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000 FXUS63 KGRR 240451 AFDGRR AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE GRAND RAPIDS MI 1150 PM EST MON NOV 23 2009 LATEST UPDATE...AVIATION... .SYNOPSIS...(415 PM EST MON NOV 23 2009) AN AREA OF LOW PRESSURE WILL SWING THROUGH THE GREAT LAKES REGION THIS WEEK...SPREADING RAIN INTO SOUTHWEST LOWER MICHIGAN TUESDAY EVENING. CHANCES FOR RAIN WILL CONTINUE INTO WEDNESDAY AND WEDNESDAY NIGHT. COLDER AIR WILL FILTER INTO THE GREAT LAKES BEHIND THE SYSTEM FROM WEDNESDAY NIGHT INTO FRIDAY. THE AIR WILL BE COLD ENOUGH WHERE SOME SNOW MAY MIX IN ON THANKSGIVING AND INTO FRIDAY. HEAVY SNOW IS NOT EXPECTED...AND FOR THE MOST PART ANY ACCUMULATION WILL BE MINIMAL. BY THE END OF THE WEEK...TEMPERATURES WILL BE MUCH CLOSER TO NORMAL WITH HIGHS AROUND 40 AND LOWS DROPPING TO AROUND 30. && .SHORT TERM...(415 PM EST MON NOV 23 2009) (TONIGHT THROUGH WEDNESDAY NIGHT) MAIN ISSUES TO DEAL WITH IN THE SHORT TERM PERTAIN TO FOG FORMATION TONIGHT...PRECIPITATION CHANCES TUESDAY NIGHT THROUGH WEDNESDAY NIGHT AND THE CHANCE FOR SNOW MIXING IN INTO THANKSGIVING MORNING. WE ARE EXPECTING FOG ONCE AGAIN TONIGHT WITH A WEAK PRESSURE GRADIENT IN PLACE AND CLEARING SKIES. BEST CHANCES OF DENSE FOG WILL BE IN AREAS THAT HAVE CLEARED OUT THIS EVENING...NAMELY ALONG AND SOUTH OF INTERSTATE 96. NOT CONFIDENT ENOUGH AT THIS POINT TO ISSUE AN ADVISORY...BUT WE WILL BE CLOSELY WATCHING VSBY/S AS WE HEAD INTO THE OVERNIGHT HOURS. THE FOG WILL LIFT OUT TOWARD MIDDAY ON TUESDAY...WITH A LULL IN THE ACTIVE WEATHER THROUGH THE AFTERNOON. RAIN WILL BE PRESS INTO THE AREA AFTER DARK ON TUESDAY EVENING IN ADVANCE OF THE DEEPENING LOW. IT APPEARS THE HEAVIEST PRECIPITATION SHOULD OCCUR TUESDAY NIGHT WITH THE SYSTEM AS STRONG LIFT PROGRESSES THROUGH THE FORECAST AREA. PRECIPITATION WILL CONTINUE INTO WEDNESDAY IN DEEP CYCLONIC FLOW. SOME LAKE ENHANCED RAIN SHOWERS WILL BE POSSIBLE BY THE END OF THE DAY AS DELTA T/S INCREASE TO AROUND 8 DEGREES C. DELTA T/S WILL INCREASE FURTHER TO AROUND 12 DEGREES C BY THANKSGIVING MORNING. RAIN SHOWERS WILL TRY TO MIX WITH SNOW SHOWERS WEDNESDAY NIGHT WITH THE LOW TO THE NORTH OF THE AREA AND COLD AIR WRAPPING INTO SOUTHWEST LOWER MICHIGAN. 850MB TEMPS WILL BE IN THE -2 TO -6 DEGREE C RANGE...SO SNOW IS A POSSIBILITY BY 12Z THURS. && .LONG TERM...(400 PM EST MON NOV 23 2009) (THURSDAY THROUGH MONDAY) MAIN CHALLENGES IN THE LONG TERM CONTINUE TO BE THE THREAT OF PCPN IN AN INCREASINGLY ACTIVE WEATHER PATTERN...AND P-TYPE THROUGH MOST OF THE PERIOD AS COLDER AIR FILTERS INTO THE STATE. COLDER AIR WILL BE ALREADY MAKING ITS WAY INTO THE AREA AT THE BEGINNING OF THE LONG TERM THU MORNING AS A SECONDARY AND MORE POTENT SHORT WAVE DIVES SE TOWARD THE GREAT LAKES. THE EXACT TRACK OF THE COLDEST AIR IS A BIT IN QUESTION DUE TO THE INTERACTION WITH THE FIRST TROUGH. EITHER WAY...THE AIR COMING IN WILL BE APPROACHING RAIN/SNOW THRESHOLDS. THE NIGHT TIME HOURS WILL SEE THE BEST THREAT OF SNOW AS THE BOUNDARY LAYER COOLS AND FREEZING LEVELS DROP TO 1K FEET OR LESS. ACCUMULATING SNOW DOES NOT LOOK LIKELY...ESPECIALLY WITH A WARM GROUND. IT IS NOT TOTALLY OUT OF THE QUESTION HOWEVER IF WE CAN COOL THE LOW LEVELS OFF ENOUGH. MODELS HAVE BEEN VARYING ON THE TIMING OF THE EXIT OF THE UPPER TROUGH FROM ANYWHERE BETWEEN FRI AFTERNOON TO SAT NIGHT/SUN. THE 12Z MODELS HAVE TIGHTENED THIS RANGE UP A BIT TO FRI NIGHT/SAT MORNING. ANY INSTABILITY SHOWERS AND/OR LAKE EFFECT WILL THEN SHUT OFF AS TEMPS AT 850 WARM. RIDGING WILL THEN MOVE IN FOR ABOUT 24-36 HOURS...AND SLIGHTLY WARM TEMPS A BIT. THE NEXT SHORT WAVE IN THE SERIES COMING IN FROM THE NW WILL MOVE IN DURING THE DAY ON SUN. TEMPS WILL BE WARM ENOUGH AHEAD OF THE SYSTEM THAT P-TYPE WILL BE ALL RAIN. THIS WILL TRANSITION TO AT LEAST A MIX IF NOT ALL SNOW BY NEXT MON AS A SHOT OF COLD AIR FOLLOWS IN THE WAKE OF THIS FRONT. && .AVIATION...(1150 PM EST MON NOV 23 2009) THE PRIMARY ISSUE REMAINS THE EXPECTED REDEVELOPMENT OF STRATUS AND FOG OVERNIGHT. THE LOW CLOUD DECK OVERSPREAD THE SOUTHERN CWA BY 8 PM. HOWEVER THERE IS AN AREA OF DRIER AIR OVER NORTHERN OH AND NRN IN HEADING INTO SOUTHWEST LOWER MICHIGAN. THAT CAN BE SEEN ON THE NAM12 925 MB RH/DEW POINT FORECAST AS WELL AS LOOKING AT LOOPS OF THE IR FOG IMAGES (SHOWING CLEARING PROGRESSING NORTHWARD TOWARD I-94). THAT BEING SO... DENSE FOG WILL QUICKLY FOLLOW AS CAN ALSO BE SEEN ON RECENT SURFACE OBS IN THE CLEAR AREAS OVER NRN IN AND OH. AT THE WESTERN TAF SITES I BROUGHT THE FOG IN AFTER BRIEFLY CLEARING THE LOW CLOUDS. IN THE EASTERN TAF SITES THE LOW CLOUDS EXTEND FATHER SOUTH... I WAS NOT SURE THE CLEARING WOULD REALLY MOVE IN THERE. SO I DID NOT BRING THE VIS DOWN AS MUCH TOWARD MORNING. SKIES WILL CLEAR BY MID AFTERNOON AS THE STORM APPROACHES FROM THE SOUTHWEST AND BRINGS IN BETTER DEEP MIXING. RAIN WILL FOLLOW IN THE 01Z TO 04Z TIME FRAME. && .MARINE...(415 PM EST MON NOV 23 2009) LIGHT EASTERLY FLOW WILL KEEP WAVE HEIGHTS IN CHECK TONIGHT AND TUESDAY. WINDS AND WAVES WILL BE ON THE INCREASE TUESDAY NIGHT INTO WEDNESDAY THOUGH AS A DEEPENING LOW MOVES INTO THE NORTHERN GREAT LAKES. WINDS WILL BECOME SOUTHERLY AS THE LOW MOVES NORTH OF THE AREA WHICH WILL BUILD WAVES TO 3 TO 5 FEET INTO WEDNESDAY MORNING. WESTERLY FLOW ON WEDNESDAY SHOULD BUILD WAVES HEIGHTS FURTHER ON WEDNESDAY INTO THE 3 TO 6 FOOT RANGE TOWARD THE END OF THE DAY. && .HYDROLOGY...(415 PM EST MON NOV 23 2009) STILL NOT EXPECTING ANY HYDRO PROBLEMS WITH THE SYSTEM MOVING THROUGH THIS WEEK. IT APPEARS MOST LOCATIONS WILL SEE RAINFALL OF A HALF INCH OR BELOW. THERE MAY BE A FEW SPOTS THAT PICK UP .50 TO .75 IN THE NORTHWEST PORTION OF THE FORECAST AREA THOUGH. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...NONE. LM...NONE. && $$ SYNOPSIS: DUKE SHORT TERM: DUKE LONG TERM: NJJ AVIATION: WDM MARINE: DUKE HYDROLOGY: DUKE
