262
FXUS61 KPBZ 180029
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
729 PM EST TUE DEC 17 2024
SYNOPSIS
RAIN RETURNS ON WEDNESDAY, WITH COLDER TEMPERATURES AND LIGHT
SNOW SHOWERS POSSIBLE TO END THE WEEK AND THROUGH THE WEEKEND.
CONFIDENCE IS INCREASING THAT BELOW AVERAGE TEMPERATURES ARE
EXPECTED OVER THE WEEKEND.
NEAR TERM /THROUGH WEDNESDAY/
KEY MESSAGES:
- INCREASING CLOUDS OVERNIGHT WITH AN APPROACHING DISTURBANCE
- RAIN CHANCES INCREASE JUST BEFORE DAWN
- CAN'T RULE OUT A BRIEF PERIOD OF WINTRY MIX MID-DAY NORTH OF
PITTSBURGH
- SNOW CHANCES INCREASE NORTH TO SOUTH AFTER SUNSET
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CLOUDS WILL INCREASE LATE TONIGHT/EARLY WEDNESDAY MORNING WITH
AN APPROACHING LOW PRESSURE SYSTEM. TEMPERATURES SHOULD
MODERATE SOME LATER IN THE NIGHT AS THE CLOUDS MOVE IN AND HELP
MITIGATE RADIATIVE COOLING.
THE NEXT WEATHER SYSTEM WILL ARRIVE IN OUR REGION BETWEEN 11Z
TO 13Z FROM THE SOUTHWEST. ANTICIPATE A DEEPENING TROUGH
TRAVERSING THE GREAT LAKES REGION WHILE A WEAK SURFACE LOW LIFTS
FROM THE TN RIVER VALLEY TOWARDS THE MID- ATLANTIC. BROAD JET
ASCENT IS EXPECTED TO DEVELOP A PLUME OF PRECIPITATION THAT
CROSSES THE UPPER OHIO RIVER VALLEY AFTER MIDNIGHT, REACHING OUR
EASTERN OHIO COUNTIES AROUND DAYBREAK.
PRECIPITATION IS EXPECTED TO REMAIN PREDOMINANTLY RAIN THROUGH
EARLY AFTERNOON AS 850MB TEMPERATURES HOVERING AROUND 2-4
DEGREES C AND SURFACE TEMPERATURES ABOVE FREEZING UNDER
SOUTHWEST FLOW. HOWEVER, AS A COLD FRONT ADVANCES INTO THE
REGION FROM THE NORTH BETWEEN 17Z AND 19Z, SOME SNOW OR ICE
PELLETS COULD MIX NEAR I-80 BEFORE PRECIPITATION TAPERS OFF
FROM MID-LEVEL DRY AIR ADVANCING IN FROM THE WEST.
A MAJORITY OF THE HEAVIER PRECIP IS EXPECTED TO END BEFORE 8PM.
CONFIDENCE IS HIGHER THAT THE HEAVIEST RAINFALL AMOUNTS WILL BE
IN NORTHERN WEST VIRGINIA, 0.60" TO 1.00" IS EXPECTED TO
ACCUMULATED THERE THROUGH LATE WEDNESDAY. ELSEWHERE, EXPECTED
0.10 TO 0.50 INCHES, WITH LOWER AMOUNTS NORTH OF PITTSBURGH.
SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY/
KEY MESSAGES:
- POTENTIAL FOR FREEZING RAIN/DRIZZLE IN EASTERN TUCKER LATE
WEDNESDAY
- COLDER TEMPERATURES ON THURSDAY.
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WITH LINGERING SHALLOW MOISTURE ALONG THE RIDGES AND FALLING
TEMPS AT THE SURFACE, FREEZING RAIN/DRIZZLE COULD OCCUR ALONG
THE RIDGES OF EASTERN TUCKER BETWEEN 8PM WED TO 1AM THURS. THIS
THREAT HAS BEEN HIGHLIGHTED IN THE HWO.
NORTHWEST WINDS BEHIND THE FRONT WILL THEN SUPPORT SCATTERED
LIGHT LAKE-EFFECT SNOW SHOWERS OVERNIGHT INTO EARLY THURSDAY
MORNING, PRIMARILY NORTHEAST OF PITTSBURGH AND IN THE RIDGES.
LITTLE OVERALL ACCUMULATION IS EXPECTED, GENERALLY A DUSTING TO
PERHAPS A HALF INCH. ALL PRECIPITATION ENDS ON THURSDAY AS HIGH
PRESSURE BUILDS INTO THE AREA, THOUGH COLD ADVECTION BEHIND
WEDNESDAY'S FRONT WILL FAVOR MORE SEASONABLE TEMPERATURES AND
CONTINUED CLOUD COVER.
LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/
KEY MESSAGES:
- HIGH PROBABILITY FOR TEMPERATURES AROUND 10 DEGREES BELOW
NORMAL FOR THE WEEKEND.
- SNOWFALL POTENTIAL CONTINUES TO APPEAR LOW END, WITH THE
THREAT FOR ANY IMPACTS LIKELY LIMITED TO NEAR LAKE ERIE.
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ANOTHER UPPER LEVEL TROUGH IS LIKELY TO DEVELOP OVER THE EASTERN
CONUS FRIDAY INTO THE WEEKEND AS IT DROPS SOUTHEAST FROM CENTRAL
CANADA. THIS PATTERN SHIFT WILL SUPPORT ANOTHER PERIOD OF
PRECIPITATION (MAINLY SNOW) WITH THE INITIAL WAVE PASSAGE FRIDAY
INTO SATURDAY) AND BELOW AVERAGE TEMPERATURE INTO THE WEEKEND.
MODEL VARIATIONS REMAIN FAIRLY HIGH ON THE OVERALL DEPTH OF THE
TROUGH AS WELL AS THE SHORTWAVE MOVEMENT WITHIN IT; THESE
FACTORS WILL PLAY LARGER ROLES IN HOW ACTIVE LAKE EFFECT SNOW
DEVELOPS AND THE BOUNDARY LAYER FLOW ANGLE FOR THOSE BANDS.
DEEPER/COLDER LEADS TO MORE EFFECTIVE SNOW BANDS (MEANING
GREATER ACCUMULATION POTENTIAL FOR FAR NORTHWEST PA AND THE
HIGHER TERRAIN) WHILE LESS DEEP/SLIGHTLY WARMER KEEPS THE REGION
DRIER AND LEADS TO MORE INCONSEQUENTIAL SNOWFALL TOTALS. STAY
TUNED AS SMALL-SCALE VARIATIONS FOR THIS WEEKEND PERIOD WILL
DETERMINE IF IMPACTS MAY DEVELOP OR NOT.
AVIATION /01Z WEDNESDAY THROUGH SUNDAY/
FAIRLY HIGH CONFIDENCE FORECAST OF VFR THROUGH THE TAF PERIOD
OVER THE NEXT 10 TO 12 HOURS.
WARM, MOIST ADVECTION AHEAD OF THE NEXT UPPER LEVEL TROUGH WILL
SPREAD RAIN AND LOWERING CEILINGS WITH RESTRICTIONS GENERALLY
DEVELOPING A FEW HOURS AFTER RAIN ONSET. THE EARLIEST
PRECIPITATION ONSET TIME IS 12Z-14Z WEDNESDAY, WITH A MOST
LIKELY TIMEFRAME OF 14Z-18Z.
WIDESPREAD RAIN AND MVFR/IFR RESTRICTIONS ARE LIKELY WEDNESDAY
AFTERNOON AND EVENING AMID WARM, MOIST ADVECTION AHEAD OF THE
NEXT UPPER LEVEL DISTURBANCE. PASSAGE OF THE SURFACE COLD FRONT
AFTER 00Z WILL SUPPORT A POTENTIAL RAIN-TO-SNOW TRANSITION.
ENSEMBLE MODELS ARE BEARISH FOR A REPRIEVE OF MVFR CIGS (MOST
TERMINALS WITH 50-80% PROBABILITY OF PERSISTENCE) UNTIL THURSDAY
EVENING.
OUTLOOK...
AN APPROACHING LOW PRESSURE SYSTEM OUT OF THE MIDWEST WILL
LIKELY KEEP RESTRICTION IN THE REGION THROUGH FRIDAY. NUMEROUS
ENSEMBLE MODELS SUGGEST THE PRECIP TYPE WITH THIS PASSING SYSTEM
WILL REMAIN AS SNOW.
PBZ WATCHES/WARNINGS/ADVISORIES
PA...NONE.
OH...NONE.
WV...NONE.
SYNOPSIS...CERMAK/HEFFERAN
NEAR TERM...CERMAK/HEFFERAN
SHORT TERM...CERMAK/22/FRAZIER
LONG TERM...CERMAK/FRAZIER
AVIATION...HEFFERAN/FRAZIER
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