Officials have issued an air quality alert for much of the Philadelphia area for higher-than-normal concentrations of ground-level pollution.

Smoke from a wildfire in Canada is a contributing factor behind the alert but it is too high up in the atmosphere to be a primary cause, said Patrick O’Hara, a meteorologist at the National Weather Service’s Mount Holly office.

The alert means that air pollution concentrations may become unhealthy for sensitive groups, including the elderly, children, and people suffering from asthma, heart disease, or other lung diseases. People in those groups should avoid strenuous activity or outdoor exercise.

Otherwise, Wednesday should be another typical, somewhat humid, summer day with sunny skies and high of about 90 degrees in Philadelphia and 84 at the Jersey Shore.

Looking ahead, showers and thunderstorms are likely Thursday afternoon and night. Some of the storms could have drenching downpours and gusty winds.

There’s a chance of showers for Friday, but there is no precipitation in the forecast for the weekend, when the daytime high temperatures are expected to be in the upper 80s.