Extended Forecast Discussion NWS Weather Prediction Center College Park MD 352 PM EDT Tue May 14 2019 Valid 12Z Fri May 17 2019 - 12Z Tue May 21 2019 ...Overview and Weather Highlights/Threats... Overall, amplified mean troughing aloft will bring a wet period to a large portion of the western U.S. and Plains states during the weekend to early next week. Much of the western US to the northern high Plains will turn colder, with much of the mid-lower MS Valley eastward turning more summerlike. Guidance is steadily trending toward resolving the leading strong trough progressing from the West and Rockies Fri/Sat and in ernest over the central then east-central states from the weekend into early next week. This neg-tilt system will spawn surface system genesis and offers rounds of locally heavy convection/severe weather as per SPC. Underneath, a gradually weakening closed low is expected to meander from the northern to eastern Gulf of Mexico and offer some heavy rain potential for southern Florida. There is some agreement that upstream flow will bring another round of strong height falls and widespread precipitation/terrain enhanced snows to the western states Fri into this weekend, continuing inland early week across the Great Basin to the High Plains. Upstream, there is a still uncertain guidance signal to develop a deeper low in the eastern Pacific early next week that offers potential to reach CA and the Great Basin/Southwest by Tuesday 21 May along with renewed unsettled weather/precipitation. Meanwhile, model and ensemble solutions continue to show above normal forecast spread with respect to downstream northeastern U.S./Mid-Atlantic flow through the medium range period as a series of potent Canadian upper systems progress within an energetic northern stream. These upper systems and surface system reflections have trended stronger into the weekend. Teleconnections relative to the negative height anomaly center associated with the West Coast mean trough then favor modest cyclonic flow aloft into early next week. ...Guidance Assessemnt and Preference... The latest deterministic models (06 UTC GFS/FV3 and 00 UTC ECMWF/UKMET/Canadian) seem to offer better than expected forecast clustering Fri into Sun morning, but confidence remains somewhat muted due to less than stellar continuity issues. Even so, the WPC product suite primarily was derived from a composite model solution during this period that seems increasingly reasonable before quickly transitioning to the much more compatable ensemble means (06 UTC GEFS/00 UTC ECMWF ensemble mean) into early next week amid growing forecast spread. 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, Fri, May 17 and Sun-Tue, May 19-May 21. - Heavy precipitation across portions of the Central Rockies, the Central Great Basin, the Northern Rockies, the Northern Great Basin, and the Northern Plains, Fri-Sat, May 17-May 18and Sun-Tue, May 19-May 21. - Heavy rain across portions of California and the Pacific Northwest, Fri-Sat, May 17-May 18and Sun-Mon, May 19-May 20. - Heavy rain across portions of the Central Plains, the Lower Mississippi Valley, the Northern Plains, the Great Lakes, the Middle Mississippi Valley, the Upper Mississippi Valley, and the Southern Plains, Fri-Sun, May 17-May 19. - Heavy rain across portions of the Central Plains, the Lower Mississippi Valley, the Northern Plains, the Middle Mississippi Valley, the Upper Mississippi Valley, and the Southern Plains, Mon-Tue, May 20-May 21. - Severe weather across portions of the Central Plains, the Middle Mississippi Valley, the Southern Plains, the Upper Mississippi Valley, and the Northern Plains, Fri, May 17. - Severe weather across portions of the Central Plains, the Middle Mississippi Valley, the Lower Mississippi Valley, the Southern Plains, and the Upper Mississippi Valley, Sat, May 18. - Severe weather across portions of the Central Plains and the Southern Plains, Mon, May 20. - Severe weather across portions of the Central Plains, the Lower Mississippi Valley, the Northern Plains, the Middle Mississippi Valley, the Upper Mississippi Valley, and the Southern Plains, Tue, May 21. - Severe weather across portions of the Middle Mississippi Valley, the Lower Mississippi Valley, the Great Lakes, the Ohio Valley, and the Tennessee Valley, Sun, May 19. - Flooding possible across portions of the Northern Rockies. - Flooding occurring or imminent across portions of the Central Plains, the Lower Mississippi Valley, the Northern Plains, the Great Lakes, the Middle Mississippi Valley, the Upper Mississippi Valley, the Southeast, the Southern Plains, and the Ohio Valley. - Flooding likely across portions of the Northern Rockies and the Northern Great Basin. - Much below normal temperatures across portions of California, the Central Great Basin, the Pacific Northwest, and the Northern Great Basin, Mon-Tue, May 20-May 21. 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