Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 291151 AFDCTP Area Forecast Discussion National Weather Service State College PA 751 AM EDT Thu Sep 29 2016 .SYNOPSIS... A widespread moderate to locally heavy rain event will continue through tonight. Minor flooding impacts are likely across the southern half of central PA. Unsettled weather with occasional lighter rain showers will persist into the weekend with a gradual drying trend by early next week. && .NEAR TERM /THROUGH TONIGHT/... 7AM: Rain event thus far has been pretty orderly/soaking with some 2+ inch amounts observed over far south-central PA. No changes with this update. -MS The 29/00z guidance remained in good agreement with the deep upper low that is forecast to settle further south from southern IN into central KY today before lifting gradually back to the north after 00-06z Friday. The ongoing rain shield is being handled pretty well by the HI-RES guidance. The highest rain amounts in the last ~6 hours generally range from 0.75 to 1.5 inches across Bedford to Adams County. Radar trends and latest HRRR suggest the north-south heavy rain band developing near the I-95 corridor from DCA to near RIC may focus into the Lower Susquehanna Valley through mid morning, as deep moisture from the Atlantic is driven inland by anomalous ESE LLJ and intersects a frontal boundary/convergence axis. This scenario is also hinted at by the HIRES NCAR ensemble mean QPF which shows a stripe of 2+ inch amounts. The strength of the upslope flow and high PW transport along with some elevated instability will maintain a favorable environment for heavy rain/efficient rainfall processes, while increasingly diffluent flow aloft supports some training bands. As the upper low settles a little further south, backing flow should shift the heavy rain focus back toward the upslope regions of the Laurel Highlands this afternoon into tonight. Overall did not change QPF amounts very much with 50/50 blend of the latest WPC guidance with the previous forecast. This should mitigate some of the detail differences between individual model QPF. Still calling for widespread 2-4" over the flood watch area with locally 4-6" most likely across the east-facing slopes and highest terrain. WPC QPF was based in large part on an ensemble of HIRES guidance. What is a little concerning is the mean 24hr QPF from the NCAR ensemble which shows the potential for 6+ inches. 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 /FRIDAY THROUGH SUNDAY NIGHT/... The upper low continues to double back to MI on Friday before slowly tracking eastward into the Lower Great Lakes over the weekend. 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. && .LONG TERM /MONDAY THROUGH WEDNESDAY/... The trend for early next week is toward dry weather as the stubborn upper low is finally is kicked to the northeast by upstream amplifying trough over the Nation`s mid section. High pressure should regain control of the large scale pattern. FWIW the 29/00z GFS is much faster vs. the ECMWF with the projected path of TC Matthew, with the system nearing the NC coast by Thursday morning. && .AVIATION /12Z THURSDAY THROUGH MONDAY/... An increasingly moist easterly flow will will produce low cigs and rain across central Pa today. Model soundings and latest SREF output support predominantly IFR cigs through this evening at the higher terrain airfields, including KBFD, KUNV, KAOO and KJST. At the lower elevation airfields, predominantly MVFR cigs are expected today at KIPT, KMDT and KLNS. However, periodic IFR is likely this morning associated with bouts of heavier rain. Outlook... Fri-Sat...Low cigs/showers likely, mainly w mtns. Sun...AM low cigs possible. Mon...Showers/cig reductions possible at KBFD. && .CTP WATCHES/WARNINGS/ADVISORIES... Flood Watch through Friday morning for PAZ024>028-033>036-056- 063>065. && $$ SYNOPSIS...Steinbugl NEAR TERM...Steinbugl SHORT TERM...Steinbugl LONG TERM...Steinbugl AVIATION...Fitzgerald

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