Extended Forecast Discussion NWS Weather Prediction Center College Park MD 255 AM EDT Tue Mar 18 2025 Valid 12Z Fri Mar 21 2025 - 12Z Tue Mar 25 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 West Coast ridge and a cooling and unsettling east- central U.S. trough. Models and ensembles again show good agreement on the weather pattern 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 late in the period. However, these seem mitigated consistent with predictability by the blending process. The WPC forecast mainly comprised of near even parts of the GFS/ECMWF/CMC/UKMET and GEFS/ECMWF/Canadian ensembles seems in line with the National Blend of Models and WPC product continuity. ...Weather/Hazards Highlights... Lead New England coastal storm genesis into Friday offers a windy heavy snow threat for northern/interior Northeast before departure as a maritimes hazard into the weekend. Well upstream, a series of Pacific systems and 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 4/Friday Excessive Rainfall Outlook maintains a Marginal Risk area for coastal northwest Oregon and Washington, with renewed focus to monitor later weekend into early next week. Compounding effects of multiple days of precipitation may lead to local runoff issues. Well downstream, less defined rainy periods over the central to eastern U.S. this week are expected to become much better organized Sunday into early next week with cyclogenesis and emerging return inflow. A deepening system track will also offer a Midwest/Great Lakes/Northeast wrapping snow threat on the colder northern portion of an expanding area of precipitation. 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