Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 AM EDT Fri Oct 26 2018 Valid 12Z Mon Oct 29 2018 - 12Z Fri Nov 02 2018 ...Pattern Overview... A moderately progressive flow pattern across the U.S. early in the medium range will gradually become quite a bit more amplified by the middle of next week. The upper ridge which as been prevalent off the West Coast is expected to return, with a downstream large scale trough expected to set up across the central U.S. This flow pattern will set the stage for transport of cold, polar air southward across the north central U.S., with wet conditions on the eastern side of the developing trough, from the lower Mississippi Valley to the Ohio Valley. ...Guidance/Predictability Assessment... Models showed sufficient consensus during the first half of the medium range to support use of a multi-model deterministic blend (including the ECMWF/GFS/UKMET) during days 3-4 (Mon-Tue). One upper trough/surface low pressure system is expected to be lift out of the eastern U.S. during this time period, while the upper ridge builds well off the West Coast, and the next significant shortwave crosses the northern Rockies and then begins to amplify across the central U.S. The 18Z and 00Z runs of the GFS were quicker than the ECMWF and the model consensus with bringing shortwave energy east from the northern Rockies into the plains Sun-Mon, and the slower 12Z GFS was preferred as part of the multi-model blend. After day 5, models show generally good agreement that the flow will become increasingly amplified with ridging expanding off the West coast and a broad/deep upper trough amplifying across the central U.S. Solutions differ, however, with respect to individual shortwave components traversing the long wave trough. As a result of decreased confidence in the specifics, boosted ECENS/GEFS ensemble means to comprise a majority of the forecast blend during days 6-7 (Thu-Fri). ...Weather Highlights/Threats... Increasingly wet conditions are expected from the lower Mississippi Valley to the Ohio Valley, especially by the middle to end of next week as the large central U.S. upper trough develops, favoring northward transport of Gulf of Mexico moisture and instability where it will interact with a surface frontal boundary. Models show a decent signal that multi-inch rainfall totals will be possible. The Pacific Northwest and the northern Rockies will also see multiple rounds of precipitation as weakening shortwaves/frontal systems traverse the northern periphery of the Pacific ridge. Initially above average temperatures across Rockies and central U.S. will quickly drop by the middle of next week as the upper trough amplifies and a surface cold front spreads polar air southward, with high temperatures 5 to 15 degrees below average across much of the Rockies and central U.S. through the middle/end of next week. Ryan 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