Area Forecast Discussion
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000 FXUS61 KPBZ 190626 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 126 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 /THROUGH TODAY/...
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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
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&& .SHORT TERM /TONIGHT 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 /07Z FRIDAY THROUGH TUESDAY/... MVFR CIGS EXPECTED OVERNIGHT WITH SITES ALONG AND NORTH OF INTERSTATE 80 POTENTIALLY SEEING IFR CIGS DEVELOP DURING PERIODS OF LIGHT SNOW. THERE IS A SLIGHT CHANCE THAT LIGHT FREEZING DRIZZLE MAY OCCUR AND SPREAD FROM NORTH TO SOUTH OVERNIGHT AS MOISTURE DECREASES ALOFT LEAVING ONLY LOW LEVEL MOISTURE IN PLACE TRAPPED UNDER THE INVERSION IN TEMPERATURES NOT SUFFICIENTLY COLD FOR ICE CRYSTALS TO DEVELOP...BUT CONFIDENCE IS NOT HIGH ENOUGH TO INCLUDE IN TAFS AT THIS TIME. POTENTIAL FOR FREEZING DRIZZLE WILL LIKELY BE OVER BY MID MORNING AS MOISTURE POOL BECOMES TOO SHALLOW. 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...NONE. PA...WINTER WEATHER ADVISORY UNTIL 6 AM EST EARLY THIS MORNING FOR PAZ007>009-013>016-022. WV...NONE. && $$

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