Probability of a tornado within 25 miles of a point. Hatched Area: 10% or greater probability of EF2 - EF5 tornadoes within 25 miles of a point.
Day 1 Tornado Risk
Area (sq. mi.)
Area Pop.
Some Larger Population Centers in Risk Area
5 %
13,501
141,272
No Major Population Center in Risk Area
2 %
35,557
3,368,214
Columbia, SC...North Charleston, SC...Sumter, SC...Summerville, SC...Goose Creek, SC...
Probabilistic Damaging Wind Graphic
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 251940
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0240 PM CDT Fri Sep 25 2020
Valid 252000Z - 261200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER FAR NORTHERN
WISCONSIN INTO UPPER MICHIGAN...
...SUMMARY...
A couple tornadoes, golf to tennis ball size hail, and damaging
winds will be possible between 5 to 10 PM CDT across far northern
Wisconsin and western Upper Michigan.
...Discussion...
No significant changes have been made to previous outlook. The
surface layer continues to destabilize across far northern WI into
Upper MI as low clouds mix out near and south of a warm front.
Storms are expected to develop generally along and north of this
boundary later this afternoon into the evening as the leading band
of deeper ascent accompanying an upstream shortwave trough and its
attendant low-level jet begins to interact with the baroclinic zone.
Supercells capable of large hail and a couple of tornadoes remain
the primary threats.
..Dial.. 09/25/2020
.PREV DISCUSSION... /ISSUED 1121 AM CDT Fri Sep 25 2020/
...Lake Superior vicinity...
A series of low-amplitude shortwave troughs will progress eastward
from the northern Rockies/Great Plains to the upper Great Lakes
through tonight. At the surface, a cyclone in west-central MN will
track east-northeast into northwest WI by about 00Z before shifting
across Lake Superior tonight. To the east of the cyclone, a warm
front will develop northward to near the southern shore of Lake
Superior by late afternoon. Surface temperatures warming into the
70s and boundary-layer dewpoints increasing into in the low 60s
beneath steep mid-level lapse rates will contribute to a narrow
corridor of MLCAPE near 1500 J/kg immediately ahead of the surface
cyclone.
The stronger forcing for ascent will likely be confined to the warm
front, with areas farther south in the warm sector remaining capped
given the modest moisture return. Thus, the more probable corridor
for surface-based storms will be across extreme northwest WI into
western Upper MI during the early evening (22-00Z). The conditional
storm environment will be rather favorable for a supercell or two
given the moderate buoyancy and large, curved hodographs with
effective bulk shear of 50-60 kt and effective SRH in excess of 300
m2/s2. There will be a window of opportunity for a couple tornadoes,
significant severe hail, and damaging winds within a spatially
confined corridor. The overall threat is expected to diminish after
about 03Z.
...SC vicinity...
The remnants of post-tropical cyclone Beta have phased with a
shortwave trough over the southern Appalachians. The surface
reflection has weakened during the past 24 hours, but there will
still be a baroclinic zone to focus isolated to scattered
thunderstorms across the Carolinas. Mid-level lapse rates will
remain poor, and low-level wind fields should continue to slowly
subside. However, deep-layer vertical shear will be sufficient for a
few transient, low-end supercells capable of isolated damaging wind
gusts and a brief tornado through about sunset.
CLICK TO GET WUUS01 PTSDY1 PRODUCT
NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 0100Z
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