Severe Thunderstorm Warning 35, NWS Grand Rapids, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
424 PM EDT SUN AUG 9 2009

LATEST UPDATE...ALL BUT AVIATION...

.SYNOPSIS...(424 PM EDT SUN AUG 9 2009)
A SOUTHWEST FLOW WILL KEEP OUR TEMPERATURES ABOVE NORMAL INTO
MONDAY.  A COLD FRONT WILL SLIP SOUTHEAST THROUGH LOWER MICHIGAN BY
MONDAY NIGHT.  A MORE SEASONABLE AIRMASS ARRIVES FOR TUESDAY.
TEMPERATURES WILL WARM UP FOR THE END OF THE WEEK AS HIGH PRESSURE
BUILDS EAST OF THE REGION.

&&

.SHORT TERM...(424 PM EDT SUN AUG 9 2009)
(TONIGHT THROUGH TUESDAY NIGHT)
THE PRIMARY CONCERNS IN THE SHORT TERM DEAL WITH THE POTENTIAL FOR
SEVERE WEATHER THIS EVENING.

PLENTY OF INSTABILITY AROUND TO SUPPORT STRONG TO SEVERE CONVECTION.
WAVE OF CONVECTION IN SOUTHERN WISCONSIN IS EXPECTED TO INTERACT
WITH THIS INSTABILITY LEADING TO A STORMY NIGHT HERE IN SOUTHWEST
LOWER MICHIGAN.  DEEP LAYER SHEAR IS STRONGEST ACROSS NORTHERN LOWER
MI INTO WI.  THE SHEAR HERE IN SOUTHWEST LOWER MICHIGAN IS EXPECTED
TO INCREASE WHICH WOULD SUPPORT ORGANIZED CONVECTION.  THE MAIN
TIMEFRAME IS FROM 6 PM TO 2 AM TONIGHT.  LOCALLY HEAVY RAIN AND
FREQUENT LIGHTNING ARE SUPPORTED BY THE SOUNDINGS.

ANOTHER ACTIVE DAY IS POSSIBLY IN STORE FOR MONDAY.  THE COLD FRONT
WILL BE SLIPPING THROUGH AND IT BECOMES UNSTABLE.  DEEP LAYER SHEAR
IS MARGINAL...SO IT SUPPORTS CLOSER MONITORING.  A SLIGHT RISK FOR
SEVERE WEATHER COVERS MUCH OF SOUTHWEST LOWER MI.

WILL KEEP A HEAT ADVISORY GOING FOR THE AREA SOUTH OF INTERSTATE 96
FOR A FEW HOURS THIS EVENING.  MANY LOCATIONS HAVE HEAT INDEX VALUES
OF JUST OVER 100 DEGREES.

&&

.LONG TERM...(424 PM EDT SUN AUG 9 2009)
(TUESDAY NIGHT THROUGH SATURDAY)
THE MID RANGE MODELS ARE IN GOOD AGREEMENT AND SHOW GOOD CONTINUITY
WITH PREVIOUS RUNS. ONLY SMALL CHANGES TO GOING GRIDS.

HIGH PRESSURE WILL BUILD INTO THE REGION AT THE SURFACE WITH RISING
HEIGHTS ALOFT. HAVE DRY WEATHER FORECAST THROUGH THE LONG TERM.

TEMPERATURES WILL BE ABOVE NORMAL THROUGH THE LONG TERM PERIOD WITH
HIGHS IN THE 80S AND LOWS MOSTLY IN THE 60S.

&&

.AVIATION...(124 PM EDT SUN AUG 9 2009)
HAZY... ESPECIALLY NEAR LAKE MICHIGAN AND FLAT CU FORMING ACROSS THE
AREA. A FEW SHOWERS OR STORMS MAY KICK UP AS THE ATMOSPHERE HEATS
UP... BUT ISOLATED AND CHANCES SMALL... SO NOT IN TAFS. STORMS IN
IOWA AROUND NOON WILL MOVE INTO THE AREA TONIGHT. TIMING NOT CERTAIN
NOR IS THE EVOLUTION OF THE STORMS SO WILL MONITOR AND UPDATE. THE
BULK OF THE DAY SHOULD FEATURE VFR CONDITIONS.

IT WILL BE RATHER BREEZY INTO THIS EVENING WITH SOUTHWEST WINDS
RUNNING BETWEEN 15 AND 25 KNOTS A GOOD PORTION OF THE DAY. EXPECT
SOME LIGHT FOG TO SETTLE BACK IN LATE TONIGHT... GIVEN THE VERY
HUMID AIRMASS IN PLACE. HAVE ALSO INCLUDED VCSH AND CB DECK TONIGHT
FOR STARTING POINT OF NEXT FORECAST ISSUANCE.

&&

.MARINE...(424 PM EDT SUN AUG 9 2009)
SOUTHWEST WINDS 30 KNOTS WILL CREATE HAZARDOUS MARINE
CONDITIONS LATE THIS AFTERNOON.  WAVES HAVE BEEN INCREASED TO UP TO
7 FEET ESPECIALLY AROUND GRAND HAVEN.  THUNDERSTORMS WITH GUSTY
WINDS AND LIGHTNING ARE POSSIBLE LATER THIS AFTERNOON INTO TONIGHT.

&&

.HYDROLOGY...(424 PM EDT SUN AUG 9 2009)
SIMILAR TO LATE SATURDAY...HIGH PRECIPITABLE WATER CONTENT AND
INSTABILITY WILL CREATE FAVORABLE CONDITIONS FOR HEAVY RAIN. SOME
STORMS MAY PRODUCE AN INCH OR TWO OF RAIN. GIVEN THE HEAVY RAIN THAT
HAS ALREADY FALLEN OVER PARTS OF THE CWA...FLOODING IS A CONCERN AND
WILL BE MONITORED.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...HEAT ADVISORY ROUGHLY SOUTH OF INTERSTATE 96 TIL 8 PM THIS
EVENING
LM...SMALL CRAFT ADVISORY ST. JOE TO MANISTEE NOW IN EFFECT THROUGH
8 PM SUNDAY.

&&

SYNOPSIS:     MJS
SHORT TERM:   MJS
LONG TERM:    IOD
AVIATION:     IOD
MARINE:       MJS
HYDROLOGY:    MJS

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
315 PM EDT SUN AUG 9 2009

MIZ037>040-043>046-050>052-056>059-064>067-071>074-101000-
MASON-LAKE-OSCEOLA-CLARE-OCEANA-NEWAYGO-MECOSTA-ISABELLA-MUSKEGON-
MONTCALM-GRATIOT-OTTAWA-KENT-IONIA-CLINTON-ALLEGAN-BARRY-EATON-
INGHAM-VAN BUREN-KALAMAZOO-CALHOUN-JACKSON-
315 PM EDT SUN AUG 9 2009

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

.DAY ONE...THIS EVENING AND TONIGHT

THE HEAT WILL BE A WEATHER CONCERN EARLY THIS EVENING AS
TEMPERATURES PUSH INTO THE LOWER 90S ACROSS A GOOD DEAL OF THE
AREA...ESPECIALLY AWAY FROM LAKE MICHIGAN. HEAT INDEX VALUES THIS
AFTERNOON WILL APPROACH 100 DEGREES WITH SLIGHTLY HIGHER VALUES
SOUTH OF INTERSTATE 96.

THUNDERSTORMS WILL BE POSSIBLE BOTH THIS EVENING AND TONIGHT WITH
THE ENTIRE AREA PLACED IN A SLIGHT RISK FOR SEVERE THUNDERSTORMS BY
THE STORM PREDICTION CENTER. THE MOST LIKELY SCENARIO HAS STORMS
REDEVELOPING IN THE AFTERNOON AND EVENING. THE MAIN THREATS WILL
BE TORRENTIAL RAIN...FREQUENT CLOUD TO GROUND LIGHTNING STRIKES AND
STRONG WIND GUSTS TO IN EXCESS OF 60 MPH. A FEW OF THE STRONGEST
STORMS MAY CONTAIN HAIL TO AROUND AN INCH IN DIAMETER. THE MAIN
STORM MOVEMENT WILL BE TO THE EAST AT 35 MPH.

RAINFALL IN THE LAST DAY OR SO HAS BEEN AS MUCH AS 3 TO 4 INCHES
IN SOME LOCATIONS...WITH MOST AREAS PICKING UP AT LEAST AN INCH.
ADDITIONAL HEAVY RAIN MAY LEAD TO FLASH FLOODING IN SOME AREAS.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

THUNDERSTORMS ARE ONCE AGAIN A GOOD POSSIBILITY MONDAY AND MONDAY
NIGHT AS A COOL FRONT SLIDES THROUGH THE AREA FROM THE NORTHWEST.
THE BULK OF THE AREA IS IN A SLIGHT RISK FOR SEVERE THUNDERSTORMS
ON MONDAY AS WELL.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS POSSIBLE THIS EVENING THROUGH MONDAY.

LMZ844>849-101000-
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-
315 PM EDT SUN AUG 9 2009

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

.DAY ONE...THIS EVENING AND TONIGHT

SOUTHERLY WINDS TO 30 KNOTS ARE EXPECTED THIS EVENING WITH WAVES
OF 4 TO 7 FEET...ESPECIALLY BETWEEN SOUTH HAVEN AND WHITEHALL.
WAVES OF THIS HEIGHT WILL POSE A HAZARD TO SMALL CRAFT. A HIGH RISK
OF RIP CURRENTS IS EXPECTED EARLY THIS EVENING. BEACHES JUST SOUTH
OF SOUTH PIERS WILL LIKELY SEE THE HIGHEST WAVE ACTION THIS EVENING.

THUNDERSTORMS ARE POSSIBLE BOTH THIS EVENING  THROUGH TONIGHT ON LAKE
MICHIGAN...SOME OF WHICH MAY BE SEVERE. STORMS WILL CONTAIN FREQUENT
CLOUD TO WATER LIGHTNING STRIKES AND TORRENTIAL RAINS. THE STRONGEST
OF STORMS MAY CONTAIN WIND GUSTS TO AROUND 60 MPH.  THE PRIMARY
STORM MOTION WILL BE EAST AT AROUND 35 MPH.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

THUNDERSTORMS ARE ONCE AGAIN A GOOD POSSIBILITY MONDAY AND MONDAY
NIGHT AS A COOL FRONT SLIDES THROUGH THE AREA FROM THE NORTHWEST.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS POSSIBLE BOTH THIS EVENING THROUGH MONDAY.

DUKE MJS

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