Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 416 PM EDT Wed Jul 31 2024 Valid 00Z Thu Aug 01 2024 - 00Z Sat Aug 03 2024 ...Dangerous heatwave expands from the Plains/Mississippi Valley into the Southeast/Mid-Atlantic as another heatwave develops over portions of the West... ...Severe weather and flash flooding expected for the Northern/Central Plains and Midwest today into Thursday... ...Another threat for flash flooding through today in northern New England... ... Locally heavy monsoonal shower and thunderstorm chances continue for the Southwest... Widespread, dangerous heat will be the big story for much of the country this week as one heatwave expands from the Plains/Mississippi Valley into the Southeast and another heatwave begins over portions of the West. A strong upper-level high will remain in place over the southern-tier of the U.S., with forecast high temperatures Wednesday and Thursday once again into the low to mid-100s over much of the Central Plains and southern High Plains and mid- to upper 90s for the Middle and Lower Mississippi Valley. High temperatures will also begin to climb into the mid- to upper 90s over much of the Southeast and southern Mid-Atlantic. High humidity values, especially for eastern portions of the Plains into the Mississippi Valley and Southeast, will bring heat indices soaring into the 105-110 degree range for many, with some locations reaching as high as 115, and many heat-related warnings and advisories are in place. The combination of hot temperatures to the west and high heat indices to the east, as well as very warm morning lows only dropping into the mid- to upper 70s, will be dangerous to anyone without access to adequate air conditioning. An approaching cold front will bring temperatures and humidity down a bit from the Middle Missouri Valley into the Central Plains Thursday. Unfortunately, an upper-level ridge will also begin to build northward over the West as well. This will quickly cause high temperatures across much of the northern tier of the West to rise 10-20 degrees above average Thursday and especially into Friday. Forecast highs will be into the upper 90s for the Pacific Northwest, northern Rockies, and northern High Plains, with 100s over much of the northern Great Basin by the weekend. Similar to areas further east, many heat-related watches and advisories have been issued as this heat will be dangerous to those without adequate air conditioning. Smoke from area wildfires will also continue to plague parts of the region, resulting in hazy conditions and poor air quality. An upper-level wave/surface frontal system along the northern side of the upper-level high over the Northern/Central Plains will continue moving southeastward, bringing a threat for severe weather and flash flooding the next couple of days. Plentiful moisture at the surface, strong to extreme instability, and accompanying strong flow aloft will help lead to some more intense thunderstorms.The Storm Prediction Center has outlined an Enhanced Risk of severe weather (level 3/5) over the Great Plains for the threats of strong wind and large hail, with a broader Slight Risk extending southeast into portions of the Middle Mississippi/Ohio Valleys and southern Appalachians to cover the threats of strong wind potential in bowing thunderstorm complexes A Slight Risk of severe weather continues tomorrow for the Ohio Valley and portions of the Midwest with the threat of large hail possible in any supercells of clusters of thunderstorms. There is a Slight Risk of Excessive Rainfall in effect across the Great Plains, Ohio, and Tennessee Valleys as clusters of thunderstorms bring the potential of dropping more than a couple of inches of rain. A Slight Risk for Excessive Rainfall is in effect for eastern parts of Illinois into the Ohio Valley on Thursday as additional rainfall concentrates along a frontal boundary in already saturated soils. Showers and thunderstorms are ongoing ahead of another upper-level wave/cold front approaching the Northeast today. High moisture lingering over the region may lead to some locally heavy downpours, 1 to 2 hour rain rates will be possible, with a heightened threat of flash flooding over portions of northern New England given the very wet antecedent conditions following historic amounts of rainfall on Tuesday. Another Slight Risk of Excessive Rainfall as well as Flood Watches are in place for the region. The front will weaken/push eastward on Thursday with some lingering shower chances, most likely over Maine. High temperatures will also rise into the upper 80s following the departure of the system, with humidity producing some muggy conditions. Showers and storms are also expected further south over portions of the Southeast/Florida through the next couple of days along with the heat. Daily Monsoonal shower and thunderstorm chances will remain over portions of the Southwest with some heavy downpours possible and an isolated threat for flash flooding. A passing upper-level shortwave will lead to greater coverage of thunderstorms over south-central Arizona today, with a Slight Risk of Excessive Rainfall in place for a locally higher threat for some flash flooding. Forecast high temperatures more broadly in the region will remain closer to average the next couple of days compared to northern areas of the West, with highs in the 60s and 70s for coastal California, middle to upper 90s for the Four Corners region and higher terrain of the Southwest, the 90s to low 100s for interior California into the central Great Basin, and mid- to upper 100s for the Desert Southwest. Putnam/Wilder Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php