Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 AM EST Mon Nov 27 2023 Valid 12Z Thu Nov 30 2023 - 12Z Mon Dec 04 2023 ...Overview... A shortwave over the Southwest on Thursday will shift across the Midwest and eventually into the Northeast next weekend, which should bring periods of moderate to heavy rainfall across parts of the South and into the Eastern U.S. late this week. Meanwhile, a shortwave or two will move into the West late week, promoting amplified mean troughing that shifts from the West into the Central U.S. and the Midwest this weekend/early next week as upper ridging builds downstream along the East Coast. This should keep the Western U.S. wet and generally unsettled with another round of possibly heavy rainfall to impact the Gulf Coast/Southeast Saturday into Sunday. ...Guidance Evaluation/Predictability Assessment... Models continue to come into better agreement on the large scale pattern across the CONUS during the medium range period, with a general blend of the latest deterministic guidance serving as a good starting point for the days 3-5 period. There continues to be some variance and timing with energy into the West late week, but overall good agreement that the pattern should turn more amplified and active. Despite good agreement right now, the guidance has struggled with the evolution over the West the past couple of days and there is still plenty of run to run variability. Blending in the ensemble guidance the second half of the period seemed to mitigate any lingering detail differences. ...Weather/Hazards Highlights... Shortwave energy into the mid-south and a warm front lifting through the Gulf of Mexico will allow for increasing moisture and instability across the Gulf Coast/Southeast region, with increasing confidence in some widespread moderate to heavy rainfall beginning Thursday and lasting into next weekend. Some uncertainty still in amounts and timing, but a marginal risk was maintained for the Day 4 (Thursday) Excessive Rainfall Outlook across the Lower Mississippi Valley. Models show some heavy rain lingering into Friday across the central Gulf Coast, so a marginal risk was added for this region on the Day 5 ERO. Amplified troughing shifting out of the West this weekend will provide a renewed surge of moisture and widespread moderate to heavy rainfall across the Southeast. Out West, precipitation will increase Thursday into next weekend as a shortwave or two move through the region, with some precipitation reaching southward into California and the Southwest. The heaviest precipitation (coastal rain and mountain snow) will be across the Washington/Oregon coast and Cascades next weekend with generally lighter amounts farther inland. The East Coast should start out with below normal temperatures on Wednesday, but should moderate back towards normal by Thursday. Mean troughing across the interior West should allow for cooler than normal temperatures lasting into next weekend. Elsewhere, there is signal for a period of above normal temperatures across the Northern Plains on Wednesday, with daytime highs 10-15 degrees above average, but as ridging builds into the Midwest and Eastern U.S. later this week, above normal temperatures should expand with time with much of the Northern Plains to Midwest and Southeast above normal by next weekend. Kebede/Santorelli 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 forecast, excessive rainfall outlook, winter weather outlook probabilities, heat indices and Key Messages 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 https://www.wpc.ncep.noaa.gov/#page=ovw