textproduct: State College

WHAT HAS CHANGED

* Refined timing of snow onset/location for Friday. * Updated products sent out.

KEY MESSAGES

1) Lake effect/upslope snow showers gradually tapering off tonight while wind chill stays in the single digits above and below zero.

2) Snow squalls are possible Saturday in the western half of the CWA as a strong cold front blasts through. Little to no impact east.

3) An arctic blast Monday will produce little snowfall, but lead to dangerous, sub-zero wind chills Monday night and Tuesday.

4) Colder than normal temperatures to prevail for the second half of January.

DISCUSSION

KEY MESSAGE 1...

Trends so far falling into timing noted below.

Not much left on radar at 8 PM, just a few light snow showers and flurries being reported. Still a gusty wind across the region.

Earlier discussion below.

SHSN ongoing. All signs continue to point to strongest LES/SHSN subsiding early this evening in the Laurels and overnight in the northern Alleghenies.

As we near sunset, the upper trough axis overhead will be sliding east of the CWA. However, continued WNW flow will keep the upslope and LES going for a few more hours along and N of I-80. Not enough support for widespread accums of 3+" to pull the trigger on an advy for the I-80 corridor nor Elk/Cameron Cos, though. Timing of LES subsiding over the NW still looks like midnight, but some more-spotty and light SHSN will linger into the wee hours.

As the wind subsides through the night to 5-10 with G15-20KT, wind chills should only dip a little at first, then level off or even rise 5F in the second half of the night.

KEY MESSAGE 2...

Only light snow due to WAA is expected Friday aftn in the W with an inch or so poss in the far NW as the highest SF totals. After a brief break, Friday night and early Sat, large-scale lift increases very slightly, but we'll be under the left- entrance region of a 150KT jet. The main forcing will be with a broad/channeled vort max caught in the SWrly flow aloft. The heights will actually be rising overhead. But, enough energy in the mid-level flow and a sharp cold front will provide an active Saturday. A little lift ahead of the front could make a very light snow patch during the morning, but timing looks favorable for SNSQs in the aftn. Sunlight and modest heating could make them stronger. Daytime maxes will be in the 40-45F range in the Lower Susq and s-cent mtns. The orientation of the flow will still be SW- NE and may confine the SHSN/SNSQs to the NW half of the CWA. The dry air and negative influence of the upper pattern could keep the SE third to half of the CWA dry/snowless.

KEY MESSAGE 3...

Another lull on Sat night into Sunday night will be followed by another - colder - cold front. 8H temps drop into the -20/-23C range for Monday. Despite the blast of bitterly cold arctic air, it will already be dry over the CWA. The front will likely generate little snowfall outside of lake effect. Min wind chills Monday night/Tuesday morning range from 0F in the LSV to minus 20F over portions of the Alleghenies which suggests a cold weather advisory may be needed. We have highlighted the extreme cold risk in the HWO.

Fcst highs in the + single digits to ~20F on Tuesday are 15 to 25 degrees below the historical average. A long duration period of sub zero wind chills is likely from Monday night through Tuesday night/AM Wednesday. With all the arctic air in place and a flow out of the west, we should have LES when the flow is best favorable at the end of the forecast period, but waggles in the mid-level flow are expected. So, a broadbrushed and decreasing PoP strategy across western PA is best at this point due to the low certainty of the details.

KEY MESSAGE 4...

The first half of January has trended a few degrees warmer than normal, but the second halft looks like it will be colder than normal. This backed up by the CPC outlooks.

AVIATION /01Z FRIDAY THROUGH TUESDAY/

A few spots of pesky IFR continue to hang on over the north west with snow showers on going behind the exiting trough. Snow showers could linger at KBFD overnight, but moist other locations should see improving visibility and rising ceilings to VFR by Friday morning. A blustery west/northwest wind will continue tonight with gusts in the 30 to 35 kt range, possibly even exceeding 40 kts at airfields across the southern half of PA late this evening. Winds stay gusty overnight and then taper off during the day on Friday.

Friday is looking to be a significant improvement over today. Confidence is high that all sites should improve to VFR by sunrise, and the day will start partly sunny. During the late afternoon a return to upslope and lake effect snow will likely occur over BFD and JST, but else where should remain dry until Saturday morning.

Outlook...

Fri...Improving to VFR areawide in the morning. Snow and restrictions return to the western mountains (KJST and KBFD) in the evening. Breezy with gusts from 180 degrees 15-25kt.

Sat...AM snow showers, PM snow squalls possible with restrictions.

Sun-Tue...Light snow/IFR possible at times.

CTP WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory until 1 AM EST Friday for PAZ004-005. Cold Weather Advisory until 1 AM EST Friday for PAZ024-033.