FXUS63 KGRR 040923
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
423 AM EST FRI DEC 4 2009

LATEST UPDATE...ALL SECTIONS EXCEPT AVIATION...

.SYNOPSIS...(423 AM EST FRI DEC 4 2009)
A STRONG WAVE OF LOW PRESSURE WILL MOVE EAST OF THE STATE THIS 
MORNING. THIS WAVE OF LOW PRESSURE COMBINED WITH ENHANCEMENT OFF OF 
LAKE MICHIGAN WILL CONTINUE TO BRING A GOOD DEAL OF SNOW SHOWERS TO 
MOST OF THE AREA. ADDITIONAL ACCUMULATIONS ARE EXPECTED THROUGH THIS 
AFTERNOON. 

SNOW SHOWERS WILL DIMINISH SOME FOR THE WEEKEND AS THE SYSTEM MOVES 
EAST OF THE STATE...HOWEVER THEY WILL NOT END. LOCATIONS NORTHWEST 
OF A LINE FROM SOUTH HAVEN...TO GRAND RAPIDS...TO CADILLAC WILL SEE 
SNOW SHOWERS LIKELY THIS WEEKEND. ADDITIONAL ACCUMULATIONS WILL BE 
AN INCH OR TWO FOR EACH 12 HOUR PERIOD.

&&

.SHORT TERM...(423 AM EST FRI DEC 4 2009)
(TODAY THROUGH SUNDAY)
PRIMARY CONCERN WITH THIS FORECAST PACKAGE IS THE ONGOING HEADLINE 
EVENT ACROSS THE WEST CENTRAL PORTION OF THE CWFA FOR TODAY. AFTER 
TODAYS EVENT...LAKE EFFECT POTENTIAL WILL HAVE TO BE DETERMINED 
THROUGH THE WEEKEND.  

WE WILL BE MAINTAINING HEADLINES AS IS THIS MORNING. IMPRESSIVE LAKE 
EFFECT/SYNOPTIC BAND THAT DUMPED BETWEEN 1 AND 2 INCHES PER HOUR AT 
TIMES IS FINALLY SHOWING SIGNS OF BECOMING DISORGANIZED. MODERATE 
OVER-LAKE INSTABILITY COMBINED WITH A TROUGH AND LOW LEVEL FGEN BAND 
ASSOCIATED WITH THE STRONG PV ANOMALY MOVING IN...AND SOME WEAKNESS 
IN THE STABILITY PROVIDED THE INGREDIENTS FOR THE HEALTHY SNOWFALL.
THE PV CENTER WILL BE CROSSING THE CWFA WITHIN THE NEXT COUPLE OF 
HOURS...AND THE STRONG BAND WILL CONTINUE TO BECOME LESS ORGANIZED.

WE EXPECT ADDITIONAL ACCUMULATIONS WILL BE GENERALLY 1 TO 3 OR 2 TO 
4 INCHES UNDER THE HEAVIEST BANDS. SFC CONVERGENCE FIELDS INDICATE 
THE HEAVIEST SNOW WILL SHIFT FROM ITS CURRENT LOCATION TO A SOUTH 
HAVEN TO IONIA ORIENTATION BY 18Z BEFORE ENTIRELY BREAKING UP. WE 
BELIEVE THAT SOME COUNTIES NOT UNDER A HEADLINE WILL SEE THIS...
HOWEVER MOST OF THE SNOW WILL FALL WHERE LITTLE HAS FALLEN SO FAR 
AND COME UP SHORT OF ADVISORY CRITERIA.

THE PERIOD FROM TONIGHT THROUGH THE DAY ON SUNDAY WILL NOT SEE A 
SIGNIFICANT AMOUNT OF CHANGE DURING THE PERIOD. SW 1000-850MB FLOW 
WILL DOMINATE THE PERIOD WITH DELTA T/S GENERALLY AROUND THE MID TO 
UPPER TEENS. INVERSION HEIGHTS WILL GENERALLY RANGE FROM 4-6K FT. IT 
APPEARS AT LEAST SOME SNOW SHOWERS WILL BE AROUND FOR A GOOD PORTION 
OF THE WEEKEND FOR THE NW HALF OF THE CWFA. THE SNOW SHOWERS DO NOT 
LOOK TO BE ALL THAT INTENSE WITH A LIMITED DGZ DEPTH AND WITH A LACK 
OF SHORT WAVE ACTIVITY. THE SW FLOW AREAS COULD SEE AN INCH OR TWO 
EACH PERIOD FROM FRI NIGHT INTO SAT NIGHT. THE MODELS DRY OUT THE 
LOWER LEVELS ON SUN...SO THE CHC DOES NOT LOOK ALL THAT EXCITING 
THEN.    

&&

.LONG TERM...(423 AM EST FRI DEC 4 2009)
(SUNDAY NIGHT THROUGH THURSDAY)
THE TWO SYSTEMS TO WATCH IN DAYS 4-7 ARE IN THE SUNDAY NIGHT AND 
MONDAY TIME FRAME...THEN THE TUESDAY NIGHT THROUGH THURSDAY PERIOD. 

THE FIRST SYSTEM IS A SHORTWAVE WHICH APPEARS TO WEAKEN/SHEAR AS IT 
HEADS NORTHEAST FROM THE CENTRAL PLAINS SUNDAY NIGHT AND MONDAY. THE 
SURFACE REFLECTION IS RATHER WEAK... BUT AT LEAST SOME TYPE OF WEAK 
SFC LOW/INVERTED TROUGH SHOULD IMPACT THE REGION. AM THINKING A 1-3 
INCH SNOWFALL CAN BE EXPECTED OVER PORTIONS OF THE CWFA AS AN EARLY 
ESTIMATE. 

THE 00Z ECWMF/GFS/GEM ARE ALL IN GOOD AGREEMENT IN TRACKING A 
DEEPENING SFC LOW ACROSS THE REGION ON WEDNESDAY... WITH A TRACK 
FROM ROUGHLY NRN IL TO NRN LK HURON. THE CENTRAL PRESSURE IS PROGGED 
TO DROP TO AROUND 970 MB BY THE TIME IT REACHES NRN LK HURON AROUND 
00Z THU. IT/S MUCH TOO EARLY TO BANK ON THAT SPECIFIC SFC LOW TRACK 
AND TIMING... BUT IT CERTAINLY APPEARS A SIGNIFICANT CYCLONE IS 
GOING TO IMPACT THE REGION MID WEEK. 

WE COULD SEE A BAND OF STRONG TSTMS SOUTH OF THE SFC LOW TRACK AND 
HEAVY SNOW NORTH OF THE LOW... WITH VERY WINDY CONDITIONS AND SNOW 
SHOWERS ON THE BACK SIDE OF THE SYSTEM WED NIGHT INTO THURS. IN THE 
GRR CWFA... IT MAY BE A SNOW TO RAIN THEN BACK TO SNOW SHOWERS 
SCENARIO.  

&&

.AVIATION...(1250 AM EST FRI DEC 4 2009)
SNOW SHOWERS PERSIST INTO THE OVERNIGHT HOURS WITH IFR CONDITIONS 
EXPECTED FOR MKG AND GRR. HEAVIER SNOW SQUALLS MAY CUT VSBYS DOWN TO 
1/2SM OR WORSE...SO WENT WITH TEMPOS THAT FEATURE LIFR CONDITIONS 
FOR MKG AND GRR THROUGH THE EARLY TO MID MORNING HOURS. LAN MAY ALSO 
GET INTO IFR AT TIMES FOR THE SAME GENERAL TIME PERIOD AS THE SNOW 
SHOWERS WILL TEND TO DRIFT BACK TOWARD THE SOUTH WITH TIME. BOTTOM 
LINE...WORST CONDITIONS WILL BE AT GRR AND MKG THROUGHOUT THE 
MORNING.

ELSEWHERE...PRIMARILY MVFR/VFR CONDITIONS ARE ANTICIPATED AS IS THE 
NATURE OF LAKE EFFECT EVENTS. EXCEPT FOR JXN...FEATURED LIGHT SNOW 
SHOWERS DURING THE EARLY AFTERNOON HOURS WITH THE TREND FOR DRIER 
CONDITIONS EXPECTED. ALL SITES SHOULD BE FREE OF IFR CONDITIONS 
AFTER 18Z...BUT WILL MONITOR CLOSELY. WITH A MORE WSW TO SW FLOW 
DURING THE AFTERNOON...WOULD EXPECT REMAINING SNOW SHOWERS TO BE 
PRIMARILY CONFINED TO THE MKG TERMINAL. 

&&

.MARINE...(423 AM EST FRI DEC 4 2009)
WE WILL BE MAINTAINING THE SMALL CRAFT ADVISORY THROUGH EARLY 
SATURDAY MORNING. GOOD COLD AIR ADVECTION COMBINED WITH GOOD OVER 
LAKE INSTABILITY AND 20-25 KNOTS 2-3K FT ABOVE THE GROUND WILL 
CONTINUE TO PRODUCE WINDS AND WAVES EXCEEDING SMALL CRAFT ADVISORY 
THRESHOLDS. 

IT DOES APPEAR WINDS WILL DROP BELOW 20 KNOTS TONIGHT AND REMAIN 
BELOW 20 KNOTS THEN THROUGH EARLY SATURDAY NIGHT. GRADIENT WILL THEN 
TIGHTEN UP A BIT AS HIGH PRESSURE MOVES EAST OF THE AREA.

&&

.HYDROLOGY...(423 AM EST FRI DEC 4 2009)
NO HYDROLOGY ISSUES EXPECTED THROUGH THE WEEKEND. ALL PRECIPITATION 
THROUGH THE WEEKEND WILL BE SNOW...AND VERY LITTLE...IF ANY RUNOFF 
IS EXPECTED WITH HIGHS EXPECTED ONLY TO BE AROUND OR SLIGHTLY ABOVE 
FREEZING.

WE COULD SEE SOME DECENT RIVER RISES NEXT WEEK IF THE STRONG STORM 
SYSTEM TAKES SHAPE AS MOST MODELS ARE INDICATING. PRECIPITATION TYPE 
WITH THIS STORM IS STILL IN QUESTION...BUT IT COULD VERY WELL BE A 
DECENT AMOUNT OF RAIN WITH A NICE SURGE OF MOISTURE FROM THE GULF. 
THAT COMBINED WITH MELTING SNOW WOULD PRODUCE QUITE A BIT OF RUNOFF.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...WINTER STORM WARNING FOR MUSKEGON...KENT...AND OTTAWA COUNTIES 
THROUGH FRIDAY AFTERNOON.
WINTER WEATHER ADVISORY FOR NEWAYGO AND ALLEGAN COUNTIES 
THROUGH FRIDAY AFTERNOON.
LM...SMALL CRAFT ADVISORY ST. JOSEPH TO MANISTEE THROUGH FRIDAY 
NIGHT.

&&

$$

SYNOPSIS:     NJJ
SHORT TERM:   NJJ
LONG TERM:    MEADE
AVIATION:     HOVING
MARINE:       NJJ
HYDROLOGY:    NJJ