138
ACUS01 KWNS 211246
SWODY1
SPC AC 211245

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0745 AM CDT Sat Sep 21 2024

Valid 211300Z - 221200Z

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

...SUMMARY...
Scattered severe storms capable of all hazards are possible this
afternoon and evening across portions of the southern High Plains.

...Southern High Plains...
Water-vapor imagery this morning shows a potent mid- to upper-level
low and associated trough moving east across AZ.  An associated
70-kt 500-mb speed max will round the base of the trough and move
into central NM by early evening before weakening overnight as it
moves into the TX Panhandle.  Southerly low-level flow will maintain
a fetch of seasonably rich moisture across the region today
(reference 12 UTC Del Rio, TX and Midland, TX raobs; 18.3 and 14.9
g/kg lowest 100-mb mean mixing ratios, respectively).  Early morning
surface analysis places a cold front pushing southward over the
central High Plains and this boundary will reach northeast NM and
parts of the Panhandles late this afternoon/early evening.

Some continuation of ongoing shower/thunderstorm activity may
continue through the morning across eastern NM into the TX
Panhandle, lending some uncertainty in airmass
destabilization/recovery in wake of this convection.  06z model
guidance (particularly the NAM) seemed to reasonably depict the
low-level moisture plume emanating from the Rio Grande
Valley/Edwards Plateau northwestward into the southern High Plains.
Steep 700-500 mb lapse rates (7.5 to 8.0 deg C/km) sampled this
morning from Albuquerque and Midland will combine with daytime
heating to yield a moderately unstable airmass by afternoon across
eastern NM into west TX.  Increasing large-scale deep-layer ascent
approaching from the west and frontal/orographic lift will likely
contribute to scattered thunderstorms developing relatively early
this afternoon.  Forecast hodographs indicate supercells will evolve
within this environment.  The risk for large hail/severe gusts will
likely accompany the stronger storms, and a threat for a few
tornadoes may be realized later this afternoon/early evening from
eastern NM into parts of adjacent west TX.

...Upper Midwest to Mid MO Valley...
A northern-stream short-wave trough will continue to move eastward
from southern MB/Dakotas into MN/northwest ON during the period.
A surface cold front will advance into MN-western IA-southern NE by
midday, before accelerating east into the Upper Great Lakes, while
the trailing portion of the boundary pushes south-southeast into
central KS by early to mid afternoon.  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.
Models suggest scattered storm coverage and forecast soundings would
imply some of the stronger storms being capable of an isolated risk
for wind damage (50-60 mph) and perhaps some hail.  This activity
will likely diminish by early evening coincident with nocturnal
cooling.

..Smith/Broyles.. 09/21/2024

$$