U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus02 kwns 210520 
Storm Prediction Center ac 210519 

Day 2 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
1219 am CDT Wed Aug 21 2019 

Valid 221200z - 231200z 

..there is a marginal risk of severe thunderstorms over the 
northern High Plains...and from Oklahoma eastward across the Ohio 

Isolated severe wind gusts are possible Thursday from Oklahoma 
eastward across the Ohio Valley, with hail or wind over the northern 
High Plains. 

Strong southwest flow aloft will remain over the northeast, with an 
upper low over Quebec. At the surface, a cold front will move across 
New England with dry air spreading southeast across the Great Lakes. 
South of the stronger winds aloft, a front will become nearly 
stationary roughly from Maryland across the Ohio Valley and into OK, with a 
moist and unstable air mass in the vicinity supporting clusters of 
storms throughout the period. 

To the west, a shortwave trough with 30-40 kt midlevel winds will 
move east across ab, sk and Mt, with attendant cold front. 
Sufficiently moist southeast low-level winds ahead of this system 
will result in destabilization from Montana into the western Dakotas, 
supporting a few strong to severe storms. 

..northern High Plains... 
A shortwave trough and cold front will move across eastern Montana and Wyoming 
during the day, and into the western Dakotas during the evening. 
Southeast surface winds ahead of the front will bring mid to upper 
50s f dewpoints westward beneath steep lapse rates aloft, resulting 
in MLCAPE in excess of 2000 j/kg. Cells or line segments are 
expected to form along this front, with a hail and wind threat. 
Winds will initially be weak in the low levels, but southeast 850 mb 
winds may aid storms as they continue into the western Dakotas where 
cin will slowly erode. Overall, shear will not be particularly 
strong, but sufficient for isolated mixed-Mode severe storms. 

..OK northeastward to the Ohio River... 
Scattered thunderstorms will be ongoing Thursday morning, from parts 
of Kansas eastward across the Ohio Valley. Models differ with placement 
and timing of these clusters, but in general, there will be an 
east/southeastward translation of the active zone as heating occurs 
to the south and new storms develop. The most unstable air will 
stretch from I-40 in Texas/OK toward the Ohio River, with 2000-3000 j/kg 
MLCAPE possible. Westerly winds aloft and only weak low-level winds 
will favor east/southeastward propagating storms capable of 
localized wind damage or marginal hail. 

..northern Virginia...MD...southeast PA and New Jersey... 
a moist air mass will remain south of an east-west oriented front 
which will move very little during the day. Winds aloft will remain 
nearly parallel to this front, and will be strongest to the north 
where the air mass is less unstable. Convergence near this front may 
be sufficient for a few thunderstorms during the afternoon, and 
perhaps into the evening as height falls occur. If destabilization 
occurs farther north than currently expected, severe probabilities 
may be needed in later updates. 

..maximum risk by hazard... 
Tornado: 2% - marginal 
wind: 5% - marginal 
hail: 5% - marginal 

.Jewell.. 08/21/2019