Colorado State Forest
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Colorado State Forest clear sky chart from 2005-11-06 to 2025-08-05.

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	4 11% 5% 10% 5% 5% 4 4 5% 6% 41%	129911
	Night	2 10% 5% 10% 5% 4 4 3 5% 6% 46%	127102
Transparency	Day	43% 5% 9% 21% 16% 5%	129615
	Night	38% 5% 11% 24% 17% 5%	126914
Seeing	Day	15% 27% 30% 18% 9% 2	16675
	Night	10% 22% 29% 27% 11% 1	26678

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 9% 7% 22% 10% 5% 3 2 3 5% 34%	3638
	11th to 20th	Day	1 11% 7% 19% 13% 9% 4 2 2 3 27%	3806
	21st to end	Day	1 10% 11% 17% 4 6% 2 1 2 3 42%	4510
February	1st to 10th	Day	1 22% 9% 16% 7% 4 3 2 3 6% 28%	1800
	11th to 20th	Day	2 16% 9% 19% 7% 4 2 2 3 5% 30%	1851
	21st to end	Day	1 15% 9% 16% 10% 4 2 2 4 5% 32%	1650
March	1st to 10th	Day	1 10% 9% 17% 5% 3 3 3 3 4 41%	4583
	11th to 20th	Day	1 13% 9% 14% 4 4 3 3 4 6% 39%	5000
	21st to end	Day	2 22% 8% 19% 5% 4 4 3 4 5% 25%	5736
April	1st to 10th	Day	4 16% 7% 11% 5% 3 4 3 6% 6% 36%	2400
	11th to 20th	Day	5% 21% 5% 11% 5% 4 4 3 5% 6% 31%	2371
	21st to end	Day	6% 19% 7% 10% 5% 4 4 4 5% 6% 30%	2400
May	1st to 10th	Day	5% 16% 7% 12% 5% 5% 5% 4 5% 6% 29%	5893
	11th to 20th	Day	4 14% 3 8% 5% 6% 6% 4 6% 7% 35%	6298
	21st to end	Day	5% 12% 3 8% 4 5% 5% 5% 6% 8% 39%	6925
June	1st to 10th	Day	6% 6% 2 6% 5% 4 5% 5% 7% 8% 45%	2800
	11th to 20th	Day	7% 5% 2 5% 4 5% 4 4 6% 7% 53%	2800
	21st to end	Day	3 4 2 5% 5% 5% 5% 5% 7% 8% 53%	2800
July	1st to 10th	Day	4 3 2 6% 5% 5% 6% 4 7% 9% 50%	6339
	11th to 20th	Day	3 3 2 6% 6% 6% 8% 7% 9% 9% 43%	6340
	21st to end	Day	4 5% 2 8% 6% 6% 7% 6% 8% 8% 41%	6688
August	1st to 10th	Day	7% 5% 3 8% 6% 7% 6% 5% 8% 9% 37%	4145
	11th to 20th	Day	7% 5% 2 7% 5% 6% 6% 5% 7% 7% 43%	3843
	21st to end	Day	6% 5% 2 6% 5% 4 5% 4 6% 8% 49%	4180
September	1st to 10th	Day	7% 4 2 6% 4 3 4 2 4 6% 58%	2280
	11th to 20th	Day	9% 5% 2 6% 4 4 4 4 5% 5% 53%	2280
	21st to end	Day	9% 7% 2 4 3 2 3 2 3 5% 61%	2052
October	1st to 10th	Day	4 7% 2 3 2 2 2 2 2 4 69%	3170
	11th to 20th	Day	5% 9% 3 7% 4 3 4 4 5% 8% 50%	3150
	21st to end	Day	4 16% 5% 6% 2 2 2 2 4 6% 50%	3376
November	1st to 10th	Day	3 12% 7% 8% 3 2 2 2 4 6% 52%	1763
	11th to 20th	Day	2 20% 4 9% 4 2 2 2 3 5% 46%	1794
	21st to end	Day	2 13% 4 13% 4 2 2 2 3 6% 49%	1600
December	1st to 10th	Day	1 10% 5% 12% 8% 3 2 2 2 3 52%	2620
	11th to 20th	Day	1 14% 8% 11% 4 3 2 2 3 6% 47%	3026
	21st to end	Day	1 18% 7% 16% 5% 5% 4 3 4 6% 31%	4004
January	1st to 10th	Night	1 9% 7% 22% 9% 6% 4 3 4 5% 31%	6327
	11th to 20th	Night	1 12% 8% 17% 10% 9% 5% 2 3 3 31%	6203
	21st to end	Night	1 11% 8% 18% 7% 5% 2 2 2 3 42%	6468
February	1st to 10th	Night	1 18% 8% 19% 8% 4 3 2 4 4 27%	2600
	11th to 20th	Night	2 15% 10% 18% 6% 5% 3 2 4 5% 30%	2434
	21st to end	Night	1 13% 9% 18% 8% 4 2 2 4 5% 35%	1980
March	1st to 10th	Night	1 12% 9% 16% 5% 3 3 2 4 4 41%	5291
	11th to 20th	Night	1 8% 4 14% 4 3 3 2 4 6% 50%	5000
	21st to end	Night	2 20% 9% 15% 4 4 4 3 4 6% 31%	5226
April	1st to 10th	Night	3 16% 4 9% 5% 3 3 3 5% 5% 42%	2000
	11th to 20th	Night	4 17% 4 9% 5% 5% 4 3 5% 6% 39%	1977
	21st to end	Night	5% 16% 5% 7% 4 3 4 3 4 5% 44%	2000
May	1st to 10th	Night	4 12% 6% 8% 5% 5% 4 3 5% 7% 41%	4080
	11th to 20th	Night	4 14% 3 6% 4 4 5% 4 6% 9% 42%	3617
	21st to end	Night	4 10% 2 4 4 4 5% 4 5% 6% 53%	3972
June	1st to 10th	Night	4 4 1 4 3 2 4 4 7% 9% 58%	1600
	11th to 20th	Night	4 4 1 4 3 4 4 3 5% 8% 61%	1600
	21st to end	Night	4 3 1 3 3 2 3 3 6% 7% 63%	1600
July	1st to 10th	Night	3 2 2 4 3 3 4 4 6% 8% 59%	3640
	11th to 20th	Night	1 2 1 4 4 4 6% 6% 8% 11% 54%	3640
	21st to end	Night	1 2 1 4 4 4 6% 5% 7% 8% 57%	4168
August	1st to 10th	Night	3 3 1 4 4 5% 5% 6% 9% 10% 50%	2883
	11th to 20th	Night	4 4 2 5% 4 5% 7% 6% 8% 9% 47%	2994
	21st to end	Night	3 3 1 5% 4 5% 5% 5% 7% 9% 52%	3487
September	1st to 10th	Night	4 4 1 4 3 3 3 3 5% 7% 62%	1900
	11th to 20th	Night	5% 4 1 4 2 4 3 3 4 7% 63%	1900
	21st to end	Night	6% 6% 1 4 2 3 3 3 4 6% 63%	2124
October	1st to 10th	Night	3 6% 1 3 2 2 2 2 3 5% 72%	3800
	11th to 20th	Night	3 8% 2 4 2 3 3 2 5% 8% 59%	3778
	21st to end	Night	4 10% 3 6% 2 2 2 2 4 6% 58%	4148
November	1st to 10th	Night	3 14% 4 6% 2 2 3 2 4 6% 54%	2535
	11th to 20th	Night	3 16% 5% 10% 4 2 2 2 3 5% 48%	2605
	21st to end	Night	2 12% 6% 9% 5% 3 3 3 4 7% 47%	2800
December	1st to 10th	Night	1 11% 5% 10% 8% 4 2 1 2 3 53%	4570
	11th to 20th	Night	1 10% 6% 17% 4 4 3 3 5% 7% 40%	5181
	21st to end	Night	1 18% 9% 15% 7% 5% 4 3 4 4 31%	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	54% 4 9% 16% 14% 3	3639
	11th to 20th	Day	62% 4 10% 11% 9% 3	3806
	21st to end	Day	48% 4 8% 15% 16% 9%	4510
February	1st to 10th	Day	60% 5% 8% 13% 12% 2	1800
	11th to 20th	Day	58% 3 8% 19% 8% 4	1860
	21st to end	Day	57% 3 10% 12% 15% 3	1650
March	1st to 10th	Day	48% 3 5% 21% 15% 8%	4583
	11th to 20th	Day	46% 5% 9% 30% 9% 1	5000
	21st to end	Day	61% 6% 9% 18% 6% 1	5736
April	1st to 10th	Day	50% 4 11% 19% 13% 3	2400
	11th to 20th	Day	56% 4 8% 18% 12% 2	2374
	21st to end	Day	56% 4 9% 23% 8%	2400
May	1st to 10th	Day	55% 6% 8% 18% 13% 1	5893
	11th to 20th	Day	46% 6% 9% 24% 14% 2	6302
	21st to end	Day	41% 6% 9% 27% 16% 1	6926
June	1st to 10th	Day	36% 7% 14% 24% 15% 5%	2800
	11th to 20th	Day	31% 4 10% 19% 26% 10%	2800
	21st to end	Day	30% 5% 8% 23% 24% 10%	2800
July	1st to 10th	Day	28% 7% 7% 14% 25% 20%	6271
	11th to 20th	Day	31% 9% 11% 23% 18% 8%	6265
	21st to end	Day	38% 7% 11% 15% 20% 9%	6495
August	1st to 10th	Day	40% 9% 14% 17% 13% 7%	4131
	11th to 20th	Day	39% 8% 9% 17% 21% 7%	3882
	21st to end	Day	35% 6% 9% 17% 21% 12%	4179
September	1st to 10th	Day	29% 5% 8% 19% 28% 12%	2280
	11th to 20th	Day	35% 4 7% 22% 24% 8%	2280
	21st to end	Day	29% 3 7% 31% 25% 5%	2052
October	1st to 10th	Day	23% 3 5% 26% 37% 7%	3170
	11th to 20th	Day	32% 4 9% 35% 17% 3	3150
	21st to end	Day	37% 4 8% 35% 15% 2	3376
November	1st to 10th	Day	36% 4 12% 25% 20% 2	1763
	11th to 20th	Day	42% 3 13% 22% 16% 4	1794
	21st to end	Day	40% 3 11% 29% 13% 4	1600
December	1st to 10th	Day	39% 4 12% 29% 14% 2	2620
	11th to 20th	Day	40% 4 16% 31% 10% 1	3024
	21st to end	Day	52% 6% 7% 18% 15% 3	4004
January	1st to 10th	Night	53% 5% 9% 17% 11% 5%	6327
	11th to 20th	Night	59% 4 9% 13% 11% 4	6203
	21st to end	Night	50% 4 8% 14% 14% 11%	6468
February	1st to 10th	Night	58% 6% 9% 15% 10% 2	2600
	11th to 20th	Night	56% 4 9% 20% 10% 2	2435
	21st to end	Night	54% 4 8% 15% 15% 4	1980
March	1st to 10th	Night	46% 4 5% 20% 16% 8%	5291
	11th to 20th	Night	36% 3 11% 29% 19% 2	5000
	21st to end	Night	53% 7% 12% 24% 4	5226
April	1st to 10th	Night	43% 6% 11% 21% 16% 3	2000
	11th to 20th	Night	47% 4 12% 24% 13% 1	1977
	21st to end	Night	43% 4 11% 30% 12%	2000
May	1st to 10th	Night	41% 6% 9% 30% 13% 1	4077
	11th to 20th	Night	37% 6% 13% 32% 11%	3618
	21st to end	Night	30% 7% 9% 33% 20% 1	3972
June	1st to 10th	Night	23% 5% 22% 31% 16% 4	1600
	11th to 20th	Night	23% 4 13% 23% 27% 10%	1600
	21st to end	Night	20% 4 10% 27% 27% 12%	1600
July	1st to 10th	Night	21% 5% 8% 18% 25% 22%	3600
	11th to 20th	Night	21% 7% 18% 30% 18% 7%	3592
	21st to end	Night	23% 6% 15% 24% 19% 12%	4050
August	1st to 10th	Night	26% 7% 23% 20% 19% 6%	2874
	11th to 20th	Night	29% 9% 17% 17% 18% 10%	3021
	21st to end	Night	28% 7% 13% 20% 24% 9%	3487
September	1st to 10th	Night	23% 4 12% 20% 30% 11%	1900
	11th to 20th	Night	23% 4 12% 25% 26% 9%	1900
	21st to end	Night	24% 4 8% 32% 28% 4	2124
October	1st to 10th	Night	19% 3 6% 26% 39% 7%	3800
	11th to 20th	Night	22% 4 12% 40% 19% 3	3778
	21st to end	Night	29% 3 10% 36% 20% 2	4148
November	1st to 10th	Night	32% 5% 11% 28% 20% 3	2535
	11th to 20th	Night	39% 3 13% 25% 15% 4	2605
	21st to end	Night	39% 4 10% 30% 13% 4	2800
December	1st to 10th	Night	37% 5% 10% 30% 16% 3	4570
	11th to 20th	Night	38% 9% 12% 29% 11%	5182
	21st to end	Night	55% 6% 6% 19% 12% 3	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	19% 33% 25% 14% 8% 1	300
	11th to 20th	Day	19% 41% 23% 13% 3 1	300
	21st to end	Day	9% 41% 30% 14% 5%	330
February	1st to 10th	Day	28% 46% 18% 6% 1 1	300
	11th to 20th	Day	26% 37% 27% 10% 1	300
	21st to end	Day	28% 39% 24% 7% 1	249
March	1st to 10th	Day	20% 44% 22% 10% 4	331
	11th to 20th	Day	20% 35% 29% 13% 3	500
	21st to end	Day	20% 44% 27% 8% 1	550
April	1st to 10th	Day	22% 40% 28% 8% 2	500
	11th to 20th	Day	28% 40% 26% 4 2	492
	21st to end	Day	23% 34% 28% 10% 3 1	500
May	1st to 10th	Day	22% 29% 28% 13% 7%	593
	11th to 20th	Day	18% 19% 31% 21% 9% 2	725
	21st to end	Day	16% 21% 29% 21% 11% 2	789
June	1st to 10th	Day	9% 17% 31% 23% 17% 3	730
	11th to 20th	Day	10% 25% 34% 22% 9% 1	730
	21st to end	Day	7% 19% 33% 26% 12% 3	730
July	1st to 10th	Day	8% 10% 29% 31% 19% 3	721
	11th to 20th	Day	6% 9% 32% 31% 19% 4	718
	21st to end	Day	7% 7% 32% 31% 19% 4	706
August	1st to 10th	Day	10% 16% 38% 28% 8% 1	504
	11th to 20th	Day	6% 14% 38% 27% 11% 3	477
	21st to end	Day	9% 16% 33% 28% 12% 2	539
September	1st to 10th	Day	9% 19% 33% 24% 11% 4	490
	11th to 20th	Day	11% 22% 37% 19% 9% 2	490
	21st to end	Day	11% 26% 27% 20% 13% 4	321
October	1st to 10th	Day	15% 25% 27% 18% 12% 4	300
	11th to 20th	Day	14% 35% 27% 16% 6% 2	300
	21st to end	Day	21% 35% 27% 14% 3 1	330
November	1st to 10th	Day	21% 39% 23% 10% 6% 1	300
	11th to 20th	Day	20% 39% 26% 11% 2 1	300
	21st to end	Day	16% 35% 30% 16% 2	300
December	1st to 10th	Day	20% 34% 26% 13% 6% 1	300
	11th to 20th	Day	15% 40% 30% 11% 3	300
	21st to end	Day	20% 38% 29% 11% 2	330
January	1st to 10th	Night	12% 30% 29% 21% 8% 1	1000
	11th to 20th	Night	11% 38% 26% 19% 5% 1	941
	21st to end	Night	7% 32% 33% 21% 5% 1	880
February	1st to 10th	Night	13% 38% 31% 14% 5%	800
	11th to 20th	Night	10% 37% 29% 20% 3	784
	21st to end	Night	13% 34% 38% 13% 2	660
March	1st to 10th	Night	10% 33% 31% 20% 6%	800
	11th to 20th	Night	10% 21% 39% 23% 8% 1	800
	21st to end	Night	10% 26% 39% 19% 5% 1	772
April	1st to 10th	Night	14% 26% 38% 20% 3	600
	11th to 20th	Night	14% 23% 37% 21% 5% 1	593
	21st to end	Night	12% 21% 35% 24% 8% 1	600
May	1st to 10th	Night	13% 15% 36% 27% 9% 1	600
	11th to 20th	Night	11% 10% 28% 36% 15% 1	591
	21st to end	Night	9% 14% 28% 32% 16% 1	650
June	1st to 10th	Night	6% 7% 28% 39% 18% 1	600
	11th to 20th	Night	7% 12% 33% 35% 13%	600
	21st to end	Night	7% 7% 23% 44% 18% 1	600
July	1st to 10th	Night	4 2 18% 41% 32% 1	585
	11th to 20th	Night	3 3 19% 42% 31% 3	582
	21st to end	Night	4 2 13% 46% 32% 3	657
August	1st to 10th	Night	6% 2 16% 47% 27% 2	579
	11th to 20th	Night	3 3 20% 42% 29% 3	564
	21st to end	Night	5% 4 17% 41% 31% 3	627
September	1st to 10th	Night	6% 5% 22% 41% 24% 2	570
	11th to 20th	Night	7% 6% 24% 42% 17% 4	570
	21st to end	Night	9% 8% 29% 32% 18% 4	626
October	1st to 10th	Night	9% 16% 29% 28% 15% 3	760
	11th to 20th	Night	11% 23% 25% 30% 9% 1	760
	21st to end	Night	15% 23% 32% 21% 8% 2	852
November	1st to 10th	Night	12% 29% 33% 19% 6% 1	975
	11th to 20th	Night	15% 32% 30% 17% 5% 1	1000
	21st to end	Night	9% 29% 35% 21% 6% 1	1000
December	1st to 10th	Night	15% 31% 29% 18% 6%	1000
	11th to 20th	Night	11% 34% 32% 19% 4	1000
	21st to end	Night	12% 35% 31% 17% 5%	1100

Page generated at 2025-08-01 23:32:29. Version ac07

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