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Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0743 AM CDT Wed Aug 10 2022

Valid 101300Z - 111200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS IN PARTS OF THE
MID-ATLANTIC REGION AND INLAND PACIFIC NORTHWEST...

...SUMMARY...
Isolated severe thunderstorms are possible in parts of the
Mid-Atlantic region and inland Pacific Northwest.

...Synopsis...
In mid/upper levels, a strong anticyclone will remain centered over
the central Rockies, with mean ridging northwestward over the
Canadian Rockies and southeastward across the Mid-South region. 
Meanwhile, heights will fall over the Great Lakes and vicinity, as a
series of shortwaves now over MB and ON contribute to amplification
of the larger-scale trough.  That action will contribute to eastward
shifting of a weak, positively tilted shortwave trough now located
from southern ON across northern IN and central IL.  The latter
trough should reach eastern NY and western PA by 00Z, then coastal
New England and Mid-Atlantic regions by the end of the period.

Meanwhile, a long-loved and pronounced synoptic-scale cyclone is
centered off the West Coast, about 150 nm west of the coastal OR/CA
line.  The associated 500-mb low should move northward to west of
the Olympic Peninsula by 12Z tomorrow, then stall on day 2. 
Associated cyclonic flow, with a substantial southerly co*ponent,
will spread northward through the Pacific Northeast today and
tonight.

At the surface, 11Z analysis showed a weak cold to quasistationary
front from south of Long Island across the PA/MD border region,
southern OH, southern MO, northern OK, then northwestward over
northeastern CO to a low near GCC.  Regional southward drift of the
front is possible in the Mid-Atlantic to Ohio Valley; otherwise it
should move very little through the period.

...Mid-Atlantic...
Widely scattered to scattered thunderstorms will develop this
afternoon near the front, and southward into the warm sector along
such features as a weak prefrontal trough, sea/bay breezes, and in
the west, preferential heating and CINH erosion over elevated
terrain.  A second convective episode may form this evening over the
mountains and move eastward to parts of the outlook area as well. 
Damaging downdrafts are expected with the most intense cells, and
isolated, marginally severe (50-55 kt) gusts are possible.

Minor large-scale ascent may affect the area ahead of the mid/upper
trough during the mid/later afternoon; however, the primary drivers
for the initial convection will be diurnal heating of a richly moist
air mass, and the mesoscale to localized boundaries.  Surface dew
points co*monly in the 70s F will contribute to MLCAPE in the
1500-2000 J/kg range, with a deep troposphere and buoyant profile
supporting water-loaded downdraft descent into a shallow but well-
mixed boundary layer.  Deep-layer flow and shear each will be weak. 
Through stronger ascent aloft is expected as the mid/upper trough
approaches closer and crosses the area tonight, stabilization from
afternoon convection makes any severe potential from later activity
more uncertain, and likely quite localized and marginal as well.

...Inland Pacific Northwest...
Isolated to widely scattered thunderstorms are expected to develop
and move northward to northeastward across the outlook area this
afternoon and evening.  Damaging to locally severe gusts, and
isolated severe hail, are possible.

As the offshore low moves northward, southerly to southeasterly flow
aloft, with pronounced difluence, will persist over the outlook
area, along with a broad plume of low-level warm advection and
moisture advection/transport.  A moist axis was analyzed on the
surface chart from the Gulf of California northward to near the LAS
and SGU areas, then north-northwestward across central NV and
eastern OR, splitting westward through the Columbia Gorge and
northward across eastern WA.  Morning low-elevation surface
dewpoints were co*monly in the 50s to low 60s along and near that
axis in the Northwestern CONUS.  While some decrease is expected
with diurnal heating, and related boundary-layer deepening/mixing,
that factor should be offset somewhat by continued moist advection
to ensure ample moisture for afternoon and evening convection across
the region.  Modified 12Z BOI/OTX RAOBs and model soundings suggest
peak/preconvective MLCAPE of 500-1000 J/kg is likely over much of
the area, with minimal MLCINH.  Modest low-level winds will limit
vertical shear, though stronger upper/anvil-level winds will aid
with cloud-layer shear and overall multicellular organization.

..Edwards/Leitman.. 08/10/2022