Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1109 AM EDT Mon Jun 11 2018 Valid 12Z Thu Jun 14 2018 - 12Z Mon Jun 18 2018 ...Pattern Overview... Coordination with the Alaska Medium Range desk led to discussion of the downstream ramifications of the ongoing extratropical transition of Maliksi offshore Japan, which is expected to lead to a more amplified flow pattern than usual for mid to late June across North America. As Maliksi swings into Alaska as a still robust system, ridging builds across the eastern Pacific which leads to a pronounced trough across the West, which leads to a similarly pronounced ridge/trough couplet across the Mississippi Valley/western Atlantic respectively. ...Model Guidance/Predictability Assessment... The guidance shows reasonable agreement for much of the period. The biggest issue involves whether or not a closed low in the western Atlantic retrogrades into the East coast, which only the operational 00z ECMWF shows beyond day 6/Sunday morning. While the Canadian is favorable across the western Atlantic late in the period, its pattern across the West and Midwest leaves a bit to be desired. Taking that into account, a compromise of the 00z ECMWF, 00z UKMET, 00z GFS, and 00z Canadian were used for the fronts/pressures/winds through Saturday. From Sunday onward, phased out the 00z Canadian and 00z ECMWF solutions substituting the 00z GFS, 00z ECMWF ensemble mean, and 00z NAEFS mean in their place. This solution led to reasonable continuity. For the remainder of the medium range grids, a more even blend of the ensemble means (leaning more ECMWF ensemble mean) and 00z GFS/06z GFS solutions was utilized. For the days 4-7 QPF, the initial template is a blend of the 00z GFS, 06z GFS, 00z ECMWF, and 12z National Blend of Models. Should the 12z GFS look reasonable in a couple hours, it could be utilized for the days 4-7 QPF as well. ...Weather Highlights/Hazards... A weakening surface front and moist air mass will support scattered to numerous showers and thunderstorms through the weekend, especially during the afternoons and evenings, across the Southeastern states, with the potential for locally heavy rainfall. A broad trough/area of disturbed weather moving westward across the Gulf of Mexico is also expected to bring the potential for more widespread rains to portions of the western Gulf Coast states from the weekend into early next week. Farther north, a shortwave, surface low pressure system crossing the northern plains and Upper Midwest will produce areas of convection with potentially heavy rainfall. The frontal boundary may slow or stall for a period of time Sat-Sun from the central plains to the Upper Midwest, resulting in several days with shower/thunderstorms potential, and potential flooding threat for some areas. Moisture associated with Tropical Storm Bud should begin to spread into the southwestern U.S. and the Rockies by the weekend, bringing the potential for areas of heavy rainfall. Interactions with a stationary frontal boundary draped from the Great Basin into the Central Rockies could lead to an enhancement of heavy rainfall potential. Some model solutions even suggest the possibility that the moisture from Bud could spread east into the central/northern plains, further enhancing heavy rain potential along the frontal boundary. Temperatures will also become a bigger story during the next week as the upper ridge expands across the central U.S. and then drifts east into the Ohio Valley. High temperature anomalies of +10 to +18 deg F are expected Thu-Sat across areas from the central plains to the Mid-Mississippi Valley, with highs approaching 100 degrees for some areas. Forecast highs and lows are expected to approach but fall short of record warm/hot values through the period. By Sunday and next Monday, the greatest temperature anomalies will shift a bit east from the Mid-Mississippi Valley into the Ohio Valley. High dew points in addition to the hot temperatures will make for dangerous heat index values for some areas, which would impact urban areas the greatest as they would receive the double whammy of high afternoon temperatures and urbanly-induced warm overnight lows. Roth/Ryan 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