Severe Thunderstorm Warning 154, NWS Grand Rapids, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
346 PM EDT MON AUG 25 2003

MANY DIFFERENT CONCERNS WITH THIS FORECAST PACKAGE. THE FIRST AND
MAIN CONCERN DEALS WITH CONVECTION OVERNIGHT TONIGHT NEAR THE
BOUNDARY THAT CONTINUES TO HANG AROUND THE AREA. ANOTHER CONCERN IS
THE CHC FOR CONVECTION TOMORROW AS THE BOUNDARY SINKS SOUTH OF THE
AREA TEMPORARILY. THEN...THE LAST MAIN CONCERN IS CHC FOR PCPN ON
THU AS THE BOUNDARY MOVES NORTH ACROSS THE AREA ONCE AGAIN.

SATELLITE AND REGIONAL RADAR IMAGERY SHOWS A LINE OF SHOWERS AND
THUNDERSTORMS EXTENDING ALL THE WAY FROM COLORADO INTO MICHIGAN.
THIS LINE OF PCPN IS RIGHT AROUND THE UPPER RIDGE IN PLACE OVER THE
SOUTHERN PART OF THE COUNTRY. ALSO IN PLACE NEAR WHERE THE
CONVECTION IS FIRING IS A NEARLY STATIONARY BOUNDARY. THIS
NEARLY STATIONARY BOUNDARY IS CURRENTLY ACROSS MICHIGAN...BUT IS
VERY POORLY DEFINED LOOKING AT SFC OBS. NOT MUCH DIFFERENCE IN AIR
MASSES ACROSS THE STATE. DEWPOINTS ARE MAINLY IN THE 70S WITH TEMPS
IN THE 80S EXCEPT FOR PLACES THAT SAW RAIN THIS AFTERNOON.

TONIGHT...THIS RING OF CONVECTION IS EXPECTED TO BRING MORE
CONVECTION INTO THE STATE. A COMPLEX IN WESTERN WI ASSOCIATED WITH
MID LEVEL THETA E ADVECTION IS BEGINNING TO MAKE ITS WAY TOWARD
MICHIGAN. THIS CONVECTION IS EXPECTED TO MOVE OVER THE AREA THIS
EVENING. MOST OF THIS CONVECTION HAS BEEN ELEVATED SO FAR. THEN
LATER TONIGHT...A 40+ KT LLJ WILL GET CRANKING AND WILL MOVE OVER
THE STATE DURING THE OVERNIGHT HOURS. PRETTY GOOD BET FOR RAIN
ACROSS MOST OF THE AREA...SO WILL CONTINUE THE LIKELY POPS ACROSS
THE AREA. WILL GO WITH A 70 POP SOUTH AND 60 NORTH PER COORDINATION
WITH SURROUNDING OFFICES. SEVERE THREAT IS PRESENT TONIGHT. 40-50 KT
WINDS WILL PRODUCE A THREAT OF WIND DAMAGE...BUT WITH THE CONVECTION
BEING MAINLY ELEVATED...IT DOESNT LOOK TO BE THE MAIN THREAT.
HELICITIES ARE FAIRLY IMPRESSIVE WITH SPEED AND DIRECTIONAL SHEAR
PRESENT. DUE TO THE ELEVATED NATURE...TORNADOES ARE POSSIBLE BUT NOT
LIKELY. HAIL POTENTIAL SEEMS TO BE SOMEWHAT LIMITED TOO WITH
FREEZING LEVELS AROUND 13K FEET. HEAVY RAIN IS POSSIBLE WITH PW/S OF
2+ INCHES ADVECTING IN.

ON TUE AND TUE NIGHT...THE FRONT IS EXPECTED TO SLOWLY SINK SOUTH
THROUGH THE AREA. AS THE FRONT SINKS SOUTH...AHEAD OF IT WILL BE A
INCREASINGLY UNSTABLE AIRMASS. HOW UNSTABLE WE WILL GET IS IN
QUESTION DUE TO THE AMOUNT OF CLOUD COVER WE WILL SEE. I ANTICIPATE
WE WILL SEE A FAIR AMOUNT OF SUN. IF WE GET ENOUGH SUN...TEMPS WILL
CLIMB INTO THE MID TO UPPER 80S AND DEWPOINTS WILL CONTINUE NEAR 70.
THIS WOULD PRODUCE CAPES OF AROUND 3K J/KG AND LI/S OF -6 TO -8. NO
MAJOR SHORT WAVE IS EXPECTED TO PASS THROUGH...BUT ANY BOUNDARY
COULD KICK CONVECTION OFF. WILL GO WILL A GENERAL 40 POP ACROSS THE
ENTIRE AREA. THE FRONT WILL PASS SOUTH OF THE AREA LATE TUE NIGHT.
UNTIL IT DOES SO...THE THREAT OF SHOWERS AND STORMS WILL CONTINUE.

WED AND WED NIGHT LOOK TO BE A COUPLE OF QUIET PERIODS. AS THE FRONT
IS EXPECTED TO STAY TO OUR SOUTH...DRY WEATHER IS EXPECTED. COOLER
AND SOMEWHAT DRIER AIR IS ALSO EXPECTED TO BE AROUND. HIGHS AROUND
80 OR SO CAN BE EXPECTED WITH A GOOD DEAL OF SUNSHINE.

THEN ON THU...THE FRONT MAKES ANOTHER NORTHWARD PUSH UP INTO THE
STATE. ALONG AND AHEAD OF THE FRONT...AN AREA OF STRONG THETA E
ADVECTION MOVES OVER THE STATE THAT SHOULD PRODUCE SOME SHOWERS AND
STORMS. WILL GO WITH A CHC OF SHOWERS AND STORMS FOR THU AHEAD AND
ALONG THIS FRONT. TEMPS ON THU WILL WARM UP A COUPLE OF DEGREES FROM
WED.

NJJ

EXTENDED FORECAST DISCUSSION...
THE GFS HAS TRENDED TOWARD A WEAKER PUSH OF THE FRONT THROUGH
THE REGION ON FRIDAY...STALLING THE FRONT OUT ACROSS THE OHIO
VALLEY FOR SATURDAY.  UPPER LEVEL HEIGHTS DO NOT FALL OFF AS
MUCH EITHER...AND THE TREND SUPPORTS ANOTHER WAVE OF LOW
PRESSURE TO APPROACH THE REGION SATURDAY.  PRECIPITABLE
WATER VALUES ARE RELATIVELY HIGH AHEAD OF THIS WAVE...SO
IT MAY END UP BEING MORE UNSETTLED THIS WEEKEND IF THIS SCENARIO
WORKS OUT.  WILL MODIFY THE EXTENDED FORECAST TO FEATURE MORE
IN THE WAY OF CLOUDS OVER WEEKEND.  BROAD CYCLONIC UPPER FLOW
FOR EARLY NEXT WEEK SHOULD KEEP OUR WEATHER SLIGHTLY COOLER THAN
NORMAL AND PERHAPS SHOWERY.

MJS

.GRR...NONE.

MIZ037>040-043>046-050>052-056>059-064>067-071>074-261000-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
213 PM EDT MON AUG 25 2003

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE SOUTHWEST QUARTER OF LOWER
MICHIGAN.

.DAY ONE...THIS AFTERNOON AND TONIGHT

SCATTERED THUNDERSTORMS SHOULD FORM THIS AFTERNOON AND NUMEROUS
STORMS ARE FORECASTED FOR TONIGHT ACROSS THE
SOUTHWEST QUARTER OF LOWER MICHIGAN. THE STORM PREDICTION CENTER HAS
PLACED THE ENTIRE AREA IN A SLIGHT RISK FOR SEVERE THUNDERSTORMS.
THE BEST CHANCE FOR STORMS WILL BE THIS EVENING AS A
WARM FRONT LIFTS NORTH THROUGH THE AREA AND THEN AGAIN OVERNIGHT AS
A COLD FRONT APPROACHES FROM THE NORTHWEST.

THE STRONGEST OF STORMS...MOST LIKELY TONIGHT...WILL BE CAPABLE OF
WINDS TO 60 MPH AND HAIL TO AROUND AN INCH IN DIAMETER.
FREQUENT CLOUD TO GROUND LIGHTNING STRIKES AND HEAVY RAIN WILL
ACCOMPANY THE STORMS.

WHERE THE STORMS PERSIST LONGER THAN AN HOUR...MORE THAN 2 INCHES OF
RAIN COULD FALL.  THIS WOULD LEAD TO URBAN AND POOR DRAINAGE
FLOODING.  THE MOST LIKELY TIME FRAME FOR THIS TO OCCUR IS AFTER
MIDNIGHT.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

THE AREA IS ALSO IN A SLIGHT RISK FOR SEVERE THUNDERSTORMS ON
TUESDAY. THE COLD FRONT WILL PROGRESS THROUGH THE AREA INTO A VERY
MOIST AND UNSTABLE AIRMASS. STRONG STORMS COULD BE ONGOING TO START
THE DAY. DURING THE AFTERNOON...ANOTHER ROUND OF THUNDERSTORMS IS
EXPECTED. THESE STORMS COULD ALSO CONTAIN WINDS TO 60 MPH AND HAIL
TO AROUND AN INCH IN DIAMETER.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED THIS EVENING OR TONIGHT.

RJD MJS