Extended Forecast Discussion NWS Weather Prediction Center College Park MD 307 PM EDT Tue Jun 08 2021 Valid 12Z Fri Jun 11 2021 - 12Z Tue Jun 15 2021 ...Locally heavy rainfall threat Friday across central Appalachians/Mid-Atlantic... ...Much above normal temperatures and record heat this weekend into early next week across much of the interior West/Northern Plains.... ...Overview... Upper pattern is forecast to amplify along 105W this weekend into early next week, promoting warm/hot temperatures over much of the West and northern High Plains that may near or break daily records. Troughing will exit but then build back into the East where rainfall will focus over the Mid-Atlantic into the Southeast. A Pacific front will push into WA/OR early next week. ...Guidance/Predictability Evaluation... The latest model guidance offers average to above average predictability for the Nation during the medium range period (Friday-Tuesday) and will be driven by a strong upper ridge or closed high over New Mexico (500mb height anomalies at least +2 to +3 sigma). Weaker ridging across the southern to central U.S. will erode as troughing becoming established over the Northeast this weekend an reinforced early next week. 00Z ECMWF and its ensembles were more bullish in troughing over the Great Lakes than the GFS/GEFS and CMC/CMC ensembles, but such a strong upstream ridge could support this deeper troughing in the ECMWF guidance. For now, opted to split the difference via a multi-model/ensemble mean blend (GFS/GEFS and ECMWF/ECMWF ensemble mean) as the lead-in evolution across the Upper Midwest will be sensitive to how some smaller-scale features track. ...Weather Highlights/Hazards... The amplification of the upper ridge over the central U.S. is expected to bring another round of much above normal to possibly record warm/hot temperatures to the northern Rockies and northern Plains late this weekend and early next week. Temperatures may be 10-25F above normal with some triple-digit readings possible across central/eastern Montana Monday and Tuesday. Nighttime lows will also remain warm for the region and likely stay 10F to 15F above normal for middle of June. Elsewhere across the CONUS, temperature anomalies are expected to be near to slightly above normal. The threat of locally heavy rainfall capable of producing flash flooding will linger on Friday across portions of the central Appalachians and Mid-Atlantic as higher moisture interacts with a southward-dropping cold front. For the weekend and early next week, the dominant upper ridge over the central CONUS will keep much of the area on the drier side with any substantial precipitation confined to the Pacific Northwest as well as portions of the Southeast and Florida along a residual frontal boundary. Fracasso/Taylor 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 Southern Appalachians, the Mid-Atlantic, the Central Appalachians, the Ohio Valley, and the Tennessee Valley, Fri, Jun 11. - Flooding possible across portions of the Lower Mississippi Valley and the Southern Plains. - Flooding occurring or imminent across portions of the Lower Mississippi Valley and the Southern Plains. - Excessive heat across portions of the Southern Plains, Fri, Jun 11. - Much above 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 Upper Mississippi Valley, and the Southwest, Sat-Tue, Jun 12-Jun 15. - Much above normal temperatures across portions of the Middle Mississippi Valley, the Great Lakes, and the Upper Mississippi Valley, Fri, Jun 11. 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