Colorado Skies Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Colorado Skies Observatory clear sky chart from 2003-08-01 to 2005-11-07.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	9% 6% 5% 6% 49%	8683
	Night	12% 5% 6% 50%	8484
Transparency	Day	13% 9% 25% 30% 20%	6034
	Night	13% 10% 27% 29% 18%	5773
Seeing	Day	17% 31% 35% 13%	532
	Night	6% 20% 40% 29%	2762

By Month

Percentage Cloud Cover
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month		Occurrence of each Forecast	Data Points
January	Day	20% 7% 5% 5% 40%	549
	Night	23% 5% 6% 44%	804
February	Day	25% 10% 5% 32%	530
	Night	22% 7% 5% 5% 6% 33%	715
March	Day	7% 5% 55%	681
	Night	9% 5% 58%	681
April	Day	14% 7% 48%	718
	Night	15% 55%	602
May	Day	5% 5% 5% 63%	812
	Night	6% 62%	552
June	Day	7% 5% 6% 62%	840
	Night	68%	477
July	Day	8% 5% 7% 10% 52%	795
	Night	10% 7% 8% 10% 40%	557
August	Day	9% 5% 10% 6% 7% 7% 36%	1163
	Night	8% 5% 5% 8% 5% 6% 8% 40%	879
September	Day	8% 5% 5% 59%	1010
	Night	7% 5% 5% 58%	934
October	Day	5% 5% 5% 6% 7% 5% 6% 8% 43%	620
	Night	14% 6% 5% 8% 46%	744
November	Day	14% 6% 6% 6% 6% 42%	470
	Night	13% 5% 6% 5% 48%	694
December	Day	12% 7% 5% 54%	495
	Night	13% 5% 53%	845

Transparency (when cloud cover <= 30%)
Color Meanings: Poor Below Average Average Above average Transparent
Month		Occurrence of each Forecast	Data Points
January	Day	28% 15% 34% 21%	275
	Night	23% 16% 39% 17%	457
February	Day	30% 9% 40% 19%	227
	Night	22% 13% 44% 17%	332
March	Day	10% 15% 26% 38% 8%	472
	Night	8% 12% 31% 35% 12%	462
April	Day	9% 6% 24% 38% 21%	427
	Night	11% 6% 23% 40% 17%	401
May	Day	7% 7% 19% 43% 21%	642
	Night	7% 9% 20% 42% 19%	419
June	Day	7% 5% 17% 32% 36%	681
	Night	6% 7% 16% 34% 35%	372
July	Day	16% 19% 20% 38%	619
	Night	15% 7% 21% 16% 39%	350
August	Day	20% 10% 23% 25% 19%	656
	Night	19% 13% 20% 21% 24%	504
September	Day	10% 8% 18% 31% 30%	755
	Night	11% 7% 16% 25% 38%	713
October	Day	15% 15% 24% 27% 16%	645
	Night	7% 12% 31% 32% 15%	757
November	Day	13% 15% 43% 24%	311
	Night	13% 16% 32% 29% 8%	454
December	Day	12% 9% 44% 30%	324
	Night	13% 5% 36% 39%	552

Seeing (when cloud cover <= 80%)
Color Meanings: Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month		Occurrence of each Forecast	Data Points
January	Night	7% 16% 39% 31%	204
February	Day	20% 60% 20%	5
	Night	8% 27% 48% 15%	185
March	Day	35% 30% 22% 11%	59
	Night	8% 31% 37% 22%	235
April	Day	33% 39% 23%	56
	Night	13% 27% 35% 22%	165
May	Day	26% 37% 34%	69
	Night	28% 41% 25%	185
June	Day	7% 28% 31% 27% 5%	119
	Night	5% 21% 40% 31%	179
July	Day	6% 30% 50% 12%	62
	Night	13% 39% 42%	183
August	Day	8% 28% 48% 14%	87
	Night	12% 38% 41%	267
September	Day	18% 29% 38% 13%	75
	Night	13% 41% 40%	287
October	Night	5% 15% 41% 34%	340
November	Night	14% 24% 36% 21%	254
December	Night	9% 22% 46% 20%	278

Page generated at 2008-06-05 21:07:24. Version ab11