Extended Forecast Discussion NWS Weather Prediction Center College Park MD 251 AM EDT Wed Oct 9 2024 Valid 12Z Sat Oct 12 2024 - 12Z Wed Oct 16 2024 ...Desert Southwest record heat moderates/lingers into Saturday... ...Overview... A shortwave diving through the north-central U.S. this weekend will amplify troughing across the East by early week, with multiple waves of impulses to reinforce it. Much below normal temperatures and frost/freeze may be a concern for some. This should initially suppress central U.S. heat southward towards the southern Plains resulting in another few days of much above normal temperatures (nearing daily records). A deep trough into the West Coast will amplify upper ridging again across the west-central U.S. which another round of above normal temperatures. ...Guidance/Predictability Assessment... Models continue to show good agreement on the overall pattern evolution across the CONUS during the period, but with some typical differences especially into next week. This allowed for an early period blend of the deterministic models. There is a lot of uncertainty by next Tuesday-Wednesday with multiple shortwave impulses that round/reinforce the trough over the East, with some models indicating potential for a cut off low over/near the Mid- Atlantic next week. The ensemble means show just amplified troughing which exemplifies the uncertainty in the evolution of the Eastern trough. Seemed prudent then to lean more heavily towards the ensemble means the second half of the period for the WPC forecast tonight. ...Weather/Hazards Highlights... A large part of the lower 48 will see fairly dry weather for a majority of the period. A compact eastern Pacific upper trough/low may bring a brief period of mostly light rainfall to the central West Coast around into Saturday, with a little light precipitation possibly reaching farther eastward into the West thereafter. Then a front approaching the Pacific Northwest may bring some moisture and light to moderate rainfall into the region by the start of next week. The amplifying upper trough and accompanying surface evolution should bring some areas of locally enhanced rainfall to parts of the Great Lakes/Northeast by late weekend into the early part of next week. A central U.S. upper ridge will continue to promote a period of well above normal temperatures with northern stream troughing and a cold front pushing the greatest warm anomalies southeast with time from the central Plains and Mid/Upper Mississippi Valley to the Southeast. Temperatures around 10 degrees above normal in the Southwest to southern High Plains could set additional daily records though the temperatures have moderated compared to recent days and the short range. The northern Rockies/High Plains may see temperatures reach up to 10-20F above normal by early next week. Meanwhile, some near to slightly above normal temperatures in the East this weekend should be replaced by temperatures generally 5-10 degrees below normal next week underneath amplified troughing. Later period cold frontal passage is also expected to provide a spread of much cooler temperatures from the north-central U.S. through the Midwest/Great Lakes and Northeast starting in about a week with some frost/freeze concerns. Santorelli Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation forecast (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: 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/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml https://www.wpc.ncep.noaa.gov/#page=ovw