Extended Forecast Discussion NWS Weather Prediction Center College Park MD 303 PM EDT Thu Apr 4 2024 Valid 12Z Sun Apr 07 2024 - 12Z Thu Apr 11 2024 ...Heavy rain and flash flooding concerns will increase in the southern U.S. next week... ...Pattern Overview... An uncharacteristically progressive Omega flow pattern will be in place over the lower 48 through middle of next week. The leading trough will be pulling offshore the Northeast with a narrow area of weak ridging and a broad trough/upper low ejecting from the West into the Plains. As the Plains 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. into next midweek to support cyclogensis/frontogenesis and lead moisture/instability return over a developing Gulf coastal front. This environment and pattern will likely be conducive for scattered to widespread heavy rain to develop across the Lower Mississippi Valley and Gulf states resulting in excessive rainfall over a multi-day period. ...Guidance/Predictability Assessment... The latest runs of global and ensemble guidance have very good clustering through much of the extended period that results in above average confidence, especially with the pattern evolution across the Plains/Mississippi Valley. However, there is still an expected amount of spread and uncertainty locally for this time range. The main differences between model solutions surround the complex evolution of the frontal systems across the central U.S. early next week starting with how/where the upper low ejects toward the Upper Midwest. These differences will affect the timing and placement of the fronts and the associated cloud cover and precipitation. In a similar approach to the previous forecast, the WPC suite of products utilized a multi model approach by using the 06Z GFS and the 00Z ECMWF/UKMET/CMC through Monday. For Tuesday and beyond the UKMET was dropped while the inclusion and weighting of the Canadian and EC ensemble means where increased. The EC and CMC solutions, particularly for QPF for the southern tier states, are a bit wetter and reflect the climatology that this pattern typically brings. ...Weather/Hazards Highlights... A strong low pressure system impacting the Northeast will move offshore this weekend, but light to locally moderate precipitation may linger over New England in brisk backside flow. Meanwhile, unsettled weather will impact the Pacific Northwest and northern and central Rockies this weekend as a cold front drops south from Canada and a low pressure system strengthens over the Plains. This will usher in snow/heavy snow for portions of the Northern Rockies into Sunday before improving for the start of the week as the system advances eastward. A large swath of showers and thunderstorms will accompany this front as it moves through the central U.S. Some of these storms that develop over the Plains, Mississippi Valley and Midwest are expected to be severe. 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. Much of the West will have below average temperatures through the weekend and into early next weeks thanks for the broad trough and upper lows tracking through. 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. Campbell/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