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
2 %
35,300
93,805
Pierre, SD...
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
15 %
42,239
113,683
Pierre, SD...
5 %
190,263
2,634,918
Amarillo, TX...Sioux Falls, SD...Rapid City, SD...Bismarck, ND...Muskogee, OK...
SPC AC 111619
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1119 AM CDT Tue Aug 11 2020
Valid 111630Z - 121200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS WESTERN NE AND
SD...
...SUMMARY...
The most likely area for severe wind and hail during the late
afternoon into tonight is across western Nebraska into South Dakota.
...SD/NE...
Low-level warm advection in conjunction with a leading mid-level
impulse has sustained general thunder across central SD this
morning. This activity should decay this afternoon as warm advection
wanes.
Late-afternoon storm development should focus where convergence is
maximized along the lee trough/dryline in the NE Panhandle vicinity.
This region will lie in the gradient between moderate mid-level
westerlies across northern WY and SD, and weaker flow across CO and
KS. The setup should favor a few multicells and a couple transient
supercells with some risk for severe hail/wind.
An upstream mid-level impulse along the MT/WY border will track into
northern SD this evening. Most guidance delays convective
development until after sunset when the low-level jet intensifies
from western KS into SD. The CAPE/shear combination in SD will be
greater relative to farther south, suggesting that an organized
cluster with severe wind/hail could form in the late evening to
overnight. Have expanded cat 2/SLGT risk east to account for this
scenario.
...Central/southern High Plains...
Isolated late-afternoon to early-evening thunderstorms are expected
along the lee trough/dryline from the CO/KS border south to west TX.
While 500-mb westerlies should hold from 15-25 kts, a belt of 50-60
kt 250-mb flow should be maintained across southern CO into the
adjacent High Plains. This will aid in isolated severe hail/wind.
...AR and eastern OK...
An MCV near the northeast OK/southeast KS border should drift
east-southeast towards AR. Regenerative convection is anticipated
through much of the period near/east/south of the MCV. Modest
enhancement to mid-level flow on the southwest flank of the MCV
across OK may aid in loosely organized multicell clusters during the
late afternoon and early evening from the Lower Red River Valley
into AR. Isolated damaging wind gusts should be the main hazard, but
marginal hail will also be possible.
...Eastern NY to western/northern New England...
A decaying shortwave trough across southeast Ontario and southwest
Quebec may support isolated thunderstorms from eastern NY to
northern ME during the late afternoon and early evening along a
trailing cold front. Convergence along the front should be weak, and
confidence in convective initiation/longevity is not particularly
high. Nevertheless, storms that can develop will pose a risk of
locally damaging wind gusts.
..Grams/Kerr.. 08/11/2020
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