PUEBLO, Colo. — Search and rescue operations are underway at Lake Pueblo after a boat overturned Sunday night, leaving multiple people stranded in the water, according to Colorado Parks and Wildlife (CPW).

CPW Public Information Officer Travis Duncan said 13 people (5 adults, 8 children) were on board when the boat capsized due to high winds around 7:30 p.m. Sunday.

Here’s an initial analysis of the role weather played in this unfortunate tragedy. There were numerous convective cells over the Palmer Divide and mountains southwest of Pueblo on Sunday afternoon that led to the gusty wind experienced at Lake Pueblo.

Virga and Downdrafts

In the timelapse below from Monument, Colorado on the Palmer Divide north of Colorado Springs you can see pockets of virga, rain evaporating before reaching the ground, with most of the cells. There is one brief shower that moved over the camera near dinner-time, but the virga evident in this timelapse is representative of what occurred over most of the area along the foothills and over the plains in southern Colorado on Sunday afternoon.

When rain falls from the base of a cloud and evaporates, it creates a pocket of air that is cooler than the air surrounding it. Because of the effects of gravity, this cooler air is denser than the surrounding warmer air and begins to descend rapidly toward the surface in a downdraft. Once this downdraft of thunderstorm outflow reaches the surface it spreads out in advance of the storm cell as a gust front.

When atmospheric conditions are right, the wind may rush down to the ground violently enough to create a microburst where speeds can reach up to 100 mph, or even higher, which is equivalent to an EF-1 tornado! Winds this high can cause major damage to homes and other structures and level hundreds of trees.

Timelapse of a microburst descending rapidly downward.

Downdrafts and microbursts are part of our thunderstorm climatology in Colorado and are pretty frequent during the late spring and summer months as sub-cloud air is often very dry.

While the storm that produced the gust front that capsized the boat at Lake Pueblo Sunday evening did not produce a microburst, the wind was still significant enough to flip the boat with 13 people on board.

Sunday’s Specifics

The atmosphere over the foothills and plains of Colorado was ripe for high-based thunderstorms with virga and downdrafts.

One such cell was visible on radar (image above) over the Wet Mountain Valley above Westcliffe at 6:25 pm. By 6:40 pm (image below) the cell had advanced east toward the Wet Mountains and was collapsing as a downdraft had developed. Notice that the intensity of the cell, indicated by darker greens, had decreased as it lifted to the northeast. At this stage, a gust front had developed.

As the gust front advanced east-northeast and descended down the east slopes of the Wet Mountains, it advanced toward Lake Pueblo State Park with wind gusts to 45 mph. At 6:50 pm (image below) the gust front was still to the west of the lake.

Sixteen minutes later the gust front was still advancing east toward Lake Pueblo as seen in the image above. A weather station just south of Highway 50, about 4 miles to the north of the lake registered a wind gust of 45 mph at 7:30 pm local (01:30 Zulu time) as the gust front from this storm arrived. This station is close enough to represent what happened on the lake as the gust front arrived.

A weather station about 4 miles to the north of the lake registered a wind gust of 45 mph at 7:30 pm local.