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Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0754 AM CDT Fri Aug 26 2022

Valid 261300Z - 271200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
EASTERN NEW YORK AND NEW ENGLAND...

...SUMMARY...
Isolated to widely scattered strong to severe thunderstorms are
possible across the Northeast, as well as parts of the northern High
Plains.

...Synopsis...
In mid/upper levels, mean troughing persists over much of the
eastern CONUS, south of a large, persistent, quasistationary cyclone
over eastern Arctic Canada.  Within the associated cyclonic-flow
field, a positively tilted shortwave trough was apparent in
moisture-channel imagery across southern ON to northern IN and
central IL.  A separate perturbation to its east was moving offshore
from the Mid-Atlantic region, and crossing southeastern New England.
The trailing trough should proceed eastward across NY and New
England through the period.

Upstream, a small cyclone is devolving into an open-wave trough over
southern AB and northwestern MT.  The trough should move to eastern
MT and southern SK by 00Z, reaching western SD late overnight.  As
this occurs, a preceding perturbation -- including an MCV now over
western SD -- should weaken and eject northeastward over eastern ND.
Farther south, a weak shortwave trough over western CO and parts of
UT will move eastward over CO, reaching the central High Plains by
the end of the period.

At the surface, 11Z analysis showed a broad area of low pressure
over Lake Ontario, with a cold front extending southwestward across
northern OH, central IN, southern IL, and central MO, beco*ing a
stationary to warm front to another low over the NE Panhandle.  A
prefrontal trough was drawn over central NY, eastern PA, central MD,
and eastern VA.  The Lake Ontario low should move/redevelop eastward
across NY and northern New England through 00Z, with the cold front
reaching southeastern NY, southern PA, and western TN.  The western
segment of the front should shift northward to northwestern NE and
northeastern WY, and beco*e somewhat better-defined baroclinically,
while intersecting a trough that will extend northward over eastern
MT.  A moist axis -- with dewpoints generally in the low/mid 60s F
-- was drawn north of and approximately parallel to the front, from
southeastern NE to near the Black Hills and eastern MT.

...Northeast CONUS...
Isolated to scattered thunderstorms are expected to form along/ahead
of the cold front from midday through the afternoon, moving
generally eastward across the region.  The most intense cells will
be capable of sporadic tree damage, isolated severe (50-kt+) gusts,
and marginally severe hail.

The greatest relative density of surface-based thunderstorms (and
therefore of strong-severe gust potential) should be in and near the
15%-wind/"slight" area during early/mid afternoon.  Although MLCINH
will weaken across much of the region throughout the day, due to
diabatic heating of a favorably moist boundary layer, the strongest
low-level instability should develop in a corridor from eastern NY
across southern/central New England, tapering northward. For the
next several hours, this region will reside between the departing
northwestern fringes of early-day clouds related to the eastern
shortwave trough, and the broken plume of clouds and occasional
precip related to the DCVA/UVV field of the approaching Great Lakes
perturbation.  Given surface dewpoints co*monly in the 60s F, this
will foster MLCAPE values in the 1000-1500 J/kg range over southern
New England, tapering to the 500-1000 J/kg range northward near the
Canadian border of VT/NH.  A tongue of favorable surface-based
buoyancy, supporting some severe potential, should extend into
western/central ME as well, between the Atlantic marine layer and a
stable, lower-theta-e boundary layer farther north.

With low-level wind speeds being limited, hodographs are forecast to
be well-curved but not particularly large over most of the area,
with the possible exception of any favorably oriented, vorticity-
enhancing outflow/differential-heating boundaries.  Effective-shear
magnitudes of 30-40 kt will support organized multicells -- in the
form of linear segments and clusters -- and perhaps short-lived
supercell structures.

...Northern Plains...
Isolated to scattered thunderstorms should form this afternoon in a
convergence zone related to a surface trough oriented roughly
north-south over the western parts of the outlook area.  Isolated
severe hail/gusts may occur from some of this convection as it moves
eastward across parts of eastern MT and northeastern WY, then into
the western Dakotas this evening.  Activity over SD may persist at
strong to marginal severe levels somewhat longer into the evening
and farther east, given its proximity to the (by then) nearly east-
west moist axis segment in low levels (surface to 800 mb).  The
moist axis will continue to bend northwestward across southwestern
SD toward eastern MT, and will underlie steep midlevel lapse rates
ahead of the mid/upper trough.  That will support a plume of MLCAPE
around 1500-2500 J/kg over parts of western SD, narrowing in width
and decreasing to around 1000-1500 J/kg over eastern MT/western ND. 
Mid/upper winds will be difluent but not particularly strong over
most of the area, but veering of low level winds with height still
yields 30-35 kt effective-shear magnitudes in eastern MT, increasing
to around 45 kt from northeastern WY to the Black Hills, nearer to
the warm front.  As such, some supercell potential exists across the
latter region.

Farther east across the eastern ND/northeastern SD region, a
conditional potential exists for strong elevated convection to form 
late this afternoon and this evening, just ahead of the ejecting/
weakening MCV, and atop a relatively stable boundary layer. 
Forecast soundings suggest 30-35-kt effective-shear magnitudes with
around 1000 J/kg MUCAPE, rooted near 850 mb.  Isolated hail near
severe limits cannot be ruled out, but in such a marginal
environment, uncertainties over convective coverage and timing
preclude extending the unconditional outlook that far at this time.

..Edwards/Goss.. 08/26/2022