Weather across America

(NATIONAL) Dangerous heat to persist across portions of the Southwest, showers and thunderstorms and cooler temperatures to spread across the Plains and the Midwest, and locally heavy rain with flash flooding possible from the southern and central Appalachians to New England. 

Temperatures will remain well-above normal and will likely reach record levels Sunday across portions of southern Texas and the southwestern U.S. Excessive heat warnings remain in effect for the lower deserts of southern California and southeastern Arizona, including the Phoenix metro, where a strong upper high will support temperatures climbing once again to near 110F in some locations.  Temperatures are forecast to start decreasing beginning Monday as the upper high begins to break down and moisture associated with tropical cyclone Jova supports increasing cloud cover.  

By Tuesday, temperatures across the Southwest are expected to be near seasonal to below-normal, with widespread shower and thunderstorms expected. Much cooler temperatures will also be spreading south and east from the northern Plains Sunday into the central Plains and the upper to mid Mississippi Valley by Monday, before reaching into the Great Lakes, Ohio Valley and parts of the southern Plains on Tuesday.  

In addition to below-normal temperatures, periods of showers and thunderstorms will follow a well-defined cold front as it moves across the region. Some storms may become strong to severe, producing large hail, damaging winds, and heavy to excessive rainfall. The greatest threat Sunday is expected to center near western Kansas and the Oklahoma Panhandle, with SPC highlighting the severe weather threat and WPC noting the excessive rainfall threat across this area.  

Showers and thunderstorms are also expected to develop farther south near the trailing end of a stalled frontal boundary that extends from the northern Gulf of Mexico northwestward into the southern High Plains. In the East, a stalled frontal boundary, ample moisture, and an upper disturbance lifting out of the Southeast, will support widespread showers and thunderstorms Sunday.  Areas of heavy rainfall are expected, with localized flash flooding possible. The greatest threat for heavy rainfall is forecast to center from the central Appalachians northeastward through the Mid Atlantic into New England.