SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0258 PM CDT Fri Aug 26 2022
Valid 262000Z - 271200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
NEW ENGLAND...
...SUMMARY...
Isolated to widely scattered strong to severe thunderstorms remain
possible possible across parts of the Northeast and northern High
Plains this afternoon and evening.
...20Z Update...
Severe probabilities have been trimmed behind ongoing convection
across New England. Both isolated large hail and scattered damaging
winds will remain possible with this activity as it spreads eastward
towards the Atlantic Coast over the next few hours. For more
information on the near-term severe threat across this area, see
Mesoscale Discussion 1723.
Across the northern High Plains, the Marginal Risk was expanded
westward to include more of eastern MT to account for ongoing strong
thunderstorms that have developed this afternoon. Even with
deep-layer shear remaining fairly modest over this region,
convection should pose an isolated severe risk through this evening
as it encounters greater low-level moisture along/near a surface
trough across eastern MT/WY into the western Dakotas.
Recent visible satellite and radar imagery shows a well-defined MCV
over northeastern SD and southeastern ND. This feature is forecast
to continue moving slowly northeastward toward MN this afternoon and
evening. While a conditional severe threat remains evident across
east-central SD given a favorable shear profile through mid levels,
the prospect for surface-based thunderstorms still appears rather
low. Have therefore not included a Marginal Risk with this update.
..Gleason.. 08/26/2022
.PREV DISCUSSION... /ISSUED 1111 AM CDT Fri Aug 26 2022/
...Northeast this afternoon/evening...
Embedded speed maxima will progress eastward from the lower Great
Lakes to New England, within the southern portion of a broad belt of
cyclonic mid-upper flow over southeast Canada. Likewise, a weak
surface cyclone will move eastward from the Saint Lawrence Valley to
ME by early tonight, as a trailing cold front moves southeastward
across PA/NY/Southern New England. Scattered, slightly elevated
thunderstorms are ongoing this morning over eastern NY in
association with a lead shortwave trough. Surface heating and
boundary-layer dewpoints in the mid 60s east of this convection and
a pre-frontal trough will result in destabilization and will support
surface-based thunderstorm development by early afternoon. Clusters
and short line segments will subsequently spread eastward across New
England in an environment of moderate buoyancy (MLCAPE of 1000-2000
J/kg) and vertical shear (effective bulk shear of 30-35 kt with
modest hodograph length/low-level clockwise curvature). Occasional
damaging gusts will be the main threat, though marginally severe
hail and an isolated tornado will be possible. Isolated strong
cells may occur farther west across NY this afternoon, near and east
of the cold front, with more veered low-level flow and weaker
vertical shear.
...Northern High Plains late this afternoon/evening...
A weak midlevel trough will continue moving eastward over MT through
this evening, and it will be preceded by a convectively-enhanced
trough/MCV moving east-northeastward over SD. The southern fringe
of the SD MCV will coincide with a corridor of boundary-layer
dewpoints in the 60s along a warm front, but it is not clear that
additional (surface-based storms) will form this afternoon across
eastern SD. Otherwise, surface heating and residual 55-60 F
dewpoints along a weak lee trough (in the zone of ascent downstream
from the midlevel trough) will support afternoon/evening
thunderstorm development from eastern MT into northeastern WY.
Steepening low-midlevel lapse rates and deeper mixing across WY/MT
will support the potential for isolated severe outflow winds/hail.
Convection will tend to become elevated and will weaken with time
while moving eastward into weakening buoyancy and larger convective
inhibition across the Dakotas late this evening into tonight.
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