Extended Forecast Discussion NWS Weather Prediction Center College Park MD 330 PM EDT Mon May 24 2021 Valid 12Z Thu May 27 2021 - 12Z Mon May 31 2021 ...Overview... A pair of shortwave troughs will track east over the northern tier of the CONUS through Monday while the next trough digs down the West Coast, closing off southern California Sunday as the pattern becomes less progressive with ridging up the central Plains. Rainfall will be focused along a cold front from the central Plains to the East Coast on Friday, sagging south to the Gulf Coast with the front Saturday before focusing ahead of the western trough/low over the central Plains Sunday/Monday. ...Guidance Evaluation and Preferences... The latest deterministic models continue to depict reasonable clustering for the Thu-Sat period as low pressure along the front moves from the Plains to the Ohio Valley to a developing cold air damming wedge over the Mid-Atlantic. By then, uncertainty increases with a southern stream shortwave through Texas/lower MS Valley as well as the unfolding western trough/low and potential stalling troughing along the East Coast. Did a typical trend toward a majority ensemble blend (GEFS/ECENS) with a small weighting of the GFS/ECMWF/Canadian deterministic runs to offer just a bit of detail where appropriate. Blended the 12Z/13Z National Blend of Models with ECMWF/GFS/ECENS/GEFS for temperatures/PoPs/QPF. ...Weather Highlights/Hazards... Highest chances of rainfall during the period are Thursday night/Friday ahead of an eastward moving low from the central Plains to the Corn Belt eastward to the central Appalachians along a wavy frontal boundary with a potential area of organized and moderate to heavy rain shifting across the mid/lower Mississippi Valley into the Ohio Valley. Areas in the Mid-Atlantic look to see light/modest showers in the developing cold air damming. Then, return flow up the Plains meets the next cold front with potential repeating rain over the central Plains Sunday/Monday. Temperatures will be cool, 10 to 15 degrees below normal, in the northern Plains to Upper Midwest to northeast Friday/Saturday, expanding south down the Mid-Atlantic Saturday with the cold air damming. Meanwhile hot conditions, 10 to 15 degrees above normal and near records, persist in the Southeast until the cold frontal passage Saturday into Sunday. For the rest of the Memorial Day weekend, expect near to slightly below normal temperatures east of the Rockies, while the Pacific Northwest looks to see a warming trend with temperatures 10 to 20 degrees above normal by Memorial Day. Jackson Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php Hazards: - Heavy rain across portions of the Central Plains, the Lower Mississippi Valley, the Great Lakes, the Middle Mississippi Valley, the Upper Mississippi Valley, the Southern Plains, and the Ohio Valley, Thu, May 27. - Heavy rain across portions of the Central Plains, the Middle Mississippi Valley, and the Southern Plains, Sat-Mon, May 29-May 31. - Heavy rain across portions of the Southern Appalachians, the Central Appalachians, and the Ohio Valley, Fri, May 28. - Severe weather across portions of the Central Plains, the Middle Mississippi Valley, the Lower Mississippi Valley, and the Southern Plains, Thu, May 27. - Flooding possible across portions of the Central Plains, the Middle Mississippi Valley, and the Northern Rockies. - Flooding occurring or imminent across portions of the Central Plains, the Middle Mississippi Valley, the Lower Mississippi Valley, and the Southern Plains. - Much above normal temperatures across portions of California, the Pacific Northwest, and the Northern Great Basin, Mon, May 31. - Much above normal temperatures across portions of the Southeast, the Mid-Atlantic, the Southern Appalachians, and the Tennessee Valley, Thu-Fri, May 27-May 28. - Much below normal temperatures across portions of the Upper Mississippi Valley and the Northern Plains, Thu, May 27. 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