Extended Forecast Discussion NWS Weather Prediction Center College Park MD 253 AM EDT Wed Mar 19 2025 Valid 12Z Sat Mar 22 2025 - 12Z Wed Mar 26 2025 ...Overview and Guidance/Predictability Assessment... Progressive upper flow with multiple embedded systems this week in two main 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. Models and ensembles seem well clustered with the weather pattern evolution through the medium range period, with reasonably good agreement on individual storm systems as well. Forecast confidence remains above average overall with a guidance blend, albeit with more uncertainty in details later period. However, these seem well mitigated consistent with predictability by the blend process and targeted manual adjustments. The WPC forecast was mainly derived from a GFS/ECMWF/CMC/UKMET composite Saturday into Monday before switching to a blend of best clustered GFS/ECMWF/Canadian model and ensemble mean guidance into longer time frames. This solution plan is mainly in line with the National Blend of Models, machine learning/00 UTC guidance and offers good WPC product continuity. ...Weather/Hazards Highlights... A series of Pacific systems and moderate moisture feeds will fuel periods of unsettled wet weather to the West/Northwest, with an enhanced moisture/rain focus for the Pacific Northwest and terrain enhanced heavy snows inland to the Rockies. The WPC Day 5/Sunday Excessive Rainfall Outlook (ERO) introduces a Marginal Risk area for coastal northwest Oregon/Washington as compounding effects of multiple bouts of precipitation may lead to local runoff issues. Downstream, less defined periods of precipitation over the central to eastern U.S. into the weekend are expected to become much better organized starting Sunday as a deepening cyclone is forecast to track northeastward from the Plains to the Great Lakes and the Northeast/eastern Canada into early next week. Return flow from the Gulf appears to support a heavy rain and a severe weather threat for parts of The South Sunday into Monday. A WPC Day 5 ERO Marginal Risk area was introduced 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. Meanwhile, reinforcing cold air wrapping around the main low appears to support a heavy snow threat for the Great Lakes region Sunday into Monday, possibly spreading over the northern and interior Northeast into Monday and Tuesday with closed upper low/trough approach and as triple-point low development is additionally possible near the coast of New England. 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