Extended Forecast Discussion NWS Weather Prediction Center College Park MD 610 PM EST Fri Nov 20 2020 Valid 12Z Mon Nov 23 2020 - 12Z Fri Nov 27 2020 ...Overview and Guidance Evaluation... The latest runs of the models and their ensemble means have shown improvement with the degree of spread within the wave that crosses through the central U.S. into the East. The preferred blend for this issuance leaned a little heavier with the 00Z ECWMF through time but also included the 00Z CMC/ECWMF ensemble mean and the 06Z GFS. There are still some uncertainties to work out in the coming days. ...Sensible Weather and Hazards... Scattered to widespread precipitation is expected to organize over portions of the Plains and the Mississippi/Tennessee/Ohio Valleys before moving into the Southeast and Mid-Atlantic regions. Most of the precipitation should fall as rain, but northern portions of the moisture shield should contain some snow and wintry mix. For Tuesday-Thursday, there is an increasing signal for a separated southern stream shortwave trough/low aloft and surface low pressure system to produce an episode of meaningful precipitation from the Southern Rockies/Plains northeastward through the East, Expect some snow will be possible this period from the upper Midwest to the upper Great Lakes under more northern stream impulse influence. Over the Northwest, it remains the case that progressive but energetic flow aloft will promote a wet period as a series of fronts approach/reach the region. There is good continuity for persistence of rain and higher elevation snow with highest totals over Coastal and Cascade Ranges and a secondary maximum into the Rockies. The supporting trough energies aloft early next weak may be followed by more flow separated/amplified systems mid-later next week that could dig organized precipitation into California, the Great Basin and then the Southwest. Campbell/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 Hazards: - Heavy rain across portions of the Lower/Middle Mississippi Valley, the Tennessee/Ohio Valley, the Southern Appalachians, and the Southeast, Wed, Nov 25. - Heavy rain across portions of the Middle/Upper Mississippi Valley, and the Great Lakes, Tue, Nov 24. - Heavy snow across portions of the Pacific Northwest and the Northern Great Basin, Tue, Nov 24. - Flooding occurring or imminent across portions of the Southeast and the Mid-Atlantic. - High significant wave heights for coastal portions of the Pacific Northwest, Wed, Nov 25. - Heavy precipitation across portions of mainland Alaska, Wed, Nov 25. - Heavy precipitation across portions of the Alaska Panhandle, Mon, Nov 23 and Thu, Nov 26. - High winds across portions of the Alaska Panhandle and mainland Alaska, Mon-Tue, Nov 23-Nov 24. - High significant wave heights for coastal portions of the Alaska Panhandle and mainland Alaska, Mon, Nov 23. - High significant wave heights for coastal portions of the Alaska Panhandle, Tue, Nov 24. 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