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Some Front Range Residents Find Ash From Colorado Wildfires On Cars Friday Morning

DENVER (CBS4) - Heavy wildfire smoke settled along Colorado's Front Range early Friday morning leaving fine particles of ash on surfaces such as cars and hot tub covers. Reports of fine ash particles have come from Mead, Boulder, Broomfield, Arvada and Aurora.

While it's not possible to say which of the three major fires burning in Colorado provided the ash there is a chance it traveled up to 300 miles to reach the Front Range. The Pine Gulch Fire north of Grand Junction was producing the highest volume of smoke while the Cameron Peak Fire's smoke plume is the closest to Denver. Smoke from the Grizzly Creek Fire is also mixed into the air.

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Small ash particles on a car in the Boulder area. (credit: R. Akasaka)

To understand why smoke is typically so bad during the early morning hours and how ash particles can land on surfaces you need a quick lesson in how the air circulates within the lowest part of the atmosphere. We are talking about the troposphere, which is where we live and where all weather happens.

As the sun rises and begins to heat the ground each day it causes the air near the surface to start a churning motion, bringing air from the surface up as air from above comes down to the ground. With each hour of sunlight the churning motion becomes bigger and bigger. We call this convection.

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On some days this mixing process can churn as much as 10,000 feet or more of the lower atmosphere. But at night the churning motion goes away without the sun. For each hour of darkness the atmosphere settles more and more.

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Wildfire smoke in Evergreen. (credit: CBS)

By sunrise the next day you typically have the calmest, most stable air of the day. So when stuff is in the air, like various types of pollution or smoke from a wildfire, it settles near the ground overnight without the daytime churning motion created by the sun. Anything in it, such as fine particles of ash, can settle out on surfaces like cars or hot tub covers.

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Thick smoke could be seen in downtown Glenwood Springs Friday morning. (credit: CBS)

One will typically notice an improvement in air quality between 11 a.m. and 1 p.m. after adequate mixing has taken place. But of course one wild card in this happening is continued smoke pouring into the area. Another is any shifts that may occur with atmospheric winds throughout the day. Cloud cover can be an additional thing to consider to a lot of the sunlight is blocked and the daily churning motion is limited.

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