979 FXUS02 KWBC 080715 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 315 AM EDT Fri May 8 2026 Valid 12Z Mon May 11 2026 - 12Z Fri May 15 2026 ...General Overview... It generally remains the case that an amplified mean flow pattern will persist through much of the period, tied to a closed low anchored over eastern Canada. This will bring deep cyclonic flow and shortwave energies ejecting into central/eastern U.S. and the western Atlantic to support a series of wavy frontal passages, which will bring showers and thunderstorms along the boundaries. As the primary cold front moves southeastward, below normal temperatures will spread into eastern U.S. through Tuesday. A strengthening ridge across the western U.S. will bring well above normal temperatures that will gradually move into the Central U.S. by midweek. Additional troughing, with much more uncertainty, may move into the West by the end of the period. ...Guidance/Predictability Assessment... Recent guidance solutions aloft remain reasonably well clustered with the larger scale pattern develolpment and maintainance through early-mid next week as highlighted by a building ridge over the West, troughing over the East, and shortwaves dropping from the Northern Plains into the Great Lakes to reinforce the trough in the East. A model composite offers a solid forecast basis for this that seems well supported by ensembles. The greatest source of uncertainty still surrounds the well upstream evolution and timing of a shortwave that drops south and eastward from near Alaska into the northeast Pacific and possibly eventually into the West. Recent ECMWF/Canadian guidance brings the bulk of energy inland. The GFS and GEFS members continue to keep this system well offshore, with less breakdown of the ridge over the West. The new 00 UTC guidance tonight does not provide much additional clarity. Given lingering unresolved uncertainty, latest WPC surface progs and sensible weather grids tried to best maintain continuity by bringing decent energy inland, but holding some stream separted troughing offshore as per a mainly ECMWF/NAEFS ensemble mean blend. ...Weather/Hazards Highlights... The closed upper-level low over eastern Canada will continue to support a mean longwave trough extending into the eastern U.S. through the period. This pattern will bring a mature and persistent cyclonic circulation aloft and multiple shortwave energies ejecting along the base of the mean trough. Each impulse will support the progression of a wavy cold front that sweeps through the eastern half of the country early next week, leading into moderate coastal low genesis. The frontal passage will bring widespread showers and thunderstorms across portions of the Great Lakes, Lower Mississippi Valley/Southern Plains, Ohio Valley into the Northeast and Mid- Atlantic, with locally heavy rainfall possible along the boundary then up the coast through Monday. As the primary cold front moves closer to the East Coast, much of the Plains and Mississippi Valley will see a short-lived drying trend by Monday with the front clearing the East Coast by Tuesday. Farther west, another frontal boundary begins to form over the Northern Tier as a potential clipper system, bringing chances for showers and thunderstorms across the northern Plains into the Upper Midwest, and eventually the Great Lakes and Northeast. In addition, deep boundary layer mixing may bring somewhat gusty winds across the Rockies and Plains through the period. System progression to the western Atlantic may also support renewed moderate coastal low genesis and inland wrapping rains/unsettled weather Wednesday into Thursday. Meanwhile, the possible mid-later trough/system ejection into/across the Northwest/West may spread some generally light and terrain induced precipitation as well. Temperatures will continue to trend below average across the eastern U.S., as the primary cold front pushes southeastward through Monday. Across the western U.S., a ridging pattern will bring well above normal highs through midweek, and will push eastward into central U.S. by Tuesday. Record tying/breaking highs will expand from California into Southern Plains on Tuesday. Some of the high temperatures across portions of central California Valleys and Desert Southwest will reach Moderate to Major HeatRisk levels into Monday/Tuesday. Moderate to major, and even spotty extreme, HeatRisk is also possible this weekend into early next week for parts of south Florida, and given continued drought and low humidities, may pose an increased fire weather risk as well. 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, 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 $$