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Small Talk
A Weather Forecasting and Analysis Blog
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How does a Meteorologist Calculate Heat Index?
The difference between temperature and heat index is quite literally YOU! Heat index take into account how hot it actually feels outside on a given day when relative humidity is taken into account. This is where the term ‘dry heat’ came to be. It is also why 90 degrees in the middle of Nevada feels nothing like 90 degrees in Eastern Oklahoma in the middle of August.
To better understand what the heat index means we first have to understand how our body cools off on a hot summers day. It’s a hot day, the temperature is 96 degrees and let’s say relative humidity is at 50%. You walk outside during the afternoon to walk the dog, work in the yard, or whatever your summer loving heart desires. Naturally, what does your body do? You sweat… you probably start sweating a lot. Your body is trying to cool you down! Sweat releases moisture onto your skin and it evaporates. Evaporation is a cooling process! When sweat evaporates from your skin it takes a little bit of your body heat with it.
Here is a great visualization on types of heat transfer!
This brings us back to our hot and humid summer afternoon. The problem is that sweat will evaporate (cool you off) at a much quicker rate in drier air. With higher humidity already in place, there isn’t much more room for additional water vapor molecules. This is why you have probably grown up hearing the phrase “warm air holds more moisture”. In addition to the already humid air around you, and when the sweat does begin to evaporate, an aura of even higher humidity builds around your body from the process. This makes it even harder to cool down. Getting rid of the air the immediate forms around you plays a role in how you feel as well. This is why a fan works, or why a breeze feels so good on a hot summer day. The hot and humid aura you are beholding from your body’s defense mechanism to battle the heat is being swept away and cleared for new evaporation processes to more easily take place.
As for calculating the actually number that we warn you about in our forecast. There is a nifty calculation that was taught to me back in my undergrad at Mississippi State University. it goes a little something like this, where (HI) is heat index:
HI = -42.379 + 2.04901523*T + 10.14333127*RH - .22475541*T*RH - .00683783*T*T - .05481717*RH*RH + .00122874*T*T*RH + .00085282*T*RH*RH - .00000199*T*T*RH*RH
Thankfully it can more easily be explained by this chart.
Take our air temperature of 96 degrees from the beginning of the article and match it up with our given relative humidity of 50%. Where they meet will give you the current heat index, or ‘feels-like’ temperature of 108 degrees. This graph also shows that even when temperatures remains the same, heat index can vary significantly by manipulating the moisture in the air.
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Lightning Facts and Safety
You may be familiar with the phrase, "When thunder roars... Go indoors!" That is because Lightning can travel up to 25 miles away from its parent storm. Meaning… it doesn’t have to be raining, or a dark cloud doesn’t need to be directly above your head for lightning to become a threat.
You may at some point have been told to get out of a swimming pool after hearing thunder from an approaching storm.
Why is being in water so dangerous in this situation?
Water is a great conductor for electric current! The same goes for metal, which is why you may have also been told to move out of a ballpark or stadium until the threat for lightning has passed.
Lightning tends to always strike the tallest object in an area. This mean it is best to stay away from tall trees, goal posts, soccer goals, or bleachers. You yourself also do not want to be the tallest object in the vicinity. Stay out of open fields, ridges, and hills.
What about your car? Is a car safe?
Actually, YES.
If you are out on the water, you should seek shelter on land, immediately, and under shelter or in a hard-topped vehicle.
Why exactly is lightning so dangerous?
There is an incredible amount of electricity flowing through that bolt, and the temperature of lightning is nearly 50,000 degrees F. That is five times hotter than the surface of the sun!
According to the National Weather Service, nearly just as many people lose their lives to lightning strikes as they do tornadoes every year. Lightning related deaths just receives less publicity because they are only happening to one, maybe two, people at a time per event.
Naturally the states with the highest amount of lightning fatalities area going to be the states that experience the most thunderstorm activity, mainly in the southeastern U.S. Louisiana and Florida are leading the country in lightning related deaths.
With a few exceptions, generally the further north and west your travel, lightning deaths become less common, mainly because there are less thunderstorms!
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Heat Advisory vs. Excessive Heat Warning
Oklahoma is no stranger to the heat during dog days of summer. On average our high temperature for the months of July and August run at a whopping 93.1 degrees. These are our warmest months of the year. Tulsa’s highest temperature ever recorded for the month of July is 113 degrees and 115 degrees for August. Both of these records were set in 1936.
When temperatures soar, you see our 2 Works for You Weather team broadcast bright colors across the counties of Northeastern Oklahoma stating ‘Heat Advisory’ or ‘Excessive Heat Warning’!
What does that mean? Should you be concerned? Why should you care?
Let’s begin with where these terms originate from. These watches and advisories are put out by local National Weather Service offices. Criteria for each varies from state to state. For example, we are much more capable to handle 90+ degree weather here in Oklahoma than our good friends in Alaska. This is where that variance of knowing when to alert people about dangerous heat comes into play. It also highlights the importance of having local NWS offices.
Oklahoma Heat Advisory Criteria:
- Issued within 12 hours of dangerous heat conditions
- Maximum heat index values reaching 105 degrees on at least two consecutive days
- Low temperatures of 75 degrees or higher
Oklahoma Excessive Heat Warning Criteria:
- Issued within 12 hours of extremely dangerous heat conditions
- Maximum heat index values reaching 110 degrees on at least two consecutive days
- Low temperatures of 75 degrees or higher
*An Excessive Heat Watch may be issued if this criteria is forecast to be met 12 to 48 hours in advance*
What precautions should YOU take under a Heat Advisory/Excessive Heat Warning?
When dangerous heat lingers for more than a day, and overnight lows don’t provide much relief, our bodies struggle to cool down. This is especially true for those without air conditioning. During a Heat Advisory/Excessive Heat Warning conditions are in place for the onset of heat exhaustion or a heat stroke. This could lead to illness or even death.
Precautionary measures include:
- Wear loose fitting clothing
- Avoid long strenuous hours of working outdoors
- Drink plenty of water…Don’t wait until you are thirsty. Stay hydrated throughout the day!
- Limit caffeine intake
Caring for others is just as important during these times. The elderly, children, and pets should always get a little extra TLC during this time.
How to help?
- Check on elderly neighbors frequently. Be sure they are safe and staying cool!
- Provide your children with lots of water
- Look before you lock! Leaving children in a hot car is deadly.
- Do not leave your pets in the car either!
- Do not walk your dog on the hot sidewalk where they could burn their paws. Reminder: You are wearing shoes, they are not! Provide them with a grassy area.
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Things to do in Green Country this Summer: Turkey Mountain Urban Wilderness
Looking for a outdoor getaway right here in Tulsa? You can escape the hustle and bustle of the city, without leaving the city! Located just across the across the Arkansas river from the beautiful Tulsa skyline you will find over 300 acres of scenic routes and lush undeveloped property. Along with the marked trails that Turkey Mountain provides, there are also 25 miles of unmarked trails that also span across the urban wilderness. The bluff rise from 300-920 feet above sea level giving you excellent views of the city while standing in an urban oasis.
I consider myself a go getter and an adventure seeker, but when it comes to hiking, I like to stick to a path. The last thing I need is to be wondering aimlessly in the woods in the heat of an Oklahoma summer afternoon. Direction is a good thing, and these trails have a lot to offer! Here are the loops that Turkey Mountain provides:
Red:
The red trail’s 0.8 mile loop is great for beginners. It is a mostly flat, even, and figure-eight shaped trail that begins at the trail head and simply loops back around.
Blue:
Looking for a bit more of a challenge? The blue trail ups the mileage to 1.5. Though this loop you will go up steep hills while making your way to the very top of Turkey Mountain. Expect to see a small pond about a third of the way into the hike. Then, back downhill you go to the trail-head!
Yellow:
No one taught me the ins and outs of Turkey Mountain when I moved here. So… what was going to be my short afternoon stroll with my dog Stratus turned into this 4.4 mile long loop! I really thought I was lost halfway through, but nope, it is just a lengthy hike with lots to see. The yellow trail runs along the eastern side of the mountain towards the Arkansas River. For the majority of the hike you will be parallel to the water, traveling north. After reaching a sharp turn, you slowly make your way back south towards the trail-head.
Pink:
If you consider yourself quite the hiking expert or have a lot of time to spare, then the pink trail might be for you! This 5.7 mile trail is the longest marked trail that Turkey Mountain offers. You can access this trail from the blue trail if you want to adventure over to the western side of the mountain. This is where views of the sunset are ON POINT! If you don’t mind a lengthy hike this zig-saggy trail is highly recommended.
While trekking through the lush greenery you may come across many common trees of Oklahoma such as blackjack oaks, post oaks, and pines. Don’t be alarmed by the woodland animals that call Turkey Mountain their home. Crossing paths with deer, fox, coyote and raccoons is not uncommon. You can also sort an array of local birds while you’re among the trees. Given the proximity to the city, you may also see some remains of Tulsa’s rich oil industry. Old piping, fountains, and coils can be spotted from when there was oil activity on the mountain itself. Don’t think of it as litter, but a little blast from the past!
Before you go!
-Bring lots of water
-Snacks may be needed if you plan on hiking the longer trails
-Restrooms are provided at the trail-head
-Dogs ARE welcomed!
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Meridian, MS
Beautiful weather took over for your Saturday afternoon, but as we go into the evening hours cloud cover will start to build in fairly quickly. Towns in Northwest Mississippi are already beginning to see showers this afternoon. The rain we be delayed until after sunset for Meridian and other areas in Southeast Mississippi. Showers and dense cloud cover moving in tonight will inhibit our low temperature from dropping below the upper 50s. Tomorrow rain becomes more wide spread and thunderstorms are likely to develop. Some of these storms do have the potential to be severe. The majority of Mississippi is put under a marginal risk for severe thunderstorms tomorrow. Sunday highs will reach the lower 70s and lows in the mid 50s.
The start of your work week continues to stay unsettled as Monday continues to stay overcast with a 20% chance of showers. Highs will remain in the lower 70s. Clouds stay put for the evening and into the night as well, lows will drop into the mid to lower 50s. More rain chances are predicted for Tuesday with a high in the mid 70s. Tuesday night remains partly cloudy with lows in the lower 50s. Rain chances continue for Wednesday as well, except we can expect to see more breaks of sunshine through the day. Highs will reach mid to upper 70s and lows will drop near 50. Overnight on Wednesday and into Thursday morning another batch of showers make their way through. These should pass before noon on Thursday, leaving us with mostly sunny skies and highs in the mid to low 70s. Lows for Thursday night drop into the low 50s.
Friday will be the same set up with mostly sunny skies and and 30% chance of rain. Highs will be in the upper 70s and lows in the lower 50s. The start of your weekend is looking nice! Saturday expect sunny skies and highs in the upper 70s. Some spots may reach near 80. Lows for Saturday night will drop into the lower 50s.
For the most part we have been staying below average for the beginning of spring. Models are showing the next big warm up to happen the first week of may.
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Until then, plenty of sunshine is on the way throughout the rest of the week with the exception of a light shower on Monday for central and southern MS regions.
Mesoscale products not picking up on showers expected in MS for Monday morning.
Hot, Cold, and Severe Weather? -MS
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Auburn, AL
A rainy week is in store for Auburn, AL. Rain chances persist well into next week. Drought-wise this is a good thing considering all of Alabama is placed under a notice whether it’s just abnormally dry or an extreme drought warning. After the rain events this upcoming week this expected to improve the drought conditions as well. The showers seen so far this past week have already taken central Alabama out of the Extreme drought that they were experiencing.
Tomorrow is going to be the last time that Auburn gets to see a mostly sunny day for quite some time. Right now the air is very dry. There is a lengthy flow of dry air aloft which is feeding into the dry and clear conditions that will be seen tonight.
This changes come Saturday, that dry air is displaced and there is more moisture thought the atmosphere over Alabama and all of the southeast as well.
Looking at the placement of the front that will be pushing through it directly aligns with the boundary of dry and maritime air coming out of the gulf. This will increase rain chances significantly as it moves through Saturday night and into Sunday.
The LI values will increase Friday night and into Saturday. This instability in the atmosphere will give way to more of those scattered changes of rain throughout the weekend.
Friday: 40% chance of light showers. No heavy rainfall starts until Saturday night. Lows will be around 52 degrees. Staying very mild as clouds move in overnight.
Saturday: 90% chance of rain with a high of 68 degrees. Lows are only dropping into the upper 50s. Very warm for an overnight low, but the winds out of the south will bring a nice warm trend overnight and into Sunday morning.
Sunday: 80% chance of rain. High of 71. Again, those south winds are really heating things up.
Overnight on Sunday, expect a low around 56 degrees. Rain still hanging around for the overnight hours.
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Snowshoe, WV
Through this geo-color image, you can see the large system that passed through Mississippi this weekend continuing to make it way eastward. Also it looks that the system has strengthened once it tapped into the Gulf’s warm and humid air mass. This sparked more convective uplift strengthening the system as it moves along the east coast.
This cold front has already passes through Snowshoe and lowered the temperatures. Tonight as they drop into the lower 20s, an upper-air trough, pictured in the mid west above, will move into the area and conditions will be suitable for winter precipitation.
Early Tuesday the 500mb chart is showing that the trough will continue to dig and amplify as the day goes on with areas of the best positive vorticity around Eastern Tennessee, Eastern Kentucky and Western West Virginia. Later on Tuesday we begin to have more positive shear voticity. Vorticity maximas are now moving into the right side of the trough, which is an indication that the trough will deamplify and lift.
At the 700mb level the system is driven by PVA.
With the 850mb level. There is a very tight gradient passing over West Virginia. There is definitely cold air advection taking place indicating a cooling trend. There is also strong thermal advection where wind vectors are blowing across the tight thermal gradient as the trough digs into eastern West Virginia.
Enhancing frontal development Tuesday morning, negative vertical velocities. The vertical velocities are supportive of convergence, and lower level development. We can expect pressure falls over eastern West Virginia again strengthening those chances for snow as the track moves over the area.
The snowfall expected out of this system is around 2-4 inches. I would predict more, but the air mass coming through is very dry, and moisture will be limited by this type of artic air mass. Temperatures will also be dropping down into the frigid single digits, around 7 degrees.
Another factor to take into consideration when forecasting snowfall in this area is the topography of West Virginia. Upslope snow will play a part in different totals throughout the area. This is an effect of moisture in the lower lying area being forced up a mountainside condensing simultaneously. This causes precipitation to form on the upslope of the mountain.
This is an elevation map of west Virginia to get an idea of where the higher elevations are and how that can effect where the higher snowfall amounts will take place. Back to the previous image, the higher elevations correspond to the 4-5 inch range while just to the west where elevation decreases by nearly 4,500 ft., those cities can expect closer to 2-3 inches. Snowshoe is in the areas of higher elevation, do they can expect those higher snowfall amounts.
Snow will continue throughout tonight and into Tuesday. Tuesday night will be the start of the clear up and sunny skies start Wednesday. Tuesday night however will be a blustery one wind chills will be in the negatives.
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New Orleans, LA
1/20/2017
High pressure is currently dominating over the Southeast bringing in a nice defrost to areas seeing frigid temperatures at the beginning of the week. The south is “something else” when it comes to winter weather places are finally recovering from winter related closures and damages. New Orleans is one place in particular that is looking forward to the weekend warm up. With the center of the high shifting to the east, the winds will become southeasterly as well moderating the temperatures and also bringing in moisture from the gulf. This will also increase the chance of rain this afternoon to around 50%. Dew points are also above what they had been earlier in the week, again due to the surge of moisture being brought in by the Gulf of Mexico.
Temperatures are also back into the mid 60s, where most locals prefer them to be at this time of year. So this is a usual set up in south Louisiana, warm temps, high dew points, and convective afternoon scattered showers. By tonight any rain should be long gone leaving a partly cloudy evening ahead. Lows will not drop off much at all due to the excessive moisture and cloud cover not allowing for effective radiational cooling. Expect a low around 55 degrees for tonight. Fog will also be an issue for tonight until Sunday night. Waters are still cool from the freeze this week and dew points are surpassing water temperatures allowing fog to form over ponds/ lakes/ coastal areas.
The southeast as a whole, not only New Orleans, is experiencing warm temperatures right now and the MJO is in correspondence with that as well being in the warm 4th ,5th and 6th phase.
Another cold front will be passing through on late Sunday night and into Monday morning. Thankfully not as strong as others we have seen so far this season, temperatures will drop by a near 10 degrees after all associated rain and cloud cover moves out. This will bring the high to around 57 degrees for Wednesday. Rain chances will be their highest on Monday morning.
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NYC, New York
A cold weekend ahead!
High pressure is currently dominating over the Northeast right now causing clouds to break up leaving clearing skies, and a mild Wednesday and Thursday with high temperatures in the mid to low 50s. This is right on average for this time of year in NYC. For today NYC can expect a decrease in cloud cover as the day goes on and a breezy wind out of the north from 10-15 mph. Lows for tonight do not deviate too much especially with having a partly cloudy night and being in close proximity to the water. The low will drop to 42 tonight with the winds still out of the north, shifting northeast as we go into Thursday. Thursday is when things become interesting for the city as the morning and afternoon are mostly sunny, but then winds shift to southerly and a strong artic front will pass through the area driving the temperatures down.
There is a trough set in the upper US shooting down cold Canadian air into New York by Thursday evening.
A very tight gradient in the Northeast which is a reason that NYC could see extreme wind gust as an artic air mass moves through.
An interesting even is going on for NYC as they may see record low temperatures for Friday night. The coldest recorded on this day was 30 degrees and both the NAM and GFS MOS are showing record breaking temps for this day. GFS and NAM are showing a low of 23 for Friday night into Saturday morning. The clear skies and light winds will really amplify the diabatic cooling processes and and really drop the overnight low temperatures. The chill continues for Saturday as well as a high of only 39 degrees will be expected. NAM MOS is predicting a little lower at 37 degrees, but it will be a clear and sunny day which could lead to efficient mixing and heating throughout the day, so I will go with GFS MOS for the high to be near 40 degrees on Veterans day.
A freeze warning will also be in affect for NYC as well.
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