Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 281713 AFDCTP Area Forecast Discussion National Weather Service State College PA 113 PM EDT THU JUL 28 2016 .SYNOPSIS... The stalled surface front over the Mason Dixon line will move northward today and tonight as a disturbance approaches from the Ohio and mid Tennessee River Valleys. This will produce a soaking rain over portions of central and south central PA tonight into Friday morning. Behind this system slightly cooler air aloft moves over the region to usher in the weekend. But the ridge may begin to build to our west again early next week. && .NEAR TERM /UNTIL 11 PM THIS EVENING/...
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Updated all grids again. Difficulty making gridded temperatures. Nearly all guidance cannot handle the slow rise in temperatures and the depth of the mid clouds blocking the sun. Pretty hard to correctly produce meaningful grids. Better where the HRRR has rain in southwest. But HRRR had really high temperatures today. Not going to happen. Now convection has broken out in the southeast along with the remnant MCS from Ohio now tracking across southwestern Pennsylvania. The more intense convective cores have stayed south of the Mason-Dixon line. But rain in Somerset county and west will move east-northeast across south-central Pennsylvania this afternoon and evening. Expect more showers to develop in southern PA in the warmer air and closer to the boundary. Each HRRR run has different scenarios with evolution and the GFS has the heavy rain axis relatively deep into the cooler air. Lots of uncertainty but from this afternoon on any lumbering convective core has the potential to produce locally heavy rainfall cannot rule out 1-2 inches in 1 hour later this afternoon and into this evening. Our grids show the blended QPF with the 15Z HRRRV1 QPF overlaidfor some convective texture. Our QPF is higher in southern/southeastern PA with HRRR based isolated maximum in western Schuylkill county. The GFS still is wetter well north of the CAMS.
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The rain with embedded heavy showers and storms will continue to over take the region. We kept lowest PoPs and QPF in northwest. Best chance of rain is clearly south and southeast. The GFS rainfall is quite impressive but likely too far north and west based on the CAMS. Things should wind down overnight and early AM. Not as hot Friday and the threat of heavy rain drops off fast in AM and the PoPs will lower as the day goes on.
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&& .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... 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 rainfall 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 /18Z THURSDAY THROUGH TUESDAY/... 12Z TAFS sent. Minor updates for showers and rain coming into southwestern areas. Earlier discussion below. Main change was to back off on fog, given slight breeze in some spots, and dewpoints not that high. Isolated showers still across the far south. Clouds will be on the increase today. Most of the day still looks dry with VFR conditions. Showers and storms will overspread the area from south to north late today into early Friday. MVFR and IFR conditions will develop overnight. Some improvement on Friday, as weak low moves east of the area. OUTLOOK... FRI...Some restrictions in SHRA/TSRA and patchy fog...mainly early. SAT-MON...Wide range of conditions expected with a chance of showers and storms. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...DeVoir NEAR TERM...Grumm SHORT TERM...Grumm LONG TERM...Lambert/Gartner AVIATION...Grumm is the U.S. government's official web portal to all federal, state and local government web resources and services.