The National Weather Service has issued a red flag warning as high temperatures continue in the Sierra Nevada range and across the northwest to the Dakotas. A Pacific low-pressure system is approaching from the west today and Friday, bringing gusty winds and dry air that could cause dry lightning this afternoon and this evening along the Interstate 80 corridor. Wetter storms are expected farther south, meteorologists said. The service warned of high winds on Lake Tahoe today; in the lower elevations, the heat is expected to come down into the 70s by the weekend.