Louisville Metro Government has issued the season’s first air quality alert .

The threshold for calling an alert is 101 on the Air Quality Index, which measures air pollution on a scale of 0 to 500. The ozone level is forecasted to be 104 this weekend.

APCD spokesman Tom Nord says the weather, rather than unexpected pollution, prompted this weekend’s alert.

“The reason we called it was because the weather system we’re in, even though it’s very beautiful out there, clear skies, sunshine, there’s not a lot of air moving and when the air doesn’t move, the pollution tends to stick around,” he said.

The air this weekend could be unhealthy for sensitive groups, which includes the young, the elderly and people suffering from lung disease.