- 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
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