San Francisco (CNN) It's unclear what caused fires to form suddenly around the same time in one night, blazing through California's wine country while many residents were caught unaware as they headed to bed.

But authorities point to a perfect storm of factors that have fanned the wildfires that began Sunday night, leaving at left 17 people dead, forcing 20,000 to evacuate and causing widespread devastation in Northern California

The investigation remains "very early in the process," Ken Pimlott, director of the California Department of Forestry and Fire Protection, said Tuesday.

"These are all fires that were in areas that are populated, and 95% of the fires in our state are started by people" in some way, he said, downplaying the chances that lightning may have played a role.

Among the factors cited behind the fires' ferocity are high winds, the start of fires at night, heavy vegetation that dried out after a hot summer and dry conditions.

1. Really strong winds

High-speed winds have played a role in the fires. The region saw powerful gusts of 50 mph, making it easier for the blazes to spread, with hurricane-force gusts of 79 mph reported in Sonoma County.

The winds also knocked down power lines in the areas where the fires started.

"The historic wind event that swept across PG&E's service area late Sunday and early Monday packed hurricane-strength winds in excess of 75 mph in some cases," Pacific Gas and Electric Co. said in a statement.

"These destructive winds, along with millions of trees weakened by years of drought and recent renewed vegetation growth from winter storms, all contributed to some trees, branches and debris impacting our electric lines across the North Bay. In some cases we have found instances of wires down, broken poles and impacted infrastructure."

Pacific Gas and Electric said it reported those events to the state utility regulator and Cal Fire.

"When we have a wind event like this ... where you have 50-mph winds bearing down on an area ... every fire that starts has a significant potential to grow into a large fire very, very quickly," Pimlott told reporters Tuesday.

Winds are likely to pick back up Wednesday, with a possibility of gusts up to 50 mph, according to the National Weather Service.

2. Timing at night

The three largest fires started between 9 and 11 p.m. Sunday, according to Cal Fire, ripping into neighborhoods when many residents had started to go to bed.

• The Tubbs fire, which has burned 28,000 acres in Sonoma and Napa counties, started at 9:45 p.m.

• The Atlas fire, which has burned 26,000 acres in Napa and Solano counties, started at 9:20 p.m.

• The Redwood/Potter fires, which have burned 21,000 acres in Mendocino County, started at 10:36 p.m.

"A fire starting after 10 o'clock at night, under 50-plus mph winds, under absolutely dry, dry fuel beds, every one of those fires had a fighting chance to get going long before our firefighters could even be able to get there. So they all grew into major fires very quickly," Pimlott said.

Survivors said they didn't know a huge fire was bearing down on their houses until the last second.

Some have raised questions about whether early notifications and alerts were adequate.

"Understand these fires started after 10 p.m. around midnight on a Sunday night," Pimlott said when reporters asked about this issue Tuesday. "They burned so quickly. There was no time to notify anybody. These fires came down into neighborhoods before anybody realized the fires were occurring in many cases."

Photos: Wildfires blaze in California Aerial images showing parts of Sonoma and Napa County that have been hit by wildfires. Hide Caption 1 of 33 Photos: Wildfires blaze in California Colby Clark, left, comforts her mother, Bonnie Trexler, after law enforcement escorted them to Trexler's home in Napa, California, to retrieve medicine and personal items on Wednesday, October 11. Trexler was one of the lucky few in her neighborhood whose home was spared. Deadly wildfires have been tearing through the state, destroying homes and businesses and prompting evacuation orders. Hide Caption 2 of 33 Photos: Wildfires blaze in California Highway Patrol officers go door to door to ask Sonoma residents to evacuate their homes as a wildfire approaches on October 11. Hide Caption 3 of 33 Photos: Wildfires blaze in California Homes are destroyed in the Coffey Park neighborhood of Santa Rosa on October 11. Hide Caption 4 of 33 Photos: Wildfires blaze in California The sign of a Firestone store malfunctions in Santa Rosa on Tuesday, October 10. Hide Caption 5 of 33 Photos: Wildfires blaze in California Damaged winemaking vats and tanks stand in ashes and debris at the Paradise Ridge Winery in Santa Rosa. Hide Caption 6 of 33 Photos: Wildfires blaze in California Smoke clouds the sun from wildfires burning in Santa Rosa and Napa Valley on October 10. Hide Caption 7 of 33 Photos: Wildfires blaze in California Mary Caughey, center in blue, reacts after finding her wedding ring in the remains of her home in Kenwood on October 10. Hide Caption 8 of 33 Photos: Wildfires blaze in California Puddles of melted metal trail away from a burned-out car near Napa on October 10. Hide Caption 9 of 33 Photos: Wildfires blaze in California A TV cameraman inches closer to a burning building at a winery in Napa Valley on Monday, October 9. Hide Caption 10 of 33 Photos: Wildfires blaze in California A firefighting plane helps battle a blaze just north of Tustin on October 9. Hide Caption 11 of 33 Photos: Wildfires blaze in California A historic barn burns in Santa Rosa on October 9. Hide Caption 12 of 33 Photos: Wildfires blaze in California The Santa Rosa Hilton Hotel burns to the ground on October 9. Hide Caption 13 of 33 Photos: Wildfires blaze in California Jim Stites watches as part of his neighborhood burns in Fountaingrove on October 9. Hide Caption 14 of 33 Photos: Wildfires blaze in California Fire burns from an open gas valve near the pool area of a Santa Rosa trailer park on October 9. Hide Caption 15 of 33 Photos: Wildfires blaze in California A man rushes to save his house as a wildfire moves through Glen Ellen on October 9. Hide Caption 16 of 33 Photos: Wildfires blaze in California Kristine Pond searches what's left of her family's home in Santa Rosa on October 9. Hide Caption 17 of 33 Photos: Wildfires blaze in California Police cars block State Route 241 as smoke rises above Orange on October 9. Hide Caption 18 of 33 Photos: Wildfires blaze in California A firefighter douses flames in Santa Rosa on October 9. Hide Caption 19 of 33 Photos: Wildfires blaze in California A woman moves horses in Orange as strong Santa Ana winds blow smoke from the Canyon 2 fire toward them on October 9. Hide Caption 20 of 33 Photos: Wildfires blaze in California A firefighter douses flames at a home in Anaheim on October 9. Hide Caption 21 of 33 Photos: Wildfires blaze in California Traffic backs up as people flee Orange on October 9. Hide Caption 22 of 33 Photos: Wildfires blaze in California Santa Rosa residents sift through the remains of a burned home on October 9. Hide Caption 23 of 33 Photos: Wildfires blaze in California The remains of fire-damaged homes and cars smolder at a Santa Rosa trailer park on October 9. Hide Caption 24 of 33 Photos: Wildfires blaze in California A tent structure built for the Safeway Open golf tournament burns in Napa on October 9. Hide Caption 25 of 33 Photos: Wildfires blaze in California Fire consumes a barn in Glen Ellen on October 9. Hide Caption 26 of 33 Photos: Wildfires blaze in California Smoke rises in the hills east of Napa on October 9. Hide Caption 27 of 33 Photos: Wildfires blaze in California A man passes a burning house in Napa on October 9. Hide Caption 28 of 33 Photos: Wildfires blaze in California The remains of fire-damaged homes are seen in Glen Ellen on October 9. Hide Caption 29 of 33 Photos: Wildfires blaze in California A wildfire burns behind the Sonoma Raceway on October 9. Hide Caption 30 of 33 Photos: Wildfires blaze in California A building burns in Napa on October 9. Hide Caption 31 of 33 Photos: Wildfires blaze in California Flames overtake a building in the Napa wine region on October 9. Hide Caption 32 of 33 Photos: Wildfires blaze in California Two women hug as they watch houses burn in Santa Rosa on October 9. Hide Caption 33 of 33

3. Lots of vegetation

A lot of dried vegetation has been fueling the flames.

California's multiyear drought ended in April after a heavy rainy season. With the bounty of rain, lots of plants flourished and bloomed across the state.

But there hasn't been much rain during the summer, causing many of the plants to wilt and dry out.

The dead vegetation "has accumulated and increases the likelihood of unusually large wildland fires," according to Cal Fire

The fires torched 20,000 acres in about 12 hours Monday alone, meaning they advanced at a rate of more than a football field every three seconds.

4. Dry conditions

October is typically when California gets its largest and most damaging wildfires.

So far, the fires have been thriving on low humidity and dry conditions.

There's no rain in the forecast for the next seven days, meaning these conditions are expected to persist.