textproduct: State College

WHAT HAS CHANGED

* No significant changes

KEY MESSAGES

1) Unseasonably mild through Friday with 2-week dry spell coming to an end

2) Trending cooler this weekend with showers downwind of Lake Erie

DISCUSSION

KEY MESSAGE 1: Unseasonably mild through Friday with 2-week dry spell coming to an end

Update... Overnight temps look on track for the most part. Still expecting some fog (or very low clouds), esp in the middle Susq and West Branch along the rivers/creeks. Should dissipate 2-3 hrs after sunrise.

Previous discussion... Anomalous upper level ridging and south-southwest flow aloft will maintain unseasonably warm temperatures through late week. Max/Min temps will be 10 to 20 degrees above the historical average for the first week of November, but should fall short of daily records.

A vertically stacked and weakening surface low pressure system will send a front through our area Wednesday night into Thursday morning. A band of rain showers will accompany this surface feature with accumulations looking to remain under half an inch. This cold frontal feature looks to stall near the coast Thursday as it becomes more strung out.

An approaching shortwave through though will likely reinvigorate precipitation development along the frontal system. The main area of uncertainty is if this new area of precipitation will impact much of our area. Global models have trended towards keeping the bulk of this precipitation closer to the coast, but some showers may still nudge into our southeastern area Thursday night into Friday.

KEY MESSAGE 2: Trending cooler this weekend with some showers downwind of Lake Erie

Update... We may want to lower the NBM MaxTs, esp on Sat. 50% or better chc of 8H temp <0C and lake effect clouds/showers will likely keep it cooler than NBM mean currently in the forecast.

Previous discussion... A compact shortwave moving through from the Great Lakes will induce a pattern of cooler cyclonic WNW flow pattern this weekend. This favors a pattern of lake effect showers off of Lake Erie moving southeastward and cooler overall temperatures. Latest model data favors this activity mostly on Saturday.

AVIATION /02Z WEDNESDAY THROUGH SUNDAY/

Current observations outline clear skies across the Commonwealth which are likely to continue overnight through 12Z Wednesday with high (~80-90%) confidence. These conditions will promote valley fog potential, especially across eastern Pennsylvania in the 06-12Z Wednesday timeframe. Recent REFS guidance has continued to indicate that IPT will have the highest probabilities (~70-80%) of fog formation, with MDT/LNS also showing modest (~40-50%) probabilities of fog potential. That being said, light winds continue at IPT and will need to trend towards calm in order for this fog to manifest. Current thinking based on NBM/REFS/GLAMP guidance is that winds will taper off over the next couple of hours and allow for fog formation. The main uncertainty with respect to the forecast is duration of fog and how dense fog will be, so have given a first-guess based off a combination of lower percentile members of the REFS.

Fog likely mixes out between ~14-16Z Wednesday, with VFR conditions likely to continue through 00Z Thursday with very high (~80-90%) confidence. Mid-to-high level cloud deck will continue to thicken based on HRRR model soundings ahead of an approaching system; however, cloud bases will likely (~100%) confidence remain above MVFR thresholds at BFD until after 00Z Thursday. After 00Z Thursday, widespread restrictions are plausible with rain showers and lowering ceilings at all of central Pennsylvania's airfields. After 00Z Thursday, there will be a slight increase in the potential for LLWS as well given the presence of a 40-50kt 850mb LLJ.

Outlook...

Thu...Rain showers, especially in the PM hours on Wednesday and continuing into Thursday. Sub-VFR conditions become more likely in showers.

Fri-Sat...Scattered to isolated rain, cloudy conditions and sub VFR ceilings possible.

Sun...Mainly VFR, isolated rain in NW PA.

CLIMATE

Current Consecutive Days streak without measurable rain:

10/17 through 11/2 (17 days) Harrisburg, Williamsport, Altoona, State College

10/18 through 11/2 (16 days) Bradford, Johnstown

CTP WATCHES/WARNINGS/ADVISORIES

None.