Extended Forecast Discussion NWS Weather Prediction Center College Park MD 303 AM EDT Thu Jul 11 2024 Valid 12Z Sun Jul 14 2024 - 12Z Thu Jul 18 2024 ...Above average temperatures forecast for much of the nation 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 temperatures to much of the nation. The ridge will gradually weaken through the week, and temperatures should become less extreme. 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 an expected amount of 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. These differences will be resolved with time. 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 another Marginal Risk area will likely be added for Day 5 (Monday) for much of the Four Corners region and portions of the southern Rockies as moisture pushes north. Flooding may also be a concern in the Great Lakes and Northeast where 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 a Marginal Risk will likely be introduced for the eastern Great Lakes and Northeast on Day 5 (Monday), especially given the heightened sensitivity in the Northeast following heavy rains this week. 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 in some locations. 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 may become less hot mid/late week for the north-central and northeastern U.S. in the wake of the frontal systems, with highs dropping from the 80s/90s to the 70s/80s. 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