Area Forecast Discussion
Issued by NWS State College, PA

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991 FXUS61 KCTP 211817 AFDCTP Area Forecast Discussion National Weather Service State College PA 217 PM EDT Fri Apr 21 2017 .SYNOPSIS... A frontal system will move south of the Commonwealth through this evening and stall south of state during the weekend. An upper level trof will form over the Tennessee Valley late this weekend, and could end up bringing a storm up the East Coast in the first part of next week. && .NEAR TERM /UNTIL 8 PM THIS EVENING/... Cold front bisecting the state this afternoon extends from Mansfield southwest to Johnstown is making it ever so slowly eastward. Warm/stationary front drops from Mansfield south to Harrisburg, with cold and cloudy conditions persisting to the east of this boundary. Only isolated showers are occurring with the front and within the warm sector. && .SHORT TERM /8 PM THIS EVENING THROUGH 6 PM SATURDAY/... Skies may clear out for a very short time this evening, but clouds will likely close back in with NW flow and a digging trough moving across the lower Grrrreat Lakes. 00Z NAM does make a push for light rain/showers late tonight and in the first half of Saturday. Will make POPs just CHCs for the south, as GFS is certain that the precip will stay well to our south with EC also less-bullish on precip north of the Mason-Dixon. Mins tonight will be mild again, but highs on Saturday will be about 5 degs below normals with a decent amount of clouds moving across from the south and sub-freezing 8H temps in the northlands. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... With a cut off low progged to form over the Mid-MS and TN Valleys this weekend, it is very difficult to be certain in many facets of forecast. The differences in model solutions show up even before the long term starts - as the NAM is farther to the north with precip than all other models. While this is usually cause to discount that one outlier, the close time horizon makes me think we should give it some creedence. In general, the flat flow aloft in place before the low gets to our longitude should keep most of the precip to our south. Then, the changes from the last forecast cycle get quite substantial. The low creeps northward as it swings to the east of GA and keeps just off the coast early in the week and may precip in off the ocean a`la a Nor`easter. However, this storm does not deepen, nor slow without a big high to the north. A frontal boundary should remain to our north/west for much of the week, but may creep close enough to make showers/storms. Warm air then seems to establish itself once again pushing temps near/above 80 late in the week. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... Cold front bisecting the airspace this afternoon extends from Mansfield southwest to Johnstown/KJST is making it ever so slowly eastward. Warm/stationary front drops from Mansfield south to Harrisburg/KMDT, with MVFR/IFR cigs persisting to the east of this boundary. Quick improved to VFR occurs behind the cold front with a noticeable wind shift to nw. Slow improvement is expcted over eastern PA this evening as cold front passes. Lower cigs will move back into NW mtns later this eve with colder air moving downwind of the lakes. Outlook... Sat...AM low CIGs possible at BFD. Sun...No sig wx expected. Mon...Rain/low CIGs possible southern Pa. Tue...Rain/low CIGs possible. Wed...Improving conds. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Dangelo/Gartner NEAR TERM...Gartner SHORT TERM...Dangelo/Gartner LONG TERM...Dangelo AVIATION...Fitzgerald/Gartner is the U.S. government's official web portal to all federal, state and local government web resources and services.