FXUS63 KGRR 012339
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
640 PM EST TUE DEC 1 2009
LATEST UPDATE...AVIATION...
.SYNOPSIS...(358 PM EST TUE DEC 1 2009)
AN AREA OF LOW PRESSURE IN THE GULF OF MEXICO WILL BEGIN TO LIFT
NORTH THIS EVENING INTO WEDNESDAY. RAIN WILL OVERSPREAD SOUTHERN
MICHIGAN WEDNESDAY EVENING AND CONTINUE TO MOVE NORTHWEST. AS COLDER
AIR FILTERS ACROSS THE AREA, RAIN WILL MIX WITH SNOW IN AREAS ALONG
WITH LAKE SHORE AND NORTH OF INTERSTATE 96 DURING THE EARLY
OVERNIGHT HORUS. ALL OF SOUTHWEST MICHIGAN WILL CHANGE TO ALL SNOW
TOWARD THURSDAY MORNING. ACCUMULATIONS AROUND AN INCH WILL BE
POSSIBLE SOUTH OF A LINE FROM MOUNT PLEASANT TO CALEDONIA TO
PLAINWELL. DURING THE DAY ON THURSDAY, LAKE EFFECT SNOW SHOWERS WILL
BE LIKELY.
&&
.SHORT TERM...(330PM EDT TUE DEC 1 2009)
(TONIGHT THROUGH THURSDAY)
FORECAST CONCERN REMAINS CENTERED ON GULF COAST LOW AND ITS
POTENTIAL IMPACTS ON MICHIGAN WEDNESDAY NIGHT INTO THURSDAY.
AFTERNOON WATER VAPOR IMAGERY DEPICTS DEVELOPING GULF LOW NICELY. AT
17Z...THE SURFACE LOW WAS POSITIONED SOUTH OF LOUISIANA. NUMEROUS
LIGHTNING STRIKES WERE EVIDENT IN THE GULF OF MEXICO. THE UPPER LOW
COULD ALSO BE SEEN WELL IN THE WATER VAPOR. AT 18Z THE UPPER SYSTEM
WAS OVER EASTERN MEXICO/WESTERN TEXAS. H5 HEIGHT FALLS WITH UPPER
LOW AT 12Z THIS MORNING WERE 70M. FURTHER NORTH, ANOTHER UPPER
SYSTEM WAS DIGGING SOUTHEAST FROM SASKATCHEWAN, CANADA. HEIGHT FALLS
ASSOCIATED WITH THIS SYSTEM WERE AN IMPRESSIVE 140M OVER CENTRAL
MONTANA.
MODELS ARE CONTINUING TO SHOW DISCREPANCIES WITH TRACK OF GULF LOW.
NAM PLACES LOW CENTERED OVER MISSISSIPPI AND EXTENDING WESTWARD INTO
NORTH LOUISIANA BY 12Z WEDNESDAY. BY 18Z WEDNESDAY, THE NAM PUTS
THIS LOW IN WESTERN TENNESSEE. GFS TRACKS THE SURFACE LOW OVER
ALABAMA DURING 12Z WEDNESDAY THEN INTO EASTERN TENNESSEE BY 18Z
WEDNESDAY. THE FIM SUGGESTS A COMPROMISE BETWEEN THE NAM AND GFS. A
COMPROMISE LOOKS LIKE AN APPROPRIATE WAY TO GO AT THIS POINT.
AMPLE MOISTURE WILL SURGE NORTHWARD WITH THE GULF SYSTEM. AS THE
NORTHERN UPPER SYSTEM MOVES SOUTHEAST INTO THE CONUS, THE UPPER LOW
FROM THE SOUTH WILL TRACK NORTHEAST. THESE SYSTEMS ARE EXPECTED TO
MEET WEDNESDAY NIGHT/THURSDAY TIMEFRAME. THE TIMING OF THIS PHASING
OF THESE UPPER SYSTEMS WILL MAKE A BIG DIFFERENCE EXTENT AND
LOCATION OF SNOW ACCUMULATION. AT THE PRESENT TIME, GIVEN THE FIM
TRACK OF THE SYSTEM, IT LOOKS LIKE THE BEST CHANCE FOR ACCUMULATING
SNOW WILL BE ALONG THE SOUTHEASTERN BORDER OF THE CWA INITIALLY.
THE NEXT TRICKY PORTION OF THE FORECAST WILL BE THE PRECIP TYPE.
BUFKIT DATA SUGGESTS TEMPERATURES WILL BE TOO WARM INITIALLY FOR
SNOW ACROSS THE SOUTHEASTERN FORECAST AREA. THIS IS REASONABLE AND
WILL KEEP MENTION OF SNOW OUT OF THE CWA UNTIL 06Z THURSDAY IN THIS
LOCATION. COOLER AIR IS EXPECTED TO FILTER ACROSS THE NORTHWESTERN
AREAS SOONER. WILL KEEP MENTION OF SNOW IN THE FORECAST AFTER 00Z
THURSDAY IN THIS AREA. LAKE EFFECT WILL BE LIKELY AS THE SYSTEM
MOVES EAST ON THURSDAY. LIGHT ACCUMULATIONS CAN BE EXPECTED.
&&
.LONG TERM...(330 PM EST TUE DEC 1 2009)
(THURSDAY NIGHT THROUGH TUESDAY)
OUR PRIMARY FCST CHALLENGE IN THE LONG TERM DEALS WITH POTENTIAL FOR
ACCUMULATING LAKE EFFECT SNOW THURSDAY NIGHT THROUGH FRIDAY INTO
SATURDAY.
CYCLONIC FLOW AND WNW TO WSW FLOW COLD AIR ADVECTION IS ANTICIPATED
THURSDAY NIGHT THROUGH FRIDAY NIGHT. A CONSENSUS OF 12Z MEDIUM RANGE
GUIDANCE 850 MB TEMP PROGS SUGGESTS THAT H8 TEMPS WILL FALL TO -11
TO -12 C BY THURSDAY EVENING AND TO -12 TO -14 C BY FRIDAY EVENING.
THIS WILL RESULT IN VERY FAVORABLE DELTA T/S IN THE UPPER TEENS
CONDUCIVE TO POTENTIAL FOR SIGNIFICANT LAKE EFFECT SNOW. UPSTREAM RH
LOOKS IMPRESSIVE TOO AND 12Z GFS GUIDANCE SHOWS ABUNDANT MOISTURE
THROUGH THE DGZ AS WELL AS ROBUST LIFT THROUGH THE DGZ IN GRR LATE
THURSDAY EVENING.
AS LOW LEVEL FLOW BACKS TO THE WSW TO SW LATE FRIDAY NIGHT INTO
SATURDAY WE WILL NEED TO MONITOR POTENTIAL FOR MORE LAKE EFFECT SNOW
PARTICULARLY FROM MKG NORTH. I HAVE TRENDED TEMPS DOWN BY
APPROXIMATELY TWO TO FOUR DEGREES FOR EARLY NEXT WEEK BASED ON MEX
NUMERICAL GUIDANCE TRENDS.
&&
.AVIATION...(640 PM EST TUE DEC 1 2009)
THE SHORT STORY IS VFR VSBY AND CIGS THROUGH WEDNESDAY AFTERNOON.
A NORTHERN STREAM WAVE WILL CONTINUE TO TRACK EAST ALONG THE
CANADIAN BOARDER TONIGHT. THAT PUTS SOUTHWEST LOWER MICHIGAN IN THE
SOUTHWEST QUAD OF THAT SYSTEM THROUGH THE NIGHT. WITH THE WARM FRONT
NORTH OF THE CWA...AND BEING IN THE SOUTHWEST QUAD OF THE SYSTEM...
I EXPECT ONLY CIRRUS CLOUDS TONIGHT WITH A STEADY SOUTH WIND
AROUND 10 KNOTS.
EVEN WEDNESDAY DURING THE DAY LIGHT HOURS... WITH THE SOUTHERN
STREAM SYSTEM HEADING NORTH...THE MOISTURE FROM THAT SYSTEM WILL NOT
GET FAR ENOUGH NORTH FAST ENOUGH TO BRING LOWER CIGS/VSBY INTO TAF
SITES UNTIL WELL AFTER 00Z.
&&
.MARINE...(330 PM EST TUE DEC 1 2009)
SOUTHWEST WINDS WILL INCREASE TO 20 TO 30 KNOTS OVERNIGHT. THIS
WILL ALLOW WAVES TO INCREASE TO UP TO 6 FEET. WINDS WILL BECOME
WESTERLY WEDNESDAY WITH 3 TO 5 FOOT WAVES POSSIBLE. THIS WILL LEAD
TO HAZARDOUS CONDITIONS FOR SMALL CRAFT. DURING THE AFTERNOON
HOURS...THE WIND DIRECTION WILL BECOME NORTHERLY AND WAVES WILL
SUBSIDE.
&&
.HYDROLOGY...(330 PM EST TUE DEC 1 2009)
NO HYDRO ISSUES.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...SMALL CRAFT ADVISORY THROUGH WEDNESDAY MORNING FROM ST JOSEPH
TO MANISTEE.
&&
$$
SYNOPSIS: JB
SHORT TERM: JB
LONG TERM: LAURENS
AVIATION: WDM
MARINE: JB
HYDROLOGY: JB
