Extended Forecast Discussion NWS Weather Prediction Center College Park MD 312 PM EDT Sun Oct 25 2020 Valid 12Z Wed Oct 28 2020 - 12Z Sun Nov 01 2020 ...Heavy precipitation threat from the Plains/Mid-Mississippi Valley eastward to the Mid-Atlantic later this week... ...Guidance Evaluation/Preferences... Through the course of the coming week a deep, closed low will exit the Southern Rockies into the Plains and progress east-northeast toward the Mid-Atlantic regions, ultimately weakening to an open wave by Friday. In additional, tropical cyclone Zeta currently located southeast of the Yucatan Peninsula, is forecast by the National Hurricane Center to track north through the Gulf of Mexico and make landfall as a hurricane on Wednesday. The two sources of moisture are expected to merge into/along the frontal boundary over the Tennessee Valley Thursday and move to the East Coast Friday. The GFS has been/continued to progress this system faster the rest of the guidance. The ECWMF, the CMC and the ensemble means were more clustered favoring higher QPF streaks along the boundary from eastern Kansas to West Virginia. QPF associated with Zeta as it transitions from a hurricane to a tropical depression or remnant low favors a combination of the ECWMF/CMC but also some GFS as well. The exact placement of the QPF swath will be closely tied to NHC's track for Zeta so there is some uncertainty of the axis and location of local maximums. ...Weather/Hazard Highlights... The recent cold spell over the Plains is expected to moderate through the extended, however many locations will continue to register temperatures 10-30 degrees colder than normal on Wednesday. To the east of the upper low, near to above normal temperatures will trend toward near to below normal as the system progresses eastward. In the Pacific Northwest, California and into the Great Basin region, temperatures will be 5-15 degrees above normal through most of the period. Deep tropical moisture streaming northward over the frontal boundary will initiate and sustain heavy rainfall for parts of the Mississippi and Tennessee Valleys. These heavy showers are expected to continue along this boundary as the system continues tracking east. Local streams and river will likely rise and localized flash flooding risk will increase. On the northwest side of the upper low, snow is likely over New Mexico to the TX/OK panhandles and southwestern KS. With marginally cold air in parts of the Northeast, snow is possible in higher elevations as the precipitation streams eastward (primarily in a warmer air mass). The Pacific Northwest will see a few bouts of mainly light rain and higher elevation snow. Campbell/Fracasso 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