Published: 2008-08-05 11:39:37
Updated: 2008-08-05 11:39:37
Posted August 5, 2008
By Jesse Richuso
MIKE MOSS SAYS: Jesse, Data that makes for a nice clean answer is a little lacking for that, but there are some numbers that tend to support the idea (and it fits with my general perception) that there is a "best season" for skywatching, and that would be the Fall in our area. Some of the reasons I lean that way are the following. For winter, we average about 25% clear skies at night, for summer about 13% clear at night, and fall about 26% clear at night. Beyond the completely clear situation however, we can also look at percent cloud cover, to allow a little more for the cases where there are some clouds around but still plenty of open sky. For winter, we average about 60% cloud cover at night, for summer it's 59% and for fall only 52%. All of those numbers are taken from cloud atlas maps available at
A couple of other comparative numbers that are more specific to climate records from RDU, for example, include that for winter RDU averages about 4.5 eigths (oktas) cloud cover, with 4.6 for sumer and 4.0 for fall, and the number of clear days per monthis 9.2 for winter, 7.4 for summer and 11.2 for fall.
The specific numbers for RDU imply a little less cloud cover than those from the cloud atlas, probably because of averaging in some nearby stations along the coast or in the mountains that may be a little cloudier on average. Still, both sources support the idea that summer isn't the best of our seasons. Just based on meteorological principles and the kinds of weather patterns that predominate, I would narrow things down a little more and say probably the "prime" period for a combination of clear or mostly clear skies, good "seeing" properties and still not too cold, would be from about late September through mid-November.