587 FXUS02 KWBC 091802 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 202 PM EDT Sat May 9 2026 Valid 12Z Tue May 12 2026 - 12Z Sat May 16 2026 ...Guidance/Predictability Assessment... The latest guidance remains reasonably well clustered with the larger scale pattern through most of next week, highlighted by a building/warming ridge over the West, troughing over the East, and shortwaves dropping from the Northern Plains/Great Lakes to reinforce troughing in the East. A guidance composite continues to offer a solid forecast basis in this time frame. The greatest source of uncertainty continues to surround the upstream evolution and timing of a main shortwave/closed low that digs over the eastern Pacific before eventually advancing inland over the Northwest/West. Initial 00/06Z guidance seemed to be split between the faster UKMET/CMC and the slower GFS, with the EC and EC-AIFS in between. The latest 12Z CMC and UKMET are now much closer to consensus for Days 3 and 4, with solutions diverging significantly for Days 5, 6, and 7. For the latter half of the period, the 12Z CMC interestingly enough is now the slowest piece of guidance, with the EC and EC-AIFS in between the faster UKMET and slower GFS. Given the uncertainty and run-to-run changes between some guidance members, continued to lean heavily on the EC and GEFS ensemble means with the remaining deterministic solutions favoring the EC, EC-AIFS, and GFS. ...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. 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, bringing periods of showers and thunderstorms through the eastern half of the country next week. By mid to late week, each system eventually works downstream to the Atlantic to spawn moderate coastal cyclogenesis with wrapping moisture feeds before lifting up/off the East Coast. Upstream, an eastern Pacific closed low will advance inland sometime mid to late next week, focusing organized light to moderate precipitation across portions of the northern Great Basin, Pacific Northwest, and northern Rockies. A developing downstream surface low and frontal boundary will form over the Northern Tier, bringing chances for showers and thunderstorms across the northern Plains into the Upper Midwest, and then the Great Lakes/East. Deep boundary layer mixing may bring some gusty winds across the Rockies and Plains with system passage. Temperatures across the eastern half of the U.S. will remain near to below normal through most of next week. Meanwhile, a ridging pattern will keep well above normal temperatures in place across much of the western U.S., with pre-frontal warmth spreading eastward into the central U.S. mid to late week. Several high temperature records are likely to be tied or broken through the period. 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 $$