FXUS63 KGRR 250019
AFDGRR

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

LATEST UPDATE...AVIATION...

.SYNOPSIS...(400 PM EST THU DEC 24 2009)
A STRENGTHENING AREA OF LOW PRESSURE WILL LIFT NORTH TONIGHT FROM 
ARKANSAS THROUGH MISSOURI. LOWER MICHIGAN WILL BE ON THE EASTERN 
FRINGES OF THE SYSTEM...WHICH IS THE WARM SIDE. WINTER STORM 
WARNINGS COVER MUCH OF THE PLAINS ON THE WESTERN...COLDER SIDE OF 
THE SYSTEM. COLD AIR NEAR GROUND LEVEL WILL COMBINE WITH A SURGE OF 
WARM AIR ALOFT TO CREATE CONDITIONS CONDUCIVE FOR A MIXTURE OF 
PRECIPITATION INTO CHRISTMAS MORNING. FREEZING RAIN AND FREEZING 
DRIZZLE WILL BE THE DOMINANT PRECIPITATION MODE. A WINTER WEATHER 
ADVISORY FOR SLEET AND FREEZING RAIN IS IN EFFECT FOR ALL OF 
SOUTHWEST LOWER MICHIGAN THROUGH CHRISTMAS DAY. THE MIXTURE OF 
PRECIPITATION WILL TRY TO CHANGE OVER TO ALL RAIN ON CHRISTMAS DAY 
BEFORE TRANSITIONING BACK TO SNOW FRIDAY NIGHT. COLDER AIR FILTERS 
INTO THE AREA FOR THE REMAINDER OF THE WEEKEND AND EARLY NEXT WEEK 
WITH SOME LIGHT ACCUMULATIONS OF SNOW POSSIBLE DURING THAT TIME. 

&&

.SHORT TERM...(400 PM EST THU DEC 24 2009)
(TONIGHT THROUGH FRIDAY NIGHT)
PULLED THE START TIME OF THE WINTER WEATHER ADVISORY FOR SLEET AND 
FREEZING RAIN BACK TO 300 PM GIVEN THE ONGOING LIGHT MIXTURE OF 
PRECIPITATION. ALL PRECIPITATION TYPES HAVE BEEN REPORTED...FROM 
SLEET...FREEZING RAIN AND SNOW. DOMINANT PRECIPITATION MODE WILL BE 
FREEZING RAIN THROUGH THE NIGHT THOUGH.

A LULL IN THE PRECIPITATION MAY OCCUR AFTER DARK...WHICH WILL LIKELY 
LEAD TO FREEZING DRIZZLE. AIR TEMPS ARE NEAR FREEZING...SO ROAD 
EFFORTS WITH SALT WILL BE EFFECTIVE. MAIN CONCERN WILL BE THE SIDE 
ROADS...PARKING LOTS AND SIDEWALKS THAT MAY NOT BE TREATED. 

FEELING IS THAT WE ARE LOOKING FOR A COUPLE BURSTS OF PRECIPITATION. 
FIRST IS THE ONE MOVING THROUGH SOUTHWEST LOWER MICHIGAN IN A ZONE 
OF WARM AIR ADVECTION...SEEN ON THE 290K ISENTROPIC SURFACE. THIS 
PRECIPITATION MAY LIFT NORTH OF THE AREA THIS EVENING LEAVING 
SOMEWHAT OF A LULL THROUGH THE OVERNIGHT WITH PERIODS OF LIGHT 
FREEZING RAIN AND DRIZZLE OCCURRING IN ITS WAKE.

MAIN BATCH OF PRECIPITATION ASSOCIATED WITH THE OCCLUDED FRONT WILL 
SPREAD IN LATE TONIGHT AND CHRISTMAS MORNING. TEMPERATURES WILL 
STILL BE FLIRTING WITH FREEZING WHICH MAKES THE RAIN/FREEZING RAIN 
CALL A HARD ONE. WARM AIR ADVECTION BURST ALOFT IS SIGNIFICANT 
THOUGH...SO SEE THE PRECIPITATION TRYING TO GO OVER TO ALL RAIN ON 
CHRISTMAS. CONCERN ARE THE SNOW AND ICE PACKED SIDE ROADS THOUGH. AS 
RAIN FALLS ONTO THESE COLDER SURFACE REFREEZING MAY STILL TAKE PLACE.

MAIN BAND OF PRECIPITATION WILL BE LIFTING NORTH OF THE AREA AS WE 
HEAD INTO FRIDAY NIGHT. NOT EXPECTING SIGNIFICANT PRECIPITATION 
FRIDAY NIGHT AS THE RAIN TRANSITIONS BACK TO SNOW. TRAVEL INTO 
SATURDAY MORNING COULD BE HAMPERED A BIT BY TEMPS FALLING BACK BELOW 
FREEZING. MOST ROADS WILL BE WET FRIDAY EVENING...BUT WITH TEMPS 
FALLING INTO THE 20S ICY CONDITIONS WILL LIKELY REDEVELOP INTO 
SATURDAY MORNING.

&&

.LONG TERM...(400 PM EST THU DEC 24 2009)
(SATURDAY THROUGH THURSDAY)

THE OCCLUDED LOW PRESSURE SYSTEM WILL BRING SOME LIGHT SNOW THIS 
WEEKEND. HOWEVER WE ARE NOT EXPECTING LAKE EFFECT SNOW SATURDAY OR 
SATURDAY NIGHT SINCE LOW LEVEL WIND FIELDS WILL BE SOUTH 
SOUTHEASTERLY. 

OUR BETTER CHC FOR LIGHT SNOW SHOULD HOLD OFF UNTIL SUNDAY WHEN 
WINDS WILL FINALLY VEER TO THE WEST TO NORTHWEST. WILL MAINTAIN HIGH 
CHC POPS SUNDAY FOR MOST OF OUR CWFA AND LIKELY POPS FOR AREAS WEST 
OF US-131. SNOW WILL LINGER SUNDAY NIGHT AND MONDAY BEFORE DRY WX 
RETURNS TUESDAY AND WEDNESDAY AS ANTICYCLONIC FLOW BUILDS IN. 

$$

.AVIATION...(718 PM EST THU DEC 24 2009)
CEILINGS HAVE BEEN QUITE VARIABLE THIS AFTERNOON AND EVENING... 
RANGING ANYWHERE FROM 800 FT TO 9000 FT. LOW LEVEL RH PROGS ARE 
SUGGESTING THAT MUCH OF THE EXISTING IFR CIGS WILL LIFT/IMPROVE AS 
THE BACK EDGE OF THE CURRENT AREA OF PCPN LIFTS NORTH THROUGH THE 
AREA. AM NOT TOTALLY CONVINCED THAT IT WILL PLAY OUT THAT WAY OR IT 
MAY JUST BE DELAYED SINCE THERE IS CURRENTLY IFR CIGS OVER SE LWR MI 
AND THE LOW LEVEL ESE WIND MAY SEND SOME THESE CIGS THIS WAY FOR A 
TIME THIS EVENING.

PCPN TYPE IS EXPECTED TO REMAIN FZRA MOST OF THE NIGHT... WITH A 
CHANGEOVER TO ALL RAIN EXPECTED AROUND 12Z. THAT IS ABOUT THE TIME 
THE MODELS SHOW THE BEST SHOT OF PCPN ARRIVING FROM THE 
SOUTH/SOUTHWEST... WITH 0.25 TO 0.50 INCHES OF RAIN POSSIBLE 
12Z-18Z. WILL FCST PREDOMINATELY IFR FOR FRIDAY DUE TO THE EXPECTED 
HEAVIER NATURE OF THE PCPN ASSOCIATED WITH THE APPROACHING SFC 
OCCLUSION. 

&&

.MARINE...(400 PM EST THU DEC 24 2009)
CONTINUED THE GALE WARNING WHICH IS IN EFFECT THROUGH CHRISTMAS DAY. 
GALE CONDITIONS SHOULD DEVELOP IN THE NEARSHORE WATERS OVERNIGHT. 
PERIOD OF HIGHEST WINDS SHOULD BE FROM ABOUT MIDNIGHT THROUGH MIDDAY 
ON CHRISTMAS. GIVEN THE OFFSHORE FLOW...HIGHEST WAVES WILL BE AT THE 
5 MILE MARK. WINDS SHOULD FALL BELOW GALE LEVELS CHRISTMAS AFTERNOON.
&&

.HYDROLOGY...(400 PM EST THU DEC 24 2009)
NOT EXPECTING ENOUGH IN THE WAY OF PRECIPITATION TO CAUSE MAJOR 
CONCERNS. AREA RIVERS ARE AT NORMAL LEVELS PER THE USGS SITE SO QPF 
ON THE ORDER OF A HALF INCH THROUGH TOMORROW EVENING SHOULD EASILY 
BE ABSORBED. WITH TEMPERATURES AROUND FREEZING THE NEXT 24 
HOURS...NOT EXPECTING ANY ICE JAM ISSUES AND HAVE HEARD NOTHING ON 
THAT FRONT YET THIS SEASON. RAINFALL ON CHRISTMAS MORNING/DAY COULD 
LEAD TO SOME LOCAL PONDING OF WATER IN AREAS THAT HAVE SNOW OR ICE 
CLOGGED STORM DRAINS.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY THIS AFTERNOON THROUGH CHRISTMAS DAY 
     FOR THE ENTIRE CWA. 

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

&&

$$

SYNOPSIS:     DUKE
SHORT TERM:   DUKE
LONG TERM:    LAURENS
AVIATION:     MEADE
MARINE:       DUKE
HYDROLOGY:    DUKE