San Francisco International, CA

Weather Underground Forecast for Tuesday, May 21, 2013.

After a devastating severe weather day in the Plains on Monday, severe weather is expected to fire up again across the nation's mid-section again on Tuesday.

The nearly stationary low over the Northern Plains will gradually weaken as it shifts eastward into the Midwest on Tuesday, while the system's associated cold front trails southwestward from the low across the Mid-Mississippi Valley through the Southern Plains. Favorable energy and conditions ahead of the cold front combined with the moisture laden conditions of the nation's mid-section will set the stage for multiple clusters of thunderstorms to develop from the Midwest into the Ozarks and the Southern Plains. Portions of northeastern Texas, extreme southeastern Oklahoma, central and southern Arkansas, and northwestern Louisiana are at moderate risk of severe thunderstorm activity as environmental conditions remain favorable for tornadoes, damaging wind gusts, and very large hail. Areas surrounding this moderate risk region from the parts of central and eastern Texas into the Upper Great Lakes are at slight risk of severe thunderstorm development with hail, damaging wind gusts, and isolated tornadoes.

Meanwhile, areas of heavy rain and widely scattered showers will continue near the low in the Northern Plains and Upper Mississippi Valley and near and to the north of a nearly stationary frontal boundary extending out ahead of the system from the Great Lakes into the Northeast. Continued precipitation in already saturated areas of the Northern Plains and Upper Midwest will maintain flood concerns from parts of North Dakota into northern Wisconsin.

Elsewhere, scattered showers and thunderstorms are expected to persist in the Mid-Atlantic and southeastern corner of the nation.