textproduct: State College

WHAT HAS CHANGED

* Extreme Cold Watch upgraded to an Extreme Cold Warning for areas along and north of I-80 and along and west of I-99. Cold Weather Advisory for the rest of the area. * Wind Advisory issued for much of Central PA.

KEY MESSAGES

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

2) Blustery with dangerous 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 today, leading to slippery travel; higher amounts in the Laurels.

Light snow will move in from west to east this morning. A secondary shot of snow/snow showers later this afternoon/evening 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. A higher-end winter weather advisory has been issued for Cambria and Somerset Counties based on a combination of snow, wind, and blowing snow preceding extreme cold. 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 instability should be limited with the front arriving near or just after sunset.

KEY MESSAGE 2: Blustery with dangerous 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 have issued an Extreme Cold Warning for areas along and north of I-80 and west of I-99. The rest of the area is under a Cold Weather Advisory. 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.

A very tight pressure gradient across the region behind the arctic front will support wind gusts in the 40 to 50 mph range on Saturday. Strong pressure rises behind the front will lead to gusts as high as 55 mph during the morning over the Laurel Highlands. A Wind Advisory has been issued for most of Central PA from midnight tonight through 10 PM Saturday. Winds remain gusty on Sunday, but should stay below advisory strength.

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 /12Z FRIDAY THROUGH TUESDAY/

Recent model guidance continues to indicate MVFR-to-IFR conditions as low-level cloud decks continue to thicken ahead of a cold frontal passage. Light radar returns across NW PA are seemingly not reaching the ground based on recent 11Z observations; however, expect that to change over the next hour at BFD with -SN likely in the cards throughout the morning and afternoon hours. Most recent GLAMP model guidance has trended slightly back on snowfall onset timing and is in better agreement with HREF/RAP model guidance, thus increasing confidence in onset timing at all airfields outside of IPT/MDT/LNS where the largest change in model guidance occurred over the past couple of model runs. IFR conditions appear more likely within heavier snow this afternoon/evening, with highest confidence at BFD/JST (~70-80%), trending slightly lower further east given a lack of low-level moisture despite ample forcing present. Snow showers (potentially some squalls) will be possible later this evening (06/18Z-07/03Z); however, confidence remains too low for inclusion in the 12Z TAF package.

Winds will increase mainly after 07/00Z and remain strong through the end of the TAF period. This may result in areas of blowing snow reducing visibility later on in the TAF package; however, confidence remains too low and might be better suited to wait until snow falls between now and 07/00Z where higher confidence would be expected. Increasing concerns for LLWS begin to eek way into the forecast after 07/06Z as a 850mb 55-65kt LLJ begins to influence the southwestern portion of the forecast area and gradually overspread the area into the end of the TAF period.

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 Warning from 1 AM Saturday to 10 AM EST Sunday for PAZ004>006-010>012-017>019-024-025-033-034-037-041-042-045- 046. Wind Advisory from 4 AM to 10 PM EST Saturday for PAZ012-027- 028-036-041-042-045-046-049>053-056>059-063>066. Wind Advisory from midnight tonight to 10 PM EST Saturday for PAZ017>019-024>026-033>035. Winter Weather Advisory from 10 AM this morning to 7 AM EST Saturday for PAZ024-033. Cold Weather Advisory from 4 AM Saturday to 10 AM EST Sunday for PAZ026>028-035-036-049>053-056>059-063>066.