850 FXUS02 KWBC 180546 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 146 AM EDT Sat Apr 18 2026 Valid 12Z Tue Apr 21 2026 - 12Z Sat Apr 25 2026 ...Overview... An active spring weather pattern will persist across CONUS with an upper level trough/low moves into the West and shortwave energy ejecting across the Intermountain West and into the Plains. The frontal system downstream will strengthen and push across the West into Central U.S. by mid-to-late next week, which will bring chances for widespread precipitation and mountain snow. Notable temperature swing will develop with above normal temperatures pushing eastward by mid-week, and below average temperatures returning for the West. ...Guidance/Predictability Assessment... Models continue to show good agreement on the overall pattern with troughing moving off of the East Coast, the ridge over western/central U.S., and the upper-level trough/low off the West Coast. Noticeable differences arise later in the period on Thursday, specifically over the Northwest/West. CMC, UKMET, and GFS seemed to show agreement with the shortwave troughs, compared to the ECMWF. GFS also showed higher run-to-run variability compared to the other models. Overall, the deterministic models seemed to show various solutions for the Pacific upper-level low/trough, but the ensemble means seemed to help eradicate some of the differences. Therefore, a multi-model blend was used for the first portion of the forecast, with phasing in the ensemble means towards mid-to- late week. ...Weather/Hazards Highlights... An unstable airmass supported by increasing return flow from the Gulf will support a broad axis of moisture convergence along a frontal boundary over the Gulf, which will trigger convection over portions of Central, South, and East Texas Tuesday. Locally heavy rainfall and isolated flash flooding may be possible, and there is a Marginal Risk of excessive rainfall for these areas in the Day 4/Tuesday Excessive Rainfall Outlooks (EROs). Meanwhile, a Pacific frontal system will continue to push east into western U.S. on Tuesday, resulting in increasing precipitation chances across much of California. Moderate rainfall and mountain snow are expected, with locally heavy rainfall possible in northern California that could lead to isolated flooding concerns. This flood threat is represented by a Marginal Risk of excessive rainfall for portions of northern California in the Day4/Tuesday EROs. The Pacific system and amplified trough will move across the Intermountain West on Wednesday and emerge in the Plains while strengthening Wednesday night into Thursday. The system is expected to bring widespread precipitation and strong gusty winds across the Intermountain West to the Plains and Mississippi Valley. Accumulating mountain snow will be possible across portions of the central and northern Rockies and into the Northern Plains. While impacts should be mainly confined to higher elevations, some travel impacts may be possible. Lower elevation rain may be moderate to heavy at times, particularly along favored upslope regions. As this energy ejects into the Plains late week, cyclogenesis will be likely, leading to increasing chances for organized convection. As a relatively cold weak front moves through Ohio Valley and across New England early next week, chances for isolated to scattered precipitation will be possible from Tuesday into Thursday. Much of the Desert Southwest and Southeast will experience mainly dry conditions next week, but a cold front will dip into the Southeast by the weekend bringing chances for showers and thunderstorms over the area. In addition, some isolated showers and storms will be possible for South Florida near a stalled frontal boundary through the week. Temperatures will continue to trend below average on Tuesday for much of the East Coast, Northeast in wake of a cold front. Texas will also see below average temperatures as a result of forecast precipitation and cloud cover. As the front moves into western U.S., temperatures over California will drop 10-20 degrees below normal on Tuesday. Above normal temperatures will develop over much of central and western U.S. ahead of the strong frontal system, with the Rockies and Plains seeing high temperatures rise to 15-25 degrees above average. By mid-week and for the remainder of the period, below normal temperatures will spread from west to east behind the western frontal system. Oudit 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, excessive rainfall outlook, winter weather outlook probabilities, heat indices and Key Messages are at: 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 $$