U.S. Severe Weather Forecast (Convective Outlook)

Heddiw
Tomorrow
Day Three

000 
acus01 kwns 201629 
swody1 
Storm Prediction Center ac 201628 


Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1128 am CDT Fri Jul 20 2018 


Valid 201630z - 211200z 


..there is a moderate risk of severe thunderstorms over parts of 
northern/western Tennessee...western/northern 
Kentucky...southern/eastern Indiana...and southwestern Ohio... 


... 
The greatest threat for severe thunderstorms will develop across the 
Ohio and Tennessee Valley regions into the mid-south today into 
early tonight, with damaging gusts, large hail and tornadoes 
possible. 


..mid MS/OH/TN valleys... 
Morning water vapor loop shows a significant upper low tracking 
southeastward across southern WI. A strong mid level jet lies to 
the south of the low, extending from the northern plains into MO. 
As this upper wind Max overspreads the warm sector over parts of the 
mid MS, OH, and Tennessee valleys, the risk of rather widespread severe 
thunderstorms will develop this afternoon into tonight. A very 
moist and unstable air mass has developed across this region with 
pockets of MUCAPE in the 5000-6000 j/kg range. Steep low and mid 
level lapse rates combined with strong effective shear values will 
result in a conditional risk of severe storms throughout the region. 
The primary forecast uncertainty is the timing and location of 
initiation. 


12z model guidance shows wide diversity in where/when the most 
intense convective clusters will occur later today. Due to this 
uncertainty, few changes have been made to the ongoing outlook. 
Discrete supercell development is possible along/ahead of the 
approaching cold front due to shear vectors orthogonal to the front 
and favorable shear magnitudes. Any storms that remain discrete 
will pose a risk of very large hail and a tornado or two. It 
appears likely that multiple clusters of storms will congeal into 
fast-moving bowing structures posing a risk of rather widespread 
damaging winds. This threat will likely spread as far east as 
eastern Kentucky/Tennessee overnight. 


..KS/MO/OK/AR this evening... 
A surface boundary will extend from western Kansas into southwest MO and 
northwest Arkansas later today. Given the intense heat to the south of 
boundary, and a corridor of high dewpoints immediately north of the 
boundary, a zone of high cape values will result. There is 
relatively good consensus of 12z models that show clusters of storms 
forming over Kansas late this afternoon and tracking along this corridor 
though the evening. Damaging winds and large hail will be possible 
if this scenario unfolds. 


.Hart/picca.. 07/20/2018 


$$ 

Mesoscale Discussion


000 
acus11 kwns 202000 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 201959 
ohz000-inz000-202100- 


Mesoscale discussion 1104 
National Weather Service Storm Prediction Center Norman OK 
0259 PM CDT Fri Jul 20 2018 


Areas affected...portions of far eastern Indiana and far western 
Ohio 


Concerning...Tornado Watch 289...290... 


Valid 201959z - 202100z 


The severe weather threat for Tornado Watch 289, 290 continues. 


Summary...threat for a few damaging gusts and a brief tornado or two 
may progress into far western Ohio. However, cells should weaken 
with eastward extent and new downstream watch issuance is not 
currently expected. 


Discussion...a line of storms, composed of bowing segments and 
embedded supercells, is moving east around 35-45 mph this afternoon. 
Backed flow and enhanced storm-relative helicity ahead of the line 
may maintain some threat for localized damaging winds and a couple 
brief tornadoes into far western Ohio. However, this line will 
encounter increasingly stable low-level air behind earlier 
convection, which should gradually reduce the severe threat. 
Therefore, downstream watch issuance is not currently anticipated. 
Local extension of ongoing watches 289 and 290 could be needed 
across far western counties of Ohio, though. 


.Picca.. 07/20/2018 


..please see www.Spc.NOAA.Gov for graphic product... 


Attention...WFO...iln...iwx...ind... 


Latitude...Lon 40298549 41378519 41478466 41418447 41078422 40558423 
40038440 39938480 39958542 39998551 40298549