Extended Forecast Discussion NWS Weather Prediction Center College Park MD 243 AM EDT Mon Oct 26 2020 Valid 12Z Thu Oct 29 2020 - 12Z Mon Nov 02 2020 ...Heavy rain threat for the Mid-Atlantic later this week from Zeta... ...Possible wintry weather in New England Friday... ...Guidance Evaluation/Preferences... Active start to the medium range in the East with the eventual merging of Zeta's remnants and a closed low exiting the Plains/Mid-Mississippi Valley on Thursday. The models have struggled with the timing of each feature but finally have shown better agreement as the lead time decreases. Per the NHC track and consensus upstream, a blend closer to the 18Z GFS for Zeta and around the 12Z ECMWF for the upper low sufficed as a starting point. Axis of QPF (including timing and intensity) remain tough to pinpoint, but a bias-corrected ensemble approach formed the idea--along Zeta's track (as it dissipates/merges with the front) and to the north across the surface boundary. Weakening ridging from the west will fall into more zonal flow over the CONUS for the weekend into next week in a much quieter pattern. Still, ensembles show a fair amount of spread and opted to rely mostly on the 12Z ECMWF, some Canadian, and mostly the ensemble means for the end of the period as the GFS runs appeared too deep with a sfc low near Vancouver/western WA late Fri. With the quicker flow by the end of the period, east-west timing of systems becomes quite large and an ensemble blend was used to temper future adjustments. ...Weather/Hazard Highlights... Cold air in the wake of the closed low and surface front over the southern Plains Thursday (temperatures 10-25 degrees below normal) will moderate into the weekend. Weakening cold fronts into the Northeast will bring in cold enough air to some locations that any northward-advancing precipitation would fall as snow, especially over higher elevations, on Friday. In the Pacific Northwest, California and into the Great Basin region, temperatures will be 5-15 degrees above normal through most of the period. Zeta and its remnants along with the frontal boundary absorbing it will yield a swath of modest to perhaps locally heavy rain from the southern Appalachians and Ohio Valley through the Mid-Atlantic and perhaps coastal Southern New England. The Pacific Northwest will see a few bouts of mainly light rain and higher elevation snow due to onshore flow in the low-amplitude upper pattern. 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