textproduct: State College

WHAT HAS CHANGED

*Trended lower with afternoon temperatures today & Thursday with cold air damming in place.

KEY MESSAGES

1) Feeling more like early Spring than late Winter this week

2) Periods of rain Wednesday, Thursday night into Friday

3) Mixed/wintry precipitation Thursday night into Friday and plowable snow possible on Sunday

DISCUSSION

KEY MESSAGE 1: Feeling more like early Spring than late Winter this week

Following one of the coldest first 2 weeks of February on record, mild weather for this time of year will be in place this week with daily max/min temperature anomalies running 10-20 degrees above the historical average. Conditions will feel more like early Spring than late Winter. Depending on the time of arrival and coverage of precipitation later this week, daytime temps may not get as quite as warm as currently forecast, but will still be above normal.

The transition to a milder pattern this week is accompanied by low clouds and fog as stagnant, warmer air moves over the colder/snow covered ground. Elevated dewpoints (higher than 32F) continue to erode lingering snow piles and that trend should persist through Friday. Fog development is likely again tonight, especially across southeast PA where a Dense Fog Advisory will most likely be needed. Additional fog concerns are likely each day this week owing to persistent moisture influx and a lack of strong forcing/winds.

KEY MESSAGE 2: Periods of rain Wednesday, Thursday night into Friday

Following one of the driest first 2 weeks of February on record, much needed periods of rainfall are likely on Wednesday and again Thursday night into Friday. Total QPF during the mid to late week period ranges between 0.50 to 1.00 inches with the highest amounts shaded toward the NW portion of the fcst area. While we do not expect the rainfall to cause flooding, the warmer temperatures and increased flows on rivers and streams should increase the risk of ice jams at least on the margin.

A few rumbles of thunder are possible in northwest PA on Wednesday afternoon and evening as a shortwave trough moves through the Great Lakes. Warm advection underneath of sufficient lapse rates could produce a few thunderstorms, with the preferential region being west of the Allegheny front up into the northwest mountains. No severe weather is expected at this time. KEY MESSAGE 3: Mixed/wintry precipitation Thursday night into Friday and plowable snow possible on Sunday

Model guidance continues to indicate a overrunning wintry/icy mix on the leading edge of returning precip late Thursday night into Friday. This would impact travel conditions for the Friday morning commute. We may begin to message the risk of slippery travel in the HWO. Marginal temperatures will be the main forecast challenge. If the cold wedge holds on a little longer, the icing threat in the Endless Mountains/Poconos could ramp up whereas a warmer solution would mitigate much concern.

There is an emerging risk of plowable snow on Sunday, although the specifics on the strength and track of the associated low pressure/coastal system are still very uncertain. A majority of deterministic and ensemble guidance (with the exception of the European models) depict a deepening coastal low with potential for significant snow along the Atlantic Coast. Such a track would keep the heaviest snow east of our area, but continue to monitor the forecast this week!

Guidance signals continue to favor a seasonably colder end to the weekend and start to the last week of February. The cool down appears to be transitory and not long lasting heading into the second half of next week/end of the month.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

Still some mid clouds at sunset, but mainly just high clouds. The combination of stale air, light winds and nearly clear skies will make for fog, as temperatures drop off quickly. I hit the fog a bit sooner and harder than the 18Z TAF package had.

Things will slowly improve Wednesday morning with the visbility as winds pick up some and rain moves into the area. However CIGS may be slow to come up, before going back down later in the day.

Overall would expect a wide range of conditions overnight, given high chance of having sites drop down to IFR conditions.

Earlier discussion below.

While this lower cloud deck erodes, mid-to-high level clouds will move across the Commonwealth as a low pressure system approaches, with VFR ceilings dropping to MVFR as these rain showers move across the northern two-thirds of the Commonwealth tomorrow morning. An exception would be KBFD, where IFR ceilings are expected with these showers.

Moreover, a downtrend in visibility is expected across the Lower Susquehanna Valley this evening as a result of favorable radiational cooling conditions and moisture advection ahead of the approaching system. As a result, IFR/LIFR visibilities are expected to develop over KLNS and KMDT after 00z. There is lower confidence in terms of persistent IFR/LIFR fog across KBFD, KIPT, KUNV, and KAOO, though NBM model guidances suggests reduced visibilities around or temporarily over these airports, resulting in mentions of VCFG or brief MVFR visibilities.

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.

CTP WATCHES/WARNINGS/ADVISORIES

None.