SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0641 AM CST Sun Dec 03 2023
Valid 031300Z - 041200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER WESTERN
PENNSYLVANIA AND SMALL PARTS OF ADJOINING STATES...
...SUMMARY...
Isolated, marginally severe thunderstorms are possible over western
Pennsylvania and small parts of adjoining states this afternoon.
...Synopsis...
In mid/upper levels, a series of shortwaves will contribute to
eastward movement of a broader-scale trough across the central CONUS
and into the Great Lakes/Mississippi Valley region. The two main
shortwave troughs involved will be:
1. A leading perturbation -- evident in moisture-channel imagery
over parts of IA, eastern MO, and the OK/AR border area. This
feature should deamplify somewhat and accelerate east-northeastward
away from the mean trough, reaching Lake Erie, western PA and WV by
00Z, then moving offshore from New England around the end of the
period.
2. A trailing perturbation -- initially apparent over central/
eastern parts of MT/WY/CO -- and forecast to reach the Mid
Mississippi Valley and Mid-South as a strong, compact shortwave
trough by 12Z tomorrow.
At the surface, 11Z analysis showed a low near PKB, with occluded
front southeastward to near LYH, warm front from there across the
Hampton Roads area, and cold front over the western Carolinas,
western GA, southeastern AL, and western FL Panhandle. That initial
low should shift/redevelop poleward over western NY through the
afternoon, at the head of the occluded front, while another low
forms and shifts along the northeast-moving triple point to near the
NJ shore by 18Z, heading seaward thereafter. By 00Z, the cold front
should extend from that low across portions of the Carolinas,
southern GA, the eastern FL Panhandle, and the northeastern Gulf.
...Western PA and vicinity...
A swath of multilayered clouds and precip now over this region is
being supported by warm advection and elevated moisture transport.
This activity should move east-northeastward into the northern
Mid-Atlantic and New England regions through the day. In its wake,
a roughly north-south corridor of convection, including a few
thunderstorms, should develop this afternoon and move east-
northeastward over the region, offering isolated damaging to
marginally severe gusts, marginally severe hail, and a conditional/
brief tornado threat.
Although the leading mid/upper-level shortwave trough will be
weakening as it approaches the area this afternoon, it still should
be preceded by a well-developed field of DCVA/ascent aloft. This
should combine with low-level warm advection and short window of
muted diabatic heating to steepen lapse rates from the surface to
midlevels and remove MLCINH, near the occluded front where weak
boundary-layer lift will be present as well. This all should
support scattered to widely scattered convection with embedded
thunderstorms, in an environment characterized by modest buoyancy
and intense mid/upper winds. Forecast soundings suggest surface
dewpoints generally in the mid-40s to low-50s F supporting MLCAPE in
the 200-500 J/kg range. Though flow should be nearly unidirectional
through most of the troposphere, 40-50 kt effective-shear magnitudes
are possible. Long, nearly straight hodographs may support storm
splitting. Activity should weaken as it moves into a more-stable
air mass across western/central NY and north-central PA by late
afternoon and early evening.
..Edwards/Kerr.. 12/03/2023
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