417
FXUS61 KCTP 200944
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
444 AM EST WED NOV 20 2024
SYNOPSIS
*MOSTLY CLOUDY AND RELATIVELY MILD WITH PATCHY RAIN AND DRIZZLE
TONIGHT AND EARLY WEDNESDAY
*GUSTY RAIN SHOWERS LATER WEDNESDAY WILL PRECEDE THE FIRST TASTE
OF WINTER WEDNESDAY NIGHT THROUGH FRIDAY
*THE FIRST SNOW ACCUMULATION OF THE SEASON IS EXPECTED IN THE
ALLEGHENY MOUNTAINS WITH SEVERAL INCHES EXPECTED AT PEAK
ELEVATIONS IN THE LAUREL HIGHLANDS BY THE WEEKEND
NEAR TERM /UNTIL 6 AM THIS MORNING/
RIDGING AT THE SURFACE AND ALOFT OVER CENTRAL AND EASTERN PA WAS
BEING AUGMENTED BY THE THERMALLY DIRECT, DESCENDING BRANCH (LEFT
ENTRANCE REGION) OF A 100 KT JET THAT WAS STRETCHED
ANTICYCLONICALLY FROM THE CENTRAL APPALACHIANS TO EAST OF THE
DELMARVA COAST.
A STATIONARY SFC FRONT WAS BANKED UP AGAINST THE ALLEGHENY FRONT
IN WEST-CENTRAL PA WITH WIDESPREAD, OVC STRATUS AND STRATOCU
BLANKETING THE ENTIRE CWA THIS EVENING AND JUST SOME LINGERING
PATCHY DRIZZLE.
MIN TEMPS WILL FALL WITHIN THE NARROW RANGE OF 45-50F WITH THE
WARMEST READINGS OVER THE HIGHER TERRAIN NEAR AND TO THE WEST OF
RT 219.
ADDITIONAL QPF THROUGH 12Z WED WILL BE ONLY 0.01" OR SO.
SHORT TERM /6 AM THIS MORNING THROUGH 6 PM THURSDAY/
SFC LOW PRESSURE CONSOLIDATING OVER LH/LE AND WRN PA WILL RESULT
IN A WEAK SOUTHEASTERLY UPSLOPE FLOW OFF OF THE ATLANTIC WILL
YIELD A LOW STRATUS OVER MUCH OF THE AREA WED, ESPECIALLY OVER
THE CENTRAL MTNS. SOME LIFTING AND SOME BREAKS ARE POSSIBLE IN
THE AFTN, ESP IN THE E/SE. FALLING HEIGHTS AND SURGING PWATS
ALONG A SOUTHERLY LOW LEVEL JET SHOULD THEN BRING IN THICKEN
CLOUDS FROM ALOFT AND SHRA/RA ACROSS THE ENTIRE AREA WED AFTN IN
THE W AND EVENING FOR THE E. WE HAVE UNDERCUT NBM MAX TEMPS
WED, DUE ITS WARM BIAS IN EASTERLY FLOW/CAD SCENARIOS.
REGARDLESS, WEDNESDAY WILL BE THE LAST MILD DAY FOR A WHILE AS
COOLER, MORE SEASONABLE AIR ARRIVES BY THURSDAY.
LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/
THE LONG TERM PERIOD KICKS OFF THE FIRST ACCUMULATING SNOW OF
THE SEASON, LIKELY TO IMPACT SPECIFICALLY THE HIGHER ELEVATIONS
ACROSS CENTRAL AND NORTHERN PA OVER 2 OR MORE ROUNDS.
THE FIRST ROUND OF WINTRY PRECIP WILL FOLLOW CLOSELY BEHIND THE
PASSAGE OF POTENT/STEEP COLD FRONT WITH STRONG ASCENT AND THE
POTENTIAL FOR SOME THUNDER IN THE OTHERWISE BKN-SOLID LINE OF
MODERATE TO HEAVY SHOWERS AND TRAILING LIGHT TO MODERATE RAIN
WEDNESDAY NIGHT.
THE PRIMARY THREAT FOR SNOW AND SOME LIGHT ACCUMS WILL BE ACROSS
THE LAUREL HIGHLANDS AND NW MTNS WHERE 850 MB TEMPS WILL FALL
BELOW -2C AROUND 06Z THURSDAY AND WILL COINCIDE WITH THE
PASSAGE OF A FAIRLY STRONG VORT LOBE AND LEFT EXIT REGION OF A
100 KT JET ROUNDING THE BASE OF SLOW MOVING/WOBBLING DEEP UPPER
LOW BECOMING CENTERED OVER OHIO THU AFTERNOON.
WITH MARGINAL TEMPS AT THE SURFACE AND ALOFT, SNOW ACCUMS WILL
BE RATHER LIGHT (A COATING TO INCH OR 2) AND LIMITED TO TERRAIN
ABOVE 2000 FT MSL THROUGH EARLY THURSDAY, WITH MAINLY
RAIN/SHOWERS ACROSS THE CENTRAL RIDGE AND VALLEY REGION (MIXING
WITH WET SNOW AT TIMES LATE AT ELEVATIONS ABOVE 1000 FT MSL AND
COATING THE GROUND ON THE RIDGE TOPS AOA 1800 FT MSL).
THE MEAT OF THIS EARLY WINTER BEAST IMPACTS CENTRAL PA, THE
ALLEGHENIES AND WESTERN POCONOS WITH VALLEY RAIN/SNOW AND
ELEVATION SNOW FALLING AT VARYING INTENSITY FROM LATE THURSDAY,
RIGHT INTO FRIDAY NIGHT.
QPF AND SNOWFALL GRIDS COVER A 36-42 PERIOD AT THIS POINT,
CENTERED ON FRIDAY. SNOW TOTALS IN EXCESS OF 3 INCHES LOOK
HIGHLY LIKELY OVER THIS TIME-SPAN ACROSS MUCH OF THE NORTHERN
AND WESTERN MTNS WITH 6 INCHES OR MORE POSSIBLE AT ELEVATIONS
AOA 2500 FT MSL (WHICH RESIDES MAINLY ACROSS THE LAUREL
HIGHLANDS - AND SPECIFICALLY SOMERSET COUNTY.
MENTIONED THIS ASPECT OF THE FORECAST IN THE HAZARDOUS WEATHER
OUTLOOK AND WE GENERATED A 1-PAGE SLIDE FOR OUR WEBPAGE.
THE MAIN AREA OF UNCERTAINTY SURROUNDS THE TIMING OF INDIVIDUAL
VORT SPOKES AND THE NWWD EXTENT/PIVOTING OF THE SFC LOW AND ANY
MORE SPECIFIC, STRONGER FGEN FORCING/MESOSCALE BANDING OF
HEAVIER SNOW ACROSS NORTHERN PA. DEEP MOISTURE AND A WELL-
ALIGNED/ORTHOGONAL FLOW AGAINST THE RIDGES OF THE LAUREL
HIGHLANDS REGION SHOULD BE A NEAR SLAM DUNK FOR HEAVY SNOW
ACCUMS AOA 6 INCHES THERE FRIDAY/FRIDAY NIGHT NEAR AND TO THE
WEST OF RT 219.
GUSTY NW WINDS EXPECTED FOR LATER THU NIGHT - FRI NIGHT AS SFC
LOW DEEPENS TO BELOW 995 MB NEAR OR JUST TO THE WEST OF KNYC.
PREVIOUS DISC WITH SOME SYNOPTIC SCALE FEATURE DETAILS FOLLOWS
BELOW...
RECENT GUIDANCE ALL TRACKS A SURFACE COLD/OCCLUDED FRONT
THROUGH CENTRAL PA WED EVENING IN ADVANCE OF THE UPPER LOW
APPROACHING FROM THE GRT LKS. STRONG LARGE SCALE FORCING AHEAD
OF THE UPPER LOW AND LOW LEVEL CONVERGENCE ALONG THE FRONT
SUPPORTS A HIGH CHANCE OF RAIN WED NIGHT. EMBEDDED LOW-TOPPED
CONVECTION IS POSSIBLE NEAR OR ALONG THE COLD FRONT GIVEN
RAPIDLY COOLING TEMPERATURES ALOFT. THE MOST LIKELY RAINFALL BY
LATE WED NIGHT IS IN THE 0.25 TO 0.75 INCH RANGE, WITH THE
HIGHEST TOTALS OVER THE EASTERN PART OF THE FORECAST AREA.
GUIDANCE INDICATES A DRY SLOT WILL WORK INTO CENTRAL PA THURSDAY
MORNING, THEN A PERIOD OF CHILLY AND UNSETTLED WEATHER LOOKS
CERTAIN LATE THIS WEEK, AS THE UPPER LOW PIVOTS ACROSS SOUTHERN
PA AND PINWHEELS NEAR THE NJ COAST. A DEEP MOIST NORTHWEST FLOW
ON THE WESTERN PERIPHERY OF THE EXITING UPPER LOW SHOULD RESULT
IN A LONG DURATION, UPSLOPE/OROGRAPHIC AND LAKE ENHANCED
PRECIPITATION EVENT FOCUSED OVER THE ALLEGHENY MTNS AND
PARTICULARLY THE LAUREL HIGHLANDS THROUGH THE END OF THE WEEK.
MODEL THERMAL PROFILES CURRENTLY LOOK COLD ENOUGH TO SUPPORT THE
FIRST ACCUMULATING SNOW OF THE SEASON ACROSS THE HIGHER
ELEVATIONS OF THE ALLEGHENIES THURSDAY INTO FRIDAY, BUT
SNOWFLAKES COULD EXTEND SOUTHEAST OF THE ALLEGHENY FRONT INTO
THE CENTRAL RIDGE AND VALLEY REGION AT TIMES.
THE LAUREL HIGHLANDS ARE POISED TO PICK UP THE MOST SNOW DUE TO
ENHANCED OROGRAPHIC FORCING, FAVORABLY NW FLOW TRAJECTORY, AND
COLDER SURFACE TEMPS. THURSDAY NIGHT LOOKS LIKE THE BEST SHOT AT
SEEING ADVISORY CRITERIA TOTALS OVER SOMERSET COUNTY WITH WPC
PWPF SHOWING HIGH PROBS (>70%) FOR SNOWFALL POTENTIALLY
EXCEEDING 4" AT ELEVATIONS ABOVE 2500FT. WE MODIFIED THE HWO TO
HIGHLIGHT THIS AREA.
IN ADDITION TO FREQUENT PRECIPITATION AND BELOW NORMAL DAYTIME
TEMPERATURES, GUSTY WEST-NORTHWEST WINDS ARE ALSO ANTICIPATED
FRIDAY AND SATURDAY, AS A TIGHT GRADIENT DEVELOPS WEST OF AN
INTENSIFYING SURFACE LOW OVER NEW ENGLAND. LATEST EPS PLUMES
INDICATE GUSTS OF AROUND 30MPH ARE LIKELY BOTH DAYS. PERSISTENT
CLOUD COVER AND COOLER TEMPERATURES ALOFT WILL KEEP HIGH
TEMPERATURES 5-10 DEGREES BELOW AVERAGE LATE THIS WEEK, WHILE
OVERNIGHT LOWS ARE CLOSE TO NORMAL.
LINGERING LAKE EFFECT OVER THE W MTNS SHOULD DWINDLE BY SUNDAY
AFTERNOON, AS INVERSION HEIGHTS FALL AND HIGH PRESSURE
APPROACHES FROM THE WEST. MILDER CONDITIONS LOOK LIKELY NEXT
MONDAY AHEAD OF AN APPROACHING COLD FRONT, WHICH COULD PRODUCE
LATE DAY RAIN SHOWERS.
AVIATION /10Z WEDNESDAY THROUGH SUNDAY/
445 AM UPDATE.
TAFS HOLDING UP RATHER GOOD SO FAR. MINOR ADJUSTMENTS MADE.
EARLIER DISCUSSION BELOW.
06Z TAFS SENT.
OVERALL LOOKING AT LOW VISIBILITY AND CIGS OVER THE MOUNTAINS AT
SITES LIKE BFD AND JST OVERNIGHT. FOR UNV AND AOO, MAINLY LOW
CIGS. MAYBE A BIT MORE CHANCE FOR FOG AT IPT AT TIMES.
FOR MDT AND LNS, LESS LIKELY TO DROP DOWN TO MVFR CONDITIONS,
GIVEN CURRENT CIG LEVELS.
BANDS OF SHOWERS THAT FORMED LATE TUESDAY AFTERNOON ARE LARGELY
EAST OF THE AREA, WITH STILL A FEW WEST OF IPT. THUS THINK MUCH
OF THE DAY LIGHT HOURS TODAY WILL FEATURE NOT MUCH GOING ON.
THE COLD FRONT MOVES INTO THE AREA TOWARD LATE AFTERNOON AND
EARLY EVENING, WITH A SHARP WIND SHIFT LINE AND A GUSTY SHOWER.
THE GREAT LAKES ARE VERY WARM, AND WITH THE LARGE SCALE PATTERN,
THIS WILL LIKELY RESULT IN WINDS MORE FROM THE WEST OR
SOUTHWEST, NOT FROM THE NORTHWEST, ONCE THE FRONT MOVES EAST OF
THE AREA. WOULD EXPECT MORE IN THE WAY OF WIND AND SNOW SHOWER
POTENTIAL LATER THURSDAY NIGHT INTO FRIDAY, ONCE WINDS CAN
SHIFT TO THE WEST AND PERHAPS A BIT TO THE NORTHWEST.
OUTLOOK...
THU-SAT...RESTRICTIONS LIKELY WITH RAIN AND SNOW SHOWERS,
MAINLY ACROSS THE MOUNTAINS (BFD AND JST). MVFR MUCH OF THE TIME
FOR UNV/IPT/AOO. MAINLY VFR AT LNS AND MDT. WINDY.
SUN...NO SIG WX.
CTP WATCHES/WARNINGS/ADVISORIES
WINTER STORM WATCH FROM THURSDAY AFTERNOON THROUGH SATURDAY
EVENING FOR PAZ024-033.
WINTER STORM WATCH FROM THURSDAY AFTERNOON THROUGH FRIDAY
AFTERNOON FOR PAZ037-042-058.
SYNOPSIS...DANGELO/STEINBUGL
NEAR TERM...LAMBERT/DANGELO
SHORT TERM...LAMBERT/DANGELO
LONG TERM...LAMBERT
AVIATION...MARTIN
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