July 31, 2012: The nation's weather

Weather Underground Forecast for Tuesday, July 31, 2012.

Unsettled weather will continue across the nation on Tuesday as monsoonal activity continues in the West, a frontal system drops across the Great Lakes and Ohio Valley, and a trough of low pressure lingers over the eastern third of the nation.

In the West, subtropical moisture from the Pacific Ocean will stream inland from the southwest across southeastern California and southern Nevada into the Four Corners through the day. Ample moisture over these areas combined with waves of energy pushing through the region will translate into heightened monsoonal activity during the afternoon and evening with areas of rain and thunderstorms.

To the east of this activity, high pressure ridging will remain locked over the south-central U.S. with scorching hot temperatures. Areas from the Southern Plains and the Lower Mississippi Valley northward into the Central Plains and the Mid-Mississippi Valley will experience daytime highs ranging from 100 to 110 degrees. A few showers and thunderstorms are anticipated in the Mid-Mississippi Valley as disturbances from the West get directed through the Central Plains, but will provide little relief from the heat. A variety of Heat Advisories and Excessive Heat Warnings are expected to remain in effect for the region.

To the north, a frontal system will drop across the Upper Great Lakes and the Ohio Valley with chances of showers and thunderstorms. This activity will spread into the Lower Great Lakes, Upper Mid-Atlantic and inner Northeast late Tuesday afternoon/evening as the system progresses to the east.

Meanwhile, a trough of low pressure over the eastern third of the nation will support more showers and thunderstorms from portions of the Mid-Atlantic through Southeast. Much of this weather activity along with possible strong winds will be focused near a frontal boundary stalling across the Southeast. Temperatures in the Lower 48 states Monday have ranged from a morning low of 32 degrees at Truckee-Tahoe, Calif. to a high of 109 degrees at Enid, Okla.