WATCHES: Severe Thunderstorm Watch Number 676

WWUS20 KWNS 211753
SEL6
SPC WW 211753
MIZ000-LHZ000-LMZ000-220100-

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 676
NWS STORM PREDICTION CENTER NORMAN OK
155 PM EDT TUE SEP 21 2010

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

NORTHERN AND CENTRAL LOWER MICHIGAN
LAKE HURON
LAKE MICHIGAN

EFFECTIVE THIS TUESDAY AFTERNOON AND EVENING FROM 155 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 65
STATUTE MILES EAST AND WEST OF A LINE FROM 35 MILES SOUTHEAST OF
ROBEN HOOD MICHIGAN TO 30 MILES NORTH OF ALPENA MICHIGAN. FOR A
COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH OUTLINE
UPDATE (WOUS64 KWNS WOU6).

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...TSTMS ARE EXPECTED TO INCREASE IN COVERAGE AND
INTENSITY THIS AFTERNOON AHEAD OF STRONG MIDLEVEL IMPULSE
PROGRESSING EWD THROUGH THE REGION. STRONG DIABATIC HEATING HAS
CONTRIBUTED TO SBCAPE OF 1000-1500 J/KG...AND EFFECTIVELY STEEPENED
LOW-LEVEL LAPSE RATES. WHEN COUPLED WITH 40-50+ KT SWLY FLOW
OBSERVED AS LOW AS 1-2 KM AGL /PER APX VWP/...ENVIRONMENT WILL FAVOR
THE DEVELOPMENT OF ORGANIZED...SEVERE STORMS CAPABLE OF MAINLY
DAMAGING WIND GUSTS.

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 26035.

...MEAD

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