textproduct: State College

WHAT HAS CHANGED

* Extended the Winter Weather Advisory for Lancaster and Lebanon Counties through 6 PM. * Increased chance for snow showers and isolated snow squalls over the Laurel Highlands and northwest mountains on Monday. * Issued a Cold Weather Advisory for much of west-central PA for Monday night and Tuesday morning.

KEY MESSAGES

1) Light snow continues across southeast PA through the rest of the afternoon.

2) Scattered snow showers and a few snow squalls on Monday ahead of an arctic front.

3) Dangerous, sub-zero wind chills Monday night and Tuesday.

4) Active weather continues through the end of the week with below normal temperatures and multiple chances for snowfall.

DISCUSSION

KEY MESSAGE 1: Light snow continues across southeast PA through the rest of the afternoon.

Snow has been light for much of the day over the Lower Susquehanna Valley, but some high res guidance continues to show steadier snow redeveloping this afternoon as a wave of low pressure moves northeastward off the coast. As a result, we have extended the Winter Weather Advisory for Lancaster and Lebanon Counties through 6 PM. Up to an inch of additional accumulation is possible, particularly in the eastern half of those two counties.

KEY MESSAGE 2: Scattered snow showers and a few snow squalls on Monday ahead of an arctic front.

A warm front will move eastward across northern Pennsylvania Monday morning as an area of low pressure tracks well to our north. A few snow showers will be possible as this front moves through, but any accumulation will be very light. Upslope flow over the Laurel Highlands will also support scattered snow showers, though the better chance for snow appears to be north of Interstate 80 ahead of an arctic front that moves across the region during the early afternoon. The snow squall parameter from both the NAM and the GFS highlight the northwest mountains for the best chance of heavier snow showers as weak instability develops ahead of the front. The flash freeze risk appears to be relatively low as surface temperatures will be well below freezing, but visibility drops and quick accumulations on roadways are possible.

Lake effect snow showers may linger across northwest PA for a few hours behind the front, but low-level flow backs to the southwest during the evening. This will help to direct the majority of the lake effect snow bands into New York. Wind gusts behind the front could will be in the 30 to 40 mph range, with a few gusts to 45 mph possible in the ridges of the Laurel Highlands.

KEY MESSAGE 3: Dangerous, sub-zero wind chills Monday night and Tuesday.

A frigid airmass characterized by 850 mb temperatures as lows as -20C moves into Pennsylvania behind the arctic front for Monday night and Tuesday. Minimum temperatures Monday night range from near zero in the Laurel Highlands and across the northwest mountains to the low teens in the Lower Susquehanna Valley. These very cold temperatures will combine with winds gusting 25 to 30 mph to produce wind chill values as low as -10 to -20 for areas north of I-80 and west of I-99. We have issued a Cold Weather Advisory for those locations. Temperatures slowly rise to the teens and low 20s for Tuesday afternoon, but wind chills likely remain sub-zero for the northern mountains into Wednesday morning.

KEY MESSAGE 4: Active weather continues through the end of the week with below normal temperatures and multiple chances for snowfall.

Temperatures moderate slightly for the end of the week, though they will remain below normal with highs in the 20s and low 30s. After a brief dry period, snow chances return to parts of the region late Wednesday into Thursday as the next shortwave rotates through the persistent trough over the eastern US. The typical lake effect and upslope snow regions will once again be favored as the surface low is expected to pass well to our north.

Temperatures trend downward as we head into next weekend, though there is a lot of spread in the ensembles as to how low they actually get. The upper level pattern supports additional chances for snow with additional shortwaves moving through the trough, but the track and timing of these systems remains unclear.

AVIATION /20Z SUNDAY THROUGH FRIDAY/

70% of models show light snow (with IFR conditions) will waggle back westward into LNS and perhaps (40% chc) into MDT/MUI/ZER for a couple of hours right around sunset. Latest HRRR and RAP just barely get the western edge of the snow to LNS. MDT and MUI are still reporting very light precip. Icing possible there, but mainly to our east. Northwest wind should be backing to the west a bit over the eastern terminals over the next few hours. The gusty west wind over the western terminals should lighten up shortly, but not go calm overnight. A warm front will approach late tonight and light snow with IFR conds should fall over FIG and BFD between 07Z-12Z. Some lighter snow with MVFR as the worst conds is expected (80% chc) at JST and UNV. AOO has very little (30%) chc of dipping below VFR. Of course, I never let my good eye off JST, and am skeptical (30% chc) that JST will also go to IFR (cig or vis) at sometime late tonight. IPT/MDT/LNS don't see any flight restrictions past 02Z tonight.

After the morning coating of snow, a short break will ensue in the "warm" sector with a mix of MVFR and VFR over the central and western terminals (VFR east). The wind will pick up during this break, with sustained 10-14KT and G15-25KT - highest on the hilltops, of course. A cold front will then blast through during the mid-day W and early aftn E. There won't be a lot of moisture to work with, but the gusts will pick up, and solar warming will generate some llvl instability as the cold air rushes in. This will create isold-sct SHSN for the western terminals, and perhaps even a stronger squall (mainly near FIG and BFD). The gusts will continue into Tuesday. Lake effect snow will stay just N of BFD.

TUE...Gusty. MVFR/IFR NW, VFR SE.

WED...Light snow/IFR NW, MVFR-VFR elsewhere.

THU...CFROPA, gusty. LIFR/IFR cigs/vis in SHSN N & W, MVFR cigs SE.

FRI...Gusty W wind. Lake effect BFD (ocnl IFR). Mainly MVFR elsewhere.

CTP WATCHES/WARNINGS/ADVISORIES

Cold Weather Advisory from 9 PM Monday to 11 AM EST Tuesday for PAZ004>006-010>012-018-019-025-034-045. Cold Weather Advisory from 9 PM Monday to 1 PM EST Tuesday for PAZ017-024-033. Winter Weather Advisory until 6 PM EST this evening for PAZ059- 066.