A weather system that meteorologists describe as “anomalously strong” is moving across metro Denver and Colorado’s Front Range Tuesday, possibly leading to severe storms in northeastern Colorado, according to the National Weather Service.

But conditions in Denver probably will remain mostly sunny with any afternoon rain showers and thunderstorms likely to be moderate, weather service officials said. Meteorologists estimated the likelihood of rain in Denver at 20%.

State health officials have issued an air quality alert due to ground-level ozone air pollution approaching levels deemed unhealthy for children, the elderly, and people with respiratory problems.

The storms Tuesday are expected to intensify in the evening, mostly east of the Interstate 25 urban corridor, though flash flooding is possible in the mountain foothills northwest of metro Denver across the forest burn scar left by the August 2020 Cameron Peak fire, weather service officials said. Storms Tuesday evening through midnight on the plains east of Denver could bring hail as big as tennis balls, bursts of wind at speeds as fast as 65 miles per hour, and possibly a brief tornado and flash flooding, forecasters said.

The high temperature in Denver Tuesday will be 87 degrees, decreasing to 57 degrees at night, forecasters said. On Wednesday, the high temperature is expected to be 84 degrees.

The Colorado Department of Public Health and the Environment air quality alert covers Douglas, Jefferson, Denver, western Arapahoe, western
Adams, Broomfield, Boulder, Larimer, and Weld counties, effective through 4 p.m., officials said.

They’ve asked residents to limit driving non-electric vehicles that burn gasoline or diesel, warning that “higher ozone concentrations are possible” and that additional air pollution will worsen air quality. Ozone concentrations considered unhealthy for sensitive groups are mostly likely in the south and western parts of metro Denver.