and heavy rain toppled trees. the pineapple express is an atmospheric river of water in the sky, funneling massive amounts of moisture from the hawaiian islands to the pacific northwest. when it hit california, it knocked out power to 80,000 homes and businesses. in san francisco, it caused flight delays of up to four hours. but despite the disruptions, the drenching rain is welcome here. >> as much as 60% to 70% of our annual rainfall comes from dramatic atmospheric river events. >> reporter: john monteverde is a meteorologist with san francisco state university. so california's in an extreme drought. will this particular weather event help us with that? >> it will help us but it's not going to end the drought. february, and march, if they are wet, then our drought-- a dent will be made into it. >> reporter: while the rain is desperately needed, this much, this fast is a big concern in san francisco's high-tech district where engineer eric stafl works