Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 271052 AFDCTP Area Forecast Discussion National Weather Service State College PA 652 AM EDT WED JUL 27 2016 .SYNOPSIS... A weak front will remain just south of the Commonwealth through tonight, as high pressure maintains warm and mainly dry conditions. An area of low pressure approaching from the west is likely to lift through the region on Friday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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H5 shear axis over wrn and central PA continues to work on deep layer moisture pooling along and south of the Mason Dixon line to produce isolated showers. Trailing shortwave now maintaining a area of sprinkles/light rain showers which will brush parts of the Laurels and South Central Mountians through 14-15z. Will maintain slight chc mentions through that timeframe across the southern tier. Across central and northern sections...drier air mass in place will prevent any showers...but clouds will skirt the west central and central mountains for much of the early to mid morning hours. Far northern areas will remain mostly clear. Richest deep layer moisture will remain pooled along and south of the Maxon Dixon line through tonight. Clouds will be most prevalent across the south, closest to the front and once again, a stray afternoon/evening shower or thunderstorm cannot be ruled out right along the border. Highs will be a few ticks higher than Tue across the north and generally unchanged south...and will range from the mid 80s north to the lower 90s southeast.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... More of the same tonight as deep layer moisture remains pooled south of the commonwealth. Slight chc pops will be confined to portions of the southern tier...with decreasing clouds occurring as one goes north. Mins will range from the upper 50s northwest to the lower 70s southeast. Moisture will slowly work northward throughout Thursday as a front approaches the region from the Ohio Valley and eastern Glaks. Most areas will remain dry for most of the day...but increasing pops to sct coverage in the afternoon and evening for most as PW approach 1.5" into the west central and central mountains...and up to 1.8" over the southern tier. Maxes will range from the lower 80s north to the lower 90s south. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... In the medium to long-range period...conditions slowly revert to near normal in temp and precip as several chunks of short wave energy in the westerly flow aloft helps to carve out a mean 500 mb trough axis over the Glakes and Ohio Valley region during the Thu-Fri timeframe. The peak in unsettled weather (with perhaps some periods of down- right rainy conditions) occurs Thursday night and Friday as a well-defined wave of sfc-850 mb low pressure lifts ENE out of the Ohio Valley and heads across the I-95 Megalopolis. Followed a blend of EC/GEFS/superblend and NBM guidance for that particular 24-36 hour period to arrive at likely pops for rain and scattered TSRA. Some uncertainty in timing and areal coverage of the convection led us to undercut the NBM by 10-20 percent for now, recognizing issues with large scale model convective parameterization schemes (and subsequent exaggeration of the areal coverage and broader qpf amounts) means that we`ll likely see more concentrated areas/bands of heavy convection, compared to the model depicted, larger cold season stratiform look to the precip shield. Portions of Southern and Central PA...close to the track of the 1006-1008 mb sfc low will likely see some localized heavy 1-2 inch,12-24 hour rainfl amounts by Friday afternoon...with even the potential for some pinpoint heavier amounts from embedded TSRA, as a tongue of 2 inch pwat air lifts north and wraps cyclonically into sern PA and the Lower Susq Valley. For later Friday through the upcoming weekend, a large area of high pressure (1020-1024 mb) near the border of southern Quebec and Ontario will try to push drier air south into the Mid Atlantic Region. Another...apparently weaker wave of low pressure at the sfc and aloft lifts NE out of the Ohio Valley over the weekend and brings an enhanced chc for showers. Slight diffs in timing/location exist between the EC/GEFS and NBM guidance. However...the target period for the best chc of showers and isolated to sctd TSRA appears to be late Sat into Sunday. Afterward, heights begin to rise from the southwest, accompanied by a ridge of surface high pressure building east into PA with mainly dry conditions and a rebound in temps for early next week. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... Broad, weak high pressure has a little weakness along the MD border and VFR clouds there are creating a few sprinkles up to about the Turnpike. Have added VCSH to JST, MDT and LNS for the next couple of hours. In general, it will remain VFR all day. But there is just the slightest chance of a reduction in visibility due to --RA. It is not worth mentioning. BFD, UNV, IPT will be dry. No hints of fog at 09z, so have removed all but the hint of it from this morning. Heating and a creep northward of the stationary front could allow stray convection in the far S later today. A PROB30 may even be too much. Wind will continue to be calm or just light and variable. High clouds do expand northeast later tonight. But, again, should not yield any reductions in vis/cig. Mainly zonal flow with just a slight troffiness to it over the OH Valley then sets up. Moisture gets thicker for the latter half of the week and remains so through the weekend. Daily heating should result in sct SHRA/TSRA each afternoon. OUTLOOK... THU-SUN...Mainly VFR. SCT PM SHRA/TSRA. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...DeVoir NEAR TERM...DeVoir SHORT TERM...DeVoir LONG TERM...Lambert/Gartner AVIATION...Dangelo

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