Extended Forecast Discussion NWS Weather Prediction Center College Park MD 233 AM EDT Fri Oct 23 2020 Valid 12Z Mon Oct 26 2020 - 12Z Fri Oct 30 2020 ...Impressive record cold for part of the West and much of the Central US Mon-Tue... ...Heavy snow for the Southern Rockies Monday... ...Heavy rain threat for the Southern Plains/Mid-Mississippi Valley next week... ...Guidance Evaluation/Preferences... Guidance remained in very good agreement on the longwave pattern next week with a deep closed low slowly exiting the Southwest and lifting back into the westerly flow by the end of the week. Trough the 12Z/18Z cycles, the GFS remained quickest to progress the low onto the southern Plains and was discounted after Monday. Preferred the larger and more consistent cluster near the 12Z ECMWF that included the Canadian/UKMET/ECMWF ensemble mean and even the 18Z GEFS mean (albeit a bit quicker). This resulted in few changes to the progression with the largest uncertainty in how quickly the upper low weakens into an open wave over the lower Mississippi Valley. The ECMWF can be too slow with opening closed lows, so trended toward the ensemble means that were in between the much quicker Canadian and the slower ECMWF. Upper ridging is forecast to hold in place over the Southeast U.S. until at least Thursday, perhaps squashed a bit as the Plains system moves eastward. ...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 threat will diminish to the east as temperatures will generally be above freezing. In the warm sector ahead of the front, showers and some storms 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 and become locally heavy. This will lift northeastward as the system tracks toward the Ohio Valley late Thu into Fri, perhaps all the way to the Mid-Atlantic and Northeast. This will depend on the track/depth of northern stream fronts out of Canada and how much moisture can be transported northward from the Gulf. Some snow may be possible at the highest elevations in northern New York/New England. 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