Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Thu Oct 24 2024 Valid 12Z Sun Oct 27 2024 - 12Z Thu Oct 31 2024 ...General Overview... A digging trough in the West will promote rain, high elevation snow, high winds and cooler temperatures across much of that region next week. This trough may generate heavy rainfall, thunderstorms and high winds over parts of the Great Plains and Mississippi Valley mid-to-late next week as well. A downstream ridge, centered over the Baja Peninsula, will support above average temperatures from the Plains to eventually the East Coast. ...Guidance/Predictability Assessment... Models were fairly well clustered regarding the overall synoptic evolution across the lower 48 next week. There's some uncertainty around whether the upper pattern will split with a southern stream trough propagating through Four Corners and into the Plains, while a northern stream trough glides across southern Canada. The deterministic 12z Canadian becomes a notable outlier due to its attempt to create a split flow pattern with an anomalous closed low over the Front Range next Wednesday. Thus, it wasn't included in the blend beyond day 5. It's worth noting that the AIFS, FuXi and Pangu ML models also signal a split flow pattern over the West beginning on Tuesday. A combination of the deterministic 12z ECMWF/CMC/UKMET and 18z GFS were utilized in the days 3 and 4 blends with the EC and GFS favored. By day 5 the Canadian and UK are removed and the 12z ECE/CMCE and 18z GEFS are introduced to the blend to mitigate some of the most anomalous split flow signals seen in some of the deterministic guidance. A more ensemble mean weighted blend is continued through day 7 due to relatively good run-to-run consistency and not much model spread around the mid-level trough over the central CONUS.. ...Weather/Hazards Highlights... A low pressure system will arrive over the Pacific Northwest on Saturday, bringing with it rain, high elevation snow to the region through Sunday. High winds will impact the lee side of the Northern Rockies this weekend as well. Rain, snow and high winds expand into the Rockies on Monday and Tuesday. Cyclogenesis over the lee of the Rockies will support high wind concerns across portions of the Great Plains and Mississippi Valley early next week. Depending on how deep the upper trough gets over the Plains next week, there could be some potential for Gulf of Mexico moisture to interact with the attendant cold front over the Plains/Mississippi Valley and generate heavy rainfall and thunderstorms. The digging trough in the West will be mirrored by a staunch downstream ridge over the southern and central U.S. next week. Kebede 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