Extended Forecast Discussion NWS Weather Prediction Center College Park MD 237 PM EDT Tue May 19 2020 Valid 12Z Fri May 22 2020 - 12Z Tue May 26 2020 ...Overview and Weather/Hazard Highlights... The large scale flow pattern across the CONUS during the medium range period will finally be transitioning from a blocky/amplified pattern to one 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. A cutoff mid/upper-level low, and associated surface frontal wave, will initially be in place across the lower Ohio Valley on Friday, but should gradually continue to weaken as it lifts into the Mid-Atlantic on Saturday and eventually out to sea. Much of the heavy rainfall associated with this system across the Mid-Atlantic/Appalachians should be in the short range period, though scattered showers and storms may linger across the region into Saturday before the system moves away. Slightly below normal temperatures across the Mid-Atlantic states will trend back towards normal for the rest of the period. Areas east of the Mississippi will see near normal temperatures while much of the Midwest and into parts of the interior Northeast are expected to see warmer than normal temperatures. Farther west, a broad and slow-moving upper-level trough is forecast to cross the West and Rockies Fri-Sat, accompanied by rain (with high elevation snow) and below average temperatures. A trailing frontal boundary associated with the system farther east is expected to linger across the Lower Mississippi Valley into the Southern Plains, which could provide some focus for development of convection and some locally heavy rain. As the trough axis shifts eastward and eventually settles across the Plains Sun-Tue, showers and thunderstorms are expected to become more widespread across parts of TX/OK into KS. Areas of heavy rain and thunderstorms are possible early next week as the guidance indicate a broad upper shortwave may linger across the region. Though details at this time frame are unclear, a broad area was highlighted in our day 3-7 Hazards Outlook. ...Guidance/Predictability Assessment... Model agreement was fair/good to start the period, though the 00Z/06Z GFS was quicker than the rest of the guidance to unfurl the upper low in the east. The 00Z ECMWF offered the closest clustering with the 06Z GEFS mean and 00Z ECMWF ensemble mean with modest agreement from the 00Z UKMET/Canadian. For next Sun-Tue, uncertainty increases especially with the evolution of amplified troughing into the Plains states late in the period. Model run-to-run consistency remained poor, especially in the details, so an ensemble-based approach was preferred. The 06Z GFS briefly came back into the preferred cluster which helped to offer some details to the late weekend/early week forecast, but then trended sharply to the ensembles (and continuity) for especially next Tue as the pattern attempts to become a bit more blocky again along 30N. 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