Severe Thunderstorm Warning 42, NWS Gaylord, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GAYLORD MI
355 PM EDT WED JUL 28 1999

FRONTAL BOUNDARY NOW EXTENDS FROM THE STRAITS AREA THROUGH NRN LAKE MI
SW INTO CENTRAL WI AND SRN MN. SFC DWPTS HAVE RISEN RAPIDLY INTO THE
UPPER 60S TO NEAR 70 ALONG AND JUST AHEAD OF THE FRONT. THETA E RIDGE
IS WORKING ITS WAY INTO THAT AREA AS WELL...AND CAPES HAVE RISEN TO
BETWEEN 2000 TO 3000 J/KG OVER LAKE MI AND WRN LOWER MI. A FEW
SHRA/TSRA HAVE DEVELOPED JUST E OF ERN UPR MI AND AROUND CAD AND
LAKE CITY. HERE IN LIES THE MAIN SHORT TERM CONCERN...THE POTENTIAL
FOR SVR TSRA THIS EVENING ALONG AND AHEAD OF THIS BOUNDARY. LATER
PERIOD CONCERNS TURN TOWARD ANOTHER SHORT WAVE AND SFC COLD FRONT
MOVING THROUGH MI ON THURSDAY.

MODELS ARE QUITE SIMILAR THROUGH 24 HOURS...DROPPING THE FRONT SE TO
THE SAGINAW BAY AREA BETWEEN 06Z AND 08Z. THETA E RIDGE STRENGTHENS
AND MOVES FURTHER E INTO LOWER MI THIS EVENING ALONG AND AHEAD OF
THE FRONT. MAIN SVR WX CONCERN IS STRONG WINDS. 500 MB W WINDS
INCREASE TO NEAR 50 KTS. LITTLE DIRECTIONAL SHEAR...BUT WITH 850 MB
WINDS HOLDING AROUND 20 KTS...GOOD 850 TO 500 MB SPEED SHEAR IS
SETTING UP FOR THIS EVENING. IN ADDITION...SOME MID LEVEL DRYING
WILL TAKE PLACE EARLY...HEIGHTENING THE CONCERN FOR DOWNBURST
POTENTIAL. THE ONLY THING THAT APPEARS TO THE LACKING IS SUFFICIENT
LOW LEVEL CONVERGENCE. ACTIVITY THAT HAS ALREADY DEVELOPED DID SO IN
AREAS OF BEST LOW LEVEL CONVERGENCE. BUT CONVECTION THUS FAR SEEMS
TO BE MISSING GOOD FOCUS. WILL MAINTAIN CHANCE POPS INTO THE
EVENING FOR ENTIRE CWA...BUT WILL WORD AS EARLY IN ERN UPR.

NGM APPEARS TO HAVE SOME ERRONEOUS DATA IN ITS UPPER LEVEL MOISTURE
FIELDS AT 24 HRS. NGM IS ALSO SLIGHTLY FASTER WITH THE SECOND SHORT
WAVE APPROACHING MI ON THURSDAY. NGM TIMING MAY BE CORRECT FOR ERN
UPR MI...SUGGESTING SCT PRECIP ARRIVING BY MID MORNING AND ENDING
AROUND MID AFTERNOON THURSDAY...BUT SUSPECT FRONT MAY SLOW A BIT
WITH DIURNAL HEATING IN THE AFTERNOON ACROSS NRN LOWER MI. BETTER
FOCUS AND MORE ORGANIZED DPVA FROM A STRONGER SHORT WAVE TO LEND
SUPPORT FOR CONVECTIVE DEVELOPMENT TOMORROW. MODEL CAPES ARE AGAIN
PROGGED TO BE AROUND 2000 J/KG...WITH AN EVEN STRONGER THETA E RIDGE
DRIVING NE INTO LOWER MI IN THE AFTERNOON. WILL GO WITH CHANCE POPS
ALL ZONES THURSDAY INTO THURSDAY EVENING...BUT WILL HOLD OFF UNTIL
AFTERNOON FOR MOST OF NRN LOWER WHEN BETTER FOCUS/INSTABILITY ARRIVES.
FRIDAY WILL BE DRY...BUT STILL VERY WARM. MOS HIGH TEMPS ARE AGAIN
TOO WARM...WILL ADJUST ACCORDINGLY.

EXTENDED FORECAST...CANADIAN AND MRF ARE SIMILAR IN GENERAL UPPER
LEVEL LONG WAVE PATTERN...KEEPING THE BROAD UPPER RIDGE IN PLACE
OVER MUCH OF THE US THROUGH TUESDAY. CANADIAN DOES SUGGEST A
SLIGHTLY DEEPER UPPER LOW OVER ERN CANADA THROUGH TUESDAY AND DOES
EXTEND THE ASSOCIATED UPPER TROFF FURTHER INTO THE GREAT LAKES.
MEANWHILE...THE EUROPEAN SEEMS TO OVERAMPLIFY THE UPPER RIDGE INTO
THE GREAT LAKES BY LATE FRIDAY. WILL TEND TO GO WITH THE MIDDLE OF
THE ROAD SOLUTION PROVIDED BY THE MRF AS IT APPEARS THE PERSISTANT
UPPER RIDGE WILL BE DIFFICULT TO OVERCOME BY THE ERN CANADIAN
LOW/TROFF...BUT DO EXPECT CWA WILL TO SEE PERIODIC SHORT WAVES SHOOT
THROUGH THE REGION IN FAIRLY FAST UPPER FLOW ON THE SRN FRINGE OF
THAT UPPER TROFF. BEST SHRA/TSRA CHANCES WILL BE LATE FRIDAY NIGHT
INTO SATURDAY AND AGAIN LATE MONDAY IN UPR MI.

.APX...NONE.

EME