Extended Forecast Discussion NWS Weather Prediction Center College Park MD 245 PM EDT Wed Apr 23 2025 Valid 12Z Sat Apr 26 2025 - 12Z Wed Apr 30 2025 ...West/Rockies to Central U.S. Spring Storm... ...Overview... Organized showers and thunderstorms with locally heavy downpours will focus across the Northeast into the weekend as a deeply wavy frontal system moves over and offshore. Meanwhile, unsettling and cooling upper troughing will move from across the West and produce widespread moderate precipitation. Expect enhanced snow for the higher elevations from the Cascades down to the Sierra and inland to the north-central Intermountain West/Rockies this weekend, with Rockies activity enhanced by lee cyclogenesis and frontogenesis into early next week. Deep moist inflow ahead of the upper trough and developing storm system will significantly increase the coverage of rains and strong to severe thunderstorms across the central to east central U.S. into early to mid next week. Temperatures will mostly remain above normal east of the Continental Divide while trending near to below normal in the West. ...Guidance/Predictability Assessment... Model guidance continues to be in good overall agreement through the upcoming weekend into early next week. Aside from minor differences with respect to smaller scale features, the depiction of the large scale pattern was generally good enough to be represented by a blend that featured mostly deterministic guidance early on, followed by roughly 50% deterministic solutions and 50% ensemble means later. Within the deterministic space, the 00Z CMC, 00Z UKMET and 06Z GFS were favored, with less weight placed on the 00Z ECMWF. This weighting was due to the 00Z ECMWF being a little too slow, weak, and less negatively tilted with the shortwave/trough lifting across the Great Lakes into the Northeast early next week compared to the other guidance. Fortunately, the 12Z ECMWF came into better alignment with the other pieces of guidance, including nearly all of the machine learning guidance, lending to a higher confidence forecast in the later forecast periods. The ensemble means featuring the 00Z EPS and 06Z GEFS were used to offer more stability for days 5, 6, and 7. ...Weather/Hazards Highlights... Modestly progressive upper shortwaves with wavy surface systems remain slated to bring some concentrated enhanced rains over the Northeast into Saturday, with trailing frontal convective activity to the south sweeping through and exiting the Eastern Seaboard by Sunday. As a result, a WPC Day 4/Saturday Excessive Rainfall Outlook (ERO) Marginal Risk area remains in place over the northeast Mid-Atlantic and New England. Meanwhile, an amplified upper trough and surface system digging across the West this weekend offers widespread rains and enhanced snows for the higher elevations from the Cascades down to the Sierra and inland over the north-central Intermountain West. Mountain snows then expand into the central and northern Rockies into early next week. Downstream, rich moisture streaming in ahead of a deeply strengthening storm system ejecting into the Plains will fuel rounds of heavy rain and thunderstorms across portions of the central U.S. from the weekend into next week. A Marginal Risk ERO area remains in place for Day 4/Saturday, which includes portions of Kansas, New Mexico, Texas, Oklahoma, Missouri and Arkansas given favorable upper trough diffluence combined with front/dryline instabilities. For Day 5, introduced a broad marginal risk from portions of Montana/North Dakota/northern South Dakota to Minnesota/northwest Wisconsin given an increasing signal for anomalous moisture and an expanding convective QPF footprint. Activity will be in the process of transforming into an emerging comma-shaped rainfall area broadly progressing over the central U.S. before tracking across some moisture laden soils of the east- central U.S. early to mid next week given further surface low and wavy frontal structure development and evolution. Episodes of severe weather will also be monitored by SPC as predictability grows closer to the event. Temperatures along and east of the Continental Divide will largely remain at or above normal through much of the medium range period as upper level ridging builds. Meanwhile, temperatures across the West will be near to below normal given unsettled conditions underneath an upper level trough. Miller/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