I'm working on a project for a GIS course, I chose to find the best locations for the placement of an observatory. To accomplish this I planned to use cloud cover (or percentage of clear nights), proximity to existing roads (probably a TIGER file), Some measure of light pollution (I have found a few good rasters for this), I was also considering adding elevation to this project too, but I think I can find a good DEM to use. I am having trouble locating any data for cloud cover. I am thoroughly inexperienced with meteorological data and some of the filetypes I've found I have no idea what to do with, I found one other question on here about it but none of the answers really got me anywhere. If anyone can point me in the right direction that would be great.
Part of the problem might be with your search term. 'Cloud Cover' is typically discussed in the context of sat imagery and specifically a percentage of blocked image. You're looking for cloud (or clear sky) frequency.
This is often a factor in studies to locate solar power facilities. Going down that route might skew your data since they're primarily concerned with clear days and you're looking for nights. But one example I noted was http://www.nrel.gov/gis/data_solar.html
Another potential source, depending on the time window and resolution you need is http://www.cgiar-csi.org/data/uea-cru-ts-v3-10-01-historic-climate-database which tracks nine climate variables globally from 1901 to 2006 at 0.5 degree resolution.