Why is the sky yellow in Boston? Canadian Wildfires turn skies orange across the US as thick smoke raises air quality concerns, nearly 100 million affected

Canadian Wildfires: Residents across parts of the northeastern United States woke up to an unusual sight this week a yellow sky, an orange sun and hazy conditions due to wildfire smoke from northern Minnesota and western Ontario. If you've been wondering why the sky is yellow right now, the answer lies hundreds of miles away in Canadian wildfires, which continue to send massive plumes of smoke across North America.

The smoke coming from wildfires burning in Canada has spread over much of the northeast, including parts of New York City, where temperatures neared 100 degrees on Wednesday.

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According to meteorologists, the smoke has traveled more than 1,000 miles from active wildfires in Canada, reaching cities across New England and parts of the Midwest. While the dramatic skies have caught many by surprise, experts are also warning that the smoke could affect air quality in several regions. The increasing concentrations of fine particulate pollution at ground level and raising the risk of unhealthy air conditions across multiple states.

Why is the sky yellow right now?

The strange yellow and orange tint isn't caused by pollution from local sources or an eclipse. It happened because smoke from Canadian wildfires changes the way sunlight reaches Earth.

Normally, shorter blue wavelengths of sunlight scatter through the atmosphere, making the sky appear blue. But wildfire smoke contains tiny particles that block and scatter blue light while allowing longer red, orange and yellow wavelengths to pass through.

As a result, the sky takes on a yellowish or orange glow, even in the middle of the day. The same effect is often seen during sunsets, but thick wildfire smoke can create it for hours.

Canadian wildfires are behind the unusual skies

According to weather officials, smoke from more than 830 active wildfires burning across Canada is drifting into the United States, with nearly 100 million people across the Midwest, Great Lakes and Northeast expected to be affected. Winds high in the atmosphere have carried the smoke plume southeast into parts of the United States.

Forecasters say the smoke will first blanket parts of the Upper Midwest before spreading eastward, bringing hazy skies and poorer air quality to major cities such as New York City, Boston, Philadelphia, Detroit and Washington, D.C. In some parts of the Upper Midwest, officials warn the skies could take on a "Mars-like" appearance, while air quality may deteriorate to levels considered unhealthy for everyone, leading to air quality alerts in multiple states.

Smoke may impact air quality too

While much of the smoke has remained high in the atmosphere, weather experts say some areas could experience poorer air quality as smoke drifts closer to the ground.

Sensitive groups—including children, older adults and people with asthma or heart and lung conditions—may notice irritation, coughing or breathing discomfort if smoke concentrations increase. Forecasters say some regions could see even thicker smoke over the coming days.

Why the sun looks orange in Boston

The smoke was thick enough to slow our temperatures from rising into the 90s and also to block out the blue light from the sun, much like we see at times during sunset, only the longer wavelength colors were able to pass through the smoke, turning our skies yellow/orange. The weather models indicate smoke concentrations could become even higher in some locations.

On Thursday, more wildfire smoke is expected with plumes charging further south and east with devastating effects on air quality for many across the Northeast. As for now, the impacts on visibility will be marginal to moderate.

Is this similar to the 2023 wildfire smoke event?

Yes. Many people have compared this week's skies to June 2023, when smoke from Canadian wildfires turned New York City's skyline orange and caused hazardous air quality across much of the eastern United States.

Meteorologists say the current smoke event may not be as severe everywhere, but in several regions it has created similar hazy skies, orange sunsets and reduced visibility.

Will the yellow sky last?

That depends on changing wind patterns.

Forecasts suggest smoke could continue drifting across parts of the Great Lakes and Northeast before gradually moving away as weather systems shift. Until then, residents in affected areas may continue to notice yellow skies, hazy sunshine and vivid orange sunsets.

What should you do if wildfire smoke reaches your area?

If air quality deteriorates, health officials generally recommend:

• Limit prolonged outdoor activity, especially strenuous exercise.
• Keep windows and doors closed if smoke is heavy.
• Use air conditioning or an air purifier if available.
• People with respiratory or heart conditions should monitor local air quality updates and reduce exposure when necessary.