174 FXUS02 KWBC 100730 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 330 AM EDT Sun May 10 2026 Valid 12Z Wed May 13 2026 - 12Z Sun May 17 2026 ...Guidance/Predictability Assessment... Guidance remains reasonably clustered with the larger scale upper pattern into mid-late week, highlighted by a West-Central U.S. warming ridge, troughing over the East, and shortwaves dropping from the Northern Plains/Great Lakes to reinforce East troughing. The greatest source of uncertainty continues to surround the upstream evolution and timing of a main closed low from the eastern Pacific that should meanwhile advance inland over the West and then downstream, leading a subsequent trailing shortwave series within increasingly zonal flow over the lower 48 into next weekend. Given the uncertainty and run-to-run changes in guidance without resolve through this forecast period, continued to lean heavily on albeit less than ideally compatible GEFS/ECMWF/Canadian ensemble mean in an effort for best feasible product continuity. ...Weather/Hazards Highlights... An eastern Canadian closed upper-level low will continue to help support a mean longwave trough down into the eastern U.S. into mid-late week. This pattern will support a persistent cyclonic circulation aloft, allowing multiple shortwave energies to approach the base of the mean trough from upstream. Impulses will lead to the progression of wavy frontal systems to bring periods of showers/thunderstorms through the eastern third of the country mid-late week. System progression to the Atlantic will also look to spawn moderate coastal cyclogenesis with wrapping moisture/rains lifting up/off the East Coast, lending into a maritime threat. Upstream, an eastern Pacific closed low is with much uncertainty slated to advance inland sometime mid-late week to focus organized light to moderate precipitation most likely across portions of the northern Great Basin, Pacific Northwest, and northern Rockies. A developing downstream surface low and frontal boundary will form down from the Northern Tier, bringing chances for showers and thunderstorms from the north-central U.S. to the Great Lakes/East. Farther upstream system energies will subseuently work inland into the West and downstream over the lower 48 with uncertain timing and weather focus in increasingly zonal flow aloft. Temperatures for the eastern third of the U.S. will be near to below normal into mid-late week before moderating into next weekend with main upper trough ejection into the Atlantic. Meanwhile, a slowly eastward shifting upper ridge will gradually spread well above normal temperatures out from the West to the Rockies and Central U.S. that may produce several high temperature records. 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 $$