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FXUS61 KCTP 270254 AFDCTP

Area Forecast Discussion National Weather Service State College PA 1054 PM EDT Fri Apr 26 2024

SYNOPSIS
A warm front will approach Pennsylvania Saturday, then lift north of the state Sunday. Upper level ridging appears likely over the area through next week, with the stalled warm front remaining just north of Pennsylvania. A cold front will likely push into the area from the Great Lakes by next Saturday.

NEAR TERM /UNTIL 7 AM SATURDAY MORNING/
Late evening satellite loop shows a thin veil of cirrus over Central PA. Mostly clear skies, light wind and relatively dry air lingering over Eastern PA should result in efficient radiational cooling and min temps a bit below NBM guidance over that part of the state. Patchy frost is possible over portions of Sullivan and Schuylkill counties, with lows in the mid 30s.

Otherwise, the focus tonight will be on an upstream shortwave lifting into the Grt Lks. Model RH fields support increasing cloudiness overspreading the region late tonight ahead of this feature. Models remain in good agreement that showers associated with the attendant low level jet and plume of higher pwats will arrive over the Allegheny Plateau around dawn. Increasing cloud cover and an active southeast breeze should result in a much milder night over the western half of the forecast than we've seen recently, with min temps in the low to mid 40s.

SHORT TERM /7 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/
The upper level shortwave and best forcing is progged to pass well north of PA Saturday. However, passage of the trailing low level jet and associated plume of higher pwats overrunning a relatively cool/stable air mass over PA should support a period of rain showers over most of Central PA. Model guidance indicates the focus of the rain will be during the morning hours over the W Mtns and during the afternoon over the Susq Valley.
Ensemble mean qpf by Sat evening ranges from around 0.25 inches over the Allegheny Plateau, to <0.05 inches in the Lower Susq Valley. Mainly cloudy skies, spotty rain and a southeast flow off of the Atlantic will result in a fairly cool day for late April, with highs mainly in the 50s.

The chance of measurable rain will diminish by Saturday night, as the shortwave passes north of PA and the plume of deep moisture along the trailing low level jet exits the area. Model RH profiles support partial clearing over much of the region Sat night. However, lingering low level moisture and an upsloping southeast flow ahead of an approaching warm front should result in areas of stratus over the N Mtns, with ridgetop fog/drizzle possible.

Brightening skies and markedly warmer conditions appear likely Sunday, as the warm front lifts north of the region. However, ensemble plumes indicate scattered "ring of fire" PM convection is possible, especially on the northern periphery of the upper ridge over Northern PA. PA should be entirely in the warm sector Sunday night with a toasty day on tap to start next week.

LONG TERM /MONDAY THROUGH FRIDAY/
Late evening update holds a slowing of the system moving in from the west at the end of the long term period (late week). This delay has brought the temps (esp the overnight mins) up quite dramatically from the previous cycle - equalling the Mon night and Tues night temps which are into the 60s in many places, with no one below 50F either night. Tues is still the highest prob for rain/thunder thru the period, and timing has not changed there.

Prev...
Fair and unseasonably warm weather is likely Monday with an upper-level ridge over the area. Mean 850mb temps near in the 10-15C range support max temps in the low-to-mid 80s areawide with temperatures pushing the upper 80s across SE PA where some clearing remains possible. Medium range guidance does outline potential for afternoon/evening convection on Tuesday as a mid- level shortwave traverses the area. At this time, best forcing looks to be across the northern half of the area, thus have upped PoPs across this area while limiting PoPs slightly to the south.

Deterministic model guidance does show diverging solutions into the second half of the week. Guidance continues to highlight ridging and above average temperatures throughout this period; however, there are slight timing differences with regards to an upstream trough and associated cold front late next week. The best timing for any precipitation will be with along a cold frontal passage Thursday PM into early Friday AM. Some uncertainty in model solutions post-frontal passage does promote a SChc of PoPs throughout Friday.

AVIATION /03Z SATURDAY THROUGH WEDNESDAY/
Quick update to winds in a few locations as the SE flow has recently gusted near 20KT. Have made a categorical change to these higher wind/gusts at JST, AOO & IPT. Also added LLWS to BFD for the next 6 hrs or so as a brief spike in llvl winds passes through. By morning, the jet max is past and up into NY.

Prev...
Unrestricted/VFR conditions should persist overnight, as clouds only gradually lower and thicken across central PA.

On Saturday, restrictive ceilings and persistent showers should reach the Allegheny Highland terminal sites (KBFD and KJST)
early in the morning. Conditions should deteriorate from MVFR/fuel alternate to IFR by midday/early afternoon, then remain low (solidly IFR) for the rest of the daylight hours.
Confidence in IFR restrictions is fairly high (60-80%).

For the ridge and valley terminal sites (KAOO and KUNV), lower clouds and showers should set in by mid-morning. MVFR-fuel alternate restrictions will likely worsen to IFR ceiling bases by mid to late afternoon. Confidence in IFR restrictions is moderate (50-70%).

For the Susquehanna Valley terminal sites (KIPT, KMDT, and KLNS), unrestricted conditions should persist for a good portion of the day, with some lower clouds and at least scattered showers (MVFR-fuel alternate restrictions) developing during the afternoon. At these terminal sites, the threat of IFR is much lower (only 10-20%).

S-SE surface winds will stay fairly gusty through the day Saturday, with periodic 18-22 kt gusts common.

Outlook...

Sun...Early morning lower ceilings possible, along with isolated late day thunderstorms. Much of the time, though, should feature VFR conditions.

Mon...No sig wx expected, with VFR/unrestricted conditions.

Tue-Wed...Scattered afternoon showers and thunderstorms possible, with at least brief restrictions.

CTP WATCHES/WARNINGS/ADVISORIES
None.

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