Eclipse Forecast Update at T-1 Day

"Eclipse viewing is about synoptic possibilities, 

but succeeding or failing based on unresolved cloud processes" 

– Slight paraphrasing of quote about storm chasing from meteorologist Chuck Doswell

Model forecasts have trended in the "right" direction since our post on outlooks for the eclipse on Friday.  At that time, the models, such as the NAM below, alled for a short-wave trough to be over Idaho at eclipse time, with at least partial cloud cover over portions of Idaho and Wyoming.

As I write this, the latest (0600 UTC) NAM forecast calls for that short-wave trough to be both further east and weaker, with the Pacific coast ridge also shifted further east.  Much of Oregon is still in a prime spot for lack of cloud cover, but the situation, at least synoptically, is better for Idaho and the Jackson area than one would have anticipated from the forecasts on Friday.

If we look at time-height sections, however, there remains one concern to give me a little heartburn, and that is a sliver of upper-level moisture coming through around the time of the eclipse, as evident in both the Sun Valley and Jackson time-height sections.  Note, in particular, the area of higher relative humidity air in both sections [note that time increases to the left and that the eclipse occurs just prior (to the right) of 18Z Mon].

Because of that sliver, one can't rule out the possibility of some high clouds being around.  The odds are low, but non-zero, an perhaps higher in Jackson than the central Idaho mountains.

There's also some smoke around, as evident in satellite imagery from 13:55 UTC this morning. 

Source: CIRA

The webcam from Stanley looks pretty good this morning, however, so perhaps it is not dense enough to be a concern.  

By and large, the synoptic odds for eclipse viewing look good.  The primary issue now is whether or not unresolved cloud processes throw a low probability monkey wrench over your location at the time of the eclipse.