Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 212003 AFDCTP Area Forecast Discussion National Weather Service State College PA 303 PM EST Sat Jan 21 2017 .SYNOPSIS... Unseasonably mild weather will continue through the weekend. A complex and dynamic storm system will bring the potential for heavy rain, accumulating snow and strong winds to portions of Central PA on Monday. The mild conditions will last into the middle of next week before a pattern change brings colder air and more seasonable temperatures to close out the month. && .NEAR TERM /THROUGH TONIGHT/... Dense fog has largely dissipated but still plenty of low clouds and 1-3SM visibility in the central and southeast valleys. Have adjusted max T down a few degrees in these areas which will not see the sun today. On the flip side, a spring-like day can be found along and west of the Allegheny Front with 55-65 degree readings over the western 1/3 of PA. Even a few cu noted on the vis sat now being overrun by increasing high clouds from the SW. Latest thinking is that low clouds and fog will expand/redevelop tonight into Sunday morning particularly from the central ridge and valley region into the Susq. valley. Later shifts may need to issue another dense fog advisory. Otherwise, cloudy and unseasonably mild overnight with minimum temperatures +20-30 degrees above normal for late January. There could be some pockets of light rain/drizzle but generally kept POPs below 20 percent. Rainfall associated with surface low tracking northeast from GA/AL is fcst by the models to stay southeast of the area. && .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/... Closed mid-level low tracks from the ARKLATEX to western VA/NC by 23/12z. Moisture and inflow will increase ahead of the mid- level system and should support rainfall pivoting northward into southern areas by the end of the period. Model QPFs indicate the main rain axis stays to the south of the PA/MD line although placement highly anomalous easterly flow of high PW air into e-w frontal zone has me a bit concerned. One thing of note is an increase in winds over the Lower Susq. valley with gusts over 40 mph possible by daybreak Monday. Temperatures stay very mild and well-above normal for this time of year. && .LONG TERM /MONDAY THROUGH SATURDAY/... The lustiest GFS/ECMWF as well as the EC ensemble are in pretty good agreement in tracking a surface low east through the Carolinas-southern Virginia before redeveloping it off the Delmarva and tracking it offshore Monday and Tuesday. We start off very warm so it`s still uncertain if or how much snow will fall. The period of most intense ascent/dynamic cooling looks to be Monday morning into the early afternoon. The GFS/ECMWF/GEFS all show very marginal cold air being generated at the peak of the storm. At this stage it looks like it will be a very elevation dependent precip type, which the EC ensemble agrees with, painting something along the lines of 2-4 inches of snow from the Laurels up into the northern mountain. The ECENS is notoriously generous with snow amounts, but I like the portrayal of my higher elevation areas. The GEFS plumes show BFD with the most snowy members, with mostly rain even down into JST. So it all points to a highly uncertain forecast. Another consideration will be the potential for heavy rain. The GEFS develops a strong ESE low level jet of about 50-60kt at 850mb. In the ensemble that figures to be a widespread 5-6 sigma easterly anomaly. The ensemble shows a high likelihood of at least an inch of rain in 24 hours between Sunday night and Monday night, with other features pointing to the Monday morning into afternoon timeframe. RFC guidance suggests rain amounts of around 2 - 2.5 inches in 6 hours will start to cause flooding problems, so as the event nears we will have another thing to focus on. After our early week storm system, the eastern ridge is made to make a rapid rebound, even if for just a short time around midweek. A fast moving shortwave quickly chews the top off the ridge with cyclonic westerly flow by week`s end. Colder air looks to advect into the region bringing in more winter like temperatures late next week. && .AVIATION /20Z SATURDAY THROUGH THURSDAY/... VFR over the western 1/3 this aftn and eve should trend toward MVFR tonight with IFR possible at KBFD. Vis satellite and obs trends indicate some improvement in cigs/vis over the central and eastern TAFs. However, expect widespread IFR-LIFR conditions to continue/redevelop overnight with local cigs/vis AOB airfield mins into Sunday morning. Outlook... Sun...MVFR/IFR. Rain spreads south-north into Sunday night. Mon...Rain/low CIGs likely. Tue...AM rain/snow and low CIGs possible. Wed...Reduced CIGs/showers possible NW. Thu...MVFR/IFR in rain/snow showers mainly west. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Steinbugl NEAR TERM...Steinbugl SHORT TERM...Steinbugl LONG TERM...La Corte AVIATION...Steinbugl is the U.S. government's official web portal to all federal, state and local government web resources and services.