851
FXUS61 KPBZ 181902
AFDPBZ
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PITTSBURGH PA
202 PM EST MON NOV 18 2024
SYNOPSIS
ABOVE AVERAGE TEMPERATURES WITH OCCASIONAL PRECIPITATION
CHANCES PREVAIL THROUGH WEDNESDAY, WITH A DRASTIC COOL-DOWN
THURSDAY THROUGH THE WEEKEND. POTENTIAL FOR AN IMPACTFUL WINTER
STORM FOR HIGHER TERRAIN IS INCREASING LATE THURSDAY THROUGH
SATURDAY.
NEAR TERM /THROUGH TONIGHT/
KEY MESSAGES:
- MILD TEMPERATURES, PATCHY CLOUDS, AND DRY CONDITIONS PREVAIL.
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A QUIET WEATHER DAY IS EXPECTED TODAY WITH LIGHT WESTERLY FLOW.
A WEAK COLD FRONT WILL MEANDER ACROSS AREAS NORTH OF THE
PITTSBURGH METRO, BUT DO LITTLE TO AFFECT LOCAL TEMPERATURES.
THE MAIN FOOTPRINT WILL BE PATCHES OF LOW CLOUD COVER WITH
NEAR- SATURATION IN THE SFC-700MB LAYER. ABOVE THIS, SUBSIDENCE
HAS ALLOWED FOR A PRONOUNCED DRY LAYER AND TEMPERATURE
INVERSION. AS MIXING PREVAILS TODAY, THESE LOW CLOUDS ARE
EXPECTED TO DECREASE IN COVERAGE AND THICKNESS AS DRIER AIR IS
INGESTED INTO THE MIXED LAYER. HIGH CLOUDS WILL CONTINUE AHEAD
OF A PLAINS LOW. HIGH TEMPERATURES ARE EXPECTED TO TOP OUT
AROUND 10 DEGREES ABOVE NORMAL.
THE WEAK FRONT WILL CONTINUE MARCHING SOUTHWARD OVERNIGHT,
CONTINUING TO HAVE LITTLE IMPACT ON LOCAL APART FROM PATCHY LOW
TO MID-LEVEL CLOUD COVER. HIGH CLOUDS WILL CONTINUE. FLOW WILL
TRANSITION LIGHT AND EASTERLY OVERNIGHT AS A SURFACE HIGH RIDGE
MOVES EAST. THIS WILL BRING IN LOWER DEWPOINT AIR INTO NORTHWEST
PENNSYLVANIA AND ALLOW LOWS TO APPROACH SEASONAL NORMALS.
ELSEWHERE, WITH HIGHER DEW POINTS AND PATCHY CLOUDS, LOWS ARE
EXPECTED TO REMAIN UP TO 10 TO 20 DEGREES ABOVE AVERAGE.
SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/
KEY MESSAGES:
- RETURNING RAIN CHANCES AND SLIGHTLY WARMER TEMPERATURES.
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THE AFOREMENTIONED PLAINS SURFACE LOW IS EXPECTED TO PULL NORTH
AND DROP UNDERNEATH OF THE UPPER LOW, OCCLUDING ALONG THE WAY
AND ALLOWING THE WEAK COLD FRONT TO SURGE BACK NORTH AS A WARM
FRONT INTO TUESDAY AND TUESDAY NIGHT. AS IT DOES SO, DAYTIME
HIGH TEMPERATURES ALONG THE SPINE OF THE APPALACHIANS AND INTO
THE PENNSYLVANIA AND WEST VIRGINIA LOWLANDS MAY INCREASE
SLIGHTLY WHEN COMPARED TO THE DAY PRIOR. THE LOWS ARE ALSO MORE
LIKELY TO BE WARMER THAN THE NIGHT PRIOR WITH A SURGE OF HIGHER
DEW POINT AIR. OVERALL, TEMPERATURES WILL REMAIN 10-20 DEGREES
ABOVE AVERAGE.
THE SURFACE TROUGH PASSAGE WITH INCREASING MOISTURE MAY ALLOW
THE RIGHT CONDITIONS FOR A LIGHT RAIN TUESDAY AFTERNOON AND
EVENING. QPF WILL REMAIN HIGHEST IN EASTERN OHIO AND PARTS OF
NORTHERN WEST VIRGINIA, DECAYING TO THE EAST AS FORCING IS
LOST. THE SPREAD BETWEEN THE LOW AND HIGH END QPF (10TH TO 90TH
PERCENTILE) IN OH/WV IS ROUGHLY 0.2" TO 0.7", WITH MOST
ENSEMBLES HONED IN ON ROUGHLY 0.25" TO 0.5" TOTALS. FOR
PENNSYLVANIA, THE SPREAD DROPS TO 0.1" TO 0.4", WITH MOST
ENSEMBLES AROUND 0.1" TO 0.25". MOST LIKELY PRECIPITATION
TIMING IS LATE MORNING AND EARLY AFTERNOON FOR OHIO, AND
AFTERNOON TO EARLY EVENING FOR PENNSYLVANIA AND WEST VIRGINIA.
LONG TERM /WEDNESDAY THROUGH SUNDAY/
KEY MESSAGES:
- STEADIER RAIN ON WEDNESDAY WITH A COLD FRONT.
- MUCH COLDER TEMPERATURE APPEARS LIKELY THURSDAY INTO THE WEEKEND,
ALONG WITH ADDITIONAL PRECIPITATION CHANCES AND A PERIOD OF GUSTY
WIND.
- MEASURABLE SNOW IS A POSSIBILITY IN MOST OF THE REGION AT SOME
POINT BETWEEN THURSDAY AND SATURDAY, WITH IMPACTFUL ACCUMULATION
POSSIBLE IN THE HIGHER ELEVATIONS.
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THE BOTTOM LINE FOR THE EXTENDED PERIOD IS THAT A STARK PATTERN
CHANGE REMAINS LIKELY: A TRANSITION TO A COLDER REGIME WITH MULTIPLE
CHANCES OF PRECIPITATION. EXACT DETAILS OF COURSE REMAIN IN
QUESTION.
VIRTUALLY ALL MODEL SOLUTIONS NOW AGREE THAT A CLOSED 500MB LOW WILL
DEVELOP IN THE VICINITY OF THE FAR WESTERN GREAT LAKES/UPPER
MISSISSIPPI VALLEY BY 12Z WEDNESDAY. THERE IS ALSO BROAD AGREEMENT
THAT THIS UPPER LOW WILL TRANSITION ACROSS THE UPPER OHIO VALLEY AND
NORTHEAST CONUS THROUGH THE THURSDAY/FRIDAY PERIOD, BEFORE LIFTING
TOWARDS THE CANADIAN MARITIMES NEXT WEEKEND. CONFIDENCE IN THIS
OVERALL SCENARIO IS NOW EDGING TOWARDS THE HIGH CATEGORY.
GIVEN THAT, DETAIL DIFFERENCES IN STRENGTH AND TIMING REMAIN. SOME
OF THIS DEPENDS ON THE STRENGTH OF THE RIDGING THAT WILL VERY LIKELY
REMAIN ALONG THE ATLANTIC SEABOARD ON WEDNESDAY. THERE REMAINS A
MINORITY OF SOLUTIONS THAT LEAN TOWARDS A STRONGER RIDGE. AS A
RESULT, THERE ARE MODEL CLUSTERS KEEPING THE UPPER LOW CENTER MORE
TOWARDS THE MIDDLE OHIO VALLEY INITIALLY INTO THURSDAY, OR PERHAPS
KEEPING THE OVERALL TROUGH FROM DIGGING AS STRONGLY, THUS KEEPING
THE CENTER MORE TOWARDS THE GREAT LAKES. THESE SCENARIOS COULD SLOW
THE ARRIVAL OF COLDER AIR A BIT. HOWEVER, THE MAJORITY OF MEMBERS
STILL ARE GOING WITH THE MORE AGGRESSIVE ARRIVAL OF THE LOW INTO OUR
VICINITY BY THURSDAY. THUS, A LEAN TOWARDS THE LOWER END OF THE
TEMPERATURE GUIDANCE ENVELOPE SEEMS PRUDENT FOR THE END OF THE WEEK.
BIMODAL SOLUTIONS OF EARLIER RUNS CONTINUE TO TREND TOWARDS A MORE
CONFIDENT DEPICTION OF COLDER TEMPERATURE. ALSO OF NOTE: A PROLONGED
PERIOD OF GUSTY WIND IS ALSO LIKELY IN THIS PATTERN. PROBABILITIES
OF GREATER THAN 45 MPH (ADVISORY-LEVEL) GUSTS REMAIN LOW OUTSIDE OF
EASTERN TUCKER COUNTY, BUT MAXIMUM GUSTS OF 30 TO 40 MPH HAVE 50% OR
BETTER PROBABILITY AREAWIDE WEDNESDAY THROUGH FRIDAY.
AT LEAST A FEW ROUNDS OF PRECIPITATION APPEAR LIKELY INTO THE
WEEKEND: AN INITIAL WAVE AHEAD OF THE MAIN COLD FRONTAL PASSAGE,
FOLLOWED BY ADDITIONAL PERIODS AS A RESULT OF WRAPAROUND MOISTURE
AND SHORTWAVES IN NORTHWEST FLOW. OF COURSE, GIVEN THE COLDER
SOLUTION, SNOW POSSIBILITIES MUST BE CONSIDERED STARTING AS EARLY AS
WEDNESDAY NIGHT. THE ENTIRE CWA HAS SOME POTENTIAL FOR MEASURABLE
SNOW. EVEN THE TYPICALLY WARMER METRO/VALLEY AREAS HAVE A 40-50%
CHANCE OF AT LEAST 0.1 INCH DURING THE 72-HOUR PERIOD ENDING AT 12Z
SUNDAY ACCORDING TO THE NBM. HOWEVER THE AREA TO WATCH WILL BE THE
LAUREL HIGHLANDS AND THE WEST VIRGINIA RIDGES. FOR THE SAME 72-HOUR
PERIOD, IMPRESSIVELY LARGE SPREADS IN MODELED SNOW ACCUMULATION
EXIST, PARTICULARLY FOR THE HIGHER ELEVATIONS OF PRESTON AND TUCKER
COUNTIES. TOTALS WILL OF COURSE DEPEND ON TEMPERATURE STRUCTURE AND
SUPPORT FOR VERTICAL MOTION FROM BOTH DYNAMIC AND UPSLOPE EFFECTS,
DETAILS WHICH NEED TO BE IRONED OUT IN FUTURE RUNS. HOWEVER, THERE
IS CERTAINLY THE POTENTIAL FOR IMPACTFUL SNOW ACCUMULATION IN THESE
FAVORED LOCATIONS. A WINTER STORM WATCH HAS BEEN ISSUED
ACCORDINGLY.
MODEL CLUSTERS SHOW SOME POTENTIAL FOR QUIETER WEATHER BY SUNDAY AS
THE UPPER LOW AND ASSOCIATED TROUGH MOVE EAST, RESULTING IN LOWER
PRECIPITATION CHANCES. HOWEVER, THE MAJORITY OF SOLUTIONS CONTINUE
TO SHOW WELL BELOW-NORMAL TEMPERATURES ON THAT DAY.
AVIATION /19Z MONDAY THROUGH SATURDAY/
A WEAK COLD FRONT REMAINS SITUATED ACROSS WESTERN PENNSYLVANIA.
THE FRONT WILL NOT MOVE MUCH FOR THE REST OF THE DAY, AND WILL
BEGIN TO PUSH BACK NORTHWARD AS A WARM FRONT TONIGHT. LINGERING
LOW-LEVEL MOISTURE CONVERGENCE ALONG THE BOUNDARY WILL CONTINUE
TO SUPPORT MVFR TO LOW-END VFR CEILINGS NEAR IT THROUGH THE
AFTERNOON. CHANCE OF MVFR ARE HIGHEST NORTH OF PIT, IN THE 50 TO
80 PERCENT RANGE. THE ONSET OF WARM ADVECTION LATE TODAY/TONIGHT
WILL LIFT CEILINGS BACK INTO THE VFR RANGE AREAWIDE BY SUNSET.
SUCH FLIGHT CONDITIONS WILL CONTINUE THROUGH THE NIGHT, WITH
MOSTLY MID-LEVEL CLOUDS EXPECTED. SOME ISOLATED PATCHES OF FOG
ARE POSSIBLE LATE TONIGHT, BUT THINK THAT CLOUD COVER WILL
LARGELY PRECLUDE THIS.
AFTER 12Z, INCREASING MOISTURE AND ISENTROPIC LIFT, ALONG WITH A
WEAK SHORTWAVE IN INCREASING SOUTHWEST FLOW ALOFT, WILL BEGIN TO
LOWER CEILINGS ONCE AGAIN. LIGHT RAIN WILL BEGIN TO DEVELOP FROM
WEST TO EAST, PERHAPS REACHING AS FAR EAST AS FKL, PIT, AND HLG
BY 18Z. MVFR CEILING RESTRICTIONS ARE MOST LIKELY AT ZZV (90%
CHANCE) BY THAT TIME, WITH A 20% CHANCE OF REACHING HLG.
OUTLOOK....
MVFR RESTRICTIONS (70% OR GREATER CHANCE) ARE LIKELY TO
OVERSPREAD THE REGION BY 00Z WEDNESDAY. THEREAFTER, A SERIES OF
INCREASINGLY POTENT LOW PRESSURE SYSTEMS WILL BRING BOUTS OF
RESTRICTIONS, GUSTY WIND, AND RAIN TURNING INTO POTENTIAL SNOW
SHOWERS FOR THE REST OF THE WEEK.
PBZ WATCHES/WARNINGS/ADVISORIES
PA...NONE.
OH...NONE.
WV...WINTER STORM WATCH FROM THURSDAY AFTERNOON THROUGH SATURDAY
EVENING FOR WVZ512>514.
SYNOPSIS...MILCAREK
NEAR TERM...MILCAREK
SHORT TERM...MILCAREK
LONG TERM...CL/MILCAREK/88
AVIATION...CL
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