Extended Forecast Discussion NWS Weather Prediction Center College Park MD 257 PM EDT Sat Jul 13 2024 Valid 12Z Tue Jul 16 2024 - 12Z Sat Jul 20 2024 ...Hazardous Heat for parts of the Central to Eastern U.S. for early-mid next week. High heat to build over the West next week... ...Overview... Heat focusing upper level ridging will persist through early-mid next week over the southern half of the nation to bring widespread above normal to hazardous temperatures. Upper trough development over the eastern/northeastern Pacific into later next week will act to build upper ridging over western North America and upper trough amplification over the east-central continent. Energy digging to the lee of the western ridge will increasingly work down into downstream southern tier upper ridging as a heatwave moderating cold front sinks down across much of the central and eastern U.S.. Meanwhile, upper level shortwaves will work over the Midwest/Great Lakes and Northeast/Mid-Atlantic. Temperature moderating fronts will sink south across the central U.S. and the East, with potential to sink down into the South/Southeast later week. Rain/thunderstorm chances will increase by these fronts. Daily rain/convection chances will linger near the Four Corners region and south-central High Plains as fueled by monsoonal moisture. ...Guidance/Predictability Assessment... The 12Z model guidance suite maintains better than average agreement on the synoptic scale across the continental U.S. through the end of the week. By Saturday, the GFS becomes a little stronger with the trough over the central U.S., but good placement overall. It is also not quite as strong with the western U.S. upper ridge when compared with the model consensus. There are also some modest differences across New England with upstream trough passages from Quebec. A general deterministic model blend sufficed as a good starting point in the forecast process through Thursday, followed by 30-40% of the ensemble means by Friday/Saturday. ...Weather/Hazards Highlights... Monsoonal moisture will linger 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 planned for Day 4 (Tuesday) and Day 5 (Wednesday) for the southern Rockies and into eastern Colorado in a region with protracted favorable upper diffluence. Favorable upper level support and well defined/wavy surface fronts set to shift southward across much of the central and eastern U.S. will lead to multiple rounds of showers and thunderstorms. With ample moisture and instability in place, locally heavy rainfall will be possible and may lead to instances of flash flooding. A WPC Day 4 (Tuesday) Marginal Risk ERO is set across the Ohio/Mid- Mississippi Valleys/central Plains, and a Slight Risk area is planned from central Indiana to central Ohio, where the strongest model signal exists along with wet antecedent conditions and anomalous PWs. The Day 5 (Wednesday) ERO extends from the Mid- South to the Mid- Atlantic as the main front shifts southeastward. Precipitation chances will progress farther southward across much of the rest of the central and eastern U.S. mid-next week as this cold front moves south, and daily precipitation chances will persist in Florida with summertime convection from sea breeze convergence. Locally heavy rain will be possible in these areas with heavy thunderstorm activity. Much of the nation will experience above average temperatures next week and a threat for widespread record values while 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 Midwest/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 tick upward again in a pattern with increasing hot conditions over the West. Hamrick/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