FXUS63 KGRR 021806
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
107 PM EST WED DEC 2 2009

LATEST UPDATE...AVIATION...

.SYNOPSIS...(406 AM EST WED DEC 2 2009)
LOW PRESSURE OVER LOUISIANA IS BEGINNING TO MOVE NORTHEAST TOWARD 
THE GREAT LAKES. CLOUDS WILL INCREASE TODAY AHEAD OF THE LOW AND 
LIGHT RAIN WILL MOVE INTO SOUTHERN LOWER MICHIGAN BY LATE AFTERNOON. 
AS COLDER AIR GETS WRAPPED IN ON THE BACK SIDE OF THE LOW TONIGHT 
THE RAIN WILL TURN TO SNOW. LIGHT ACCUMULATIONS ARE POSSIBLE. LAKE 
EFFECT SNOW SHOWERS WILL THEN DEVELOP THURSDAY AND CONTINUE INTO THE 
WEEKEND. ACCUMULATIONS ARE POSSIBLE FROM THURSDAY THROUGH SATURDAY. 
 

&&

.SHORT TERM...(1228 PM EST WED DEC 2 2009)
(THIS AFTERNOON)
LOW PRESSURE IS MOVING FROM NORTHERN MISSISSIPPI AT MIDDAY INTO 
TENNESSEE. PRESSURE FALLS PLACE IT ON A PATH TOWARD EASTERN 
KENTUCKY. A LARGE RAIN SHIELD IS IN PLACE NORTH OF THE LOW SURGING 
OUT OF THE OHIO VALLEY. GOING FORECAST WAS IN GOOD SHAPE...WITH RAIN 
SPREADING INTO THE SOUTH LATE IN THE DAY AND HIGH TEMPERATURES IN 
THE UPPER 40S TO AROUND 50.

FOCUS IS ON THE LOW MOVING INTO THE EASTERN LAKES TONIGHT AND THE 
CHANCES FOR SNOW THE NEXT FEW DAYS. AT FIRST GLANCE...LOOKS LIKE 
RAIN CHANGING TO SNOW TONIGHT WITH THE POTENTIAL FOR SOME SMALL 
ACCUMULATIONS. MAYBE AROUND AN INCH OF SLUSHY SNOW BEFORE IT ENDS.  
THERE IS SOME DISCREPANCY THOUGH WITH THE NAM SHOWING MAINLY RAIN 
WITH LITTLE IN THE WAY OF SNOW...GFS IS WARMER. ISSUES TONIGHT FOR 
SNOW REVOLVE AROUND THE FACT THAT WE ARE IN THE UPPER 40S NOW AND WE 
HAVE A WARM GROUND (2 INCH DEPTH SOIL TEMPS AROUND 40). 
THEREAFTER...LAKE EFFECT SNOW IS THE FOCUS. DEPTH OF MOISTURE MAY BE 
AN ISSUE WITH THE LAKE EFFECT...BUT MORE ON THIS WITH THE AFTERNOON 
FORECAST ISSUANCE.

&&

.LONG TERM...(406 AM EST WED DEC 2 2009)
(FRIDAY NIGHT THROUGH TUESDAY)

OUR PRIMARY FCST CHALLENGE IN THE LONG TERM DEALS WITH POTENTIAL FOR 
ACCUMULATING LAKE EFFECT SNOW FRIDAY NIGHT THROUGH SATURDAY.

CONTINUED COLD AIR ADVECTION FRIDAY NIGHT ALONG WITH A FAVORABLE 
MOISTURE PROFILE SUPPORTS ACCUMULATING LAKE EFFECT SNOWS.  THE BEST 
LOW LEVEL CONVERGENCE IS ROUGHLY ALONG AND WEST OF HIGHWAY 131.  IF 
THE NAM ENDS UP RIGHT WE WILL LIKELY NEED HEADLINES AS IT FEATURES 
STRONGER UPWARD MOTION IN THE DGZ.

FOR SAT...THE FLOW BACKS FROM WSW TO SSW.  THE LOW LEVEL CONVERGENCE 
AXIS SHIFTS UP TO NEAR LDM.  AT 12Z THE COLDEST AIR AT 850 MB IS 
STILL ADVECTING IN FROM THE SW.  SO IT APPEARS TO ME THAT 
ACCUMULATIONS ARE LIKELY FOR MY NW COUNTIES.  I ADDED LIKELY POPS TO 
THE FORECAST FOR SAT MAINLY FOR THE LAKESHORE COUNTIES NORTH OF 
LWA.  I DO FEEL THAT WE WILL NEED TO MONITOR THE FORECAST CLOSELY 
FOR SAT AS INCREASING FETCH AND POTENTIAL MOISTURE ADVECTION AT 700 
MB...COULD ENHANCE THE SNOW RATES.

THE MOISTURE DEPTH FALLS SAT NIGHT INTO SUNDAY...THUS I WILL GO NO 
HIGHER THAN CHANCE POPS. 

&&

.AVIATION...(107 PM EST WED DEC 2 2009)
BETTER THAN IFR CONDITIONS ACROSS THE TAF SITES WILL CONTINUE INTO 
THE EVENING. A SYSTEM MOVING NORTHWARD TOWARD THE REGION WILL BRING 
IN HIGH AND MID LEVEL CLOUDS THIS AFTERNOON WITH SOME MVFR CEILINGS 
MOVING IN THIS EVENING. THIS WILL BE FOLLOWED BY RAIN AND FOG... 
WHICH WILL HELP TO REDUCE VISIBILITIES TO BELOW 3 MILES FROM 
APPROXIMATELY 04Z THROUGH 11Z.  

COLDER AIR WILL MOVE INTO THE AREA FROM THE NORTHWEST AND WEST 
TONIGHT WITH LOW LEVEL LAKE EFFECT CLOUDS AND SHOWERS. LOOKING FOR 
CEILINGS TO REMAIN MOSTLY ABOVE IFR LEVELS. DELAYED THE MIX WITH 
SNOW UNTIL LATE TONIGHT... AS THE WARMER PUSH FROM THE SOUTHERN 
SYSTEM SHOULD DOMINATE. KEPT PRECIPITATION GOING THROUGH THE DAY 
TOMORROW... THOUGH IT/S POSSIBLE THAT THERE MAY BE A BREAK LATE IN 
THE MORNING INTO THE AFTERNOON AS THE SOUTHERN SYSTEM PULLS OUT AND 
LAKE EFFECTS INCREASE AND REORIENT.

&&

.MARINE...(1225 PM EST WED DEC 2 2009)
NORTH WINDS WILL INCREASE TODAY INTO TONIGHT WHICH WILL BUILD WAVES 
INTO THE 5 TO 8 FOOT RANGE. EXTENDED THE SMALL CRAFT ADVISORY 
THROUGH THURSDAY AT THIS POINT AS WAVES WILL COME UP THIS EVENING 
AND REMAIN A HAZARD TO SMALL CRAFT AT LEAST INTO THE DAY ON THURSDAY.

&&

.HYDROLOGY...(406 AM EST WED DEC 2 2009)
NO HYDRO ISSUES EXPECTED. A QUARTER TO HALF INCH OF RAIN/SNOW EQUIV 
IS EXPECTED DURING THE NEXT 36 HRS. THAT AMOUNT OF LIQUID LIKELY 
WON/T BE ENOUGH TO CAUSE ANY HYDRO CONCERNS.  

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...SMALL CRAFT ADVISORY ST. JOSEPH TO MANISTEE THROUGH THURSDAY.
&&

$$

SYNOPSIS:     93
SHORT TERM:   93
LONG TERM:    MJS
AVIATION:     IOD
MARINE:       DUKE
HYDROLOGY:    93