textproduct: State College

SYNOPSIS

*Breezy with wet snow of varying intensity over the Northern Mountains of Pennsylvania with areas of snow changing to mixed precip or rain across Central and Southern PA today into this evening *Snow showers and localized, narrow bands of snow squalls continue late tonight through Thursday. Wind gusts of 35 to 45 mph from the West or Northwest on Thursday. *Additional bouts of winter weather possible Friday-Sunday

NEAR TERM /UNTIL 6 PM THIS EVENING/

Widespread clouds and a light south to southwest sfc breeze with fairly uniform temps between 25-30F were noted this morning across the CWA. Leading edge of steady light snow at 09Z was seen near the RT 219 corridor. Max wet bulb temps in the 950 to 900 mb layer range from 0-1C across Warren, Elk and McKean Counties to -2 to -5C across the rest of the region with the coldest air locked in across the Ncent Mtns of PA. A focused area of deeper ascent beneath the coupled jets (right entrance/left exit regions will occur over a slow moving warm front (extending Southeastward from a 990 mb sfc low over SW Lower Michigan at daybreak) and the steepest part of the LLVL cold dome over Northern PA. This UVVEL will lead to snow of varying intensity today to the North of Interstate 80, and periods of lighter snow, that will become mixed with or change to intermittent light rain this afternoon across the southern half of the state.

Max wet bulb temps in the 950-900 mb layer dont get above zero from the mid Susq Valley NE to the Endless Mtns and Poconos, so the precip type there should stay mainly, or ALL snow today.

All snow for the bulk of this synoptic event with anywhere from 2-6 inches of wet snow across the Northern Mtns and 1-3 inches over the Laurels.

Local max ~6" may be found in the higher terrain in Sullivan County. Snow rates are projected to be in the 0.50-1 in/hr range in the NW mtns during the 5-10AM window before shifting eastward across north central PA toward the Poconos.

The main period of impact to travel by this winter weather across the Central Mtns, Lower Susq Valley and Laurel Highlands will be through 15Z today, followed by the precip type transition and sfc temps warming into the mid/upper 30s and low 40s (south).

Temps are expected to rise above the freezing mark particularly along and southeast of I99/I80 corridor by the afternoon. Temps could stay a few degrees colder in the northern tier, but road snow will likely become more limited after midday given the marginal air/road temps.

Intermittent snow/rain in the valleys along I99/US220 corridor from Blair/Centre County east along I80/US220 should result in a slushy coating to 1 inch. There is a scenario where wetbulb effects help to lock in colder air for a longer duration over the central ridge/valley region, which may result in a bit more snow than currently fcst.

No change in Winter Weather Advisories for this initial, clipper event.

SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/

Precip tapers off this evening as the approx 990 mb sfc low moves to near KART, and the bulk of the CWA falls within the warm sector for up to several hours.

The lows southwestward trailing cold front pushes through the state early tonight followed by a transition to windy and notably colder conditions with long, narrow bands of LES snow showers/squalls with a multi-lake upstream connection.

Extended Winter Weather Advisories for LES across our NW Mtns through much of Thursday night, with another 2-5 inches likely and localized amounts around 6 inches. This could bring 48 hour snow totals to around 12 inches across parts of the NW Mtns near and to the North of Rt 6 INVOF KBFD.

Winds increase late tonight through Thursday with frequent gusts in the 30-35 mph range; locally higher gusts up to 40-45 mph are likely, esp across the Laurel Highlands. Given the wet character of the snow early on Wednesday, blowing and drifting impacts are not a concern at least initially. However, as temps fall into tonight, expect the character of the snow to become drier or more fluffy which increases the potential for blowing and drifting over the higher terrain tonight. Wet surfaces and slush areas will be prone to refreezing and icy spots overnight tonight into early Thursday morning.

LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/

Pattern supports fast moving weaker systems, mainly to the north and south. Wide swings in guidance at times, given the large scale pattern.

For the next system, the highest chance for snow later Friday is mainly south of our area again.

Pattern supports an abnormally cold period.

Earlier discussion below.

Lake effect snow showers and gusty northwesterly winds continue on Thursday with additional snow accums expected over the northwestern mountains and Laurel Highlands. A few long fetch bands or locally heavy snow showers/squalls are possible on Thursday and could extend as far southeast as I81.

Winter weather/periods of snow continue from Friday through the weekend and into early next week with a series of upper troughs and clippers followed by reinforced cold NW flow and lake effect/upslope snow showers. Temperatures remain below the historical average heading into mid-December.

AVIATION /09Z WEDNESDAY THROUGH SUNDAY/

A clipper system will bring periods of light to moderate snow to the region on Wednesday morning and into the afternoon, initially moving into BFD by 09Z. Ceilings will fall to MVFR from west to east as precipitation arrives, and BFD should see IFR ceilings by 09Z. The main uncertainty arises from the precipitation type forecast. BFD should see all snow, but all other TAF sites will have the potential for mixed precip. IFR visibilities are likely outside of AOO, MDT, and LNS during the late morning and afternoon as snow rates increase.

LLWS will be a concern through the rest of the night and into the afternoon as a 45 to 60 knot low-level jet traverses the region. Behind the cold front Wed evening into Thu, winds will turn out of the west and increase with sfc gusts 15-35 kts (highest in the Laurels).

Precipitation ends for most of Central PA by 00Z Thursday as the system exits to the east, but lake effect and upslope snow showers continue for BFD and JST.

Outlook...

Thu...Snow showers continue, mainly N/W PA. Windy.

Fri-Sun...Additional rounds of light snow possible with multiple clipper systems.

CLIMATE

Bradford, PA had two records in one night! Their temp of -4F just before midnight EST on 12/8 broke the previous record of -2F set in 1970.

As the temp continued falling through the night, they tied the 12/9 record low of -12F at 618 AM EST. This tied the record set in 2002.

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

CTP WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory until 4 AM EST Friday for PAZ004>006- 010-011-017. Winter Weather Advisory until 10 PM EST this evening for PAZ012-018-037-041-042. Winter Weather Advisory from 10 AM this morning to 10 AM EST Thursday for PAZ024-033.