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 2024-02-20.

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	6% 5% 2 5% 5% 3 5% 5% 6% 8% 51%	78405
	Night	5% 5% 2 5% 5% 3 4 4 5% 7% 54%	80847
Transparency	Day	31% 5% 11% 25% 21% 7%	78109
	Night	29% 5% 12% 27% 20% 7%	80665
Seeing	Day	11% 11% 31% 27% 15% 4	14646
	Night	9% 12% 35% 32% 11% 1	24835

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 7% 6% 4 5% 3 5% 7% 54%	2538
	11th to 20th	Day	2 6% 3 8% 8% 4 5% 4 5% 8% 47%	2540
	21st to end	Day	1 4 2 4 5% 2 4 5% 5% 8% 61%	3091
February	1st to 10th	Day	3 8% 3 8% 6% 3 4 3 6% 9% 48%	1710
	11th to 20th	Day	1 7% 3 7% 5% 3 4 5% 5% 8% 52%	1796
	21st to end	Day	2 9% 3 6% 5% 3 4 4 5% 7% 53%	1480
March	1st to 10th	Day	4 7% 3 6% 5% 2 4 4 4 7% 54%	1800
	11th to 20th	Day	6% 7% 3 6% 5% 3 4 4 6% 9% 47%	1928
	21st to end	Day	6% 8% 3 7% 5% 3 6% 6% 5% 8% 44%	2326
April	1st to 10th	Day	7% 7% 3 5% 4 3 4 5% 6% 8% 49%	2160
	11th to 20th	Day	10% 10% 4 6% 5% 3 5% 4 5% 8% 40%	2131
	21st to end	Day	10% 9% 3 5% 5% 4 4 5% 6% 8% 40%	2160
May	1st to 10th	Day	15% 8% 3 5% 4 4 5% 4 6% 8% 38%	2359
	11th to 20th	Day	16% 8% 3 6% 4 3 5% 4 6% 8% 37%	2478
	21st to end	Day	9% 7% 3 6% 6% 3 6% 6% 8% 8% 38%	2724
June	1st to 10th	Day	6% 4 2 5% 4 4 5% 6% 7% 10% 47%	2520
	11th to 20th	Day	8% 4 2 4 4 3 5% 6% 6% 9% 48%	2520
	21st to end	Day	4 2 1 3 4 3 6% 7% 7% 8% 53%	2520
July	1st to 10th	Day	8% 4 2 4 5% 3 6% 7% 8% 9% 45%	2520
	11th to 20th	Day	4 3 2 3 6% 3 5% 6% 7% 9% 52%	2520
	21st to end	Day	6% 3 2 5% 6% 5% 6% 7% 8% 9% 44%	2742
August	1st to 10th	Day	6% 4 2 5% 6% 4 6% 6% 8% 10% 43%	2366
	11th to 20th	Day	5% 3 2 4 5% 4 5% 6% 7% 8% 53%	2148
	21st to end	Day	5% 3 2 4 5% 3 5% 6% 6% 8% 53%	2376
September	1st to 10th	Day	7% 4 1 3 4 2 4 4 5% 7% 59%	2160
	11th to 20th	Day	7% 4 1 3 4 2 3 5% 6% 6% 59%	2133
	21st to end	Day	6% 5% 1 3 3 2 3 3 3 6% 64%	1980
October	1st to 10th	Day	9% 5% 2 4 4 2 3 4 4 6% 58%	1823
	11th to 20th	Day	5% 5% 2 4 4 2 3 3 4 6% 63%	1800
	21st to end	Day	6% 5% 2 3 3 2 4 3 5% 6% 60%	1868
November	1st to 10th	Day	3 5% 1 5% 4 3 4 4 5% 10% 58%	1673
	11th to 20th	Day	3 6% 2 4 3 2 3 5% 5% 8% 59%	1710
	21st to end	Day	2 5% 3 6% 4 3 4 5% 6% 7% 55%	1565
December	1st to 10th	Day	2 4 2 5% 6% 3 4 4 6% 8% 56%	1520
	11th to 20th	Day	4 7% 3 5% 5% 2 4 4 4 6% 57%	1926
	21st to end	Day	2 6% 3 6% 6% 4 5% 5% 5% 6% 52%	2794
January	1st to 10th	Night	2 6% 2 5% 6% 3 4 5% 6% 7% 52%	4417
	11th to 20th	Night	1 4 4 7% 5% 3 5% 5% 6% 7% 53%	4430
	21st to end	Night	2 6% 2 6% 5% 2 3 4 5% 7% 57%	4604
February	1st to 10th	Night	2 6% 3 7% 5% 3 5% 4 4 9% 52%	2470
	11th to 20th	Night	3 6% 3 6% 6% 3 4 5% 5% 8% 50%	2255
	21st to end	Night	2 9% 4 6% 5% 3 4 3 4 6% 54%	1776
March	1st to 10th	Night	3 8% 3 6% 5% 3 4 4 5% 7% 53%	2160
	11th to 20th	Night	6% 7% 2 5% 4 3 4 5% 5% 7% 53%	2030
	21st to end	Night	7% 9% 3 5% 5% 3 6% 5% 6% 8% 45%	2030
April	1st to 10th	Night	5% 8% 3 5% 5% 3 4 4 5% 8% 51%	1800
	11th to 20th	Night	9% 8% 3 6% 5% 3 5% 4 4 7% 47%	1777
	21st to end	Night	13% 8% 3 5% 3 2 4 4 5% 7% 47%	1800
May	1st to 10th	Night	13% 7% 3 5% 5% 3 5% 5% 8% 8% 39%	1595
	11th to 20th	Night	15% 7% 2 5% 3 3 4 4 5% 9% 42%	1417
	21st to end	Night	8% 5% 3 5% 5% 3 5% 5% 7% 8% 46%	1552
June	1st to 10th	Night	6% 3 1 4 4 2 3 6% 8% 11% 52%	1440
	11th to 20th	Night	7% 2 1 3 4 3 5% 5% 6% 8% 56%	1440
	21st to end	Night	5% 3 2 3 4 2 3 4 6% 8% 60%	1440
July	1st to 10th	Night	7% 4 2 3 5% 3 5% 5% 7% 9% 50%	1440
	11th to 20th	Night	2 2 2 3 4 3 5% 5% 6% 8% 59%	1440
	21st to end	Night	5% 3 1 4 5% 4 5% 6% 7% 9% 50%	1576
August	1st to 10th	Night	6% 4 2 5% 4 2 5% 5% 7% 9% 50%	1569
	11th to 20th	Night	4 3 2 4 4 2 4 4 6% 9% 58%	1752
	21st to end	Night	5% 3 1 5% 5% 3 4 6% 6% 7% 56%	1980
September	1st to 10th	Night	8% 3 2 4 4 4 2 4 5% 7% 57%	1800
	11th to 20th	Night	8% 4 2 3 4 2 3 3 4 6% 61%	1826
	21st to end	Night	7% 4 2 3 4 2 3 4 5% 6% 62%	1980
October	1st to 10th	Night	10% 5% 2 3 4 2 3 3 5% 6% 56%	2132
	11th to 20th	Night	6% 4 1 3 4 3 3 3 4 5% 64%	2160
	21st to end	Night	6% 7% 2 4 3 3 3 3 5% 6% 58%	2468
November	1st to 10th	Night	4 5% 2 4 4 2 3 4 5% 9% 57%	2405
	11th to 20th	Night	3 6% 2 4 4 3 4 3 5% 7% 59%	2470
	21st to end	Night	3 6% 3 5% 4 2 4 5% 6% 7% 56%	2612
December	1st to 10th	Night	2 7% 3 5% 5% 3 4 4 5% 7% 56%	2660
	11th to 20th	Night	3 6% 3 4 4 3 4 4 6% 7% 55%	3271
	21st to end	Night	3 5% 3 6% 5% 3 5% 5% 6% 8% 51%	4873

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	30% 4 12% 28% 21% 5%	2539
	11th to 20th	Day	34% 8% 16% 20% 18% 4	2540
	21st to end	Day	22% 4 18% 32% 20% 5%	3091
February	1st to 10th	Day	34% 5% 13% 26% 16% 5%	1710
	11th to 20th	Day	31% 5% 9% 28% 21% 6%	1806
	21st to end	Day	31% 4 11% 29% 19% 6%	1480
March	1st to 10th	Day	30% 3 10% 30% 23% 5%	1800
	11th to 20th	Day	34% 3 14% 24% 20% 5%	1928
	21st to end	Day	36% 6% 12% 28% 15% 3	2326
April	1st to 10th	Day	32% 6% 13% 27% 15% 8%	2160
	11th to 20th	Day	42% 6% 9% 23% 15% 5%	2134
	21st to end	Day	41% 4 9% 28% 17% 1	2160
May	1st to 10th	Day	44% 5% 12% 23% 13% 2	2359
	11th to 20th	Day	45% 6% 13% 23% 13% 1	2482
	21st to end	Day	39% 8% 13% 24% 14% 3	2724
June	1st to 10th	Day	30% 7% 17% 24% 16% 6%	2520
	11th to 20th	Day	30% 6% 10% 21% 20% 12%	2520
	21st to end	Day	25% 6% 9% 25% 22% 13%	2520
July	1st to 10th	Day	32% 6% 11% 21% 20% 11%	2451
	11th to 20th	Day	25% 6% 10% 22% 22% 15%	2445
	21st to end	Day	32% 7% 11% 24% 21% 6%	2590
August	1st to 10th	Day	33% 6% 13% 24% 16% 9%	2350
	11th to 20th	Day	27% 5% 9% 23% 24% 12%	2148
	21st to end	Day	27% 6% 8% 22% 26% 12%	2376
September	1st to 10th	Day	24% 5% 6% 21% 28% 16%	2160
	11th to 20th	Day	24% 5% 7% 23% 28% 14%	2133
	21st to end	Day	23% 4 6% 22% 36% 8%	1980
October	1st to 10th	Day	30% 3 6% 24% 27% 10%	1823
	11th to 20th	Day	24% 4 8% 27% 27% 10%	1800
	21st to end	Day	25% 4 10% 30% 24% 8%	1868
November	1st to 10th	Day	23% 5% 11% 27% 26% 9%	1673
	11th to 20th	Day	24% 3 10% 31% 26% 7%	1710
	21st to end	Day	27% 4 9% 27% 26% 7%	1565
December	1st to 10th	Day	27% 3 15% 29% 19% 7%	1520
	11th to 20th	Day	29% 4 9% 31% 24% 3	1924
	21st to end	Day	32% 5% 12% 26% 21% 5%	2794
January	1st to 10th	Night	29% 5% 11% 32% 19% 4	4417
	11th to 20th	Night	28% 7% 18% 20% 19% 8%	4430
	21st to end	Night	28% 4 18% 31% 16% 3	4604
February	1st to 10th	Night	32% 5% 15% 26% 18% 4	2470
	11th to 20th	Night	32% 5% 10% 28% 20% 4	2255
	21st to end	Night	33% 3 9% 26% 23% 7%	1776
March	1st to 10th	Night	33% 3 8% 27% 23% 5%	2160
	11th to 20th	Night	31% 4 10% 26% 25% 5%	2030
	21st to end	Night	37% 6% 12% 28% 15% 3	2030
April	1st to 10th	Night	31% 5% 13% 27% 19% 6%	1800
	11th to 20th	Night	37% 4 10% 28% 16% 4	1777
	21st to end	Night	38% 4 10% 27% 21% 1	1800
May	1st to 10th	Night	40% 7% 13% 27% 12% 1	1595
	11th to 20th	Night	40% 5% 16% 27% 12%	1418
	21st to end	Night	34% 7% 18% 23% 13% 4	1552
June	1st to 10th	Night	24% 6% 24% 28% 13% 5%	1440
	11th to 20th	Night	24% 6% 15% 23% 20% 13%	1440
	21st to end	Night	22% 6% 10% 30% 25% 9%	1440
July	1st to 10th	Night	30% 6% 13% 27% 19% 6%	1400
	11th to 20th	Night	22% 6% 10% 26% 23% 13%	1392
	21st to end	Night	27% 6% 16% 30% 16% 6%	1488
August	1st to 10th	Night	30% 6% 20% 23% 15% 6%	1561
	11th to 20th	Night	22% 5% 10% 29% 22% 12%	1752
	21st to end	Night	26% 5% 9% 26% 23% 11%	1980
September	1st to 10th	Night	27% 4 7% 21% 23% 18%	1800
	11th to 20th	Night	25% 4 8% 25% 25% 13%	1826
	21st to end	Night	24% 4 7% 26% 30% 9%	1980
October	1st to 10th	Night	29% 4 11% 21% 26% 8%	2132
	11th to 20th	Night	22% 4 9% 29% 23% 12%	2160
	21st to end	Night	28% 4 12% 25% 23% 9%	2468
November	1st to 10th	Night	24% 5% 11% 26% 26% 8%	2405
	11th to 20th	Night	25% 4 9% 31% 24% 7%	2470
	21st to end	Night	27% 4 9% 27% 25% 7%	2612
December	1st to 10th	Night	28% 5% 14% 29% 18% 7%	2660
	11th to 20th	Night	27% 5% 10% 34% 21% 2	3272
	21st to end	Night	31% 5% 12% 28% 19% 5%	4873

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% 14% 34% 24% 9% 3	270
	11th to 20th	Day	11% 22% 42% 19% 6%	270
	21st to end	Day	5% 22% 53% 13% 5% 2	297
February	1st to 10th	Day	11% 24% 47% 13% 4 1	270
	11th to 20th	Day	9% 21% 47% 18% 4 1	267
	21st to end	Day	11% 24% 45% 16% 3 1	198
March	1st to 10th	Day	5% 22% 42% 24% 6% 1	240
	11th to 20th	Day	13% 16% 39% 24% 8% 1	368
	21st to end	Day	16% 16% 40% 21% 5% 1	462
April	1st to 10th	Day	15% 22% 38% 16% 7% 1	420
	11th to 20th	Day	21% 18% 37% 18% 5% 1	412
	21st to end	Day	22% 14% 29% 23% 9% 4	420
May	1st to 10th	Day	21% 10% 31% 23% 12% 4	591
	11th to 20th	Day	23% 5% 25% 25% 16% 5%	625
	21st to end	Day	13% 8% 29% 27% 19% 5%	679
June	1st to 10th	Day	7% 5% 21% 33% 25% 9%	630
	11th to 20th	Day	10% 5% 32% 34% 16% 4	630
	21st to end	Day	6% 3 26% 38% 21% 6%	630
July	1st to 10th	Day	9% 2 16% 33% 32% 7%	621
	11th to 20th	Day	5% 4 18% 38% 28% 8%	618
	21st to end	Day	7% 1 18% 34% 32% 7%	684
August	1st to 10th	Day	10% 2 19% 40% 25% 5%	485
	11th to 20th	Day	5% 4 24% 36% 25% 7%	437
	21st to end	Day	6% 3 27% 34% 22% 7%	495
September	1st to 10th	Day	10% 4 25% 36% 18% 6%	450
	11th to 20th	Day	9% 5% 25% 34% 21% 7%	423
	21st to end	Day	9% 7% 27% 29% 16% 12%	270
October	1st to 10th	Day	12% 6% 27% 30% 17% 8%	270
	11th to 20th	Day	8% 18% 39% 19% 13% 4	270
	21st to end	Day	10% 18% 38% 21% 11% 2	297
November	1st to 10th	Day	9% 14% 41% 20% 11% 4	270
	11th to 20th	Day	12% 19% 40% 21% 6% 1	270
	21st to end	Day	10% 15% 47% 20% 6% 3	270
December	1st to 10th	Day	9% 25% 40% 21% 6%	270
	11th to 20th	Day	12% 23% 47% 17% 1	270
	21st to end	Day	10% 24% 42% 18% 4 1	297
January	1st to 10th	Night	8% 23% 39% 22% 7% 2	950
	11th to 20th	Night	7% 27% 42% 19% 5% 1	950
	21st to end	Night	7% 18% 49% 21% 5%	880
February	1st to 10th	Night	5% 23% 48% 19% 4	760
	11th to 20th	Night	8% 19% 46% 24% 4	742
	21st to end	Night	8% 19% 50% 22% 1	592
March	1st to 10th	Night	7% 16% 44% 27% 5% 1	720
	11th to 20th	Night	9% 13% 38% 31% 8% 1	720
	21st to end	Night	11% 11% 42% 27% 7% 1	644
April	1st to 10th	Night	11% 16% 42% 26% 5%	540
	11th to 20th	Night	15% 12% 39% 27% 6% 1	533
	21st to end	Night	18% 11% 29% 34% 7% 1	540
May	1st to 10th	Night	17% 8% 29% 34% 11% 1	540
	11th to 20th	Night	18% 3 27% 37% 13% 2	531
	21st to end	Night	10% 6% 32% 34% 16% 2	584
June	1st to 10th	Night	8% 4 23% 43% 20% 2	540
	11th to 20th	Night	8% 5% 28% 45% 14%	540
	21st to end	Night	5% 3 26% 45% 19% 2	540
July	1st to 10th	Night	8% 1 13% 44% 32% 1	525
	11th to 20th	Night	2 1 16% 53% 25% 2	522
	21st to end	Night	6% 1 12% 48% 31% 2	591
August	1st to 10th	Night	9% 1 15% 46% 26% 3	537
	11th to 20th	Night	6% 1 15% 52% 23% 1	534
	21st to end	Night	5% 3 16% 46% 28% 3	594
September	1st to 10th	Night	8% 3 19% 44% 23% 3	540
	11th to 20th	Night	10% 3 21% 40% 21% 4	540
	21st to end	Night	9% 3 27% 45% 14% 1	540
October	1st to 10th	Night	12% 7% 30% 33% 15% 2	692
	11th to 20th	Night	8% 10% 37% 33% 11% 1	720
	21st to end	Night	12% 11% 38% 30% 7% 1	884
November	1st to 10th	Night	8% 10% 43% 31% 7% 1	925
	11th to 20th	Night	7% 17% 44% 27% 3 1	950
	21st to end	Night	7% 15% 44% 28% 6% 1	950
December	1st to 10th	Night	8% 22% 44% 22% 4	950
	11th to 20th	Night	7% 19% 48% 21% 4 1	950
	21st to end	Night	8% 25% 42% 20% 4 1	1045

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