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Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0747 AM CDT Fri May 27 2022

Valid 271300Z - 281200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE
MID-ATLANTIC REGION AND NORTHERN HIGH PLAINS...

...SUMMARY...
Damaging thunderstorm winds and a few tornadoes are possible today
over parts of the Mid-Atlantic region.  Thunderstorms may produce
severe gusts this afternoon into early evening over portions of the
northern High Plains.

...Synopsis...
A progressive synoptic pattern in mid/upper levels will feature two
dominant cyclones and their associated troughs:
1.  A long-lived circulation now centered over the lower Wabash
River area, with trough south-southwestward across southern MS to
the north-central Gulf.  As a closely phased, northern-stream
perturbation amplifies across ON, the cyclone should move
east-northeastward to PA and beco*e an open-wave trough today.  By
00Z, the co*bined trough should extend across north-central through
south-central QC and southern New England, having moved offshore
from the Mid-Atlantic a few hours prior. 
2.  A co*plex cyclone over the northeastern Pacific, covering much
of the area from the southern Gulf of Alaska to the coastal Pacific
Northwest.  The main low -- evident in moisture-channel imagery west
of Vancouver Island -- should move slowly northeastward to the
mainland BC coastline north of Vancouver Island by 12Z.  A series of
mostly low-amplitude shortwave perturbations will be embedded in the
cyclonic-flow field to its southeast, as heights fall across the
Northwest, northern Rockies, and northern Plains. 

The 11Z surface analysis showed a co*plex, elongated area of low
pressure from southwestern QC across Lake Huron to southwestern
Lower MI.  A cold front was drawn across western PA, WV,
southwestern VA, the western Carolinas, and western FL Panhandle. 
The western part of the same boundary has beco*e quasistationary
approximately along the northern Gulf Coast to the middle TX Coast,
to near DRT, and a low near FST. By 12Z tomorrow the cold front
should reach western New England, the eastern Carolinas, southern
GA, still quasistationary near the north-central Gulf Coast, and
dissipating across south TX.

...Mid-Atlantic/Northeast/Carolinas...
Scattered thunderstorms -- mainly in a
north-northeast/south-southwest line already underway in western
parts of the area -- are expected to offer sporadic damaging gusts
and a few tornadoes.  See tornado watch 276 and related mesoscale
discussions for near-term details over portions of MD/VA/NC/DC and
eastern WV Panhandle.

Activity should move into a moist, low-LCL boundary layer that will
destabilize from south to north via a co*bination of theta-e
advection and diurnal heating tempered by cloud cover.  MLCAPE of
1500-2000 J/kg already is apparent over eastern parts of the
Carolinas, and may expand over southern/eastern VA in the
preconvective sector.  Values will decrease gradually northward to
around 500 J/kg in southern/eastern NY and parts of New England.  

Meanwhile, height falls and strengthening mid/upper winds will
overspread the area ahead of the progressive cyclone and trough
aloft.  Favorable deep shear (effective-shear magnitudes in the
40-55-kt range) will exist for supercells, though deep-shear and
mean-wind vectors will have a substantial co*ponent parallel to the
axis of convective lift.  Hodographs will be long but not particular
large in the low levels over most of the area.  As such,
predominantly quasi-linear mode, with embedded bows/LEWPs and
related mesocirculations, will pose a threat for damaging gusts and
brief tornadoes, while any relatively discrete supercells that still
may form in the foregoing warm sector offer a cyclic tornado threat.
The favorably unstable warm sector will narrow with weaker buoyancy
northward extent toward southern NY and northern New England,
beneath stronger upper-level winds.  However, strong/isolated severe
surface-based convection is possible as far north as northern New
England.  

...Northern High Plains, northern Rockies...
Widely scattered to scattered thunderstorms are excepted to develop
this afternoon over the southern MT/northern WY area, with the
best-organized activity perhaps initiating over or near the northern
Bighorns.  Convection should move eastward astride a low-level
moisture/instability axis, and atop a well-mixed boundary layer with
upper 30s to mid 40s F surface dewpoints, supporting 500-800 J/kg
MLCAPE, with even larger DCAPE values.  Some upscale growth and
cold-pool organization are possible.  The main concern will be
severe gusts, some of which may reach or exceed 65 kt.  Activity
should weaken this evening as it moves into a stabilizing boundary
layer. 

Father southwest, isolated to widely scattered, high-based
thunderstorms will develop today across parts of the northern
Rockies into southern ID amidst weak MLCINH and marginal moisture. 
meanwhile cooling aloft and diurnal heating will steepen
low/middle-level lapse rates and remove MLCINH, with just enough
boundary-layer moisture to support 200-500 J/kg MLCAPE.  With
deep/well-mixed subcloud layers expected, strong/isolated severe
gusts may be noted this afternoon into early evening.

..Edwards/Mosier.. 05/27/2022