007
ACUS01 KWNS 210551
SWODY1
SPC AC 210550

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1250 AM CDT Sat Sep 21 2024

Valid 211200Z - 221200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE
SOUTHERN HIGH PLAINS...

...SUMMARY...
Scattered severe storms are expected this afternoon and evening
across the southern High Plains. Isolated strong to severe
thunderstorms are also possible from the mid Missouri Valley to the
Upper Midwest, and also from western Pennsylvania into
northern/central Virginia.

...Southern High Plains...

Notable upper trough has advanced into the lower CO River Valley
early this morning. Strong 500mb speed max will soon round the base
of the trough and eject across southern AZ into southern NM by late
afternoon. This feature will greatly influence convective
development/intensity across the southern High Plains by peak
heating. Northern-stream short-wave trough will shift east today
which will allow a sharp surface cold front to surge south across
the High Plains into eastern CO by early afternoon, likely arcing
across the northern TX Panhandle into northeast NM by 22/00z. Strong
boundary-layer heating is expected across southern NM with more
modest warming forecast within southeasterly upslope flow from the
TX/NM border into the Sangre de Cristo range, just southwest of the
cold front. Forecast soundings suggest convective temperatures will
be breached fairly early, aided in part by frontal/orographic
influences. Scattered convection will easily develop ahead of the
short wave, and this activity will be strongly sheared as the speed
max approaches. Supercells are expected to evolve within this
environment as 0-6km shear will be on the order of 50kt, along with
veering winds with height. Large hail should develop with this
activity along with some risk for a few tornadoes.

...Upper Midwest to Mid MO Valley...

Northern-stream short-wave trough is progressing across SK/eastern
MT into the northern Plains, in line with latest model guidance.
This feature is forecast to suppress the height field immediately
downstream across eastern ND into northern MN, though the strongest
falls will remain north of the international border. Even so,
notable surface front will advance into MN-western IA-southern NE by
18z, then steadily surge east into the early evening hours. This
boundary will serve as the focus for potential convective
development during the late afternoon, though surface heating is not
expected to be particularly strong ahead of the wind shift. With the
strongest forcing expected to spread across northwest ON, convection
may be more isolated along the front trailing across the Upper
Midwest. Even so, some hail/wind threat will exist with this
activity which should peak in intensity during the early evening.

...Western PA into western VA...

Weak short-wave trough will dig southeast across the upper OH Valley
later this afternoon with modest mid-level northwesterly flow
expected to extend across western PA/VA. This feature will encourage
scattered convection later this afternoon along a frontal zone that
will be draped across the Delmarva-western PA into western NY.
Convection that evolves near this wind shift will move southeast
with an attendant risk for gusty winds and some hail.

..Darrow/Thornton.. 09/21/2024

$$