Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 251800 AFDCTP Area Forecast Discussion National Weather Service State College PA 200 PM EDT Sat Mar 25 2017 .SYNOPSIS... A cold front will sag southward across Pennsylvania this afternoon and tonight, before returning north as a warm front late Sunday and Sunday night. Unsettled conditions will continue through the middle of next week before high pressure returns with drier air. && .NEAR TERM /THROUGH TONIGHT/... Meso-anal shows an west-east boundary strung out just north of I-80. The thickest clouds are over northern PA along and north of the front with brighter skies over southern PA where a mix of sun and clouds is common. The boundary will continue to settle slowly south throughout the day so by mid afternoon, it will actually start to cool over the northern half or so of the forecast area. The HRRR suggests that by nightfall it will have moved through southern PA, with the possible exception of the far SW. Rainfall amounts are expected to be on the light side. More likely we will see a pattern developing where we have widespread low clouds with scattered rain showers and areas of drizzle and fog. Overnight lows will range from the mid 30s over the NE to mid 40s over the SW. These will average some 10-20 deg above normal. && .SHORT TERM /SUNDAY/... The light showers...with areas of drizzle/ridge top fog are likely to continue through much of the day Sunday. Local experience suggests we lean away from blended model guidance for max temps in such low level cold air damming situations. As such, I lowered tomorrrow`s highs by a few degrees counting on a day not nearly as nice as today, temperature-wise. && .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/... The main precip event impacts central PA Sun night into early Mon as low moves through. QPF looks to be around 0.50 inch. Above average temperatures (especially nighttime) appear very likely through early next week, as GEFS indicates PA remains beneath a mean upper level ridge and plume of anomalous PWATs. The chance of showers again spikes with passage of next shortwave Tuesday into Wednesday and another one to start the weekend. U.S. 25/00Z and 06Z GFS and GEFS differs drastically with the 25/00Z EC and its ensembles during the second half of the week, as the EC guidance is dominated by stronger southern stream troughs and associated northward advection of warmer air and higher 500 mb heights. In contrast, the GFS and its ensemble mean appears to maintain a several decameter deeper and more persistent upper low over nrn New England and the Canadian Maritimes, while also latching onto a piece of northern stream energy that breaks away from a potent upper low that will be digging SE across the Four Corners area Tuesday, before heading east across the High Plains of E New Mexico and West Texas later Wednesday and Wed evening. The presence of this aforementioned northern stream short wave has big implications for maintaining/reinforcing colder NW flow aloft across southern Canada and the NE U.S., while shearing its initially potent southern stream "parent" low harmlessly east (for us here in Central PA) across the Carolinas. Considering the several-run persistence in the GFS, along with the amount of snow cover across intact parts of the nrn Mid Atlantic and New England States, (not to mention the persistence of cold air there and points north across Ont and Quebec), I slightly favor the GFS/GEFS solution at this point in time with a more extended period of drier and cooler conditions for Wed- Sat. The northern edge of the precip shield associated with the shearing srn stream wave and mdtly strong forcing via the R.E. region of a 100-120 kt upper jet across the Lower Great Lakes and Mid Atlantic region may support a period of cold rain...mix...or even a light accumulation of snow across the southern half of PA late in the week. The "Less likely" EC solution (at this point) would help to develop a stronger upper ridge across the eastern U.S. for the second half of the week with the upper low lifting NNE to the upper midwest by 00Z Sat with warmer air at the surface and aloft surging northward through the Ohio River Valley and Appalachians. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... Frontal boundary over northern PA will be pushed southward through the airspace toward the PA/MD line by 25/00z as strong high pressure builds over eastern Canada. Increasing low level moisture and wind shift to the east-northeast should translate into a lower trend in ceilings and visibility from north to south with widespread MVFR to IFR restrictions likely by tonight, lasting into Sunday. Scattered light rain showers will be possible today especially near the southward-moving frontal zone with pockets of fog/drizzle overnight into early Sunday morning. The front should lift back to the north on Sunday which should allow for at least some marginal improvement especially over portions of the southern airspace. Outlook... Sun...VFR-MVFR western 1/4 with low risk for thunderstorm in the evening. MVFR-IFR central and east with drizzle/fog. Mon-Tue...Sub-VFR with periods of rain. Wed-Thu...Becoming VFR. No sig wx. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...La Corte NEAR TERM...La Corte SHORT TERM...La Corte LONG TERM...Lambert/RXR AVIATION...La Corte is the U.S. government's official web portal to all federal, state and local government web resources and services.