FXUS63 KGRR 262046
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
345 PM EST SAT DEC 26 2009

LATEST UPDATE...ALL EXCEPT AVIATION...

.SYNOPSIS...(345 PM EST SAT DEC 26 2009)
A SLOW MOVING LOW PRESSURE SYSTEM OVER NORTHWESTERN ILLINOIS WILL 
KEEP THE WEATHER COLD WITH SNOW SHOWERS IN LOWER MICHIGAN THROUGH 
THE WEEKEND. THE BEST SNOW ACCUMULATIONS ARE EXPECTED NEAR THE 
LAKESHORE.  THE UPPER LEVEL SYSTEM WILL MOVE EAST OF THE AREA 
MONDAY...ALLOWING COLD AIR AND LAKE EFFECT SNOW SHOWERS TO FILTER 
INTO THE AREA. TUESDAY THROUGH WEDNESDAY SHOULD BE MOSTLY DRY. A 
WEAK SYSTEM MAY BRING SOME SNOW WEDNESDAY NIGHT THROUGH THURSDAY. 
THIS WILL BE FOLLOWED BY MUCH COLDER TEMPERATURES INTO THE WEEKEND. 

&&

.SHORT TERM...(345 PM EST SAT DEC 26 2009)
(TONIGHT THROUGH SUNDAY NIGHT)

THE MAIN CHALLENGE IN THE SHORT TERM DEALS WITH THE SNOWFALL AMOUNTS 
ESPECIALLY NEAR THE LAKESHORE. A WINTER WEATHER ADVISORY FOR SNOW 
WILL BE NEEDED TONIGHT FOR THE LAKESHORE COUNTIES FROM OTTAWA COUNTY 
NORTH.

SURFACE LOW OVER NORTHWESTERN ILLINOIS IS EXPECTED TO TRACK 
NORTHEAST INTO SRN WI BY THIS EVENING AS AN ASSOCIATED UPPER PV 
ANOMALY SWINGS TOWARDS THE AREA AROUND THE STACKED UPPER LOW. RADAR 
INDICATES INCREASED COVERAGE IN SNOW AS MINOR VORT LOBES ROTATE INTO 
SW LOWER AHEAD OF THE MORE SUBSTANTIAL PV ANOMALY CROSSING FROM IA 
INTO IL. THIS AREA OF SNOW IS MAKING SLOW PROGRESS TOWARDS OUR 
CWFA...POSSIBLY DUE TO DRY LOWER LEVELS OVER OUR SW ZONES NOTED IN 
THE LAPS SOUNDINGS. EXPECT DEEP SATURATION TO BE REALIZED WITHIN A 
MATTER OF HOURS.

FAVORED NAM12 IS SHOWING IMPRESSIVE CONVERGENCE ASSOCIATED WITH A 
WIND CONFLUENCE AXIS ALONG THE LAKESHORE. THIS COMBINED WITH 
FRICTIONAL SHORELINE CONVERGENCE AND DEEP SATURATED PROFILES ALL 
SUGGEST THAT ADVISORY SNOWS WILL BE LIKELY NEAR THE LAKESHORE.

AHEAD OF THIS PV FEATURE...FORECAST SOUNDING SHOW CONVECTIVE LAYER 
DEPTH GROWING TO NEARLY 700 MB WITH CONVECTIVE INSTABILITY IN THE 
DGZ. BASED ON THIS...WOULD NOT BE SURPRISED TO SEE SOME LOCALIZED 
HIGHER SNOWFALL REPORTS APPROACHING 10 INCHES. AS WE EXPECT THESE 
REPORTS TO BE VERY LOCALIZED...WE ARE NOT INCLINED TO GO WITH A 
WARNING AT THIS POINT. SNOW IN THE ADVISORY AREA SHOULD BEGIN TO 
TAPER OFF AROUND SUNRISE SUNDAY. 

&&

.LONG TERM...(345 PM EST SAT DEC 26 2009)
(MONDAY THROUGH SATURDAY)

LAKE EFFECT SNOW SHOWERS ARE ANTICIPATED MONDAY AS H8 TEMPS FALL TO 
AROUND -14 C. LES WILL GRADUALLY WIND DOWN MONDAY NIGHT AS HIGH 
PRESSURE BUILDS IN. TRANQUIL WX WILL CONTINUE THROUGH MIDDAY 
WEDNESDAY WITH HIGH PRESSURE IN CONTROL. 

THE NEXT LOW PRESSURE SYSTEM WILL MOVE IN WEDNESDAY NIGHT BRINGING 
SOME LIGHT SNOW WEDNESDAY NIGHT THROUGH THURSDAY NIGHT.  

IT WILL TURN COLDER FRIDAY AND SATURDAY BEHIND THAT LOW PRESSURE 
SYSTEM AND AS HIGH PRESSURE BUILDS INTO THE NORTHERN PLAINS STATES. 
THIS WILL RESULT IN STRONG NORTH FLOW CAA FRIDAY AND SATURDAY. WE 
HAVE TRENDED THE MAX TEMP FCST COLDER FOR THAT TIME FRAME BASED ON 
THIS NOTION AND MEX NUMERICAL GUIDANCE TRENDS. 

&&

.AVIATION...(1240 PM EST SAT DEC 26 2009)
AREA OF LAKE ENHANCED SNOW IS APPROACHING SW LOWER MI...SO HAVE 
THEREFORE GONE MORE PESSIMISTIC WITH CIGS/VSBYS BEGINNING AROUND 
18Z. BIGGEST IMPACTS SHOULD BE AT KMKG. EXPECT FUEL ALTERNATE 
CONDITIONS TO PREVAIL WITH A BRIEF PERIOD OF LIFR OVERNIGHT AS 
HEAVIEST LAKE ENHANCED SNOW GETS GOING AFT 00Z. 

EXPECT GENERALLY BETTER CONDITIONS FROM W TO E OVERNIGHT WITH ONLY 
BRIEF MVFR CONDS AT KJXN AND KLAN. CONFIDENCE IN FORECAST DECREASES 
FROM EAST TO WEST. IT IS POSSIBLE THAT MORE PESSIMISTIC IFR 
CONDITIONS COULD BE SEEN AT GRR...AZO...AND BTL. CONDITIONS ARE 
EXPECTED TO IMPROVE AT INLAND TAF SITES AFT 12Z.

&&

.MARINE...(345 PM EST SAT DEC 26 2009)
THE LATEST LOCAL RUN OF THE GLERL WAVE MODEL SUGGESTS WAVES HAVE 
SUBSIDED...ESPECIALLY SOUTH OF HOLLAND. WILL THEREFORE MAINTAIN THE 
SMALL CRAFT ADVISORIES NORTH OF HOLLAND AS GREATER FETCH...GUSTY 
WINDS AND COLD AIR ADVECTION WILL LIKELY KEEP CONDITIONS HAZARDOUS 
FOR SMALL CRAFT THROUGH THIS EVENING. REDUCED VISIBILITIES AT 
COASTAL WEBCAMS DUE TO SNOW MAKE IT A BIT DIFFICULT TO CORROBORATE 
THE WAVE HEIGHTS ADVERTISED BY THE WAVE MODEL...SO WILL ERR ON THE 
SIDE OF CAUTION. EXPECT REMAINING ADVISORY CAN BE DROPPED BY EVENING.

AFTER A BRIEF BREAK IN THE ACTION SUNDAY...AN ARCTIC FRONT MONDAY 
SHOULD PUT WINDS AND WAVES WELL BACK INTO SCA TERRITORY.

&&

.HYDROLOGY...(345 PM EST SAT DEC 26 2009)
NO CONCERNS ARE ANTICIPATED IN THE SHORT TERM DUE TO MODEST RUNOFF 
AND COLD TEMPERATURES. UNSEASONABLY COLD TEMPERATURES FRIDAY AND 
SATURDAY COULD RESULT IN INCREASED ICE JAM POTENTIAL INTO THE 
WEEKEND.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY THIS EVENING AND TONIGHT FOR    
     MASON...OCEANA...MUSKEGON...AND OTTAWA COUNTIES.

LM...SMALL CRAFT ADVISORY THROUGH 06Z SATURDAY NIGHT FOR 
     THE ENTIRE NEAR SHORE.

&&

$$

SYNOPSIS:     TJT
SHORT TERM:   TJT
LONG TERM:    LAURENS
AVIATION:     TJT
MARINE:       TJT
HYDROLOGY:    TJT