Extended Forecast Discussion NWS Weather Prediction Center College Park MD 315 PM EDT Thu Apr 30 2020 Valid 12Z Sun May 03 2020 - 12Z Thu May 07 2020 ...Much above normal temperatures for the south central U.S. early next week, shifting to the Southwest by midweek... ...Guidance/Predictability Assessment... The WPC medium range product suite was primarily derived from a composite blend of the 00Z UTC ECMWF/UKMET and 06Z GFS, along with GEFS/ECMWF ensemble means days 3-7. Deterministic solutions were weighted more heavily during days 3-5 (Sun-Tue), with ensembles weighted more during days 6-7 (Wed-Thu), consistent with increasing forecast spread/uncertainty. Relatively small timing/intensity differences with the upper shortwave crossing the Great Lakes days 3-4 lead to differences in the evolution of the surface system, particularly on day 4 with potential low development off the New England coast. In this case, a multi-model blend appeared to be the best way to represent the overall model consensus. The new surface low is forecast to quickly move away from the Northeast, with relatively limited impacts. Later in the forecast, growing timing differences with the next shortwave crossing the Northern Tier Mon-Wed, and reaching the Pacific Northwest on Wed, lended to a ramp up of ensemble guidance through time. ...Weather/Hazard Highlights... Above normal temperatures will spread from the Southwest/Rockies through the South this weekend and linger early next week. Temperatures will range up to 10-20F above normal, with daily records most likely over the southern Plains. Upstream upper ridge rebuilding over the West may support hot temperatures by next midweek to include some record southern CA/Southwest U.S. values. Upper trough and jet energies in two streams will amplify/dig from the north-central U.S. through the East Sun. Rainfall may focus through the Mid-MS/OH Valleys and central Appalachians/Mid-Atlantic. Dynamics, instability and progressive frontal pushes may support some organized strong to severe convection with locally heavier downpours. Upstream, robust eastern Pacific trough energy/height falls will work inland across the West Sun into Mon and spread moderate precipitation mainly from the Northwest through the northern Rockies. Favored higher elevations may see periods of locally enhanced snow. The dynamic system should emerge over the north-central U.S. Mon before digging into the East through next midweek. Forecast spread and guidance uncertainty quickly increases at these longer time frames, but the larger scale flow suggests that an associated frontal system and lead instability may favor a risk of strong to severe convection with some heavy downpours from the north-central Plains southeastward through the MS Valley then onward to the Appalachians/Mid-Atlantic/Northeast. Ryan/Schichtel 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 rain across portions of the Upper Mississippi Valley and the Northern Plains, Sun-Tue, May 3-May 5. - Heavy rain across portions of the Lower/Middle Mississippi Valley, the Central Appalachians, the Tennessee Valley, the Mid-Atlantic, the Southern Appalachians, the Southeast, and the Ohio Valley, Mon-Tue, May 4-May 5. - Heavy rain across portions of the Southern/Central Appalachians, the Ohio Valley, and the Tennessee Valley, Sun, May 3. - Flooding possible across portions of the Northeast, the Central Appalachians, the Middle/Upper Mississippi Valley, the Mid-Atlantic, the Great Lakes, and the Ohio Valley. - Flooding occurring or imminent across portions of the Southeast, the Mississippi Valley, and the Northern Plains. - Flooding likely across portions of the Middle Mississippi Valley, the Great Lakes, and the Northern Rockies. - Much above normal temperatures across portions of California, the Central/Northern Great Basin, the Pacific Northwest, and the Southwest, Wed-Thu, May 6-May 7. - Much above normal temperatures across portions of the Southern/Central Rockies, the Southern Plains, the Southwest, and the Central Great Basin, Sun-Thu, May 3-May 7. - Much above normal temperatures across portions of the Southern/Central Rockies, the Southern/Central Plains, and the Central Great Basin, Sun-Mon, May 3-May 4. - Much above normal temperatures across portions of the Southern Rockies and the Southern Plains, Sun-Tue, May 3-May 5. 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