This week in America it pays to know your cumulus from your cirrus and your nimbostratus from your plain old regular stratus.
They are all types of cloud, with cloud cover forecast to play havoc with the plans of hundreds of thousands of people preparing to watch the eclipse on Monday.
Unusually for this time of the year, the northeast of the US is likely to have better conditions than the southwest. States like Texas and Arkansas are expected to be covered by a veil of cloud which could seriously diminish prospects of a clear view of a historic total eclipse.
But it depends what type of cloud, with the sheet-like stratus clouds a much bigger problem than the wispy cirrus clouds.
“For any eclipse you want the clearest view possible,” says Brett Tingley, avid eclipse viewer and editor of Space.com, “if it’s just a bit overcast you will see the eclipse but not the definition of the moon going over the sun”.
Mr Tingley is watching the eclipse with his family in Cape Girardeau, Missouri, a small town which is in the so-called “path of totality,” where the total eclipse will be visible. It is an eight-hour drive from his home in North Carolina and he booked a hotel six months ago for $120 a night. Prices for a hotel room in the area are now going for $700 a night and more.
The most keen eclipse viewers have been furiously checking the weather forecast for days, looking for the latest on where the clouds are likely to be a nuisance.
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A sign on Interstate 81 in Binghamton, New York. ahead of the eclipse. Pic: AP
“I’m looking at the forecast every four hours,” says Mr Tingley, “The latest shows there should be a big hole in the cloud cover over Missouri so that’s good.
“I’m bringing my children with me,” he adds, “they’re nine and six and will be grown and out of the house by the time of the next eclipse in 2044 so it’s very special to share this with them. It will be great if we have a clear view.”
American network television has been featuring regular updates from its meteorologists about conditions in the path of totality. CNN has its own weather centre and has set up an “eclipse central” team which has been monitoring weather and cloud cover from 10 days out.
Fredericksburg in Texas was supposed to be an eclipse-watching hotspot in the centre of the path of totality. Just a few days ago hotel rooms there were selling for around $800 a night and now people are trying to offload them because the forecast is for 75% cloud cover, which would make it much less of a spectacle. But most of those hotel rooms are non-refundable.
Solar eclipse marketing at a Wegmans grocery store in Syracuse, New York. Pic: AP
There is better news for people travelling to the northeast. New England is basking in an almost perfect eclipse-viewing weather forecast.
It has come as a surprise to those who live there, too. Michael Hibben is director of the Pierson Library in Shelburne, Vermont, and is organising a viewing party. He was expecting hundreds of visitors but now says it could be thousands because of the weather.
“It says sunny and clear skies, which is fortuitous and unexpected,” he says, “we had a snow storm this past weekend and most people were thinking the southwest would be better. People who are serious about seeing the eclipse are willing to move location so we could definitely have more visitors than expected.
“We’re hearing of people potentially rerouting private plane routes to see the eclipse here instead. To see a total eclipse is so rare and extraordinary, I don’t know anyone personally who has seen one.”