The Fourth of July weather forecast calls for temperatures in the mid- to upper-80s and clear skies, although in the evening, fireworks might affect air quality, according to officials.

Those participating in the local Fourth of July 5k/10k run-walk don’t necessarily need to be concerned, as the air quality is expected to be moderate until about mid-afternoon.

Later in the day, however, the onset of fireworks is expected to be considered “unhealthy for sensitive groups,” according to the South Coast Air Quality Management District.

“(For the Fourth of July), the air quality index is more driven by ozone, because during the summertime, it’s hotter so there are more stagnant air conditions that can lead to more smog or ozone,” said Nahal Mogharabi, director of communications for the AQMD.

The anticipated onset of fireworks also plays a significant role for the next two days, she added.

“(Air pollutants) start to rise during the early evening, and they tend to stay elevated overnight and through the morning of July 5,” she said.

A regularly updated forecast for air quality for the Santa Clarita Valley is available online at the South Coast Air Quality Management District website at http://www.aqmd.gov.

When the air quality reaches an unhealthy level, Los Angeles County Health Officer Dr. Muntu Davis advises people living or working in the SCV who have heart disease, asthma or other respiratory diseases to minimize outdoor activities.

“Children who have sensitive conditions, including heart disease, asthma, and other chronic respiratory diseases, should not participate in outdoor physical activity at schools, camps and other recreational programs and should stay indoors as much as possible (when the air is ‘unhealthy’),” according to a warning from Davis’ office.

The weather calls for warming with temperatures peaking in the low-90s on Saturday, according to Alex Arnold, intern meteorologist with the National Weather Service.

“The rest of the week is in the mid- to high 80s,” she said Wednesday, “and then Saturday has a high of 91 forecast.”