textproduct: State College

SYNOPSIS

* Mostly cloudy and colder today; bitterly cold/frigid tonight * Not as cold Tuesday; quick shot of snow in the NW mtns * Windy with snow/rain mix followed by lake effect snow through midweek; additional snow accumulation possible Friday-Sunday

NEAR TERM /THROUGH TONIGHT/

A cold northerly wind is sending arctic air southward to the MD line early this morning as 1030mb high pressure builds across the eastern Great Lakes. Despite brief clearing north of I80 after midnight, expect a partly to mostly cloudy and cold day with mid and high clouds streaming northward in association with a 500mb trough tracking eastward from the TN Valley to the VA/NC coast.

Sub-freezing max temps (below 32F) today in the upper teens to upper 20s are quite cold by early December standards or 15 to 20 degrees below the historical average. Hires model data shows mid/high clouds peeling off to the northeast by tonight, setting up favorable radiational cooling under the modified and reoriented arctic sfc high channeling down the east-side of the Allegheny Front/Blue Ridge by 12Z Tue. This will translate into a bitter cold to frigid night across CPA with lows ranging from 5 below to 15 above or 15 to 25 degrees below climo. It should be noted that some daily record lows could be within reach particularly if the min temps prints on 12/8 (before midnight) vs. 12/9 or after midnight. (See climate section for 12/8 and 12/9 record mins)

SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/

High pressure shifts east of the I95 corridor by Tuesday afternoon yielding to lead/low amplitude northern stream mid level shortwave disturbance moving swiftly across the eastern Great Lakes. Blended model data continues to favor a quick shot of light snow ~1" btwn 18Z Tue-06Z Wed with this feature over the NW mtns which could impact the evening commute.

Meanwhile upstream, an intense mid-980s mb clipper low will be racing through WI and into Michigan's Mitten btwn 06-12Z Wed. WAA out ahead of this anomalously deep Alberta clipper (one of the strongest for this time of year by historical/climatological MSLP standards) is expected to spread accumulating light to mdt snow across the NW 1/2 of the CWA for the Wednesday morning commute. By Wednesday afternoon, 24-hour snow totals are projected to reach 2-4" in the NW mtns with C-1" fcst elsewhere in areas along and north of I80. As the precip expands eastward into Wednesday afternoon, marginal temperatures/thermal profiles will favor a snow/rain mix or just plain rain from the central ridges eastward into the mid and lower Susquehanna Valley.

As the storm tracks through the St. Lawrence River Valley Wednesday night, much colder cyclonic/NWly flow will trigger lake effect snows with minor snow accums over the typical NW PA snow belts and favored upslope areas along the Allegheny Front and Laurel Highlands. The other factor to account for with this powerful clipper tracking to the north of CPA is the wind field which should generate max gusts 30-40+ mph range.

36-48hr snowfall is generally 2-4/3-6" over the NW mtns with odds of a pending winter headline better than 50/50. Lower snow amounts (C-1/1-2") are fcst for locations along and northwest of I99/US220.

LONG TERM /THURSDAY THROUGH SUNDAY/

Lake effect snow and gusty NW winds continue on Thursday with additional snow accums expected over the NW mtns and Laurel Highlands.

The next winter wx system is progged to arrive later Friday into Friday night, although models are showing some variance with the evolution and track. More lake effect snow/snow showers continue over the weekend with temperatures staying below the historical average heading into mid-December.

AVIATION /12Z MONDAY THROUGH FRIDAY/

High pressure moving across Pennsylvania will keep VFR conditions in place through the day, but a wave of low pressure passing to our south will lead to increasing mid and high clouds during the morning. Skies will clear out again during the evening from northwest to southeast and winds will decrease to less than 5 knots.

Low stratus should expand northward into southwestern PA after 06Z as low-level flow takes on more of a southerly component. Most guidance suggests that this shouldn't reach much farther than JST and AOO, and ceilings likely remain VFR in the 3000 to 4000 foot range.

Outlook...

Tue-Fri...Restrictions possible with snow or mixed ptype, especially across the northern half of Pennsylvania, as multiple low pressure systems track through the northeastern US. Gusts 15-30 kts, and up to 40 kts in the Laurels late Wed.

CLIMATE

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

Record lows for 12/8: MDT 12 in 2002 IPT 3 in 1901 AOO 7 in 2005 BFD -2 in 1970

Record lows for 12/9: MDT 7 in 1989 IPT 3 in 2002 AOO -3 in 1989 BFD -12 in 2002

CTP WATCHES/WARNINGS/ADVISORIES

None.