Colorado National Monument
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Colorado National Monument clear sky chart from 2005-11-06 to 2025-11-03.

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	2 3 1 4 3 4 4 4 6% 8% 60%	135399
	Night	2 4 2 5% 4 4 4 4 6% 8% 58%	132140
Transparency	Day	20% 7% 12% 22% 24% 15%	130250
	Night	22% 8% 13% 23% 22% 12%	128292
Seeing	Day	4 7% 22% 34% 26% 7%	16667
	Night	5% 3 18% 46% 25% 2	26811

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 6% 2 7% 5% 5% 5% 5% 8% 9% 48%	4034
	11th to 20th	Day	1 3 2 6% 4 5% 5% 5% 7% 8% 54%	4100
	21st to end	Day	3 5% 2 5% 4 4 4 3 4 6% 60%	4510
February	1st to 10th	Day	2 6% 3 6% 5% 5% 6% 4 6% 8% 51%	1800
	11th to 20th	Day	3 8% 2 6% 4 5% 5% 4 6% 7% 50%	1755
	21st to end	Day	3 6% 1 6% 5% 4 5% 4 5% 6% 55%	1667
March	1st to 10th	Day	2 6% 2 5% 4 5% 5% 4 6% 7% 55%	4954
	11th to 20th	Day	3 7% 3 6% 4 5% 5% 5% 7% 8% 47%	5000
	21st to end	Day	2 5% 2 6% 5% 6% 7% 6% 7% 8% 45%	5486
April	1st to 10th	Day	3 4 2 4 4 5% 5% 4 6% 8% 56%	2361
	11th to 20th	Day	3 5% 1 6% 4 3 5% 4 6% 8% 55%	2371
	21st to end	Day	2 3 1 4 4 4 5% 5% 6% 9% 56%	2467
May	1st to 10th	Day	3 3 1 4 4 4 5% 4 7% 9% 56%	5880
	11th to 20th	Day	3 3 1 4 3 3 4 4 7% 8% 59%	5841
	21st to end	Day	1 2 1 3 2 3 4 4 7% 8% 64%	6880
June	1st to 10th	Day	2 2 1 3 3 3 5% 3 6% 7% 66%	2800
	11th to 20th	Day	2 2 2 2 3 2 2 4 7% 73%	2800
	21st to end	Day	1 1 1 2 2 3 3 3 6% 8% 71%	2800
July	1st to 10th	Day	1 1 1 2 2 3 3 3 4 5% 74%	6208
	11th to 20th	Day	1 2 1 2 2 3 4 4 9% 13% 60%	5880
	21st to end	Day	2 2 1 2 3 3 4 4 6% 9% 64%	6401
August	1st to 10th	Day	1 2 1 3 2 3 5% 4 8% 10% 60%	5779
	11th to 20th	Day	2 1 1 2 2 3 4 4 6% 7% 68%	5798
	21st to end	Day	4 3 1 4 3 4 4 4 7% 9% 57%	5989
September	1st to 10th	Day	4 2 1 3 2 2 3 3 5% 7% 68%	2400
	11th to 20th	Day	2 2 1 4 2 3 4 4 5% 7% 67%	2304
	21st to end	Day	3 2 1 3 3 3 3 2 4 5% 71%	2156
October	1st to 10th	Day	3 2 1 2 1 2 2 2 3 4 78%	3270
	11th to 20th	Day	4 3 1 4 3 4 4 4 6% 10% 58%	3250
	21st to end	Day	2 3 1 3 2 2 3 2 5% 8% 68%	3548
November	1st to 10th	Day	2 4 1 3 2 3 3 3 5% 7% 66%	1979
	11th to 20th	Day	3 2 1 4 3 3 4 3 5% 7% 65%	1681
	21st to end	Day	3 5% 2 4 3 3 3 3 5% 7% 62%	1600
December	1st to 10th	Day	1 4 2 5% 3 3 3 3 4 9% 64%	2620
	11th to 20th	Day	2 4 2 4 4 4 4 3 6% 9% 59%	3026
	21st to end	Day	3 8% 3 7% 4 5% 5% 4 6% 8% 49%	4004
January	1st to 10th	Night	1 7% 3 8% 5% 5% 6% 4 6% 8% 48%	5959
	11th to 20th	Night	2 5% 2 6% 5% 5% 4 4 6% 9% 51%	5880
	21st to end	Night	3 6% 2 6% 4 4 4 3 5% 6% 56%	6468
February	1st to 10th	Night	1 5% 3 7% 4 4 4 4 6% 9% 52%	2600
	11th to 20th	Night	2 7% 3 6% 3 5% 5% 4 6% 8% 49%	2532
	21st to end	Night	3 6% 2 6% 5% 5% 4 4 5% 7% 52%	1958
March	1st to 10th	Night	2 8% 2 5% 4 4 5% 4 5% 6% 54%	4940
	11th to 20th	Night	3 7% 3 6% 4 4 4 4 7% 9% 50%	5000
	21st to end	Night	2 5% 3 6% 6% 6% 6% 5% 7% 8% 46%	5489
April	1st to 10th	Night	3 4 2 4 5% 5% 5% 5% 5% 8% 53%	2038
	11th to 20th	Night	4 5% 2 5% 5% 5% 5% 4 5% 9% 52%	1977
	21st to end	Night	4 4 2 4 4 4 4 5% 8% 10% 52%	1930
May	1st to 10th	Night	5% 5% 2 5% 4 5% 4 5% 7% 8% 50%	4100
	11th to 20th	Night	2 3 1 5% 4 4 5% 5% 7% 9% 55%	4074
	21st to end	Night	2 2 1 3 3 3 4 4 6% 8% 63%	3999
June	1st to 10th	Night	1 3 1 3 3 3 4 4 5% 9% 65%	1600
	11th to 20th	Night	3 3 1 3 3 2 3 3 5% 6% 68%	1600
	21st to end	Night	1 2 2 2 3 3 3 6% 8% 70%	1600
July	1st to 10th	Night	2 1 1 3 2 3 4 4 6% 7% 67%	3766
	11th to 20th	Night	2 2 1 3 3 4 6% 5% 9% 13% 54%	4100
	21st to end	Night	1 2 1 3 3 3 5% 4 7% 9% 61%	4472
August	1st to 10th	Night	2 2 1 3 3 4 6% 5% 9% 10% 56%	4033
	11th to 20th	Night	2 2 1 3 3 3 4 4 6% 8% 65%	4051
	21st to end	Night	3 2 1 4 3 4 6% 6% 8% 9% 55%	4986
September	1st to 10th	Night	3 2 1 3 3 3 3 3 6% 6% 67%	2000
	11th to 20th	Night	2 2 1 3 3 3 4 2 5% 7% 68%	2092
	21st to end	Night	3 2 1 3 2 2 3 3 4 5% 72%	2242
October	1st to 10th	Night	3 2 1 2 2 2 2 2 4 5% 77%	3920
	11th to 20th	Night	3 2 1 3 3 4 5% 4 7% 7% 61%	3898
	21st to end	Night	4 4 2 4 3 3 2 2 4 5% 67%	4252
November	1st to 10th	Night	2 4 1 3 3 3 4 3 4 6% 66%	2364
	11th to 20th	Night	2 3 1 4 3 3 3 3 4 6% 68%	2695
	21st to end	Night	4 6% 2 4 4 3 3 3 5% 6% 60%	2800
December	1st to 10th	Night	2 4 2 4 3 3 3 2 3 5% 69%	4570
	11th to 20th	Night	2 4 1 4 3 3 5% 4 7% 8% 58%	5181
	21st to end	Night	4 7% 3 7% 5% 5% 4 4 6% 7% 48%	6974

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	28% 12% 23% 26% 10% 1	4035
	11th to 20th	Day	23% 11% 20% 25% 17% 4	4100
	21st to end	Day	26% 6% 16% 28% 20% 4	4510
February	1st to 10th	Day	29% 9% 20% 24% 14% 3	1800
	11th to 20th	Day	31% 8% 16% 27% 15% 2	1764
	21st to end	Day	27% 10% 10% 27% 21% 6%	1667
March	1st to 10th	Day	24% 8% 12% 24% 25% 6%	4954
	11th to 20th	Day	30% 8% 15% 27% 17% 3	5000
	21st to end	Day	30% 12% 14% 27% 15% 2	5486
April	1st to 10th	Day	24% 8% 10% 25% 23% 11%	2361
	11th to 20th	Day	24% 7% 11% 23% 26% 9%	2374
	21st to end	Day	20% 7% 12% 25% 28% 8%	2467
May	1st to 10th	Day	19% 11% 12% 21% 30% 9%	5880
	11th to 20th	Day	17% 7% 10% 22% 30% 14%	5844
	21st to end	Day	13% 7% 8% 18% 41% 13%	6881
June	1st to 10th	Day	14% 5% 8% 18% 32% 23%	2800
	11th to 20th	Day	13% 4 6% 10% 24% 43%	2800
	21st to end	Day	11% 4 6% 12% 26% 42%	2800
July	1st to 10th	Day	12% 3 6% 7% 15% 57%	6142
	11th to 20th	Day	13% 4 8% 16% 31% 28%	5811
	21st to end	Day	14% 5% 9% 17% 27% 29%	6217
August	1st to 10th	Day	19% 6% 13% 24% 18% 20%	4208
	11th to 20th	Day	16% 7% 12% 19% 25% 22%	4197
	21st to end	Day	18% 6% 9% 21% 25% 20%	4316
September	1st to 10th	Day	16% 4 9% 16% 25% 31%	2400
	11th to 20th	Day	15% 7% 9% 20% 26% 24%	2304
	21st to end	Day	17% 3 6% 15% 38% 21%	2156
October	1st to 10th	Day	12% 4 6% 15% 33% 31%	3270
	11th to 20th	Day	21% 4 7% 27% 33% 8%	3250
	21st to end	Day	16% 4 12% 33% 31% 5%	3548
November	1st to 10th	Day	17% 6% 11% 28% 32% 6%	1979
	11th to 20th	Day	20% 5% 12% 35% 24% 4	1681
	21st to end	Day	22% 6% 15% 34% 22% 2	1600
December	1st to 10th	Day	19% 6% 25% 36% 13% 1	2620
	11th to 20th	Day	22% 8% 27% 33% 9%	3024
	21st to end	Day	32% 8% 22% 21% 17% 1	4004
January	1st to 10th	Night	29% 11% 22% 25% 12% 2	5959
	11th to 20th	Night	25% 12% 17% 26% 18% 2	5880
	21st to end	Night	29% 7% 18% 23% 21% 2	6468
February	1st to 10th	Night	27% 10% 20% 27% 13% 3	2600
	11th to 20th	Night	31% 10% 14% 26% 17% 3	2533
	21st to end	Night	27% 10% 12% 27% 19% 4	1958
March	1st to 10th	Night	27% 9% 9% 25% 24% 6%	4940
	11th to 20th	Night	25% 9% 13% 28% 19% 5%	5000
	21st to end	Night	28% 14% 13% 27% 16% 2	5489
April	1st to 10th	Night	27% 7% 9% 21% 25% 10%	2038
	11th to 20th	Night	27% 8% 11% 19% 23% 12%	1977
	21st to end	Night	24% 9% 12% 20% 27% 8%	1930
May	1st to 10th	Night	25% 11% 12% 17% 27% 7%	4097
	11th to 20th	Night	19% 10% 11% 21% 29% 10%	4075
	21st to end	Night	15% 7% 8% 19% 37% 14%	3999
June	1st to 10th	Night	15% 5% 10% 16% 29% 25%	1600
	11th to 20th	Night	17% 5% 8% 11% 19% 41%	1600
	21st to end	Night	12% 4 6% 12% 23% 43%	1600
July	1st to 10th	Night	15% 4 7% 8% 13% 53%	3724
	11th to 20th	Night	18% 4 10% 16% 28% 23%	4046
	21st to end	Night	16% 5% 9% 14% 26% 30%	4344
August	1st to 10th	Night	23% 8% 14% 20% 15% 21%	2928
	11th to 20th	Night	22% 7% 14% 15% 20% 23%	2928
	21st to end	Night	19% 7% 11% 16% 23% 23%	3590
September	1st to 10th	Night	17% 5% 8% 15% 21% 35%	2000
	11th to 20th	Night	16% 5% 9% 20% 22% 27%	2092
	21st to end	Night	15% 5% 6% 15% 32% 27%	2242
October	1st to 10th	Night	12% 3 5% 14% 35% 31%	3920
	11th to 20th	Night	20% 5% 10% 23% 33% 9%	3898
	21st to end	Night	21% 4 7% 36% 28% 5%	4252
November	1st to 10th	Night	17% 6% 10% 27% 30% 9%	2364
	11th to 20th	Night	16% 6% 12% 34% 29% 4	2695
	21st to end	Night	24% 7% 10% 30% 24% 4	2800
December	1st to 10th	Night	19% 5% 24% 35% 16% 1	4570
	11th to 20th	Night	23% 8% 25% 37% 7%	5182
	21st to end	Night	32% 12% 17% 25% 14% 1	6974

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	6% 5% 24% 36% 21% 7%	300
	11th to 20th	Day	5% 5% 24% 40% 21% 5%	300
	21st to end	Day	5% 3 14% 46% 25% 7%	330
February	1st to 10th	Day	4 6% 26% 47% 13% 3	300
	11th to 20th	Day	7% 6% 27% 44% 15% 2	300
	21st to end	Day	7% 10% 23% 44% 13% 4	303
March	1st to 10th	Day	8% 12% 30% 30% 17% 3	500
	11th to 20th	Day	7% 12% 28% 32% 18% 4	500
	21st to end	Day	8% 15% 35% 29% 12% 2	550
April	1st to 10th	Day	5% 17% 29% 28% 16% 4	500
	11th to 20th	Day	8% 19% 31% 28% 10% 3	492
	21st to end	Day	5% 17% 29% 28% 16% 5%	500
May	1st to 10th	Day	7% 12% 33% 27% 17% 3	503
	11th to 20th	Day	5% 10% 25% 35% 19% 6%	528
	21st to end	Day	4 9% 24% 31% 26% 6%	770
June	1st to 10th	Day	3 6% 20% 33% 32% 6%	730
	11th to 20th	Day	3 6% 25% 35% 25% 6%	730
	21st to end	Day	2 5% 20% 38% 30% 5%	730
July	1st to 10th	Day	2 2 13% 32% 40% 10%	670
	11th to 20th	Day	2 1 12% 32% 38% 15%	524
	21st to end	Day	2 2 11% 33% 38% 15%	575
August	1st to 10th	Day	3 2 17% 33% 35% 9%	527
	11th to 20th	Day	3 2 11% 32% 37% 15%	517
	21st to end	Day	3 2 15% 32% 38% 10%	583
September	1st to 10th	Day	3 3 15% 28% 35% 16%	530
	11th to 20th	Day	2 6% 24% 33% 27% 8%	530
	21st to end	Day	4 7% 17% 29% 32% 11%	486
October	1st to 10th	Day	6% 8% 15% 23% 32% 15%	330
	11th to 20th	Day	3 9% 19% 29% 32% 8%	330
	21st to end	Day	6% 6% 17% 34% 31% 7%	363
November	1st to 10th	Day	5% 8% 21% 35% 25% 6%	306
	11th to 20th	Day	2 5% 22% 42% 22% 7%	300
	21st to end	Day	5% 5% 20% 37% 25% 8%	300
December	1st to 10th	Day	7% 3 18% 41% 19% 11%	300
	11th to 20th	Day	4 3 22% 43% 23% 5%	300
	21st to end	Day	8% 7% 20% 43% 17% 5%	330
January	1st to 10th	Night	5% 3 18% 47% 23% 4	840
	11th to 20th	Night	5% 3 20% 45% 23% 4	800
	21st to end	Night	6% 3 18% 50% 20% 4	880
February	1st to 10th	Night	4 3 25% 50% 16% 3	800
	11th to 20th	Night	5% 4 25% 50% 15% 1	784
	21st to end	Night	5% 4 26% 54% 10%	660
March	1st to 10th	Night	5% 5% 26% 45% 17% 1	800
	11th to 20th	Night	7% 3 21% 48% 20% 1	800
	21st to end	Night	5% 7% 22% 51% 15% 1	880
April	1st to 10th	Night	6% 7% 29% 44% 14%	638
	11th to 20th	Night	7% 8% 25% 46% 13% 1	593
	21st to end	Night	5% 7% 28% 40% 19% 2	600
May	1st to 10th	Night	9% 4 24% 46% 16% 1	600
	11th to 20th	Night	4 4 19% 47% 24% 3	591
	21st to end	Night	5% 6% 20% 39% 27% 2	650
June	1st to 10th	Night	2 3 17% 47% 29% 2	600
	11th to 20th	Night	4 3 22% 48% 21% 2	600
	21st to end	Night	2 1 13% 49% 34% 1	600
July	1st to 10th	Night	2 1 12% 41% 41% 3	585
	11th to 20th	Night	2 1 6% 38% 48% 4	582
	21st to end	Night	3 7% 35% 51% 4	657
August	1st to 10th	Night	3 1 9% 39% 47% 2	597
	11th to 20th	Night	4 2 7% 43% 43% 3	594
	21st to end	Night	3 1 9% 40% 43% 4	660
September	1st to 10th	Night	4 1 9% 43% 40% 3	600
	11th to 20th	Night	2 1 12% 48% 35% 2	692
	21st to end	Night	4 2 15% 36% 38% 6%	800
October	1st to 10th	Night	7% 4 14% 44% 28% 3	800
	11th to 20th	Night	4 2 17% 45% 28% 3	800
	21st to end	Night	7% 4 17% 41% 28% 3	880
November	1st to 10th	Night	4 4 18% 45% 27% 2	788
	11th to 20th	Night	3 2 21% 52% 19% 3	960
	21st to end	Night	7% 4 20% 42% 24% 3	1000
December	1st to 10th	Night	6% 3 16% 54% 20% 2	1000
	11th to 20th	Night	7% 3 22% 46% 21% 2	1000
	21st to end	Night	7% 5% 21% 50% 14% 2	1100

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