Extended Forecast Discussion NWS Weather Prediction Center College Park MD 120 AM EDT Sat Jul 25 2020 Valid 12Z Tue Jul 28 2020 - 12Z Sat Aug 01 2020 ...Overview... A subtropical high initially centered over the Southern High Plains is forecast to slowly retrograde toward the Four Corners region through the medium range period. Meanwhile, an upper low in east-central Canada should spread troughing into the Midwest/Great Lakes and then into the Northeast/Mid-Atlantic by midweek, pushing a cold front through those areas. Lowering heights across the Northwest will replace initial upper ridging as troughing establishes itself off the West Coast. ...Weather/Hazard Highlights... Tropical Storm Hanna will likely have dissipated over northern Mexico by the start of the medium range period, although lingering tropical moisture and instability along the Gulf Coast may result in periods of locally heavy rainfall into Wednesday. To the north, a cold front should push across the Northeast on Tuesday, while becoming stationary across the Tennessee/mid-Mississippi Valleys and back into the Central Plains through midweek. Rain and thunderstorms should focus along this boundary with locally heavy rainfall possible, aided by Southwestern U.S. monsoonal moisture. Upper level energy rounding the top of the Southern tier ridge looks to settle into the Midwest states by Thursday, with several pieces of guidance indicating the potential for additional rounds of organized rainfall and thunderstorms from the middle Mississippi Valley into the Tennessee and lower Ohio Valleys Wednesday into Friday. The cold front across the Northeast may become stationary along the Mid-Atlantic coast bringing a chance for moderate to locally heavy rainfall to parts of the Carolina Coasts through Friday as well. Above normal temperatures (+5 to +10 degrees above average) initially across parts of the Northwest and East Coast on Tuesday should moderate back towards normal the remainder of the week. Gulf Coast to Southern Plains states begin the period below normal with abundant cloud cover/moisture, but by the middle of the week should also warm up to near normal. ...Guidance/Predictability Assessment... The guidance continues to show relatively good agreement on the overall large scale pattern, with expected variances in the smaller scale, less predictable, features especially later in the period. A majority deterministic blend (between the ECMWF and the GFS) worked well for days 3-4, but spread especially concerning height falls into the Northwest increases beyond day 5. The ensemble means remain well clustered with this system and so opted to blend increasing percentages of the ECENS and GEFS means days 5-7. Continued smaller contributions from the ECMWF and GFS through the period just to maintain some level of definition of features. This approach maintains good WPC continuity. 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