935 FXUS02 KWBC 101800 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 PM 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 overall larger scale upper pattern from mid-late week into the weekend, highlighted by a western U.S. ridge that slides eastward into the Central U.S., 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 smaller scale details regarding the upstream evolution and timing of a main closed low from the eastern Pacific that should advance inland over the West and then downstream later on in the period. Models continue to struggle with this feature, with poor agreement both run-to-run and within the larger modeling suite as a whole. There was enough agreement to utilize a composite blend of deterministic guidance from the EC, GFS, UKMET, and EC-AIFS for Days 3 and 4. However, weighting shifted dramatically towards the ensemble means for the rest of the period, with 100% of the blend split between the EC and GEFS ensemble means by Day 7. This strategy seemed to best preserve continuity while maintaining integrity with the 13Z National Blend of Models. ...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. through mid to 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. 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. The persistent troughing looks to break down heading into next weekend as low amplitude ridging builds in from the west. Upstream, an eastern Pacific closed low is slated, with much uncertainty, 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 subsequently 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 from the West to the Rockies and Central U.S. that may produce several high temperature records. Schichtel/Miller 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 $$