Severe Thunderstorm Warning 141, NWS Grand Rapids, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1040 PM EDT WED AUG 23 2006

.UPDATE...
LATEST SFC ANALYSIS AT 02Z SHOWS THE QUASI-STATIONARY FRONT
EXTENDING FROM JUST SOUTH OF KMSN...TO JUST NORTH OF KORD...AND THEN
NEAR THE SW TIP OF LOWER MICHIGAN. A FEW SMALL CLUSTERS OF SFC BASED
CONVECTION HAVE BEEN ONGOING RIGHT ALONG THIS FRONT. THE MOST
NOTABLE STORM WAS THE RIGHT MOVER THAT MOVED THROUGH MICHIGAN CITY
INDIANA AND PRODUCED A MEASURED 106 MPH WIND GUST AT THE COAST AND
REPORTS OF A TORNADO. THIS SFC BASED CONVECTION IS STAYING JUST
SOUTH OF THE CWFA...RIDING ALONG THE SFC INSTABILITY GRADIENT NEAR
THE FRONT.

OVER THE GRR CWFA...WE HAVE BEEN IN A LULL BETWEEN THE DYING AREA OF
PCPN EARLIER THIS AFTERNOON AND THE PCPN NEAR THE FRONT. THE DRY
ATMOSPHERE HAS BEEN GRADUALLY MOISTENING...WITH MANY LOCATIONS NOW
REPORTING CLOUD LAYERS AROUND 6K TO 8K FEET. IN THE LAST HALF AN
HOUR OR SO...ISOLATED CONVECTION HAS BEEN FIRING SOUTH OF A LINE
FROM KGRB TO KMBL. THIS ISOLATED CONVECTION IS EVIDENCE THAT THE
ATMOSPHERE HAS MOISTENED ENOUGH AND BECOME UNSTABLE ENOUGH TO ALLOW
THE MID LEVEL WAA/THETA E ADVECTION AHEAD OF THE INCOMING WAVE TO
START PRODUCING PCPN. SHOWALTER INDICES ARE FORECAST TO FALL DOWN TO
AROUND -3 OR SO OVERNIGHT. WE EXPECT THAT THIS DEVELOPMENT OF
UNORGANIZED CONVECTION WILL CONTINUE OVER THE NEXT FEW HOURS AND
BEGIN AFFECTING MORE OF THE CWFA. THE BEST THREAT OF RAIN WILL
CONTINUE TO BE FOUND CLOSER TO THE FRONT AS THE ORGANIZED CONVECTION
CONTINUES ALONG THE FRONT. WITH THE ELEVATED NATURE OF THE
CONVECTION OVER THE AREA...THE SEVERE THREAT IS DIMINISHING AS TIME
GOES ON AS THE BOUNDARY LAYER COOLS. THE THREAT WILL NOT COMPLETELY
END AS FREEZING LEVELS AROUND 12K FT OR SO WILL KEEP MARGINALLY
LARGE HAIL POSSIBLE IN THE BETTER UPDRAFTS. ALSO WITH DEEP LAYER
SHEAR VALUES OF 30 TO 45 KNOTS /HIGHEST NORTH/ AN ISOLATED REPORT OF
WIND DAMAGE CAN NOT BE RULED OUT.

THE FORECAST HAD THINGS WELL IN HAND AND ONLY MINOR ADJUSTMENTS WERE
MADE.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...NONE.

NJJ

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
150 PM EDT WED AUG 23 2006

LMZ844>849-MIZ037>040-043>046-050>052-056>059-064>067-071>074-241030-
ST JOSEPH TO SOUTH HAVEN-SOUTH HAVEN TO HOLLAND-
HOLLAND TO GRAND HAVEN-GRAND HAVEN TO WHITEHALL-
WHITEHALL TO PENTWATER-PENTWATER TO MANISTEE-MASON-LAKE-OSCEOLA-
CLARE-OCEANA-NEWAYGO-MECOSTA-ISABELLA-MUSKEGON-MONTCALM-GRATIOT-
OTTAWA-KENT-IONIA-CLINTON-ALLEGAN-BARRY-EATON-INGHAM-VAN BUREN-
KALAMAZOO-CALHOUN-JACKSON-
150 PM EDT WED AUG 23 2006

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTHWEST LOWER
MICHIGAN.

.DAY ONE...TODAY AND TONIGHT

SHOWERS AND THUNDERSTORMS MAY DEVELOP LATE THIS EVENING INTO THE
OVERNIGHT HOURS ACROSS PORTIONS OF SOUTHWEST LOWER MICHIGAN. THERE
IS A SLIGHT CHANCE A FEW THUNDERSTORMS COULD BECOME SEVERE AFTER
MIDNIGHT. LARGE HAIL AND LOCALLY HEAVY RAINFALL WILL BE THE MAIN
HAZARDS. GREATEST THREAT WILL BE ALONG AND SOUTHWEST OF A LINE FROM
MUSKEGON TO JACKSON.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

A CHANCE FOR SHOWERS AND THUNDERSTORMS REMAIN THROUGH SUNDAY FOR
PORTIONS OF SOUTHWEST LOWER MICHIGAN.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED LATE TONIGHT.

BEACHLER

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