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000
FXUS61 KPBZ 052153
AFDPBZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
453 PM EST THU DEC 5 2013

.SYNOPSIS...
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RAIN WILL CHANGE OVER TO A WINTRY MIX OF PRECIPITATION AFTER
MIDNIGHT AND CONTINUE INTO FRIDAY EVENING BEFORE ENDING AS SNOW.
ANOTHER STORM WILL BRING ANOTHER CHANCE FOR A WINTRY MIX SUNDAY
INTO SUNDAY NIGHT.
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&&

.NEAR TERM /THROUGH FRIDAY NIGHT/...
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A COLD FRONT IS NOW ACROSS EASTERN OHIO...WITH LOWER 50S AND A
WESTERLY WIND AT ZZV AND PHD...WHILE HLG REMAINS IN THE UPPER 50S
WITH A SOUTHERLY WIND. THE FRONT SHOULD CROSS THE ENTIRE FORECAST
AREA BY MIDNIGHT...BRINGING A DRAMATIC DROP IN TEMPERATURES OVER
THE NEXT 48 HOURS. LOWS TONIGHT WILL DROP INTO THE 30S.
PRECIPITATION IS EXPECTED THROUGH THE NIGHT...WITH MORE INTENSE
RAINFALL DURING THE LATE EVENING AND EARLY MORNING HOURS AS A
SHORTWAVE MOVES THROUGH. ALTHOUGH LOW LEVEL TEMPERATURES WILL BE
DROPPING TOWARDS FREEZING...A WARM LAYER WILL REMAIN
ALOFT...COMPLICATING PRECIPITATION TYPE. AFTER MIDNIGHT...THINK
THAT PROFILES WILL BE FAVORABLE FOR SLEET TO MIX IN AT MANY
LOCATIONS.

THERE MAY BE A BIT OF A LULL IN PRECIPITATION EARLY FRIDAY MORNING
BEFORE A MORE INTENSE SHORTWAVE ARRIVES FRIDAY AFTERNOON.
TEMPERATURES SHOULD BE CONSTANT THROUGH THE MORNING...THEN SLOWLY
DROP DURING THE AFTERNOON. AGAIN...PRECIPITATION TYPE WILL BE
QUITE DIFFICULT DURING THIS TIME PERIOD. MODELS STILL HAVE NOT
COME INTO ANY SOLID AGREEMENT OF P-TYPE. SOUTH AND EAST OF
LATROBE TO MORGANTOWN...WARMER TEMPERATURES SHOULD GENERALLY ALLOW
FOR ALL RAIN. ACROSS THE REST OF THE REGION...SURFACE TEMPERATURES
WILL SUPPORT EITHER RAIN OR SNOW...WITH A POSSIBILITY OF SLEET
MIXING IN. COMPARED TO YESTERDAY MODEL RUNS...MODEL RUNS TODAY ARE
MUCH MORE SUPPORTIVE OF SLEET FALLING...POSSIBLY FOR SEVERAL
HOURS. ALTHOUGH A LOT OF PRECIPITATION MAY FALL AS SOMETHING OTHER
THAN RAIN...THE THREAT OF SLEET SHOULD GREATLY REDUCE SNOW/SLEET
ACCUMULATION. IF THE WARM LAYER ERODES MORE QUICKLY THAN
FORECAST...SNOW ACCUMULATIONS COULD BE SIGNIFICANTLY HIGHER. THE
ONE AREA THAT MAY BE LIMITED IN SLEET ACCUMULATION WOULD BE NORTH
OF INTERSTATE 80...WHERE PROFILES INDICATE THAT PRECIPITATION
SHOULD CHANGE OVER TO ALL SNOW BY EARLY AFTERNOON...ALLOWING FOR A
FEW INCHES OF SNOW.

ALTHOUGH RAIN AND SLEET MAY BRIEFLY HOLD ON EARLY FRIDAY
EVENING...PRECIPITATION SHOULD CHANGE OVER TO ALL SNOW BY
MIDNIGHT. BULK OF PRECIPITATION WILL HAVE MOVED OFF TO THE EAST BY
THIS TIME...SO ANY ADDITIONAL SNOWFALL ACCUMULATION SHOULD
GENERALLY BE LIGHT. THE COLD AIR WILL CONTINUE TO STREAM INTO THE
REGION...WITH LOWS RANGING FROM THE MID TEENS TO THE MID 20S.

AS FOR WEATHER HEADLINES...ALL OHIO COUNTIES AND MANY PENNSYLVANIA
COUNTIES ARE UNDER WINTER WEATHER ADVISORIES FOR THE WINTRY MIX.
THE FARTHEST NORTH AND WEST COUNTIES SHOULD HAVE A LIMITED RISK
FOR FREEZING RAIN...WITH SNOWFALL ACCUMULATION THE DRIVING FACTOR
FOR THE ADVISORY. ELSEWHERE...AN ADVISORY WAS ISSUED BECAUSE OF
THE THREAT FRIDAY AFTERNOON FOR A PERIOD OF FREEZING RAIN AND
SLEET AS PRECIPITATION TRANSITIONS. WINTER WEATHER ADVISORIES
CANNOT BE RULED OUT IN THE FUTURE FOR THE REST OF THE FORECAST
AREA...BUT WITH UNCERTAINTY IN PRECIPITATION TYPE 24 TO 30 HOURS
OUT...FELT ANY ADDITIONAL HEADLINES WOULD BE BETTER HANDLED BY
LATER SHIFTS.
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&&

.SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
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THE WEATHER SHOULD BE BENIGN DURING THIS TIME...ALTHOUGH SOME
LIGHT SNOW MAY WRAP UP DURING THE MORNING HOURS. WEST-
NORTHWESTERLY WINDS WILL KEEP CLOUDS DUE TO LAKE ERIE MOISTURE
THROUGH THE DAY...BUT CLOUDS COULD CLEAR OUT SATURDAY NIGHT AS
WINDS BECOME LIGHT. TEMPERATURES WILL BE ABOUT 15 DEGREES BELOW
NORMAL. DEPENDING ON HOW MUCH CLOUDS CAN CLEAR OUT SATURDAY NIGHT
AND HOW MUCH SNOW/SLEET ACCUMULATION OCCURS...TEMPERATURES COULD
REALLY BOTTOM OUT...WITH SINGLE DIGIT LOWS NOT OUT OF THE
QUESTION.
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&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
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MORE ACTIVE WEATHER IS EXPECTED EARLY NXT WEEK AS PTN OF CNTRL
CONUS TROFG AND WRN ATLANTIC RIDGING MAINTAINS OVRALL SWLY FLOW
OVR THE UPR OH REGION. ECMWF AND GFS AGAIN INDICATE RAPID
EMERGENCE OF LOW PRES FM THE LWR MS VALLEY TO THE GREAT LAKES ON
SUNDAY AND MONDAY.

AS THESE MDLS HAVE CONSISTENTLY SHOWN A TRACK WEST OF THE
IMMEDIATE AREA OVR THE LAST CPL OF DAYS...MAINTAINED THE WARMER
WPC SOLN AS IS TYPICAL OF THAT WINTER PATH. UNFORTUNATELY...THE
WARM ADVCTN ON THE ERN FLANK OF THE LOW...COMBINED WITH COLD AIR
ENTRENCHMENT REINFORCED VIA NEW ENGLAND HIGH PRES...MAY SPPRT
PROLONGED FREEZING RAIN FOR PART OF THE AREA...NAMELY COUNTIES
NORTH AND EAST OF PITTSBURGH. FOR NOW...HAVE OPTED FOR A MORE
AGGRESSIVE PCPN PHASE CHANGE FOR MOST ZONES FM SNOW AND FREEZING
RAIN TO ALL RAIN AS WRM AIR ADVCTN SPREADS NWD SUNDAY NGT. A
HAZARDOUS WEATHER OUTLOOK WILL ALSO BE INCLUDED AND MONITORING
WILL CONTINUE.

OTHERWISE...COLDER AND DRIER AIR WL BE SHUNTED OVR THE UPR OHIO
REGION IN THE WAKE OF THAT SYSTEM...WITH TEMPS AND POPS FORECAST
USING A COMBO OF WPC AND MOS GUIDANCE.
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&&

.AVIATION /21Z THURSDAY THROUGH TUESDAY/...
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A CDFNT WL MOVE SLOWLY ACRS THE AREA THIS AFTN/ERLY EVE. GENLY
MVFR CONDS EXPD...WITH OCNL IFR IN HEAVIER SHWRS S AND E OF PIT.
EXPTG A DCRS TO IFR CONDS OVRNGT INTO FRI AS WAVES OF LOW PRES
MOVE NE ALG THE FNT SPREADING ADDNL PCPN ACRS THE RGN. TEMPS WL
COOL AS WELL...AND EXPG A WINTRY MIX OF PCPN ACRS THE AREA LT TNGT
INTO FRI. MGW SHOULD STAY WARM ENOUGH FOR ALL RAIN HOWEVER THRU
FRI. PCPN SHOULD CHG TO ALL SNW THU EVE BEFORE ENDG.

.OUTLOOK.../FRIDAY NIGHT THROUGH TUESDAY/...
RSTRNS ARE LIKELY THRU SAT MRNG AS LOW PRES EXITS THE RGN. RSTRNS
ARE LIKELY AGAIN SUN AND MON AS LOW PRES BRINGS A WINTRY MIX TO
THE RGN. VFR SHOULD RTN TUE UNDER BLDG HIGH PRES.
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&&

.HYDROLOGY...
THURSDAY UPDATE: THE CHANGE FROM WEDNESDAY IS AN EXPANSION OF THE
HEAVIER RAINFALL A BIT FARTHER EASTWARD OVER THE CHEAT AND
YOUGHIOGHENY RIVER BASINS. THIS WILL RESULT IN SLIGHTLY HIGHER
CRESTS ON SATURDAY. CRESTS ARE STILL EXPECTED TO REMAIN BELOW
FLOOD STAGES, BUT ACTION LEVELS ARE STILL PROJECTED TO BE REACHED
ALONG THE MONONGAHELA AND OHIO RIVERS.

SUMMARY: A RIVER RISE OF 5 TO 9 FEET IS COMING THIS SATURDAY (DEC
7, 2013) ON THE MONONGAHELA AND OHIO RIVERS. AND THEN A SECOND
RISE IS LIKELY MONDAY (DEC 9, 2013). CURRENT WEATHER MODELS HAVE
BEEN CONSISTENT FOR THE PAST 3 DAYS AND CONTINUE TO INDICATE A
FORECAST OF 2 TO 3 INCHES OF RAIN OVER THE MONONGAHELA AND UPPER
OHIO RIVER BASINS FRIDAY. THAT HEAVIER RAINFALL AREA HAS BEEN
EXPANDED INTO THE CHEAT AND YOUGHIOGHENY RIVER BASINS.

A GENERAL 5 TO 9 FOOT RISE IS EXPECTED SATURDAY ON THE
MONONGAHELA AND UPPER OHIO RIVERS. AT THIS POINT PROJECTIONS ARE
TO BRING GRAYS LANDING UP 17.9 FEET SATURDAY LATE MORNING AND
PITTSBURGH 20.2 FEET SATURDAY AFTERNOON. THE MON PARKING WHARF
WILL BE AFFECTED STARTING SATURDAY.

STILL ANOTHER RAINSTORM IS PROJECTED OVER THE SAME AREA SUNDAY
THAT WILL CONTINUE TO KEEP RIVER LEVELS AND FLOWS ON THE
MONONGAHELA AND OHIO RIVERS ELEVATED THROUGH TUESDAY. THE RAINFALL
AMOUNTS ON SUNDAY ARE MORE UNCERTAIN AT THIS TIME. INITIAL
ESTIMATES ARE PROJECTED TO BE 1 AND 2 INCHES, BUT THE GROUND WILL
BE SATURATED AND IT WILL TAKE LESS RAIN TO THE CAUSE THE SAME
RUNOFF.

RIVER LEVELS SHOULD RECEDE SATURDAY NIGHT AND SUNDAY THEN
A SECOND RISE IS EXPECTED MONDAY THAT COULD CREST AT HIGHER THAN
SATURDAY LEVELS. THE CURRENT PROJECTIONS DO NOT INCLUDE THE
PROJECTED RAINFALL FOR SUNDAY AT THIS POINT.

THE PRECIPITATION OVER THE ALLEGHENY WILL BE MINIMAL AND WILL
LIKELY FALL IN THE FORM OF SNOW.

RIVERS WILL RECEDE TUESDAY AND FOR THE REST OF THE WEEK.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
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MD...NONE.
OH...WINTER WEATHER ADVISORY FROM 10 AM FRIDAY TO MIDNIGHT EST
     FRIDAY NIGHT FOR OHZ049-050-057>059-068-069.
     WINTER WEATHER ADVISORY FROM 4 AM FRIDAY TO MIDNIGHT EST
     FRIDAY NIGHT FOR OHZ039>041-048.
PA...WINTER WEATHER ADVISORY FROM 10 AM FRIDAY TO MIDNIGHT EST
     FRIDAY NIGHT FOR PAZ014>016-020.
     WINTER WEATHER ADVISORY FROM 4 AM FRIDAY TO MIDNIGHT EST
     FRIDAY NIGHT FOR PAZ007>009-013.
WV...WINTER WEATHER ADVISORY FROM 10 AM FRIDAY TO MIDNIGHT EST
     FRIDAY NIGHT FOR WVZ001.
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&&

$$