We are publishing regular cloud forecast updates leading up to the total solar eclipse on Aug. 21. Confidence is still fairly low but will get higher and our predictions more specific in the days leading up to the big event.
Overall forecast confidence: Low to medium
- Increased partly cloudy risk for lower Mississippi Valley
- Cloudiest risks still reside in upper Midwest and parts of Four Corners area
- Afternoon thunderstorms in Southeast still look hit or miss
Forecast confidence: Medium
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 look likely
Forecast confidence: Low to medium
Grand Island, Neb.: Greatest risk area for mostly cloudy conditions
St. Joseph, Mo.: Partly cloudy, occasional interference a concern
St. Louis: Partly cloudy, occasional interference possible
Carbondale, Ill.: Partly cloudy, occasional interference possible
Hopkinsville, Ky.: Scattered clouds, limited interference
Nashville: Scattered clouds, limited interference
Forecast confidence: 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
Also notable: We are well-within range of the best global forecast models, including the GFS. This is the cloud cover that model is predicting as of Thursday.
In this graphic, clouds are shown in blue. It doesn’t exactly match what we’ve illustrated above. That’s because these are just single predictions by individual models; the Capital Weather Gang forecast takes into account all of the models’ predictions as well as what we know about typical August conditions. So, as always, take these with a grain of salt.
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.