Marine Thunderstorm Winds in Lake St. Clair, July 21, 2002

SOUTHEAST MICHIGAN AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1145 AM EDT SUN JUL 21 2002

SEVERE WEATHER THREAT AND THE HEAT WILL BE THE MAIN CONCERNS FOR
THIS AFTERNOON. THE STRONG SURFACE COLD FRONT EXTENDING FROM
NORTHERN LAKE MICHIGAN BACK INTO THE MID MISSISSIPPI VALLEY WILL
PUSH THROUGH SOUTHEAST MICHIGAN FROM 20Z TO 00Z...PER THE LATEST RUC
SOLUTION. VERY HIGH INSTABILITY AHEAD OF THIS FRONT IS ALREADY
ALLOWING THUNDERSTORMS TO DEVELOP IN FAR SOUTHERN LOWER MICHIGAN AND
NORTHERN INDIANA. UPPER LEVEL SUPPORT FOR THE THUNDERSTORMS WILL
COME FROM SOME LIFT AHEAD OF THE SHORT WAVE TROUGH OVER THE UPPER
MISSISSIPPI VALLEY AND DIVERGENCE ALOFT IN ENTRANCE REGION OF UPPER
JET OVER THE NORTHERN GREAT LAKES. MODIFIED 12Z KDTX SOUNDING FOR A
TEMP OF 94 AND DEWPOINT OF 75 GIVES A CAPE OF 5200 J/KG. MODEL
SOUNDING FOR THIS AFTERNOON ARE STILL SHOWING SOME DRYING IN THE MID
LEVELS. THIS DRIER MID LEVEL AIR WAS NOTED ACROSS ILLINOIS ON THE
12Z RAOBS. SO ALTHOUGH 0-6KM SHEAR PROFILES ARE NOT THAT
STRONG...NEGATIVE BUOYANCY POTENTIAL AND THE INSTABILITY SHOULD BE
ENOUGH TO ALLOW SOME STORMS TO PRODUCE DAMAGING WINDS. PRECIPITABLE
WATER VALUES NEAR 2 INCHES AND K INDICES IN THE UPPER 30S WILL ALSO
SPELL GOOD POTENTIAL FOR HEAVY RAINFALL WITH THE STORMS. TIMING THE
ONSET OF THE STORMS WILL BE DIFFICULT AS DIFFERENTIAL HEATING
BOUNDARIES AND THUNDERSTORM OUTFLOW WILL AID DEVELOPMENT WELL IN
ADVANCE OF THE SURFACE COLD FRONT.

A HEAT ADVISORY HAS ALSO BEEN ISSUED FOR THE SOUTHERN 2/3RDS OF THE
FORECAST AREA BASED ON CURRENT HEAT INDICES. SOME LOCATIONS MAY NOT
ATTAIN ADVISORY CRITERIA DUE TO ONGOING THUNDERSTORMS. WITH A GOOD
BIT OF CLEARING UPSTREAM THOUGH...THINK THAT THERE WILL BE SEVERAL
LOCATIONS THAT HAVE HEAT INDICES AROUND 105 DEGREES FOR MUCH OF THE
AFTERNOON.

.DTX...HEAT ADVISORY...THIS AFTERNOON...
       MIZ060>063-068>070-075-076-082-083

CONSIDINE

MIZ047>049-053>055-060>063-068>070-075-076-082-083-212100-

HAZARDOUS WEATHER OUTLOOK FOR SOUTHEAST MICHIGAN
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
1045 AM EDT SUN JUL 21 2002

...HOT...HUMID WEATHER AND THUNDERSTORMS TODAY AND
MONDAY...

DISPATCHERS...PLEASE NOTIFY YOUR EMERGENCY MANAGERS IMMEDIATELY.

HAZARDS...
EXCESSIVE HEAT AND HUMIDITY WILL AFFECT ALL OF SOUTHEAST MICHIGAN
TODAY...WITH TEMPERATURES INCHING ABOVE 90 AND HEAT INDICES
APPROACHING 100.

IN ADDITION...NUMEROUS THUNDERSTORMS ARE EXPECTED THROUGH EARLY TO
MID AFTERNOON NORTH OF M59. THESE THUNDERSTORMS ARE EXPECTED TO
PRODUCE WIND GUSTS TO 45 MPH AND PEA SIZE HAIL. NO SEVERE WEATHER IS
EXPECTED AT THIS TIME.

DISCUSSION...
LOW PRESSURE NORTH OF LAKE SUPERIOR WILL CONTINUE TO TRACK EAST
TODAY...AND SOUTHWEST WINDS AHEAD OF THIS SYSTEM WILL PUMP HOT AND
HUMID AIR INTO SOUTHEAST MICHIGAN. HIGH TEMPERATURES WILL CLIMB
ABOVE THE 90 DEGREE MARK THIS AFTERNOON WITH DEWPOINTS CLIMBING
ABOVE THE 70 DEGREE MARK... ESPECIALLY IN AREAS SOUTH OF M59. THIS
COMBINATION WILL RESULT IN HEAT INDEX VALUES REACHING AROUND THE 100
DEGREE RANGE. AS HEAT INDICES APPROACH OR EXCEED THE 100 MARK...IT
IS BEST TO AVOID PROLONGED OUTSIDE ACTIVITIES TO PREVENT HEAT
STRESS.

IN ADDITION...THE INCREASE IN MOISTURE WILL LEAD TO AN UNSTABLE
AIRMASS...WHICH WILL CONTRIBUTE TO NUMEROUS THUNDERSTORMS NORTH OF
M59 THIS AFTERNOON AND THIS EVENING. VERY HEAVY RAINFALL...PEA SIZE
HAIL AND WIND GUSTS UP TO 45 MPH WILL BE THE MAIN HAZARDS WITH THESE
STORMS. THE STORMS WILL MOVE TO THE SOUTHEAST AT 25 MPH.

SPOTTER ACTIVATION...
SPOTTER ACTIVATION NOT ANTICIPATED AT THIS TIME... ALTHOUGH
THUNDERSTORM DEVELOPMENT WILL BE MONITORED FOR INCREASES IN
INTENSITY.

OUTLOOK FOR MONDAY AND TUESDAY...
A COLD FRONT WILL MOVE THROUGH SOUTHEAST MICHIGAN MONDAY AFTERNOON.
MORNING SUNSHINE WILL ALLOW TEMPERATURES TO RISE WELL INTO THE 90S.
HEAT INDICES ARE EXPECTED TO REACH INTO THE 105 TO 110 DEGREE RANGE
FOR AREAS ALONG AND SOUTH OF INTERSTATE 69. IN ADDITION...SEVERE
THUNDERSTORMS WILL BE POSSIBLE WITH THE PASSAGE OF THE COLD FRONT
MONDAY AFTERNOON AND EVENING. NO HAZARDOUS WEATHER IS EXPECTED ON
TUESDAY AS CONDITIONS WILL BE DRY AND COOLER.

STAY TUNED TO NOAA WEATHER RADIO... OR LOCAL MEDIA OUTLETS... FOR
THE LATEST FORECAST INFORMATION FROM THE NATIONAL WEATHER SERVICE.
YOU CAN ALSO OBTAIN THE LATEST FORECAST ON THE NATIONAL WEATHER
SERVICE WEB SITE.

HTTP://WWW.CRH.NOAA.GOV/DTX/ (ALL LOWER CASE)

SF/RBP