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Dixie Alley: The New Tornado Alley

Here is a paper I wrote back in May of 2016 about tornadoes and their trends based on location over the past decades. The main goal of this paper is to explain why we need to move on from the term “Tornado Alley”, as well as start constructing better homes in the Southeastern US.

Dixie Alley: The New Tornado Alley

 The area stretching from North Texas to South Dakota has commonly been referred to as “Tornado Alley.” Although the Great Plains do have a tornado season from mid-March to the end of May in which more tornadoes spin up than anywhere else on Earth, Dixie Alley has more tornado related fatalities in nine of eleven months out of the year, largely due to the population density. May and June the only months where the Plains Tornado Alley has more fatalities than Dixie, with July being the least active month for both areas. The winter months are a concern for the Southeast unlike the Great Plains. Moisture off the Gulf of Mexico can combat cold fronts out of the west, and if conditions are right, tornadoes can spawn. Warmer temperatures and higher dew points can create an unstable atmosphere ¾ of the year. The summer months are not as active because the horizontal temperature gradient is extended northward. While most buildings or residences in the Great Plains have basements or storm shelters, much of the Southeast is vulnerable because a lot of buildings do not have nearby shelters or basements. The objective of this paper is to explain why the Southeast needs a better preparedness system for future storms to come.

To make an argument about which tornado alley is the true tornado alley is wrong. Both areas produce many tornadoes every year, however Dixie Tornado Alley (DTA) is believed to be the most dangerous area to live in because of tornadoes. The Plains Tornado Alley (PTA) is significant because of its very active spring season. When comparing the two, many methods are gathered by using recorded data.

           The National Oceanic and Atmospheric Administration (NOAA) provides data dating back to 1800’s, but proper tornado recordings didn’t appear until the 1950’s. NOAA created the Storm Prediction Center, which has provided organized data that has benefited numerous weather-related research teams. The database provides physical attributes of tornadoes, for instance the Fujita damage scale, the width, the path length, and its’ location, as well as tornado related injuries or fatalities.

           To obtain specific comparisons between the two alleys, the alleys needed to be separated by location. Nebraska, Kansas, Oklahoma, and Texas all fall in the PTA, while Arkansas, Louisiana, Tennessee, Mississippi, Alabama, and Georgia comprise the DTA. It’s important to note that the PTA has larger total area than the DTA, but the DTA has 7,000,000 more people than the PTA. Then the overall number of tornadoes by each alley can be obtained and compared between the two. F2/EF2 or higher rated tornadoes are considered violent tornadoes. Mississippi has the most counties that have seen at least eight or more tornadoes rated F3 to F5 per 1,000 square miles from 1880 to 2003, which is nearly 3000 more square miles than state with the 2nd most, Oklahoma (Broyles, 3).  When first reviewing the data, there were substantially more tornadoes (3000+) in PTA compared to DTA, but there was an average of only 400 more ‘violent’ tornadoes in the PTA. Since there is so much data on numerous tornadoes, and most of them are EF1 or lower, the EF2 or higher tornadoes will be compared due to the significance of the rating, because they do substantial damage. Many comparisons can be made, like comparing the alleys based on the average number of violent tornadoes by month. The frequency of tornadoes can be obtained by number of tornadoes per a certain number of square miles. Most tornadoes occur in the afternoon or evening, and time of day can be compared between the two alleys. More nighttime violent tornadoes could mean more injuries or fatalities, because a lot of people would be asleep. The DTA has technically two tornado seasons, one in late fall through early winter, and the other in the late spring, but the PTA has a very active spring, so it will be interesting to see how things change throughout a typical year. Another comparison to make is on the number of tornado related injuries or deaths. An issue with this is the population density of the DTA. To properly make comparisons, a sample size will need to be used.

           Research on tornadoes dates back to 1950 when records began. The Dixie Tornado Alley (DTA) and the Plains Tornado Alley (PTA) are the main areas in the United States where the most tornadoes occur. More tornadoes occur in the PTA every year, mainly due to the peak season of May being the perfect time for tornadoes to spawn across the Central US. However, 80% of tornadoes that occur are EF0 or EF1. EF2 tornadoes and higher are less common, but are more significant due to the amount of damage they can produce. EF2 is defined by having 111-135 mph winds, meaning significant or considerable damage. Weather teams including the National Weather Service survey the damage done by a tornado the day after the event. Since wind speeds cannot currently measure wind speeds, the NWS assess the damage and comes up with a conclusion based on structural signs, trees, and power lines. An EF2 rating is determined when roofs are ripped off their homes, some exterior walls may have collapsed, vehicles can be lifted off the ground, mobile homes being totally destroyed, or tress snapping or up-rooted. Anything worse than this would be considered higher on the Enhanced Fujita scale. For this research, EF2 or higher will be considered as strong or violent tornadoes, and therefore this will be the focus of the research. The Fujita scale changed in 1973 to the Enhanced Fujita scale. They did this because often times, ratings were recorded higher than they should have been, so they implemented a guideline the NWS follows when going out to survey the damage the next day. Figure 1 highlights this change in the graphic below. After 1973, the number of significant tornadoes decreased as expected, at a rate of 1.5 per year (Schaefer). The overall reported tornadoes in the US have been increasing each year ever since recordings began. This is because population was less dense, so a lot of tornadoes went unnoticed. On average, 15 more tornadoes occur each year compared to the previous year (Schaefer). With the development of radar technology, meteorologists can notice where the tornado signatures like a “hook echo” or a strong coupling of changing winds. Survey teams can then pinpoint exactly where all the tornadoes tracked. Storm spotter networks have continuously expanded since the 1990’s (McCarthy). Figure 2 is a breakdown of Figure 1 based on location. The Great Plains has had a large drop in significant tornadoes since 1972. The Southeast has had fewer significant tornadoes since 1972, but the average has not decreased that much. There are more peaks in the Southeast, indicating the DTA has more significant tornado outbreak years than the PTA.

 (Fig. 1): a) Overall trend of reported tornadoes since 1950, b) Significant tornadoes by year

(Fig. 2): a) and b) show EF0 and EF1 rated tornadoes for the Great Plains and Southeast respectively; c) and d) show EF2 or higher rated tornadoes for the same areas.

             Using data from NOAA’s Storm Events Database, all tornadoes can be assessed and the information can be gathered easily based on the state. Adding up the number of EF2 tornadoes in Alabama, Tennessee, Mississippi, Arkansas, Georgia, and Louisiana, 916 strong tornadoes have occurred in the DTA, from the years 2000-2015. In the PTA, Nebraska, Kansas, Oklahoma, and Texas have accounted for 542 strong tornadoes for the same time period (NCDC). This is interesting because the PTA usually has more tornadoes annually, but this includes EF0 or EF1 ratings. The PTA spans roughly more than 400,000 square miles, compared to DTA’s 275,000 square miles. However, data gathered from the government’s census page shows that 32,270,000 people live in DTA and 35,700,000 live in PTA. This is pretty close, even with though Texas accounts for 27,000,000 of the 35,700,000 people. Obviously, the population density is much higher in the DTA. Rural areas make up most of the Central Plains, while suburbs and growing cities are more common in the Southeast. From this we can expect more deaths to occur in the DTA due to more strong/violent tornadoes and a higher population density. DTA had 627 fatalities from tornadoes over the past 15 years, while the PTA has had just 150 (NCDC). This is determined by adding up all the fatalities by state from NOAA’s Storm Events Database.

           Overall frequency of tornadoes is much higher in the PTA with roughly 13,500 tornadoes reported since 1950. The DTA has had around 7,500 since records began. By averaging the number of strong tornadoes annually based on month, we can determine when these violent tornadoes will likely occur. The PTA has only one tornado season and it lasts only a few months (April-June), nearly 76% of strong tornadoes occur in this time frame (Gerard, 148). The DTA however has recorded many strong tornadoes occurring between November and May, and only 40% of these tornadoes occur in the spring months. The time of day is very important as well. Overnight tornadoes are less common, but are very important because most people are asleep. By using the data, we can determine the frequency of when strong tornadoes occur. Since NOAA’s page has everything from population, to tornado width and length, to duration, and much more, many comparisons can be made. Most tornadoes occur in the late afternoon to evening hours, but the DTA has a 50% greater risk for overnight strong tornadoes than the PTA (Gerard, 154). The PTA has a shorter time frame for tornadoes, 3pm -8pm. Roughly 1/3 of deaths by tornadoes in the DTA occur at night, compared to 1/5 in PTA (Gerard, 153).

Topography is much different between the two areas. The Southeast has more hills and trees, making it difficult to see an oncoming tornado. This and many other factors likely increase the number of fatalities seen in the DTA.  Alabama has had more strong tornadoes than Texas over the past 15 years, but Texas has had substantially more since 1985. April 27, 2011 was a major severe weather outbreak day across the Southeast; this abnormal event can skew average data. An event like this occurs roughly every 25 years. NOAA’s page has many variables that can be assessed. Other variables can then be compared like damage costs to rebuild or even comparing the duration of strong tornadoes between the alleys. Figure 3 shows the average annual number of significant tornadoes passing within 25 miles of a point between 1973 and 2010 (Dixon). The graphic changed drastically after 2011 due to the outbreak in late April, as seen in Figure 4.

Fig. 3) Average annual number of significant tornadoes from 1972 to 2010

Fig. 4) Average annual number of significant tornadoes from 1972-2011

Fig. 5) Average annual number of tornadoes with a path length >10 miles from 1972-2010

The pathlength of a tornado is also important. The longer they stay on the ground, the more destructive they can be. Figure 5 highlights where the longest-lived tornadoes typically occur. Central Mississippi up to Northern Alabama could see nine long-tracked tornadoes every year.

The data and comparisons have been made between the Dixie Tornado Alley and the Plains Tornado Alley. The PTA has been known to be the true tornado alley in the past, but with this research it has come apparent that the DTA is the most dangerous area when it comes to tornadoes. Although the PTA has the most tornadoes annually, most of these tornadoes are weaker tornadoes (EF0, EF1), and their tornado season only spans a few months in the spring. The DTA has technically two tornado seasons: September to December and February to May. This is because of how the systems set up during the spring and fall months. The DTA experiences tornadoes in the fall because the Gulf of Mexico is warmer than in the springtime because water takes longer to warm up and cool down. After the summer months, the water is warmer; therefore higher dew points seep into the Southeastern states. High dew points, or a high relative humidity is a major ingredient in the formation of tornadoes. Tornadoes also need lift, or convergence of winds at the surface, instability in the atmosphere, a large angle between surface winds and winds aloft, and a high CAPE, or convective area of potential energy. In the springtime, a dry line sets up in the Plains, and when a low-pressure system moves through the area, sever weather breaks out. The PTA in May has the most tornadoes out of any month in both locations. Since the PTA does not have source of moisture as well as the DTA does with the Gulf, the PTA relies on daytime heating to create instability in the atmosphere. When the Sun heats the ground, latent heat is release, which adds water vapor and instability in the atmosphere. Overnight this boundary level lowers and cools due to the lack of sunlight causing warmth in the air. As a result, the PTA sees substantially less overnight tornadoes than the DTA does. The DTA still has access to the abundant moisture off the Gulf of Mexico at night. Therefore, the DTA has a 50% greater risk of strong tornadoes during the overnight hours than the PTA. Although more tornadoes occur in the PTA annually, the DTA has more strong/ violent tornadoes annually. The PTA has a high-risk peak season compared to a more moderate risk longer season the DTA has. Over the pass 30 years, 75% of tornado fatalities in the US have occurred in the DTA. The population density of the DTA is much higher than the PTA, so there’s a higher chance for a tornado to hit a building in the Southeast than in the Plains. The PTA is very rural, and a lot of the tornadoes that touch down go unreported because no one sees them. Even if there is a tornado signature on Doppler radar, a tornado may go unrecorded, which could skew research. In the PTA, topography is flat, so people can see the storm coming from a few miles away. In the DTA however, there are more hills, valleys, and trees, and a lot of tornadoes “sneak” up on people who cannot see them. In conclusion, the DTA is more dangerous than the PTA for all the reasons stated. There’s a longer season for a chance of a tornado outbreak, but the PTA does have more tornadoes, even if most of them are weaker ones. Both areas have the most tornadoes in the world, so they are both dangerous areas to live in. The PTA has been known to have more shelters than the DTA. Most houses built in the Plains have basements or storms shelters, unlike the Southeast. Perhaps in the past when they built the houses, it was less common to see dangerous tornadoes in the Southeast and more in the Plains.

Today the Southeast faces a greater risk of a tornado threat than in the Great Plains. The Southeast needs to better construct homes to have a shelter, or communities should just build more storm shelters. Mainly, people in the Southeast need to be aware of the risks of living in the DTA. Apathy has been a concern for the Southeast in the past, but after April 27, 2011, a lot people recognized the importance of taking these tornadoes seriously. With the ever-increasing population, expansion of urban areas, and therefore the expansion of suburbs around the cities, chances of a tornado hitting a populated community can only increase. The assumption of tornadoes being more dangerous in the tornado alley (PTA) is no longer true. Although the most dangerous alley is the South, including Oklahoma and Texas, all the way to Georgia, and south of Kentucky to Northern Alabama.

 References:

·               Gerard, Alan, The National Weather Service: National Weather Digest, Jackson, MS. December 2010

http://www.nwas.org/digest/papers/2010/Vol34No2/Pg145-Gagan-etal.pdf

·               Dixon, P. Grady, Mississippi State University, Mississippi State, MS; Coleman, Timothy, University of Alabama Huntsville, An Objective Analysis of Tornado Risk in the United States. American Meteorological Society.

http://journals.ametsoc.org/doi/full/10.1175/WAF-D-13-00057.1

(Where all the figure came from)

·               McCarthy, D. W., and J. T. Schaefer, 2004: Tornado trends over the past 30 years, 14th Conference of Applied Climatology, Seattle, WA, American Meteorological Society, 3.4

https://ams.confex.com/ams/84Annual/techprogram/paper_72089.htm

·               Dolce, Chris, The Weather Channel, March 2015: How Many Tornadoes Has Your City Seen Since 1950?

https://weather.com/storms/tornado/news/tornadoes-by-month-cities

·               Schaefer, Joseph T., Norman, OK: The SPC Tornado/Severe Thunderstorm Database

https://ams.confex.com/ams/99annual/abstracts/1360.htm

·               Broyles, Chris and Crosbie, Casey, Storm Prediction Center, 2004: Evidence of Smaller Tornado Alleys Across the United States Based on Long Track F3 to F5 Tornado Climatology Study from 1880 to 2003.

http://www.spc.noaa.gov/publications/broyles/longtrak.pdf

·               https://www.census.gov/popest/data/maps/2011/PopDensity_11.pdf

·               http://www.esrl.noaa.gov/psd/data/

·               http://www.ncdc.noaa.gov/stormevents/

·               http://w2.weather.gov/climate/index.php?wfo=lsx

If you have any questions or concerns, please comment below!

Thanks for reading!

Merritt Turner

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Houston Floods

Houston has already been hit hard by rainfall, and it’s not expected to end until Wednesday. An upper-level low over Colorado has been rotating in place seen in the water vapor imagery. Dry air from Mexico and dry air pushing down into Florida are squeezing the more moist air in a small area. The result is a stationary boundary, a line of converging winds with abundant moisture due to the proximity to the Gulf of Mexico. The jet stream has been too far north and has yet to push the upper level low forward, keeping the system stalled. Precipitation totals have climbed into the 1-foot level over the past 2 days in Northwest Houston, and similar numbers are expected for areas the southeast of the city. Some areas could see over 2 feet of rain by Wednesday. The Buffalo Bayou drains the city, but it expected to crest tomorrow, so additional flooding is expected, even for areas that have not received as much rainfall as NW Houston. Over 100 water rescues have taken place this morning and 6 counties are under a Flood Emergency.

The 250 mb shows the lack of strength of the jet stream and a very strong ridge in Eastern Canada. The ridge is expected to dig through the New England by Wednesday, allowing the front to move through. The surface winds show high pressure over Atlanta, which rotates clockwise. Winds out of the Gulf are typically out of the South, but this set up has changed the direction to the west, feeding the system with abundant moisture. The 850mb shows just how moist the air is. 90% relative humidity extends through the Central Plains, but due to the convergence of winds and abundant moisture, SE Texas is in for a record-breaking flood event.

High pressure dominates the entire Continental US, but there is a line of lower pressure that extends up through the Plains. The temperature anomaly lines up with the MSLP graphic. Much colder temperatures exist from Colorado down to Western Mexico. The Great Lakes region has been much hotter than normal. The line between the two is where our precipitation has been taking place. This setup will continue today and tomorrow, and it will finally start moving east by Wednesday.

Houston is very prone to flooding due to the urbanization of the city. A lack of soil to absorb moisture, a close proximity to the Gulf, and only one main drainage system (Buffalo Bayou), Houston is very prone to flooding. With a stationary front sitting over the area, this is a big concern for the Texas city. On top of the amount rain that has already fallen, 6-12 more inches of rain is expected through Thursday. GEM and GEFS models disagree with the totals, but extensive flooding is expected within and around Houston, with an increased concern near rivers and flood plains. If you’re in the SE Texas region: Turn around, Don’t Drown.

-Merritt Turner

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Little Rock Severe Threat- Interesting Setup

The Southeast has experienced a rather windy week this week. The severe threat is back this week for eastern Texas, Louisiana, and Arkansas tonight and tomorrow. Little Rock is expected to receive the tail-end of the severe weather tomorrow evening, so this week we will focus on the ingredients near the Arkansas capitol. At 6pm on Monday, the 850mb shows the lower level winds rotating over Arkansas. Moist winds are out of the Southwest, which usually are not a concern to spawn tornadoes, but the drier winds out of the north seem to come in from the north/northwest. This larger than normal angle is expressed by the darker yellow colors over Arkansas, indicating an increased rotation in the winds. The dew point model (NAM) agrees with the wind orientation of the Euro model. Dew points reach the low 70′s in Arkansas, which is plenty of moisture for severe weather.

By looking at the anomaly, we can see the strong high pressure system over the North Central US. This will deepen Southeast this week, shoving the low pressure system over Texas through the East Coast. This interesting setup has an inverted trough over East Texas and an increasing inverted ridge over North Texas. This uncommon setup is not rare, but it’s difficult to forecast due to the abnormality of it. It’s easy to predict where this low pressure will go though due to the lower level winds and the strong gradient between the low over Eastern Canada and the high in the Atlantic Ocean. The precipitable water shows which air has the most moisture in it, and we can see an increase of it along the Mississippi River all the way up into Tennessee. 

However, the upper air dynamics do not support the lower dynamics in producing severe weather. Jet streaks are not noticeable within the system over Texas, therefore there is not much diverging aloft occurring. This will slow convergence at the surface since the air will have little room to move. Cloud tops will likely be lower since the outflow is not at strong as the inflow. Isolated tornadoes are a possibility, but they would likely be weaker and short-lived due to the lack of sustainment the ingredients provide. Small hail is expected with some of these storms. Little Rock and eastern Arkansas also have the chance for some overnight tornadoes, as the front isn’t expected to pass until around midnight.

If we check out Bufkit’s files, we can see the CAPE is pretty high at around 7pm. The main thing to look at is the wind profile. Surface winds are out of the southeast at this time, which is a big concern for forecasters. The backing winds are out of the west the more you rise in the atmosphere. This angle is big enough to spawn tornadoes, and the second graphic shows a strong CAPE backing this up in the evening hours. The red line indicates CAPE values, and there are actually two spikes, one in the morning and one in the evening, meaning storms that pop up ahead of the squall line will have the potential energy to produce tornadoes. Although, our main concern is in the evening when cyclonic vorticity is highest in the lower levels due to opposing surface winds seen the 850mb level graphic above.

-Merritt Turner

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Presque Isle, Maine

This week we will check out Presque Isle’s weather forecast to mix things up. Currently, the cold front split is through Oklahoma and Missouri. It will cross through this Midwest and transfer into a Nor’Easter early this week. The system seems to strengthen once it makes contact with the Atlantic Ocean, seen in the 700mb chart. The gradients are much tighter Monday evening, increasing the likelihood for abundant precipitation.

Tuesday morning, the winds show flow off the NE coast help fuel the system. Temperatures will be cold enough for 4-6 hours to produce enough snowfall to accumulate. Roughly, a 16:1 snow ratio indicates Presque Isle could receive 1-3 inches of snow. However, the relative humidity shows heavy rainfall Monday evening, and temperatures are above freezing at the surface. This can slow sticking for the first few hours when transitioning to snow. The snow growth region can be seen lowering in the atmosphere, representing the backside of the system.

Comparing the GFS and NAM models, the GFS has the system arriving a few hours earlier than the NAM, but the NAM model seems to be stronger, with darker colors indicating heavier precipitation. The rain should start Monday evening, and then it will transition into snow by 3:00am. It will move out midday, and high pressure will transition into the South. The high for Tuesday is 34 degrees, Wednesday we will warm up to 45 with cloudy skies, then more rain is on the way for Thursday and Friday.

Temperature’s will be winter-like Tuesday, but the system is not dragging a whole lot of polar air from the North. South Dakota will warm up around 30 degrees from where it is now. As we move more into the spring months, the less-likely these Nor’Easters will bring snow to the Northeast. If you live in the Northeast, I’m sure you’re sick of seeing snow, but this system could be your last chance to enjoy it this season.

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Warmer than Normal, and A Wet Weekend Ahead

We have had a warmer than normal winter, but the precipitation has been high as well the past few months. Nashville will continue to be warmer than normal for the near future. A nice start to the week comes to an end on Thursday when we are expected to get rain off and on for 4 days. The 850mb level shows a stout high pressure system off the Atlantic coast rotating clockwise. A low pressure system increases the flow in the lower atmosphere over Louisiana. That low centred over East Texas sits there for a few days, keeping moisture flowing north through Deep South. The climatology report shows Wednesday will be nearly 14 degrees celsius warmer than normal this time of the year. The warmer trend continues after the rain this weekend.

The 250mb level shows us a very deep trough extending into Mexico the upper air. The low is not as stout, which explain why it will stay relatively stationary for a few days. Increased flow in the upper atmosphere over the Gulf of Mexico can create rising motion in the right-rear region of the jet streak. The duration of this jet streak will help determine the amount of rain we will receive this weekend. The 500mb Geopotential Height Anomaly shows the ensemble for this week. The low pressure system digs deep enough to be cut-off from the ridge like conditions to the north and east. Since there is no connection to the polar regions, we can assume this system will “rain itself out”.

The precipitable water on Thursday, highlights the strength of the high pressure system off the Atlantic coast. It seems to wrap the moisture from the Gulf of Mexico up into the Northeast. This set-up will bring decent amounts of rain to the greener areas on the graphic for a few days straight. Off to the west, we can see the Pineapple Express creating a focused area of rain to parts of the dry California Coast. Atmospheric flows like the Pineapple Express can be beneficial to a lot of people, but rapid amounts of rainfall can cause landslides in areas that have received little rainfall prior and floods.

Dewpoints on Friday are still in the 60′s on Friday, indicating the amount of moisture present in the atmosphere. We can see a tighter gradient to the west on the back side of the system. These dew points won’t reach us until Sunday, when the system finally moves out. The 250mb chart on Saturday shows extreme weakening within the system. The negative tilt of the trough and the lack of strong winds indicates the system has run its course.

The 7-day accumulation model shows Nashville receiving roughly 3 inches of rain. The main threat is in central Louisiana and extends up the Mississippi River. Some areas of Louisiana are expected to receive up to 9 inches of rain with the system, increasing the flood threat for the area. Even Northern California is expected to see around 10 inches of rain, a huge amount after very little rainfall this past year. The 14 day outlook shows local conditions over the next 2 weeks. The dotted lines indicate the 30-year average highs and lows. The yellow line is our temperature forecast. Every day for next 2 weeks, we are expected to be above normal temperatures, as we never drop below 60 degrees for the high temperature.

-Merritt Turner

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Another Stormy Tuesday

The past few weeks, it seems as if the low pressure systems are on a weekly cycle, bringing storms to Nashville the past 2 Tuesdays, and this week will be no different. The water vapour image shows drier air is heading this way for the next couple of days in the upper atmosphere. A system is organising just west of South Dakota, that will bring a few showers through our area early Monday morning. The sounding for tomorrow at noon, shows faster winds than normal coming out of the southwest, where the dry air is currently located. However, high pressure over the panhandle of Florida will continue east and more concerning system will move in on Tuesday.

The high pressure over NW Florida can be seen from the 850mb chart. Although drier air is the upper atmosphere, the clockwise flow from the high pressure system actually sends moisture in the lower levels of the atmosphere, that can be seen in the lower 5,000 km of the atmosphere from the bufkit data. Some early morning showers are possible Monday morning due to moisture in the snow growth region, but not much rain is expected due to the weakness of the system. The red line indicates CAPE, and we can see on Tuesday evening is when the highest risk for severe weather is predicted to occur.

Here is the sounding for Tuesday evening at 6:00 pm. We can see the CAPE (yellow line adjacent to red line) extends high up into the atmosphere, but it’s very skinny, meaning a small amount of convective potential energy is there, but it’s not strong enough to cause serious concerns. Still the chance is available, so it will be important to stay weather aware on Tuesday. The main threat will be  straight line winds associated with the front. The sounding shows from the wind profile, fairly parallel wind direction out of the west throughout the atmosphere. If surface winds were coming from the south, then there would be more of a concern for rotation to spin up. Instead, they are out of the west pretty fast near the surface.

We can see how the upper air dynamics support the system as it drives through the area. Due to the axis of rotation within the trough being mostly N and S (vertical) on Tuesday evening, this when we can expect the strongest storms of this system. After the axis tilts negative by Wednesday morning, we can start to expect occlusion in the system. The 500mb chart highlights the relative vorticity in middle part of the atmosphere. It’s pretty substantial on Tuesday evening, indicating there is rotation in the atmosphere, but due to lower dew points, surface winds out of the west, and a skinny CAPE the threat for severe weather is marginal to moderate. At best I predict there is 20% chance for a tornado within a 50 mile radius.

From the ensemble, we can see that Tuesday will not be the only day that brings us rain this week, because Thursday another front is expected. Sunny skies and 60 degree weather will be the outlook for the next couple of days. Temperatures will drop to the mid-50s for Wednesday and Thursday after the front moves through on Tuesday, so severe weather is not expected with this system. We can see that we will quickly be back under ridge conditions by the weekend. The 7 day precipitation anomaly shows the annual average conditions for this upcoming week. Areas north and south of us will be drier than normal, but most of Tennessee will be a bit wetter than we usually are this time of year.

-Merritt Turner

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Last Chance for Snow?

We’ve had a few showers today and that’s due to the overall convergence of surface winds from the NW and SE. Our relative humidity is rather high, but I don’t see Nashville receiving anymore rain tonight. Surface flow from the north is extending into Texas, although it’s air is low in humidity, it’s converging with air off the Gulf of Mexico, ramping up the system. The Enhanced IR shows the system in Texas and the trough to the north start to merge, trying to take over the drier air. We can expect to see mostly cloudy conditions over the next couple of days as the system in Texas organizes, and the system to our north moves east.

We have a skinny CAPE this evening, however there isn’t enough moisture for the rain like it’s calling for. Drier air is dominant in the upper atmosphere. The relative humidity graphic shows us when our most likely chance of rain will be. Tomorrow afternoon, if the sun is able to peer through the clouds long enough in the morning, we have a higher chance for some lighter rain. Tuesday evening into Wednesday is when our best chance of rain will be.

Monday afternoon, we can see drier air 7km up. Winds slow down in the bottom of the atmosphere. The relative vorticity shows these slower winds as a result of the system in Texas suppressing natural flow from the Gulf of Mexico from entering our area. The backside of the trough seems to have to strongest relative vorticity by early Tuesday, indicating it’s going to strengthen more before it weakens.

The NAM 850mb model has the system relatively close to where it is now, meaning it needs to rotate and organize before it moves. Severe weather is not a huge threat for us on Wednesday, but a few thunderstorms may be associated with this system. By Wednesday evening, most of the moisture will be off to our northeast, but the moisture that remains may result in some snowfall. The Bufkit sounding for Wednesday at 6pm shows complete freezing throughout the atmosphere, except for the surface which is just above freezing. Winds are very high on the backside of this system as we can see them sinking down into our area. This lowers the snow ration from 11:1 to 8:1 due to the near freezing level atmosphere and high compacting winds. No accumulation is expected with this because the low pressure system will move northeast before enough snow has time to stick on the already wet ground, and because temperatures are not predicted to drop below 34 degrees.

The ensemble shows the probabilities over the next few days, and we can observe the low pressure system continue northeast after it passes us Wednesday. The system seems to merge with the colder arctic air north of Canada, indicating a colder spell for the Northeastern states. The precipitation probability outlook for the end of February and first week of March shows we are more likely in for drier than normal weather 8-14 days from now. Once the system moves through this week, we will cool off a bit, but not too much. A high of 46 for Thursday and in the mid-50′s for the weekend is our forecast. The 8-14 day outlook for temperature shows the Eastern US will be colder than normal, and the Western half will be warmer than normal.

-Merritt Turner

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Wet Beginning of the Week for Nashville

Currently in Nashville, we are siting at 36 degrees and tonight we will drop to only 34 degrees. We are expected to get some of the precipitation associated with Winter Storm Olympia, but we will receive only rain and a small chance of sleet over the next couple of days. Our surface analysis shows our dew point at 17, which is low, but will grow overnight as the moisture tracks east. Kentucky has received moderate amounts of snow today, but in Nashville our temperatures are just warm enough to melt the snow before it reaches the surface.

The NAM’s model shows the system gaining strength over the next 24 hours, all while we receive its’ rain, until early Tuesday. It will continue up the coast Tuesday and into Wednesday,causing problems for the Northeast. Once the system moves out, high pressure will settle in and we will warm up on Thursday. Over the weekend, temperatures are expected to reach the mid-60′s, and as far as long-range forecasting goes, we are getting very close to switching to a more spring-like pattern. The relative humidity seems to concentrate itself across Tennessee through tomorrow, which will help fuel the system for rain. 

This evening we could see a wintry mix for a little while, but not enough to make an impact. The first sounding is for tonight at 7pm. All the way down the atmosphere, we only reach 2.8 degrees celsius as a max, and we need 4 to fully melt an ice crystal. However, after we go back behind freezing for a few hundred feet, we approach 2 degrees the rest of the way down, roughly 2500 feet. This means there is a lot of time available to melt the ice crystal, but a few degrees can change this from rain to sleet to freezing rain in a short period. Tomorrow morning we can expect the rain to pick up momentum. At around 4000 feet, we are warm enough to completely melt a particle at 5.5 degrees celsius (42 Fahrenheit). This trend will continue for most of the day on Monday and into Monday night.

The relative humidity can be seen over the next few days using Bufkit data. Although there is moisture in the snow growth region, mainly just Monday, it’ll be too warm for us to receive any snow. Monday evening we have another chance to drop below freezing, but the sounding shows that we are above freezing for 5000 feet at 8pm, meaning complete melting. Winds are speeding up and turning south, indicating the back-end of the system. The moisture will move out by the end of Tuesday and high pressure will begin to move in.

Two pockets of colder air can be seen from the 300mb level as of this evening. They begin to phase together tomorrow morning and you can see it strengthen into Monday evening.The trough combines the energy of the two systems into one. By Tuesday morning, the trough digs towards the northeast, indicating its next direction. After this system moves on, we will warm up again for a nice weekend ahead.

-Merritt Turner

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Snow Chance This Week

The front that brought some severe weather to Nashville this week is off the coast of the Carolinas, continuing to push offshore. It brought some cooler air, but another front is right behind it that will bring some cold air and snow to our area. At the 700mb level you can see the low pressure system over the Minnesota/Canada border with a decent amount of moisture. Heights extend way up into Northern Canada, meaning the stream of cold air is coming from very cold regions. The analysis shows snow already associated with the system that will dig southwest and affect us Monday into Tuesday.

The NAM model backs up what I just mentioned, showing a surge of cold air will push in by Tuesday morning. Monday, we can see some of the surface winds our out of the South, which will help fuel the system as it approaches. We will warm up to 42 degrees on Monday, but we will drop throughout the afternoon, with a low of 24 overnight. Tuesday we will struggle to break freezing point, and overnight we will be in the teens. Wednesday’s high will be 28 degrees as the snow tapers out of our region.

Here are the Bufkit files to show the chance of snow for Nashville this week. Starting with the top graphic, at Monday at 2pm we may be seeing some flurries start to come down, but the surface is at 4 degrees Celsius, which is the temperature needed to completely melt an ice crystal. If it does start snowing in the afternoon, it will likely melt on the warmer surface as we are predicted to reach up to 42 on Monday. Rain will likely lead the system as it tries to push its cold air in. But by Monday evening, the precipitation rate increases. The air at the surface is getting colder, so the likely hood of snow sticking increases. Wind speed is fairly high, which can impact the compactness of the snow. The snow ratio increases with the first graphic at 7:1 to the second graphic at 10:1.

Tuesday will be cold enough for the ratios to increase. The snow growth region has expanded to over 8000 feet at 10:00 am on Tuesday. Drier air won’t filter into the upper levels until late Tuesday and early Wednesday. Tuesday’s soundings look similar throughout the day, meaning accumulation is expected with this system. Riming occurs when we exit the snow growth region of -10 degrees celsius. Less riming on Tuesday compared to Monday is what we can take away from these soundings. The snow ratio increases to 15:1 on Tuesday. There needs to be a substantial enough of moisture in the snow growth region for us to get a good amount of snow.

Here is the relative humidity and snow growth regions for the early part of the week in Nashville. Early Monday morning, we have some moisture in the SGR, but it will be too warm near the surface so the snow will melt into rain once it reaches us. But starting Monday evening, moisture returns to the SGR, and continues to produce until early Wednesday. I predict that we will get 2-4 inches of snow from this system, with the bulk of it coming on Tuesday. I’ll keep a close eye on it as it approaches our area and the forecasts change.

-Merritt Turer

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Severe Weather Tuesday into Wednesday

Tonight we will drop to around 30 degrees in Nashville, TN. Partly cloudy skies are in the forecast for tomorrow with a high near 48. We will warm back up this weekend with sunny skies and a high of 64 for Saturday. The warm humid air will help fuel our next system moving through next week, but we do get a few days of 60+ degree weather.

From the 300mb chart from this afternoon, the trough split of the low pressure has brought rain and storms for the deep south, including Florida. The backside of the trough is bringing sinking air, which will clear up the skies tomorrow into Saturday. The next system to keep an eye on is out West, but it will be moving this way over the next few days. 60 degree weather in January must result in storms as the front pushes through, and after that, cooler air will drive its way in.

The IR image shows a few clouds sticking around the area, but they are moving out. Clearer skies are in behind this, but more clouds are on the way ahead of the next system. These clouds will be here by Sunday. The station plot shows faster winds associated with trough off to our north. 49 was recorded at BNA in Nashville earlier. Once this trough moves out, we will see more winds out of the south, increasing our dew points leading up to front coming in around Tuesday. Some forecasts have us up to 55 degrees for dew points on Monday, which combined with 60 degree weather, can cause a lot of instability in the atmosphere, a recipe for storms.

The 500mb ensemble shows a deepening of low pressure will occur across the Eastern US mid-week. The timing for this is a 6pm on Tuesday, so we can assume storms will arrive before this that day. A 40% chance rain will likely lead the front on Monday, but clouds could cap the atmosphere, slowing rain production. The 850mb GFS model shows how this system sets up. It’s time frame is from Saturday night to Monday morning. By Sunday evening, we can see the low pressure real ramp up over Southern California as is begins its track west. Meanwhile, the winds for our area are coming up from the Gulf of Mexico, increasing the humidity substantially.

The Storm Prediction Center has put out an early advisory for this system. For now, there’s a 15% chance for severe weather on Tuesday within 25 miles of any point inside the yellow box. From the precipitation and MSLP chart, the low pressure system seems very organised around 6am on Tuesday. If it’s cloudy early Tuesday, I do not expect it the weather to be too bad , but if it’s sunny, the heat from the sun can help destabilize the atmosphere, increasing our chance for severe weather in the afternoon and evening. Once the squall line from the front pushes through, we will begin to cool off again. The highs will be around the low forties, while the lows will drop into the mid-20′s for Wednesday and Thursday.

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Post-Snowmaggedon 2016, Nashville, TN

The big storm has come and gone, but there’s a lot of snow to melt over the next couple of days. Some areas received up to 9″, while my house received 5″ on the east side of Nashville. The clouds have been clearing out some to help melt the snow, but temperatures have struggled today to reach above freezing. Still take caution on ice because tonights low will be in the upper-teens. Tomorrow, most of the snow will melt when we reach 40 degrees and clearing skies.

According to this morning’s sounding, the colder air has been driving in behind Winter Storm Jonas. The winds are veering out of the north indication sinking dense cold air. Winds seem to speed up around 700mb, which means it’s sinking rapidly. The water vapor image shows the drier air in behind the front and the moisture that is being wrapped around the Northeast coast, causing a lot of problems for them as well. Areas of WV received up to 41″ of snow, and now New York City and Boston are at the brunt of Jonas. Our next system that can bring us scattered showers on Tuesday, is up near the Canadian border and Minnesota.

Jonas’ strength can be seen from the visible satellite image above. The circulation is strongest off the coast of New Jersey. Clouds are moving SW in the Northeast, while the clouds off the coast are moving NE, fuelling the moisture for a lot of snow. In our area, the clouds can be seen falling apart as the dry air moves in. We will continue to see clerking skies over the next couple of days.

Here we have the 300mb charts from the NAM model and GFS model, respectively. The top image shows the forecast over the next 36 hours. We can see Jonas being blocked by a High pressure system off the coast. If that high was not in place, Jonas would’ve been far out into the Atlantic by now, but since it’s been blocked, it’s been able to dump loads of snow over the Northeast coast. We can see the next system set up with winds increasing in the upper atmosphere over the mid-state. This right-front region of the jet streak indicates rising motion, which results in clouds and rain. The GFS model for Tuesday and Wednesday indicates a bit of trough-splitting with the system, which creates an uncertainty of showers. 50% is my prediction for Tuesday’s chance of rain.

The 500mb height and sea level pressure show Jonas exiting the US by Monday morning. High pressure will dominate the area for the next couple of days. Sunday overnight, we’ll drop back below freezing, Monday’s high will be in the lower-50′s as humidity begins to rebuild into our area, the overnight low will be in the low-40′s. Tuesday’s high will reach up to 45 degrees, and will drop to below freezing again overnight as the front pushes through. The rest of the week looks dry and warming up the mid-50′s by the weekend.

-Merritt Turner

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Finally Fall

The big front that pushed through this past weekend has brought very cold temperatures to the Eastern US. We’ve had a slow start to Fall, but it’s definitely here now. At the 250mb level we can see where our cold air is coming from. The water vapor shows the dry air has pushed it’s way through, and sunny skies are a result for us for the next few days. The front has reached the east coast where it’s still releasing rain in the Northeast, although it’s occlusion has left it as less of a concern.

After the front pushed through, the backside of low produced snow for many states along the Corn Belt. It can be seen circled in the satellite image spreading from Iowa to northern Indiana. The Appalachian Mountains also received a good bit of snow cover due how cold it is in higher elevations. The surface temperature from this afternoon (Nov. 22) shows how this front has pulled a lot of cold air from the north. Today’s high is not expected to get above 41 degrees for Nashville. The snow along the Corn Belt is helping keep the temperatures below freezing for their area.

The lifted index shows how stable the atmosphere is. Areas less than zero represent areas that have unstable air that could produce thunderstorms. Values greater than 10 indicate dry conditions and typically clear skies. As you can see, we are well above that number and will continue to be so, tomorrow and into Tuesday. The 700mb level has blue and purple colors representing sinking air of the vertical velocities. Tonight’s low is expected to reach 23 degrees, and tomorrow we will get up to 55. Tomorrow night we will fall below freezing again, but then we will warm back up into the 60′s for the rest of the week.

The right front quadrant of the jet streak stretching from Tennessee all the way up into Western Canada indicates more sinking air will drive its way in over the next 24 hours. The air here is sinking because the fast winds that are approaching the base of the trough must slow down. And since they have nowhere to go, they are forced down and we experience drier and cooler conditions. The GFS 850mb model forecasts the next days. The cold air moves out and up towards the Northeast and we warm back up by Wednesday. The next front to push through will come around the weekend and a lot of rain is expected with this system. You can see it start to set up Wednesday off of the Rocky Mountains. We’ll keep a close eye on it as we get further into the week.

Merritt Turner

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A Couple Inches of Rain Expected this Week

A strong cold front will be making it’s way through our area on Wednesday. The radar from this morning has shown some light rain, but the high pressure to our east has kept us dry so far. That will change as the high pressure continues to move east. We can see the dry air from the sounding this morning in the lower atmosphere. Although we will get some rain today, the main threat is going to come Wednesday when the main front pushes through.

Today there is a threat for severe weather across parts of the deep South as the front pushes through Texas. The threat will continue tomorrow for areas just west of the Mississippi River. Once it reaches our area, the front will not be as strong as it will be today and tomorrow, but the chance for a lot of rain will still be high.

The NAM 700mb level shows very strong vertical vorticity across the South associated with this front. This means updraft will be high and the wind shear in the upper levels will create environments capable of producing tornadoes. The GFS model plays it out, showing the front strengthen by tomorrow, and then weaken by Wednesday once it reaches Nashville. Roughly 2 inches of rain is expected over the next few days. Once the front passes, we will be back to cooler conditions, with highs reaching the mid-50′s and lows reaching the lower 30′s later this week.

The National Weather Service predicts 2.36″ of rain for Nashville by Thursday, with higher numbers to our west. Some areas could receive up to 3 inches of rain. The precipitable water and lifted index chart shows us where our greatest areas of concern are. We will continue to monitor this system over the next couple of days to see if the threat for severe weather increases, but as of now the main concern is flash flooding due to rainfall.

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Severe Weather Chance This Week

We’ve had a wet weekend in Nashville, and it’s not quite done yet. The radar shows a few showers to our south that will head northeast over the next couple of days. We may get a bit of this rain tomorrow, but a few models have different predictions on this (more on this later). Another front will push through late Wednesday and into Thursday, rain is predicted to be minimal due to the amount of high pressure and dry air that will in place the next two days, however isolated severe storms are a possibility.

From the water vapor imagery, it seems as if the dry air has taken over the area, and the system is propagating northeast, but from the surface analysis, we can see the surface winds are coming out of the east. As the system will move up the coast, some of the rain could clip us tomorrow even with the drier air already in place. The next system that will push through is up in the Northwest US. It will swing down into the Southeast by Thursday, and it has the potential to have severe storms associated with it.

We can see the negative tilt of the axis of the trough centered over the Central Plains at the 500mb level indicating it will propagate Northwest. The 12-hour forecast at 850mb level shows some fast winds coming out of the Southeast. This is due to counter-clockwise rotation about a low pressure center over the MS coast, and clockwise rotation and high pressure off the Atlantic coast. This is why the NAM model predicts we will get up to an inch of rain tomorrow. If there is enough uplift in the air, there will be enough moisture in the lower-levels to produce rain.

The models disagree on the amount of moisture this system will produce. The NAM is predicting up to 3 inches of rain in some locations and up to and 1.5″ for Nashville. The RAP models resembles the GFS model in the amount of precipitation expected. The GFS has the high pressure over the Northeast, suppressing the system and not allowing it to push as fast as the NAM is predicting it. At the 700mb level, we can see a strong core of rising motion push   up through Eastern Tennessee. The GFS model has this core pushing more along the Atlantic coast compared to the NAM.

Tomorrow’s high is 51 degrees, but warmer temperatures will push eastward and we will warm up until Wednesday. The Convective Outlook for Wednesday is calling for a 15% chance of severe weather for our area. The biggest concern is to our west in cities like Memphis or Little Rock, who have a 30% chance for severe weather. This is something to keep an eye on as we get closer to Wednesday. I expect the SPC will alter this area of affect over the next few days as the models start to come in agreeance with each other, but it is something to look out for. After the front pushes through, high’s are predicted to be in the upper-50′s for the remainder of the week.

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Another Rainy Weekend for Nashville

Here we are again with another wet weekend in store for Nashville. At the 700mb level, we can see there is a lot of humidity with the system that is headed this way. The shortwaves in trough are on the east side of it, so we can assume that it will stop digging toward the southeast and start propagating toward the northeast. We are expected to get rain tomorrow, but how much rain is the question.

The high pressure is starting to move out of our area, and more moist air is starting to push it’s way in. From the water vapor image, we can see the center of rotation of the system is located over the intersection of Arizona, New Mexico, and Mexico. Out ahead of it the cooler air is converging with the moist Gulf of Mexico air, creating thundershowers. The sea level pressure gradient is tight between Arkansas and Texas, increasing surface winds at these locations. The low will continue to move this way, bringing showers with it.

According to the MOS by NAM, the dew points will keep increasing over the next 60 hours. As the surface winds start coming out of the south, cloud cover increases. Pressure will decrease by about 15mb over the next 2 days. The vertical velocities at the 700mb level show very strong uplift with this system over the next 48 hours. They are predicting that we will get 2 inches of rain total by Sunday.

However, the GFS model disagrees with this. It’s predicting the northern low over Montana to push deeper south than the NAM. Because it’s pushing deeper south, the backend of the trough associated with this northern low will send anticyclonic and sinking air to Nashville. This would keep the storms in Texas moving more east rather than northeast. They are predicting that we will only get 0.5 inches of rain. It’ll be interesting to see which model is more accurate by Sunday.

The trough-splitting is more prominent in the NAM model over the next 2 days, as well as the jet streaks have faster winds than the GFS model over the Southeast. The right-rear quadrant of the jet streak indicates rising motion. The GFS model has slower winds in the upper atmosphere meaning not as much air needs to be replaced due to upper level divergence. I predict that the total precipitation we get is closer to the GFS forecast, say 1 inch. Temperatures will stay in the mid-60′s this weekend with cloudy skies, but we clear up a bit and warm up come Monday, with temperatures reaching the 70′s once again.

Merritt Turner

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Cooler and Wetter Days Ahead

Nashville has enjoyed another sunny dry week of weather, but as we move more into the cooler season, cold fronts become more frequent as troughs dig deeper into more southern latitudes. A low pressure system has brought a lot of rain to Texas, while we are still under high pressure and dry conditions. This will be the same story tomorrow, but the front will push northeast and will reach us by Saturday. We are expected to get some rain, but it will not be a washout as the high pressure will stop the low from pushing south and direct it northeast toward the Great Lakes.

From the water vapor imagery, we can see storms pop up across the dry line in Texas. Another low is stalled just of the coast of Texas, and this is squeezing the dry air between the the coast and the front extending up to Iowa. Another thing to keep an eye on is Hurricane Patricia in the Pacific. It was only a tropical storm yesterday with winds at 50 mph, but it has since strengthened to a category 4 hurricane with 150 mph winds. This infrared image shows just how quickly its eye formed over the past 12 hours. It’s going to make landfall in Mexico tomorrow evening and is forecasted to track northeast towards the Southeastern US. It will continue to weaken once it reaches the land. If it stays on its track it will bring a good bit of rain to our area by the mid-week.

Dewpoints have been in the 40′s and low 50′s this week, but that will change tomorrow as the moisture feeding into Louisiana and Texas will continue to shift east. Surface analysis shows the strong surface winds off of the Gulf of Mexico flow into the front aligned through Texas. This front will continue to propagate northeast, and the further it gets from the Gulf of Mexico, the less moisture it has to feed off of. Dewpoints will not drop that much because a bit of trough splitting in the upper atmosphere will keep energy and moisture around for the next few days.

The relative vorticity this evening is strong over the Colorado and Wyoming border. It is forecasted to weaken according to the NAM 500mb level by tomorrow as it’s negative axis continues to occlude itself. With that includes the trough-splitting I mentioned earlier, which will keep our weekend cloudy as the front comes through Saturday. Temperatures will reach 83 tomorrow and 74 on Saturday. They will struggle to reach 70 degrees for the rest of the early work week. The GFS model shows the front pushing through Saturday, but the main concern is Hurricane Patricia that is predicted to cross Mexico, brush Texas, and extend up the Mississippi River by Tuesday. It’ll weaken substantially by then, but we’ll keep an eye out for it as it marches this way.

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First Frost Already?

A special weather statement has been issued for Nashville for this weekend. Saturday, Sunday, and Monday mornings are all days of concern for our first frost of the year. Temperatures are forecasted to drop into the mid-30s for each of these early mornings, with highest concern being early Sunday with a low temperature of 35 degrees. This is due to a cold front that will be pushing through tonight. Rain will not be an issue due to the lack of moisture and position of the system, although our northern county neighbors may see a few showers overnight.

From this mornings sounding, Thursday October 15, we can see we’ve been under some relatively dry conditions. Winds are fast in the upper atmosphere as an upper level trough is digging through the Ohio Valley. Analysis this afternoon shows that this front is pushing towards high pressure in the Southeast. This high pressure is what is stopping Gulf of Mexico moisture from flowing into the area. The front will push through tonight, and high pressure will take over the next few days. It’s a pretty strong pressure gradient between the front and the high pressure behind it meaning it will be a bit windy this weekend, but it will also be sunny as the sinking cooler air drives its way in.

Some showers are moving east in Missouri and into Kentucky this evening. They will extend a bit more south tonight, but Nashville will stay dry as the rain will affect areas just to our north. From the surface analysis, we can see the strong winds out of the northwest headed this way. Convergence of surface winds are what have created some showers to pop up just to our north. Temperatures are not vastly different right behind the front, but the next couple of days will be cooler as the colder air continues to flow in from the north. Drier air has extended across the Deep South due to the front that pushed through a few days ago, and so it has blocked moisture from naturally flowing up into the Southeast. This is why no rain will be associated with the current front for our area.

At the 850mb level, it’s more clear where the front is actually located. To be clear, 850mb is near the surface, but not right at the surface, therefore temperatures at the surface will be a bit higher than at this level. Areas of light blue coloring represent the freezing mark at 32 degrees. According to the NAM model over the next 48 hours, this cold air begins to creep its way towards us. The GFS model has us staying just above the freezing mark for Saturday and Sunday mornings, but it’s only by a few degrees. Areas that are more likely to receive their first frost include the more northern counties and the Cumberland Plateau to our east. Still, it’s better to be safe than sorry when it comes to protecting your plants and pets, as predictions can easily change, even a few degrees, over the next 24-48 hours. I recommend covering plants every evening this weekend until Monday morning. Conditions will be nice early next week as the high pressure settles in and sunny skies emerge, while temperatures will warm up into the low-mid-70s.

This is NOAA’s 3-month outlook for November through January. Temperatures are predicted be above normal for our northern and western states, but cooler for areas of Texas. For Nashville, temperatures will be at our normal average winter levels, but precipitation is predicted to be above average for most of the southern states due to the strong El Nino. Although Nashville is in the “equal chance” zone, it’s closer to above average moisture, therefore the ingredients will be in place for possible winter weather events.

-Merritt Turner