textproduct: State College

SYNOPSIS

* Cloudy and damp with light showers across the Northwest Half of PA and areas of dense fog in the southeast early today * A strong cold front will bring a few additional showers later this morning and this afternoon, followed by strong gusty winds and much colder temps tonight through Friday * Lake effect snow may result in significant Thanksgiving holiday travel disruptions across northwest Pennsylvania, while scattered snow showers and a few squalls impact the weather across the Central Mtns, Laurel Highlands and possibly the Middle Susquehanna Valley Thursday into Friday

NEAR TERM /UNTIL 6 PM THIS EVENING/

Weak llvl warm advection and the presence of a 95 kt jetlet at 300 mb lifting NE across Wrn and Central PA was supporting plenty of clouds and numerous, albeit light rain showers through the predawn hours.

SFC cold front was pushing into Western Ohio attm and will move across PA during the late morning and afternoon hours, with another brief/gusty shower mainly over the Western half of the CWA.

Elsewhere this morning, Foggy conditions with vsbys varying between 1/4-1/2SM will persist for the next few to several hours and will be under a Dense Fog Advisory through 13Z today. The fog formed yesterday evening as a result of significant breaks in the cloud cover and radiational cooling near, and just to the north of a slow-moving warm front where llvl moisture was pooling.

Forecast high temperatures today will be very mild for late November (ranging from the low to mid 50s across the Northern and Western Mtns to the low and mid 60s in the southern Valleys

These values could end up being several deg F too high if the fog lingers longer than expected. This cold front will usher in much colder air for tonight through Friday.

SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY NIGHT/

Model soundings show the potential for widespread wind gusts tonight and Thursday morning in the 40 to 55 mph range as winds at the top of the mixed layer approach 50 knots and the 40 kt isotach is noted more than half of the way to the ground from the 4-5 kft top of the mixed layer.

Confidence is highest in the Laurel Highlands, so a Wind Advisory remains in effect from 00z Thu to 00z Fri. The Wind Advisory was expanded over the past few hours to include Clearfield County which contains the heavily traveled I-80 and where the interstate reaches its highest peak east of the Mississippi.

Gusty winds continue into Friday, perhaps just a little less windy than Thursday.

The main focus for this period is still the potential for heavy lake effect snow across northwest PA. While the low-level flow will initially be out of the southwest, favoring areas north of the Pennsylvania-New York border for the heaviest snow, winds quickly become more westerly by Thursday morning, directing the snow bands into northwest PA.

Most guidance shows the flow remaining favorable for snow to continue over northwest PA through Friday. With confidence continuing to increase in at least portions of Warren and McKean counties seeing from 6 to 12+ inches of snow, we have upgraded the Winter Storm Watch to a Lake Effect Snow Warning. Areas that see the most persistent snow bands may even see snowfall amounts as high as 15 to 18 inches (if they sit beneath a true LES band for a several hours where snowfall rates could be in the 2-3 inch per hour range.

Heavy snow combined with wind gusts up to 40 mph may make travel difficult to impossible at times. Lake effect snow bands will almost certainly make it farther south and east than those two counties, but confidence in placement and snowfall amounts remains too low to issue any Winter Weather Advisories yet.

Snow showers will also impact the Western Mountains tonight/Thursday and again on Friday with model RH profiles showing saturation in the DGZ along with favorable upslope wind trajectories. Friday may also feature a few snow showers or squalls that could impact the the I-80 and I-99 corridors, leading to rapidly changing travel conditions.

LONG TERM /SATURDAY THROUGH TUESDAY/

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 returning precip to 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 /12Z WEDNESDAY THROUGH SUNDAY/

LIFR in fog currently locked in the southeast corner of the forecast area but this will dissipate in the next hour or so as winds increase aheads of an approaching cold front. Scattered -SHRA ahead of this front will move across the central portions of the state through the morning with isolated MVFR.

As the day progresses, conditions will gradually become VFR elsewhere. Along and behind the front, winds will become westerly (240-280 degrees) and it will turn quite blustery.

Blustery westerly winds will continue overnight. As colder air continues to filter into the region, snow showers will develop across the western highlands (BFD/JST) but will occur near the end of the forecast period and poiints beyond.

Outlook...

Thu-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.

CTP WATCHES/WARNINGS/ADVISORIES

Lake Effect Snow Warning from 1 AM Thursday to 1 AM EST Saturday for PAZ004-005. Winter Weather Advisory from 7 AM Thursday to 1 AM EST Saturday for PAZ006-010-011. Wind Advisory from 7 PM this evening to 7 PM EST Thursday for PAZ017-024-025-033-034. Dense Fog Advisory until 8 AM EST this morning for PAZ036- 057>059-063>066.