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.
Milwaukee, WI...St. Louis, MO...Grand Rapids, MI...Sioux Falls, SD...Lansing, MI...
SPC AC 091627
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1127 AM CDT Mon Aug 09 2021
Valid 091630Z - 101200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
INTO EARLY TONIGHT ACROSS NORTHERN IL AND NORTHWESTERN IN...AND
ACROSS EASTERN ND AND VICINITY...
...SUMMARY...
Severe storms are expected this afternoon into tonight over parts of
the northern Plains and Midwest/Ohio Valley, primarily across
eastern North Dakota and northern Illinois.
...Northern IL area this afternoon into early tonight...
Clouds and convection have been relatively widespread across
WI/IL/IN this morning in association with multiple thunderstorm
clusters, though some cloud breaks are becoming apparent from west
central into northeast IL. Storms are ongoing along the WI/IL
border along the southern/southeastern flank of an MCV, and
additional storm development should occur toward the south and
southwest as the low levels destabilize from west-to-east this
afternoon across northern IL. Enhanced low-level flow/warm
advection along the south flank of the MCV will result in
substantial hodograph curvature/SRH, while deep-layer shear will be
sufficiently strong for supercells. The net result will be a band
of convection developing southward across northern IL with embedded
supercells capable of producing damaging winds, large hail, and a
couple of tornadoes.
...Eastern ND and vicinity this afternoon into early tonight...
A pronounced midlevel shortwave trough over MT this morning will
progress eastward across ND through tonight. The midlevel trough
will be preceded by a surface cyclone and cold front in eastern ND,
which will combine with ascent downstream from the midlevel trough
to focus thunderstorm development through tonight. Surface heating
in the warm sector will contribute to MLCAPE up to 2000 J/kg, while
midlevel lapse rates will be relatively steep (close to 8 C/km) and
effective bulk shear will reach 35-45 kt in a narrow corridor along
the front. A mix of supercells and clusters/line segments is
expected along the front late this afternoon through late evening,
with an attendant threat for isolated very large hail of 2 to 2.5
inch diameter and severe outflow winds of 60-70 mph.
..Thompson/Bentley.. 08/09/2021
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NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 2000Z
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