FXUS63 KGRR 070523
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1220 AM EST MON DEC 7 2009

LATEST UPDATE...AVIATION...

.SYNOPSIS...(356 PM EST SUN DEC 6 2009)
LIGHT SNOW WILL BE ACROSS AREAS NORTH OF INTERSTATE 96 TONIGHT BUT 
ONLY LIGHT ACCUMULATIONS OF AN INCH OR TWO AREA EXPECTED WITH 
PERHAPS ANOTHER INCH ON MONDAY AS WEAK LOW PRESSURE MOVES ALONG A 
STALLED FRONT. THEN ALL EYES TURN TO THE SOUTHWEST WHERE A WINTER 
STORM WILL BE GATHERING BY TUESDAY. THIS STORM WILL BRING HIGH WINDS 
AND HEAVY SNOW OR MIXED PRECIPITATION FOR THE WEDNESDAY MORNING 
COMMUTE. THEN LAKE EFFECT SNOW COMBINED WITH 40 MPH WIND GUSTS COULD 
IMPEDE TRAVEL WEDNESDAY NIGHT AND THURSDAY.

&&

.SHORT TERM...(356 PM EST SUN DEC 6 2009)
(TONIGHT THROUGH TUESDAY NIGHT)
FORECAST ISSUES IN THE NEAR TERM ARE FOR LIGHT SNOW TONIGHT AND 
HEAVY SNOW POTENTIAL TUESDAY NIGHT. FOR TONIGHT...AREA OF LIGHT SNOW 
WAY BACK ACROSS WESTERN IOWA ASSOCIATED F-GEN FORCING AND THIS WILL 
TRANSLATE EAST ALONG AND NORTH OF THE PATH OF THE WEAK SFC LOW THAT 
WILL BE MOVING ALONG THE STATIONARY FRONT NOW DRAPED OVER OUR 
NORTHERN FORECAST AREA.

THIS FRONT IS ALSO PROVIDING SOME LOW LEVEL CONVERGENCE AND 
ENHANCING THE FEW REMAINING LAKE EFFECT SNOW SHOWERS ACROSS THE 
NORTHERN ZONES. DECIDED TO KEEP LOW CHANCE POPS UP NORTH FOR THIS 
EVENING TO ACCOUNT FOR THIS. THE DEEPER MOISTURE AND BETTER LIFT 
ARRIVES AFTER 06Z...AND WITH SOME LAKE ENHANCEMENT...SHOULD SEE 
LIGHT ACCUMS ACROSS ROUGHLY THE NORTHERN HALF OF THE FORECAST AREA 
BETWEEN 06Z AND 18Z MONDAY. MADE ONLY SLIGHT TWEAKS TO CURRENT SNOW 
GRIDS FOR THIS PERIOD...WITH ABOUT 2 INCHES OF ACCUMS FROM NORTH OF 
MKG TO RQB AND OVER TO MOP.

ONCE THIS WEAK SYSTEM MOVES EAST BY MONDAY NIGHT...THERE SHOULD BE A 
LULL IN THE ACTION UNTIL TUESDAY NIGHT WHEN DEEP MOISTURE ARRIVES 
AND ISENTROPIC ASCENT INCREASES ASSOCIATED WITH MAJOR SOUTHERN 
PLAINS CYCLONE. TRACK OF THE LOW HAS BEEN PRETTY CONSISTENTLY 
HANDLED BY THE GFS AND EXPECT HEAVY SNOW TO MOVE FROM SOUTHWEST TO 
NORTHEAST ACROSS THE FORECAST AREA DURING THE EVENING. MIX TO SLEET 
AND FREEZING RAIN POSSIBLE ACROSS THE SOUTH AFTER 06Z WEDNESDAY AS 
SEEN IN GFS THERMAL PROFILES. DRY SLOT MAY ALSO BE AN ISSUE ACROSS 
THE SOUTH...BUT PROBABLY NOT UNTIL BEYOND 12Z WEDNESDAY. 

&&

.LONG TERM...(356 PM EST SUN DEC 6 2009)
(WEDNESDAY THROUGH SUNDAY)
THE MID RANGE MODELS CONTINUE TO TRACK A STRONG LOW PRESSURE SYSTEM
THROUGH THE GREAT LAKES REGION EARLY WEDNESDAY INTO WEDNESDAY NIGHT. 
THE 12Z GFS HAS A LOW OF 984 MB DEEPENING TO 986 MB AS IT MOVES 
FROM GARY INDIANA TO EASTERN LAKE HURON. THE 12Z ECMWF HAS THE LOW 
DEEPENING FROM 980 MB TO 970 MB AS IT MOVES FROM SOUTH OF GARY 
INDIANA TO CENTRAL LAKE HURON. PRECIPITATION MAY BE IN THE FORM OF 
RAIN... ICE PELLETS OR SNOW ACROSS SOUTHERN LOWER MICHIGAN WEDNESDAY 
MORNING AS A WARM WEDGE MOVES THROUGH. THIS WILL LIMIT THE SNOW 
ACCUMULATIONS ACROSS THE SOUTH. A GOOD PRESSURE GRADIENT AND 
CYCLONIC FLOW AS COLD AIR FLOWS IN BEHIND THE SYSTEM WILL KICK UP 
LAKE EFFECT SNOWS BEHIND THIS SYSTEM OVERNIGHT WEDNESDAY THROUGH 
THURSDAY.
 
THE MODELS THEN SHOW SPLIT FLOW AROUND AN AREA OF HIGH PRESSURE 
THAT BUILDS INTO THE CENTER OF THE CONTINENT. LOW PRESSURE SYSTEMS 
WILL MOVE BY TO THE NORTH AND SOUTH OF THE AREA LATE FRIDAY AND 
SATURDAY. COLD AIR WILL CONTINUE TO FLOW ACROSS LAKE MICHIGAN AND 
LIGHT LAKE EFFECT SNOW SHOWERS AND FLURRIES WILL CONTINUE TO BE 
POSSIBLE.

TEMPERATURES IN THE LONG TERM WILL BE MOSTLY BELOW NORMAL FOR THIS 
TIME OF THE YEAR WITH A FEW PERIODS NEAR NORMAL. NORMAL HIGHS ARE IN 
THE MID 30S AND NORMAL LOWS ARE IN THE LOWER 20S.
&&

.AVIATION...(1220 AM EST MON DEC 7 2009)
VFR CONDITIONS STILL IN PLACE ACROSS MOST OF SOUTHWEST LOWER 
MICHIGAN...INCLUDING ALL THE TAF SITES. WEAK LOW PRESSURE IN 
MISSOURI WILL DRIFT OUR DIRECTION THE NEXT 12 HOURS...SPREADING SNOW 
INTO THE REGION...ESPECIALLY ACROSS CENTRAL LOWER MICHIGAN. 
CONTINUED TO PLACE THE WORST CONDITIONS AT KMKG. BURST OF SNOW OVER 
ILLINOIS IS FORECAST TO WEAKEN WITH TIME OVERNIGHT AND DRIFT INTO 
INDIANA...VIA THE HRRR RUC MODEL. RAN WITH THAT IDEA STILL AND WE 
WILL SEE HOW IT PLAYS OUT. DID BRING SOME MVFR CEILINGS INTO MOST 
TAF SITES MONDAY AFTERNOON AS THE SWATH OF LOWER CEILINGS TO THE 
WEST IS PRETTY HARD TO IGNORE.

&&

.MARINE...(356 PM EST SUN DEC 6 2009)
OFFSHORE FLOW AND DECREASING WAVES TONIGHT. BIG STORM FOR WEDNESDAY 
AND THURSDAY WITH GALES LIKELY WEDNESDAY NIGHT...MAYBE STORM FORCE 
WIND GUSTS.

&&

.HYDROLOGY...(356 PM EST SUN DEC 6 2009)
NO HYDRO ISSUES AT LEAST THROUGH TUESDAY. STILL LOOKS LIKE WEDNESDAY 
STORM WILL BE MORE SNOW OR MIXED PRECIP THAN RAIN. STAY TUNED.  

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE. 
LM...NONE.

&&

$$

SYNOPSIS:     OSTUNO
SHORT TERM:   OSTUNO
LONG TERM:    IOD
AVIATION:     DUKE
MARINE:       OSTUNO
HYDROLOGY:    OSTUNO