Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 280250 AFDCTP Area Forecast Discussion National Weather Service State College PA 1050 PM EDT Thu Jul 27 2017 .SYNOPSIS... A slow moving low pressure system, located over southeast Missouri this evening, will strengthen as is tracks south of Pennsylvania late Friday and Saturday. Behind this system, high pressure over Great Lakes will slowly build into the region into early next week. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... 0230Z radar loop showing just a few isolated showers/storms forming ahead of shortwave tracking through central Pa this evening. SPC mesoanalysis indicates some decent MLCAPES of around 1000 J/KG across the Lower Susq Valley, where we will place the highest POPs of a shower or storm through about 06Z. Elsewhere, radar trends and cooling/stabilizing boundary layer suggest little chance of rain this evening. Large scale subsidence indicated after 06Z in wake of shortwave. Only mention of precip late tonight will be in vicinity of quasi-stationary boundary along the Maryland border. Near term models support a 20-30 pct chance of showers after midnight across that part of the state. Given low dewpoint depressions, partly cloudy skies and a calm wind late this evening, expect some fog development. However, setup for significant fog formation is not ideal with an increasing gradient between low over the Ohio Valley and high over the Grt Lks likely resulting in a northeasterly breeze late tonight. A blend of latest model guidance supports min temps tonight from near 60F across the northern mountains, to near 70F over the Lower Susq Valley. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... Did cut back POPS some early Friday. Models still show several sfc lows and QPF max with each. Behind this, a digging upper level low to follow and result in deepening. Not clear how all this will phase and how much rain will fall. For now went with a flash flood watch southern PA starting at 18Z. Some plumes very wet. Key will be how convection over the plains this afternoon comes into play. Models been showing several sfc lows and the upper lvl low digging for several days now, thus after touching base, went with a flash flood watch. Watch extends out to 18Z Saturday, later shift can push it further out in time and space. Did not go as far north as Lycoming County, very wet there, but QPF is fcst to be lower. Still have to watch how the moisture is advected up the mid Susquehanna Valley, the mountain range to the south of IPT often has a large influence on things. Only adjusted max temperature a little on Friday. Later starting time of the heavy rain may allow high temperatures to be not that cold. Main concern would be on Saturday. More info. below. Max temps Friday and Saturday will almost certainly be several Deg or more lower than most MOS guidance given the widespread light to moderate rain and a trajectory of the anomalously strong llvl wind from the New England Coast in contrast to the Mid Atl Coast. && .LONG TERM /SATURDAY THROUGH THURSDAY/... Weather highlights are front-end loaded this period with rare (unusually strong for late July) rainstorm continuing to impact southern portions of the area on Saturday. Model and ensemble guidance shows an anomalously strong minus 3.5-4.0 sigma below normal closed 500mb low over the southern Mid Atlantic by the weekend. Organized heavy rainfall is expected along and north of its associated surface wave which is projected to consolidate and gradually amplify as it tracks east- northeast along frontal zone from the OH Valley across northern VA/D.C. into the Delmarva Friday night-Saturday morning before shearing and weakening off the coast Saturday-Sunday. A secondary low is fcst to develop and lift north off the Mid Atlantic coast Mon- Tue but at this time does not look to impact the wx here in central PA. Steadier rains early Saturday across the southern tier counties should generally taper off from northwest to southeast later Saturday into Saturday night. High pressure and accompanying push of abnormally dry/below normal PW air will work into the area by Sunday with dry and pleasant wx continuing early next week. A stray shower to T`storm is possible Tue-Wed as warmer temperatures and higher dewpoints return to the area. NAEFS and ECENS favor a continuation of the western ridge/eastern trough pattern which should allow for one or more weakening cold front to push southeast from the Great Lakes later next week. Temperatures will start off well below average on Saturday with fcst departures on the order of -10 to -15 degrees. Following the unseasonably cool start, a gradual warming trend is expected with max/min temperatures returning to seasonal normals heading into August. && .AVIATION /03Z FRIDAY THROUGH TUESDAY/...
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Isold heavy showers will continue through midnight. Clearing skies and light winds will again lead to areas of fog, some of it locally dense overnight and into Friday morning. Widespread showers and storms with heavy rain expected later Friday into Sat. .OUTLOOK... Friday night-Sat morning...Scattered SHRA north. Widespread showers and heavier SHRA/TSRA across the southern airfields. Saturday afternoon...improving conds from west to east through the evening. Sun...Areas of fog and low cigs Sunday morning. Mon-Tue...No sig wx.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch from Friday afternoon through Saturday afternoon for PAZ024>028-033>036-056-057-059-063>066. && $$ SYNOPSIS...Fitzgerald NEAR TERM...Fitzgerald SHORT TERM...Lambert/Martin LONG TERM...Steinbugl AVIATION...Gartner/Martin is the U.S. government's official web portal to all federal, state and local government web resources and services.