Which US regions are likely to offer clear skies when the eclipse occurs?

August weather may bring clear skies to millions of people gathered across the country as the moon's shadow crosses the continent during the upcoming eclipse.

Aug. 21 marks the first total solar eclipse visible from the continental United States in nearly four decades. The path of totality will occur along a 68-mile-wide stretch traversing 2,500 miles across the continent from Oregon to South Carolina.

"Overall, the chances of clear skies increase the farther west you are across the country," AccuWeather Meteorologist Dave Samuhel said.

This is simply due to the fact that the Atlantic Ocean and Gulf of Mexico are closer in proximity to the eastern third of the country, which brings more rain, Samuhel said, citing his recent post on AccuWeather's astronomy blog.

Nearly 12 million people live in the path of totality, and many more are expected to travel to see the celestial event.

Roughly two-thirds of the entire U.S. population live within a day's drive from the path, according to Space.com.

The chances for clear skies in the western U.S. are greater for those viewing the event east of the Cascades in Oregon and away from the coast, Samuhel added, stating that "low clouds are likely to be a problem, especially along the immediate Pacific Coast."

For those closer to the southeastern portion of the path, clouds are more likely, Samuhel said.

"This is especially true given the timing of the eclipse in the Southeast," he added. "The eclipse will occur after noon in the Southeast, where building clouds and showers and thunderstorms are often found on August afternoons."

In the Southeast, tropical storms and hurricanes can also bring widespread areas of clouds.

However, Samuhel said it is important to note that no matter where people are viewing the eclipse, clouds could occur nearly anywhere.

"By Aug. 21, we start to see the first Pacific cold fronts of the season," he said. "These will tend to just be an issue for the Northwest, Oregon and Idaho."

In mountainous areas, clouds are more likely to develop as the day progresses, Samuhel said.

"The mountains in Oregon would be a fine place to see the eclipse, as many more clouds would likely be in lower elevations near the Pacific."

Clouds will be more likely to build during the afternoon hours after the eclipse has passed, which makes it more likely for clear skies during the event, he added.

"Elsewhere, building clouds over the mountains will likely make them cloudier than nearby lower elevations," he said.

In addition, the Plains are always under a threat for thunderstorm clusters during the month of August.