000
FXUS63 KGRR 211207
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
707 AM EST SAT DEC 21 2013

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 329 AM EST SAT DEC 21 2013

A STORM SYSTEM DEVELOPING TO OUR SOUTHWEST WILL BEGIN TO MOVE INTO
THE AREA FROM THE SOUTH TODAY AND CONTINUE TO IMPACT THE AREA
THROUGH THE DAY ON SUNDAY. THIS SYSTEM WILL BRING MAINLY SNOW TO THE
NORTHWEST PORTION OF THE AREA...FREEZING RAIN ACROSS SOUTH CENTRAL
AND SOUTHEAST LOWER MICHIGAN...WITH A WINTRY MIX IN BETWEEN.

COLDER AIR WILL THEN MOVE IN ACROSS THE AREA LATER ON SUNDAY AND
REMAIN IN PLACE MOST OF THE UPCOMING HOLIDAY WEEK. OCCASIONAL
CHANCES OF SNOW SHOWERS CAN BE EXPECTED WITH SOME ACCUMULATIONS
LIKELY...ESPECIALLY CLOSER TO THE LAKESHORE.

&&

.SHORT TERM...(TODAY THROUGH SUNDAY NIGHT)
ISSUED AT 329 AM EST SAT DEC 21 2013

THE MAIN FOCUS OF THE SHORT TERM IS THE STORM SYSTEM EXPECTED TO
IMPACT THE AREA BEGINNING TODAY AND LASTING THROUGH SUNDAY. WE HAVE
TRANSITIONED THE HEADLINES FROM THE WATCH...TO AN ICE STORM WARNING
ACROSS THE FAR SE CORNER OF THE CWFA. ADVISORIES HAVE BEEN ISSUED
FOR THE REMAINDER OF THE CWFA FOR SNOW ACROSS THE NORTH AND A WINTRY
MIX ACROSS THE MIDDLE SECTION OF THE CWFA. NO MAJOR CHANGES IN THE
FCST HAVE BEEN MADE AS THE CONSENSUS OF THE MODELS IS GENERALLY
CONSISTENT WITH THE PREVIOUS RUNS.

WE WILL NEED TO DEAL WITH SOME FOG ISSUES ACROSS THE SOUTH THIS
MORNING.

THE GREATEST IMPACT OF THE INCOMING STORM SYSTEM LOOKS TO BE THE
THREAT OF RELATIVELY SIGNIFICANT AMOUNTS OF FREEZING RAIN/ICING
EXPECTED ROUGHLY SE OF I-69 LATER TODAY AND INTO THE EARLY OVERNIGHT
HOURS TONIGHT. WE EXPECT RAIN AND OR FREEZING RAIN TO START PUSHING
UP INTO THE SRN COUNTIES TOWARD THE AFTERNOON TODAY. AREAS ALONG AND
SOUTH OF I-94 COULD START OUT BARELY ABOVE FREEZING AT THE ONSET OF
PCPN. WE EXPECT ALL PCPN DOWN ACROSS THE SE CORNER TO TRANSITION TO
FREEZING RAIN AS THE COLD AND SOMEWHAT DRIER NE FLOW WILL BRING
TEMPS DOWN DUE TO ADVECTION AND EVAPORATIVE COOLING.

QPF ACROSS THE SE COUNTIES LOOKS TO BE OVER AN INCH THROUGH THE
EARLY OVERNIGHT HOURS AS THEY BARELY GET UNDER THE NRN PERIPHERY OF
THE BEST MOISTURE AXIS WITH THIS SYSTEM. AN ABOVE FREEZING LAYER
ALOFT IS MAINTAINED MOST OF THE TIME AS THE SFC TEMPS DROP TO AROUND
OR JUST BELOW FREEZING. NOT ALL OF THIS QPF WILL GO INTO THE ICING
EXPECTED DUE TO LATENT HEAT AND RUNOFF PROCESSES. HOWEVER WITH THAT
MUCH QPF...EVEN A PORTION OF IT FREEZING WILL CREATE A GOOD COATING
OF ICE...UP AROUND HALF AN INCH WILL BE LIKELY.

THE TRANSITION IN P-TYPE WILL BE SOMEWHAT TRICKY ACROSS THE CENTRAL
PORTION OF THE CWFA NW OF I-69 TO ROUGHLY M-20. HOWEVER WE EXPECT
THAT FREEZING RAIN AND SLEET TO BE MORE PREVAILING WITH SOME SNOW
POSSIBLE. A SLIGHT ABOVE FREEZING LAYER WILL BE PRESENT WITH THE
LAYER THINNER AND COOLER AS YOU MOVE NW. QPF AMOUNTS WILL BE QUITE A
BIT LESS AS THE MOISTURE AXIS REMAINS SE OF THIS AREA. IT WILL BE
TOUGH TO GET HIGH IMPACT FREEZING RAIN AMOUNTS IN THIS AREA. HOWEVER
ONE THING TO CONSIDER IS THE GLAZE IN PLACE ALREADY FROM THE THU
NIGHT/FRI EVENT.

THE PCPN IN BOTH OF THESE AREAS IS EXPECTED TO LIGHTEN UP
SIGNIFICANTLY BETWEEN 06-12Z SUN AS THE DRY SLOT IS EXPECTED TO MOVE
OVER THESE AREAS. SOME LIGHT PCPN WILL REMAIN...HOWEVER WE COULD
SEE IT TRANSITION TO FZDZ AS THE DGZ BECOMES UNSATURATED.

BY THE TIME PCPN REACHES THE NRN PORTION OF THE CWFA...THE COLUMN
SHOULD BE MAINLY COLD ENOUGH TO SUPPORT MAINLY SNOW. THE SNOW SHOULD
START OUT LIGHT...AND PICK UP LATE TONIGHT/SUN MORNING AS THE BEST
DEFORMATION SLIDES ACROSS THE NRN COUNTIES AND NW OF THE CWFA. SNOW
AMOUNTS ARE GENERALLY EXPECTED TO REMAIN IN THE ADVISORY CATEGORY AS
THE UPPER LOW EJECTING WILL HAVE OPENED UP BY THE TIME IT REACHES
HERE AND THE FGEN IN THE DEFORMATION WILL NOT BE AS STRONG AS TO OUR
SW. ONE THING GOING FOR BETTER SNOW AMOUNTS HERE IS THE FACT THAT
THE DGZ IS EXPECTED TO REMAIN SATURATED AS THE DRY SLOT REMAINS SE
OF THIS AREA.

THE CAVEAT TO ALL OF THIS IS IF THE OUTLIER NAM IS CORRECT...ALL OF
THIS WOULD BE SHIFTING TO THE NW A LITTLE. WE BELIEVE AT THIS TIME
THAT WE HAVE A GOOD CONSENSUS OF THE TRACK OF THE SYSTEM WITH GOOD
RUN TO RUN CONSISTENCY FROM MOST OF THE GLOBAL MODELS AND IT SHOULD
BE WELL SAMPLED BY NOW WITH IT BEING WELL WITHIN THE RAOB NETWORK.

WE WILL SEE A TRANSITION TO SOME LAKE EFFECT SNOW SHOWERS ON SUN
NIGHT AS COLDER AIR COMES IN BEHIND THE SYSTEM. THE FLOW SHOULD BE
NNW WHICH WOULD FAVOR THE IMMEDIATE LAKESHORE FOR BEST SNOW SHOWER
CHANCES. THERE IS SOME DECENT MOISTURE UP THROUGH 15K FEET AND
OVER-LAKE INSTABILITY IS SUFFICIENT.

.LONG TERM...(MONDAY THROUGH FRIDAY)
ISSUED AT 329 AM EST SAT DEC 21 2013

THE UPCOMING CHRISTMAS WEEK WILL BE MORE LIKE WHAT WE HAVE SEEN FOR
MUCH OF DECEMBER: COLDER THAN NORMAL WITH FREQUENT CHANCES FOR SNOW
SHOWERS. THE NORTHERN BRANCH OF THE JET AND ARCTIC AIR WILL DOMINATE
THROUGHOUT THE WEEK... WITH SEVERAL SHORTWAVES AND SFC
TROUGHS/FRONTS SWINGING THROUGH THE GRTLKS RGN. TEMPERATURES ARE
EXPECTED BE BELOW FREEZING ALL WEEK... AND THE COLDEST DAY OF THE
WEEK WILL BE TUESDAY WHEN HIGHS SHOULD STRUGGLE TO REACH 20 BEHIND
THE FIRST NRN STREAM WAVE.

GFS/ECMWF ARE IN GOOD AGREEMENT SHOWING A POTENT SHORTWAVE IMPACTING
THE AREA MONDAY AFTERNOON AND NIGHT. SNOW SHOWERS ARE LIKELY AND
LAKE ENHANCEMENT WILL BE IN PLAY AS THIS FEATURE COMES THROUGH.
HOWEVER CONFIDENCE IN WIND DIRECTION IS LOW SINCE MODELS INDICATE A
WEST TO EAST ORIENTED SFC TROUGH SETTING UP SOMEWHERE ACROSS LWR MI
AND ARE NOT IN GREAT AGREEMENT WITH IT/S LOCATION AND RESULTANT
WINDS. NEVERTHELESS THE TROUGH SHOULD RESULT IN LOCALLY ENHANCED
CONVERGENCE WITH A LARGE PORTION OF THE CWFA SEEING SNOW SHOWERS AND
AT LEAST SOME LIGHT ACCUMULATIONS. IF A WESTERLY FLOW DEVELOPS THEN
AREAS ALONG AND WEST OF HWY 131 COULD SEE SEVERAL INCHES BUT AGAIN
WIND DIRECTION IS VERY QUESTIONABLE AT THIS TIME.

A BRIEF PERIOD OF SHORTWAVE RIDGING MOVES ACROSS FOR TUESDAY
AFTERNOON AND EVENING... THEN SOME WAA/ISENTROPIC LIFT LIGHT SNOW
POSSIBLE ON CHRISTMAS DAY AHEAD OF THE NEXT APPROACHING SHORTWAVE.
THE ECMWF HAS A MUCH STRONGER SHORTWAVE THAN THE GFS FOR THE 26TH
AND WOULD SUGGEST A DECENT ROUND OF ACCUMULATING LAKE ENHANCED SNOW
SHOWERS FOR THURSDAY AND THURSDAY NIGHT.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 706 AM EST SAT DEC 21 2013

WIDESPREAD LIFR CONDITIONS DUE TO LOW CLOUDS AND FOG WILL CONTINUE
TO PLAGUE ALL OF THE TERMINALS TODAY AND TONIGHT. FREEZING RAIN WILL
BREAK OUT AGAIN THIS AFTERNOON... STARTING EARLY THIS AFTERNOON
ALONG THE I-94 CORRIDOR THEN SPREADING NORTH TO THE I-96 CORRIDOR
BY LATE AFTERNOON WHERE SOME SLEET AND SNOW MAY MIX WITH THE FREEZING
RAIN AT THE ONSET. MKG SHOULD TEND TO BE MOSTLY SNOW AND SLEET AS
PRECIP DEVELOPS THERE EARLY THIS EVENING.

THE INTENSITY OF THE FREEZING RAIN/ICING IS EXPECTED TO BE
HEAVIEST DURING THE EVENING HOURS THEN DIMINISH AFTER 06Z TONIGHT.
MKG SHOULD BE THE EXCEPTION TO THIS... WHERE SNOW WILL CONTINUE
OVERNIGHT.


&&

.MARINE...
ISSUED AT 534 PM EST FRI DEC 20 2013

NORTHEAST FLOW WILL CONTINUE INTO SATURDAY NIGHT. THIS OFFSHORE FLOW
WILL HELP KEEP WAVES LOWER. HOWEVER AS WINDS PIVOT TO THE NORTH
NORTHWEST LATE SATURDAY NIGHT/EARLY SUNDAY MORNING WAVES WILL BUILD
AND WE WILL LIKELY NEED A SMALL CRAFT ADVISORY BY THEN.


&&

.HYDROLOGY...
ISSUED AT 325 PM EST FRI DEC 20 2013

THE FORECAST TREND IS TOWARDS LESS QPF OVER THE WEEKEND AS THE
TRACK OF THE LOW LOOKS TO STAY FURTHER SOUTH AND EAST OF THE RIVER
BASINS IN SOUTHWEST LOWER MICHIGAN. TOTAL QPF IS NOW EXPECTED TO
BE LESS THAN AN INCH FOR THE HEADWATERS OF THE GRAND AND ST.
JOSEPH BASINS.

SHARP RISES ARE STILL POSSIBLE AT THE JACKSON FORECAST POINT ON
THE GRAND RIVER AND WE WILL HAVE TO WATCH THE MODEL TRENDS CLOSELY
TONIGHT AND THE ACTUAL STORM DEVELOPMENT ON SATURDAY. SNOW MELT
COULD ALSO CONTRIBUTE TO RISES ACROSS THE ST. JOSEPH AND KALAMAZOO
BASINS BEFORE THE ARCTIC AIR RETURNS ON MONDAY...WITH ICE
REFORMING ON THE RIVERS.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...WINTER WEATHER ADVISORY FROM 4 PM THIS AFTERNOON TO NOON EST
     SUNDAY FOR MIZ051-052-056>059-064-065-071-072.

     ICE STORM WARNING FROM 1 PM THIS AFTERNOON TO 7 AM EST SUNDAY
     FOR MIZ066-067-073-074.

     WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 7 PM EST
     SUNDAY FOR MIZ037>040-043>046-050.

LM...NONE.
&&

$$

SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...MEADE
AVIATION...MEADE
HYDROLOGY...OSTUNO
MARINE...JK