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 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 3 1 4 3 4 4 4 6% 7% 60%	156658
	Night	3 4 2 5% 4 4 4 4 6% 7% 57%	152650
Transparency	Day	19% 5% 9% 21% 27% 20%	151676
	Night	20% 5% 9% 20% 27% 19%	148639
Seeing	Day	9% 12% 25% 29% 20% 6%	17555
	Night	7% 9% 26% 37% 19% 2	27664

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 9% 4 7% 4 4 4 3 6% 6% 53%	5318
	11th to 20th	Day	1 3 3 4 2 2 2 2 3 4 73%	5340
	21st to end	Day	3 8% 3 6% 4 3 3 3 4 4 58%	5844
February	1st to 10th	Day	2 4 2 5% 4 3 4 3 6% 7% 61%	1919
	11th to 20th	Day	3 5% 2 6% 4 3 3 3 6% 6% 58%	2049
	21st to end	Day	2 5% 2 4 4 3 4 3 4 5% 65%	1730
March	1st to 10th	Day	1 5% 2 4 4 4 4 3 5% 6% 62%	4928
	11th to 20th	Day	2 5% 3 8% 5% 4 6% 3 5% 7% 54%	5110
	21st to end	Day	1 4 2 5% 4 4 5% 4 5% 8% 58%	5740
April	1st to 10th	Day	3 3 1 4 4 4 4 3 5% 6% 63%	2520
	11th to 20th	Day	4 5% 1 3 3 4 3 3 4 5% 64%	2491
	21st to end	Day	2 4 1 3 3 3 3 2 4 6% 68%	2520
May	1st to 10th	Day	2 5% 1 4 3 4 5% 4 6% 8% 59%	7057
	11th to 20th	Day	2 3 1 3 3 3 4 3 4 6% 70%	7192
	21st to end	Day	2 2 1 3 2 3 3 3 5% 7% 70%	8824
June	1st to 10th	Day	3 3 1 3 3 4 4 4 7% 9% 58%	2940
	11th to 20th	Day	2 2 1 2 2 2 4 3 4 6% 72%	2940
	21st to end	Day	5% 4 1 4 4 5% 5% 5% 6% 7% 55%	2940
July	1st to 10th	Day	3 2 1 4 4 4 5% 4 6% 8% 59%	7737
	11th to 20th	Day	2 2 1 4 4 6% 6% 6% 10% 12% 46%	7650
	21st to end	Day	4 4 2 5% 5% 6% 7% 6% 9% 11% 40%	8304
August	1st to 10th	Day	1 1 1 3 3 4 6% 5% 8% 10% 56%	7332
	11th to 20th	Day	3 2 1 4 4 5% 5% 5% 8% 12% 51%	7003
	21st to end	Day	3 3 1 4 4 5% 6% 6% 9% 12% 47%	7751
September	1st to 10th	Day	4 3 2 6% 5% 5% 5% 5% 6% 8% 51%	2520
	11th to 20th	Day	5% 3 1 4 4 4 4 5% 5% 6% 58%	2520
	21st to end	Day	4 3 1 3 3 3 4 3 4 5% 67%	2272
October	1st to 10th	Day	3 3 1 3 2 2 2 2 3 3 75%	3370
	11th to 20th	Day	3 3 1 3 4 4 3 3 4 6% 66%	3280
	21st to end	Day	2 1 2 2 2 2 2 3 5% 78%	3548
November	1st to 10th	Day	2 2 1 3 3 3 4 3 4 6% 69%	2059
	11th to 20th	Day	2 3 1 5% 3 3 3 2 4 5% 69%	1900
	21st to end	Day	2 5% 2 5% 2 3 3 3 5% 5% 64%	1890
December	1st to 10th	Day	2 3 1 3 2 2 2 2 4 5% 75%	2799
	11th to 20th	Day	2 4 2 5% 4 4 3 3 5% 6% 64%	3106
	21st to end	Day	2 4 1 4 2 3 3 2 5% 6% 68%	4215
January	1st to 10th	Night	2 7% 4 9% 5% 5% 5% 4 5% 5% 48%	7605
	11th to 20th	Night	1 2 1 4 2 2 3 2 3 4 76%	7650
	21st to end	Night	3 6% 2 5% 3 4 5% 4 5% 7% 57%	8370
February	1st to 10th	Night	2 5% 2 5% 3 3 3 3 4 6% 65%	2698
	11th to 20th	Night	3 6% 2 6% 4 5% 4 3 5% 8% 54%	2458
	21st to end	Night	3 4 1 5% 3 3 3 3 5% 6% 63%	2076
March	1st to 10th	Night	2 4 3 5% 3 4 4 3 4 5% 62%	5164
	11th to 20th	Night	4 6% 4 9% 5% 4 4 3 4 5% 54%	5110
	21st to end	Night	2 3 1 5% 4 3 3 3 5% 7% 64%	5470
April	1st to 10th	Night	3 4 2 4 3 3 3 3 5% 6% 64%	2100
	11th to 20th	Night	3 4 2 5% 4 4 3 2 5% 5% 63%	2077
	21st to end	Night	3 3 1 5% 3 4 3 2 5% 6% 64%	2100
May	1st to 10th	Night	5% 7% 2 6% 4 4 5% 4 5% 6% 53%	5890
	11th to 20th	Night	2 3 1 4 3 3 3 3 5% 6% 64%	5695
	21st to end	Night	3 3 1 4 4 4 4 3 4 6% 65%	5365
June	1st to 10th	Night	4 4 2 6% 5% 5% 5% 5% 7% 8% 51%	1680
	11th to 20th	Night	3 3 1 3 3 3 3 3 6% 7% 65%	1680
	21st to end	Night	5% 5% 2 5% 4 5% 5% 6% 8% 8% 47%	1680
July	1st to 10th	Night	3 4 2 6% 5% 6% 6% 4 6% 8% 50%	5218
	11th to 20th	Night	5% 3 2 6% 5% 6% 6% 6% 10% 12% 39%	5340
	21st to end	Night	7% 5% 2 7% 6% 6% 7% 7% 10% 12% 31%	5805
August	1st to 10th	Night	2 3 2 6% 6% 6% 7% 6% 9% 11% 40%	5486
	11th to 20th	Night	4 4 2 8% 6% 6% 7% 7% 10% 13% 34%	5853
	21st to end	Night	5% 4 2 8% 7% 7% 8% 7% 10% 13% 30%	6465
September	1st to 10th	Night	5% 4 2 6% 4 7% 6% 5% 6% 9% 47%	2100
	11th to 20th	Night	5% 4 2 5% 3 3 5% 4 6% 7% 55%	2100
	21st to end	Night	6% 3 2 4 3 4 3 3 4 6% 63%	2343
October	1st to 10th	Night	3 2 1 3 2 2 2 2 3 5% 74%	4040
	11th to 20th	Night	4 3 1 4 3 4 4 3 4 5% 66%	3934
	21st to end	Night	2 2 1 2 2 2 2 2 4 5% 76%	4252
November	1st to 10th	Night	2 2 1 3 2 2 3 3 4 5% 73%	2460
	11th to 20th	Night	1 3 1 4 2 3 3 3 4 4 71%	2695
	21st to end	Night	4 5% 2 5% 4 3 3 3 4 6% 62%	2730
December	1st to 10th	Night	2 2 1 3 2 3 3 2 4 6% 72%	4606
	11th to 20th	Night	2 3 1 4 4 4 4 3 6% 8% 63%	5321
	21st to end	Night	2 5% 2 5% 3 3 3 2 4 6% 64%	7034

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% 3 5% 32% 31% 7%	5321
	11th to 20th	Day	11% 4 7% 21% 35% 22%	5340
	21st to end	Day	22% 5% 5% 17% 29% 23%	5844
February	1st to 10th	Day	17% 4 8% 23% 31% 18%	1919
	11th to 20th	Day	20% 4 7% 24% 28% 16%	2059
	21st to end	Day	17% 2 6% 17% 32% 26%	1730
March	1st to 10th	Day	16% 4 4 12% 33% 31%	4928
	11th to 20th	Day	16% 9% 7% 17% 30% 21%	5110
	21st to end	Day	17% 4 6% 20% 41% 12%	5740
April	1st to 10th	Day	18% 3 6% 16% 36% 21%	2520
	11th to 20th	Day	18% 3 6% 16% 30% 28%	2494
	21st to end	Day	15% 3 5% 19% 38% 21%	2520
May	1st to 10th	Day	20% 4 7% 19% 30% 19%	7057
	11th to 20th	Day	12% 4 5% 15% 31% 33%	7195
	21st to end	Day	13% 4 6% 14% 21% 43%	8825
June	1st to 10th	Day	18% 5% 10% 19% 25% 24%	2940
	11th to 20th	Day	13% 3 5% 12% 22% 44%	2940
	21st to end	Day	24% 5% 9% 18% 21% 24%	2940
July	1st to 10th	Day	21% 7% 9% 12% 21% 30%	7674
	11th to 20th	Day	24% 8% 22% 27% 13% 6%	7581
	21st to end	Day	32% 8% 19% 27% 11% 2	8120
August	1st to 10th	Day	22% 7% 14% 34% 16% 7%	5805
	11th to 20th	Day	22% 8% 17% 27% 18% 8%	5519
	21st to end	Day	27% 7% 16% 33% 15% 2	6078
September	1st to 10th	Day	28% 6% 12% 20% 24% 10%	2520
	11th to 20th	Day	24% 6% 10% 16% 26% 18%	2520
	21st to end	Day	18% 4 7% 22% 31% 19%	2272
October	1st to 10th	Day	14% 3 5% 13% 31% 34%	3370
	11th to 20th	Day	17% 2 5% 19% 32% 24%	3280
	21st to end	Day	8% 2 4 15% 41% 31%	3548
November	1st to 10th	Day	13% 3 5% 21% 39% 20%	2059
	11th to 20th	Day	15% 2 6% 22% 38% 17%	1900
	21st to end	Day	19% 3 6% 21% 35% 17%	1890
December	1st to 10th	Day	12% 2 6% 29% 34% 18%	2799
	11th to 20th	Day	17% 4 7% 22% 37% 13%	3104
	21st to end	Day	14% 3 6% 27% 36% 14%	4215
January	1st to 10th	Night	24% 5% 6% 26% 32% 7%	7605
	11th to 20th	Night	9% 4 5% 20% 42% 20%	7650
	21st to end	Night	19% 7% 6% 14% 29% 25%	8370
February	1st to 10th	Night	16% 3 10% 22% 30% 20%	2698
	11th to 20th	Night	20% 4 8% 23% 28% 17%	2458
	21st to end	Night	16% 3 5% 17% 34% 24%	2076
March	1st to 10th	Night	14% 4 4 15% 35% 28%	5164
	11th to 20th	Night	20% 7% 6% 19% 31% 18%	5110
	21st to end	Night	11% 3 8% 25% 37% 15%	5470
April	1st to 10th	Night	17% 2 7% 17% 35% 23%	2100
	11th to 20th	Night	18% 3 7% 16% 27% 29%	2077
	21st to end	Night	17% 3 7% 17% 34% 21%	2100
May	1st to 10th	Night	26% 4 10% 19% 25% 17%	5888
	11th to 20th	Night	14% 5% 7% 14% 30% 29%	5696
	21st to end	Night	17% 3 6% 12% 17% 44%	5366
June	1st to 10th	Night	25% 6% 11% 16% 17% 25%	1680
	11th to 20th	Night	17% 3 6% 14% 20% 40%	1680
	21st to end	Night	28% 6% 12% 14% 15% 24%	1680
July	1st to 10th	Night	28% 8% 10% 15% 16% 23%	5173
	11th to 20th	Night	30% 7% 25% 24% 10% 4	5286
	21st to end	Night	38% 6% 21% 24% 9% 1	5677
August	1st to 10th	Night	32% 7% 18% 25% 13% 5%	4337
	11th to 20th	Night	33% 7% 18% 22% 14% 6%	4613
	21st to end	Night	38% 7% 20% 24% 10% 2	5069
September	1st to 10th	Night	30% 6% 14% 20% 20% 10%	2100
	11th to 20th	Night	25% 7% 11% 16% 22% 20%	2100
	21st to end	Night	21% 4 8% 16% 31% 21%	2343
October	1st to 10th	Night	13% 4 5% 12% 32% 34%	4040
	11th to 20th	Night	18% 3 7% 18% 25% 29%	3934
	21st to end	Night	10% 2 4 16% 38% 31%	4252
November	1st to 10th	Night	11% 2 4 22% 39% 21%	2460
	11th to 20th	Night	13% 3 5% 20% 37% 22%	2695
	21st to end	Night	21% 4 6% 18% 33% 19%	2730
December	1st to 10th	Night	12% 3 6% 29% 30% 20%	4606
	11th to 20th	Night	14% 3 6% 21% 36% 19%	5322
	21st to end	Night	16% 3 7% 24% 37% 14%	7034

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% 12% 30% 31% 12% 1	330
	11th to 20th	Day	13% 15% 34% 24% 13% 2	330
	21st to end	Day	10% 15% 33% 27% 15% 2	363
February	1st to 10th	Day	12% 18% 33% 23% 13% 2	330
	11th to 20th	Day	20% 14% 37% 26% 4	330
	21st to end	Day	14% 27% 32% 21% 5% 1	273
March	1st to 10th	Day	13% 22% 32% 23% 9% 1	477
	11th to 20th	Day	18% 20% 29% 21% 12% 1	540
	21st to end	Day	13% 28% 31% 20% 7% 1	594
April	1st to 10th	Day	11% 21% 34% 24% 7% 2	540
	11th to 20th	Day	16% 23% 34% 19% 7% 1	532
	21st to end	Day	14% 23% 30% 23% 8% 1	540
May	1st to 10th	Day	10% 17% 39% 22% 10% 1	543
	11th to 20th	Day	10% 14% 32% 26% 14% 4	568
	21st to end	Day	4 15% 29% 35% 15% 1	772
June	1st to 10th	Day	4 8% 21% 35% 27% 5%	780
	11th to 20th	Day	5% 8% 23% 36% 25% 3	780
	21st to end	Day	6% 6% 19% 33% 28% 7%	780
July	1st to 10th	Day	4 3 16% 35% 30% 12%	602
	11th to 20th	Day	4 8% 29% 38% 21%	564
	21st to end	Day	6% 10% 27% 35% 22%	619
August	1st to 10th	Day	2 1 10% 33% 40% 15%	567
	11th to 20th	Day	4 1 13% 33% 37% 11%	557
	21st to end	Day	5% 1 11% 37% 34% 12%	627
September	1st to 10th	Day	5% 3 15% 32% 34% 11%	570
	11th to 20th	Day	5% 4 22% 34% 28% 8%	570
	21st to end	Day	8% 8% 22% 31% 23% 8%	402
October	1st to 10th	Day	7% 8% 29% 28% 23% 6%	360
	11th to 20th	Day	13% 11% 22% 27% 21% 6%	339
	21st to end	Day	12% 12% 21% 29% 20% 6%	363
November	1st to 10th	Day	8% 15% 28% 31% 16% 2	330
	11th to 20th	Day	9% 11% 27% 30% 18% 5%	330
	21st to end	Day	13% 16% 32% 23% 15% 1	330
December	1st to 10th	Day	11% 13% 32% 27% 15% 2	330
	11th to 20th	Day	8% 16% 33% 27% 13% 2	330
	21st to end	Day	15% 16% 34% 23% 10% 2	363
January	1st to 10th	Night	7% 10% 29% 38% 14% 2	840
	11th to 20th	Night	8% 12% 31% 36% 13% 1	840
	21st to end	Night	8% 14% 29% 34% 14% 2	924
February	1st to 10th	Night	7% 13% 32% 35% 13% 1	840
	11th to 20th	Night	12% 14% 34% 33% 7%	824
	21st to end	Night	9% 16% 37% 33% 4	692
March	1st to 10th	Night	6% 17% 37% 31% 8% 1	840
	11th to 20th	Night	10% 15% 29% 33% 12% 1	840
	21st to end	Night	7% 15% 33% 37% 8%	861
April	1st to 10th	Night	8% 13% 39% 33% 5%	630
	11th to 20th	Night	8% 19% 33% 33% 6%	623
	21st to end	Night	7% 14% 40% 33% 5% 1	630
May	1st to 10th	Night	7% 11% 37% 38% 7%	630
	11th to 20th	Night	8% 11% 27% 37% 16% 1	621
	21st to end	Night	5% 9% 33% 42% 12%	683
June	1st to 10th	Night	5% 5% 27% 45% 17%	630
	11th to 20th	Night	3 5% 27% 47% 18%	630
	21st to end	Night	6% 4 21% 41% 27% 2	630
July	1st to 10th	Night	5% 1 17% 41% 32% 3	615
	11th to 20th	Night	4 1 12% 33% 45% 4	612
	21st to end	Night	7% 1 10% 31% 45% 6%	690
August	1st to 10th	Night	5% 1 10% 30% 46% 8%	627
	11th to 20th	Night	6% 1 10% 38% 41% 4	624
	21st to end	Night	4 1 10% 37% 44% 5%	693
September	1st to 10th	Night	7% 2 14% 41% 34% 3	630
	11th to 20th	Night	6% 4 16% 45% 26% 3	630
	21st to end	Night	7% 4 19% 43% 25% 2	705
October	1st to 10th	Night	5% 5% 26% 43% 19% 2	840
	11th to 20th	Night	6% 8% 22% 44% 17% 2	812
	21st to end	Night	6% 10% 23% 36% 22% 3	880
November	1st to 10th	Night	4 9% 24% 40% 20% 2	820
	11th to 20th	Night	5% 8% 27% 40% 18% 2	1015
	21st to end	Night	8% 14% 23% 33% 20% 2	1050
December	1st to 10th	Night	8% 11% 27% 38% 15% 1	1050
	11th to 20th	Night	7% 12% 29% 38% 13%	1050
	21st to end	Night	9% 13% 29% 40% 8% 1	1113

Page generated at 2026-10-11 03:06:27. Version ac07

Copyright © 2026 Attilla Danko.