Extended Forecast Discussion NWS Weather Prediction Center College Park MD 240 AM EDT Thu Sep 24 2020 Valid 12Z Sun Sep 27 2020 - 12Z Thu Oct 01 2020 ...Overview... Latest guidance continues to indicate a high-confidence large-scale pattern amplification next week to a strong western ridge/upper high and east-central trough/upper low. Smaller-scale details within the synoptic eastern trough remain somewhat uncertain. The amplified pattern will bring another warm-up for much of the West (and record highs in California/Arizona) versus mid- or late-fall temperatures for the East. Rainfall will focus over the Midwest/Northeast and Florida next week. ...Guidance/Predictability Assessment... Through the 12Z/18Z guidance, only the UKMET was different enough to exclude from a blended solution that trended toward more ensemble inclusion with time. The new FV3-based GEFS mostly aligned with the 12Z ECMWF ensemble mean though its 12/18Z cycles differed on timing/strength of eastern shortwaves through the mean trough. The GFS runs continued to favor incoming Pacific shortwaves to add to the eastern trough at a slightly lower latitude from the ECMWF/Canadian, leading to a quicker progression of the GFS vs ECMWF/Canadian. Leaned more toward the slower ECMWF-led cluster though the GFS/GEFS was not discounted as it was within the acceptable spread. ...Weather/Hazard Highlights... Rainfall will primarily be confined to areas east of the Rockies/Plains, around low pressure near the Great Lakes and along/ahead of the cold fronts pushing well south into the Gulf of Mexico. As southerly flow off the Atlantic lifts into the Northeast, rainfall could be locally modest but otherwise generally light. Frontal passages in Florida will touch off some showers as well as drier air tries to reach the southern Gulf. In the West, any rainfall over WA/ID will retreat northward Monday as ridging strengthens up the West Coast and through western Canada. Dry conditions will hold through the rest of next week; however, offshore flow and low relative humidity may aggravate fire concerns. See SPC for their extended outlook on fire danger. Sunday will be a transition day for much of the CONUS, as any western coolness and eastern warmth will flip for the work week. Temperatures 10 to 15F above normal will be common over many areas of the West right to the coast, especially northern CA and southwestern OR. Record highs/warm lows look to be approached/exceeded especially over parts of California and Arizona, where highs of 100 to 110F will be common over the lower deserts. The Plains to East Coast will see slightly below normal highs behind the lead cold front Sunday into Monday. Reinforcing cold front late Mon into Tue will bring much cooler temperatures into the Upper Midwest/Great Lakes and Ohio/Tennessee Valleys Wed/Thu. Highs may be 5-15 deg F below normal over a large area of the East, between the Plains and Appalachians southward to the Gulf Coast. Fracasso 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