textproduct: State College

WHAT HAS CHANGED

* Cold Weather Advisory and Extreme Cold Watch issued for Friday afternoon through early Saturday morning

KEY MESSAGES

1) Frigid temperatures and dangerous wind chills expand from northwest to southeast Friday afternoon into Saturday morning

2) Increasing odds for double digit heavy snow accumulation and widespread moderate to major winter storm impacts Saturday night through Sunday night/AM Monday

3) Arctic blast persists with frigid temperatures and sub-zero to dangerous wind chills expected next Monday through Wednesday

DISCUSSION

KEY MESSAGE 1: Frigid temperatures and dangerous wind chills expand from northwest to southeast Friday afternoon into Saturday morning

Following a relatively mild afternoon, arctic air is poised to return to the forecast area - filtering in from northwest to southeast through Friday night. High confidence in -10 to -20F wind chills across all of CPA Friday afternoon into early Saturday morning approaching extreme cold criteria in the Laurel Highlands. Frigid arctic air will remain in place prior to the onset of the winter storm/heavy snowfall this weekend.

KEY MESSAGE 2: Increasing odds for double digit heavy snow accumulation and widespread moderate to major winter storm impacts Saturday night through Sunday night/AM Monday

Double-digit snowfall and widespread moderate to major winter storm impacts are becoming more likely across most of CPA Saturday night through Sunday night/AM Monday. As northern and southern branches of the jet stream interact and merge, pronounced WAA and accompanying 850-700mb fgen response will drive deep ascent into a rapidly moistening column thanks to IVT above the 90th climatological percentile. This phase transition along with favorable jet dynamics will spell an impressive snowfall for most of the area with rates >1"/hr likely. As secondary low pressure develops offshore (in a Miller B type evolution), banded structures within the WAA zone may pivot over the area Sunday night/AM Monday. Latest odds for >10" are better than 50/50 over most of the area peaking 70-85% range across the south central and eastern portions of the CWA. The arctic air would favor a dry, fluffy snowfall over the weekend and be more prone to blowing/drifting impacts.

We still can't rule out some mixing with sleet/zr at the peak of warm air advection aloft, and this trend will need to be monitored as it could cut down on max snowfall. NBM wx grids did begin to introduce a slight chance of ip/zr along the southern tier later Sunday into Sunday night.

Please continue to check for the latest forecast as it evolves and details become more clear. Now is the time to prepare. Think snow blowers, re-arranging travel plans to avoid travel during the storm, what to do in case of a power outage, etc. Remember it will be very cold before, during and after the storm. Never run a generator indoors due to carbon monoxide.

KEY MESSAGE 3: Arctic blast persists with frigid temperatures and sub-zero to dangerous wind chills expected next Monday through Wednesday

A prolonged stretch of frigid temperatures continues next week through the end of January. Sub-zero to dangerous wind chills will also persist with the most likely timing for another round of cold wx headlines (-10 to -20F wind chills) Monday night through Tuesday morning. Given the prolonged nature of the bitter cold, we may begin to see more infrastructure impacts (frozen pipes) by next week.

Occasional lake effect/upslope snow showers are likely next week under a very cold cyclonic flow aloft.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

Mostly clear skies are expected across the forecast area overnight outside of BFD/JST and MDT/LNS which will likely experience cloud cover overnight based on most recent HREF model guidance. Across southwestern Pennsylvania (JST), highest probabilities for cloud cover come between 23/00Z-04Z with more dry air in place further east, which will limit cloud cover at AOO with high (~70-80%) confidence. Cloud cover currently across western New York will continue to gradually shift southward and get into BFD after 23/01Z and is likely to continue through the rest of the 00Z TAF package, with MVFR conditions becoming more likely after 23/09Z. Recent model guidance does indicate some scattering out of the low-level (below 3000ft AGL) cloud deck at BFD with a period of VFR conditions in the 23/10Z-13Z timeframe; however, low (~20%) confidence in this solution at this juncture. Cloud cover is also progged by the bulk of model guidance to begin filtering into southeastern Pennsylvania after 23/09Z, thus have included mentions in VFR ceilings at MDT/LNS with moderate-to-high (~60-80%) confidence.

Gusty to breezy winds are expected to continue overnight with some periods of relatively lighter winds progged by recent GLAMP/HREF model guidance. The 00Z TAF package has increased winds and gusts slightly higher than previous forecasts based on current observations with winds expected to stay stead and/or increase overnight across the area ahead of a moisture-starved Arctic Front passage across central Pennsylvania expected early Friday morning. Gusty winds are expected with high (~80-90%) confidence after the passage of this Arctic Front with gusts between 20 and 30 knots expected area wide.

Outlook...

Sat...Dry most of the day, then SN begins to enter south-to- north late spreading across region and intensifying overnight. Widespread IFR likely Sat night.

Sun...Impactful snow storm continues with widespread IFR restrictions, LIFR possible.

Mon...Storm lifts to the NE and cold northwest flow takes over, bringing snow showers and continued restrictions to the NW, and improving conditions to the SE.

Tue...Lake effect snow across NW PA with restrictions possible; otherwise, dry and breezy.

CTP WATCHES/WARNINGS/ADVISORIES

Cold Weather Advisory from 1 PM Friday to 10 AM EST Saturday for PAZ004>006-010>012-017-018-037-041-042. Winter Storm Watch from Saturday evening through Monday afternoon for PAZ004>006-010>012-017>019-024>028-033>037-041- 042-045-046-049>053-056>059-063>066. Cold Weather Advisory from 6 PM Friday to 10 AM EST Saturday for PAZ019-025>028-034-035-045-046-049>053. Extreme Cold Watch from Friday evening through Saturday morning for PAZ024-033. Cold Weather Advisory from 10 PM Friday to 10 AM EST Saturday for PAZ036-056>059-063>066.