7/23 - 1:15pm - Heat Continues, No End in Sight

The entrenched heat we've had over the eastern half of the nation has been making headlines for quite some time now and it appears that it will continue for a while more. The strong ridge of hot, stagnant air is staying firmly in place and most forecast models are keeping it over the same area for at least the next week or two. A big portion of the Plains, Midwest, and East Coast is covered in heat advisories and warnings, which you'll see shaded in orange and purple on left.

Around Louisville, temperatures are going to stay in the 90's for the foreseeable future. For some perspective, we're hotter right now than Jackson, MS, Birmingham, AL, Memphis, TN, Jackson, TN, and Nashville, TN. Cloud cover, surface winds bringing in cooler air, and easterly flow aloft is keeping these locations cooler than Louisville even though they're all to the south. This really highlights the Midwest and Plains as being the primary target for the heatwave since we have been and will continue to be feeding off of the entrenched hot air from those regions.

A few pop-up showers and storms are possible today in Louisville, but a bigger chance for storms comes tomorrow as a "cool" front approaches the area that will cross through on Monday. I think tomorrow afternoon and evening will be the best time period for storms, most likely lasting into the early part of Monday. Behind this "cool" front temperatures won't really drop much, but dew points will take a tumble.

Check out the dew point output from the GFS for early Wednesday on the left. Those dew points are a good 15 degrees lower than the average this week and that translates to markedly lower humidity. That won't last long though... higher dew points with the same old hot temperatures will be back before the weekend. Until then, remember that an Excessive Heat Warning continues for the Louisville area until Sunday night. Stay safe!

7/21 - 2pm - Enough Excessive Heat to Go Around

93° in Louisville is hot on its own, but when you couple that with a very high 77° dew point (which puts relative humidity at 60%), you're talking about a heat index of 107°. We're well on our way to a high near 97° this afternoon. It's just hot. An Excessive Heat Warning, on left shaded in purple, remains in effect for the entire Louisville area until Saturday night as heat index values soar past 110° during the maximum heating of the day. Regardless of where you're from and the weather you're used to, your body cannot sustain itself in the hot, humid air we have in Louisville and much of the Midwest right now. Be sure to drink plenty of water and limit your activity outside this week to avoid heat-related illness.

Heat Index?

NC State Climate Office

I've been mentioning the term heat index for weeks now, so what exactly is the heat index you ask? Most people know it as the "feels like" temperature or what it feels like because of the humidity. That's basically it in a nutshell, but there's more to it. Mathematically, the heat index is a product of an equation that uses temperature and relative humidity. Factors like perspiration and body size averages are held constant, so the heat index is an educated guess at the "temperature" that most people are feeling. Don't let the "educated guess" usage fool you though, because higher humidity and in turn heat index values lessen the amount of evaporational cooling on your skin. If your body can't cool properly through this evaporation, you can overheat quite easily. It's interesting and useful to note that heat index values are based on what it feels like in the shade. Being in the sun can increase the heat index by up to 15°. Below is a table from NWS Pueblo, CO with heat index values and associated heat disorders:

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With the heat we'll have a chance for afternoon scattered storms, which will increase significantly as we get closer to the passage of a cold front on Monday. Today's storms have been and should be staying south of Louisville, so we'll see no relief from the heat today!

7/18 - 12pm - Heat, Storms on the Way this Week

Many areas across Louisville saw heavy rain yesterday as scattered storms slowly made their way through the area. A setup like that will likely happen this afternoon as well with storms again coming from the north. Any chance of severe storms will stay to our north as the ingredients for this will be in better supply. Look for a high just over 90 degrees this afternoon in the city and a degree or two lower in the suburbs.

Disturbance over IN at 700mb

Tomorrow will be a different story. A small upper-level disturbance will be swinging our direction around a high centered in the Midwest. This should spawn an MCS (Mesoscale Convective System - a big complex of storms) in the afternoon that will move our way from the northwest. The whole evolution of the MCS and exactly who it will affect most is still murky at this point, but it seems the parameters for severe weather will be in place and the SPC has issued a 15% Slight Risk for the region. Damaging winds from bowing segments and even a few spin-up tornadoes are possible with this MCS tomorrow, so be on the lookout for warnings as they're issued.

Let's not forget about the heat! The National Weather Service has issued an Excessive Heat Watch along and west of I-65 from Tuesday afternoon to Friday evening due to heat index values reaching up to 110 degrees. Actual forecast highs in Louisville will be in the mid to upper 90's throughout the week, so get ready for an extended heat wave. Humidity won't be as extreme as last week, but even so we'll be seeing dew points getting into the mid 70's near the latter part of the week. Uncomfortable humidity starts with a 60 degree dew point, so you can imagine that mid 70's are pretty bad!

7/12 - 10am - Another Day of Incredible Heat

Here we go again. It's already 87° with a dew point of 81° in Louisville and we're just getting started. See that condensation on my door to the left? That started at 10pm last night when the temperature dropped a couple degrees and just now cleared up with sunlight and a bit of heating. That's some crazy humidity right there. I think we'll get near yesterday's high of 97 again today, but like yesterday the dew point is the bigger story. With such a high temperature and high dew point in the low 80's (which is almost unheard of in Louisville), heat index values will be exceeding 110° again. An Excessive Heat Warning has been issued that goes from 11am this morning to 8pm this evening.

...But wait! There's more. We're under a Slight Risk from the Storm Prediction Center for severe weather this afternoon as a cold front approaches the area from the north. This is mainly a wind threat (notice the 30% wind risk red area on the right), but there's also a small chance for hail. A lack of wind shear and helicity (turning of the atmosphere) will eliminate any tornado threat for the most part. This front should be the trigger for some southward-moving clusters of scattered storms this afternoon. With all the heat energy and moisture in the area, there's no question that some of these could reach severe limits as the SPC indicates. Not everyone will see storms this afternoon, but those who do will receive quite a bit of rainfall, lightning, damaging wind, and a break from the heat. The cold front is positioned just south of Indianapolis right now and is moving fairly slow, so there will be quite a bit of time for storms to fire today and tonight before the front passes through sometime early tomorrow.

7/11 - 6:45pm - It's So Hot You Can (sorta) Fry an Egg!

It's 96° outside in Louisville with a heat index of 114°, making this the hottest day of the year so far. This got me thinking: Is it hot enough to fry an egg outside? I grabbed an infrared thermometer (measures temperature without having to make contact with the surface) and did some tests to see how hot various surfaces around my house were. The wooden deck was 149.3°, the tan concrete of our patio was 130.6°, and our driveway was 129.5°. While all very hot surfaces with direct sunlight, the deck was a clear winner.

Now to the egg frying part. I didn't want to fry an egg on the surface of the wooden deck because it may stain it. So, I put a metal cookie sheet right on top of the deck surface. This not only protects the deck, but easily heats up in the direct sunlight. After a few minutes in the sun, the temperature of the cookie sheet with non-stick spray applied about equaled the temperature of the deck surface.

Since the refrigerator at my house was void of eggs, I poured out the one-egg equivalent of egg beaters, the made-from-eggs substitute that you find at the grocery store, into a measuring cup. This may have thrown my results a bit, but hey, this is supposed to be fun right? Once the cup of egg beaters warmed to the ambient air temperature (around 96°), I poured it out on to the cookie sheet.

The results were interesting. I spread the liquid eggs around on the pan to resemble a flat pancake or crepe to increase surface area for heating. After a few minutes the edges of this "pancake" turned crispy and the middle became a thicker liquid with solid "chunks" (yeah, don't read this if you're getting ready to eat dinner) embedded in it. The surface of the deck was cooling down just before five o'clock, so this marked the end of the experiment. Had the temperature outside been a little hotter, and hence the deck a little warmer, it could have cooked more thoroughly. The temperature of a safely cooked egg is about 160°. Check out the video below to see the end result:

Today felt so hot because the dew point was near or at 80° for a good portion of the afternoon. That's a rare occurrence and signals the presence of an intense amount of moisture in the air. Humid is an adjective that doesn't even describe how it felt. Tomorrow should be almost as hot with the high topping out near 93 and heat indices near 110. This has prompted the National Weather Service to issue another Heat Advisory from 1pm to 8pm tomorrow. A "cold" front accompanied by a little southward dip in the jet stream (a trough) will increase scattered thunderstorm chances tomorrow afternoon in Louisville. The Storm Prediction Center places us under a Slight Risk for severe weather, mainly due to the threat for some hail and strong winds. The chance for storms could continue into Wednesday morning as the front passes through, but the lack of surface heating should suppress most of the development. We should dry out for the rest of the week with highs near 90. Stay cool out there!

7/10 - 3:30pm - Heat Advisories and Warnings

The hottest days of summer are yet to come, with today and tomorrow being just the start. A ridge of high pressure has locked itself into the eastern half of the nation, and many are feeling its hot and humid effects. It's 91° at Louisville International Airport, 88° in the southeastern suburbs of Louisville, 91° in Bowling Green, KY,  and 95° in Jackson, TN as of 3pm EDT/2pm CDT. Doesn't take me to tell you that those are some hot readings! Areas near the Louisville area have been placed under a Heat Advisory until 8pm tomorrow while areas to the west of Owensboro have been placed under a more strongly-worded Excessive Heat Warning. Highs in Louisville could reach near 96° tomorrow with heat indices ("feels like" temperatures) up to 110.

Most of West Tennessee is under an Excessive Heat Warning until tomorrow at 10pm. Jackson could get up to 100 tomorrow with Memphis easily passing into the triple digits. Heat indices near or above 110 are expected, so limit your time outside if possible and drink lots of water.

As a trough and associated "cool" front dip down from the north, we should see chances for storms enter the forecast by Tuesday, which will help to break the heat a bit. While more scattered in Tennessee, Kentucky will likely see a good helping of storms during Tuesday afternoon and evening, some of which may be strong. The Storm Prediction Center has placed portions of Kentucky (including the Louisville area) under a Slight Risk for severe storms. I don't think there will be much, if any, of a tornado and hail threat from these, but gusty winds could present some issues across the region.

7/22 - 10pm - Could We Get Another Shot at 100 Degrees?

100 degrees might not be that far off as high pressure has settled into the eastern half of the country. As it draws up warm, moist air from the south over the next couple days, temperatures and heat index values will skyrocket. The National Weather Service in Louisville has issued a Heat Advisory from noon to 7pm for both tomorrow and Saturday in lieu of the heat and humidity. Temperatures both tomorrow and Saturday could get very close to 100 degrees and even hit it in areas influenced by the urban heat island effect (like downtown Louisville and the larger suburbs). As dew points get into the lower to mid 70's, heat index values will surge past 100 or even 105 over the next couple days. In other words, be careful and stay hydrated if you have to go outside anytime soon!

Relief will come in the form of a front on Sunday, which should bring us a chance for thunderstorms until Monday morning. Temperatures will stay in the lower 90's after that with a small daily chance of rain through the remainder of the workweek.

Tropical Storm Bonnie (formerly Tropical Depression Three) has formed off the coast of Florida and is expected to hit the South Florida Coast before heading out to the Gulf of Mexico. It should remain a tropical storm until it makes landfall somewhere near Louisiana according to both the National Hurricane Center and the spaghetti chart (a compilation of various computer model forecast tracks - see right image). We'll have to keep a close eye on any intensification of this storm, especially when it exits the Florida Peninsula and heads into the Gulf.

6/20 - 5:30pm - Summer Starts Tomorrow, but it's Already HOT!

After a nice week on the Gulf Coast in Florida, I'm back home in Louisville. There were no sightings of tar balls or oil between Destin and Panama City while I was there, but both were creeping closer to shore according to reports. That area is just too beautiful to be spoiled by such an environmental catastrophe. Let's hope the spill doesn't go as far as forecast and that the right solutions are found to clean up the mess that many in Alabama, Mississippi, and Louisiana are already dealing with.

It's 91 in Southeast Louisville right now, but when you add on the 72 degree dew point, it feels like 100 out there. A Heat Advisory is in effect until 6pm this evening, but I'm sure we'll see quite a few of those issued this week. Our average high temperature in Louisville for this time of year is 84 degrees, so we are definitely quite a bit above average. With high pressure and southerly winds in place, that heat will stick around for quite a while. I'd like to point out that summer starts tomorrow and we've already had quite a few days in the 90's already. Looks like we could be in for a scorcher of a summer!

Severe weather is cranking up across Kansas right now and Nebraska is in line for some later this evening. Parameters like instability, surface winds, and EHI are looking ripe for supercells with tornadoes possible. The SPC has issued a 10% risk for tornadoes and a Moderate Risk for severe weather across the Northern Plains, so the storm reports could be quite interesting as they come in this evening.

6/23 - 3:30pm - Hot Weather, Storm Chasing Videos and Photos

92 may not sound too bad, but couple that with humidity and you have quite a scorcher! We'll be in the 90's for the rest of the week, with heat indices soaring above 100 on Wednesday and maybe thereafter. The computer models are now putting rain in here on Thursday afternoon as opposed to Friday and they've gotten rid of the weekend rain completely. We'll see if this holds up on the next few model runs.

I just posted a new page at ryanweather.org with pictures and videos from my storm chasing trip. Click here to view it.

6/11 - 3pm - Not Too Bad Today!

Temperatures right now are holding in the upper 80's and dew points are in the mid 40's. That's not so bad is it? 90's are expected tomorrow with 80's and some rain for Friday and Saturday. It won't feel too hot since the humidity will be lower than last week.

A question was raised about the relationship between humidity and dew points and I'd like to clear that up since we're heading into the time when this is pretty crucial for heat index. The dew point is the temperature where the air is completely saturated. For instance... If the temperature is 90 degrees and the dew point is 90 degrees, then the air is completely saturated... no more water can be added or else the water in the air will condense (that's why its the DEW point, the temperature where dew forms on the grass). This also means that the humidity is 100%, which does make the air feel heavy and sweat on your body cannot evaporate, thus making it feel hotter than it really is. The higher the humidity, the less sweat can evaporate from your skin into the surrounding air. If the temperature is 100 degrees, but the dew point is 80, then the humidity is at 80%. To give you an idea how dew point feels, 65-69 feels oppressive, but anything over 70 is just unbearable.

So... Humidity is just a ratio of temperature and dew point. Humidity influences heat index (how it really feels outside), and you can find charts relating heat index and humidity on the web. That's my weather sermon for today...

I'll be at the Bonnaroo Music Festival in Manchester, TN this weekend, so this will be my last post until Monday or Tuesday. Stay cool!

9/6 - 9pm - Weather or Not...

Alright, so there's a big area of disorganized shower activity and a low just off the coast of Florida and Georgia. This thing is just drifting around in prime development waters just waiting. There's a pretty good bit of shear associated with an upper level jet that's almost ready to bug on out of New England, and I think that's when this thing is going to go tropical. The models don't know what's going on because of this jet being so finicky and thus they can't seem to get strength or placement for this next storm right. So by this weekend, once a ridge builds and the jet clears, we've got ourselves a tropical storm, possibly hitting the Carolinas.

Tomorrow is our last day in the 90's for the whole year! Then we'll have a rousing round of storms this weekend that will lead to upper 70's for highs next week. That's right, 90's to 70's in one week! Here's the new motto for Kentucky that I made up in place of "Unbridled Spirit": "Kentucky, where seasons change in less than a week." Pretty accurate, eh? It always seems that we don't have any buffer time between seasons. It's always ridiculously hot or freezing. No such thing as "warm" or "mild" in the Ohio Valley. But of course that's an exaggeration.

8/9 - 5pm - Last Day of Triple Digits (for now...)

Yes, it will not break 100 tomorrow like it has done for the past few days! We will instead turn down the humidity and temperature down. How does lower 90's sound?

Yet we are not done with triple digits. I think by this time next week we could be seeing more of them as another pesky ridge sits on us. This one should feel the same as the one we're experiencing now and last a couple days. As for now, my thermometer reads 99 degrees at home and the airport is sitting at 101. We may even see some storms tonight as we get the cold front in here, which is the catalyst for this break in heat. I think it will be widely scattered at best though.

8/8 - 5pm - 102 Degree Record Tied

We have tied the 102 degree record for this day back in 1930. Wow. I can't believe we're seeing multiple days in a row with triple digit temperatures after years without any. My home thermometer topped out at 99.7 degrees today because I live in a suburb with a lessened heat island effect. But still, 99 is HOT! I can't remember a time in Louisville in the past decade when it was this hot for this long, although it has happened before. Breaking two records yesterday (for the highest high and highest low temperature) was also unfathomable. Tomorrow promises more of the same, but we will "cool" down into the lower to mid 90's for the weekend. The heat index for tomorrow will breach 110... Yuck. I don't know if I can bear this much longer. It is so hot that I start sweating the minute I open the front door!

8/7 - 5pm - HEAT INDEX OF 108!

That's right everyone, tomorrow's heat index is going to push near 110. The NWS has issued a Heat Advisory for today and probably will stay in place for at least two more days. The high for tomorrow WILL breach 100. Period. I don't care what kind of humidity or heat index you factor in, because 100 degrees alone is just awful. Here's my advice: Stay indoors after 11am and don't come back out until after 5pm. We will get a break from this heat after Friday, but you can't really call lower 90's relief...

8/6 - 4pm - 96°

My weather station is showing a blistering 96° right now. Humidity is reading in at 41%, which puts the heat index at around 103°. Here are the current readings (updated every 5 mins):

6/4 - 9am - Things to Watch for This Week

Since I'll be gone this week, here are a few things to look out for this week in terms of weather. Number one is severe weather. Friday and Saturday look like our best chances for severe weather, according to the SPC. After cringing and waiting for this severe weather season, I think this could be the real kick off. Luckily, it looks like more of a wind/hail threat right now than a tornado threat. Of course the minute we get severe weather, I'm not here to do my video coverage...

The second thing is rain later today. I think some areas may get more than a quarter of an inch. Like the rain yesterday, which went east of here for the most part, it will be hit and miss. I think Louisville will make out better today though, at least I'm hoping.

The third and final thing to look out for is the heat. As I mentioned in my video forecast, we could have a heatwave on our hands by late this week. I think at least Thursday, Friday, Saturday, Sunday, and also Tuesday through Thursday next week will be in the 90's. Unfortunately the humidity is also going to skyrocket next week too. So we may have to pull out a word I've not used yet in the six month history of this blog. Heat index.

Well, I hope for the best in Louisville while I'm gone. When I come back, I'm hoping everything (like the trees in my backyard and the shingles on my roof) is where I left it.