FXUS63 KGRR 240034
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
730 PM EST WED DEC 23 2009
LATEST UPDATE...AVIATION...
.SYNOPSIS...(412 PM EST WED DEC 23 2009)
STRENGTHENING LOW PRESSURE WILL FORM IN THE LOWER MISSISSIPPI VALLEY
LATE TONIGHT AND MOVE NORTH INTO SOUTHERN IOWA BY CHRISTMAS MORNING.
LOWER MICHIGAN WILL BE ON THE EASTERN SIDE OF THE STORM
SYSTEM...WHICH WILL BE THE WARMER SIDE. SOME LIGHT SNOW AND SLEET
WILL BE POSSIBLE THIS EVENING OVER FAR SOUTHWEST LOWER
MICHIGAN...OTHERWISE A DRY NIGHT IS EXPECTED.
THE MAIN STORM SYSTEM WILL BEGIN TO AFFECT THE AREA WITH FREEZING
RAIN FROM CHRISTMAS EVE AFTERNOON INTO CHRISTMAS MORNING. A WINTER
STORM WATCH IS IN EFFECT FOR ICE ACCUMULATION. THE BEST POTENTIAL
FOR ACCUMULATING ICE WILL BE ACROSS CENTRAL LOWER MICHIGAN. STAY
TUNED TO LATER FORECASTS FOR POSSIBLE WARNINGS AND ADVISORIES.
AS THE LOW IN THE PLAINS DRIFTS OUR DIRECTION OVER THE
WEEKEND...SNOW WILL BE A POSSIBILITY FROM SATURDAY INTO MONDAY. THE
SNOW WILL TREND TOWARD LAKE EFFECT BY LATE IN THE WEEKEND...WITH
SOME ACCUMULATION EXPECTED ALONG AND WEST OF HIGHWAY 131.
&&
.SHORT TERM...(412 PM EST WED DEC 23 2009)
(THIS EVENING AND TONIGHT)
MAIN ISSUE IN THE SHORT TERM WILL BE THE INITIAL PUSH OF SOME WARM
AIR ADVECTION PRECIPITATION THIS EVENING. THE PRECIPITATION IS
ASSOCIATED WITH A SHORTWAVE LIFTING NORTHEAST AHEAD OF THE MAIN
SYSTEM. A MIXTURE OF PRECIPITATION IS OCCURRING ACROSS NORTHERN
ILLINOIS AND NORTHERN INDIANA. AS THE PRECIPITATION MOVES FURTHER
NORTH INTO THE COLDER AND DRIER AIR WE SHOULD MAINLY SEE SNOW OR
SLEET. FOLLOWED SREF POPS AS IT DOES LOOK LIKE THE PRECIPITATION
WILL MAKE A MOVE INTO THE FAR SOUTHWEST CORNER OF THE STATE.
ALLEGAN...VAN BUREN AND KALAMAZOO COUNTIES WILL STAND THE BEST
CHANCE AT SEEING PRECIPITATION. OTHERWISE EXPECTING INCREASING
CLOUDS WITH A BRISK EAST WIND.
&&
.STORM TERM...(412 PM EST WED DEC 23 2009)
(THURSDAY THROUGH FRIDAY)
COMPLEX SYSTEM TO UNFOLD THROUGH THE HOLIDAY PERIOD. LOW PRESSURE
WAS DEEPENING OVER THE TX PANHANDLE TODAY...WHILE AN UPPER LEVEL LOW
WAS WEST OF LAKE WINNIPEG. THESE TWO FEATURES WILL MERGE OVER THE
MIDDLE OF THE NATION. DUE TO INFLUENCE OF THE NORTHERN STREAM
LOW...THE TRACK OF THE SURFACE LOW WILL BE UNUSUAL...DRIFTING ALMOST
DUE NORTH FROM EASTERN TX INTO IA BY FRIDAY.
THE RESULT WILL BE A PUSH OF GULF MOISTURE AND WARM AIR TOWARD THE
GREAT LAKES. THIS WARM AIR ARRIVES FIRST IN THE LOW/MID LEVELS...
WHILE STUBBORNLY COLD BOUNDARY LAYER AIR HOLDS ON. THEREFORE...
INITIALLY THE EXPECTED PCPN TYPE CONTINUES TO BE FREEZING RAIN.
HAVE LEFT THE WINTER STORM WATCH INTACT. HOWEVER...WITH THE SYSTEM
MOVING MORE NORTH THAN IT IS EAST FOR THE NEXT 24 HOURS...WESTERN
MICHIGAN WILL CONTINUE TO STAY ON THE EASTERN FRINGES ON THE PCPN
SHIELD. THE LAKESHORE AREAS COULD SEE MIXED PCPN AS EARLY AS MID
DAY ON THURSDAY...BUT THIS SHOULD BE LIGHT. THE ADVANCEMENT
EASTWARD WILL BE VERY SLOW UNTIL THE SYSTEM IS GIVEN A EASTWARD PUSH
BY THE NORTHERN MERGER LATE THURSDAY NIGHT. AT THIS POINT IT
APPEARS THE PCPN WILL ONLY MAKE IT TO U.S. 131 DURING THE EVENING
HOURS...THEN FINALLY PUSH ACROSS THE REST OF THE CWA AFTER
MIDNIGHT. SO...ALTHOUGH THE WATCH WILL REMAIN INTACT FROM LATE
THURSDAY AFTERNOON THROUGH LATE FRIDAY AFTERNOON...WILL SPELL OUT
THE FINE DETAILS IN THE TEXT OF THE WSW.
MOST AREAS WILL CHANGE OVER TO RAIN CHRISTMAS MORNING FROM SOUTH TO
NORTH AS THE WARM AIR MAKES IT DOWN TO THE SURFACE. ICING COULD BE
PROLONGED SINCE GROUND TEMPS ARE NEAR THE FREEZING MARK AND ALTHOUGH
WE MAY REACH 33-34 DEGREES ICING AT THE SURFACE MAY CONTINUE.
HOWEVER WITH MID AND UPPER 30S EXPECTED BY MID DAY...MOST OF THE ICE
ACCUMS WILL END. ONE AREA WHERE THE PCPN MAY NOT CHANGE OVER WILL
BE THE NORTHERN COUNTIES FORM LUDINGTON TO CLARE. HERE IS WHERE THE
HIGHEST ICING ACCUMS CAN BE EXPECTED.
COLD AIR WRAPS AROUND THE SYSTEM AND PUSHES IN FROM THE SW LATE IN
THE DAY ON CHRISTMAS. THIS WILL BEGIN TO CHANGE THE PCPN TO SNOW
TOWARD EVENING.
&&
.LONG TERM...(412 PM EST WED DEC 23 2009)
(FRIDAY NIGHT THROUGH WEDNESDAY)
STILL LOOKS LIKE LOWER MICHIGAN IS DRY SLOTTED FRIDAY NIGHT AND MUCH
OF SATURDAY AS THE OCCLUDED CYCLONE BEGINS TO FILL OVER IOWA.
RAISED HPC POPS ESPECIALLY NEAR THE LAKE SHORE SUNDAY AND SUNDAY
NIGHT AS WE EXPECT LAKE ENHANCED SNOW COMBINED WITH DEEP MOISTURE
WITH THE UPPER LOW. OVERALL...THE INTENSITY OF THE LAKE ENHANCED
SNOW LOOKS LESS IMPRESSIVE THAN IT DID YESTERDAY DUE TO THE TRACK OF
THE LOW AND LOWER CONVECTIVE LAYER DEPTHS IN THE FORECAST SOUNDINGS
THAN PREVIOUSLY ADVERTISED.
SNOW WILL GRADUALLY DIMINISH MONDAY AS THE LOW MOVES EAST AND THE
DGZ DESATURATES. FOLLOWING ON THE PREVIOUS DISCUSSION...WILL KEEP
CHANCES FOR SNOW IN THE FORECAST TUESDAY AND WEDNESDAY DUE TO THE
POSSIBILITY OF AN ARCTIC FRONT MOVING THROUGH THE AREA. THE ECMWF
APPEARS TO SHUNT THE COLDER AIR MORE TOWARDS THE NORTHEAST STATES
COMPARED TO THE GFS...SO THIS REMAINS A LOW CONFIDENCE PART OF THE
FORECAST.
.AVIATION...(730 PM EST WED DEC 23 2009)
RADAR SHOWS PRECIPITATION MOVING IN FROM THE SOUTHWEST...NOW INTO
KSBN. FORECAST SOUNDING DATA SUGGESTS THE DRY AIR NEAR THE GROUND
WILL ACT TO DELAY AND WEAKEN THE PRECIPITATION AS IT MOVES IN. AN
ELEVATED WARM LAYER MAY ALLOW FOR THE SNOW TO MELT...BUT THE FACT
THAT IT IS SO COLD NEAR THE GROUND...THE PRECIPITATION SHOULD
REFREEZE INTO SLEET BEFORE REACHING THE GROUND. UNFORTUNATELY NO
TAMDAR FLIGHTS NEARBY TO CONFIRM THIS...SO WE WILL NEED TO MONITOR
THIS CLOSELY THROUGH THE NIGHT.
UNLESS THE PRECIPITATION FALLS HARD TONIGHT AND REDUCES THE
VSBYS...VFR WEATHER IS EXPECTED TO PREVAIL.
THIS FIRST BATCH OF PRECIPITATION IS EXPECTED TO WEAKEN EARLY
THURSDAY MORNING...BY 15Z. THEN WE WILL BE AWAITING THE
NEXT...STRONGER AREA OF FREEZING RAIN TO ARRIVE AFT 00Z FRI FROM THE
SOUTHWEST.
&&
.MARINE...(412 PM EST WED DEC 23 2009)
HAVE HOISTED A GALE WARNING FROM MIDDAY ON CHRISTMAS EVE THROUGH
CHRISTMAS DAY. EASTERLY GALES ARE EXPECTED TO REACH THE 35-40 KNOT
RANGE DURING THAT PERIOD. WAVES WILL NOT BE REAL HIGH IN THE
NEARSHORE WATERS AS THE FETCH LENGTH WILL BE LIMITED TO ABOUT 5
MILES WITH THE OFF SHORE WIND.
&&
.HYDROLOGY...(412 PM EST WED DEC 23 2009)
QPF POTENTIAL THURSDAY NIGHT AND FRIDAY WILL NOT BE HIGH ENOUGH TO
CAUSE HYDRO ISSUES.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...WINTER STORM WATCH FROM THURSDAY EVENING THROUGH FRIDAY
AFTERNOON ALL ZONES.
LM...GALE WARNING FROM MIDDAY THURSDAY THROUGH FRIDAY AFTERNOON FOR
THE ENTIRE NEAR SHORE.
&&
$$
SYNOPSIS: DUKE
SHORT TERM: DUKE
STORM TERM: JK
LONG TERM: TJT
AVIATION: MJS
MARINE: DUKE
HYDROLOGY: DUKE
