Area Forecast Discussion
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000 FXUS61 KPBZ 181138 AFDPBZ AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PITTSBURGH PA 638 AM EST THU DEC 18 2014 .SYNOPSIS... IT WILL BE CLOUDY WITH NEAR SEASONAL TEMPERATURES THROUGH THE END OF THE WEEK. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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NO UPDATES NEEDED EARLY THIS MORNING AS THE ONGOING FORECAST ALIGNS WELL WITH LATEST OBSERVATIONAL TRENDS...PREV DISCUSSION BELOW.. TEMPS THIS MORNING HAVE STAGNATED AS LLVL CAA HAS CEASED AND WITH ABUNDANT CLOUD COVER BLANKETING THE AREA. LIGHT UPSLOPE SNOW SHOWERS AND FLURRIES ACROSS THE NORTH WILL CONTINUE TO DWINDLE THIS MORNING. LAKE ENHANCED MOISTURE...SATURATING AND DEEPENING THE BOUNDARY LAYER...WILL RETURN OVER OUR NRN 1/3 OF THE CWA BY MID-MORNING WITH CHANCES OF SNOW SHOWERS PERSISTING THROUGHOUT THE NEAR TERM. THIS AFTERNOON HI-RES MODELS KEEP LAKE EFFECT SNOW PRODUCTION ACTIVE DESPITE NAM BUFR SOUNDINGS SHOW INVERSION HEIGHTS LOWERING AND A SLIGHT WARMING OF THE MID-LEVELS. WILL MAINTAIN CHC POPS ACROSS THE NRN TIER OF THE CWA. ELSEWHERE...CLOUDS WILL CONTINUE TO BE EVER-PRESENT...BUT INSUFFICIENT MOISTURE WILL PRECLUDE ANY PRECIPITATION. WITH LACK OF SUNSHINE AND NO REAL CHANGE TO THE AIR MASS TO SPEAK OF...HIGH TEMPS WILL REMAIN BELOW AVERAGE WITH MOST LOCATIONS FLIRTING WITH THE FREEZING MARK. WINDS COULD MAKE IT FEEL ABOUT 5-10 DEGREES COLDER. TAX
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&& .SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY NIGHT/... ANOTHER WEAK WAVE WILL PASS THROUGH THE AREA TONIGHT DEEPENING THE BOUNDARY LAYER ACROSS THE NRN 1/2 OF THE CWA BY INJECTION OF UPSTREAM LAKE MOISTURE. 00Z NAM SHOWS H85 MOISTURE PUSHING SOUTH ACROSS LAKE ERIE LATE TONIGHT EMBEDDED IN THE BROAD WEAK TROF AXIS. A COLD POOL COINCIDENT WITH THIS FEATURE WILL BRING H85 TEMPS BACK TO NEAR -11C. WHILE NOT OPTIMAL...THE COLDER TEMPS ALOFT SHOULD AID IN SNOW GENERATION WITH THE WEAK WAVE. WILL KEEP LIKELY POPS CONFINED TO THE AREA NORTH OF I-80 WHERE LAKE ERIE ENHANCEMENT WILL OCCUR...BUT DO EXPAND POPS SOUTH NEARING THE PITTSBURGH METRO AREA AND SOUTH ALONG THE LAUREL AND CHESTNUT RIDGES. LITTLE TO NO ACCUMULATION IS EXPECTED. HIGH PRESSURE WILL FINALLY SQUASH ANY REMAIN CHANCE OF LIGHT SNOW FRI. THE LLVL INVERSION WILL HOLD STEADY THROUGH FRI WITH MOISTURE REMAINING TRAPPED UNDERNEATH...BUT EROSION OF THAT MOISTURE DOES OCCUR. THIS SHOULD BE THE FIRST CHANCE TO HAVE AT LEAST SOME SUNSHINE RETURN TO THE AREA. THE NEXT SYSTEM IS POISED TO SKIRT OUR SOUTH AND EAST SAT IN THE FORM OF AN OPEN WAVE. MODELS REMAIN SPLIT ON THE NRN EXTENT OF THE PRECIPITATION AS DEEPER MOISTURE WILL BE FIGHTING HIGH PRESSURE THROUGH ITS PROGRESSION THROUGH THE TN VALLEY. BACKED OFF POPS AND SLOWED TIMING TO FALL IN LINE WITH THE LATEST GFS/ECMWF. AS OF THIS ISSUANCE...EVEN THE SREF MEAN HAS FALLEN MORE IN LINE WITH THE AFOREMENTIONED MODELS...BUCKING THE NRN TRACK IT CLUNG TO EARLIER. TAX && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... THE LONGWAVE PATTERN WILL BECOME MORE MERIDIONAL SUNDAY THROUGH THE FIRST HALF OF NEXT WEEK AS A TROUGH OF LOW PRESSURE DIGS SOUTH OVER THE CENTRAL US AND DEEPENS AS IT TRANSITIONS EASTWARD. LATEST GUIDANCE SHOWS GOOD CONTINUITY WITH THIS FEATURE AND OVERALL ARE IN FAIRLY GOOD AGREEMENT. WITH THAT AND LATEST RMOP AND MODTRENDS VERY SIMILAR TO 24HRS AGO...OPTED TO ADJUST THE EXTENDED TO BE MORE IN LINE WITH A BLEND OF THE 00Z WPC...EC...AND GEFS....WHICH RESULTED IN A FAIRLY BIG INCREASE IN BOTH LOW AND MAX TEMPERATURES TOWARDS THE MIDDLE OF THE WEEK WITH HIGHER CONFIDENCE IN TIMING. CURRENTLY...THE BRUNT OF PRECIPITATION LOOKS TO FALL OVERNIGHT TUESDAY THROUGH WEDNESDAY MORNING AS RAIN AHEAD OF THE COLD FRONT UNDER STRONG WAA AND MOISTURE ADVECTION...WITH LATEST ENSEMBLE GUIDANCE INDICATING V-COMPONENT ANOMALIES BY TUESDAY AFTERNOON AROUND 2 STANDARD DEVIATIONS ABOVE NORMAL. TEMPERATURES ARE FORECAST TO BE AROUND 10 DEGREES ABOVE NORMAL BY TUESDAY AFTERNOON...AND STAYING RELATIVELY WARM TUESDAY NIGHT AS STRONGER SOUTHWEST SURFACE WINDS AHEAD OF THE SYSTEM KEEPS STRONG WAA IN PLAY AND THE LOWER LEVELS MIXED. WHILE THE FINER DETAILS CERTAINLY COULD CHANGE...LATEST MODEL PROGS SHOW COLD AIR BEHIND THE FRONT FULLY INTO THE FORECAST AREA BY CHRISTMAS MORNING AT WHICH TIME ALL PRECIPITATION WOULD CHANGEOVER TO SNOW. CHANGEOVER SHOULD HAPPEN RELATIVELY QUICKLY...BUT THERE IS SOME UNCERTAINTY ON HOW LONG WE MAY SEE MIXED PRECIPITATION BASED ON LATEST PROGGED CRITICAL THICKNESSES. IN GENERAL...CURRENTLY AROUND ONE HALF INCH OF LIQUID PRECIPITATION IS EXPECTED AT THIS TIME AHEAD OF THE COLD FRONT WITH LIGHT SNOWFALL ON THE BACKSIDE. NOMADS REANALYSIS BASED ON THE LATEST 00Z RUN GIVES AROUND A 50 PERCENT CHANCE OF AN INCH OR SO OF SNOW FALLING ON THE BACKSIDE OF THE FRONT THE NIGHT OF THE 24TH AND INTO THE 25TH. && .AVIATION /12Z THURSDAY THROUGH MONDAY/...
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A PERSISTENT LOW LEVEL DECK OF STRATOCUMULUS WILL KEEP SITES UNDER MVFR CIG RESTRICTIONS THROUGH THE MORNING...WITH SITES SOUTH OF INTERSTATE 80 OCCASIONALLY IMPROVING TO VFR AND SLIGHT CHANCE SITES NORTH OF INTERSTATE 80 MAY BRIEFLY SEE IFR AT TIMES WITH OCCASIONAL LIGHT FLURRIES. OUTLOOK.../TUESDAY NIGHT THROUGH SUNDAY/... PERIODIC CIG RESTRICTIONS WILL CONTINUE UNTIL BOUNDARY LAYER FLOW BACKS TO THE SOUTHWEST ON SATURDAY AHEAD OF AN APPROACHING MID-LEVEL TROUGH OF LOW PRESSURE.
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&& .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...NONE. OH...NONE. PA...NONE. WV...NONE. && $$

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