FXUS63 KGRR 151159
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
655 AM EST TUE DEC 15 2009

LATEST UPDATE...AVIATION...

.SYNOPSIS...(428 AM EST TUE DEC 15 2009)
COLDER AIR WILL FLOW INTO THE REGION THROUGH THE END OF THE WEEK. 
LAKE 
EFFECT SNOW SHOWERS WILL MAINLY AFFECT THE WESTERN PORTION OF LOWER 
MICHIGAN. ACCUMULATIONS UP TO 5 INCHES ARE POSSIBLE NORTH OF 
MUSKEGON AND WEST OF US-131 TODAY.    

&&

.SHORT TERM...(428 AM EST TUE DEC 15 2009)
(TODAY THROUGH THURSDAY)
FORECAST CONCERNS DEAL WITH LAKE EFFECT SNOW POTENTIAL THROUGH THE 
PERIOD. 

THIS EVENT IS A LITTLE SLOW TO UNFOLD BUT IS SLOWLY BEGINNING. 
KGRR-88D SHOWS LIGHT SHSN DEVELOPING OVER THE LAKE. NAM/GFS BUFKIT 
SHOW THE DGZ FALLING AND BECOMING SATURATED TOWARD SUNRISE. AROUND 
12Z OMEGA INCREASES DRAMATICALLY AS A SHORT WAVE...CURRENTLY SEEN ON 
IR IMAGERY CROSSING NRN WISCONSIN...MOVES OVER LAKE MICHIGAN. AS 
OMEGA NOSES INTO THE DGZ...PCPN EFFICIENCY WILL BE MAXED AND 
SNOWFLAKE SIZE WILL INCREASE. WE COULD SEE SNOWFALL RATES APPROACH A 
HALF INCH PER HOUR THIS MORNING IN THE ADVISORY AREA. WE/LL KEEP THE 
ADVISORY GOING AS THE HEAVIEST SNOW IS YET TO COME. 

NW FLOW IN THE BOUNDARY LAYER WILL CONTINUE TODAY. H8 TEMPS QUICKLY 
FALL TO AROUND -16C AS THE SHORT WAVES MOVES ACROSS AND THEN 
INCREASES LATE IN THE DAY. SHSN SHOULD DIMINISH A BIT LATE IN THE 
DAY AND MOVE WWD TOWARD THE LAKE. LIGHT SHSN WILL PERSIST INTO 
THURSDAY BUT WE DON/T ANTICIPATE MUCH ACCUMS. INVERSION HGTS FALL 
BEGINNING TONIGHT TO AROUND 3-4KFT. THAT TYPE OF CLOUD DEPTH WON/T 
PRODUCE MUCH SNOWFALL. 

TEMPS SHOULD FALL THIS AFTERNOON AS THE CORE OF THE ARCTIC AIR MOVES 
ACROSS THE LAKE. 

.LONG TERM...(428 AM EST TUE DEC 15 2009)
(THURSDAY NIGHT THROUGH MONDAY)
THERE IS SOME DISCREPANCY IN HOW THE UPPER PATTERN EVOLVES DURING 
THE LONG TERM...BUT BOTH THE GFS AND THE EURO INDICATE UPPER 
TROUGHING OVER THE GREAT LAKES THIS WEEKEND. SURFACE RIDGING SHOULD 
KEEP THINGS FAIRLY DRY TOWARD THE END OF THE WEEK...WITH THE 
POTENTIAL FOR SNOW SHOWERS THIS WEEKEND. TONIGHT/S MODEL RUNS DO NOT 
LOOK AS IMPRESSIVE AS LAST NIGHT/S IN REGARD TO THE WEEKEND LAKE 
EFFECT SNOW POTENTIAL. AT THIS POINT THOUGH MAINTAINED THE SNOW 
SHOWERS IN THE FORECAST. TEMPERATURES CONTINUE TO LOOK AT OR 
SLIGHTLY BELOW NORMAL.

&&

.AVIATION...(655 AM EST TUE DEC 15 2009)
COMPLEX WEATHER ACROSS SOUTHWEST LOWER MICHIGAN THIS MORNING WITH A 
SURFACE TROUGH SLIDING SOUTHEAST OF THE AREA. LOW CEILINGS REMAIN 
NEAR THE TROUGH AT KLAN AND KJXN. CEILINGS POP UP CONSIDERABLY RIGHT 
BEHIND IT WITH VFR CEILINGS PRESENTLY AT KAZO AND KGRR. LAKE EFFECT 
SNOW HAS COMMENCED IN THE WAKE OF THE TROUGH WITH SNOW NOW OCCURRING 
AT KMKG. CEILINGS SHOULD REBOUND INLAND THIS MORNING...BEFORE ALL 
SITES DROP DOWN ONCE AGAIN INTO THE MVFR CATEGORY. 

LAKE EFFECT SNOW SHOWERS SHOULD REACH THERE PEAK ACROSS ALL THE TAF 
SITES BETWEEN 14Z AND 20Z AS A MID LEVEL SHORTWAVE TROUGH SWINGS 
ACROSS THE AREA GIVING THE LAKE EFFECT A BOOST. EXPECT THE SNOW 
SHOWERS TO LOSE INTENSITY AND COVERAGE TOWARD EVENING...WITH MAINLY 
FLURRIES EXPECTED OVERNIGHT. MVFR CEILINGS WILL REMAIN THOUGH 
THROUGH THE NIGHT. 

&&

.MARINE...(428 AM EST TUE DEC 15 2009)
WAVES ARE INCREASING AS COLD AIR FLOWS OVER THE LAKE. WE EXTENDED 
THE SCA THROUGH WEDNESDAY MORNING TO ACCOUNT FOR THE WAVES. 

&&

.HYDROLOGY...(428 AM EST TUE DEC 15 2009)
NO HYDRO ISSUES.
 

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...LAKE EFFECT SNOW ADVISORY FOR MASON...LAKE...OCEANA...NEWAYGO 
AND MUSKEGON COUNTIES TODAY. 
LM...SMALL CRAFT ADVISORY IN EFFECT THROUGH WEDNESDAY MORNING FOR 
THE ENTIRE NEAR SHORE.

&&

$$

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