Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1200 PM EDT Sun Aug 11 2019 Valid 12Z Wed Aug 14 2019 - 12Z Sun Aug 18 2019 ...Overview and Guidance/Predictability Assessment... Early in the medium range period, low amplitude troughing will prevail over the east as ridging once again builds centered over the Southwest/Southern Plains. Another trough is expected to approach the Pacific Northwest Wed and enter around Thu. It appears the 00Z UKMET is too fast with the track of this trough by Thu and especially Fri, and the 00Z CMC is weaker than other guidance initially (though eventually looks similar to other model guidance with its strength and position by Sat). The trough and energy is expected to move eastward through the northwest and north-central CONUS over the weekend, but the details are rather uncertain, as its progression depends on the evolution of an upper low moving southward in the vicinity of the Alaska panhandle on Fri/Sat. Solutions diverge with this upstream feature especially by Sat, and the 00Z ECMWF looks like an outlier with the GFS having somewhat better run-to-run continuity. Thus, used a 06Z/00Z GFS and 00Z ECMWF blend early on, with some incorporation of the NAEFS and EC means. Leaned much more toward the means by the weekend forecast and eliminated the 00Z ECMWF. Also of note is the GFS spinning up a mid-level low by Sat along the eastern Gulf Coast over its past several runs, possibly from the dying front at the surface and likely convection in the vicinity. With the ECMWF weaker and the usually aggressive CMC showing nothing, was not willing to fully latch onto this feature yet. The main change made to the fronts/pressures from the overnight forecast was slowing down the low pressure/frontal system moving through the Northern Plains over the weekend, due to models trending slower with the shortwave entering the area. ...Weather Highlights/Threats... A wavy lead frontal system will shift southward through the eastern and central states, stalling out over the South/Southeast later week. Widespread showers and thunderstorms including a threat of local cell training/runoff issues are expected to move southward from the Mid-Atlantic to focus into the Southeast/Gulf Coast from midweek onward as deepened Gulf moisture streams into the vicinity of the front. Upstream, upper trough amplification over Northwest/northern Rockies mid-later this week and robust system/height fall ejections into the north-central U.S. next weekend should both provide dynamics and instabilities supportive of periods of locally enhanced rainfall and thunderstorms. Expect warmer than average pre-frontal temperatures for the Gulf Coast states/Southeast into mid-later week. There is a threat of excessive heat with widespread record high minimum temperatures through Wed morning. Additionally, the Southwest to Southern Plains should also experience hot temperatures through the period under the upper high/ridge. Tate/Schichtel Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indices are 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