Forecast prepared on Aug. 11, 2017.

We are publishing regular cloud forecast updates leading up to the total solar eclipse on Aug. 21. We can begin to assemble some likelihoods from historical cloud cover tendencies and very generalized weather patterns predicted by models. But confidence is still quite low. Our confidence will get higher and our predictions more specific as we approach the big event.

The eclipse is now just 10 days away, and we are about at the point where forecast models can start piecing together the general weather pattern for Aug. 21. However, not until about three to five days prior to the eclipse — or even later — will regional details start to come into focus. So we still must paint the cloudiness outlook with a very broad strokes. Continue to take it with a grain of salt and we would not recommend altering plans based on it.

Forecast notes as of Aug. 11:

Forecast confidence: Low

  • The possibility of an approaching cold front raises the risk of clouds for Washington and Oregon. Smoke in Pacific Northwest could be less extensive as the front could push smoke north into Canada
  • Possible storm system in center of country poses greatest risk for extensive cloud cover.
  • Midday to afternoon storm chances exist in many areas in the South and Southeast but, for most, would still allow breaks in the cloud cover.
  • The Northern Rockies still appear to be best bet for clear viewing, but nothing is yet locked in.

Our next forecast will be issued Aug. 14, one week before the eclipse.


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.

Link: More eclipse coverage from The Washington Post

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 on Aug. 21 focuses 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)