At no other time in history has the summer climatology of a narrow strip of land spanning from the salt marshes of South Carolina to the rugged coast of Oregon been under such scrutiny.
In a 70-mile wide path on Aug. 21, day will turn to night as the moon slips between the sun and Earth, casting a shadow that will create the first total solar eclipse to travel sea to shining sea in 99 years.
Prime viewing of the celestial ballet can be pricey for anyone outside the path, but no amount of money can buy the key ingredient to a successful show — clear skies.
“The most important thing is what will the weather be like,” said Vanessa Griffin, director of the National Oceanic and Atmospheric Administration’s Office of Satellite and Product Operations. “If you are looking at the coasts, you will see more clouds because of higher humidities.”
That’s why for hardcore eclipse chasers, it wasn’t enough to just find a seat in the path of totality. The climatological history was also a consideration that ruled out many cities, such as Columbia, S.C., which has just a 44 percent chance of clear skies despite being in the path of highest impact, according to the National Centers of Environmental Information, or NCEI.
Palm Beach County is hundreds of miles from the path of totality. It will still experience 81 percent of the sun being obscured, with the first bite taken at 1:25 p.m. and maximum eclipse happening at 2:57 p.m.
But the chances of clear skies are just 50 percent.
Thank South Florida’s reliable summertime thunderstorms for that. The afternoon storms build with the sea breeze, making a 3 p.m. viewing time less than ideal.
“Some of this has to do with the time of day that the eclipse is passing over the cities,” said Ronald Leeper, a research associate with NCEI. “In the afternoon, you just have more clouds in general, and it will hit the eastern half of the U.S. in the afternoon”
Leeper worked with cloud data collected from surface weather observation stations throughout the U.S. to compile an interactive map of areas most likely to have clear skies on Aug. 21. The stations gather five types of cloud cover: clear (no clouds), few, scattered, broken, and overcast.
What he found were cloud-free August skies in a sweeping swath of the Intermountain West.
In fact, if historical conditions hold true, towns such as Rexburg, Idaho, Casper, Wyo., and Lincoln, Neb., are the best bets for seeing the eclipse.
“Experts will tell you to stay mobile,” said Deborah Byrd, editor-in-chief of the online astronomy magazine Earth and Sky. “I’ve rarely viewed a total or annular eclipse without having to be in the car at the last moment chasing down a hole in the clouds.”
Rob Cox, a meteorologist with the National Weather Service in Cheyenne, Wyo., said the state’s rainy season is May through July when a high pressure system across the southwest feeds in moisture from the Pacific Ocean.
But by August, dry air prevails. Casper has an 88 percent chance of clear skies on Aug. 21.
“Another situation that is kind of unique is our higher elevation allows you to see the sun as a bit larger,” said Cox, noting that Casper is 5,200 feet above sea level. “Because you are at a higher elevation, a dry air mass is usually in place. It won’t be hazy.”
Rexburg, Idaho has a 91 percent chance of clear skies. Officials in the 30,000-resident town are expecting an additional 60,000 people for the eclipse — not including day trippers.
“Every hotel we know of within 100 miles is booked,” said Scott Johnson, Rexburg’s director of economic development and community relations. “It’s pretty crazy. We’ve heard prices as high as $1,500-a-night.”
Full solar eclipses viewable from populated areas are rare. The last full solar eclipse in the United States was in 1979, but it only covered five states.
The next total solar eclipse in the U.S. is 2024. The next coast-to-coast solar eclipse in the U.S. is 2045
The Pacific Northwest will first see the Agu. 21 eclipse at about 10:15 a.m. Pacific Daylight Time. A 90-minute journey will take it across the U.S. where South Carolina will be the last to see it beginning in Clemson at 2:37 p.m. Eastern Daylight Time.
About 12 million people live within the narrow path of the total eclipse, which includes the capital cities of Salem, Ore., Lincoln, Neb., Jefferson City, Mo., Nashville, Tenn., and Columbia, S.C.
“If you can possibly get into the eclipse path, take the family, take the kids, because it will be one of the most amazing natural phenomena that you will ever see,” said retired NASA astrophysicist Fred Espenak, who has traveled to see 27 solar eclipses but was clouded out seven times.
In 2012, Espenak took his family to Australia to see a total solar eclipse. Clouds moved in as the moon took its place between Earth and sun. Totality was supposed to last two minutes. Espenak caught three seconds of it between breaks in the clouds.
In Florida, Key West has the highest chances for clear skies on Aug. 21 at 78.7 percent, according to Leeper’s climatology. Fort Myers is second with a 68 percent chance of clear skies.
“It is so nice to see people interact with climate data and be able to use it to help them make decisions,” Leeper said. “I would recommend having a Plan A and Plan B.”
Keep up with weather reporter Kimberly Miller’s dispatches on the solar eclipse at http://pbpo.st/kmillerweather