Weather Underground Forecast for Saturday, August 20, 2011.
Active weather was expected to persist across most of the nation on Saturday. A low pressure system north of the Great Lakes was expected to continue spinning over eastern Canada. Flow around this system was expected to push a cold front over the Great Lakes and Midwest, and into the Central and Southern Plains. The leading edge of this front was expected to pull abundant moisture in from the Gulf of Mexico and create favorable conditions for afternoon thunderstorm development. Some of these storms were forecast to turn severe with strong winds, large hail, and heavy downpours. Rainfall totals were expected to range from 1 to 2 inches, while up to 3 inches are likely in areas of severe storm development. As the system tracks over the Missouri River and into the Mississippi River Valley, heavy rainfall was expected to create possible flash flooding across the already swollen rivers. Tornado development is not likely because the system does not have a history of producing tornadoes.
Behind this system, noticeably cooler air is expected to filter into the Central U.S. Temperatures were forecast to remain near seasonable, but range from 5 to 10 degrees cooler.
In the South, hot and humid conditions were expected to prevail across the Southern Plains. High temperatures were expected to remain just above 100 degrees, with heat index values up to 110 degrees.
Out West, a trough of low pressure was expected to dip southward from just off the coast of the Pacific Northwest. This is expected to create onshore flow, pushing low clouds onshore and brings slightly cooler temperatures to the Pacific Northwest and California. Temperatures in the Lower 48 states Friday ranged from a morning low of 30 degrees at Stanley, Idaho to a high of 109 degrees at Shawnee, Okla.