Black Canyon of the Gunnison
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Black Canyon of the Gunnison clear sky chart from 2005-11-06 to 2025-07-06.

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 8% 3 6% 4 4 4 4 6% 7% 52%	124005
	Night	5% 9% 3 6% 4 3 4 3 5% 6% 52%	123740
Transparency	Day	29% 8% 9% 22% 23% 10%	123764
	Night	31% 6% 9% 23% 22% 8%	123568
Seeing	Day	9% 13% 29% 32% 15% 2	16250
	Night	10% 6% 23% 41% 19% 1	26397

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	3 11% 5% 14% 5% 5% 5% 4 5% 5% 39%	3911
	11th to 20th	Day	5% 12% 4 11% 5% 4 4 4 5% 5% 42%	4100
	21st to end	Day	3 10% 4 8% 4 3 3 2 4 5% 54%	4510
February	1st to 10th	Day	7% 12% 4 9% 5% 4 4 3 5% 6% 41%	1800
	11th to 20th	Day	7% 15% 5% 8% 4 3 4 3 6% 6% 40%	1789
	21st to end	Day	4 16% 6% 9% 4 3 4 3 4 4 41%	1650
March	1st to 10th	Day	4 14% 4 8% 4 3 4 3 5% 5% 46%	4926
	11th to 20th	Day	3 13% 5% 9% 5% 5% 5% 4 5% 6% 41%	5000
	21st to end	Day	4 14% 4 9% 5% 5% 5% 4 6% 6% 37%	5519
April	1st to 10th	Day	7% 11% 3 6% 4 3 4 4 4 7% 46%	2400
	11th to 20th	Day	7% 11% 4 7% 5% 5% 4 4 6% 7% 42%	2371
	21st to end	Day	6% 9% 3 6% 5% 4 5% 4 7% 8% 45%	2400
May	1st to 10th	Day	5% 11% 3 7% 5% 4 5% 4 6% 8% 43%	5806
	11th to 20th	Day	3 6% 2 6% 4 5% 5% 4 6% 8% 50%	5973
	21st to end	Day	4 5% 1 4 3 3 4 3 6% 7% 60%	6925
June	1st to 10th	Day	3 4 1 4 4 3 4 4 6% 8% 59%	2800
	11th to 20th	Day	4 3 1 4 3 3 4 3 5% 6% 65%	2800
	21st to end	Day	2 3 1 4 3 4 4 4 5% 7% 63%	2800
July	1st to 10th	Day	2 3 1 4 2 3 3 3 4 5% 69%	4501
	11th to 20th	Day	2 2 1 3 3 4 6% 6% 10% 13% 50%	4149
	21st to end	Day	3 3 1 4 4 4 5% 4 7% 8% 57%	4454
August	1st to 10th	Day	4 3 1 5% 4 5% 6% 7% 10% 12% 42%	4092
	11th to 20th	Day	4 3 1 5% 4 5% 5% 5% 7% 8% 53%	3918
	21st to end	Day	3 3 2 5% 4 4 6% 5% 8% 10% 51%	4180
September	1st to 10th	Day	5% 3 1 4 3 4 4 5% 6% 7% 58%	2280
	11th to 20th	Day	5% 4 1 4 3 3 4 4 5% 7% 60%	2273
	21st to end	Day	5% 4 1 4 3 3 3 2 4 6% 65%	2001
October	1st to 10th	Day	5% 3 1 2 2 2 2 2 3 4 75%	3170
	11th to 20th	Day	5% 4 2 5% 4 4 5% 4 7% 8% 52%	3150
	21st to end	Day	6% 6% 2 4 3 3 2 2 4 5% 63%	3438
November	1st to 10th	Day	4 7% 2 4 3 2 3 2 5% 6% 62%	1912
	11th to 20th	Day	7% 7% 2 5% 3 3 2 2 3 4 60%	1757
	21st to end	Day	5% 10% 2 7% 3 2 3 3 4 4 57%	1600
December	1st to 10th	Day	5% 10% 3 4 3 2 2 2 3 5% 62%	2620
	11th to 20th	Day	5% 9% 4 7% 3 3 3 3 4 7% 52%	3026
	21st to end	Day	4 11% 4 8% 5% 4 5% 4 5% 7% 44%	4004
January	1st to 10th	Night	3 12% 7% 13% 5% 4 4 3 4 5% 39%	6097
	11th to 20th	Night	5% 16% 4 8% 4 3 2 2 4 5% 46%	5880
	21st to end	Night	3 14% 5% 7% 4 3 3 2 4 4 50%	6468
February	1st to 10th	Night	6% 15% 3 8% 4 3 3 3 5% 5% 45%	2600
	11th to 20th	Night	6% 14% 4 9% 4 3 3 3 5% 5% 43%	2497
	21st to end	Night	5% 16% 4 7% 3 4 4 3 4 5% 46%	1980
March	1st to 10th	Night	5% 16% 4 7% 5% 4 3 3 4 5% 44%	4950
	11th to 20th	Night	3 13% 5% 8% 4 4 4 3 5% 6% 46%	5000
	21st to end	Night	6% 18% 4 8% 5% 4 4 3 5% 5% 39%	5454
April	1st to 10th	Night	8% 13% 3 6% 5% 4 3 3 5% 5% 45%	2000
	11th to 20th	Night	8% 13% 4 8% 4 4 3 3 5% 5% 43%	1977
	21st to end	Night	10% 9% 2 5% 4 4 3 3 6% 6% 48%	2000
May	1st to 10th	Night	9% 10% 2 6% 4 4 4 4 7% 7% 43%	4158
	11th to 20th	Night	6% 6% 2 6% 4 4 5% 4 5% 7% 51%	3937
	21st to end	Night	6% 4 1 4 2 2 3 3 4 6% 64%	3972
June	1st to 10th	Night	3 3 2 4 4 3 5% 4 5% 8% 60%	1600
	11th to 20th	Night	4 3 1 3 3 3 2 3 4 5% 68%	1600
	21st to end	Night	3 2 1 3 3 4 4 4 6% 7% 63%	1600
July	1st to 10th	Night	2 2 1 3 3 3 4 3 5% 6% 68%	2580
	11th to 20th	Night	1 2 1 4 4 4 4 5% 10% 12% 53%	2817
	21st to end	Night	2 3 2 5% 4 5% 5% 4 7% 9% 55%	3109
August	1st to 10th	Night	4 4 2 7% 5% 6% 7% 6% 9% 10% 40%	2847
	11th to 20th	Night	3 3 1 5% 4 4 6% 5% 7% 9% 53%	2921
	21st to end	Night	4 4 1 6% 5% 5% 5% 4 7% 8% 50%	3487
September	1st to 10th	Night	4 4 2 5% 3 4 4 4 6% 7% 59%	1900
	11th to 20th	Night	5% 4 1 4 4 3 4 3 5% 7% 61%	1904
	21st to end	Night	6% 3 1 4 2 3 2 2 3 5% 69%	2177
October	1st to 10th	Night	5% 3 1 2 2 2 2 2 3 4 75%	3800
	11th to 20th	Night	5% 4 2 5% 4 4 4 3 5% 8% 56%	3778
	21st to end	Night	7% 7% 2 5% 2 3 2 2 2 3 64%	4120
November	1st to 10th	Night	5% 7% 2 4 3 3 3 3 4 5% 62%	2365
	11th to 20th	Night	7% 8% 2 3 3 2 2 3 4 5% 61%	2640
	21st to end	Night	7% 10% 3 5% 3 2 2 3 4 5% 55%	2800
December	1st to 10th	Night	5% 7% 2 4 2 1 2 2 4 6% 64%	4570
	11th to 20th	Night	5% 11% 3 7% 4 3 3 3 4 6% 51%	5181
	21st to end	Night	5% 15% 5% 9% 5% 4 3 2 4 5% 43%	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	42% 10% 13% 21% 13%	3912
	11th to 20th	Day	38% 9% 13% 16% 20% 3	4100
	21st to end	Day	31% 7% 9% 28% 20% 5%	4510
February	1st to 10th	Day	44% 8% 13% 19% 12% 4	1800
	11th to 20th	Day	44% 7% 7% 23% 16% 3	1798
	21st to end	Day	45% 7% 4 21% 19% 4	1650
March	1st to 10th	Day	35% 10% 6% 22% 20% 8%	4926
	11th to 20th	Day	38% 6% 11% 31% 12% 2	5000
	21st to end	Day	41% 12% 8% 26% 11% 1	5519
April	1st to 10th	Day	36% 7% 7% 24% 20% 6%	2400
	11th to 20th	Day	39% 7% 7% 21% 21% 4	2374
	21st to end	Day	34% 8% 7% 25% 23% 3	2400
May	1st to 10th	Day	32% 12% 9% 21% 21% 4	5806
	11th to 20th	Day	27% 8% 7% 24% 28% 5%	5976
	21st to end	Day	20% 8% 5% 23% 37% 7%	6926
June	1st to 10th	Day	21% 6% 6% 23% 29% 15%	2800
	11th to 20th	Day	20% 5% 5% 12% 28% 30%	2800
	21st to end	Day	18% 6% 4 15% 27% 29%	2800
July	1st to 10th	Day	18% 5% 5% 9% 20% 43%	4432
	11th to 20th	Day	19% 7% 10% 26% 25% 12%	4078
	21st to end	Day	21% 7% 11% 19% 19% 22%	4314
August	1st to 10th	Day	26% 11% 19% 19% 14% 11%	4078
	11th to 20th	Day	26% 8% 11% 16% 26% 13%	3957
	21st to end	Day	24% 9% 11% 18% 24% 13%	4179
September	1st to 10th	Day	25% 7% 7% 14% 29% 18%	2280
	11th to 20th	Day	23% 7% 8% 18% 29% 15%	2273
	21st to end	Day	22% 5% 4 18% 39% 12%	2001
October	1st to 10th	Day	16% 3 4 16% 38% 23%	3170
	11th to 20th	Day	26% 5% 7% 30% 28% 5%	3150
	21st to end	Day	23% 4 6% 30% 32% 4	3438
November	1st to 10th	Day	24% 5% 8% 25% 33% 4	1912
	11th to 20th	Day	28% 5% 7% 31% 24% 4	1757
	21st to end	Day	32% 5% 8% 26% 24% 4	1600
December	1st to 10th	Day	27% 3 10% 37% 20% 2	2620
	11th to 20th	Day	33% 5% 12% 28% 22% 1	3024
	21st to end	Day	37% 8% 11% 21% 21% 2	4004
January	1st to 10th	Night	45% 7% 10% 22% 15% 1	6097
	11th to 20th	Night	38% 8% 11% 17% 22% 4	5880
	21st to end	Night	36% 6% 10% 21% 21% 5%	6468
February	1st to 10th	Night	41% 5% 14% 21% 16% 3	2600
	11th to 20th	Night	41% 7% 9% 24% 17% 2	2498
	21st to end	Night	40% 6% 6% 24% 20% 4	1980
March	1st to 10th	Night	38% 8% 5% 21% 22% 6%	4950
	11th to 20th	Night	36% 7% 8% 26% 20% 3	5000
	21st to end	Night	43% 10% 9% 27% 11% 1	5454
April	1st to 10th	Night	40% 6% 6% 22% 20% 6%	2000
	11th to 20th	Night	41% 7% 6% 18% 22% 6%	1977
	21st to end	Night	35% 6% 8% 23% 25% 3	2000
May	1st to 10th	Night	33% 10% 10% 23% 21% 4	4155
	11th to 20th	Night	28% 8% 8% 28% 25% 3	3938
	21st to end	Night	19% 6% 6% 19% 39% 10%	3972
June	1st to 10th	Night	21% 7% 7% 19% 30% 17%	1600
	11th to 20th	Night	19% 4 5% 15% 21% 36%	1600
	21st to end	Night	17% 6% 6% 16% 24% 32%	1600
July	1st to 10th	Night	17% 5% 8% 9% 18% 43%	2540
	11th to 20th	Night	19% 7% 11% 31% 15% 17%	2765
	21st to end	Night	22% 8% 14% 19% 18% 19%	3011
August	1st to 10th	Night	33% 10% 21% 14% 12% 12%	2838
	11th to 20th	Night	26% 7% 18% 13% 17% 19%	2948
	21st to end	Night	28% 8% 11% 17% 22% 14%	3487
September	1st to 10th	Night	23% 7% 8% 16% 24% 22%	1900
	11th to 20th	Night	23% 6% 10% 16% 27% 18%	1904
	21st to end	Night	20% 4 4 19% 39% 14%	2177
October	1st to 10th	Night	15% 3 4 16% 41% 20%	3800
	11th to 20th	Night	26% 5% 7% 29% 26% 7%	3778
	21st to end	Night	26% 4 5% 30% 31% 5%	4120
November	1st to 10th	Night	25% 5% 8% 27% 29% 5%	2365
	11th to 20th	Night	27% 4 8% 31% 26% 5%	2640
	21st to end	Night	31% 5% 6% 26% 27% 4	2800
December	1st to 10th	Night	23% 3 9% 43% 21% 1	4570
	11th to 20th	Night	34% 5% 8% 34% 19%	5182
	21st to end	Night	43% 7% 9% 20% 20% 2	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	15% 8% 33% 30% 12% 1	300
	11th to 20th	Day	11% 16% 35% 27% 10%	300
	21st to end	Day	9% 8% 35% 35% 12% 1	330
February	1st to 10th	Day	14% 20% 35% 25% 4 2	300
	11th to 20th	Day	19% 16% 38% 22% 4 1	300
	21st to end	Day	12% 19% 38% 26% 4 1	249
March	1st to 10th	Day	16% 19% 30% 25% 9% 1	485
	11th to 20th	Day	12% 19% 28% 28% 12%	500
	21st to end	Day	17% 23% 33% 21% 6%	550
April	1st to 10th	Day	14% 19% 32% 22% 12% 2	500
	11th to 20th	Day	16% 24% 31% 20% 7% 1	492
	21st to end	Day	14% 20% 33% 23% 9% 1	500
May	1st to 10th	Day	14% 18% 33% 26% 9%	503
	11th to 20th	Day	9% 13% 32% 28% 16% 2	582
	21st to end	Day	9% 15% 28% 31% 14% 2	789
June	1st to 10th	Day	5% 9% 29% 35% 20% 2	730
	11th to 20th	Day	6% 12% 34% 31% 16% 1	730
	21st to end	Day	3 12% 27% 40% 16% 1	730
July	1st to 10th	Day	3 6% 20% 47% 21% 3	697
	11th to 20th	Day	4 4 16% 44% 29% 4	508
	21st to end	Day	5% 5% 17% 39% 30% 4	531
August	1st to 10th	Day	5% 8% 21% 43% 20% 4	487
	11th to 20th	Day	5% 5% 24% 40% 24% 3	477
	21st to end	Day	4 4 21% 46% 24% 2	539
September	1st to 10th	Day	6% 6% 25% 38% 23% 3	490
	11th to 20th	Day	6% 8% 33% 39% 13% 2	490
	21st to end	Day	7% 10% 25% 34% 21% 1	401
October	1st to 10th	Day	9% 11% 22% 32% 23% 3	300
	11th to 20th	Day	5% 16% 29% 30% 18% 2	300
	21st to end	Day	10% 11% 30% 33% 15% 1	330
November	1st to 10th	Day	8% 17% 30% 31% 13% 1	300
	11th to 20th	Day	7% 12% 35% 31% 13% 2	300
	21st to end	Day	12% 11% 32% 29% 13% 2	300
December	1st to 10th	Day	10% 14% 33% 30% 11% 2	300
	11th to 20th	Day	11% 12% 34% 30% 12% 1	300
	21st to end	Day	13% 13% 37% 25% 10% 1	330
January	1st to 10th	Night	12% 7% 25% 39% 15% 1	900
	11th to 20th	Night	12% 9% 23% 41% 14% 1	800
	21st to end	Night	11% 7% 27% 41% 12% 1	880
February	1st to 10th	Night	13% 10% 30% 38% 9%	800
	11th to 20th	Night	11% 8% 29% 40% 10%	784
	21st to end	Night	13% 7% 33% 39% 7%	660
March	1st to 10th	Night	12% 9% 28% 39% 11% 1	800
	11th to 20th	Night	7% 8% 26% 41% 17%	800
	21st to end	Night	15% 9% 26% 38% 11%	870
April	1st to 10th	Night	13% 11% 28% 40% 9%	600
	11th to 20th	Night	15% 11% 24% 37% 12% 1	593
	21st to end	Night	13% 8% 27% 37% 14% 1	600
May	1st to 10th	Night	13% 8% 26% 40% 13% 1	600
	11th to 20th	Night	10% 4 25% 40% 18% 3	591
	21st to end	Night	8% 7% 26% 37% 19% 2	650
June	1st to 10th	Night	3 5% 22% 43% 26% 2	600
	11th to 20th	Night	5% 4 23% 47% 19% 2	600
	21st to end	Night	5% 3 18% 46% 27% 2	600
July	1st to 10th	Night	4 1 13% 47% 33% 2	570
	11th to 20th	Night	3 1 10% 41% 41% 4	552
	21st to end	Night	4 2 10% 42% 40% 2	624
August	1st to 10th	Night	6% 3 12% 40% 37% 3	567
	11th to 20th	Night	4 3 11% 45% 34% 2	564
	21st to end	Night	6% 3 12% 42% 34% 4	627
September	1st to 10th	Night	4 4 13% 49% 29% 1	570
	11th to 20th	Night	6% 3 17% 43% 29% 2	574
	21st to end	Night	7% 4 18% 41% 26% 3	760
October	1st to 10th	Night	9% 4 20% 46% 20% 1	760
	11th to 20th	Night	6% 6% 20% 44% 21% 3	760
	21st to end	Night	12% 4 20% 42% 20% 2	836
November	1st to 10th	Night	8% 6% 23% 43% 18% 2	805
	11th to 20th	Night	10% 6% 24% 41% 17% 2	1000
	21st to end	Night	11% 8% 24% 40% 16% 1	1000
December	1st to 10th	Night	13% 7% 23% 46% 11% 1	1000
	11th to 20th	Night	15% 9% 28% 36% 12%	1000
	21st to end	Night	14% 9% 29% 40% 8%	1100

Page generated at 2025-07-02 23:30:13. Version ac07

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