Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 190949 AFDCTP Area Forecast Discussion National Weather Service State College PA 549 AM EDT Wed Jul 19 2017 .SYNOPSIS... Pennsylvania will be on the northern periphery of a subtropical high passing over southern states the rest of the week. A cold front will likely push through the region early next week, as the the upper ridge pushes off the east coast. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Early morning satellite loop showing fairly extensive valley fog across central Pa, which should burn off by 13Z-14Z based on latest HRRR and LAMP guidance. Upper level ridging and associated capping inversion should put a lid on convection across most of the forecast area today. However, a few updrafts will likely break through cap during max afternoon heating. Will keep POPs in the 15-25 pct range, with the highest chance over the elevated heating source of the Allegheny Mountains. Model soundings showing very weak shear, so any thunderstorms that form will be of the pulse variety, with little chance of organized severe weather. GEFS mean 850 temps of around 18C should support max temps a bit higher than Tuesday, ranging from the mid 80s across the Allegheny Mountains, to the low 90s across the Susq Valley. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... Any widely scattered, diurnally-driven convection should die around sunset. A dying cold front will work into northern Pa overnight, but almost no large scale forcing will be present as parent shortwave passes well north of the region. Therefore, expecting a rain free overnight, with patchy fog the main concern once again. Fog should be most prevalent across the western half of the state, where pressure gradient will be the weakest and SREF probs of reduced visibility are the greatest. Focus Thursday will be on the possibility of strong storms moving into the northwest late in the day ahead of shortwave traversing the Grt Lks. Increasing mid level winds and associated deep layer shear could support a threat of organized severe tstorms, with damaging wind gust the primary threat given relatively limited CAPE. 850 temps suggest Thursday`s max temps will be similar to today`s, ranging from the mid 80s to low 90s. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Medium range models generally agree that a continued/gradual weakening and east-southeast shift of the persistent central U.S. upper ridge can be expected with time, as shortwave troughing shifts slowly southeast out of the Canadian Prairie across the northeast quarter of the country by early next week. POPs fairly low Friday, when bulk of model data shows large scale subsidence over the region. Over the weekend, fast west-northwest flow aloft on the northern periphery of the upper ridge will reside over the area. The evolution of convection-producing waves within this belt of westerlies is depicted differently within various models and specifics, such as timing and location will depend on details not well resolved until the very short term time frame. Therefore the later periods will show a broad-brushed, redundant 40-60 percent POP given lack of confidence in highlighting any specific areas/timeframes with concentrated pcpn potential. The other concern is for a several-day period of hot/humid conditions punctuated across the Lower Susquehanna Valley with blended guidance showing 2-3 days of 90+F max temps with max heat index potential approaching 100F. The heat risk was added to the HWO yesterday. A heat advisory may be needed for at least 1 day based on NDFD max HI and WPC D3-7 HI probs. The hot temperatures should be eroded from the NW with time, as the frontal boundary gradually sinks to the south in response to mean troughing developing late in the period. Above average temperatures (+5-10 degree max T departures) should trend toward mid to late July climo numbers by next Mon-Tue. && .AVIATION /09Z WEDNESDAY THROUGH SUNDAY/... Latest radar shows the only remaining showers and storms in southern Franklin county. Many areas that received precipitation today will also see light winds, high dewpoints and mainly clear sky which should allow radiation fog to form once again tonight in the valleys. IFR restriction are expected. AOO, which saw rain, is already IFR. So periods of IFR is expected at MDT, LNS and UNV as well. Fog/low stratocu should begin to develop between 08Z to 12Z. Conditions should improve by late morning as winds mix out. A short-wave trough passing overhead at a favorable time Wed mid-day to aftn will likely create isold shra. So Wed will likely be a similar day to today except with even less coverage of shra/tsra. The flow does become a little more westerly then today, but wind remains light. Fog psbl again Wed night. .OUTLOOK... Thu...AM fog psbl...otherwise no sig wx. Fri-Sun...isold-sct tsra psbl - mainly pm. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Fitzgerald NEAR TERM...Fitzgerald SHORT TERM...Fitzgerald LONG TERM...Fitzgerald/Steinbugl AVIATION...Dangelo/Ceru

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