textproduct: State College

SYNOPSIS

*Snow showers and gusty winds gradually taper off tonight *Accumulating snow possible this weekend followed by another arctic blast *Signs of a warmer pattern change on the horizon by the end of next week

NEAR TERM /THROUGH FRIDAY/

Transient snow showers continue across central Pennsylvania, mainly along and north of the I-80 corridor this evening with intensity gradually on a downward trend. A couple of stronger snow showers could still impact the I-80 corridor between 11PM Thursday and 1AM Friday before precipitation mentions shift further north/west. Recent observations and radar observations continue to outline light snow across the northern tier and western Pennsylvania where Winter Weather Advisories continue through 4AM. At this time, no modifications seem to be necessary to existing WSW products with the aforementioned snow showers brining light accumulations to areas under the Advisory.

00Z HREF continues to outline moderate (40-60%) chances of snow showers across NW PA through 08Z/3AM EST Friday before chances begin a steady decline supporting little in the way of mentions after sunrise. Outside of far western Warren County, the bulk of Friday will remain dry with partly to mostly cloudy skies and well-below average high temperatures for the middle of December.

In terms of winds, the highest wind gust over the past 24 hours was reported at Lancaster Airport (KLNS) at 48 mph late Thursday morning, with multiple stations across the region reporting over 40 mph readings throughout the day. Winds have drastically dropped off across the area, with much of the area reporting winds generally under 20KT as of 04Z/11pm EST. Consensus of model data continues these winds on a decreasing trend through the overnight with slight increases after sunrise on Friday.

SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/

An approaching surface low pressure tracking across the Upper Great Lakes will bring increased chances of light WAA snow (less than 1" of accumulation) downwind of Lake Erie into northwestern Pennsylvania late Friday night into early Saturday. Upslope flow will likely lead to a slightly earlier arrival time compared to recent model guidance, thus have mentions beginning slightly after midnight Friday night.

To the south of the main upper low center near Lake Superior, another fast moving system will streak around the southern periphery of the upper trough from the Northern Plains through the Ohio Valley and into the Central Appalachians and Mid Atlantic Saturday night through Sunday morning. The upper trough is fcst to dig/amplify as it pivots eastward and should drive coastal low development while dragging a pocket of -20C air at 850mb into southwest PA/WV by Sunday afternoon.

Odds are rising for a broad area of expanding/accumulating snow Saturday night through early Sunday across CPA. NBM probs for >3" are highest over the southern Laurels and southeast portion of the Lower Susquehanna Valley. The arrival of arctic air ensures snow character will be very dry and fluffy.

Max temps Sunday will drop by 10-20 degrees vs. Saturday with mean departures from climo on the order of 15 to 25 degrees. A few locations could see highs close to the daily record low max. Gusty winds and very cold temps will send min wind chills near and below zero Saturday night through Sunday night/AM Monday.

Lake effect/upslope snow showers continue through Sunday night.

LONG TERM /MONDAY THROUGH THURSDAY/

One more shortwave trough could brush the area with light snow early next week; otherwise there is growing confidence in a mid to late December thaw as the pattern transitions to a milder SW flow aloft with mean troughing shifted westward into the Central U.S. Dry wx is favored Tue-Thu with highs climbing toward the 40-50F range late in the week - possibly in advance of the next widespread precip event.

AVIATION /04Z FRIDAY THROUGH TUESDAY/

Snow showers continue mainly across the northern half of the forecast area and will continue to bring likely MVFR conditions to BFD through ~06Z before model guidance begins to indicate lower probabilities in snowfall at the airfield. Based on current radar, could see a brief reprieve with even some observations peaking up to VFR; however, generally expect these to be minimal before trending back towards MVFR with some IFR if heavier snow bands are able to get into the airfield. Further east, IPT will be next up for concerns with the northern snow showers; however, there remains some uncertainty with these features given low-level dry air in place based off of recent observations. The bulk of model guidance does indicate some snowfall but have brought back mentions considerably from the previous package and highlighted a two hour window where this is most plausible based off of recent observations/radar. Upslope snow appears to be slightly underdone in the most recent GLAMP at JST, so have also increased snow mentions over the next three hours with lower confidence throughout the rest of the evening.

Consensus of model guidance indicates that MVFR will prevail at BFD/JST throughout much (if not all at BFD) of the 00Z TAF package with continued VFR conditions elsewhere. Snow shower potential at BFD is generally expected to continue through ~12Z Friday with lower confidence towards the end of this timeframe as showers gradually diminish. At JST, lower ceilings are the main concern in terms of aviation. Recent GLAMP guidance has started to hint towards some bouts of IFR at JST between 13-18Z Friday; however, this seems like a lower probability (~10-20%) solution at this time based on RAP model soundings and HREF probabilities in ceilings below 700ft AGL, thus have kept any IFR mentions out of the 00Z TAF package at this time.

Outlook...

Sat-Sun...Rounds of light snow expected with highest chances for snow late Sat into early Sun, restrictions possible.

Mon...Snow becomes confined to N/W PA, restrictions possible.

Tue...Lingering showers NW PA early before trending dry across the area.

CLIMATE

Astronomical winter (solstice) begins at 10:03 a.m. on Sunday, December 21st.

CTP WATCHES/WARNINGS/ADVISORIES

Lake Effect Snow Warning until 4 AM EST Friday for PAZ004-005. Winter Weather Advisory until 4 AM EST Friday for PAZ006-010- 011-017-037.