FXUS63 KGRR 300456
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1154 PM EST SUN NOV 29 2009

LATEST UPDATE...AVIATION...

.SYNOPSIS...(322 PM EST SUN NOV 29 2009)
LOW PRESSURE WILL EXIT THE REGION THIS EVENING BRINGING AN END TO 
THE LIGHT RAIN AND SNOW OVERNIGHT.  MONDAY MORNING WILL BE DRY... 
HOWEVER ANOTHER TROUGH OF LOW PRESSURE WILL MOVE TOWARD THE STATE 
LATE IN THE DAY AND COULD BRING SCATTERED LIGHT SNOW BACK TO THE 
AREA.  THE SNOW WILL BECOME ENHANCED BY LAKE MICHIGAN MONDAY 
EVENING.  AREAS NORTH OF INTERSTATE 96 AND INLAND FROM THE LAKE 
COULD SEE UP TO AN INCH OF SNOW ACCUMULATION BY EARLY TUESDAY 
MORNING.  TUESDAY AND TUESDAY NIGHT LOOK DRY AS HIGH PRESSURE FLOATS 
BY.

&&

.SHORT TERM...(1057 PM EST SUN NOV 29 2009)
(TONIGHT THROUGH TUESDAY NIGHT)
UPDATED THE GRIDS TO REFLECT PCPN OVERNIGHT. CURRENTLY KGRR-88D 
SHOWS SCT SHRA MOVING SOUTH ALONG US-31. AS COLDER AIR ADVECTS SOUTH 
OVERNIGHT THE PCPN WILL TURN TO SHSN. NOT EXPECTING ACCUMS DUE TO AN 
UNSATURATED DGZ AND LIMITED OVERALL MOISTURE PROFILE...BUT SCT SHSN 
WILL LINGER DUE TO INSTABILITY OVER THE LAKE.

WILL REMOVE THE LOW CHANCE POPS MONDAY MORNING AS THE SURFACE RIDGE 
WILL BE IN PLACE.  HOWEVER...BY LATER IN THE DAY A SURFACE TROUGH 
WILL APPROACH THE AREA.  A RATHER SHEARED UPPER SHORT WAVE 
ACCOMPANIES THE TROUGH.  NOT AN OVERLY IMPRESSIVE SYSTEM...SO WILL 
JUST LEAVE LOW CHANCE POPS IN FOR THE AFTERNOON. 

THE SHORT WAVE ITSELF AND DEEPER MOISTURE ARRIVES MONDAY NIGHT.  WE 
SHOULD ALSO SEE A BOOST FROM THE LAKE.  HAVE DECIDED TO INCREASE 
POPS TO LIKELY ALONG THE LAKE AND ACROSS THE NORTHERN HALF OF THE 
CWA.  THIS APPEARS TO BE MAINLY AN EVENING EVENT...WITH THE PCPN 
DIMINISHING AFTER MIDNIGHT AS THE WAVE PASSES.  PCPN TYPE SHOULD BE 
MAINLY SNOW...WITH A MIX OVER THE SW CORNER.  SOME AREAS NORTH OF 
I-96 AND INLAND FROM THE LAKE COULD SEE UP TO AN INCH OF SNOW 
ACCUMULATION ON GRASSY AREAS BY EARLY TUESDAY MORNING.

WILL MAINTAIN THE DRY FORECAST FOR TUESDAY AND TUESDAY NIGHT.  THERE 
WILL BE A NORTHERN STREAM SYSTEM APPROACHING...BUT THIS SHOULD 
MAINLY IMPACT NORTHERN LOWER AND THE U.P.

&&

.LONG TERM...(322 PM EST SUN NOV 29 2009)
(WEDNESDAY THROUGH SUNDAY)
VERY FEW LONG RANGE FCST CHANGES WERE NECESSARY. 12Z GFS/ECMWF/FIM 
GUIDANCE CONTINUES TO SUGGEST THAT THE GULF COAST LOW WILL STAY FAR 
ENOUGH EAST OF OUR AREA (ALONG THE APPALACHIANS) LATE WEDNESDAY 
NIGHT AND THURSDAY SUCH THAT WE WILL MISS OUT ON THE SYNOPTIC PCPN 
FROM THAT SYSTEM.

HOWEVER WE WILL BE IN A STRONG WNW FLOW CAA REGIME THURSDAY THROUGH 
FRIDAY LEADING TO LAKE EFFECT SNOW AS 850 MB TEMPS FALL TO AT LEAST 
-10 TO -12 C BY THURSDAY NIGHT. MAX TEMPS THURSDAY AND FRIDAY WILL 
ONLY REACH THE LOWER 30S. WE HAVE EXPANDED THE AREA OF LIKELY POPS 
FOR LAKE EFFECT SNOW SHOWERS TO ENCOMPASS THE WESTERN HALF OF OUR 
CWFA...WITH HIGH CHC POPS FURTHER INLAND. THE THOUGHT IS THAT WNW 
WINDS WILL BE BRISK ENOUGH TO CARRY SNOW SHOWERS WELL INLAND. 

THIS CERTAINLY HAS POTENTIAL TO BE THE FIRST SIGNIFICANT LAKE EFFECT 
SNOW EVENT OF THE SEASON FOR PORTIONS OF OUR CWFA...PARTICULARLY IN 
OUR FAVORED WNW FLOW SNOW BELT AREAS. MUCH WILL DEPEND ON NUMEROUS 
OTHER FACTORS THOUGH INCLUDING INVERSION HEIGHTS...DEPTH OF MOISTURE 
AND UPSTREAM RH AND AMOUNT OF WIND SPEED/DIRECTIONAL SHEAR WITH 
HEIGHT. IT IS STILL A LITTLE TOO EARLY TO DRILL DOWN INTO THOSE 
TYPE OF SPECIFICS. 

&&

.AVIATION...(1154 PM EST SUN NOV 29 2009)
CEILINGS FOR THE MOST PART ACROSS THE AREA ARE VFR (UP CONSIDERABLY 
FOR EARLIER THIS EVENING) AND ARE EXPECTED TO STAY THAT WAY THE 
MAJORITY OF THE NIGHT. MID LEVEL MOISTURE IS PEELING AWAY AND AS 
EXPECTED THE LAKE EFFECT PRECIPITATION IS TONING DOWN. FOR THE 
REMAINDER OF THE NIGHT EXPECTING VFR CEILINGS...WITH SOME SPOTTY 
SPRINKLES/FLURRIES TOWARD THE COAST. 

MVFR CEILINGS WILL TRY TO SPREAD BACK IN ACROSS THE TAF SITES DURING 
THE DAY ON MONDAY AS THE FLOW GOES WESTERLY. BY EVENING VFR CEILINGS 
ARE ONCE AGAIN EXPECTED. A WEAK SYSTEM MOVING THROUGH THE AREA 
MONDAY EVENING MAY BRING A BURST OF SOME RAIN AND SNOW AFTER SUNSET. 
WILL BE KEEPING AN EYE ON THIS ESPECIALLY FOR THE NORTHERN TAF 
SITES. IT WILL TURN BREEZY AS WELL TOMORROW EVENING WITH GUSTY WINDS 
OUT OF THE SOUTHWEST.

&&

.MARINE...(322 PM EST SUN NOV 29 2009)
A SMALL CRAFT ADVISORY WAS ALREADY IN EFFECT.  WINDS AND WAVES WILL 
BE BUILDING THIS EVENING AND WILL REMAIN HAZARDOUS TO SMALL CRAFT 
INTO TUESDAY AFTERNOON.

&&

.HYDROLOGY...(322 PM EST SUN NOV 29 2009)
NO HYDRO ISSUES.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...SMALL CRAFT ADVISORY THROUGH TUESDAY AFTERNOON FROM ST JOSEPH 
TO MANISTEE.

&&

$$

SYNOPSIS:     JK
SHORT TERM:   JK 93
LONG TERM:    LAURENS
AVIATION:     DUKE
MARINE:       JK
HYDROLOGY:    JK