534
FXUS61 KPBZ 210651
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
151 AM EST SUN DEC 21 2025
SYNOPSIS
DRY COLD FRONT PASSING THIS MORNING MEANS TEMPERATURE GENERALLY
FALLING THROUGH THE DAY WITH BREEZY WIND CREATING WIND CHILLS IN
THE TEENS AND TWENTIES.
THE NEXT WEATHER SYSTEM WILL ARRIVE LATE MONDAY INTO TUESDAY
WITH MOSTLY RAIN, THOUGH A WINTRY MIX PERIOD IS POSSIBLE FOR
PORTIONS OF NORTHWEST PENNSYLVANIA AND THE HIGHER TERRAIN.
TEMPERATURE IS FAVORED TO RISE THE REST OF THE WEEK WITH
PERIODIC PRECIPITATION CHANCES.
NEAR TERM /THROUGH TONIGHT/
KEY MESSAGES:
- PASSING COLD FRONT OFFERS LITTLE PRECIPITATION BUT COMES WITH
FALLING TEMPERATURE
- CALM AND CLEARING CONDITIONS FAVOR SEASONABLY COOL OVERNIGHT
LOWS
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THOUGH MODEL DEPICTIONS HAVE GENERALLY BEEN TOO FAST WITH THE
SOUTHEAST PROGRESSION OF A SURFACE COLD FRONT (RESULTING IN MILD
OVERNIGHT TEMPERATURE), IT IS STILL FAVORED TO DROP SOUTHEAST
THIS MORNING AS THE UPPER TROUGH AXIS PASSES OVERHEAD. NOTABLY
DRY AIR PRESENT AND LITTLE ADVECTING IN WITH THE FRONT MEANS DRY
CONDITIONS ARE HIGHLY LIKELY SAVE FOR A NON-ZERO POSSIBILITY OF
A FEW FLURRIES BEING SQUEEZED OUT OF LOWER CLOUD DECKS
DEVELOPING OFF LAKE ERIE. THE MAIN FOCUS, THEN, IS AREA
TEMPERATURE GENERALLY FALLING DURING THE DAYLIGHT HOURS; TODAY'S
HIGHS WILL BE THE READINGS SEEN JUST AFTER MIDNIGHT. BREEZY
WINDS WITH A MIXED LAYER AND SURFACE GRADIENT ALSO MEANS
AFTERNOON WIND CHILLS FALLING INTO THE TEENS TO 20S.
SURFACE HIGH PRESSURE WILL CENTER OVER THE UPPER OHIO RIVER
VALLEY OVERNIGHT AS NORTHWEST FLOW ALOFT WANES SLIGHTLY. THE
RESULTANT CLEAR AND CALM CONDITIONS FAVOR STRONG RADIATIONAL
COOLING THAT DROPS AREA TEMPERATURE BELOW SEASONAL AVERAGES (AND
COULD END UP A FEW DEGREES LOWER THAN FORECASTED).
SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/
KEY MESSAGES:
- TEMPERATURE MODERATION MONDAY WITH INCREASING CLOUDS
- MONITORING FREEZING RAIN POTENTIAL NE OF PITTSBURGH EARLY
TUESDAY MORNING
- RAIN AREAWIDE THROUGH THE DAY TUESDAY BEFORE TAPERING OFF AT
NIGHT
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A DEVELOPING UPPER LEVEL SHORTWAVE WITHIN NORTHWEST FLOW WILL
ENCROACH THE AREA THROUGH THE DAY MONDAY, FOSTERING WARM
ADVECTION ALOFT THAT HELPS INCREASE MID TO HIGH LEVEL CLOUDS. A
COOL START TO THE DAY IS EXPECTED TO WARM AS ENOUGH SOUTHERLY
SURFACE FLOW DEVELOPS WITH HIGH PRESSURE SLIDING EAST; THAT
SAID, EXCESSIVE CLOUD COVER COULD STUNT SOME OF THIS WARMING
(NOTABLY ACROSS WEST CENTRAL TO NORTHWEST PA) UNTIL LATE IN THE
EVENING WHEN SW FLOW BETTER DEVELOPS. THE REGION IS LIKELY TO
REMAIN DRY WITH HIGH PRESSURE INFLUENCE BUT A WARM-NOSE ALOFT
WITH ENOUGH JET LIFT COULD SQUEEZE SOME LIGHT RAIN OR SNOW
(DEPENDING LOCATIONS THERMAL PROFILES) DURING THE LATE AFTERNOON
AND EVENING HOURS.
THE FOCUS WILL BE A MORE NOTABLE PUSH OF THE SHORTWAVE AND LOW
MOVEMENT OVERNIGHT MONDAY INTO TUESDAY MORNING, WHICH WILL
FEATURE A LIFTING SURFACE WARM FRONT AIDING IN PRECIPITATION
PRODUCTION. MODEL MEAN 850MB TEMPERATURES WILL RISE TOWARD 2 TO
5 DEGREES CELSIUS WHILE SURFACE TEMPERATURE STARTS TO RISE AS
WELL AND CAUSE FALLING PRECIPITATION TO BE RAIN FOR A VAST
MAJORITY OF THE REGION. THE LATER ARRIVAL OF THIS WARM NOSE, AN
INITIAL DRIER LOWER PROFILE RIPE FOR WET-BULBING, AND SOME
VARIANCES IN LOW POSITIONING THAT COULD ALLOW FOR E TO SE FLOW
TO REINFORCE SUB-FREEZING SURFACE AIR ALL PAINT A PICTURE FOR
MORE OF A WINTRY MIX FOR PORTIONS OF NORTHWEST PA. CURRENT
ENSEMBLE MODEL MEANS AN INITIAL PERIOD OF SNOW THAT TRANSITIONS
TO RAIN, WITH SNOW ACCUMULATIONS LIKELY TO BE LESS THAN 1"
(85-95% PROBABILITY). HOWEVER, THERE ARE SOME LOW PROBABILITIES
(10-20%) SUGGESTING A PERIOD OF FREEZING RAIN PRIOR TO THAN RAIN
TRANSITION THAT COULD LEND TO A GLAZE OF ICE ACCUMULATION. WILL
ADD A MENTION FOR THESE ZONES AS WELL AS EASTERN TUCKER THAT
CAN BE MORE PRONE/STUBBORN IN HOLDING SUB-FREEZING TEMPERATURE
IN THESE REGIMES AS IT BEARS MONITORING MOVING FORWARD.
THE GENERALLY LIGHT RAIN AREAWIDE BY THE AFTERNOON WILL TAPER
OFF SLOWLY THROUGH TUESDAY EVENING AS THE SYSTEM DIVES TOWARD
NEW ENGLAND AND THE SURFACE COLD FRONT PUSHES THROUGH. ENSEMBLE
MEANS FAVOR DRY CONDITIONS OVERNIGHT BUT EVEN THERE, LINGERING
MOISTURE WITH UPSLOPE FLOW COULD CREATE AREAS OF LIGHT RAIN,
DRIZZLE, AND EVEN FREEZING DRIZZLE IN PLAY FOR THE HIGHER
ELEVATIONS.
LONG TERM /WEDNESDAY THROUGH SATURDAY/
KEY MESSAGES:
- SEASONABLY WARM PATTERN FAVORED THROUGH FRIDAY BUT REMAINS
HIGHLY VARIABLE ON DEGREE OF WARMING
- PERIODIC PRECIPITATION CHANCES DRIVEN BY SUBTLE SHORTWAVE
MOVEMENT
- NON-ZERO LIGHTNING PROBABILITY OVERNIGHT WEDNESDAY
INTO CHRISTMAS MORNING SOUTHWEST OF PITTSBURGH
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THERE IS HIGH CONFIDENCE IN THE DEVELOPMENT OF RIDGING OVER THE
CENTRAL CONUS WEDNESDAY THROUGH FRIDAY WITH THE UPPER OHIO RIVER
VALLEY SITTING ON ITS NE PERIPHERY UNDERNEATH NORTHWEST FLOW. IF
THE CALENDAR DIDN'T SAY 'DECEMBER', YOU'D ALMOST THINK THIS WAS
A SUMMER-ESQUE PATTERN WHERE SUBTLE SHORTWAVES ROUNDING THE
RIDGE AXIS COULD POSE VARIOUS THUNDERSTORM OR SEVERE WEATHER
RISKS FOR THE FORECAST AREA. WELL, IT WILL BE TRUE BUT WILL NOT
FEATURE 'SEVERE WEATHER' CONCERNS; IT WILL FEATURE TEMPERATURE
BECOME ABOVE TO WELL ABOVE NORMAL WHILE EMBEDDED SHORTWAVES
(THE FIRST OF WHICH ARRIVES LATER ON CHRISTMAS EVE INTO
CHRISTMAS DAY) GENERATES PRECIPITATION (VERY LIKELY RAIN) AND A
NON-ZERO LIGHTNING THREAT. IT IS ALSO A PATTERN THAT CAN BE
HIGHLY VARIABLE AS SUBTLE CHANGES COULD DRASTICALLY ALTER THE
DEGREE OF WARMING, THE FAVORED AREAS FOR PRECIPITATION, AND THE
PATH OF SUBSEQUENT SHORTWAVES.
MONITORING THE PROGRESSION OF TUESDAY'S SHORTWAVE TROUGH AND
HOW DEEP IT BECOMES JUST OFF THE ATLANTIC COAST IS KEY FOR
IRONING SOME OF THE VARIANCES. IN GENERAL, A DEEPER TROUGH WILL
STUNT THE INFLUENCE OF THE EASTWARD-MOVING RIDGE AND DELAY THE
MEAN TEMPERATURE RISE WEDNESDAY/THURSDAY WHILE PUSHING THE
FAVORED PRECIPITATION AREA MORE SOUTHWEST OF THE CURRENT POP
PEAKS. A SHALLOWER, MORE PROGRESSIVE TROUGH WOULD ALLOW THAT
EASTWARD RIDGE MOVEMENT AND PUSH TEMPERATURE NEAR/ABOVE CURRENT
FORECASTED VALUES WEDNESDAY/THURSDAY WHILE CENTERING
PRECIPITATION OVER THE AREA. THIS IS BEST EXEMPLIFIED IN LOOKING
AT ENSEMBLE MODEL MAXT SPREADS WEDNESDAY/THURSDAY THAT SHOW
LARGE RANGE OFF OUTCOMES WITHIN A ZONE THAT IS APPROXIMATELY
ALONG/NORTH OF I-70 AND MEANS FLUCTUATION IN FORECASTED VALUES
IS LIKELY TO OCCUR FOR THIS PERIOD AS IT APPROACHES UNTIL THESE
DETAILS BETTER COALESCE.
VARIABILITY IN THE SYNOPTIC PATTERN ONLY GROWS FRIDAY INTO
SATURDAY IN PART DUE TO HOW WEDNESDAY/THURSDAY'S SYSTEM PLAYS
OUT, BUT THE CURRENT CONSENSUS MAINTAINS THE ABOVE NORMAL
TEMPERATURE WITH PERIODIC PRECIPITATION CHANCES.
AVIATION /06Z SUNDAY THROUGH THURSDAY/
KEY MESSAGES:
- VFR WITH LLWS OVERNIGHT.
- RESTRICTIONS LIKELY AT BVI, DUJ, AND FKL SUNDAY.
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CONDITIONS ACROSS THE AREA FAVOR A VFR FORECAST THROUGH MUCH OF
THE PERIOD. A PASSING DRY COLD FRONT WILL PROVIDE PLENTY OF MID
LEVEL CLOUD COVER AS IT CROSSES THE AREA. AS WELL, WITH A MID
LEVEL JET CROSSING THE FORECAST AREA, THERE MAY BE A PERIOD OR
TWO OF SOME LOW LEVEL WIND SHEAR. HOWEVER, THERE HAVE BEEN SOME
INSTANCES OF GUSTS AT THE SURFACE THROUGH 06Z SO WILL HOLD OFF
ON THE LLWS THREAT FOR NOW. FURTHER NORTH, THE FKL TERMINAL MAY
HAVE A STRONGER PART OF THE JET PASSING SO DID HINT TO AT LEAST
SOME LLWS THERE. GUSTS MAY APPEAR TO LAST THROUGH THE NIGHT AT
THE SURFACE FOR OTHER TERMINALS SO WILL HOLD OFF ON THE LLWS FOR
NOW.
THE EVENING SOUNDING SHOWS A VERY DRY SURFACE WITH LITTLE CHANCE
OF A LOW LEVEL DECK COMING IN. FURTHER NORTH, CLOSER TO THE
LOW, THERE MAY BE A BIT MORE MOISTURE AS THE COLD FRONT PASSES
THIS MORNING IN THE 06Z TO 12Z TIMEFRAME. THIS MAY LEAD TO A
SHORT INSTANCE OF MVFR CIGS AT FKL AND DUJ. THIS WILL MAINLY BE
IN THE 14Z TO 20Z TIMEFRAME. EXPECT WINDS TO GUST UP TO 20 KNOTS
FROM THE NORTHWEST BEFORE DECOUPLING SUNDAY NIGHT 00Z.
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...FRAZIER
NEAR TERM...FRAZIER
SHORT TERM...FRAZIER
LONG TERM...FRAZIER
AVIATION...SHALLENBERGER
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