Severe Thunderstorm Watch 792

Issued

Aug 20, 2011, 1:41 PM EDT (17:41 UTC)

Expired

Aug 20, 2011, 6:04 PM EDT

In force

4 hr

Issued by

the Storm Prediction Center

Largest hail expected

1.5 in

Strongest gust expected

60 kt

The Grand Rapids radar (KGRR), 81 km from the middle of the area, began a volume at 17:44 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

Two or more tornadoes

10%

One or more EF2 to EF5 tornadoes

2%

Ten or more severe wind reports

40%

One or more gusts of 65 knots or more

30%

Ten or more severe hail reports

20%

One or more hailstones of 2 inches or more

10%

Six or more combined severe hail and wind reports

70%

• Mesoscale Discussion 2026Aug 20, 12:04 PM EDT
• Mesoscale Discussion 2027Aug 20, 4:37 PM EDT

331 
WWUS20 KWNS 201741
SEL2
SPC WW 201741
MIZ000-LEZ000-LHZ000-210100-

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 792
NWS STORM PREDICTION CENTER NORMAN OK
140 PM EDT SAT AUG 20 2011

THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

       SOUTHERN LOWER MICHIGAN
       LAKE ERIE
       LAKE HURON

EFFECTIVE THIS SATURDAY AFTERNOON AND EVENING FROM 140 PM UNTIL
900 PM EDT.

HAIL TO 1.5 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70
MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 85
STATUTE MILES EAST AND WEST OF A LINE FROM 40 MILES SOUTHWEST OF
JACKSON MICHIGAN TO 30 MILES NORTH NORTHEAST OF FLINT MICHIGAN.
FOR A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH
OUTLINE UPDATE (WOUS64 KWNS WOU2).

REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE
FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
AND POSSIBLE WARNINGS. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY
DO PRODUCE TORNADOES.

DISCUSSION...A LINEAR CLUSTER OF THUNDERSTORMS IS MOVING EWD FROM
LAKE MI INTO SW LOWER MI.  THOUGH DOWNSTREAM ANVIL HAS LIMITED
SURFACE HEATING...SURFACE TEMPERATURES NEAR 80 AND DEWPOINTS NEAR 70
ARE STILL SUPPORTING MLCAPE AOA 2000 J/KG.  LOW-LEVEL FLOW IS NOT
PARTICULARLY STRONG OVER LOWER MI...BUT 40 KT WLY MIDLEVEL FLOW IS
CONTRIBUTING TO SUFFICIENT BULK SHEAR FOR ORGANIZED BOWING SEGMENTS
AND CLUSTERS.  A FEW DAMAGING GUSTS AND MARGINALLY SEVERE HAIL WILL
BE THE PRIMARY SEVERE THREATS THIS AFTERNOON AS THE CONVECTION
SPREADS EWD TOWARD SE LOWER MI.

AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT
TO 1.5 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60
KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM
MOTION VECTOR 27030.


...THOMPSON

Severe Thunderstorm Watches in Michigan, 2011Every severe thunderstorm watch in 2011

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.