Extended Forecast Discussion NWS Weather Prediction Center College Park MD 258 AM EDT Fri May 31 2019 Valid 12Z Mon Jun 03 2019 - 12Z Fri Jun 07 2019 ...Overview and Weather/Threats Highlights... It remains the case that an active 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 linger over southern California and the desert Southwest, only very slowly moving eastward. Meanwhile, a hot subtropical ridge will migrate westward and reposition over the south central U.S. and the Gulf of Mexico. A persistent and amplified upper low over southeastern Canada to the lee of a mean upper ridge 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 allows heights to fall for much of the Great Lakes/Ohio Valley and the Mid-Atlantic/Northeast. 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 and lower Ohio Valleys. This offers a risk of episodes of locally heavy rainfall/flash flooding as well as strong to severe thunderstorms/MCS activity. This may be especially evident if the slow moving closed low over the unsettled Southwest ejects into the central U.S. later next week in response to amplified approach of kicker Pacific energy upstream across the West Coast. Kicker trough/height falls may themselves support the spread of modest to moderate precipitation across the Northwest quarter of nation later next week. ...Guidance/Uncertainty Assessemnt... The WPC medium range product suite was mainly derived from a composite blend of well clustered 18/00 UTC GFS/FV3/GEFS mean and 12 UTC ECMWF/ECMWF ensemble mean mass field guidance. This bolsters forecast confidence in the overall pattern evolution. The main heavy convective rainfall focus is less predictable within this pattern, but there remains a good signal supporting a threat from the south-central Plains to the Mid-Mississippi/Lower Ohio Valleys. Schichtel 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