Issued by NWS Grand Rapids, MI
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000 FXUS63 KGRR 081148 AFDGRR AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAND RAPIDS MI 745 AM EDT FRI MAY 8 2009 LATEST UPDATE...AVIATION... .SYNOPSIS...(405 AM EDT FRI MAY 8 2009) PARTLY SUNNY AND MILD WEATHER IS ANTICIPATED TODAY. THE NEXT LOW PRESSURE SYSTEM WILL BRING SHOWERS AND SOME THUNDERSTORMS LATE TONIGHT INTO SATURDAY MORNING. IT WILL TURN MUCH COOLER THIS WEEKEND WITH HIGH TEMPS BOTH SATURDAY AND SUNDAY ONLY IN THE 50S. IT WILL ALSO BE QUITE BREEZY SATURDAY. && .SHORT TERM...(405 AM EDT FRI MAY 8 2009) (TODAY THROUGH SUNDAY) PRIMARY SHORT TERM FCST CONCERNS REVOLVE AROUND DETERMINING PROBABILITIES FOR SHOWERS THROUGH SATURDAY. WE ALSO NEED TO ASSESS POTENTIAL FOR CONVECTIVE DEVELOPMENT LATE TONIGHT. WE HAVE RAMPED UP FCST WIND SPEEDS FROM SATURDAY MORNING THROUGH LATE SATURDAY EVENING. IT WILL BE PARTLY SUNNY AND MILD TODAY WITH MAX TEMPS REACHING THE LOW TO MID 70S... EXCEPT MUCH COOLER RIGHT ALONG THE LAKE MI SHORELINE. ISOLATED SHOWERS MAY REDEVELOP ACROSS MAINLY OUR SOUTHERN CWFA LATER TODAY... THOUGH PREDOMINANTLY DRY CONDITIONS WILL PREVAIL THROUGH THIS AFTERNOON AND EVENING. MOST OF THE 00Z GUIDANCE AND 4KM WRF NMM SIM REFL STILL SHOWS POTENTIAL FOR ISOLATED SHOWERS TO DEVELOP SOUTH/SE LATER THIS MORNING AND AFTN. THE LOW PRESSURE SYSTEM AND COLD FRONT WILL BRING AN INCREASING THREAT FOR SHOWERS AND THUNDERSTORMS LATE TONIGHT INTO SATURDAY MORNING. OUR BEST CHC FOR SOME STORMS WILL COME FROM AROUND 06Z SATURDAY THROUGH 12Z SATURDAY COINCIDENT WITH AN INCREASE IN ELEVATED INSTABILITY AS 850 LI/S FALL TO AROUND -1 TO -2. VIGOROUS PVA AND UPPER LEVEL DIFFLUENCE WILL DEVELOP IN THAT TIME FRAME IN ADDITION TO ROBUST POTENTIAL VORTICITY AS THE WAVE OVER MONTANA EARLY THIS MORNING RACES EAST TO IMPACT OUR CWFA LATE TONIGHT INTO SATURDAY MORNING. IT WILL TURN VERY BREEZY AND SHARPLY COOLER BEHIND THE COLD FRONT SATURDAY WITH TEMPS ONLY IN THE 50S. WNW WINDS OF 20 TO 30 MPH ARE ANTICIPATED WITH HIGHER GUSTS POTENTIALLY IN THE 35 TO NEAR 40 MPH RANGE. SOME SHOWERS WILL LINGER SATURDAY... MAINLY IN THE MORNING. TEMPS COULD DIP DOWN TO NEAR THE FREEZING MARK BY 10-11Z SUNDAY PARTICULARLY ACROSS OUR NORTH AND NE CWFA. HOWEVER MODEL TIME HEIGHT RH PROGS SUGGEST SOME CLOUDS WILL LINGER THROUGH THE NIGHT. THIS AND WNW SFC WINDS OF AROUND 5 TO 7 KTS COULD RESULT IN SUFFICIENT BOUNDARY LAYER MIXING TO MITIGATE WIDESPREAD FROST FROM FORMING. AT THIS TIME WE WILL CONTINUE MENTION OF PATCHY FROST DEVELOPMENT DURING THE EARLY MORNING HOURS SUNDAY. IT WILL BE PARTLY SUNNY AND CONTINUED COOL SUNDAY WITH THE SFC RIDGE IN CONTROL. MAX TEMPS SUNDAY WILL ONLY REACH THE MID TO UPPER 50S. && .LONG TERM...(405 AM EDT FRI MAY 8 2009) (SUNDAY NIGHT THROUGH THURSDAY) COOL AND DRY SFC HIGH PRESSURE WILL PREVAIL SUNDAY NIGHT THROUGH TUESDAY... WITH FROST AND FREEZING TEMPERATURES AT NIGHT AND DAYTIME HIGHS ONLY NEAR 60. WARM ADVECTION COMMENCES TUESDAY NIGHT AS THE SFC HIGH MOVES TO THE EAST COAST... WHICH MAY RESULT IN A FEW SHOWERS OVERNIGHT. HOWEVER THE BEST CHANCE OF RAIN AND TSTMS LOOKS TO EXIST ON WEDNESDAY INTO WEDNESDAY NIGHT. THIS IS WHEN AN ACTIVE WARM FRONT LIFTS NORTH AND SETS UP ACROSS THE AREA WHILE A POTENT NRN PLAINS H5 UPR LOW/TROUGH SHIFTS EWD. THE SHOWER AND TSTM THREAT MAY LINGER INTO THURSDAY... BUT THE COLD FRONT ARRIVING FROM THE WEST SHOULD EVENTUALLY DRY THINGS OUT BY LATE IN THE DAY IF NOT EARLIER. && .AVIATION...(745 AM EDT FRI MAY 8 2009) VFR CONDITIONS EXPECTED TODAY AND THIS EVENING... ALTHOUGH LATE TONIGHT SOME LIGHT MVFR FOG MAY FORM AGAIN AND SHOWERS WILL BE ARRIVING FROM THE WEST. CIGS SHOULD LOWER INTO MVFR/IFR CATEGORY TOWARD 12Z AS THE RAIN BECOMES MORE WIDESPREAD/HEAVIER... PARTICULARLY ALONG/NORTH OF THE I 96 CORRIDOR. A FEW TSTMS ARE ALSO POSSIBLE TOWARD 12Z... BUT LEFT THAT THREAT OUT OF THE TAFS FOR NOW. && .MARINE...(405 AM EDT FRI MAY 8 2009) MINIMAL WAVE ACTION LESS THAN TWO FEET IS ANTICIPATED TODAY DUE TO FAIRLY LIGHT SW TO WEST WINDS. THUNDERSTORMS WILL DEVELOP LATE TONIGHT AND POSE A HAZARD TO MARINERS. WINDS AND WAVE HEIGHTS WILL INCREASE SIGNIFICANTLY SATURDAY. WNW WINDS SATURDAY WILL RAMP UP TO 20 TO 30 KTS WITH HIGHER GUSTS RESULTING IN INCREASING WAVE HEIGHTS TO 3 TO 6 FEET. IN FACT A GALE WATCH HEADLINE MAY BE NEEDED LATER TODAY... WE HELD OFF ON IT FOR NOW BASED ON COORD WITH LOT. && .HYDROLOGY...(405 AM EDT FRI MAY 8 2009) RIVER LEVELS CONTINUE TO FALL AT ALL SITES AND WILL CONTINUE TO FALL THROUGH THE WEEKEND INTO EARLY NEXT WEEK. RAINFALL LATE TONIGHT INTO SATURDAY WILL NOT BE SIGNIFICANT ENOUGH TO CAUSE RIVER LEVELS TO RISE. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...NONE. LM...NONE. && $$ SYNOPSIS: LAURENS SHORT TERM: LAURENS LONG TERM: MEADE AVIATION: MEADE MARINE: LAURENS HYDROLOGY: LAURENS
