Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1143 AM EDT Thu May 30 2019 Valid 12Z Sun Jun 02 2019 - 12Z Thu Jun 06 2019 ...Overview and weather highlights... An active northern stream flow pattern is expected to continue next week with a strong North Pacific upper-level jet splitting as it approaches the West Coast of North America. An upper-level low will persist in the vicinity of southern California through much of the extended period, only very slowly moving eastward. Meanwhile, the subtropical ridge will migrate westward and reposition over the south central U.S. and the Gulf of Mexico. Farther north, an upper ridge axis initially across central Canada is forecast to slowly move east and weaken, with some potential for ridging to become reestablished across western Canada and the northern U.S. Rockies by the middle of next week. Downstream, a persistent and initially fairly deep upper low across southeastern Canada will cause incoming northern stream shortwaves to periodically amplify as they dig into the Great Lakes and Northeast, traversing the broader anticyclonic flow. These digging waves along with the westward migration of the subtropical ridge will allow for heights to fall across much of the Great Lakes/Ohio Valley and the Mid-Atlantic/Northeast, ushering in cooler high temperatures (near or several degrees below average) and lower dew points through much of next week. Relatively slow-progressing southern stream shortwaves will periodically eject eastward from the upper low, reaching the central U.S. and potentially interacting with amplifying northern stream energy. These waves along with return flow across a persistent baroclinic zone may continue to support areas of increased convective potential from the Southern/Central Plains into the Mid-Mississippi Valley, with the potential for at least locally heavy rainfall/flash flooding as well as strong thunderstorms. Predictability in location/amounts is low due to a less-dynamic pattern overall compared to the previous two weeks. ...Guidance evaluation and preferences... The WPC medium range product suite was initially derived from a blend of the 06Z GFS/FV3-GFS and the 00Z ECMWF/CMC/UKMET solutions during days 3-5 (Sun-Tue). These solutions handled features similarly enough and any differences were favorably smoothed out by the blend. This included some shifting of the surface low and attendant cold front in the east Sun-Mon. By days 6-7 (Wed-Thu), differences with upper ridging through the west favored a middle ground solution given wavering in how long to maintain ridging before Pacific height falls push inland. Teleconnections supported the idea of stronger ridging but both the GEFS/ECMWF ensemble means have trended toward allowing troughing to push east. Fracasso/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