Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 201452 AFDCTP Area Forecast Discussion National Weather Service State College PA 1052 AM EDT Thu Oct 20 2016 .SYNOPSIS... A storm system will move into Western Pennsylvania today. The associated cold front will move slowly across the state tonight and Friday. Windy and much colder weather will move in for the weekend with the first bout of lake effect and upslope rain and snow showers Saturday into Saturday night. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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The meso anal early today shows a very complicated surface pattern with an inverted trough poking up into NWRN Pa, and cool air damming scenario in place further east over much of central and eastern Pa. The warm front aloft extends from the northern mountains SSE into the lower Susq Valley where marginally unstable air has helped support showers and isolated thunderstorms. Some locally heavy rains in excess of 1 inch have already been observed over portions of the northern mountains with radar estimates in excess of 2 inches over parts of Warren County. The NW looks to remain the focus for the best rains today as a wave of low pressure forms over the lower Ohio Valley and ripples up into western Pa by nightfall. As the associated upper trough deepens and moves toward the NERN US, the wavy front will slow down with the best rains concentrating along and behind the front, in almost classic anafront fashion. The models show a strengthening upper jet entrance region which will support strong deep layer frontogenetic forcing moving slowly across the forecast area, mainly tonight through the first half of Friday. We are outlooked for a Slight Risk of severe storms which is not unreasonable given the strong surge of moisture and expected development of several hundred Joules of Cape by mid to late afternoon as the front enters western Pa. Model depicted deep layer shear will be similarly intensifying under the deepening upper trough so the potential for damaging wind gusts will be enhanced if any discreet convection can manage to organize. As far as temps go, right now we already have a very mild - for the time of year - day forecast. If more sun than is currently expected manages to break out, we could end up warmer still.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... The first in a series of surface waves will be lifting out of NW PA late this afternoon. The surface pattern will be rather complex by that time with a low and potent cold front moving slowly across the western part of the state, and a warm front extending east before dog-legging down through the Central Mountains and east to the coastal plain. The forecast surface based LI`s depict this cool air damming scenario lasting at least through mid afternoon before we mix out and see the warm front become established to the NE of the region. The models have converged significantly with the timing/strength of an amplifying upper trough moving into the Eastern U.S. over the next couple of days. The trough axis takes on a slightly negative tilt as it chugs from the Ohio Valley...east across Pennsylvania. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... The amplifying upper trough will dig through Mid MS/TN Valley and eventually closes off, taking on a negative tilt moving through the Mid-Atlantic/Northeast States Fri-Sat. The right entrance region of 100+kt upper level jet should be in a favorable position to provide dynamical support and enhanced synoptic scale lift. Low level 850mb winds accelerate ahead of the surface low which helps to draw in precipitable water values +2SD above normal over Central PA into western NY. The deep layer upward vertical motion afforded by the upper level divergence and the sustained moisture flux convergence along the pivoting frontal boundary should result in 24-36 hour rainfall totals of 2-3 inches across northwest into north- central PA by Friday night. A colder day with a gusty northwest wind (between 30-40 mph at times - based on BUFKIT depicted mixing depth up through 6-8 kft agl in some places). A deep, northwest flow pattern will set up Friday night into early Saturday with wrap around/deformation precipitation on the backside of the low giving way to a cold advection lake effect/upslope shower regime focused downwind of Lake Erie and over the higher terrain of the Alleghenies/Laurel Highlands. Surface- 850mb temps will be marginally cold enough to support rain/snow showers Saturday (and especially Saturday night) over the NW mtns and Laurel Highlands with a low probability for a light coating of snow at the highest elevations. Some wet snow flakes or pellets may even be possible in the lee of the Alleghenies over the central ridges and valleys especially in heavier bands/pcpn rates. 25-35 mph wind gusts will add an additional blustery chill to below normal temps on Saturday. GFS/EC still show a fast-moving low diving through the Great Lakes into early next week. This system has low predictability given it weak state embedded within a progressive WNW flow aloft. Temperatures will trend noticeably colder/below normal by the weekend with highs easily 20-25 degrees colder than today. The roller-coaster up and down swing in temperatures is not uncommon for this time of year and will only continue as the calendar turns towards winter. Overall the pattern looks to stabilize into early next week with temperatures returning to normal for late October. && .AVIATION /15Z THURSDAY THROUGH MONDAY/...
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A complex low and frontal system will dictate the weather over the next 2 days. A warm front will progress through the flying area today with conditions improving to VFR by mid day or early afternoon where they have not already. BFD being closest to the front will be the exception likely holding onto MVFR conditions most if not all day. The rain will become more widespread later today along with deteriorating conditions from west to east as low pressure enters from the Ohio Valley. We will be unstable enough for the possibility of a potent thunderstorm with strong wind gusts, mainly western sections. Overnight and Friday will feature widespread MVFR/IFR developing over the entire region as the wavy slow moving front crawls through the area. Outlook... Sat...Scattered showers with restrictions NW. Brisk NW wind. Sun...No sig wx. Mon...Mainly VFR. MVFR with rain showers possible NW.
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&& .CLIMATE... Another new daily record maximum temperature was set at Harrisburg Wednesday. Here are the current records for 10/19: Harrisburg: 82 in 1945 (New record set 85) Williamsport: 82 in 1963 (High temp just shy of the record at 81F) && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...La Corte/Lambert NEAR TERM...Lambert SHORT TERM...Lambert LONG TERM...Lambert/Steinbugl AVIATION...La Corte/Ceru CLIMATE... is the U.S. government's official web portal to all federal, state and local government web resources and services.