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
No Risk Areas Forecast
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.
Probability of hail 1" or larger within 25 miles of a point. Hatched Area: 10% or greater probability of hail 2" or larger within 25 miles of a point.
Day 1 Hail Risk
Area (sq. mi.)
Area Pop.
Some Larger Population Centers in Risk Area
5 %
10,059
16,215
No Major Population Center in Risk Area
SPC AC 210545
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1245 AM CDT Thu Oct 21 2021
Valid 211200Z - 221200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE SOUTHERN AND CENTRAL APPALACHIANS...LOWER GREAT LAKES AND IN
WEST TEXAS...
...SUMMARY...
Thunderstorms associated with isolated strong wind gusts will be
possible today across parts of the southern and central Appalachians
into the lower Great Lakes. Isolated storms capable of marginally
severe hail and strong gusts may also occur over a small part of
west Texas.
...Southern and Central Appalachians/Lower Great Lakes...
An upper-level low will move eastward across the southern Great
Lakes region today as an associated upper-level trough moves across
the mid Mississippi Valley. Ahead of the system, a narrow corridor
of maximized low-level moisture will be in place across the Ohio and
Tennessee Valleys. This corridor will shift eastward during the day
as a cold front advances southeastward. By afternoon, weak
instability will be in place from western Pennsylvania
south-southwestward across eastward Ohio, eastern Kentucky and
eastern Tennessee. Thunderstorms will develop along and just ahead
of the much of the front by mid afternoon with this convection
moving eastward into western parts of the southern and central
Appalachians.
RAP forecast soundings along the axis of strongest instability by
21Z, from Pittsburgh to Knoxville, have 0-6 km shear in the 40 to 50
kt range. This combined with steep low-level lapse rates and weak
instability should be enough for multicell line segments capable of
strong wind gusts. The current thinking is that a line segment will
develop ahead of the front during the mid to late afternoon. This
line segment will move eastward into the western foothills of the
Appalachians where a few marginally severe wind gusts may occur. At
this time, instability appears to be the factor that will minimize
severe threat coverage. Although an isolated supercell can not be
ruled out, any threat should remain very localized and strongly tied
to destabilization.
...West Texas...
An upper-level ridge will move eastward across the Intermountain
West today as northwest mid-level flow remains over the southern and
central Plains. At the surface, the western edge of a moist airmass
will be in place across west Texas. Moderate instability will
develop by midday across west Texas, where convective initiation
appears likely in the Davis Mountains. The storms should remain
isolated due to minimal large-scale ascent. However, the instability
combined with steep mid-level lapse rates and moderate deep-layer
shear should be enough for hail and strong gusty winds.
..Broyles/Wendt.. 10/21/2021
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NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z
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