It's probably the most anticipated weather forecast in recent memory. Millions of people across the United States are eagerly tuning in to their local meteorologists or refreshing their favorite apps, all hoping for the same thing: clear skies overhead Monday for the total solar eclipse.
By now you have probably heard about the Eclipse of the Century, the first total eclipse to occur in the United States since 1979 and the first to cross from coast to coast in 99 years.
If you are one of the 200 million Americans who live within a one-day drive of the path of totality, hopefully you have made plans to view the awe-inspiring event.
But as predictable and consistent as we know the eclipse will be -- we know to the second when and where the moon will cast its shadow upon the Earth -- the weather remains the biggest wild card when it comes to a successful viewing experience.
"When eclipse day dawns, weather will trump all the geometric calculations and careful planning that eclipse-chasers have worried about for years," said Kelly Beatty, senior editor of Sky & Telescope magazine and veteran eclipse-chaser.
"That day's forecast is the one element that can't be determined in advance. It's a simple truth," he said. "In the end, the best place to observe the eclipse will be from wherever it's clear."
Weather for the eclipse
The weather forecast for the eclipse is becoming clearer, and luckily the skies are looking clearer as well. What earlier in the week was looking rather gloomy for some of the key locations in the path, especially in the southeast, now looks a bit more encouraging for all but in the coastal southeast.
While there doesn't appear to be a major weather feature that will bring widespread bad weather to a specific region, there are a few trouble spots to keep an eye on for potential poor visibility.
The Pacific Northwest, which will be the first location to see the eclipse, looks like it might have some of the best weather. The Northwest looks to be clear of any large-scale storm systems, though some clouds are likely along a trailing front from Montana into Wyoming and Idaho.
The Western United States will have the advantage of experiencing the eclipse in the morning, before the heat of the day has had a chance to build up clouds and storms.
Coastal locations could still be dealing with some morning fog and low clouds, however, which is a risk for those wanting to be the first to observe the eclipse on Oregon's Pacific coast.
Over the central United States, an area of low pressure will be spreading from the northern Great Plains to the Midwest, which will bring clouds and rain. It looks like most of the unsettled weather will stay north of the eclipse's path of totality, from Iowa and Minnesota east to the Great Lakes region.
The system will bring enough unstable and humid air from the south that it may create some partly- to mostly-cloudy conditions over the key states of Nebraska and Missouri, especially in the afternoon -- which could mean cloud-dodging could be required for a clear view in some locations.
The biggest trouble spots, weather-wise, will likely be in the Southeast. A stalled frontal boundary and onshore flow will trigger clouds and storms in Georgia and the Carolinas. The extent of the clouds and storms should increase as the heat of the day builds, which could start happening by the 2 p.m. hour when the eclipse is peaking in the region.
Clouds and storms will be most likely along the coast (looking at you, Charleston) and in the elevation of the Appalachian Mountains.
What will you see if the weather is bad?
"It's called being clouded-out," said Beatty, who has had three of eclipse chases disrupted by the weather: 1991 in Hawaii, 2004 in South Africa and 2013 in Kenya. "All were disappointing," he admitted.
As long as you are in the path of totality, you will still "experience the eclipse," even if there are clouds obscuring your view.
"Remember, the sun is 93 million miles away. The shadow of the moon will still darken the sky," said Dave Jones, founder and CEO of StormCenter Communications, whose group is helping states in the path of the eclipse prepare for the event. "If it is cloudy ,it will get even darker" than if the skies were clear.
A lot of the effect from the clouds will depend on their thickness.
High, thin clouds may still allow for a view of the sun's oval and the eclipsing moon moving across.
As long as the clouds are not too thick, "the temperature should drop a bit too," according to Beatty.
Scattered clouds, as you might expect, can be hit or miss, leaving eclipse viewers to play the odds as to whether one of those puffy white monsters will block their much-anticipated view.
But some good news: Total eclipses can actually improve local weather conditions in the moments before totality.
Cumulus clouds, the "fair-weather clouds" that occur frequently on warm summer days (such as in August), will tend to disappear as the sun's rays begin to darken.
"Because they are driven by convective currents (from the sun's heat), cumulus clouds tend to dissipate as totality nears," Beatty revealed.
Unfortunately, if the clouds are too thick, and especially if rain is present, much of the magic of the eclipse is lost.
Beatty said bluntly, "if it's raining, it'll still get dark too -- but I can't think of anything more depressing."
So it's going to rain -- now what?
Your bag is packed, you've got your camera and eclipse glasses, your hotel room that you booked last year is waiting for you -- but the forecast is calling for persistent rain. Now what?
"If you're in the path of totality and committed to seeing the eclipse," Beatty said, "get in the car the night before and hit the road. ... Sleeping in the car for a night won't kill you."
Just remember, you won't be the only one chasing those clear skies for a pristine view of the heavens.
"Traffic is expected to be very congested, especially around urban areas," according to Jones. "Make sure you have a tank full of gas and enough food and water for three days."
If fighting traffic or sleeping in your vehicle doesn't sound worth it, Beatty has a few other suggestions.
"If you are stuck under bad weather, watch one of the many eclipse webcasts available online and start planning ahead -- either for the 2019 total eclipse in Chile or the 2024 total eclipse that crosses the US from Texas to Maine."