Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Mon Apr 24 2023 Valid 12Z Thu Apr 27 2023 - 12Z Mon May 01 2023 ...Overview and Guidance/Predictability Assessment... Guidance shows a transitional pattern over North America over the next week. Rex/Omaga style blocky flow from eastern Canada down across the northeast quarter of the lower 48 is slated to slowly breakdown later this week. Meanwhile in this period, a separated southern stream cutting underneath remains challenging with less than stellar run to run continuity on which embedded wave to place emphasis as a series of impulses and trailing main upper trough progress eastward from the south-central U.S. through the southeast/eastern states. Each wave offers an uncertain opportunity for locally enhanced rainfall/convection and subsequent coastal low potential offshore up over the western Atlantic. Even so, latest model and ensemble solutions seem a bit better clustered for this period and then also generally agree in showing a stark amplification of the continental upper pattern Friday into next week, bolstering forecast confidence to a degree despite flow complexity/nature. This pattern will be highlighted by a gradual inland shift of an amplified/warming ridge from the eastern Pacific into the western North America and the downstream carving out of an amplified/closed central Canadian through east-central U.S. trough that will produce a protracted period of unsettled/cooled conditions. The WPC medium range product suite was primarily derived from a composite of the 18 UTC GFS/GEFS mean, the 12 UTC ECMWF/Canadian/UKMET and ECMWF ensemble mean along with the 01 UTC National Blend of Models. The blend process tends to mitigate embedded system variances consistent with individual system predictability. WPC product continuity is reasonably maintained with this plan and remains overall in line with a composite of newer 00 UTC guidance. ...Weather/Hazards Highlights... Late week main system ejection across the South/Southeast along with less certain lead impulses will act to re-focus lower atmospheric convergence/baroclinicity with a series of frontal waves. There will be several opportunities for ingredients to come together to fuel swaths of moderately heavy convective rainfall given influx of Gulf of Mexico to western Atlantic moisture and instability. Downstream, guidance has trended away from deep coastal low development. A blocky upper trough/closed low flow to the north should steadily lose influence later this week but still favor cooled and unsettled weather/widespread light-side precipitation from the Great Lakes/Midwest though the Northeast. Meanwhile, northern stream upper trough energy remains slated to dig southeastward into the north-central U.S. late next week and then in earnest within an amplifying pattern that settles in late week/weekend coincident with upstream strong upper ridge translation and building inland across the West Coast. Run to run continuity is not stellar, but this general track would increasingly focus precipitation across the north-central states. The pattern favors development of much below normal temperaturesdown through the central to east-central U.S. as frontal surges of cold Canadian air sink into the U.S. with system development and overall flow amplification. 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