Extended Forecast Discussion NWS Weather Prediction Center College Park MD 100 PM EDT Sat Mar 23 2019 Valid 12Z Tue Mar 26 2019 - 12Z Sat Mar 30 2019 ...Overview... An upper low in the eastern Pacific on day 3/Tue will approach the western CONUS on day 4/Wed, with troughing traversing the western/central U.S. days 5-7. At the surface, fronts in the West will help create heavy precipitation early in the period, and low development in the Plains and movement into the MS Valley/Midwest could cause heavy precipitation in those areas by day 6-7, but uncertainty remains high. ...Guidance Assessment/Preferences... For days 3-4, a multi-model blend worked well for the large-scale features while de-emphasizing the small-scale differences in the forecast--models were in general agreement for the upper low in the eastern Pacific moving eastward into the CONUS. By day 4-5, the 00Z CMC became much deeper with the trough than other models, and sent upper-level energy around the upper high in the Gulf of Alaska in a manner that seemed unlikely, so did not utilize the CMC for this forecast. Additionally, the operational 00Z ECMWF began exhibiting differences from its mean and other models at day 5, moving the large upper low in central Canada eastward more quickly. Moving into day 6-7, this meant that the trough in the CONUS was cut off from the northern stream flow, and thus was moving eastward more slowly and much stronger compared to other models, which affected surface low placement as well. There is plenty of spread in the ensembles in the degree of separation of these features and other aspects of the CONUS trough's evolution, but preferred to stay away from the deterministic ECMWF solution for now in favor of the means. Used the GEFS and EC means at day 7 with some WPC continuity, with a slight emphasis on the GEFS mean due to how it handled the transitioning pattern in Alaska. ...Weather Highlights and Hazards... With the upper low approaching the West, a couple of fronts will make their way through the West, and heavy precipitation is expected for day 3-5. Heavy valley rain/mountain snows will threaten northern California/Oregon through the Northern Rockies, and heavy snow is forecast for the Central Rockies as well later in the week. As the trough energy ejects out through the West, it is expected to induce cyclo/frontogenesis in the Plains, and this plus another cold front dropping southward out of Canada, as well as deepening return flow from the Gulf of Mexico, would all fuel an expanding risk of enhancing rains/convection. The emerging heavy rain area threatens areas of the Mississippi Valley/Midwest (where flooding is ongoing) heading into next weekend. 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. The cold front moving quickly southward through the Plains and Mississippi Valley is expected to change the ongoing regime of above average temperatures there in the short/early medium range period to below normal by day 6-7 (Fri-Sat). Ahead of this front, the Eastern Seaboard is expected to be warmer than average by Sat after the cold high pressure dominates midweek. Tate 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