textproduct: State College

SYNOPSIS

* Mostly cloudy to overcast skies continue today through Saturday morning. * A period of light rain lasting about 6 hours late today and tonight and focused mainly over the southern half to two thirds of Pennsylvania night, precedes a drying trend with more sunshine over the weekend * Mild pattern with rain prior to Thanksgiving turns decidedly colder with temperatures below average by next weekend

NEAR TERM /UNTIL 6 PM THIS EVENING/

Two fairly weak upper-level short waves in the Northern and Southern streams will move across the NE US and Ohio Valley/Central Appalachians - out of phase - today and tonight.

The Northern short wave will be in the lead supporting a few scattered light showers along and ahead of its associated weak cold front. The southern stream wave will have the greatest impact on our CWA precip-wise (Mainly over the southern half to two thirds of PA) as an approx 5-8 hour period of weak to MDT uvvel linked to the thermally indirect, left exit region of an upper level jet late today and tonight. Forecast rainfall from AOB 0.10 inch near the I-80 corridor to between 2 and 3 tenths of an inch near and south of the PA Turnpike looks good at this point. Many locations across the northern mountains could escape the next 24 hour with very little or no measurable rainfall.

Thick, layered cloud cover covered all of the CWA early today which will minimize any further temp drop early today, considering a light south to southwest breeze and T/Td spreads of generally 3 deg F or less.

Previous discussion pertaining to low clouds and fog on the Western high terrain...

Drizzle is falling here and there, mainly in the SW quarter of the CWA right now. Forcing is so weak that it is tough to pick out the mechanism generating it. However, the NAM does have a bead on it, and slides the light QPF it makes to the east slowly tonight. Have added areas of DZ and FG to most of the area. The conditions may get worse overnight (vsby) but they won't get any better. We will consider a dense fog advy if the vsby creeps lower than the ridge tops. Thankfully, unlike last night, the temps and dewpoints are above freezing and no black ice/freezing fog is expected to form. Temps will waggle within a couple of degrees of current, and may even rise a tiny bit in some places.

High temps today will rebound by 5-10F, reaching the 45-55F range respectively from North to South across the state.

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

Lead upper level wave in the northern stream of the split flow will move from the Glakes to the new England states today, pushing a weak cold front SE across PA late today (north) and tonight across Central and Southern PA.

Prior to this frontal passage the southern half to 2/3rds of PA will see light rain - beginning in SW PA/Laurel Highlands late today/this evening, before spread ENE between 04Z and 13Z Saturday. The period of rainfall in any one location should be about 7-8 hours.

Some pockets of mixed precip may be possible on the northern edge of the precip by early Saturday morning, but the southward suppression of QPF would render this precipitation type uncertainty a moot point.

LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/

Somewhat zonal pattern will start the medium range period with the southern branch of the jet stream extending from northern Mexico ENE across the Gulf Coast States as a slow moving Upper Low drifts across northern Baja California. Several pieces of energy diving SE from NW Canada, combined with a potent upper level trough crashing into the Wash/Oregon Coast, will amplify the flow across N American and the mean trough over the NE U.S. Saturday night into early next week.

Drying trend expected over the weekend behind the cold frontal passage. Upper level trough pivoting through the Great Lakes may deliver some rain/snow showers to the northern tier on Sunday. On balance, it should be a quiet weekend with temps remaining close to the historical average. We'll see much more sunshine later Saturday through Monday, which will be a welcome change. Sunday morning is the coldest morning of the week ahead, with partly cloudy skies supporting lows in the 20s.

A reinforcing shot of cold air will push south across PA late Sunday/Sunday night as a rather compact but potent shortwave moves SE from the Glakes. A brief shower of rain (south) and a few rain/snow showers (North) could occur with this frontal boundary.

The 2 aforementioned storms (the upper troughs over Nrn Mexico and the NW U.S.) will move to the NE/E respectively and merge across the Nrn Plains states as 500 mb heights/flow at that level back about 30-45 deg to a more swrly direction across the NE US and Ohio/Tennessee Valleys.

This storm system will eventually move through the eastern US toward the middle of next week. While the exact timing remains uncertain (typical fast/low biases evident in the GFS/ECMWF), a period of rain appears most likely in the Tuesday or Wednesday time frame ahead of the next split stream system tracking eastward from the Central U.S. Temperatures will be mild as the main slug of moisture moves through, with rain as the predominant precipitation type. Colder air wrapping around the system could produce some snow showers in the northwest mountains late in the week. By next week, ensemble model data continues to advertise a pattern shift toward colder/below average temperatures after Thanksgiving.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

No big changes in store for the 12Z TAF package.

Conditions have been up and down all night. I would expect conditions to do the same over the next few hours.

Earlier discussion below.

Low clouds and fog will prevail much of the time overnight into Friday morning or early aft.

Sites that can keep a bit of a breeze like JST will have the best chance of not having as much fog.

Some showers with the cold front, but overall not much on Friday.

A fast moving wave is likely to form along the cold front. This wave may bring some more rain to the area Friday night, mainly across the southern part of PA.

Outlook...

Sat...Improvement to VFR at most terminals. Fog may return Sat night.

Sun-Mon...Mainly VFR.

Tue...Restrictions in widespread rain possible.

CTP WATCHES/WARNINGS/ADVISORIES

None.