Forecast confidence: Low to medium
- The cloudiest conditions continue to be in the Midwest
- Low cloud issues and fog along the West Coast will most likely burn off in time for the eclipse, except for maybe the northern Washington coast
- Afternoon thunderstorms in the Southeast will be an issue, but there’s no way to know exactly where those will pop up
- Some parts of the West near wildfires will be prone to haze
Corvallis, Ore.: Morning fog likely to burn off in time for good view
Madras, Ore.: Mostly clear but light smoke haze possible
Rexburg, Idaho: Mostly clear — just few clouds possible
Casper, Wyo.: Partly cloudy, breaks possible
Grand Island, Neb.: Greatest risk area for mostly cloudy conditions
St. Joseph, Mo.: Partly cloudy, occasional interference a concern
St. Louis: Partly cloudy, some slight interference possible
Carbondale, Ill.: Scattered clouds, limited interference
Hopkinsville, Ky.: Scattered clouds, limited interference
Nashville: Scattered clouds, limited interference
Confidence: Very low
Greenville, S.C.: Partly cloudy, occasional interference possible
Columbia, S.C.: Partly cloudy, occasional interference a notable concern
Charleston: Partly cloudy, occasional interference possible
Average weather conditions for Aug. 21
The timing of the eclipse is ideal, at least for the West. It begins just after 10 a.m. local time on the West Coast, which is usually enough time to burn off the fog that often occurs there.
The intermountain areas sometimes see thunderstorms bubble up in the afternoons during this time of year. These are associated with the Southwest monsoon, a period of increased thunderstorms and rain during the late summer and early fall. But the eclipse passes through this region around noon, before most of the storms develop, so the storm risk should be low there.
Clouds often pop up along the rest of the path throughout the day simply because of warmth and moisture. Those two things combined lead to rising air, which creates clouds. So the cloud risk gets greater the farther east you go. On top of that, South Carolina will see totality the latest in the day — after 2:30 p.m.
NASA created the map below, which shows how, on average, the best chance of clear skies Aug. 21 focuses in western areas, and the chance of cloud cover increases as you head east.
Additional cloud cover resources:
Jason Samenow contributed to this post.