Extended Forecast Discussion NWS Weather Prediction Center College Park MD 257 PM EDT Wed Jun 12 2024 Valid 12Z Sat Jun 15 2024 - 12Z Wed Jun 19 2024 ...Early season heatwave expected from the Central Plains to the East Coast with widespread highs in the 90s... ...Gradually improving conditions for Florida while western Gulf becomes more active early next week... ...General Overview and Guidance/Predictability Assessment... Guidance generally remains in good overall agreement into next week with respect to the overall pattern, featuring a building upper ridge across the eastern half of the U.S., and a developing trough over the Intermountain west. The 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 over Florida this week will slowly retrograde over the Gulf of Mexico this weekend into next week. This will bring gradually improving conditions for Florida, while increasing rainfall chances for the central and western Gulf Coast going into Sunday and early next week The WPC medium range product suite was primarily derived from a multi-deterministic model blend for the weekend, along with some previous WPC continuity. There is a gradual increase of the GEFS/ECMWF ensemble means through next Wednesday to account for 40% of the blend amid growing forecast model differences typical at this time range. ...Weather/Hazards Highlights... The coverage of heavy showers and storms over the central and southern Florida Peninsula is forecast to decrease going into this weekend, as the main axis of tropical moisture is forecast to drift westward across the Gulf of Mexico and then affect the western Gulf Coast region. A Day4/Saturday ERO Marginal Risk remains valid for lingering convective activity over the southern half of Florida. However, as the weekend progresses and into early next week, there is some model guidance signal that moisture influx and possible heavy rainfall may refocus and increase near the central Gulf Coast and vicinity. A Day 5/Sunday Marginal Risk ERO remains valid given the moist pattern. Uncertainty remains, particularly with the potential amount of rainfall and with westward extent into the western Gulf through early-mid next week. Elsewhere, a convective precipitation event is likely across the Northern Plains and then the Upper Midwest/western Great Lakes this weekend as southern stream troughing ejects northeastward toward the region from the Southwest, with an MCS likely to develop. A Slight Risk is now planned for portions of southern Minnesota, northern Iowa, and western Wisconsin to account for the improved model signal for an axis of 1-3 inch totals, with locally higher values possible, where some convective training could develop. A broader Marginal Risk area remains across much of this same region going into the Day 5 period as the overall weather pattern doesn't change all that much. 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 into next week as the upper-level ridging builds in. Highs are forecast well into the 90s, potentially near 100 degrees for some areas, and with lows in the middle 60s to middle 70s providing little relief from the heat overnight. The Climate Prediction Center continues a heat threat into week 2. Schichtel/Hamrick 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