By Chris Spears
DENVER (CBS4) – Did you wake up Saturday morning wondering where the fog came from?
Believe it or not, western Nebraska and northwest Kansas played a role!
While you were sleeping early Saturday a wind pattern developed that pulled air from the northeast and into the Front Range.
Because that air was colder and more dense it settled into areas with a lower elevation, such as river valleys, including the South Platte.
That’s why the fog was mostly found from downtown Denver and to the north and east of the city. Those on the south side of town woke up to mostly sunny skies and temperatures that were 10-15 degrees warmer.
HOW FOG FORMS
As the sun sets each day, the ground immediately begins to cool as longwave energy escapes into the atmosphere.
By sunrise the next day, when maximum cooling has been reached, if air near the ground can become saturated, or cool down to the dewpoint temperature, radiation fog can form.
Fog is a cloud that has a base at the ground and it is usually pretty shallow. The fog bank Saturday morning was less than 1,000 feet thick.
At times you could see the tallest buildings in downtown Denver poking through.
Once the sun rises and begins to heat the surface of the Earth, a process called convection begins, which mixes the atmosphere.
It will bring dry air above the fog down to the ground, and the bank of fog up into the dry air. Over time this mixing will disperse the fog and make for a mostly sunny day.
It tooks less than two hours after Saturday’s sunrise for this process to make for a significant reduction in the fog over Denver, as seen below.