FXUS63 KGRR 020906
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
406 AM EST WED DEC 2 2009

LATEST UPDATE...ALL BUT AVIATION...

.SYNOPSIS...(406 AM EST WED DEC 2 2009)
LOW PRESSURE OVER LOUISIANA IS BEGINNING TO MOVE NORTHEAST TOWARD 
THE GREAT LAKES. CLOUDS WILL INCREASE TODAY AHEAD OF THE LOW AND 
LIGHT RAIN WILL MOVE INTO SOUTHERN LOWER MICHIGAN BY LATE AFTERNOON. 
AS COLDER AIR GETS WRAPPED IN ON THE BACK SIDE OF THE LOW TONIGHT 
THE RAIN WILL TURN TO SNOW. LIGHT ACCUMULATIONS ARE POSSIBLE. LAKE 
EFFECT SNOW SHOWERS WILL THEN DEVELOP THURSDAY AND CONTINUE INTO THE 
WEEKEND. ACCUMULATIONS ARE POSSIBLE FROM THURSDAY THROUGH SATURDAY. 
 

&&

.SHORT TERM...(406 AM EST WED DEC 2 2009)
(TODAY THROUGH FRIDAY)

FORECAST CONCERNS DEAL WITH PCPN TRENDS THROUGH THE PERIOD. MOST OF 
TODAY LOOKS DRY...WHICH MAY BE THE LAST DRY DAY FOR A WHILE. THE LOW 
IN LOUISIANA WILL MOVE TO KENTUCKY BY 00Z. RAIN WILL HAVE ALREADY 
MOVED INTO THE SRN CWA BY THEN. THIS SYSTEM IS VERY DYNAMIC. 30KT 
WINDS ACROSS THE 295K ISENTROPIC PRESSURE SFC WILL QUICKLY SATURATE 
THE COLUMN AS THE SYSTEM MOVES NORTH. WE ONCE AGAIN ARE FOLLOWING 
SREF POPS FOR GUIDANCE WHICH BRINGS CATEGORICAL POPS INTO MOST OF 
THE CWA BY EVENING. COLD AIR WILL BE TRYING TO MOVE SOUTHEAST 
TONIGHT. A COLD FRONT CURRENTLY STRETCHING FROM EASTERN WISCONSIN TO 
WRN ILLINOIS WILL GET CAUGHT UP IN THE CIRCULATION AROUND THE LOW. 
LOOK FOR THE RAIN TO CHANGE OVER TO SNOW BY LATE EVENING FROM 
NORTHWEST TO SOUTHEAST. MOST OF THE PCPN WILL FALL AS RAIN...BUT 
THERE WILL BE A FEW HRS OVERNIGHT WHERE WE SEE STEADY SNOWFALL AS 
THE RAIN CHANGES OVER. I THINK SNOWFALL ACCUMS WILL BE LIGHT...AN 
INCH OR TWO...THOUGH AS BOUNDARY LAYER TEMPS ARE ONLY MARGINAL FOR 
SNOW FROM SAGINAW BAY TO ST JOE BY 06Z. THE SYNOPTIC SYSTEM LOOKS 
MORE OF A RAIN EVENING FOR THE SRN 2/3 OF THE CWA AS A TROWAL MOVES 
ACROSS THE SE CWA. 

LATE TONIGHT THROUGH MID MORNING THURSDAY WILL BE A TRANSITION 
PERIOD FROM SYNOPTIC SNOW TO LAKE EFFECT SNOW. BOUNDARY LAYER WINDS 
WILL BACK TO THE NORTHWEST AND THEN WEST BY MID DAY AND H8 TEMPS 
WILL DROP TO -10C BY 00Z FRIDAY. I INCREASED POPS TO CATEGORICAL 
ACROSS THE WRN CWA THURSDAY NIGHT AND FRIDAY AS MOISTURE REMAINS 
FAIRLY DEEP AND TEMPS COLD. IN ADDITION...THE DGZ REMAINS SATURATED 
FROM THU NIGHT THROUGH FRIDAY. 

BOTH THE GFS AND NAM HINT AT THE POSSIBILITY OF AN ENHANCED PERIOD 
OF SNOW LATE THURSDAY NIGHT/FRIDAY MORNING...AND AGAIN LATE FRIDAY. 
THIS IS WHEN SHORT WAVES ROTATING AROUND THE UPPER TROUGH MOVING 
INTO THE AREA WILL RESULT IN OMEGA INTERSECTING THE DGZ. FAVORED 
AREAS WILL BE THE I-96 CORRIDOR DUE TO WRLY BOUNDARY WINDS. A FEW 
INCHES OF SNOW ARE POSSIBLE LATE THURSDAY NIGHT TO LATE FRIDAY. 

&&

.LONG TERM...(406 AM EST WED DEC 2 2009)
(FRIDAY NIGHT THROUGH TUESDAY)

OUR PRIMARY FCST CHALLENGE IN THE LONG TERM DEALS WITH POTENTIAL FOR 
ACCUMULATING LAKE EFFECT SNOW FRIDAY NIGHT THROUGH SATURDAY.

CONTINUED COLD AIR ADVECTION FRIDAY NIGHT ALONG WITH A FAVORABLE 
MOISTURE PROFILE SUPPORTS ACCUMULATING LAKE EFFECT SNOWS.  THE BEST 
LOW LEVEL CONVERGENCE IS ROUGHLY ALONG AND WEST OF HIGHWAY 131.  IF 
THE NAM ENDS UP RIGHT WE WILL LIKELY NEED HEADLINES AS IT FEATURES 
STRONGER UPWARD MOTION IN THE DGZ.

FOR SAT...THE FLOW BACKS FROM WSW TO SSW.  THE LOW LEVEL CONVERGENCE 
AXIS SHIFTS UP TO NEAR LDM.  AT 12Z THE COLDEST AIR AT 850 MB IS 
STILL ADVECTING IN FROM THE SW.  SO IT APPEARS TO ME THAT 
ACCUMULATIONS ARE LIKELY FOR MY NW COUNTIES.  I ADDED LIKELY POPS TO 
THE FORECAST FOR SAT MAINLY FOR THE LAKESHORE COUNTIES NORTH OF 
LWA.  I DO FEEL THAT WE WILL NEED TO MONITOR THE FORECAST CLOSELY 
FOR SAT AS INCREASING FETCH AND POTENTIAL MOISTURE ADVECTION AT 700 
MB...COULD ENHANCE THE SNOW RATES.

THE MOISTURE DEPTH FALLS SAT NIGHT INTO SUNDAY...THUS I WILL GO NO 
HIGHER THAN CHANCE POPS. 

&&

.AVIATION...(1145 PM EST TUE DEC 1 2009)
IT SEEMS THE LATEST RUN OF THE GFS CONTINUES TO BRING THE STORM ON A 
MORE WESTERLY TRACK...WHICH IS CLOSER TO THE TRACK FORECAST BY THE 
NAM FOR SEVERAL RUNS NOW. SO I NOW FELL THERE WILL BE RAIN BY 8 PM 
ACROSS THE CWA WEDNESDAY AND CIGS/VSBY WILL GO MVFR BY 02Z AND IFR 
WITH MODERATE RAIN BY 04Z. THE CHANGE TO SNOW WILL BE FROM NW TO SE 
IN 05Z TIME FRAME AT MKG...AFTER 06Z FOR THE OTHER TAF SITES. 

OTHERWISE IN THE SHORT TERM NOT MUCH TO WRITE ABOUT...MKG WILL HAVE 
THE STRONGEST WINDS BEING CLOSEST TO THE LAKE SHORE...AND WARMER AIR 
TO MIX DOWN THE 35 KNOT WINDS NEAR 1000 FT OVERNIGHT. 

&&

.MARINE...(406 AM EST WED DEC 2 2009)
THE SCA WILL CONTINUE THIS MORNING. WAVE WILL LIKELY DECREASE TO 
LESS THAN 4 FEET BY THE AFTERNOON. WE/LL PROBABLY NEED ANOTHER SCA 
TONIGHT AS COLD AIR ADVECTION INCREASES WAVE ACTIVITY OVERNIGHT. 

&&

.HYDROLOGY...(406 AM EST WED DEC 2 2009)
NO HYDRO ISSUES EXPECTED. A QUARTER TO HALF INCH OF RAIN/SNOW EQUIV 
IS EXPECTED DURING THE NEXT 36 HRS. THAT AMOUNT OF LIQUID LIKELY 
WON/T BE ENOUGH TO CAUSE ANY HYDRO CONCERNS.  

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...SMALL CRAFT ADVISORY THIS MORNING FROM ST JOSEPH TO MANISTEE.
&&

$$

SYNOPSIS:     93
SHORT TERM:   93
LONG TERM:    MJS
AVIATION:     WDM
MARINE:       93
HYDROLOGY:    93