8/7 - 5:15pm - More Storms in Our Future

Did the storms in Louisville wake you up this morning? I slept through them, which is probably a good thing because those that couldn't sleep through them early this morning sure looked tired today. Locations near Downtown Louisville saw rainfall amounts exceed one inch this morning, but most of the suburbs and outlying areas received under an inch. Click the image on the left from NWS Louisville to see a complete map of the rainfall totals from this morning. More storms are possible this afternoon and especially tomorrow as a cold front to our north provides a focus for development.

I've been watching the radar and satellite image for the past couple hours and it appears that ongoing storms dropping southeastward near Indianapolis may send out a some outflow boundaries toward Louisville over the next few hours. Outflow boundaries are like miniature cold fronts created by the cool air flowing out from a thunderstorm's downdraft. They also can cause storms to develop because they are a source of lift and that's why they're so important when forecasting short-term storm development. Since we have a little bit of wind shear and a very unstable atmosphere over the Louisville area right now, a kick from one of these southward-moving outflow boundaries may cause a few isolated storms to develop this evening. Storms may also form without the boundary if another small-scale feature or surface heating gets things going first. So, a vast majority of the area will stay dry, but if you happen to get under one of these wildcard isolated storms get ready for some heavy rain and wind.

There's a much better chance for storms tomorrow as a shortwave disturbance moves through the region. These storms will likely cluster together into an MCS (Mesoscale Convective System - complex of storms) and severe weather is possible. These scattered or MCS storms will roll through Louisville sometime tomorrow late afternoon or evening. Damaging winds, frequent lightning, and small hail will be the main threats from these storms. If they cluster together in a line, wind damage probabilities will be higher. The Storm Prediction Center has placed much of Kentucky, including Louisville, in a 30% Slight Risk area for severe weather tomorrow due to these factors.

8/4 - 11:30am - Finally, a Break in Sight!

Ridge breaking at 500mb on Wed.

The weather here in Louisville is about the same as when I left it last week on vacation in California! The good thing is that a cold front that came through yesterday will keep temperatures in the lower 90's today, as opposed to mid 90's for the last few days, and the humidity will be a little less oppressive. That said, daily afternoon storm chances will increase tomorrow and especially Saturday when an area of surface low pressure will pass right over us. That low and the accompanying cold front will finally begin the breakdown of this hot, humid ridge that we've been stuck under for so long, but not before some higher heat and humidity sneaks its way into the region for the weekend. Temperatures will be in the 80's next week as this pattern breaks, which could be temporary at best if some of the long-range models are to be believed.

So far we've had 40 days with highs at 90 or above in Louisville, with 18 consecutive days at 90 or above on our current streak. At this point last year we were counting 46 days in the 90's so far, so it seems this summer is a fairly close repeat of last.

Talk of development in the tropics has come to a fever pitch lately as Tropical Storm Emily seems to be taking a path that will pass very close to the southeast coast of Florida. The forecast path has been flip flopping around a little bit over the last couple of days, but at least right now it appears that Florida will not see a landfall from this storm. Emily has sustained winds at 50 mph, which is still a ways from the 74 mph needed to be declared a hurricane. The National Hurricane Center's forecast includes Emily reaching hurricane status by Monday well off the coast of South Carolina.

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 RyanHoke.com:

This video is available in 720p or 1080p HD

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!

7/16 - 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:

GFSX MOS (MEX)
 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!