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FXUS61 KCTP 061424 AFDCTP

Area Forecast Discussion National Weather Service State College PA 924 AM EST Wed Dec 6 2023

SYNOPSIS
A chilly wind from the northwest will maintain intermittent snow/rain showers today especially over the western and northern Alleghenies. Another quick shot of light snow/rain is forecast mainly over the northern tier Thursday morning. A significant warming trend Friday through the weekend will precede a strong cold frontal passage that will bring the potential for heavy rain, strong wind gusts, and sharply colder temperatures later Sunday through Sunday night into early Monday.

NEAR TERM /THROUGH TONIGHT/
Base of 5H upper trough tracking east of the area through this afternoon with continued forcing and NW-flow lake enhancement for scattered snow showers and flurries. Higher elevations of the Allegheny Plateau may see another coating through the day, and localized accums around Laurel Summit may be an inch or two, but overall accums will be minimal with mainly melting on roadways.

As the upper trough is nudged east by tonight, the large scale flow transitions to coupled northwest flow aloft, while sfc ridge axis builds across central PA tonight. As the ridge axis moves east of the area Thursday morning, warm advection aloft and isentropic lift combined with approaching shortwave and 100kt upper jet max will likely result in a quick shot of light snow/rain translating over northern/eastern parts of the area Thursday morning. Although confident in amounts remaining well below advisory criteria, timing around the morning commute may produce impacts given traffic volumes at that time of day. Min temps trend slightly colder night/night with lows in the 25-30F range.

SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/
Snow accumulation Thursday should be less than 1 inch based on blend of latest HRRR/NBM. Precip should end by 00Z Fri as warming aloft ramps up Thursday night-Friday AM.

Expect plenty of clouds to hold max temps to near or a bit below seasonal normals Thursday, with highs ranging from the mid 30s to mid 40s. Lows Thursday night will vary from west (warmer) to east (cooler) thanks to elevation/gradient WSW flow and boundary layer decoupling. Some sites in the western part of the CWA may even see a non diurnal temp trend.

Noticeable warmup on Friday with max temps +10-15F warmer than Thursday with highs in the mid 40s to mid 50s. Similar west to east breakdown in min temps Friday night with relatively mild conditions (upper 30s to around 40F or +15-20F DFN) over the western & northern Alleghenies and colder readings in the central and eastern valleys.

LONG TERM /SATURDAY THROUGH TUESDAY/
*Heavy rain and strong wind gusts possible Sunday-Sunday night followed by sharp drop in temperatures into Monday

The bulk of guidance tracks a deepening surface low west of PA this weekend. Without a blocking high to the northeast of PA, expect well above normal temps to continue until the arrival of a trailing cold front Sunday PM or Monday AM. High temperatures on Saturday and Sunday are progged to be +10 to +15F above normal corresponding to highs in the 50s across the region. A slower arrival of the cold front on Sunday afternoon could allow temperatures to crest the 60 degree mark.

A deep plume of GOMEX moisture and strong upper level divergence ahead of an upstream trough should produce a period of moderate to heavy rain ahead of the front Sunday afternoon and evening.
Latest guidance has trended a bit slower on the arrival of precipitation, but some uncertainty remains. Ensemble plumes indicate most likely rainfall will fall between 0.75 and 1.50 inches. Strong/gusty southerly winds are possible if the region can break into the warm sector Sunday PM. However, climatology suggests the strongest winds will come in the cold advection regime behind the cold front Sunday night into Monday. Latest ECENS plumes indicate a possibility of wind gusts in excess of 40kts during this time frame. A return to cooler weather appears likely Monday, as upper level trough shifts into the region, accompanied by lingering orographic rain/snow showers over the W Mtns. Wind gusts will be on the decrease by Tuesday as the deep cyclone pulls away.

AVIATION /14Z WEDNESDAY THROUGH SUNDAY/
Trough aloft and a bit of an inverted trough at the sfc is keeping lots of clouds over the state. There are still patches of flurries over much of the area, and improvement looks like it will be a little slower than anticipated. There is enough moisture coming down from LO to continue to generate very light precip all morning over much of the area.

The weak subsidence associated with a high pressure ridge nearing and a gusty NW wind should help break up the lowest clouds downwind of the mountains. The clouds will hang tough for the west on the WNW upslope with some flurries still possible in the afternoon. The cigs will continue to bounce around as the multiple levels of clouds drift overhead and away again very quickly. From mid-aftn on into the the night (Wed night) should settle down to will then be as is typical with a NW flow, MVFR/IFR BFD and JST, and mainly VFR elsewhere.

Warm air starts to flow in aloft from the west late tonight and Thursday. Snow will likely fall along and east of the warm front which will cross the area. The forcing from a shortwave trough rolling southeast along the warm front will drop into the state from the N during the day on Thurs. Expect light snow, esp in BFD and IPT. Have nudged timing up (a little faster)
with this pkg. But, this still only gets snow restrictions back into north (BFD around 06Z). IPT and UNV are the other sites most likely to see constant MVFR conditions and a period of IFR in the morning.

This wave shall pass to the south & east and yield improvements in the aftn on Thurs. BFD will be the only terminal to have a >50% chc of an IFR cig later in the day.

Outlook...

Fri...Mainly VFR.

Sat...VFR early. Showers late.

Sun...CFROPA. Widespread reductions in rain/snow. Windy.

CTP WATCHES/WARNINGS/ADVISORIES
None.

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Market Street Bridge
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Wed -- 12:31 AM EST     Moonrise
Wed -- 02:37 AM EST     0.45 feet Low Tide
Wed -- 07:07 AM EST     Sunrise
Wed -- 08:10 AM EST     5.26 feet High Tide
Wed -- 01:10 PM EST     Moonset
Wed -- 02:55 PM EST     0.62 feet Low Tide
Wed -- 04:35 PM EST     Sunset
Wed -- 08:26 PM EST     5.55 feet High Tide
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Market Street Bridge, Schuylkill River, Pennsylvania, Tide feet

Philadelphia
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Wed -- 12:30 AM EST     Moonrise
Wed -- 02:46 AM EST     0.46 feet Low Tide
Wed -- 07:07 AM EST     Sunrise
Wed -- 08:36 AM EST     5.43 feet High Tide
Wed -- 01:10 PM EST     Moonset
Wed -- 03:04 PM EST     0.64 feet Low Tide
Wed -- 04:35 PM EST     Sunset
Wed -- 08:52 PM EST     5.72 feet High Tide
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Philadelphia, Pennsylvania, Tide feet

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