Extended Forecast Discussion NWS Weather Prediction Center College Park MD 220 PM EDT Wed Apr 3 2024 Valid 12Z Sat Apr 06 2024 - 12Z Wed Apr 10 2024 ...Heavy rain and flash flooding concerns will increase in the southern U.S. next week... ...Pattern Overview... Initially an omega style blocking pattern will be in place over the continental U.S. late this week, with a deep upper low over the Northeast and another deep low over the West, sandwiching a central nation upper ridge. This pattern will be slowly progressive over the weekend as the northeastern upper low exits into the Atlantic and the western low lifts northeastwards towards the Upper Midwest through mid-next week. As the low lifts, it will be accompanied by a surface frontal system that could bring a chance of showers to parts of the Central U.S. and the Ohio, Tennessee, and Lower Mississippi Valleys (this will likely have implications for eclipse viewing on Monday). Another upper low will dig down the West Coast into the Southwest early in the week and move into the south- central U.S. by mid-next week. This pattern will likely produce excessive rainfall that could lead to flash flooding in the southern Plains and Lower Mississippi Valley mid-next week. ...Guidance/Predictability Assessment... Model guidance remains in reasonably good agreement on the weather pattern through the medium range period; however, there is still an expected amount of spread and uncertainty for this time range. The main differences between model solutions surround the complex evolution of the frontal system moving across the central U.S. next week. There are differences in how the models are handling the ejection of the upper low towards the Upper Midwest, which will in turn affect timing and location of fronts, precipitation, and cloud cover. The WPC forecast was mainly derived from a multi-model blend of the 06 UTC GFS and 00 UTC ECMWF/UKMET/CMC for maximum system detail through this weekend into Monday. For Tuesday and Wednesday, ensemble means from the GEFS and EC ensemble were added to the blend in increasing amounts to smooth out model differences and maintain trends with the amplified upper pattern. ...Weather/Hazards Highlights... The strong low pressure system that will impact the Northeast late this week will move offshore by this weekend, but light to locally moderate precipitation may linger over New England and downwind of the Great Lakes on Saturday. Brisk northwesterly flow on the backside of the system will persist across the Northeast on Saturday, then decrease on Sunday as the pressure gradient weakens. Meanwhile, unsettled weather will impact the Pacific Northwest and northern and central Rockies as a cold front drops south from Canada and a low pressure system strengthens over the Plains. Heavy snow will be possible for parts of the northern Rockies Saturday into Sunday, then conditions will improve as the system progresses east. Early next week, this system will bring a large swath of showers and thunderstorms (with some severe thunderstorms possible) across the Plains and Mississippi Valley into the Midwest. This system will be relatively slow moving, which could result in locally heavy rainfall in some areas. Behind the system, high winds will spread from the Rockies into the Plains, which will combine with dropping humidity to produce a critical wildfire risk over eastern New Mexico, the western Half of Texas, and the Oklahoma panhandle this weekend. Upstream, a renewal of mainly light to moderate precipitation is possible along the West Coast early next week as a new Pacific upper trough/closed low digs down towards the Southwest. The focus for precipitation will then shift to the south-central U.S. Tuesday into Wednesday, and moist Gulf inflow may be re-energized as a low pressure system sweeps across the southern tier of the nation. Heavy rainfall seems likely across the southern Plains, Lower Mississippi Valley, and Mid-South, which may lead to flash flooding concerns. Temperatures will be below average this weekend into early next week across the western U.S. as upper level troughing dominates the weather in this region. Temperatures for much of the West should rebound to near or slightly above average by Tuesday, except for in the Southwest where temperatures will remain cooler than average. In the Central U.S., temperatures should remain near to slightly above average with areas of below average temperatures under cloud cover and precipitation. In the East, colder air will move into the region behind the departing coastal low, which will result in below normal temperatures this weekend. Morning lows are forecast to be near freezing from the Northeast and Great Lakes into the Mid- Mississippi, Ohio, and Tennessee Valleys, which could affect sensitive vegetation. A warming trend should take root in the East and Midwest early next week. Dolan/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