textproduct: State College

WHAT HAS CHANGED

* Watching trends on radar etc. in regard to fast moving weather systems into the weekend. * Flood Watch for ice jams issued for southwest PA tonight into Friday. * Winter Weather Advisory for light ice accumulation issued for Sullivan and Schuylkill County late tonight into Friday morning.

KEY MESSAGES

1) Cloudy and foggy overnight into Friday with fast moving bands of rain. 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 overnight into Friday with fast moving bands of rain. Ice jam risk continues into the weekend.

First batch of rain weaken as it moved east, heaviest now south of our area. Some bright banding on the radar earlier with this batch, so use caution with pcpn estimates.

CAD continues with a very slow drop in temperature. Will continue to monitor obs for temperatures and fog. Similar to last night in this regard.

Main area that got the heavier rain earlier was JST, around a half inch. So far rivers not a problem.

With the expected rainfall and ongoing snowmelt through the end of the week, the risk of ice jams will remain elevated. A Flood Watch remains in effect until 1PM Friday for southwest PA (Blair, Bedford, Cambria, Fulton, Huntingdon, and Somerset Counties) where the risk for ice jams is highest.

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

Been watching temperatures across southeast NY state and NW New Jersey. Much of the pcpn has been south of where the colder air is. Next batch of rain likely to be more to the northwest than what we had earlier, and might not reach into the northeast part of the CWA much before sunrise.

Earlier discussion below.

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 hoisted a Winter Weather Advisory for Sullivan and Schuylkill County where confidence in cold enough temperatures and light enough precipitation for ice accretion is highest. Farther west through Northern Lycoming, Tioga, Northern Clinton, and Northern Centre County, ridgetop ice accretion is possible if temperatures trend a bit lower than currently expected. Higher rainfall rates will limit the efficiency of ice accretion there and confidence in any impacts is sufficiently low at this time to preclude Advisory issuance.

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.

Main chance for snow on Sunday would be more from the inverted trough, still a ways out to pinpoint location and amts of snow with such a feature. Upper level low dynamics might be the key for our area as well.

Earlier discussion below.

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. This is a low confidence forecast at this time 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. Confidence in accumulating snowfall continues to increase, but significant details remain TBD as it relates to the potential for significant snowfall.

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 /02Z FRIDAY THROUGH TUESDAY/

Widespread IFR-to-LIFR conditions are expected as moisture continues to flow overtop a cool/moist airmass overnight, with lower visibilities expected where precipitation is falling through 20/15Z. Localized areas of light freezing rain or sleet is possible across northern Pennsylvania overnight; however, have continued to keep mentions out of the 00Z TAF package due to lower confidence with respect to FZRA at IPT. Further south and east, very high (~90-100%) confidence in rain being the main precipitation type through 20/20Z. Some potential exists after 20/20Z at BFD for SHSN; however, low (~30%) probability warrants only mentions of PROB30s this cycle.

Guidance continues to struggle with respect to recovery tomorrow; however, recent GLAMP/NAM model guidance continues to outline IFR conditions across much of the region, with HREF/NBM model guidance also trending in that direction. Thus, slightly higher confidence compared to the earlier TAF packages, but still would only describe confidence as moderate (~40-50%) for the 00Z TAF cycle.

High confidence in LLWS thresholds being met overnight across the western terminals, with the presence of an 850mb LLJ. More recent HREF guidance has tracked back on the strength of this LLJ, but based on recent NBM/NAM model guidance, seems like LLWS concerns at BFD/JST/AOO/UNV seem well-founded. Further east, slightly lower confidence, so have continued to leave out of the TAF package at this time.

Outlook...

Sat...Lingering rain and snow showers.

Sun-Mon...Potential for restrictions in snow showers.

Tue...No significant weather expected.

CTP WATCHES/WARNINGS/ADVISORIES

None.