Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Fri May 19 2023 Valid 12Z Mon May 22 2023 - 12Z Fri May 26 2023 ...Pattern Overview and Guidance/Predictability Assessment... Models and ensembles offer a reasonably similar mid-larger scale pattern evolution aloft into next week to include split stream upper troughs dug over both the West Coast and the Eastern U.S. that sandwich warming upper ridging set to work over the central U.S. that may with much uncertainty spread over the Midwest later next week. However, there are widespread embedded smaller scale impulse differences and interactions. A favored composite model blend should act to mitigate these differences consistent with individual predictability through early next week, but growing forecast spread and uncertainty portends increasing usage of the much more compatible GEFS/ECMWF ensemble means for mid-later next week. Overall through this forecast period, guidance differences seem most noticable with surface system reflection and local warm season convection/weather focus, but in particular with the potential for modest to moderate southeast U.S. coastal low genesis and associated coastal to offshore rainfall. An overall guidance trend over the past few cycles seems to gradually favor amplitude and shift over the West along with more pronounced stream separation with a resultant southeast U.S. upper trough position that may offer more opportunity for coastal frontal lows as energies rotate into/around the slow moving feature. This overall solution maintains broadly good WPC product continuity. ...Weather/Hazards Highlights... A slow moving/separated southeast U.S. upper trough position and associated surface feature proximity should focus moder to locally heavier rainfall/convection over portions of the Southeast, but espeically with wave/frontal development from Florida to up the Southeast coast and potentially the eastern Mid-Atlantic into mid-later week with uncertain coastal wave developments to monitor. Otherwise, the aforementioned upper ridge position should support summertime temperatures with values upwards to 15-20 degrees above normal through early next week should shift slowly east with time across the Northern Plains and eventually the Midwest later next week as tempered locally by scattered and potentially strong thunderstorm activity both with ejection of impulses from the West and interaction with northern stream system/frontal approaches from southern Canada. Locally heavy thunderstorm activity may focus heavy local downpours down over the southern Plains as well with moisture/instability pooling with southern stream impusles. Above to much above normal overnight temperatures and a pattern favoring scattered to widespread showers and thunderstorms are also expected to linger all next week over much of interior West through the Rockies in moistened flow channeled between West Coast upper troughing and the downstream central U.S. upper ridge. Schichtel Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, experimental excessive rainfall outlook, 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/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml