Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 300327 AFDCTP Area Forecast Discussion National Weather Service State College PA 1127 PM EDT Thu Sep 29 2016 .SYNOPSIS... Showery conditions will prevail overnight. Any flooding would be localized and minor with little in the way of impacts. Unsettled weather with occasional lighter rain showers will persist into the weekend with a gradual drying trend by early next week. && .NEAR TERM /UNTIL 8 AM FRIDAY MORNING/... Still a neat little box around 95 pct of central PA where no radar echoes exist. It is drizzly at may locations, but that stuff is too low (and the droplets too tiny for most 10cm radars) to pick up. A slight increase in radar echoes is starting to move in from the south and precip in DE also sliding just a little to the west of north. HRRR and RAP doing well with the first couple of hours in the past few runs, so higher than normal confidence exists that they will do well with the rest of the night. 00Z NAM arriving and continues to make heavier rain than other mdls. The placement of the heavier rain is mainly to the east of the Susq and is an area where generally less rainfall occurred. That area has also had a decent break of time since any real rain has occurred. Grid work with this update was mainly to dip the POPs to =<20pct in the north for the next few hrs. However, the guidance is big on developing the precip associated with a wave moving up the MidAtlantic coast. This area would then blossom as it enters eastern PA and make the heaviest rain in the east for a few hours either side of sunrise while lifting north. The northern mtns should then have their best shot at some rain during the daytime on Fri. Prev... Rainfall down to nil at the moment with central PA in the dry slot between a higher plume of moisture to the east and another to the west. Newest progs yield only light to what might be considered modest amounts of rainfall through sunrise. 18Z NAM seems like a high-end outlier on QPF amount - and only for a small area. Stream response has been very little if anything on the medium to larger streams. Even NAM amounts and placement will not cause widespread flooding problems. The ground and still-growing vegetation are gladly soaking it up. Have decided to chop the rest of the Flood Watch off. Have adjusted POPs in the very near term to account for the dry slot and GFS/HRRR/RAP evolution of the rain for the rest of the night. Prev... 2.5 to 3.5 inch amounts feel across southern tier overnight through midday...with higher amounts likely on the east facing slopes occurred across the southern tier. Flooding threat remains...albeit low...with upslope areas susceptible to any persistent upslope or training convective showers over the next 18 hours which could add another 1 to as much as 2 inches in some spots. Dry slot over western PA with high cloud covering eastern brought transition to low topped open cellular activity propagating from southeast to northwest today. Thus a more showery regime took over with times of little or no rainfall and other times with brief moderate to heavy rates accumulating a few tenths of an inch at time. Moderate PW transport along with some elevated instability will maintain a favorable environment for mdt-heavy rain/efficient rainfall processes through this evening, while increasingly diffluent flow aloft supports some training bands in addition to the trend to low topped open cellular character. In fact...training bands have organized over nrn VA/MD at mid afternoon and are moving into the Laurels and South Central Mountains...as anticipated earlier. Still expecting storm totals of 2-4" over the remaining flood watch area with locally 5"+ possible along the east-facing slopes and highest terrain. Very dry antecedent conditions resulting in 3-6hr FFG values of 4+ inches along with below normal stream flows should help to mitigate flooding to some extent, however if the higher end amounts are realized flooding impacts/runoff issues could become more serious. && .SHORT TERM /8 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/... The Large low will be quasi stationary and will continue to stream moisture into Southwestern PA through tomorrow. Strong E-SE LLJ and above normal PW along with associated forcing on east/southeast side of upper low favors scattered to numerous lighter rain showers through the period. The mid range models are keying in on a mid level short wave trough that forms to the east of the low and should increase rainfall rates and amounts through Central PA as it is coupled with the LLJ and the PWATS. && .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/... The upper level low will continue to spin slowly northward into MI and continue on into Southern Canada. The low will slowly be pulled into the upper level flow and cold air advection will filter into the region early into next week. The final vestiges of the low that has dominated our weather pattern this week will finally lift and move off coast by mid next week by the upstream amplifying trough over the central CONUS. High pressure should regain control of the large scale pattern. The 12Z GFS comes more into alignment with the EC however the EC continues the path of the TC Matthew much slower and keeps it off the coast of Florida, where the GFS brings the projected path up the Atlantic coast and has the system nearing the NC coast by Thursday morning. Temperatures will be slightly below normal through the weekend, before shifting to slightly above normal by the middle of next week. && .AVIATION /04Z FRIDAY THROUGH TUESDAY/... Minor changes made to 03Z TAFS. Low clouds and areas of light rain, drizzle, and fog will linger across the area, given strong easterly flow of moisture off the ocean. MVFR to LIFR conditions will prevail into at least Friday. Again, not much change expected overnight or on Friday. Outlook... Sat...Low cigs/showers likely, mainly w mtns. Sun...AM low cigs possible. Mon...Showers/cig reductions possible at KBFD. Tue...Fair. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...DeVoir/Steinbugl NEAR TERM...Dangelo/DeVoir/Steinbugl SHORT TERM...DeVoir/Ceru/Steinbugl LONG TERM...Ceru/Steinbugl AVIATION...Martin

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