The eclipse is just a day away, and our confidence in the forecast continues to grow. We wish that it could be clear across the entire United States for this awesome event, but unfortunately there will be clouds in many places, including along the path of totality.

Forecast notes

Overall forecast confidence: Medium to high

  • The Southeast and Midwest are still the areas expected to have the most challenging viewing.
  • In the southern Midwest, be prepared to drive to identify better viewing; high cloud cover present here may allow for some less obstructed viewing.
  • Generally, the West is still best, but scattered smoke and haze issues are difficult to predict.

Local forecasts

Forecast confidence: Medium to high

  • Corvallis, Ore.: Morning fog likely to burn off in time for good view
  • Madras, Ore.: Mostly clear but light smoke or haze possible
  • Rexburg, Idaho: Scattered clouds, light haze or smoke possible
  • Casper, Wyo.: Mostly sunny, smoke possible, limited interference
  • Grand Island, Neb.: Partly cloudy, frequent interference possible
  • St. Joseph, Mo.: Partly cloudy, frequent interference possible
  • St.  Louis: Partly cloudy, occasional interference possible
  • Carbondale, Ill.: Partly cloudy, occasional interference possible
  • Hopkinsville, Ky.: Partly cloudy, occasional interference possible
  • Nashville: Scattered clouds, limited interference

Forecast confidence: Medium

  • Greenville, S.C.: Partly to mostly cloudy, occasional to frequent interference
  • Columbia, S.C.: Partly to mostly cloudy, occasional to frequent interference
  • Charleston: Partly to mostly cloudy, frequent interference possible

Model forecasts

We are well within range of our best forecast models, including the American Global Forecast System (GFS), North American Model (NAM) and European models. Below are illustrations of the cloud cover that these models are predicting as of Sunday.

In the graphic below, showing the GFS model, clouds are displayed in gray — the darker the gray, the more cloud cover predicted. It doesn’t exactly match what we’ve illustrated in our forecast map at the top of this article. That’s because it is just a single prediction from a single model.


GFS model cloud cover forecast at 2 p.m. Monday, Aug. 21. (StormVistaWxModels.com)

For another point of view, below is the cloud cover forecast from the European model:


European model cloud cover forecast at 2 p.m. Monday, Aug. 21. (StormVistaWxModels.com)

And lastly, this is the cloud cover forecast from the North American model:


NAM model cloud cover forecast at 2 p.m. Monday, Aug. 21. (StormVistaWxModels.com)

For the Capital Weather Gang cloud cover forecast, we take into account all the models’ predictions as well as what we know about typical August conditions.

Finally, note that the above maps display the model forecasts for total cloud cover, which take into account both high and low clouds. In some areas, their illustration is probably overly pessimistic because the eclipse may still be viewable through high, thin clouds.


Average weather 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 Monday is focused in western areas, and the chance of cloud cover increases as you head east.


(NASA)

Additional cloud cover resources:

Jason Samenow contributed to this post.

Capital Weather Gang's Angela Fritz breaks down what will happen when a total solar eclipse crosses the U.S. on Aug. 21. (Claritza Jimenez,Daron Taylor,Angela Fritz/The Washington Post)