Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1141 AM EDT Wed Sep 23 2020 Valid 12Z Sat Sep 26 2020 - 12Z Wed Sep 30 2020 ...Overview... Latest guidance continues to indicate a high-confidence large scale pattern amplification next week from a nearly zonal flow across the northern tier of the CONUS to a strong western continental ridge/upper high and east-central continental trough/low. Smaller-scale details of the embedded troughs driving the amplification remain somewhat uncertain. The amplified pattern will bring another warm-up for much of the West (and perhaps near record highs in California/Arizona) versus mid-fall temperatures for the East along with precipitation shifting from the northern tier this weekend across the Midwest/Northeast next week. ...Guidance/Predictability Assessment... The initial concern is the trough axis shifting east across the northern Plains Saturday and amplifying over the Great Lakes Sunday. The 00Z CMC quickly becomes the less amplified/quicker with this trough axis while the 00Z ECMWF/06Z GFS are slower/more amplified while the 00Z UKMET is the most amplified. So an initial general model blend quickly shifts to a preference for the 00Z ECMWF/06Z GFS for Days 4/5. The main amplifying shortwave enters the continent near the AK/BC border late Sunday and quickly shifts southeast to the northern Plains Sunday and the eastern central Plains/Midwest Tuesday. The deterministic ECMWF/GFS diverge with this wave by Day 6 with the GFS more progressive. However, there is good trough axis agreement with the 00Z ECENS/06Z GEFS means which dominate the preference for Days 6/7. ...Weather/Hazard Highlights... Precipitation over the weekend will be limited to the Northwest CONUS, the Great Lakes region and the Southeast Coast/Florida with high pressure dominating the Southwest and East. A cold front races down the Plains and across the Midwest Monday through Tuesday as the east-central trough develops and low pressure swings through the Great Lakes. This front then sweeps across the Eastern Seaboard Wednesday. Gulf/Atlantic moisture streams in ahead of the front and enhances rainfall from the Midwest to the Mid-Atlantic and Northeast Monday night to Tuesday night. In the West, Pacific Northwest/extreme northern Rockies rainfall will retreat northward Monday as ridging strengthens up the West Coast and through western Canada Monday through Wednesday. The upper ridge and surface high pressure centered over the northern High Plains will favor dry conditions for areas west of the Plains next week, including offshore flow/fire concern for the West Coast. The temperature anomaly pattern this weekend will be cool in the Northwest (by 5 to 10F on Saturday) and warm over the Southwest/central Plains to Northeast will give way to much above normal temperatures for the West Coast and Southwest with much below normal temperatures spreading from the Northern Plains to the entire east through the first half of next week. Coverage of positive 10 to 15F anomalies for highs will increase with time west of the Rockies beginning Sunday. Some locations in California and the southwest corner of Oregon will see the best potential for max temperatures above 15F more than normal with offshore flow and an increased risk of fire conditions. Record highs/warm lows look to be approached/exceeded especially over parts of California and Arizona. Highs of 100 to 110F will be common over the lower deserts. The Plains to East will have an initial warm-up this weekend ahead of the leading cold front. Greatest anomalies for warm sector daytime highs this weekend (at least plus 10F) should be from the central Plains into the Great Lakes/Northeast this weekend into Monday. Next Tuesday and Wednesday, expect moderately below normal highs (5-10F below normal) from the Upper Midwest into the Great Lakes and Ohio/Tennessee Valleys behind the cold front/under the upper trough/low. Many areas look to stay below 60F for the Upper Midwest the Great Lakes. Jackson 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