Extended Forecast Discussion NWS Weather Prediction Center College Park MD 330 PM EDT Mon Apr 01 2019 Valid 12Z Thu Apr 04 2019 - 12Z Mon Apr 08 2019 ...Overview... This period will feature a steady progression of Pacific features into the West that continue onward to produce several episodes of active weather over the east-central U.S. Heaviest precipitation should extend from the central/northern West Coast to the northern Rockies as well as downstream from the southern Plains/South to the Appalachians/Mid-Atlantic. ...Guidance Assessment/Preferences... Latest models and ensembles remain remarkably stubborn in maintaining their spread for shortwave energy aloft and associated surface lows tracking across the eastern half of the country late this week into the start of the weekend. As has been the case in recent days there is decent clustering for low pressure over the south-central Plains early Thu. Then individual models/ensemble members rapidly diverge for the latitude of best-defined low centers farther east. In forecasts valid early Fri the one trend of note is a reduction of ensemble members in the northern part of the spread in the Great Lakes. On the other hand recent ECMWF/CMC runs remain on the southern part of the spread. By early Sat there is still the potential for low pressure centers anywhere from northern New England to southern coastal Mid-Atlantic. Confidence remains low for system specifics due to the sensitivity to small scale details aloft that include a combination of initial Plains shortwave and northern tier energy that could interact by Fri. WPC progs now favor a weakening northern stream surface wave tracking through the Ohio Valley and Northeast as a southern stream surface wave focuses potential for deeper moisture/rainfall/convection underneath over the South and Mid-Atlantic. Upstream, a fairly strong northeastern Pacific storm should bring a decent front (with vigorous upper shortwave support) into the West by Sat, potentially followed a day later by another system tracking near Vancouver Island and bringing a front/energy aloft to the Northwest. Guidance has been fairly consistent in weakening shortwave energy that crosses the Northwest and heads into a downstream ridge, while southern stream shortwaves cross the Southwest U.S./northern Mexico and then southern Plains/Mississippi Valley by the weekend. There is still a rapid increase in forecast spread for details of flow aloft from the Pacific into the western U.S., but relative agreement among the ensemble means. ...Weather Highlights/Hazards... Aside from the typically variable finer details, there is good continuity in the forecast of multiple periods of significant rainfall/higher elevation snow from northern California/Sierra Nevada and Pacific Northwest into the northern Rockies. Highest five-day totals will likely be over favored terrain in the West Coast states with somewhat less moisture reaching the Rockies. Heaviest precipitation should occur along the West Coast during Fri-Sun. Meanwhile the system tracking out of the Plains Thu onward will spread a decent moisture shield across the eastern half of the country, but with continued lack of confidence in specifics. Today there is somewhat more of a signal for heavy rainfall potential over the Lower Mississippi/Tennessee Valley/Gulf Coast region, and some convection over this area could be strong to severe. Check SPC outlooks for latest info on severe threats. Some snow may be possible into the northern Great Lakes/New England. Behind this system, most guidance continues to suggest a heavy rainfall threat next weekend/Monday for the southern Plains/Lower Mississippi Valley. This activity will be encouraged by the approaching southern stream shortwave aloft and a healthy flow of Gulf moisture interacting with a stalled front that should return north as a warm front. Rainfall of varying intensity should also spread farther northward across the central and eventually eastern U.S. 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 Hazards: - Heavy precipitation across portions of California, the Central Great Basin, the Pacific Northwest, and the Northern Great Basin, Thu-Sun, Apr 4-Apr 7. - Heavy rain across portions of California and the Pacific Northwest, Thu-Sun, Apr 4-Apr 7. - Heavy rain across portions of the Lower Mississippi Valley and the Southern Plains, Sat-Sun, Apr 6-Apr 7. - Heavy rain across portions of the Southeast, the Lower Mississippi Valley, and the Tennessee Valley, Thu-Fri, Apr 4-Apr 5. - Heavy snow across portions of the Northern Rockies and the Northern Great Basin, Sat-Sun, Apr 6-Apr 7. - Heavy snow across portions of the Northeast, Fri-Sat, Apr 5-Apr 6. - Severe weather across portions of the Southeast, the Lower Mississippi Valley, the Southern Plains, and the Tennessee Valley, Thu, Apr 4. - Flooding possible across portions of the Middle Mississippi Valley. - Flooding occurring or imminent across portions of the Central Plains, the Lower Mississippi Valley, the Northern Plains, the Tennessee Valley, the Middle Mississippi Valley, the Upper Mississippi Valley, the Great Lakes, and the Ohio Valley. - Flooding likely across portions of the Middle Mississippi Valley and the Northern Plains. - High significant wave heights for coastal portions of California and the Pacific Northwest, Sat-Sun, Apr 6-Apr 7. 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