SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1221 AM CDT Thu Sep 22 2022
Valid 221200Z - 231200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE
MID-ATLANTIC AND NEW ENGLAND COASTS AND OVER PORTIONS OF THE
NORTHERN HIGH PLAINS...
...SUMMARY...
Thunderstorms with damaging winds will be possible this morning into
the early afternoon hours from the Mid-Atlantic to the New England
coasts. Strong to severe winds are also possible across portions of
the northern High Plains this afternoon.
...Synopsis...
Early-morning water-vapor imagery reveals an upper-level wave
continuing to slowly amplify over the Great Lakes region as it
migrates east. At the surface, an associated surface low over
eastern Canada will undergo some deepening over the next 12-24 hours
as it lifts northeast. A trailing surface cold front is noted in
surface observations stretching from the Lower Great Lakes into the
central Plains. Thunderstorm coverage has increased along this front
across portions of PA and NY during the 04-05 UTC period with
additional development likely through the late morning hours. To the
west, an upper low over the northern Great Basin/northern Rockies
will meander to the east/northeast, supporting ascent and
thunderstorm chances across portions of the northern High Plains
this afternoon.
...New England and Mid-Atlantic Coasts....
Elevated thunderstorms will likely be ongoing at the start of the
period across the New England region due to a combination of focused
ascent along the front and 500-1000 J/kg MUCAPE. Mean flow along the
boundary will maintain a linear mode with winds in the 925-850 mb
layer strengthening to 35-45 knots between 12-16 UTC. Limited
diurnal heating will modulate low-level lapse rates and the
potential for convection to become rooted in the boundary layer.
However, more robust downdrafts may mix the stronger low-level winds
to the surface and support isolated damaging winds. The wind threat
may increase for locations that can see temperatures climb into the
low 70s via daytime heating by late morning, but this scenario
appears limited and will likely be confined closer to the coast.
To the south across the Mid-Atlantic/Carolinas, thunderstorm
development is expected along the front by early to mid afternoon.
While mid-level lapse rates will be modest, steepening 0-3 km lapse
rates and gradually increasing deep-layer shear will support a few
strong cells capable of isolated damaging winds. Isolated to
scattered thunderstorms are likely along the front into the Southern
states, but weak deep-layer flow will limit the potential for
organized severe convection.
...Southeast Montana and Northeast Wyoming...
Increasing mid-level flow and upper-level difluence ahead of the
Great Basin upper low will support lee troughing along the northern
High Plains through the day. 7-8 C/km mid-level lapse rates, sampled
in upstream 00 UTC soundings, are expected to advect into the region
by mid afternoon amid the west/southwest flow regime. Modest
moisture in the 850-700 mb layer should support adequate buoyancy
for convection within the left-exit region of the upper-level speed
max. Storms maturing in a deep, well-mixed boundary layer to the
west of the sharpening surface trough will be capable of a few
strong to severe wind gusts.
..Moore/Jewell/Weinman.. 09/22/2022
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