Sunday, July 24, 2011

7/24 - 4pm - 2011 Great Plains Storm Chase Video

From May 7th to June 4th this year I had the privilege of again being a tour guide with Storm Chasing Adventure Tours, a company I've worked with for four years. We traveled well over 10,000 miles during my time in the Great Plains and saw numerous supercell thunderstorms with wall clouds and even a few funnel clouds. There were also a few episodes when we came very close to tornadoes, with one touching down right in front of us at night in South Dakota. Check out my "mini documentary" video of all the things I saw this year below or on my storm chasing page at

This video is available in 720p or 1080p HD

Saturday, July 23, 2011

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!

Thursday, July 21, 2011

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:

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!

Monday, July 18, 2011

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!

Saturday, July 16, 2011

7/16 - 11am - Heat Building Back In

Ridge over Central US on Wednesday
It's been cooler and quiet over the past couple of days in Louisville with temperatures around and just below 90. That's going to change fast though as a hot and dry upper-level ridge begins to build into the eastern half of the nation next week. Today and tomorrow don't look particularly bad with temperatures in the low 90's and a slight chance of some afternoon pop-up thunderstorms

Thursday Eve. temperatures (GFS)
By Monday we'll be talking temperatures in the mid 90's and not a chance of rain in sight. The warming temperatures aloft with this ridge will limit instability for thunderstorm development significantly. Surface features like fronts will also be very hard to come by once this thing moves over us, so there won't be a trigger for storms either. What this means is that while the heat is building in we won't have any relief via the normal summertime afternoon storms that form. The compounding of the heat and dry air over the course of next week could send our temperatures to the 100 degree mark for the first time this season. Humidity-wise next week won't be as bad as it was earlier this week with dew points exceeding 80 degrees, but dew points in the mid 70's, still very humid, are possible especially on Tuesday and Wednesday. Below is some raw data from the GFS MOS output, which is basically a combination of numerical and statistical weather models. This output usually runs a  degree or two on the warm side this time of year, but I've highlighted the warmest temperatures of the week in red and highest dew points in green:

 KSDF   GFSX MOS GUIDANCE   7/16/2011  0000 UTC                       
 FHR  24| 36  48| 60  72| 84  96|108 120|132 144|156 168|
 SAT  16| SUN 17| MON 18| TUE 19| WED 20| THU 21| FRI 22|
 X/N  89| 73  93| 75  95| 78  96| 79  98| 78  99| 78  97|
 TMP  85| 75  88| 77  90| 80  91| 81  92| 80  93| 80  91|
 DPT  69| 70  69| 72  70| 75  74| 75  72| 72  71| 71  70| 
 CLD  PC| PC  PC| CL  PC| PC  PC| PC  PC| PC  PC| PC  PC| 
 WND   6|  6   7|  6   9|  9   9|  9   8|  7   8|  7   8|
 P12  24| 13  14|  7   9| 19  40| 27  20| 12  25| 14  19|
 P24    |     19|      9|     40|     40|     25|     34|
 Q12   0|  0   0|  0   0|  0   1|  0   0|  0   0|  0    |
 Q24    |      0|      0|      1|      1|      0|       |
 T12  26|  8  32| 10  24| 37  49| 49  39| 29  28| 21  36|
 T24    | 30    | 40    | 50    | 71    | 49    | 44    |

Looks pretty hot doesn't it? A span of three or more 90 degree plus days is usually considered a heat wave, so I think we'll meet and exceed that definition easily. Next week will be a good time to take it easy and drink lots of fluids when working or playing outside. Here comes the heat!

Tuesday, July 12, 2011

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.

Monday, July 11, 2011

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!

Sunday, July 10, 2011

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.

Friday, July 8, 2011

7/8 - 3:30pm - Here Comes the Sun!

It's been a rainy one around Louisville today. The airport has had .45", my house in Southeast Louisville received .88", and Shelbyville got .72" of rain since midnight. Bullitt, Hardin, and Meade Counties in Kentucky all received well over an inch of rain, but Frankfort is the winner coming in at 2.13" since midnight. Check out some of the rain amounts since midnight in the map below from the Kentucky Mesonet. The clouds are still hanging around just east of Louisville, but Louisville and westward is seeing some sunshine. That trend should continue eastward as the afternoon goes on. There's a chance that some scattered storms could redevelop later today around the area, so a few locations could receive more rain today before the cold front triggering these storms moves south.

Sunshine and warmer temperatures will be the rule this weekend around Kentuckiana. High pressure will keep the clouds out of the picture through Monday and temperatures above 90 degrees are a sure bet until then as well. Monday will likely be the hottest day (low to mid 90's) in the near future before another front approaches the area and increases afternoon storm chances yet again.

Tuesday, July 5, 2011

7/5 - 6pm - Scattered Storms in Louisville

Hope everyone had a great Independence Day! Some scattered small thundershowers have popped up across the Louisville Metro area this afternoon with the heating of the day. These will likely stay well below severe limits, but watch out for some heavy rain and a few lightning strikes as they move very slowly through the city.

More storms like this are possible tomorrow afternoon through Friday with severe weather chances remaining very low. We should be completely dry this weekend in Louisville as a surface front slides to our south and an upper-level ridge slides in from the west.

Sunday, July 3, 2011

7/3 - 12:30pm - Fantastic Fourth Forecasts

A cold front sliding southward through Indiana and Kentucky this morning has triggered some thunderstorms in Southwest Indiana that likely won't make it to the Louisville area this afternoon, but more storms could develop later on. While any storm that forms this afternoon could have heavy rain, lightning, and some gusty winds, most if not all will stay below severe limits. Temperatures are already in the upper 80's around the Louisville area, so a high near 93 today looks good at this point.

How about those Fourth of July forecasts? Hot and humid will be the rule for most locations, but scattered afternoon thunderstorms covering quite a large area could drench a few of those outdoor barbecues. The storms will be large in coverage due to a trough hanging around the eastern half of the US and a stationary front near the Ohio River.

Here are some Independence Day forecasts for selected regional locations from the National Weather Service:

Louisville, KY: Partly Sunny | 89 degrees | 40% afternoon storms
Lexington, KY: Partly Sunny | 86 degrees | 40% afternoon storms
Evansville, IN: Mostly Cloudy | 87 degrees | 50% afternoon storms
Indianapolis, IN: Mostly Sunny | 85 degrees
Cincinnati, OH: Partly Sunny | 86 degrees | 20% afternoon storms
Jackson, TN: Mostly Sunny | 93 degrees | 30% afternoon storms
Memphis, TN: Mostly Sunny | 95 degrees | 30% afternoon storms
Nashville, TN: Mostly Cloudy | 92 degrees | 30% afternoon storms
Knoxville, TN: Partly Sunny | 91 degrees | 40% afternoon storms
Tupelo, MS: Mostly Sunny | 96 degrees | 20% afternoon storms
Starkville, MS: Mostly Sunny | 96 degrees | 20% afternoon storms
Jackson, MS: Mostly Sunny | 97 degrees | 30% afternoon storms
Birmingham, AL: Partly Sunny | 94 degrees | 30% afternoon storms
Atlanta, GA: Mostly Sunny | 94 degrees | 50% afternoon storms