CSU-Pueblo Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the CSU-Pueblo Observatory clear sky chart from 2005-11-06 to 2025-04-26.

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 1 4 3 3 4 4 6% 8% 59%	117537
	Night	5% 5% 2 5% 3 3 4 3 5% 7% 59%	119937
Transparency	Day	20% 6% 10% 23% 26% 15%	117283
	Night	23% 5% 10% 23% 26% 13%	119781
Seeing	Day	6% 6% 22% 33% 24% 9%	16046
	Night	6% 3 26% 45% 18% 1	26204

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	2 8% 2 4 2 2 2 3 4 10% 61%	3638
	11th to 20th	Day	1 4 2 6% 4 4 3 4 5% 6% 61%	3847
	21st to end	Day	3 7% 3 5% 4 3 3 3 4 6% 60%	4510
February	1st to 10th	Day	3 6% 2 5% 3 3 4 3 5% 7% 59%	1848
	11th to 20th	Day	1 5% 2 6% 4 3 5% 3 7% 8% 56%	1949
	21st to end	Day	2 6% 2 7% 4 4 4 4 4 5% 60%	1650
March	1st to 10th	Day	1 4 1 3 3 3 3 3 4 7% 67%	4500
	11th to 20th	Day	5% 7% 2 5% 4 4 4 3 5% 8% 54%	4898
	21st to end	Day	2 4 1 4 3 3 3 4 6% 8% 62%	5854
April	1st to 10th	Day	4 5% 2 3 3 3 3 4 5% 8% 60%	2400
	11th to 20th	Day	7% 6% 2 4 2 3 4 4 6% 8% 55%	2371
	21st to end	Day	8% 4 1 4 3 4 4 3 7% 8% 53%	2341
May	1st to 10th	Day	8% 5% 2 4 3 3 4 4 5% 8% 54%	3960
	11th to 20th	Day	6% 5% 2 5% 4 4 5% 5% 8% 9% 48%	4203
	21st to end	Day	3 3 1 3 2 3 4 5% 8% 11% 57%	4825
June	1st to 10th	Day	4 4 1 3 3 4 5% 5% 8% 11% 52%	2660
	11th to 20th	Day	4 2 1 3 2 3 4 4 7% 8% 61%	2660
	21st to end	Day	3 3 1 4 4 5% 5% 5% 8% 10% 52%	2660
July	1st to 10th	Day	3 3 1 4 3 4 4 5% 7% 9% 57%	4430
	11th to 20th	Day	2 2 1 4 4 4 5% 5% 9% 12% 52%	4430
	21st to end	Day	3 3 1 4 3 4 5% 4 8% 9% 57%	4649
August	1st to 10th	Day	5% 4 2 5% 4 5% 6% 5% 10% 12% 43%	3974
	11th to 20th	Day	3 2 1 3 3 3 5% 5% 9% 10% 56%	3726
	21st to end	Day	3 3 1 4 3 4 6% 5% 9% 11% 51%	4180
September	1st to 10th	Day	4 3 2 3 3 3 3 3 5% 7% 63%	2280
	11th to 20th	Day	4 2 1 3 2 3 4 3 5% 7% 65%	2237
	21st to end	Day	5% 3 1 3 2 2 3 2 4 6% 68%	2090
October	1st to 10th	Day	4 2 1 2 1 2 2 1 3 4 78%	3268
	11th to 20th	Day	4 3 1 4 2 2 3 4 4 7% 65%	3150
	21st to end	Day	4 3 1 2 2 2 2 2 3 4 75%	3330
November	1st to 10th	Day	3 3 1 2 2 2 2 2 5% 7% 70%	1763
	11th to 20th	Day	1 5% 1 3 3 3 3 3 5% 5% 69%	1800
	21st to end	Day	4 5% 1 4 2 2 3 3 4 6% 65%	1800
December	1st to 10th	Day	1 5% 1 3 2 2 3 2 4 6% 71%	2626
	11th to 20th	Day	2 3 1 4 3 2 3 2 5% 8% 68%	3026
	21st to end	Day	2 5% 1 4 3 3 4 3 6% 7% 60%	4004
January	1st to 10th	Night	2 9% 3 6% 3 2 3 3 5% 8% 56%	6327
	11th to 20th	Night	1 5% 2 6% 3 3 4 4 5% 6% 61%	6175
	21st to end	Night	3 5% 2 4 3 3 3 3 5% 6% 63%	6468
February	1st to 10th	Night	3 7% 2 6% 3 3 3 2 4 7% 59%	2550
	11th to 20th	Night	3 9% 3 5% 3 4 4 3 5% 8% 52%	2338
	21st to end	Night	3 6% 2 5% 2 2 3 3 5% 6% 62%	1980
March	1st to 10th	Night	4 8% 2 3 2 2 2 2 4 5% 66%	5374
	11th to 20th	Night	9% 7% 2 5% 3 3 4 3 4 5% 56%	5095
	21st to end	Night	5% 5% 2 5% 3 3 4 4 5% 7% 58%	5089
April	1st to 10th	Night	4 5% 1 5% 3 3 3 3 5% 6% 61%	2000
	11th to 20th	Night	9% 7% 2 5% 2 2 3 3 5% 8% 54%	1977
	21st to end	Night	11% 6% 2 5% 3 3 4 3 6% 8% 51%	1955
May	1st to 10th	Night	10% 5% 2 4 3 3 3 3 4 6% 58%	2996
	11th to 20th	Night	12% 6% 2 5% 3 3 4 4 6% 9% 47%	2685
	21st to end	Night	7% 4 1 4 3 3 4 4 5% 7% 57%	2762
June	1st to 10th	Night	5% 3 1 4 3 4 3 4 8% 8% 57%	1520
	11th to 20th	Night	4 3 1 4 3 4 3 4 6% 7% 61%	1520
	21st to end	Night	4 4 2 4 4 4 5% 5% 8% 10% 50%	1520
July	1st to 10th	Night	8% 3 1 5% 4 5% 5% 5% 8% 8% 47%	2540
	11th to 20th	Night	3 3 1 5% 5% 5% 6% 6% 9% 11% 47%	2540
	21st to end	Night	4 3 2 5% 4 4 5% 4 9% 9% 51%	2910
August	1st to 10th	Night	9% 6% 2 8% 6% 6% 7% 6% 8% 8% 34%	2965
	11th to 20th	Night	4 3 2 5% 5% 6% 6% 5% 9% 11% 45%	3113
	21st to end	Night	3 3 2 5% 4 5% 7% 6% 9% 11% 44%	3487
September	1st to 10th	Night	4 4 2 5% 4 4 4 3 6% 9% 54%	1900
	11th to 20th	Night	6% 1 1 3 2 2 4 3 4 9% 64%	1943
	21st to end	Night	8% 3 1 4 2 3 3 3 4 6% 64%	2090
October	1st to 10th	Night	4 2 1 2 2 2 2 2 4 4 74%	3695
	11th to 20th	Night	7% 3 1 4 2 2 3 3 5% 7% 63%	3778
	21st to end	Night	4 4 1 3 2 2 2 2 4 5% 71%	4195
November	1st to 10th	Night	4 4 1 2 2 2 2 2 4 7% 69%	2535
	11th to 20th	Night	2 5% 2 3 2 2 2 2 4 5% 71%	2600
	21st to end	Night	3 6% 2 4 2 2 3 3 4 6% 65%	2600
December	1st to 10th	Night	1 4 1 3 2 2 2 2 4 6% 73%	4560
	11th to 20th	Night	2 4 1 4 3 3 3 2 5% 8% 65%	5181
	21st to end	Night	5% 6% 2 5% 3 4 4 3 5% 7% 56%	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	20% 4 9% 34% 25% 9%	3639
	11th to 20th	Day	21% 5% 8% 22% 28% 16%	3847
	21st to end	Day	25% 4 7% 24% 27% 12%	4510
February	1st to 10th	Day	23% 5% 9% 25% 25% 13%	1848
	11th to 20th	Day	24% 4 10% 25% 28% 9%	1959
	21st to end	Day	25% 4 6% 19% 25% 21%	1650
March	1st to 10th	Day	16% 4 6% 15% 31% 27%	4500
	11th to 20th	Day	26% 6% 7% 19% 29% 12%	4898
	21st to end	Day	18% 5% 10% 33% 28% 6%	5854
April	1st to 10th	Day	20% 5% 10% 24% 24% 16%	2400
	11th to 20th	Day	24% 6% 10% 24% 21% 15%	2374
	21st to end	Day	25% 6% 12% 24% 24% 9%	2341
May	1st to 10th	Day	24% 7% 11% 25% 18% 15%	3960
	11th to 20th	Day	25% 12% 15% 22% 19% 8%	4207
	21st to end	Day	14% 9% 15% 23% 20% 18%	4825
June	1st to 10th	Day	21% 8% 15% 24% 19% 13%	2660
	11th to 20th	Day	17% 7% 11% 17% 25% 23%	2660
	21st to end	Day	22% 7% 12% 19% 23% 17%	2660
July	1st to 10th	Day	20% 6% 11% 18% 27% 17%	4361
	11th to 20th	Day	19% 7% 14% 24% 25% 11%	4355
	21st to end	Day	20% 7% 12% 21% 20% 20%	4502
August	1st to 10th	Day	29% 9% 19% 27% 10% 6%	3960
	11th to 20th	Day	20% 6% 14% 20% 22% 18%	3762
	21st to end	Day	22% 6% 14% 23% 24% 11%	4179
September	1st to 10th	Day	20% 5% 9% 21% 26% 18%	2280
	11th to 20th	Day	17% 5% 9% 18% 26% 26%	2237
	21st to end	Day	18% 4 7% 18% 32% 21%	2090
October	1st to 10th	Day	12% 3 6% 13% 33% 33%	3268
	11th to 20th	Day	19% 3 7% 23% 32% 16%	3150
	21st to end	Day	14% 2 3 18% 40% 22%	3330
November	1st to 10th	Day	15% 3 8% 22% 31% 21%	1763
	11th to 20th	Day	16% 4 7% 26% 33% 15%	1800
	21st to end	Day	20% 4 7% 16% 32% 21%	1800
December	1st to 10th	Day	15% 3 7% 28% 36% 11%	2626
	11th to 20th	Day	15% 3 8% 28% 34% 12%	3024
	21st to end	Day	21% 5% 9% 25% 29% 11%	4004
January	1st to 10th	Night	26% 4 7% 33% 25% 6%	6327
	11th to 20th	Night	21% 5% 9% 24% 24% 16%	6175
	21st to end	Night	20% 5% 11% 26% 29% 9%	6468
February	1st to 10th	Night	26% 4 9% 25% 25% 11%	2550
	11th to 20th	Night	28% 4 10% 27% 22% 9%	2338
	21st to end	Night	22% 3 7% 21% 31% 16%	1980
March	1st to 10th	Night	21% 3 5% 17% 35% 19%	5374
	11th to 20th	Night	28% 5% 9% 16% 27% 14%	5095
	21st to end	Night	23% 6% 11% 33% 22% 5%	5089
April	1st to 10th	Night	22% 5% 11% 23% 24% 16%	2000
	11th to 20th	Night	27% 5% 13% 22% 20% 13%	1977
	21st to end	Night	29% 6% 15% 22% 20% 9%	1955
May	1st to 10th	Night	24% 7% 12% 22% 21% 14%	2996
	11th to 20th	Night	29% 9% 16% 24% 10% 11%	2686
	21st to end	Night	21% 10% 15% 20% 20% 14%	2762
June	1st to 10th	Night	21% 9% 18% 25% 15% 13%	1520
	11th to 20th	Night	19% 6% 14% 19% 20% 22%	1520
	21st to end	Night	25% 9% 13% 19% 18% 16%	1520
July	1st to 10th	Night	31% 7% 11% 18% 22% 10%	2500
	11th to 20th	Night	25% 7% 20% 26% 17% 5%	2492
	21st to end	Night	26% 8% 13% 20% 21% 12%	2819
August	1st to 10th	Night	43% 9% 18% 16% 8% 7%	2956
	11th to 20th	Night	30% 9% 18% 17% 20% 6%	3143
	21st to end	Night	29% 8% 15% 26% 17% 6%	3487
September	1st to 10th	Night	26% 5% 12% 21% 23% 13%	1900
	11th to 20th	Night	16% 6% 10% 20% 25% 23%	1943
	21st to end	Night	21% 4 7% 17% 30% 20%	2090
October	1st to 10th	Night	14% 4 6% 17% 36% 23%	3695
	11th to 20th	Night	21% 3 6% 28% 28% 15%	3778
	21st to end	Night	17% 3 5% 21% 36% 18%	4195
November	1st to 10th	Night	16% 2 9% 24% 30% 19%	2535
	11th to 20th	Night	16% 2 6% 25% 36% 14%	2600
	21st to end	Night	21% 4 8% 21% 30% 16%	2600
December	1st to 10th	Night	15% 3 7% 37% 28% 10%	4560
	11th to 20th	Night	17% 3 7% 25% 38% 10%	5182
	21st to end	Night	25% 5% 9% 22% 29% 10%	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% 39% 21% 5%	300
	11th to 20th	Day	6% 7% 26% 43% 16% 2	300
	21st to end	Day	5% 4 25% 46% 15% 5%	330
February	1st to 10th	Day	4 7% 38% 37% 10% 3	300
	11th to 20th	Day	3 6% 33% 42% 14% 1	300
	21st to end	Day	4 9% 27% 47% 12%	249
March	1st to 10th	Day	5% 9% 28% 36% 21% 2	300
	11th to 20th	Day	11% 10% 28% 33% 14% 4	450
	21st to end	Day	9% 17% 32% 29% 11% 1	550
April	1st to 10th	Day	6% 15% 37% 27% 12% 3	500
	11th to 20th	Day	9% 15% 36% 27% 10% 2	492
	21st to end	Day	12% 11% 27% 33% 13% 2	481
May	1st to 10th	Day	11% 11% 30% 31% 14% 3	558
	11th to 20th	Day	9% 7% 23% 31% 24% 6%	675
	21st to end	Day	6% 6% 24% 35% 23% 7%	734
June	1st to 10th	Day	5% 4 20% 29% 32% 10%	680
	11th to 20th	Day	5% 4 22% 33% 28% 8%	680
	21st to end	Day	3 5% 22% 32% 29% 9%	680
July	1st to 10th	Day	6% 3 14% 26% 38% 14%	671
	11th to 20th	Day	3 1 12% 25% 41% 19%	668
	21st to end	Day	3 2 9% 25% 37% 24%	648
August	1st to 10th	Day	3 2 15% 30% 33% 17%	487
	11th to 20th	Day	3 3 16% 33% 26% 19%	477
	21st to end	Day	3 3 12% 35% 32% 14%	539
September	1st to 10th	Day	6% 2 17% 31% 27% 17%	490
	11th to 20th	Day	6% 3 18% 33% 29% 11%	447
	21st to end	Day	7% 4 12% 27% 33% 17%	300
October	1st to 10th	Day	8% 2 21% 29% 21% 19%	300
	11th to 20th	Day	3 6% 17% 36% 26% 12%	300
	21st to end	Day	8% 5% 18% 36% 26% 8%	330
November	1st to 10th	Day	5% 5% 20% 41% 23% 6%	300
	11th to 20th	Day	4 4 23% 42% 20% 7%	300
	21st to end	Day	8% 5% 18% 40% 23% 6%	300
December	1st to 10th	Day	3 6% 27% 41% 16% 8%	300
	11th to 20th	Day	4 4 25% 47% 18% 3	300
	21st to end	Day	4 6% 35% 41% 12% 3	330
January	1st to 10th	Night	4 4 28% 48% 14% 2	1000
	11th to 20th	Night	5% 3 35% 43% 13% 1	926
	21st to end	Night	5% 1 29% 50% 13% 1	880
February	1st to 10th	Night	5% 3 36% 47% 8% 1	800
	11th to 20th	Night	5% 4 36% 45% 10%	784
	21st to end	Night	7% 3 42% 43% 5%	660
March	1st to 10th	Night	5% 6% 34% 46% 9% 1	800
	11th to 20th	Night	10% 4 28% 44% 13% 1	800
	21st to end	Night	7% 6% 35% 45% 6%	713
April	1st to 10th	Night	7% 8% 41% 37% 7%	600
	11th to 20th	Night	12% 9% 31% 39% 9%	593
	21st to end	Night	11% 6% 29% 43% 10% 1	587
May	1st to 10th	Night	10% 6% 31% 42% 11%	570
	11th to 20th	Night	13% 4 21% 42% 20% 1	561
	21st to end	Night	9% 5% 29% 40% 17% 1	617
June	1st to 10th	Night	4 2 24% 44% 24% 2	570
	11th to 20th	Night	5% 3 23% 51% 17% 1	570
	21st to end	Night	4 3 19% 46% 27% 1	570
July	1st to 10th	Night	8% 2 13% 40% 36% 2	555
	11th to 20th	Night	4 1 9% 42% 39% 4	552
	21st to end	Night	7% 2 8% 33% 46% 4	624
August	1st to 10th	Night	9% 1 8% 38% 42% 2	567
	11th to 20th	Night	6% 2 12% 43% 35% 2	564
	21st to end	Night	4 2 8% 43% 40% 3	627
September	1st to 10th	Night	5% 2 11% 45% 33% 4	570
	11th to 20th	Night	6% 2 14% 46% 28% 3	570
	21st to end	Night	8% 4 17% 46% 24% 2	570
October	1st to 10th	Night	10% 2 21% 45% 21% 2	694
	11th to 20th	Night	6% 2 21% 46% 24% 2	760
	21st to end	Night	7% 3 23% 43% 22% 2	875
November	1st to 10th	Night	4 2 23% 52% 17% 1	975
	11th to 20th	Night	4 4 27% 50% 14% 2	1000
	21st to end	Night	6% 4 28% 43% 18% 1	1000
December	1st to 10th	Night	4 2 30% 50% 14% 1	1000
	11th to 20th	Night	5% 4 31% 49% 12% 1	1000
	21st to end	Night	6% 4 33% 48% 9%	1100

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