068
FXUS61 KCTP 190117
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
817 PM EST MON NOV 18 2024
SYNOPSIS
A RIDGE OF HIGH PRESSURE WILL BUILD ACROSS PENNSYLVANIA
TONIGHT, THEN A WEAKENING SHORTWAVE WILL GRAZE THE AREA AS IT
LIFTS NORTH THROUGH THE GREAT LAKES LATE TUESDAY. A CUT-OFF
UPPER LOW WILL TRACK FROM THE GREAT LAKES INTO PENNSYLVANIA
LATE THIS WEEK, PRECEDED BY AN OCCLUDED FRONT PASSAGE WEDNESDAY
NIGHT.
NEAR TERM /UNTIL 7 AM TUESDAY MORNING/
SURFACE RIDGING BUILDING ACROSS THE REGION WILL ENSURE FAIR
WEATHER AND LIGHT WINDS TONIGHT ACROSS CENTRAL PA. WARM
ADVECTION NORTH OF A STALLED FRONT IN THE OHIO VALLEY WILL
RESULT IN MOSTLY CLOUDY SKIES ACROSS THE SOUTHWEST PORTION OF
THE FORECAST AREA, WHILE THE REST OF THE REGION EXPERIENCES A
MOSTLY CLEAR START TO THE NIGHT, THEN VARIABLE CLOUDINESS LATE.
LATEST SREF AND NAMNEST BOTH TARGET THE N MTNS FOR VALLEY FOG
LATE TONIGHT ASSOCIATED WITH EFFICIENT RADIATIONAL COOLING AND
TUMBLING TEMPS THE FIRST HALF OF THE NIGHT. FURTHER SOUTH,
DEWPOINT DEPRESSIONS ARE ALREADY LOW ACROSS THE SOUTHWEST
COUNTIES CLOSER TO THE STALLED FRONT. ANY BREAKS IN THE CLOUD
COVER IN THAT AREA SHOULD ALSO RESULT IN PATCHY LATE NIGHT
VALLEY FOG.
EXPECT MIN TEMPS TO RANGE FROM THE LOW 30S IN THE VALLEYS OF
NORTHERN PA, WHERE CONDITIONS ARE MOST FAVORABLE FOR RADIATIONAL
COOLING, TO THE MID 40S OVER SOMERSET COUNTY, WHERE SKIES SHOULD
REMAIN MOSTLY CLOUDY OVERNIGHT.
SHORT TERM /7 AM TUESDAY MORNING THROUGH WEDNESDAY/
UPPER LEVEL RIDGING OVER THE AREA SHOULD PROVIDE CENTRAL PA
WITH MILD AND RAIN-FREE CONDITIONS FOR MOST OF TUESDAY. WEAK
MIXING UNDER THE RIDGE AXIS SHOULD RESULT IN SLIGHTLY LOWER
TEMPS TUESDAY, DESPITE WARMING ALOFT. SEE NO REASON TO DEVIATE
FROM NBM GUIDANCE, WHICH PROJECTS HIGHS IN THE 50S TO NEAR 60F
ACROSS THE LOWER SUSQ VALLEY.
WARM ADVECTION ASSOCIATED WITH A WEAKENING SHORTWAVE LIFTING
INTO THE GRT LKS SHOULD LEAD TO INCREASING CLOUDS LATE
TUESDAY/TUESDAY NIGHT WITH THE CHANCE OF A LITTLE LIGHT RAIN,
MAINLY OVER THE W MTNS. ANY LIGHT RAIN SHOULD TAPER OFF
FROM WEST TO EAST LATE TUE EVENING, AS THE LOW LEVEL JET AND
DEEPEST MOISTURE EXITS. HOWEVER, MODEL SOUNDINGS INDICATE PATCHY
DRIZZLE MAY LINGER OVER THE ALLEGHENIES, WHERE THE SFC-850MB
LAYER REMAINS NEARLY SATURATED AND A LIGHT SOUTHEAST FLOW
ASCENDS THE HIGH TERRAIN. LATEST ENSEMBLE QPF SUGGEST MOST
LIKELY RAINFALL BY LATE TUE NIGHT RANGES FROM NEAR A TENTH OF AN
INCH ACROSS THE LAUREL HIGHLANDS, TO LITTLE IF ANY RAIN IN THE
SUSQ VALLEY.
FOCUS THEN SHIFTS TO A CUT-OFF UPPER LOW DROPPING INTO THE
MIDWEST. MODEL SOUNDINGS INDICATE AN EASTERLY FLOW OFF OF THE
ATLANTIC WILL LIKELY YIELD STRATUS OVER MUCH OF THE AREA WED,
ESPECIALLY OVER THE CENTRAL MTNS. FALLING HEIGHTS AND SURGING
PWATS ALONG A SOUTHERLY LOW LEVEL JET SHOULD THEN BRING
THICKENING CLOUDS AND AN INCREASING CHANCE OF SHOWERS ACROSS THE
ENTIRE AREA BY LATE WEDNESDAY OR WED EVENING. 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 /WEDNESDAY NIGHT THROUGH MONDAY/
A VERY MATURE CYCLONE WILL INTERACT WITH THE GREAT LAKES AND
PLENTY OF MOISTURE AVAILABLE THERE (WITH NO ICE FLOATING AROUND
YET). THE OCCLUDED/COLD FRONT WILL LIKELY PUSH ACROSS PA WED
EVENING. THE TRIPLE POINT MAY RUN W-E ACROSS PA OR JUST TO THE
SOUTH OF THE STATE. I HAD INITIALLY PUT IN SCHC THUNDER FOR
LATER WED FOR THE SE, BUT WITHDREW IT WITHOUT SUPPORT FROM OTHER
FORECASTERS. THE COLD AIR ADVECTION IS STRONGEST FROM THE WSW
BUT LAGS A BIT BEHIND THE INITIAL DRY SLOT/OCCLUSION.
THE PATTERN IN FIRST 48HRS OF THE LONG TERM IS THE MOST
INTERESTING OF THE SEASON THUS FAR, AND HAS THE MOST
SPREAD AND THEREFORE LOWEST CONFIDENCE. STILL, EVEN WITH THE
MASS FIELDS DIFFERING AMONGST GUIDANCE, THE END RESULT IS GOING
TO BE THE FIRST SNOWFALL OF THE SEASON FOR THE MOUNTAINS. THE
LAURELS (SPECIFICALLY SOMERSET CO WHICH ARE THE VERY HIGHEST
ELEVS OF PA) COULD PICK UP SIGNIFICANT AMOUNTS OF SNOW THANKS TO
A PERSISTENT UPSLOPE FLOW CARRYING GREAT LAKES (AND MAYBE
HUDSON BAY) MOISTURE IN FROM THE N/NW. COLLABORATION WITH
NEIGHBORING OFFICES AND WPC HAS RESULTED IN US NOT ISSUING A
WATCH AT THIS POINT. THERE MAY BE A COUPLE WAVES/PERIODS OF BEST
CONDITIONS FROM THURS-SAT INSTEAD OF A SINGULAR PERIOD/EVENT.
PROBABILISTIC GUIDANCE USING NBM FOR BASIS HAS <40% CHC OF
WARNING CRITERIA (6+") SNOW OCCURRING. BUT, THE EVENT COULD LAST
48+ HRS. THUS, EVEN THOUGH WE ARE STILL 4+ DAYS FROM THE PEAK
OF THE SNOWFALL INTENSITY/ACCUMS, THERE WAS SERIOUS
CONSIDERATION TOWARD STARTING A WATCH WITH THIS PKG. IN THE END,
THE COLLAB EFFORT SETTLED ON US NEEDING A BIT MORE CONFIDENCE
IN THOSE HIGHER AMOUNTS TO POST WATCHES IN PA (INCL SOMERSET
CO). IN ADDITION, THE HIGHER ELEVS OF THE POCONOS COULD ALSO
SEE ACCUMS AS THE COLD AIR COMES IN NEAR THE END OF THE INITIAL
PUSH OF PRECIP (WED PM-THURS AM). BUT, THE QPF POSSIBLE THERE
IS MUCH LOWER THAN ENOUGH TO WORRY FOR A WATCH.
A NORTHWEST FLOW PATTERN REMAINS (READ:LAKE EFFECT/UPSLOPE SHSN)
UNTIL SUNDAY WHEN HIGH PRESSURE STARTS TO SLIDE TO THE SOUTH
OF PA. BUT, WE CAN'T TOTALLY REMOVE THE CHC/SCHC POPS FROM THE
NW AT THIS POINT WITH SO MUCH UNCERTAINTY. COOLER THAN NORMAL
WEATHER WITH BLUSTERY WIND IS ANTICIPATED FOR THURS- SAT, AND
ONLY A MODEST WARM UP LATE IN THE WEEKEND/FIRST PART OF NEXT
WEEK.
AVIATION /01Z TUESDAY THROUGH SATURDAY/
CONDITIONS ARE GENERALLY VFR ACROSS A LARGE CHUNK OF CENTRAL
PENNSYLVANIA THIS EVENING. THE EXCEPTION BEING KJST WHERE A MVFR
CEILING PERSISTS ACROSS THAT HIGHER ELEVATION SITE. EXPECT THIS
TO CONTINUE OVERNIGHT.
ELSEWHERE, VFR WILL PERSIST OVERNIGHT AND INTO TUESDAY
AFTERNOON. PATCHY FOG IS POSSIBLE ACROSS THE NORTHWEST MOUNTAINS
AND LAURELS BY TUESDAY MORNING. NOT ENOUGH CONFIDENCE (<20%) TO
INCLUDE FOG AT ANY TAF SITES AT THIS POINT (HIGHEST PROBABILITY
AT JST/BFD, POSSIBLE AT IPT, UNV, AND AOO).
CLOUDS WILL BEGIN TO INCREASE TOMORROW AHEAD OF A WARM FRONT
THAT WILL BRING LIGHT SHOWERS TO WESTERN AIRFIELDS TUESDAY
AFTERNOON. RESTRICTIONS SHOULD HOLD OFF UNTIL AFTER 21Z IN THE
WEST WITH IFR CONDITIONS DEVELOPING OVERNIGHT.
OUTLOOK...
TUE NIGHT...RESTRICTIONS LIKELY WEST
WED...RESTRICTIONS LIKELY, MAINLY NW. MORE WIDESPREAD
RESTRICTIONS WITH RAIN AND LLWS WED NIGHT.
THU-FRI...RESTRICTIONS LIKELY WITH RAIN AND SNOW SHOWERS, MAINLY
ACROSS THE MOUNTAINS. WINDY.
CTP WATCHES/WARNINGS/ADVISORIES
NONE.
SYNOPSIS...LAMBERT/FITZGERALD
NEAR TERM...FITZGERALD
SHORT TERM...FITZGERALD/BANGHOFF
LONG TERM...FITZGERALD/DANGELO
AVIATION...TYBURSKI
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