January 10, 2025
Los Angeles is no stranger to bushfires. Its dry, near-desert climate (just 350 mm of rain annually) and the infamous Santa Ana Winds create the perfect storm for disaster. But even for LA, this event is extreme. Let’s break down the factors driving these catastrophic fires.
Just 4 mm in 6 Months
Downtown LA has been bone-dry, recording just 4 mm of rain over the past six months. This prolonged dryness has turned vegetation into fuel for wildfires. The "La Niña Modoki" weather pattern worsens the situation, as cooler eastern Pacific waters shift pressure systems, reducing Southern California’s already scarce rainfall.
It could be argued that the Pacific Ocean is in a "La Nina Modoki" - meaning a similar but different to normal La Nina" Source: NOAA.
Santa Ana Winds: Cyclonic Intensity
The topography of LA plays a key role in its fire risk. Towering mountains to the north and east, some over 3,000 metres high, block direct wind flow. When a high-pressure system forms inland and low pressure builds over the Pacific, air rushes toward the coast.
These winds are forced through narrow mountain passes and canyons, where they compress and accelerate—much like water speeding through a partially blocked garden hose.
Note the very localised nature of the strong winds near Los Angeles (bottom left of image). Source: MetCentre.
The result? Dry winds often exceeding 100km/h roaring through the mountains. For this event, the US National Weather Serviced recorded winds of up to 160 km/h! That's nearly as strong as a Category 3 tropical cyclone. Unlike tropical cyclones, however, Santa Ana winds are bone-dry, with humidity levels near zero.
A Perfect Storm for Fires
When you combine LA’s unusually dry conditions with these hurricane-force winds, it doesn’t take much for a fire to ignite. Once it starts, the winds spread flames rapidly, leaving devastation in their path.
Fire Risks Aren’t Just in Summer
It’s not just LA—northern Australia also sees its peak bushfire season during winter, thanks to dry conditions and windy weather. Wet vegetation doesn’t burn as easily, which is why low humidity and wind often have a greater impact than high temperatures. However, prolonged heat can dry vegetation and worsen the fire risk.
Could the Same Happen in Australia?
One could argue that it already has. On Black Saturday 2009, devastating bushfires tore through Victoria, with entire towns destroyed as 90 km/h winds and temperatures soaring into the high 40s created horrendous fire conditions. Every year, bushfires threaten suburbs and towns across Australia. However, there are notable differences between Australia and Los Angeles.
LA’s unique topography creates very localised, and sometimes persistent, strong winds that can last for days. In contrast, winds of similar magnitude near Australian capital cities are much rarer. Hobart is an exception, with Mt Wellington recording gusts over 130–140 km/h multiple times a year. While strong winds can occur in Melbourne, Canberra, and Sydney, they rarely reach the intensity of this current burst of Santa Ana winds.
The winds for this event were very extreme, ranging from 84mph (134km/h) to 100mph (160km/h). These winds are not normally experienced near major Australian cities during bushfire conditions.
That said, Australia’s elevated rainfall in recent years, driven by successive La Niña events, has resulted in significant vegetation growth. When the inevitable return to drier years comes—as it always does—there is growing concern about the fuel loads that could exacerbate bushfire conditions. Vigilance and preparation will be critical as these patterns shift.
It's been a wet few years across Australia with above average rainfall fueling elevated bushfire loads. Source: BoM.
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