April 18th Severe Weather Potential

Keeping in mind yesterdays Storm Prediction Center Outlook for Day 1 had a moderate risk area and a 15% hatched area for tornadoes ..The storm reports look like this so far...

Not one tornado was reported for the day thus far. 

The above is our outlook for today the 18th. Once again the red zone is where we think the greatest risk of severe will be based off the NAM/SREF and ECM ..and also would be the area that would have a chance of a Tornado.

A stationary front goes from off the coast around the carolinas back towards the west across Ohio to Illinois to a low pressure on the Kansas /Missouri border to another area of low pressure around the panhandle of Tx with a cold front trailing off to the SW.. 

The stationary front will lift north as a warm front and the low pressures will move to the NE and  in doing so a cold front will be marching to the east. It is this cold front that will be responsible for another day of severe weather across parts of the USA..
The timing of this cold front looks to be around 06 Z or 2 AM EST (1 AM CDT) across western KY and TN and closer to 8 AM friday morning EST (7 AM ) for central and Eastern Areas of KY and TN..

Due to the timing of this front we think that places in Western to Central KY and TN will be dealing with more in the way of Garden Variety type thunderstorms and heavy rains then actual severe weather. There could be some isolated severe in those regions which would be in the form of gusty winds with the front and possible hail..

12 Z ECM has no CAPE across any of KY or TN and CAPE is one ingredient necessary for severe weather. However ...lets take a look at the severe weather parameters from the NAM..

CAPE is generally 500-1500 which is on the meager side. Generally when one thinks of a severe outbreak they would like to see CAPE in the 2000 + range..

Lift index will be about -4 to -5 but greater across the south around Louisiana 

Shear depending on what time of the day will be 30-50 knots and 60 + knots down across eastern TX but the greatest shear will be further to the west where 90 + will be. 

Helicity a thin stripe stretching from N to S which is in the 500 range ..

EHI +1 or higher again allocated fairly well with the higher Helicity. Now keep in mind this image is at 5 PM in the afternoon ..so those that are in central and western KY and TN are not really dealing with any precipitation at that time frame as the front does not arrive till the overnight hours and by the time the front does arrive the EHI looks like this..

Well below 1 except for locations further to the south .. 
Finally temperatures will be in the 70s and 80s..

So in summary the greatest parameters are actually to the west and south of KY and TN  so we have put the greatest risk to allocate with the greatest parameters. As the storms move towards the east with the cold front they will be going into parameters which are not really conducive for severe weather and with the timing of the front and the heaviest precipitation any storms should weaken and the main threat would be garden variety thunderstorms with heavy rains. In areas to the west they will be looking at Gusty winds along with Large Hail and the potential for tornadoes...