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 200532
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1232 AM CDT Sun Jun 20 2021
Valid 201200Z - 211200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM EASTERN
IOWA TO SOUTHERN LOWER MICHIGAN...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
ENHANCED RISK FROM THE MID MISSISSIPPI VALLEY INTO THE LOWER GREAT
LAKES ALONG WITH PARTS OF THE SOUTHEAST...
Scattered severe storms are expected across the Midwest into the
lower Great Lakes/upper Ohio Valley. Large hail, severe/damaging
winds, and a few tornadoes are possible. Damaging winds and a couple
of tornadoes are also possible across the Southeast.
...Midwest to Lower Great Lakes...
Late Saturday central High Plains convection has spread downstream
and matured into a significant MCS as it tracks east along the NE/KS
border. Forward propagation appears to be reasonably similar to the
latest NAM with the leading edge of the MCS likely spreading across
southwestern into south-central IA early in the period. One concern
is how poorly the models are handling the strong, sustained
convection across northern MO. This activity continues to propagate
northwest and will likely be absorbed into a larger complex by
daybreak. The disruptive potential of this interaction is unknown.
Even so, it appears a corridor of strong instability should evolve
from northern IL into southern lower MI. Approaching convectively
induced short-wave trough, strong heating, and the potential for a
low-level confluence zone to be draped across this region suggest
the potential for significant severe. Have opted to extend the ENH
Risk downstream across southern lower MI and adjacent portions of
northern IN/northwest OH as forecast soundings are impressively
buoyant and strongly sheared. Profiles favor supercells but the
early-day MCS will likely continue, in some form, through the day as
it spreads downstream. If supercells evolve, tornadoes and large
hail threat will increase with this activity. Otherwise, damaging
winds can be expected.
Later in the afternoon, surface heating should contribute to frontal
convection that will initiate across the upper MS Valley, then
spread/develop along the wind shift into eastern KS. Steep lapse
rates, strong surface-6km shear, and abundant instability suggest
the potential for very large hail with supercells in the wake of the
Remnants of Claudette continue to shift downstream across AL into
GA/northern FL. Low-level shear will remain strong from northern FL
into coastal NC much of the period. While numerous showers/storms
will be ongoing at daybreak, latest NAM suggests a narrow corridor
of steeper surface-3km lapse rates within the zone of stronger shear
from northeast FL through coastal SC. This may increase the
potential for damaging winds and tornadoes. For these reasons have
increased severe probabilities across this region.
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