Extended Forecast Discussion NWS Weather Prediction Center College Park MD 135 AM EDT Mon Jul 20 2020 Valid 12Z Thu Jul 23 2020 - 12Z Mon Jul 27 2020 ...Overview and Weather/Hazard Highlights... The flow pattern across North America is forecast undergo some amplification during the extended period. Models/ensembles show consensus that a ridge axis should gradually strengthen by late in the week across the east-central U.S./Canada, with positive 500 hPa height anomalies forecast to extend from the Gulf of Mexico to the Arctic. Both upstream and downstream of the ridge axis, cyclonic flow and upper-level troughing will be favored through time, across the Pacific Northwest, as well as New England and the Canadian Maritime provinces. An active jet with several shortwaves/frontal waves traversing the CONUS northern tier should bring a multiple rounds of showers and thunderstorms during the medium range from the Northern Plains/Midwest to the Northeast/Mid-Atlantic, generally spaced 1-2 days apart. The first of these during the medium range will affect the Northeast/Mid-Atlantic on Thu, bringing at least a temporary respite from the dangerous heat affecting those areas during the short range. Another round of convection should move from the Upper Midwest/Great Lakes Thu to the Northeast by the weekend, by which time yet another round of storms should affect the north central U.S. Farther south, a broad trough moving west in the Gulf of Mexico will keep the central/western Gulf Coast states wet late this week into the weekend, with scattered to numerous showers and storms. Finally, monsoonal moisture should increase across the Four Corners region by later this week, with diurnal showers/storms increasing through the weekend as the central U.S. ridge intensifies. The building central U.S. ridge will also support another round of above average temperatures, beginning across the Northern Plains/Midwest Fri-Sat, where highs are forecast to be 5 to 10 deg F above average. Temperatures should increase once again across portions of the Mid-Atlantic Sun-Mon as well. ...Guidance/Predictability Assessment... As seen over recent days, models/ensemble continued to show relatively good consensus at larger scales, with increasing detail differences through time. This scenario lends well to a heavily deterministic blend (12Z ECMWF/18Z GFS) during days 3-4 (Thu-Fri), and gradually increasing emphasis on ECENS/GEFS ensemble means during days 5-7 (Sat-Mon). Overall forecast confidence was average to slightly above average. Ryan 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