textproduct: State College

WHAT HAS CHANGED

* Issued a Special Weather Statement for generally light snow accumulations occurring over a 24 to 30 hour period across the Northwest Mountains and Laurel Highlands.

KEY MESSAGES

1) Light upslope and lake enhanced snow showers will bring a few inches of total snow accumulation (with locally as much as 4 or 5 inches along the summit of Laurel Ridge and Mount Davis in Somerset County) late today through Thursday, mainly across Warren and Mckean Counties and the Laurel Highlands.

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

DISCUSSION

KEY MESSAGE 1: Light upslope and lake enhanced snow showers will bring a few inches of total snow accumulation (with locally as much as 4 or 5 inches along the summit of Laurel Ridge and Mount Davis in Somerset County) late today through Thursday, mainly across Warren and Mckean Counties and the Laurel Highlands.

Vertically growing/cooling boundary layer (with the upper half of the cloud layer falling within the DGZ this evening through Thursday) will initially compete/be offset by large scale subsidence beneath the left entrance region of an upper level jet.

Rather steady, albeit light snow will develop across primarily the NW Mtns and Laurel Highlands late this afternoon and evening, continuing overnight. FLurries or more brief, isolated snow showers will occur across the Ncent Mtns and Central Ridge and Valley region, where a light coating to one half of an inch is possible on the higher terrain near and just to the NW of the I-99 and Route 220 corridors.

Based on this larger scale subsidence aloft and the lack of any significant cross-haired signature within the cloud layer on model time-height cross sections ala BUFKIT, we feel that the snow will be slow to accumulate with rates under 1/2 inch per hour.

Otherwise, the wind stays gusty for the rest of this afternoon and tonight - likely generating some gusts up near 40KT on the highest ridges (mainly the Allegheny Front/Babcock Mtn). We'll continue hold off on a wind advy at this point.

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 /00Z THURSDAY THROUGH MONDAY/

Northwest flow over the region continues to produce scattered lake effect snow showers west of UNV. MVFR ceilings will persist at BFD, JST, and AOO through the night, gradually expanding to UNV as well. There is a low chance for MVFR ceilings to reach IPT for a brief period later tonight, but with the LAMP showing VFR conditions prevailing and the HREF only suggesting a 40-50% chance of MVFR, we will keep VFR conditions in the TAF for now.

Snow showers increase in coverage through the night as a shortwave rotates through the region. While MVFR conditions are favored at BFD and JST, brief periods of IFR are possible in any snow showers that move directly over the airfield.

Northwest winds sustained at 10 to 15 knots with gusts of 25 to 30 knots will remain likely through the night. There is low-end potential for LLWS for airfields south of UNV as wind at 2000 feet will be around 40 knots, but with surface winds not expected to remain above 10 knots, we will hold off on including any mentions of wind shear.

Ceilings at AOO and UNV quickly rise to VFR during the morning, while BFD and JST likely remain MVFR through the 00Z TAF period with continuing snow showers. Some guidance does show the potential for MVFR ceilings to redevelop at UNV and IPT during the afternoon, but continued VFR appears to be the more likely outcome

Outlook...

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

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

CTP WATCHES/WARNINGS/ADVISORIES

None.