Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 072329 AFDCTP Area Forecast Discussion National Weather Service State College PA 729 PM EDT Fri May 7 2021 .SYNOPSIS... Rain will push through eastern Pennsylvania this evening ahead of a deep upper level trough. Unseasonably chilly conditions will follow for Saturday, with mostly cloudy skies, isolated to scattered rain showers and a northerly breeze. After a partly cloudy and cold Saturday night with relatively lighter wind and areas of frost across the Central and Northern Mountains and Laurel Highlands, clouds will thicken on Sunday morning with a cold rain developing across much of the region and lasting into Sunday evening. Scattered showers will linger on Monday, but drier conditions will return by Tuesday and Wednesday of next week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... A potent shortwave is pushing through central Pa early this evening, accompanied by a band of rain. Some convective elements, and even a few lightning strikes, were noted earlier across Franklin Co. However, latest RAP cape forecast indicates the chance of additional lightning is low. HRRR, which should perform well with this strongly forced feature, indicates the back edge of the rain will slowly edge eastward this evening, exiting the easternmost part of the forecast area by around 06Z. Wet ground, clearing skies and light winds will likely promote patchy valley fog late tonight over parts of the region. However, expect increasing clouds with a renewed chance of showers toward dawn across the western counties in association with approach of next shortwave diving into based of upper trough. Lows tonight will vary from the low to mid 30s across the northwest mountains, to the low 40s in the Susq Valley. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/... Scattered showers should be focused across the Allegheny Plateau and south central mountains early Saturday, associated with a potent shortwave diving through southwest Pa. Model soundings indicate the air mass could be just could enough to support the possibility of mixed rain/snow showers over the higher terrain of the Alleghenies until around noon. More widespread showers are expected to develop by afternoon due to diurnal heating beneath upper trough axis. Have ramped POPs up to 60-70 pct across much of the forecast area based on latest guidance. Some minimal surface based instability could support a few lightning strikes during the afternoon, primarily over the central and eastern counties. Mostly cloudy skies and numerous showers, combined with pool of chilly air aloft, will result in well below normal temperatures Saturday. High temps will vary from the upper 40s across the ridge tops of the Laurel Highlands to the 50s in most other locations. An increasingly gusty northwest wind will make it feel even a chillier. Bufkit soundings support gusts between 15-25kts by afternoon, with the highest gusts across the southwest portion of the forecast area. Exiting upper trough and approach of surface ridge should result in breaking clouds toward sunset with a rapidly diminishing chance of showers. && .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/... *Cool pattern for early May continues through next week *Brief window for frost Saturday night-A.M. Sunday *Soaking cold rain for Mother`s Day *Drying out and staying cool Monday-Wednesday; A.M. Wed. frost? *Wet weather returns by late week Some clearing early Saturday night associated with narrow ridge of HP and light winds may allow for some patchy frost to form by early Sunday morning. Clouds will be increasing into Sunday morning so it`s a tough call for now. Soaking cold rain expected on Sunday (Mother`s Day). WAA precip spreading into retreating cold/dry airmass will result in favorable evap cooling/web bulb effects to hold temps in the upper 40s across the NW Alleghenies. Trended fcst MaxT below NBM using 25th percentile. 24-hr QPF show 0.50-1" amounts over the northwest 2/3 of CPA with some point amounts >1" shaded toward the Laurel Highlands. 1hr FFG values remain low, however it does not appear that there is enough instability to result in sufficiently high rain rates to cause problems. That said, some minor runoff and ponding issues are possible and WPC plans to extend the D3 MRGL risk ERO over west-central PA. Rain totals trend lower to the southeast of I-81 (0.50" or less). Wave of low pressure passes to the south Sunday night with rain tapering to showers into Monday morning. Cooler and drier NW flow should end precip by Monday afternoon. Breezy start to the week with gusts in the 20-25 mph range. Reinforcing shortwave drives another surge of chilly air into the region on Tuesday. Some spotty showers will be possible especially across the northern tier. Still breezy and cool. Another potential frost window may open late Tuesday night into Wednesday morning as HP migrates into PA. Rain likely returns to the area by late week (Thu) with moisture extending northward as potential low pressure system develops near the southern Mid Atlantic coast. Operational GFS/EC consensus supported trending POPs above NBM PPI into the likely range. Also lowered MaxT on Thu by several degrees given the synoptic and precip patterns. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
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Steady rain will move off to the east early tonight with a few showers lingering for a time. With clearing moving in from the west and plenty of moisture from the earlier rain, there is the potential for a period of fog, especially over the western airspace overnight with IFR conditions possible. Another round of showers will move through late tonight, then more showers are expected to pop up Saturday afternoon which could lead to brief reductions in vsbys. Outlook... Sat...Brief MVFR to IFR cigs and MVFR vsbys possible in rain. Sun...Deteriorating conditions with a steady rain likely. Mon...Poor conds early. Improving west to east late in the day. Tue...Mainly dry, but still breezy.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert/DeVoir NEAR TERM...Fitzgerald SHORT TERM...Fitzgerald LONG TERM...Steinbugl AVIATION...DeVoir/Travis is the U.S. government's official web portal to all federal, state and local government web resources and services.