Extended Forecast Discussion NWS Weather Prediction Center College Park MD 401 PM EDT Fri Mar 22 2019 Valid 12Z Mon Mar 25 2019 - 12Z Fri Mar 29 2019 ...Overview... The 00Z and 06Z suite of models continued to portray general agreement in the overall pattern of an upper low in the eastern Pacific (off the U.S. West Coast), ridging into the western and central CONUS, and a deep upper low in eastern Canada that creates troughing in the eastern CONUS on day 3 (Mon). This pattern will be slow-moving on days 3-5 (Mon-Wed), before the upper low in the eastern Pacific begins breaking down and sends energy into the western CONUS by Thu and the central CONUS on Fri. ...Guidance Assessment/Preferences... Days 3-5 in the medium range were marked by general model agreement between the 00Z/06Z GFS, 00Z GEFS, 00Z ECMWF/its ensemble, and the 00Z UKMET, so was able to include components of all these models in the blend, rather than attempting to select which model's small-scale features would prevail. Did exclude the CMC from the blend as it broke down the eastern Pacific upper low more quickly than the other models, by day 5/Wed. Model spread increases quite a bit as the upper low moves into the West and weakens/becomes associated with a deep trough in central Canada, as each model handles shortwaves embedded in the trough differently. Thus by day 6-7 we leaned toward the 00Z GEFS and EC means, with a lower percentage of the operational ECMWF from 00Z. The 00Z GFS strengthened a trough in the central CONUS more than other models, while the 06Z GFS focused on a trough oriented differently in the western U.S. The 00Z ECMWF seemed like a compromise of these features and seemed similar enough to the means to incorporate some of it, and wanted to stay away from the inconsistency of the GFS runs. ...Weather Highlights and Hazards... This medium range period starts Monday/Tuesday as a southern stream front with several moisture/enhanced precipitation focusing waves ejects across the South/Southeast/and Mid-Atlantic. These waves cut underneath/interact with a cooling northern stream frontal drape whose post-frontal high pressure builds down through the central and eastern U.S. Meanwhile, a protracted series of Pacific systems with associated height falls and enhanced precipitation swaths will track onshore and across much of the West early through mid next week in advance of an mean closed low/trough reinforced just off West Coast. Expect heaviest precipitation/heavy mountain snows threats from northern California/Oregon to the northern Rockies. Indication that the bulk of Pacific trough energy will eject through the West Wed/Thu to emerge over the Plains later next week to induce cyclo/frontogenesis. This may occur just as a renewed northern stream may force cool air down into the unsettled n-central states. This airmass would prove to be in stark contrast to a rapidly warming airmass spreading over the e-central U.S. where moist Gulf return flow may fuel an expanding risk of enhancing rains/convection channeling between the surging fronts and retreating eastern U.S. high pressure. Thus, heavy rain is possible somewhere in the Mississippi Valley/Midwest (where flooding is ongoing) by late in the medium range period, but uncertainty remains high regarding rainfall amounts and placement of the heaviest rainfall. 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 Hazards: - Heavy precipitation across portions of the Central Great Basin, California, and the Southwest, Mon-Thu, Mar 25-Mar 28. - Flooding possible across portions of the Northern/Central Plains, the Northeast, the Central Appalachians, the Upper/Middle Mississippi Valley, the Mid-Atlantic, and the Great Lakes. - Flooding occurring or imminent across portions of the Northern/Central Plains, the Mississippi Valley, the Tennessee Valley, the Great Lakes, and the Ohio Valley. - Flooding likely across portions of the Northern/Central Plains, the Upper/Middle Mississippi Valley, and the Great Lakes. - Much above normal temperatures across portions of the Northern/Central Plains, the Upper/Middle Mississippi Valley, and the Great Lakes, Wed-Thu, Mar 27-Mar 28. 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