Weather Across America 8/24/25

(NATIONAL) A Slight Risk of excessive rainfall over parts of the Sierra Nevada Mountains, Central/Southern High Plains, and Great Basin, a Slight Risk of excessive rainfall over parts of the Southwest, Central/Southern Rockies, and Central/Southern Plains and Extreme Heat Warnings and Heat Advisories along the West Coast and just inland.

Anomalous moisture will continue to surge into the Western U.S. Sunday. Upslope enhancement of moisture over parts of the Sierra may produce flash flooding, particularly over the central Sierra, where a slight risk (at least 15% chance) of excessive rainfall leading to flash flooding is in effect. Another slight risk area is over portions of southern Utah, where any storms that produce heavy rainfall could produce instances of flash flooding in slot canyons. A high end slight risk (at least 25% chance) of excessive rainfall is in effect from parts of eastern Colorado into the Texas/Oklahoma panhandles and western Kansas, where a complex of thunderstorms moving south could encounter increased instability leading to enhanced rain rates Sunday afternoon/evening.

The slight risk areas shift into portions of central/southern Colorado, northeastern New Mexico and Oklahoma, southern Kansas and western Arkansas on Monday. An upper trough, coming from the East Pacific, will begin to degrade the upper ridge centered over the Southwest early this week. Stormy monsoon conditions in the Southwest will likely alleviate the heat wave in the Southwest beginning on Monday, while continued southerly flow and clearer skies should allow for an expansion of the heatwave in the Northwest through early this week.

Extreme heat warnings and watches remain in effect across portions of the Desert Southwest, southern California, Washington, Oregon and northern California. For many areas there will be little nighttime relief from the extreme heat, with overnight lows remaining well above normal. Numerous nighttime temperature records are likely. Extreme heat is dangerous even at night when temperatures don't cool down.

Without A/C or cooling, the body can't recover, increasing the risk of heat illness. Elsewhere, a cool and dry continental airmass associated with surface high pressure will descend on the Central U.S. from Canada over the next few days. High temperatures in the 60s and 70s will be 15-30 degrees below average from the Great Plains to the Midwest. Some isolated record low maximum temperatures may be realized on Monday and Tuesday. These cool and dry conditions spread into the Eastern U.S. later this week.