Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1129 AM EDT Sat Jul 20 2019 Valid 12Z Tue Jul 23 2019 - 12Z Sat Jul 27 2019 ...Overview and Guidance/Predictability Assessment... Amplified upper-level pattern expected to be in place through much of the medium range, with persistent upper ridging centered across the Four Corners region and amplified upper troughing, transitioning to broad cyclonic flow, across the eastern half of the CONUS. Upper troughing is expected to push a cold front off the Eastern Seaboard by day 3 (Tue), with the trailing end of the front extending from the Florida Panhandle to South Texas. Models show consensus that this front should stall by day 4 (Wed) and linger through the remainder of the forecast period as it gradually washes out. Farther west, shortwave energy reaching the Pacific Northwest on days 3-4 should move a cold front inland, reaching the northern High Plains by day 5 (Thu), where forward progress should begin to slow somewhat as the southern end of the front runs into the higher heights from the southern Rockies to the Southern Plains. Overall, the majority of model/ensemble guidance was relatively agreeable through much of the extended forecast period. A multi-model deterministic blend (00Z ECMWF/UKMET/CMC/06Z GFS) was used as a basis for the forecast during days 3-4. The UKMET/CMC were dropped starting on day 5 as their solutions begin to differ from consensus, particularly the CMC which differed substantially with the evolution of the shortwave expected to reach the Northern Plains by late Thu, closing off the feature and holding it farther west across the Canadian Rockies. The forecast during days 5-7 was based heavily on the ECMWF/GFS and ECENS/GEFS ensemble means, with gradually increasing weight on the means trough time. ...Weather Highlights/Threats... The frontal boundary expected to stall off the Eastern Seaboard through the medium range is expected to focus numerous showers and thunderstorms. The most widespread convection and the greatest potential for areas of heavy rainfall should occur from eastern/coastal North Carolina southward across the coastal plain to the Florida Panhandle Tue-Thu. Showers/storms may lessen in coverage/intensity by late next week as the surface front washes out. The shortwave/frontal system moving from the Pacific Northwest to the Northern Plains/Upper Midwest should bring an increase in shower/storm chances to the Upper Midwest by late next week. Meanwhile, daily scattered storms will be possible across the central/southern Rockies as some degree of monsoonal moisture manages to spread into the upper ridge. Below average temperatures are expected across a large area in the wake of the cold front moving off the East Coast Tue. High temperatures are forecast to be 5 to 10 deg F below average from the Southern/Central Plains to the Southeast/Mid-Atlantic Tue through late in the week. Temperatures are expected to gradually moderate some by Thu-Sat across the Mid-Atlantic, but areas from the Southern Plains to the Southeast should remain below average due to elevated clouds and scattered precipitation north of the frontal boundary. 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