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When it comes to forecasting the conditions for catastrophic California wildfires, there are two main ingredients: fuels (think grasses, shrubs, trees – basically anything that’s available for fires to burn) and winds.
When analyzing fuels, forecasters look mainly at the levels of drought, along with any recent rains that may help diminish the effect of longer-term drought. With winds, in southern California at least, it’s all about anticipating the Santa Anas – the fierce winds that blow offshore, from the deserts to the coast, bringing loads of dry air with them.
Looking ahead to the next week, a range of weather and climate models bring good and bad news for southern California:
The good news is there’s no sign on the horizon of a windstorm close to last week’s Santa Anas, which brought record-setting 100mph wind gusts to Los Angeles.
The bad news is that it looks like Los Angeles’s record-dry start to its rainy season will keep getting worse.
Over the next three days
A stalled low pressure system offshore this week will usher in the return of strong Santa Ana winds.
The US National Weather Service (NWS) in Los Angeles has upgraded this week’s fire weather outlook to a “particularly dangerous situation” – its highest level of alert. “Winds will be strong enough to potentially cause explosive fire growth,” it said in a forecast briefing. “Do not do anything that could spark a fire.” In California, about 95% of fires are “human caused”. That rarely means arson, more commonly things such as a truck’s dragging trailer chain, downed power lines or discarded cigarettes.
The NWS expects offshore winds gusting to 70mph, especially in Ventura and Los Angeles counties between Tuesday morning and Wednesday afternoon, bringing relative humidity down as low as 5% and allowing for extreme fire behavior and long-range transport of burning embers. Conditions in Ventura county in particular could be worse than last week.
Within the next few days, fuels will reach record-dry for this time of year all the way up the central coast and potentially into the Bay Area. Fuel dryness – the amount of water that has been removed from trees, grasses and shrubs by the current drought – is approaching and will soon exceed what’s typically seen at the peak of the wildfire season in mid-summer across coastal southern California.
Over the next three weeks
This year’s rainy season is running at just 2% of normal for Los Angeles, which has only seen 0.16in of rain so far.
Weather models increasingly indicate that southern California will receive no rain at all during the rest of January, and potentially no rain during the first week or two of February as well.
That’s really unusual. January and February are the wettest months of the year for Los Angeles, averaging more than 7in of the city’s 13in of rain in a typical year. Even in the winter of 2006-2007, LA’s driest year in history, the city still received a little more than 3in of rain.
Intensifying drought conditions mean that the current round of extremely out-of-season fire weather will continue with the resurgence of any moderate-to-strong Santa Ana winds.
There are emerging signs in longer-range weather models that the current weather pattern could get sticky – and settle into what’s called a blocking pattern. If a blocking pattern, specifically a “Rex block” sets up, it would continue to shunt Pacific moisture either north into Alaska or further south into Mexico, worsening California’s drought.
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Over the next three months and beyond
According to the NWS, drought intensified last week across southern California, and will continue to worsen into March.
This year’s historically low rainfall comes after more than 25in of rain fell in each of the last two rainy seasons, boosting the growth of shrubs and grasses that now serve as potential fuel.
This kind of “weather whiplash” is a hallmark signal of the climate crisis.
If and when the rains do come later this year, chances are they will come courtesy of an atmospheric river of moisture that would heighten the risk of flooding and mudslides in the vast burn scars of the Palisades and Eaton fires.
Early January also marked the official arrival of La Niña conditions in the tropical Pacific Ocean, which tend to precede drought years in southern California.
Factoring in the next seven months of seasonal climate forecasts, Los Angeles is on track for between 4-7in of rain for the remainder of this year’s rainy season, with some potential wiggle room above and below that range.
Should this forecast hold, dangerous fire weather would continue not just during the next several weeks, but well into the summer and beyond – and could spread north in California.
