textproduct: State College

WHAT HAS CHANGED

* Forecast remains highly consistent

KEY MESSAGES

1) Patches of ice may glaze over the Laurel Highlands this morning, and result in locally hazardous travel conditions

2) Winter weather threat for Sun-Mon timeframe continues to trend very slightly lower.

DISCUSSION

KEY MESSAGE 1: Patches of ice may glaze over the Laurel Highlands this morning, and result in locally hazardous travel conditions

Temps are dropping in the wake of a cold front, both at the sfc and in the low clouds over the W. Model soundings portray a thermal profile in the shallow clouds which would be mainly/all supercooled water this morning. With sfc temps now dipping near 32F, we could see some patches of -ZL/ZR as the orographic lift helps wring out some of that moisture as the air ascends the Laurels and the tops of the highest spots on the Allegheny Plateau this AM. Will hold onto the Winter Weather Advisory for the Laurels, and continue to only mention patches elsewhere in the wrn mtns. A kicker/help for any precip this AM/early aftn is a secondary front poised to cross the mtns from N-S from just before sunrise in the N to mid-morning S. Then, the thermal profile will get cold enough for SHSN instead. Cross-lake flow will make a deposit of 1-2" over the highest terrain of the Laurels and and inch or so in the far NW. Otherwise the wind gets stronger after the second FROPA - likely generating some gusts up near 40KT on the highest ridges (mainly the Allegheny Front/Babcock Mtn. We'll hold off on a wind advy at this point, but are mentioning the gusty winds in the WSW for the Laurels where the wind will be strongest/gustiest. ---------------------

KEY MESSAGE 2: Winter weather threat for Sun-Mon timeframe continues to trend very slightly lower.

A wave of low pressure is set to develop/deepen over the desert SW and TX on Fri-night. The upper feature which is expected to drive this development is still off the CA coast. Thus, upper air sampling/initialization is not infused with any actual sounding data. Old forecaster once told me to not trust anything still over the Pacific at model runtime. Advances in model init with sat data and better first-guesses have improved our long- range forecasting since then (along with the extinction of the dinosaurs). Yet, I can't shake the large amount of doubt that this upper low/trough brings to a forecast for >3000SM away and ~5 days in the future.

While many deterministic model solutions now take all of the precip associated with the low to the south of PA, all of the ensemble systems continue to keep a relatively high (50-60pct) chc of measurable precip falling over PA sometime Sun into Mon.

Thus, the main message here is that a winter storm - or at least a meager amount of light precip - remains possible. Progged temps on Sat night and Sun morning look sub-freezing over all of the forecast area as a high pressure/cold dome moving down from the N/NE could make a wedge of CAD. However, Sunday may hold a warming up to 35F N and 42F S. So, arrival time of (any) precip would be key to (any) precip type. With so much uncertainty, we've only shown a slight nudge downward in PoPs Sun-Mon by about 10-15pct from the previous model cycle, leaning toward the drier forecast that the deterministic model solutions continue to trend toward.

AVIATION /07Z WEDNESDAY THROUGH SUNDAY/

Mixed bag of VFR-to-MVFR conditions will continue across western Pennsylvania through 11/12Z with restrictions mainly in the form of low ceilings. At this point, continues to look like MDT/LNS are least likely to experience MVFR conditions, but any restrictions would likely occur between 11/09Z and 11/12Z Wed. A period of IFR ceilings is possible at KBFD and KJST over a similar timeframe with a slight increase in low-level moisture. Lake effect/upslope snow showers will develop Wednesday afternoon and could bring IFR/LIFR visibility if they move over any airfields. KBFD and KJST are the most likely locations to experience restrictions.

LLWS will also continue as a moderately strong southwesterly LLJ passes overhead. Once the front passes through, winds will shift to the northwest and become gusty. Gusty WNW winds in excess of 30 kts will be likely mainly after 10-12Z Wednesday with some periods of light snow/snow showers - focused across the Western Mtns of PA. Wind gusts elsewhere will at least be in the mid to upper 20KT range.

Outlook...

Wed-Thu...Sub-VFR most likely at KBFD and KJST with periods of snow showers.

Fri-Sat...Improving conditions late week into the weekend

Sun...Monitoring potential for winter weather on Sunday. Most likely restrictions are in southern PA at this time.

CTP WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory until 3 PM EST this afternoon for PAZ024-033.