Another air quality alert for Philly Sunday, as temperatures approach 90 under smoky residue

The winds of change are imminent, and we are all but promised a decent soaking rain Monday, but yet one more dreaded “air quality alert” is in effect for Southeastern Pennsylvania Sunday as temperatures approach 90 — and likely to feel even warmer.

Canadian wildfire smoke has mercifully thinned, but enough of the residue will linger to interact with the heat to produce unhealthful “code orange” levels of ozone, according to the interagency Air Quality Partnership. The air may be harmful to those with background respiratory and heart conditions. Fine particle levels also may remain in the “moderate” range.

Thermal comfort being relative, Sunday “is not going to feel great considering how cool it’s been,” said Sarah Johnson, the warning coordination meteorologist at the National Weather Service Office in Mount Holly.

“People aren’t acclimated.”

The heat is due to end quite an impressive cool spell for June. Temperatures have been below normal in Philly for eight consecutive days through Saturday, in part due to that siege of smoke which veiled some of the sunshine during the week.

The warmth does represent a positive sign: It is being driven by winds from the south and southwest, which should further rout the smoke.

The Quebec smoke has ridden steady winds from the north, generated by a low-pressure storm system that was centered over New England, so areas to the west and south tend to experience breezes from the north country.

The next weather-maker is centered to the west of the region, said Johnson, so the winds will be blowing from the south to the east of the center.

Those winds, she said, “should continue the rest of the week.”

They also should coincide with a change of rain fortunes, she added. “The chances are looking pretty darn good” for rain, sometime from Sunday night through Monday night.

“The amounts probably are not as much as people would like,” she said, maybe up to an inch.

If that does happen, that would be about four times more than the total we have received in the last six weeks.

In its weekly update, the U.S. Drought Monitor placed all of Chester and Delaware Counties and parts of Bucks and Montgomery Counties in “moderate drought.”