A severe thunderstorm watch in effect in most of Connecticut. And why is the sky so hazy? Western wildfires bring smoke eastward.

Western wildfires, from states as far as away as Oregon, have brought hazy skies across the country to Connecticut. But the sky is about to get darker: A severe thunderstorm watch is in effect Wednesday afternoon for most of the state.

The severe thunderstorm watch is in effect for Hartford, Middlesex, Tolland, Windham, New London, New Haven and Fairfield counties, the National Weather Service says.

Where is the smoke coming from?

Smoke from wildfires out west has traveled all the way to Connecticut.

“I think they’ve been citing Oregon as the origin, but just the way the jet stream has been set up, it’s been able to carry smoke from out that far west, into Northern Canada, down through the Great Lakes and eventually all the way out here in Northeastern United States, including Southern New England,” Rob Megnia from the National Weather Service said.

It’s not entirely uncommon, Megnia added.

“It probably happens a couple times a year. You get a big wildfire and the jet stream is able to carry it across the country,” he said.

What kind of storms will Connecticut see Wednesday?

Severe thunderstorms will be seen across the whole state, Megnia said.

They’ll likely be between 2 p.m. through 9 p.m., with potentially damaging wind gusts, and a “pretty decent, large hail threat as well,” Megnia said.

Central Connecticut is expected to see the most action, but all eight counties will be affected.

There’s also chances for an isolated tornado, Megnia added.

The weather service announced the severe thunderstorm watch about noon.

How is the air quality?

An air quality warning was in effect until midnight Tuesday, Megnia said.

AirNow, which tracks air quality across the country, had parts of the state in the red zone of elevated levels of fine particles (PM2.5) in the air.

Healthy levels usually are below 50 PM2.5, but parts of Connecticut, including Hartford, Danbury, Torrington, Stratford and Bridgeport saw unhealthy levels between 153-161 PM2.5. By Wednesday, levels are supposed to drop to moderate.

Storms and showers Wednesday afternoon, into the evening, will also help clear the smoke and improve air quality, Megnia said.

The state Department of Energy and Environmental Protection urged residents to keep outdoor activities limited.

What about flooding?

As of Tuesday night, there was only one active flood warning which was isolated to Middle Haddam, Megnia said.

“They’re in flood stage right now,” Megnia added. The NWS was warning residents to avoid near Route 17A.

The good news, he said, was that the water was receding.

For the rest of the state though, it’s just a matter of watching for additional rainfall.

Courant staff writer Christine Dempsey contributed to this report.

Jessika Harkay can be reached at jharkay@courant.com.