Extended Forecast Discussion NWS Weather Prediction Center College Park MD 258 AM 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 with wrapped flow 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 acorss the West and produce widespread moderate precipitation. Expect enhanced snow for 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 a spread of rains and strong thunderstorms across the central to east central U.S. into early-mid next week. ...Guidance/Predictability Assessment... Model and ensemble forecast spread remains reasonable for most systems within a broadly similar larger scale pattern evolution, albeit with continued uncertainties with wave timing and local convection foci. There is still a growing signal favoring flow amplitude and energetic main system cyclogenesis and frontogenesis. Accordingly, the WPC medium range product suite was primarily derived from a broad composite blend of best clustered guidance from the 18 UTC GFS/GEFS mean and the 12 UTC ECMWF/UKMET/Canadian and ECMWF ensemble means along with a compatible 01 UTC National Blend of Models. This plan maintains good WPC product continuity, generally in line with recent machine learning guidance and latest available 00 UTC model and ensemble guidance. ...Weather/Hazards Highlights... Slowly 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. A WPC Day 4/Saturday Excessive Rainfall Outlook (ERO) Marginal Risk area is in place over the northeast Mid-Atlantic and New England. Meanwhile, amplified upper trough and surface system drive over the West this weekend offers widespread rains and enhanced snows for higher elevations from the Cascades down to the Sierra and inland over the north-central Intermountain West. North-central Rockies snow threats ramp into next week with continued storm genesis. The WPC Winter Weather Outlook as linked below along with other WPC products depicts the most likely mountain locations. Downstream, return moisture streaming in ahead of deep system genesis 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 for Day 4/Saturday includes portions of Texas and Oklahoma and a large portion of Kansas given favorable upper trough diffluence combined with front/dryline instabilities. While no WPC Day 5/Sunday risk area was introduced at this time due to coverage/local uncertainties, scatterred convective downpours both over the northern Plains and down over the south- central Plains will be monitorred for a more defined guidance signal to issue an ERO upgrade. Activity will be in the process of increasingly transforming into an emerging comma-shaped rainfall area broadly progressing over the central U.S. and then into some moisture laden soils of the east-central U.S. early-mid next week given further surface low and wavy frontal structure development and evolution. Episodes of severe weather will also continued to be monitorred by SPC as predictability grows closer to the event. 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