You can also see if there is a sponsored ClearSky Clock in your area. If so
you can get past forecasted data for cloud cover, seeing transparency, etc.
If have found these forecast clocks to be very accurate. Here is the one
for my observatory.
http://cleardarksky.com/clmt/c/JATObPAct.html

-JATO
http://jatobservatory.org



On Mon, 21 Feb 2005 18:58:57 -0600, Jim wrote:

On Sun, 20 Feb 2005 11:43:58 GMT, "W. Wat son"
wrote:

Is there a source that will tell me how many clear days a particular region
(city) has had over some period of time? In particular, I'd like to know
how many clear (reasonably cloudless) days we've had since Oct. 1, 2004.


Try

http://www.wrh.noaa.gov/climate/index.php?wfo=sto

Select "Monthly Weather Summary CLM" Sacremento

and select each of the months that you want data for.

CLIMATE REPORT
NATIONAL WEATHER SERVICE SACRAMENTO, CA
952 AM PST TUE FEB 1 2005

...................................
snip
SKY COVER
POSSIBLE SUNSHINE (PERCENT) MM
AVERAGE SKY COVER 0.80
NUMBER OF DAYS FAIR 3
NUMBER OF DAYS PC 8
NUMBER OF DAYS CLOUDY 20

AVERAGE RH (PERCENT) 87

snip

and total it all up.

Jim