LIVE MAP (ABOVE) ... SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1127 AM CDT Fri Aug 25 2023
Valid 251630Z - 261200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM CENTRAL IL
INTO SOUTHWEST IN...
...SUMMARY...
Isolated to scattered thunderstorms associated with strong wind
gusts and marginally severe hail are possible this afternoon and
evening from Kansas to Virginia and across Upper Michigan, with the
somewhat greater threat focused from central Illinois into southwest
Indiana.
...IL/IN this afternoon/evening...
An outflow-reinforced front extends from WV/southern OH to central
IL, while a second outflow surge is moving southeastward into
northern MO and west central IL. The merger zone of these two
boundaries appears to be the more probable area for thunderstorm
development this afternoon into IL, along the north gradient of the
78-80 F boundary-layer dewpoints. Modified 12z soundings and
short-term model forecasts suggest that MLCAPE could exceed 4000
J/kg with weakening convective inhibition, while steep midlevel
lapse rates will also result in large DCAPE (> 1200 J/kg). With
most of the vertical shear (25-30 kt magnitudes) concentrated in the
lowest 3 km, the primary convective mode is expected to be multicell
clusters and perhaps a relatively short-lived supercell or two
capable of producing damaging outflow winds.
...Eastern KY to VA through this evening...
The remnants of overnight convection persist from WV into eastern
KY. The warmest surface temperatures and higher dewpoints to the
west across KY suggest that the preferred development of new storms
will also be toward the west and southwest this afternoon, where
isolated strong downburst winds will be possible.
Farther east into VA, somewhat lesser boundary-layer moisture (mixed
mainly into the mid-upper 60s) and lesser midlevel lapse rates will
support weaker buoyancy (MLCAPE in the 1500-2000 J/kg range)
compared to KY/southern OH. Despite the early passage of the
convectively-enhanced midlevel trough, 25-30 kt midlevel flow will
linger over VA/MD this afternoon. Thunderstorm development will be
possible this afternoon along a weak lee trough, as well as any
persistent differential heating zones (mainly across southwest VA)
and along a cold front moving southeastward from PA. The overall
threat for damaging winds with downbursts still appears to be best
categorized as MRGL, so will maintain the 5% wind probabilities.
...Northeast MN into Upper MI this afternoon/evening...
A pronounced midlevel shortwave trough is moving east-southeastward
over the MN Arrowhead/Lake Superior. A narrow zone of
destabilization coincident with a band of ascent will support at
least widely thunderstorms through the afternoon. Though buoyancy
will be modest (MLCAPE of 500-1000 J/kg), long hodographs will
support organized/supercell storms capable of producing isolated
wind damage and marginally severe hail.
...Eastern CO to KS/NE border this afternoon/evening...
As the surface warms with daytime heating, high-based thunderstorm
development is expected along a slow-moving front in KS and in a
zone of low-level upslope flow in CO by mid-late afternoon.
Vertical shear will be relatively weak, but deep inverted-V profiles
with large DCAPE will support the potential for strong to isolated
severe outflow gusts this afternoon into this evening.
..Thompson/Smith.. 08/25/2023
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