Extended Forecast Discussion NWS Weather Prediction Center College Park MD 234 AM EDT Sat Sep 26 2020 Valid 12Z Tue Sep 29 2020 - 12Z Sat Oct 03 2020 ...Guidance/Predictability Assessment... The models agree to develop a highly amplified pattern over the CONUS next week, with upper ridging over the West and a deep east-central U.S. upper trough. Some uncertainty remains with respect to the degree of flow separation within the main upper trough, but forecast spread is finally improving. In general recent ECMWF/UKMET and ECMWF ensembles showed more separation and surface frontal wave/enhanced QPF response than recent GFS/Canadian and GEFS runs. However, a day 3-5 (Tue-Thu) model blend and day 6/7 ensemble mean composite now seems reasonable given latest guidance trends toward amplification and separation, especially with the 00 UTC GFS and GEFS. Upstream, the mean upper ridge along the west coast persists due to warm advection downstream from a slow moving north Pacific cyclone. The ridge is slow moving and persistent, so the models and ensembles have better than average agreement, also favoring a consensus-based approach. ...Weather/Hazard Highlights... The amplified upper ridge will return hot and dry conditions to the West, so a growing fire danger is again a concern all next week. Temperatures of 5-15 degrees F above normal are forecast from California/Nevada through the Pacific Northwest that may include some record-breaking values, especially over parts of California. Cold fronts will work through the central and eastern U.S. and provide focus for showers/storms, with moderate to locally heavy rainfall possible up the Eastern Seaboard Tue/Wed dependent on frontal wave details under influence of base of upper trough stream separation and timing uncertainties. Cold air aloft will meanwhile provide instability for scattered showers across the Midwest/Great Lakes/Appalachians under the upper trough, including some Great Lake enhancement. Amplitude and slow eastward progression of the upper trough may also support later next week frontal waves that could maintain unsettled/rainy East Coast and maritime conditions. Cold air surges should support below to much below normal temperatures for much of the central to eastern U.S. next week of 5-15 degrees F below normal. In this pattern, there remains a chance for a first frost/freeze of the season for the Northern Plains and Upper MS Valley into later next week. 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