Extended Forecast Discussion NWS Weather Prediction Center College Park MD 224 AM EDT Wed May 20 2020 Valid 12Z Sat May 23 2020 - 12Z Wed May 27 2020 ...Overview and Weather/Hazard Highlights... The large scale flow pattern across the CONUS during the medium range period should finally look more typical of summer as a ridge builds across the southern tier, and northern stream energies shift east and north towards the U.S./Canadian border. In the west, a broad and slow-moving upper level trough is forecast to cross the Rockies this weekend, 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. 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. Model guidance is beginning to show this could increase the threat for 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 dissipates over Texas. Given model uncertainties, the details of this setup remain unclear at this time frame, although a broad heavy rain area is highlighted in our day 3-7 Hazards Outlook. Elsewhere, a stubborn and slow to move cutoff low over the Mid-Atlantic in the short range period should continue to weaken at the start of the Medium Range period as it finally shifts out to sea. Temperatures in the East should trend back towards normal through this weekend and early next week. Meanwhile, temperatures in the Midwest and interior Northeast should be warmer than average underneath of upper level ridging. 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. ...Guidance/Predictability Assessment... Model agreement was fair/good to start the period, although the GFS was still different from consensus with handling of the upper low out of the Mid-Atlantic days 3-4. The 12z/May 19 ECMWF and UKMET offered the closest clustering with the ensemble means. For Sun-Tues, uncertainty continues especially with the evolution of the amplified troughing into the Plains. Model run to run consistency remains poor, especially in the details, although the GFS seems blendable with the ECMWF and the means late in the period. Across the board, a mostly deterministic blend (ECMWF/UKMET) was preferred early in the period, though trended towards the ensemble means (replacing the UKMET with the GFS) days 6-7. This approach fits with previous WPC continuity as well. 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