Issued by NWS Grand Rapids, MI
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000 FXUS63 KGRR 271137 AFDGRR AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAND RAPIDS MI 730 AM EDT MON OCT 27 2008 LATEST UPDATE...AVIATION... .SYNOPSIS...(407 AM EDT MON OCT 27 2008) CHILLY CANADIAN AIR WILL RESIDE OVER THE GREAT LAKES TODAY AND TUESDAY. DAYTIME TEMPERATURES WILL ONLY STRUGGLE TO REACH 40. THIS COLD AIR...OVER THE RELATIVE WARMER WATERS OF LAKE MICHIGAN WILL PRODUCE LAKE EFFECT PRECIPITATION THROUGH TUESDAY. RAIN WILL BECOME MIXED WITH SNOW TODAY...THEN CHANGE TO ALL SNOW BY THIS EVENING. AREAS WITHIN 50 MILES OF LAKE MICHIGAN COULD SEE UP TO TWO INCHES OF SNOW ACCUMULATION TONIGHT INTO TUESDAY. THE SNOW WILL WIND DOWN TUESDAY NIGHT. WARMER TEMPERATURES ARE EXPECTED FOR THE LATTER HALF OF THE WEEK ALONG WITH SOME SUNSHINE. && .SHORT TERM...(407 AM EDT MON OCT 27 2008) (TODAY THROUGH WEDNESDAY) THE LONG ANTICIPATED COLD AIR HAS ARRIVED THIS MORNING. LAKE MICHIGAN HAS RESPONDED WITH LAKE EFFECT RAIN SHOWERS BREAKING OUT SINCE ABOUT 1 AM. THICKNESS VALUES ARE STILL TOO WARM TO SUPPORT MUCH MORE THAN RAIN EARLY THIS MORNING. HOWEVER...IN SOME OF THE MORE INTENSE SHOWERS...SOME SNOW OR EVEN HAIL WILL BE POSSIBLE. THE CHILLY AIR WILL CONTINUE TO ADVECT IN THROUGH THE DAY AND SNOW MIXING WITH THE RAIN WILL BECOME MORE COMMON FROM NW TO SE. THE THINKING NOW IS THAT SNOW WILL APPEAR NW OF A GRAND HAVEN TO RQB LINE BY MID DAY...WITH THE REST OF THE CWA SEEING SNOW MIXING IN THROUGH THE AFTERNOON. DUE TO THE MIXED NATURE...ANY DAYTIME ACCUMULATION WILL BE LESS THAN AN INCH AND MAINLY OVER THE NW CWA. THERE WILL BE A BETTER CHANCE OF ACCUMULATING SNOW TONIGHT. ONE CONCERN HOWEVER IS THAT THERE IS A TREND FOR THE FLOW TO BE MORE NNW THAN NW. THIS WOULD LEAVE THE BEST LAKE BANDS HUGGING THE LAKE SHORE COUNTIES. AGAIN I/M THINKING THE BULK OF THESE AREAS WILL SEE LESS THAN AN INCH...HOWEVER LOCALIZED 2-3 INCHES IS NOT OUT OF THE QUESTION. MUCH OF THIS WILL BE A GRASSY SURFACES AND CAR TOPS. FURTHER INLAND...EAST OF U.S. 131...MOST AREAS WILL ONLY SEE A DUSTING...IF THAT. THE LAKE EFFECT WILL CONTINUE INTO TUESDAY...BUT THE RISK OF ACCUMULATIONS WILL BE REDUCED AS THE DIURNAL IMPACTS CAUSE THE SHOWERS TO BECOME MORE OPEN CELLS. THE MODELS HAVE BACKED OFF THE TIMING OF THE SURFACE RIDGE APPROACHING FROM THE WEST. THIS MEANS THE LAKE EFFECT COULD LINGER INTO TUESDAY NIGHT...SO HAVE ADDED POPS. SKIES WILL GRADUALLY CLEAR ON WEDNESDAY AS THE RIDGE FINALLY MOVES IN. TEMPS WILL RESPOND TO THE SUNSHINE AND CLIMB TO 45 TO 50. && .LONG TERM...(407 AM EDT MON OCT 27 2008) (WEDNESDAY NIGHT THROUGH SUNDAY) RATHER STRONG WARM AIR ADVECTION IS SHOWN BY THE MEDIUM RANGE MODELS ACROSS THE GREAT LAKES REGION FOR THU INTO FRI. THEN A BACKDOOR COLD FRONT SLIPS DOWN FROM THE NORTH FOR FRI EVENING. THIS FRONTAL PASSAGE LOOKS DRY. AN IMPRESSIVE 1040+ MB HIGH WILL BE DROPPING DOWN FROM CENTRAL CANADA DRAWING A SHALLOW COLD AIRMASS INTO THE REGION FOR FRI NIGHT INTO SAT NIGHT. HOWEVER THE PATTERN WILL BE PROGRESSIVE DESPITE THE AMPLIFICATION AND STRONG WARM AIR ADVECTION RETURNS FOR SUN. MODELS ARE IN RELATIVE AGREEMENT FOR THIS SCENARIO. NO PRECIPITATION FORECASTED FOR THE EXTENDED PERIOD. I MODIFIED WINDS UPWARD FOR MOST PERIODS GIVEN THE STRONG TEMPERATURE ADVECTION PATTERN SEEN. I DID LOWER TEMPERATURES FRI NIGHT INTO SAT GIVEN THE STRENGTH OF THE COLD AIR ADVECTION AND THE SHALLOW NATURE OF THE COLD AIRMASS. && .MARINE...(407 AM EDT MON OCT 27 2008) WILL MAINTAIN THE GALE WARNING THIS MORNING...HOWEVER IT MAY BE ABLE TO BE CANCELED BY MID/LATE THIS MORNING AS THE PRESSURE GRADIENT RELAXES A BIT. ONCE THIS IS DONE A SMALL CRAFT ADVISORY WILL BE NEEDED THROUGH AT LEAST TUESDAY NIGHT AS WAVES WILL REMAIN HIGH WITH THE UNSTABLE NATURE OF THE LAKE. && .AVIATION...(730 AM EDT MON OCT 27 2008) COLD AIR ADVECTION ACROSS LAKE MI WILL CONTINUE TO GENERATE SHOWERS THROUGH THE DAY TODAY AND INTO TONIGHT. MOST LOCATIONS WILL SEE A MIXTURE OF VFR AND MVFR CLOUD HEIGHTS THROUGH THE DAY. AS WE GO INTO TONIGHT...HEIGHTS SHOULD IMPROVE TO VFR. MOST OF THE PRECIPITATION IS EXPECTED AROUND KAZO. THERE IS SOME INSTABILITY PRESENT...SO WE WILL NEED TO MONITOR THE THUNDER THREAT...BUT AT THIS TIME THE POTENTIAL APPEARS LIMITED. WITH TEMPERATURES ABOVE FREEZING NEAR THE GROUND...IT WILL BE TOUGH FOR SNOW TO REACH THE GROUND...SO I DID NOT MENTION IT IN THE TAFS. && .HYDROLOGY...(407 AM EDT MON OCT 27 2008) NO HYDRO CONCERNS AS PCPN NEXT 72 HOURS WILL BE GENERALLY SCATTERED IN NATURE WITH QPF AMOUNTS BELOW HALF INCH. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...NONE. LM...GALE WARNING IN EFFECT ST. JOE TO MANISTEE THROUGH THIS AFTERNOON. && $$ SYNOPSIS: JK SHORT TERM: JK LONG TERM: MJS MARINE: JK AVIATION: MJS HYDROLOGY: JK
