FXUS63 KGRR 160221
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
920 PM EST TUE DEC 15 2009

LATEST UPDATE...SHORT TERM...

.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...(920 PM EST TUE DEC 15 2009)
(TONIGHT THROUGH THURSDAY NIGHT)
WE HAVE GONE AHEAD AND UPDATED THE FORECAST TO LOWER POPS A BIT FOR 
TONIGHT. 

AT FIRST GLANCE...LATEST RADAR IMAGERY SHOWS QUITE A FAIR AMOUNT OF 
ECHOES ACROSS THE CWFA. FILTERING OUT THE ECHOES BELOW 20 DBZ LEAVES 
VERY LITTLE IF ANY RETURNS. IN ADDITION...VISIBILITIES ACROSS THE 
ENTIRE CWFA REMAIN AOA 7SM. FLURRIES/VERY LIGHT SNOW SHOWERS ARE 
BEING OBSERVED HERE IN GRR UNDER SOME OF THESE ECHOES...HOWEVER IT 
IS JUST TRACE TYPE OF PCPN. INVERSION HTS ARE AROUND 4K FEET WITH 
VERY DRY AIR MOVING IN. WITH ALL OF THIS IN MIND...WE HAVE LOWERED 
POPS DOWN TO 30 PCT ACROSS THE WRN 3/4 OF THE CWFA TO ACCOUNT FOR 
THAT ISOLATED LOCATION THAT MAY SEE SLIGHTLY MORE THAN A DUSTING OF 
SNOW. 

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/NJJ
LONG TERM:    63
AVIATION:     OSTUNO
MARINE:       WDM
HYDROLOGY:    WDM