Severe Thunderstorm Warning 121, NWS Grand Rapids, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
400 PM EDT WED JUL 16 2008

LATEST UPDATE...ALL SECTIONS BUT AVIATION AND HYDROLOGY...

.SYNOPSIS...(400 PM EDT WED JUL 16 2008)
A FRONTAL BOUNDARY EXTENDING FROM CENTRAL LOWER MICHIGAN TO SOUTH
DAKOTA WEDNESDAY AFTERNOON WILL LIFT NORTH ON THURSDAY THEN SINK
SOUTH AGAIN ON FRIDAY. SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE
PERIODICALLY ALONG AND NORTH OF THIS FRONTAL BOUNDARY... WITH VERY
WARM AND HUMID CONDITIONS SOUTH OF THE FRONT.

&&

.SHORT TERM...(400 PM EDT WED JUL 16 2008)
(TONIGHT THROUGH FRIDAY NIGHT)
MAIN CHALLENGE IN THE SHORT TERM IS CONVECTIVE TRENDS. BELIEVE
CURRENT ACTIVITY OVER IN WISCONSIN WILL PROBABLY REMAIN THERE AND
BUILD SOUTHWARD ACROSS THE MSN AND MKE AREAS WHERE MAX INSTABILITY
WITH CAPES OF 4000-5000 J/KG EXISTS.

MEANWHILE IN OUR NECK OF THE WOODS... BELIEVE WE/LL PROBABLY SEE
SOME WIDELY SCATTERED STORMS LATE THIS AFTERNOON AND EVENING NORTH
OF I-96 AND EAST OF HWY 131 WHERE DECENT SFC CONVERGENCE WILL EXIST
IN THE VICINITY OF THE WEAK SFC FRONTAL BOUNDARY AND AT THE
INTERSECTION OF THE LAKE BREEZE FRONT. OUR CAPES AREN/T TOO SHABBY
EITHER... AROUND 3000 J/KG... SO CANT RULE OUT A SVR CELL OR TWO.
ALL OF THIS DIURNAL/SFC BASED ACTIVITY SHOULD TEND TO DISSIPATE
TOWARD SUNSET.

THEN THE QUESTION FOR LATER TONIGHT BECOMES WHETHER OR NOT WE/LL SEE
A LATE NIGHT MCS ROLLING ACROSS NRN LWR MI...POSSIBLY AFFECTING OUR
NRN CWFA. THERE IS CURRENTLY A SHORTWAVE SEEN ON WATER VAPOR IMAGERY
SCOOTING EAST ACROSS NORTH DAKOTA... AND THIS FEATURE COULD
CERTAINLY BE AN IMPETUS FOR NOCTURNAL MCS ACTIVITY AS IT HEADS ESE
WITH 500 MB HGT CONTOURS. WILL MAINTAIN THE THOUGHTS OF PREVIOUS
FORECASTER... WITH POPS RANGING FROM ONLY 15 PCT OR SO SOUTH OF I-96
TO 50-60 PCT IN THE FAR NRN CWFA AFTER 06Z.

THE SURFACE FRONT SHOULD LIFT NORTH OF THE AREA ON THURSDAY...
LEADING TO A DRY/HOT/HUMID AFTERNOON OVER ALL OF THE CWFA. NOTE THAT
AN OZONE ACTION DAY HAS BEEN ISSUED FOR PARTS OF OUR AREA. WILL
CARRY POPS IN THE NORTH THURSDAY MORNING TO ACCOUNT FOR POSSIBILITY
OF LINGERING AFOREMENTIONED NOCTURNAL MCS... THEN DRY FOR CWFA WIDE
FOR THE AFTERNOON.

THE FRONT IS PROGGED TO SLIP SOUTH AGAIN LATER THURSDAY NIGHT AND
FRIDAY... SO WILL ACCORDINGLY HAVE CHANCE POPS SPREADING BACK
SOUTHWARD INTO THE CWFA. HOWEVER CHANCES WILL STILL ONLY BE 15-20
PCT FOR AREA SOUTH OF I-96.

&&

.LONG TERM...(400 PM EDT WED JUL 16 2008)
(SATURDAY THROUGH WEDNESDAY)
WE WILL STILL BE COPING WITH THE FRONTAL BOUNDARY INTO THE EXTENDED
PERIOD.  IT APPEARS THE BOUNDARY WILL BE ACROSS THE SOUTHERN
PORTION OF THE CWA BY EARLY SATURDAY.  WITH HIGHER CONFIDENCE THE
MODELS ARE POINTING TO A WET BEGINNING TO THE WEEKEND AS A MID LEVEL
SHORT WAVE CROSSES THE GREAT LAKES SATURDAY OR SATURDAY NIGHT.  HAVE
INCREASED POPS ACROSS THE SOUTHERN AND CENTRAL PORTIONS OF THE CWA
FOR BOTH SATURDAY AND SATURDAY NIGHT.  THIS WAVE AND IT/S PCPN COULD
LINGER INTO SUNDAY AS THE GFS SUGGESTS...HOWEVER THE ECMWF WAS
MOVING IT EAST BY THIS TIME SO WILL KEEP POPS ON THE LOW SIDE.

THERE IS UNCERTAINTY HOW FAR SOUTH THE FRONT WILL SAG INTO THE EARLY
PART OF NEXT WEEK.  WILL HOLD ON TO LOW POPS SUNDAY NIGHT AND
MONDAY...HOWEVER BY MONDAY NIGHT IT APPEARS CANADIAN HIGH PRESSURE
WILL SHOVE THE FRONT FURTHER SOUTH AND WE SHOULD FINALLY START TO
DRY OUT.  HAVE LEFT SLGT CHC POPS IN FOR POSSIBLE DAYTIME CONVECTION
ACROSS THE SOUTHERN CWA FOR BOTH TUESDAY AND WEDNESDAY AS THE FRONT
APPEARS TO ONLY SAG TO CENTRAL IN/OH AND SOME MOISTURE MAY TRY TO
CROSS NORTH OF THE FRONT.

&&

.MARINE...(400 PM EDT WED JUL 16 2008)
VERY WARM/HUMID AIR MASS MOVING ACROSS THE LAKE MAY RESULT IN SOME
HAZE OVER THE NEXT FEW DAYS. RELATIVELY WEAK WIND FIELDS ARE PRESENT
ATTM WITH THE FRONT NEARBY... BUT THEY MAY STRENGTHEN A BIT OUT OF
THE SW ON THURSDAY AS THE FRONT LIFTS NORTH. STILL... THE FLOW
PROBABLY WONT BECOME STRONG ENOUGH TO WARRANT ANY SMALL CRAFT
ADVISORIES. WE WILL PROBABLY HAVE A WIND SHIFT TO THE N/NE NORTH OF
HOLLAND ON FRIDAY AFTERNOON AND NIGHT AS THE FRONT SLIPS SOUTH
AGAIN.

&&

.AVIATION...(148 PM EDT WED JUL 16 2008)
INSTABILITY WAS INCREASING THIS AFTERNOON RESULTING IN A GROWING CU
FIELD.  BELIEVE THERE WILL BE POP UP SHOWERS AND THUNDERSTORMS INTO
THE MID/LATE AFTERNOON AS THE INSTABILITY IS MAXIMIZED.  THIS
CONVECTION SHOULD REMAIN WIDELY SCATTERED HOWEVER...SO WILL JUST
MENTION VCTS AT THIS POINT AWAY FROM THE LAKE.  ANY STORMS WILL DIE
OFF PRIOR TO MIDNIGHT WITH THE LOSS OF SURFACE HEATING.  SOMEWHAT
DRIER AIR ARRIVES OVERNIGHT...SO FEEL THAT THURSDAY MORNING INTO THE
EARLY AFTERNOON WILL BE STORM FREE FOR THE TAF SITES.

&&

.HYDROLOGY...(400 PM EDT WED JUL 16 2008)
USGS RIVER GAGES CONTINUE TO SHOW LEVELS ACROSS THE AREA AT OR ABOVE
NORMAL. AIR MASS IS BECOMING INCREASINGLY MOIST WITH PRECIPITABLE
WATERS APPROACHING 1.50 INCHES OVER THE CWFA THIS MORNING. THE MOST
WIDESPREAD RAINFALL THROUGH THE END OF THE WEEK LOOKS TO REMAIN JUST
NORTH OF THE CWFA...CLOSER TO THE NOSE OF THE LOW LEVEL JETS
EXPECTED TO IMPACT THE AREA. ANY STORMS THAT DO DEVELOP WILL HAVE
THE POTENTIAL TO PRODUCE LOCALLY HEAVY DOWNPOURS. BASIN AVERAGES ARE
EXPECTED TO REMAIN RATHER LOW ATTM...GENERALLY LESS THAN A QUARTER
OF AN INCH FOR EACH PERIOD.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...NONE.

&&

SYNOPSIS:     MEADE
SHORT TERM:   MEADE
LONG TERM:    JK
MARINE:       MEADE
AVIATION:     JK
HYDROLOGY:    NJJ

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
632 PM EDT WED JUL 16 2008

LMZ844>849-MIZ037>040-043>046-050>052-056>059-064>067-071>074-171015-
ST JOSEPH TO SOUTH HAVEN MI-SOUTH HAVEN TO HOLLAND MI-
HOLLAND TO GRAND HAVEN MI-GRAND HAVEN TO WHITEHALL MI-
WHITEHALL TO PENTWATER MI-PENTWATER TO MANISTEE MI-MASON-LAKE-
OSCEOLA-CLARE-OCEANA-NEWAYGO-MECOSTA-ISABELLA-MUSKEGON-MONTCALM-
GRATIOT-OTTAWA-KENT-IONIA-CLINTON-ALLEGAN-BARRY-EATON-INGHAM-
VAN BUREN-KALAMAZOO-CALHOUN-JACKSON-
632 PM EDT WED JUL 16 2008

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

.DAY ONE...TONIGHT

THUNDERSTORMS WILL AFFECT AREAS NORTH OF A LINE FROM ROUGHLY
SAUGATUCK TO MASON THIS EVENING. SOME OF THE STORMS MAY BE SEVERE
WITH DAMAGING WINDS AND LARGE HAIL. TORRENTIAL RAINFALL IS ALSO
POSSIBLE WHICH WILL CREATE AREAS OF URBAN AND SMALL STREAM FLOODING.

ADDITIONAL THUNDERSTORMS MAY DEVELOP LATE TONIGHT NORTH OF
INTERSTATE 96.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

SHOWERS AND THUNDERSTORMS WILL CONTINUE TO BE POSSIBLE THURSDAY
THROUGH TUESDAY AS LOW PRESSURE MOVES ALONG A WAVERING FRONT ACROSS
LOWER MICHIGAN.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION SHOULD NOT BE NEEDED THIS AFTERNOON AND TONIGHT
BECAUSE THE COVERAGE OF STORMS WILL BE RATHER LIMITED.

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