The eclipse is Monday, and our confidence in the forecast is about as high as it’s going to get, but not perfect.

The good news is that viewing conditions should be decent over a substantial portion of the path of totality, with our highest confidence in mostly clear skies in western areas.

But all it takes is a small patch of clouds to spoil viewing — especially if it arrives during the one or two minutes of eclipse totality. The zone from Nebraska to South Carolina is where unwelcome clouds have the best chance to cover parts of the sky — especially along the western and eastern parts of this zone.

You can track cloud cover at this link: National Weather Service satellite image

Forecast notes

Overall forecast confidence: Medium to High

  • Viewing in the West should be great with just some patchy areas dealing with light haze and smoke (and smoky skies could enhance colorization).
  • The coastal Southeast and northern Midwest have the best chance of cloud cover and compromised viewing.
  • While passing clouds are possible, viewing conditions look pretty good in the interior Southeast.

Local forecasts

Forecast confidence: High

  • Corvallis, Ore.: Looks great!
  • Madras, Ore.: Looks great!
  • Rexburg, Idaho: Looks great!
  • Casper, Wyo.: Mostly sunny, patchy smoke/haze possible, limited interference
  • Grand Island, Neb.: Partly cloudy, frequent interference possible
  • St. Joseph, Mo.: Partly cloudy, some interference
  • St.  Louis: Partly cloudy, occasional interference possible
  • Carbondale, Ill.: Partly cloudy, occasional interference possible
  • Hopkinsville, Ky.: Partly cloudy, occasional interference possible
  • Nashville: Scattered clouds, some limited interference possible

Forecast confidence: Medium-High

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

Model forecasts

In the graphic below, showing the high-resolution NAM 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.


High-resolution NAM model cloud cover forecast at 2 p.m. Monday. (StormVistaWxModels.com)

The model shows prime viewing in the West while patchy cloud cover is seen in the Midwest and East, especially in the northern Midwest and toward the Southeast coast.

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.

You can compare our cloud cover forecast with the National Weather Service’s outlook, provided below (in its map, blue indicates clear skies, gray indicates cloudy skies):


(National Weather Service)

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 report.

The first coast-to-coast solar eclipse in almost 100 years moved across the U.S. at 2,000 mph on Aug. 21. Here are some highlights. (Erin Patrick O'Connor/The Washington Post)