Extended Forecast Discussion...updated NWS Weather Prediction Center College Park MD 414 AM EDT Fri Sep 14 2018 Valid 12Z Mon Sep 17 2018 - 12Z Fri Sep 21 2018 ***Hurricane Florence to bring flash flooding and prolonged significant river flooding to parts of the Appalachians into early next week*** ...Hurricane Florence... The National Hurricane Center forecasts Hurricane Florence to make landfall over southeastern North Carolina Friday morning. The cyclone should gradually weaken as it tracks across northern South Carolina before lifting northward, roughly along and just west of the Appalachians through Tuesday as it accelerates northeastward. Flooding will be the main threat owing to heavy and persistent rainfall as it interacts with the mountainous terrain. Although the majority of the prolific rainfall will happen before the medium range period begins, a swath of enhanced rain will follow along the track of Florence as it becomes extratropical. This will be a multi-day and multi-faceted event, and the National Hurricane Center and local NWS forecast offices have additional information pertaining to this event. ...Pattern Overview and Guidance/Predictability Assessment... The forecast period begins on Monday with a trough centered near the West Coast, an upper level ridge over the southern plains, and a broad trough over the Ohio Valley that captures the remnants of Florence. The upper ridge expands across the south-central U.S. and then the Southeast states by the end of the week with a progressive flow pattern across the northern tier of the nation. The trough over the western third of nation becomes re-established by the end of the week. The forecast was based primarily on a blend of the deterministic GFS, ECMWF, and their respective ensemble means, with a greater percentage of the means by next Thursday and Friday owing to timing differences noted with the West Coast trough axis. The upper level ridge has better model agreement overall. ...Weather Highlights/Hazards... Florence is forecast to spread a large area of significant rainfall across the central and northern Appalachians early next week despite its acceleration ahead of an approaching cold front. Rainfall amounts on the order of 2 to 4 inches appear likely with isolated higher totals of 6 inches possible. Flash flooding will be possible for flood prone areas and this is something that WPC will continue to monitor as the event enters the short range forecast period. Farther to the west, with the upper level trough moving out of the northwest, a cold front will advect a cooler air mass to the northern plains and Upper Midwest/Great Lakes through mid week as a Canadian surface high build into the region, and then to the east coast next Thursday. Above normal temperatures are expected for the southern tier of the U.S. courtesy of the upper ridge in place, with the potential for some daily record highs and record high minimums. Hamrick/Schichtel WPC medium range 500 mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indexes are found at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml