Most of the Bay Area will be under a red flag warning starting Tuesday for expected dry conditions and strong winds, according to the National Weather Service. Critically dry fuels, low humidity and gusty winds prompted the red flag warning from 11 a.m. Tuesday to 7 a.m. Thursday, the weather service said. The combination of those gusty winds and dry conditions can cause fire to spread quickly, weather officials said. Outdoor burning is not recommended. Despite recent rain, prolonged offshore northerly winds at 20 to 30 mph, with gusts up to 50 mph, will dry fuels out very quickly, the weather service said. Relative humidity is expected to drop as low as 15%, forecasters said. The fire weather conditions also could lead to possible power shutoffs in parts of the Bay Area, according to PG&E. The utility has notified 15,000 customers in 17 counties that their power may be proactively shut off.