Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 PM EST Sat Nov 14 2020 Valid 12Z Tue Nov 17 2020 - 12Z Sat Nov 21 2020 ...Overview... The start of the period early Tue should feature a fairly amplified upper air pattern across the U.S. as a strong cyclone will likely bring strong winds and heavy precipitation into the Pacific Northwest. The mean pattern should then flatten over the following couple days as the Pacific cyclone pushes through the southern Canadian Rockies into the Canadian prairies. The trailing cold front should become nearly stationary from across the central Plains to the Northeast by the end of next week. The highest precipitation potential will gradually shift eastward into the central Rockies and upper Midwest by the end of the week. ...Guidance Evaluation/Preferences... Model guidance this morning still indicates appreciable uncertainty regarding the speed of motion of a rather strong cyclone forecast to track northward off the Pacific Northwest coast toward Vancouver Island during the day Tue. The 00Z ECMWF and the CMC went back to a slower solution in contrast with the consistently faster GFS. On the other hand, the GEFS solutions had been slower than the deterministic GFS. The WPC blend starts out the medium range period using more ensemble means for Day 3 than normal with 20% each from the 00Z ECMWF, 00Z EC mean, 06Z GEFS, 06Z GFS, and 00Z NAEFS. Going forward into Wed-Thu there remains decent agreement with respect to energy from this system ejecting inland and supporting a southern Canada/northern tier U.S. low and frontal system. By the end of next week, models generally agree that the trailing front will become nearly stationary across the central Plains and Midwest. The ECMWF dips the front farther south than its ensemble mean. The GFS and GEFS as well the NAEFS were supportive of keeping the front farther north. Thus, more of the ensemble means were incorporated for Days 6 and 7 with only a small portion from the ECMWF, which yielded a solution fairly close to WPC continuity. ...Sensible Weather and Hazards... The heaviest rain and high elevation snow over the West will extend from northern California through the Pacific Northwest and to a lesser extent into the northern Rockies--especially Tue-Wed in the moist flow ahead of the strong Tue Pacific storm/trailing front followed by residual troughing aloft. Generally expect precipitation to trend lighter with time over the West Coast states while moisture spreads farther inland, eventually reaching into the central Rockies. Toward the end of next week, there is decent agreement on the idea that the trailing front should settle over the Plains/Mississippi Valley as the upper flow flattens. This front would provide a focus and/or areal expansion of precipitation depending on timing and strength of upstream shortwave energy. Some rain/snow may accompany the anchoring system over parts of the Upper Great Lakes/Northeast Thu-Fri, and before then the eastern Lakes may see lingering lake effect snow. Easterly low level flow may bring periods of mostly light rain to the Florida Peninsula early and late in the period with a drier period in-between. Pattern evolution will lead to a northwest-to-southeast erosion of above to well above normal temperatures initially over much of the western and central U.S. Expect the warmest anomalies to be over the north-central/central portions of the Plains on Wed with highs potentially exceeding 20F above normal at some locations. Double-digit warm anomalies may be confined to only the far southern High Plains by Sat. Best potential for daily records will be over the Southwest around midweek while isolated records may be possible over the High Plains. Incoming cooler air should bring highs down to near or slightly below normal over the West. The coolest day over the East should be Wed when highs may be 10-15F below normal from the southern Mid-Atlantic into the Northeast. After midweek, a modified form of the Plains warmth will spread eastward to bring some double-digit anomalies into the Midwest and then by Sat plus 5-10F anomalies for highs in the East. Kong/Rausch 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