Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1203 PM EDT Mon May 27 2019 Valid 12Z Thu May 30 2019 - 12Z Mon Jun 03 2019 ...Episodes of heavy rain possible for portions of the central U.S... ...Overview and Guidance Evaluation/Preferences... Split flow is expected to persist across North America during the medium range. The subtropical ridge is expected to remain entrenched across the Gulf of Mexico, keeping a feed of warm and moist air into the central and southeastern states. Flow associated with an active North Pacific upper-level jet will split as it approaches the West Coast of North America where a ridge axis will be in place through much of the period before gradually shifting eastward to the central U.S./Canada by late in the weekend into early next week. As northern stream energy periodically encounters a persistent upper low in the vicinity of Hudson Bay, the energy will amplify in the broad cyclonic flow with shortwaves digging into the north central and northeastern U.S. Meanwhile slower progressing southern stream energy will move from the Great Basin/Rockies to the central U.S. and Great Lakes, where interaction with amplifying northern stream energy is a possibility. There is relatively good agreement amongst the various model solutions for days 3-4. Beyond that, differences begin to arise in some of the deterministic runs. The 06z run of the GFS is less amplified/weaker with the Hudson Bay upper low which allows for a quicker progression of the ridge into central Canada on days 6-7. Farther south, it's also a bit faster with a shortwave exiting the Mid-Atlantic on Day 5 compared to its previous runs, the ECMWF, and the ensemble means. The Canadian is also on the quick side with that wave, as well as much more amplified with shortwave energy digging into the Great Lakes Sunday into Monday. Thus, the 06z GFS and the 00z Canadian were rejected. The ensemble means show good agreement with each other as well as with the 00z ECMWF throughout the entire medium range period. This cycle of the WPC medium range progs were comprised using a blend of 00z GFS, 00z ECMWF, and the EC and NAEFS ensemble means, with more weighting placed on the 00z ECMWF than the 00z GFS because of better run to run continuity. Increased the weighting of the ensemble means by days 6-7 to mitigate some differences with smaller scale details. This blend results in a forecast reasonably close to that of the previous shift. ...Weather Highlights and Hazards... Areas of showers and thunderstorms with locally heavy rain are possible Thu-Fri from the Southern Plains to the Ohio Valley and Northeast along a surface cold front and around the periphery of the subtropical ridge. Another round of more significant and widespread convection and heavy rainfall is possible across the Southern/Central Plains Sat-Sun as the trailing end of the frontal boundary lifts north as a warm front and weakens, and another cold front dives south across the central U.S. before stalling by the weekend and providing additional focus for areas of showers and thunderstorms. Farther west, periodic showers are expected from the Great Basin to the central/northern Rockies as a couple weak southern stream shortwaves traverse the region. Hot temperatures will persist into Thu across portions of the Southeast and southern Mid-Atlantic, where highs may be 10-20 deg F above average. A gradual cooling trend is expected from Fri into early next week as the upper ridge retreats a bit into the Gulf of Mexico allowing heights to fall across the Southeast - although any cooling will be relatively modest with highs expected to remain 5-10 deg above average. Santorelli/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