562
FXUS61 KPBZ 210558
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
1258 AM EST SAT DEC 21 2024
SYNOPSIS
THE PASSAGE OF LOW PRESSURE WILL BRING AN END TO GENERAL LIGHT
SNOW LATE TONIGHT. COLDER NORTHWESTERLY FLOW SHOULD PROVIDE
LAKE-EFFECT AND UPSLOPE SNOW SHOWERS ON SATURDAY. DRY AND COLD
WEATHER SUNDAY WILL BE FOLLOWED BY A WARMING TREND NEXT WEEK.
NEAR TERM /THROUGH TODAY/
KEY MESSAGES:
- STEADIER SNOW CONTINUES TO TAPER OFF INTO THIS EVENING.
- BEST CHANCE OF ACCUMULATING SNOW OVERNIGHT LIES IN THE RIDGES
WITH DEVELOPING NORTHWEST FLOW.
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LIGHT SNOW IS EVIDENT ACROSS ERN OH THIS EVENING ALONG AND AHEAD
OF A SURGE OF COLD AIR THAT WILL INCREASE POTENTIAL FOR A HIGH-
CONFIDENCE, NARROW LAKE-EFFECT BAND LATE TONIGHT INTO SAT.
POPS WERE ADJUSTED TO REFLECT ONGOING SNOW OVER MUCH OF ERN OH,
WHICH SHOULD DIMINISH TO FLURRIES WITH TIME THIS EVENING. VERY
LIMITED ACCUMULATION IS EXPECTED, AS THE THERMAL PROFILE IS
LEADING TO POOR SLR. PREVIOUS DISCUSSION FOLLOWS...
LIGHT SNOW CONTINUES OVER ROUGHLY THE NORTHERN HALF OF THE CWA,
AS EARLIER ASCENT FORCED BY ISENTROPIC LIFT AND 700MB
FRONTOGENESIS CONTINUES TO WEAKEN. SEVERAL REPORTS OF 1 TO 1.5
INCHES OF SNOW HAVE BEEN RECEIVED.
COVERAGE WILL CONTINUE TO GENERALLY WANE THROUGH THE REST OF
THE AFTERNOON AS SYNOPTIC FORCING CONTINUES TO WEAKEN. SOME
RAIN MAY MIX IN WITH ANY LINGERING SNOW TO THE SOUTH OF
PITTSBURGH, WHERE SOME LOCATIONS HAVE WARMED INTO THE UPPER 30S.
STEADIER PRECIPITATION, ASSOCIATED WITH THE VORTICITY MAXIMUM AT
THE BASE OF A CROSSING SHORTWAVE TROUGH, SHOULD CONTINUE TO DIVE
INTO CENTRAL AND SOUTHERN WEST VIRGINIA FOR THE MOST PART,
ALTHOUGH THE EDGE OF THIS PRECIPITATION SHIELD MAY STILL CLIP
THE ZANESVILLE AREA THIS AFTERNOON.
MOST OF THE SHORT-RANGE CAMS STILL DEPICT A RELATIVE LULL IN
ACTIVITY THROUGH MUCH OF THE NIGHT BETWEEN THE DEPARTING SURFACE
LOW AND THE ONSET OF NORTHWEST FLOW/COLD ADVECTION TOWARDS
SUNRISE. THE BEST POTENTIAL FOR OVERNIGHT SNOW ACCUMULATION WILL
LIE IN THE RIDGES, AS LOW-LEVEL NORTHWEST FLOW SETS UP BEFORE
THE COLDER 850MB TEMPERATURES. AN INCH OR TWO IS POSSIBLE HERE
OVERNIGHT, BUT NBM/HREF PROBABILITIES OF ADVISORY-LEVEL SNOW
ARE TOO LOW TO CONSIDER A HEADLINE.
SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/
KEY MESSAGES:
- LAKE EFFECT/UPSLOPE SNOW SHOWERS EXPECTED INTO SATURDAY
EVENING.
- PLACEMENT/ORIENTATION OF MAIN LAKE-EFFECT BAND REMAINS IN
QUESTION. HIGHLY LOCALIZED ACCUMULATIONS UP TO 3 INCHES
POSSIBLE.
- COLD AND DRY SUNDAY.
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COLD ADVECTION AND NORTHWEST FLOW WILL BE IN PLACE BY 12Z SATURDAY
BEHIND THE DEPARTING TROUGH, LEADING TO NARROWLY-BANDED LAKE
EFFECT/SCATTERED UPSLOPE SNOW SHOWERS. MOST OF THE HI-RES MODELS
AGREE ON THE OCCURRENCE OF BANDING AND A LAKE HURON CONNECTION, BUT
DIFFERENCES REMAIN IN BAND ORIENTATION AND INTENSITY. THE MAJORITY
APPEAR TO FAVOR THE GENERAL OH/PA BORDER REGION, AND THIS IS WHERE
HIGHER POPS WILL BE PLACED, BUT PLACEMENT FURTHER WEST OR EAST WILL
NEED TO BE CONSIDERED IN UPCOMING RUNS OF CAMS. HREF/NBM
PROBABILITIES OF GREATER THAN 2 INCHES ARE VERY LOW, GENERALLY LESS
THAN 20 PERCENT, SO THE CHANCES OF A HIGHER-IMPACT, ADVISORY-LEVEL
EVENT DO NOT LOOK GREAT. DESPITE THIS, WITH SHORT PERIODS OF
DECENT MOISTURE AND VERY MODEST INSTABILITY IN THE DENDRITIC
GROWTH ZONE, TEMPORARY HEAVIER SNOW RATES COULD LEAD TO VERY
LOCALIZED HIGHER ACCUMULATIONS OF UP TO 3 INCHES, WITH PORTIONS
OF MERCER/LAWRENCE/COLUMBIANA COUNTIES BEING POSSIBLE
LOCATIONS. LOCALIZED ACCUMULATIONS OF THIS LEVEL ARE ALSO
POSSIBLE IN THE RIDGES, BUT AGAIN, HEADLINE-WORTHY AMOUNT
CHANCES APPEAR TOO LOW AT THIS TIME GIVEN THE OVERALL MOISTURE
CHALLENGES.
BY SATURDAY NIGHT, INCREASING SUBSIDENCE IN THE FACE OF RISING 500MB
HEIGHTS SHOULD LOWER INVERSION HEIGHTS, LEADING TO A DECREASE IN
SNOW SHOWER COVERAGE AND INTENSITY. SNOW IS LIKELY TO CEASE
OVERNIGHT, BUT NOT BEFORE TEMPERATURES SINK INTO THE 10 TO 20 DEGREE
RANGE DESPITE LINGERING CLOUD COVER AND A LITTLE WIND.
FORECAST CONFIDENCE TICKS UP FOR SUNDAY, AS CROSSING SURFACE HIGH
PRESSURE SHOULD LEAD TO DRY WEATHER AND CONTINUED BELOW-NORMAL
TEMPERATURE. A MOSTLY CLEAR SKY AND LIGHT WIND WILL LIKELY MAKE
SUNDAY NIGHT THE COLDEST OF THIS CHILLIER RUN, WITH SOME VALUES IN
THE SINGLE DIGITS POSSIBLE NORTH OF PITTSBURGH.
LONG TERM /MONDAY THROUGH FRIDAY/
KEY MESSAGES:
- COLD AND DRY WEATHER CONTINUES INTO MONDAY.
- 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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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
WARMER TEMPERATURES, WITH MAX VALUES PERHAPS AROUND 10 DEGREES
HIGHER THAN SUNDAY, DEPENDING ON HOW QUICKLY CLOUDS THICKEN AHEAD OF
THE NEXT SYSTEM.
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 /06Z SATURDAY THROUGH WEDNESDAY/
MODERATE TO HIGH CONFIDENCE REMAINS IN THE MAINTENANCE OF MVFR
DECKS WITH LOW LEVEL COLD ADVECTION IN NORTHERLY FLOW THROUGH AT
LEAST SATURDAY MORNING BEFORE SOME LIFTING IS POSSIBLE IN
MIXING AND SUBSIDENCE COME EARLY AFTERNOON WHEN ENSEMBLE
PROBABILITIES FOR MVFR TAKE A TUMBLE TO <50%. THERE IS HIGH
CONFIDENCE IN A NORTH/SOUTH ORIENTED SNOW BAND SETTING UP
SOMEWHERE IN EASTERN OH, THE WV PANHANDLE, AND/OR FAR WESTERN
PA. PLACEMENT OF THIS BAND STILL REMAINS LOW CONFIDENCE TONIGHT
WITH SPREAD STILL EXHIBITED IN THE HI RES MODEL GUIDANCE. THE
HIGHEST CHANCES OF ANY PORT TO SEE RESTRICTIONS FROM THIS
FEATURE WILL BE BVI WHERE A TEMPO GROUP DOWN TO IFR HAS BEEN
MAINTAINED. OTHERWISE, PROB30S ARE NOTED AT PIT, AGC, AND HLG
FOR NOW. PREDICTABILITY OF THIS BAND WILL BE RATHER SHORT-FUSED
AND UNTIL WE SEE IT TAKE SHAPE, IT WILL BE TOUGH TO PIN DOWN
EXACT IMPACTS. WITHIN THE BAND, AT LEAST TEMPORARY IFR IS
POSSIBLE IN SNOW, BUT ELSEWHERE ESPECIALLY AFTER 18Z, VFR SEEMS
MOST LIKELY WITH THE CONTINUATION OF MIXING AND UPPER
SUBSIDENCE. NORTHERLY WIND WILL REMAIN ELEVATED OVERNIGHT AND
TOMORROW WITH GUSTS TO 20 KNOTS AT 40-60% LIKELIHOOD. SNOW
CHANCES AND SURFACE WINDS DROP OFF TOMORROW NIGHT WITH HIGH
PRESSURE DIRECTLY OVERHEAD.
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...CL
NEAR TERM...KRAMAR
SHORT TERM...CL
LONG TERM...CL
AVIATION...MLB/MILCAREK
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