The science behind the LA wildfires
Epic events like the Southern California wildfires do not have a singular cause.
While we don't yet know the official causes of the fires, we do know that the weather and climate conditions when they started made for a perfect storm for the rapid spread of the flames.
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The first problem is that Los Angeles has been very dry. The city has only seen 0.16 inches of rain since May 6, so the regions rainy season is off to an unusually dry start. This created a lot of fuel for potential fires. But a lack of rain alone didn't lead to the devastating fires we saw this week.
It was the wind that spread the fires so rapidly once they were ignited. An exceptionally strong mountain wave wind event, with northerly 80 to 100 mile per hour gusts, spread the fires faster than anyone could stop them.
And we knew the weather conditions were coming. Thirty-six hours before the fires started, the National Weather Service in Los Angeles warned of "life threatening and destructive winds, extreme fire behavior and likely the strongest north winds in southern California since 2011.
That event on Dec. 1, 2011, also brought powerful and destructive wind gusts to much of Southern California, including the Los Angeles metro area.
Wind gusts up to 97 mph were recorded in the mountains of northwestern Los Angeles County, according to the National Weather Service. But unlike last week, no large wildfires broke out like they did in 2011. A more normal rainfall amount from October to December of that year may have helped avoid the same disaster.
PHOTOS: Powerful images show destruction from deadly Southern California fires
Santa Ana events typically are associated with northeast to east-northeast winds in Los Angeles County and usually result in very little wind in the San Gabriel Valley and eastern San Fernando Valley areas, which are home to many high-populated sections of the LA metro area.
The atmospheric setup during this recent event oriented winds in a more northerly to north-north easterly direction. This sent the high winds right over the regions San Gabriel Mountains in a trajectory that not only helped amplify their strength, but made the air even drier as it came rushing down the other side. This brought powerful wind gusts to areas that dont typically experience winds at such an intensity.
What made this a devastating Santa Ana event is that conditions higher up in the atmosphere helped to further enhance winds at the surface.
In this case, an area of low pressure in the upper atmosphere was moving over Baja California. The cold, dense air associated with this system was positioned at a favorable north-northeast to northeast trajectory over the region. The particular setup allowed for the colder air located higher up in the atmosphere to come rushing down towards the surface and enhance the winds already blowing. This brought surges of powerful winds across the Los Angeles and Ventura County Mountains, crashing into the foothills and some coastal communities.
The wind direction and topography played a major role as well. The San Gabriel Mountains and the wind orientation interacted to produce a damaging wind event that doesn't occur often. The mountains can also make the winds more erratic because additional whirls of wind, known as wind eddies, can form as the air moves across the peaks and through the canyons.
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So while both the 2011 and 2025 events brought powerful, destructive winds, one big difference is how dry it is right now in the LA area.
As far as climate change, we won't know the direct impact until climate attribution studies are done. While climate change likely amplified some of the conditions that contributed to the massive, destructive nature of the wildfires, it is just one part of a long list which also includes more direct human impacts like rapid urbanization and land management.
But we do know that wildfires in the West have become larger, more intense and more destructive and that human-amplified climate change is one of the key reasons.
And new research explains how climate change is making hydroclimate whiplash more common. Those are rapid swings between intensely wet and dangerously dry weather.
As Daniel Swain, the lead author of the research and a climate scientists with UCLA explain, "This whiplash sequence in California has increased fire risk twofold: first, by greatly increasing the growth of flammable grass and brush in the months leading up to fire season, and then by drying it out to exceptionally high levels with the extreme dryness and warmth that followed."
Less than a year ago, Los Angeles had historic flooding and is now facing severe drought conditions. That literally adds fuel to the fire.
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Finally, its important to reiterate that California has and will always be particularly vulnerable to wildfires simply due to its natural climate. The state historically experiences highly variable weather and climate conditions, typically shifting from periods of very dry to very wet weather.
Across the continental U.S., California has the most year-to-year variability between wet and dry conditions. As you move down into Southern California, that variability increases even more, according to Julie Kalansky, a climate scientist and deputy director of operations at the Center for Western Weather and Water Extremes at the University of California, San Diego's Scripps Institution of Oceanography.
Take a look at the latest stories and videos on the devastating Southern California wildfires here.
ABC News chief meteorologist and chief climate correspondent Ginger Zee, ABC News meteorologist Dan Peck, ABC News Climate Units Matthew Glasser and ABC News meteorologist Dan Manzo contributed to this report.
