FXUS63 KGRR 231119
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
618 AM EST WED DEC 23 2009

LATEST UPDATE...AVIATION...

.SYNOPSIS...(430 AM EST WED DEC 23 2009)
A STRONG WINTER STORM WILL SPREAD HEAVY SNOW ACROSS THE UPPER 
MISSISSIPPI VALLEY AND MIXED SLEET SNOW AND FREEZING RAIN INTO LOWER 
MICHIGAN...BEGINNING LATE THURSDAY. 

TRAVEL CONDITIONS WILL DETERIORATE CHRISTMAS EVE FROM SOUTH TO NORTH 
AS FREEZING RAIN AND SLEET MOVE INTO THE REGION. WARMER AIR WILL 
CHANGE THE PRECIPITATION TO MAINLY RAIN CHRISTMAS MORNING. COLDER 
AIR WILL MOVE BACK IN LATE CHRISTMAS DAY AGAIN CHANGING THE 
PRECIPITATING BACK TO SNOW. COLDER AIR WILL THEN REMAIN IN PLACE 
THROUGH THE WEEKEND. SNOW SHOWERS ARE EXPECTED FRIDAY NIGHT THROUGH 
THE WEEKEND.     

&&

.SHORT TERM...(430 AM EST WED DEC 23 2009)
(TODAY THROUGH FRIDAY)
A COMPLEX WEATHER SCENARIO IS UNFOLDING. LATEST WV LOOP SHOWS A 
UPPER LOW MOVING THROUGH THE SRN ROCKIES. THIS STORM WILL PRODUCE A 
DEEP SFC LOW IN THE SOUTHERN PLAINS TONIGHT. ISENTROPIC LIFT AHEAD 
OF THE SYSTEM IN THE WARM AIR ADVECTION REGIME IS ALREADY PRODUCING 
SHOWERS/STORMS OVER THE MISSOURI VALLEY. STABILITY INDICES SUGGEST 
THAT STORMS WILL REMAIN WELL SOUTH OF THE CWA. HOWEVER...PCPN WILL 
CONTINUE TO SPREAD NWD TODAY THROUGH IL/IN. THERE IS A CHANCE OF 
LIGHT SNOW IN THE FAR SW CWA LATE THIS AFTERNOON AND A BIT FARTHER 
NORTH THIS EVENING AS THIS PCPN MOVES NWD AND BATTLES THE DRY AIR IN 
PLACE. FOLLOWED THE SREF FOR POP GUIDANCE WITH THIS FCST. 

AS THE SFC LOW DEEPENS AND MOVES NWD...PCPN WILL TEND TO PULL BACK 
TO THE WEST OVERNIGHT. I THINK MOST OF TONIGHT WILL BE CLOUDY AND 
DRY ACROSS THE CWA. 

PCPN WILL MOVE INTO THE CWA THURSDAY...MAINLY DURING THE AFTERNOON. 
BUFKIT RH PROFILES SHOW A LARGE WEDGE OF DRY AIR IN THE LOW LEVELS 
THURSDAY AS LOW DEWPOINTS ADVECT IN FROM THE EAST AROUND THE HIGH TO 
THE NORTH. THIS WILL DELAY THE ONSET OF PCPN. THE MAIN THRUST OF THE 
PCPN WILL MOVE IN THURSDAY NIGHT. FORECAST SOUNDINGS POINT TOWARD 
FREEZING RAIN AND SLEET...WITH SOME SNOW OVER THE NRN CWA. THE MAIN 
THREAT IS ICE ACCUMULATION...ESPECIALLY OVER THE NRN CWA WHERE UP TO 
A QUARTER INCH IS POSSIBLE. WINDS MAY ALSO BE 
PROBLEMATIC...ESPECIALLY ALONG THE LAKE SHORE WHERE THEY MAY GUST UP 
TO 40 MPH AND COMBINE WITH A COATING OF ICE ON THE TREES. WE MAY SEE 
SOME TREE LIMBS FALL AND RESULT IN SCATTERED POWER OUTAGES.  

THE HIGHEST THREAT FOR A QUARTER INCH OF ICE WILL BE NORTH OF A ALMA 
TO PENTWATER LINE AS THIS AREA WILL BE THE LAST TO SEE THE WARM AIR 
THAT WILL BEGIN MOVING INTO THE CWA LATE THURSDAY NIGHT.

EXPECT A CHANGEOVER TO RAIN FROM SOUTH TO NORTH CHRISTMAS DAY. THE 
FAR NORTH MAY NEVER CHANGE OVER COMPLETELY. FORECAST SOUNDINGS OVER 
THE NRN CWA SUGGEST SFC TEMPS IN THE LOWER 30S. BUT AS WE/VE SEEN 
MANY TIMES...SFC OBS MAY BE IN THE LOWER 30S...BUT ROAD TEMPS MAY BE 
A DEGREE OR TWO COLDER...JUST ENOUGH TO CREATE REAL PROBLEMS. 

COLDER AIR WRAPPING AROUND THE OCCLUDED LOW WILL RESULT IN COLD AIR 
ADVECTION FROM THE SOUTH FRIDAY AFTERNOON. THIS WILL CAUSE THE PCPN 
TO MIX WITH AND CHANGE TO SNOW. LITTLE SNOW ACCUMULATION IS 
EXPECTED. 

&&

.LONG TERM...(430 AM EST WED DEC 23 2009)
(FRIDAY NIGHT THROUGH TUESDAY)
LOOKS LIKE LOWER MICHIGAN IS DRY SLOTTED FRIDAY NIGHT AND MUCH OF 
SATURDAY AS THE OCCLUDED CYCLONE BEGINS TO SPIN DOWN ACROSS IOWA. 
WENT WITH CHANCE POPS AND TWEAKED THEM A BIT LOWER UNTIL THE UPPER 
LOW FINALLY MOVES EAST ON SUNDAY. TWEAKED POPS UP FOR SUNDAY AND 
MONDAY WITH THE DEEP MOISTURE OF THE UPPER LOW COMBINING WITH SOME 
LAKE ENHANCEMENT TO PRODUCE SNOW SHOWERS. MAY EVENTUALLY HAVE TO GO 
LIKELY POPS FOR PART OF SUNDAY OR MONDAY.

SNOW WILL GRADUALLY DIMINISH AS THE LOW MOVES EAST LATE MONDAY. 
CHANCE POPS FOR SNOW ON TUESDAY AS AN ARCTIC FRONT MAY BRING SOME 
LOW LEVEL CONVERGENCE.

&&

.AVIATION...(618 AM EST WED DEC 23 2009)
LOW CLOUDS MOVING WES TOFF LAKE HURON HAVE MADE IT INTO LAN THIS 
MORNING...BUT SATELLITE TRENDS SHOW THEY ARE NOT GOING TO REACH JXN. 
THEY MAY MAKE IT INTO GRR BETWEEN 12Z AND 14Z. BOTH LAN AND GRR WILL 
BE RIGHT ON THE EDGE OF THESE LOW CLOUDS...WITH CEILINGS AROUND 2000 
FEET. ELSEWHERE CEILINGS WILL REMAIN NEAR 10 THOUSAND FEET THROUGH 
TODAY. DO NOT EXPECT ANY PRECIPITATION TODAY OR TONIGHT EXCEPT FOR 
SOME FLURRIES THIS MORNING NEAR AZO AND JXN.

&&

.MARINE...(430 AM EST WED DEC 23 2009)
GALE WATCH CONTINUES THURSDAY INTO FRIDAY. WINDS WILL 
INCREASE...ESPECIALLY THURSDAY NIGHT...AS A STRONG STORM APPROACHES.
&&

.HYDROLOGY...(430 AM EST WED DEC 23 2009)
QPF POTENTIAL THURSDAY NIGHT AND FRIDAY ISN/T HIGH ENOUGH TO CAUSE 
HYDRO CONCERNS.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...WINTER STORM WATCH FROM THURSDAY EVENING THROUGH FRIDAY 
     AFTERNOON ALL ZONES.
LM...GALE WATCH FROM MID MORNING THURSDAY THROUGH FRIDAY MORNING FOR 
     THE ENTIRE NEAR SHORE.

&&

$$

SYNOPSIS:     93
SHORT TERM:   93
LONG TERM:    OSTUNO
AVIATION:     OSTUNO
MARINE:       93
HYDROLOGY:    93