FXUS63 KGRR 081206 CCA
AFDGRR

AREA FORECAST DISCUSSION...CORRECT TIME ISSUED
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
705 AM EST TUE DEC 8 2009

LATEST UPDATE...AVIATION...

.SYNOPSIS...(527 AM EST TUE DEC 8 2009)
AN INTENSE WINTER STORM WILL MOVE TOWARD MICHIGAN TODAY AND BEGIN TO 
SPREAD SNOW INTO THE REGION BY EARLY TO MID AFTERNOON.  
ACCUMULATIONS BY THIS EVENING SHOULD BE AROUND AN INCH OR LESS.  
HOWEVER...AS THE LOW MOVES CLOSER THE SNOW WILL INTENSIFY THIS 
EVENING.  AREAS NORTH OF INTERSTATE 96 CAN EXPECT TO RECEIVE AN 
ADDITIONAL 6 TO 9 INCHES OF SNOW OVERNIGHT.  ALONG AND SOUTH OF 
INTERSTATE 96 WARMER AIR IS EXPECTED TO CHANGE THE SNOW TO A MIX OF 
FREEZING RAIN...SLEET AND SNOW LATE TONIGHT.  THIS WILL KEEP SNOW 
ACCUMULATION TO 1 TO 4 INCHES ALONG WITH A LIGHT COATING OF ICE.   
FURTHER SOUTH...NEAR AND SOUTH OF INTERSTATE 94...THE SNOW IS 
EXPECTED TO CHANGE TO RAIN LATE TONIGHT...KEEPING SNOW ACCUMULATIONS 
TO TWO INCHES OR LESS.

COLDER AIR WILL RETURN WEDNESDAY AFTERNOON WHEN LAKE EFFECT SNOW 
SHOWERS WILL INCREASE IN INTENSITY.  SOME OF THE AREAS DOWN WIND 
FROM THE LAKE COULD PICK UP SEVERAL ADDITIONAL INCHES OF SNOW.  
BLUSTERY WINDS COULD CREATE NEAR BLIZZARD CONDITIONS AT TIMES.

&&

.SHORT TERM...(527 AM EST TUE DEC 8 2009)
(TODAY THROUGH WEDNESDAY NIGHT)
HAVE UPGRADED MUCH OF THE WATCH AREA TO A WARNING ALONG AND NORTH OF 
A SOUTH HAVEN TO ST. JOHNS LINE.

GOOD AGREEMENT IN THE MODELS SHOWING AN INTENSIFYING LOW PRESSURE 
THAT WAS CENTERED JUST SW OF DEN THIS MORNING WILL TRACK TO JUST 
NORTH OF STL LATE TONIGHT...THEN CROSS LOWER MICHIGAN ON WED.

BURST OF WARM ADVECTION SNOW IS ON TRACK TO MOVE IN THIS 
AFTERNOON...A BIT QUICKER THAN EARLIER THOUGHT.  HAVE ADJUSTED THE 
HEADLINES OVER SOUTHERN LOWER ACCORDINGLY.  MAIN BURST OF SNOW WILL 
ARRIVE IN THE CWA WITH THE ASSISTANCE OF THE LOW LEVEL JET BETWEEN 
00-06Z.  MUCH OF SOUTHERN HALF OF THE CWA WILL PICK UP A QUICK 1-4 
INCHES OF SNOW THROUGH THE EVENING.  THEN THE PCPN SHOULD CHANGE 
OVER TO A MIX.  THE MODEL SOUNDINGS APPEAR SLIGHTLY COOLER...SO THIS 
CHANGE OVER MAY TAKE A BIT LONGER...AND COULD CAUSE THE SNOW TOTALS 
TO BE ON THE HIGHER END.  HOWEVER WITH THE LOW EXPECTED TO TRACK 
ACROSS CENTRAL LOWER...THE PCPN SHOULD EVENTUALLY MIX ALONG 
I96...AND CHANGE TO ALL RAIN ALONG I94 LATE TONIGHT.  

FURTHER NORTH....MKG TO MOP...THE PCPN WILL LARGELY STAY SNOW.  HERE 
IS WHERE WE WILL SEE THE HIGHEST SNOW TOTALS.  SNOWFALL RATES IN 
EXCESS OF AN INCH AN HOUR APPEARS LIKELY AS STRONG LIFT WILL BE 
ACCOMPANIED BY INSTABILITY IN THE MID LEVELS.  4 TO AS MUCH AS 10 
INCHES OF SNOW CAN BE EXPECTED BY DAYBREAK WED.  

THERE SHOULD BE A BIT A LULL IN THE PCPN AROUND MID DAY WED AS THE 
DRY SLOT ACCOMPANIES THE PASSAGE OF THE SURFACE LOW.  HOWEVER ON THE 
BACKSIDE OF THE LOW THE BRISK WEST WINDS WILL KICK IN AND BEGIN TO 
CHURN UP LAKE EFFECT SNOW SHOWERS.  MEAN FLOW WILL BE 280-295 BY WED 
AFTERNOON AND OVERNIGHT.  THE STRENGTH OF THE WINDS WILL PUSH THE 
HEAVIEST SNOW INLAND TOWARD U.S. 131.  MANY AREAS WILL SEE ANOTHER 
2-4 INCHES OF SNOW WED AFTERNOON THROUGH WED NIGHT...HOWEVER THE 
AREAS S OF GRR COULD PICK ANOTHER 6+ INCHES OF SNOW.  HAVE GONE WITH 
A WATCH OVER THE SW PORTION OF THE CWA WHERE THERE WILL BE A LULL IN 
THE TWO SNOW PERIODS.  THE OTHER ASPECT OF THIS PERIOD WILL BE THE 
WINDS WHICH COULD GUST TO 40 MPH AT TIMES CAUSING BLOWING AND 
DRIFTING AND NEAR BLIZZARD CONDITIONS.  A BLIZZARD WARNING IS STILL 
A POSSIBILITY WITH LATER FORECAST PACKAGES IF CONFIDENCE INCREASES.

IT IS VERY POSSIBLE HEADLINES WILL NEED TO BE EXTENDED INTO THURSDAY 
AS THE WINDS MAY REMAIN STRONG AND THE LAKE EFFECT IS EXPECTED TO 
CONTINUE.  HOWEVER AT THIS POINT WILL LET LATER SHIFTS DETERMINE 
THIS POTENTIAL.

&&

.LONG TERM...(527 AM EST TUE DEC 8 2009)
(THURSDAY THROUGH MONDAY)
LITTLE QUESTION SNOW SHOWERS...BLOWING SNOW AND GUSTY WINDS WILL 
DOMINATE SOUTHWEST LOWER MICHIGAN'S WEATHER DURING THE DAY TIME 
HOURS OF THURSDAY. AS OUR UNUSUALLY STRONG STORM CONTINUES TO DEPART 
THE AREA WEST WINDS IN THE 950 TO 850 MB LAYER (CLOUD LAYER) WILL BE 
FROM THE WEST AROUND 35 KNOTS. THE MEAN RH IN THAT LAYER WILL BE 
NEAR 95 PCT (RH OVER ICE) AND WITH 850 MB TEMPS FCST NEAR -20C... 
LITTLE QUESTION THERE WILL BE EXTREME LAKE INSTABILITY TO AID IN  
THE PRODUCTION OF SNOW SHOWERS OVER LAKE MICHIGAN THAT WILL SPREAD 
INLAND WITH THE WIND.  THE WEST WIND WILL RESULT IN A I-94 TO I-96 
CONVERGENCE BAND AND WITH THE 35 KNOTS WINDS WILL BLOW THE SNOW 
SHOWERS ACROSS OUR CWA WITH LITTLE PROBLEM. COULD BE NEAR BLIZZARD 
CONDITIONS NEAR THE LAKE SHORE INTO THE MIDDAY HOURS OF THURSDAY. 
THE SMALL FLAKES (DGZ BELOW THE CLOUD BASE)AND STRONG WINDS WILL 
COMBINE TO CREATE LOW VISIBILITIES TOO. WE MAY NEED TO EXPAND OUR 
HEADLINES UNTIL THURSDAY EVENING BASED ON THE STRENGTH OF ALL THESE 
FEATURES. 

THERE ARE TWO BLOCKING UPPER LEVEL RIDGES THAT WORKING TOGETHER ARE 
CAUSING THE CHANGE TO COLDER WEATHER OF LATE. THE MORE SIGNIFICANT 
IS THE LARGE BLOCKING RIDGE OVER ALASKA. AN EVEN MORE PERSISTENT 
UPPER RIDGE FORMS OVER GREENLAND BY SAT 00Z. THESE FEATURES WILL 
KEEP THE GREAT LAKES IN AN AIR FLOW THAT CROSSES THE NORTH POLE FOR 
SOME TIME TO COME. 

SO...AFTER THIS MAJOR STORM MOVES OUT OF THE WAY WE WILL SEE A 
PARADE OF NORTHERN BRANCH SYSTEMS (COLD FRONTS). NONE OF THESE WAVES 
SEEM OUTSTANDINGLY STRONG... SO FORECASTING THE TIMING AND DETAILS 
AT THIS TIME RANGE IS NOT MORE THAN AN EDUCATED GUESS. SO... I DID 
NOT CHANGE THE GRID FORECAST SIGNIFICANTLY THROUGH NEXT TUESDAY.  
SO...SINCE WE HAD SNOW SHOWERS IN OUR FORECAST FOR THROUGH THE LONG 
RANGE PART OF THE FORECAST THEY SHALL REMAIN THERE.    

&&

.AVIATION...(705 AM EST TUE DEC 8 2009)
FOR THE MOST PART MVFR VSBY PREVAILED AT 6 AM THIS MORNING AT OUR 
TAF SITES WHILE CEILING REMAIN VFR.  LATEST DATA SHOWS DRY AIR 
BEING ADVECTED NORTHWARD INTO THE GRR CWA FROM THE SOUTH. THAT 
SHOULD KEEP THE CEILING VFR MOST OF THE DAY.  THE MAIN SNOW BAND 
SHOULD NOT REACH OUR TAF SITES UNTIL LATE IN THE DAY.  THE STRONG 
LIFT COME IN AFTER 03Z. WE CONTINUE TO BRING THE SNOW INTO THE TAF 
SITES AROUND 21Z JUST AHEAD OF THE BETTER MID LEVEL LIFT. FREEZING 
RAIN WAS ADDED TO THE I-94 TAF SITES BASED ON THE  DEPTH OF THE 0C ON
BUFKIT SOUNDING. 
 
&&

.MARINE...(527 AM EST TUE DEC 8 2009)
A GALE WARNING HAS BEEN POSTED.  GALES WILL BE POSSIBLE TOWARD 
MIDNIGHT TONIGHT...AND THEN AGAIN LATE WED MORNING THROUGH AT LEAST 
WED NIGHT.

&&

.HYDROLOGY...(527 AM 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:     JK
SHORT TERM:   JK
LONG TERM:    WDM
AVIATION:     WDM
MARINE:       JK
HYDROLOGY:    JK