Thomas Fire: 10% contained

Rye Fire: 93%

Creek Fire: 95%

Ventura

CALIFORNIA

Los Angeles

Long Beach

Lilac

Fire:

75%

Pacific

Ocean

25 MILES

Extent of fire perimeters reported as of Dec. 10

San Diego

Thomas Fire: 10% contained

Rye Fire: 93% contained

 

Creek Fire: 95% contained

Ventura

San Bernardino

Los Angeles

Long Beach

CALIFORNIA

Lilac Fire:

75% contained

Pacific

Ocean

50 MILES

San Diego

Extent of fire perimeters reported as of Dec. 10

MEXICO

Rye Fire: 93% contained

VENTURA

COUNTY

Creek Fire: 95% contained

Ventura

Thomas Fire:

10% contained

San Bernardino

Los Angeles

Long Beach

CALIFORNIA

Lilac Fire

75% contained

Pacific

Ocean

50 MILES

San Diego

Extent of fire perimeters reported as of Dec. 10

MEXICO

The Santa Ana winds did not start the fires that have been rampaging through Southern California since Dec. 5. But the near-hurricane-force gusts created ideal conditions for fire and then spread flames with deadly efficiency.

CALIFORNIA

50 MILES

Thomas Fire

Rye Fire

Ventura

Creek Fire

San

Bernardino

Los Angeles

Long Beach

Satellite imagery from Friday morning shows strong winds from the northeast fueling fires and blowing smoke over the Pacific Ocean.

—Lilac

Fire

Pacific

Ocean

San Diego

MEXICO

50 MILES

CALIFORNIA

Thomas Fire

Rye Fire

—Creek Fire

Ventura

San Bernardino

Los Angeles

Long Beach

—Lilac Fire

Pacific

Ocean

Satellite imagery from Friday morning shows strong winds from the northeast fueling fires and blowing smoke over the Pacific Ocean.

San Diego

MEXICO

50 MILES

CALIFORNIA

Thomas Fire

Rye Fire

—Creek Fire

Ventura

San Bernardino

Los Angeles

Long Beach

—Lilac Fire

Pacific

Ocean

Satellite imagery from Friday morning shows strong winds from the northeast fueling fires and blowing smoke over the Pacific Ocean.

San Diego

MEXICO

Any wind can exacerbate a wildfire, but unique traits of Santa Ana winds make them particularly effective at sending flames rushing into new areas.

Jack Oren, 50-year resident of La Conchita south of Carpinteria, uses a garden hose to try and fight flames from the Thomas Fire. (Photo by Stuart Palley for The Washington Post)

The Thomas Fire burned 90,000 acres and destroyed an estimated 150 structures. (Photo by Stuart Palley for The Washington Post)

Pressure changes create wind

Santa Ana winds occur from spring to late fall or even early winter, when a high-pressure system forms over the deserts of the Great Basin. The high pressure circulates clockwise, pushing air westward toward the lower-pressure areas of the coast.

NEV.

CALIF.

GREAT

BASIN

Sacramento

Carson

City

San

Francisco

Los Angeles

San Diego

CALIFORNIA

GREAT

BASIN

Carson City

Sacramento

NEVADA

San Francisco

San Jose

Los Angeles

Santa Ana

San Diego

Air gets hotter and drier

As the wind flows over the Sierra Nevada and Santa Ana mountains, it drops from high elevation to sea level. The sinking air becomes compressed and heats up, and its relative humidity drops.

Cold

air

Warm, dry

air

Mountains

Valley

Coast

Cold

air

Warm, dry

air

Mountains

Valley

Coast

Cold air

Mountains

Warm, dry

air

Valley

Coast

Cold air

Mountains

Warm, dry

air

Valley

Coast

Gaps in the mountains form wind tunnels

The wind speeds up as it pours over the mountains, particularly where it is forced through passes and canyons like water through a funnel. Gusts of 40 to 60 mph or even stronger are common.

Suddenly dry, warm — or downright hot — air is whooshing toward the coast.

Mountains

Warm, dry air

Fast-moving,

hot, dry air

Valley

Coast

Warm, dry air

Mountains

Fast-moving,

hot, dry air

Valley

Coast

Warm, dry air

Mountains

Fast-moving,

hot, dry air

Valley

Coast

The result is like a giant hair dryer

The wind careens over low-lying Southern California, parching vegetation in its path that can easily become fuel for a fire. The wet winter made for a particularly leafy spring and summer in California in 2017.

Gusty

wind

Dry

vegetation

Fires

expand

Wind

carries

embers

and debris

Flames

Wind

carries

embers

and debris

Gusty

wind

Dry

vegetation

Fires

expand

Flames

Wind

carries

embers

and debris

Gusty

wind

Dry

vegetation

Fires

expand

Flames

Once a fire starts, gusty winds speed it along and carry burning debris to new areas.

Angela Fritz, Tim Meko and Denise Lu contributed to this report.

Sources

National Weather Service. Maps4News/HERE. Fire perimeters from GEOMAC Wildland Fire Support. Wind map imagery from ESA Sentinel, Dec. 7. Wind directions generalized from the Global Forecast System (GFS) spectral model accessed via Global Forest Watch Fires. Percent containment of fires from CAL FIRE.

Originally published Dec. 8, 2017.

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