textproduct: State College

SYNOPSIS

* A quick-hitting system will bring snow and perhaps a snow squall (north) and a wintry mix (south) tonight and Sunday. Freezing drizzle is possible in the Laurels. * A brief period of lake effect snow may affect the far NW Sunday night. * A more widespread/significant winter storm is possible on Tuesday.

NEAR TERM /UNTIL 6 AM SUNDAY MORNING/

Had some sun for a brief time earlier this afternoon, but mid and high clouds started to move in before sunset. Some returns on the radar as of early evening, but nothing making it to the ground yet, rather dry at low levels.

Earlier discussion below.

Not much to see for the evening hours. Deepening low pressure to our west will slide into the Great Lakes area tonight. Warm advective precip/snow will approach by midnight, but it will take some time to work down from aloft. So, despite some radar echos this evening and early tonight, we don't expect anything to stick until close to midnight in Warren Co, with some flurries starting about that time along the rest of the western CWA border.

SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY/

Still looks like the far northwest will have the highest chance for several inches of snow later tonight into late Sunday. Most of the snow will be from warm advection, but some snow showers and perhaps a squall along the cold front later Sunday, followed by limited lake effect late Sunday. The cold air is not as deep as on Friday, so heavy snow showers and perhaps a squall will be more limited with this system.

Earlier discussion below.

One wave of light WAA snow will lift across the far NW early tonight with a second and maybe third wave by sunrise. As the moisture thickens up overnight, some snow may stick over the rest of the Alleghenies. A worry has developed for freezing drizzle to occur on the higher elevations of the Laurels. Model soundings indicate a thick cloud layer of super-cooled liquid water there before sunrise. Temps will be below freezing there despite the thickening clouds. Without (many) snow crystals in the cloud there, the more-likely precip type is freezing drizzle. The forcing and upslope flow are poor and non-existent, respectively. It is even more of a downslope flow, esp for Cambria and Bedford. After confab with PBZ/LWX, we came to the consensus that a WW.Y was necessary to highlight a light ice accum on the highest elevations.

The moisture does inch upward slightly before a cold front sweeps through the CWA from W to E during mid-day. The better lift and instability will be over the NW, and they could get above freezing just before the front arrives. Almost all other locations will likely get to or above freezing, too. The soundings look like snow N of a line from JST-UNV-IPT before the front passes despite the above freezing air temps. Therefore, there could be some heavier snow showers or even squalls that could ice up the previously warmed roads/bridges. Something to be aware of at this point. The highest risk for SQWs would be over the Alleghenies where the SNSQ parameter start to light up as we see some instability develop in the "warm" sector. The vertical profiles look more like mix or rain as you move farther south toward I-81, especially the later in the day things arrive/occur. Maxes will be in the 40s S of I-80 and below 1500ft.

For now, only mentions of SNSQ will be in the NW third. FROPA 18Z BFD, 22Z IPT/AOO, 00Z at LNS. Wind will get gusty in the unstable/mixed air, but should be under 30KTs. Some hilltops in the west could get into the 30s. The flow behind the front goes NWrly and still has some kick. So, that means...lake effect. The time period where the NW flow will be confined to late Sun and Sunday night coincident with a secondary cold front pushing thru the NW. Moisture decreases and inversion lowers by sunrise Monday. Monday should be bland/fair with high pressure arriving and centering overhead. Clouds will probably linger in the W very much like today (Sat) before high clouds move in later in the day Mon.

LONG TERM /MONDAY NIGHT THROUGH SATURDAY/

The main event will be the potential for widespread snow on Tuesday. The limiting factor will be the speed of the low.

At this point, Wednesday looks to be dry. The flow favors fast moving systems, but systems for later in the week look to move along and are weaker than the low for Tuesday.

Earlier discussion below.

Unsettled weather will continue into the first week of December as cold air in the middle of the country sets up a strong baroclinic zone over the eastern US. High pressure in the Plains should keep cold air in place on the northern side of the precipitation shield from a wave of low pressure progged to move out of the Gulf. This system should move northeast around the base of the aforementioned high pressure system, bringing increasing moisture to the Mid-Atlantic Tuesday into Wednesday.

The system at this time looks to be somewhat progressive with the lack of a strong area of high pressure to slow the advance of the system. Despite the expected fast forward movement, a deepening coastal low could still provide enough forcing juxtaposed with favorable upper jet dynamics to produce significant snowfall across the region. Snow looks to arrive later Monday night and lift across the region during the day on Monday, though confidence is still low on timing given the spread in current guidance this far out. The eventual track and intensity of the low will have big implications on observed snowfall totals and the northward extent of any mix/rain scenarios.

The latest WPC probabilities of 0.25" or greater liquid equivalent snow/sleet paint medium probabilities (40-70%) across most of the region, with slightly lower amounts expected in northwest PA. The latest Winter Storm Outlook highlights a 30-50% chance of Warning criteria snowfall (5"+) in northeast PA. GEFS and ECENS probabilities of 6"+ continue to outline probabilities <30% with a higher likelihood in northeast PA up through coastal New England. If confidence increases in higher amounts, Watches may be needed in the next 24-48 hours. At this time, though, a plowable snowfall seems like a reasonable bet for most of the region. Guidance has remained consistent overall for snowfall amounts with the last two runs, however some uncertainty remains whether or not warm nosing above the surface could limit snow across the PA/MD boarder. Continue to monitor the forecast in the days ahead, especially if you have plans to travel.

Later in the week, high pressure will regain control of our weather. Prevailing upper troughing brings high confidence in continued below normal temperatures and a chilly start to December. Low temperatures in the teens or single digits are possible and our active storm pattern appears likely to continue.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

Some radar returns across north/western Pennsylvania are likely struggling to reach the ground in the near-term with low- level dry air in place. Better chances for precipitation come after 06Z Sunday based on a consensus of GLAMP/HREF guidance, thus have trended back any mentions of precipitation at BFD until after 06Z Sunday. Snowfall will begin with restrictions to MVFR/high-end IFR at BFD as there remains some uncertainty with respect to how east the heaviest band of snowfall will extend between 06-08Z Sunday. There remains a lower probability solution where the heavier band sneaks into BFD closer to 07Z and brings (V)LIFR restrictions; however, confidence remains too low (~20-30%) to include in the 00Z TAF package and might be better resolved in the 06Z TAF package with current radar trends available at that time.

Precipitation is expected (based on GLAMP/RAP/HREF guidance) to enter JST/AOO closer to the 11-12Z timeframe and gradually extend eastward with prevailing MVFR restrictions limited to JST/AOO/UNV at this time. There remains a lower confidence solution where lower ceilings develop at IPT (~30% probability) so have outlined a PROB30 group for this outcome. IFR restrictions after 12Z will look confined to western terminals (BFD/JST) for the 00Z TAF package.

Moderate-to-high (~60-70%) confidence in LLWS exists at all airfields outside of UNV/IPT/MDT/LNS after 11Z with the cold frontal passage and increased low-level flow behind the frontal passage across central Pennsylvania. Recent TAF package continues mentions for these restrictions, with slight timing adjustments based on RAP/GLAMP model guidance.

Outlook...

Mon...Mixed/wintry precip likely early on. MVFR likely. IFR possible.

Tue...Snow possible, before a possible mix later in the day across the south. Restrictions possible.

Wed-Thu...Trending drier, lingering snow across NW PA.

CTP WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory from 3 AM to noon EST Sunday for PAZ033.