As of Friday, the forecast for Monday's total solar eclipse shows Oregon and Idaho as the most promising for clear sky views, while South Carolina is the most likely to find the sun and moon blocked by clouds.
The National Weather Service also is optimistic about good viewing from St. Louis to Nashville, but forecasts can change.
Overall, about half the nation is likely to get favorable eclipse viewing weather, said Mike Musher, a meteorologist at the weather service's Weather Prediction Center.
The troublesome area, not easy to forecast and not likely to be all clear, is from Wyoming to western Missouri.
"It's going to be twitchy for everybody from Nebraska eastward," said retired Canadian meteorologist Jay Anderson, who has been forecasting eclipse weather since 1978.
Anderson, who runs the Eclipsophile weather website, said people east of Idaho and west of the Appalachian Mountains may have to drive a bit to find clear skies, but with a little effort they can find them. Officials and eclipse watchers have fretted, though, about roads being too clogged as the eclipse approaches.
The full eclipse will cover a 70-mile-wide (112-kilometer) swath from Oregon to South Carolina. The moon will pass between Earth and the sun for America's first coast-to-coast total solar eclipse since 1918. When this happens, the classic image appears of a black dot surrounded by a feathery red ring, the sun's corona.
A partial eclipse will be visible outside the path, extending up to Canada and down to the top of South America.
Anderson, who is staying in Jackson, Wyoming, fears heart-breaking weather in Wyoming where clouds could hide the eclipse with tantalizing clear skies just off in the distance.
If a cloud moves over the sun, you miss the corona, Anderson said. "That's everybody's No. 1 target."
It will still get dark and cooler and animals may act differently, but the sky show won't be the same, Anderson said.
Computer-generated forecasts don't quite agree about cloud cover, except for the Pacific Northwest and South Carolina.
This is still early. The forecast can still change and has been changing, but Musher said "we are getting into that window where there shouldn't be a dramatic adjustment to weather development and cloud coverage."
Musher cautioned that wildfires in the Northwest could cause smokiness that might worsen the eclipse view in Oregon and Idaho, but Anderson and Oregon State University climate scientist Kathie Dello said smoke is looking like less of an issue.
No area on the eclipse path had high chances of rain Monday afternoon, Musher and Anderson agreed.
Hardcore eclipse chasers pore over weather forecasts, especially the day before the action so they can alter their plans.
"I've travelled overseas three times for this. One that I can drive to, I don't want to miss because of the weather," said Alabama plastic surgeon Gordon Telepun, who is leading a group of about 20 people.
He is leaving nothing to chance. Telepun has booked six separate sites - five camping areas and one hotel - along a 400-mile-long swath from Missouri to Tennessee, ready to get ahead of the weather.
Telepun said he won't even pay attention to Friday's forecast, despite how promising it looks for him.
"We'll be making the decision Sunday morning where to go," Telepun said.
Follow AP's coverage of the total solar eclipse here.
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