Extended Forecast Discussion NWS Weather Prediction Center College Park MD 222 AM EDT Sun Jun 21 2020 Valid 12Z Wed Jun 24 2020 - 12Z Sun Jun 28 2020 ...Overview and Weather/Hazard Highlights... Medium range period begins Wednesday with an upper low meandering south of Hudson bay before lifting northeast by Friday. Height falls across the Ohio Valley/Northeast will drive a cold front into the Eastern states Wednesday and Thursday with showers and thunderstorms likely along and ahead of the boundary from the Mid-Atlantic to the South. Upper level energy combined with the stalled trailing portion of the boundary could support a period of focused convection from the Southern Plains to the Lower Mississippi Valley, with the best chance for heavy rainfall along the Texas Gulf Coast region on Thursday. Unsettled weather should continue into the weekend across the South as the trailing boundary lingers and eventually weakens. Meanwhile out West, upper level ridging dominates across the Southwest much of the period, with early period ridging across the Northwest/Rockies keeping temperatures above normal. A progressive upper level trough will push a frontal system from the Northwest/northern Rockies on Wednesday into the Plains by Friday. The most organized precipitation is likely ahead of the trough and surface warm front as it lifts from the northern Plains into the Upper Midwest late this week, with showers and storms also developing by next weekend into the Central Plains/Mid-Mississippi Valley. Troughing reinforcement arrives out West late in the period which should also help moderate temperatures back towards normal. ...Guidance/Predictability Assessment... A majority deterministic model blend produces a reasonable forecast for days 3-4 when model agreement is good. The ECMWF remains the strongest with energy along the western Gulf Coast and resulting QPF may be overdone, but it's not unreasonable given the setup and most models show at least some heavy rainfall potential. After day 4, model spread begins to increase dramatically particularly with upper troughing digging across the Northwest into the north-central U.S. late this week and next weekend. Deterministic runs remain wildly inconsistent run to run, but ensemble means at least show some reasonable agreement. Forecast confidence in the evolution of this feature remains low, but there may be a slight trend towards more progressive troughing at least compared to previous forecasts. In accordance with these thoughts, WPC trended quickly towards the ensemble means for days 5-7. 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