456 FXUS02 KWBC 181933 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 333 PM 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 the CONUS next week as a potent mid/upper level low swings across northern California and the Pacific Northwest before ejecting eastward into the northern Plains. This system will bring strong winds and widespread precipitation, including the potential for moderate to heavy rain and mountain snow. Heavy rain and severe weather threats then expand into the Central U.S. by late week as a surface low strengthens and rich moisture is drawn northward from the Gulf. This active pattern will foster significant temperature swings, with above normal temperatures pushing from the Central U.S. eastward, while below normal temperatures return across the West. ...Guidance/Predictability Assessment... The latest guidance continues to have a relatively good handle on the large scale pattern through most of the medium range period. Most of the uncertainty stems from the evolution of smaller scale waves within and rotating around the inland penetrating mid/upper level low/trough across the Western/Central U.S., with these details affecting surface low placement and development and sensible weather. Forecast preferences leaned more heavily towards the ECMWF and EC-AIFS given slightly better run-to-run stability, but most weight was placed on the ECMWF and GEFS ensemble means, particularly for Days 5 and 6. This composite blend seemed to provide a good foundation of large scale features while still maintaining an acceptable level of finer scale details. ...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 southeast TX Tuesday. Locally heavy rainfall and isolated flash flooding may be possible, and there remains a Marginal Risk of excessive rainfall for this area in the Day 4/Tuesday Excessive Rainfall Outlook (ERO). 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 also represented by a Marginal Risk of excessive rainfall for portions of northern California in the Day 4/Tuesday ERO. 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, a strong developing surface low is likely to lead to increasing chances for organized convection and severe weather. As a relatively weak cold front moves through the Ohio Valley, Mid- Atlantic, and Northeast early next week, chances for isolated to scattered showers will be possible from Tuesday into Thursday. Much of the Desert Southwest and Southeast will be mainly dry next week, but a cold front will dip into the Southeast by the weekend bringing chances for showers and thunderstorms. 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 in the wake of a cold front. Temperatures in Texas will also be below normal as a result of precipitation and cloud cover. Below normal temperatures will spill into California and much of the West as the strong mid/upper level low pushes inland. Above normal temperatures will develop over much of central and western U.S. ahead of this strong system, with the Rockies and Plains seeing high temperatures rise to 20-30 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. Miller/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 $$