textproduct: State College

WHAT HAS CHANGED

* Still a threat of light freezing rain in the Endless Mountains late Thursday night into early Friday, although it looks more spotty in nature at this point

KEY MESSAGES

1) Early Spring-like pattern continues through late week with periods of rain, areas of dense fog, and elevated ice jam risk

2) Ice glaze possible late Thursday night into Friday morning across the Endless Mountains of north-central and northeast PA

3) Seasonably colder to close out the weekend into early next week, with some potential for accumulating snow from Sunday into Sunday night

DISCUSSION

KEY MESSAGE 1: Early Spring-like pattern continues through late week with periods of rain, areas of dense fog, and elevated ice jam risk

Patchy light rain continues to traverse the Commonwealth late this afternoon, as low-level warm advection combines forces with an upper-level wave crossing northwest PA and western NY. As the upper system tracks farther northeast and away from the region tonight, rain should taper down overall, but with plenty of lower clouds and patchy fog/drizzle in its wake. Particularly over some of the higher elevations, fog could be locally dense overnight into early Thursday morning. Thereafter, much of the day Thursday should continue with a low overcast, and perhaps some spotty drizzle and fog.

From late in the day Thursday, through Thursday night, and into early Friday, another spoke of upper-level energy will encroach on PA, along with renewed low-level warm and moist advection. As a result, we expect an area of rain (mostly light) to translate across the region. Although the mid-levels of the atmosphere are expected to stay warm and support rain drops as the hydrometeor type, surface temperatures could drop to near the freezing mark late Thursday night into early Friday over the Endless Mountains (particularly areas north and northeast of Williamsport). As a a result, we're continuing to monitor these areas for the potential of at least patches of freezing rain.

Given the expectation of some rainfall and continued snowmelt through the end of the week, we'll remain vigilant of the ice jam risk.

KEY MESSAGE 2: Ice glaze possible late Thursday night into Friday morning across the Endless Mountains of north-central and northeast PA

As mentioned in the above section, a period of steady rainfall and near 32f surface temperatures are foreseen later Thursday night and early Friday across the Endless Mountains. From this early vantage point, it seems that the higher elevations would stand the best chance of seeing light ice accretions (we're talking 0.1" or less). Although an eventual Winter Weather Advisory remains in the cards, we want to see higher confidence in sub-freezing boundary layer conditions before issuing.

A slow climb in surface temperatures is expected by Thursday afternoon, with even the colder spots in the Endless Mountains likely above freezing by early afternoon. Steadier rain should also be tapering off by then, as the latest upper wave pushes northeast of the Commonwealth.

KEY MESSAGE 3: Seasonably colder to close out the weekend into early next week, with some potential for accumulating snow from Sunday into Sunday night

There is high confidence in the influx of colder air from Sunday into early next week, as a larger-scale and progressive upper- level trough drops into the eastern CONUS.

As this pattern evolves, cyclone development appears likely along the east coast Sunday into Monday. Although the track and intensity of the surface storm center still differ from model to model, there appears to be reasonable model consensus that an upper low will close off and deepen as it pivots across the Commonwealth. The result could be a period of snow for portions of PA from Sunday into Sunday night, with early indications favoring the Alleghenies for potentially several inches of snowfall.

Since we're still a number of days out and significant uncertainty remains, please stay tuned to the latest forecast updates over the coming days.

AVIATION /00Z THURSDAY THROUGH MONDAY/

Low clouds and reduced visibilities will continue to stick around for this evening and through Thursday morning. light winds and shallow moisture suggests fog redevelopment overnight, with widespread MVFR/IFR visibilities expected. LIFR has already been observed over portions of central PA with fog present near UNV and IPT. Periods of LIFR fog may also be observed across areas such as the Lower Susquehanna Valley early in the morning, along the lines of how last night's fog progressed.

Thursday afternoon, some parts of south central PA have a very low probability of observing thunder with the rain showers moving through during afternoon and evening, though probabilities were low enough to keep out of TAFs. Some elevated instability will be present, but overall confidence is low for thunder reaching the airspace. There will be a brief period of improving conditions on Thursday as ceilings will raise to MVFR or low end IFR, but with additional rain expected to arrive these improvements will not last long.

Outlook...

Thu...Dry early, then rain later in the day with restrictions possible.

Fri...Rain with restrictions likely. Some snow may mix in over northern PA.

Sat...Lingering rain and snow showers.

Sun...Potential for restrictions in snow showers.

Mon...Potential for restrictions in snow showers.

CTP WATCHES/WARNINGS/ADVISORIES

None.