Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 241209
AFDGRB

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREEN BAY WI
609 AM CST WED DEC 24 2014

UPDATED AVIATION PORTION FOR 12Z TAF ISSUANCE

.SHORT TERM...TODAY...TONIGHT...AND THURSDAY
ISSUED AT 351 AM CST WED DEC 24 2014

PRIMARY FORECAST CONCERN WILL BE AREAS OF DENSE OF FOG OVER
EASTCENTRAL WISCONSIN THIS MORNING...THEN CHANCES FOR A MIX OF
LIGHT RAIN OR SNOW ALONG THE LAKESHORE AS DEEPENING SURFACE WAVE
MOVES ALONG BAROCLINIC ZONE TO OUR SOUTHEAST THIS AFTERNOON.

OF IMMEDIATE CONCERN EARLY THIS MORNING IS AREAS OF DENSE FOG THAT
HAD DEVELOPED OVERNIGHT OVER CENTRAL AND EASTCENTRAL WISCONSIN.
FOG IS THE RESULT AMPLE LOW-LEVEL MOISTURE IN VICINITY OF FRESH
SNOW COVER FROM YESTERDAYS SYSTEM...AND LIGHT WINDS NEAR SURFACE
TROUGH SITUATED OVER THE EASTERN HALF OF THE FORECAST AREA. THE
DENSE FOG WITH VISIBILITIES 1/4 MILE OR LESS HAS BEEN GENERALLY
CONFINED TO THE FOX VALLEY FROM OCONTO...TO GRB...SOUTH ACROSS THE
FOX RIVER VALLEY. IN ADDITION..CANNOT RULE OUT PATCHY FREEZING
DRIZZLE IN AREAS WHERE SURFACE TEMPERATURES MAY FALL AT OR BELOW
FREEZING. GIVEN LOCALIZED NATURE OF THE DENSE FOG...WILL CONTINUE
TO HANDLE WITH SPECIAL WEATHER STATEMENTS THIS MORNING. EXPECT
CONDITIONS TO GRADUALLY IMPROVE OVER THE FOX VALLEY AS SURFACE
NORTHERLY BOUNDARY LAYER WINDS DEVELOP IN THE WAKE OF DEPARTING
SURFACE TROUGH.

FURTHER WEST OVER CENTRAL WISCONSIN MAY STILL SEE SOME SCATTERED
FLURRIES...DRIZZLE OR FREEZING DRIZZLE NEAR MID-LEVEL TROUGH AXIS
THROUGH EARLY AFTERNOON.

APPEARS MODEL GUIDANCE HAS FINALLY LOCKED ON TO CYCLOGENESIS ALONG
BAROCLINIC ZONE TO OUR SOUTHEAST FOR LATER TODAY. VAST MAJORITY
OF GUIDANCE IS NOW TAKING DEEPENING SURFACE LOW ACROSS INDIANA TO
SOUTHEAST LOWER MICHIGAN DURING THE AFTERNOON AND EARLY EVENING.
WESTERN PERIPHERY OF THE ASSOCIATED DEFORMATION PRECIPITATION COMMA
HEAD LOOKS TO JUST GRAZE OUR LAKESHORE COUNTIES DURING THE MID TO
LATE AFTERNOON HOURS. APPEARS SURFACE BASED ABOVE FREEZING LAYER
WILL BE SUFFICIENTLY DEEP FOR MIXED LIGHT RAIN AND SNOW ALONG THE
LAKESHORE WITH ONLY MINOR SNOW ACCUMULATIONS AT BEST.

WEAK SURFACE RIDGE SHOULD THEN BUILD INTO THE FORECAST AREA
OVERNIGHT WITH WINDS TURNING WESTERLY...WITH CLOUDS PERSISTING
OVERNIGHT. GENERALLY CLOUDY WITH TEMPERATURES IN THE 30S EXPECTED
FOR CHRISTMAS DAY AS SURFACE RIDGE SLOWLY DRIFTS OFF TO THE EAST
LATE IN THE DAY. CONFLUENT MID-LEVEL FLOW UPSTREAM OVER THE
DAKOTAS IS CONDUCIVE FOR BROAD FRONTOGENETIC FORCING AT LOW TO
MID-LEVELS. MODELS ARE PICKING UP ON THE SIGNAL RATHER NICELY AND
DO GENERATE A NARROW BAND OF SNOW ALONG THE DEFORMATION AXIS FROM
SOUTH DAKOTA...EASTWARD ACROSS CENTRAL MINNESOTA INTO NORTHWEST
WISCONSIN. AT THE MOMENT...APPEARS ANY LIGHT SNOW WITH THIS FGEN
BAND WILL REMAIN NORTHWEST OF THE FORECAST AREA UNTIL AROUND 00Z.

.LONG TERM...THURSDAY NIGHT THROUGH TUESDAY
ISSUED AT 351 AM CST WED DEC 24 2014

SEVERAL ISSUES TO DEAL WITH DURING THE PERIOD INCLUDING PRECIPITATION
CHANCES THURSDAY NIGHT INTO FRIDAY NIGHT...AND THEN MUCH COLDER
TEMPERATURES LATER IN THE PERIOD AS THE WESTERN RIDGE RE-EMERGES
AFTER A FEW WEEKS IN HIBERNATION.

FORECAST TRICKY THURSDAY NIGHT AND FRIDAY DUE TO MOISTURE CONCERNS
AT THE LOW AND MID LEVELS...AND MUST ACCOUNT FOR MODEL BIASES IN
PRECIPITATION TYPES. BEST CHANCE FOR LIGHT SNOW WILL BE ACROSS THE
NORTH WHERE SEEDER FEEDER MECHANISM IS AT WORK...PRODUCING ICE
CRYSTALS. LITTLE MID LEVEL MOISTURE NOTED ACROSS EASTERN WISCONSIN.
THE MAIN PROBLEM WITH THIS PERIOD IS THAT THE GFS IS MUCH SLOWER
DEVELOPING DEEPER MOISTURE TRAPPED BELOW AN INVERSION WHILE NAM
MODEL WAS MUCH QUICKER. WEAK 850MB WARM ADVECTION AND WEAK 700MB
LIFT WOULD PROBABLY SUPPORT A QUICKER DEVELOPMENT OF FREEZING
DRIZZLE. HOWEVER...NAM MODEL HAS A TENDENCY TO BE TOO QUICK WITH
THE DEEPER MOISTURE...THUS WILL NOT ADD TO THE FORECAST FOR NOW.
LATER SHIFTS WILL NEED TO MONITOR AND ADD IT IF NEEDED. THE SAME
ISSUES APPLY FOR FRIDAY AS WELL AS BEST MID LEVEL MOISTURE REMAINS
NORTH AND WEST OF THE FOX VALLEY. THE GFS FINALLY DEEPENS THE LOW
LEVEL MOISTURE TO SUPPORT THE ADDITION OF DRIZZLE LATE FRIDAY
AFTERNOON. AGAIN WILL LET LATER SHIFTS ADD DRIZZLE TO THE
FORECAST.

NEW DEVELOPMENT TONIGHT IS THE WRF/GFS/ECMWF BRING WEAK WAVE
ACROSS THE REGION FRIDAY NIGHT. HAVE INCREASE PRECIPITATION CHANCES
FOR THIS FEATURE. IF THE MODELS CONTINUE WITH THIS FEATURE...LATER
SHIFTS WILL NEED TO BUMP UP PRECIPITATION CHANCES.

FOR THE WEEKEND INTO MUCH OF NEXT WEEK...WESTERN RIDGE WILL
AMPLIFY AS UPPER TROUGH ESTABLISHES ITSELF OVER EASTERN NORTH
AMERICA. THE MILD WEATHER OF RECENT WEEKS WILL COME TO AN END AS
SUBZERO TEMPERATURES WILL RETURN TO MUCH OF THE AREA FOR THE LAST
FEW DAYS OF THE YEAR WHICH SHOULD LINGER INTO THE FIRST WEEK OF
THE NEW YEAR.
&&

.AVIATION...FOR 12Z TAF ISSUANCE
ISSUED AT 608 AM CST WED DEC 24 2014

LIGHT WINDS AND AMPLE BOUNDARY LAYER MOISTURE HAVE CONTRIBUTED
IFR/LIFR CONDITIONS OVER EASTCENTRAL WISCONSIN WHERE AREAS OF
DENSE FOG AND DRIZZLE HAVE DEVELOPED OVERNIGHT. AS WEAK SURFACE
LOW PRESSURE SYSTEM/TROUGH MOVES EAST LATER THIS MORNING
VISIBILITIES SHOULD IMPROVE AS NORTHERLY BOUNDARY LAYER WINDS
INCREASE SOMEWHAT. HOWEVER...IFR CIGS WILL LIKELY PERSIST INTO
THE EVENING HOURS UNTIL MID-LEVEL TROUGH AXIS SWINGS ACROSS THE
AREA. PATCHY FREEZING DRIZZLE IS ALSO POSSIBLE THROUGH MID-MORNING
OVER CENTRAL AND NORTHCENTRAL WISCONSIN. AFTER MIDNIGHT...CIGS
SHOULD IMPROVE TO MVFR AS SLIGHTLY DRYER AIR AND WEAK SURFACE HIGH
PRESSURE RIDGE MOVES INTO THE AREA FROM THE WEST.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM.....ESB
LONG TERM......ECKBERG
AVIATION.......ESB






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