FXUS63 KGRR 142323
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
623 PM EST MON DEC 14 2009

LATEST UPDATE...AVIATION...

.SYNOPSIS...(442 PM EST MON DEC 14 2009)
A STORM SYSTEM TRACKING THROUGH LOWER MICHIGAN LATE THIS AFTERNOON 
WILL BE FOLLOWED BY ARCTIC AIR THAT WILL BRING LAKE EFFECT SNOW 
SHOWERS TO SOUTHWEST LOWER MICHIGAN LATE TONIGHT THROUGH WEDNESDAY. 
THE HEAVIEST SNOW SHOWERS WILL BE WEST OF ROUTE 131 AND NORTH OF 
MUSKEGON LATE TONIGHT INTO TUESDAY AFTERNOON. THE CENTER OF A LARGE 
HIGH PRESSURE SYSTEM WILL MOVE SOUTH OF THE GREAT LAKES WEDNESDAY 
AND THAT WILL BRING A RETURN FLOW OF SLIGHTLY MILDER AIR FOR 
THURSDAY.  

&&

.SHORT TERM...(442 PM EST MON DEC 14 2009)
(TONIGHT THROUGH WEDNESDAY NIGHT)
THE MAIN FOCUS WILL BE THE LAKE EFFECT SNOW SHOWERS BETWEEN 06Z AND 
22Z TUESDAY AS THE ARCTIC AIR SURGES IN BEHIND THE DEPARTING STORM 
SYSTEM. 

THIS EVENING THE COLD FRONT AT 4 PM WAS OVER LAKE MICHIGAN AND 
SHOULD CROSS THE ENTIRE CWA BY 8 PM. THERE IS A BAND OF SHOWERS WITH 
THE FRONT AND IT JUST MAY MIX WITH SNOW AT TIMES AS THE FRONT IS 
COMING THROUGH. THE MAIN AREA OF SNOW NORTH OF THE TRACK OF THE 
SURFACE LOW WAS OVER THE NORTHERN 1/3 OF LOWER MICHIGAN AND WILL BE 
EXITING THE STATE BY 8 PM. WHAT FOG THAT IS AROUND WILL BE LIFTED AS 
THE COLD FRONT MOVES THROUGH THE AREA EARLY THIS EVENING. 

AS IT TURNED OUT...USING THEN NAM12 WITH THE RH IN THE DGZ COMBINED 
WITH THE LIFT IN THAT LAYER HAS BEEN MATCHING THE AREA OF 
PRECIPITATION BEST OF ANY TOOL I HAVE USED TODAY. SO I USED THAT TO 
MAKE THE REST OF THE FORECAST. THIS TOOL SHOWS MOST OF THE LIFT OUT 
OF THE CWA BY 8 PM SO IF YOU DO NOT SEE PRECIPITATION BY 8 PM MORE 
THAN LIKELY YOU WILL NOT SEE ANY UNTIL THE LAKE EFFECT SNOW SHOWERS 
KICK IN AFTER MIDNIGHT. 

LATE TONIGHT THE COLD AIR COMES IN AT LOW AND MID LEVELS AND THAT 
BRINGS ENOUGH LIFT WITH THE NORTHWEST FLOW TO SATURATE THE DGZ OVER 
THE NORTHWEST MOST FIVE COUNTIES IN OUR CWA. WITH THE BEST LIFT IN 
THE DGZ IN THOSE COUNTIES I DECIDED TO ISSUE A LAKE EFFECT SNOW 
ADVISORY SINCE THERE IS A STRONG CORRELATION BETWEEN HAVING THE BEST 
LIFT IN THE DGZ (SURFACE AIR BEING COLD ENOUGH) AND HAVING HEADLINE 
CRITERIA SNOWFALLS. SINCE THIS ONLY LAST FOR ABOUT 18 HOURS... I 
WOULD SEEM THERE WOULD NOT BE ENOUGH SNOW FOR A WARNING BUT IT WOULD 
BE ENOUGH FOR 3 TO 5 INCHES. SOUTH OF MKG NOT MUCH LIFT AND 
INVERSION HEIGHTS ARE MUCH LOWER SO I DO NOT EXPECT MORE THAN LIGHT 
SNOW SHOWERS THERE.

TUESDAY NIGHT AND WEDNESDAY THE HIGH MOVES INTO THE AREA AND 
INVERSION HEIGHTS ARE WAY TO LOW FOR SIGNIFICANT SNOWFALL EVEN IF 
THE WINDS ARE FROM THE WEST AND 850 MB TEMPS BELOW -10C. 

.LONG TERM...(442 PM EST MON DEC 14 2009)
(THURSDAY THROUGH MONDAY)
MID RANGE MODELS SHOWING SIMILAR SOLUTIONS BUT SETUP GIVES ME LOW 
CONFIDENCE. ONLY SMALL GRID CHANGES MADE DUE TO LOW CONFIDENCE.

LOW PRESSURE PASSING THROUGH THE AREA TODAY IS SHOWN PULLED INTO A 
STRONG GYRE OVER THE NORTHEASTERN PORTION OF THE CONTINENT. THE 12Z 
ECMWF SHOWS THE CENTER MOVING BACK TO THE WEST WITH A LOBE SWINGING 
TO THE SOUTH AND DEVELOPING OVER THE GREAT LAKES FRIDAY NIGHT INTO 
SATURDAY. THE 12 GFS HAS THE ENTIRE ROTATION RETROGRADING AND 
PASSING TO THE SOUTH SOUTHEAST OVER THE REGION. BOTH SOLUTIONS HAVE 
AIR AT 850 MB COLD ENOUGH FOR LAKE EFFECT SNOW FOR MOST OF THE 
EXTENDED PERIOD IN NORTHWEST FLOW. 

TEMPERATURES THROUGH THE PERIOD LOOK TO SLIGHTLY BELOW NORMAL.

&&

.AVIATION...(623 PM EST MON DEC 14 2009)
COLD FRONT WILL BE MOVING THROUGH THIS EVENING...PUTTING AN END TO 
THE DRIZZLE AND FOG. CEILINGS WILL SLOWLY COME UP OVERNIGHT BUT LAKE 
EFFECT SNOW SHOWERS WILL BE DEVELOPING AND COULD AFFECT VISIBILITY 
AT MKG AND TO A LESSER EXTENT GRR AND AZO. LOOKING AT MOSTLY MVFR 
CONDITIONS IN LAKE EFFECT CLOUDS AND SNOW SHOWERS AFTER 06Z. 
NORTHWEST WINDS WILL BE PICKING UP AFTER 12Z...WITH GUSTS OVER 20 
KNOTS BY 18Z.

&&

.MARINE...(442 PM EST MON DEC 14 2009)
COLD AIR AND NORTHWEST WINDS OF 15 TO 25 KNOTS WILL BE ENOUGH TO 
BUILD WAVES TO UP TO 8 FEET TUESDAY. THUS THE SMALL CRAFT ADVISORY 
WAS CONTINUED THROUGH TUESDAY NIGHT.

&&

.HYDROLOGY...(442 PM EST MON DEC 14 2009)
WITH LITTLE IN THE WAY OF RAIN AND TEMPERATURES EXPECTED TO BE BELOW 
FREEZING FOR SEVERAL DAYS THERE ARE NO SIGNIFICANT HYDRO ISSUES.
 

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...LAKE EFFECT SNOW ADVISORY FOR MASON...LAKE...OCEANA...NEWAYGO 
AND MUSKEGON COUNTIES FROM 1 AM THROUGH 5 PM ON TUESDAY. 
LM...SMALL CRAFT ADVISORY IN EFFECT FROM 1 AM TUESDAY TO 5 AM EST
WEDNESDAY FOR THE ENTIRE NEAR SHORE.

&&

$$

SYNOPSIS:     WDM
SHORT TERM:   WDM
LONG TERM:    63
AVIATION:     OSTUNO
MARINE:       WDM
HYDROLOGY:    WDM