Extended Forecast Discussion NWS Weather Prediction Center College Park MD 301 PM EDT Thu Mar 20 2025 Valid 12Z Sun Mar 23 2025 - 12Z Thu Mar 27 2025 ...Overview and Guidance/Predictability Assessment... Progressive upper flow into the weekend in two streams will amplify into next week with the development of a warming/building West Coast ridge and a cooling/deepening and unsettling east- central U.S. trough. Operational and ML models capture the evolution of the overall synoptic pattern across the lower 48 for next week. All models are in reasonably good agreement on the day 3 pattern, save for several 00z GEFS members which depict a slower Central U.S. trough. This trend continues through the rest of the period. Deterministic guidance are more progressive than the ensembles and operational AIFS with the upper low propagating through the Great Lakes region on day 4. The upper pattern simplifies into mean troughing in the East and mean ridging in the West beginning on day 5. A Euro- centric general model blend is used from day 5 through 7. ...Weather/Hazards Highlights... Shortwave troughs riding a Western ridge will shift from the northeast Pacific into BC Sunday with a potent moisture plume to the south that pushes across western WA. A Marginal Risk for excessive rainfall is maintained only into Day 4/Sunday for coastal Washington as compounding effects of multiple preceding bouts of precipitation may lead to local runoff issues. Amplified upper trough development and deep system genesis early-mid next week should prove slow to approach the West Coast, but should spread organized precipitation back into the Northwest in about a week. The amplifying low over the northern Plains into the Great Lakes Sunday will draw broad scale Gulf moisture up the MS Valley and support a heavy rain and a severe weather threat for parts of Mid- South and lower MS Valley into the TN Valley. The Day 4/Sunday ERO Marginal Risk area is maintained for the Lower Mississippi and Tennessee Valleys. Enhanced rains then spread as a wavy cold front sweeps across the Southeast/Eastern Seaboard Monday into Tuesday. A WPC Day 5/Monday ERO Marginal Risk area was maintained to cover lingering and training cell potential over the eastern Gulf Coast. Meanwhile on the northern periphery of the expanding precipitation shield, reinforcing cold air wrapping around the main deep low appears to support a heavy snow threat for the Great Lakes region Sunday into Monday, spreading over the northern and interior Northeast into Monday and Tuesday with closed upper low/trough approach and with coastal New England triple-point low development. An amplifying ridge in the West will support an early return of spring-like temperatures in the West next week. Highs are expected to be between 15-30 degrees above average for much of the region. There's increasing potential for widespread high/low records to be tied/broken next Tuesday/Wednesday. This includes much of the Desert Southwest, where some places may experience daytime highs over 100 degrees. Kebede/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 forecast (QPF), excessive rainfall outlook (ERO), winter weather outlook (WWO) probabilities, heat indices, and Key Messages can be accessed from: 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