Extended Forecast Discussion NWS Weather Prediction Center College Park MD 400 PM EDT Tue Sep 23 2025 Valid 12Z Fri Sep 26 2025 - 12Z Tue Sep 30 2025 ...Heavy rain threat for portions of the Mid-Atlantic to the Southeast beginning on Friday, with heavy rains likely across the Southwest through the weekend... ...Overview... An upper-level pattern that features eastward progressive waves across Canada will be contrasted with a slow-to-evolve omega block across mainland U.S. through the medium-range period. As a large Bermuda High remains anchored over the Atlantic, the progression of troughing near both the West and East Coasts will be further obstructed. Meanwhile, occasional injections of energy coming from the progressive higher latitude troughs in conjunction with two tropical disturbances/lows approaching from the Bahamas and western Atlantic could detach the upper low over the Southeast with highly uncertain potential interactions of the two tropical lows off the coast of the Southeast U.S. late in the period. The closed low over the Southwest is forecast to eventually open up and lift toward the northern/central Plains early next week as a longwave trough is forecast to edge toward the West Coast from the Pacific late in the period. The associated cold front will focus widespread rains from the Gulf Coast/Southeast in parts of the Mid- Atlantic through at least Friday. Meanwhile, Pacific moisture ahead of another cutoff low near the California coast could lead to daily rain chances over parts of California into much of 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 and the Northeast. ...Guidance/Predictability Assessment... The latest guidance continues to show good agreement on the aforementioned synoptic set up through much of the period, with much of the uncertainty centered over the Southeast U.S. into the western Atlantic. Persistent upper troughing near the East Coast and into the Southeast will tend to maintain a frontal boundary near or just off the coast through the period. A pair of potential tropical lows rounding the west side of the Bemuda High will add considerable uncertainty to the forecasts for the Southeast for early next week. The upper trough may tend to steer the tropical system just offshore although complex interaction between the upper trough and the tropical systems cannot be ruled out. Out West, there has not been too much of a change from the previous forecast cycle apart from some expected fluctuations in the placement of the QPF footprint across the Southwest, with focus sliding east into New Mexico from Sunday into Monday. The WPC forecast package today was based the consensus of the deterministic and ensemble means of 40% from the 06Z GFS/GEFS, 40% from the 00Z ECMWF/EC mean, and 20% from the 00Z CMC/CMC mean. Overall, maintained good continuity with the previous shift's forecasts. ...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, a broad marginal risk on the Days 4/Friday ERO stretching from the Gulf Coast to the Mid-Atlantic is maintained. Dry antecedent conditions may limit the overall flood threat, but future upgrades remain possible within the broader marginal risks, and will be reevaluated should the guidance show better consensus. Rainfall may linger across parts of the East into the weekend, and a marginal risk was included on the Day 5/Saturday ERO from eastern Georgia to southeast Virginia. A heavy rain area is expected across Virginia into North Carolinas on the Hazards Map. Meanwhile, Pacific moisture ahead of an upper low near California will result in increasing rainfall chances across much of the Southwest into 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 Friday and Saturday EROs with a more targeted slight risk on both days across southeast Arizona to southwest New Mexico where QPF amounts look greatest. This activity will continue into at least Sunday as the upper low drops slowly south and eastward through the region and may begin to taper off by Monday. 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 with only a gradual eastward shift. Temperatures across the Southwest will be below normal underneath the lingering upper low, with near normal temperatures elsewhere across the CONUS. Kong/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