Denver
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Denver clear sky chart from 2005-11-06 to 2026-03-18.

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 5% 2 5% 4 4 4 4 6% 8% 54%	140006
	Night	5% 6% 2 5% 3 3 4 3 5% 7% 58%	138966
Transparency	Day	26% 5% 10% 23% 25% 11%	134958
	Night	26% 5% 10% 24% 26% 9%	135021
Seeing	Day	8% 7% 25% 33% 20% 7%	17370
	Night	7% 4 27% 45% 15% 1	27546

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 7% 3 6% 3 3 3 3 5% 7% 59%	4720
	11th to 20th	Day	1 4 2 6% 4 3 4 3 4 7% 63%	4877
	21st to end	Day	1 4 3 7% 4 3 3 3 5% 7% 62%	5844
February	1st to 10th	Day	3 6% 3 7% 4 4 4 3 5% 6% 55%	1890
	11th to 20th	Day	1 5% 2 7% 4 4 4 4 5% 9% 56%	2029
	21st to end	Day	2 6% 3 6% 3 3 3 3 5% 7% 59%	1730
March	1st to 10th	Day	4 10% 2 4 3 3 3 2 4 7% 59%	4600
	11th to 20th	Day	5% 7% 2 6% 4 4 4 4 6% 9% 49%	5001
	21st to end	Day	4 6% 2 5% 4 3 4 4 5% 8% 55%	5830
April	1st to 10th	Day	6% 6% 2 5% 3 3 4 3 7% 7% 55%	2400
	11th to 20th	Day	8% 8% 3 6% 3 4 4 4 6% 7% 48%	2371
	21st to end	Day	10% 7% 2 4 3 3 5% 4 7% 8% 47%	2400
May	1st to 10th	Day	9% 7% 2 6% 4 4 5% 4 6% 8% 44%	5752
	11th to 20th	Day	7% 6% 2 6% 4 4 5% 5% 7% 8% 45%	6269
	21st to end	Day	7% 5% 2 5% 5% 5% 5% 5% 7% 9% 46%	6925
June	1st to 10th	Day	5% 4 2 4 4 4 5% 5% 8% 9% 50%	2800
	11th to 20th	Day	5% 3 1 4 4 4 6% 5% 7% 10% 51%	2800
	21st to end	Day	4 3 2 4 4 4 6% 6% 8% 10% 50%	2800
July	1st to 10th	Day	4 3 1 4 3 4 5% 4 7% 9% 56%	6339
	11th to 20th	Day	2 2 1 5% 4 5% 7% 6% 9% 11% 45%	6340
	21st to end	Day	4 4 2 6% 5% 5% 6% 5% 8% 8% 47%	6797
August	1st to 10th	Day	6% 4 2 5% 5% 6% 8% 7% 9% 10% 39%	5762
	11th to 20th	Day	2 2 1 4 3 5% 5% 5% 8% 9% 54%	5366
	21st to end	Day	6% 5% 2 6% 5% 5% 6% 5% 7% 9% 45%	5984
September	1st to 10th	Day	4 3 1 4 4 3 4 4 5% 7% 61%	2400
	11th to 20th	Day	5% 3 1 4 3 3 4 4 6% 8% 59%	2372
	21st to end	Day	5% 5% 1 4 2 3 3 3 4 6% 64%	2200
October	1st to 10th	Day	4 2 1 2 2 2 2 2 3 5% 75%	3307
	11th to 20th	Day	4 4 2 5% 3 3 3 3 5% 7% 61%	3250
	21st to end	Day	5% 6% 1 3 2 2 2 3 4 5% 65%	3420
November	1st to 10th	Day	3 5% 1 4 2 2 2 3 5% 8% 65%	1853
	11th to 20th	Day	2 5% 2 4 3 3 2 3 5% 8% 63%	1890
	21st to end	Day	3 6% 2 5% 3 2 3 3 5% 7% 60%	1790
December	1st to 10th	Day	1 4 2 4 3 3 3 2 4 6% 69%	2700
	11th to 20th	Day	2 3 1 4 2 2 3 3 5% 7% 69%	3106
	21st to end	Day	2 6% 3 7% 4 4 4 4 6% 7% 54%	4092
January	1st to 10th	Night	2 9% 4 6% 3 3 3 2 4 7% 58%	8201
	11th to 20th	Night	1 6% 3 6% 4 3 3 2 4 6% 62%	8158
	21st to end	Night	2 5% 3 7% 3 3 3 2 4 5% 61%	8370
February	1st to 10th	Night	2 8% 2 6% 3 3 4 3 5% 7% 57%	2730
	11th to 20th	Night	2 8% 3 6% 4 5% 5% 3 4 6% 53%	2475
	21st to end	Night	2 8% 2 6% 3 3 3 3 4 5% 61%	2076
March	1st to 10th	Night	5% 9% 2 5% 3 3 4 3 5% 5% 55%	5494
	11th to 20th	Night	7% 9% 2 5% 3 3 3 3 4 6% 54%	5135
	21st to end	Night	7% 9% 3 5% 3 4 3 3 5% 6% 50%	5127
April	1st to 10th	Night	6% 7% 2 5% 3 3 4 3 5% 6% 57%	2000
	11th to 20th	Night	11% 7% 2 5% 3 3 4 3 5% 6% 51%	1977
	21st to end	Night	12% 8% 2 5% 3 3 3 3 5% 7% 49%	2000
May	1st to 10th	Night	13% 7% 2 6% 4 4 4 3 5% 7% 45%	4226
	11th to 20th	Night	8% 6% 2 7% 4 4 4 4 6% 8% 47%	3630
	21st to end	Night	10% 6% 2 4 3 3 4 3 5% 6% 55%	3972
June	1st to 10th	Night	5% 3 1 3 3 3 4 4 6% 9% 59%	1600
	11th to 20th	Night	5% 3 1 3 3 3 3 4 7% 7% 63%	1600
	21st to end	Night	4 3 1 4 3 3 4 5% 8% 8% 58%	1600
July	1st to 10th	Night	2 2 1 4 3 4 4 4 6% 7% 62%	3640
	11th to 20th	Night	3 3 1 4 3 4 6% 5% 8% 12% 51%	3640
	21st to end	Night	4 3 2 5% 4 4 5% 5% 8% 11% 50%	4060
August	1st to 10th	Night	6% 4 2 5% 4 4 5% 5% 7% 9% 50%	4049
	11th to 20th	Night	3 2 1 4 3 4 5% 5% 8% 11% 54%	4483
	21st to end	Night	6% 5% 2 6% 5% 5% 5% 4 7% 9% 45%	4993
September	1st to 10th	Night	6% 3 2 4 4 4 4 3 5% 7% 59%	2000
	11th to 20th	Night	7% 3 1 4 2 3 3 2 5% 8% 63%	2026
	21st to end	Night	7% 3 2 4 3 2 3 2 4 6% 64%	2200
October	1st to 10th	Night	5% 4 1 2 2 2 2 2 3 5% 72%	3878
	11th to 20th	Night	6% 3 2 4 3 2 3 2 4 8% 62%	3898
	21st to end	Night	5% 6% 2 4 2 2 2 2 3 6% 66%	4348
November	1st to 10th	Night	3 4 1 3 2 3 2 3 4 6% 68%	2665
	11th to 20th	Night	3 5% 1 4 2 3 3 3 4 6% 66%	2730
	21st to end	Night	4 6% 2 4 3 3 3 3 5% 6% 61%	2826
December	1st to 10th	Night	1 4 2 3 3 2 2 2 4 6% 72%	4710
	11th to 20th	Night	1 4 2 4 2 2 3 2 4 8% 67%	5321
	21st to end	Night	4 8% 2 6% 4 4 4 3 5% 6% 54%	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	25% 4 7% 30% 24% 9%	4723
	11th to 20th	Day	22% 3 10% 27% 28% 10%	4877
	21st to end	Day	23% 3 8% 27% 27% 12%	5844
February	1st to 10th	Day	28% 4 10% 26% 23% 8%	1890
	11th to 20th	Day	25% 5% 7% 29% 27% 7%	2039
	21st to end	Day	23% 4 8% 22% 29% 14%	1730
March	1st to 10th	Day	26% 3 7% 16% 32% 16%	4600
	11th to 20th	Day	30% 6% 11% 22% 26% 6%	5001
	21st to end	Day	26% 6% 12% 36% 18% 3	5830
April	1st to 10th	Day	27% 5% 11% 25% 23% 10%	2400
	11th to 20th	Day	33% 6% 10% 21% 21% 9%	2374
	21st to end	Day	31% 6% 12% 24% 22% 4	2400
May	1st to 10th	Day	34% 6% 13% 26% 17% 5%	5752
	11th to 20th	Day	32% 8% 11% 19% 21% 9%	6273
	21st to end	Day	31% 7% 14% 23% 20% 5%	6926
June	1st to 10th	Day	26% 8% 15% 23% 19% 9%	2800
	11th to 20th	Day	25% 7% 11% 17% 24% 16%	2800
	21st to end	Day	25% 7% 11% 19% 24% 14%	2800
July	1st to 10th	Day	21% 5% 8% 17% 27% 23%	6271
	11th to 20th	Day	25% 8% 13% 23% 20% 11%	6265
	21st to end	Day	30% 7% 11% 18% 17% 16%	6601
August	1st to 10th	Day	36% 9% 14% 20% 15% 6%	4191
	11th to 20th	Day	26% 7% 13% 17% 22% 15%	3882
	21st to end	Day	26% 5% 11% 19% 25% 14%	4311
September	1st to 10th	Day	22% 5% 7% 21% 26% 19%	2400
	11th to 20th	Day	22% 4 8% 20% 28% 18%	2372
	21st to end	Day	21% 3 6% 18% 36% 15%	2200
October	1st to 10th	Day	14% 3 5% 15% 37% 26%	3307
	11th to 20th	Day	23% 4 8% 23% 32% 10%	3250
	21st to end	Day	21% 3 4 23% 37% 12%	3420
November	1st to 10th	Day	19% 3 7% 26% 29% 16%	1853
	11th to 20th	Day	19% 4 6% 26% 35% 10%	1890
	21st to end	Day	24% 3 8% 21% 31% 13%	1790
December	1st to 10th	Day	18% 3 7% 33% 29% 10%	2700
	11th to 20th	Day	16% 4 6% 29% 35% 10%	3104
	21st to end	Day	28% 4 7% 25% 27% 9%	4092
January	1st to 10th	Night	27% 3 6% 32% 25% 6%	8202
	11th to 20th	Night	24% 5% 8% 25% 26% 13%	8158
	21st to end	Night	25% 4 9% 23% 29% 10%	8370
February	1st to 10th	Night	27% 4 9% 26% 26% 6%	2730
	11th to 20th	Night	32% 4 8% 27% 22% 7%	2475
	21st to end	Night	26% 4 4 23% 29% 14%	2076
March	1st to 10th	Night	29% 4 7% 16% 36% 9%	5494
	11th to 20th	Night	30% 6% 10% 14% 29% 11%	5135
	21st to end	Night	33% 5% 10% 33% 17% 2	5127
April	1st to 10th	Night	28% 5% 11% 24% 22% 10%	2000
	11th to 20th	Night	35% 5% 10% 21% 21% 8%	1977
	21st to end	Night	35% 6% 10% 25% 20% 5%	2000
May	1st to 10th	Night	36% 7% 13% 26% 11% 7%	4223
	11th to 20th	Night	32% 8% 14% 21% 17% 7%	3631
	21st to end	Night	29% 7% 18% 25% 16% 4	3972
June	1st to 10th	Night	20% 8% 19% 31% 15% 8%	1600
	11th to 20th	Night	19% 6% 15% 21% 24% 16%	1600
	21st to end	Night	21% 7% 11% 24% 28% 9%	1600
July	1st to 10th	Night	21% 5% 11% 19% 34% 11%	3600
	11th to 20th	Night	23% 7% 18% 26% 20% 6%	3592
	21st to end	Night	25% 7% 17% 21% 20% 11%	3944
August	1st to 10th	Night	34% 9% 15% 22% 16% 4	2944
	11th to 20th	Night	22% 9% 19% 20% 20% 10%	3243
	21st to end	Night	25% 6% 15% 22% 25% 6%	3597
September	1st to 10th	Night	24% 4 11% 21% 24% 15%	2000
	11th to 20th	Night	21% 4 10% 24% 26% 16%	2026
	21st to end	Night	23% 3 8% 20% 34% 13%	2200
October	1st to 10th	Night	17% 4 7% 18% 32% 22%	3878
	11th to 20th	Night	21% 3 10% 26% 30% 10%	3898
	21st to end	Night	22% 3 5% 24% 33% 13%	4348
November	1st to 10th	Night	18% 4 8% 25% 29% 15%	2665
	11th to 20th	Night	20% 4 6% 27% 34% 10%	2730
	21st to end	Night	24% 4 8% 23% 30% 10%	2826
December	1st to 10th	Night	16% 3 7% 35% 31% 7%	4710
	11th to 20th	Night	18% 3 6% 32% 35% 6%	5322
	21st to end	Night	31% 4 8% 23% 27% 7%	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	6% 6% 29% 42% 12% 4	330
	11th to 20th	Day	6% 7% 32% 39% 14% 1	330
	21st to end	Day	3 6% 39% 37% 13% 2	363
February	1st to 10th	Day	4 12% 38% 36% 7% 2	330
	11th to 20th	Day	4 4 42% 39% 8% 3	330
	21st to end	Day	5% 10% 36% 39% 10%	273
March	1st to 10th	Day	5% 9% 33% 36% 15% 2	330
	11th to 20th	Day	12% 13% 31% 29% 12% 2	491
	21st to end	Day	14% 16% 29% 30% 9% 2	550
April	1st to 10th	Day	11% 15% 32% 29% 12% 2	500
	11th to 20th	Day	15% 18% 32% 23% 10% 2	492
	21st to end	Day	17% 11% 31% 26% 12% 3	500
May	1st to 10th	Day	15% 12% 26% 29% 15% 3	633
	11th to 20th	Day	16% 8% 23% 29% 19% 6%	725
	21st to end	Day	11% 9% 23% 31% 20% 7%	789
June	1st to 10th	Day	6% 5% 19% 32% 26% 11%	730
	11th to 20th	Day	6% 7% 25% 34% 21% 7%	730
	21st to end	Day	6% 6% 22% 34% 25% 8%	730
July	1st to 10th	Day	7% 3 15% 29% 33% 13%	721
	11th to 20th	Day	4 3 12% 31% 38% 11%	718
	21st to end	Day	5% 3 12% 29% 38% 12%	750
August	1st to 10th	Day	7% 5% 21% 29% 25% 13%	527
	11th to 20th	Day	3 4 20% 33% 26% 13%	517
	21st to end	Day	7% 5% 17% 33% 30% 10%	583
September	1st to 10th	Day	5% 3 19% 33% 26% 13%	530
	11th to 20th	Day	5% 5% 22% 37% 22% 10%	502
	21st to end	Day	6% 6% 18% 33% 22% 15%	330
October	1st to 10th	Day	9% 6% 22% 27% 24% 12%	330
	11th to 20th	Day	5% 8% 28% 36% 18% 5%	330
	21st to end	Day	12% 7% 24% 37% 16% 4	363
November	1st to 10th	Day	7% 7% 28% 39% 14% 5%	330
	11th to 20th	Day	6% 6% 29% 42% 13% 4	330
	21st to end	Day	7% 7% 28% 41% 14% 3	330
December	1st to 10th	Day	5% 8% 31% 37% 16% 3	330
	11th to 20th	Day	5% 5% 41% 38% 10% 1	330
	21st to end	Day	6% 6% 32% 45% 9% 2	363
January	1st to 10th	Night	4 4 35% 46% 10% 2	1050
	11th to 20th	Night	4 4 39% 43% 9% 1	1023
	21st to end	Night	5% 3 35% 47% 9% 1	924
February	1st to 10th	Night	6% 2 42% 44% 6%	840
	11th to 20th	Night	5% 3 41% 44% 7%	824
	21st to end	Night	7% 5% 40% 45% 3	692
March	1st to 10th	Night	6% 3 37% 45% 9%	840
	11th to 20th	Night	11% 4 29% 46% 10%	828
	21st to end	Night	10% 6% 36% 42% 7%	725
April	1st to 10th	Night	11% 7% 37% 40% 6%	600
	11th to 20th	Night	15% 8% 30% 38% 9%	593
	21st to end	Night	16% 6% 29% 40% 10% 1	600
May	1st to 10th	Night	15% 5% 24% 43% 13% 1	600
	11th to 20th	Night	16% 3 17% 45% 18% 1	591
	21st to end	Night	11% 5% 23% 39% 21% 1	650
June	1st to 10th	Night	6% 4 16% 47% 25% 2	600
	11th to 20th	Night	7% 3 22% 50% 17% 1	600
	21st to end	Night	5% 2 17% 48% 27% 1	600
July	1st to 10th	Night	7% 3 13% 42% 33% 2	585
	11th to 20th	Night	3 2 11% 45% 37% 2	582
	21st to end	Night	5% 2 8% 44% 38% 4	657
August	1st to 10th	Night	5% 3 11% 45% 34% 2	597
	11th to 20th	Night	4 2 15% 47% 30% 1	594
	21st to end	Night	5% 1 16% 45% 31% 2	660
September	1st to 10th	Night	6% 2 13% 45% 28% 5%	600
	11th to 20th	Night	7% 2 14% 50% 25% 3	600
	21st to end	Night	7% 2 18% 49% 21% 2	600
October	1st to 10th	Night	12% 4 18% 46% 18% 3	771
	11th to 20th	Night	5% 3 26% 49% 15% 2	800
	21st to end	Night	8% 4 25% 46% 15% 2	940
November	1st to 10th	Night	5% 3 32% 47% 12% 2	1025
	11th to 20th	Night	5% 5% 32% 49% 9% 1	1050
	21st to end	Night	7% 4 28% 48% 12% 1	1050
December	1st to 10th	Night	5% 4 33% 49% 9%	1050
	11th to 20th	Night	5% 4 35% 46% 8% 1	1050
	21st to end	Night	7% 4 37% 44% 7% 1	1155

Page generated at 2026-03-15 00:23:56. Version ac07

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