Extended Forecast Discussion NWS Weather Prediction Center College Park MD 241 AM EDT Wed Apr 05 2023 Valid 12Z Sat Apr 08 2023 - 12Z Wed Apr 12 2023 ...Overview and Guidance/Predictability Assessment... The upper level pattern will transition to one that is more zonal with a series of inherently low predictable northern and southern stream shortwave troughs and impulses later this week before re-amplifying with increasing uncertainty next week. Guidance run to run continuity has not been stellar with the numerous flow embedded systems. Later period East Pacific to West Coast upper trough amplification and downstream upper ridge building over the west-central U.S. has been a fairly consistent guidance theme, but the extent of northern and stream interaction/upper trough amplification over the East and low genesis has varied, albeit with a recent guidance trend away from stream phasing aloft. The 12 UTC ECMWF was the last model to follow this emerging trend. Overall, the WPC medium range product suite was primarily derived from a more diverse than usual blend of the 18 UTC GFS/GEFS mean, the 12 UTC ECMWF/UKMET/Canadian and the 01 UTC National Blend of Models. Applied marginally more blend weighting to the models for this weekend before shifting focus strongly/increasingly to the more compatible and run to run stable ensemble means by next week to better mitigate system differences. 00 UTC guidance remains overall in line. ...Weather/Hazards Highlights... A leading front will track offshore and settle over the Atlantic Ocean and back over the Gulf of Mexico through this period. The experimental Day 4 WPC Excessive Rainfall Outlook (ERO) introduces a "Marginal" threat area across parts of the Southeast Saturday given recent wetter guidance trends as the passage of impulse energy aloft and frontal waves now seems more likely to organize activity. The proximity of the wavy front should support some additional precipitation across the Southeast Sunday, lingering mainly over Florida into early next week with renewed low developments. Northern stream system progression early-mid next week offers modest precipitation chances, but digs trailing cold fronts down into the central and eastern states. Meanwhile, activity across the Southeast has a growing signal for a separated southern stream upper trough/low with potential for moderate coastal/maritime low developments out over the western Atlantic, but ample uncertainties remain. Well upstream as the flow becomes more zonal, multiple shortwaves will move onshore the West Coast. This favors moderate precipitation across the Pacific Northwest/northern California this weekend along with modest terrain snows further inland across the Northwest. This pattern will transition into early next week with the expected amplification of an eastern Pacific upper trough and a downstream/warming upper ridge across the West Coast. A slow eastward translation of the trough across the West Coast early-mid next week would reinvigorate wet flow for the Northwest as the eastward slide of the ridge shifts warmth across the West/Rockies to the Plains where some record values may become possible. 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