Extended Forecast Discussion NWS Weather Prediction Center College Park MD 252 AM EDT Sun Sep 27 2020 Valid 12Z Wed Sep 30 2020 - 12Z Sun Oct 04 2020 ...Hot and dry conditions return for the West... ...Overview and Guidance/Predictability Assessment... Models and ensembles show upper level flow settling into a highly amplified pattern featuring a western U.S./Canada ridge and east-central trough. This configuration will support very warm/hot and dry conditions west of the Rockies and below normal temperatures over much of the central/eastern states. Wavy fronts ahead of the upper trough may produce areas of significant rainfall over the East. The large scale/amplified nature of the pattern provides above average to high predictability for the mean flow. In particular a series of strong North Pacific systems tracking toward or near the Alaska Peninsula will likely help to maintain the western upper ridge through at least the end of the period. There has been quite a bit of forecast spread and run-to-run variability for early period middle/lower Mississippi Valley upper trough energy which may separate for a time before rapidly ejecting northeastward ahead of upstream flow. Latest guidance is coming into better agreement and WPC progs reflect an increasing separation signal supporting a wavy and slowly translating eastern U.S./western Atlantic front. The WPC medium range product suite was primarily derived from a GFS/ECMWF/Canadian model blend Wed/Thu to include better system detail and amplitude consistent with improved predictability before also blending in GEFS/ECMWF ensemble means days 5-7. ...Weather/Hazard Highlights... The West will see increasing fire danger once again this week as the amplified upper ridge over the region brings a return of hot and dry conditions. Expect temperatures will reach 5-15 degrees F above normal (perhaps isolated higher values) from California/Nevada through the Pacific Northwest. Some record-breaking values will be possible, mainly over parts of California. Cold fronts working through the central and eastern U.S. will provide focus for showers/storms, with moderate to locally heavy rainfall possible Wed into Thu over from the Mid-Atlantic to the Northeast. 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 week frontal waves that could maintain unsettled/rainy East Coast and maritime conditions. Cold air surges should support below to much below normal temperatures of 5-15 degrees F for much of the central to eastern U.S. this week. In this pattern there remains a chance for a first frost/freeze of the season for the Northern Plains and Upper Mississippi Valley by later in the 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