Cloudiness trends for the 2017 eclipse
Average percent cloud cover in the images:
The solar eclipse on August 21st 2017 will be visible over the contiguous United States from the west coast to the eastern seaboard, with the band of totality stretching from Newport OR to Charleston SC (more information from NASA). The last total solar eclipse visible in the contiguous US was in 1979; the next will be in 2024, with the path of totality going from Mexico through Texas and Maine to eastern Canada.
For enthusiasts traveling to see the total solar eclipse, an important question is: where should one go for the best chance of clear skies, to get the best views of eclipse and associated phenomena such as Bailey’s beads and the shadow bands? We try to answer that question by looking at historic cloud cover data. Using NASA satellite images from MODIS, on the Terra satellite, for the 12 years 2005-2016, we look at cloud cover percentage both for August 21 itself and for a week centered around 21st Aug; i.e. from 18th – 24th Aug. For each pixel, we average the cloud cover fraction over the 12 years, and report that fraction. Therefore, a 20% chance of cloud cover can be interpreted as either a 20% chance of 100% clouds (and therefore an 80% chance of it being clear) or as 100% chance of 20% cloud cover. Either way one would seem to have a 20% chance of not seeing the eclipse, though in practice the latter case might give one a better opportunity of driving a few miles for a clear view.
The widget at the upper right of the map lets you choose whether to look at cloud coverage for just the eclipse path or the whole contiguous US, and whether to show the average for just 8/21 or averaged over the week centered on 21st Aug (18th – 24th Aug).