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Area Forecast Discussion
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000
FXUS61 KPBZ 190839
AFDPBZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
339 AM EST FRI DEC 19 2014

.SYNOPSIS...
A WEAK DISTURBANCE WILL CROSS THE REGION TONIGHT. BUILDING HIGH
PRESSURE IS EXPECTED THROUGH THE WEEKEND...THOUGH CLOUDS WILL
REMAIN.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
CURRENTLY TWO DIFFERENT TYPES OF PRECIPITATION BEING GENERATED 
PRODUCED BY TWO DIFFERENT MODES OF GENERATION. LIGHT SNOW SHOWERS 
EXIST ACROSS THE SOUTH AND HIGHER ELEVATIONS OF THE SOUTHEAST 
PRODUCED BY SEEDER-FEEDER METHODS WITH MOISTURE FROM ABOUT 
500MB-600MB SEEDING THE MOISTURE TRAPPED BELOW THE INVERSION AT 
850MB. THE 00Z UPPER AIR SOUNDING SAMPLED THIS ENVIRONMENT RATHER 
NICELY AND THE HI-RES MODELS HAVE PICKED UP ON THIS...EVEN 
GENERATING QPF. AS THE SW TROF AXIS SWINGS THROUGH N TO S THE UPPER 
LEVEL MOISTURE MOVES QUICKLY OUT WHILE DRYING UP. THIS SHOULD 
EFFECTIVELY SQUASH ANY REMAINING SEEDER-FEEDER GENERATED SNOW 
SHOWERS ACROSS OUR SOUTH.

ELSEWHERE...ACROSS THE NORTHERN TIER OF THE CWA THE BL MOISTURE 
DEPTH HAS BEEN ENHANCED BY AN INJECTION OF UPSTREAM LAKE MOISTURE 
THAT HAS RAISED INVERSION HEIGHTS. LAST NIGHT MODELS WERE INDICATING 
A BL TOP TEMP IN THE -10C TO -11C RANGE WHICH WOULD BE COLD ENOUGH 
TO PRODUCE ICE CRYSTALS AND GENERATE LIGHT SNOW. THE 00Z SOUNDING 
VERIFIED THIS OCCURRENCE WITH 850MB TEMPS RIGHT AT -10C...WHICH WOULD 
LEAD ONE TO BELIEVE THAT SNOW WOULD RESULT. HOWEVER...LOOKING AT RAP 
BUFR SOUNDINGS...THE -10C ISOTHERM LAYER IS RATHER SMALL SPATIALLY 
AT 850MB AND THE SAMPLE TAKE SEEMS MORE LIKE THE EXCEPTION THAN THE 
RULE. IN ACTUALITY THE BL TOP TEMP IS CLOSER TO -8C WHICH KEEPS 
SUPERCOOLED LIQUID INTO PLAY...THUS THE REPORTS OF FZDZ MIXING IN 
WITH LIGHT SNOW. AN ADVISORY IS OUT FOR THE AREA DIRECTLY IMPACTED 
BY THE FZDZ...AND DEPENDING ON THE DRIFT OF THE DOWN-LAKE 
MOISTURE...AN EXPANSION SOUTHWARD MAY BE NECESSARY. 

HI-RES MODELS INDICATING A FEED OF ENHANCED LLVL MOISTURE WILL SAG 
SOUTHWARD THROUGH THE EARLY MORNING HOURS...REACHING THE PITTSBURGH 
METRO AREA NEAR SUNRISE. THIS IS IN RESPONSE TO THE MI-LEVEL TROF 
AXIS AND ATTENDANT MID-LEVEL DEFORMATION ZONE. AS IT CONTINUES IT 
TREK SOUTH OF LAKE ERIE...THE MOISTURE BEGINS TO ERODE ALONG WITH 
THE DEFORMATION ZONE GETTING WASHED OUT. ATTM...HAVE INCLUDED LIGHT 
SNOW SHOWERS INTO THE METRO AND AREAS NW TO SE SURROUNDING. WILL SHY 
AWAY FROM FZDZ MENTION FOR NOW...AS CONFIDENCE IS NOT HIGH IN THE 
POTENTIAL FURTHER SOUTH. CLOUDS WILL CONTINUE TO PLAGUE THE CWA FOR 
YET ANOTHER DAY.
TAX

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY/...
SFC HIGH PRES IS PROGGED TO BLD IN UNDER UPR TROFG OVR THE GT LKS
FRI...ENDING ANY LINGERING MRNG SNW SHWRS. THE SFC HIGH IS EXPD TO
BRING DRY WEA THRU THE WKEND...THOUGH PERSISTENT MSTR BLO AN
INVERSION MAY KEEP SKIES MCLDY. A SHRTWV MOVG ACRS THE SERN CONUS
LT SAT/SAT NGT IS NOW PROGGED TO STAY FAR ENOUGH S TO REMOVE ALL
PCPN FM THE FCST FOR AREAS S OF PIT. A WK SHRTWV IS PROGGED FOR
ERLY SUN ACRS THE GT LKS...BUT WITH A LACK OF DEEP MSTR AND THE
SFC HIGH OVERHEAD KEPT THE FCST DRY.

SLGTLY BLO AVG TEMPS SHOULD RTN TO NR SEASONAL LVLS BY SUN.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
WHILE THE MODELS AGREE ON A DEEPENING UPPER LEVEL TROUGH TO CLOSE
OFF OVER THE GREAT LAKES THROUGH THE PERIOD THE DETAILS OF HOW
THIS EXACTLY UNFOLDS WILL BE CRITICAL. BY MONDAY SOUTHERN STREAM
SHORTWAVE AHEAD OF MAIN NORTHERN STREAM UPPER TROUGH DIGGING INTO 
THE NORTHERN PLAINS WILL PRODUCE LOW PRESSURE ACROSS THE CAROLINAS
MOVING OFF SHORE OF THE EAST COAST. THE SOUTHEAST RIDGES MAY BE
BRUSHED BY LIGHT RAIN FROM THIS SYSTEM. NEXT UP IS DEEPENING LOW
PRESSURE OVER THE OHIO VALLEY AHEAD OF SHARPLY DIGGING UPPER
TROUGH AND CLOSED LOW MOVING INTO THE WESTERN GREAT LAKES. UPPER
OHIO VALLEY LOOKS TO BE ON THE WARM SIDE OF THE SYSTEM TUESDAY
INTO WEDNESDAY WITH RAIN...FOLLOWED BY STRONG COLD FRONT AND COLD
ADVECTION LATER WEDNESDAY NIGHT AND THURSDAY WITH SNOW SHOWERS.
WITH SUCH A STRONG SYSTEM ALOFT AND FAST DEEPENING LOW PRESSURE AT
THE SURFACE TIMING OF COLD AIR AND EXACT TRACK WILL LIKELY CHANGE
AS WE GET CLOSER TO CHRISTMAS. ALL IN ALL PREVIOUS FORECAST IS
LITTLE CHANGED WITH ONLY MINOR ADJUSTMENTS BASED ON NEWEST WPC
EXTENDED PROGS.

&&

.AVIATION /09Z FRIDAY THROUGH TUESDAY/...
UPDATED TAFS TO INCLUDE MENTION OF FREEZING DRIZZLE FOR SITES
NORTH OF INTERSTATE 70 THROUGH EARLY THIS MORNING BASED ON LATEST
OBS AND LATEST HI RES AND RAPID REFRESH GUIDANCE SHOWING
INDICATING MOISTURE IN THE COLUMN LIMITED TO LOWER LEVELS NOT COLD
ENOUGH FOR ICE CRYSTAL FORMATION...THUS...FINE MIST AND LIGHT
DRIZZLE EXPECTED THROUGH 9AM WILL REMAIN LIQUID AND FREEZE ON
CONTACT. DO NOT EXPECT ANY PERIODS OF RAPID ICE DEVELOPMENT BUT
WILL LIKELY FOR A LIGHT GLAZE OVER THE NEXT SEVERAL HOURS.
ICE POTENTIAL WILL LIKELY BE OVER BY MID MORNING AS MOISTURE POOL
BECOMES TOO SHALLOW...WITH CIG RESTRICTIONS LARGELY MVFR THROUGH
MUCH OF THE DAY...IMPROVING TO VFR STARTING LATE THIS AFTERNOON.


OUTLOOK.../FRIDAY NIGHT THROUGH TUESDAY/...
STRATUS AND RESTRICTIONS MAY PERSIST INTO THE WEEKEND. NEXT STORM
SYSTEM WILL BRING RESTRICTIONS TUESDAY.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...NONE.
OH...WINTER WEATHER ADVISORY UNTIL 9 AM EST THIS MORNING FOR 
     OHZ039>041-048>050.
PA...WINTER WEATHER ADVISORY UNTIL 9 AM EST THIS MORNING FOR 
     PAZ007>009-013>016-020>022.
WV...WINTER WEATHER ADVISORY UNTIL 9 AM EST THIS MORNING FOR WVZ001.

&&

$$






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