Severe Thunderstorm Warning 72, NWS Grand Rapids, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
330 AM EDT WED AUG 22 2001

THE PRIMARY CONCERNS WITH THIS FORECAST PACKAGE DEAL WITH THE
POTENTIAL FOR HEAVY RAIN AND SEVERE WEATHER THIS MORNING...AND
SCATTERED SHOWERS AND THUNDERSTORMS TONIGHT.

AN AREA OF SHOWERS AND THUNDERSTORMS OVER WESTERN WI APPEARS TO BE
EVOLVING INTO AN MCS.  THIS SYSTEM IS FORMING ON THE NOSE OF A 30 TO
40 KNOT 925/850 MB JET.  MEANWHILE ALOFT 250 MB JET IS PROVIDING
UPPER LEVEL DIVERGENCE...ENHANCING LIFT.  MOISTURE IN LOWER MI
INCREASES THIS MORNING WITH PRECIPITABLE WATER VALUES PROGGED TO
CLIMB TO OVER 1.5 INCHES.  THE STORMS ARE ELEVATED WITH THE SURFACE
WARM FRONT STILL OVER IA AND CENTRAL IL.  ADDITIONAL STORMS WERE
FORMING IN FAR SOUTHWEST LOWER MI.

CONCERNING THE HEAVY RAIN TODAY...THE AIRMASS WILL BE VERY MOIST
WITH LOW LIFTED CONDENSATION LEVELS.  THE LOW LEVEL JET LIFTING INTO
THE AREA WILL HELP TO ENHANCE THE HEAVY RAINFALL THREAT.  THESE
SITUATIONS COULD LEAD TO AN EFFICIENT RAINFALL SYSTEM...POSSIBLY
PRODUCING EXCESSIVE AMOUNTS.  WILL BE WATCHING RAINFALL TOTALS
UPSTREAM ACROSS WI OVER THE NEXT SEVERAL HOURS.  WILL HOLD OFF ON A
FLOOD WATCH AT THIS TIME...BUT MAY NEED ON IF RAINFALL TOTALS
UPSTREAM CONTINUE TO INCREASE AS THIS MCS EVOLVES.  FLASH FLOOD
GUIDANCE SUGGESTS THAT MY MOST PRONE COUNTIES NEED 2.5 INCHES IN 6
HOURS TO INITIATE FLOODING.

STEEPENING LAPSE RATES ADVECTING INTO THE BACKSIDE OF THE MCS...AND
THE SYSTEM MOVING INTO AN AREA OF STRONGER MID LEVEL WINDS AROUND 40
KNOTS AT 500 MB COULD LEAD TO SOME HAIL AND STRONG WINDS
GUSTS...ESPECIALLY FOR MY SOUTHERN COUNTIES.

THE MODELS ALL POINT TO THIS DEVELOPING MCS TRACKING THROUGH
SOUTHWEST LOWER MI.  THE BULK OF THE PRECIPITATION IS EXPECTED PRIOR
TO 18Z.  WILL INCREASE THE PROBABILITY OF RAIN TO CATEGORICAL FOR
NEARLY ALL OF MY AREA FOR TODAY.  THIS AFTERNOON SHOULD FEATURE A
DECREASE IN THE RAINFALL...FROM NORTHWEST TO SOUTHEAST.

WILL HOLD ONTO A LOW CHANCE FOR SHOWERS AND THUNDERSTORMS THIS
EVENING IN MY SOUTHERN COUNTIES OTHERWISE...WILL KEEP IT DRY.  AM
CONCERNED ABOUT THE WEAK COLD FRONT THAT IS PROGGED TO DROP DOWN
THROUGH LOWER MI TONIGHT POSSIBLY LEADING TO ADDITIONAL SCATTERED
PRECIPITATION.  CURRENTLY MODELS ARE NOT HANDLING THIS FEATURE WELL
AS THERE ARE NUMEROUS SHOWERS IN NORTHERN MINNESOTA.  LATER
FORECASTS CAN UPDATE THIS IF NEEDED.  WILL KEEP IT DRY FOR NOW.

BACKED OFF ON TEMPERATURES SLIGHTLY FOR THURSDAY DUE TO THE MODELS
TRENDING COOLER.

MJS

EXTENDED FORECAST DISCUSSION...
LATEST MEDIUM RANGE MODEL GUIDANCE CONTINUES TO SHOW FRONTAL PASSAGE
ON SUNDAY. 00Z AVN AND CANADIAN MODELS SHOW PCPN FOR SAT NIGHT AND
SUN MORNING AHEAD OF FRONT. WILL LEAVE MONDAY AND TUESDAY FORECAST
AS IS. ECMWF APPEARS TO BE THE MOST AGGRESSIVE WITH THE COLD
ADVECTION EARLY NEXT WEEK...BUT PREFER THE MRF/AVN SOLUTION AT THIS
POINT.

GREENE

.GRR...NONE

MIZ037>040-043>046-050>052-056>059-064>067-071>074-231000-

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
415 AM EDT WED AUG 22 2001

...HAZARDOUS WEATHER POTENTIAL STATEMENT FOR THE SOUTHWEST QUARTER OF
LOWER MICHIGAN FOR TODAY AND TONIGHT...

DISPATCHERS...PLEASE PASS ALONG THIS INFORMATION TO YOUR EMERGENCY
MANAGERS.

HAZARDS...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS IN
SOUTHWEST LOWER MICHIGAN TODAY...PRIMARILY SOUTH OF INTERSTATE 96.
THUNDERSTORMS...ESPECIALLY THIS MORNING...WILL BE CAPABLE OF LARGE
HAIL AND DAMAGING WINDS TO 60 MPH.

HEAVY RAIN IS LIKELY WITH SOME OF THE THUNDERSTORMS.  LOCALLY 2 TO 3
INCHES ARE POSSIBLE...WHICH COULD LEAD TO POOR DRAINAGE FLOODING AND
RAPID RISES ON SMALL STREAMS.

DISCUSSION...
A WARM FRONT OVER INDIANA...WILL LIFT NORTHWARD INTO LOWER MICHIGAN
TODAY AND BECOME STATIONARY.  MEANWHILE...A LOW PRESSURE SYSTEM
DEVELOPING OVER WISCONSIN THIS MORNING...WILL TRACK EASTWARD ALONG
THIS FRONT...BRINGING WIDESPREAD SHOWERS AND THUNDERSTORMS TO
SOUTHWEST LOWER MICHIGAN ESPECIALLY THIS MORNING.  THE AREA THAT
WILL MOST LIKELY SEE THE STRONGEST THUNDERSTORMS...FEATURING HEAVY
RAIN AND PERHAPS LARGE  HAIL AND DAMAGING WINDS WILL BE ALONG AND
SOUTH OF A MUSKEGON...TO GRAND RAPIDS...TO LANSING LINE.  ALREADY
SOME SEVERE WEATHER AND HEAVY RAINFALL HAS OCCURRED IN NORTHERN
INDIANA.  THE STORMS THAT DO DEVELOP WILL MOVE EAST SOUTHEAST AT
AROUND 30 MPH.  THE BULK OF THE PRECIPITATION IS EXPECTED TO PUSH
SOUTH OF SOUTHERN LOWER MICHIGAN THIS EVENING.

SPOTTER ACTIVATION...MAY BE NEEDED THIS MORNING.

...HAZARDOUS WEATHER POTENTIAL FOR WEDNESDAY THROUGH SATURDAY...

HIGH PRESSURE IS EXPECTED TO BUILD IN FOR THURSDAY AND FRIDAY.  THE
WARM FRONT IS EXPECTED TO RETURN FOR SATURDAY BRINGING THE
OPPORTUNITY FOR MORE SHOWERS AND THUNDERSTORMS.

MJS

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE GRAND RAPIDS, MI
827 AM EDT WED AUG 22 2001

TIME(EDT)  .....CITY LOCATION.....STATE   ...EVENT/REMARKS...
           ....COUNTY LOCATION....

0818 AM    CITY OF HOLLAND           MI   .75 INCH HAIL
08/22/01   OTTAWA                         NEAR M40 AND I196 BY
                                          SPOTTER

0820 AM    CITY OF HOLLAND           MI   .75 INCH HAIL
08/22/01   OTTAWA                         NEAR M40 AND US31

GEO