FXUS63 KGRR 051133
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
633 AM EST SAT DEC 5 2009

LATEST UPDATE...AVIATION...

.SYNOPSIS...(424 AM EST SAT DEC 5 2009)
LIGHT LAKE EFFECT SNOW SHOWERS AND FLURRIES CAN BE EXPECTED FOR MOST 
OF THE AREA THROUGH MOST OF THE WEEKEND. ACCUMULATIONS WILL BE ON 
THE LIGHT SIDE WITH ONLY AN INCH OR SO FOR EACH PERIOD THROUGH 
SUNDAY FOR LOCATIONS MAINLY WEST OF A LINE FROM SOUTH HAVEN TO 
CADILLAC.

A COUPLE OF STORM SYSTEMS WILL THEN IMPACT THE AREA NEXT WEEK. ONE 
WILL BRING AT LEAST A COUPLE OF INCHES OF SNOW TO THE AREA LATE 
SUNDAY NIGHT AND ON MONDAY. ANOTHER WILL MOVE IN ACROSS THE AREA 
FROM LATE TUESDAY AND THROUGH WEDNESDAY.

&&

.SHORT TERM...(424 AM EST SAT DEC 5 2009)
(TODAY THROUGH MONDAY)
PRIMARY CHALLENGES WITH THIS FORECAST PACKAGE ARE LAKE EFFECT 
POTENTIAL THROUGH THE DAY ON SUN...AND DETERMINING PCPN CHCS WITH 
THE SHORT WAVE MOVING THROUGH LATE SUN NIGHT AND ON MON.

BASIC INGREDIENTS ARE IN PLACE FOR LAKE EFFECT TO CONTINUE THROUGH 
MOST OF THE WEEKEND FOR AT LEAST THE NW HALF OF THE CWFA. SNOW 
SHOWERS DO LOOK LIKE THEY WILL REMAIN ON THE LIGHTER SIDE HOWEVER. 
DELTA T/S IN THE MID TEENS WILL BE SUFFICIENT...HOWEVER MOISTURE IS 
FAIRLY SHALLOW BELOW 6K FEET AND ALMOST ALL OF THE LIFT IS BELOW THE 
DGZ. WE WILL ALLOW FOR AN INCH OR SO BASICALLY W AND NW OF GRAND 
RAPIDS FOR EACH PERIOD AS GENERAL FLOW WILL BE FROM THE SW. 

MODELS ARE IN FAIRLY GOOD AGREEMENT CONCERNING THE SHORT WAVE TROUGH 
THAT WILL BE MOVING ACROSS THE CWFA DURING THE DAY ON MON. THIS 
SHORT WAVE IS CURRENTLY DIVING SSE ACROSS THE PACIFIC NW...AND WILL 
BEGIN TO HEAD NE AFTER REACHING THE FOUR CORNERS REGION.  MOISTURE 
WILL INCREASE IN THE MID TO UPPER LEVELS SUN EVENING...AND WILL BE 
ESTABLISHED ENOUGH FOR PCPN TO BEGIN FALLING TO THE GROUND ACROSS 
THE WRN CWFA LATE SUN NIGHT.

MOST OF THE PCPN WILL OCCUR DURING THE DAY ON MON. COLD AIR WILL BE 
FIRMLY ENTRENCHED SO THAT ALL PCPN WITH THIS WILL BE OF THE FROZEN 
VARIETY. THIS IS A QUICK MOVING SYSTEM AND IT DOES NOT HAVE ALL THAT 
MOIST OF AIR COMING IN WITH SPECIFIC HUMIDITIES ONLY APPROACHING 2 
IN THE MID LEVELS. THIS WOULD SUPPORT A MAX OF 2 TO 4 INCHES OF 
SNOW. BEST FGEN FORCING WITH THE DEFORMATION/TROWAL IS EXPECTED TO 
MOVE ACROSS THE NRN HALF OF THE CWFA. LAKE ENHANCEMENT DOES NOT LOOK 
TO BE A PLAYER WITH MOST OF THIS SYSTEM WITH AN ERLY COMPONENT TO 
THE FLOW.

&&

.LONG TERM...(424 AM EST SAT DEC 5 2009)
(MONDAY NIGHT THROUGH FRIDAY)
THE LATEST 00Z GFS/FIM/ECMWF/GEM GUIDANCE STILL SHOWS A SIGNIFICANT 
CYCLONE PASSING THROUGH THE REGION ON WEDNESDAY... ALTHOUGH NOT 
QUITE AS LOW OF A CENTRAL PRESSURE AS IN PREVIOUS RUNS. 

NEVERTHELESS... THE SYSTEM IS STILL PROGGED TO BE DEEPENING TO ABOUT 
985 MB AS IT TRACKS FROM ROUGHLY INDIANAPOLIS TO DETROIT. THIS PATH 
WOULD KEEP THE PCPN TYPE ALL SNOW OVER THE GRR CWFA WITH SEVERAL 
INCHES OF ACCUMULATION POSSIBLE... BUT IT IS STILL WAY TOO EARLY TO 
NAIL DOWN THE EXACT TRACK. THE FIM SOLUTION AND TWO OF THE GFS 
ENSEMBLE PERTURBATIONS SHOW A FARTHER WEST TRACK WHILE THE UKMET IS 
MUCH FARTHER SOUTH AND EAST WITH THE LOW TRACK. IT IS WORTH NOTING 
TOO HOWEVER THAT THE TIMING HAS NOT CHANGED MUCH AT ALL. 

VERY WINDY CONDITIONS ARE STILL POSSIBLE WEDNESDAY NIGHT INTO 
THURSDAY IN TIGHT GRADIENT ON THE BACK SIDE OF THE SYSTEM. ALSO H8 
AIR AS COLD AS -20C MAY BE PULLED DOWN AS THE SYSTEM DEPARTS ON 
THURSDAY... WHICH COULD LEAD TO SOME SIGNIFICANT LAKE EFFECT SNOW 
SHOWERS WITH CONSIDERABLE BLOWING AND DRIFTING SNOW.  

&&

.AVIATION...(633 AM EST SAT DEC 5 2009)
DESPITE LAKE EFFECT CLOUDS AND LIGHT SNOW SHOWERS... PRIMARILY VFR 
CONDITIONS CAN BE EXPECTED TODAY AND TONIGHT. CIGS SHOULD BE AROUND 
3500 FEET WITH VSBYS MOSTLY ABOVE 5 MILES. EVERY NOW AND THEN THE 
MKG AND GRR TAF SITES MAY DIP DOWN TO 4-5 MILES IN THE LAKE EFFECT 
SNOW SHOWERS.  

&&

.MARINE...(424 AM EST SAT DEC 5 2009)
WE WILL KEEP THE SMALL CRAFT ADVISORY UP THROUGH THE 12Z EXPIRATION 
AS WINDS CONTINUE TO BARELY EXCEED CRITERIA. WINDS ARE EXPECTED TO 
CONTINUE TO DIMINISH THROUGH TODAY AND WAVES WILL FOLLOW SUIT. A 
BRIEF BREAK IN THE STRONGER WINDS WILL OCCUR TODAY. MODELS INDICATE 
WINDS PICKING UP A LITTLE TONIGHT AS THE TROUGH FROM THE NORTH TRIES 
STRENGTHENING THE GRADIENT.

WINDS WILL THEN DIMINISH ONCE AGAIN FROM SUNDAY INTO MONDAY AS A 
RIDGE OF HIGH PRESSURE WILL INITIALLY BE AFFECTING THE AREA. THE 
NEXT SYSTEM WILL MOVE IN SUNDAY NIGHT AND MONDAY...HOWEVER THE 
GRADIENT ASSOCIATED WITH THIS SYSTEM WILL BE ON THE WEAK SIDE.

&&

.HYDROLOGY...(424 AM EST SAT DEC 5 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. THE STORM NEXT WEEKEND MAY BE RAIN OR SNOW...IT IS STILL 
TOO EARLY TO TELL HOW MUCH IF ANY RUNOFF WILL OCCUR.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE. 
LM...SMALL CRAFT ADVISORY ST. JOSEPH TO MANISTEE THROUGH 12Z THIS  
MORNING.

&&

$$

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