Special Weather Statement, NWS Grand Rapids, MI

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
738 PM EDT WED MAY 11 2011

LATEST UPDATE...AVIATION...

.SYNOPSIS...(436 PM EDT WED MAY 11 2011)
A WARM FRONT JUST SOUTHWEST OF LOWER MICHIGAN WILL INCH NORTHEAST
TONIGHT AND THURSDAY... TRIGGERING SCATTERED SHOWERS AND
THUNDERSTORMS.

ANOTHER FRONTAL BOUNDARY NOW SITUATED FROM MINNESOTA SOUTH TO KANSAS
WILL EDGE SLOWLY EAST OVER THE NEXT FEW DAYS AS WAVES OF LOW
PRESSURE MOVE NORTHEAST ALONG IT. THIS PATTERN... COMBINED WITH A
WARM AND HUMID AIR MASS... WILL KEEP SCATTERED SHOWERS AND
THUNDERSTORMS IN THE FORECAST ALL THE WAY THROUGH THE WEEKEND.

&&

.SHORT TERM...(436 PM EDT WED MAY 11 2011)
(TONIGHT THROUGH FRIDAY NIGHT)

WARMER MID LEVEL TEMPS AND SUBSIDENCE ASSOCIATED WITH AMPLIFYING
RIDGE OVERHEAD HAS HALTED ANY SOUTHWARD MOVEMENT/DEVELOPMENT OF THE
NRN LWR MI MCS TODAY. ALL THE ACTION REMAINS NORTH OF HIGHWAY U.S.
10 WHICH APPROXIMATES THE NRN EDGE OF THE MID LEVEL CAP.

HOWEVER THE RIDGE AXIS AND WARMER TEMPS ALOFT WILL BE SHIFTING OFF
TO THE EAST TONIGHT AND THURSDAY AND THERE ARE CURRENTLY SEVERAL
CLUSTERS/BANDS OF CONVECTION MOVING N/E THROUGH THE WRN SIDE OF THE
RIDGE. WILL CARRY LIKELY POPS TONIGHT AND THURSDAY OVER THE NRN AND
WRN PORTIONS OF THE CWFA WHERE THE SHORT WAVES WITHIN THE
INCREASINGLY SW FLOW ALOFT SHOULD HAVE THE MOST IMPACT. MEANWHILE
WILL CONTINUE CHANCE POPS IN THE SE CWFA CLOSER TO UPR RIDGE AXIS.

THE MAIN SVR WX THREAT SHOULD CONTINUE TO BE LARGE HAIL DUE TO STEEP
MID LEVEL LAPSE RATES AND FAT CAPE PROFILES ALOFT. OBVIOUSLY BASED
ON WHAT HAS BEEN HAPPENING ACROSS THE FAR NRN CWFA TODAY... HEAVY
RAIN/LOCAL FLOODING REMAINS A THREAT. PWATS ARE NEAR 1.5 INCHES AND
DEEP LAYER SHEAR VALUES ARE LOW.

OVERALL SYNOPTIC PATTERN CHANGES LITTLE FRIDAY AND FRIDAY NIGHT...
WITH A CONTINUATION OF SCATTERED SHOWERS AND TSTMS EXPECTED IN WARM
AND HUMID AIR MASS... HIGH CAPE/LOW SHEAR. THE UPPER LOW NEAR THE
FOUR CORNERS REGION HEADS SOUTHEAST WHILE ANOTHER UPPER LOW DROPS
INTO THE NRN PLAINS REGION. THIS KEEPS US IN SW FLOW ALOFT... WITH
OCNL IMPULSES HEADING NE AND TOUCHING OFF ROUNDS OF STORMS. ALSO...
SFC BASED CAPES NEAR 2000 THUR AND FRI COULD LEAD TO AREAS OF
STRONGER STORMS WHERE/WHEN LOW LEVEL CONVERGENCE IS MAXIMIZED.

&&

.LONG TERM...(436 PM EDT WED MAY 11 2011)
(SATURDAY THROUGH WEDNESDAY)
THE MAIN FOCUS OF THE FORECAST IS THE COMPLEX UPPER SYSTEM THAT
LOOKS TO BE AFFECTING THE CWFA AT LEAST THROUGH THE WEEKEND...IF NOT
LONGER. NO MAJOR CHANGES WERE MADE TO THE FORECAST WITH A HIGHER
THAN NORMAL AMOUNT OF UNCERTAINTY.

UPPER LOW TO OUR SW AND IS BRINGING THE WARMER AND UNSETTLED WEATHER
IS EXPECTED TO ONLY SLOWLY ROTATE TO THE EAST INTO THE EARLY PORTION
OF THE UPCOMING WEEKEND. IT APPEARS THAT WE WILL EVENTUALLY END UP
ON THE COOLER SIDE OF THE SYSTEM BY SAT...AND SHOWERS WITH SOME
THUNDER WILL BE POSSIBLE AS WAVES ROTATE AROUND THIS LOW. IT WILL
NOT BE RAINING THE ENTIRE TIME...BUT THE THREAT OF RAIN WILL BE
THERE.

THE UNCERTAINTY AND COMPLEXITY OF THE LONG TERM PORTION OF THE FCST
THEN COMES IN BEGINNING SAT NIGHT AND SUN AS ALL THE MODELS ARE
SHOWING ANOTHER STRONG UPPER SYSTEM DIVING ESE CLOSE BEHIND THE
FIRST SYSTEM. SHOWERS WILL REMAIN POSSIBLE AT LEAST THROUGH
SUN...AND EVEN MON REGARDLESS OF WHAT MODEL ONE LOOKS AT. THE LAST
COUPLE RUNS OF THE EURO SHOW THE FIRST LOW WRAPPING AROUND THE
SECOND UPPER LOW. THIS WOULD WRAP RAIN BACK ACROSS THE AREA THROUGH
THE END OF THE PERIOD. THE GFS HAS THE SECOND LOW STRONG ENOUGH AND
COMBINES WITH AN UPPER TROUGH ACROSS CANADA TO CLEAR OUT EVERYTHING
FROM THE CWFA.

THIS FCST IS BASED ON THE LATTER SCENARIO IN WHICH THE PCPN GETS
CLEARED OUT BY TUE. THAT IS BASED A BIT ON CONSISTENCY WITH THE
PREVIOUS FCST AND DUE TO THE GREAT AMOUNT OF UNCERTAINTY THAT
REMAINS. NOT COMFORTABLE IN ADDING A LOT OF ADDITIONAL POPS AT THIS
POINT WITH THE AMOUNT OF UNCERTAINTY THAT STILL EXISTS. AS
CONFIDENCE INCREASES...THE CHC OF RAINFALL WILL NEED TO BE FINE
TUNED.

&&

.AVIATION...(738 PM EDT WED MAY 11 2011)
CONVECTIVE TRENDS ARE ONCE AGAIN THE MAIN FOCUS OF THE NEW SET OF
TERMINALS. A COUPLE OF WAVES OF SCATTERED-NUMEROUS STORMS ARE POISED
TO MOVE THROUGH THE TERMINALS A LITTLE LATER THIS EVENING AND DURING
THE EARLY OVERNIGHT HOURS TONIGHT. EXTRAPOLATING THIS CONVECTION IN
ACROSS THE AREA WOULD BRING IT FIRST TO KAZO BY 02Z AND THEN LAST TO
KLAN AROUND 03-04Z. THERE WILL BE A FEW HOURS OF POTENTIAL
CONVECTION ONCE IT MOVES IN. THE STORMS MAY HAVE A TENDENCY TO
WEAKEN/DIMINISH OVERNIGHT AS THE DIURNAL HEATING COMPONENT IS LOST.
INSTABILITY WILL REMAIN IN PLACE ABOVE THE SFC...SO IT MAY NOT
DISSIPATE ENTIRELY. THE WAVE SHOULD MOVE OUT BETWEEN 06-08Z WHICH
SHOULD DIMINISH THE CHCS FOR AT LEAST A FEW HOURS.

AFTER A GOOD CHANCE OF A BREAK IN THE CONVECTION...INSTABILITY WILL
BUILD ONCE AGAIN LATE THU MORNING AND THU AFTERNOON. IT WILL BE
TOUGH TO PIN DOWN ANY DETAILS WITH REGARDS TO TIMING WAVES IN...SO
WE HAVE JUST WENT WITH A VCTS FOR THE TIME BEING. THIS WILL NEED TO
BE FINE TUNED IN FUTURE TERMINAL PACKAGES.

&&

.MARINE...(436 PM EDT WED MAY 11 2011)
A RATHER BRISK EAST FLOW HAS DEVELOPED TODAY DUE TO MESOSCALE
EFFECTS ASSOCIATED WITH THE NRN LWR MI MCS. EVENTUALLY LATER THIS
EVENING... THE FLOW SHOULD WEAKEN AND BECOME MORE SE/S.

VISIBILITY ISSUES RELATED TO FOG AND HAZE WILL LIKELY BECOME AN
ISSUE LATER TONIGHT THROUGH THURSDAY INTO FRIDAY. IT/S BEEN
OCCURRING ON THE OTHER SIDE OF THE LAKE AND THE DEVELOPING SOUTH
FLOW/HIGHER SFC DEW PTS MAY INCREASE THAT PROBABILITY ON THIS SIDE
OF THE LAKE.

IN ADDITION...THE THREAT OF THUNDERSTORMS/HAIL WILL POSE A HAZARD TO
MARINERS THROUGH FRIDAY.

&&

.HYDROLOGY...(436 PM EDT WED MAY 11 2011)
HEAVY RAIN HAS IMPACTED THE FAR NRN CWFA TODAY BUT IT WAS VERY
LOCALIZED AND COVERED WITH FLASH FLOOD WARNINGS/URBAN AND SMALL
STREAM ADVISORIES.

THE OVERALL AREAL/BASIN AVERAGE COVERAGE OF RAINFALL SHOULD CONTINUE
TO BE SCATTERED AND RELATIVELY LOW. THAT MEANS THAT THE LARGER
MAINSTEM RIVERS PROBABLY WON/T BE IMPACTED TOO MUCH. HOWEVER THE
SMALLER CREEKS AND STREAMS WHERE HEAVIER CONVECTION PERSISTS COULD
SEE SHARP AND SIGNIFICANT RESPONSES OVER THE NEXT FEW DAYS.

&&

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

&&

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

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
245 PM EDT WED MAY 11 2011

MIZ037>040-043>046-050>052-056>059-064>067-071>074-121000-
MASON-LAKE-OSCEOLA-CLARE-OCEANA-NEWAYGO-MECOSTA-ISABELLA-MUSKEGON-
MONTCALM-GRATIOT-OTTAWA-KENT-IONIA-CLINTON-ALLEGAN-BARRY-EATON-
INGHAM-VAN BUREN-KALAMAZOO-CALHOUN-JACKSON-
245 PM EDT WED MAY 11 2011

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

.DAY ONE...TODAY AND TONIGHT

SCATTERED THUNDERSTORMS THIS AFTERNOON NORTH OF HIGHWAY U.S. 10
COULD PRODUCE SOME HAIL AND LOCALLY HEAVY RAINFALL AS THEY MOVE EAST
AT AROUND 15 MPH. STORMS ARE POSSIBLE OVER THE ENTIRE AREA TONIGHT
AND SOME MAY BE SEVERE WITH LARGE HAIL.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

SCATTERED THUNDERSTORMS ARE POSSIBLE INTO SATURDAY. AN ISOLATED
SEVERE THUNDERSTORM MAY OCCUR...WITH DAMAGING WINDS AND LARGE
HAIL THE PRIMARY RISKS. LOCALLY HEAVY RAINFALL IS POSSIBLE.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED TONIGHT.

LMZ844>849-121000-
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-
245 PM EDT WED MAY 11 2011

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

.DAY ONE...TODAY AND TONIGHT

SCATTERED THUNDERSTORMS NORTH OF LUDINGTON THIS AFTERNOON COULD
PRODUCE SOME HAIL AND LOCALLY HEAVY RAINFALL AS THEY MOVE EAST AT
AROUND 15 MPH.  STORMS ARE POSSIBLE OVER THE ENTIRE AREA TONIGHT AND
SOME MAY BE SEVERE WITH LARGE HAIL.

AREAS OF FOG COULD LEAD TO AREAS OF LOW VISIBILITY.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

A RISK FOR THUNDERSTORMS WILL EXIST INTO SATURDAY. IN ADDITION
WINDS AND WAVES WILL BE ON THE INCREASE THIS WEEKEND. AREAS OF FOG
COULD LEAD TO AREAS OF LOW VISIBILITY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED TONIGHT.

MEADE

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