Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 182355 AFDCTP Area Forecast Discussion National Weather Service State College PA 755 PM EDT Mon Mar 18 2024 .SYNOPSIS...
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An amplifying upper level trough will drift across Pennsylvania through tonight, followed by a reinforcing shortwave and associated cold front Wednesday. High pressure is likely to build over the area Thursday. A dying cold front is likely to approach from the Great Lakes late next week, as a southern stream shortwave passes south of the state.
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&& .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... Water vapor loop at 22Z shows a deep upper level trough pushing into PA from the Grt Lks. Modest instability ahead of it is producing mostly light snow showers across the Alleghenies and central mountains, while dry air and downsloping flow is maintaining fair but chilly dry conditions across the Susq Valley. Large scale subsidence behind the exiting trough should result in breaking clouds east of the mountains tonight, while lake- enhanced orographic snow showers persist across the Allegheny Plateau. Near term model guidance indicates the plume of best lake moisture will begin the evening over the NW Mtns, then pivot south into the Laurel Highlands late tonight. Progged inversion heights are fairly low and the airmass remains dry outside of lake bands, so overnight accumulations will be light. Latest ensemble mean qpf supports overnight accums ranging from a dusting over most of the Alleghenies, to around an inch over the Laurel Highlands. A well mixed boundary layer and only weak cold advection suggest temperatures will fall slowly tonight, with daybreak readings ranging from the mid 20s over the higher terrain of the Alleghenies, to the low 30s in the Lower Susq Valley. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
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Latest guidance continues to track a clipper across the Northern Grt Lks Tuesday. Backing flow ahead of this feature should result in a break in the lake effect activity early Tuesday. However, warm advection along the attendant low level jet is likely to support some light snow across primarily the N Mtns Tuesday. Latest ensemble mean qpf indicates accumulations of less than an inch are likely. Temperatures will edge up a bit Tuesday under warm advection regime, but plenty of cloud cover should still result in max temps several degrees below average, ranging from the 30s over the N Mtns, to the low and mid 40s in the southern valleys. The best isentropic lift shifts north of the border Tuesday night. However, residual low level moisture ascending the Allegheny Plateau should result in a few lingering snow showers overnight in that part of the state, with clearing skies expected downwind (east) of the mountains.
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&& .LONG TERM /WEDNESDAY THROUGH MONDAY/...
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The passage of the trailing cold front Wednesday should be accompanied by scattered rain/snow showers, a few of which could survive into the Susq Valley, due to strong forcing ahead of the upper level shortwave. Steep lower tropospheric lapse rates indicate the potential of some heavier snow squalls across the N Mtns. Deep cold advection and passage of a strong isallobaric couplet signal a period of gusty northwest winds behind the cold front late Tuesday. Latest Bufkit soundings support gusts in the 30-40mph range late Tuesday into Tue evening. Fair, but still cool, weather appears likely Thursday, as the trough lifts out and surface ridging builds in from the Grt Lks. Medium range guidance suggests a few rain showers are possible Friday, mainly over the N Mtns, associated with the approach of a dying cold front. The bulk of guidance tracks a more significant southern stream shortwave and associated area of low pressure well south of PA next weekend. Therefore, fair and seasonal conditions currently appear likely next Sat/Sun.
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&& .AVIATION /00Z TUESDAY THROUGH SATURDAY/... Mainly VFR will continue into Tuesday across much of the central and SE PA airspace under varying amounts of stratocu based AOA 3500 ft AGL. There will be occasional to persistent MVFR across PA`s northern and western mtn airfields tonight and even some brief periods of MVFR Cigs at KUNV and KAOO in -SHSN this into this evening. West-northwest winds will be moderately gusty this evening and tonight for all TAF sites. A dual or multi-layered cloud shield (mainly VFR) will spread across the region Tuesday as the low level flow backs a bit more to the west-southwest, helping to confine most of the snow showers across the far NW zones, with generally mostly cloudy skies and breezy and dry conditions elsewhere. Outlook... Tuesday-Saturday...Periodic snow showers and reductions, primarily across the higher terrain of northern and western PA. This will be enhanced by reinforcing shots of unseasonably cold air and gusty W/NW winds. West to northwest wind gusts could peak in the 35 to 40 mph range on Wednesday. && .CLIMATE... Astronomical Spring (vernal equinox) begins on Tuesday March 19 at 11:06 PM EDT. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert NEAR TERM...Fitzgerald SHORT TERM...Lambert/Fitzgerald LONG TERM...Fitzgerald AVIATION...Lambert/Gartner CLIMATE...Steinbugl

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