textproduct: State College

SYNOPSIS

* Occasional light freezing rain or freezing drizzle will continue across north-central and northeast PA early today along with areas of dense fog * A strong cold front pushing east across the state this morning will usher in very windy and much colder conditions from this afternoon into Tuesday * Accompanying the colder weather this week will be the development of a few heavy lake-effect snow bands that will stretch across northwest PA with snow showers and brief squalls elsewhere

NEAR TERM /THROUGH TONIGHT/

KEY MESSAGES: - Patchy freezing rain and freezing drizzle and higher elevation dense fog will continue to be an issue for a time early today across parts of north-central and northeast PA - A broken line of convective showers along a strong cold front will push east across the Commonwealth this morning, ushering in gusty winds and plummeting temperatures with a 20 to 30 degrees drop in temperatures within about 10 hours after the cold frontal passage. --------------------------------------------------------------

Warm frontal boundary having a difficult time (so far) pushing east into the cooler, dense air, trapped in the deeper valleys of Central PA where temps were slowly inching up through the low to mid 30s. The lingering light freezing rain/freezing drizzle will continue in some areas, and thought it prudent to extend the Winter Weather Advisory until 09Z (4 am).

Areas of dense fog and freezing drizzle will end shortly across the Ncent Mtns and Wrn Poconos as most observation sites are now up to 33-34F.

As moist and relatively mild air overruns a colder ice/sleet/snow covered ground over parts of Nort-Central PA and the Western Poconos, areas of very dense fog will persist at least through daybreak. Dense Fog Advisory for parts of the region (roughly the NE 1/3 of the CWA the until 7 am.

The combination of low visibilities and locally slippery travel on untreated surfaces overnight will be a hazard to motorists from parts of the Endless Mountains and Middle Susquehanna Valley into the Pocono plateau.

Better mixing via an increased P-gradient and southerly llvl flow, just ahead of the incoming arctic front, will support some rise in temperatures during the pre-dawn and early morning hours today.

We'll continue to monitor this situation closely.

The aforementioned strong cold front will plow east across the Commonwealth this morning, likely accompanied by a broken band of briefly heavy, gusty rain showers.

Behind the front, strong low-level cold advection will commence, along with very windy conditions. Regarding high wind potential, although the strongest isallobaric forcing is progged over upstate NY and southern Canada, very impressive pressure rises, good post-frontal downward momentum transfer, and an overall strong wind field into the upper part of the boundary layer across PA, argue for widespread wind gusts of 40-50 mph, and isolated gusts of 55-65 mph over the Alleghenies and points just downstream. A High Wind Warning is in effect for several of our Western and SW zones, with a Wind Advisory for the rest of the area. The period of strongest winds is anticipated from early Monday afternoon through the evening hours, when BUFKIT Time/Height cross-sections show the 60 kt wind contour as low as 1000 ft AGL and within the lower third of the well-mixed Blyr. This is almost a slam dunk for 50 kt gusts across the Warned Area.

A vivid, non-diurnal temperature trend will today (particularly across the Laurel Highlands where sfc temps have surged well into the 50s), with morning highs in the 40s-mid 50s elsewhere, plummeting into the 20s-mid 30s by late afternoon.

The other primary issue is the expected development of lake- effect snow bands today, tonight, and Tuesday. the mean low- level flow orientation is expected to slowly veer from about 260 (west- southwest) to 290 (west-northwest) with time.

75th to 90th percentile snowfall totals (a good bet where the most persistent bands reside) argue for 3-8" of snow from northern Warren into northwest McKean county, where a Winter Storm Watch was upgraded to a Lake Effect Snow Warning. A favorable fetch off the lakes along with upslope effects should support efficient snowfall accumulation in the Laurels through Tuesday afternoon as well. Have hoisted a Winter Weather Advisory for Elk down to Somerset for the potential of a few inches of snow along with blustery winds and reduced visibility in blowing snow.

SHORT TERM /TUESDAY/

Snow showers and areas of more persistent, heavier LES will continue Tonight and Tuesday with the deep cloud layer occupied by the favorable DGZ of -12 to -18C.

Frigid wind chills will also become an issue tonight and Tuesday morning in particular (apparent temperatures +/- single digits). These values don't quite reach cold weather headline criteria (-10f).

LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/

On the large-scale, a cold, cyclonic NW flow pattern will reside over much of the eastern CONUS this period, underneath a deep upper low in eastern Canada. This will support a reinforcing shot of arctic air in the Thursday-Friday time frame, followed by gradual moderation next weekend, as heights aloft slowly start to build.

A prolonged period of lake enhanced/upslope snowfall may well continue across northwest PA and the Alleghenies through at least Thursday-Friday. However, it does appear that the ambient air mass could be fairly dry later in the week vs. earlier, which could eventually cut down on snowfall potential. However, there is considerable uncertainty in this regard, and we'll continue to monitor over time.

Of high confidence, though, is very cold temperatures (highs only in the teens-mid 20s later this week), along with frigid wind chills. As alluded to above, readings should gradually moderate by later next weekend.

AVIATION /12Z MONDAY THROUGH FRIDAY/

IFR/LIFR continues ahead of the frontal passage with brief dips up and down at IPT/MDT/LNS. GLAMP/HREF model guidance suggest a continuation of these LIFR ceilings through 14Z at MDT/LNS when the cold frontal passage allows for some scattering out of the low-level cloud decks and improvements in visibility. While the cold front has promoted VFR conditions, expect deterioration at BFD/JST as lake effect and upslope snow begins based on a combination of RAP/HREF model guidance. Locally heavier snow showers with gusty winds are expected to develop at BFD and potentially (~30% chance) at JST in the 18Z Monday to 06Z Tuesday timeframe and could promote blowing snow at the airfields which could allow for even lower visibility for longer durations. The 12Z TAF package continues these mentions and tries to find more targeted windows for this potential. Some improvement expected after closer to 12Z Tuesday as snow showers begin to taper off, with fair chances (~40-50%) of MVFR.

Elsewhere, after the cold frontal passage model guidance indicates an overall improving trend compared to the previous twelve hours with MVFR the main rule after 12Z at AOO/UNV/IPT before trending VFR. There remains some uncertainty at UNV where recent GLAMP model guidance continues to outline some lower- level decks hovering just at MVFR, thus have leaned onto this possibility with low (~30-40%) confidence. Gusty winds will be the primary hazard at all airfields outside of BFD/JST, with gusty winds exceeding 50kts at AOO/JST and 40kts at UNV/IPT/MDT/LNS through the rest of the 12Z TAF package. LLWS ahead of the front remains possible at MDT/LNS through 14Z with renewed LLWS concerns in recent NAM/NBM model guidance after 00Z at all airfields outside of MDT/LNS.

Outlook...

Tue...Windy and cold with snow showers N/W. Dry southeast.

Wed...Chance of snow showers across the north and west, dry southeast.

Thu...Chance of snow showers.

Fri...Mainly dry. Slight chance of a snow shower at BFD.

CTP WATCHES/WARNINGS/ADVISORIES

Wind Advisory until noon EST Tuesday for PAZ004>006-010>012- 019-026>028-035>037-041-045-046-049-050-056-063-064. Lake Effect Snow Warning until 4 PM EST Tuesday for PAZ004-005. Dense Fog Advisory until 8 AM EST this morning for PAZ006-012- 037-041-042-045-046-049>053-057>059-065-066. Winter Weather Advisory from 1 PM this afternoon to 1 PM EST Tuesday for PAZ010-017-024-033. High Wind Warning until 4 PM EST Tuesday for PAZ017-018-024- 025-033-034. Wind Advisory until noon EST Tuesday for PAZ042-051>053- 057>059-065-066.