Cheyenne
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cheyenne clear sky chart from 2005-11-06 to 2026-08-15.

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	5% 6% 2 6% 4 4 5% 4 6% 8% 51%	152859
	Night	5% 6% 2 6% 4 4 4 3 6% 7% 53%	146608
Transparency	Day	30% 5% 10% 24% 22% 9%	147770
	Night	29% 5% 11% 26% 22% 7%	142709
Seeing	Day	11% 11% 31% 27% 15% 4	18182
	Night	9% 12% 36% 32% 10% 1	28109

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% 3 8% 5% 5% 4 3 5% 6% 53%	4720
	11th to 20th	Day	1 4 2 7% 5% 4 4 3 6% 8% 55%	4740
	21st to end	Day	1 4 2 6% 4 3 3 3 5% 7% 62%	5761
February	1st to 10th	Day	2 8% 3 8% 5% 4 3 3 6% 9% 49%	1890
	11th to 20th	Day	1 7% 3 8% 5% 4 5% 4 6% 8% 50%	2002
	21st to end	Day	2 8% 2 6% 4 3 3 3 5% 6% 57%	1730
March	1st to 10th	Day	4 9% 3 6% 3 3 4 3 4 7% 52%	4600
	11th to 20th	Day	4 8% 4 8% 4 4 4 3 5% 7% 48%	4985
	21st to end	Day	5% 9% 3 7% 4 5% 4 4 6% 9% 43%	5983
April	1st to 10th	Day	6% 8% 2 5% 4 4 4 4 6% 7% 50%	2520
	11th to 20th	Day	9% 12% 3 7% 4 4 5% 4 5% 7% 40%	2491
	21st to end	Day	10% 10% 3 7% 5% 4 4 4 6% 8% 40%	2520
May	1st to 10th	Day	11% 9% 2 5% 4 4 4 3 4 6% 47%	7737
	11th to 20th	Day	9% 7% 2 6% 4 5% 5% 4 6% 8% 45%	8191
	21st to end	Day	10% 7% 2 6% 4 5% 5% 4 7% 8% 41%	9026
June	1st to 10th	Day	6% 5% 2 5% 4 5% 5% 5% 8% 9% 47%	2940
	11th to 20th	Day	7% 4 1 5% 4 5% 5% 5% 6% 8% 49%	2940
	21st to end	Day	4 3 1 5% 4 5% 5% 5% 8% 8% 52%	2940
July	1st to 10th	Day	4 3 1 4 4 5% 6% 5% 8% 9% 50%	8249
	11th to 20th	Day	2 2 1 4 4 5% 5% 4 7% 8% 56%	8250
	21st to end	Day	6% 4 2 6% 5% 6% 6% 5% 8% 10% 43%	8957
August	1st to 10th	Day	8% 3 2 5% 4 5% 6% 5% 7% 10% 46%	6005
	11th to 20th	Day	3 3 1 4 4 5% 5% 5% 7% 8% 54%	5466
	21st to end	Day	8% 5% 2 7% 4 5% 5% 4 6% 7% 46%	5984
September	1st to 10th	Day	6% 4 1 4 3 3 4 3 6% 7% 58%	2400
	11th to 20th	Day	7% 4 1 4 3 3 4 4 6% 6% 58%	2369
	21st to end	Day	6% 4 1 4 3 3 4 3 3 6% 63%	2200
October	1st to 10th	Day	5% 4 1 3 2 2 2 2 2 4 73%	3307
	11th to 20th	Day	5% 6% 2 4 3 3 3 3 4 7% 60%	3250
	21st to end	Day	6% 5% 2 4 2 3 4 3 5% 6% 61%	3336
November	1st to 10th	Day	4 5% 1 5% 3 3 3 4 6% 9% 57%	1853
	11th to 20th	Day	3 6% 2 4 3 3 3 4 6% 8% 59%	1890
	21st to end	Day	2 7% 2 6% 4 4 4 4 6% 7% 54%	1729
December	1st to 10th	Day	2 4 2 5% 3 2 3 2 4 6% 68%	2700
	11th to 20th	Day	2 6% 3 5% 4 3 3 3 5% 6% 60%	3106
	21st to end	Day	3 6% 3 7% 5% 5% 5% 5% 6% 7% 49%	4092
January	1st to 10th	Night	2 7% 3 7% 5% 4 4 4 5% 7% 52%	8201
	11th to 20th	Night	1 4 3 8% 4 4 4 4 5% 6% 56%	8250
	21st to end	Night	1 5% 3 8% 4 3 3 3 5% 6% 58%	8509
February	1st to 10th	Night	2 6% 3 8% 4 4 5% 4 4 8% 52%	2730
	11th to 20th	Night	3 8% 2 7% 6% 4 5% 4 5% 8% 49%	2505
	21st to end	Night	2 8% 3 6% 4 4 4 2 4 5% 58%	2076
March	1st to 10th	Night	4 12% 4 7% 4 3 3 2 4 5% 53%	5494
	11th to 20th	Night	4 9% 3 6% 3 3 4 3 5% 8% 52%	5228
	21st to end	Night	7% 9% 3 7% 5% 5% 5% 4 6% 8% 42%	5217
April	1st to 10th	Night	4 8% 2 6% 4 4 4 4 6% 7% 52%	2100
	11th to 20th	Night	9% 8% 2 6% 4 3 5% 3 5% 6% 48%	2077
	21st to end	Night	13% 9% 3 5% 3 4 3 3 5% 7% 45%	2100
May	1st to 10th	Night	11% 8% 3 6% 4 4 4 3 6% 6% 44%	5204
	11th to 20th	Night	10% 6% 2 6% 4 5% 5% 4 6% 8% 44%	4701
	21st to end	Night	10% 8% 3 6% 4 4 5% 4 6% 7% 44%	5181
June	1st to 10th	Night	6% 3 1 4 4 3 4 5% 8% 10% 52%	1680
	11th to 20th	Night	6% 3 1 3 4 3 4 4 6% 7% 57%	1680
	21st to end	Night	5% 3 2 4 3 3 4 3 6% 8% 59%	1680
July	1st to 10th	Night	3 3 2 5% 4 5% 6% 5% 7% 9% 52%	4740
	11th to 20th	Night	2 2 1 3 3 4 4 4 6% 9% 61%	4740
	21st to end	Night	5% 4 2 6% 5% 6% 6% 5% 8% 9% 43%	5152
August	1st to 10th	Night	10% 4 2 5% 3 4 5% 4 7% 9% 48%	4023
	11th to 20th	Night	3 3 2 6% 4 4 5% 5% 7% 9% 52%	4470
	21st to end	Night	8% 5% 2 6% 4 4 5% 5% 7% 8% 47%	4993
September	1st to 10th	Night	7% 3 1 4 4 4 3 4 5% 7% 58%	2000
	11th to 20th	Night	8% 4 2 4 3 3 3 3 4 6% 60%	2030
	21st to end	Night	7% 5% 1 3 3 2 3 3 5% 6% 62%	2200
October	1st to 10th	Night	6% 3 1 3 2 2 2 2 3 4 71%	3877
	11th to 20th	Night	6% 5% 2 5% 4 3 3 3 4 6% 58%	3898
	21st to end	Night	5% 6% 2 4 3 3 3 2 5% 7% 60%	4430
November	1st to 10th	Night	4 5% 2 4 3 3 4 3 5% 9% 57%	2665
	11th to 20th	Night	3 6% 2 4 4 3 4 3 6% 7% 59%	2730
	21st to end	Night	3 6% 2 6% 4 3 4 4 6% 7% 56%	2888
December	1st to 10th	Night	1 5% 2 4 3 3 3 2 4 5% 67%	4710
	11th to 20th	Night	2 6% 2 5% 3 3 4 3 6% 7% 59%	5321
	21st to end	Night	3 6% 3 7% 4 5% 5% 4 6% 8% 49%	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	32% 4 11% 27% 23% 4	4723
	11th to 20th	Day	25% 6% 14% 23% 25% 7%	4740
	21st to end	Day	22% 4 12% 28% 27% 7%	5761
February	1st to 10th	Day	33% 5% 13% 27% 17% 6%	1890
	11th to 20th	Day	32% 5% 9% 28% 20% 6%	2012
	21st to end	Day	28% 3 10% 27% 24% 8%	1730
March	1st to 10th	Day	32% 4 6% 22% 29% 8%	4600
	11th to 20th	Day	34% 4 12% 25% 21% 4	4985
	21st to end	Day	34% 8% 13% 31% 12% 1	5983
April	1st to 10th	Day	32% 6% 12% 27% 16% 7%	2520
	11th to 20th	Day	41% 6% 9% 21% 17% 6%	2494
	21st to end	Day	41% 5% 9% 27% 17% 2	2520
May	1st to 10th	Day	37% 4 9% 28% 16% 4	7737
	11th to 20th	Day	35% 6% 9% 22% 23% 6%	8195
	21st to end	Day	37% 7% 9% 24% 19% 4	9027
June	1st to 10th	Day	30% 7% 17% 24% 17% 6%	2940
	11th to 20th	Day	29% 6% 10% 22% 21% 13%	2940
	21st to end	Day	25% 6% 9% 24% 23% 13%	2940
July	1st to 10th	Day	25% 6% 7% 18% 26% 18%	8181
	11th to 20th	Day	22% 5% 8% 24% 20% 22%	8175
	21st to end	Day	32% 7% 12% 17% 18% 13%	8759
August	1st to 10th	Day	34% 6% 12% 21% 18% 9%	4407
	11th to 20th	Day	28% 7% 9% 18% 22% 15%	3970
	21st to end	Day	27% 5% 8% 19% 26% 15%	4311
September	1st to 10th	Day	24% 5% 6% 21% 30% 14%	2400
	11th to 20th	Day	24% 5% 7% 22% 28% 13%	2369
	21st to end	Day	23% 4 6% 22% 35% 10%	2200
October	1st to 10th	Day	18% 2 4 18% 32% 26%	3307
	11th to 20th	Day	24% 3 10% 28% 26% 9%	3250
	21st to end	Day	24% 3 6% 31% 29% 6%	3336
November	1st to 10th	Day	24% 4 11% 27% 26% 9%	1853
	11th to 20th	Day	23% 3 9% 31% 27% 7%	1890
	21st to end	Day	28% 4 9% 28% 25% 6%	1729
December	1st to 10th	Day	19% 2 9% 33% 30% 7%	2700
	11th to 20th	Day	25% 4 8% 36% 23% 4	3104
	21st to end	Day	32% 5% 11% 26% 20% 5%	4092
January	1st to 10th	Night	30% 5% 9% 31% 20% 5%	8202
	11th to 20th	Night	27% 5% 13% 24% 23% 8%	8250
	21st to end	Night	27% 4 11% 26% 25% 7%	8509
February	1st to 10th	Night	31% 5% 14% 26% 20% 4	2730
	11th to 20th	Night	33% 5% 11% 27% 19% 5%	2505
	21st to end	Night	29% 3 8% 25% 26% 9%	2076
March	1st to 10th	Night	34% 3 5% 20% 30% 8%	5494
	11th to 20th	Night	31% 4 9% 19% 30% 6%	5228
	21st to end	Night	38% 6% 16% 26% 12% 2	5217
April	1st to 10th	Night	31% 5% 12% 27% 20% 5%	2100
	11th to 20th	Night	36% 5% 10% 26% 18% 5%	2077
	21st to end	Night	39% 4 10% 27% 20% 1	2100
May	1st to 10th	Night	39% 5% 10% 28% 14% 3	5205
	11th to 20th	Night	36% 5% 13% 26% 14% 5%	4702
	21st to end	Night	38% 7% 17% 24% 13% 2	5182
June	1st to 10th	Night	25% 6% 23% 29% 14% 4	1680
	11th to 20th	Night	24% 6% 14% 24% 20% 13%	1680
	21st to end	Night	22% 6% 10% 28% 24% 10%	1680
July	1st to 10th	Night	26% 5% 9% 27% 24% 8%	4700
	11th to 20th	Night	20% 5% 13% 24% 23% 15%	4692
	21st to end	Night	34% 7% 15% 20% 16% 7%	5038
August	1st to 10th	Night	34% 5% 16% 21% 20% 4	2945
	11th to 20th	Night	31% 7% 12% 23% 17% 11%	3242
	21st to end	Night	26% 6% 12% 22% 22% 11%	3597
September	1st to 10th	Night	26% 4 8% 23% 24% 16%	2000
	11th to 20th	Night	26% 4 7% 24% 26% 12%	2030
	21st to end	Night	24% 4 7% 25% 30% 11%	2200
October	1st to 10th	Night	19% 2 6% 20% 30% 23%	3877
	11th to 20th	Night	27% 4 8% 28% 25% 7%	3898
	21st to end	Night	25% 3 8% 29% 26% 9%	4430
November	1st to 10th	Night	24% 4 10% 27% 26% 8%	2665
	11th to 20th	Night	25% 4 8% 30% 25% 8%	2730
	21st to end	Night	27% 4 10% 29% 24% 7%	2888
December	1st to 10th	Night	21% 4 10% 36% 25% 6%	4710
	11th to 20th	Night	24% 4 8% 40% 21% 4	5322
	21st to end	Night	32% 5% 10% 28% 21% 4	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	15% 16% 35% 22% 8% 3	330
	11th to 20th	Day	11% 25% 40% 19% 5%	330
	21st to end	Day	5% 24% 51% 13% 4 2	363
February	1st to 10th	Day	10% 26% 45% 15% 3 1	330
	11th to 20th	Day	9% 19% 48% 21% 3 1	330
	21st to end	Day	13% 25% 43% 16% 3	273
March	1st to 10th	Day	7% 22% 42% 22% 6% 1	330
	11th to 20th	Day	13% 18% 40% 21% 7% 1	480
	21st to end	Day	16% 16% 42% 20% 5% 1	594
April	1st to 10th	Day	14% 21% 39% 18% 7% 1	540
	11th to 20th	Day	21% 18% 36% 19% 5% 1	532
	21st to end	Day	20% 15% 33% 22% 7% 3	540
May	1st to 10th	Day	21% 11% 31% 23% 11% 4	740
	11th to 20th	Day	20% 7% 27% 26% 15% 4	775
	21st to end	Day	12% 9% 30% 27% 17% 4	844
June	1st to 10th	Day	8% 6% 23% 33% 23% 8%	780
	11th to 20th	Day	9% 7% 32% 33% 15% 4	780
	21st to end	Day	6% 5% 27% 37% 19% 6%	780
July	1st to 10th	Day	8% 2 17% 36% 29% 8%	771
	11th to 20th	Day	5% 3 17% 36% 31% 8%	768
	21st to end	Day	6% 2 18% 34% 32% 7%	849
August	1st to 10th	Day	9% 2 19% 41% 24% 5%	611
	11th to 20th	Day	4 4 23% 36% 25% 7%	534
	21st to end	Day	7% 3 26% 35% 22% 6%	583
September	1st to 10th	Day	9% 5% 24% 36% 19% 7%	530
	11th to 20th	Day	8% 5% 26% 33% 20% 6%	499
	21st to end	Day	8% 7% 26% 29% 18% 12%	330
October	1st to 10th	Day	12% 5% 26% 33% 16% 8%	330
	11th to 20th	Day	7% 19% 38% 18% 13% 4	330
	21st to end	Day	9% 18% 39% 21% 11% 1	363
November	1st to 10th	Day	9% 16% 43% 19% 9% 3	330
	11th to 20th	Day	10% 19% 43% 21% 7% 1	330
	21st to end	Day	10% 16% 46% 20% 6% 2	330
December	1st to 10th	Day	8% 26% 39% 20% 6% 1	330
	11th to 20th	Day	13% 25% 45% 15% 1	330
	21st to end	Day	11% 24% 42% 18% 4 1	363
January	1st to 10th	Night	8% 22% 41% 22% 6% 2	1050
	11th to 20th	Night	7% 28% 42% 18% 4 1	1050
	21st to end	Night	7% 17% 49% 22% 4	972
February	1st to 10th	Night	5% 23% 49% 19% 3	840
	11th to 20th	Night	8% 18% 48% 23% 3	824
	21st to end	Night	8% 22% 47% 22% 1	692
March	1st to 10th	Night	8% 16% 43% 28% 5%	840
	11th to 20th	Night	10% 14% 39% 30% 7%	840
	21st to end	Night	11% 12% 43% 28% 6% 1	751
April	1st to 10th	Night	11% 15% 41% 27% 5%	630
	11th to 20th	Night	15% 12% 39% 28% 5% 1	623
	21st to end	Night	19% 10% 32% 33% 6% 1	630
May	1st to 10th	Night	16% 10% 29% 34% 10% 1	630
	11th to 20th	Night	17% 4 30% 36% 12% 2	621
	21st to end	Night	11% 7% 32% 34% 14% 2	683
June	1st to 10th	Night	8% 4 26% 43% 18% 2	630
	11th to 20th	Night	8% 5% 29% 44% 13%	630
	21st to end	Night	5% 3 29% 44% 17% 2	630
July	1st to 10th	Night	8% 2 16% 45% 28% 1	615
	11th to 20th	Night	3 1 16% 54% 24% 2	612
	21st to end	Night	5% 1 13% 50% 30% 2	690
August	1st to 10th	Night	8% 2 17% 48% 22% 3	627
	11th to 20th	Night	6% 2 16% 52% 23% 1	606
	21st to end	Night	6% 3 17% 46% 26% 2	660
September	1st to 10th	Night	8% 3 18% 45% 23% 3	600
	11th to 20th	Night	10% 4 22% 42% 20% 4	600
	21st to end	Night	9% 3 26% 45% 15% 1	600
October	1st to 10th	Night	12% 7% 29% 35% 15% 2	770
	11th to 20th	Night	9% 10% 37% 33% 10% 1	800
	21st to end	Night	11% 11% 39% 31% 7% 1	983
November	1st to 10th	Night	8% 11% 43% 31% 6% 1	1025
	11th to 20th	Night	7% 17% 44% 28% 3 1	1050
	21st to end	Night	7% 15% 44% 29% 5% 1	1050
December	1st to 10th	Night	8% 21% 44% 23% 4	1050
	11th to 20th	Night	8% 20% 46% 21% 4 1	1050
	21st to end	Night	8% 24% 44% 20% 3 1	1155

Page generated at 2026-08-12 01:37:15. Version ac07

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