FXUS63 KGRR 011135 RRA
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
630 AM EST TUE DEC 1 2009

LATEST UPDATE...AVIATION...

.SYNOPSIS...(400 AM EST TUE DEC 1 2009)
LOW PRESSURE DEVELOPING OVER THE NORTHWEST GULF OF MEXICO WILL MOVE 
NORTHEAST TOWARD THE GREAT LAKES TODAY AND WEDNESDAY. RAIN WILL MOVE 
INTO THE REGION LATE WEDNESDAY. AS THE LOW MOVES ACROSS OHIO COLDER 
AIR WILL FLOW INTO LOWER MICHIGAN WEDNESDAY CAUSING THE RAIN TO MIX 
WITH AND CHANGE TO SNOW. LIGHT ACCUMULATIONS ARE POSSIBLE MAINLY 
SOUTH OF A BATTLE CREEK TO MOUNT PLEASANT LINE. LAKE EFFECT SNOW 
SHOWERS WILL CONTINUE FROM THURSDAY THROUGH THE END OF THE WEEK. 

&&

.SHORT TERM...(400 AM EST TUE DEC 1 2009)
(TODAY THROUGH THURSDAY)
FORECAST CONCERNS DEAL WITH PCPN TRENDS LATE WEDNESDAY INTO THURSDAY 
AS THE LOW IN THE NW GULF MOVES NORTHEAST.

PCPN IS JUST NOW DEVELOPING ACROSS THE SOUTH TEXAS COAST. MID AND 
HIGH CLOUDS ARE SPREADING NORTH INTO ARKANSAS AND THESE WILL ARRIVE 
THIS EVENING. A WELL DEFINED UPPER LOW OVER NRN MEXICO IS BEING 
KICKED OUT BY A STRONG SHORT WAVE MOVING SOUTHEAST ACROSS THE SRN 
CANADIAN ROCKIES. THE SHORT RANGE MODELS ARE IN PRETTY GOOD 
AGREEMENT IN BRINGING THE SFC LOW THROUGH KENTUCKY AND 
CENTRAL/EASTERN OHIO. THAT TRACK PLACES THE BULK OF THE PCPN FROM 
THE EASTERN CWA EWD. HAVE PRETTY MUCH FOLLOWED SREF POPS AND BROUGHT 
PCPN INTO THE SRN CWA WED AFTERNOON AND ACROSS THE REST OF THE CWA 
BY WED EVE. THE PCPN WILL BEGIN AS RAIN AND THEN CHANGE OVER THE 
SNOW FROM NW TO SE AS THE COLDER AIR GETS WRAPPED IN BEHIND THE 
SYSTEM. THE NRN STREAM WAVE HAS IT/S OWN SFC LOW TOO THAT WILL BE 
MOVING ACROSS THE UP/NRN LWR. THIS LOW WILL HELP TO DRIVE THE COLDER 
AIR SOUTH A LITTLE QUICKER THAN IF THE ONLY LOW IN PLAY WAS THE ONE 
MOVING NORTH FROM THE GULF. 

THERE IS THE POSSIBILITY OF LIGHT ACCUMULATIONS ACROSS THE SOUTHEAST 
CWA WEDNESDAY NIGHT. SINCE WE ONLY EXPECT LOWS BY THURSDAY MORNING 
TO BE IN THE LOWER 30S...MUCH OF THE SNOW WILL LIKELY MELT. FARTHER 
NORTHWEST...THE SNOW WILL FALL FOR A LONGER PERIOD OF TIME...BUT QPF 
IS LIGHTER. 

LAKE EFFECT SNOW SHOWERS WILL DEVELOP IN THE COLD AIR PATTERN BY 
THURSDAY MORNING. AS BOUNDARY LAYER WINDS BACK TO THE WEST...MUCH OF 
THE CWA SHOULD SEE SOME LIGHT SNOW THURSDAY. SFC TEMPS IN THE 30S 
WILL LIMIT ACCUMS A BIT. 

&&

.LONG TERM...(400 AM EST TUE DEC 1 2009)
(THURSDAY NIGHT THROUGH MONDAY)

THE MAIN FCST CHALLENGE IN THE LONG TERM DEALS WITH POTENTIAL FOR 
ACCUMULATING LAKE EFFECT SNOW FOR THE END OF THE WEEK.

CYCLONIC LOW LEVEL COLD AIR ADVECTION WILL BE UNDERWAY FOR THURSDAY 
NIGHT AND IT PERSISTS INTO FRIDAY NIGHT.  THE FLOW BACKS FROM NW TO 
WSW DURING THIS TIME.  850 MB TEMPS FALL TO AROUND -14 DEG 
C...GENERATING SOME FAVORABLE DELTA T VALUES. A 700 MB TROUGH IS 
SHOWN BY THE MODELS TO ARRIVE ROUGHLY 12Z FRI...WHICH SHOULD HELP 
ENHANCE THE SNOWFALL.   GIVEN THE CONTINUED FAVORABLE ENVIRONMENT 
FOR LAKE EFFECT SNOW INTO FRIDAY NIGHT...I INCREASED POPS TO 
LIKELY.  

WITH THE LOW LEVEL FLOW TURNING MORE SOUTHWEST ON SATURDAY...WILL 
NEED TO MONITOR POSSIBILITY OF CONTINUED ACCUMULATING SNOW MUSKEGON 
COUNTY NORTH.  MODELS VARY WITH THE LOW LEVEL TEMPERATURES TRENDS 
THEN...SO SOME UNCERTAINTY EXISTS WITH THE EXTENT OF ANY SNOWFALL.

THUS SEVERAL PERIODS OF ACCUMULATING LAKE EFFECT SNOW ARE PREDICTED 
FOR THE END OF THE WEEK...ESPECIALLY ALONG AND WEST OF HIGHWAY 131. 

&&

.AVIATION...(630 AM EST TUE DEC 1 2009)
THE MAIN CHALLENGE WITH THE AVIATION FORECAST DEALS WITH THE 
POTENTIAL FOR LOWER CLOUDS THIS MORNING.  SATELLITE AND SURFACE 
OBSERVATION DATA SHOWS LOWER CLOUDS DEVELOPING FROM NEAR KMKG TO 
JUST SOUTH OF KLAN.  FORECAST DATA SUGGESTS THESE CLOUDS EXPANDING 
IN THE NEXT HOUR OR TWO.  THUS TAFS WILL FEATURE AT LEAST A COUPLE 
HOUR PERIOD OF MVFR CLOUDS MAINLY FOR THIS MORNING.  THE AFTERNOON 
IS EXPECTED TO FEATURE VFR CONDITIONS AS MIXING BREAKS UP THE LOWER 
CLOUDS.

LOW LEVEL MOISTURE DOES TRY TO INCREASE UPON SUNSET. THIS RAISES THE 
RISK FOR FOG OR LOW STRATUS CLOUDS TONIGHT.  HOWEVER WINDS REMAIN UP 
THROUGH THE NIGHT AND THE MOISTURE IS LIMITED AT THIS POINT. WILL 
KEEP THE FORECAST VFR FOR TONIGHT AS WELL.

&&

.MARINE...(400 AM EST TUE DEC 1 2009)
WINDS HAVE DECREASED BELOW GALE FORCE AND WILL REMAIN BELOW GALE 
FORCE TODAY. ISSUED A SMALL CRAFT ADVISORY MAINLY FOR WAVES AS THEY 
WILL REMAIN AOA 3 FEET THROUGH WEDNESDAY MORNING. 

&&

.HYDROLOGY...(400 AM 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:     93
SHORT TERM:   93
LONG TERM:    MJS
AVIATION:     MJS
MARINE:       93
HYDROLOGY:    93