12:00 Noon, Thursday, August 17, 2017
We are just 4 days away from the total eclipse and I wish the potential for clear skies was greater than it is. This blog will focus on Colorado (where a partial eclipse will occur), and the narrow totality path across Wyoming and Nebraska where most Front Range folks seeking totality will end up on Monday.
Let me start by saying that the chance for midday clear skies this time of year according to climatology is on the order of 80%. It’s a bit less than 80% directly over the mountains where daytime cumulus clouds get their start, and also a little less in central and eastern Nebraska where it is typically more humid.
So what I look for is whether the atmospheric moisture is likely to be below average, average, or above average. When I wrote last week it appeared that atmospheric moisture would be near or below average on the 21st. But now it appears that our flow will be from the south and southwest at different levels of the atmosphere which will likely increase the moisture content, especially on the plains. Let me point out that atmospheric moisture does not necessarily result in clouds (water vapor is invisible), but it makes it easier for clouds to form. A moister atmosphere may result in early development of thundershowers over the mountains on Monday and lingering patches of cirrus clouds from the previous day’s thunderstorms across any part of the region. The worst case scenario is a frontal boundary that could trigger development of a broad area of clouds. Current indications are that there may be an east-west frontal boundary somewhere in the northern Kansas-Nebraska-South Dakota region extending westward toward the Front Range. There is a chance the front will be weak, or north of the eclipse path, but for now this is what I see as the likely scenario:
- western & central Wyoming has a good chance of clear skies (similar to climatology)
- eastern Wyoming and Colorado have less than the climatological chance for clear skies, but still a little better than 50%
- as you go eastward along the total eclipse path in Nebraska, the chance of clear skies slips below 50%
There are of course a lot of opinions about the complicated cloud forecast. For another opinion see the Washington Post’s Capital Weather Gang: https://www.washingtonpost.com/news/capital-weather-gang/wp/2017/08/17/total-solar-eclipse-weather-forecast-as-of-aug-17/?utm_term=.41adcb6ae557