Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM EDT Fri Oct 23 2020 Valid 12Z Mon Oct 26 2020 - 12Z Fri Oct 30 2020 ...Impressive record cold for the West and Central U.S. Mon-Tue... ...Heavy snow threat Southern Rockies/High Plains Mon-Tue... ...Heavy rain threat spreads eastward over the South Wed-Fri... ...Guidance Evaluation/Preferences... Overall, guidance remains in good agreement on the longwave pattern next week with a deep closed low slowly exiting the Southwest and ejecting into the westerly flow in a separated southern stream. However, the GFS remains quickest to progress the low onto the southern Plains and eastward, faster than the GEFS, and was downplayed given the closed nature of the system. Preferred the larger and more consistent cluster near the 00 UTC ECMWF, but especially the ECMWF ensemble mean. The ECMWF can be too slow with opening closed lows, so trended toward the ECMWF ensemble mean that was a bit more progressive. Upper ridging is forecast to hold in place over the Southeast U.S. until Thursday, perhaps squashed a bit as the Plains system moves eastward. A significant complicating factor is that NHC is now following a Caribbean tropical disturbance that may develop and work into the Gulf of Mexico in some capacity/uncertainty next week whose deep moisture would lift northward from the Gulf in advance of the ejecting closed low to enhance rainfall/runoff issues. ...Weather/Hazard Highlights... By Monday morning, arctic front will have driven to the Mexican border with cold Canadian high pressure sinking through the Rockies. This will spread cold air down the east side of the Rockies as well as spill over westward through the Great Basin. Widespread record cold is likely for areas of the West and many areas of the central Plains Monday, focusing on the Plains Tuesday. Some areas may break record lows by 5-20 degrees and may set records for being so cold so early in the season (e.g., earliest below zero readings). Monday will see the largest negative anomalies as high temperatures may remain 10-40 degrees below normal, especially just east of the central Rockies into the western Plains. The cold airmass will moderate as it pushes eastward through the week. By next Thu/Fri, temperatures may only be 5-15 degrees below normal from the Upper Midwest/Mississippi Valley to the Great Lakes/Northeast. Areas of the Northwest and California will moderate quickly by mid week back to above normal temperatures by about 5-10 degrees. Upslope flow behind the front will lead to widespread snow over the Rockies with significant accumulations possible. The snow/ice threat will diminish to the east as temperatures will generally be above freezing. In the warm sector ahead of the front, showers and thunderstorms will focus over the Ohio/Tennessee/lower Mississippi Valleys Monday with heavy rain possible. Once the upper low over the Southwest moves toward Texas, rainfall could expand over Oklahoma and nearby areas early next week and become more widespread and locally heavy. This system will continue east-northeastward and track to the Tennessee Valley to the Southeast/Mid-Atlantic Thu-Fri. Schichtel/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