FXUS63 KGRR 090540
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1240 AM EST WED DEC 9 2009

LATEST UPDATE...AVIATION...

.SYNOPSIS...(415 PM EST TUE DEC 8 2009)
A POWERFUL WINTER STORM WILL IMPACT THE REGION TONIGHT THROUGH 
THURSDAY.  THIS STORM WAS DEVELOPING IN COLORADO...AND WILL TRACK 
THROUGH LOWER MICHIGAN ON WEDNESDAY.  SNOW WILL OVERSPREAD MUCH OF 
THE AREA THIS EVENING.  AS WARMER AIR MOVES IN FROM THE SOUTH THE 
SNOW IS EXPECTED TO CHANGE OVER TO RAIN FOR SOUTHERN LOWER 
MICHIGAN.  THEN AS ARCTIC AIR FILTERS IN FROM THE SOUTHWEST ON 
WEDNESDAY ALL THE PRECIPITATION WILL CHANGE BACK TO SNOW.  STRONG 
GUSTY WINDS ARE EXPECTED WITH THIS STORM.

&&

.SHORT TERM...(1033 PM EST TUE DEC 8 2009)
(TONIGHT THROUGH 1 PM WED)
FORECAST SEEMS TO BE ON TRACK.  WARMER AIR AND DRY SLOT WILL KEEP 
MOST ACCUMS SOUTH OF I-96 TO 2-4 INCHES AS A MIX OR COMPLETE CHANGE 
OVER OCCURS OVERNIGHT.  HOWEVER...NORTH OF A MUSKEGON TO GRATIOT 
COUNTY LINE WE WILL LIKELY SEE A SHARP GRADIENT IN THE SNOW ACCUMS 
OVERNIGHT.  THIS AREA WILL ESCAPE THE DRY SLOT AND WILL ALSO LARGELY 
REMAIN SNOW.  4 TO 8 INCHES CAN BE EXPECTED BY MORNING ACROSS THIS 
AREA.  AND THE 00Z NAM SUGGEST THIS WILL BE THE PIVOT REGION OF THE 
DEFORMATION ZONE TOWARD DAYBREAK...LEADING TO MORE SNOW IN THIS AREA 
INTO WED MORNING.  A FOOT OF SNOW IS POSSIBLE IN SOME SPOTS BY NOON 
IN THIS AREA. 

ELEVATED INSTABILITY ARRIVES FROM 06Z TO 12Z AND THAT WILL LEAD TO A 
RISK FOR AN ISOLATED THUNDERSTORM. SOME SLEET COULD MIX IN DURING 
ANY BURST OF HEAVIER PRECIPITATION.

COLD AIR ADVECTION WILL STRENGTHEN WED AM.  BY 1 PM SNOW SHOULD BE 
MIXING IN WITH ANY RAIN.  WINDS WILL BE ON THE INCREASE AND GUSTS 
OVER 45 MPH ARE EXPECTED AS MIXING HEIGHTS INCREASE BY NOON... 
ESPECIALLY ALONG THE LAKESHORE AND SOUTH OF INTERSTATE 96.  THE WIND 
DATA WILL BE INCORPORATED INTO THE WINTER WEATHER HEADLINES. 
 
&&

.MID TERM...(415 PM EST TUE DEC 8 2009)
(1 PM WEDNESDAY THROUGH THURSDAY NIGHT)
BIGGEST CONCERNS DURING THIS TIME FRAME WILL BE LAKE EFFECT 
POTENTIAL...WINDS...AND RESULTING POTENTIAL FOR POSSIBLE NEAR 
BLIZZARD CONDITIONS. WE WILL BE LEAVING UP THE WINTER STORM WATCH 
FOR THE SW CORNER OF THE CWFA FOR THIS PERIOD...AND EXPECT THAT IT 
WILL BE UPGRADED IN THE NEXT FCST PACKAGE DUE TO A COMBINATION OF 
CONDITIONS. 

LOW WILL BE JUST EXITING THE CWFA AT 18Z WED. COLDER AIR WILL BE 
WRAPPING IN FROM THE W/NW FAIRLY QUICKLY...CHANGING ALL PCPN BACK 
OVER TO SNOW SHOWERS FOR THE AFTERNOON HOURS. THERE MAY BE A BRIEF 
LULL IN THE HEAVIER PCPN AS THE SYNOPTIC PCPN MOVES OUT...AND BEFORE 
THE LAKE EFFECT CAN GET GOING. 

H850 TEMPS WILL PLUMMET FROM AROUND -3C AROUND 18Z WED TO -20C OR SO 
BY EARLY THU MORNING. LAKE EFFECT SNOW SHOWERS WILL GET GOING BY WED 
EVENING...AND CONTINUE RIGHT ON THROUGH THU NIGHT FOR THE ENTIRE 
CWFA. THE FLOW IS EXPECTED TO BECOME WRLY WED EVENING AND REMAIN SO 
SO THROUGH THU NIGHT. THIS WILL FAVOR THE LAKESHORE LOCATIONS AND 
LOCATIONS OVER THE SW QUARTER OF THE CWFA WHICH ARE DOWNWIND OF THE 
LARGEST FETCH OF THE LAKE. SNOW SHOWERS WILL REACH WELL INLAND WITH 
THE STRONG FLOW.

AS FAR AS ACCUMULATIONS ARE CONCERNED...THE HEAVIEST ACCUMS WILL BE 
FOUND IN THE AFOREMENTIONED FAVORED AREAS LISTED ABOVE. SOME HEALTHY 
ACCUMS ARE EXPECTED WED NIGHT WITH INSTABILITY BECOMING MODERATE TO 
EXTREME...AND MOISTURE REMAINING RATHER DEEP /THROUGH 10K FT/ AS THE 
SYSTEM IS STILL PULLING AWAY. WINDS WILL TEND TO SPREAD THE ACCUMS 
INLAND A BIT...KEEPING AMOUNTS FROM GETTING TOO HIGH. THE POTENTIAL 
FOR ACCUMS WILL DIMINISH A BIT FOR THU AND THU NIGHT AS THE LOW DGZ 
AND COLDER TEMPS WILL LIMIT FLAKE SIZE. COMBINING ALL THREE 
PERIODS...SOME LOCATIONS IN ALLEGAN...KENT...OTTAWA...AND BARRY 
COUNTIES COULD SEE A FOOT OF SNOW FROM WED NIGHT THROUGH THU NIGHT.

IN ADDITION TO THE LAKE EFFECT...THE WINDS WILL BECOME A MAJOR 
FACTOR. MOST MODELS ARE INDICATING THAT MOST OF THE CWFA WILL SEE 
WIND GUSTS AROUND 40 TO LOCALLY 50 MPH WED NIGHT AND ON THU. THESE 
WINDS WILL PRODUCE WIDESPREAD BLOWING AND DRIFTING SNOW...WITH 
VISIBILITIES GOING DOWN TO NEAR ZERO AT TIMES NEAR THE LAKESHORE. IF 
THE CONFIDENCE IN THE FREQUENT WIND GUSTS AND VISIBILITIES 
CONTINUES...A BLIZZARD WARNING MAY BE NEEDED. INLAND AREAS WILL NOT 
SEE CONDITIONS QUITE AS BAD WITH LESS SNOW AND SLIGHTLY WEAKER 
WINDS...BUT CONDITIONS WILL STILL BE QUITE BLUSTERY. AN ADVISORY 
WILL LIKELY BE NEEDED INLAND FOR THIS PART OF THE EVENT.

WIND CHILLS WILL ALSO BE AN ISSUE WITH VALUES DROPPING BELOW ZERO 
LATE WED NIGHT AND CONTINUING ON THU WITH TEMPS HOLDING IN THE 
TEENS. 

&&

.LONG TERM...(245 PM EST TUE DEC 8 2009)
(FRIDAY THROUGH TUESDAY)
A FEW RELATIVELY MINOR SYSTEMS ARE EXPECTED DURING THIS TIME PERIOD. 
CONFIDENCE IS LOW REGARDING THE TIMING AND PLACEMENT OF ANY OF THESE 
SYSTEMS. ANY LINGERING LAKE EFFECT SHOULD SHUT DOWN QUICKLY FRIDAY 
WITH INCREASINGLY ANTICYCLONIC FLOW.

FOR SATURDAY NIGHT...PREVIOUS RUNS OF THE ECMWF ADVERTISE CYCLONIC 
FLOW TO SHARPEN AS A CANADIAN PV ANOMALY BRUSHES THE NORTHERN GREAT 
LAKES AND AN ASSOCIATED COLD FRONT CROSSES THE CWFA. THE GFS AGREES 
WITH THE TIMING OF THIS SYSTEM BUT IS A BIT WEAKER. HOWEVER...THE 
LATEST 12Z ECMWF SHOWS A LATER FRONTAL PASSAGE...SO CONFIDENCE IN 
THIS TIME FRAME FOR POPS REMAINS RATHER LOW. HAVE ONLY INTRODUCED 
CHANCE OF SNOW AT THIS TIME IN LINE WITH HPC GUIDANCE.

MODEL SOLUTIONS REMAIN DIVERGENT FROM SUNDAY INTO THE MIDDLE OF THE 
WORK WEEK...KEEPING CONFIDENCE IN THE FORECAST LOW. HAVE THEREFORE 
STAYED CLOSE TO HPC GUIDANCE OF CHANCE SNOW EACH DAY AS BROAD 
CYCLONIC FLOW ALOFT SHOULD DOMINATE THE PATTERN. IT IS WORTH NOTING 
THAT THE 12Z ECMWF ADVERTISES A PV ANOMALY SWEEPING ACROSS THE CWA 
MONDAY...SUGGESTING HIGHER THAN CHANCE POPS. SINCE THIS IS THE FIRST 
INDICATION...WILL NOT MAKE ANY CHANGES AT THIS TIME.

THE PATTERN BEGINS TO AMPLIFY AN UPSTREAM RIDGE BY MIDWEEK...WHICH 
SHOULD RESULT IN SURFACE HIGH PRESSURE AND COLDER THAN NORMAL 
TEMPERATURES.

&&

.AVIATION...(1240 AM EST WED DEC 9 2009)
AT LEAST IFR CONDITIONS ARE EXPECTED THE NEXT 24 HOURS WITH LOW 
CEILINGS MOST OF THE TIME...AND VISIBILITIES DROPPING WEDNESDAY 
EVENING. INITIAL BAND OF SNOW IS WORKING NORTHWARD THROUGH THE TAF 
SITES CURRENTLY...WITH A LULL IN THE PRECIPITATION EXPECTED FROM 
LATE TONIGHT INTO WEDNESDAY MORNING. SNOW WILL BRIEFLY MIX TONIGHT 
WITH SOME SLEET AT KLAN AND KJXN...BEFORE GOING OVER TO RAIN AND 
DRIZZLE AT ALL SITES TOWARD MORNING. THE RAIN AND DRIZZLE WITH 
CHANGE BACK TO SNOW WEDNESDAY AFTERNOON AS COLD AIR POURS INTO THE 
STATE BEHIND A FRONTAL PASSAGE. CONDITIONS WILL LIKELY DETERIORATE 
RAPIDLY WEDNESDAY EVENING AS HEAVY LAKE EFFECT SNOW DEVELOPS IN 
CONJUNCTION WITH STRONG WINDS. EXPECTING NEAR ZERO VISIBILITY AT 
KGRR AND KAZO DURING THE EVENING.
 
&&

.MARINE...(415 PM EST TUE DEC 8 2009)
A GALE WARNING CONTINUES.  GALES WILL BE POSSIBLE THIS 
AFTERNOON AND EVENING...AND THEN AGAIN LATE WED MORNING THROUGH AT 
LEAST WED NIGHT.

&&

.HYDROLOGY...(415 PM EST TUE DEC 8 2009)
NO HYDRO ISSUES EXPECTED ALTHOUGH SOME RISES ARE POSSIBLE IN 
KALAMAZOO RIVER BASIN DEPENDING ON HOW MUCH QPF FALLS IN THE FORM OF 
RAIN EARLY WEDNESDAY MORNING.   

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...WINTER STORM WARNING ALLEGAN...KENT...IONIA...GRATIOT COUNTIES  
     NORTHWARD THIS EVENING THROUGH WEDNESDAY NIGHT.
     WINTER WEATHER ADVISORY ELSEWHERE LATE THIS AFTERNOON AND       
     TONIGHT.
     WINTER STORM WATCH VAN BUREN...KALAMAZOO AND BARRY COUNTIES     
     LATE WEDNESDAY AFTERNOON THROUGH WEDNESDAY NIGHT.
LM...GALE WARNING ST. JOSEPH TO MANISTEE TONIGHT THROUGH 
THURSDAY.

&&

$$

SYNOPSIS:     MJS
SHORT TERM:   MJS JK
LONG TERM:    TJT
MID TERM:     NJJ
AVIATION:     DUKE
MARINE:       MJS
HYDROLOGY:    MJS