textproduct: State College

WHAT HAS CHANGED

* Dense Fog Advisory expanded into the Lower Susquehanna Valley

KEY MESSAGES

1) Cloudy and foggy today with rain spreading south to north by tonight; elevated ice jam risk continues into the weekend

2) Mixed/wintry precip remains possible overnight into Friday morning across the higher terrain of north/east central PA

3) Reminder that it's still winter with potential for accumulating snow Sunday followed by a brief cold spell with brisk winds Monday and Tuesday

DISCUSSION

KEY MESSAGE 1: Cloudy and foggy today with rain spreading south to north by tonight; elevated ice jam risk continues into the weekend

Low clouds and fog will be prevalent again today as CAD pattern sets up across CPA. This will again introduce several degrees of downside risk daytime max temps.

Downstream of strengthening surface low tracking from Kansas to Lake Michigan, surging WAA on 850mb SW flow will send plume of high pwats and accompanying light to moderate precip from south to north later today/tonight into Friday. Forecast rainfall totals are in the 0.25-0.75" range through 00Z Saturday.

With the expected rainfall and ongoing snowmelt through the end of the week, the risk of ice jams will remain elevated.

KEY MESSAGE 2: Mixed/wintry precip remains possible overnight into Friday morning across the higher terrain of north/east central PA

The location and orientation of the retreating banana high appears only marginally conducive for wintry precip later tonight into Friday morning. The higher terrain ridges over the northern and eastern portions of the forecast area remain most susceptible for mixed precip. The latest ptype output suggests more of a mixed precip evolution (rain/sleet/snow) with sfc temps largely above the freezing at the onset. Freezing rain is still possible, but coverage should be limited with the best odds for an ice glaze =>0.01" over the interior north central mtns in Potter/N. Lycoming and Tioga Counties as well as along the northeast periphery of the CWA in higher elevations of Sullivan and Schuylkill Counties. The marginal boundary layer thermal profiles and weak/retreating position of the high suggests any wintry precip may be relatively short-lived and provide limited/low impact having difficulty accumulating on roads. We will the allow dayshift to assess the setup one more time and make a final call on a winter wx advisory.

KEY MESSAGE 3: Reminder that it's still winter with potential for accumulating snow Sunday followed by a brief cold spell with brisk winds Monday and Tuesday

There remains a strong potential for a low pressure system off the Mid-Atlantic coast Sunday intensifying into a nor'easter by Monday. However, the track of the low remains uncertain with plenty of variability in the model guidance. The ECMWF and the UKMET remain farther south and offshore as it exits the coast, whereas the GFS is closest and has the greatest impacts to the Mid-Atlantic region. Low confidence forecast with northern and southern stream phasing differences still to be resolved. It seems that even with a more suppressed and eastward track, the associated upper trough and inverted trough axis may be able to provide sufficient forcing/lift to produce a broad area of accumulating snow. This will continue to be monitored closely.

Confidence is much higher in a reality check back to winter temperatures as a brisk northerly wind behind the departing nor'reaster directs a much colder Canadian airmass back into the region. Max temps on Monday and Tuesday will be 5 to 15 degrees below the historical average. The cold spell won't last long with a moderating trend commencing through midweek as low level winds turn more southwesterly.

AVIATION /12Z THURSDAY THROUGH MONDAY/

Low stratus clouds and dense fog was found on the cool side of a sinuous stationary surface frontal boundary that extended from near KBFD to KFIG, KAOO and KCBE at 11Z. Widespread IFR through VLIFR conditions were noted in this shallow/moist cool airmass.

On the warm western side of this front, more in the way of high based, generally MVFR to VFR clouds were found.

Some slight improvement in these conditions will occur late this morning and this afternoon, but most airfields will be IFR to low-end MVFR w/respect to CIGS and MVFR based on VSBYS.

For this Thursday afternoon, some parts of south central PA have a very low probability of observing thunder followed by a shield of rain moving northeast across much of the SW half of PA by mid evening, and overspread the rest of Ncent and NE PA later this evening and overnight.

Though probabilities for TSRA were low enough to keep out of TAFs. Some elevated instability will be present, but overall confidence is low for thunder reaching the airspace.

Conditions lower again tonight with widespread IFR CIGS and VSBYS and periods of rain and drizzle.

Outlook...

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

Dense Fog Advisory until 9 AM EST this morning for PAZ004>006- 010>012-017>019-037-041-042-045-046-049>053-057>059-065-066.