Extended Forecast Discussion NWS Weather Prediction Center College Park MD 219 PM EST Tue Nov 17 2020 Valid 12Z Fri Nov 20 2020 - 12Z Tue Nov 24 2020 ...Overview and Guidance Evaluation... The latest guidance continues to have spread in timing, strength, location and intensity with specific details over the next week; however, the general consensus shows mostly progressive, cyclonic flow that setups up mean troughiness over the western/central CONUS. The first feature of note will be a shortwave moving into the West late this week and continuing across the country thereafter, interacting with a leading surface front initially extending from the northeastern U.S. through the central Plains into the Four Corners states. This caused spread in where the band of higher QPF sets up over the central U.S- the ECWMF favored the Midwest/Mississippi Valley while the CMC, GFS, UK were further north from the Central Plains/Mid-Upper Mississippi Valley to the Great Lakes. Consensus favors faster, less amplified solutions over the West for the leading energy forecast to approach/reach the West by around Sun. This reflects greater influence of strong North Pacific flow upstream, which should ultimately develop a broad trough aloft over the northeastern Pacific by the end of the period next Tue, and suggests that the positive height anomaly expected to be near 40N 170W may not be strong enough to support a more amplified eastern Pacific/West Coast trough aloft recommended by teleconnections. The preferred blend for this forecast issuance included the 00 ECWMF/CMC/UKMET 06 GFS with increasing weight of the means beyond Sunday. ...Sensible Weather and Hazards... Snow and lower elevation rain near the Central Rockies will spread east across the Plains this weekend as mid-level shortwave energy interacts with a southwest-northeast orientated surface cold front. With time, the front is expected to slow while maintaining the orientation with waves along the boundary possible. This boundary will provide a focus for scattered to widespread precipitation from the South, Plains, Midwest and into the Great Lakes region. Within the cool sector, particularly portions of the Central Plains and Great Lakes, may have some snow if any falls. The exact location, coverage and intensity of the precipitation across the central and eastern states are a bit uncertain given spread in forecast solutions. The Pacific Northwest and surrounding areas will be in an increasingly wet pattern as troughing over the Pacific favors onshore flow/surface fronts to approve the coast. Light to moderate precipitation is expected for parts of California, with intensity becoming heavier further north and into the Northern Rockies through Tuesday. Precipitation at lower levels will mostly by in the form of rain with mountain snow at the the mid-highest elevations of the Coastal ranges, Cascades and eastward to the Northern Rockies. Areas from Arizona, the Southern Rockies northeastward will see well above normal temperatures in the warm sector ahead of the initial northeast-southwest front, with a decent area of plus 10-20F anomalies along with min temps possibly exceeding 20F above normal over parts of the central Plains. System/front progression will bring plus 5-15F anomalies into the East around Sun-Mon. Trailing cooler air will offer near to moderately below normal anomalies spreading from the West into the southern half of the Plains Fri-Mon before moderating farther east thereafter. The West will see temperatures rebound to near or slightly above normal by next Mon-Tue. The northern Plains should be moderately above normal most of the period, with a late warming trend possibly bring some highs at least 10F above normal by next Tue. Campbell/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