Extended Forecast Discussion NWS Weather Prediction Center College Park MD 342 PM EDT Tue Aug 11 2020 Valid 12Z Fri Aug 14 2020 - 12Z Tue Aug 18 2020 ...Guidance/Predictability Assessment... Decent agreement was seen in 06Z GFS and 00Z ECMWF which compose most of the forecast, with increasing reliance on the GEFS and ECENS starting on Day 5. The 12Z GFS has since come more in line with the 00Z ECMWF. The general pattern is a trough lingering over New England into this weekend, a ridge just upstream drifting east from the Great Lakes and over/near New England into next week, an active flow pattern over the Canadian Prairies through this weekend that becomes a trough over the Great Lakes next week, a ridge over the Southwest that builds over the northern/Canadian Rockies Sunday/Monday and a retrograding low along the northern CA coast that gets lifted north in the flow ahead of the next low moving across the Gulf of Alaska. ...Weather/Hazard Highlights... Surface high pressure will expand down the Eastern Seaboard this weekend, causing damming that will linger into next week/until the cold front associated with the Great Lakes trough pushes through. A wavy surface front ahead of the damming and extending west into the TN Valley will act to focus convection, with heavy rain likely for across south-central Appalachians this weekend. The cold front ahead of the trough moving from the Canadian Prairies will be another focus for convective development for the upper Midwest and down the Plains this weekend. This broad cold front shifts to New England, the Eastern Seaboard, and approaches the central Gulf coast by Tuesday with diurnally enhanced rounds of convective development ahead of it. This is all east of the ridge that builds over the Desert SW and continues to limit any monsoon conditions in The West through at least the middle of next week. The building ridge will spread max temp anomalies of 10 to 15 degrees above and possible daily records from the southern High Plains and Four Corners Desert Southwest and up across The West west of the Rockies this weekend. The cold front will shift max temps of 5 to 10 degrees below from the Northwest across the northern Plains this weekend then across the central and southern Plains and Midwest through early next week. 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 across portions of the Upper Mississippi Valley, Fri, Aug 14. - Heavy rain across portions of the Southeast, the Southern/Central Appalachians, and the Mid-Atlantic, Fri-Sun, Aug 14-Aug 16. - Flooding occurring or imminent across portions of the Middle Mississippi Valley. - Excessive heat across portions of the Central Great Basin, California, and the Southwest, Fri-Tue, Aug 14-Aug 18. - Excessive heat across portions of California, Sat-Sun, Aug 15-Aug 16. - Excessive heat across portions of the Southern Plains, Fri, Aug 14. - Excessive heat across portions of the Lower Mississippi Valley and the Southern Plains, Fri-Sun, Aug 14-Aug 16. - Much above normal temperatures across portions of California, the Pacific Northwest, the Great Basin, and the Northern Rockies, Sat-Mon, Aug 15-Aug 17. - Much above normal temperatures across portions of the Southern Plains, Fri, Aug 14. 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