697
FXUS61 KCTP 201543
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
1043 AM EST WED NOV 20 2024
SYNOPSIS
*BRIEF PERIOD OF MODERATE TO LOCALLY HEAVY RAIN SPREADS FROM
WEST TO EAST THIS EVENING INTO EARLY TONIGHT
*BIG PATTERN CHANGE FOR LATE WEEK ASSOCIATED WITH THE FIRST
WINTER STORM OF THE SEASON
*HEAVY, ELEVATION-DRIVEN WET SNOW ACCUMULATION POSSIBLE IN THE
LAUREL HIGHLANDS AND POCONOS THURSDAY NIGHT-FRIDAY NIGHT
NEAR TERM /THROUGH TONIGHT/
LOW THICK CLOUDS AND FOG CONTINUE TO HANG ON ACROSS MUCH OF THE
CENTRAL AND NORTHERN MOUNTAINS IN THE LATTER HALF OF THIS
MORNING. SUN HAS BROKEN OUT ACROSS THE SOUTHERN HALF OF THE
COMMONWEALTH, AND TEMPERATURES ARE BEGINNING TO RISE. MOST OF
CENTRAL PA SHOULD BREAK OUT INTO PARTLY SUNNY SKIES AHEAD OF THE
OCCLUDED FRONT EXPECTED TO REACH US LATER THIS EVENING, WHICH
WILL PROMOTE THE WEAK INSTABILITY FOR THE CONVECTIVE RAIN
SHOWERS TONIGHT.
PREVIOUS DISCUSSION...
EXPECT LATE DAY HIGHS IN THE MID 50S TO LOW 60S OR +10-15
DEGREES ABOVE DAILY CLIMO.
HIRES MODELS SHOW A BAND OF SOAKING RAIN ACCOMPANYING AN
OCCLUDED FRONT SWEEPING THROUGH THE AREA THIS EVENING THROUGH
EARLY TONIGHT. A BRIEF PERIOD OF CONVECTIVELY ENHANCED/LOCALLY
HEAVY RAINFALL IS POSSIBLE GIVEN WEAK/SLIGHTLY ELEVATED
INSTABILITY PARTICULARLY OVER PORTIONS OF SOUTH CENTRAL PA. THE
SHORT DURATION DOWNPOURS COULD CAUSE SOME MINOR STREET OR
ROADWAY PONDING ESPECIALLY DUE TO LEAF-CLOGGED STORM DRAINS.
CONDITIONS WILL TURN WINDY AND SHARPLY COLDER IN THE WAKE OF THE
FRONTAL PASSAGE WITH TEMPERATURES FALLING ABOUT 20 DEGREES
IN 12 HOURS BETWEEN 7PM-7AM. 3-6MB PRESSURE RISES IN 3HR ALONG
WITH STRONG CAA WILL PROMOTE BRISK WIND GUSTS BETWEEN 30-40 MPH.
MIN TEMPS WILL BE 10-20 DEGREES LOWER VS. LAST NIGHT IN THE
30-40F RANGE BY DAYBREAK THURSDAY WITH AN ADDED WIND CHILL
FACTOR.
SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/
BIG PATTERN CHANGE UNFOLDS FOR LATE WEEK AS COMPLEX BUT HIGHLY
ANOMALOUS UPPER LEVEL CLOSED LOW SPAWNS THE FIRST WINTER STORM
OF THE SEASON.
TWO KEY AREAS OF CONCERN:
1) NORTHEAST ZONES ADJACENT TO THE POCONOS: ELEVATION DRIVEN
HEAVY WET SNOW POTENTIALLY SETTING UP OVER A 24HR PERIOD
THURSDAY EVENING INTO FRIDAY EVENING AS ROBUST DEFORMATION ZONE
PIVOTS OVER NORTHEAST PA. WE WERE KEEN TO ISSUE A WINTER STORM
WATCH FOR THE HIGHER TERRAIN ZONES ADJACENT TO WFOS BGM AND PHI
WITH MULTI MODEL/ENSEMBLE TRENDS SIGNALING INCREASING
CONFIDENCE IN >6" NEAR OR ABOVE 1500FT.
2) LAUREL HIGHLANDS: MULTI-DAY UPSLOPE FLOW SNOW EVENT IS SET
TO OCCUR FROM THURSDAY NIGHT THROUGH SATURDAY NIGHT IMPACTING
THE LAUREL HIGHLANDS. THIS IS OUR HIGHEST CONFIDENCE HEAVY SNOW
RISK AREA GIVEN A VERY PREDICTABLE LONG DURATION NW FLOW
PATTERN. ENSEMBLE GUIDANCE HAS BEEN ALL OVER THIS GOING BACK
MORE THAN A WEEK AND NOW SHORT RANGE BLENDS INDICATE HIGH ODDS
FOR >6" OF SNOW ABOVE 2000 FEET. A WINTER STORM WATCH WAS ALSO
ISSUED FOR SOMERSET AND CAMBRIA COUNTIES.
A GENERAL 1-3 INCHES IS FORECAST OVER THE NORTHWEST ALLEGHENY
MOUNTAINS WITH SOME POTENTIAL FOR LOCAL 3-6". LOWER ELEVATIONS
ALONG AND TO THE SOUTHEAST OF I99/I80 CORRIDOR COULD PICK UP A
SLUSHY COATING TO AN INCH OR SO BY THE WEEKEND, WITH VERY LITTLE
TO NO SNOW ACCUM EXPECTED IN THE LOWER SUSQ VALLEY. BLUSTERY
WINDS AND HEAVY WET SNOW COULD RESULT IN MODERATE IMPACTS (WSSI)
PARTICULARLY IN THE HIGHER ELEVATIONS, BUT ANY ACCUMS IN THE
VALLEYS WOULD LIKELY OCCUR ON GRASS AND ELEVATED SURFACES. THERE
ARE STILL SOME DETAILS TO RESOLVE, BUT FEEL WATCH ISSUANCE WAS A
SOLID STEP IN THE HEADLINE PROGRESSION AT THIS STAGE/FCST
LENGTH.
LONG TERM /SATURDAY THROUGH TUESDAY/
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 /16Z WEDNESDAY THROUGH SUNDAY/
7 AM UPDATE.
12Z TAFS SENT.
STARTING TO SEE MORE VARIATION IN THE OBS, FOG AND PERHAPS SOME
SMOKE MIXING WITH THE FOG, IS STARTING TO LIFT UP. STILL EXPECT
DECENT IMPROVEMENT IN A FEW HOURS.
MAIN THING WAS TO CUT OFF PRECIPITATION A BIT FASTER THAN
GUIDANCE, BEHIND THE COLD FRONT TONIGHT. THIS BASED ON SEVERAL
FACTORS GIVEN LACK OF HIGH DEWPOINTS AND WINDS SHIFTING TO THE
WEST RATHER QUICKLY IN SPOTS LIKE MDT.
EARLIER DISCUSSION BELOW.
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...STEINBUGL
NEAR TERM...STEINBUGL/BOWEN
SHORT TERM...STEINBUGL
LONG TERM...LAMBERT
AVIATION...MARTIN
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