Many Maine municipalities will open cooling centers this week with the National Weather Service issuing a variety of heat advisories covering the next few days.

The Maine DEP also issued an air quality alert for Wednesday with ground-level ozone expected to reach levels that are unhealthy for sensitive groups.

York County, interior Cumberland and Androscoggin counties, and the southern half of Oxford County are under an extreme heat warning from 11 a.m. Wednesday to 8 p.m. Friday.

The warning calls for “dangerously hot conditions” that could feature heat index values of up to 110 degrees. The index measures how hot it feels to the human body when relative humidity is combined with the air temperature. Overnight lows are only expected to fall into the 70s, according to the weather service office in Gray.

The warnings prompted Lewiston Public Schools to call off summer school for Thursday.

The rest of the state — save northern Aroostook, Piscataquis and Somerset counties — falls under a heat advisory this week. However, the weather service has also placed a number of counties under an extreme heat watch for Thursday.

In Kennebec, Lincoln and Sagadahoc counties, as well as coastal Cumberland and interior Waldo counties, heat index values are expected to reach up to 104 degrees during the heat advisory period, the weather service warns. They could reach 110 degrees Thursday, when the extreme heat watch is in effect.

Southern Somerset and Franklin Counties are under a heat advisory Wednesday through Friday, with heat index values up to 104 expected, according to the weather service. Coastal Hancock County is under an advisory Thursday and Friday, with values also expected to reach 104 degrees, while most of Washington County is also under a heat advisory Thursday and Friday, with heat index values of up to 102 degrees expected there.

Southern Piscataquis and Penobscot counties, as well as interior Hancock County, are under heat advisories through Friday. Heat index values could reach 99 degrees Wednesday and up to 103 Thursday and Friday, the weather service warns.

Northern Oxford and Franklin counties, and central Somerset County fall under a heat advisory until 8 p.m. Thursday and can expect a heat index value of up to 100 degrees according to the weather service.

Northern Penobscot and southeast Aroostook counties will be under a heat advisory Thursday when a heat index of 97 degrees is expected. Central Penobscot County is under an advisory Wednesday through Friday. The heat index could reach 98 degrees there Wednesday, according to the weather service, and up to 100 on Thursday and Friday.

The weather service advises people to drink plenty of fluids, stay in air-conditioned rooms when possible, avoid extended periods in the sun, and check up on relatives and neighbors. It also warns not to leave young children and pets in unattended vehicles, as “car interiors will reach lethal temperatures in a matter of minutes.”

A list of cooling centers is also available on the Maine Emergency Management Association’s website.

The Maine Department of Environmental Protection has also issued an air quality alert from 10 a.m. to 11 p.m. on Wednesday along the coast from Kittery to Acadia National Park. The agency warns that ground-level ozone concentrations are expected to reach levels that are unhealthy for sensitive groups.

Ozone levels may reach “moderate levels” further inland, according to the Maine DEP, including in all of Androscoggin and Kennebec counties, as well as parts of Cumberland, Knox, Lincoln, Penobscot, Sagadahoc, Waldo, Washington and York counties.

Elevated ozone levels can pose a risk to children, older adults and people suffering from respiratory or heart diseases, according to the Maine DEP. Anyone exerting themselves outdoors may also experience health effects, which could include coughing, shortness of breath, throat irritation and mild chest pain.

Ozone levels were already climbing in southern New England on Tuesday, according to the Maine DEP, and winds are expected to bring those conditions to Maine on Wednesday.

The Maine DEP recommends that vulnerable populations avoid strenuous outdoor activities, keep windows closed, and circulate indoor air with fans or air conditioners. Those with asthma are also advised to keep quick-relief medication handy.

Particle pollution levels are also expected to be moderate across the state on Wednesday due to wildfire smoke, the Maine DEP said in its announcement Tuesday. Wildfires in Colorado, which have claimed the lives of three firefighters, had burned nearly 90,000 acres as of Tuesday, according to the Denver Post.