Extended Forecast Discussion NWS Weather Prediction Center College Park MD 346 PM EDT Thu Apr 23 2020 Valid 12Z Sun Apr 26 2020 - 12Z Thu Apr 30 2020 ...Extended Period of Much Above Normal Temperatures Across the West... ...Cool With Two Storm Systems Affecting Eastern States... ...Guidance/Predictability Assessment... There are two areas of concern model-wise. One area of disagreement lies near the Canadian Maritimes where the 00z ECMWF and its ensemble mean phase two systems aloft faster that the remainder of the guidance which led to a faster low track, which would impact the period/intensity of cold advection over the Northeast. Preferred the non-ECMWF camp there. The other issue was a trough expected to carve out in the Midwest and progress eastward to the Great Lakes. The 06z GFS was more northeast of the other guidance, including ensemble means, with this system, though it was showing some slowing when compared to its 00z run. Due to the increasing amplitude of the progressive flow pattern, there's room for this trough to dig/lie farther west so stayed closer to a 00z ECMWF and 00z Canadian-like solution for this system, using ensemble means to help account for uncertainty. The pressure and wind blends were weighted accordingly, and the starting point for the other grids tend to weight against the GFS which would work out better with time (best outside New England early on) considering this model spread and preference. ...Weather/Hazard Highlights... Most guidance is stable in showing a persistent western ridge/eastern trough pattern aloft through next Thursday, and likely beyond given the Climate Predication Center 8-14 day forecast. The western ridge will promote much above normal temperatures with the strongest upper ridging and greatest temperature anomalies likely to be mid next week, with the hottest temperatures in the Desert Southwest where highs of 100-110F are expected. Fairly persistent southwest flow off the Pacific should bring periods of precipitation to parts of the Pacific Northwest and extreme northern Rockies. At the same time, the eastern U.S. will see below normal temperatures due to the mean trough aloft. There will be two primary storm systems of note. One will track northeast from the Mid-Atlantic early Sunday onward which could bring snow to interior and elevated sections of New England Sunday. Upstream northwestern U.S. energy will amplify and generate another system that should intensify as it tracks from the Plains/Midwest into or near the Great Lakes mid-week while progressing eastward. Both systems should produce meaningful rainfall over some areas with locally moderate/heavy activity possible, with the highest precipitation totals expected to be in the Northeast. As more heavy rainfall is possible in saturated areas in and around northern Louisiana, flash flooding/excessive rainfall is a concern Tuesday into Wednesday, should the guidance remain stable. Roth/Rausch Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php Hazards: - Heavy precipitation across portions of the Pacific Northwest and the Northern Great Basin, Sun-Mon, Apr 26-Apr 27. - Heavy precipitation across portions of the Northeast, Sun, Apr 26. - Heavy rain across portions of the Lower Mississippi Valley and the Southern Plains, Tue, Apr 28. - Heavy rain across portions of the Northeast, the Central Appalachians, the Mid-Atlantic, the Southern Appalachians, the Great Lakes, and the Ohio Valley, Wed-Thu, Apr 29-Apr 30. - Heavy rain across portions of the Mid-Atlantic, the Northeast, and the Central Appalachians, Sun, Apr 26. - Flooding possible across portions of the Northern Plains. - Flooding occurring or imminent across portions of the Lower Mississippi Valley, the Northern Plains, the Middle Mississippi Valley, the Upper Mississippi Valley, the Southeast, and the Southern Plains. - Flooding likely across portions of the Southeast and the Tennessee Valley. - Much above normal temperatures across portions of the Central Plains, the Central Rockies, the Central Great Basin, the Northern Plains, the Southern Plains, the Northern Great Basin, the Southern Rockies, California, the Northern Rockies, the Pacific Northwest, and the Southwest, Sun-Thu, Apr 26-Apr 30. - Much below normal temperatures across portions of the Northeast, the Central Appalachians, the Tennessee Valley, the Mid-Atlantic, the Southern Appalachians, the Great Lakes, and the Ohio Valley, Sun-Mon, Apr 26-Apr 27. - High winds across portions of the Alaska Panhandle, Sun-Wed, Apr 26-Apr 29. - High winds across portions of the Aleutians, Tue-Wed, Apr 28-Apr 29. WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, 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/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml