Extended Forecast Discussion NWS Weather Prediction Center College Park MD 245 AM 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 omega style flow pattern will be uncharactistically on the move over the continental U.S. this weekend into early next week, with a closed upper trough/low slowly working offshore from the Northeast and another deep closed trough low ejecting from the West to the Plains, shunting an amplified/sandwiched central nation upper ridge into the east-central U.S.. 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 pattern will likely produce excessive rainfall that could lead to flash flooding in the southern Plains/Lower Mississippi Valley and vicinity 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 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. 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 18 UTC GFS and 12 UTC ECMWF/UKMET/CMC for maximum system detail through this weekend into Monday. For Tuesday-next Thursday, Canadian and ECMWF ensemble means were increasing relied upon over time to smooth out model differences consistent with predictability. These ensemble systems are overall less progressive with systems than the GEFS and this solution seems a better match with models and pattern ampitude. Latest 00 UTC guidance maintains these trends. ...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. Heavy snow will be possible for parts of the northern Rockies 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. 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