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000
FXUS63 KGRR 081718
AFDGRR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1218 PM EST SUN DEC 8 2013

LATEST UPDATE...
AVIATION

.SYNOPSIS...
ISSUED AT 325 AM EST SUN DEC 8 2013

A WEAK LOW PRESSURE SYSTEM WILL BRING LIGHT SNOW THIS AFTERNOON
THROUGH TONIGHT WITH AN INCH OR TWO OF ACCUMULATION BY MONDAY
MORNING. COLD WEATHER WILL CONTINUE THROUGH THE UPCOMING WEEK WITH
OCCASIONAL SNOW SHOWERS.

&&

.UPDATE...
ISSUED AT 1157 AM EST SUN DEC 8 2013

DID NOT MAKE MUCH IN THE WAY OF CHANGES TO THE GOING FORECAST AS
IT STILL APPEARS ON TRACK. THE BULK OF THE SNOW WILL HOLD OFF
UNTIL AFTER DARK...SO ANY ACCUMULATIONS THIS AFTERNOON WILL BE
LIMITED. THE BEST CHANCE AT SEEING SOME LIGHT ACCUMULATIONS THOUGH
PRIOR TO NIGHTFALL WILL BE ALONG THE I-94 CORRIDOR. DRY AIR
REMAINS IN THE LOWER LEVELS THIS MORNING...WHERE THE DTX SOUNDING
WAS QUITE DRY BELOW 700MB/S. ILX/S SOUNDING ON THE OTHER HAND
SHOWED A DISTINCT MOISTENING ABOVE 850MB/S. THE MOISTENING OVER
SOUTHWEST LOWER MICHIGAN WILL OCCUR THIS AFTERNOON AND EARLY
EVENING. SNOW WILL SPREAD INTO THE AREA THIS AFTERNOON...IT WILL
JUST BE ON THE LIGHT SIDE. HAVE LIKELY POPS IN ALL AREAS AFTER
21Z. TEMPERATURES WILL BE ON THE COLD SIDE ONLY TOPPING OUT AROUND
20 ACROSS CENTRAL LOWER AND THE LOWER 20S FOR THE MOST PART
ELSEWHERE.

&&

.SHORT TERM...(TODAY THROUGH TUESDAY AFTERNOON)
ISSUED AT 325 AM EST SUN DEC 8 2013

PRIMARY SHORT TERM FORECAST CONCERNS INVOLVE DETERMINING SNOW
ACCUMULATIONS THIS AFTERNOON THROUGH TONIGHT AND WITH LAKE EFFECT
SNOW SHOWERS EARLY IN THE WEEK.

LIGHT SNOW WILL DEVELOP FROM SW TO NE ACROSS OUR FCST AREA THIS
AFTERNOON AND EVENING AS A WEAK LOW PRESSURE SYSTEM MOVES INTO THE
REGION. SNOW SHOULD BECOME STEADIEST THIS EVENING WITH A BURST OF
WARM AIR ADVECTION ENHANCEMENT AND AS STRONG MID LEVEL PVA OCCURS.

A CONSENSUS OF LATEST SHORT RANGE GUIDANCE AND SNOW TOOL DATA
SUGGESTS ACCUMULATIONS FROM THIS AFTERNOON THROUGH TONIGHT WILL BE
RATHER LIGHT WITH ONLY AROUND AN INCH OR TWO. THE RELATIVELY HIGHEST
TOTALS ARE EXPECTED NEAR TO NORTH OF A LINE FROM MUSKEGON TO MOUNT
PLEASANT AND LOCALIZED HIGHER TOTALS TO NEAR 3 INCHES ARE POSSIBLE
OVER OUR NORTHERNMOST COUNTIES. WE ALSO CANNOT RULE OUT SOME PATCHY
FREEZING DRIZZLE MONDAY MORNING AS DEEPER MOISTURE MOVES OUT BUT
DECENT LOW LEVEL MOISTURE LINGERS.

WESTERLY FLOW LAKE EFFECT SNOW SHOWERS WILL DEVELOP MONDAY THROUGH
MONDAY NIGHT AS H8 TEMPS FALL TO AROUND -14 TO -16 C BY MONDAY
AFTERNOON. MOISTURE DEPTH IS NOT IMPRESSIVE BUT SOME LIGHT
ACCUMULATIONS ARE EXPECTED MAINLY NEAR TO WEST OF US-131... ALTHOUGH
BRISK WEST WINDS WILL CARRY THE SNOW SHOWERS WELL INLAND MONDAY
MORNING AND AFTERNOON BEFORE WIND SPEEDS DIMINISH MONDAY NIGHT.
LIGHT SNOW SHOWERS AND FLURRIES WILL LINGER TUESDAY.

.LONG TERM...(TUESDAY NIGHT THROUGH SATURDAY)
ISSUED AT 325 AM EST SUN DEC 8 2013

PERSISTENT COLD CYCLONIC FLOW WILL RESULT IN MORE LAKE EFFECT SNOW
SHOWERS TUESDAY NIGHT AND WEDNESDAY WITH SOME ADDITIONAL
ACCUMULATIONS LIKELY.

THE ECMWF AND GFS ARE IN GOOD AGREEMENT IN SHOWING A WELL DEFINED
SHORTWAVE DROPPING DOWN FROM THE NORTHWEST DURING THIS TIME...WHICH
SHOULD PROMOTE AN INCREASE IN THE INTENSITY AND COVERAGE OF SNOW
SHOWERS DUE TO DEEPER MOISTURE AND A BUMP IN INVERSION HEIGHTS.

THERE IS ALSO A SURFACE TROUGH WHICH IS PROGGED TO COME THROUGH ON
WEDNESDAY AND THE ECMWF IS MOST PRONOUNCED WITH THIS FEATURE. THE
SFC TROUGH SHOULD ENHANCE LOW LEVEL CONVERGENCE AND POSSIBLY LEAD TO
A HEALTHY I-94/I-96 CONVERGENCE BAND WITH SOME OF THE HEAVIER SNOW
SHOWERS SPREADING WELL INLAND TOWARD JXN FOR A TIME.

THE FLOW SWINGS AROUND TO THE NORTHWEST BEHIND THE SFC TROUGH BY
LATE WEDNESDAY WITH MORE -20C AIR AT H8 COMING IN BEHIND IT.
MOISTURE BECOMES SHALLOWER WEDNESDAY NIGHT AND THURSDAY WITH A
SURFACE HIGH/ANTICYCLONIC FLOW BUILDING IN. THIS SHOULD LEAD TO AN
OVERALL DECREASE IN THE INTENSITY OF THE LAKE EFFECT... BUT A FEW
LIGHT SNOW SHOWERS WILL LIKELY STILL PERSIST WEST OF HIGHWAY 131.

FORECAST CONFIDENCE DECREASES SUBSTANTIALLY TOWARD THE END OF THE
WEEK AS ECMWF AND GFS SOLUTIONS ARE VERY DIFFERENT. THE ECMWF KEEPS
THE COLD AIR LOCKED IN ACROSS THE GRTLKS RGN WITH NORTH/NORTHEAST
LOW LEVEL FLOW WHILE THE GFS SHOWS WARM ADVECTION /SOUTHWEST FLOW/
AHEAD OF A PLAINS LOW. 00Z MOS GUIDANCE HIGH TEMPS FROM THE ECMWF
FOR FRI/SAT FOR GRR ARE 22/18 WHILE THE GFS HAS 33/36.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 1218 PM EST SUN DEC 8 2013

LATEST RADAR SHOWS LIGHT SNOW TRYING TO OVERCOME THE DRY AIR IN
THE LOWER LEVELS. A FEW MVFR CIGS NOTED SOUTH OF THE TAF SITES IN
ADDITION TO KJXN. WOULDN/T BE SURPRISED TO SEE KJXN GO VFR FOR A
COUPLE OF HOURS. CENTRAL IL/IN SEEMS TO BE THE AREA WHERE CIGS
CONSISTENTLY GO MVFR. THAT WILL EVENTUALLY MOVE INTO LOWER
MICHGIAN LATER THIS AFTERNOON AS LIGHT SNOW CONTINUES TO TRY TO DEVELOP.

A FEW HOUR PERIOD OF FREEZING DRIZZLE POSSIBLE OVERNIGHT TOO
BEFORE PCPN ENDS EARLY MONDAY MORNING.

&&

.MARINE...
ISSUED AT 325 AM EST SUN DEC 8 2013

FAIRLY MINIMAL WAVE ACTION IS ANTICIPATED TODAY THROUGH THIS EVENING
DUE TO OFFSHORE FLOW. WAVE HEIGHTS WILL BEGIN TO RAMP UP VERY LATE
TONIGHT AND ESPECIALLY MONDAY AS WINDS VEER TO THE WEST AND
STRENGTHEN TO AROUND 20 TO 30 KTS. A SMALL CRAFT ADVISORY WILL
LIKELY BE NEEDED FOR MONDAY. WAVE HEIGHTS MONDAY SHOULD REACH AT
LEAST 5 TO 8 FEET.


&&

.HYDROLOGY...
ISSUED AT 325 AM EST SUN DEC 8 2013

ICE FORMATION ON AREA RIVERS WILL CONTINUE AS TEMPERATURES REMAIN
BELOW FREEZING THROUGH THE UPCOMING WEEK. RIVER WATER TEMPERATURES
AROUND THE AREA RANGE FROM 0C TO +4C AND CONCERN REMAINS FOR
POTENTIAL ICE JAM ISSUES. WE WILL CONTINUE TO MONITOR AREA RIVER
LEVELS.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
LM...NONE.
&&

$$

UPDATE...DUKE
SYNOPSIS...LAURENS
SHORT TERM...LAURENS
LONG TERM...MEADE
AVIATION...93
HYDROLOGY...LAURENS
MARINE...LAURENS