Extended Forecast Discussion NWS Weather Prediction Center College Park MD 244 AM EDT Mon Sep 28 2020 Valid 12Z Thu Oct 01 2020 - 12Z Mon Oct 05 2020 ...Hot and dry conditions return for the West... ...Overview and Guidance/Predictability Assessment... Guidance continues to 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 a swath of significant rainfall over the Northeast with a well-defined New England wave into Thu. The 18 UTC GFS and 12 UTC ECMWF offer similar solutions for this system as it enters the short range. 00 UTC runs remain in line. Amplified pattern nature and good guidance continuity suggests high predictability for the CONUS Thu-Sat and a composite of the similar GFS/ECMWF seems reasonable. Strong northeast Pacific systems should help maintain the strength of the western North American upper ridge into the weekend. By Sun/Mon guidance begins to diverge regarding possible weakening of the ridge as the upstream trough begins to drift a bit eastward and ejecting impulses possibly filter into/through the ridge. Opted for a solution in line with the more amplified ECMWF/ECMWF ensemble mean as high amplitude flow tends to linger. However, the sheared nature of shortwave support in this pattern lowers predictability for the details of frontal waviness along/off the East Coast and for a wave digging through the central to east-central U.S. Sat-Mon. ...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 to reach 5-15 degrees F above normal (isolated higher values) from California/Arizona/Nevada through the Pacific Northwest. Some record-breaking values will be possible, mainly over parts of California but perhaps into western Oregon/Washington as well. By next weekend modest weakening of the upper ridge could allow for some moderation of the heat close to the West Coast. Parts of the Northeast may see moderate to heavy rain/storms into Thu as a vigorous wave lifts up an East Coast front. A trailing front with one or more weak waves, reaching the East Coast later week, may provide another focus for rainfall over the Mid-Atlantic/Northeast along with unsettled maritime conditions. Rain with this front should be lighter due to less moisture being available than with the first system. Both fronts will tend to decelerate and possibly stall near/south of the southern Florida Peninsula and Keys where periods of rain are possible through the period. Tropical moisture influx there could fuel some heavy downpours. 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. A wave expected to drop into the central then east-central U.S. Sat-Mon may produce light to locally moderate rain from the Plains to the Great Lakes and Ohio Valley. Cold air surges will support temperatures of 5-15 degrees F below normal for much of the central to eastern U.S.. There is a chance for a first frost/freeze of the season for the Northern Plains and Upper Mississippi Valley late 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