Extended Forecast Discussion NWS Weather Prediction Center College Park MD 420 PM EDT Wed May 15 2019 Valid 12Z Sat May 18 2019 - 12Z Wed May 22 2019 ...Guidance/Predictability Assessment... The 06 UTC GFS/FV3 and 00 UTC ECMWF/UKMET/Canadian offer good forecast clustering this weekend. Despite some common longer term model similarities, forecast confidence next week remains below normal due to less than stellar continuity issues. Accordingly, the WPC product suite primarily was derived from a composite model solution this weekend before quickly transitioning to more compatable 06 UTC GEFS mean and 00 UTC ECMWF ensemble mean into early next week amid growing forecast spread....Guidance Assessment and Weather Highlights/Threats... ...Weather Highlights and Hazards... Model and ensemble solutions continue to show above normal forecast spread with respect to northeastern U.S./Mid-Atlantic flow through this weekend as a series of potent Canadian upper systems progress within an energetic northern stream. Favor a composite. Upstream, a dynamic mid-upper level trough will lift northeastward from the southern Rockies to the central then northeastern U.S. Sat-Tue. This system will spawn surface system/low genesis with lead moisture inflow and instability providing the foundation for a threat of heavy convection/rainfall and severe weather as per SPC. Underneath, a gradually weakening closed low/convection will weaken over the eastern Gulf of Mexico. There remains a strong signal that Pacific flow will bring another round of strong height falls and widespread precipitation/terrain enhanced snows to the West later this weekend into early-mid next week before ejecting over the central U.S. Further 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 again early next week along with renewed unsettled weather/precipitation. 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, Sat-Sun, May 18-May 19. - Heavy precipitation across portions of California, the Northern Plains, and the Northern Rockies, Sat, May 18. - Heavy precipitation across portions of the Central Great Basin, the Northern Rockies, and the Northern Great Basin, Sun, May 19. - Heavy precipitation across portions of the Central Rockies, the Northern Plains, and the Northern Rockies, Sun-Mon, May 19-May 20. - Heavy precipitation across portions of the Northern Plains, Wed, May 22. - Heavy rain across portions of the Central Rockies, California, the Pacific Northwest, and the Central Plains, Mon-Tue, May 20-May 21. - 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, the Southern Plains, and the Ohio Valley, Sat-Wed, May 18-May 22. - Heavy rain across portions of the Black Hills of South Dakota, Wed, May 22. - 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 Middle Mississippi Valley, the Lower Mississippi Valley, the Great Lakes, the Ohio Valley, and the Tennessee Valley, Sun, May 19. - Severe weather across portions of the Central Plains and the Southern Plains, Mon, May 20. - Severe weather across portions of the Central Plains, the Middle Mississippi Valley, the Lower Mississippi Valley, the Southern Plains, and the Ohio Valley, Tue, May 21. - Flooding possible across portions of the Northern Great Basin. - Flooding occurring or imminent across portions of the Lower Mississippi Valley, the Northern Plains, the Great Lakes, the Northern Rockies, 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 the Central Plains, the Central Great Basin, the Northern Plains, the Northern Rockies, the Central Rockies, California, the Northern Great Basin, the Pacific Northwest, and the Southwest, Sat-Wed, May 18-May 22. - Much below normal temperatures across portions of the Central Plains, the Upper Mississippi Valley, the Great Lakes, the Northern Plains, and the Northern Rockies, Sat-Tue, May 18-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