Extended Forecast Discussion NWS Weather Prediction Center College Park MD 152 PM EDT Sun Mar 22 2020 Valid 12Z Wed Mar 25 2020 - 12Z Sun Mar 29 2020 ...Guidance/Predictability Assessment... The upcoming medium range upper flow pattern will feature cold troughing across the western U.S. with zonal to southwesterly flow over the central/eastern U.S overtop an amplified Gulf of Mexico to Florida upper ridge. 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 with warm lead southern tier flow. The WPC forecast was initially based heavily on a blend of the 00Z ECMWF/UKMET during days 3-5 (Wed-Fri). These solutions showed good consensus with the ensemble means on a system moving from the central Appalachians on Wed to off the Northeast U.S. coast on Thu. Farther west, the GFS was on the fast side of the spread, almost to the point of being an outlier, with the positively tilted upper-level trough digging into the Western U.S. during that time frame, then becomes slower than consensus by the time the system reaches the Four Corners and central U.S. Fri-Sun). These speed differences also result in downstream phasing differences with northern stream energy, with the more phased ECMWF spinning up a relatively strong low pressure system across the Midwest/Great lakes, and the GFS maintaining more separate streams with a more suppressed low pressure system. Ensembles provided a bit more support for the ECMWF idea, with the GFS only supported by a minority cluster of GEFS members. By Sat-Sun (days 6-7), ensemble means (ECENS/GEFS) were much more heavily weighted in the forecast, with some continued limited use of the ECMWF. ...Weather/Hazard Highlights... Expect an active winter-like 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 and the Cascades. The Great Basin/Southwest and Rockies will see episodes of organized precipitation as well, especially with main system passage. Ejecting lead system energy offers potential for a swath of rain/convection from the Mid-Atlantic/Northeast through midweek with low/frontal system passage and moderate lead return moisture inflow. Progressive flow nature should limit heavy rainfall/runoff issue potential. This system could produce another round of accumulating snows for portions of the Northeast with coastal low development. A potentially deeper low pressure system across the central U.S. Fri into the weekend would produce broad areas of showers and thunderstorms from the Central Plains/Mid-Mississippi Valley to the eastern U.S. The system also has some potential to produce some severe warm sector fueled thunderstorms as per latest SPC Day 4-8 Convective Outlook/Discussion. The heaviest rainfall risk may focus over the OH Valley and vicinity given system organization/depth and deeper moisture influx/instability. There is also some guidance signal for a swath of snow from the Upper Midwest/Great Lakes to the Northeast on the northern tier of the wrapping/expanding precipitation shield, although confidence in this aspect is a bit lower given the spread among solutions by that time. Schichtel/Ryan 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