Probability of damaging thunderstorm winds or wind gusts of 50 knots or higher within 25 miles of a point. Hatched Area: 10% of greater probability of wind gusts 65 knots or greater within 25 miles of a point.
SPC AC 290544
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1244 AM CDT Tue Jun 29 2021
Valid 301200Z - 011200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM CENTRAL PA
THROUGH MUCH OF THE NORTHEAST...
Several severe thunderstorms are possible Wednesday afternoon and
evening from the Upper Ohio Valley into Northeast States. Isolated
severe thunderstorms may also occur across the Great Basin.
Subtropical ridging is forecast to persist across the southern
Plains and Southeast States on Wednesday, while a weak upper flow
regime continues over the Southwest and Great Basin. Upper ridging
centered of southern Alberta early Wednesday is expected to
gradually shift eastward throughout the day as a compact shortwave
trough traverses its western periphery over British Columbia.
Farther east, a series of shortwave troughs will likely progress
through the base of an upper trough extending from the Hudson Bay
into the Upper Midwest early Wednesday. Evolution of these
shortwaves coupled with the eastern moving upper ridge will likely
result in an overall eastward progression of the upper trough, with
some deepening also possible.
A largely nondescript surface pattern is expected east of the
Rockies, with a tropical air mass covering all but the northern and
central Plains. Some low-level convergence is possible from central
KS northeastward into Lower MI, along the weak stationary front
separating the tropical air mass to the south/east and more
continental air mass to the north/west.
...OH Valley into the Northeast...
Upper 60s to low 70s dewpoints are expected to be in place across
the OH Valley and much of the Northeast early Wednesday morning.
This moist air mass will destabilize quickly amid daytime heating,
with moderate buoyancy anticipated by early afternoon. Given the
lack of convective inhibition, scattered to widespread thunderstorm
development is possible across the region with both surface
convergence and subtle large-scale forcing for ascent acting as
Closer proximity to the shortwave troughs moving through the parent
upper trough will result in both stronger large-scale forcing ascent
and stronger vertical shear over the Northeast. A predominantly
multicellular storm mode is anticipated, but stronger vertical shear
in the region could result in a few more organized line segments,
with an attendant threat for damaging wind gusts. Given the
favorable overlap between buoyancy and shear, a greater severe
potential appears to exist from central PA through central/eastern
NY into much of New England. This includes much of VT and NH as well
as central/eastern Maine, where stronger low-level flow could
support a few supercells.
Increasing mid-level moisture will help support isolated to
scattered thunderstorms development Wednesday afternoon. Weak
vertical shear should limit storm organization, but high cloud bases
amid a deeply mixed boundary layer could still result in a few
strong gusts with more robust storms.
...North-Central/Northwest MN into Northwest WI...
Shortwave trough dropping south through western Ontario is forecast
to reach northern MN during the afternoon, contributing to
thunderstorm development amid modest buoyancy. Storm coverage
remains uncertain, but moderate northwesterly flow aloft could
result in a few strong storms. Coverage uncertainty precludes adding
probabilities with this outlook.
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NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z