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Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0750 AM CDT Mon Sep 12 2022

Valid 121300Z - 131200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE MID-ATLANTIC AND NORTHEAST...AND OVER PORTIONS OF ARIZONA...

...SUMMARY...
Isolated strong to severe thunderstorms may occur across parts of
the Mid-Atlantic and Northeast, and over portions of Arizona.

...Synopsis...
A highly amplified yet progressive mid/upper-level pattern is
forecast across most of the CONUS through the period.  A well-
developed, nearly stacked, deep-tropospheric low is centered over
northeastern IL, with associated cyclonic flow covering much of the
CONUS between the Great Plains and the Appalachians.  Through the
day-1 period, the mid/upper low is forecast to move across northern
IN and northwestern OH to Lake Erie near CLE.  By 12Z tomorrow, a
positively tilted trough should trail southwestward across the
Tennessee Valley region.

Upstream, high-amplitude ridging -- now located from central MX
across the Four Corners and ID to the Canadian Rockies -- will
weaken and shift eastward, reaching far west TX and the central/
northern High Plains by 12Z.  This will occur as a southern-stream
shortwave trough -- related to the remnants of former eastern
Pacific tropical cyclone Kay -- moves slowly eastward/inland during
the middle/latter part of the period.  By 12Z, the associated 500-mb
trough should extend from the lower Colorado River Valley of AZ/CA
southward over northern Baja, then southwestward from the Baja spur.

At the surface, 11Z analysis showed a cold front -- related to the
southern Upper Great Lakes cyclone aloft -- across eastern Lake
Erie, to near an ERI-HLG-TYS-PIB line then southwestward across deep
south TX.  By 00Z, the front should reach western/central NY,
central/eastern PA, northern to southwestern VA, the western
Carolinas, then southwestward near PNS and across the north-central/
west-central Gulf.  By 12Z, the cold front should reach eastern NY,
NJ, the Delmarva/NC Tidewater region, southern GA, near AAF, and
beco*ing quasistationary over the northern/western Gulf.  A warm
front -- initially drawn over central PA and southern NJ -- will
move slowly northward over eastern PA and NJ today.

...Mid-Atlantic/Northeast...
Scattered thunderstorms are expected to develop from midday through
afternoon, mainly ahead of the cold front, both over higher terrain
near/west of the Blue Ridge, and near a prefrontal surface trough. 
As convection impinges on a very moist and diurnally destabilizing
airmass across the outlook area, intensification should occur, with
occasional downdrafts capable of tree damage and isolated severe
gusts/hail possible.

Surface dewpoints from the upper 60s to low 70s, and PW around
1.75-2 inches, should remain co*mon over the central/eastern
portions of NC/VA, as well as much of the region from the Delmarva
Peninsula and MD to parts of southeastern PA and NJ along and south
of the warm front.  This will counterbalance modest mid/upper-level
lapse rates enough to support peak/preconvective MLCAPE in the
1000-2000 J/kg range, based on modified 12Z WAL RAOB and model
soundings.  Near-surface flow should remain weak across this region,
limiting both low-level shear magnitudes and hodograph size. 
However, difluent yet strong upper flow will contribute to deep-
layer speed shear, with nearly straight low/middle-level hodographs
and effective-shear magnitudes around 30-40 kt over much of the
area.  Organized multicells and at least transient supercell
structures are possible, especially near outflow/marine-breeze
boundaries.

...AZ...
Widely scattered to scattered thunderstorms are possible today over
the outlook area, offering sporadic strong/isolated severe gusts and
isolated, marginally severe hail.

Morning clouds/convection across primarily the central/northern
parts of the outlook area are diminishing based on radar and
satellite imagery -- a trend that should continue through the early
afternoon.  Airmass recovery from the prior day's convection -- not
always a given this time of year -- also will be aided from south to
north by theta-e advection ahead of the slowly ejecting mid/upper
trough.  The next/diurnal round(s) of convection should initiate
both over areas of heated higher terrain in the northern and eastern
parts, but also across the deserts and smaller Sky Island ranges of
southern AZ, where diurnal destabilization will be longer and
stronger.

Activity already over the Mogollon Rim will only have a narrow
corridor of favorable boundary-layer air to support wind/hail
potential before moving farther north to northeast and dissipating,
but may send outflows southwestward to lower elevations.  Initially
separate convection over the central/southern parts, however, should
move over well-mixed, deeper subcloud layers across the deserts,
with large-scale lift related to the approaching trough overlying
favorable moisture and weak MLCINH near the surface.  Steep low/
middle-level lapse rates will contribute to MLCAPE generally around
1500 J/kg (locally higher), based on a modified 12Z TUS RAOB and
model soundings.  Outflow collisions/interactions may support
additional development into the evening, before stabilization from
both diabatic cooling and outflow spread will lessen convective
organization/coverage.

..Edwards/Smith.. 09/12/2022