Firefighters need better weather to fight California's flames. When will they get relief?

Fire danger remains high in parts of Los Angeles that have been ablaze for days, but there is hope that better weather over the weekend will give firefighters battling the flames some much-needed relief.

After calmer weather on Tuesday helped firefighters snuff out fires, a rare warning of a "Particularly Dangerous Situation" was issued for Wednesday in an area near the two fires that killed at least 25 people and destroyed thousands of homes. A red flag warning was issued by the National Weather Service from Central Coast to the border with Mexico from 3 a.m. to 3 p.m.

Forecasts suggest that conditions for firefighting will improve later in the week.

What conditions are best for firefighting?

Just like wind and drought were major factors in why the fires spread so quickly, calmer wind speeds, more humidity, lower temperatures and more wind or rain can all help extinguish fires.

Humidity in the air exchanges moisture with soil, trees and other organic matter. When potential fuels are more moist, then fire danger is reduced because they're less combustible. Forecasters look out for relative humidity — or how much water vapor the air is holding. Fire warnings are issued when relative humidity is 15% or lower, combined with higher wind speeds.

Calmer or no winds also contribute to better conditions. Strong winds give oxygen to flames and can dry out vegetation, making it more combustible. While fires will continue even with no wind, they don't spread as easily, making it easier for firefighters to put it out or for firefighting planes to fly overhead.

Rain or snow can also help put out fires, but often not completely, as it can evaporate quickly.

When will LA get relief?

The Wednesday forecast looks set to make things worse before they get better, with low humidity and strong Santa Ana winds fanning the flames. But there may be relief later in the week.

Forecasts predict higher humidity and lower wind speeds by Friday and into the weekend, but there's little rain forecast. While rain can help, heavier rain could trigger mudslides in affected areas.

When when the fire does finally subside, climate change makes wildfires more frequent and intense, with drought-like conditions in the western United States more likely, creating the conditions for more extreme wildfires in the future.

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