Damaging Winds in Michigan, June 18, 2001

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
355 AM EDT MON JUN 18 2001

SHORT TERM DISCUSSION...
FORECAST CONCERNS RIGHT THROUGH THE SHORT TERM PERIOD (TODAY-WED
NIGHT) WILL PERTAIN TO PRECIPITATION CHANCES. COLD FRONT CURRENTLY
EXTENDS FROM NORTH CENTRAL WI...SOUTHWEST INTO IOWA. THIS FRONT WILL
PROGRESS STEADILY EAST TODAY...BEING PUSHED BY A STRONG SHORTWAVE
THAT MOVES FROM NORTHERN MN AT PRESENT TO EAST OF JAMES BAY BY 00Z.
SURFACE BOUNDARY MOVES SOUTH OF THE AREA TONIGHT...BUT CLOSE ENOUGH
TO WORRY ABOUT PRECIPITATION CHANCES. ON WEDNESDAY...SECONDARY COLD
FRONT APPROACHES THE FORECAST AREA FROM THE NORTH...AS THE TRAILING
VORT AXIS MOVES OVERHEAD ALOFT. WEDNESDAY NIGHT...THE SECONDARY
FRONT PUSHES INTO SOUTHWEST LOWER AS ITS ASSOCIATED SHORTWAVE MOVES
INTO THE NORTHERN GREAT LAKES. NAILING DOWN PRECIPITATION CHANCES
OBVIOUSLY THE MAIN CONCERN...NOT TO MENTION THE CHANCES FOR SVR WX
TODAY. ETA AND THE AVN ARE SIMILAR WITH THE MAIN FIELDS AND WILL USE
A COMPROMISE OF BOTH.

FOR TODAY...CONVECTION TO THE WEST IS SHOWING A MARKED DECREASING
TREND IN BOTH INTENSITY AND AREAL COVERAGE. CONVECTION ACROSS
SOUTHERN WI DOMINATED BY THERMODYNAMICS...WHEREAS
CONVECTION FURTHER NORTH IS BEING AIDED BY THE SUBSTANTIAL SHORTWAVE
OVER MN. STRONG LOW LEVEL JET THAT IS CURRENTLY IN PLACE IS
BOTHERSOME FOR THE CHANCES FOR SEVERE...BUT IT QUICKLY WEAKENS/MOVES
EAST THIS MORNING. KGRR VAD WIND PROFILE SHOWING 60KTS AT 3000FT AT
230AM. IT WOULD NOT TAKE MUCH FOR THIS WIND TO REACH THE SURFACE IN
A DOWNDRAFT...BUT AS STATED EARLIER...BY MIDDAY...PROGD WINDS ARE
35KTS OR LESS THROUGH 7000FT. WILL MAINTAIN THE 40 POPS FOR THE
MAJORITY OF THE FORECAST AREA FOR SHOWERS AND THUNDERSTORMS...AND
BUMP THE SOUTHEAST TO 50 GIVEN THE FACT THAT THE FRONT WILL BE
MOVING THROUGH THE LAN/JXN AREAS DURING THE MIDDAY HOURS AND THE
AIRMASS MAY BE ABLE TO RECOVER SOME. WILL USE A CONSIDERABLE CLOUDS
WORDING TO ACCOUNT FOR THE AMOUNT OF CONVECTIVE DEBRIS THAT WILL BE
OVERHEAD. HIGHS SHOULD RANGE FROM THE LOWER 80S NORTHWEST...TO THE
MIDDLE 80S IN THE SOUTHEAST.

IN TERMS OF SEVERE TODAY...IF THE LINE CAN REINTENSIFY ALONG THE
COLD FRONT THIS MORNING...DAMAGING WINDS WILL OBVIOUSLY BE A THREAT
ACROSS THE WESTERN PORTIONS OF THE FORECAST AREA THIS MORNING.
SEVERE ALSO A THREAT LATE THIS MORNING AND AFTERNOON IN THE EASTERN
PORTION OF THE FORECAST AREA AS THE COLD FRONT PUSHES THROUGH.
FRONTAL CONVERGENCE ALONG WITH DECENT MOISTURE (SFC DEW PTS IN THE
60S F / 850MB DEW PTS IN THE LOW TEENS C) SHOULD BE ENOUGH TO TOUCH
OFF SCATTERED SHOWERS AND STORMS.

TONIGHT...BOUNDARY SLIPS INTO NORTHERN PORTIONS OF INDIANA AND
OHIO...WITH A SHORTWAVE APPROACHING FROM THE WEST LATE. 300MB JET
STREAK OFF TO THE NORTH WILL PLACE THE AREA IN THE RIGHT ENTRANCE
REGION. THIS UPPER DIVERGENCE RESULTS IN A LOW LEVEL RESPONSE IN THE
FORM OF SOME WEAK WARM AIR ADVECTION OVER THE FRONTAL BOUNDARY. BOTH
THE ETA AND AVN ARE SHOWING A BLOSSOMING OF PRECIPITATION OVER SRN
LWR MI OVERNIGHT. WILL BUMP THE CURRENT 30/40 POPS THAT ARE
STRATIFIED NORTH TO SOUTH TO 40/50 PCT. CONFIDENCE NOT ESPECIALLY
HIGH WITH THE OVERNIGHT PRECIPITATION...BUT IT SEEMS REASONABLE
ENOUGH TO BUMP POPS UP A TAD. LOWS SHOULD RANGE FROM ARND 60 IN THE
SOUTH TO THE UPPER 50S NORTH...CLOSE TO GUIDANCE.

WEDNESDAY...THE SECONDARY COLD FRONT SLIPS INTO NORTHERN LOWER MI BY
THE EVENING HOURS. ALOFT...THE UPPER TROF IS DROPPING INTO THE
AREA... WITH A COOLER DAY EXPECTED. GOING FORECAST HAS SCATTERED
SHOWERS WITH PARTLY SUNNY SKIES NORTH AND MOSTLY CLOUDY WORDING
SOUTH. CANNOT ARGUE AND WILL CONTINUE WITH THE SAME WORDING. HIGHS
SHOULD GENERALLY BE IN THE LOWER 70S.

WEDNESDAY NIGHT...SUBSTANTIAL SHORTWAVE MOVES TOWARD THE
REGION...WITH THE SECONDARY COLD FRONT PRESSING INTO THE FORECAST
AREA. WILL MAINTAIN THE GOING WORDING OF SCATTERED SHOWERS.
SHORTWAVE TO APPROACH FOR LATE WEDNESDAY NIGHT IS CURRENTLY SEEN IN
THE WATER VAPOR IMAGERY DIVING INTO NORTHERN SASK/MB. MUCH COOLER
NIGHT ON TAP FOR WEDNESDAY NIGHT (LOW TO MID 50S) AS COMPARED TO THE
UPPER 70S IN PLACE THIS MORNING.

DUKESHERER

EXTENDED FORECAST DISCUSSION...
PREVIOUS EXTENDED FORECAST WILL REMAIN UNCHANGED AS MODELS HAVE COME
INTO BETTER AGREEMENT WITH HANDLING OF ERN U.S. TROUGH PASSAGE FOR
LATTER PART OF THE WORK WEEK. FAIRLY IMPRESSIVE SHORTWAVE TROUGH
WILL PASS ACROSS FORECAST AREA ON THURSDAY...WITH GOOD DYNAMICS BUT
LIMITED LOW LEVEL MOISTURE. UPPER LEVEL NWRLY FLOW PATTERN WILL
BECOME ESTABLISHED FOR FRI WITH COOLER THAN NORMAL SFC TEMPS
EXPECTED. RETURN TO NEAR NORMAL CLIMATOLOGICAL TEMPS FOR THE WEEKEND
AS UPPER TROUGHING GIVES WAY TO RIDGING. RIDGE AXIS PASSES MONDAY
WITH POTENTIAL FOR CONVECTION AHEAD OF UPSTREAM SHORTWAVE. SFC TEMPS
BY MONDAY EXPECTED TO RISE ABOVE NORMAL AS SWRLY LOW LEVEL FLOW
KICKS IN AND ADVECTS HEAT AND INCREASING HUMIDITY.

GREENE

.GRR...NONE.