Extended Forecast Discussion NWS Weather Prediction Center College Park MD 447 PM EDT Fri Mar 20 2020 Valid 12Z Mon Mar 23 2020 - 12Z Fri Mar 27 2020 ...Guidance/Predictability Assessment... The synoptic pattern across the CONUS over the medium range period (Mon-Fri) next week is expected to feature troughing across the western U.S. with zonal to southwesterly flow over the central/eastern U.S.. In this setup, several shortwaves will traverse through the active northern stream, bringing episodes of precipitation with some of that coming as heavy rainfall. The phasing or lack of between the northern and southern stream and multiple weaker storm systems through the flow lead to an overall average to below average forecast confidence for individual storms and associated weather impacts. The WPC medium range blend preferences was derived initially from a near equal weight of the latest deterministic guidance but quickly transitioned toward heavier weights of the ECMWF for day 4-5. Beyond that time frame, with increasing model spread and lower forecast confidence, the ECENS/GEFS were gradually increased with the most emphasis on the ECENS. ...Weather/Hazard Highlights... Expect an active wintry pattern for much of the West next week as broad areas of moderate rains and terrain enhanced snows periodically overspread the region with approach and passage of several lead systems and eventual upper trough amplification. Highest totals for the period should be over the Sierra Nevada while favored terrain along much of the West Coast. The Great Basin/Southwest and Rockies will likely see episodes of organized precipitation as well. The potential still exists for some locally heavy rains across portions of the Mid-South and vicinity early next week. Specifics will take more time to resolve though. Precipitation coverage and intensity farther north Mon-Tue will depend on uncertain details of expected surface low development near the East Coast on Mon-Tue. Current solutions for track remain far enough apart for some considerable sensible weather differences between only precipitation versus a potentially significant snowfall event over portions of the Northeast and New England. The latest WPC winter weather probabilities show at least 30 percent for a quarter inch or more liquid equivalent in the form of snow over parts of NY and New England. Some higher values exceeding 70 percent exist across the terrain areas of interior NY State. Modestly below normal temperatures over the eastern U.S. Sun-Mon will be followed by increasing coverage of above normal readings to the east of the Rockies, while the amplifying West Coast trough and the eventual start of its eastward progress will bring a cooling trend to much of the West. By next Wed-Thu expect a fairly broad area of plus 10-20F anomalies over the eastern half of the country and generally minus 5-15F anomalies for highs (with more moderate temperatures for morning lows) over the West. Schichtel/Taylor Hazards: - Heavy precipitation across portions of the Olympic Peninsula, Fri, Mar 27. - Heavy rain across portions of the coastal section of New Jersey, Long Island and southeastern New England, as well as across the Mid-Mississippi Valley through the southern Appalachians, Mon-Tue, Mar 23-Mar 24. - Heavy rain from the Mid-Mississippi Valley through much of the Ohio Valley into the southern Appalachians, Fri, Mar 27. - Heavy snow along the southern Cascades, Mon-Tue, Mar 23-Mar 24 and Fri, Mar 27. - Heavy snow along the northern Cascades, Thu-Fri, Mar 26-Mar 27. - Heavy snow along much of the Sierra Nevada, Mon-Tue, Mar 23-Mar 24. - Heavy snow from across the higher elevations of western Wyoming down into northern Utah, Tue, Mar 24. - Heavy snow across portions of central Idaho, Mon, Mar 23. - Severe weather across portions of the southern Plains, Mon, Mar 23. - Flooding possible across portions of the Mid-Mississippi Valley, the southern Plains, and the Upper Midwest. - Flooding occurring or imminent across portions of the lower and middle Mississippi Valley, scattered locations in the northern and southern Plains, and a couple of areas in the Southeast. - Flooding likely across portions of the central and southern Plains, as well as the middle Mississippi Valley. 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