Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1154 AM EDT Wed May 16 2018 Valid 12Z Sat May 19 2018 - 12Z Wed May 23 2018 ...Guidance and Predictability Assessment... Models have been showing shortwave trough ejecting from the Rockies and will slide across the Mississippi Valley and into the Ohio Valley by the beginning of the medium range period. This shortwave will slide off to the northeast as it gets absorbed into the trough over eastern Canada by the end of the weekend. Both the 06Z GFS and 00Z ECMWF are in good agreement with this energy. By the beginning of the medium range period, an upper ridge will be centered over the western U.S. Meanwhile, by Sunday and into Monday, a 500 mb trough will dig across the West Coast. Once again, both the GFS and ECMWF are in agreement with the timing and strength of this trough as it moves toward the Desert Southeast by Tuesday and Wednesday. The upper ridge will persist across western Canada and into the Plains. Once again, models and ensemble clustering continues to improve and is in good agreement through the medium range period. As such, WPC took a blend of 06Z GFS/00Z ECMWF and 06Z GEFS/00Z ECENS. The blend uses more of the operational models through Day 6 due to their good agreement and by Day 7 split the difference between the operational and ensembles. ...Weather/Threats Highlights... Showers and thunderstorms are expected along a cold front that will move over the Upper Mississippi Valley and northern/central Plains in the beginning of the weekend. Meanwhile, anomalous moisture will continue to stream from the Gulf of Mexico across the Southeast and into the Mid-Atlantic and Northeast this weekend. At the surface, a wavy front will remain over coastal Mid-Atlantic into the Ohio Valley throughout the medium range period and will eventually stretch into the Plains by midweek. Thus, more rounds of showers and thunderstorms will be possible especially along the East Coast and into the Ohio Valley. By the beginning of the work week, mid-level shortwave energy will move over the southern Plains eastward into the mid-Mississippi Valley by Tuesday. Showers and thunderstorms are expected to develop along West Texas/Texas Panhandle and move eastward toward the mid-MS Valley by Tuesday/Wednesday. The Southeast and Florida will see typical summertime scattered showers and thunderstorms driven by diurnal heating next week. In terms of temperatures, the central U.S. will be warmer than normal this weekend with high temperatures up to 10 degrees above normal. In fact, record high temperatures could occur on Saturday especially in the Southeast and Mississippi Valley. Record high minimum temperatures will also be possible in the Mid-Atlantic on Saturday and lasting through the beginning of next week. Behind the cold front sweeping across the northern Plains, high temperatures will be much colder being up to 15-20 degrees below average on Saturday. WPC medium range forecasts of 500 mb heights, surface systems, weather grids, quantitative precipitation, and winter weather outlook probabilities can be found at: http://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif http://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif http://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html http://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml http://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 Reinhart