Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 291531 AFDCTP Area Forecast Discussion National Weather Service State College PA 1131 AM EDT Wed Mar 29 2017 .SYNOPSIS...
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Cooler and drier air will overspread Pennsylvania today and Thursday as high pressure builds southward from southern Canada. A new storm system will approach the region on Thursday, bringing showery conditions Thursday night through Saturday. Cooler and unsettled conditions will last into Sunday.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Sky has cleared out over most of the area, with only a patch of high-MVFR clouds in the NE. These should dissipate for the most part as they try to drift to the S, but will remain over the nrn tier for the rest of the day thanks to cool air aloft. Wind a little gusty right now in the north and east with mixing, and the wind should also pick up a little in the SW but not as much as the other areas. Have bumped temps up a little in the south with N/downslope wind in the lower Susq Valley and sunshine in the srn mountains. Expect some higher clouds to spread in from the west through the night. But, temps will still drop into the 25-35F range as the wind slackens in most places to less than 5 MPH.
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&& .SHORT TERM /THURSDAY/...
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Fair and cool conditions will continue Thursday as strong surface ridge axis remains nosed in from the north. Clouds will increase by late Thu morning and Thu afternoon from west to east (respectively) as the sfc ridge axis moves offshore and return flow arrives. Late day showers are expected to develop west of the Alleghenies and may reach the central mountains by nightfall...which will be the start of another lengthy stretch of gloomy and showery conditions set to last through most of the weekend. Mins tonight will be much chillier than recent nights..ranging from the upper 20s north to the mid 30s south. Highs on Thursday will be a few degrees cooler than Wednesday thanks to decreased mixing and increasing cloud cover in the morning and afternoon hours especially...and will range from the mid 40s north to the lower 50s south.
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&& .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... GFS/EC and their respective ensembles are in good agreement with the onset timing of warm frontal rain that streaks quickly east from the Ohio Valley by Thursday evening. Evaporational/dynamic cooling of the airmass *may* help 925-850 mb temps dip to near 0C across our NE counties Thursday night and Friday as the steadier light- mdtly heavy, Warm Advection rain begins there. 00z cycle has warmed boundary layer from earlier solutions...and have included only isolated mentions of rain/sleet mix to the North and East of a KIPT and KSEG line. There`s a low prob for a light coating of snow on the high terrain across Sullivan County...and have a few tenths of an inch of snow accumulation forecast there. Model consensus is also for a quasi Miller-B type of low track heading just north of the Ohio River during the day Friday, then a pressure jump and slight intensification of the sfc low (to 996 mb) off the southern NJ and New England Coast Saturday. Under normally colder winter-time circumstances, this low track would be pretty favorable for a significant snowfall across much of central and northern PA. However, a quite warm boundary layer (and 850 mb temps) to begin with, coupled with the lack of a stronger anchoring high over southeast Canada and New England will mean a widespread/soaking rain evening with 24-36 hour rainfall at the majority of places here in Central PA coming in between 0.75-1.00 inch. This rainfall will add a healthy spike to the flow and levels on smaller streams and creeks across the region with broader mdt rises on rivers, but no significant threat for flooding as headwater flash flood guidance is averaging 2-2.5 inches for a 12 and 24 hour period respectively. Periods of light rain, drizzle, and ridge shrouding dense fog will persist Friday night into Saturday as slightly colder air wraps around behind the storm. Some breaks in the cloud cover should occur Saturday afternoon, esp across the Lower Susq Valley where drying downslope flow will be enhanced. Forecast temps Friday may be a bit warm considering the aforementioned storm track just to our south, and amount of rain expected. Max temps Saturday will near to a few deg F above normal in many locations. High pressure building over the region (coupled with the offsetting effect of abundant sunshine and GEFS mean 850 mb temps cooling by 3-4 deg C imply max temps close to what we`ll see Saturday, which is upper 40s to lower 50s across the nrn mtns...and mid to upper 50s elsewhere. Dry and slightly milder conditions are in the forecast for Monday as the ridge of high pressure slides just to our east and ens mean 850 mb temps rebound by a few to svrl deg C (atop a light serly sfc flow). The next, rather potent and moisture laden southern stream wave heads our way for Mon night and Tuesday, bringing a likelihood of a widespread rain. && .AVIATION /15Z WEDNESDAY THROUGH SUNDAY/...
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MVFR ceilings left over the NE, but these should both break up and rise to VFR bases. VFR conditions will continue tonight most of Thursday with increasing high-to-mid level clouds/cigs AOA 10kft AGL. Some sprinkles are possible before 00Z Fri in the west. But, the storm approaching from the WSW should not produce any widespread showers or lowered cigs/vis before then. Outlook... Thu Night-Fri: MVFR/IFR. Occasional rain/showers. Sat: Sub-VFR restrictions early; then gradually improving conditions into Sat night. Sun: VFR/No sig wx.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Dangelo NEAR TERM...Dangelo SHORT TERM...Grumm/Dangelo/DeVoir LONG TERM...Lambert/Gartner AVIATION...Dangelo/Steinbugl

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