textproduct: State College

WHAT HAS CHANGED

* Cold Weather Advisory extended until noon for the Laurel Highlands * Cold Weather Advisory issued for this evening into Friday morning * Odds for plowable snow/winter driving impacts trend lower and shift south and east of US-15 and I-81

KEY MESSAGES

1) Prolonged Extreme Cold/Wind Chills through the end of January 2) Low to declining risk of plowable snow/minor winter weather impacts this weekend in the eastern Lower Susquehanna Valley 3) Extreme cold retreats early next week, but temperatures remain below the historical average into February

DISCUSSION

KEY MESSAGE 1: Prolonged Extreme Cold/Wind Chills through the end of January

The coldest wind chills will be somewhat variable this morning as clouds and flurries have spread over the forecast area.

The peak of the "elite" cold is approaching with record challenging minimum temperatures forecast tonight and Friday night/AM Saturday. We would not be surprised to see a few local observations (overnight min temps or wind chills) getting close to extreme cold criteria into the weekend. We are into the late innings of the prolonged extreme cold period which should end as the calender flips to February.

KEY MESSAGE 2: Low to declining risk of plowable snow/minor winter driving impacts this weekend in the eastern Lower Susquehanna Valley

Confidence growing that plowable/impactful snow (>2" footprint) will not impact the eastern portion of the Lower Susquehanna Valley this weekend based on the latest NBM and associated ensemble portfolios. 29/00Z deterministic GFS and ECMWF both keep this area snow-free while WPC/NBM/NBMv5 data indicate some potential for a coating to less than 1" amounts on the northwest extent of the broader/heavier snows expected closer to the Mid Atlantic coast. Odds for both minor and moderate winter weather/driving impacts have also trended lower and shifted southeastward in the Probabilistic Winter Storm Severity Index (WSSI-P).

KEY MESSAGE 3: Extreme cold retreats, but temperatures remain below the historical average into February.

Risk of cold weather headlines comes off the table on Monday as temperatures moderate a bit - but remain below the historical average through early February. The run of sub-freezing temperatures (consecutive days <32F) rolls on across the majority of CPA.

Additional forecast information:

The seemingly endless cold cyclonic flow aloft with reinforced shots of arctic air (850mb temps -18 to -24C are below the 10th climatological percentile) will allow for periods of terrain enhanced snow showers with minor snow accums focused across the Laurel Highlands and NW Alleghenies. Flurries will also extend into the central ridge/valley region through late week and may continue over the weekend. Recent Great Lakes ice cover analysis from GLERL/NIC shows 100% concentration on Lake Erie, so available moisture will be limited to upstream lake connections as mean llvl flow shifts from WNW to NNW by Friday.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

Widely scattered snow showers will continue through the day, potentially leading to periods of IFR vsby at BFD and JST. Otherwise, expect conditions to mainly be VFR. Wind gusts of 20 to 25 knots will be possible through the afternoon. MVFR or IFR ceilings should redevelop at BFD overnight, with MVFR ceilings persisting at JST. Model soundings suggest there is limited potential for fog to develop across southeast PA as skies clear out and winds decrease to less than 5 knots, but there is a less than 20 percent chance of visibility restrictions developing at MDT and LNS.

Outlook...

Fri-Sat...Periods of lake effect and upslope snow showers remain possible across N/W PA, with restrictions possible; otherwise, chilly and breezy areawide.

Sun...Light snow possible in southeast PA. Breezy with gusts between 20 and 30 knots.

Mon...Mainly VFR. A few light snow showers possible at BFD and JST in the afternoon and evening.

CLIMATE

Daily record minimum temperatures possible to close out January:

01/30 MDT: 2 in 1934 IPT: -6 in 1948 AOO: -3 in 2019 BFD: -14 in 1965 STC: -10 in 1977

01/31 MDT: 2 in 1948 IPT: -14 in 1948 AOO: -4 in 2019 BFD: -13 in 2019 STC: -9 in 1948

State College has a very good shot of tying the second longest run (7) of consecutive days with max temp <= 20F (1/25-1/31).

The last time this occurred was post-Christmas 2017 (12-28-2017 to 01-03-2018). The longest run of 10 days occurred in January 1893 from the 11th-20th.

CTP WATCHES/WARNINGS/ADVISORIES

Cold Weather Advisory from 7 PM this evening to 10 AM EST Friday for PAZ004>006-010>012-017>019-024>028-033>037-041-042- 045-046-049>053-056>059-063>066.