Area Forecast Discussion
Issued by NWS State College, PA

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982 FXUS61 KCTP 291919 AFDCTP Area Forecast Discussion National Weather Service State College PA 319 PM EDT WED JUN 29 2016 .SYNOPSIS... High pressure over the western great lakes region this afternoon will drift east and bring generally dry weather with comfortable humidity into early friday. A few, isolated showers and thunderstorms are possible across the Susquehanna Valley and South-Central part of the state late Thursday afternoon and evening. A cold front will move east across the state Friday afternoon and evening, bringing scattered showers and thunderstorms. Another area of high pressure will move in for Saturday with mainly clear, dry conditions and low humidity. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... Strong cold advection focused near the 925mb level helped to strengthen the subsidence inversion and trap/maintain a shield of bkn-ovc stratocu across much of the region outside of the mid/lower Susq Valley. Skies in those areas were mainly sct...but as the colder air aloft spreads across that region through the rest of the afternoon/early evening hours, expect periods of bkn high based strato cu invof kthv and kmdt too. Max temps in most places will occur between 21-23z as the strato deck dissolves, and the coldest air in the upper blyr drifts south toward the mason/dixon line. A transition to mainly clear skies and light wind will occur from 00z through 06z Thursday as the center of high pressure moves across the Ohio River Valley and into western PA. Areas of Valley Fog are likely during the early to mid morning hours as a result of strong radiational cooling and the air/water temp diff expands to exceed 20F in the typically colder central and nrn PA mtn/river valleys. Min temps will range from the unseasonably very chilly lower 40s across the NW the mid 50s and lower 60s in most other locations. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/... Thursday remains somewhat of an interesting forecast, with the potential for a very minor short wave trough lifting NE from the Ohio Valley and Central Appalachians and dampening out a bit while moving across southern and eastern PA and during the daytime hours. The airmass will be pretty dry, and there will be just a few triggers for isolated/weak convection across the south (especially on the ridge tops) where dewpoints will be closer to 60F. Maxes will warm significantly in most places compared to the cool temps of Wed...especially across the nrn and western mtns. highs will be in the upper 70s to lower 80s. However...the Laurel Highlands may hold in the mid 70s. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... A vorticity lobe rotating around the south-side of a closed mid level low over James Bay will send a cold front from the Great Lakes through the Mid Atlantic and Northeast states on Friday. Model QPF continues to point toward spotty light to moderate rain amounts with local maxes from upstate NY southward along the Mid Atlantic piedmont. The best combination of low level moisture (60+F surface dewpoints) and marginal instability will be located over the eastern 1/2 to 1/3 of the area including the middle and Lower Susquehanna Valley. The severe T-storm outlook from SPC indicates severe storm potential is very low at this time. The front shifts off the coast Friday night with high pressure and abnormally dry airmass moving into central PA for the weekend. What appeared to be a fairly predictable/confident forecast in dry weather lasting through the 4th of July has begun to degrade with recent deterministic model runs showing increasing differences in shortwave details from the Central U.S. into southeastern Canada. More specifically, the 29/12z GFS and CMC show a northward trend or shift in the stationary boundary located along/north of the I-70 corridor with pcpn arriving in western PA around the time fireworks are getting underway. The 29/00z ECMWF keeps the boundary and bulk of associated pcpn further south of the Mason Dixon line along the I-64 corridor. Given the increasing model differences, will utilize a blend of the latest guidance with the previous forecast which increases POPs a bit over the southern counties around Mon-Tue but still keeps continuity for a mainly dry and seasonable Holiday weekend. && .AVIATION /19Z WEDNESDAY THROUGH MONDAY/... The mvfr to low end vfr cloud deck will persist through the late afternoon...before quickly dissipating early this evening as high pressure builds in from the west. NW winds of 7-11 kts will contain some minor gusts into the mid teens. be gusty in the upper teens to around 20 kts this afternoon...especially across the Susq Valley where more sun and a greater depth of vertical mixing will occur. The next chc for showers and storms will be late Thursday afternoon and Thursday Night across the south and east. Maybe across the entire area on a cold front approaches from the west. OUTLOOK... Fri...Isold tsra impacts possible. Sat and Sun...No sig wx expected. Mon...a slight increase in humidity for Monday with a low chance of showers and thunderstorms across the south. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert NEAR TERM...Lambert SHORT TERM...Lambert LONG TERM...Steinbugl AVIATION...Lambert is the U.S. government's official web portal to all federal, state and local government web resources and services.