Up in the air: Heat, humidity, ozone, storms

The forecast calls for varying degrees of discomfort today through the weekend, with heat, high humidity, an ozone alert and looming thunderstorms.

If the high hits 90 for the third straight day today - and the fourth in the past five days - we'll officially be in an early heat wave.

Last year, the first heat wave was in August.

Not only will the air feel sticky today - a dewpoint in the mid 60s assures that - but ozone could be at unhealthful levels.

An orange alert for ozone - only the second this year - has been issued for about a dozen counties across Southeastern Pennsylvania, so anyone with breathing problems, such as asthma, should avoid strenuous activity, as should small children and the elderly, according to the Air Quality Partnership (hotline 1-800-872-7261).

People are asked to avoid idling cars, mowing lawns and topping off gas tanks.

Showers and thunderstorms are possible this afternoon, tomorrow and Sunday, with the chances of rain in the city and the suburbs rising from 20 percent today to 60 percent on Sunday, according to the National Weather Service. At the Shore, the probability of rain Sunday is 40 percent.

Temperatures will gradually decline through Wednesday, but weekend highs should stay in the mid to upper 80s in the Philadelphia area, and in the low to mid 80s at the Shore.

For more on the forecast, go to http://go.philly.com/weather.