textproduct: State College

SYNOPSIS

* Slightly milder temperatures today with steady rain followed by even milder conditions Wednesday with a few showers along and ahead of a strong cold front * Becoming windy and much colder Wednesday night 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

NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/

Rain will continue across much of Central PA through the rest of the day and may actually increase slightly in intensity for the rest of the afternoon as forcing for ascent increases slightly ahead of an approaching 30 to 40 knot low-level jet. Precipitable water values will increase to around 1 inch, which is around the 95th percentile for this time of year. Total rainfall amounts through tonight will range from around a half of an inch to three quarters of an inch. The rain gradually tapers off to a few showers overnight as the axis of the LLJ exits the region to the east. Temperatures remain mild overnight, with lows ranging from the low 40s to near 50.

SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY NIGHT/

Additional showers will be possible on Wednesday afternoon along and ahead of a strong cold front. Temperatures on Wednesday will be even milder, with highs in the 50s and 60s, though these values could end up being slightly high if the front arrives earlier than currently anticipated. This cold front will usher in much colder air for Wednesday night through Friday.

Model soundings show the potential for widespread wind gusts Wednesday night and Thursday morning in the 45 to 50 mph range as winds at the top of the mixed layer will range from 45 to 55 knots. If confidence continues to increase in these gusts mixing down to the surface, a Wind Advisory may be needed for much of Central PA. Gusty winds continue through the end of the week, but may peak just below Wind Advisory criteria for both Thursday and Friday afternoons.

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 early 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 anywhere 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. 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 Wednesday night and 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. 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 a mixed ptype transitioning 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 /00Z WEDNESDAY THROUGH SUNDAY/

Steady rain will taper off from west to east this evening, with patchy light rain/drizzle lingering overnight. Low clouds will persist, with predominantly IFR conds expected overnight across central PA. Borderline LLWS conds this evening should diminish overnight.

Wednesday will be mild and showery ahead of a cold front that will cross the region from west to east as the day progresses. Conds should improve to at least MVFR across the western highlands as the day progresses, and 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 Wed eve/night. As colder air continues to filter into the region, snow showers will develop across the western highlands (BFD/JST).

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. Wind Advisory from 7 PM Wednesday to 7 PM EST Thursday for PAZ024-025-033-034.