Extended Forecast Discussion NWS Weather Prediction Center College Park MD 221 AM EDT Sat Oct 19 2024 Valid 12Z Tue Oct 22 2024 - 12Z Sat Oct 26 2024 ...General Overview... The weather pattern across the continental U.S. on Tuesday will be featured with an upper ridge and surface high over the Eastern U.S., accompanied by above average temperatures. An incoming trough from the Midwest will then dislodge this ridge and the associated cold front will herald the arrival of cooler weather towards the end of the week, but it will have limited moisture to work with so rainfall amounts from the Great Lakes to the Northeast will be generally light. Meanwhile, the next Pacific storm system is expected to approach the Pacific Northwest by late Thursday and into Friday, bringing a return to rain and high mountain snow from northern California to Washington state. An upper ridge and milder temperatures are likely ahead of this Pacific storm system. ...Guidance/Predictability Assessment... The latest model guidance features reasonably good agreement across the continental U.S. to begin the forecast period Tuesday, and a blend of the GFS/ECMWF/CMC along with some previous WPC continuity served as a good starting point in the forecast process. There is still quite a bit of uncertainty across the Western U.S. in regards to the placement of the upper ridge axis ahead of the approaching Pacific low, which also has considerable model uncertainty. There is more confidence in the forecast across the South and the Eastern U.S. with the large scale surface high that is progged to be in place. The ensemble means accounted for about 60% of the forecast blend by next Saturday. ...Weather/Hazards Highlights... The cold front crossing the Great Lakes and into the Northeast for the middle of the week will likely have just enough moisture and lift to produce some mainly light to moderate showers for the middle of the week, mainly north of the Interstate 70 corridor. It should continue to remain dry and mostly sunny for areas farther to the south across the Mid-Atlantic and the Southeast U.S., where the very pleasant fall weather will continue for a while. There are no risk areas in the Day 4 and Day 5 excessive rainfall outlooks. Out West, showers are expected to return to the Pacific Northwest coast by Thursday and become heavier going into Friday as the cold front from the Pacific low moves ashore. This currently does not look like an atmospheric river event, but some areas could get 1 to locally 2 inches of rainfall by Saturday morning. Lighter precipitation is possible for the Northern Rockies by this time. Snow is likely for the highest terrain of the Cascades. In terms of temperatures, it will feel more like September across much of the east-central U.S. for the middle of the week, with highs running 10-20 degrees above average for late October. The cold front will bring a return to more typical conditions for this time of year, but still quite pleasant. A warming trend then commences for the western High Plains and the Rockies by the end of the week and into next weekend as the upper ridge rebuilds ahead of the Pacific storm system. Hamrick 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