FXUS63 KGRR 241738
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1235 PM EST THU DEC 24 2009

LATEST UPDATE...AVIATION...

.SYNOPSIS...(750 AM EST THU DEC 24 2009)
A DEEP LOW OVER THE PLAINS WILL DRAW ABUNDANT MOISTURE NORTH FROM 
THE GULF OF MEXICO. FREEZING RAIN AND SLEET WILL MOVE INTO LOWER 
MICHIGAN TODAY AND TONIGHT...RESULTING IN SOME ICY ROADS. THESE ICY 
CONDITIONS WILL CONTINUE INTO FRIDAY MORNING BEFORE WARMER AIR WILL 
ARRIVE AND TURN THE PRECIPITATION OVER TO RAIN. HOWEVER NORTH OF 
M-46...THE FREEZING RAIN MAY LINGER INTO THE AFTERNOON. COLDER AIR 
WILL THEN WRAP INTO LOWER MICHIGAN FROM THE SOUTH CHRISTMAS 
AFTERNOON. LIGHT RAIN WILL TURN TO SCATTERED SNOW SHOWERS. THE 
COLDER AIR WILL LINGER THROUGH THE WEEKEND ALONG WITH SNOW SHOWERS. 

&&

.SHORT TERM...(1215 PM EST THU DEC 24 2009)
(THIS AFTERNOON)
COMPLEX FORECAST SCENARIO UNFOLDING WITH ANOTHER LIGHT BURST OF WARM 
AIR ADVECTION PRECIPITATION LIFTING NORTH INTO THE FORECAST AREA AT 
THIS TIME. VERY DRY AIR CONTINUES TO TRY AND HOLD ON WITH CEILINGS 
THAT ARE VFR ACROSS SOUTHWEST LOWER MICHIGAN. IN THE BAND LIFTING 
INTO THE AREA NOW...CEILINGS DO FALL INTO THE 4000-6000FT RANGE. 
QUESTION IS WHICH WILL CARRY THE DAY...THE DRY AIR OR THE WARM AIR 
ADVECTION RELATED PRECIPITATION. CONFIDENCE IS NOT HIGH IN HOW 
THINGS WILL PLAY OUT THIS AFTERNOON BETWEEN A LIGHT TRACE EVENT 
VERSUS A FEW HUNDRETHS OF PRECIPITATION.

CONSIDERED PULLING THE CURRENT ADVISORY THAT GOES INTO EFFECT AT 700 
PM THIS EVENING BACK TO THE CURRENT TIME IN THE LAST COUPLE OF 
HOURS. CONSENSUS IS THAT THE DRY AIR SHOULD HAVE A SIGNIFICANT 
AFFECT ON THE PRECIPITATION TRYING TO ERODE IT WITH TIME. SO FAR 
VSBY/S IN THE BAND HAVE BEEN BETWEEN 7 AND 10 MILES. SO IT IS QUITE 
LIGHT. WE WILL CONTINUE TO PERUSE THE LATEST SATELLITE AND RADAR 
TRENDS...OBSERVATIONS AND THE SHORT RANGE MODELS LIKE THE RUC TO SEE 
IF CHANGES NEED TO BE MADE. 

&&

.LONG TERM...(310 AM EST THU DEC 24 2009)
(SATURDAY NIGHT THROUGH WEDNESDAY)
OCCLUDED LOW MOVING THROUGH OVER THE WEEKEND WILL BRING SNOW SHOWERS 
AND POSSIBLY SOME ACCUMULATIONS IN THE 2 TO 4 INCH RANGE WITH LAKE 
ENHANCEMENT. WILL HAVE 50 POPS FOR SATURDAY NIGHT AND SUNDAY BUT 
WILL PROBABLY NEED LIKELY ONCE THE TIMING IS PINNED DOWN A LITTLE 
BETTER. LAKE EFFECT SNOW SHOWERS ON THE BACK SIDE OF THE UPPER LOW 
PASSAGE BUT THESE WILL BE WINDING DOWN BY TUESDAY AS SFC RIDGING 
BUILDS IN.

$$

.AVIATION...(1235 PM EST THU DEC 24 2009)
VERY COMPLEX FCST THE NEXT 24 HRS DUE TO A LIGHT WINTRY MIX OF PCPN. 
PREDOMINANTELY VFR CONDITIONS ARE ANTICIPATED THIS AFTERNOON BUT 
THERE WILL BE SOME REDUCTIONS INTO THE MVFR TO IFR FLIGHT CATEGORY 
PARTICULARLY AT LAN AND JXN WHERE A LOW STRATUS DECK REMAINS IN 
PLACE. IN ADDITION... SLEET AND LIGHT FREEZING RAIN MAY IMPACT OUR 
SOUTHERN TAF SITES (AZO... BTL AND JXN) AS WELL AS MKG THIS 
AFTERNOON. HOWEVER LOCAL AND RGNL RADAR TRENDS CORROBORATED WITH SFC 
OBS INDICATE MUCH OF THE ACTIVITY ON RADAR IS EITHER VERY LIGHT OR 
NOT REACHING THE GROUND AT ALL DUE TO BRISK AND DRY EASTERLY WINDS 
AND LOW LEVEL DRY AIR. 

EASTERLY WINDS OF 15 TO 25 KTS WILL CONTINUE THIS AFTERNOON AND 
INCREASE TO 20 TO 30 KTS OVERNIGHT THROUGH 18Z FRIDAY.

LIGHT FREEZING RAIN AND SLEET COULD REDEVELOP OVERNIGHT AND 
GRADUALLY TRANSITION OVER TO PLAIN RAIN SHOWERS FROM SOUTH TO NORTH 
DURING THE EARLY MORNING HOURS FRIDAY. HOWEVER IT IS NOTED THAT 
OVERALL SHORT RANGE COMPUTER MODEL GUIDANCE TRENDS SUGGEST THAT DRY 
CONDITIONS SHOULD PREVAIL MOST OF THE NIGHT AND THAT ANY FROZEN PCPN 
WOULD BE RATHER LIGHT BEFORE THE TRANSITION TO PLAIN RAIN. LIGHT 
PLAIN RAIN SHOWERS AND SPRINKLES ARE ANTICIPATED FROM MID MORNING 
FRIDAY THROUGH EARLY FRIDAY AFTERNOON WITH CONDITIONS IN THE IFR TO 
LIFR FLIGHT CATEGORY. 

&&

.MARINE...(310 AM EST THU DEC 24 2009)
GALE WARNING REMAINS FOR ENE WINDS GUSTING TO 40 KNOTS THROUGH 
CHRISTMAS DAY. 
&&

.HYDROLOGY...(310 AM EST THU DEC 24 2009)
QPF POTENTIAL THURSDAY NIGHT AND FRIDAY WILL NOT BE HIGH ENOUGH TO 
CAUSE HYDRO ISSUES.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY TONIGHT AND FRIDAY ENTIRE CWA. 

LM...GALE WARNING FROM MIDDAY TODAY THROUGH FRIDAY AFTERNOON FOR 
     THE ENTIRE NEAR SHORE.

&&

$$

SYNOPSIS:     93/OSTUNO
SHORT TERM:   DUKE
LONG TERM:    OSTUNO
AVIATION:     LAURENS
MARINE:       93
HYDROLOGY:    93