textproduct: State College

WHAT HAS CHANGED

* Winter Storm Warnings remain in effect through 1 PM Monday with significant snowfall expected across all of central Pennsylvania. * Increased snowfall totals across much of the area due to higher confidence in a band of heavier snow occurring across north-central Pennsylvania. * Updated precipitation types across the southern tier of Pennsylvania to account for more snowfall, still some sleet/freezing rain mentions retained.

KEY MESSAGES

1) A major winter storm will impact all of central Pennsylvania bringing widespread travel impacts across the Commonwealth through Monday morning.

2) Frigid temperatures and breezy-to-gusty winds will bring bitterly cold wind chills in the wake of the winter storm and continue throughout much of the upcoming week. Periods of snow showers expected in this timeframe.

DISCUSSION

KEY MESSAGE 1: A major winter storm will impact all of central Pennsylvania bringing widespread travel impacts across the Commonwealth through Monday morning.

Current (as of 4 AM EST 01/25/2026) radar outlines precipitation expanding across the southern half of Pennsylvania with recent observations outlining light snow as far north as Bradford (KBFD) with ample lift with a trough across western portions of Pennsylvania. Some low-level dry air remains further northeast; however, expect enough moisture to filter into the region with more than sufficient lift to allow for snowfall to expand across the entire region by sunrise.

Moderate snow rates are already being observed across portions of southwestern Pennsylvania with recent observations at AOO/JST outlining periods of SN. Webcams across the region also outline more efficient rates along the I-99 corridor where higher radar returns can be observed; however, the overall trend is that moderate snow will continue on/off for the next couple of hours before rates begin to amp up near/after sunrise due to better isentropic ascent from low-level frontogenesis. Snowfall rates over 1"/hr are increasingly likely across the bulk of central Pennsylvania in the 12Z/07 AM EST to 00Z (Mon)/7PM EST timeframe, starting off across southern Pennsylvania and spreading northward throughout the morning/afternoon. Of more recent concern based on more recent model guidance will be the potential for snowfall rates pushing close to (and potentially exceeding) 2"/hr rates across portions of the north-central mountains where frontogenesis at 850mb and 700mb have remained fairly constant and more recent hi-res model guidance paints a more concerning picture for increased snowfall totals. The beginning rumblings of this tale can already be observed on radar with a frontogenetic/convergent band beginning to set up across portions of western Pennsylvania and extending into portions of central Ohio with heavier radar returns further west into Indiana. If this band continues to hold stout, snowfall totals are nearly certain to exceed a foot and potentially push over 18", which the newest forecast package attempts to get in there with Storm Total Snowfall.

Some uncertainty remains with regards to the snowfall forecast across the southern tier, where the main concern will be the potential for freezing rain and sleet, which could knock down snowfall totals slightly. Overall, a slight increase across the region has been issued in the newest forecast package to account for current radar/observational trends. At this time it's looking increasingly likely that southeastern portions of the forecast will be flirting with the 8-12" forecast range and have taken more of a midpoint approach to best account for the slight north/southward discrepancies in recent model guidance. Either way, significant snowfall is expected and will likely impact travel today and into Monday across southeastern Pennsylvania.

Wrap around snow showers in the wake of the low pressure system Sunday evening and into Monday will continue to allow for light-to-moderate snow before the system begins shifting north and east of the region. Some more recent guidance does bring in a quicker end to snowfall compared to previous forecast with low-level dry air attempting to make way into the region, so have blended in with previous forecast in order to get some lower mentions but still hold onto mentions into Monday morning before becoming more confined to upslope snow Monday afternoon and evening with higher confidence in snowfall ending by late Monday evening.

Lots of words with meteorology above, so the long and short of it across central Pennsylvania: - While light-to-moderate snowfall is currently being observed across the region, we are expecting rates to increase closer to sunrise and continuing through the afternoon/evening hours. - In terms of "increased rates": 1"/hr (possible even 2"/hr) rates are *likely* this morning and afternoon across much of central Pennsylvania. - Travel is expected to be hazardous through Monday morning, we're highlighting this in our WSW's (no changes this cycle) that travel will be "extremely difficult to impossible". - Impacts are likely to continue into Monday morning with most locations across central Pennsylvania likely to observed over 12" of snow. Accumulations might be less across southeastern Pennsylvania; however, 8-12" of snowfall will still be difficult for travel purposes.

KEY MESSAGE 2: Frigid temperatures and breezy-to-gusty winds will bring bitterly cold wind chills in the wake of the winter storm and continue throughout much of the upcoming week. Periods of snow showers expected in this timeframe

Very high confidence in cold air settling into the region in the wake of the aforementioned winter storm with 850mb temperatures in the -15C to -20C range through Saturday. The most recent NBM forecast outlines the Monday night into Tuesday morning as one of the coldest period of the week. Digging into the why for this; 850mb temperatures across the entire region right around -20C, some potential clearing across the southeastern half of the forecast area, breezy-to-gusty winds with a fairly tight pressure gradient across central Pennsylvania is more than supportive of widespread negative wind chills across the region with widespread Cold Weather Advisory and potentially Extreme Cold criteria being met across the Laurel Highlands and all of north-central Pennsylvania. A very similar setup will be in place Thursday night into Friday morning, so we're looking at these two nights for the most potential for Extreme Cold mentions; however, a longer duration of cold temperatures are expected with much of the area not reaching above the freezing mark in the current forecast (runs through Sunday 02/01). The main concern with pushing out any products right now for Monday night would be timing with respect to the incoming winter system. Want to make sure the cold weather products do not get drowned out with the current high- end Winter Storm Warning we have out, so will message it in the Additional Details of the WSW & HWO and will likely issue headlines where they would get more visibility.

Cyclonic flow aloft will allow for continued mentions for upslope snow showers across the Laurels and NW Alleghenies throughout the week. In terms of the favored lake effect regions of northwestern Pennsylvania, current ice coverage on Lake Erie outlines a fair amount of ice coverage which will limit mentions with cold temperatures likely allowing for a shutoff across the region. Any Lake Huron connections will still be fair game at this point, so will need to keep monitoring potential along that front but looks like until we get a solid warm up the Lake Erie lake effect machine will be slowing down for the near future.

AVIATION /12Z SUNDAY THROUGH THURSDAY/

Widespread IFR-to-LIFR conditions with pockets of (V)LIFR within the heaviest bands of snow across central Pennsylvania over the next couple of hours. Heavier snowfall rates are progged by all model guidance, gradually overspreading south- to- north after 12Z Sun and continuing through 00Z Mon. Given the increasing rates, have went ahead and leaned towards more pessimistic guidance solutions which outline widespread 1/4SM +SN through 00Z Monday, leaning towards a combination of HREF/GLAMP model guidance. Wind shear concerns increase across the western terminals in the 15Z Sun to 04Z Mon timeframe with the presence of 50kt LLJ at 850mb, thus have included mentions in the 12Z TAF package with moderate (50-70%) confidence. Further east, lower confidence in LLWS thresholds being met, thus have continued no mentions in this timeframe.

After 06Z Monday, considerable uncertainty remains with respect to precipitation being ejected out of central Pennsylvania with some of the more recent hi-res model guidance indicating a quicker end to precipitation across southern and eastern portions of Pennsylvania while upslope snow showers continue further west. There is higher confidence across areas generally along and west of the Allegheny Front retaining IFR mentions under snow showers, with UNV/IPT outlining slightly lower probabilities for measurable snowfall compared to BFD/JST/AOO this model cycle. Further east, recent GLAMP model guidance does indicate some instances of precipitation tapering off after 06Z Monday with a brief period of IFR persisting before MVFR conditions become more certain closer and slightly after 12Z Monday.

Outlook...

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.

Wed-Thu...Light upslope snow over W PA, elsewhere dry.

CLIMATE

The winter system impacting the central/eastern United States will be bringing significant snowfall to all of central Pennsylvania, with the bulk of snowfall expected to fall on Sunday, January 25th. This section provides some context on the magnitude of snowfall based on some records at the two long- standing climate sites across central Pennsylvania; Harrisburg International Airport (KMDT) and Williamsport Regional Airport (KIPT) which have periods of records dating back to 1888 and 1895, respectively. The current forecast for Harrisburg does not break the top five one-day snowfall records; however, forecast does bring snowfall accumulations towards exceeding the record snowfall for January 25th in Harrisburg. Current forecast for Williamsport will be pushing close to the top five one-day snowfall accumulations and will also be pushing close to the snowfall record for January 25th.

Top 5 One Day Snowfall (All Year) KMDT: 1. 26.4" on 01/23/2016 2. 24.0" on 02/11/1983 3. 20.3" on 03/13/1993 4. 19.8" on 01/07/1996 5. 19.7" on 01/16/1945

KIPT: 1. 23.0" on 02/22/1902 2. 20.0" on 02/19/1972 3. 19.6" on 01/13/1964 4. 18.3" on 03/14/2017 T5. 16.0" on 02/04/1926 T5. 16.0" on 02/14/1914

Record Snowfall for January 25th: KMDT: 5.4" in 1988 KIPT: 9.2" in 1958

CTP WATCHES/WARNINGS/ADVISORIES

Winter Storm Warning until 1 PM EST Monday for PAZ004>006- 010>012-017>019-024>028-033>037-041-042-045-046-049>053- 056>059-063>066.