Gunnison Valley Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Gunnison Valley Observatory clear sky chart from 2005-11-06 to 2025-06-10.

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	2 4 2 5% 4 5% 6% 5% 8% 9% 50%	123610
	Night	2 5% 2 6% 4 5% 5% 5% 7% 9% 51%	123562
Transparency	Day	26% 7% 14% 24% 21% 7%	123366
	Night	26% 8% 15% 27% 20% 5%	123394
Seeing	Day	5% 11% 24% 33% 20% 7%	16171
	Night	4 4 24% 45% 21% 2	26334

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 3 10% 6% 6% 8% 6% 10% 12% 37%	3758
	11th to 20th	Day	3 1 5% 5% 7% 9% 7% 10% 11% 41%	4100
	21st to end	Day	4 3 8% 5% 6% 6% 6% 8% 11% 43%	4510
February	1st to 10th	Day	5% 3 6% 4 5% 5% 6% 8% 12% 47%	1800
	11th to 20th	Day	1 4 2 5% 5% 5% 6% 5% 9% 13% 45%	1840
	21st to end	Day	4 3 7% 7% 5% 5% 4 8% 9% 48%	1650
March	1st to 10th	Day	1 5% 2 5% 4 5% 6% 5% 8% 11% 49%	4810
	11th to 20th	Day	1 5% 2 8% 5% 5% 7% 7% 9% 10% 40%	5000
	21st to end	Day	1 7% 3 6% 5% 4 6% 5% 7% 10% 45%	5607
April	1st to 10th	Day	1 5% 2 5% 4 4 5% 4 8% 9% 53%	2400
	11th to 20th	Day	1 5% 2 6% 4 5% 5% 4 8% 11% 49%	2371
	21st to end	Day	2 4 2 5% 4 4 5% 4 8% 10% 51%	2400
May	1st to 10th	Day	3 5% 2 6% 5% 5% 6% 5% 8% 10% 44%	5653
	11th to 20th	Day	2 4 2 6% 5% 5% 6% 5% 7% 8% 50%	6132
	21st to end	Day	2 2 1 4 3 4 5% 5% 7% 8% 59%	6925
June	1st to 10th	Day	2 3 2 4 4 4 4 5% 7% 8% 57%	2788
	11th to 20th	Day	3 3 1 4 4 4 4 4 5% 7% 63%	2660
	21st to end	Day	2 2 1 5% 4 5% 4 5% 7% 9% 57%	2660
July	1st to 10th	Day	3 3 2 5% 3 3 4 4 6% 6% 62%	4430
	11th to 20th	Day	2 3 2 5% 5% 6% 7% 7% 10% 12% 43%	4279
	21st to end	Day	3 4 1 5% 5% 5% 6% 5% 7% 8% 51%	4454
August	1st to 10th	Day	4 5% 2 6% 5% 7% 6% 6% 8% 12% 39%	4092
	11th to 20th	Day	4 3 2 6% 5% 6% 6% 5% 7% 9% 47%	3848
	21st to end	Day	2 4 2 6% 5% 6% 7% 6% 8% 10% 45%	4180
September	1st to 10th	Day	4 4 2 6% 4 4 5% 4 7% 7% 53%	2280
	11th to 20th	Day	4 4 2 5% 4 4 4 3 6% 8% 57%	2280
	21st to end	Day	4 4 1 5% 3 3 4 3 4 6% 65%	2025
October	1st to 10th	Day	2 2 1 2 2 2 2 3 4 5% 74%	3170
	11th to 20th	Day	2 3 2 5% 4 5% 6% 4 6% 8% 54%	3150
	21st to end	Day	2 3 2 3 3 3 4 3 5% 6% 66%	3438
November	1st to 10th	Day	1 2 1 3 3 3 4 3 6% 8% 66%	1852
	11th to 20th	Day	1 4 1 4 3 3 4 4 6% 7% 64%	1800
	21st to end	Day	1 5% 1 4 4 4 4 4 7% 9% 56%	1618
December	1st to 10th	Day	4 2 4 4 5% 6% 7% 10% 11% 48%	2620
	11th to 20th	Day	4 2 5% 4 5% 5% 5% 10% 12% 48%	3026
	21st to end	Day	1 3 2 7% 5% 5% 6% 6% 10% 12% 42%	4004
January	1st to 10th	Night	4 4 11% 7% 8% 8% 7% 8% 9% 33%	6235
	11th to 20th	Night	3 3 7% 6% 8% 9% 6% 7% 9% 42%	5880
	21st to end	Night	1 8% 4 10% 6% 6% 7% 5% 6% 7% 39%	6468
February	1st to 10th	Night	4 2 8% 5% 4 5% 4 8% 11% 46%	2600
	11th to 20th	Night	1 6% 3 6% 4 4 5% 5% 8% 11% 47%	2447
	21st to end	Night	1 7% 3 7% 4 5% 4 5% 7% 9% 48%	1980
March	1st to 10th	Night	7% 3 6% 5% 6% 5% 4 6% 10% 47%	5076
	11th to 20th	Night	1 8% 3 7% 4 4 5% 5% 7% 10% 46%	5000
	21st to end	Night	1 7% 3 8% 5% 5% 6% 4 7% 7% 46%	5362
April	1st to 10th	Night	2 6% 2 6% 4 4 4 4 6% 8% 54%	2000
	11th to 20th	Night	2 7% 2 7% 4 4 4 4 6% 8% 51%	1977
	21st to end	Night	2 6% 2 5% 3 4 4 4 6% 8% 55%	2000
May	1st to 10th	Night	4 7% 2 6% 4 5% 5% 4 7% 10% 47%	4324
	11th to 20th	Night	3 5% 2 5% 5% 5% 5% 4 6% 9% 51%	3766
	21st to end	Night	2 3 1 3 2 3 3 3 5% 7% 67%	3972
June	1st to 10th	Night	2 2 1 4 3 4 3 3 6% 7% 66%	1596
	11th to 20th	Night	2 3 1 3 3 3 3 3 4 6% 69%	1520
	21st to end	Night	1 1 1 3 3 4 4 4 5% 10% 64%	1520
July	1st to 10th	Night	2 2 1 4 4 3 4 4 5% 6% 64%	2540
	11th to 20th	Night	2 3 1 4 4 4 6% 5% 8% 13% 51%	2687
	21st to end	Night	2 3 1 5% 4 4 5% 5% 7% 10% 53%	3109
August	1st to 10th	Night	5% 4 2 7% 5% 5% 6% 6% 9% 12% 38%	2847
	11th to 20th	Night	3 4 2 4 4 5% 6% 5% 8% 10% 51%	2991
	21st to end	Night	3 4 2 6% 5% 6% 7% 6% 8% 10% 45%	3487
September	1st to 10th	Night	4 3 1 5% 3 4 4 4 7% 8% 55%	1900
	11th to 20th	Night	4 4 1 5% 3 3 3 3 6% 8% 60%	1900
	21st to end	Night	3 3 2 4 3 3 3 3 4 5% 68%	2150
October	1st to 10th	Night	2 3 1 3 2 2 2 2 3 5% 74%	3800
	11th to 20th	Night	3 3 1 4 3 4 5% 4 6% 8% 59%	3778
	21st to end	Night	3 4 2 5% 3 3 2 2 4 7% 65%	4120
November	1st to 10th	Night	1 4 1 4 2 2 3 3 4 8% 67%	2425
	11th to 20th	Night	1 3 2 4 3 4 4 3 6% 7% 64%	2600
	21st to end	Night	2 5% 2 5% 4 4 4 4 5% 8% 56%	2780
December	1st to 10th	Night	1 3 1 4 3 5% 9% 7% 7% 10% 50%	4570
	11th to 20th	Night	1 4 2 5% 4 5% 6% 7% 9% 9% 48%	5181
	21st to end	Night	1 6% 4 11% 6% 7% 7% 6% 9% 11% 35%	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	31% 8% 22% 25% 14% 1	3759
	11th to 20th	Day	30% 10% 15% 21% 21% 4	4100
	21st to end	Day	26% 9% 13% 28% 20% 4	4510
February	1st to 10th	Day	26% 12% 21% 22% 15% 5%	1800
	11th to 20th	Day	28% 9% 13% 27% 20% 4	1849
	21st to end	Day	30% 8% 12% 24% 22% 4	1650
March	1st to 10th	Day	25% 7% 13% 26% 24% 6%	4810
	11th to 20th	Day	31% 8% 15% 32% 13% 2	5000
	21st to end	Day	31% 8% 22% 27% 11% 1	5607
April	1st to 10th	Day	27% 8% 14% 26% 19% 6%	2400
	11th to 20th	Day	27% 8% 16% 24% 22% 4	2374
	21st to end	Day	25% 8% 16% 29% 20% 2	2400
May	1st to 10th	Day	29% 7% 16% 24% 18% 5%	5653
	11th to 20th	Day	25% 8% 12% 27% 24% 5%	6136
	21st to end	Day	19% 6% 13% 26% 31% 6%	6926
June	1st to 10th	Day	21% 8% 13% 22% 26% 10%	2788
	11th to 20th	Day	20% 6% 9% 18% 25% 22%	2660
	21st to end	Day	20% 6% 11% 18% 25% 20%	2660
July	1st to 10th	Day	22% 5% 8% 12% 21% 32%	4361
	11th to 20th	Day	28% 7% 17% 26% 15% 6%	4204
	21st to end	Day	26% 8% 13% 20% 15% 16%	4314
August	1st to 10th	Day	36% 9% 20% 15% 13% 6%	4078
	11th to 20th	Day	32% 8% 14% 14% 24% 9%	3887
	21st to end	Day	31% 8% 13% 20% 20% 7%	4179
September	1st to 10th	Day	28% 7% 12% 16% 24% 13%	2280
	11th to 20th	Day	24% 7% 11% 20% 25% 12%	2280
	21st to end	Day	22% 5% 7% 22% 34% 10%	2025
October	1st to 10th	Day	14% 4 7% 22% 37% 16%	3170
	11th to 20th	Day	27% 4 9% 30% 24% 6%	3150
	21st to end	Day	18% 5% 8% 35% 29% 4	3438
November	1st to 10th	Day	17% 5% 12% 27% 34% 5%	1852
	11th to 20th	Day	18% 5% 13% 36% 24% 4	1800
	21st to end	Day	23% 6% 13% 32% 21% 5%	1618
December	1st to 10th	Day	25% 10% 16% 36% 12% 2	2620
	11th to 20th	Day	22% 8% 19% 35% 15%	3024
	21st to end	Day	27% 8% 19% 23% 19% 4	4004
January	1st to 10th	Night	37% 10% 16% 25% 12% 1	6235
	11th to 20th	Night	33% 9% 14% 23% 18% 3	5880
	21st to end	Night	33% 9% 14% 22% 19% 3	6468
February	1st to 10th	Night	27% 9% 19% 26% 16% 3	2600
	11th to 20th	Night	28% 9% 15% 28% 18% 3	2448
	21st to end	Night	28% 7% 11% 27% 23% 4	1980
March	1st to 10th	Night	26% 8% 10% 28% 27% 1	5076
	11th to 20th	Night	27% 9% 14% 32% 18% 1	5000
	21st to end	Night	29% 10% 22% 29% 9% 1	5362
April	1st to 10th	Night	25% 8% 14% 26% 22% 5%	2000
	11th to 20th	Night	29% 8% 13% 24% 22% 4	1977
	21st to end	Night	23% 9% 14% 30% 22% 2	2000
May	1st to 10th	Night	28% 7% 18% 25% 20% 2	4321
	11th to 20th	Night	22% 8% 14% 32% 21% 2	3767
	21st to end	Night	15% 4 14% 24% 36% 6%	3972
June	1st to 10th	Night	15% 7% 14% 24% 27% 13%	1596
	11th to 20th	Night	15% 5% 11% 18% 26% 25%	1520
	21st to end	Night	15% 5% 12% 21% 25% 21%	1520
July	1st to 10th	Night	21% 7% 10% 15% 16% 32%	2500
	11th to 20th	Night	22% 7% 28% 26% 10% 7%	2639
	21st to end	Night	23% 10% 19% 25% 8% 15%	3011
August	1st to 10th	Night	34% 13% 21% 13% 11% 8%	2838
	11th to 20th	Night	26% 11% 20% 12% 23% 8%	3018
	21st to end	Night	32% 9% 16% 23% 16% 5%	3487
September	1st to 10th	Night	25% 7% 14% 18% 22% 13%	1900
	11th to 20th	Night	20% 7% 15% 17% 28% 13%	1900
	21st to end	Night	17% 6% 8% 26% 35% 8%	2150
October	1st to 10th	Night	14% 4 7% 24% 39% 12%	3800
	11th to 20th	Night	23% 4 13% 34% 22% 5%	3778
	21st to end	Night	21% 4 6% 41% 25% 3	4120
November	1st to 10th	Night	17% 5% 12% 33% 28% 5%	2425
	11th to 20th	Night	18% 5% 13% 35% 26% 3	2600
	21st to end	Night	25% 6% 9% 30% 26% 3	2780
December	1st to 10th	Night	22% 13% 13% 37% 13% 1	4570
	11th to 20th	Night	23% 8% 16% 39% 14%	5182
	21st to end	Night	34% 8% 16% 23% 17% 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	3 11% 21% 39% 21% 5%	300
	11th to 20th	Day	6% 11% 24% 40% 16% 3	300
	21st to end	Day	1 6% 21% 48% 19% 5%	330
February	1st to 10th	Day	4 13% 32% 39% 10% 2	300
	11th to 20th	Day	3 16% 32% 38% 9% 2	300
	21st to end	Day	2 17% 30% 40% 10% 1	249
March	1st to 10th	Day	6% 15% 31% 29% 16% 2	429
	11th to 20th	Day	5% 15% 29% 33% 15% 3	500
	21st to end	Day	6% 22% 34% 28% 9% 1	550
April	1st to 10th	Day	7% 23% 29% 27% 11% 3	500
	11th to 20th	Day	7% 26% 33% 24% 9% 1	492
	21st to end	Day	7% 20% 32% 28% 11% 2	500
May	1st to 10th	Day	11% 23% 32% 21% 10% 3	503
	11th to 20th	Day	5% 12% 28% 32% 20% 3	650
	21st to end	Day	7% 14% 24% 30% 19% 6%	789
June	1st to 10th	Day	4 10% 22% 30% 28% 6%	726
	11th to 20th	Day	4 8% 28% 35% 20% 5%	680
	21st to end	Day	3 8% 22% 34% 27% 5%	680
July	1st to 10th	Day	5% 3 16% 30% 35% 10%	671
	11th to 20th	Day	4 3 13% 33% 32% 15%	582
	21st to end	Day	8% 3 16% 34% 25% 15%	531
August	1st to 10th	Day	8% 5% 21% 32% 21% 14%	487
	11th to 20th	Day	4 5% 24% 34% 20% 14%	477
	21st to end	Day	5% 4 20% 36% 24% 11%	539
September	1st to 10th	Day	7% 4 21% 30% 23% 15%	490
	11th to 20th	Day	4 9% 27% 33% 19% 8%	490
	21st to end	Day	4 10% 23% 27% 24% 13%	366
October	1st to 10th	Day	9% 10% 14% 23% 25% 19%	300
	11th to 20th	Day	9% 9% 24% 27% 23% 8%	300
	21st to end	Day	8% 12% 22% 31% 21% 6%	330
November	1st to 10th	Day	3 15% 21% 36% 19% 6%	300
	11th to 20th	Day	5% 11% 16% 42% 20% 6%	300
	21st to end	Day	4 9% 21% 39% 23% 4	300
December	1st to 10th	Day	4 8% 24% 39% 14% 10%	300
	11th to 20th	Day	4 10% 20% 46% 18% 3	300
	21st to end	Day	3 13% 25% 42% 13% 3	330
January	1st to 10th	Night	2 6% 28% 45% 16% 2	960
	11th to 20th	Night	2 5% 30% 46% 15% 2	800
	21st to end	Night	3 3 28% 50% 13% 3	880
February	1st to 10th	Night	2 6% 37% 45% 9% 1	800
	11th to 20th	Night	3 5% 39% 44% 10%	784
	21st to end	Night	3 5% 36% 50% 5%	660
March	1st to 10th	Night	3 5% 35% 46% 10% 1	800
	11th to 20th	Night	3 4 28% 50% 15% 1	800
	21st to end	Night	3 6% 32% 49% 10%	830
April	1st to 10th	Night	5% 7% 34% 45% 9%	600
	11th to 20th	Night	5% 9% 32% 42% 11%	593
	21st to end	Night	5% 6% 29% 46% 14% 1	600
May	1st to 10th	Night	6% 7% 27% 45% 15%	600
	11th to 20th	Night	8% 4 17% 48% 21% 2	591
	21st to end	Night	6% 5% 22% 44% 21% 2	650
June	1st to 10th	Night	2 2 17% 45% 33% 1	599
	11th to 20th	Night	2 3 19% 55% 19% 1	570
	21st to end	Night	2 2 14% 48% 33% 1	570
July	1st to 10th	Night	4 1 8% 42% 41% 3	555
	11th to 20th	Night	3 1 4 34% 51% 6%	552
	21st to end	Night	5% 2 5% 32% 50% 7%	624
August	1st to 10th	Night	7% 2 6% 34% 46% 5%	567
	11th to 20th	Night	4 2 6% 45% 39% 4	564
	21st to end	Night	6% 2 6% 40% 40% 6%	627
September	1st to 10th	Night	5% 2 8% 45% 37% 3	570
	11th to 20th	Night	5% 2 10% 49% 31% 2	570
	21st to end	Night	3 2 14% 43% 32% 6%	697
October	1st to 10th	Night	4 4 18% 46% 25% 3	760
	11th to 20th	Night	4 4 21% 47% 22% 3	760
	21st to end	Night	5% 4 23% 44% 20% 3	836
November	1st to 10th	Night	4 3 27% 46% 18% 2	865
	11th to 20th	Night	3 6% 27% 47% 16% 2	1000
	21st to end	Night	5% 7% 27% 43% 17% 1	1000
December	1st to 10th	Night	4 6% 29% 47% 12% 2	1000
	11th to 20th	Night	4 5% 34% 43% 13% 1	1000
	21st to end	Night	3 8% 31% 47% 10% 1	1100

Page generated at 2025-06-07 08:28:14. Version ac07

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