Whatever your plans are for this month’s eclipse, there is one thing that can easily render them moot. Clouds.
Unfortunately, traditional weather forecasts can’t reliably predict weather significantly in advance, so looking at the weather for next Monday hasn’t really been a possibility until now, except for one forecast designed by a team from the North Carolina Institute for Climate Studies.
“We’re using historical information to make inferences about the future,” said Ronald Leeper, a research associate at NCICS. “Essentially what we’ve done is look at all of the historical cloud information for Aug. 21 and used that as a best guess of what we should expect typical cloud cover to be for Aug. 21.”
NCICS has hour by hour cloud data from across the country for the day of the eclipse, so they are able to calculate likelihood of cloud coverage at the specific times the eclipse will appear as it moves across the country. Those likelihoods will change as the eclipse moves east.
“In the west coast the eclipse is going to come earlier in the morning whereas on the east coast it is going to be closer to 2 p.m.,” said Leeper. “You can kind of see in the cloud data that, in the morning, atmospheric conditions are generally stable, so you’ll have clear conditions. By the time you get to the afternoon you expect some vertical development and some pop up clouds.”
The forecast does not treat all cloudiness the same. It takes into account cloud variability, or how cloudy it was historically at the time of the eclipse on a scale from clear to completely overcast. Using this information, the forecast weights the likelihood of being able to see the eclipse based on the extent of past cloud coverage in a given area.
According to the NCICS’ work, across South Carolina there is a 52.6 percent chance of the eclipse being viewable as it reaches totality in Charleston, a 73.2 percent chance of visibility in Orangeburg, a 48.3 percent chance in Sumter Shaw, and a 75.5 percent chance in downtown Columbia. Further west in the state chances range from roughly 65 to 75 percent.
The closest city to Beaufort County with available predictions in the NCICS forecast is Savannah, which has forecasts available for two locations, one of which has a 41.5 percent chance of eclipse visibility, while the other has a 52.6 percent chance.
As for more traditional forecasting methods, AccuWeather is predicting partly cloudy conditions with a 30 percent chance of rain throughout Beaufort County on the day of the eclipse. They are predicting the same probabilities in Charleston and Santee, the closest spot to Beaufort County that will spend more than two and a half minutes in totality.
The National Weather Service will have their first look at the big day on Tuesday.