Weather across America

(NATIONAL) Heavy rain and flash flooding possible across much of the Southwest and southern Rockies, isolated severe thunderstorms are possible throughout the Lower Great Lakes, upper Ohio Valley, and Tennessee Valley, and a break in the heat and humidity expected to arrive across the South, but with heat continuing to build throughout much of the West. 

Additional rounds of showers and thunderstorms are likely to impact the Southwest and southern Rockies into Sunday night as moisture remains in place along with a front extending from West Texas to Arizona. 

Much of this region will gladly welcome more rain, given the longer term drought conditions that are in place, but locally there will continue to be sufficient heavy rain to result in some flash flooding. A Slight Risk (level 2/4) of excessive rainfall has been issued for much of central/northern New Mexico and southern Colorado through Sunday night to highlight this concern, with a Slight Risk also maintained for Monday over west-central to northern New Mexico. 

Additional rainfall totals of 1 to 2 inches, with locally higher amounts, could lead to rapid runoff and flooding concerns particularly near burn scars. The threat of widespread shower and thunderstorm activity is expected to gradually diminish and shift southward on Tuesday.

A cold front advancing across the eastern and southern U.S. will create the potential for isolated severe thunderstorms through Sunday evening, with the greatest threat extending from the Lower Great Lakes to the Tennessee Valley. A few storms could contain damaging wind gusts, frequent lighting, and heavy rain. An isolated threat of flash flooding will also extend along much of the cold front as it reaches the East Coast on Monday.

Meanwhile, a hot and sultry airmass initially across the Deep South and Southeast will be supportive of scattered afternoon and evening thunderstorms through early this week as the aforementioned cold front slowly settles down across this region. Slow-moving thunderstorms will have the capability of producing intense rainfall rates and isolated flash flooding.

A gradual frontal passage should occur for much of the South over the next couple of days, and this should bring about a break in the recent high heat and humidity. High temperatures for Monday and Tuesday should trend down closer to normal across the Gulf Coast states, but turn below normal across the southern Plains and adjacent areas of the lower Mississippi Valley and Mid-South. 

Conversely, for the West, a building upper-level ridge will allow for highs to surge into the 90s and near 100 degrees from central California through the Intermountain West and into the Pacific Northwest. The greatest high temperature anomalies will be over the Pacific Northwest where daytime highs will be as much as 20 to 25 degrees above normal for this time of the year. 

Heat Advisories remain in effect across large areas of Washington, western Oregon, and northern California, as well as areas farther south including the San Joaquin Valley and southern California. The heat will be relatively short-lived over the Northwest, as an approaching storm system and associated cold front crosses the region and ushers in cooler air by Tuesday.