Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Fri Sep 25 2020 Valid 12Z Mon Sep 28 2020 - 12Z Fri Oct 02 2020 ...Guidance/Predictability Assessment... There is an increasing guidance signal supporting development of a highly amplified pattern across the CONUS next week, with ridging across the West and a deep upper trough/low over the central and eastern U.S. This will lead to warm to hot temperatures once again in the West, and cool temperatures more reminiscent of mid- to late fall farther east. Rainfall should focus from the Great Lakes/Mid-South toward the Appalachians and East Coast next week. However, there remains quite a bit of forecast spread with respect to the degree of flow separation within the main upper trough. The 12/18 UTC GFS and 12 UTC Canadian showed minimal flow separation compared to the 12 UTC ECMWF/UKMET/NAVGEM that even show a closed low development threat. I placed emphasis on the 12 UTC ECMWF ensemble mean for the WPC medium range product suite that leaned 2/3 the way toward the more amplified solution composite given upstream guidance amplification trends. Newer 00 UTC guidance has trended this way as well, but still leaves the door open for closed low development. ...Weather/Hazard Highlights... Ample energy seems set to dig into the potent upper trough/low position will push cold fronts across the central and eastern U.S. through the period and provide focus for rain. Amplification trends have slowed the eastward translation of a main lead front and reinforcement as contingent on uncertain stream separation. A significant WPC frontal continuity adjustment was applied to address timing. Modest to locally heavy rainfall totals may focus from the Appalachians eastward for the first part of the workweek, albeit with trough axis differences affecting wave development and moisture inflow potential. Florida will also see some rain along the fronts as they try to push across the state and bring drier air. Unsettled conditions are expected to linger across the Midwest/Mid-South to Great Lakes region under the upper trough. Given the upper-level pattern and the cold fronts, below normal temperatures are forecast to push across the Plains toward the Eastern Seaboard, especially in terms of daytime highs, which should be 5-15 degrees F below normal. But by Thu/Fri, below average lows are also forecast for the Central/Northern Plains toward the Midwest, and there is a chance for a first frost or freeze of the season in portions of those areas. Upper ridge re-emergence will return hot, dry conditions to the West, so fire danger is a concern. Much above normal high temperatures are forecast to build from the Desert Southwest and California/Nevada to the Pacific Northwest. Some record-breaking highs/warm lows look to be approached/exceeded especially over parts of California. 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 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