Extended Forecast Discussion...amended NWS Weather Prediction Center College Park MD 350 AM EDT Sun May 19 2019 Valid 12Z Wed May 22 2019 - 12Z Sun May 26 2019 ...Overall Weather Pattern... The upper level pattern across the continental U.S. will remain amplified and slow to change next week. A hot upper level ridge over the southeast U.S. becomes anchored over the region and gradually becomes stronger for the second half of the upcoming work week. Across the western U.S., a large scale upper trough will be dominant as multiple shortwave perturbations keep conditions cool and unsettled. This will also be slow to move given the expected development of an omega block type pattern upstream over the eastern Pacific. Lead main weather features include a strong low pressure system for the Plains and Upper Midwest mid-week, followed by weaker lows and slow moving fronts from the Southwest to the Northeast U.S. later in the week on the western and northern periphery of the Southeast ridge. ...Models and Preferences... The models and ensemble means are in relatively good agreement on Wednesday, with the GFS more progressive with the trough axis over the Desert Southwest and the CMC slower than the model consensus. By Friday, the GFS becomes an outlier solution regarding the intensity of an upper low over California, whereas the other operational guidance, including the FV3, is more indicative of an open trough over this region. There has also been a westward and slower adjustment to the surface low over the Plains through the end of the week, compared to earlier forecasts. By the end of the forecast period on Sunday, the GFS is suggesting less upper level ridging over the eastern U.S. compared to the model consensus. The FV3 was given greater weighting in the forecast process given its better agreement with the ensemble means, and the ECMWF/EC mean/GEFS mean were also incorporated into the forecast. ...Weather Highlights and Hazards... The main things that will make weather headlines for the second half of the week and extending into next weekend will be the anomalous heat and humidity building across the southeastern quadrant of the nation, the unseasonably cool weather expected for the interior western U.S. and northern plains, and the ongoing threat of heavy rainfall and potential severe weather across the central U.S. High temperatures are forecast to be on the order of 10 to 15 degrees above late May averages from the Midwest to the Southeast U.S., with the hottest readings expected for the Friday to Sunday time period. There is a good chance that the first 100 degree temperatures of the season could be realized across inland portions of southern Georgia and South Carolina. The opposite will hold true for the western U.S. under the influence of the upper level trough, with daytime highs of 15 to 25 degrees below normal for mid-week, and then moderating to 5 to 15 degrees below normal by the end of the forecast period. Heavy rain will likely be an issue again for parts of the central plains and Midwest with the stalled frontal boundary in place for the end of the week and into the weekend. There are some differences in the model placements of the heaviest QPF axis, but the consensus is for the heaviest rain to develop from northern Texas to Iowa with the potential for flash flooding. Strong to severe thunderstorms are also likely in this same general area. D. Hamrick 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