Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Thu Jun 13 2024 Valid 12Z Sun Jun 16 2024 - 12Z Thu Jun 20 2024 ...Early season heatwave to spread from the West/Southwest out through the South-Central Plains to the Midwest/East Coast next week... ...Improved conditions for Florida while the central to western Gulf becomes more active into next week... ...Multi-episode Heavy rain/convection pattern for the north- central U.S. next week... ...General Overview and Guidance/Predictability Assessment... The latest models and ensembles generally remain in good overall agreement into next week with respect to the overall pattern, featuring a strongly building upper ridge across the eastern half of the U.S., and a developing amplified upper trough over the West. Guidance indicates a southern stream shortwave over the Southwest will lift northeast, and around the western periphery of the building ridge with additional embedded waves crossing the northern tier as the main upper trough begins to take hold over the West. An upper-level disturbance now over Florida should slowly work westward over the Gulf of Mexico this weekend into next week. This will bring improving conditions for Florida, while increasing rainfall chances for the central and western Gulf Coast and vicinity going into Sunday and early-mid next week. The WPC medium range product suite was primarily derived from a composite blend of best clustered guidance of the 18 UTC GFS/GEFS mean and 18 UTC ECMWF/ECMWF ensemble mean, the 01 UTC National Blend of Models through medium range time scales all next week in a pattern with near average predictability overall. ...Weather/Hazards Highlights... A main axis of tropical moisture is forecast to shift westward across the Gulf of Mexico and affect the central to western Gulf Coast region next week. Day 4/Sunday and Day 5/Monday ERO Marginal Risk areas have been introduced for the west-central Gulf Coast given the moist pattern. Uncertainty remains, particularly with the potential amount of rainfall and with westward extent into the western Gulf into later next week. The 12 UTC Canadian offered an outlier solution with tropical development and northward inland track not supported by NHC guidance. The 00 UTC run backed off. Elsewhere, convective precipitation event is likely across an unstable Northern Plains and the Upper Midwest/western Great Lakes as southern stream troughing ejects northeastward from the Southwest as well as lagging northern stream upper trough approach. WPC ERO Marginal Risk areas have been introduced for Day 4/5 Sunday/Monday. There is now a more consistent signal that the subsequent upstream march of an amplified upper trough out from the West/Northwest will act to also support the Marginal Risk of heavy rains over the Northern Rockies/High Plains Day5/Monday. This focus is expected to slowly work across the north-central U.S. Tuesday into next Thursday as aided by renewed cyclo/frontogenesis. As for anomalous temperatures, an amplified upper ridge slated to steadily/broadly shift from the Southwest through the south- central U.S. to the East over the coming week will produce widespread anomalous heat and humidity, with the potential for some daily record highs to be established. Temperatures will already be rather hot over portions of the South before the even broader region of heat expands into the Midwest/Ohio Valley then Mid- Atlantic/Northeast next week as the upper-level ridging builds in. Highs are forecast well into the 90s and with lows in the middle 60s to middle 70s providing little overnight heat relief. Latest guidance trends are slower to alieviate the heatwave with more steadfast persistence of the supporting upper high/ridge. 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