San Francisco, CA

Weather Underground midday recap for Saturday, May 18, 2013.

Multiple areas of unsettled weather developed over the nation on Saturday. In the center of the nation, a broad low pressure system moved off the Rockies and into the Central and Northern Plains. This system created a warm front that developed over the Northern Plains and Upper Midwest, which stretched eastward into the Great Lakes. Scattered showers and thunderstorms developed along and ahead of this frontal boundary with some parts of Minnesota reporting over 2 inches of rain by mid-day Saturday. These storms have not yet turned severe, but have a history of producing strong winds, large hail, and even a few tornadoes. The back side of this broad low pressure system continued to pull a cold front across the Western states. This allowed for onshore flow to persist from the Pacific Ocean, maintaining sufficient moisture to kick up scattered showers across the Intermountain West, Rocky Mountains, and Great Basin. Some snow showers developed at the highest elevations of Wyoming and Montana. As moisture and energy from this front moved off the Rockies and into the Central and Northern Plains, threats of severe thunderstorm development increased. There was a moderate risk for severe storms with large hail, strong winds, and tornadoes from eastern Colorado through western Nebraska and Kansas, but severe storms have not yet developed.

Meanwhile in the East, a trough of low pressure slowly moved offshore and allowed for more showers and thunderstorms to persist for the Eastern Valleys, the Central and Southern Appalachians, and the Mid-Atlantic States. Severe storms were not anticipated in these areas.