Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1244 PM EST Mon Nov 16 2020 Valid 12Z Thu Nov 19 2020 - 12Z Mon Nov 23 2020 ...Overview/Model Preferences... A persistent negative anomaly across Nunavut/north-central Canada favors troughing across the Great Lakes and Midwest, of which the guidance agrees. The eastern Pacific is another matter, as a positive anomaly near 40N 180 favors troughing offshore the West Coast which is at odds with preferences relating to the negative anomaly in northern Canada. This implies a fast flow pattern with systems of low amplitude moving near the West Coast late in the period, weaker than seen in the 00z ECMWF/00z ECWMF ensemble mean solutions. From Thursday into Saturday, a compromise of the 00z ECMWF, 06z GFS, 00z Canadian, and 00z UKMET was preferred for pressures, 500 hPa heights, and winds. Thereafter, weighted the ECMWF-related solutions minimally, placing more weight on the other guidance, including the 00z NAEFS mean. This preference maintained reasonably good continuity. No matter which solution you prefer, the precipitation forecast through Sunday is in reasonable agreement amongst the guidance. For next Monday, ECMWF-based solutions are less preferred for QPF. ...Sensible Weather and Hazards... System from the eastern Pacific into the West late this week will lead to a lighter trend for rain/high elevation snow over the Pacific Northwest/northern Rockies and bring some precipitation into the central Rockies. By the weekend, the shortwave will interact with the front draped over the central U.S. into Lower Great Lakes, leading to an expansion of precipitation and development of a wave along the front. Currently the best potential for highest totals extends over and a little south of the Midwest as well as into parts of the Great Lakes. Expect mostly rain to the east of the Rockies, with modest potential for a little snow in the northern fringe of the moisture shield. Meanwhile precipitation should increase again over the Pacific Northwest during the weekend/early next week. Orientation of flow aloft is uncertain given the model and ensemble spread so specifics of terrain enhancement and timing/coverage at a particular point in time have low confidence. However there is a more common signal for precipitation to be increasing in this time frame, and the guidance is most agreeable on the precipitation forecast this weekend. Initially very warm temperatures from the Southwest/southern Rockies through much of the Plains and into the Great Lakes on Thursday will moderate and push southeastward with time, especially from the weekend into next week as the main frontal boundary over the country accelerates. Some plus 15-20F or slightly higher anomalies will be possible Thursday and to a lesser extent Friday with scattered daily records also a possibility from Arizona into the southern Rockies and parts of the Plains Monday through Thursday. By next Monday, above normal readings should be confined to the eastern states. The cooler air pushing into the western and central U.S. will likely yield near to modestly below normal anomalies. Roth/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