textproduct: State College

WHAT HAS CHANGED

* Uncertainty exists with how far east across the Commonwealth heavier snow showers and possibly snow squalls make it later this morning into the afternoon - low confidence in this regard * Confidence continues to increase in only a short time window for lake-effect and upslope snow showers across northwest PA and the Alleghenies later this afternoon and tonight

KEY MESSAGES

1) Persistent snow showers /and possibly a few squalls/ are expected across the Alleghenies today. Snow showers will become more scattered in nature as they progress to eastern Pennsylvania this afternoon.

2) Gusty winds anticipated this afternoon and evening.

3) Quieter/mainly dry weather to start the week, with moderating temperatures from Tuesday into Wednesday.

4) The potential remains for a storm system to develop over the Mid-Atlantic and impact Pennsylvania later in the week, with snow, or a wintry mix. However, a wide range of outcomes are still on the table, including that the storm will fail to form at all. Stay tuned for later forecasts.

DISCUSSION

KEY MESSAGE 1... Persistent snow showers /and possibly a few squalls/ are expected across the Alleghenies today. Snow showers will become more scattered in nature as they progress to eastern Pennsylvania this afternoon.

A lead surface frontal system is slicing across PA early this morning, and it should be east of the Commonwealth before sunrise. As this system passes, drier air is mixing out any residual fog, with skies also partially clearing.

A vigorous upper low and secondary surface cold front are making quick progress through the OH Valley early this morning. The cold front should reach northwest PA between 7 and 9 am, with subsequent eastward progress through the state into this afternoon. Given strong height falls and cold advection aloft tied to the aforementioned upper low, the front will have access to some instability and mid to upper-level forcing, with relatively high confidence that locally heavier snow showers and potential squalls make it to northwest PA later this morning. Things get more fuzzy farther east, as a pool of instability is still likely to be present, but with convective cells having to downslope off the Alleghenies and generally move farther away from the better forcing well north of PA. We'll monitor this situation closely later today.

Lingering moisture, low-level cold air advection, and upslope W-NW flow will keep lake-enhanced snow showers going over northwest PA and the Laurels into this evening. A quick approach of the surface-850 mb ridge axis later tonight into early Monday should bring this activity to a relatively quick end.

KEY MESSAGE 2... Gusty winds anticipated this afternoon and evening.

The best surface pressure rises and downward momentum transfer characteristics will reside over northwest and central PA during the late afternoon and evening hours. Based on model sounding projections, wind gusts will likely top out in the 30-35 kt range for most, which is below Wind Advisory criteria. However, downsloping W-NW flow off the Laurels will add some acceleration just downstream, and thus we've maintained the Wind Advisory for Cambria, Somerset, Blair, and Bedford counties.

KEY MESSAGE 3... Quieter/mainly dry weather to start the week, with moderating temperatures from Tuesday into Wednesday.

High pressure at the surface and short-wave ridging aloft are expected to provide fair/uneventful weather to start the week.

Monday looks seasonably chilly, but with less wind as compared to Sunday. Readings should warm back into the 40s for most on Tuesday, as warm advection commences on increasing SW flow.

KEY MESSAGE 4... The potential remains for a storm system to develop over the Mid-Atlantic and impact Pennsylvania later in the week, with snow, or a wintry mix. However, a wide range of outcomes are still on the table, including that the storm will fail to form at all. Stay tuned for later forecasts.

An initial mid-week cold frontal passage, accompanied by rain showers, could turn more interesting Wednesday night and Thursday, as the front stalls just east and south of the Commonwealth. Some model projections bring a surface wave northeast along the front, with wintry precipitation developing back into at least parts of central PA.

However, key model differences remain, and sensible weather during this period will be driven by small-scale sensitivities in the upper-level pattern, which are inherently hard to pin down this far out. Please stay tuned for later forecast updates.

AVIATION /12Z SUNDAY THROUGH THURSDAY/

The cold front is now east of the area, resulting in the low CIGS and fog to the east being replaced by a gusty west wind.

The main issue today into this evening will be gusty winds, especially from late afternoon into the early evening hours. I held onto the strong winds a bit later tonight than the guidance.

Some potential for a band of snow showers and perhaps a brief squall to enter the northwest mountains (BFD) by mid morning, the remains of the band to be just west of the IPT area by mid afternoon. The band of snow showers may not make it to MDT, and LNS, so will leave this out of those 2 sites for now.

Better conditions expected for Monday, as high pressure builds toward the area and winds shift more to the west and southwest.

Outlook...

Mon...A few lingering lake effect snow showers early, giving way to mainly VFR conditions.

Tue-Wed...Mainly VFR.

Thu...Chance of snow showers, perhaps mixing with rain in the southeast.

CTP WATCHES/WARNINGS/ADVISORIES

Wind Advisory from 10 AM this morning to 1 AM EST Monday for PAZ024-025-033-034. Winter Weather Advisory until 1 AM EST Monday for PAZ033.