[AZ-Observing] Clear Sky Chart History Plots for Vekol Rd.
- From: Tom Polakis <tpolakis@xxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Tue, 10 Feb 2009 17:46:25 -0500
I learned recently that sponsored Clear Sky Charts have a “Forecast
History/Climate” link. I am interested in the astro-climate of the Arizona
desert, and paying for something I use all the time seemed like a good idea.
So I sent webmaster Attilla Danko some PayPal funds, and sponsored the existing
Vekol Road Clear Sky Chart.
There is now a CSC “history” page for Vekol Road (about 50 miles south of
Phoenix). He points out up front that these are only summaries of past
forecasts, and are not to be confused with actual climate data, which of course
does not exist as this level. The cloud, transparency, and seeing forecast
data for the past 2 ¼ years are here:
http://www.cleardarksky.com/clmt/c/VklRdAZct.html
It’s probably best to skip over the “Observing Conditions” charts, and just
scroll a quarter of the way down to Individual Forecasts. In the overall
summary, the percent of “clear” hours is 69%. Deep-sky observing requires
perfectly transparent nights, however, and that number is 47%. Since he
summarizes transparency only for nights with 30% or less cloud cover (and I
wish he wouldn’t), the percentage of perfectly transparent hours is actually
about 37%. That sounds about right; 1 in 3 nights is photometric. The summary
shows 8% of the nights having 5-out-of-5 seeing, and another 36% as 4/5. My
experience has been that even 3/5 seeing makes a mess out of planets.
Following the overall summary is a breakdown by month, which predictably shows
the most cloudless conditions in June and October, and the most cloudy nights
in August. I’m not so sure about April looking as good as it does on the
summary, as it seems in reality to be a period of dry conditions, but frequent
cirrus clouds.
The monthly seeing summary is interesting, as it shows the best seeing
occurring in August, followed by July. I wonder if the forecast models used by
the CSC are missing sources of poor seeing located near the surface, or if I’m
just not out enough in that miserable time of year to see how good it is.
Maybe the lack of good seeing during the Spring months is real, and due to the
ever-present strong winds aloft.
In case you’re disappointed with how clear it really is in the Arizona desert,
it’s a good morale booster to compare it side-by-side with the data for
Buffalo, New York.
http://www.cleardarksky.com/clmt/c/BuffaloNYct.html
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