401 FXUS02 KWBC 080710 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 310 AM EDT Thu Oct 8 2026 Valid 12Z Sun Oct 11 2026 - 12Z Thu Oct 15 2026 ...Isaias will bring heavy rainfall and potential flash flooding across parts of the Mid-Atlantic and Northeast through Sunday... ...Remnants of Rachel to increase heavy rainfall potential across the Southwest and Intermountain West this weekend into early next week... ...Pattern Overview... The remnants of Isaias and associated deep tropical moisture will lift northeastwards bringing heavy rainfall and flash flooding potential across portions of the Mid-Atlantic and Northeast through Sunday. Meanwhile, the amplified western trough will interact with remnants of Rachel, bringing widespread rainfall a cross the Southwest into the Great Basin and Rockies/Plains. Additionally, chances for widespread snow arrives for the high elevations of the northern Rockies this weekend into early next week. ...Guidance/Predictability Assessment... The models continue to show relatively good agreement with the large-scale pattern of a trough moving southeastward and interacting with moisture from the tropical system Rachel. The models seem to also capture the progression of the northern-stream wave. The primary forecast uncertainty is resolving how quickly the western trough ejects into the Plains and how strongly it amplifies as it interacts with the developing ridge downstream. Additionally, confidence is lower concerning the timing and amplitude of shortwaves by mid-period. The ensemble means and the AI guidance seems to have a better handle on some of the smaller- scale differences. The forecast favored a multi-model blend approach through the early next week, with increasing reliance on ensemble means and AI guidance where deterministic solutions diverge. ...Weather/Hazards Highlights... The heavy rainfall concerns from Sunday into Monday will be associated with the lingering tropical moisture from Isaias. The remnants of Isaias will continue to move northeastward from the Mid- Atlantic, with rainfall gradually becoming more stratiform and shifting offshore. Some locally moderate to heavy rainfall could persist across portions of the Northeast and Mid- Atlantic on Sunday into Monday, leading to isolated flash flooding risk. The higher likelihood for flash flooding will occur particularly where the circulation interacts with frontal boundaries and where repeated convection develops. Farther west, the remnants of Rachel and the associated western trough will continue interact, leading to widespread heavy rainfall and localized flash flooding from the Southwest into the Great Basin, Rockies, and eventually the northern Plains on Sunday into Monday. Furthermore, cold air surging behind the cold front will lower snow levels, leading to accumulating snow over high elevations across the northern Rockies through Monday causing possible minor to moderate impacts. Moments of wet and heavy snow may cause impacts to power lines and trees. Another shortwave progresses eastward across the northern- tier, bringing another chance for showers along a frontal boundary across the north/central Rockies and Plains and Upper Midwest on Monday into Tuesday. Farther south across the Southwest into the Rockies and central/southern Plain, renewed chances for heavy rainfall develops as tropical moisture from Simon moves northward into the area. The moisture will move northeastward along the frontal boundary, spreading widespread showers across the Rockies, Plains, and Midwest. Oudit 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, excessive rainfall outlook, winter weather outlook probabilities, heat indices and Key Messages 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/#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 $$