Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 PM EDT Thu Oct 24 2024 Valid 12Z Sun Oct 27 2024 - 12Z Thu Oct 31 2024 ...General Overview... An upper-level trough digging into the Pacific Northwest this weekend will spread unsettled weather across much of the western U.S. early next week with high-elevation snow, gusty winds and colder temperatures. This trough will then push eastward against an expansive warm high pressure system anchored over the eastern U.S., resulting in a wavy sharp front across the mid-section of the country where a moderate to heavy rain event appears to emerge across the mid-Mississippi Valley to the Midwest by midweek next week. ...Guidance/Predictability Assessment... Model guidance maintains fairly good agreement with the overall synoptic evolution across the mainland U.S. through the medium- range period. The digging trough over the western U.S. early next week is forecast to attain maximum amplitude by about Tuesday while on the verge of splitting into a southern stream upper low. The Canadian model is most pronounced with this scenario while all other models show a decent amount of trough splitting, before the entire trough lifts and heads eastward into the mid-section of the country by midweek. There is more noticeable model spread on how fast the trough will lift northeast toward the upper Midwest or Great Lakes by next Thursday. Otherwise, models today generally show better agreement on the timing of the precipitation moving through the western U.S. through early next week. Therefore, the WPC medium-range forecasts were based on a general model compromise of 40% from the 06Z GFS/GEFS, 40% from the 00Z ECMWF/EC mean, and 20% from the CMC/CMC mean. Higher weightings were given to the ensemble means for Day 6 and 7. This blend yielded a solution compatible with the previous WPC forecasts. ...Weather/Hazards Highlights... The cold front associated with a digging upper-level trough from the Pacific Northwest will continue to penetrate further inland as the medium-range period begins on Sunday. Periods of rain, high- elevation snow, windy and colder conditions are expected to overspread much of the rest of the western U.S. through early next week behind the front. High winds could locally impact the lee of the northern Rockies this weekend, and then down into the southern Rockies and southern High Plains by about Tuesday. Modest cyclogenesis across the Canadian prairies will advance a front across the northern Plains and upper Midwest through early next week. This front is forecast to sharpen with time as it continues to push against an expansive high pressure system anchoring across the eastern and southern U.S. Snow will appear to linger over the northern to central Rockies and into the northern High Plains behind a low pressure wave where accumulating snowfall appears likely. Ahead of the sharpening front, a long fetch of return flow from the Gulf of Mexico could lead to a moderate to heavy rain event to emerge across the mid- Mississippi Valley to the Midwest with embedded thunderstorms by midweek next week especially if a low pressure wavy is able to consolidate along the front. In the meantime, precipitation associated with the next Pacific system is forecast to move into the Pacific Northwest during midweek next week. The digging trough in the West will be mirrored by a staunch downstream ridge over the southern and central U.S. next week. This ridge will support temperatures between 20-30 degrees above average across the Plains on Monday before spreading into the Mississippi Valley and East on Tuesday, Wednesday and Thursday. There's also a potential for widespread high temperature records to be tied or broken across from Arizona to Texas on Sunday followed by an expansion into the Plains and Upper Midwest on Monday. Kong/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