Capilla Peak Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Capilla Peak 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 4 3 4 4 4 5% 7% 61%	123005
	Night	3 4 2 5% 4 4 4 4 5% 7% 59%	124135
Transparency	Day	18% 5% 8% 20% 28% 20%	122769
	Night	19% 5% 8% 19% 28% 20%	123958
Seeing	Day	8% 11% 24% 29% 22% 6%	15714
	Night	6% 9% 26% 38% 19% 2	25945

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	2 8% 3 6% 4 3 3 3 5% 5% 58%	4098
	11th to 20th	Day	1 3 3 6% 3 2 3 3 3 5% 67%	4100
	21st to end	Day	2 8% 3 7% 4 3 3 4 4 4 57%	4510
February	1st to 10th	Day	2 4 2 5% 4 3 4 3 6% 7% 60%	1827
	11th to 20th	Day	3 5% 2 6% 4 3 3 3 6% 6% 59%	1949
	21st to end	Day	2 6% 2 4 4 3 4 3 4 5% 64%	1650
March	1st to 10th	Day	1 5% 2 5% 4 4 4 3 5% 6% 62%	4821
	11th to 20th	Day	2 5% 3 8% 5% 4 6% 3 5% 7% 53%	5000
	21st to end	Day	1 4 2 5% 4 4 5% 4 5% 7% 58%	5616
April	1st to 10th	Day	3 3 1 4 3 3 4 3 5% 6% 63%	2400
	11th to 20th	Day	4 5% 1 3 3 4 3 3 4 5% 65%	2371
	21st to end	Day	3 4 1 3 3 3 3 2 4 6% 68%	2400
May	1st to 10th	Day	2 4 1 4 3 4 4 3 5% 8% 61%	5440
	11th to 20th	Day	3 3 1 3 3 3 4 3 5% 6% 67%	5526
	21st to end	Day	1 1 1 2 2 2 3 3 5% 7% 72%	6779
June	1st to 10th	Day	3 4 1 3 3 4 4 4 7% 9% 60%	2788
	11th to 20th	Day	2 2 1 2 2 3 4 3 4 5% 71%	2660
	21st to end	Day	5% 4 2 4 4 5% 5% 5% 6% 7% 54%	2660
July	1st to 10th	Day	3 2 1 4 4 4 6% 5% 7% 10% 54%	4156
	11th to 20th	Day	2 3 1 4 4 6% 7% 6% 9% 11% 47%	4110
	21st to end	Day	6% 4 2 5% 5% 6% 7% 6% 10% 11% 38%	4454
August	1st to 10th	Day	2 2 1 5% 5% 5% 6% 6% 9% 11% 47%	3975
	11th to 20th	Day	3 2 1 3 3 4 4 4 7% 11% 57%	3726
	21st to end	Day	4 4 2 5% 5% 6% 6% 6% 9% 10% 44%	4180
September	1st to 10th	Day	5% 4 1 6% 5% 5% 5% 5% 6% 8% 51%	2280
	11th to 20th	Day	5% 3 1 4 3 4 4 4 5% 6% 60%	2280
	21st to end	Day	3 2 1 3 3 3 3 3 4 5% 70%	2056
October	1st to 10th	Day	3 3 1 3 2 2 2 2 3 3 75%	3170
	11th to 20th	Day	3 2 1 3 4 4 3 3 4 6% 66%	3150
	21st to end	Day	2 1 2 2 2 2 2 3 5% 79%	3438
November	1st to 10th	Day	2 2 1 3 3 3 4 4 4 6% 68%	1959
	11th to 20th	Day	2 3 1 5% 3 3 3 2 4 5% 70%	1810
	21st to end	Day	2 5% 2 6% 2 3 3 3 5% 5% 64%	1800
December	1st to 10th	Day	2 3 1 3 2 2 2 2 4 5% 75%	2716
	11th to 20th	Day	2 4 2 5% 4 4 3 3 5% 6% 64%	3026
	21st to end	Day	2 4 1 4 2 3 3 2 5% 6% 68%	4124
January	1st to 10th	Night	2 6% 3 8% 5% 5% 5% 3 5% 5% 54%	5867
	11th to 20th	Night	2 2 2 5% 3 3 3 2 4 4 70%	5880
	21st to end	Night	2 6% 2 5% 4 4 5% 4 5% 6% 57%	6468
February	1st to 10th	Night	2 5% 2 5% 3 3 3 3 4 6% 64%	2570
	11th to 20th	Night	4 6% 2 6% 4 5% 4 3 5% 8% 55%	2338
	21st to end	Night	3 5% 1 5% 3 3 3 3 5% 6% 62%	1980
March	1st to 10th	Night	2 4 3 5% 3 4 4 4 4 5% 62%	5051
	11th to 20th	Night	4 6% 4 9% 5% 4 4 3 4 5% 53%	5000
	21st to end	Night	2 3 1 5% 4 3 3 3 5% 7% 64%	5352
April	1st to 10th	Night	3 3 2 4 3 3 3 3 5% 6% 65%	2000
	11th to 20th	Night	3 4 2 5% 3 3 3 2 5% 5% 63%	1977
	21st to end	Night	3 3 1 5% 3 4 3 2 5% 6% 65%	2000
May	1st to 10th	Night	4 6% 2 6% 5% 4 4 4 5% 5% 56%	4540
	11th to 20th	Night	3 3 1 4 4 4 4 4 5% 7% 61%	4384
	21st to end	Night	2 2 1 3 3 3 3 3 4 6% 69%	4114
June	1st to 10th	Night	4 4 2 5% 4 5% 5% 5% 7% 8% 52%	1596
	11th to 20th	Night	3 3 1 3 3 3 3 3 6% 7% 66%	1520
	21st to end	Night	5% 5% 2 6% 5% 5% 5% 6% 7% 8% 47%	1520
July	1st to 10th	Night	3 4 2 6% 5% 7% 6% 5% 7% 8% 49%	2794
	11th to 20th	Night	5% 4 2 6% 5% 5% 6% 5% 8% 11% 42%	2860
	21st to end	Night	9% 6% 2 6% 6% 5% 6% 6% 9% 12% 33%	3109
August	1st to 10th	Night	3 3 2 7% 6% 6% 8% 7% 9% 12% 37%	2960
	11th to 20th	Night	4 3 1 7% 5% 5% 6% 6% 10% 10% 42%	3113
	21st to end	Night	5% 4 2 8% 7% 6% 8% 7% 9% 10% 33%	3487
September	1st to 10th	Night	5% 4 2 5% 5% 7% 6% 5% 5% 9% 48%	1900
	11th to 20th	Night	5% 4 2 5% 3 3 5% 4 6% 6% 57%	1900
	21st to end	Night	4 3 2 4 3 3 3 3 4 6% 66%	2119
October	1st to 10th	Night	3 3 1 3 2 2 2 2 3 5% 74%	3800
	11th to 20th	Night	3 2 1 4 3 3 4 3 4 5% 67%	3778
	21st to end	Night	2 2 1 2 2 2 2 2 4 5% 76%	4120
November	1st to 10th	Night	2 2 1 3 2 2 3 3 4 6% 72%	2340
	11th to 20th	Night	1 2 1 4 2 3 3 3 4 4 73%	2566
	21st to end	Night	4 5% 2 5% 4 3 3 3 4 6% 62%	2600
December	1st to 10th	Night	2 2 1 3 2 3 3 2 4 6% 72%	4469
	11th to 20th	Night	2 3 1 4 4 4 4 3 6% 8% 62%	5181
	21st to end	Night	2 5% 2 5% 3 3 3 2 4 6% 64%	6882

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	21% 4 6% 25% 35% 9%	4099
	11th to 20th	Day	14% 5% 8% 24% 30% 20%	4100
	21st to end	Day	21% 6% 6% 18% 29% 19%	4510
February	1st to 10th	Day	18% 4 8% 23% 30% 17%	1827
	11th to 20th	Day	21% 4 7% 23% 28% 17%	1959
	21st to end	Day	18% 2 6% 16% 31% 27%	1650
March	1st to 10th	Day	16% 5% 4 12% 32% 31%	4821
	11th to 20th	Day	17% 9% 7% 17% 30% 20%	5000
	21st to end	Day	17% 4 6% 20% 41% 12%	5616
April	1st to 10th	Day	17% 3 6% 17% 36% 22%	2400
	11th to 20th	Day	18% 3 6% 16% 29% 28%	2374
	21st to end	Day	15% 3 5% 18% 38% 21%	2400
May	1st to 10th	Day	19% 4 7% 19% 29% 22%	5440
	11th to 20th	Day	14% 5% 6% 15% 32% 28%	5529
	21st to end	Day	10% 4 6% 14% 19% 47%	6780
June	1st to 10th	Day	17% 5% 9% 20% 25% 24%	2788
	11th to 20th	Day	13% 3 5% 12% 22% 45%	2660
	21st to end	Day	25% 5% 10% 18% 20% 22%	2660
July	1st to 10th	Day	21% 8% 14% 14% 18% 25%	4092
	11th to 20th	Day	25% 8% 18% 28% 16% 5%	4041
	21st to end	Day	32% 9% 17% 29% 12% 1	4314
August	1st to 10th	Day	25% 8% 18% 27% 15% 8%	3961
	11th to 20th	Day	20% 8% 11% 25% 24% 12%	3762
	21st to end	Day	29% 7% 17% 26% 18% 3	4179
September	1st to 10th	Day	28% 6% 11% 20% 24% 11%	2280
	11th to 20th	Day	23% 6% 11% 15% 27% 19%	2280
	21st to end	Day	16% 4 7% 21% 32% 21%	2056
October	1st to 10th	Day	13% 3 5% 13% 30% 35%	3170
	11th to 20th	Day	17% 2 5% 20% 32% 24%	3150
	21st to end	Day	8% 2 4 15% 40% 31%	3438
November	1st to 10th	Day	13% 3 5% 21% 37% 20%	1959
	11th to 20th	Day	15% 2 6% 21% 38% 18%	1810
	21st to end	Day	19% 3 6% 21% 33% 18%	1800
December	1st to 10th	Day	12% 2 6% 29% 34% 18%	2716
	11th to 20th	Day	17% 4 7% 22% 37% 12%	3024
	21st to end	Day	14% 3 6% 27% 36% 14%	4124
January	1st to 10th	Night	22% 6% 8% 20% 35% 10%	5867
	11th to 20th	Night	12% 6% 6% 21% 34% 21%	5880
	21st to end	Night	19% 8% 8% 15% 27% 22%	6468
February	1st to 10th	Night	17% 3 10% 22% 28% 20%	2570
	11th to 20th	Night	21% 4 8% 23% 28% 17%	2338
	21st to end	Night	17% 3 6% 17% 33% 25%	1980
March	1st to 10th	Night	14% 4 5% 15% 35% 27%	5051
	11th to 20th	Night	20% 7% 6% 19% 31% 17%	5000
	21st to end	Night	12% 3 8% 25% 37% 14%	5352
April	1st to 10th	Night	16% 2 7% 16% 35% 23%	2000
	11th to 20th	Night	18% 3 7% 15% 27% 30%	1977
	21st to end	Night	17% 3 8% 16% 34% 22%	2000
May	1st to 10th	Night	24% 4 10% 17% 26% 19%	4537
	11th to 20th	Night	15% 6% 9% 14% 30% 26%	4385
	21st to end	Night	13% 3 6% 12% 16% 50%	4114
June	1st to 10th	Night	24% 7% 11% 16% 17% 25%	1596
	11th to 20th	Night	17% 3 6% 13% 19% 42%	1520
	21st to end	Night	29% 7% 12% 14% 15% 23%	1520
July	1st to 10th	Night	31% 8% 14% 12% 13% 22%	2749
	11th to 20th	Night	29% 7% 17% 31% 12% 4	2806
	21st to end	Night	37% 7% 17% 30% 9% 1	3011
August	1st to 10th	Night	32% 9% 18% 21% 14% 7%	2951
	11th to 20th	Night	28% 7% 14% 23% 19% 8%	3143
	21st to end	Night	37% 8% 18% 21% 12% 3	3487
September	1st to 10th	Night	29% 6% 13% 20% 20% 11%	1900
	11th to 20th	Night	24% 7% 10% 15% 22% 21%	1900
	21st to end	Night	19% 4 7% 15% 32% 22%	2119
October	1st to 10th	Night	14% 4 5% 12% 31% 35%	3800
	11th to 20th	Night	17% 3 7% 19% 25% 29%	3778
	21st to end	Night	10% 2 4 16% 37% 31%	4120
November	1st to 10th	Night	12% 2 5% 22% 38% 21%	2340
	11th to 20th	Night	13% 3 5% 20% 37% 23%	2566
	21st to end	Night	21% 4 6% 17% 33% 20%	2600
December	1st to 10th	Night	12% 3 6% 29% 30% 20%	4469
	11th to 20th	Night	15% 3 6% 21% 36% 18%	5182
	21st to end	Night	16% 3 7% 24% 37% 14%	6882

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	11% 12% 30% 34% 13% 1	300
	11th to 20th	Day	12% 14% 35% 24% 14% 2	300
	21st to end	Day	8% 13% 33% 28% 16% 2	330
February	1st to 10th	Day	12% 16% 34% 24% 13% 1	300
	11th to 20th	Day	15% 13% 39% 28% 4	300
	21st to end	Day	13% 26% 32% 22% 5% 1	249
March	1st to 10th	Day	12% 21% 32% 25% 10% 1	440
	11th to 20th	Day	17% 18% 29% 22% 12% 1	500
	21st to end	Day	14% 27% 31% 20% 7% 1	550
April	1st to 10th	Day	11% 21% 35% 24% 7% 2	500
	11th to 20th	Day	14% 23% 35% 20% 7% 1	492
	21st to end	Day	12% 23% 31% 25% 9% 1	500
May	1st to 10th	Day	7% 18% 39% 24% 11% 1	503
	11th to 20th	Day	9% 12% 32% 27% 15% 4	528
	21st to end	Day	4 15% 30% 35% 16% 1	721
June	1st to 10th	Day	4 7% 20% 36% 29% 5%	726
	11th to 20th	Day	4 6% 21% 37% 28% 4	680
	21st to end	Day	6% 4 16% 34% 31% 8%	680
July	1st to 10th	Day	3 2 13% 33% 34% 14%	519
	11th to 20th	Day	5% 5% 25% 41% 24%	484
	21st to end	Day	5% 1 7% 24% 38% 25%	531
August	1st to 10th	Day	2 1 6% 29% 45% 17%	487
	11th to 20th	Day	4 1 10% 32% 39% 13%	477
	21st to end	Day	5% 1 8% 34% 37% 14%	539
September	1st to 10th	Day	5% 3 11% 31% 38% 12%	490
	11th to 20th	Day	4 3 18% 35% 32% 9%	490
	21st to end	Day	6% 7% 18% 33% 27% 9%	338
October	1st to 10th	Day	6% 7% 26% 29% 26% 7%	300
	11th to 20th	Day	9% 8% 23% 30% 24% 7%	300
	21st to end	Day	12% 10% 19% 31% 21% 6%	330
November	1st to 10th	Day	9% 14% 26% 32% 18% 1	300
	11th to 20th	Day	8% 10% 28% 31% 18% 5%	300
	21st to end	Day	11% 15% 32% 24% 16% 1	300
December	1st to 10th	Day	8% 10% 33% 30% 17% 2	300
	11th to 20th	Day	7% 15% 35% 29% 12% 2	300
	21st to end	Day	14% 16% 33% 24% 11% 2	330
January	1st to 10th	Night	6% 9% 29% 40% 14% 2	800
	11th to 20th	Night	7% 11% 31% 37% 13% 1	800
	21st to end	Night	7% 13% 29% 35% 15% 2	880
February	1st to 10th	Night	6% 13% 32% 35% 13% 1	800
	11th to 20th	Night	10% 14% 35% 34% 7%	784
	21st to end	Night	8% 15% 39% 33% 4	660
March	1st to 10th	Night	7% 17% 36% 31% 9% 1	800
	11th to 20th	Night	9% 14% 29% 35% 12% 1	800
	21st to end	Night	7% 15% 32% 37% 8%	820
April	1st to 10th	Night	7% 13% 40% 34% 5% 1	600
	11th to 20th	Night	7% 17% 34% 34% 6% 1	593
	21st to end	Night	6% 14% 41% 34% 5% 1	600
May	1st to 10th	Night	6% 11% 38% 39% 7%	600
	11th to 20th	Night	8% 9% 28% 37% 16% 1	591
	21st to end	Night	4 8% 32% 42% 12%	650
June	1st to 10th	Night	4 4 27% 46% 18%	599
	11th to 20th	Night	3 4 26% 49% 18%	570
	21st to end	Night	6% 2 19% 42% 29% 2	570
July	1st to 10th	Night	5% 1 15% 41% 35% 4	555
	11th to 20th	Night	4 1 9% 33% 49% 5%	552
	21st to end	Night	6% 8% 31% 48% 7%	624
August	1st to 10th	Night	5% 1 8% 28% 50% 9%	567
	11th to 20th	Night	5% 1 8% 38% 44% 4	564
	21st to end	Night	3 8% 38% 45% 5%	627
September	1st to 10th	Night	6% 1 14% 42% 35% 2	570
	11th to 20th	Night	6% 3 15% 45% 28% 3	570
	21st to end	Night	4 5% 18% 44% 26% 2	637
October	1st to 10th	Night	5% 4 25% 45% 19% 2	760
	11th to 20th	Night	5% 6% 22% 47% 18% 2	760
	21st to end	Night	6% 9% 23% 36% 23% 3	836
November	1st to 10th	Night	4 8% 24% 41% 21% 2	780
	11th to 20th	Night	4 8% 27% 40% 19% 2	966
	21st to end	Night	7% 13% 23% 33% 21% 2	1000
December	1st to 10th	Night	7% 10% 28% 40% 16% 1	1000
	11th to 20th	Night	6% 12% 29% 39% 13% 1	1000
	21st to end	Night	9% 12% 29% 40% 8% 1	1060

Page generated at 2025-06-07 08:28:15. Version ac07

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