Extended Forecast Discussion NWS Weather Prediction Center College Park MD 258 PM EDT Wed Oct 23 2024 Valid 12Z Sat Oct 26 2024 - 12Z Wed Oct 30 2024 ...General Overview... A predominantly zonal pattern across the mainland U.S. will give way to a more amplified pattern by next week. The prevailing tranquil weather this weekend across much of the country will become more unsettled across the western U.S. with periods of rain, high- elevation snow and gusty winds. The trough that brings the unsettled weather in the West early next week will likely be pushing east against a warm high pressure system in the eastern U.S., resulting in a sharp and wavy frontal boundary to drape across the mid-section of the country where bands of moderate to locally heavy rain appear possible. ...Guidance/Predictability Assessment... Models are in reasonable agreement regarding the overall synoptic pattern across the CONUS through the medium range period. The main discrepancy among the guidance suite has to do with the timing of the western U.S. trough and the associated precipitation. The ECMWF and CMC tend to be faster with the eastward progression of the trough compared with the GFS. Nevertheless, the spread is relatively small given the predicted depth of the trough even out to Day 7. Therefore, the WPC medium-range forecasts are based on a general consensus of 40% 00Z ECMWF/EC mean, 40% 06Z GFS/GEFS, and 20% 00Z CMC/CMC mean, with higher percentages from the ensemble means for Day 6 & 7. This blend yielded a solution that compares well with the previous WPC forecasts. ...Weather/Hazards Highlights... A cold front ahead of a closed mid-level low over the Gulf of Alaska will reach the Pacific Northwest this weekend. This cold front will gradually work its way through much of the western U.S. by midweek next week, bringing unsettled weather with periods of rain and lowering of snow levels across the higher elevations behind the front along with gusty winds. The Pacific Northwest will see the precipitation moving through this weekend, followed by the northern to central Rockies early next week, with some snow lingering over the central Rockies by midweek. With the passage of the cold upper trough, temperatures will be well below average. Portions of the Great Basin and Intermountain West may experience minimum temperature anomalies between 10-20 degrees below average from Monday to Wednesday. Meanwhile, an upper ridge with a broad southerly return flow at the surface behind a large high pressure system will promote increasingly warm temperatures first across much of the Plains this weekend and especially by Monday. The warmth will then expand eastward to encompass much of the Great Lakes into New England by Wednesday. The trough that will bring the unsettled weather across the West will be pushing east against the warm high pressure system in the eastern U.S., resulting in a sharp and wavy frontal boundary to drape across the mid-section of the country by midweek. There is some signal for an organized moderate to heavy rain event to unfold over parts of the lower Missouri Valley into the upper Midwest midweek if a low pressure wave is able to consolidate and remains relatively slow-moving along the front, where bands of moderate to locally heavy rain with embedded thunderstorms could develop midweek. In addition, some locally strong Chinook winds are possible as modest cyclogenesis is currently forecast to occur on the lee side of the northern Rockies late Sunday into Monday, as well as across parts of the Intermountain West behind the cold front as far south as interior southern California. Kong 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