

615 

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

