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04/20/2017

Chance for Strong to Severe Storms Today

Severe Risk:

The Storm Prediction Center has issued a "Slight Risk" for severe weather for this afternoon and evening for our northern counties. A slight risk is defined by SPC as an area of organized severe storms, which is not widespread in coverage with varying levels of intensity. Majority of the rest of the viewing area, to the south, is under a "Marginal Risk".  This is the second lowest of six categories and is defined as an area of severe storms of limited organization and longevity, or very low coverage and intensity. 

Scattered thunderstorms are expected to develop this afternoon and evening.  The main threats will be isolated, damaging gusty winds, small to marginally severe hail and localized heavy rain. 

Image 1

Set up:

Surface low pressure has dropped south and is now centered between Northern IL and Southern WI and will continue to track east through the Great Lakes and will drag a cold front through the area tonight and significantly drop our temperatures by tomorrow and into the weekend. Say goodbye to the 80s! We are currently in the warm sector, which is a warm, moist air mass and I'm sure you have noticed! We are already in the 80s and the dew point is sitting at 60 degrees. That is enough moisture to develop strong to severe storms. 

Speaking of ingredients... 

Image 2

Ingredients:

Instability: Models are showing CAPE or Convective Available Potential Energy, a measurement of instability, around 1000 - 1500 J/kg during the afternoon. Which is certainly enough for strong to severe storms to develop.  The timing of the front is later than peak instability, but there will still be showers and storms at that time or 21z (the time of the image below), which is 5 pm. Models suggest that the instability falls slightly in the hours following.   

Image 3

As of 1 pm, as clouds begin to increase ahead of the front, a few pop up showers have developed as well. Checking SPC's Mesoanalysis Page, The current CAPE values are around 600 J/kg, which is not super impressive, but enough to produce a few thunderstorms. It is probably a bit lower due to mid/high level cloud cover over the past few hours. It will need to increase a bit over the next few hours in order to develop strong to severe storms.  Image 4

Below is an image of the mid level winds. It is showing them around about 25-30 kts. Sufficient for strong to severe storms, but it is not overly impressive.  The lack of wind energy will keep this from being a widespread severe weather event, but we cannot rule out a few strong to severe storms or two with this wind energy. The winds are unidirectional with height in the atmosphere and the best chance for tornadoes is much further north toward Northern Ohio and Southern Michigan.

Timing: 

As I mentioned above, we are already seeing a few showers and they will continue to increase in coverage over the next few hours. By 3 pm, scattered showers will be likely and the trend will continue through the late afternoon and evening. I should note, there is only a 60% for showers and storms. This means not everyone is going to see showers and storms. Scroll through the images of Advancetrack below to get an idea of the timing and coverage of storms for today and tonight. 

At 1

At 2

At 3

The front will push through tonight after the instability has dropped. Notice that not all areas will be created equal. Some will see more rain than others and other areas might not see a drop of rain. 

At 4

So what do I think?? 

I think severe weather is certainly possible today. The ingredients are not overwhelming, but there is certainly enough to produce a few strong to severe storms with localized damaging wind gusts and small hail.

A few more scattered showers and storms are expected tomorrow, but the data has been flip-flopping the amount/coverage/intensity for Friday. Plus, Thunder Over Louisville is looking like a wet one. Be sure to join Marc and Rick this evening on WDRB News to hear about that! If and when storm become severe, we will be keeping you informed in a variety of ways. One of those is on social media. The links to my pages are below! 

Katie McGraw's Facebook Page

Katie McGraw's Twitter Page

-Katie McGraw 

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