Extended Forecast Discussion NWS Weather Prediction Center College Park MD 256 AM EDT Mon Mar 23 2020 Valid 12Z Thu Mar 26 2020 - 12Z Mon Mar 30 2020 ...Guidance/Predictability Assessment... The WPC medium range forecast was primrily derived from a blend of the GEFS mean and especially the ECMWF ensemble mean for better WPC continuity as the deterministic models offer significant system timing and development differences. Speed differences with respect to the ultimate ejection of a main southern stream trough out of the Southwest heading into the weekend also results in downstream phasing differences with northern stream energy, with the more phased ECMWF and to a lesser extent the UKMET/Canadian spinning up a stronger low pressure system to the Midwest/Great Lakes. In contrast, the GFS maintains more separate streams with a more suppressed low pressure system. While an outlier solution, the GFS is plausible considering inital system amplitude, while the expectation for later period phasing/deeper low development most notably in the ECMWF often comes with increased uncertainty. Nevertheless, GEFS and especially ECMWF ensembles provide more support for a deeper low and preference in that direction seems to make more sense considering potential main trough support, with the GFS only supported by a minority cluster of GEFS members. ...Weather/Hazard Highlights... The upper pattern Thursday into Friday will feature an amplified and cooling southern stream trough over California and the south-central Great Basin/Rockies/Southwest and a series of more modest systems from the Gulf of Alaska inland across the Northwest. Expect an active winter-like pattern with moderate rains and terrain enhanced snows. Downstream flow over the central and eastern U.S will lift ejecting impulses and modest shower/thunderstorm focusing surface based systems overtop an amplified and warming Gulf of Mexico to Florida upper ridge. Main southern stream upper trough ejection offers potential for a robust low pressure system across the central U.S. Friday into the weekend that could produce broad areas of showers and strong thunderstorms from the south-central Plains/Mid-Mississippi Valley through the Ohio Valley and Northeast. In this scenario, the heaviest rainfall and runoff risk may focus over the Ohio Valley and vicinity given system organization/depth and deeper moisture influx/instability. There is also a decent guidance signal for a swath of snow from the central Plains and Upper Midwest/Great Lakes to the Northeast on the northern tier of a wrapping/expanding precipitation shield, although confidence in this aspect/timing is a bit lower given the spread among solutions by that time. 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