Extended Forecast Discussion NWS Weather Prediction Center College Park MD 255 AM EDT Sun Oct 20 2024 Valid 12Z Wed Oct 23 2024 - 12Z Sun Oct 27 2024 ...General Overview... The weather pattern across the continental U.S. for the middle of the week will be featured with a surface high over the Eastern U.S., accompanied by above average temperatures and continued dry conditions from the Mid-Atlantic and the Southeast states. 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. 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... It remains the case that model spread is higher than usual throughout the entire forecast period, and thus below average confidence in forecast specifics. The models are still struggling with the flow pattern across the eastern Pacific and into the Pacific Northwest, and this in turn affects 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. Changes in future forecasts are a near certainty as the weather pattern comes into better focus in future model runs. Upon examination of the available guidance, the GFS and GEFS mean, and to a slightly lesser extent the CMC, were generally in better agreement with the ML guidance from the ECMWF, which differed in many areas from the operational ECMWF. The GFS based guidance appeared to have a better overall handle on the forecast evolution, so the forecast was hedged more in that direction. Some previous WPC continuity was also used for days 3 through 6. The GEFS and NAEFS accounted for about 60-70% of the forecast blend by next weekend amid the high model spread. ...Weather/Hazards Highlights... The cold front crossing the Great Lakes and into the Northeast Wednesday into early Thursday will likely have just enough moisture and lift to produce some mainly light to moderate showers, 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 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 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 the 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 precipitation is forecast to reach the Northern Rockies by the weekend. 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 and possibly even a little higher over parts of the Upper Midwest/northern Great Lakes on Tuesday. A cold front pushing rapidly eastward from the northern Plains will bring a return to more seasonable 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 on the order of 10-20 degrees above normal. 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