Waterspouts in Lake Huron, August 19, 2002

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GAYLORD MI
345 AM EDT MON AUG 19 2002

SCATTERED SHOWERS -- AND EVEN A FEW THUNDERSTORMS -- WERE ADVANCING
STEADILY EAST ACROSS WI AND LAKE MI THIS MORNING. PRECIPITATION WAS
ASSOCIATED WITH A FAST MOVING SHORT WAVE TROUGH ENTERING WRN WI. THE
IMPACT OF THIS FEATURE ON TODAY/S WEATHER IS THE MAIN SHORT TERM
FORECAST CONCERN.

TODAY...SHORT WAVE TROUGH -- AND ASSOCIATED 50-60 KT 500 MB JET
MAX -- ARE FORECAST TO MOVE VERY QUICKLY ACROSS THE FORECAST AREA...
PROVIDING REGION WITH A QUICK SHOT OF DPVA THIS MORNING. MID/UPPER
CLOUDS WERE THICKENING RAPIDLY EARLY THIS MORNING ACROSS NRN MI AS
FEATURE APPROACHED. EXTRAPOLATION OFF IR SATELLITE LOOP SUGGESTS
THAT BACK EDGE OF MID CLOUDS (AND PRECIPITATION) ASSOCIATED WITH
SHORT WAVE WILL EXIT E UPPER AND NW LOWER BY 14Z...AND NE LOWER BY
16Z. WILL THEREFORE LIMIT SCATTERED PRECIPITATION TO THIS MORNING...
WITH AT LEAST PARTLY SUNNY SKIES DEVELOPING AREAWIDE BY AFTERNOON.

UPSTREAM ELEVATED THUNDERSTORMS ARE THE RESULT OF A RAPID INFLUX OF
A LAYER MID LEVEL MOISTURE CENTERED NEAR OR JUST ABOVE ABOUT 700 MB.
THIS HAS RESULTED IN A LAYER OF CONVECTIVE INSTABILITY -- WITH A
SHARP DECREASE IN THETA-E WITH HEIGHT NOTED ACROSS CENTRAL/SRN WI --
BETWEEN ROUGHLY 700 AND 500 MB (PER ETA MODEL SOUNDINGS...AND N-S
CROSS SECTIONS ACROSS WI VALID AT 06Z). MODEL FORECAST SOUNDINGS
ACROSS NRN MI DON/T APPEAR AS CONDUCIVE TO ELEVATED THUNDERSTORMS AS
THOSE JUST UPSTREAM. HOWEVER...WILL STILL INCLUDE THUNDER IN
FORECAST GIVEN UPSTREAM CONDITIONS -- BUT LIMIT TO AREAS S OF A TVC
TO APN LINE. OTHERWISE...SCATTERED SHOWERS WILL IMPACT MOST AREAS
THIS MORNING -- WITH BEST COVERAGE S OF TVC-APN. PER RADAR TRENDS...
WILL LIMIT SHOWER WORDING TO SCATTERED SPRINKLES ACROSS E UPPER.
AFTER A COOL/DAMP START...INCREASING SUNSHINE BY AFTERNOON WILL
ALLOW TEMPERATURES TO REBOUND INTO THE 70 TO 75 DEGREE RANGE.

TONIGHT AND TUESDAY...HIGH PRESSURE WILL EXPAND EWD FROM THE UPPER
MS VALLEY INTO THE GREAT LAKES...TAKING UP RESIDENCE ACROSS LOWER MI
BY 12Z TUE. EXPECT SCATTERED AFTERNOON CU TO DISSIPATE THIS
EVENING...WITH MOSTLY CLEAR SKIES AND SLACKENING WINDS THEN
RESULTING IN EXCELLENT RADIATIONAL COOLING CONDITIONS. PREFER THE
COOLER FWC LOWS TONIGHT...WITH WIDESPREAD 40S EXPECTED (ESPECIALLY
INLAND). WILL ALSO INCLUDE SOME PATCHY FOG (MOST LIKELY TO FORM LATE
NEAR WARM BODIES OF WATER). LOTS OF SUNSHINE EXPECTED TUE...THANKS
TO WEAK 850/700 MB WARMING AND A DRY BOUNDARY LAYER THAT WILL RESULT
IN MINIMAL CU.

TUESDAY NIGHT AND WEDNESDAY...HIGH PRESSURE WILL PUSH E INTO NEW
ENGLAND BY 12Z WED...AS WAA SPREADS EWD INTO THE GREAT LAKES OUT
AHEAD OF DEVELOPING CENTRAL PLAINS SYSTEM. THETA-E ADVECTION AND
PASSAGE OF SHORT WAVE RIDGE AXIS ALOFT WILL ALLOW SKIES TO BECOME
PARTLY CLOUDY LATE TUE NIGHT -- ESPECIALLY W. ON WED...WARM FRONT
LIFTING NE TOWARD REGION AND INCREASING LOW LEVEL MOISTURE WILL
RESULT IN A CHANCE OF SHOWERS/STORMS BY AFTERNOON -- PER GOING
FORECAST.

.APX...NONE.

SMITH