textproduct: State College

SYNOPSIS

* Gusty winds with abundant sunshine for the rest of today and just some very light snow/flurries from shallow lake effect clouds across the Northwest Mountains that could bring an additional dusting of snow. * A quick-hitting system will bring a few to several hour period of snow with a coating to 2 inches across Central and Northern PA Monday night, followed by a light wintry mix of precipitation early Tuesday morning; travel impacts possible * Wintry mix possible Christmas Eve * Turning milder with several chances for rain Christmas Day into the weekend

NEAR TERM /THROUGH TONIGHT/

Some shallow strato cu across NW PA, within the deepened cold air across the state is nestled within the favorable DGZ, so we're seeing very light snow with vsbys of 3-6SM for the most part and maybe a light dusting on the ridges near KBFD and points west.

This strato cu layer across the north goes mainly SCT late tonight while the rest of the CWA is generally SKC with diminishing wind and quite cold temps in the low to mid teens for most (with a spattering of upper single digits temps likely throughout the perennial cold rural valleys in Central and Northern PA). Expect WNW wind gusts into the 20s and 30s for much of the area through dusk or shortly after, but not high enough for an advy. If anyone gets close to 40KT gusts it will be the Laurels (as deeper layer subsidence associated with the thermally direct branch of a 145KT upper jet moves over that part of the state). We've seen peak gusts in the low to mid 30s (kts) there over the past several hours.

The deepening and moderately strong CAA won out against the low sun angle and sfc temps few a few deg F in many places compared to values late this morning.

SHORT TERM /MONDAY/

1035mb high pressure dome will float in overnight and become centered just south of the state on Monday. The wind will gradually decrease and back to the west then WSW by daybreak Monday.

Plenty of sunshine Monday morning will be followed by increasing and thickening clouds Monday afternoon and evening. A quick- hitting system will bring a few to several hour period of snow during the first half of Monday night with a coating to 2 inches across Central and Northern PA, followed by a light wintry mix of precipitation early Tuesday morning that could end as some light drizzle or freezing drizzle.

High temps Monday, prior to the thickening clouds and any precip will range from the low 30s across the Northern Mtns to the low 40s in the Southern Valleys. Sfc dewpoints will be only in the teens, setting the stage for good low level wet-bulbing as the precip moves in late in the day/Monday evening.

LONG TERM /MONDAY NIGHT THROUGH SUNDAY/

For the bulk of the steadier precip during the first half or so of the event Monday night/early Tuesday (warm frontal precip within the ascending portion of the thermally direct cell of a jet lifting NE across the state), wet bulb temps are slightly below zero C through the entire column, so we're confident that we'll see some light snow accums to slicken up travel on untreated/secondary roads Monday night.

Early Tuesday, near to slightly above zero C wet bulb temps advect NE across the CWA within about a 2-3 KFT layer between about 3-6 kft AGL (as the cloud tops lower lower and warm) and any lingering light precip will likely turn to intermittent light sleet/freezing rain then light rain/drizzle by the afternoon.

We will continue to mention ZR in the wx grids and show a small patch of ice accum in the central mtns late Mon night and early Tues AM. We have 3 more periods to become more confident in the forecast, but may eventually need a wint wx advy for that time frame.

Since snow will be the primary precip type with temps hovering in the 30-32F range for much of the CWA late Mon night and early Tues, the changeover to RA could occur without creating dangerous ZR, and act as more of a thin crust on the snow/slush.

The highest threat of ice accumulations appears to be around AOO and UNV before sunrise Tuesday. QPF will be almost nothing on the MD border, but a widespread 0.20" in the nrn half of the CWA. Most of that would be falling when it would be SN. SLRs are very low (<10:1), and accums will be a max of 1-2" with the highest accums in Tioga & Sullivan Cos. A coating (<1") is expected for much of the area before the SN turns to RA. The precip should lift off to the NE and be over around noon Tues. Temps max out in the upper 30s NE and near 50F between AOO and HGR. Gusts will increase Tuesday evening to the teens and 20s, but drop off through the day on Wed as high pressure moves in.

Wed holds some potential for temps to get warmer than will be a milder day as 8H temps rise to the mid-single digits (C). But, the subsidence inversion will be holding the top of the mixed layer down around 2kft. Therefore, we'll hang close to the NBM guidance for the time being.

The fast flow will keep pushing high clouds in from the NW. Forcing comes over the top ridge over TX and the Deep South after coming ashore in SoCal.

Clouds will thicken up Wed night (Christmas Eve) and eventually could bear some precip - mainly for the SW half of the CWA. The timing is still moderately uncertain, but the trend on the GFS is centering on any precip starting after 06Z. The ECMWF is much drier and would delay precip until Thurs. Temps Wed night will probably be very much like Monday night, but the precip lighter. So, there is a chc for --ZR over the NErn half of the CWA early Christmas morning. However, the moisture feed and precip amounts are still suspect.

Christmas day will hold a good warm up, turning any potentially frozen or freezing precip to plain rain. Maxes certainly not Christmas-like for PA with the Laurels 15-20F above normal (esp if the clouds can break a little), with the eastern zones about 5F warmer than normal. After Thursday, the GFS and ECMWF diverge with the former making a cold front push thru Fri and the latter surging warm air into the Great Lakes and PA. That would delay the arrival of a colder airmass until later in the weekend. Therefore, the forecast for the weekend is highly uncertain. NBM seems to be weighted heavily toward having the cold air arrive earlier rather than later. Without any confidence then, we'll just defer to the NBM output for that period.

AVIATION /19Z SUNDAY THROUGH FRIDAY/

VFR for the bulk of Central PA TAF sites for the rest of this afternoon with some higher end MVFR CIGS at KJST through 19-20Z and at KBFD into this evening.

Gusty WNW sfc winds (up to 30 KTS at times) are expected into this evening before and area of high pressure approaches from the west leads to diminishing wind tonight.

Increasing, but mainly VFR cloud levels will occur Monday as warmer air aloft streams in from the southwest. A several hour period of snow/sleet is expected Monday night with MVFR highly probable with areas of IFR possible.

Outlook...

Mon...Trending drier with VFR favored. Snow enters W PA Monday evening with restrictions possible.

Tue...Rain/snow becomes increasingly possible, restrictions possible.

Wed...A few lingering rain and snow showers. Trending VFR.

CLIMATE

Astronomical winter (solstice) began at 10:03 a.m. today - December 21st.

CTP WATCHES/WARNINGS/ADVISORIES

None.