Special Marine Warning 2, NWS Gaylord, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GAYLORD MI
405 AM EDT THU APR 18 2002

SFC HIGH CENTER IS BEGINNING TO PUSH NE OF MI EARLY THIS MORNING...
WITH MOIST SE RETURN FLOW QUICKLY APPROACHING THE STATE. SEVERAL
AREAS OF CONVECTION HAVE DEVELOPED OVERNIGHT...AND ARE NOW AFFECTING
ERN ND...MUCH OF MN AND PORTIONS OF WRN WI AND NE IA. SVR TSRA WATCH
BOX WAS RECENTLY ISSUED FOR PORTIONS OF THIS AREA WHERE CONVECTION
IS BEING FUELED BY A 60 KT 850 MB JET AND THETA-E RIDGE...AND
FOCUSED NORTH OF A WARM FRONT ASSOCIATED WITH A DEVELOPING LOW PRES
SYSTEM IN THE PLAINS. MAIN SHORT TERM CONCERN IS TSRA AND SVR WX
POTENTIAL FOR TODAY AND TONIGHT AS THIS SYSTEM MOVES THRU MI. THEN
WX QUIETS AND COOLS FOR FRIDAY AND SATURDAY AS COLD CANADIAN HIGH
PRES SETTLES INTO THE REGION.

TODAY...WARM FRONT REACHES NRN LWR MI BY MIDDAY AND THEN PROGRESSES
NORTHWARD TO ERN UPR MI BY 00Z FRI. THERE WILL BE QUITE OF BIT OF
DRY/STABLE AIR TO OVERCOME DURING THE ONSET PER 00Z APX AND GRB
SOUNDINGS. NO SURPRISE THAT THE LEADING EDGE OF SCT SHRA/TSRA OVER
CENTRAL WI HAS SHOWS SOME DIMINISH IN INTENSITY AS IT MOVES NE
TOWARD THE SFC HIGH CENTER. HOWEVER...EXPECT LOW LEVELS WILL MOISTEN
QUICKLY DURING THE MORNING WITH THE RAPID APPROACH OF THE WARM
FRONT. SFC DWPTS HAVE ALREADY RISEN INTO THE MID 40S ACROSS PORTIONS
OF WI AS HIGHER THETA-E VALUES ADVECT INTO THIS REGION. THETA-E WILL
CONTINUE TO INCREASE THROUGHOUT THE DAY...BUT AREA OF MAX THETA-E
WILL STAY TO THE W OVER THE UPPER MISSISSIPPI VALLEY UNTIL LATE
AFTERNOON/EARLY EVENING WHEN THE 50 KT 850 MB JET MAX MOVES ACROSS
THE CWA. MODEL CAPES INCREASE TO AROUND 2000-3000 J/KG BY 18Z ACROSS
SRN SECTIONS OF THE CWA...AND THEN SPREAD NORTHWARD INTO THE REST OF
THE CWA LATE IN THE DAY. 850-500 MB SHEAR WILL BE SUFFICIENT TO
SUPPORT SUSTAINABLE UPDRAFTS WITHIN CONVECTION THAT DEVELOPS.
CERTAINLY THINK SVR TSRA POTENTIAL EXISTS...ESPECIALLY DURING PEAK
HEATING OF LATE AFTERNOON AND EARLY EVENING. WILL KEEP SCATTERED
SHRA/TSRA IN THE FORECAST FOR ALL ZONES TODAY...AND CLOSELY MONITOR
ANY STORMS THAT DO DEVELOP FOR SVR POTENTIAL.

TONIGHT...HIGHLY UNSTABLE ENVIRONMENT CONTINUES INTO THIS EVENING
BEFORE COLD FRONT PASSES THRU THE CWA OVERNIGHT. SFC LOW RIDES ALONG
THE WARM FRONT...REACHING UPR MI BY 00Z FRI AND THEN MOVING NE OF
THE STATE OVERNIGHT. SVR WX THREAT WILL CONTINUE AND MAY EVEN BE
HEIGHTENED BY INCREASING LOW LEVEL CONVERGENCE PROVIDED BY THE SFC
LOW AND COLD FRONT. WILL MAINTAIN LIKELY POPS FOR ALL ZONES TONIGHT
AND CONTINUE TO MONITOR THE SITUATION CLOSELY AS THE EVENT UNFOLDS.

FRIDAY THROUGH SATURDAY...COLD CANADIAN HIGH PRES MOVES INTO THE
REGION...DROPPING TEMPS BACK TO MORE SEASONAL VALUES. STILL LOOKS
LIKE A DRY PERIOD...BUT EXPECT BKN-OVC CLOUDS WILL LINGER OVER THE
REGION AS AMPLE LOW LEVEL MOISTURE REMAINS IN PLACE.

NO CHANGES MADE TO THE REST OF THE FORECAST.

THANKS TO DTX AND GRR FOR COORDINATION.

.APX...NONE.

EME