Extended Forecast Discussion NWS Weather Prediction Center College Park MD 255 AM EDT Thu Apr 6 2023 Valid 12Z Sun Apr 9 2023 - 12Z Thu Apr 13 2023 ...Synoptic Overview... A large surface high will be in place across the northeastern U.S. this weekend, and this high should remain in place across the eastern U.S. through the middle of next week. Meanwhile, a stalled front offshore will likely support a surface low well off the southeast coast that will provide onshore flow from Florida to the Mid-Atlantic. Across the western U.S., a Pacific front moves inland followed by a building upper trough over the West Coast region and a downstream ridge building over the Midwest and Plains states. An upper low will likely develop near the Gulf Coast region by the middle to end of the week. ...Guidance/Predictability Assessment... The 00Z guidance suite is generally in good agreement on the synoptic scale through Monday, with some mesoscale uncertainties remaining near the southeast coast and the offshore low evolution. There is now stronger model agreement for a closed low developing near the central Gulf Coast by midweek, but disagree to some extent on the building ridge north of it. For the western U.S., the ECMWF takes the developing closed low farther south, whereas the GFS is a bit slower and the CMC weaker and farther east. The WPC front/pressures forecast was weighted more towards the ECMWF/GFS/CMC early on, and then gradually increased contributions from the ensemble means to about 50% by next Wednesday and Thursday. ...Weather/Hazards Highlights... The proximity of the wavy front to the southeast coast should support some additional precipitation across mainly coastal portions of the Southeast Sunday, lingering mainly over Florida into the middle of next week with continued onshore flow and the presence of a weak upper trough/closed low. The models continue to indicate the higher rainfall totals will likely be just offshore the Southeast Coast, and therefore no need for any Marginal Risk areas in the excessive rainfall outlook for this region. Things will likely be unsettled across western Washington and Oregon with a potential atmospheric river accompanying the next cold front to move inland, favoring moderate to locally heavy precipitation across this region in the Sunday to Monday time period. A Marginal Risk of excessive rainfall was introduced for the Day 4 period Sunday from the central Oregon Coast to the Olympic Peninsula with the potential for 1 to 3 inches of rain across the southwest-facing terrain. As the week progresses, this trough will move eastward across the northwestern U.S., and result in snow for the northern Rockies. Temperatures are expected to be slightly below early April averages across the southeastern U.S. early in the forecast period, owing to increased cloud cover and rainfall, and slightly above average from the Desert Southwest to the Great Lakes region. By Thursday, warmer weather returns to most of the central and eastern U.S., with highs running up to 20 degrees above average from the Upper Midwest to the eastern Great Lakes, and about 5-15 degrees below average for the Intermountain West. Hamrick 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