Why Tuesday turned gusty in Denver, even though the storms were miles away

Posted at 12:49 PM, Aug 21, 2019

DENVER – If you noticed the strong gusts of wind that rolled through Denver late Tuesday afternoon, you might have thought a storm was soon to follow.

But the severe weather wasn't anywhere close to the city. Instead, it was out on the plains, to the north and east of the metro area.

The wind we felt in Denver was the result of an outflow, the moist, cool air produced by a thunderstorm that can cause a wind shift miles away.

An outflow boundary is one of those meteorological terms you probably hear all the time during storm season, especially in Colorado. The boundary can trigger another round of storms, or, in Tuesday's case, just make the atmosphere unstable enough to create windy conditions.

Watch the radar image below, posted on Twitter by Kris Karnauskas, a professor at the Oceans and Climate Lab at CU Boulder. The heart of the storms was out east, from Bennett and then up to Interstate 70, near Roggen. As the storms drifted east, the moist air sank toward the ground and pushed back toward the west. This was the outflow of the storm.

KFTG - Super-Res Reflectivity Tilt 1 6:29 PM MDT

— Kris Karnauskas (@OceansClimateCU) August 21, 2019

Jim Kalina, a meteorologist with the National Weather Service in Boulder, explained the outflow as being similar to ripples extending across the surface of a pond. The cool air from a storm slams to the ground and goes wherever it can.

"It's almost like when you throw a rock in a pond," said Jim Kalina, a meteorologist with the National Weather Service in Boulder. "As [the moist air] is coming straight down, it has nowhere to go."

On Tuesday, the outflow air traveled back toward Denver. The weather here was likely too hot and dry to fuel thunderstorms from the outflow boundary, Kalina said, but the winds and dust kicked up.

"Additional moisture comes into the area," Kalina said, "and it changes the whole atmosphere. It can make things unstable."