U.S. Severe Weather Forecast (Convective Outlook)

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Day Three

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Storm Prediction Center ac 201730 


Day 2 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1230 PM CDT Wednesday Aug 20 2014 


Valid 211200z - 221200z 


..no severe thunderstorm areas forecast... 


... 
thunderstorms...a few of which could be strong to severe...may occur 
over parts of the Great Lakes and Ohio Valley as well as a portion 
of Nebraska and northern Kansas. Some hail and gusty winds will be 
possible with the strongest storms. 


... 


Blocking synoptic pattern will persist through Thursday with mean 
ridge over the central U.S. Flanked by upper troughs over the eastern and 
western states. The eastern U.S. Upper trough will deamplify as a shortwave 
trough within its base continues eastward and off the Atlantic Seaboard 
early Thursday. A low amplitude shortwave trough will move from the 
upper MS valley into southwestern Ontario Thursday morning. Cutoff low over 
Southern California will drift slowly east into Arizona. At the surface a Lee trough will 
reside across the Central Plains and a cold front will advance southeastward 
through the northern plains during the day. A warm front is expected to 
lift slowly northward through northern portions of the Ohio Valley and into the 
Great Lakes. 


..upper MS valley...Ohio Valley and Great Lakes area... 


Thunderstorms are expected to be ongoing and fairly widespread from 
a portion of the upper MS valley southeastward into the Great Lakes and Ohio 
Valley within zone of isentropic ascent north of warm front. Some of 
this activity will likely persist during the day. However...the warm 
sector south of these storms should gradually destabilize with onset 
of diabatic warming supporting 2000-3000 j/kg MLCAPE. There will be 
some potential for additional storms to develop or ongoing storms to 
reintensify near the convectively reinforced warm front and where 
moist and unstable inflow from the destabilizing warm sector will be 
maximized. Activity will be embedded within modest northwesterly flow aloft 
with 30-35 knots effective shear. There is concern that as storms 
reintensify/redevelop they could evolve into a southeastward advancing 
organized cluster...posing a threat for damaging wind. 
However...uncertainty regarding evolution of morning storms and weak 
forcing aloft with modest height rises lowers confidence in a more 
organized severe event. Nevertheless...this area will continue to be 
monitored for a possible slight risk in later outlooks. 


..neb and northern Kansas... 


A few storms could develop in vicinity of Lee trough from Nebraska into 
northern Kansas where steep lapse rates...moderate instability and inverted-v 
boundary layers will exist. Isolated downburst winds and some hail 
will be possible with the stronger storms. 


.Dial.. 08/20/2014