683 FXUS02 KWBC 300657 PMDEPD Extended Forecast Discussion NWS Weather Prediction Center College Park MD 257 AM EDT Thu Apr 30 2026 Valid 12Z Sun May 03 2026 - 12Z Thu May 07 2026 ...Overview... Several disturbances rotating around a persistent upper level closed low centered over Ontario and Quebec will help to reinforce broadly deep troughing across the eastern U.S. from late this weekend through much of next week. This pattern will keep conditions cool and unsettled at times across parts of the Upper Midwest, Great Lakes, Mid-Atlantic, and Northeast as multiple frontal systems move through. Meanwhile, what's left of a frontal boundary will continue to be a focus for showers and thunderstorms across central and southern Florida Sunday into Monday. Then another Pacific closed low pushes inland early next week, bringing low elevation showers and thunderstorms along with mountain snow showers to parts of the West. ...Guidance/Predictability Assessment... The latest guidance continues to have a very good handle on the large scale pattern evolution through the period, featuring an initial large upper low and broad troughing across the eastern U.S., and a Rex block across the western U.S. By late in the period, the Rex block breaks down as a closed upper level Pacific low pushes inland and an upper level ridge builds in from the west. Despite above average agreement amongst the models, there are still some smaller scale differences. The main sources of uncertainty deal with several smaller waves rotating around the large primary upper low spinning over southeast Canada, as well as how quickly the cut-off Pacific low portion of the Rex block pushes inland over the Southwest. An equal model composite blend between the ECMWF, GFS, CMC, UKMET, and EC-AIFS sufficed for the first half of the forecast period, with more weighting placed on the ensemble means for the latter half. This approach remains in line with the previous WPC forecast as well as the 01z NBM, which served as a good starting point for the WPC Day 4-7 forecast. ...Weather/Hazards Highlights... As a large upper level low spins over southeast Canada, multiple disturbances rotating around the low are likely to push a few cold fronts and chances for showers and thunderstorms into the Upper Midwest, Great Lakes, Ohio Valley, and Northeast Sunday into the middle of next week. A little snow may even mix in with the rain closer to the U.S./Canada border. In addition to shower chances, the fronts will bring reinforcing surges of cool air, keeping temperatures near to below seasonal norms. Chilly nighttime lows may also lead to frost and freeze concerns over parts of the Ohio Valley, Mid-Atlantic, and the central Appalachians Sunday night into early Monday morning. A cold front sagging southward across central and southern Florida will be a focus for heavy rain on Sunday. Anomalous moisture pooling along the front combined with increasing instability will lead to the development of scattered to numerous clusters of showers and thunderstorms, mainly during the afternoon and evening. This activity may contain heavy rainfall rates which could lead to localized poor drainage and urban flooding. As a result, the Day 4/Sunday Marginal Risk ERO remains in place. While some showers and storms are likely to linger into Monday, waning coverage and intensity should keep any remaining flooding threat to a minimum. Thus, no additional Marginal Risk was introduced for the new Day 5/Monday ERO. A slow-moving Pacific low spinning off the coast of California will begin to push inland across California and the Great Basin during the first half of next week. Increasing moisture and instability ahead of this low will support scattered low elevation showers and storms along with mountain snow showers across portions of the West Monday and Tuesday. After several days of unseasonable warmth, temperatures trend cooler for the first half of the week given plenty of showers and clouds around. Once the low moves out mid to late week, a ridge builds in and temperatures rebound back above seasonal norms once again. Miller 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, excessive rainfall outlook, winter weather outlook probabilities, heat indices and Key Messages are at: 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 $$