Weather Underground Forecast for Friday, August 17, 2012.
A cold front moving through the Eastern US will produce more showers and thunderstorms on Friday. This system will advance southeastward and move over the Ohio River Valley and Mid-Mississippi River Valley, reaching into the Tennessee Valley and Lower Mississippi River Valley. This system will pull in moisture from the Gulf of Mexico, allowing for more thunderstorms to develop. Some of these storms may turn severe across the Tennessee Valley with main threats of strong winds, large hail, and periods of heavy rainfall. AT the same time, the northern side of this system will pull moisture in from the Atlantic Ocean and produce scattered showers across the Northeast, moving into the Mid-Atlantic states in the evening.
Behind this cold front, noticeably cooler temperatures will return to the Midwest, Ohio River Valley, and Mid-Mississippi River Valley as flow from the north continues. This will pull cool air in from Canada, allowing for highs to range in the 70s across the Upper Midwest, Great Lakes, and Mid-Mississippi River Valley.
Meanwhile in the West, an area of low pressure slides up the West Coast and allows of onshore flow to continue. This will keep temperatures slightly cooler across most of California. In the north, a ridge of high pressure strengthens over the Pacific Northwest and keeps the region warm and dry. Expect high heat advisories and dangerous fire weather conditions will remain in effect on Friday. In the Southwest, monsoonal moisture will maintain thunderstorm activity across Arizona, New Mexico, and parts of southern California. Temperatures in the Lower 48 states Thursday have ranged from a morning low of 32 degrees at West Yellowstone, Mont. to a high of 101 degrees at Zapata, Texas