FXUS63 KGRR 152311 CCA
AFDGRR

AREA FORECAST DISCUSSION...CORRECTED TIME
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
611 PM EST TUE DEC 15 2009

LATEST UPDATE...AVIATION...

.SYNOPSIS...(405 PM EST TUE DEC 15 2009)
A LARGE ARCTIC HIGH PRESSURE SYSTEM FROM ALASKA HAS MOVE SOUTHEAST 
TO THE CENTRAL PLAINS AS OF MIDDAY TUESDAY. THIS LARGE COLD HIGH 
PRESSURE SYSTEM WILL MOVE SLOWLY TO THE NORTHEAST OVER THE NEXT 
SEVERAL DAYS... REACHING THE EASTERN GREAT LAKES BY FRIDAY. THE COLD 
DRY AIR WILL SIGNIFICANTLY LIMIT THE POTENTIAL FOR LAKE EFFECT SNOW 
SHOWERS. THIS MOST SIGNIFICANT IMPACT THIS HIGH WILL HAVE ON 
SOUTHWEST LOWER MICHIGAN IS FOR COLDER THAN NORMAL TEMPERATURES TO 
PREVAIL THROUGH FRIDAY. 

&&

.SHORT TERM...(405 PM EST TUE DEC 15 2009)
(TONIGHT THROUGH THURSDAY NIGHT)
THE FOCUS OF THIS FORECAST IS BOTH THE ARCTIC AIR MOVING IN AND THE 
LACK FOR POTENTIAL FOR LAKE EFFECT SNOW DUE TO THE SHALLOW INVERSION 
HEIGHTS AND SUBSEQUENT DRY AIR. 

SHORTWAVE RIDGING IN COMBINATION WITH THE LARGE ARCTIC HIGH PASSING 
SOUTH OF MICHIGAN WEDNESDAY WILL LOWER INVERSION HEIGHTS TO LESS 
THAN 5000 FT TONIGHT. SO...EVEN WITH THE WEST WINDS...850 MB 
TEMPERATURES BELOW -10C THROUGH WEDNESDAY AND THE DGZ WELL WITHIN 
THE LAKE GENERATED CLOUDS...SNOW SHOWERS WILL BE LIGHT AT BEST DOWN 
WIND OF LAKE MICHIGAN AS WILL THE ACCUMULATIONS. MORE THAN ANYTHING 
ELSE... IT WILL JUST BE COLD OUTSIDE. LOW LEVEL THICKNESS (1000-925 
MB) SUPPORT HIGHS WED IN THE LOWER TO MID 20S. 

A WEAK NORTHERN STREAM WAVE WILL BRING LAYERED MID CLOUDS TO THE 
AREA LATER THURSDAY INTO THURSDAY NIGHT. TEMPERATURES WILL REMAIN 
BELOW NORMAL.

.LONG TERM...(405 PM EST TUE DEC 15 2009)
(THURSDAY THROUGH MONDAY)
THE MID RANGE MODEL SOLUTIONS HAVE DIVERGED A BIT... DECREASING 
CONFIDENCE IN THE FORECAST. COORDINATION KEEPS FORECAST CLOSER TO 
THE ECMWF. ONLY SMALL GRID CHANGES MADE DUE TO LOW CONFIDENCE.

MODELS SHOW A STRONG GYRE OVER THE NORTHEASTERN PORTION OF THE 
CONTINENT THURSDAY. THE 12Z ECMWF SHOWS THE CENTER OF ROTATION 
RETROGRADING AND PASSING TO THE SOUTH SOUTHEAST OVER THE REGION 
TUESDAY. THE 12Z GFS SOLUTION HAS A LOBE MOVING THROUGH THE REGION 
WITH LITTLE MOISTURE. THE MORE ACTIVE ECMWF HAS THE AIR AT 850 MB 
COLD ENOUGH FOR LAKE EFFECT SNOW FOR MOST OF THE EXTENDED PERIOD IN 
NORTHWEST FLOW. IT ALSO HAS SEVERAL SHORT WAVES MOVING THROUGH THE 
REGION AND ADDING SOME KICK TO THE LAKE EFFECT SHOWERS. THEREFORE... 
KEPT 30 POPS BROAD BRUSHED OVER THE EXTENDED PERIODS.

TEMPERATURES THROUGH THE PERIOD LOOK TO BE SLIGHTLY BELOW NORMAL.

&&

.AVIATION...(611 PM EST TUE DEC 15 2009)
LIGHT LAKE EFFECT SNOW SHOWERS WILL CONTINUE TONIGHT BUT CONDITIONS 
WILL BE MOSTLY MVFR AS INVERSION HEIGHTS LOWER AND SFC HIGH PRESSURE 
BUILDS IN. LOW CLOUDS WILL BEGIN TO BREAK UP WEDNESDAY MORNING AS 
DRIER AIR MOVES IN WITH VFR CONDITIONS EXPECTED IN THE AFTERNOON.

&&

.MARINE...(405 PM EST TUE DEC 15 2009)
WAVES OF 4 TO 8 FEET ARE EXPECTED TO CONTINUE AS THE ARCTIC AIR 
CONTINUES TO BLOW ACROSS THE WARMER WATERS OF LAKE MICHIGAN AT 20 TO 
25 KNOTS. WINDS AND WAVES WILL START TO DIMINISH DURING WEDNESDAY 
AFTERNOON.  

&&

.HYDROLOGY...(405 PM EST TUE DEC 15 2009)
NO HYDRO ISSUES ARE EXPECTED THROUGH THIS WEEK.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE
LM...SMALL CRAFT ADVISORY IN EFFECT THROUGH WEDNESDAY MORNING FOR 
THE ENTIRE NEAR SHORE.

&&

$$

SYNOPSIS:     WDM
SHORT TERM:   WDM
LONG TERM:    63
AVIATION:     OSTUNO
MARINE:       WDM
HYDROLOGY:    WDM