Severe Thunderstorm Warning 60, NWS Gaylord, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GAYLORD MI
258 AM EDT THU AUG 30 2001

CURRENT SATELLITE WV LOOPS SHOW A SERIES OF SHORTWAVES UPSTREAM OF
THE WRN GREAT LAKES. ONE (PROBABLY THE MOST OBVIOUS GIVEN THE DRY
AIR INTRUSION) IS CURRENTLY NUDGING INTO NW MINNESOTA. MEANWHILE,
ANOTHER MORE CONVECTIVELY-INDUCED VORT MAX IS MOVING THROUGH THE MN
ARROWHEAD. LASTLY, OTHER SHORTWAVES WERE NOTED ACROSS SASKATCHEWAN
AND NRN MANITOBA IT IS THESE TWO FEATURES THAT WILL BE THE DRIVING
FORCE IN TERMS OF THE FORCING/FRONTAL PASSAGE LATER TODAY/TONIGHT
ACROSS THE REGION. MAIN FCST CONCERNS WILL BE WITH TIMING/COVERAGE
OF PRE-FRONTAL CONVECTION, ALONG WITH THE SEVERE WEATHER THREAT.

TODAY, GOOD LOW LEVEL MOISTURE/THETA-E INFLOW (35-40 KTS AT 850 MB
PER PROFILER DATA) IS FUELING THE CURRENT WIDESPREAD AREA OF
NOCTURNAL CONVECTION ACROSS MN/WI. 300/200 MB DIVERGENCE IS HIGHEST
IN THIS REGION, WITH SUBTLE RRQ/LFQ COUPLING OF 300 MB WIND SPEED
MAXES. THE MCS WILL DIMINISH UPON REACHING ERN UPR/WRN LWR MI THIS
MORNING AS IT BECOMES FARTHER DISPLACED FROM THE MAIN DYNAMICAL
SUPPORT (INTO A REGION OF 850/300 MB THICKNESS DIFLUENCE). WHILE
WEAKENING, REGION OF UPPER DIVERGENCE/DPVA AND 850/500 MB QS
CONVERGENCE AHEAD OF THE SHORTWAVE CURRENTLY OVER SASKATCHEWAN BUILD
INTO THE REGION DURING THE AFTERNOON. A PRE-FRONTAL TROUGH IS
REFLECTED AT THE SURFACE AS A RESULT, ALBEIT WEAKENING UPON MOVING
THROUGH THE REGION THIS AFTERNOON. WHILE NEITHER OVERWHELMING, THE
DEGREE OF DYNAMICS/THERMODYNAMICS COMBINED IS SUFFICIENT TO CONTINUE
WITH THE LIKELY PROBS OVER WESTERN/CENTRAL ZONES TODAY (CHANCE EAST),
AND CHANCE WEST/CENTRAL THIS EVENING (LIKELY EAST).

SEVERE WX CHANCES WILL DEPEND HEAVILY ON THE DEGREE OF DAYTIME
HEATING (SURFACE-BASED DESTABILIZATION) WE CAN GET, AS MID LEVEL
(700/500 MB) LAPSE RATES ARE EXPECTED TO BE A MEAGER 6.0 C/KM WITH
TOTAL-TOTALS ONLY IN THE MID 40S. EXPECT MCS DEBRIS TO FACTOR IN
THIS MORNING, ESPECIALLY TOWARD LAKE MI. LIMITED SUN OVER WEST/
CENTRAL COUNTIES WILL LIKELY KEEP TEMPS AOB 80F BEFORE THE INITIAL
TROUGH APPROACHES THIS AFTERNOON. SURFACE/BOUNDARY LAYER MOISTURE
CONVERGENCE APPEARS LIMITED AS WELL. DECAYING MCS REMNANTS WILL
RESULT IN A MORE TRANSPARENT CLOUD COVER IN THE SE PORTION OF NRN
LWR MI, HOWEVER OVER THIS AREA MOISTURE POOLING AT THE SURFACE IS
NOT REAL STRONG EITHER. LINEAR SHEAR PROFILES WITH 40-50KT 700-500MB
WINDS WILL MAKE BOWING SEGMENTS POSSIBLE, ASSUMING OF COURSE ENOUGH
POSITIVE BUOYANCY CAN BE GENERATED.

TONIGHT, MAIN COLD FRONT (ASSOCIATED FROM THE MANITOBA SHORTWAVE)
PUSHES THROUGH THE REGION PER THE ETA/AVN. AGAIN WILL MAINTAIN
EVENING POPS, WITH THE CONCERN THEN REGARDING THE EXTENT OF POST-
FRONTAL CLOUDS AS DOWNWARD Q-G FORCING DOES NOT ARRIVE UNTIL LATE
(8-12Z). MODEL SOUNDINGS SUGGEST AT LEAST SCT LOW/MID CLOUDS
LINGERING, WITH MORE POST-FRONTAL SC (POSSIBLY LAKE-GENERATED) ACROSS
ERN UPR WITH THE COLD ADVECTION INITIATING QUICKLY AT LOW LEVELS.

FRI/FRI NIGHT, COOL/DRY CONDITIONS AGAIN EXPECTED, THOUGH THE
850/800 MB THERMAL TROUGH IN PLACE EXPECT NUMEROUS DAYTIME CU TO POP
BY FRI AFTERNOON (WILL CONTINUE WITH THE MOSTLY CLOUDY MENTION AS A
RESULT). 850 MB TEMPS CONTINUE TO COOL FRI NIGHT, TO AROUND 2-3C
ACROSS LAKES SUPERIOR AND MI. EXPECT LAKE CLOUDS TO DEVELOP GIVEN
LAKE/850 MB DELTA TS IN THE MID/UPPER TEENS, THOUGH LIKELY TO AFFECT
A SMALL PORTION OF THE REGION (DOWNWIND OF LAKES SUPERIOR/MICHIGAN)
WITH THE MEAN N/NNW FLOW AT LOW LEVELS.

.APX...NONE.

HURLEY