textproduct: State College

WHAT HAS CHANGED

* Added mention of SNSQs in the wx grids for 14-19Z Sun

KEY MESSAGES

1) Snow accumulation /and possibly a few squalls/ expected across the western highlands Sunday. A few snow showers could even make it into eastern Pennsylvania Sunday afternoon. Wind picks up behind a broken line of snow showers/squalls.

2) Quieter wx for Mon-Tues. Warmer than normal for Tues-Wed.

3) Still a possibility for a low pressure area to develop later in the week over the Mid-Atlantic. But, many factors are in question.

DISCUSSION

KEY MESSAGE 1...

A cold front will cross the commonwealth overnight, ushering in colder temperatures. It will turn blustery on Sunday, with wind gusts of 40-50 mph expected. A second front with the deeper arctic air immediately behind it will blow through during the daylight hrs, mainly between 13Z NW and 20Z SE.

Refining the forecast for Sunday. Have added mention of SNSQs to the W and N for mid-morning into mid-aftn. We have a decent chance for just enough heating to allow for development of some CAPE before the arctic front arrives in the central and northern mtns. Wind along and behind this front should be well- aligned to allow for momentum transfer to the sfc. Deep (for winter scenario) mixing up to ~12kft possible. That should allow for gusts into the 30s along the line/squalls. Afterward, the 50KT winds get down to about 3kft at UNV, and just 2kft or less above the ridge tops at JST. SNSQ parameter does light up. Tried to refine timing of said SNSQs based on blend of latest HRRR and RAP with some influence from NAMNest and GFS to allow for a bit of broadening to the PoPs to reflect some uncertainty on timing by 1hr either side of the consensus timing.

A relatively short period of LES and upslope SHSN will affect the Alleghenies and Laurels. The heaviest snow will occur on the ridges of Somerset Co and far NW Warren Co.

KEY MESSAGE 2...

Wind gets a little lighter Sun night, and SHSN lift NE. Both wind and winter wx advys should be good to drop around midnight.

Look for improving conditions early next week, with little if any precip and moderating temperatures Monday & Tuesday. The next chance of precip will be as a northern stream wave will drop in from the Great Lakes Tues night-Wed. At this point, temps look marginal for RA/SN in the NW, but RA elsewhere.

KEY MESSAGE 3...

Precipitation chances will increase in the middle to later part of next week in response to an amplifying upper trough carving out over the Eastern US. Temps trend colder to more typical levels for mid January by Thursday and Friday. Thus, the potential for a widespread snowfall for Central PA is there, but the uncertainty of the development/strength/timing all point to a middle of the road PoP and broadbrushed QPF/snow picture. Will hang with NBM guidance for the time being without a strong enough reason to stray.

AVIATION /02Z SUNDAY THROUGH THURSDAY/

IFR/LIFR conditions remain the rule of central Pennsylvania as of 00Z Sunday, with rainfall mainly stationed across the northern and western halves of the forecast area, with rainfall observed at all TAF sites outside of MDT/LNS. Ample low-level moisture remains in place across the southeast; however, so cannot rule out an hour-two of light drizzle/rain before limited precipitation mentions are expected. Some signal for clearing across the eastern half of the forecast area does promote some potential for fog formation at IPT/MDT/LNS with the threat lower (but still notable) at UNV given light/calm winds in the near- term. The 00Z TAF package hits eastern airfields with fog formation, leaning towards a blended GLAMP/RAP model solution that outlines ample low-level moisture that is trending well with current observations. Lower probability solution trends towards no fog mentions at any of the airfields; however, IFR conditions are expected (> 80%) confidence at all airfields through ~06Z Sunday.

Winds begin to pick up west-to-east near the 04Z-06Z Sunday timeframe, which will allow for lower confidence in IFR conditions prevailing area wide. Recent GLAMP/HREF model guidance does indicate improvement overnight towards MVFR ceilings and potentially VFR conditions should the low-level deck scour out completely. Highest uncertainty remains at BFD/JST, where low-level moisture remains present in most recent RAP model guidance, so have trended slightly towards the RAP solution in this timeframe with lower (30-40%) confidence. Elsewhere, a period of VFR conditions are virtually certain (~90-100% confidence) with the most uncertainty coming with respect to timing and duration of VFR flight categories.

Secondary cold front (see Key Message #3) will allow for lake effect and upslope snow showers across the western highlands of Pennsylvania, with BFD/JST (higher confidence, 60-80%) and AOO/UNV/IPT (lower confidence, 20-40%) having the potential for snow showers. The 00Z TAF package introduces mentions based on a RAP/HREF model blend, that tracks fairly well with recent GLAMP guidance; however, there remains some uncertainty with respect to a faster arrival time, so could realistically see onset of precipitation/restrictions moving up one-two hours in the next couple of TAF cycles. IFR conditions within snow showers are increasingly likely based on visibility restrictions; however, based on the lower confidence further east have trended back mentions towards MVFR. Some LLWS concerns begin to come towards the end of the TAF package; however, given time horizon and lower confidence based on NBM/NAM model guidance, have kept mentions out this cycle with low (~20%) confidence.

Outlook...

Mon...A few lingering lake effect snow showers early, giving way to mainly VFR conditions.

Tue-Wed...Mainly VFR.

Thu...Ceiling restrictions poss NW, VFR SE.

CTP WATCHES/WARNINGS/ADVISORIES

Wind Advisory from 10 AM Sunday to 1 AM EST Monday for PAZ024- 025-033-034. Winter Weather Advisory from 8 AM Sunday to 1 AM EST Monday for PAZ033.