textproduct: State College

WHAT HAS CHANGED

* The Wind Advisory has been expanded a bit further into parts of the Middle and Lower Susquehanna Valleys, as well as the Poconos, through early Saturday.

KEY MESSAGES

1) Strong winds expected through tonight and into Saturday morning for most of Central PA, along with a coating to a few inches of snow for the northern mountains.

2) Gusty winds return Sunday afternoon through Tuesday, with a temperature roller coaster, and potential for strong to severe thunderstorms Monday afternoon and evening.

DISCUSSION

KEY MESSAGE 1: Strong winds expected through tonight and into Saturday morning for most of Central PA, along with a coating to a few inches of snow for the northern mountains.

A potent upper-level disturbance will track across upstate NY late this afternoon, and eventually through southeast Canada tonight and early Saturday. As it does so, a trailing surface cold front will cross the Commonwealth through this evening.

Most of our near-term guidance is suggesting that a band of rain and snow showers will form along the above mentioned cold front later this afternoon, and quickly cross PA this evening. For areas north of I-80, where temperatures are colder, a quick burst of snow is foreseen, which could sharply reduce visibilities and produce locally slick roads. We will be monitoring the far northern tier of the state for any flash freeze/snow squall potential into the evening. Farther south, where surface temperatures are milder, just a brief shot of gusty rain showers are anticipated.

Late tonight and into Saturday, strong westerly winds are still expected. Isallobaric forcing and a deeper layer of steep lapse rates in the lower part of the atmosphere points to the strongest gust potential (perhaps as high as 45-55 mph) across the Laurel Highlands and also areas near and north of I-80. However, even a bit farther to the southeast into parts of the Susquehanna Valley and the Pocono plateau, occasional gusts could eclipse 45 mph, thus the above mentioned expansion of the Wind Advisory. Winds should gradually subside Saturday afternoon into Saturday evening, as the pressure gradient relaxes.

A relatively brief period of cold advection crossing Lake Erie and interacting with downstream terrain will produce periods of snow for the northern snow belt areas (Warren, McKean, and parts of Potter counties). Current expectations are for 1-3" of snow locally, mostly over the higher terrain and north of US-6.

KEY MESSAGE 2: Gusty winds return Sunday afternoon through Tuesday, with a temperature roller coaster, and potential for strong to severe thunderstorms Monday afternoon and evening.

Another potent disturbance will emerge out of the Plains states on Sunday, eventually tracking through the Great Lakes and the northeastern states by early next week. A strong cold front tied to the main surface wave is expected to slice through the Commonwealth Monday afternoon and evening.

Strengthening S-SW flow in the expanding warm sector will overspread PA later Sunday and into Monday, with gusty conditions again returning.

We continue to monitor the potential for strong-severe thunderstorms along and just ahead of the aforementioned cold frontal passage later Monday afternoon into the early evening hours. We have high confidence at this early stage that it will relatively warm for mid-March, as well as strongly sheared. However, smaller scale and less predictable factors like cloud cover/associated instability, as well as convective mode (discrete vs. linear, or a combination thereof), still need to be worked out, and probably won't really be known until we head into Monday. Stay tuned for later forecasts/updates.

We also have relatively high confidence that it will remain windy and turn sharply colder later Monday night and Tuesday. Some areas may see a 30+ degree temperature difference on the negative side for Tuesday, as compared to Monday.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

Potent/energetic system moving through will be ramping up the wind speeds and gusts shortly. Some have already gusted near 40kt (JST AOO). Despite the gustiness, we have included mentions of LLWS for tonight. While we don't regularly include LLWS mentions when gusts are almost as high as the shearing layer, we felt it importnat to highlight them this time to bring some extra attention to the wind forecast for the next 24 hrs. Strong srly flow now will switch to the west as the cold front moving through OH at 18Z arrives and passes thru PA. The clouds/visbys are all VFR at the moment, but BFD is expected to dip to IFR for a few hours - or at least parts of hours - for two periods: later this aftn and then again after midnight. The reductions are not certain with cross-lake flow very strong and mostly straight westerly. That will likely keep much of the SHSN up in wrn NY. Other than BFD's problems, the wind will be just about the only flying-condition trouble elsewhere. While some MVFR (bkn-ovc030) clouds re-establish themseleves across many terminals overnight, they will be gone in the morning. The wind will be slowing in the morning, too. But, gusts will remain in the 20s for most sites for the entire day Sat even as upper heights rise and sfc high nears. Sat night, the ridge will be overhead, and wind should finally die off. But...another storm system will move toward the state from the northern Plains.

Then, Sun: Low clouds creep in from the S. MVFR cigs certain (90%), IFR possible (50%). Rain and snow showers possible across the northern half of PA as a warm front lifts thru. LLWS certain (80%).

Outlook...

Mon...VERY strong cold fropa. Pre-frontal SHRA/TSRA with IFR possible. Then turning blustery and colder. Post-frontal MVFR cigs for most of the area. IFR likely N/W (60%) due to clouds and/or SHSN.

Tue...Blustery. Sct SHSN NW. IFR poss (50%) at BFD, (30%) JST.

Wed...Warm fropa. -SN or -RA poss (30%) NW.

CTP WATCHES/WARNINGS/ADVISORIES

Wind Advisory until 8 AM EDT Saturday for PAZ004-005-010-017- 018-024-025-033-034. Wind Advisory until 11 AM EDT Saturday for PAZ006-011-012-019- 026>028-035>037-041-042-045-046-049>053-056>059-063.