San Francisco International, CA

Weather Underground midday recap for Monday, May 20, 2013.

Heavy rains and chances of severe thunderstorm activity continued for areas of the Plains into the Midwest on Tuesday as a broad, nearly stationary low remained over the Northern Plains. As the system lingered, ample moisture streamed northward from the Gulf of Mexico, while an associated cold front reached from the low southward through Central and Southern Plains. The sharpening cold front combined with a dry line in the Southern Plains and the moisture laden conditions of the Central U.S. set the stage for multiple clusters of thunderstorms to develop across the Plains and into the Mid-Mississippi Valley. Portions of eastern/central Oklahoma, north-central Texas, northwestern Arkansas, southern Missouri, far southeastern Kansas remained at moderate risk of severe thunderstorm activity as environmental conditions remained favorable for strong tornadoes, damaging wind gusts, and very large hail. Areas surrounding this moderate risk region from the parts of the central Texas into the Upper Great Lakes and Upper Mississippi Valley were at slight risk of severe thunderstorm development with hail and isolated tornadoes.

Meanwhile, areas of heavy rain and widely scattered showers persisted near the low and it\\\\'s associated warm front in portions of the north-central U.S. Continued precipitation in this already saturate region combined with rapid runoff maintained flood concerns from parts of North Dakota into northwestern Wisconsin.

Elsewhere, scattered showers and thunderstorms developed in the Mid-Atlantic and southeastern corner of the nation as a weak upper trough of low pressure dropped southward over the region. To the north, additional showers were possible in the Northeast.