Extended Forecast Discussion NWS Weather Prediction Center College Park MD 256 PM EDT Thu Jul 11 2024 Valid 12Z Sun Jul 14 2024 - 12Z Thu Jul 18 2024 ...Hazardous to dangerous heat likely for parts of the Central to Eastern U.S. next week... ...Overview... Persistent upper level ridging will be in place next week across the interior West, Southeast, and south-central U.S. and will bring above normal to hazardous temperatures to much of the nation. The ridge across the West will gradually weaken into early next week, but may build again by later in the period. Meanwhile, a series of potent upper level shortwaves will swing across the Upper Midwest, Great Lakes, and Northeast, and a couple of frontal boundaries will sink south across the north- central U.S. and the Northeast. Precipitation chances will increase along these frontal boundaries, and daily precipitation chances will also exist in the Four Corners region as monsoonal moisture focuses over the area. ...Guidance/Predictability Assessment... Model guidance remains in good agreement on the overall pattern, with typical spread/uncertainty in the details. The most impactful uncertainty will likely surround the timing of northern stream shortwaves, which will affect the timing and location of fronts and sensible weather at the surface. There is uncertainty that increases later in the period with amplified troughing off the West Coast and any energy into the Pacific Northwest ahead of it too. Given pretty good overall agreement, the WPC forecast model blend was comprised of a general deterministic blend of the GFS/ECMWF/CMC/UKMET, with slightly more weight placed on the GFS/ECMWF, for the first half of the period. Ensemble means from the GEFS/ECENS were added to the blend for the second half of the period to smooth out some differences. ...Weather/Hazards Highlights... Monsoonal moisture will focus over portions of the Four Corners region, which will allow for daily rounds of precipitation that could result in flash flooding, especially near steep terrain and burn scars. A Marginal Risk of Excessive Rainfall remains in place for much of the region on Day 4 (Sunday) and Day 5 (Monday) for much of the Four Corners region and portions of the southern Rockies as moisture pushes north. Across the Great Lakes and Northeast, upper level shortwaves and surface fronts will provide support for multiple rounds of showers and thunderstorms. With ample moisture and instability in place across these regions, locally heavy rainfall will be possible and may lead to isolated instances of flash flooding. A Marginal Risk of Excessive Rainfall remains in place for much of the Great Lakes region on Day 4 (Sunday), and the eastern Great Lakes and Northeast on Day 5 (Monday), especially given the heightened sensitivity in the Northeast following heavy rains this week. The Storm Prediction Center also highlights parts of this region for severe weather potential as well. Elsewhere, precipitation chances will progress south across the rest of the central and eastern U.S. mid-next week as a cold front moves south, and daily precipitation chances will persist in Florida with summertime convection. Locally heavy rain will be possible in these areas with any heavier thunderstorm activity. The West Coast and much of the Pacific Northwest will remain dry through next week. Much of the nation will experience above average temperatures next week, becoming dangerously hot for many from especially the central to eastern U.S.. Hazardous heat should slowly suppress south and eastward with time as amplified troughing dips into the Great Lakes and Northeast/Mid-Atlantic. Temperatures in the 110s are likely to continue across the Desert Southwest, and highs near or above 100 will be common in the central/southern Plains. Temperatures across the Northwest may be marginally above normal through early next week, but as upper ridging builds back in, anomalies may tick upward again. Santorelli/Dolan 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