426 FXUS02 KWBC 120738 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 338 AM EDT Tue May 12 2026 Valid 12Z Fri May 15 2026 - 12Z Tue May 19 2026 ...Guidance/Predictability Assessment... Guidance forecast clustering has improved across much of the lower 48 valid Friday into Sunday, bolstering confidence in a GFS/ECMWF/UKMET/Canadian model composite blend that is well supported by ensembles. Model forecast clustering is not as stellar with details and system/stream interactions heading into next week as upstream energies work into the western to central U.S., but a more compatible GEFS/ECMWF/Canadian ensemble means and machine learning guidance composite blend seems to provide a decent forecast basis and product continuity given growing uncertainties. ...Weather/Hazards Highlights... Amplified upper troughing will persist over the East into Friday. System progression to the Atlantic will spawn moderate coastal cyclogenesis with moderate wrapping moisture/rains/winds lifting into New England while acting as a maritime threat. Upstream guidance finally agrees to progress a current main eastern Pacific upper level closed low/trough bodily inland to the north- central U.S./south-central Canada by Friday to spawn surface cyclogenesis and focus light-moderate Midwest/Great Lakes trailing frontal QPF. Activity diminishes with weekend downstream system progression over eastern Canada and the Northeast. Farther upstream system energies subsequently work into the West and downstream up across the central U.S. with less certainty this weekend into early next week. However, there is am emerging signal that weekend upper trough passage over the West will focus some organized precipitation chances broadly over the Northwest and north-central Intermountain West/Rockies. Wavy downstream frontal genesis and lead Gulf return flow of moisture and instability may set the stage to fuel an emerging later weekend/early next week enhanced central U.S. convective rainfall pattern to monitor. Meanwhile, an eastward spreading upper ridge will spread well above normal pre-frontal temperatures across the Central to Eastern U.S. this period that may support local high temperature values. To the south, low level onshore flow will bring shower into Florida in proximity to upper low development near/east of the Bahamas. 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 $$