Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1200 PM EDT Sun Mar 24 2019 Valid 12Z Wed Mar 27 2019 - 12Z Sun Mar 31 2019 ...Overview... A closed eastern Pacific upper trough will reach the West midweek, with height falls working eastward over the nation Thu-next Sun. Surface fronts in the West will support some heavy precipitation including heavy elevation snows, and low developments in the Plains and subsequent movement through the MS Valley/Midwest will combine with a surge of deepening moisture/warmth from the Gulf of Mexico, which may fuel some enhanced rain/thunderstorms in those areas later in the week. The pattern also includes a risk of wrap-around post-frontal snows on the cooled northwest periphery of the main precipitation shield. ...Guidance Assessment/Preferences... For the beginning of the medium range period, a multi-model blend served us well for the large-scale features (upper trough/low entering the West with some downstream ridging) while de-emphasizing the small-scale differences. This blend included the 00Z GFS, ECMWF, and UKMET, as well as the 00Z EC mean and 06Z GEFS mean. By day 5 (Fri), preferred the 00Z deterministic GFS rather than the 06Z run, as most other models have come into better agreement with the the location/orientation of the closed upper high in western Canada compared to yesterday, and this placement is unlike the 06Z GFS. Deterministic models quickly diverge by day 6-7, especially by day 7 (Sun) as the 00Z EC combines the northern and southern streams into one deep upper trough across the central/eastern CONUS, whereas the GFS runs separate the streams but have been rather inconsistent regarding placement of troughs in the central to western U.S. Thus preferred the EC and GEFS means, which were reasonably well-aligned, for this more uncertain portion of the forecast. ...Weather Highlights and Hazards... With the upper trough/low approaching the West, a couple of fronts will make their way through the West and some heavy precipitation is expected Wed/Thu. Heavy valley rain/mountain snows will threaten northern California/Oregon through the Northern Rockies, with heavy snow forecast for the Central Rockies by Thu/Fri. As the trough energy ejects out through the West, it is expected to induce cyclo/frontogenesis in the Plains. This plus another cold front dropping southward out of Canada in tandem with deepening lead return flow from the Gulf of Mexico would fuel an expanding risk of enhanced rains/convection. The Upper/Middle Mississippi Valley (where flooding is ongoing) is currently forecast to receive rainfall by Thu-Fri, with rain expected in the Lower Mississippi Valley by Sat. Uncertainty remains regarding heaviest rainfall amounts/placement, but the guidance signal for development continues to grow. In the cold air behind the aforementioned cold front coming from Canada, late-season snow is possible in the Northern/Central Plains to Midwest. Warmer than average temperatures are expected to prevail across the Plains/MS Valley before the series of cold fronts dropping south through those areas changes the regime to cooler than average temperatures. The Eastern Seaboard could have above normal temperatures next weekend ahead of these cold fronts. Tate/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