Extended Forecast Discussion NWS Weather Prediction Center College Park MD 244 PM EDT Sun Oct 20 2024 Valid 12Z Wed Oct 23 2024 - 12Z Sun Oct 27 2024 ...General Overview... A generally benign weather pattern is expected for many areas across the continental U.S. for the middle of the week to be featured with a surface high over the Eastern U.S., accompanied by above average temperatures and continued dry conditions from the Mid- Atlantic to the Southeast U.S.. An incoming trough from the Midwest 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 to occasionally moderate. There may be another chance for some organized rains there again next weekend. Meanwhile, the next Pacific storm system is expected to approach the Pacific Northwest late in the week, 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 across much of the Central U.S. ...Guidance/Predictability Assessment... Recent model cycles have struggled with the flow pattern across the eastern Pacific and into the Pacific Northwest, and this in turn affected the amplitude and position of both upper ridge over the Rockies and western High Plains, and also the evolving closed low off the Northwest Coast and its eventual evolution as it tracks inland. The 06 UTC GFS/GEFS and 00 UTC ECMW/ECMWF ensemble means converged upon a better clustered solution over medium range time periods, bolstering forecast confidence to a degree, probably closer to average levels. A prefered composite blend of these guidance pieces also seems to provide a solid forecast basis for the rest of the nation along with the NBM, but latest 12 UTC guidance run clustering is not quite as good. ...Weather/Hazards Highlights... A leading cold front crossing the Great Lakes/Ohio Valley and into the Northeast Wednesday into Thursday will likely have just enough moisture and lift to produce some mainly light to moderate showers. Later period system approach has more uncertainty, but would support another period of organized rain potential there into next weekend. 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 currently no risk areas in the Day 4 and Day 5 excessive rainfall outlooks. The pattern will become favorable for the return of precipitation to the Pacific Northwest late this week into the weekend. However despite some recent improvement in the area, there is continued model spread for a system expected to develop over the eastern Pacific by midweek and lift northeastward thereafter. Rain and high elevation northern Cascades snow could commence as early as late Thursday per the fast side of recent spread, or take until late Friday or so on the slower side. Currently this looks more like a broad precipitation event rather than a focused atmospheric river, but some locally enhanced totals will be possible. Lighter weekend precipitation is forecast to reach the Northern Rockies. Temperatures will feel more like September across areas from the central U.S. into the Northeast mid-week, with highs running 10-20 degrees above average for late October. A main cold front pushing rapidly southeastward from the northern Plains will bring a return to more seasonable to conditions for the end of the week. From late week into the weekend, a building Western U.S. upper ridge that pushes eastward ahead of the Pacific storm system should promote a warming trend first over the Intermountain West and Rockies/western High Plains, and then covering much of the central U.S. where many areas should see highs upwards to 10-15 degrees above normal. Hamrick/Schichtel 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