534 FXUS02 KWBC 210455 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1255 AM EDT Tue Apr 21 2026 Valid 12Z Fri Apr 24 2026 - 12Z Tue Apr 28 2026 ...Overview... A fairly active and progressive large-scale pattern will persist across much of CONUS as a mid/upper-level low and trough will gradually translate east across the northern Plains into through the weekend, with troughing extending back into the West. This system will bring strong winds across the West and Plains, with some lingering rain and mountain snow through Friday. As the trough and strengthening surface low interacts with a northern stream of Gulf moisture, episodes of heavy rain and severe weather will become more likely across parts of the central U.S. and much of the eastern U.S. through the period. The system will bring periods of anomalous warmth ahead of it for the East and late- season cool intrusions as below average temperatures expand from the western U.S. to the central U.S. behind a strong eastward advancing cold front. ...Guidance/Predictability Assessment... The latest deterministic model suite remains in reasonably good agreement on the synoptic-scale evolution through Day 5 (Sunday), particularly regarding the progression of the Pacific trough over western/central U.S. into south-central Canada. Later in the period, spread increases with respect to the timing and amplitude of the shortwave energy embedded within the mean flow. Differences are also apparent in a Pacific energy developing towards Day 6-7. The NBM provides a good baseline for the sensible weather fields, with incorporating the ensemble means to mitigate some of the finer and small scale differences. Therefore, the forecast maintained a multi-model blend weighted towards deterministic guidance for the first portion of the period, and the ensemble means toward the later in the period. ...Weather/Hazards Highlights... The upper low over the northern High Plains will gradually lift into south-central Canada late this week, carrying multiple embedded shortwaves rotating around the base of the trough. This will continue to bring periods of low elevation rain and mountain snow, with locally heavy precipitation possible along favored terrain over the Intermountain West, Rockies, and Plains. Accumulating snow will primary be confined to higher elevations, with impacts limited to high mountain passes and mountain towns. In addition, strong gusty winds are expected across parts of the Rockies into the Plains. This system will support the eastward projection of a surface low and cold front across the Plains into the Midwest by the end of the week and eventually the East by the weekend. The cold front will interact with warm Gulf moisture and an unstable airmass, which will support a corridor of showers and thunderstorms across the Plains into much of the eastern U.S. through the weekend. The combination of the large scale forcing and increasing instability along and ahead of a strengthening surface low and strong cold front, will support widespread clusters of strong to severe thunderstorms with the potential for locally heavy rainfall and isolated flash flooding over the parts of Mid/Lower Mississippi Valley into Ohio/Tennessee Valley. This flooding threat is highlighted by a Marginal Risk in the Day 4/Friday ERO. Given increasing soil moisture from previous bouts of convection, an upgrade to a Slight Risk is not out of the question in future updates. The front will begin to drape across much of the southern U.S. and will slowly move across the Southeast through the weekend, with a chance for a weak area of low pressure redeveloping along the front. This will reinforce showers and thunderstorm threats across the south-central Plains, Ohio Valley, and Southeast through Monday, with locally heavy rainfall and possible flood threat to monitor. Over into the West, the upper-level trough lingering over the West will maintain unsettled conditions through Monday, including lower elevation rain and mountain snow. Below normal temperatures over much of western U.S. will expand east into the Northern/Central Plains by Friday and parts of the Mississippi Valley by the weekend behind the cold front. Parts of the Northern Plains/Rockies will drop to 20-25 degrees below normal, where highs will drop between 30s and 40s on Friday through Sunday. Ahead of the frontal system, above average temperatures will persist through Friday across the southern parts of central U.S. into much of the eastern U.S. before temperatures moderate into the weekend into the beginning of the next week. Over the Pacific Northwest, temperatures will begin to trend slightly above average late in the period as upper level ridging sneaks into the region. 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 $$