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/...

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

&&

.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/...
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. &&

.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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