-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPBZ 042043
AFDPBZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
343 PM EST WED DEC 4 2013

.SYNOPSIS...
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RAIN WILL SPREAD OVER THE REGION ON THURSDAY AS A COLD FRONT
SLIDES TOWARD THE REGION. AS THE COLD FRONT PASSES...RAIN WILL
CHANGE TO SNOW ON FRIDAY.
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&&

.NEAR TERM /THROUGH THURSDAY/...
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LOW PRESSURE WILL DEEPEN AS IT MOVES FROM ILLINOIS NORTHEAST INTO
CANADA. OUR REGION WILL REMAIN IN THE WARM SECTOR
OVERNIGHT...AND SOUTHERLY FLOW WILL ALLOW OVERNIGHT LOWS TO REMAIN
WARMER THAN NORMAL DAYTIME HIGHS FOR EARLY DECEMBER. THE BULK OF
THE RAINFALL SHOULD REMAIN TO THE WEST OVERNIGHT...WITH THE FRONT
CROSSING THROUGH THE REGION THURSDAY. WITH THE FRONT ARRIVING LATE
IN THE DAY...TEMPERATURES WILL RISE INTO THE UPPER 50S AND 60S.
-- End Changed Discussion --

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
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THE FRONT WILL ESSENTIALLY STALL OUT JUST TO THE EAST OF THE
FORECAST AREA THURSDAY NIGHT INTO FRIDAY...WITH MULTIPLE
SHORTWAVES RIDING ALONG THE FRONT TO THE NORTHEAST. ONE SHORTWAVE
IS LIKELY THURSDAY NIGHT...WITH ANOTHER MOVING UP THE FRONT ON
FRIDAY. MANY LOCATIONS WILL PICK UP HALF AN INCH OF RAINFALL
THURSDAY NIGHT.

AS THE FRONT PASSES...TEMPERATURES WILL TUMBLE SOME 20 TO 25
DEGREES THURSDAY NIGHT. ON FRIDAY...TEMPERATURES MAY NOT EVEN RISE
FROM THE OVERNIGHT VALUES. A CONCERN WITH THE FRONT IS THAT WHILE
TEMPERATURES WILL SIGNIFICANTLY DROP AT THE SURFACE...A WARM LAYER
COULD REMAIN ALOFT...BRINGING THE CHANCE FOR MIXED PRECIPITATION.
HARD TO PIN DOWN EXACTLY HOW THIS PRECIPITATION TYPE EVOLUTION
COULD OCCUR...BUT FOR NOW THE FORECAST HAS RAIN CHANGING OVER TO
SNOW...WITH A FEW HOURS OF SLEET AS A POSSIBILITY AS WELL. IN
ADDITION...FRIDAY AFTERNOON IS WHEN THE GREATEST AMOUNT OF
PRECIPITATION IS EXPECTED TO FALL...RIGHT AS TEMPERATURES WILL BE
CRITICAL FOR DETERMINING WHAT TYPE OF PRECIPITATION IS FALLING.
THAT TIME PERIOD COULD FIND RAIN ACROSS THE SOUTH...WITH HEAVY
SNOW FALLING TO THE NORTH. SNOWFALL TOTALS HAVE BEEN BUMPED UP BY
A COUPLE OF INCHES. THE FRIDAY AFTERNOON AND FRIDAY EVENING TIME
PERIOD WILL NEED TO BE CLOSELY MONITORED DURING FUTURE FORECASTS.

AFTER FRIDAY EVENING PRECIPITATION SHOULD RAPIDLY MOVE OFF TO THE
EAST...WITH JUST A SLIGHT CHANCE OF SNOW PERSISTING ON THE RIDGES
SATURDAY MORNING. ALTHOUGH THE FLOW WILL BE FAVORABLE FOR LAKE
EFFECT OR UPSLOPE SNOW...PROFILES JUST APPEAR TO BE WAY TOO DRY
WITH INVERSION LEVELS ONLY REACHING ABOUT 3000 FT. HAVE KEPT
MOSTLY CLOUDY SKIES IN THE FORECAST...BUT LITTLE PRECIPITATION.
HIGH TEMPERATURES ON SATURDAY WILL BE ABOUT 10 DEGREES BELOW
NORMAL.
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&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
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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 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...HAVE ACCEPTED A 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. FOR NOW...HAVE OPTED
FOR A MORE AGGRESSIVE PCPN PHASE CHANGE FM SNOW AND FREEZING RAIN
TO ALL RAIN AS SUNDAY NGT PROGRESSES. 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.
-- End Changed Discussion --

&&

.AVIATION /21Z WEDNESDAY THROUGH MONDAY/...
GENL VFR CONDS EXPD INTO TNGT. SC IS EXPD TO INCR THIS EVE BUT
SHOULD REMAIN VFR. THE EXCEPTION IS FKL AND DUJ WHERE MVFR CIGS
MAY DVLP OVRNGT AS LLVL MOISTURE BEGINS TO INCR. LLVL WNDS INCR
ABV THE SFC OVRNGT AS WELL. LEFT LLWS OUT OF THE FCST
ATTM...HOWEVER THIS WL HAVE TO BE MONITORED. AN APCHG CDFNT WL
SPREAD MVFR SHWRS ACRS THE AREA THU MAINLY IN THE AFTN.

.OUTLOOK.../THURSDAY NIGHT THROUGH MONDAY/...
RSTRNS ARE LIKELY THRU SAT MRNG AS A SLOW MOVG CDFNT...ALG WITH A
SERIES OF DISTURBANCES...CROSS THE RGN. RSTRNS ARE PSBL AGAIN SUN
AND MON AS LOW PRES MOVES ACRS THE AREA.

&&

.HYDROLOGY...
A RIVER RISE OF 4 TO 6 FEET IS EXPECTED SATURDAY ON THE
MONONGAHELA AND OHIO RIVERS. AND THEN A SECOND RISE IS LIKELY
MONDAY. CURRENT QPF FORECASTS SHOW THE POTENTIAL OF OVER 2 INCHES
OF RAINFALL OVER THE MONONGAHELA AND UPPER OHIO RIVER BASINS
FRIDAY. THEN ANOTHER RAIN EVENT 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. A GENERAL 4
TO 6 FOOT RISE IS EXPECTED SATURDAY ON THE MONONGAHELA AND UPPER
OHIO RIVERS THAT MAY AFFECT THE MON PARKING WHARF. AT THIS POINT
PROJECTIONS ARE TO BRING GRAYS LANDING (15 FOOT ACTION STAGE) UP
16.7 FEET SATURDAY MORNING AND PITTSBURGH (18 FOOT ACTION STAGE)
TO 18.8 FEET SATURDAY EVENING. THESE STAGE PROJECTIONS WOULD
STILL BE BELOW FLOOD STAGES. RIVER LEVELS SHOULD RECEDE ON SUNDAY
THEN A SECOND RISE IS EXPECTED MONDAY THAT COULD CREST AT NEARLY
THE SAME LEVELS OR PERHAPS 1 TO 2 FEET HIGHER THAN SATURDAY
LEVELS. THE PRECIPITATION OVER THE ALLEGHENY BASIN WILL BE
MINIMAL.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...NONE.
OH...NONE.
PA...NONE.
WV...NONE.

&&

$$