textproduct: State College

SYNOPSIS

* Gusty west to northwest winds and much colder temperatures to end the week * Lake effect snow will result in significant Thanksgiving holiday travel disruptions across northwest Pennsylvania * Scattered snow showers and a few squalls will impact the weather across the Central Mtns, Laurel Highlands and possibly the Middle Susquehanna Valley Thanksgiving Day into Friday * A few periods of snow (Northern PA) and snow/or a wintry mix (Southern PA) late Saturday Night and Sunday * A more significant/widespread winter storm possible Tuesday and Tuesday night

NEAR TERM /UNTIL 6 PM THIS EVENING/

Lake effect snow will be the primary and significant concern across Northwest PA for this Thanksgiving Day. No changes were made to the current Winter headlines for several counties in NW PA or or the Wind Advisory for the Laurel and Wcent Mtns.

Mean low level flow to start the day will be from 250-255 deg, which will keep the significant single band of heavy LES along and just inland from the south shore of Lake Erie in NW PA and SW NY.

This will be short-lived though today as slight veering of the wind by 5-10 degrees will push the single, intense snow band into Northern Warren and NW Mckean County by 12Z.

This LES band will transition to 2 or 3, long and more narrow bands of LES, extending well to the east of RT 219 in NW PA by late this morning. The bands will then waggle throughout the next 36 hrs, but fetch will keep the heaviest accums over the normal snow belt of Warren county and NWrn McKean county.

Limited Glake moisture and deep layer cooling will bring fairly widespread flurries today across much of the Central and Northern Mtns, Laurel Highlands and even the Middle Susq Valley as the depth of the well mixed layer occupied by the dendritic growth zone of -12C or lower increases from about a 1 kft thickness this morning to around 2 kft by 00Z Friday. Drying, low-level downslope flow across the Lower Susq Valley will result in some significant breaks of sunshine in that part of the CWA for the mid to late afternoon hours.

Temps today will display only a few to several deg F rise at best across the Northern and Western Mtns considering the deepening cold advection and widespread bkn-ovc skies, while the Susq Valley sees a 6-8 deg F rise from morning lows.

Highs will range from the upper 20s to low 30s across much of the Northern and Western Mtns to the lower 40s in the Greater York, Harrisburg, Lancaster areas.

SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/

The next concern would be if a long band from Lake Huron eventually meets up with LE water and develops at least one longer band that could extend deep into the CWA. At this point, most models keep the large Huron-connected band well to the N of UNV (and along the RT 6 corridor) later tonight through daybreak Friday, with focus for the Central Mtns being placed more on a Lake Superior/Nrn Lake Mich and Central Lake Erie fetch producing another extensive band on a 285 to 90 deg axis pointed at KDUJ, KFIG and KUNV by 12Z Friday.

There is potential for this band to become quasi-stnry for a few to several hours which could result in locally 2-3 inches of wind blown snow along a 15-30 mile stretch of I-80.

The big take-away: Snow for PA will be most-widespread and heaviest on tonight and Friday AM.

The positions and strength of snow bands on Friday are difficult to precisely nail down. There is some disagreement on just how fast/completely the wind will back/turn to the west and southwest and make the snow go away. Current forecast of lower PoPs on Friday aftn is reasonable, but we may need to delay the exit/ending of the snow for 6+ hrs.

LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/

The lake effect snow pattern comes to an end Saturday morning as low-level flow backs and high pressure begins to build in, resulting in a lowering subsidence inversion. There is still some uncertainty with speed/timing, but overall guidance agrees in bringing another round of precipitation for the area on Sunday. Thermal profiles appear to be cold enough to initially support snow, then perhaps mixing with or changing to rain for the last day of November. Unsettled weather will continue into early next week as cold air in the middle of the country sets up a strong baroclinic zone over the eastern US.

AVIATION /10Z THURSDAY THROUGH MONDAY/

Gusty west winds will persist through the TAF period and perhaps linger all the way through Friday. Meanwhile, lake effect snow showers across upstate New York will gradually sag south into PA today and tonight. Restrictions are likely at KBFD, with IFR/LIFR visibility restrictions expected after 22Z. A few scattered snow showers during the day today could also bring intermittent restrictions to KBFD.

Some snow showers could start to work into JST later this afternoon or evening as winds shift more to the northwest late in the day. Restrictions become increasingly likely at KJST overnight tonight and Friday. A few snow showers could bring brief restrictions to UNV, AOO, and IPT late tonight into Friday as well. MDT and LNS should remain restriction-free with nothing more than a snow flurry expected.

Conditions will improve by Saturday, but a storm tracking north and west of central PA on Sunday will bring a chance of some snow and rain. Track to the west supports some rain. Most of this would taper off by Monday. Models show some chance for more snow and rain on Tue.

Outlook...

Fri...Windy with gusts 30-35kt from 270-300 degrees; frequent snow showers/squalls across the NW 1/2 of the airspace.

Sat...Improving conds; diminishing winds with lingering snow showers ending.

Sun...Light rain/wintry mix developing from west to east; restrictions possible. Precip may turn to rain across the south during the day.

Mon...Mixed/wintry precip likely. MVFR likely. IFR poss.

CTP WATCHES/WARNINGS/ADVISORIES

Lake Effect Snow Warning until 1 AM EST Saturday for PAZ004- 005. Winter Weather Advisory until 1 AM EST Saturday for PAZ006-010- 011. Wind Advisory until 7 PM EST this evening for PAZ017-024-025- 033-034.