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Colorado weather: Why wildfires can start just before snowstorms

The Sunshine Wildland Fire is just the latest example of a fire starting just before a snowstorm.
Credit: KUSA

COLORADO, USA — The Sunshine Wildland Fire on Monday is just the latest example of a recent Colorado trend: Major wildfires sparking just before a major snowstorm.

And it's likely not a coincidence.

Dry, gusty winds ahead of snowstorms are common and, perhaps combined with some social science, likely behind an elevated fire danger threat just ahead of a snowstorm.

Let's start with some meteorological basics. During the winter, winds in Colorado tend to be much stronger than the summer. That's thanks to a stronger temperature gradient and a stronger jet stream.

Ahead of a cold front, Colorado winds tend to pick up because of both the changing weather and the usual placement of the jet stream near or over Colorado ahead of a storm. 

Here's another meteorological 101: Colder air is heavier than warmer air. That colder, denser air pushing in tends to accelerate winds ahead of a front. Those stronger winds also tend to come out of the west, which is a downsloping wind for the Front Range. That's a drying and warming wind.

And finally, the Front Range's relatively dry climate usually means that we have several days in between snow events. So if a snowstorm is coming, it's probably been dry for at least a few days. That could lead to drier grasses, and a higher threat for a wildfire.

In 2020, the East Troublesome wildfire sparked on Oct. 14. But it wasn't until a week later that a significant wind event fanned the fire's flames, exploding it into one of Colorado's largest fires on record.

The Marshall Fire sparked on the eve of a significant snowstorm (and after the driest and warmest fall on record along the Front Range). Colorado's most destructive wildfire was fanned by winds that gusted up to 100 mph and, again, just ahead of a snowstorm.

Gusty winds upwards of 40 mph on Monday took a structure fire west of Boulder and turned it into the Sunshine Wildland Fire, forcing the evacuations of hundreds of residents from their homes. This comes, of course, on the doorstep of a major cold and snow event across Colorado on Wednesday.

And finally, there's probably at least a degree of social science behind the trend of wildfires starting just before a snowstorm. Snow and cold are high-impact weather events that garner the attention of the majority of the public (and, admittedly, meteorologists), often leading to an overlooked factor with fire danger.

But the next time you hear a snowstorm is coming, consider the likelihood that fire danger may be notably higher just ahead of one.

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