Extended Forecast Discussion NWS Weather Prediction Center College Park MD 256 AM EDT Tue Apr 04 2023 Valid 12Z Fri Apr 07 2023 - 12Z Tue Apr 11 2023 ...Overview and Guidance/Predictability Assessment... A much less stormy pattern is slated to develop for much of the nation by later this week. The upper flow pattern over the lower 48 becomes rather zonal with a series of inherently low predictable northern and southern stream shortwave troughs and impulses before re-amplifying with increasing uncertainty next week. Nevertheless, this overall flow transition remains well depicted among the latest guidance into next week and preference is for a composite blend of the reasonably clustered mid-larger scale guidance from the 18 UTC GFS/GEFS mean, 12 UTC ECMWF/CMC/UKMET and ECMWF ensemble mean along with the 01 UTC National Blend of Models. The composite tends to mitigate, consistent with predictability, still rampant small-mid scale flow embedded system differences in guidance throughout the medium range period. This forecast plan maintains good WPC product continuity, but latest 00 UTC guidance now trends away from flow amplification over the eastern lower 48 into late period, lowering forecast confidence. ...Weather/Hazards Highlights... A lead front will settle down through the Gulf Coast/Southeast and persist through this forecast period. Lingering thunderstorms and flash flooding issues appear most likely across the western Gulf Coast region into Friday, where a low pressure wave is forecast to form near the front just offshore. Accordingly, the experimental Days 4 WPC Excessive Rainfall Outlook (ERO) is planned to maintain a "Marginal" threat area from the Texas coastal Plain to southwestern Louisiana. The proximity of the wavy front should support some additional periods of moderate precipitation across the South through the weekend into early next week. The WPC product suite still limits the northern lift of later week/weekend activity given overall flow. Increasing northern and southern stream interaction into early next week and the digging of cooling cold fronts with modest precipitation themselves down across the central and eastern states offers renewed potential for some northward spread of activity down across the Southeast given some signal for moderate coastal/maritime low development, but ample uncertainties remain with the system. Out West, the switch to a flatter flow pattern opens the Pacific Northwest to repeating shortwave troughs and onshore flow. These energetic Pacific systems should favor moderate to locally heavier precipitation across the Pacific Northwest into Friday/Saturday along with modest snows further inland across the Northwest and vicinity, but activity is set to weaken/lift north over the weekend into early next week when a strong upper ridge builds up the West Coast and shifts gradually inland over time. This will usher in a warmer and broadly benign weather conditions for much of the West, but eastern Pacific upper trough amplification and slow approach may portend a renewed wet pattern for especially the Pacific Northwest in about a week. 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