Severe Thunderstorm Warning 22, NWS Grand Rapids, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
400 PM EDT FRI JUN 18 2010

LATEST UPDATE...ALL BUT AVIATION...

.SYNOPSIS...(400 PM EDT FRI JUN 18 2010)
SHOWERS AND THUNDERSTORMS...SOME POSSIBLY SEVERE...WILL MOVE THROUGH
THE AREA TONIGHT AHEAD OF A COLD FRONT. AFTER THE FRONT PASSES
THROUGH EARLY SATURDAY...DRIER CONDITIONS AND MORE SEASONAL
TEMPERATURES ARE EXPECTED FOR THE REST OF THE WEEKEND. THE FOLLOWING
WORK WEEK WILL BE CHARACTERIZED BY HUMID CONDITIONS...SOMEWHAT ABOVE
NORMAL TEMPERATURES...AND CHANCES FOR THUNDERSTORMS EACH DAY.

&&

.SHORT TERM...(400 PM EDT FRI JUN 18 2010)
(TONIGHT THROUGH SATURDAY)
MAIN CONCERN IS TIMING...PLACEMENT...AND STRENGTH OF THUNDERSTORMS
TONIGHT.

RADAR AND SATELLITE SHOW A FORWARD PROPAGATING MCS RACING E ACROSS
NRN IL AT THIS TIME. LATEST RUC SOUNDINGS SHOW A GREATER SURGE OF
BOUNDARY LAYER MOISTURE S OF I-96 LATE THIS AFTERNOON AND EARLY
EVENING. CURRENT MOTION SUGGESTS THE MCS WILL AFFECT THE SW CWFA
AROUND 6 PM. IT IS SOMEWHAT UNCERTAIN IF THE MCS WILL BE WEAKENED
WHILE CROSSING LAKE MICHIGAN. THE MCS APPEARS TO BE DRIVEN BY A
MODERATE JET STREAK MOVING NE TOWARDS THE GREAT LAKES...WHICH
SUGGESTS IT WILL REMAIN ORGANIZED. WOULD NOT BE SURPRISED TO SEE A
SEVERE THUNDERSTORM WATCH ISSUED FOR THE MENTIONED AREA.

ANOTHER SURGE OF STORMS WILL OCCUR AHEAD OF THE FRONT MORE IN THE
MIDNIGHT TIMEFRAME. WE ARE SKEPTICAL OF THE HIGHLY KINEMATIC GFS
SOLUTION DUE TO THE LARGE AMOUNT OF GRID SCALE PRECIPITATION / LOW
LEVEL PV GENERATION OVERNIGHT...WHICH IN TURN LIKELY
OVER-STRENGTHENS THE DOWNSTREAM LOW LEVEL JET. TEND TO FAVOR THE
NAM...WHICH HAS LESS IMPRESSIVE SHEAR PROFILES. HOWEVER...THE
ALREADY IMPRESSIVE INSTABILITY ALONE JUSTIFIES A CONTINUED MENTION
OF SEVERE. EXPECT CONVECTION TO WIND DOWN AROUND SUNRISE SATURDAY AS
THE FRONT SWEEPS THROUGH THE AREA.

&&

.LONG TERM...(400 PM EDT FRI JUN 18 2010)
(SATURDAY NIGHT THROUGH FRIDAY)

A HIGH PRESSURE RIDGE WILL BUILD IN AND PRODUCE FAIR WX SATURDAY
NIGHT THROUGH SUNDAY NIGHT. THE SFC RIDGE AXIS WILL SHIFT EAST WITH
A LOW PRESSURE SYSTEM OVER THE PLAINS STATES BY MONDAY. THIS WILL
RESULT IN SOUTHERLY RETURN FLOW AND INCREASING HEAT AND HUMIDITY
OVER OUR AREA MONDAY THROUGH TUESDAY NIGHT.

THE INCREASING INSTABILITY WILL RESULT IN POTENTIAL FOR TSTORMS
MONDAY THROUGH TUESDAY AND PERHAPS LINGERING INTO WEDNESDAY UNTIL A
COLD FRONT COMES THROUGH. DRY WX WITH SEASONABLE TEMPS IS EXPECTED
FOR THURSDAY AND FRIDAY AS HIGH PRESSURE BUILDS IN.

&&

.AVIATION...(145 PM EDT FRI JUN 18 2010)
EXPECT A LESS THAN 20 PERCENT PROBABILITY FOR THUNDERSTORMS OVER SW
LOWER MI THROUGH 00Z...BUT ANY STORMS THAT DEVELOP COULD BE SEVERE
WITH GUSTS GREATER THAN 50KT. THE LIKELIHOOD OF A TERMINAL BEING
AFFECTED IS VERY LOW. IF STORMS WERE TO DEVELOP EARLY...THEY WOULD
MOST LIKELY BE OVER FAR SW LOWER MI CLOSE TO AZO.

EXPECT A BETTER COVERAGE OF THUNDERSTORMS APPROACHING FROM THE WEST
AFTER 04-05Z AHEAD OF A COLD FRONT. LATEST TAFS CARRY ONLY CB FOR
THIS TIME FRAME...BUT THERE IS A GOOD CHANCE THAT MOST TAF SITES
WILL SEE AROUND AN HOUR OF TSRA OVERNIGHT. THERE IS A GOOD CHANCE
FOR THUNDERSTORM WIND GUSTS GREATER THAN 40 KNOTS...MOST LIKELY OUT
OF THE W-NW...AND AT LEAST A SLIGHT CHANCE FOR GUSTS GREATER THAN 50
KTS.

ALTHOUGH NOT MENTIONED IN THE TAFS...EXPECT VFR CIGS AND VSBYS AFTER
12Z FOR ALL TAF SITES.

&&

.MARINE...(400 PM EDT FRI JUN 18 2010)
NO HAZARDS ARE ANTICIPATED. ONE CONCERN...BESIDES STRONG TO SEVERE
CONVECTION...IS FOG DUE TO HIGH DEWPOINTS STREAMING OVER THE COOL
WATERS. WILL MONITOR THIS IF WINDS ARE ABLE TO DECOUPLE IN SPITE OF
AN INCREASING PRESSURE GRADIENT.

&&

.HYDROLOGY...(421 PM EDT FRI JUN 18 2010)
THERE WILL NOT BE ANY LOWER OR UPPER JET TO FOCUS AN AREA OF HEAVY
PCPN WITH THIS APPROACHING SYSTEM.  GENERALLY RIVER BASIN AVERAGE
QPF WILL BE AROUND A QUARTER.  HOWEVER LOCALLY HEAVY AMOUNTS WILL
OCCUR WITH PRECIPTABLE WATER VALUES AROUND 1.75 INCHES.  GIVEN THE
MOIST GROUNDS ALREADY IN PLACE...SOME URBAN AND SMALL STREAM
FLOODING WILL BE POSSIBLE TODAY AND TONIGHT.

&&

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

&&

SYNOPSIS:     TJT
SHORT TERM:   TJT
LONG TERM:    LAURENS
AVIATION:     TJT
MARINE:       TJT
HYDROLOGY:    JK

HAZARDOUS WEATHER OUTLOOK...CORRECTED SPOTTER INFO SECTION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
445 PM EDT FRI JUN 18 2010

LMZ844>849-MIZ037>040-043>046-050>052-056>059-064>067-071>074-191000-
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-
445 PM EDT FRI JUN 18 2010

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

.DAY ONE...THIS AFTERNOON AND TONIGHT

SEVERE THUNDERSTORM WATCH NUMBER 0344 IS IN EFFECT UNTIL MIDNIGHT
FOR AREAS SOUTH OF HIGHWAY 10. DAMAGING WINDS ARE THE MAIN THREAT.
STORM MOTION WILL BE TO THE EAST AROUND 45 MPH.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

THUNDERSTORMS ARE POSSIBLE MUCH OF NEXT WEEK WITH THE HIGHEST
CHANCES ON MONDAY AND AGAIN ON WEDNESDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS REQUIRED THIS EVENING FOR ALL OF SOUTHWEST
LOWER MICHIGAN. SKYWARN LIKELY WILL NEED TO CONTINUE UNTIL
AFTER MIDNIGHT AS ANOTHER ROUND OF STORMS MOVE EAST ACROSS THE AREA.

TJT

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