Red flag warnings issued in 5 states: See wildfire, smoke map of US, Canada

Correction: A previous version of this story misstated the number of states under red flag warnings.

Five states were under red flag warnings Tuesday due to hot, dry and unstable conditions, the National Weather Service said.

Parts of Pennsylvania, New Jersey, Michigan, Washington and Alaska will remain under the warning until 8-10 p.m. local time, the weather service said.

In Pennsylvania, lightning strikes may cause fires to start in dry areas. In Washington, dry and unstable air mass with warm temperatures could contribute to a fire.

“Be careful with any activities that could potentially lead to a wildfire,” the weather service warned Michigan residents. “Camping, outdoor grills, smoking materials, chain saws and all-terrain vehicles all have the potential to throw a spark and ignite a dangerous and destructive fire.”

What is a red flag warning?

The weather service issues a “red flag warning” when weather conditions in an area are ripe for the spread of wildfires due to a combination of strong winds, low relative humidity and dry fuels.

“Any fires that develop will likely spread quickly,” the weather service said. “Outdoor burning is not recommended.”

Wildfires in Canada affecting air quality in US

Millions of Americans are exposed to unsafe air quality levels as eastern Canada experiences one of its worst reported wildfire seasons, officials said last week.

The weather service issued air quality alerts to several U.S. states warning “sensitive groups” such as older adults, children and those with preexisting respiratory conditions like asthma to limit prolonged or strenuous outdoor activity.

Air pollution increases the risk of respiratory infections, heart disease and lung cancer, according to the World Health Organization.

Wildfire, smoke map for US, Canada

US weather warnings

US Air Quality Index

More coverage from the USA TODAY Network

Air quality: Smoke, haze impact US air quality as Canadian wildfires continue to rage

Grayling, Michigan wildfire: More than 3,000 acres burned; 85% contained

Map: Smoke from wildfires in Canada prompt US air quality alerts. Here's a wildfire, smoke map.

Insurance: Allstate no longer offering new policies in California due to wildfires, other costs

Home insurance: State Farm will no longer insure new homes in California because of wildfire risks

This article originally appeared on USA TODAY: Wildfire, smoke map of US, Canada: Red flag warnings in 5 states