FXUS63 KGRR 022130
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
430 PM EST WED DEC 2 2009

LATEST UPDATE...LONG TERM...

.SYNOPSIS...(348 PM EST WED DEC 2 2009)
LOW PRESSURE ENTERING KENTUCKY THIS EVENING WILL RACE NORTHEAST 
TONIGHT AND BE CENTERED NEAR LAKE ONTARIO BY THURSDAY MORNING. THE 
LOW PRESSURE SYSTEM WILL SPREAD RAIN INTO SOUTHERN LOWER MICHIGAN 
THIS EVENING PUSHING NORTHWARD OVERNIGHT. COLDER AIR WILL GRADUALLY 
FILTER INTO SOUTHWEST LOWER MICHIGAN AFTER MIDNIGHT AS NORTHERLY 
WINDS INCREASE. RAIN WILL TRY TO MIX WITH AND CHANGE OVER TO SNOW 
LATE. ANY ACCUMULATION SHOULD BE AN INCH OR LESS.

COLDER AIR WILL INVADE THE STATE ON THURSDAY...PERSISTING INTO THE 
WEEKEND. LAKE EFFECT SNOW WILL OCCUR MUCH OF THIS TIME. ACCUMULATING 
SNOW WILL BE POSSIBLE THURSDAY NIGHT AS A LAKE EFFECT BAND SETS UP. 
LOCATIONS ALONG AND WEST OF U.S. HIGHWAY 131 WILL SEE SOME 
ACCUMULATION OF SNOW BY THE WEEKEND.

&&

.SHORT TERM...(348 PM EST WED DEC 2 2009)
(TONIGHT THROUGH FRIDAY NIGHT)
MAIN CONCERNS OBVIOUSLY PERTAIN TO SNOW...SPECIFICALLY WHEN DOES IT 
CHANGE OVER FROM RAIN TONIGHT AND HOW MUCH FALLS EACH FORECAST 
PERIOD AFTER TONIGHT. 

TRACK OF THE LOW IS SIMILAR IN THE MODELS...WELL EAST OF THE 
FORECAST AREA. ALL OF THE SHORT TERM MODELS HAVE A LOW CENTERED NEAR 
LAKE ONTARIO AT 700AM THURSDAY MORNING. RAIN WILL SPREAD INTO THE 
SOUTHERN HALF OF THE FORECAST AREA THIS EVENING AS THE LOW MOVES 
INTO KENTUCKY. THE BOUNDARY LAYER AT THIS POINT IS WARM...WITH TEMPS 
IN THE MIDDLE TO UPPER 40S. DEW POINTS ARE IN THE LOWER TO MIDDLE 
30S...SO WE WILL WET BULB DOWN AS THE PRECIP STARTS...BUT IT MAY 
TAKE A GOOD PORTION OF THE NIGHT BEFORE WE CAN MIX/CHANGE TO SNOW. 
THINK THE WARMER NAM IS THE BETTER OPTION TONIGHT...SO NOT THINKING 
MUCH IN THE WAY OF ACCUMULATIONS. HALF INCH OR LESS IN MOST 
LOCATIONS ON GRASSY AREAS.

THE COLD AIR MAKES ITS MOVE IN EARNEST ON THURSDAY AS 850MB TEMPS 
DROP TO AROUND -9C BY EVENING. THIS WILL PUSH DELTA T/S INTO THE 
UPPER TEENS C WITH A LAKE AROUND +8C. DEEP MOISTURE IS LACKING ON 
THURSDAY THOUGH AS LOWER MICHIGAN WILL BE IN BETWEEN THE UPPER WAVE 
THAT WILL PUSH EAST OF THE AREA AND THE UPPER TROUGH TO THE WEST. 
ANY ACCUMULATIONS ON THURSDAY SHOULD BE ON THE LIGHT SIDE...AN INCH 
OR LESS.

FIRST TIME FRAME OF CONCERN IS THURSDAY NIGHT. BOTH THE GFS AND THE 
NAM ARE INDICATING A CONVERGENT DOMINANT LAKE BAND SETTING UP IN 
VICINITY OF INTERSTATE 96. IT APPEARS SOMEWHAT TRANSIENT THOUGH...AS 
RIDGING TRIES TO BUILD NORTH OUT OF THE PLAINS. THE AREA FROM SOUTH 
HAVEN TO GRAND RAPIDS TO MUSKEGON WILL BE THE MAIN SNOWBAND 
LOCATION...FUNNELING TOWARD LANSING. AT THIS POINT THINKING 2-4 
INCHES WILL BE POSSIBLE IN THE ABOVE MENTIONED AREA...WITH LOWER 
AMOUNTS AWAY FROM THIS ZONE. WE WILL BE WATCHING THIS TIME FRAME 
CLOSELY...AS WE MAY NEED AN ADVISORY WITH TIME. WE STILL HAVE SOME 
TIME TO WATCH THIS THOUGH. 

LAKE EFFECT SNOW WILL CONTINUE FRIDAY AND FRIDAY NIGHT AS THE FLOW 
GRADUALLY SWINGS TOWARD THE SOUTHWEST. LOCATIONS FROM SOUTH HAVEN TO 
GRAND RAPIDS AND NORTH UP THE LAKESHORE WILL BE THE AREAS THAT ARE 
FAVORED. MOISTURE LOOKS TO BE A BIT ON THE SHALLOW SIDE...BUT MORE 
THAN SUFFICIENT FOR SNOW...UP THROUGH ABOUT 5000FT. WILL HAVE 
CATEGORICAL/LIKELY POPS DURING THIS TIME FRAME TOWARD THE COAST WITH 
LIGHT ACCUMS. IT APPEARS 1-3 INCHES WILL BE POSSIBLE NORTH AND WEST 
OF GRAND RAPIDS ON FRIDAY FROM FREMONT TOWARD SCOTTVILLE AND BALDWIN.

&&

.LONG TERM...(430 PM EST WED DEC 2 2009)
(SATURDAY THROUGH WEDNESDAY)
THE PRIMARY FORECAST CHALLENGE IS DEALING WITH THE TIMING... 
LOCATION AND OCCURRENCE OF SNOW FALL. THE MID RANGE MODELS HAVE 
LARGE DIFFERENCES AND CONFIDENCE IS LOW. WENT CLOSER TO THE ECMWF 
12Z SOLUTION... THOUGH THE GRIDS RESEMBLE NO MODEL SOLUTION.

WINDS WILL BE OUT OF THE SOUTHWEST WITH CYCLONIC FLOW SATURDAY INTO 
SATURDAY NIGHT... AS A LOW PRESSURE SYSTEM MOVES AWAY FROM THE AREA. 
LAKE EFFECTS WILL BE WINDING DOWN... WITH THE FOCUS MAINLY ON WEST 
CENTRAL LOWER MICHIGAN. ACCUMULATIONS WILL BE POSSIBLE NEAR AND 
INLAND FROM BIG AND LITTLE SABLE POINTS. THE NEXT LOW MAY APPROACH 
THE AREA EARLY MONDAY MORNING. HAVE BROAD BRUSHED 30 POPS MONDAY 
THROUGH WEDNESDAY FOR SYSTEM AND LAKE EFFECT SNOWS. WILL VERY LIKELY 
HAVE TIMES WITH NO SNOW... BUT NOT CONFIDENT ENOUGH TO LIMIT 
PRECIPITATION. 

TEMPERATURES WILL BE AROUND TO A LITTLE BELOW AVERAGE FOR THIS TIME 
OF YEAR... WITH HIGHS IN THE LOWER TO MID 30S AND LOWS IN THE 20S.

&&

.AVIATION...(107 PM EST WED DEC 2 2009)
BETTER THAN IFR CONDITIONS ACROSS THE TAF SITES WILL CONTINUE INTO 
THE EVENING. A SYSTEM MOVING NORTHWARD TOWARD THE REGION WILL BRING 
IN HIGH AND MID LEVEL CLOUDS THIS AFTERNOON WITH SOME MVFR CEILINGS 
MOVING IN THIS EVENING. THIS WILL BE FOLLOWED BY RAIN AND FOG... 
WHICH WILL HELP TO REDUCE VISIBILITIES TO BELOW 3 MILES FROM 
APPROXIMATELY 04Z THROUGH 11Z.  

COLDER AIR WILL MOVE INTO THE AREA FROM THE NORTHWEST AND WEST 
TONIGHT WITH LOW LEVEL LAKE EFFECT CLOUDS AND SHOWERS. LOOKING FOR 
CEILINGS TO REMAIN MOSTLY ABOVE IFR LEVELS. DELAYED THE MIX WITH 
SNOW UNTIL LATE TONIGHT... AS THE WARMER PUSH FROM THE SOUTHERN 
SYSTEM SHOULD DOMINATE. KEPT PRECIPITATION GOING THROUGH THE DAY 
TOMORROW... THOUGH IT/S POSSIBLE THAT THERE MAY BE A BREAK LATE IN 
THE MORNING INTO THE AFTERNOON AS THE SOUTHERN SYSTEM PULLS OUT AND 
LAKE EFFECTS INCREASE AND REORIENT.

&&

.MARINE...(348 PM EST WED DEC 2 2009)
SURFACE LOW PRESSURE TRACKING FROM THE OHIO VALLEY INTO THE EASTERN 
GREAT LAKES WILL TIGHTEN A PRESSURE GRADIENT OVER LAKE MICHIGAN. 
WINDS WILL INCREASE TO AROUND 30 KNOTS TONIGHT...BUILDING WAVES INTO 
THE 5 TO 8 FOOT RANGE. WAVES WILL GRADUALLY SUBSIDE INTO THE 3 TO 5 
FOOT RANGE BY THURSDAY AT SUNSET...BUT WINDS WILL INCREASE ONCE 
AGAIN THURSDAY NIGHT. WAVES WILL LIKELY BE A HAZARD TO SMALLER CRAFT 
ALL THE WAY INTO SATURDAY.

&&

.HYDROLOGY...(348 PM EST WED DEC 2 2009)
ALL RIVER SITES ARE REPORTING VALUES WELL WITHIN BANK. PRECIPITATION 
TONIGHT WILL RANGE FROM POSSIBLY A TENTH OF AN INCH IN THE FAR 
NORTHWEST NEAR LUDINGTON TO BETWEEN A QUARTER AND A HALF INCH CLOSER 
TO THE TRACK OF THE LOW AT JACKSON. THESE VALUES WILL NOT AFFECT 
RIVER LEVELS MUCH AT ALL. THURSDAY INTO SATURDAY LAKE EFFECT SNOW 
WILL BE THE DOMINANT MODE AND WILL NOT AFFECT RIVER LEVELS EITHER. 

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...SMALL CRAFT ADVISORY ST. JOSEPH TO MANISTEE THROUGH THURSDAY.

&&

$$

SYNOPSIS:     DUKE
SHORT TERM:   DUKE
LONG TERM:    IOD
AVIATION:     IOD
MARINE:       DUKE
HYDROLOGY:    DUKE