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 2025-04-11.

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 4 4 6% 8% 51%	117427
	Night	4 6% 2 6% 4 4 4 3 5% 7% 54%	119759
Transparency	Day	30% 5% 10% 24% 22% 9%	117168
	Night	29% 5% 11% 26% 22% 7%	119608
Seeing	Day	11% 11% 31% 27% 15% 4	16207
	Night	9% 12% 35% 32% 10% 1	26377

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 7% 4 10% 5% 5% 5% 3 5% 6% 50%	3638
	11th to 20th	Day	1 6% 2 9% 5% 5% 4 3 6% 7% 52%	3640
	21st to end	Day	1 5% 2 4 3 3 3 3 5% 7% 63%	4441
February	1st to 10th	Day	2 8% 3 9% 5% 4 3 3 6% 9% 49%	1800
	11th to 20th	Day	1 7% 3 8% 5% 4 5% 4 5% 7% 51%	1904
	21st to end	Day	2 8% 2 6% 5% 3 3 3 5% 6% 55%	1650
March	1st to 10th	Day	4 9% 3 6% 3 4 4 3 4 7% 53%	4500
	11th to 20th	Day	4 8% 4 8% 4 4 4 4 5% 7% 47%	4878
	21st to end	Day	5% 9% 3 7% 4 5% 4 5% 6% 9% 42%	5854
April	1st to 10th	Day	6% 8% 2 5% 4 4 4 4 6% 7% 49%	2400
	11th to 20th	Day	10% 12% 3 7% 5% 4 4 4 5% 8% 39%	2252
	21st to end	Day	10% 9% 3 6% 5% 4 4 3 7% 8% 40%	2280
May	1st to 10th	Day	13% 12% 3 6% 5% 4 5% 3 5% 6% 39%	4165
	11th to 20th	Day	10% 7% 2 6% 4 5% 6% 4 7% 9% 41%	4388
	21st to end	Day	8% 7% 2 6% 4 5% 5% 4 8% 8% 42%	4825
June	1st to 10th	Day	5% 5% 2 5% 4 5% 5% 5% 7% 9% 47%	2660
	11th to 20th	Day	8% 4 2 5% 4 5% 5% 5% 7% 8% 48%	2660
	21st to end	Day	4 3 1 5% 3 5% 6% 6% 8% 8% 52%	2660
July	1st to 10th	Day	7% 5% 2 4 4 4 5% 4 7% 8% 50%	4430
	11th to 20th	Day	3 3 1 5% 5% 5% 6% 6% 8% 10% 49%	4430
	21st to end	Day	4 3 2 5% 4 5% 5% 5% 8% 8% 51%	4802
August	1st to 10th	Day	11% 4 2 5% 4 5% 6% 5% 7% 10% 42%	4158
	11th to 20th	Day	4 3 2 5% 5% 5% 6% 5% 7% 8% 50%	3763
	21st to end	Day	4 3 2 5% 4 4 5% 4 6% 8% 54%	4180
September	1st to 10th	Day	6% 4 1 4 3 3 4 3 6% 7% 58%	2280
	11th to 20th	Day	7% 4 1 3 3 3 4 4 6% 6% 59%	2251
	21st to end	Day	6% 5% 1 4 3 2 3 3 3 6% 64%	2090
October	1st to 10th	Day	5% 3 1 3 2 1 2 2 2 4 74%	3206
	11th to 20th	Day	5% 6% 2 4 3 3 3 3 4 7% 60%	3150
	21st to end	Day	6% 5% 2 4 2 3 4 3 5% 6% 60%	3232
November	1st to 10th	Day	4 5% 1 5% 3 3 4 4 6% 9% 56%	1763
	11th to 20th	Day	3 6% 2 4 2 3 3 4 5% 8% 59%	1800
	21st to end	Day	2 6% 3 7% 4 4 4 4 6% 7% 55%	1647
December	1st to 10th	Day	2 4 1 4 3 2 3 2 4 6% 69%	2620
	11th to 20th	Day	2 6% 3 5% 4 3 3 3 5% 6% 60%	3026
	21st to end	Day	3 6% 3 7% 5% 5% 5% 5% 6% 7% 49%	4004
January	1st to 10th	Night	2 8% 3 8% 5% 4 4 4 5% 7% 50%	6327
	11th to 20th	Night	1 4 4 8% 5% 5% 5% 4 6% 6% 54%	6340
	21st to end	Night	2 5% 3 7% 4 3 3 3 4 7% 60%	6579
February	1st to 10th	Night	2 6% 3 8% 4 4 5% 4 4 9% 51%	2600
	11th to 20th	Night	3 7% 2 7% 6% 4 5% 4 5% 8% 49%	2383
	21st to end	Night	2 9% 3 6% 4 4 4 2 4 5% 57%	1980
March	1st to 10th	Night	3 12% 4 7% 4 3 3 2 4 5% 54%	5374
	11th to 20th	Night	4 10% 3 6% 3 3 4 3 5% 8% 51%	5115
	21st to end	Night	7% 9% 3 7% 5% 5% 5% 4 6% 8% 42%	5104
April	1st to 10th	Night	4 8% 2 6% 4 4 4 4 6% 7% 52%	2000
	11th to 20th	Night	9% 8% 2 7% 4 3 5% 3 5% 6% 47%	1882
	21st to end	Night	13% 9% 3 5% 3 4 3 3 5% 7% 46%	1900
May	1st to 10th	Night	10% 7% 3 8% 5% 5% 5% 3 7% 7% 41%	2799
	11th to 20th	Night	10% 6% 2 5% 3 5% 5% 4 7% 9% 44%	2517
	21st to end	Night	9% 6% 2 6% 3 3 4 3 6% 7% 50%	2762
June	1st to 10th	Night	6% 3 1 4 3 3 4 5% 8% 11% 52%	1520
	11th to 20th	Night	7% 3 1 3 4 3 5% 4 6% 7% 56%	1520
	21st to end	Night	5% 3 2 4 3 3 3 4 6% 8% 59%	1520
July	1st to 10th	Night	5% 3 2 4 4 5% 5% 4 6% 8% 54%	2540
	11th to 20th	Night	2 2 1 3 4 5% 5% 4 7% 11% 55%	2540
	21st to end	Night	4 3 1 4 4 6% 5% 4 8% 8% 52%	2761
August	1st to 10th	Night	12% 5% 2 5% 3 4 5% 4 7% 9% 44%	2777
	11th to 20th	Night	4 4 2 7% 5% 5% 6% 5% 7% 9% 48%	3075
	21st to end	Night	4 2 1 5% 4 4 5% 5% 7% 8% 53%	3487
September	1st to 10th	Night	8% 3 2 4 4 4 3 4 5% 7% 57%	1900
	11th to 20th	Night	8% 4 2 4 3 3 3 2 4 6% 62%	1928
	21st to end	Night	6% 5% 1 3 3 2 3 3 5% 6% 62%	2090
October	1st to 10th	Night	6% 3 1 3 2 2 2 2 3 4 72%	3758
	11th to 20th	Night	6% 5% 2 5% 4 3 3 3 4 6% 58%	3778
	21st to end	Night	5% 6% 2 4 3 3 3 2 4 7% 60%	4293
November	1st to 10th	Night	4 6% 2 4 4 3 4 3 5% 9% 56%	2535
	11th to 20th	Night	3 6% 1 4 3 3 4 3 6% 7% 60%	2600
	21st to end	Night	3 6% 2 6% 4 3 4 4 6% 7% 56%	2750
December	1st to 10th	Night	1 5% 2 4 3 3 3 2 4 5% 68%	4570
	11th to 20th	Night	2 6% 3 5% 3 3 4 3 6% 7% 59%	5181
	21st to end	Night	3 6% 3 7% 4 5% 5% 4 6% 8% 49%	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	35% 4 10% 27% 20% 4	3639
	11th to 20th	Day	30% 6% 12% 20% 27% 5%	3640
	21st to end	Day	20% 4 13% 27% 28% 8%	4441
February	1st to 10th	Day	33% 5% 13% 26% 17% 6%	1800
	11th to 20th	Day	32% 5% 9% 28% 20% 6%	1914
	21st to end	Day	29% 4 10% 28% 22% 8%	1650
March	1st to 10th	Day	32% 4 6% 22% 29% 8%	4500
	11th to 20th	Day	35% 4 12% 25% 21% 3	4878
	21st to end	Day	34% 8% 13% 32% 12% 1	5854
April	1st to 10th	Day	32% 6% 12% 27% 16% 8%	2400
	11th to 20th	Day	43% 6% 9% 22% 16% 5%	2255
	21st to end	Day	41% 4 9% 28% 17% 1	2280
May	1st to 10th	Day	45% 5% 9% 21% 13% 6%	4165
	11th to 20th	Day	35% 7% 13% 26% 16% 2	4392
	21st to end	Day	33% 9% 11% 25% 19% 4	4825
June	1st to 10th	Day	30% 7% 17% 24% 16% 6%	2660
	11th to 20th	Day	30% 6% 10% 21% 20% 12%	2660
	21st to end	Day	25% 6% 9% 25% 22% 13%	2660
July	1st to 10th	Day	28% 5% 8% 17% 23% 19%	4361
	11th to 20th	Day	25% 6% 9% 22% 20% 17%	4355
	21st to end	Day	26% 6% 8% 18% 24% 18%	4651
August	1st to 10th	Day	35% 6% 12% 21% 18% 8%	4143
	11th to 20th	Day	28% 7% 9% 18% 22% 16%	3799
	21st to end	Day	26% 5% 8% 19% 26% 16%	4179
September	1st to 10th	Day	24% 5% 6% 20% 30% 15%	2280
	11th to 20th	Day	24% 5% 7% 23% 28% 14%	2251
	21st to end	Day	22% 4 6% 22% 36% 10%	2090
October	1st to 10th	Day	18% 2 4 18% 32% 26%	3206
	11th to 20th	Day	24% 3 10% 28% 26% 9%	3150
	21st to end	Day	24% 3 7% 31% 29% 6%	3232
November	1st to 10th	Day	24% 4 11% 26% 26% 9%	1763
	11th to 20th	Day	23% 3 9% 30% 27% 8%	1800
	21st to end	Day	27% 4 9% 27% 26% 7%	1647
December	1st to 10th	Day	18% 2 9% 33% 30% 7%	2620
	11th to 20th	Day	25% 4 8% 36% 23% 4	3024
	21st to end	Day	32% 5% 11% 26% 20% 5%	4004
January	1st to 10th	Night	32% 5% 11% 26% 20% 6%	6327
	11th to 20th	Night	29% 6% 13% 19% 25% 8%	6340
	21st to end	Night	25% 4 13% 26% 26% 7%	6579
February	1st to 10th	Night	31% 5% 15% 26% 19% 4	2600
	11th to 20th	Night	33% 6% 11% 27% 19% 4	2383
	21st to end	Night	31% 3 8% 25% 25% 8%	1980
March	1st to 10th	Night	34% 3 5% 19% 30% 8%	5374
	11th to 20th	Night	31% 4 9% 19% 30% 6%	5115
	21st to end	Night	38% 6% 16% 26% 12% 1	5104
April	1st to 10th	Night	31% 5% 12% 28% 19% 5%	2000
	11th to 20th	Night	37% 5% 10% 27% 17% 4	1882
	21st to end	Night	38% 4 10% 27% 20% 1	1900
May	1st to 10th	Night	40% 7% 11% 24% 14% 5%	2799
	11th to 20th	Night	33% 7% 18% 30% 10% 3	2518
	21st to end	Night	32% 6% 19% 25% 15% 3	2762
June	1st to 10th	Night	24% 6% 24% 28% 13% 4	1520
	11th to 20th	Night	24% 6% 14% 23% 20% 12%	1520
	21st to end	Night	22% 6% 10% 29% 24% 9%	1520
July	1st to 10th	Night	27% 5% 10% 25% 24% 10%	2500
	11th to 20th	Night	22% 6% 13% 24% 25% 10%	2492
	21st to end	Night	26% 5% 13% 26% 18% 11%	2674
August	1st to 10th	Night	35% 5% 17% 21% 19% 4	2769
	11th to 20th	Night	30% 7% 13% 23% 16% 11%	3105
	21st to end	Night	25% 5% 12% 23% 23% 12%	3487
September	1st to 10th	Night	27% 4 7% 21% 24% 17%	1900
	11th to 20th	Night	25% 4 7% 25% 26% 13%	1928
	21st to end	Night	23% 4 7% 25% 31% 10%	2090
October	1st to 10th	Night	19% 2 6% 19% 30% 23%	3758
	11th to 20th	Night	27% 4 8% 29% 25% 7%	3778
	21st to end	Night	26% 3 8% 29% 25% 9%	4293
November	1st to 10th	Night	25% 4 10% 26% 26% 8%	2535
	11th to 20th	Night	24% 4 9% 30% 25% 8%	2600
	21st to end	Night	27% 4 9% 28% 25% 7%	2750
December	1st to 10th	Night	20% 4 9% 36% 25% 6%	4570
	11th to 20th	Night	24% 4 8% 40% 21% 3	5182
	21st to end	Night	32% 5% 10% 28% 20% 4	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	16% 14% 35% 24% 9% 3	300
	11th to 20th	Day	10% 23% 42% 20% 5%	300
	21st to end	Day	5% 23% 52% 14% 5% 2	330
February	1st to 10th	Day	11% 26% 45% 14% 3 1	300
	11th to 20th	Day	9% 20% 48% 19% 3 1	300
	21st to end	Day	13% 24% 43% 16% 3	249
March	1st to 10th	Day	6% 22% 41% 24% 6% 1	300
	11th to 20th	Day	13% 16% 40% 22% 7% 2	443
	21st to end	Day	16% 16% 41% 20% 5% 1	550
April	1st to 10th	Day	14% 22% 38% 18% 7% 1	500
	11th to 20th	Day	22% 18% 36% 19% 5% 1	453
	21st to end	Day	21% 13% 30% 23% 8% 3	460
May	1st to 10th	Day	22% 11% 31% 22% 11% 3	641
	11th to 20th	Day	22% 5% 25% 26% 16% 5%	675
	21st to end	Day	12% 8% 30% 27% 18% 4	734
June	1st to 10th	Day	7% 5% 22% 33% 24% 8%	680
	11th to 20th	Day	9% 6% 33% 33% 15% 4	680
	21st to end	Day	6% 4 26% 39% 19% 6%	680
July	1st to 10th	Day	10% 2 17% 33% 30% 8%	671
	11th to 20th	Day	4 3 18% 37% 29% 7%	668
	21st to end	Day	7% 1 19% 34% 32% 8%	739
August	1st to 10th	Day	10% 2 18% 40% 24% 5%	527
	11th to 20th	Day	5% 5% 24% 36% 24% 6%	477
	21st to end	Day	6% 3 27% 35% 23% 7%	539
September	1st to 10th	Day	9% 4 24% 36% 20% 7%	490
	11th to 20th	Day	9% 5% 26% 33% 21% 7%	461
	21st to end	Day	8% 7% 27% 31% 16% 11%	300
October	1st to 10th	Day	11% 6% 26% 33% 16% 8%	300
	11th to 20th	Day	8% 17% 37% 19% 14% 5%	300
	21st to end	Day	10% 18% 40% 21% 10% 2	330
November	1st to 10th	Day	9% 15% 42% 19% 10% 4	300
	11th to 20th	Day	11% 20% 42% 20% 6% 1	300
	21st to end	Day	9% 15% 48% 20% 6% 2	300
December	1st to 10th	Day	8% 25% 39% 21% 6% 1	300
	11th to 20th	Day	12% 25% 46% 16% 1	300
	21st to end	Day	11% 25% 41% 18% 5% 1	330
January	1st to 10th	Night	8% 22% 40% 22% 6% 2	1000
	11th to 20th	Night	7% 27% 42% 19% 5% 1	1000
	21st to end	Night	7% 17% 49% 22% 5%	926
February	1st to 10th	Night	5% 23% 49% 19% 4	800
	11th to 20th	Night	8% 18% 47% 23% 3	784
	21st to end	Night	8% 20% 49% 22% 1	660
March	1st to 10th	Night	8% 16% 43% 28% 5% 1	800
	11th to 20th	Night	10% 13% 38% 31% 8% 1	800
	21st to end	Night	11% 12% 42% 28% 6% 1	715
April	1st to 10th	Night	11% 16% 41% 28% 5%	600
	11th to 20th	Night	15% 12% 38% 27% 5% 1	565
	21st to end	Night	19% 11% 30% 34% 7% 1	570
May	1st to 10th	Night	16% 9% 30% 33% 10% 1	570
	11th to 20th	Night	17% 3 28% 37% 13% 2	561
	21st to end	Night	11% 6% 32% 34% 15% 2	617
June	1st to 10th	Night	7% 4 24% 43% 19% 2	570
	11th to 20th	Night	9% 5% 29% 44% 13%	570
	21st to end	Night	5% 3 27% 45% 18% 2	570
July	1st to 10th	Night	8% 2 14% 44% 31% 1	555
	11th to 20th	Night	2 1 16% 54% 25% 2	552
	21st to end	Night	6% 1 12% 49% 30% 2	624
August	1st to 10th	Night	9% 2 14% 47% 25% 3	567
	11th to 20th	Night	6% 2 16% 52% 22% 2	564
	21st to end	Night	5% 3 17% 47% 27% 3	627
September	1st to 10th	Night	8% 3 18% 44% 24% 3	570
	11th to 20th	Night	10% 3 22% 41% 21% 4	570
	21st to end	Night	9% 3 27% 45% 14% 1	570
October	1st to 10th	Night	12% 7% 30% 34% 15% 2	731
	11th to 20th	Night	8% 9% 36% 34% 11% 1	760
	21st to end	Night	11% 11% 39% 31% 7% 1	934
November	1st to 10th	Night	8% 10% 43% 31% 6% 1	975
	11th to 20th	Night	7% 17% 44% 28% 3 1	1000
	21st to end	Night	7% 15% 44% 28% 5% 1	1000
December	1st to 10th	Night	8% 21% 43% 23% 5%	1000
	11th to 20th	Night	7% 20% 47% 21% 4 1	1000
	21st to end	Night	8% 24% 43% 20% 3 1	1100

Page generated at 2025-04-08 07:17:24. Version ac07

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