LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1246 AM CDT Fri Sep 22 2023
Valid 221200Z - 231200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
THE NORTHERN AND CENTRAL HIGH PLAINS...AND OVER THE SOUTHERN COASTAL
MIDDLE ATLANTIC...
...SUMMARY...
Severe thunderstorms are possible across parts of the central and
northern High Plains, mainly this afternoon and this evening. A few
tornadoes are also possible along the Mid-Atlantic Coast early
Saturday morning in association with the approaching potential
tropical system.
...Northern/Central High Plains...
Strong upper low that has settled into the northern Great Basin will
advance into western WY by late afternoon as a 70kt 500mb speed max
rotates through the base of the trough to near WY/UT/CO border by
23/00z. Seasonally cold mid-level temperatures (-20C at 500mb
beneath the upper low) will spread east in association with this
feature, and the exit region of aforementioned jet will overspread
the High Plains of eastern WY by early afternoon.
Latest model guidance suggests boundary-layer flow will remain
decidedly easterly across NE and the Dakotas into eastern WY. As a
result, strongest boundary-layer heating will be noted across the
higher plateau region of WY immediately ahead of the approaching
trough. Forecast soundings suggest convective temperatures will be
breached by 19z, and thunderstorms should develop shortly
thereafter. Soundings across eastern WY exhibit substantial SBCAPE
with steep lapse rates through 8km. NAM 21z forecast sounding for
LUS strongly favors supercells with 60kt surface-6km bulk shear.
Very large hail may accompany some of this activity as it spreads
toward the southern Black Hills region/northwestern NE.
Additionally, relatively moist boundary-layer conditions and low
LFCs suggest some tornado threat. It's not clear how far this
activity will spread east before weakening, as the updrafts will
likely decouple from the boundary layer due to much cooler surface
temperatures and weaker low-level lapse rates. For this reason have
focused higher severe probabilities across the High Plains where
stronger surface heating is expected.
...Potential Tropical Cyclone Sixteen...
PTC 16, currently located well southeast of the Carolina Coast, is
forecast to move north-northwest over the next 24hr, likely
intensifying as it approaches the NC Coast early Saturday. As this
system intensifies, low-level shear will increase markedly across
the southern Middle Atlantic Coast. Probabilities for supercells
will increase late, especially after 06Z, along with some risk for
tornadoes, primarily east of the low track.
Reference
https://www.nhc.noaa.gov for more information on this
developing system.
..Darrow/Moore.. 09/22/2023
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