Extended Forecast Discussion NWS Weather Prediction Center College Park MD 204 PM EDT Fri Jul 30 2021 Valid 12Z Mon Aug 02 2021 - 12Z Fri Aug 06 2021 ...Lingering monsoonal moisture and heavier rain for parts of the Interior West on Monday.. ...Heavy rainfall threat for parts of the South and the Southeast... ...Overview... Positive height anomalies over western/central Canada and southwest of California will favor continued troughing in the eastern states next week. This will promote cooler than normal temperatures east of the Plains with highest rainfall chances along and ahead of a slowly southward-moving cold front into the Southeast. The Interior West will see diminishing rainfall, focused along the Rockies and perhaps shifting to the Plains later next week. ...Guidance/Predictability Evaluation... Latest models and ensembles remain in good agreement on the large scale pattern through the week. The differences lie in the details difficult to resolve at this time scale. Recent deterministic runs continue to waver on how quickly (or slowly) to bring height falls into the Pac NW later in the week with ECMWF/ECENS mean a little bit slower than the GFS/GEFS mean. The lack of a clear upstream kicker over Alaska would favor the slower solutions, but a general blend of the ECMWF/GFS with the means gets us a good starting point. The CMC seems too quick to bring lower heights into the West and also quicker to erode troughing over the Ohio Valley and push it eastward the latter half of the week. Thus, the CMC was excluded from the blend during the late periods. This cycle of the WPC forecast favored a blend of the deterministic guidance days 3-5, with modest weighting towards the means by days 6 and 7. Continued more than usual blending of the ECMWF/GFS later in the period just for some added strength and definition to individual features typically washed out by the means. This approach also maintains good continuity with the previous WPC forecast. ...Weather Highlights/Hazards... With the upper high around the lower CO River Monday, mid-level energy will spur afternoon convection over the northern/central Rockies, some of which may contain heavier rain. As heights build a bit over the Southwest, the moisture source will decrease and rain coverage/intensity will decrease through the week. In the East/Southeast, troughing will push a cold front close to or into the Gulf of Mexico by midweek. Abundant moisture ahead of the boundary will support heavier rain chances anywhere from Texas eastward to the Carolinas. As the upper pattern remains mostly in place, the front may wobble about due, in part, to areas of low pressure that may act to enhance rainfall into the Mid-Atlantic. Temperatures will slowly moderate from below normal in much of the Interior West (owing to clouds and rainfall) early in the week to near or slightly above normal by the end of next week. Areas along the Canadian border may see the warmest anomalies of +5 to +10 from eastern Montana to the western Great Lakes. Much of the East/Southeast will see near to below normal temperatures along and behind the cold front, perhaps as much as 10 degrees below normal for early August on some days. Santorelli/Fracasso Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook 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