Extended Forecast Discussion NWS Weather Prediction Center College Park MD 413 PM EDT Tue Apr 04 2023 Valid 12Z Fri Apr 07 2023 - 12Z Tue Apr 11 2023 ...Overview and Guidance/Predictability Assessment... The upper level pattern will transition to one that is more zonal with a series of inherently low predictable northern and southern stream shortwave troughs and impulses before re-amplifying with increasing uncertainty next week. The latest runs of global guidance and their ensemble means are handling the evolution fairly well three fore utilized a general blend of the 00Z CMC/UKMET/ECWMF, 06/00Z GFS, 00Z GEFS and EC ensemble means, and the 13Z NBM. This approach maintains run to run continuity. ...Weather/Hazards Highlights... The leading front will track offshore and then settle over the Atlantic Ocean and the Gulf of Mexico through much of the extended period. Showers and thunderstorms will linger across portions of the Southern Plains, Lower Mississippi Valley and Gulf Coast into Friday, where a low pressure wave is forecast to form near the front just offshore. An experimental Days 4 WPC Excessive Rainfall Outlook (ERO) with "Marginal" threat was already in place across parts of the Gulf Gulf and was expanded a little to the north and east to account for the latest QPF trends. The proximity of the wavy front should support some additional periods of moderate precipitation across the South through the weekend into early next week. Most of the guidance and WPC forecast limits the northward lift of the precipitation for the late week/weekend activity. Increasing northern and southern stream interaction into early next week and the digging of cooling cold fronts with modest precipitation themselves down across the central and eastern states offers renewed potential for some northward spread of activity down across the Southeast given some signal for moderate coastal/maritime low development, but ample uncertainties remain with the system. As the flow becomes more zonal multiple shortwaves will move onshore the West Coast, which should favor moderate to locally heavier precipitation across the Pacific Northwest into Friday/Saturday along with modest snows further inland across the Northwest and vicinity. This pattern will weaken by early next week in response to a strong upper ridge building along the West Coast. With this feature comes generally warmer and drier conditions for a vast majority of the western states. However, eastern Pacific upper trough amplification and slow approach may portend a renewed wet pattern for especially the Pacific Northwest in about a week. Campbell/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 Hazards: - Heavy rain across portions of the Lower Mississippi Valley, the Tennessee Valley, the Mid-Atlantic, the Southern Appalachians, the Southeast, and the Southern Plains, Fri-Sat, Apr 7-Apr 8. - Heavy snow across portions of the Pacific Northwest and the Northern Great Basin, Sun, Apr 9. - Flooding possible across portions of the Great Lakes, the Upper Mississippi Valley, and the Northern Plains. - Flooding occurring or imminent across portions of the Southeast and the Lower Mississippi Valley. - Flooding likely across portions of the Southeast. - Much below normal temperatures across portions of the Upper Mississippi Valley and the Northern Plains, Fri, Apr 7. WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, experimental excessive rainfall outlook, winter weather outlook probabilities and heat indices 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