308
FXUS61 KPBZ 201711
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
1211 PM EST FRI DEC 20 2024
SYNOPSIS
WIDESPREAD SNOW SHOWERS ARE LIKELY TODAY INTO SATURDAY WITH THE
APPROACH AND PASSAGE OF LOW PRESSURE. WELL BELOW NORMAL
TEMPERATURE WILL SWEEP IN BEHIND THE COLD FRONT BEFORE
TEMPERATURE SLOWLY MODERATES NEXT WEEK.
NEAR TERM /THROUGH TONIGHT/
KEY MESSAGES:
- STEADY SNOW THIS MORNING TAPERS OFF BY THIS AFTERNOON, WITH
MORE ISOLATED ACTIVITY LATER TODAY AND TONIGHT.
- HIGHEST ACCUMULATIONS EXPECTED OVER NORTHWEST PA AND THE
RIDGES.
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BROAD ASCENT ASSOCIATED WITH ISENTROPIC LIFT/WARM ADVECTION, AS
WELL AS AN AREA OF 700MB FRONTOGENESIS, IS OCCURRING AHEAD OF
AN APPROACHING UPPER TROUGH IS SPREADING AN AREA OF LIGHT TO AT
TIMES MODERATE SNOW ACROSS THE REGION, WITH THE BACK EDGE OF THE
INITIAL BATCH MOVING ACROSS EASTERN OHIO. SNOW HAS
OVERPERFORMED A BIT RELATIVE TO MODEL EXPECTATIONS, WITH SEVERAL
OBSERVATIONS NOTING ACCUMULATION OF AROUND AN INCH, INCLUDING
HERE AT THE OFFICE. COVERAGE WILL GENERALLY WANE FROM WEST TO
EAST THROUGH THE REST OF THE MORNING INTO EARLY AFTERNOON, WITH
MOST ACCUMULATIONS TOPPING AROUND AN INCH, WITH ISOLATED
LOCATIONS PERHAPS APPROACHING 2 INCHES. SOME RAIN MAY MIX IN
WITH ANY LINGERING SNOW AS TEMPERATURES WARM INTO THE MIDDLE AND
UPPER 30S, MAINLY SOUTH OF PITTSBURGH.
MODEL TRENDS STILL INDICATE THAT THE BETTER FORCING/MOISTURE
WILL DIVE MOSTLY SOUTH OF THE CWA THIS AFTERNOON IN THE BASE OF
THE PASSING TROUGH, LEAVING OUR REGION IN A RELATIVE LULL OF
ACTIVITY INTO TONIGHT, WITH ANY ACTIVITY STARTING TO FOCUS ON
AREAS NORTH OF I-80 AND ALONG THE RIDGES AS NORTHWEST FLOW AND
COLD ADVECTION TAKE OVER BEHIND THE CROSSING SURFACE LOW. NBM
PROBABILITIES OF 3+ INCHES OF SNOW IN THESE AREAS STILL REMAIN
LOW, AND HEADLINES ARE STILL NOT ANTICIPATED AT THIS TIME.
SHORT TERM /SATURDAY THROUGH SUNDAY/
KEY MESSAGES:
- WIDESPREAD SNOW EXPECTED INTO SATURDAY MORNING, AREAL
COVERAGE MAY BE SPOTTIER AT TIMES.
- ACCUMULATIONS ARE LIKELY HIGHEST FOR THE RIDGES AND PORTIONS
OF THE I-80 CORRIDOR.
- LAKE EFFECT AND UPSLOPE SNOW POSSIBLE SATURDAY.
- COLD AND DRY SUNDAY.
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TRANSITION OF THE UPPER TROUGH AXIS EAST SATURDAY WILL ENABLE
STRONGER 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 WHILE OTHER AREAS REMAIN SNOW FREE.
GLOBAL AND HI-RES MODELS REMAIN BULLISH ON THIS FEATURE, 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 PRODUCE 1-2" OF SNOWFALL ACCUMULATION, BUT
FURTHER ANALYSIS WILL BE REQUIRED AS HI-RES MODEL DATA BEGINS TO
COVER THE BANDS.
HEIGHT RISES AND STRONG SUBSIDENCE OF THE MEAGER MOISTURE
COLUMN SHOULD END ALL SNOWFALL BY LATE SATURDAY NIGHT.
THERE IS HIGH CONFIDENCE IN DRY WEATHER WITH BELOW AVERAGE
TEMPERATURE SUNDAY UNDER THE INFLUENCE OF HIGH PRESSURE WHILE
HEIGHT RISES CONTINUES ALOFT.
LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/
KEY MESSAGES:
- COLD DRY WEATHER CONTINUES INTO MONDAY.
- INCREASING LIKELIHOOD FOR PRECIPITATION, INCLUDING SNOW, FOR
NORTHERN AREAS CHRISTMAS EVE.
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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 /17Z FRIDAY THROUGH TUESDAY/
THE SURFACE LOW CENTER AND UPPER TROUGH AXIS WILL CROSS THIS
AFTERNOON AND EVENING AND SHUNT CURRENT AREAS OF SNOWFALL ENE OF
THE REGION, WITH A LACK OF LIFT TRENDING DOWN SHOWER ACTIVITY.
RESTRICTIONS NORTH OF A LLVL BOUNDARY NEAR KPIT MAY LINGER IN
IFR THROUGH 00Z WHILE SOUTHERN TERMINALS VARY BETWEEN LOW VFR TO
MVFR. FARTHER TO THE WEST, JET-AIDED BANDS OF SNOW MAY CLIP
ZZV/MGW TO OFFER SOME REDUCTIONS AFT 20Z, BUT MODELS FAVOR A
SHORT DURATION IMPACT BEFORE SNOW FOCUS OVER THE HIGHER
TERRAIN.
TRANSITION OF THE SYSTEM EAST WILL BRING THE COLD FRONT THROUGH
AROUND 00Z THAT WILL LEAD TO A NW WIND SHIFT, MORE UNIFORM MVFR
(WITH POCKETS OF IFR) CEILINGS, AND CONTINUED ISOLATED SNOW
SHOWERS (TOO LOW PROBABILITY FOR TAF MENTION). GREATER ADVECTION
WITH MORE IDEAL WIND ANGLES MAY FAVOR A FEW, NARROW BANDS OF
LAKE ENHANCED SNOW SHOWERS FAVORING WEST CENTRAL TO NORTHWEST PA
AFTER 12Z SATURDAY. WHILE MIXING AND DRY ADVECTION SLOWLY LIFT
CIGS, THESE SHOWERS COULD OFFER PERIODIC AND LOCALIZED MVFR
CIG/IFR VSBY RESTRICTIONS. OUTSIDE OF THE SHOWERS, EXPECT A
RETURN TO VFR SATURDAY AFTERNOON WITH DEEPER MIXING YIELDING
15-25KT GUSTS AND POTENTIAL FOR SCATTERING OF THE STRATOCU
FIELD.
OUTLOOK...
VFR UNDER THE INFLUENCE OF HIGH PRESSURE IS FAVORED
SUNDAY INTO MONDAY BEFORE THE NEXT UPPER LEVEL SYSTEM CROSSES
THEN REGION LATE MONDAY INTO TUESDAY, BRINGING ANOTHER ROUND OF
LIGHT SNOW AND AREAWIDE RESTRICTIONS.
PBZ WATCHES/WARNINGS/ADVISORIES
PA...NONE.
OH...NONE.
WV...NONE.
SYNOPSIS...22/FRAZIER
NEAR TERM...22/FRAZIER/CL
SHORT TERM...22/FRAZIER
LONG TERM...FRAZIER
AVIATION...FRAZIER
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