textproduct: State College

WHAT HAS CHANGED

* Freezing rain threat increased slightly late Thursday night into early Friday morning over the north central ridges into the Coal Region/Poconos/Endless Mtns

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 north central ridges into the Endless Mtns/Poconos and Coal Region

3) Seasonably colder to close out the weekend into early next week with uncertain wintry impacts

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

Mild weather for this time of year will remain in place through late 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. Max temps still have some downside risk (verifying cooler than fcst) with persistent low clouds and onset/timing of precip occurring in the morning or early in the day.

The transition to a milder pattern this week is accompanied by low clouds, areas of dense fog, and poor air quality as stagnant, warmer air moves over the colder/snow covered ground. Melting snow is also helping to increase residual low level moisture. DFA continues until 10AM for York and Lancaster Counties; so far the 06-08Z obs do not favor an expansion of the DFA.

Following one of the driest first 2 weeks of February on record, much needed rainfall arrives today 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 will result in an elevated risk of ice jams.

SPC continues to highlight the NW Alleghenies with a general t-storm outlook for today. HREF data shows a narrow zone of marginal instability spreading eastward from the Upper Ohio Valley this evening within a region of warm air advection. Any storms that can develop are expected to remain sub-severe; it's been a while since we've had a t-storm so this is more of a callout or heads up that you may see a flash of lightning or hear a rumble of thunder in this part of the forecast area.

KEY MESSAGE 2: Ice glaze possible late Thursday night into Friday morning across the north central ridges into the Endless Mtns/Poconos and Coal Region

After a brief break or lull on Thursday, another round of precip is expected to spread across the forecast area Thursday night through Friday. A strengthening storm system in the Midwest will direct a plume of above normal moisture/pwats into a somewhat weak CAD pattern signature forming over central PA. This will set the stage for a potential overrunning wintry to icy mix set up over the interior north central ridges into the Endless Mtns and Coal Region. Ice glaze chances >=0.01" are 30-50% over these areas with lower probs in the 10-30% range for >=0.10 inch. Any ice accumulation would impact the early morning commute on Friday and a winter wx advy may be needed. However, sfc temps continue to look rather marginal hovering around the freezing mark which reduces forecaster confidence on the margin. If the cold wedge holds longer like the NAM would suggest, then odds for ice impacts would rise substantially. KEY MESSAGE 3: Seasonably colder to close out the weekend into early next week with uncertain wintry impacts

Another break in the action/drying trend for Saturday. We have high confidence in progressively lower temperatures and colder trend Sunday through early next week. Max temps on Tuesday are likely to be 5 to 15 degrees below the historical average. The cool down appears to be transitory and not long lasting with a gradual warm-up heading into month-end.

There is a growing potential for a coastal low/nor'easter by Sunday and early Monday for the East Coast. That said, when it comes to winter weather impacts for central PA, confidence remains very low given the ongoing uncertainty in the storm track. FWIW the 18/00Z guidance has trended a little more in the direction of the ECMWF which has been more suppressed with the intensifying offshore low. The GFS has really backed off from a snowstorm over the past 3 runs. Continue to monitor the forecast as details begin to unfold over the next few days.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

Shallow cool and moist airmass in place across all of the Central PA airfields with a light east-southeast sfc wind.

Increasing wind aloft from the west-southwest will overrun a slow moving frontal boundary that extended from near chicago and Cleveland southeast to Morgantown WVA and Central VA.

This low level jet will enhance lift over the boundary and lead to periods of rain/showers across all airfields today into tonight accompanied by IFR to ocnl LIFR CIGS and IFR to MVFR vsbys in -RA/BR. These conditions will persist through most or all of this 06Z TAF cycle.

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

Dense Fog Advisory until 10 AM EST this morning for PAZ065-066.