Extended Forecast Discussion NWS Weather Prediction Center College Park MD 315 AM EDT Mon Sep 22 2025 Valid 12Z Thu Sep 25 2025 - 12Z Mon Sep 29 2025 ...Heavy rain threat for portions of the Eastern U.S. late week... ...Overview... An amplified trough/closed low will move slowly from the Midwest on Thursday to the East by the weekend, with some energy meandering over the Southeast. The associated cold front will focus potentially heavy rainfall from the Gulf Coast/Southeast into the Appalachians and the Mid-Atlantic mainly Thursday and Friday. Meanwhile, Pacific moisture ahead of another cutoff low near the California coast could lead to daily rain chances over southern California into the Southwest as it drifts southeastward. An upper level ridge in between these two systems will allow for above normal temperatures much of the period from the interior West to the northern Plains. ...Guidance/Predictability Assessment... The latest numerical guidance remains in relatively good agreement with the large scale pattern through the medium range period. With the eastern trough/upper low, the CMC was notably faster as early as Day 3 with the UKMET also slightly faster, particularly by Day 5. Otherwise, a blend of the GFS and ECMWF was reasonable for much of the period. The GFS was stronger with holding a closed low over the Southeast next weekend, but there is consensus that some sort of weak energy may be left behind as the northern stream energy exits the Northeast. Good agreement in the models with the upper low over California that drifts into the Southwest. The greatest uncertainty is the latter half of the period with shortwaves moving through the Northwest. The WPC forecast today was based on a blend of the ECMWF with the GFS and UKMET for days 3 and 4 and the ECMWF with the ensemble means beyond. Overall, this maintains good agreement with the previous WPC forecast as well. ...Weather/Hazards Highlights... Widespread rain and convection will focus along and ahead of a cold front as it slowly moves into the East later this week. Anomalous moisture and ample instability will be in place, warranting broad marginal risks on the Days 4 and 5 (Thursday- Friday) ERO stretched from the Gulf Coast to the Mid- Atlantic. Dry antecedent conditions may limit the overall flood threat, but there continues to be enough of a heavy rainfall signal for the more vulnerable southern Appalachians region on Thursday where a slight risk is highlighted in the ERO. Additional slight risk upgrades are not out of the question within the broader marginal risks, and will be reevaluated with future issuances should the guidance show better consensus. Rainfall may linger across the Northeast and the immediate East Coast this weekend as well. Meanwhile, Pacific moisture ahead of an upper low near California will result in increasing rainfall chances across much of the Southwest into southern California. Moisture anomalies 2 to 3 standard deviations above normal and sufficient instability will result in at least a localized flash flood threat, particularly for vulnerable burn scar areas. This entire region is highlighted with a marginal risk for both Thursday and Friday's EROs. A more targeted slight risk was added on both days across southeast Arizona where QPF amounts look greatest. This activity will continue into the weekend as the upper low drops slowly south and eastward through the region. A ridge axis will build from the Four Corners states into the West with the most anomalously warm temperatures expected from the Northwest into the northern Rockies and Plains which may hold much of the period. The Desert Southwest should also see temperatures reaching or exceeding 100F, mainly into Thursday before the ridge shifts east. Expect near to below normal temperatures for the Central U.S. and Midwest under the large upper trough/low. As the low drifts eastward, temperatures will cool across the East as well. 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