715
FXUS61 KPBZ 191849
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
149 PM EST THU DEC 19 2024
SYNOPSIS
WIDESPREAD SNOW IS LIKELY FRIDAY INTO SATURDAY WITH THE APPROACH
AND PASSAGE OF A LOW PRESSURE SYSTEM, WITH ACCUMULATIONS
FAVORING NORTHWEST PENNSYLVANIA AND THE WEST VIRGINIA HIGHER
TERRAIN. WELL BELOW AVERAGE TEMPERATURE WILL DEVELOP BEHIND THE
COLD FRONT BEFORE TEMPERATURE SLOWLY MODERATES NEXT WEEK.
NEAR TERM /THROUGH TONIGHT/
KEY MESSAGES:
- DRY WEATHER EXPECTED WITH MINIMAL DIURNAL HEATING UNDER A
STAGNANT CLOUD DECK.
- INCREASING POTENTIAL FOR LIGHT SNOWFALL ACCUMULATIONS IN
NORTHWEST PA AHEAD OF MORNING COMMUTE.
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HIGH PRESSURE POSITIONED NEAR NORTHERN NY WILL HELP TO MAINTAIN
DRY WEATHER TODAY AS THE NEXT UPPER LEVEL TROUGH APPROACHES FROM
THE NORTHWEST. AREA STRATUS IS LIKELY TO REMAIN STAGNANT INTO
THE EVENING AS MOISTURE REMAINS TRAPPED BENEATH A POST-FRONTAL
INVERSION AND LITTLE FORCING/ADVECTION WILL AID ITS EROSION.
THUS, EXPECT DIURNAL TEMPERATURE TO BE MUTED THROUGH THE REST OF
THE AFTERNOON AND EVEN SHOW LIMITED COOLING OVERNIGHT AS ANY
CLEARING IS SOON COVERED BY HIGHER CLOUD LAYERS.
APPROACH OF THE UPPER TROUGH FROM THE NW IS EXPECTED OVERNIGHT
AS THE SURFACE LOW TRACKS TOWARD WEST CENTRAL OH. THERE IS
POTENTIAL FOR ENOUGH JET ASCENT COMBINING WITH AN EMBEDDED 700MB
WAVE TO GENERATE SNOW AFT 06Z IN THE NE QUADRANT OF THE SYSTEM.
THIS POTENTIAL IS FAVORED WITHIN THE INITIAL HI-RES MODEL RUNS
REACHING THE TIME PERIOD; SUCH DEVELOPMENT COULD FOSTER A QUICK
1" OF SNOW AHEAD OF THE MORNING COMMUTE MAINLY ALONG THE I-80
CORRIDOR. OTHERWISE, ANY LIGHT PRECIPITATION THAT DEVELOPS
SHOULD REMAIN FARTHER WEST NEAR THE LOW CENTER OR ALONG THE
EASTERN SLOPES OF THE HIGHER TERRAIN WITH WEAK UPSLOPE FLOW.
SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/
KEY MESSAGES:
- WIDESPREAD SNOW FAVORED FRIDAY INTO SATURDAY MORNING, THOUGH
AREAL COVERAGE MAY BE SPOTTIER AT TIMES.
- ACCUMULATIONS ARE LIKELY TO HIGHEST FOR THE WV HIGHER TERRAIN
AND ALONG THE HIGHER TERRAIN SPINE TOWARD THE I-80 CORRIDOR.
- LAKE EFFECT AND UPSLOPE SNOW POSSIBLE ON SATURDAY.
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THE UPPER TROUGH WILL TRANSITION ACROSS THE REGION THROUGH THE
DAY FRIDAY WHILE THE SURFACE MOVES INTO EASTERN OH BEFORE
PHASING WITH THE DEVELOPING COASTAL LOW. BROAD FORCING/ASCENT
PLUS COLD ADVECTION WILL FUEL MAINLY SNOW SHOWER DEVELOPMENT
THROUGH MUCH OF THE DAY INTO SATURDAY MORNING. CONFIDENCE IS
HIGH IN GENERALLY LESS THAN 1" ACCUMULATIONS FOR LOWER ELEVATION
AREAS THROUGH 6AM SATURDAY (80 TO NEAR 100% PROBABILITY) WHILE
HIGHEST AMOUNTS WILL BE TETHERED TO THE HIGHER WV TERRAIN AND
ALONG THE LAUREL HIGHLANDS TOWARD THE I-80 CORRIDOR. FOR THE
I-80 CORRIDOR TOWARD CENTRAL PA, AVAILABLE GUIDANCE SUGGESTS THE
PRIMARY ACCUMULATION WINDOW BEING ~4AM TO 2PM FRIDAY BEFORE
MOISTURE VACATES NE. FOR THE LAUREL HIGHLANDS INTO THE WV HIGH
TERRAIN, AVAILABLE GUIDANCES SUGGESTS THE PRIMARY ACCUMULATION
WINDOW BEING ~2PM FRIDAY THROUGH 6AM SATURDAY.
THE BIGGEST UNCERTAINTY LAYS IN TOTAL QPF AVAILABLE AS SHOWERS
GENERATE AS WELL AS SHORTWAVE PLACEMENT ON THE SW EDGE OF THE
TROUGH AND ITS UPSLOPE WIND COMPONENT AS IT REACHES THE HIGH
TERRAIN. CIPS AND GLOBAL GUIDANCE ARE MORE BULLISH FOR
ADVISORY-LEVEL ACCUMULATIONS IN THE WV HIGH TERRAIN (AND LESSER
FOR NW PA CORRIDOR) WHEREAS INITIAL HI-RES MODELS PUSH THE WAVE
FARTHER SOUTH, LIMITING THE UPSLOPE COMPONENT AND KEEPING
MOISTURE DEPTHS ON THE LOWER END OF THE DGZ. THESE LATEST TRENDS
LOWERS THE PROBABILITY OF 3+" FOR WV HIGH TERRAIN (20-50%),
RESULTING IN NO ACTION ON WINTER HEADLINES AT THIS TIME.
TRANSITION OF THE UPPER TROUGH AXIS EAST SATURDAY WILL ENABLE
GREATER COLD ADVECTION WITHIN NORTHERLY TO NORTHWESTERLY
BOUNDARY-LAYER FLOW. THIS FLOW OVER THE WARM LAKE WATERS WILL
FOSTER NARROW BANDS OF LAKE ENHANCED SNOW SHOWERS FOR LOCALIZED
PORTIONS OF THE REGION (FAVORING 15Z/10AM THROUGH 03Z/10PM)
WHILE SNOW ENDS FOR OTHER AREAS. GLOBAL AND INITIAL HI- RES
MODELS HAVE REMAINED BULLISH ON THIS FEATURE DEVELOPMENT, THOUGH
VARIATION REMAINS IN BAND INTENSITY/ORIENTATION/LOCATION BUT
SHOULD GENERALLY START AS A FETCH OF LAKE HURON AND MOVE TOWARD
THE OH/PA BORDER NW OF PITTSBURGH. IT STILL APPEARS THAT THESE
BANDS WILL ONLY ADD AN 1-2" OF SNOWFALL ACCUMULATION TO THE SUB-
ADVISORY AMOUNTS IN THE AREA, BUT FURTHER ANALYSIS AS MORE HI-
RES MODELS REACH THIS TIMEFRAME IS NEEDED TO ASSESS POTENTIAL
FOR GREATER IMPACTS/ACCUMULATIONS.
HEIGHT RISES AND STRONG SUBSIDENCE OF THE MEAGER MOISTURE
COLUMN SHOULD END ALL SNOWFALL BY SATURDAY NIGHT.
LONG TERM /SUNDAY THROUGH WEDNESDAY/
KEY MESSAGES:
- COLD BUT DRY WEATHER LIKELY SUNDAY INTO MONDAY.
- INCREASING LIKELIHOOD FOR PRECIPITATION, INCLUDING SNOW, FOR
NORTHERN AREAS CHRISTMAS EVE.
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THERE IS HIGH CONFIDENCE IN DRY WEATHER WITH BELOW AVERAGE
TEMPERATURE SUNDAY UNDER THE INFLUENCE OF HIGH PRESSURE WHILE
HEIGHT RISES CONTINUES ALOFT.
ENSEMBLES FAVOR SHORTWAVE RIDGING TO QUICKLY TRAVERSE THE AREA
AHEAD OF THE NEXT WEAKER BUT LIKELY SWIFT MOVING SHORTWAVE
ARRIVES LATE MONDAY INTO TUESDAY. EXPECT TEMPERATURE MODERATION
MONDAY WITH THE DEGREE OF MODERATION DEPENDENT ON TIMING OF MID
AND HIGH LEVEL CLOUD ARRIVALS.
THOUGH TIMING AND STRENGTH OF THE AFOREMENTIONED SHORTWAVE
REMAINS VARIABLE, ITS CROSSING SHOULD GENERATE AN AREA OF
PRECIPITATION FAVORING NORTHWEST PA (DUE TO CLOSER PROXIMITY TO
THE WAVE). LATEST GUIDANCE SUGGESTS A 30-70% CHANCE FOR
ACCUMULATING SNOWFALL NORTH OF THE MASON-DIXON LINE THROUGH
TUESDAY EVENING/CHRISTMAS EVE, BUT THE LACK OF DEEPER MOISTURE
AND COLDER AIR LIKELY WILL PREVENT NOTABLE ACCUMULATIONS (ONLY
NORTHWEST PA SEES 20-30% PROBABILITY FOR GREATER THAN 1" OF
SNOW). OTHERWISE, THE WARMING TREND IS LIKELY TO CONTINUE INTO
WEDNESDAY/CHRISTMAS DAY WITH GRADUAL HEIGHT RISES THAT LIKELY
WILL RESULT IN SLIGHTLY ABOVE NORMAL TEMPERATURE.
AVIATION /18Z THURSDAY THROUGH TUESDAY/
A STRATOCUMULUS DECK REMAINS IN PLACE ACROSS THE REGION THIS
AFTERNOON, AS A THIN LAYER OF MOISTURE REMAINS TRAPPED
UNDERNEATH AN INVERSION AT AROUND 825MB. CEILINGS ARE STILL
STRADDLING THE MVFR/VFR THRESHOLD. EXPECT THIS TO CONTINUE THIS
AFTERNOON, WITH A TREND TOWARDS VFR THIS EVENING AS WEAK WARM
ADVECTION ENSUES - HREF MVFR PROBABILITIES BACK OFF TO 50
PERCENT OR LESS AREAWIDE.
TONIGHT, CEILINGS SHOULD DRIFT BACK DOWN TO MVFR AS LOW PRESSURE
APPROACHES THE GREAT LAKES. HREF PROBABILITIES INCREASE BACK
ABOVE 70 PERCENT FOR MUCH OF WESTERN PA/NORTHERN WV. LIGHT SNOW
MAY BREAK OUT JUST PRIOR TO 12Z, MAINLY NORTH OF PIT. VCSH WAS
USED AT THE MAJORITY OF TAF SITES, BUT CONFIDENCE IN AT LEAST
MVFR VISIBILITY RESTRICTION IS HIGHEST AT FKL/DUJ, WHERE IFR
CEILINGS ARE ALSO A STRONG POSSIBILITY.
OUTLOOK...
MORE WIDESPREAD RESTRICTIONS ARE LIKELY FRIDAY AFTERNOON AND
NIGHT AS LOW PRESSURE CROSSES THE REGION. OCCASIONAL
RESTRICTIONS MAY THEN CONTINUE THROUGH SATURDAY AS COLD
ADVECTION UNDER NORTHWEST FLOW PROMOTES THE CONTINUATION OF
LAKE-EFFECT CLOUDS AND SCATTERED SNOW SHOWERS. THE NEXT CHANCE
FOR VFR LOOKS TO BE LATER SATURDAY NIGHT OR SUNDAY.
PBZ WATCHES/WARNINGS/ADVISORIES
PA...NONE.
OH...NONE.
WV...NONE.
SYNOPSIS...FRAZIER
NEAR TERM...FRAZIER
SHORT TERM...FRAZIER
LONG TERM...FRAZIER
AVIATION...CL
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