FXUS63 KGRR 261150
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
645 AM EST SAT DEC 26 2009

LATEST UPDATE...AVIATION...

.SYNOPSIS...(435 AM EST SAT DEC 26 2009)
A SLOW  MOVING LOW PRESSURE SYSTEM OVER ILLINOIS WILL KEEP THE 
WEATHER COLD WITH SNOW SHOWERS HERE IN LOWER MICHIGAN THROUGH THE 
WEEKEND.  ACCUMULATIONS ARE POSSIBLE...ESPECIALLY NEAR THE 
LAKESHORE.  THIS SYSTEM WILL PULL AWAY SLOWLY EARLY NEXT WEEK WITH 
TEMPERATURES EXPECTED TO BE CLOSE TO NORMAL. 

&&

.SHORT TERM...(435 AM EST SAT DEC 26 2009)
(TONIGHT THROUGH MONDAY)

THE MAIN CHALLENGE IN THE SHORT TERM DEALS WITH THE SNOWFALL AMOUNTS 
AND TRENDS THROUGH THE WEEKEND.

FIRST OFF..THE FREEZING RAIN HAS ENDED... BUT A LAYER OF ICE IS 
UNDERNEATH THE SNOW.  CONDITIONS ARE LIKELY TO REMAIN SLICK ON ANY 
UNTREATED SURFACES THROUGH THIS MORNING.  SOME OF THE SNOW WILL BE 
LOCALLY HEAVY AS THE LOW LEVEL VORT MAX LIFTING NORTHWARD OUT OF 
INDIANA PIVOTS THROUGH SOUTHWEST LOWER MI.  CLOUD TOPS HAVE BEEN 
COOLING WITH THIS FEATURE AND RECENTLY KGSH DROPPED TO 3/4SM.  
MODELS DATA SUGGESTS THIS FEATURE WILL STRENGTHEN AS IT MIGRATES 
THROUGH THE AREA.  I WILL KEEP THE WINTER WEATHER ADVISORY GOING 
THROUGH THE MORNING AS TRAVEL IMPACTS ARE LIKELY DUE TO THE ICY 
SURFACES AND AREAS OF REDUCED VISIBILITIES.  

RATHER INTERESTING SETUP FOR LATER THIS AFTERNOON INTO TONIGHT.  
ANOTHER VORT LOBE PIVOTS IN FROM THE SOUTHWEST.  THE MOISTURE 
DEEPENS AS A THERMAL TROF AT 850 MB TO 700 MB ARRIVES. LOW LEVEL 
CONVERGENCE IS FOCUSED MAINLY WEST OF  HIGHWAY 131 FROM 00Z TO 06Z 
FROM THE NAM.  THIS RAISES THE RISK FOR SOME LOCALLY HEAVIER 
SNOW...ESPECIALLY UP THE LAKESHORE NORTH OF HOLLAND.     MAY NEED TO 
COVER THE SITUATION WITH ADVISORIES AND THERE IS EVEN A LOW RISK FOR 
A WARNING EVENT DEPENDING ON HOW THE SITUATION UNFOLDS.

ANOTHER LOW OF VORTICITY ARRIVES SUNDAY WITH THE ACTUAL COLD POOL 
ALOFT.  WILL FEATURE LIKELY POPS FOR MAINLY WESTERN COUNTIES AS 
ACCUMULATING SNOW IS EXPECTED.

WHILE THE UPPER COLD POOL IS PULLING AWAY ON MONDAY...A REINFORCING 
SHOT OF SHALLOW COLD AIR DROPS DOWN FROM THE NORTH.  THIS FEATURE 
WILL LIKELY KEEP THE SNOW SHOWERS GOING...ESPECIALLY NEAR THE 
LAKESHORE.  

&&

.LONG TERM...(435 AM EST SAT DEC 26 2009)
(MONDAY NIGHT THROUGH FRIDAY)
THE MID RANGE MODELS ARE IN DECENT AGREEMENT IN A SETUP WITH SLOW 
MOVING SYNOPTIC SCALE FEATURES. TIMING OF A SYSTEM APPROACHING THE 
REGION WEDNESDAY OR WEDNESDAY NIGHT IS THE MAIN ISSUE WITH THIS 
FORECAST PACKAGE. ONLY SMALL CHANGES NEEDED AND/OR MADE TO THE GRIDS.

LAKE EFFECT SNOW SHOWERS WILL BE WINDING DOWN AS HIGH PRESSURE 
BUILDS INTO THE REGION BEHIND A SLOW MOVING LOW PRESSURE SYSTEM 
MONDAY NIGHT. FAIRLY QUIET WEATHER IS THEN EXPECTED THROUGH TUESDAY 
NIGHT... AS THE RIDGE OF HIGH PRESSURE MOVES THROUGH THE GREAT LAKES 
REGION. 

THE NEXT LOW WILL APPROACH THE REGION LATE WEDNESDAY OR WEDNESDAY 
NIGHT. THE ECMWF MOVES THE LOW NORTH OF THE AREA WHILE THE GFS MOVES 
IT SLOWLY OVER THE AREA AS AN UPPER LEVEL LOW MEANDERS ACROSS THE 
REGION. WITH EITHER SOLUTION... SNOW AND UNSETTLED WEATHER WILL BE 
POSSIBLE FOR OUR FORECAST AREA THROUGH FRIDAY. THE SNOW LOOKS TO BE 
LIGHT IN THE LONG TERM PERIODS.

THE HIGH TEMPERATURES TUESDAY AND FRIDAY SHOULD BE A BIT BELOW 
NORMAL AS COOLER AIR IS MOVING IN ON THESE DAYS AND TEMPERATURES FOR 
THE REST OF THE LONG TERM SHOULD BE AROUND NORMAL. NORMAL LOWS ARE 
IN THE UPPER TEENS WITH NORMAL HIGHS AROUND 30 DEGREES F.

$$

.AVIATION...(645 AM EST SAT DEC 26 2009)
THE MAIN CHALLENGE WITH THE AVIATION FORECAST DEALS WITH THE TIMING 
OF THE ROUNDS OF SNOW.  AT KMKG...ANY IMPROVEMENT OF IFR IS EXPECTED 
TO BE TEMPORARY.

ONE WAVE OF LOW PRESSURE WAS TRACKING NORTHWARD  INTO THE AZO AREA 
AT 12Z.  TO THE NORTH OF THIS FEATURE CONDITIONS DUE TO SNOW WILL 
FALL DOWN TO AT LEAST IFR FOR PART OF THIS MORNING.  SOME 
IMPROVEMENT IS EXPECTED TO THE SOUTH OF THE WAVE FOR A FEW HOURS AT  
 MOST TAF SITES LATER THIS MORNING.  

ANOTHER WAVE WILL BE MOVING IN THIS AFTERNOON AND IS EXPECTED TO 
CAUSE CONDITIONS TO DROP BACK DOWN TO IFR...ESPECIALLY CLOSER TO THE 
LAKESHORE.  A RISK FOR LIFR EXISTS...ESPECIALLY AT KMKG AS THE 
MOISTURE WILL BE DEEP AND SOME LIFT WILL BE LOCATED WITHIN THIS 
MOISTURE.

&&

.MARINE...(435 AM EST SAT DEC 26 2009)
WILL MAINTAIN THE SMALL CRAFT ADVISORIES AS GUSTY WINDS AND COLD AIR 
ADVECTION WILL LIKELY KEEP CONDITIONS HAZARDOUS FOR SMALL CRAFT 
THROUGH TODAY.

&&

.HYDROLOGY...(435 AM EST SAT DEC 26 2009)
TEMPERATURES ARE FALLING AND THAT WILL LIKELY LOCK UP ANY ADDITIONAL 
RUNOFF FROM THE SNOW MELT AND RECENT RAINFALL.  SO WHILE RISES ARE 
EXPECTED ON AREA STREAMS AND RIVERS...THEY ARE EXPECTED TO BE 
MINIMAL.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY ALL COUNTIES UNTIL 11 AM SAT. 

LM...SMALL CRAFT ADVISORY THROUGH 6Z SATURDAY NIGHT FOR THE ENTIRE 
NEAR SHORE.

&&

$$

SYNOPSIS:     MJS
SHORT TERM:   MJS
LONG TERM:    63
AVIATION:     MJS
MARINE:       MJS
HYDROLOGY:    MJS