124 FXUS02 KWBC 201924 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 324 PM EDT Tue Oct 20 2026 Valid 12Z Fri Oct 23 2026 - 12Z Tue Oct 27 2026 ...Southern Rockies to Southern High Plains Heavy Rain threat this weekend... ...Overview... An upper-level trough and associated moisture plume will bring a threat for heavy rainfall to parts of the Southern Rockies to Southern High Plains this weekend into early next week. This trough should split next week with a short wave/surface front racing across the Northern tier and weak energy lingering over the Southwest. Another Pacific shortwave may move into the Northwest bringing precipitation across the region next week. Across the Southeast, onshore flow will support additional rainfall across especially southeast Florida through much of the period. ...Guidance/Predictability Assessment... Model guidance is pretty well clustered for the beginning of the period featuring an elongated Western trough that splits with a shortwave moving through the northern tier into early next week and a weak upper low lingering over the Southwest. The greatest source of uncertainty during the period surrounds shortwave energy moving out of the Gulf of Alaska with a likely cutoff low forming off the British Columbia coast this weekend. There is a lot of run to run variability on the evolution of this, whether the low amplifies and moves into the Northwest U.S. late period or lingers off the British Columbia coast. This impacts the downstream evolution of the pattern over the north-central U.S. as well and the strength of a shortwave and also ridging over the West. The EC-AIFS and CMC bring the upper low farther south into the Northwest, resulting in amplified troughing over the West late period, while the GFS and ECMWF are less excited about this, with more ridging over the West. Ensembles are also pretty split, resulting in a highly uncertain forecast. The WPC forecast today leaned pretty heavy on the ensemble means late period, which seemed to be a fairly good middle ground solution for now, and consistent with the previous WPC forecast as well. ...Weather/Hazards Highlights... Across the Western U.S., the upper trough will continue to support periods of rain and embedded thunderstorms across the Four Corners region by late week. Anomalous moisture transport into the region, combined with ascent associated with the lingering upper low and forcing, could produce locally heavy rainfall, especially into the weekend across the southern Rockies to High Plains region. Any persistence of deep moisture and slow storm motion would increase the potential for excessive runoff, particularly over vulnerable terrain and burn scars. Therefore, a Marginal Risk of excessive rainfall for portions of the New Mexico into western Texas continues for Friday, while a Slight Risk is introduced for Saturday across portions of New Mexico and Texas into the Southern/Central High Plains. Further north, an upper low/trough digging southeastward from the Gulf of Alaska may move into the Northwest by later in the weekend. Depending on the evolution, this may bring increased precipitation chances to at least the Pacific Northwest. Elsewhere, a broad upper trough extending towards the western Atlantic may support persistent easterly flow and moisture transport into Florida. Periods of showers and thunderstorms could develop along the Florida coast, with rainfall potentially becoming more widespread across the southern peninsula if onshore flow persists. Repeated rainfall over urbanized areas and locations with poor drainage could lead to localized flash flooding concerns through the weekend into early next week. Santorelli/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 $$