Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 291001 AFDCTP Area Forecast Discussion National Weather Service State College PA 601 AM EDT Wed Mar 29 2017 .SYNOPSIS... 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, with scattered valley rain and mountain snow showers possible. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Cooler and drier air mass filtering southward over central PA early this morning. Low clouds persist across most of central PA...but early morning IR imagery shows breaks evolving and back edge settling southward through the Fingerlakes region. After a cloudy start...expect to see sun breaks increase as the early morning progresses. Building sfc high pressure will eventually bring a mix of sun and clouds across northern areas, and a bright sunny day over southern areas by mid to late morning. Highs in the 40s and 50s will be near to slightly above normal. It will be breezy out of the north between 10 and 20 mph. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... Fair and cool conditions will continue tonight and Thursday... as strong surface ridge axis remains nosed and anchored across central PA tonight and Thursday. 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. && .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 /10Z WEDNESDAY THROUGH SUNDAY/... MVFR/IFR ceilings will persist across the western 3/4 of the airspace into the mid-late morning. The far southeast 1/4 including KMDT/KLNS should stay low VFR with bases 4-5kft AGL. All guidance is in agreement with high confidence in improving conditions/return to VFR this afternoon. VFR will continue tonight with increasing high level clouds/cigs AOA 15kft AGL. Outlook... Thu: VFR/No sig wx. Chance of rain NW 1/2 late. Thu Night-Fri: MVFR/IFR. Rain. Sat: Sub-VFR restrictions early; then gradually improving conditions into Sat night. Sun: VFR/No sig wx. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...DeVoir NEAR TERM...Grumm/DeVoir SHORT TERM...Grumm/DeVoir LONG TERM...Lambert/Gartner AVIATION...Steinbugl is the U.S. government's official web portal to all federal, state and local government web resources and services.