Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0700 AM CDT Sat Jun 28 2025
Valid 281300Z - 291200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE UPPER
MIDWEST TO THE BLACK HILLS...AND PARTS OF NEW YORK AND
PENNSYLVANIA...
...SUMMARY...
Scattered severe thunderstorms are possible across portions of the
Upper Midwest into the north-central Great Plains. All severe
hazards are possible centered on southern Minnesota and eastern
South Dakota. Scattered damaging gusts are possible across parts of
New York into Pennsylvania.
...Upper Midwest to the Black Hills of South Dakota...
Broad weak troughing per morning water-vapor imagery over the
northern Rockies/High Plains will gradually shift eastward and
become centered over MB/SK and the Dakotas by the end of the period.
A somewhat ill-defined boundary this morning will become draped from
parts of the upper MS Valley west-southwestward into the Black Hills
later this afternoon/evening.
Residual clusters of showers/weak thunderstorms this morning will
likely dissipate by mid-late morning over the Upper Midwest. The
resultant convective outflow will probably prove instrumental in
renewed thunderstorm activity later this afternoon where
differential heating/convergence will become focused.
Isolated to scattered thunderstorms should readily develop along the
front/composite outflow by late afternoon when buoyancy will be
maximized. Forecast soundings show 3000-4500 J/kg MLCAPE developing
from eastern SD into MN/western WI. It appears sufficient hodograph
curvature and effective shear magnitudes around 30 kt will support a
supercell mode, at least initially. All severe hazards will be
possible. Gradual upscale growth into a cluster may occur during
the evening --supported by a persistent southwesterly LLJ-- with the
risk gradually favoring more of a wind threat.
Stronger heating across the Plains of NE into eastern WY will aid
isolated-scattered thunderstorms across this portion of the SLGT
Risk. Higher-based updrafts, but steep lapse rates suggest hail/wind
will be the primary concerns.
...Northeast into the Mid-Atlantic region and upper Ohio Valley...
Morning satellite imagery indicates a weak mid-level trough near
Georgian Bay/southern ON. This feature is forecast to move eastward
to the VT/NH/QC vicinity by early evening and glance NY/PA. In
agreement with earlier forecast thinking, the southern extent of the
disturbance's influence will aid in storm development within the
northeast extent of richer moisture extending from the upper OH
Valley into the PA/southern NY area. Initial extensive low cloud
cover will gradually abate as diurnal heating aids in moderate
destabilization by midday from southern NY southwestward into the
upper OH Valley. Bands of smaller storm clusters preferentially
developing on the front/wind shift will predominately be
multicellular, and pose a wind-damage risk across parts of PA during
the afternoon/early evening. Slightly stronger low to mid-level
flow over NY may favor a mix of strong to severe multicells and
perhaps transient, weak supercell structure. Farther south,
slow-moving isolated to scattered pulse-like storms will yield an
isolated risk for 50-60 mph gusts capable of wind damage with the
more intense water-loaded downdrafts.
..Smith/Broyles.. 06/28/2025
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