Area Forecast Discussion
Issued by NWS State College, PA

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679 FXUS61 KCTP 272118 AFDCTP Area Forecast Discussion National Weather Service State College PA 518 PM EDT WED JUL 27 2016 .SYNOPSIS... A weak trough to our north and the subtropical ridge to our south have setup a frontal boundary just to our south. This boundary will move northward as a shortwave moves over the ridge Thursday night. This should produce some rain Thursday into Friday. Behind this system system slightly cooler air aloft moves over the region. But the ridge may begin to build to our west again early next week. && .NEAR TERM /UNTIL 10 PM THIS EVENING/... Stayed close to guidance values nudging forecast with blend and HRRR. Cooler to the north with open cell cumulus in northern Pennsylvania. Warmer and more humid to south with some clouds moving over the northern edge of the low-level frontal boundary to our south. The HRRRV2 shows little or no QPF with a few spotty rogue elements and the HRRRV1 is tad more active. So kept slight chance showers in extreme southwest. Lower than hydrostatic model blend PoPs which were in the 20-30 percent range. Any showers would be really isolated and weak. Have no QPF. Central and northern along with eastern areas will be partly cloudy though the cumulus will dissipate close to sunset. Higher clouds in westerly flow aloft will persist. Most areas on south-southeast will likely top 90 again today. Many locations are close or have already done so. && .SHORT TERM /10 PM THIS EVENING THROUGH 6 PM THURSDAY/... Guidance implies areas of patchy fog overnight. Better chance in western areas. Clouds slowly increase southwest to northeast overnight. Overnight lows mainly near 60 in northwest to lower 70s southeast. Tomorrow clouds increase in southern and central areas. Increased moisture will produce haze. Best chance rain in southwestern areas. The HRRRV2 keeps the rain out of our area through 0300 UTC tonight and implies it is well to our west back over KY. Tweaked grids with new 12Z blends which had slight chance PoPs overnight in southwest increasing to chance in the morning. Chance of rain will increase southwest to northeast during the day. But most guidance continues to imply most of northern PA should be rain free most of the day. Best chance in south and southwest. Higher PoPs are likely in the next period. && .LONG TERM /THURSDAY 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 /21Z WEDNESDAY THROUGH MONDAY/... VFR conditions will prevail into early tonight. Patchy fog will develop in the valleys and elevated valleys of central PA. Expect areas of MVFR and IFR to develop near or shortly after midnight. Fog will lift early Thursday. Rain and an isolated thunderstorm could move into southwestern areas Thursday morning and afternoon. This would produce areas of MVFR and perhaps IFR conditions in heavier showers. More MVFR and IFR conditions possible overnight Thursday into Friday morning with the potential for rain/thunderstorms and patchy fog. Conditions should improve Friday into Saturday. OUTLOOK... THU-FRI...areas MVFR and IFR in Rain/TSTMS and patchy fog SAT-SUN...Mainly VFR. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Grumm NEAR TERM...Grumm SHORT TERM...Grumm LONG TERM...Lambert/Gartner AVIATION...Grumm/Jung is the U.S. government's official web portal to all federal, state and local government web resources and services.