281 FXUS02 KWBC 071901 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 301 PM EDT Thu May 7 2026 Valid 12Z Sun May 10 2026 - 12Z Thu May 14 2026 ...General Overview... 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. to support a series of 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... The latest guidance shows good agreement on the large scale for the first half of the period which mainly features a building ridge over the West, troughing over the East, and a shortwave dropping from the Northern Plains into the Great Lakes to reinforce the trough in the East. The greatest source of uncertainty surrounds the evolution and timing of a shortwave that drops south and eastward from near Alaska into the northeast Pacific and possibly eventually the West. Some of the 00z guidance seemed to suggest a possible trend towards this system moving into the West late period, rather than a cut-off low well off the Coast like was the consensus yesterday. But the timing of this solution is highly uncertain, with the ECMWF fast, and the CMC/EC-AIFS slower. The GFS and GEFS members continue to keep this system well offshore, with less breakdown of the ridge over the West. The new 12z guidance this afternoon do not provide any additional clarity, and generally look similar to the 00z runs. There does seem to be somewhat of a suggestion that more troughing will come into the West late period than suggested by the previous forecasts, so the WPC surface progs and sensible weather grids tried to trend in that direction showing more of a ridge breakdown than the previous shift. The WPC forecast today was weighted more towards the middle ground CMC and EC-AIFS solutions, along with the ensemble means. Also introduced additional, albeit light, QPF across the West for the Wednesday and Thursday time period compared to what the 13z NBM initially offered. ...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 strong cold front that will sweep through the eastern half of the country early in the period. 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 through Monday. Across the southern tier, the primary heavy rainfall threat is expected to focus near the quasi-stationary frontal boundary extending from eastern Texas through the Gulf Coast region on Sunday. Deep- layer Gulf moisture transport and weak impulses moving through the southern stream will support repeated convective redevelopment along the boundary. With flooding concerns over the area, a Marginal Risk continues for the Day 4/Sunday ERO across parts of the Southeast. On Monday, the boundary weakens as the primary cold front moves into the area. 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. The late period possible trough into the West may spread some generally light and terrain induced precipitation mid week next week 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 by Monday into 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. Santorelli/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 $$