Extended Forecast Discussion NWS Weather Prediction Center College Park MD 227 AM EDT Sat Mar 28 2020 Valid 12Z Tue Mar 31 2020 - 12Z Sat Apr 04 2020 ...Overview... Main player over North America next week will be an incredibly strong upper high moving east from the North Slope of Alaska through the Canadian archipelago. With 500mb heights likely above +3.5 sigma (and sea level pressure perhaps into the low 1060s mb which would be higher than records for all of April), this teleconnects to modestly zonal flow over the CONUS but mean/averaged troughing near both coasts. After a lead system departs the Southeast late Tuesday/early Wednesday, overall pattern will become drier and relatively cool for areas between the Rockies and Appalachians but mild for California into the Southwest. ...Guidance/Predictability Assessment... The models and ensembles show little convergence on the evolution of the medium-scale features out of the Pacific and across the lower 48 with forecaster confidence no better than average. The ensembles were generally split (about 60/40) with how to handle a closed low south of the Aleutians Mon-Tue and the downstream ridge/trough either quicker (slight majority of ensembles) or slower (nearly all deterministic models + slight minority of ensembles + continuity). The latter group was preferred in order to limit changes to the ongoing forecast as well as to give deference to the deterministic cluster that can lead the ensembles in some cases. The 12Z/18Z GFS runs were quite different (18Z much quicker than the 12Z run, both of which more or less book-ended the 12Z ECMWF and somewhat the Canadian/UKMET), though perhaps nothing could really be discounted. Favored the 12Z ECMWF/Canadian/UKMET overall Tue-Thu before transitioning to a multi-model/ensemble blend with the very washed-out ensemble means as the two camps in the members became nearly exactly out of phase). ...Weather/Hazard Highlights... System moving out of the southern Appalachians Tue will spread modest rainfall and maybe some snowfall over the higher elevations into the Mid-Atlantic and Northeast Wed/Thu as it skirts the coast. In the West, precipitation will taper to lighter rain/snow showers as an upper low weakens over British Columbia. Temperatures will oscillate between cooler and milder than normal between the lead system and subsequent northern stream cold front later in the week. Larger area of cold temperatures will remain over Montana with some readings 15-20 deg below normal. Milder temperatures are expected over California into the Southwest. 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