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 2026-10-14.

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% 5% 5% 7% 9% 52%	158007
	Night	2 5% 2 6% 4 5% 5% 5% 7% 9% 52%	151355
Transparency	Day	25% 6% 14% 25% 21% 9%	152925
	Night	25% 7% 15% 27% 19% 6%	147446
Seeing	Day	5% 11% 24% 33% 20% 7%	18050
	Night	4 4 24% 45% 21% 2	28075

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	4 3 10% 6% 6% 7% 5% 9% 11% 39%	4882
	11th to 20th	Day	2 1 4 4 6% 8% 6% 9% 10% 51%	5340
	21st to end	Day	4 3 7% 5% 5% 5% 5% 7% 10% 48%	5844
February	1st to 10th	Day	5% 3 5% 4 5% 5% 6% 8% 11% 48%	1890
	11th to 20th	Day	1 4 2 6% 5% 5% 6% 5% 9% 13% 44%	1934
	21st to end	Day	4 2 7% 6% 5% 5% 4 8% 9% 49%	1730
March	1st to 10th	Day	1 5% 2 5% 4 5% 6% 5% 8% 11% 49%	4916
	11th to 20th	Day	1 4 2 8% 5% 5% 7% 7% 9% 10% 41%	5110
	21st to end	Day	1 7% 3 6% 5% 5% 5% 5% 7% 10% 46%	5730
April	1st to 10th	Day	1 5% 2 5% 4 4 5% 4 8% 9% 54%	2520
	11th to 20th	Day	2 5% 2 6% 4 5% 5% 4 8% 11% 50%	2491
	21st to end	Day	2 4 2 5% 4 4 5% 4 7% 10% 52%	2520
May	1st to 10th	Day	2 5% 2 6% 4 4 6% 5% 8% 9% 49%	7334
	11th to 20th	Day	2 4 2 6% 5% 5% 6% 5% 7% 8% 51%	7971
	21st to end	Day	2 2 1 4 4 4 5% 5% 7% 8% 59%	9026
June	1st to 10th	Day	2 3 2 4 4 4 4 5% 7% 8% 58%	2940
	11th to 20th	Day	2 3 1 3 3 4 4 4 5% 7% 64%	2940
	21st to end	Day	2 2 1 4 4 4 4 5% 7% 8% 59%	2940
July	1st to 10th	Day	2 2 1 3 3 3 3 3 5% 6% 69%	8249
	11th to 20th	Day	2 2 2 5% 4 6% 7% 6% 8% 10% 48%	7959
	21st to end	Day	2 3 1 5% 5% 5% 7% 6% 10% 11% 46%	8304
August	1st to 10th	Day	3 3 1 5% 4 5% 5% 5% 7% 10% 54%	7549
	11th to 20th	Day	3 3 1 5% 4 5% 5% 5% 7% 9% 52%	7229
	21st to end	Day	3 4 2 6% 5% 6% 7% 6% 8% 11% 41%	7751
September	1st to 10th	Day	4 4 2 6% 4 4 4 4 6% 8% 54%	2520
	11th to 20th	Day	4 4 2 5% 4 4 5% 3 6% 8% 55%	2520
	21st to end	Day	4 4 2 5% 3 3 4 3 4 6% 62%	2237
October	1st to 10th	Day	2 2 1 2 2 2 2 3 4 5% 73%	3370
	11th to 20th	Day	2 3 2 5% 4 5% 6% 4 6% 8% 55%	3280
	21st to end	Day	2 3 2 3 3 3 3 3 5% 6% 66%	3548
November	1st to 10th	Day	1 2 1 3 3 3 4 3 5% 8% 67%	1946
	11th to 20th	Day	1 4 1 4 3 3 4 4 6% 7% 64%	1890
	21st to end	Day	1 5% 1 4 4 4 4 4 7% 9% 57%	1699
December	1st to 10th	Day	4 2 4 4 5% 6% 7% 9% 11% 48%	2700
	11th to 20th	Day	4 2 5% 4 5% 5% 5% 10% 12% 48%	3106
	21st to end	Day	1 3 2 7% 5% 5% 6% 6% 10% 12% 42%	4092
January	1st to 10th	Night	1 5% 4 11% 7% 8% 8% 7% 8% 9% 32%	8081
	11th to 20th	Night	2 2 5% 4 7% 7% 5% 6% 8% 52%	7650
	21st to end	Night	1 9% 4 9% 5% 5% 6% 4 5% 6% 46%	8370
February	1st to 10th	Night	4 2 8% 5% 4 5% 4 8% 11% 48%	2730
	11th to 20th	Night	1 6% 3 6% 4 5% 5% 5% 8% 11% 46%	2572
	21st to end	Night	1 6% 3 6% 4 5% 4 5% 6% 9% 50%	2076
March	1st to 10th	Night	7% 3 6% 5% 6% 5% 4 6% 10% 48%	5189
	11th to 20th	Night	1 8% 3 7% 4 4 5% 5% 7% 10% 47%	5110
	21st to end	Night	1 7% 3 8% 5% 5% 6% 4 7% 7% 46%	5481
April	1st to 10th	Night	2 6% 2 5% 4 4 4 4 6% 8% 54%	2100
	11th to 20th	Night	2 7% 2 7% 4 4 4 4 6% 8% 50%	2077
	21st to end	Night	2 6% 2 5% 3 4 4 4 6% 8% 55%	2100
May	1st to 10th	Night	3 6% 2 6% 4 5% 5% 4 7% 10% 48%	5610
	11th to 20th	Night	3 5% 2 4 4 4 5% 4 6% 9% 54%	4904
	21st to end	Night	2 3 1 4 2 3 4 3 5% 7% 65%	5181
June	1st to 10th	Night	2 1 1 4 3 4 3 3 6% 7% 67%	1680
	11th to 20th	Night	2 3 1 3 3 2 3 3 4 6% 70%	1680
	21st to end	Night	1 1 1 3 3 4 4 4 5% 9% 65%	1680
July	1st to 10th	Night	1 2 1 3 2 3 4 4 6% 7% 67%	4740
	11th to 20th	Night	2 3 1 5% 4 4 6% 6% 9% 12% 48%	5013
	21st to end	Night	2 3 1 5% 4 5% 6% 6% 9% 13% 46%	5805
August	1st to 10th	Night	3 3 1 4 3 3 4 4 6% 9% 59%	5273
	11th to 20th	Night	2 4 1 4 4 4 5% 4 8% 11% 54%	5627
	21st to end	Night	4 5% 2 6% 5% 6% 7% 6% 9% 13% 39%	6465
September	1st to 10th	Night	4 3 1 5% 3 4 4 4 7% 7% 56%	2100
	11th to 20th	Night	4 4 1 5% 3 3 3 4 6% 8% 59%	2100
	21st to end	Night	3 4 2 4 3 3 3 3 5% 5% 66%	2378
October	1st to 10th	Night	2 3 1 3 2 2 3 2 3 5% 73%	4040
	11th to 20th	Night	3 3 1 4 3 4 5% 4 6% 8% 59%	3934
	21st to end	Night	3 4 2 5% 3 3 2 2 4 7% 65%	4252
November	1st to 10th	Night	1 4 1 3 2 2 2 3 4 8% 68%	2549
	11th to 20th	Night	1 3 2 4 3 3 4 3 6% 7% 63%	2730
	21st to end	Night	2 5% 2 6% 4 4 4 4 6% 8% 55%	2919
December	1st to 10th	Night	1 4 2 4 3 5% 9% 7% 7% 9% 51%	4710
	11th to 20th	Night	1 4 1 5% 4 5% 6% 7% 9% 8% 49%	5321
	21st to end	Night	1 6% 4 10% 6% 7% 6% 6% 9% 11% 35%	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	33% 6% 21% 27% 12% 1	4885
	11th to 20th	Day	24% 8% 16% 25% 22% 4	5340
	21st to end	Day	24% 7% 13% 29% 24% 3	5844
February	1st to 10th	Day	25% 12% 20% 24% 15% 5%	1890
	11th to 20th	Day	30% 8% 13% 26% 19% 4	1943
	21st to end	Day	29% 8% 12% 25% 22% 4	1730
March	1st to 10th	Day	24% 7% 13% 26% 24% 6%	4916
	11th to 20th	Day	30% 7% 14% 32% 13% 3	5110
	21st to end	Day	31% 8% 21% 28% 12% 1	5730
April	1st to 10th	Day	26% 8% 14% 26% 19% 6%	2520
	11th to 20th	Day	27% 7% 15% 24% 22% 4	2494
	21st to end	Day	25% 7% 16% 28% 20% 3	2520
May	1st to 10th	Day	27% 6% 14% 29% 19% 5%	7334
	11th to 20th	Day	26% 6% 10% 27% 25% 6%	7975
	21st to end	Day	20% 5% 14% 27% 29% 6%	9027
June	1st to 10th	Day	21% 7% 12% 23% 26% 10%	2940
	11th to 20th	Day	19% 6% 8% 17% 26% 24%	2940
	21st to end	Day	19% 6% 10% 17% 25% 23%	2940
July	1st to 10th	Day	17% 4 6% 9% 22% 43%	8181
	11th to 20th	Day	27% 5% 16% 26% 16% 10%	7884
	21st to end	Day	27% 7% 21% 20% 15% 10%	8120
August	1st to 10th	Day	28% 7% 15% 17% 19% 14%	5978
	11th to 20th	Day	31% 7% 18% 18% 19% 7%	5700
	21st to end	Day	32% 7% 21% 20% 15% 5%	6078
September	1st to 10th	Day	27% 6% 12% 18% 24% 12%	2520
	11th to 20th	Day	25% 6% 12% 21% 24% 11%	2520
	21st to end	Day	24% 5% 8% 22% 32% 9%	2237
October	1st to 10th	Day	14% 4 6% 23% 37% 16%	3370
	11th to 20th	Day	27% 3 9% 30% 24% 6%	3280
	21st to end	Day	18% 5% 8% 35% 30% 4	3548
November	1st to 10th	Day	16% 5% 12% 29% 33% 5%	1946
	11th to 20th	Day	18% 5% 13% 37% 23% 4	1890
	21st to end	Day	23% 6% 14% 32% 21% 5%	1699
December	1st to 10th	Day	25% 10% 16% 35% 11% 2	2700
	11th to 20th	Day	22% 7% 19% 36% 15%	3104
	21st to end	Day	27% 8% 19% 23% 19% 3	4092
January	1st to 10th	Night	40% 8% 16% 26% 10%	8082
	11th to 20th	Night	26% 7% 17% 30% 17% 3	7650
	21st to end	Night	30% 7% 13% 25% 21% 5%	8370
February	1st to 10th	Night	26% 8% 18% 28% 16% 3	2730
	11th to 20th	Night	29% 9% 15% 27% 18% 3	2573
	21st to end	Night	27% 7% 12% 28% 23% 4	2076
March	1st to 10th	Night	26% 7% 10% 28% 27% 1	5189
	11th to 20th	Night	26% 8% 14% 33% 18% 1	5110
	21st to end	Night	28% 10% 21% 30% 9% 1	5481
April	1st to 10th	Night	25% 8% 13% 27% 22% 4	2100
	11th to 20th	Night	29% 8% 13% 25% 22% 4	2077
	21st to end	Night	23% 9% 14% 30% 22% 2	2100
May	1st to 10th	Night	29% 6% 17% 29% 18% 2	5608
	11th to 20th	Night	22% 7% 13% 32% 24% 3	4905
	21st to end	Night	18% 4 15% 25% 33% 5%	5182
June	1st to 10th	Night	15% 7% 13% 24% 28% 13%	1680
	11th to 20th	Night	15% 5% 10% 17% 26% 27%	1680
	21st to end	Night	15% 5% 12% 20% 24% 24%	1680
July	1st to 10th	Night	16% 5% 9% 10% 20% 40%	4700
	11th to 20th	Night	26% 6% 27% 25% 9% 8%	4965
	21st to end	Night	26% 9% 26% 21% 9% 9%	5677
August	1st to 10th	Night	25% 9% 16% 16% 20% 14%	4168
	11th to 20th	Night	26% 11% 23% 16% 18% 6%	4432
	21st to end	Night	29% 9% 30% 18% 11% 3	5069
September	1st to 10th	Night	25% 6% 14% 20% 23% 12%	2100
	11th to 20th	Night	22% 6% 15% 18% 26% 12%	2100
	21st to end	Night	20% 6% 9% 26% 33% 8%	2378
October	1st to 10th	Night	15% 4 7% 25% 38% 11%	4040
	11th to 20th	Night	23% 3 12% 34% 23% 5%	3934
	21st to end	Night	20% 4 7% 41% 25% 3	4252
November	1st to 10th	Night	16% 5% 12% 35% 28% 5%	2549
	11th to 20th	Night	18% 4 13% 36% 25% 3	2730
	21st to end	Night	26% 6% 10% 30% 25% 3	2919
December	1st to 10th	Night	23% 13% 14% 37% 12% 1	4710
	11th to 20th	Night	23% 8% 16% 39% 14%	5322
	21st to end	Night	34% 8% 16% 24% 17% 2	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	3 11% 22% 40% 20% 4	330
	11th to 20th	Day	5% 11% 24% 42% 15% 4	330
	21st to end	Day	1 6% 22% 49% 18% 5%	363
February	1st to 10th	Day	4 12% 31% 38% 11% 3	330
	11th to 20th	Day	4 15% 32% 39% 8% 2	330
	21st to end	Day	3 17% 29% 38% 12% 1	273
March	1st to 10th	Day	5% 16% 31% 30% 16% 2	465
	11th to 20th	Day	5% 17% 29% 32% 14% 3	540
	21st to end	Day	6% 21% 34% 28% 9% 1	594
April	1st to 10th	Day	6% 23% 29% 27% 11% 4	540
	11th to 20th	Day	7% 26% 33% 24% 9% 1	532
	21st to end	Day	8% 21% 31% 27% 11% 2	540
May	1st to 10th	Day	10% 22% 32% 21% 11% 4	543
	11th to 20th	Day	6% 12% 28% 32% 19% 4	696
	21st to end	Day	6% 14% 24% 30% 19% 6%	844
June	1st to 10th	Day	4 10% 22% 30% 28% 7%	780
	11th to 20th	Day	4 8% 29% 34% 20% 6%	780
	21st to end	Day	3 9% 23% 33% 26% 5%	780
July	1st to 10th	Day	4 4 17% 30% 34% 11%	771
	11th to 20th	Day	4 3 12% 33% 32% 16%	672
	21st to end	Day	7% 3 16% 33% 25% 16%	619
August	1st to 10th	Day	7% 5% 22% 33% 21% 12%	567
	11th to 20th	Day	4 4 22% 32% 22% 15%	557
	21st to end	Day	5% 4 19% 36% 25% 11%	627
September	1st to 10th	Day	6% 5% 21% 30% 24% 14%	570
	11th to 20th	Day	4 8% 27% 34% 19% 7%	570
	21st to end	Day	5% 9% 21% 28% 24% 13%	432
October	1st to 10th	Day	9% 8% 13% 25% 26% 19%	360
	11th to 20th	Day	9% 11% 25% 27% 22% 7%	339
	21st to end	Day	7% 12% 21% 31% 23% 6%	363
November	1st to 10th	Day	3 14% 21% 36% 20% 5%	330
	11th to 20th	Day	5% 10% 15% 41% 23% 6%	330
	21st to end	Day	4 9% 20% 39% 24% 3	330
December	1st to 10th	Day	4 8% 24% 41% 13% 9%	330
	11th to 20th	Day	3 9% 19% 45% 19% 4	330
	21st to end	Day	2 13% 24% 44% 14% 3	363
January	1st to 10th	Night	2 6% 29% 45% 16% 1	1008
	11th to 20th	Night	2 5% 30% 47% 15% 2	840
	21st to end	Night	3 3 28% 51% 12% 2	924
February	1st to 10th	Night	2 6% 36% 45% 10% 1	840
	11th to 20th	Night	3 5% 38% 44% 10%	824
	21st to end	Night	3 5% 36% 50% 5%	692
March	1st to 10th	Night	3 5% 35% 47% 10% 1	840
	11th to 20th	Night	3 4 29% 49% 14% 1	840
	21st to end	Night	3 6% 32% 49% 10%	872
April	1st to 10th	Night	5% 7% 33% 45% 9%	630
	11th to 20th	Night	5% 9% 33% 43% 11%	623
	21st to end	Night	5% 6% 29% 46% 14%	630
May	1st to 10th	Night	6% 7% 27% 46% 15%	630
	11th to 20th	Night	8% 3 18% 48% 21% 2	621
	21st to end	Night	6% 5% 22% 45% 21% 2	683
June	1st to 10th	Night	2 2 18% 45% 32% 1	630
	11th to 20th	Night	2 3 20% 55% 19% 1	630
	21st to end	Night	2 2 16% 49% 30% 1	630
July	1st to 10th	Night	4 1 9% 44% 40% 3	615
	11th to 20th	Night	3 1 5% 35% 50% 6%	612
	21st to end	Night	5% 2 5% 32% 49% 7%	690
August	1st to 10th	Night	7% 2 6% 37% 44% 4	627
	11th to 20th	Night	4 2 6% 44% 40% 4	624
	21st to end	Night	6% 2 6% 39% 41% 6%	693
September	1st to 10th	Night	5% 2 8% 46% 36% 3	630
	11th to 20th	Night	5% 2 10% 51% 30% 2	630
	21st to end	Night	4 2 13% 43% 32% 5%	771
October	1st to 10th	Night	4 3 18% 46% 25% 4	840
	11th to 20th	Night	4 3 22% 46% 21% 2	812
	21st to end	Night	5% 4 23% 45% 20% 3	880
November	1st to 10th	Night	4 3 28% 46% 17% 2	909
	11th to 20th	Night	3 6% 27% 48% 15% 1	1050
	21st to end	Night	5% 7% 27% 43% 17% 1	1050
December	1st to 10th	Night	4 6% 30% 47% 12% 2	1050
	11th to 20th	Night	3 5% 34% 43% 13% 1	1050
	21st to end	Night	3 7% 32% 47% 9% 1	1155

Page generated at 2026-10-11 03:06:26. Version ac07

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