textproduct: State College

WHAT HAS CHANGED

* Extreme Cold Watch expanded through Sunday morning to include all of central PA * Winter Weather Advisory issued for the Laurel Highlands

KEY MESSAGES

1) A clipper system will bring a coating to a couple inches of light, powdery snow to much of the area on Friday, leading to slippery travel; higher amounts in the Laurels.

2) Blustery with dangerous to extremely cold wind chills Friday night through Sunday morning; coldest weekend of winter

3) Moderating temperatures during the second week of February

DISCUSSION

KEY MESSAGE 1: A clipper system will bring a coating to a couple inches of light, powdery snow to much of the area on Friday, leading to slippery travel; higher amounts in the Laurels.

Initial wave of light snow (accum rates <0.50 in/hr) spreads from NW to SE across CPA Friday morning through the afternoon. Secondary shot of snow/snow showers later Friday through Friday night will be driven by a strong arctic frontal passage followed by plummeting temperatures and blustery winds into Saturday morning. Although moisture will be modest in an environment with well below normal PWs, the orographic/upslope forcing/ascent into a deepening DGZ will be sufficient to wring out a moderate to locally heavy (fluffy) snowfall in the Laurel Highlands. Higher-end winter weather advisory has been issued (based on a combination of snow+wind+blowing snow preceding xcold) with near-blizzard conditions possible at times. The usual summits and ski resorts along Laurel Mtn could pick up as much as 6-8 inches of high SLR fluff. Elsewhere along the Allegheny Plateau, a general 1-2" is expected with a 0.5-1" most likely in the central and southern ridge/valley region. We still can't rule out a couple of heavier snow showers or brief squalls along the arctic front, but timing is not ideal and SNSQ parameter signal is weak.

KEY MESSAGE 2: Blustery with dangerous to extremely cold wind chills Friday night through Sunday morning; coldest weekend of winter

Prepare for the coldest weekend of winter with wind chills 20 to 30 below zero possible/likely early Saturday morning. We expanded the extreme cold watch to cover the rest of the CWA and extended in time; however we would anticipate a warning and/or advisory to be issued in the next 1-2 fcst cycles. The lowest wind chills occur early Saturday morning, but remain below zero through Saturday afternoon before dropping back to double digits below zero Saturday night into early Sunday morning. Blustery winds may exceed advisory criteria (>40kt) especially over the southern half of the forecast area on Saturday; a wind advisory may be needed. Blowing and drifting snow is also a concern given the dry snow character and gusty winds.

KEY MESSAGE 3: Moderating temperatures during the second week of February

For those looking for a break in the cold pattern, here you go. Confidence continues to increase that temperatures will moderate during the second week of February and climb back to seasonal levels or near the historical average for early to mid February. This "warmup" puts mixed precipitation on the table with the next weather system that could arrive Wed/Thu next week. The guidance has come into better agreement concerning the precip pattern evolution with best odds around the middle of next week.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

Stratus with bases 1500-2500 ft progged to move into BFD and JST between 05z and 10z Fri as a clipper system approaches the area. Light stratiform snow will break out across central PA after sunrise, with max coverage during the afternoon. Guidance generally keeps cigs 1000 ft or higher through much of the day, with some lowering cigs later into the evening. JST has the highest chance of IFR cigs (60 pct chc) in the late afternoon and evening. Vsby will likely range from 3/4 to 4 SM in light snow across the area. Stratiform snow will dissipate across the west towards 00z Sat, as snow showers along and behind the Arctic front become the dominant mode. Across east central PA, stratiform light snow will continue later into the night (through 6-9z Sat).

Temps will fall quickly behind the front during the second half of Fri night. Winds will increase and stay strong through the day Sat with gusts 35-45 kts. This may result in areas of blowing snow reducing vsby into the day Sat even after the snow ends. Winds slowly decrease later Sunday.

Outlook...

Sat...Sct SHSN/MVFR AM (IFR poss) BFD/JST. Strong NW wind.

Sun...-SN/MVFR poss W. VFR E.

Mon-Tue...No sig wx.

CTP WATCHES/WARNINGS/ADVISORIES

Extreme Cold Watch from late Friday night through Sunday morning for PAZ004>006-010>012-017-018-024-025-033-034-037-041- 042. Extreme Cold Watch from late Friday night through Sunday morning for PAZ019-026>028-035-036-045-046-049>053-056>059- 063>066. Winter Weather Advisory from 10 AM Friday to 7 AM EST Saturday for PAZ024-033.