Extended Forecast Discussion NWS Weather Prediction Center College Park MD 301 PM EDT Tue Apr 22 2025 Valid 12Z Fri Apr 25 2025 - 12Z Tue Apr 29 2025 ...Overview... Widespread showers and thunderstorms with locally heavy downpours will gradually spread from portions of the central U.S. eastward into the Northeast later this week into the weekend as a low pressure/frontal system moves through. Meanwhile, ample upper troughing will move from the eastern Pacific into the West and promote modest precipitation, with a main focus over the Northwest. Snow is likely for the higher elevations across the north-central Rockies, enhanced by lee cyclogenesis and frontogenesis. Deep moist inflow ahead of the ejecting upper trough and developing storm system will significantly increase the spatial coverage of rain and thunderstorm chances across the central U.S. once again over the weekend and into early next week. ...Guidance/Predictability Assessment... Model guidance remains in good overall agreement with its depiction of the large scale pattern through most of the medium range period. Generally minor differences begin to crop up by days 6 and 7, particularly with respect to the evolution of the smaller scale shortwaves within the parent trough ejecting from the Intermountain West into the central U.S. Despite the differences, there was enough of a consensus as to not drastically impact predictability. As a result, the WPC forecast was largely derived from deterministic solutions stemming from the 00Z ECMWF, 00Z CMC, and the 06Z GFS. Ensemble means from the 00Z EPS and the 06Z GEFS gradually became more heavily weighed by the end of the period, but combined were still slightly less than 50/50 of the total blend by day 7. This blend offered a desirable compromise of higher resolution details and large scale stability. ...Weather/Hazards Highlights... A number of slowly progressive upper features and surface based systems will continue to work over mainly the eastern half of the nation into late week and the weekend. Recent and ongoing rainfall over some portions of this broad region will make some areas susceptible to additional rains. By Friday, a low pressure system and its trailing front is likely to move across the Mississippi Valley toward the Great Lakes and interior Northeast, spreading thunderstorm chances into those areas. The Day 4/Friday WPC Excessive Rainfall Outlook Marginal Risk area was expanded northward into the eastern Great Lakes and interior Northeast given a growing signal for heavier and more widespread QPF. The risk across portions of the Northeast continues into Day 5/Saturday, with the Marginal Risk area expanded into more of northern New England and Maine from the inherited risk area of the northeastern Mid-Atlantic to southern New England given higher QPF. Meanwhile, upper trough amplification from the eastern Pacific into the West late this week into the weekend, along with surface system genesis and slow but steady system translation, will still offer increasingly widespread rain chances and mountain snows. Renewed moisture streaming in ahead of the trough plus lingering boundaries in the area will allow for additional rounds of possibly heavy rain and thunderstorms across portions of the central U.S. by the weekend. The inherited Marginal Risk ERO for Day 5/Saturday was expanded northward from portions of Texas and Oklahoma to a large portion of Kansas and eastern Nebraska given favorable upper trough difluence combined with front/dryline instabilities. Organized activity should then increasingly transform into an emerging comma- shaped rainfall area broadly sweeping over the central U.S. into early next week given expected surface low and wavy frontal structure development and evolution. Episodes of severe weather are possible along with the marginal heavy rain threat. 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