- Day Three
acus02 kwns 201731
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
..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.