Severe Thunderstorm Warning 59, NWS Detroit, MI

SOUTHEAST MICHIGAN AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DETROIT/PONTIAC MI
325 PM EDT TUE AUG 7 2001

SHOWERS AND THUNDERSTORMS FIRING ALONG INCREASINGLY STRONG SURFACE
CONVERGENCE LINE STRETCHING FROM PHN NORTH INTO LAPEER AND GENESEE
COUNTIES. MESOETA SHOWS THE SURFACE CONVERGENCE DRIFTING SLOWLY
SOUTH TO METRO DETROIT AREA...THEN DISSIPATING BETWEEN 00Z AND 03Z.
TEMPERATURES IN THE LOW TO MID 90S ALONG WITH DEW POINTS WELL INTO
THE 70S HAS PRODUCED CAPE VALUES IN THE 6000 PLUS RANGE...PER LAPS
DATA. MESOETA SOUNDINGS SHOW A CAP IN PLACE THROUGH THE EVENING.
HOWEVER...12Z MESOETA SOUNDINGS LOOKED AGGRESSIVE WITH CAP VS ACTUAL
DTX SOUNDING. AIDING DEVELOPMENT OF TSRA ACTIVITY IS DPVA ACROSS
NORTHERN THIRD OF CWA AS DEPICTED BY RUC MODEL. THIS DPVA WILL ALSO
BE WORKING SOUTH DURING THE EVENING HOURS. WITH CAPES IN THE 4000 TO
6000 J/KG RANGE...AND DRY AIR OBSERVED ACROSS CWA PER H20 VAPOR
LOOP...PULSE TYPE STORMS PRODUCING MARGINALLY SEVERE HAIL/WIND
CANNOT BE RULED OUT THROUGH ABOUT 9 PM.

WITH COMBINATION OF TEMPERATURES AND DEW POINTS PRODUCING HEAT
INDICES IN THE 105 TO 108 RANGE WILL MAINTAIN HEAT ADVISORY INTO
THE EARLY EVENING HOURS FOR ALL ZONES...EXCEPT HURON/SANILAC
COUNTIES. THERE...DRIER AIR HAS FILTERED INTO THE REGION BRINGING
HEAT INDICES BELOW ADVISORY CRITERIA.

SKIES WILL CLEAR TONIGHT. FLY IN THE OINTMENT IS PROGGED MCS
DEVELOPMENT OVER NORTHERN MINNESOTA OVERNIGHT. 300-850MB THICKNESS
PROGS AND CORFIDI VECTORS SUGGEST A SOUTHEAST DRIFT TO THE MCS
OVERNIGHT INTO THE MORNING HOURS WEDNESDAY. MCS PRECIPITATION FIELDS
BRING REMNANT PRECIPITATION CLOSE TO NORTHERN PART OF THE CWA
TOMORROW AFTERNOON. ELEVATED AND SURFACE INSTABILITIES BECOME
CONDUCIVE TO SHOWER ACTIVITY TOMORROW AFTERNOON. HOWEVER...GIVEN THE
EVER PRESENT TIMING AND LOCATION PROBLEMS INHERENT WITH MCS
DEVELOPMENT WILL LEAVE THE DAY DRY. 850MB TEMPERATURES WARM A DEGREE
OR TWO FROM TODAY/S LEVELS...SO GIVEN EXPECTED LEVELS OF SUNSHINE
EXPECT ANOTHER DAY OF MID 90S TEMPERATURES. MODEL GUIDANCE...MAVS
AND ETA 2M...SHOW DEW POINTS SOME 6 TO 10 DEGREES LOWER TOMORROW
THAN TODAY. THEREFORE...WILL HOLD OFF ON ANY HEAT ADVISORIES.
RECORDS FOR TOMORROW AT MBS/FNT/DTW RESPECTIVELY ARE 99/93/97. WILL
HIGHLIGHT RECORD TEMPERATURES FOR FNT ZONE.

ANOTHER TRICKY DAY ON THURSDAY. ETA AND AVN SUGGEST SOME MOISTURE
FROM THE REMNANTS OF BARRY WILL BE TRANSPORTED INTO AT LEAST THE
SOUTHERN HALF OF THE CWA. MODELS DIVERGE THOUGH ON PRECIPITATION
CHANCES WITH THIS MOISTURE AVAILABILITY. AVN KICKS OFF MEASURABLE
PRECIP...WHILE ETA KEEPS THINGS DRY. WHILE ACKNOWLEDGING THE
MOISTURE...WILL HOLD OFF ON INSERTING ANY POPS FOR THURSDAY...GIVEN
LACK OF ANY SURFACE CONVERGENCE. LOOKS LIKE ANOTHER 90 DEGREE DAY
ACROSS MOST OF THE CWA...WITH 850MB TEMPERATURES OFF A DEGREE OR TWO
FROM TOMORROW/S VALUES...LOW 90S LOOKS BETTER THAN MID 90S.

POTENT COLD FRONT WILL APPROACH CWA LATE IN THE DAY THURSDAY.
DPROG/DT ON ETA MODEL SHOWS A SLIGHTLY SLOWER SOLUTION THIS MODEL
RUN. WILL LEAVE FRONTAL INDUCED PRECIPITATION OUT OF NORTHERN ZONES
ON THURSDAY...BUT INSERT SCT SHRA/TSRA CWA-WIDE FOR THURSDAY NIGHT.

EXTENDED...
FRONT WILL CLEAR CWA IN TIME TO KEEP FRIDAY DRY...AND USHER IN
PROLONGED PERIOD OF COOLER TEMPERATURES. UPPER LEVEL HIGH WILL
RETROGRADE EARLY IN THE PERIOD AND ESTABLISH ITSELF ALONG THE GREAT
BASIN BY THE END OF THE PERIOD. THIS WILL ALLOW HEIGHTS TO LOWER
ACROSS THE GREAT LAKES. MRF IS THE MOST AGGRESSIVE OF THE EXTENDED
MODELS IN ROTATING SEVERAL CLOSED LOWS JUST NORTH OF THE BORDER
THROUGH THE PERIOD. CANADIAN IS THE MOST SUBDUED...WITH THE ETA-XX
INTERMEDIATE. ETA-XX AND MRF BOTH IN REASONABLY GOOD AGREEMENT IN
PUSHING A POTENT COLD FRONT ACROSS THE CWA ON MONDAY. WILL NEED TO
INTRODUCE A CHANCE OF SHOWERS AND THUNDERSTORMS FOR MONDAY. EXTENDED
PERIOD WILL BE MARKED BY A SIGNIFICANT COOL DOWN FROM CURRENT
LEVELS...WITH TEMPERATURES TRENDING NEAR TO EVEN SLIGHTLY BELOW
NORMAL.

.DTX...HEAT ADVISORY...EARLY THIS EVENING...
       MIZ047-048-053-054-060>063-068>070-075-076-082-083

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