Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Sat Mar 21 2020 Valid 12Z Tue Mar 24 2020 - 12Z Sat Mar 28 2020 ...Guidance/Predictability Assessment... The upper flow pattern for next week is expected to feature cold troughing across the western U.S. with zonal to southwesterly flow over the central/eastern U.S. In this flow, a series of progressive shortwaves and associated/complex surface based systems will traverse through the active southern stream, bringing episodes of organized precipitation in a warm pattern. The phasing or lack of between northern and southern streams 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. WPC medium range products valid Tue-Thu were mainly derived from a composite blend of reasonably well clustered guidance from the 18 UTC GFS/GEFS mean, the 12 UTC ECMWF/ECENS mean and the National Blend of Models. The 00 UTC GFS/ECMWF and GEFS mean now also seem in line for this period. Accordingly, forecast confidence has been elevated to average levels. Prefer an ensemble mean solution Fri-next Saturday considering growing forecast spread. The ECENS mean seems more reasonable in offering more Plains to OH Valley cyclogenesis than the GFS/GEFS as the main western U.S. upper trough finally ejects northweastard. It seems premature to favor a solution as deep as the ECMWF, but it is plausible. ...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. Energy ejecting from the West in flat flow offers potential for a swath of rain/convection from the Mid-MS Valley/Mid-South to the Mid-Atlantic/Northeast Tue-Wed with low/frontal system passage and moderate lead return moisture inflow. Progressive flow nature should limit heavy rainfall/runoff issue potential. Expected ejection of the main western U.S. upper trough Fri/Sat may offer greater potential for a more amplified central to eastern U.S. surface system response, possibly more in line with ECMWF ensembles and yesterdays 12 UTC GFS/ECMWF that offered at least a moderate OH Valley low by next Saturday. If so, modest WPC QPF depiction, considering uncertainty, would prove conservative. Schichtel 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