SAN FRANCISCO (AP) – Firefighters and aircraft from 10 states have begun arriving in California to help weary crews battling some of the largest blazes in state history. But weekend weather is threatening to renew the advance of flames that have killed six people and incinerated hundreds of homes. Some 560 wildfires are burning throughout the state but the most damaging are three clusters of blazes in the San Francisco Bay Area and the wine country. State fire officials say their forces are stretched thin and they’re grateful for reinforcements. They’re hoping to make progress before unsettled weather beginning Sunday brings the threat of lightning strikes that could spark new blazes.