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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KPBZ 070139 AAC
AFDPBZ

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PITTSBURGH PA
839 PM EST FRI DEC 6 2013

.SYNOPSIS...
SNOW AND SLEET THIS EVENING WILL DIMINISH AFTER MIDNIGHT. ANOTHER
STORM WILL LIKELY BRING A WINTRY MIX ONCE AGAIN ON SUNDAY AND
EARLY MONDAY.

&&

.NEAR TERM /THROUGH SATURDAY/...
MADE A COUPLE SMALL CHANGES TO THE EVENING FORECAST AS THE
CHANGEOVER FROM RAIN TO SNOW IS TRENDING SLIGHTLY FASTER THAN
ANTICIPATED...BUT OVERALL THE FORECAST IS IN GOOD SHAPE.

EVEN WITH THE EARLIER TRANSITION...SNOWFALL AMOUNTS FOR TONIGHT
STILL LOOK ON TARGET...BUT MAY END UP BEING LARGELY IN THE HIGHER
END OF FORECAST RANGES. SNOWFALL RATES WILL FLUCTUATE BETWEEN
THREE QUARTERS OF AN INCH TO ONE INCH PER HOUR IN GENERAL...WITH
BRIEF PERIODS OF UP TO 1.5 INCHES PER HOUR THROUGH THE
EVENING...BEFORE TAPERING OFF AFTER MIDNIGHT.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
REPRIEVE IN PCPN IS STILL INDICATED FOR SATURDAY INTO SATURDAY NIGHT
WITH COLD HIGH PRESSURE ACROSS THE REGION. ANOTHER WINTER SCENARIO
WILL DEVELOP TOWARD SUNRISE ACROSS THE SOUTH AS AN INVERTED TROUGH
AT THE SURFACE MOVES NORTHEAST WHILE STRONGER LOW PRESSURE DEVELOPS
ACROSS THE WESTERN LAKES WITH AN ADVANCING UPPER LEVEL TROUGH. WITH
DOME OF COLD AIR IN PLACE WARM ADVECTION WILL OVERRIDE COLD LOW
LEVELS WITH SNOW ADVANCING NORTHWARD SUNDAY MORNING WITH LIGHT
ACCUMULATIONS. EXPECT A MIX OF PRECIP BY AFTERNOON SOUTH OF
PITTSBURGH WITH LIGHT SNOW MIXING WITH SLEET NORTH. IN THE SOUTHERN
RIDGES AND ESPECIALLY GARRETT AND TUCKER COUNTIES LOW LEVEL COLD AIR
WILL DAM UP AGAINST THE EASTERN SLOPES FOR MUCH OF SUNDAY NIGHT AS
THE MID LEVELS WARM TO CHANGE PRECIP OVER TO FREEZING RAIN.

MODELS SOUNDINGS NOW IN GENERAL AGREEMENT FOR POSSIBLE ICE
ACCUMULATIONS GREATER THAN ONE QUARTER INCH ACROSS EASTERN PORTIONS
OF GARRETT AND TUCKER COUNTIES ESPECIALLY SUNDAY AFTERNOON AND NIGHT
AND HAVE ISSUED A WINTER STORM WATCH FOR THIS POSSIBILITY.
ELSEWHERE MODEL SOLUTIONS KEEP BEST PROLONGED DEEP MOISTURE AND LIFT
FARTHER SOUTH THAN PREVIOUS RUNS WHILE STILL WARMING LOW LEVELS
ABOVE FREEZING LATE SUNDAY NIGHT INTO MONDAY MORNING. MIXED PRECIP
WITH LIGHT SNOW AND ICE AMOUNTS EXPECTED SUNDAY INTO SUNDAY NIGHT
AND WILL LIKELY BE AN ADVISORY EVENT.

BY MONDAY MORNING WARMER LOW LEVEL AIR WILL PUSH ACROSS THE REGION
AND BRING TEMPERATURES ABOVE FREEZING WITH SIGNIFICANT PRECIP
ENDING.

A COLD FRONT ASSOCIATED WITH THE ADVANCING UPPER TROUGH WILL CROSS
THE UPPER OHIO VALLEY BY LATE MONDAY WITH A FEW RAIN OR SNOW
SHOWERS.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
MUCH COLDER AND DRIER AIR WILL BE SHUNTED OVR THE UPPER OHIO VALLEY
REGION IN THE WAKE OF THE MONDAY COLD FRONT. COLD TEMPS AND GENLY
PCPN FREE POPS WERE FORECAST USING A COMBO OF WPC AND MOS GUIDANCE.
ONLY LOW POPS ACROSS THE FAR NORTH WERE MAINTAINED.

&&

.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
MVFR/IFR CIGS OVERNIGHT...WITH MVFR BECOMING MORE PREVALENT AROUND
DAWN. SNOW WILL REDUCE VIS TO IFR/LIFR THROUGH 06Z. MGW WILL FINALLY
CHANGE TO ALL SNOW BY 03Z...WITH FZRA IN THE MEANTIME. VIS WILL
RAPIDLY IMPROVE AFT 06Z-08Z AS THE SNOW MOVES EAST.

IMPROVEMENT TO VFR CIGS IS EXPECTED AT ALL PORTS BY LATE MORNING.

.OUTLOOK.../SATURDAY NIGHT THROUGH WEDNESDAY/...
RSTRNS ARE LIKELY AGAIN SUN AND MON AS LOW PRES BRINGS A WINTRY
MIX TO THE RGN. VFR SHOULD RTN TUE AND WED UNDER BLDG HIGH PRES.
-- End Changed Discussion --


&&

.HYDROLOGY...
FRIDAY UPDATE: ONLY MINOR CHANGES FROM THURSDAYS UPDATE. THE
CREST LEVELS ARE ABOUT THE SAME OR SLIGHTLY HIGHER ON THE
MONONGAHELA RIVER WITH THE CREST TIMES 6 TO 8 HOURS LATER THAN
PREDICTED YESTERDAY.

RADAR SHOWS A CONVEYER BELT OF PRECIPITATION ALONG THE OHIO RIVER
DIRECTLY INTO OUR AREA. AS OF FRIDAY MORNING WIDE SPREAD RAINFALL
OF OVER 1.5 INCHES HAS OCCURRED OVER SOUTHERN OHIO AND NORTHERN
WEST VIRGINIA OVER THE UPPER MONONGAHELA AND MAINSTEM OF THE OHIO.
RISES ARE OCCURRING ON THE UPPER WEST FORK AND TYGART.

ANOTHER 1 TO 1.8 INCHES OF RAIN ARE FORECAST THROUGH SATURDAY
MORNING. A BREAK IN THE PRECIPITATION WILL OCCUR ON SATURDAY AND
THEN THE NEXT STORM SYSTEM APPROACHES SUNDAY BRINGING ANOTHER 1 TO
1.5 INCHES ACROSS THE UPPER MONONGAHELA AND CHEAT. 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 MONDAY (DEC 9, 2013). FLOWS AND VELOCITIES WILL BE ELEVATED
INTO TUESDAY.

CURRENT WEATHER MODELS HAVE BEEN CONSISTENT FOR THE PAST 4 DAYS
AND CONTINUE TO PREDICT A STORM TOTAL RAINFALL FROM THE FIRST
STORM OF 2 TO 3 INCHES OF RAIN OVER THE MONONGAHELA/CHEAT AND
UPPER OHIO RIVER BASINS BY SATURDAY MORNING. 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 TO
18.3 FEET SATURDAY AROUND NOON AND PITTSBURGH 20.0 FEET SATURDAY
EVENING. THE MON PARKING WHARF WILL BE AFFECTED STARTING SATURDAY.
STILL ANOTHER RAINSTORM IS PROJECTED OVER THE SAME AREA SUNDAY
INTO MONDAY THAT WILL CONTINUE TO KEEP RIVER LEVELS AND FLOWS ON
THE MONONGAHELA AND OHIO RIVERS ELEVATED THROUGH TUESDAY. IN
BETWEEN RAINSTORMS, SATURDAYS TEMPERATURES WILL BE CHILLY (UPPER
20S TO LOWER 30S), AND COULD SLOW DOWN SOME OF RESIDUAL RUNOFF
FROM THE FIRST STORM. FORECAST RAINFALL AMOUNTS ON SUNDAY/SUNDAY
NIGHT ARE PROJECTED TO BE AN ADDITIONAL 1 TO 1.5 INCHES ACROSS THE
UPPER MONONGAHELA AND CHEAT. WITH THE GROUND SATURATED, IT WILL
TAKE LESS RAIN TO THE CAUSE THE SAME RUNOFF FROM THE SECOND STORM.

RIVER LEVELS SHOULD RECEDE SATURDAY NIGHT AND SUNDAY THEN A SECOND
RISE IS EXPECTED MONDAY THAT SHOULD BE CLOSE TO SATURDAY CREST
LEVELS. THE CURRENT PROJECTIONS NOW INCLUDE 72 HOUR FORECAST
RAINFALL FORECAST THROUGH MONDAY MORNING. THE PRECIPITATION OVER
THE ALLEGHENY WILL BE MINIMAL AND WILL LIKELY FALL IN THE FORM OF
SNOW.

COLD AIR WILL MOVE INTO THE IMMEDIATE PITTSBURGH AREA FRIDAY
AFTERNOON AND NIGHT AND PRECIPITATION COULD FALL IN THE FORM OF
SNOW/SLEET OR FREEZING PRECIPITATION, CAUSING ICY CONDITIONS
ONBOARD VESSELS. THE SAME MIXTURE COULD OCCUR IN THE IMMEDIATE
PITTSBURGH AREA FOR SUNDAY BEFORE CHANGING TO RAIN LATER SUNDAY,
BUT WILL BE ALL RAIN IN THE HEADWATERS OF THE MONONGAHELA CAUSING
THE SECONDARY RISE.

ARCTIC AIR THEN MOVES INTO THE ENTIRE REGION TUESDAY AND RIVERS
WILL RECEDE TUESDAY AND FOR THE REST OF THE WEEK.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
MD...WINTER WEATHER ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR MDZ001.
     WINTER STORM WATCH FROM SUNDAY MORNING THROUGH LATE SUNDAY
     NIGHT FOR MDZ001.
OH...WINTER WEATHER ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR
     OHZ039>041-048>050-057>059-068-069.
PA...WINTER WEATHER ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR
     PAZ007>009-013>016-020>023-029-031-073>076.
WV...WINTER WEATHER ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR
     WVZ001>004-012-021>023-041.
     WINTER STORM WATCH FROM SUNDAY MORNING THROUGH LATE SUNDAY
     NIGHT FOR WVZ041.
-- End Changed Discussion --

&&

$$