406
FXUS61 KPBZ 202335
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
635 PM EST SAT DEC 20 2025
SYNOPSIS
A "MOSTLY DRY" COLD FRONT PASSES OVERNIGHT, WITH DRIZZLE
CHANCES IN THE HIGH TERRAIN. COOL AND DRY SUNDAY WITH THE NEXT
DISTURBANCE FORECAST MONDAY NIGHT INTO TUESDAY, ACCOMPANIED BY
A WARMUP. ODDS OF A "WHITE CHRISTMAS" ARE NULL THIS YEAR WITH
ABOVE AVERAGE TEMPERATURES.
NEAR TERM /THROUGH SUNDAY/
KEY MESSAGES:
- DRIZZLE POSSIBLE OVERNIGHT IN THE RIDGES.
- LIGHT SNOW SHOWERS POSSIBLE NORTH OF I-80 ON SUNDAY.
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HIGH CLOUDS WILL CONTINUE TO INCREASE OVERNIGHT, GIVING WAY TO A
"MOSTLY DRY" SURFACE COLD FRONT PASSAGE. AT THIS TIME, FORCING
APPEARS WEAK AND THE LOW LEVELS TOO DRY TO SUPPORT ANY PRECIPITATION
ALONG IT, UNTIL IT REACHES THE RIDGES WHICH AID IN OROGRAPHIC LIFT.
SOUNDINGS HAVE HIGH CONFIDENCE IN SATURATION LESS THAN -10C AT
ONSET, INDICATING DRIZZLE MAY BE THE PRIMARY PRECIPITATION TYPE IN
THE RIDGES. THE ONLY QUESTION BETWEEN DRIZZLE AND FREEZING DRIZZLE
IS WHETHER THE RIDGES WILL BE BELOW FREEZING BY THEN (FORECAST TO
DROP BY 07Z TO 09Z). NONETHELESS, EVEN THE WARM SURFACE FROM TODAY,
IMPACTS TO SIDEWALKS OR ROADWAYS SEEM MINIMAL, EVEN SHOULD IT OCCUR.
ON SUNDAY, A SURFACE BASED HIGH WILL BUILD IN AS AN UPPER-LEVEL
TROUGH SWINGS THROUGH THE AREA BEHIND TODAY'S WEAK LOW. THIS WILL
INCREASE LOW CLOUDS FROM THE NORTH ESPECIALLY AS A NORTHWESTERLY
FLOW KICKS IN. THERE MAY BE SHALLOW ENOUGH SATURATION TO SUPPORT
SOME LIGHT SNOW SHOWERS NORTH OF I-80. ENSEMBLES ARE SHOWING A WEAK
LAKE EFFECT SIGNATURE WITH A 40%-70% CHANCE TO ACCUMULATE MEASURABLE
SNOW (>0.1") ACROSS PARTS OF VENANGO, FOREST, CLARION, AND JEFFERSON
(PA) COUNTIES. THERE IS UNCERTAINTY ON THEIR TIMING & LOCATION,
HOWEVER, THERE IS NO SIGNIFICANT SNOW ACCUMULATION EXPECTED WITH
THESE POTENTIAL LIGHT BANDS AS THE CHANCE FOR >0.25" OF SNOW IS LESS
THAN 25%. CHANCES FOR SNOW SHOWERS IN THESE AREAS WILL DECREASE
AFTER SUNSET SUNDAY EVENING.
SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/
KEY MESSAGES:
- COOL MONDAY MORNING; CLOUDS AND WARMING TREND AFTERWARD.
- LOW CHANCE OF FREEZING RAIN NORTH OF PITTSBURGH MONDAY NIGHT.
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BEHIND THE SHORTWAVE TROUGH PASSAGE WILL ENSUE SHORTWAVE RIDGING
AND A BRIEF BOUT OF SURFACE HIGH PRESSURE SUNDAY NIGHT INTO
EARLY MONDAY. THIS WILL ACT TO CLEAR THE SKIES AND LEND TO AN
EFFICIENT RADIATIVE COOLING NIGHT, BRINGING LOWS AROUND 10
DEGREES BELOW NORMAL, THROUGH LIGHT TO CALM WINDS SHOULD KEEP
WIND CHILLS AT BAY. WARMING TEMPERATURES AND INCREASING CLOUDS
ARE EXPECTED FOR THE DAY MONDAY AS THE NEXT DISTURBANCE
APPROACHES FROM THE WEST. HIGHS ARE EXPECTED TO BE NEAR NORMAL.
MONDAY NIGHT, A SYSTEM IS EXPECTED TO SWEEP THROUGH THE AREA AS
A WARM FRONT BRINGS PRECIPITATION. THIS IS >90% LIKELY TO FALL
AS ALL RAIN OUTSIDE OF THE I-80 CORRIDOR. IN VENANGO, FOREST,
CLARION, JEFFERSON, AND INDIANA COUNTIES, THERE IS SOME
UNCERTAINTY IN PRECIPITATION TYPE. WHILE MOST ENSEMBLES FAVOR
RAIN, MODELS TEND TO PREFORM POORLY WITH EVACUATING EXISTING
COLD AIR.
IN THE WARM SCENARIO WHERE THE WARM FRONT ARRIVES AFTER
DAYBREAK TUESDAY, THE AFOREMENTIONED COUNTIES MAY REMAIN ALL
RAIN AND HAVE NO IMPACTS. IN THE COOLEST SCENARIO, WHERE THE
WARM FRONT ARRIVES EARLY OVERNIGHT, COUNTIES COULD SEE T-1" OF
SNOW, WHICH TRANSITIONS TO A LIGHT COATING OF FREEZING RAIN. IN
THE CURRENT FORECAST, WE MAINTAIN MORE OF A MEDIAN SOLUTION OF A
LIGHT COATING OF FREEZING RAIN RAPIDLY OVERRODE BY RAIN.
LONG TERM /TUESDAY THROUGH SATURDAY/
KEY MESSAGES:
- RAIN CHANCES TUESDAY AFTERNOON
- ABOVE-NORMAL TEMPERATURES OVER CHRISTMAS
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LONG-RANGE GUIDANCE STRONGLY FAVORS A WARM PATTERN FROM TUESDAY
AFTERNOON INTO FRIDAY, SUPPORTED BY A PRONOUNCED RIDGE OVER THE
GREAT PLAINS. DURING THIS PERIOD, ANY DISTURBANCE THAT ADVANCES
THROUGH THE REGION WILL MAINLY FALL AS RAIN, WITH PERHAPS A
BRIEF RAIN/SNOW MIX NORTH OF PITTSBURGH WITH NO IMPACTS. SOME
MODEL SOUNDINGS EVEN SUGGEST THE POTENTIAL OF THUNDERSTORMS
EARLY CHRISTMAS MORNING ALONG A WARM FRONT, DRIVEN BY ELEVATED
INSTABILITY. AS THE EVENT APPROACHES, CONFIDENCE WILL INCREASE
IN ASSESSING ANY THREATS BEYOND THE POTENTIAL FOR LIGHTNING.
AVIATION /00Z SUNDAY THROUGH THURSDAY/
KEY MESSAGES:
- VFR WITH LLWS OVERNIGHT.
- RESTRICTIONS LIKELY AT BVI, DUJ, AND FKL SUNDAY.
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THERE IS HIGH CONFIDENCE IN VFR AND LIGHT SOUTHWEST WINDS
THROUGH MUCH OF TONIGHT AS A MID-LEVEL CLOUD DECK OVERSPREADS
THE AREA. THE LOW-LEVEL WIND SHEAR THREAT INCREASES OVERNIGHT
GIVEN THE LIGHT SURFACE WINDS AND SOUTHWEST FLOW AT 2KFT AGL
INCREASING TO AROUND 45 KNOTS. A DRY COLD FRONT IS EXPECTED TO
PASS THROUGH IN THE 06Z TO 12Z TIMEFRAME, BRINGING SURFACE WIND
GUSTS BACK TO THE FORECAST (ENDING LLWS THREAT) AND POTENTIALLY
AN MVFR STRATOCU DECK IN ITS WAKE. THE BEST CHANCE FOR MVFR
CEILINGS IS NORTH OF PIT WHILE THE LOWEST CHANCES ARE AT ZZV AND
MGW.
THERE IS STILL SOME UNCERTAINTY REGARDING THE DENSITY OF CLOUD
COVER (SCT VS. BKN/OVC) AND CEILING (MVFR VS. LOW-END VFR). FOR
THIS FORECAST CYCLE, ERRED ON THE PESSIMISTIC SIDE WITH
COVERAGE AND INTRODUCED BKN INSTEAD OF SCT EVERYWHERE EXCEPT
ZZV, HLG, AND MGW. MEANWHILE, MAINTAINED CEILINGS AROUND 3-4KFT
AGL FOR MOST TERMINALS EXCEPT FKL/DUJ/BVI WHERE LOWER BASES IN
THE 1.5-2.5KFT AGL RANGE WERE FAVORED GIVEN HIGHER PROBABILITIES
FOR MVFR AT THOSE LOCATIONS.
OUTLOOK...
VFR RETURNS AREAWIDE SUNDAY NIGHT INTO MONDAY. WIDESPREAD
RESTRICTIONS RETURN OVERNIGHT MONDAY INTO TUESDAY WITH CHANCES
OF RAIN (AND -FZRA AT DUJ).
PBZ WATCHES/WARNINGS/ADVISORIES
PA...NONE.
OH...NONE.
WV...NONE.
SYNOPSIS...MILCAREK
NEAR TERM...MILCAREK/LUPO
SHORT TERM...MILCAREK
LONG TERM...HEFFERAN
AVIATION...CERMAK/MILCAREK
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