226 FXUS02 KWBC 200714 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 314 AM EDT Tue Oct 20 2026 Valid 12Z Fri Oct 23 2026 - 12Z Tue Oct 27 2026 ...Southern California/Southwest/Rockies Heavy Precipitation... ...Overview... A upper-level trough and associated moisture plume will bring chances for showers and thunderstorms across the Southwest into the Rockies and Plains, with potential accumulating snow over higher terrain. The system will continue to move eastward into the Plains bringing additional showers and thunderstorms into early next week. Another Pacific shortwave will move into the Northwest bringing precipitation across the region. Across the Southeast, onshore flow will support additional rainfall across portions of Florida through the Monday. ...Guidance/Predictability Assessment... Model guidance remains well clustered for the start of the period with the troughing over western U.S., ridging over central U.S., and troughing beginning to exit offshore over eastern U.S. However, differences arise in regard to the timing, amplitude, and eastward progression of the western trough, especially with the GFS/GEFS serving as outliers compared to the ECMWF and CMC. These differences will influence the location and organization of precipitation across western U.S. Otherwise, models seem to capture the eastward progression of the ridge through early next week. Therefore, the forecast favored a multi-model blend with the ECMWF/CMC, with increasing emphasis on the ensemble means toward the latter portion of the period. ...Weather/Hazards Highlights... Across western U.S., the upper trough extending into the Southwest will continue to support periods of rain and embedded thunderstorms from California and the Great Basin into the Four Corners region and central Rockies by late week. Anomalous moisture transport into the region, combined with ascent associated with the upper low and forcing, could produce locally heavy rainfall. Any persistence of deep moisture and slow storm motion would increase the potential for excessive runoff, especially 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 central Plains. Furthermore, snow levels and precipitation type will depend on the strength of the cold advection accompanying the upper low. Higher elevation of the Sierra Nevada and south/central Rockies could receive accumulating snow, particularly as the system shifts inland and colder air becomes more established. As the system continues to push eastward, strengthening southerly flow may promote lee cyclogenesis over the High Plains. Therefore, showers and thunderstorms will expand across portions of the High Plains and adjacent central or southern Plains through the weekend into early next week. Gulf moisture and frontal convergence will may lead to organized convection. Further north, an upper low/trough digging southeastward from the Gulf of Alaska is expected to move into the Northwest by the weekend. Increasing ascent and Pacific moisture transport may support renewed precipitation across the Pacific Northwest/Intermountain West. The highest terrain could experience accumulating snow as cold air accompanies the system. 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. This is reflected with a Slight Risk of excessive rainfall for portions of southeast Florida for Saturday. 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 $$