Stargate Colorado Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Stargate Colorado Observatory clear sky chart from 2005-11-06 to 2026-04-17.

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	3 4 2 5% 4 4 5% 4 6% 8% 56%	140053
	Night	3 5% 2 5% 3 3 4 3 5% 7% 59%	139577
Transparency	Day	15% 38% 6% 14% 18% 10%	135091
	Night	16% 37% 5% 14% 18% 9%	135547
Seeing	Day	8% 17% 31% 27% 14% 3	17261
	Night	7% 12% 35% 33% 12% 1	27416

By Month

Percentage Cloud Cover SW (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	1 5% 4 6% 3 3 3 3 5% 7% 60%	4720
	11th to 20th	Day	1 3 2 3 2 2 3 3 4 5% 72%	5177
	21st to end	Day	1 6% 2 4 3 4 4 3 5% 6% 62%	5844
February	1st to 10th	Day	1 4 3 6% 3 2 3 3 5% 8% 63%	1995
	11th to 20th	Day	1 4 2 4 3 4 4 3 5% 9% 61%	2049
	21st to end	Day	1 5% 2 5% 4 3 3 3 5% 6% 63%	1730
March	1st to 10th	Day	1 9% 3 4 3 2 2 3 4 5% 65%	4600
	11th to 20th	Day	4 11% 4 6% 3 3 3 3 6% 6% 51%	5005
	21st to end	Day	2 6% 2 4 3 3 4 3 6% 8% 58%	6000
April	1st to 10th	Day	3 5% 1 4 3 3 4 3 5% 8% 60%	2520
	11th to 20th	Day	5% 6% 2 5% 3 4 4 3 5% 7% 56%	2444
	21st to end	Day	4 6% 2 5% 3 3 5% 4 6% 9% 53%	2400
May	1st to 10th	Day	7% 7% 2 5% 3 3 4 4 5% 7% 53%	5578
	11th to 20th	Day	5% 5% 1 4 3 4 4 4 5% 7% 58%	5862
	21st to end	Day	3 4 1 4 4 4 4 4 8% 9% 55%	6925
June	1st to 10th	Day	4 4 2 4 3 5% 7% 7% 8% 10% 47%	2800
	11th to 20th	Day	3 3 1 3 3 4 5% 5% 8% 9% 57%	2800
	21st to end	Day	5% 4 2 6% 4 5% 6% 6% 8% 9% 46%	2800
July	1st to 10th	Day	3 3 1 3 4 5% 6% 6% 9% 10% 50%	6339
	11th to 20th	Day	2 3 1 5% 5% 6% 9% 6% 9% 11% 43%	6340
	21st to end	Day	5% 4 2 7% 7% 7% 7% 7% 8% 9% 37%	6524
August	1st to 10th	Day	3 3 1 6% 5% 6% 8% 7% 10% 10% 40%	5489
	11th to 20th	Day	3 3 1 5% 4 6% 7% 6% 9% 12% 44%	5366
	21st to end	Day	4 4 2 7% 6% 6% 7% 6% 8% 10% 40%	5984
September	1st to 10th	Day	4 5% 2 5% 4 5% 5% 4 6% 8% 52%	2400
	11th to 20th	Day	5% 3 1 5% 3 4 4 4 6% 7% 59%	2345
	21st to end	Day	4 3 2 4 3 3 3 3 5% 5% 64%	2200
October	1st to 10th	Day	3 3 1 3 2 2 3 2 4 6% 71%	3405
	11th to 20th	Day	5% 3 1 3 2 2 3 4 6% 9% 62%	3250
	21st to end	Day	3 3 1 3 2 2 2 2 3 4 74%	3489
November	1st to 10th	Day	2 4 1 3 2 2 3 3 4 6% 72%	1853
	11th to 20th	Day	1 3 1 5% 3 3 3 2 4 6% 68%	1890
	21st to end	Day	3 5% 2 5% 3 2 3 3 3 6% 64%	1890
December	1st to 10th	Day	1 3 2 3 2 1 2 2 3 6% 76%	2842
	11th to 20th	Day	1 4 2 4 3 2 3 3 5% 8% 65%	3106
	21st to end	Day	1 3 2 5% 3 3 3 3 5% 7% 64%	4092
January	1st to 10th	Night	1 7% 4 8% 4 3 4 3 5% 7% 55%	8201
	11th to 20th	Night	1 2 1 5% 3 3 3 3 4 5% 71%	7858
	21st to end	Night	1 4 2 5% 3 3 3 3 4 7% 63%	8370
February	1st to 10th	Night	1 6% 2 5% 3 3 3 2 4 6% 64%	2623
	11th to 20th	Night	2 5% 3 4 4 3 3 4 6% 6% 60%	2458
	21st to end	Night	1 4 1 4 2 3 3 2 4 6% 69%	2076
March	1st to 10th	Night	2 8% 2 4 3 2 3 2 3 5% 66%	5494
	11th to 20th	Night	5% 9% 3 5% 3 3 3 3 4 6% 56%	5207
	21st to end	Night	2 6% 2 3 3 2 3 3 5% 7% 65%	5199
April	1st to 10th	Night	3 4 2 3 3 3 3 3 5% 6% 65%	2100
	11th to 20th	Night	4 6% 2 5% 3 3 3 3 5% 7% 59%	2037
	21st to end	Night	6% 7% 2 4 3 3 3 3 5% 8% 56%	2000
May	1st to 10th	Night	8% 10% 3 4 3 2 2 2 4 6% 56%	4388
	11th to 20th	Night	6% 5% 1 4 3 3 3 3 5% 8% 59%	4036
	21st to end	Night	5% 6% 2 5% 4 3 4 4 5% 7% 57%	3972
June	1st to 10th	Night	4 4 2 4 3 3 4 5% 7% 9% 55%	1600
	11th to 20th	Night	2 3 1 4 4 3 4 4 7% 7% 61%	1600
	21st to end	Night	5% 4 2 5% 4 5% 6% 4 9% 11% 47%	1600
July	1st to 10th	Night	5% 4 2 4 4 5% 5% 5% 8% 10% 48%	3640
	11th to 20th	Night	4 3 1 5% 5% 6% 7% 6% 9% 10% 44%	3640
	21st to end	Night	6% 5% 2 6% 5% 6% 6% 6% 9% 10% 39%	4331
August	1st to 10th	Night	5% 4 2 6% 5% 6% 7% 6% 8% 10% 44%	4323
	11th to 20th	Night	4 3 1 4 3 5% 5% 6% 11% 15% 43%	4483
	21st to end	Night	6% 6% 3 7% 5% 6% 6% 5% 10% 12% 35%	4993
September	1st to 10th	Night	5% 4 2 4 3 4 4 4 7% 9% 55%	2000
	11th to 20th	Night	5% 4 1 3 3 3 2 3 5% 8% 63%	2055
	21st to end	Night	3 4 1 4 3 3 3 3 5% 7% 64%	2200
October	1st to 10th	Night	3 3 1 3 2 3 3 2 4 5% 71%	3778
	11th to 20th	Night	5% 3 1 4 2 2 3 3 5% 7% 64%	3898
	21st to end	Night	3 4 2 4 2 2 2 2 3 4 74%	4279
November	1st to 10th	Night	2 3 1 3 2 2 2 3 4 6% 72%	2665
	11th to 20th	Night	1 3 1 3 2 2 2 3 4 6% 73%	2730
	21st to end	Night	2 5% 2 4 2 3 3 3 6% 7% 64%	2730
December	1st to 10th	Night	1 3 2 4 2 2 2 3 4 6% 70%	4564
	11th to 20th	Night	1 3 1 4 3 3 3 3 5% 9% 66%	5321
	21st to end	Night	1 5% 2 5% 3 3 4 3 5% 7% 61%	7128

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	22% 21% 4 19% 25% 9%	4723
	11th to 20th	Day	12% 21% 5% 17% 30% 15%	5177
	21st to end	Day	19% 23% 4 14% 27% 13%	5844
February	1st to 10th	Day	7% 58% 3 10% 12% 8%	1995
	11th to 20th	Day	8% 58% 3 12% 14% 6%	2059
	21st to end	Day	7% 60% 2 7% 14% 11%	1730
March	1st to 10th	Day	15% 28% 2 4 26% 25%	4600
	11th to 20th	Day	25% 29% 4 9% 22% 12%	5005
	21st to end	Day	16% 28% 5% 29% 20% 3	6000
April	1st to 10th	Day	10% 59% 4 11% 12% 4	2520
	11th to 20th	Day	12% 61% 4 9% 9% 6%	2447
	21st to end	Day	12% 62% 4 10% 10% 2	2400
May	1st to 10th	Day	22% 31% 7% 16% 14% 11%	5578
	11th to 20th	Day	17% 30% 3 9% 20% 20%	5866
	21st to end	Day	14% 32% 7% 16% 14% 17%	6926
June	1st to 10th	Day	9% 65% 7% 9% 7% 3	2800
	11th to 20th	Day	7% 63% 5% 7% 10% 9%	2800
	21st to end	Day	11% 62% 5% 10% 7% 5%	2800
July	1st to 10th	Day	14% 31% 9% 15% 20% 11%	6271
	11th to 20th	Day	21% 31% 14% 20% 12% 2	6265
	21st to end	Day	27% 31% 10% 14% 13% 6%	6337
August	1st to 10th	Day	22% 41% 13% 16% 7% 2	3995
	11th to 20th	Day	14% 40% 11% 15% 11% 9%	3882
	21st to end	Day	20% 40% 10% 18% 9% 3	4311
September	1st to 10th	Day	11% 59% 5% 11% 9% 5%	2400
	11th to 20th	Day	10% 58% 3 9% 13% 7%	2345
	21st to end	Day	11% 58% 3 8% 13% 8%	2200
October	1st to 10th	Day	7% 36% 3 8% 32% 14%	3405
	11th to 20th	Day	12% 38% 6% 17% 19% 7%	3250
	21st to end	Day	8% 35% 2 9% 28% 18%	3489
November	1st to 10th	Day	8% 53% 3 9% 17% 11%	1853
	11th to 20th	Day	9% 54% 2 9% 17% 9%	1890
	21st to end	Day	12% 55% 3 9% 13% 8%	1890
December	1st to 10th	Day	6% 34% 2 16% 33% 9%	2842
	11th to 20th	Day	12% 30% 2 12% 29% 15%	3104
	21st to end	Day	14% 25% 3 17% 26% 14%	4092
January	1st to 10th	Night	25% 22% 3 19% 24% 7%	8202
	11th to 20th	Night	13% 22% 5% 21% 26% 13%	7858
	21st to end	Night	17% 24% 4 16% 26% 13%	8370
February	1st to 10th	Night	8% 59% 3 11% 12% 8%	2623
	11th to 20th	Night	10% 58% 4 12% 11% 5%	2458
	21st to end	Night	7% 59% 2 7% 15% 10%	2076
March	1st to 10th	Night	16% 28% 1 4 29% 21%	5494
	11th to 20th	Night	23% 29% 4 9% 20% 14%	5207
	21st to end	Night	14% 29% 2 31% 18% 5%	5199
April	1st to 10th	Night	9% 59% 4 13% 11% 4	2100
	11th to 20th	Night	11% 61% 5% 9% 9% 5%	2037
	21st to end	Night	12% 63% 6% 8% 9% 1	2000
May	1st to 10th	Night	23% 30% 5% 19% 10% 12%	4385
	11th to 20th	Night	16% 29% 4 14% 19% 17%	4037
	21st to end	Night	20% 32% 8% 11% 12% 17%	3972
June	1st to 10th	Night	10% 63% 8% 10% 6% 3	1600
	11th to 20th	Night	7% 63% 5% 7% 9% 8%	1600
	21st to end	Night	12% 62% 5% 8% 8% 4	1600
July	1st to 10th	Night	20% 30% 11% 16% 14% 9%	3600
	11th to 20th	Night	25% 30% 17% 20% 7% 1	3592
	21st to end	Night	28% 30% 11% 15% 12% 5%	4207
August	1st to 10th	Night	32% 40% 10% 12% 5% 1	3141
	11th to 20th	Night	14% 41% 16% 13% 13% 3	3243
	21st to end	Night	24% 41% 14% 16% 5% 1	3597
September	1st to 10th	Night	10% 59% 6% 13% 9% 4	2000
	11th to 20th	Night	9% 58% 5% 9% 11% 7%	2055
	21st to end	Night	9% 58% 4 9% 14% 7%	2200
October	1st to 10th	Night	11% 36% 2 10% 26% 15%	3778
	11th to 20th	Night	16% 38% 7% 14% 17% 7%	3898
	21st to end	Night	11% 35% 2 10% 29% 14%	4279
November	1st to 10th	Night	9% 53% 2 9% 18% 8%	2665
	11th to 20th	Night	7% 53% 2 11% 18% 9%	2730
	21st to end	Night	12% 54% 4 11% 12% 8%	2730
December	1st to 10th	Night	9% 34% 2 20% 27% 7%	4564
	11th to 20th	Night	11% 31% 2 12% 31% 14%	5322
	21st to end	Night	17% 26% 5% 16% 24% 12%	7128

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	7% 20% 40% 22% 10% 1	330
	11th to 20th	Day	9% 18% 40% 25% 6% 2	330
	21st to end	Day	4 23% 36% 23% 11% 2	363
February	1st to 10th	Day	6% 25% 39% 22% 7% 1	330
	11th to 20th	Day	11% 29% 35% 20% 4 1	330
	21st to end	Day	17% 24% 34% 20% 4	273
March	1st to 10th	Day	10% 27% 35% 21% 8%	330
	11th to 20th	Day	13% 25% 33% 20% 7% 1	487
	21st to end	Day	15% 34% 32% 14% 4 1	594
April	1st to 10th	Day	14% 28% 37% 15% 5% 1	540
	11th to 20th	Day	16% 34% 35% 12% 3 1	517
	21st to end	Day	12% 33% 35% 16% 3	500
May	1st to 10th	Day	11% 26% 37% 20% 6% 1	563
	11th to 20th	Day	11% 17% 33% 25% 12% 2	725
	21st to end	Day	9% 20% 35% 25% 10% 2	789
June	1st to 10th	Day	5% 14% 27% 30% 20% 4	730
	11th to 20th	Day	5% 13% 35% 29% 15% 2	730
	21st to end	Day	6% 9% 33% 29% 20% 3	730
July	1st to 10th	Day	5% 7% 23% 32% 27% 5%	721
	11th to 20th	Day	4 1 17% 38% 32% 8%	718
	21st to end	Day	4 2 16% 37% 30% 10%	633
August	1st to 10th	Day	5% 4 24% 34% 24% 8%	527
	11th to 20th	Day	3 4 26% 43% 19% 5%	517
	21st to end	Day	5% 4 25% 43% 19% 4	583
September	1st to 10th	Day	5% 5% 27% 39% 19% 5%	530
	11th to 20th	Day	5% 12% 30% 31% 19% 4	475
	21st to end	Day	7% 12% 25% 32% 20% 4	330
October	1st to 10th	Day	7% 19% 25% 25% 17% 6%	330
	11th to 20th	Day	9% 21% 27% 24% 14% 5%	330
	21st to end	Day	12% 17% 29% 27% 13% 2	363
November	1st to 10th	Day	5% 22% 33% 26% 12% 2	330
	11th to 20th	Day	7% 16% 33% 29% 12% 3	330
	21st to end	Day	11% 18% 34% 24% 10% 3	330
December	1st to 10th	Day	6% 22% 36% 25% 10% 1	330
	11th to 20th	Day	6% 18% 42% 27% 7% 1	330
	21st to end	Day	9% 23% 40% 23% 5%	363
January	1st to 10th	Night	5% 13% 36% 35% 10% 1	1050
	11th to 20th	Night	7% 12% 38% 33% 8% 2	918
	21st to end	Night	5% 12% 38% 35% 10%	924
February	1st to 10th	Night	7% 16% 42% 29% 7%	840
	11th to 20th	Night	7% 21% 44% 22% 6%	824
	21st to end	Night	6% 17% 46% 28% 2	692
March	1st to 10th	Night	8% 20% 39% 29% 5%	840
	11th to 20th	Night	9% 15% 38% 29% 7%	840
	21st to end	Night	8% 22% 40% 24% 6%	746
April	1st to 10th	Night	8% 20% 45% 23% 3	630
	11th to 20th	Night	9% 23% 38% 26% 3	611
	21st to end	Night	12% 17% 39% 25% 7%	600
May	1st to 10th	Night	11% 14% 35% 32% 8% 1	600
	11th to 20th	Night	12% 11% 33% 32% 10% 1	591
	21st to end	Night	9% 14% 38% 29% 8% 1	650
June	1st to 10th	Night	6% 9% 37% 32% 15% 1	600
	11th to 20th	Night	5% 11% 42% 34% 9%	600
	21st to end	Night	7% 8% 29% 39% 16% 2	600
July	1st to 10th	Night	4 8% 25% 40% 21% 2	585
	11th to 20th	Night	6% 2 22% 43% 24% 3	582
	21st to end	Night	7% 2 21% 37% 29% 3	657
August	1st to 10th	Night	5% 2 19% 37% 32% 5%	597
	11th to 20th	Night	7% 3 25% 39% 24% 2	594
	21st to end	Night	4 3 28% 39% 24% 3	660
September	1st to 10th	Night	5% 6% 27% 42% 19% 2	600
	11th to 20th	Night	7% 10% 29% 36% 17% 2	600
	21st to end	Night	6% 12% 31% 34% 15% 2	600
October	1st to 10th	Night	8% 14% 34% 30% 13% 2	710
	11th to 20th	Night	5% 9% 33% 37% 13% 2	800
	21st to end	Night	8% 9% 31% 36% 13% 3	895
November	1st to 10th	Night	5% 13% 32% 36% 13% 1	1025
	11th to 20th	Night	4 14% 37% 34% 10% 2	1050
	21st to end	Night	6% 14% 32% 34% 12% 2	1050
December	1st to 10th	Night	4 12% 41% 34% 8% 1	1050
	11th to 20th	Night	5% 12% 41% 33% 9%	1050
	21st to end	Night	8% 15% 37% 33% 6% 1	1155

Page generated at 2026-04-14 00:44:24. Version ac07

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