Extended Forecast Discussion NWS Weather Prediction Center College Park MD 231 PM EDT Wed May 20 2020 Valid 12Z Sat May 23 2020 - 12Z Wed May 27 2020 ...Overview and Weather/Hazard Highlights... The rather blocky flow in the short term will attempt to transition to zonal flow next week but appears destined to again fall back to a pattern with weaker steering currents along/south of 40N. This is due, in part, to the nearly stationary positive height anomalies over NW and SE Canada, favoring troughing over the middle of the continent. In the West, troughing is forecast to exit the Rockies this weekend (with some higher elevation snow around Yellowstone), pushing a cold front out into the Plains. Moisture ahead of the front should support modest rainfall amounts across the northern/central Plains on Saturday along with a chance of severe weather (NE/SD). As this first shortwave lifts into central Canada, energy in the base of the main trough should settle across the southern Plains Sunday into Tuesday, and begin to tap return moisture from the Gulf of Mexico. Threat is increasing for locally heavy rainfall and thunderstorms across portions of the southern and central Plains Sunday into Memorial Day, weakening some and dropping southward on Tuesday towards the western Gulf Coast as the surface front weakens over Texas. Given model uncertainties, the details of this setup remain unclear at this time frame, but a broad heavy rain area is highlighted in our day 3-7 Hazards Outlook. Elsewhere, a stubborn and slow-moving cutoff low over the Mid-Atlantic in the short range period should continue to weaken at the start of the medium range as it finally shifts out to sea. Temperatures in the East will trend back toward normal through this weekend and early next week. Meanwhile, temperatures in the Upper Midwest/Great Lakes/interior Northeast will be warmer than normal due to southwest flow and rising heights. Out west, the upper level trough will bring below normal temperatures on Saturday across the Rockies/Great Basin states, but should transition to above normal by the end of the period as ridging builds in behind the trough and in advance of another upper low in the eastern Pacific Ocean. Temperatures could again rise into the low 100s over much of the inland deserts and near 110 in the favored warmer locations. Some areas could approach record highs over the Great Basin. ...Guidance/Predictability Assessment... Model agreement was fair/good to start the period, although the 00Z/06Z GFSs were still displaced (quicker) from the ECMWF-led consensus with the handling of the upper low out of the Mid-Atlantic this weekend. The 00Z ECMWF/UKMET/Canadian offered the closest clustering with the ensemble means (06Z GEFS and 00Z ECMWF ensemble mean). For Mon-Tue, uncertainty continues/increases with the evolution of the amplified troughing into the Plains though in principle agreement remains acceptable. Model run-to-run consistency remained poor in the details and a trend toward increased ensemble weighting was preferred. This approach fits well with previous WPC continuity. Fracasso/Santorelli 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 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