087
FXUS61 KPBZ 212030
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
330 PM EST SAT DEC 21 2024
SYNOPSIS
LAKE ENHANCED SNOW SHOWERS WILL CONTINUE INTO THE EVENING WITH
NORTHWESTERLY WINDS GUSTING TO AROUND 20 MPH ON AVERAGE DURING
THE AFTERNOON. WITH THE EXCEPTION OF LATE MONDAY AND TUESDAY
MORNING, DRY CONDITIONS ARE LARGELY EXPECTED NEXT WEEK WITH AN
INCREASING TREND IN TEMPERATURES.
NEAR TERM /UNTIL 6 AM SUNDAY MORNING/
KEY MESSAGES:
- LAKE ENHANCED SNOW BANDS INTO THE EVENING HOURS IS RESULTING
IN LOCALIZED AREAS OF ADVISORY LEVEL ACCUMULATING SNOW.
- SNOW SHOWER COVERAGE AND INTENSITY WILL SLOWLY WANE THROUGH
THE EVENING AND NIGHT.
- COLD OVERNIGHT LOWS IN THE 10 TO 20 DEGREE RANGE.
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THE MAIN LAKE-EFFECT BAND IS SHOWING MORE OF A BROKEN NATURE
THAN SEVERAL HOURS AGO, AND REFLECTIVITIES/SNOW RATES HAVE
DECREASED A BIT. THIS TREND SHOULD CONTINUE INTO THE EVENING
HOURS, AS MOST MODEL SOUNDINGS AGREE THAT INVERSION HEIGHTS WILL
BE SLOWLY LOWERING WITH TIME. THIS WILL DECREASE AVAILABLE
MOISTURE IN THE DGZ AND THUS LEAD TO CONTINUED WEAKENING. STILL,
AN ADDITIONAL 1 TO AS MUCH AS 3 INCHES CANNOT BE RULED OUT ON A
VERY LOCALIZED BASIS. WILL BE WATCHING AREAS IN BEAVER/ALLEGHENY
COUNTIES THAT HAVE RECEIVED 4-6 INCHES ALREADY. SUSTAINED
HEAVIER SNOW OVER AN HOUR OR TWO IN THIS AREA COULD JUSTIFY A
WARNING ISSUANCE. HOWEVER, CURRENT EXPECTATIONS ARE THAT SNOW
SHOWERS WILL BE INTERMITTENT ENOUGH SUCH THAT THE CURRENT
ADVISORY WILL HANDLE THE SITUATION.
GRID UPDATES WERE MAINLY FOCUSED ON EXPANDING THE AREA OF
ISOLATED/SCATTERED SNOW SHOWERS AWAY FROM THE MAIN BAND, WHICH
ARE BEING FED BY THE COLD ADVECTION AND DAYTIME
HEATING/INSTABILITY. COVERAGE OF THESE WILL ALSO FADE AS WE
APPROACH AND PASS SUNSET.
PREVIOUS DISCUSSION...
COLD NORTHWESTERLY FLOW OVER THE 41 TO 44 DEGREE WATER
TEMPERATURES OFF OF LAKE ERIE WILL RESULT IN LAKE ENHANCED SNOW
SHOWER BANDING THROUGH THE EVENING, GIVEN THE FAVORABLE FLOW AND
COLD AIR ALOFT. THE NATIONAL BLEND OF MODELS, HREF, AND PRETTY
MUCH ALL GUIDANCE HAS WAY UNDERDONE POTENTIAL SNOW TOTALS,
WHICH ISN'T SURPRISING WITH THIS SETUP. AN ADVISORY HAS BEEN
ISSUED VALID UNTIL MIDNIGHT FOR AREAS WHERE BANDING HAS SET UP
AND WILL CONTINUE TO MEANDER.
SNOW SHOWERS WILL THEN TAPER OFF OVERNIGHT UNDER INCREASING
SUBSIDENCE AS RIDGING BUILDS IN FROM THE WEST.
SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY/
KEY MESSAGES:
- COLD AND DRY SUNDAY AND MONDAY MORNING.
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BY SUNDAY, HIGH PRESSURE IS EXPECTED TO BE JUST TO THE NORTH OF
THE FORECAST AREA AS THE CORE OF THE COLDEST AIR FINALLY
DESCENDS ON THE UPPER OH VALLEY. TEMPERATURES IN OUR FAR
NORTHEASTERN COUNTIES ADVERTISE A 60% TO 80% CHANCE OF LESS THAN
10 DEGREES FOR A LOW SUNDAY MORNING. ITS EVEN COLDER FOR MONDAY
MORNING AS THE PROBS IN THE NORTHEAST (FOREST COUNTY) NOW
INCREASES TO AROUND 90% BUT ALSO SHOWING AROUND 40% FOR THE
RIDGES AND SOUTH INTO THE WV COUNTIES. HIGHS ARE EXPECTED TO BE
BELOW NORMAL FOR SUNDAY BUT THE AIR MASS WILL MODIFY
SIGNIFICANTLY AFTER A COLD MORNING ON MONDAY AS HIGHS SOAR INTO
THE LOW 40S. THE NBM ENSEMBLE SUGGESTS A 40% TO 60% PROBABILITY
OF HIGH TEMPERATURES ABOVE 40 DEGREES FOR MONDAY. THIS PROVIDES
QUITE A SHIFT IN TEMPERATURES JUST BEFORE CHRISTMAS.
ENSEMBLE GUIDANCE CONTINUES TO INDICATE FLAT MID-LEVEL RIDGING
MOVING ACROSS THE UPPER OHIO VALLEY ON MONDAY, WITH CONTINUED DRY
WEATHER LIKELY. WARM ADVECTION AND RISING HEIGHTS SHOULD LEAD TO
THE PREVIOUSLY DISCUSSED WARMER TEMPERATURES, WITH MAX VALUES
PERHAPS AROUND 10 DEGREES HIGHER THAN SUNDAY, DEPENDING ON HOW
QUICKLY CLOUDS THICKEN AHEAD OF THE NEXT SYSTEM.
LONG TERM /MONDAY NIGHT THROUGH SATURDAY/
KEY MESSAGES:
- GENERALLY LIGHT PRECIPITATION APPEARS LIKELY MONDAY NIGHT INTO
CHRISTMAS EVE DAY, WITH A MINOR SNOW ACCUMULATION POSSIBLE
NORTH OF PITTSBURGH.
- A WARMING TREND AND LOWER PRECIPITATION CHANCES MAY FOLLOW FOR
CHRISTMAS DAY THROUGH THE END OF THE WEEK.
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A FAIRLY WEAK SHORTWAVE APPEARS MOST LIKELY TO CROSS THE AREA MONDAY
NIGHT INTO CHRISTMAS EVE DAY. MODEL CLUSTERING SHOWS GENERALLY MINOR
DIFFERENCES IN STRENGTH AND TIMING, BUT MOST AGREE THAT QPF WILL
GENERALLY BE LIGHT AND FOCUSED NORTH OF PITTSBURGH CLOSER TO THE
WAVE TRACK. PROBABILITIES OF ACCUMULATING SNOW ARE BEING MODULATED
BY TEMPERATURE, WITH HIGHS LIKELY IN THE MID TO UPPER 30S FROM
PITTSBURGH NORTH AND IN THE RIDGES, AND IN THE LOWER 40S TO THE
SOUTH. THESE LIKELIHOODS RANGE FROM NEAR 10 PERCENT AT ZANESVILLE,
TO 40 PERCENT AT PITTSBURGH, AND 90 PERCENT AT DUBOIS.
PROBABILITIES OF AN INCH OR MORE REMAIN CONFINED TO AREAS NORTH
OF I-80 AND MAX OUT AT AROUND 40-50%. THIS WOULD BE THE AREA
THAT HAS THE BEST CHANCE OF HAVING AN INCH OF SNOW ON THE GROUND
COME CHRISTMAS MORNING, BUT THE ABOVE-FREEZING TEMPERATURE
COULD PLAY A ROLE IN LIMITING SNOW DEPTH.
THEREAFTER, ENSEMBLES CONTINUE TO SHOW GOOD PROBABILITIES OF RIDGING
DURING THE MIDWEEK PERIOD, WHICH WILL CONTINUE THE WARMING TREND
THROUGH CHRISTMAS DAY AND THE REMAINDER OF THE WEEK. TEMPERATURES
COULD PERHAPS RISE TO AROUND 10 DEGREES ABOVE NORMAL BY FRIDAY. A
MINORITY OF ENSEMBLE MEMBERS ARE SHOWING LOWER HEIGHTS/FLATTER
RIDGING, PERHAPS LEADING TO LESS OF A WARMUP. ALONG WITH THE
WARMING, THE MAJORITY MODEL OPINION WOULD LEAD TO FAIRLY LOW CHANCES
OF LIGHT PRECIPITATION AT BEST FOR THE SECOND HALF OF THE HOLIDAY
WEEK.
AVIATION /21Z SATURDAY THROUGH THURSDAY/
CONDITIONS EXPECTED TO BE PREDOMINANTLY VFR SOLUTION TODAY
OUTSIDE OF SNOW SHOWERS. WITHIN THE SNOW BAND OVER EASTERN OH,
THE WV PANHANDLE, AND WESTERN PA PRODUCE RESTRICTIONS OF
VISIBILITY BETWEEN 1/4 -1 1/2 SM AND CEILINGS BETWEEN 300-1000
FEET. THE HIGHEST CHANCES TO SEE RESTRICTIONS FROM THIS FEATURE
WILL BE PIT, AGC, BVI, LBE, AND HLG WHERE A TEMPO GROUP DOWN TO
IFR/LIFR. THE SNOW BANDS LOOK TO START WEAKENING AROUND 21Z
TODAY.
WEST-NORTHWESTERLY WIND WILL REMAIN ELEVATED TODAY WITH GUSTS TO 20
KNOTS AT MAJORITY OF TERMINALS, ESPECIALLY NEAR THE APPALACHIANS.
OVERNIGHT, WE WILL SEE SURFACE WIND DROP OFF BECOMING LIGHT AND
VARIABLE BY TOMORROW MORNING.
OUTLOOK...
VFR UNDER THE INFLUENCE OF HIGH PRESSURE IS FAVORED SUNDAY AFTERNOON
INTO MONDAY BEFORE THE NEXT UPPER LEVEL SYSTEM CROSSES INTO THE REGION
LATE MONDAY INTO TUESDAY, BRINGING ANOTHER ROUND OF LIGHT SNOW
AND AREAWIDE RESTRICTIONS.
PBZ WATCHES/WARNINGS/ADVISORIES
PA...WINTER WEATHER ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR PAZ013-
014-020-021-029-073>076.
OH...WINTER WEATHER ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR OHZ041-
050.
WV...WINTER WEATHER ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR WVZ001-
002-510>512.
SYNOPSIS...CL/88
NEAR TERM...CL/88
SHORT TERM...SHALLENBERGER/88
LONG TERM...SHALLENBERGER/88
AVIATION...LUPO
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