Extended Forecast Discussion NWS Weather Prediction Center College Park MD 247 PM EDT Wed Sep 18 2019 Valid 12Z Sat Sep 21 2019 - 12Z Wed Sep 25 2019 ...Imelda moisture brings an East-Central Plains to Midwest Heavy Rainfall Threat... ...Overview and Guidance Evaluation/Preferences... The main flow pattern features are an exiting trough over the northern Plains Saturday that drags a cold front across the eastern CONUS through Tuesday and a trough digging south off the Pacific Northwest Coast Saturday into Sunday before closing a cutting off over California Monday. The 06Z GFS is much farther east with this low with the center over the Great Basin while the 00Z GFS/ECMWF/CMC/UKMET all have the center over California. Therefore the 06Z GFS was not included in the model blend beyond Day 3. The more consistent ECMWF was preferred and by Day 5 a blend of the 00Z ECENS mean and the 00Z GEFS mean took heavier weight through Day 7. ...Weather Highlights/Threats... Deep tropical moisture with the remains of Imelda will offer a significant threat of locally excessive rainfall into the weekend over the central CONUS. Expected inland lifting/entrainment into the flow with approaching mid-latitude upper trough crossing to the north and a cold front that pivots over the east-central plains will focus moisture/heavy convective storm potential with cell training from the east-central Plains to the Mid-MS Valley/Midwest, in particular eastern Kansas, northern Missouri into Illinois. Meanwhile, an aforementioned upper trough will lift northeastward over the northern Plains. This will support an organized convective focus with locally heavy downpours and a severe thunderstorm risk over the Dakotas into Saturday as per SPC. Deepened lead moisture may also support some record high minimum temperatures ahead of the front Saturday morning. Upstream, upper low/trough energies will reload back into an again unsettled West/Southwest Sunday into next week with a precipitation swath over the Northwest then Great Basin for Days 4/5. The risk then shifts to the southwest where moisture from Lorena is drawn into AZ/NM as the low cuts off over CA. The combination of monsoonal/tropical moisture and maybe some Lorena remnants leads to a prolonged heavy rain threat Monday through Wednesday. Jackson 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 rain from portions of the Central Plains to the Midwest, Sat-Sun, Sep 21-Sep 22. - Heavy rain across portions of the Central Plains and the Middle Mississippi Valley, Mon-Tue, Sep 23-Sep 24. - Heavy rain across portions of the Southwest, Sun-Tue, Sep 22-Sep 24. - Flooding possible across portions of the Southern Plains, the Upper Mississippi Valley, and the Northern Plains. - Flooding occurring or imminent across portions of the Northern Plains and the Great Lakes. - Flooding likely across portions of the Central Plains and the Middle Mississippi Valley. 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