864
FXUS61 KPBZ 210556 AAA
AFDPBZ
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PITTSBURGH PA
1256 AM EST THU NOV 21 2024
SYNOPSIS
MUCH COLDER AIR WILL OVERSPREAD THE AREA OVERNIGHT. A LARGE
UPPER LEVEL SYSTEM WILL BRING MORE RAIN AND SNOW INTO SATURDAY.
WITH A SIGNIFICANT WINTER STORM POSSIBLE IN THE HIGHER
ELEVATIONS.
NEAR TERM /UNTIL 6 AM THIS MORNING/
KEY MESSAGES:
- A DRASTIC COOL DOWN EXPECTED OVERNIGHT BEHIND THE COLD FRONT.
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QUICK UPDATE TO EXPIRE THE WIND ADVISORY FOR THE RIDGES.
OTHERWISE, NO SIGNIFICANT CHANGES TO THE CURRENT FORECAST.
PREVIOUS DISCUSSION...
STRONG COLD AIR ADVECTION IS EXPECTED TONIGHT WHICH WILL TANK
TEMPERATURES DOWN TO THE LOW 30S OR EVEN UPPER 20S OVERNIGHT.
THIS WILL ALSO ALLOW WINDS BEHIND THE FRONT TO REMAIN ELEVATED,
JUSTIFYING A WIND ADVISORY FOR THE HIGH TERRAIN THAT IS SET TO
EXPIRE AT 06Z. A DRY SLOT ALOFT WILL CROSS THE REGION OVERNIGHT
WHICH SHOULD LIMIT THE THREAT FOR ANY SNOW SHOWERS UNTIL
THURSDAY MORNING IN EASTERN OHIO.
SHORT TERM /6 AM THIS MORNING THROUGH SATURDAY/
KEY MESSAGES:
- RAIN AND SNOW CHANCES CONTINUE THURSDAY AND FRIDAY WITH
IMPACTFUL ACCUMULATIONS LIKELY FOR THE HIGHER TERRAIN.
- WINTER STORM CONDITIONS FOR THE HIGHER TERRAIN CONTINUES INTO
SATURDAY AS DO THE GUSTY WINDS.
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THE UPPER LOW WILL MOVE ACROSS THE UPPER OHIO VALLEY ON
THURSDAY. THIS WILL INITIATE MORE PRECIPITATION AND BRING
ANOTHER SHOT OF COLD AIR. A MIX OF RAIN AND SNOW IS EXPECTED AT
THE ONSET, BUT SNOW BECOMES MORE LIKELY THROUGH THE DAY THURSDAY
AS THE PARENT LOW AND DEVELOPING COASTAL LOW PIVOT AROUND EAST
OTHER. AS THE PARENT LOW DIVES SOUTHEAST, LIFT WILL INCREASE
AHEAD OR IT AND DAYTIME HEATING AND DESTABILIZATION MAY ALLOW AN
INCREASE IN SHOWERS INTO THURSDAY AFTERNOON. DAYTIME HIGH
TEMPERATURES WILL LIKELY BE BELOW AVERAGE BUT ABOVE FREEZING FOR
THE LOWLANDS WHICH WILL CHALLENGE DAYTIME ACCUMULATIONS. THE
SAME CANNOT BE SAID FOR RIDGES OVER 2KFT, WHERE DAYTIME
ACCUMULATIONS WILL BE POSSIBLE. THE WINTER STORM WARNING AND
WINTER WEATHER ADVISORY BEGINS THURSDAY AFTERNOON FOR THE WEST
VIRGINIA RIDGES ACCORDINGLY. THE HIGHEST SNOWFALL RATES APPEAR
THE MOST LIKELY FRIDAY MORNING FOR THE PA ADVISORY/WARNING AREA,
AND DURING THE DAYTIME FRIDAY FOR THE HIGH TERRAIN OF WV.
WHEN COMPARED TO THE LAST UPDATE, THE PARENT LOW IS EXPECTED TO
DIVE WELL TO THE SOUTH INTO KENTUCKY AND SOUTHWEST VIRGINIA. SO
ON THE FRONT END OF THE WINTER SYSTEM DURING THE EARLY OVERNIGHT
HOURS ON FRIDAY, ACCUMULATIONS WILL MOSTLY BE OROGRAPHIC AS
DAYTIME INSTABILITY WANES. IN THE EARLY MORNING HOURS FRIDAY,
THE TRIPLE-POINT LOW WILL BEGIN TO FEEL THE INFLUENCE OF THE
PARENT LOW SWINGING TO THE SOUTH WHILE IT TRIED TO RELOCATE
UNDER THE UPPER LOW. THIS WILL ATTEMPT TO PULL THE LOW BACK TO
THE EAST, WITH SOME EVIDENCE THAT A DEFORMATION DONE MAY SET UP
IN AN AREA OF CONVERGENCE ORIENTED FROM WEST TO EAST ON THE EAST
SIDE OF THE LOW.
THIS IS THE PRIMARY UNCERTAINTY FOR COUNTIES NORTH OF
PITTSBURGH. JUST HOW FAR EAST THIS LOW PULLS BACK WITH BOTH
AFFECT THE DEGREE OF CONVERGENCE AND THE PROXIMITY TO THE I-80
COUNTIES. ACCORDINGLY, PRODUCT EXPANSIONS OR UPGRADES MAY BE
NECESSARY ON A SHORTER FUSE SHOULD CONFIDENCE INCREASE. WHILE
THERE IS FAIRLY HIGH CONFIDENCE (75%) IN SUB-ADVISORY SNOWS IN
ALLEGHENY AND POINTS SOUTH.
INTO THE DAYTIME HOURS ON FRIDAY, WARM ADVECTION WILL ACTUALLY
DROP DOWN FROM THE NORTHWEST COMBINED WITH DAYTIME HEATING. THIS
WILL BE ENOUGH TO BRING TEMPERATURE ABOVE FREEZING FOR THE
LOWLANDS INTO FRIDAY AFTERNOON, CUTTING OFF ACCUMULATIONS AND
POTENTIAL TRANSITIONING SOME AREAS TO RAIN. THE MOST NOTABLE
EXCEPTION WILL BE THE HIGHER ELEVATIONS OF PENNSYLVANIA AND
WEST VIRGINIA. THIS WILL ALLOW ADDITIONAL CHANCES OF SNOW FOR
THE RIDGES. OROGRAPHIC LIFT, SYNOPTIC FORCING FROM A SHORTWAVE,
AND DRY ADIABATIC PROFILES INTO A SATURATED DGZ ARE ALL
CONDUCIVE TO HEAVY SNOWFALL AND RAPID ACCUMULATION IN THE RIDGES
OF PENNSYLVANIA AND WEST VIRGINIA DURING THE DAYLIGHT HOURS ON
FRIDAY. RATES ABOVE 1"/HR FOR MULTIPLE HOURS ARE POSSIBLE. AS
THIS WAVE COMPLETES ITS PASSAGE FRIDAY NIGHT, SNOWFALL RATES
WILL DROP OFF. WITH THE EXCEPTION OF EASTERN TUCKER, THE WINTER
PRODUCTS WILL BE ALLOWED TO EXPIRE AT 7AM SATURDAY. WITH
SHALLOW SATURATION AND THE POTENTIAL FOR BELOW FREEZING
TEMPERATURES, PRECIPITATION MAY END AS A BRIEF FREEZING DRIZZLE
SATURDAY IN EASTERN TUCKER, WHICH WILL JUSTIFY HOLDING ONTO THE
WARNING UNTIL 7PM THERE. MOST LIKELY ACCUMULATIONS IN THE RIDGES
VARY FROM 6-12" FOR PA TO UP TO 10-18" FOR WV. THERE IS ALMOST
90% CHANCE OF A 6" IN THE WARNING AREA. ON THE VERY HIGH END,
(90TH PERCENTILE) 10-16" IN THE PA RIDGES AND 18-24" IN THE WEST
VIRGINIA RIDGES COULD NOT BE RULED OUT.
WIND CHANCES DROP OFF SLIGHTLY, BUT THERE IS STILL A
WIDESPREAD 60% TO 80% CHANCE OF GUSTS EXCEEDING 30MPH FOR THE
DURATION OF THE EVENT. THIS WILL ALSO JUSTIFY BLOWING SNOW AND
LOW VISIBILITY CONCERNS FOR THE HIGH ELEVATIONS.
HERE'S THE TAKE HOME MESSAGE: A NOTABLE WINTER STORM WITH A 75%
TO 90% CHANCE OF EXCEEDING 6" IS LIKELY FOR THE HIGH TERRAIN OF
PRESTON COUNTY AND TUCKER COUNTY BETWEEN THURSDAY AND SATURDAY
MORNING. THIS IS 50% TO 75% LIKELY FOR THE RIDGES OF PA. GUSTY
WINDS ARE LIKELY THROUGH THE WHOLE PERIOD, AND BLOWING SNOW MAY
BE A HAZARD FOR THE RIDGES. THE HIGHEST SNOWFALL RATES APPEAR
THE MOST LIKELY FRIDAY MORNING FOR THE PA ADVISORY/WARNING AREA,
AND DURING THE DAYTIME FRIDAY FOR THE HIGH TERRAIN OF WV.
LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/
KEY MESSAGES:
- DRY ON SUNDAY.
- UNSETTLED PATTERN FOR THE BEGINNING OF NEXT WEEK.
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PRECIPITATION CHANCES DECREASE SUNDAY AND MONDAY AS THE LARGE
UPPER LOW RACES OUT OVER THE ATLANTIC AND A WEAK RIDGE MOVES
OVER THE UPPER OHIO VALLEY. THE END OF THE LONG TERM LOOKS
UNSETTLED ONCE AGAIN, BUT WITH MILDER TEMPERATURES.
AVIATION /06Z THURSDAY THROUGH MONDAY/
FRONTAL BOUNDARY HAS CROSSED THE LAUREL HIGHLANDS, TAKING HEAVY
RAIN AND ISOLATED THUNDERSTORMS WITH IT. AN AREA OF MOSTLY
LIGHT RAIN/DRIZZLE WILL LINGER BEHIND IT FOR A FEW HOURS, ALONG
WITH MVFR CEILINGS. AFTER GUSTING BETWEEN 35 AND 50 KNOTS
AREAWIDE EARLIER, GUSTS ARE NOW MAINLY IN THE 20 TO 30 KNOT
RANGE. THESE WILL CONTINUE TO SLOWLY DIMINISH OVERNIGHT AS THE
SURFACE PRESSURE GRADIENT RELAXES TEMPORARILY. ALSO, AS A DRY
SLOT WORKS INTO THE AREA, SKIES WILL CLEAR FOR SEVERAL HOURS
OVERNIGHT, REPRESENTING A RETURN TO VFR.
AFTER 10Z OR SO, MVFR CEILINGS ARE EXPECTED TO REDEVELOP OVER
THE REGION AS UPPER LEVEL LOW PRESSURE ROTATES INTO THE UPPER
OHIO VALLEY. AN INITIAL MIX OF RAIN/SNOW SHOWERS SHOULD TURN TO
MORE SNOW THAN RAIN DURING THE MORNING HOURS, AND CONTINUE INTO
THE AFTERNOON. FOR NOW, HAVE KEPT MVFR VISIBILITY WITH THIS
ACTIVITY. THERE WILL CERTAINLY BE PERIODS IFR OR POTENTIALLY
EVEN LIFR VISIBILITY IN SNOW WILL BE POSSIBLE ON A LOCALIZED
BASIS. HOWEVER, CONFIDENCE IN LOCATION AND TIMING OF SUCH
SHOWERS IS LOW AT PRESENT. WESTERLY WIND GUSTS WILL ALSO PICK UP
INTO THE 15 TO 25 KNOT RANGE DURING THE DAY.
OUTLOOK...
RESTRICTIONS ARE EXPECTED THURSDAY THROUGH SATURDAY AS A SERIES
OF LOW PRESSURE SYSTEMS SPIN ACROSS THE NE CONUS, BRINGING
PERIODS OF RAIN AND SNOW SHOWERS TO THE AREA. VFR SHOULD RETURN
SUNDAY AS HIGH PRESSURE BUILDS IN.
PBZ WATCHES/WARNINGS/ADVISORIES
PA...WINTER WEATHER ADVISORY FROM 1 PM THIS AFTERNOON TO 7 AM EST
SATURDAY FOR PAZ009-016-077-078.
WINTER STORM WARNING FROM 1 PM THIS AFTERNOON TO 7 AM EST
SATURDAY FOR PAZ074-076.
OH...NONE.
WV...WINTER WEATHER ADVISORY FROM 1 PM THIS AFTERNOON TO 7 AM EST
SATURDAY FOR WVZ510.
WINTER STORM WARNING FROM 1 PM THIS AFTERNOON TO 7 AM EST
SATURDAY FOR WVZ511>513.
WINTER STORM WARNING FROM 1 PM THIS AFTERNOON TO 7 PM EST
SATURDAY FOR WVZ514.
SYNOPSIS...22/MILCAREK
NEAR TERM...WM/22/MLB/MILCAREK
SHORT TERM...22/MILCAREK
LONG TERM...22/MILCAREK
AVIATION...CL
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