Observatorio Carl Sagan Cerro Azul
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatorio Carl Sagan Cerro Azul clear sky chart from 2005-11-06 to 2026-05-02.

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	3 3 1 4 3 4 4 4 5% 6% 62%	140813
	Night	3 3 1 4 3 3 4 3 5% 7% 63%	139230
Transparency	Day	20% 5% 6% 11% 23% 35%	135731
	Night	20% 4 6% 11% 25% 34%	135316
Seeing	Day	10% 12% 27% 29% 17% 5%	16863
	Night	6% 4 16% 38% 30% 5%	27039

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 4 2 4 3 3 4 3 5% 6% 62%	5318
	11th to 20th	Day	1 2 1 3 2 2 2 3 4 5% 76%	5340
	21st to end	Day	6% 6% 2 6% 3 3 3 3 5% 6% 56%	5844
February	1st to 10th	Day	5% 4 2 5% 2 2 3 3 5% 5% 63%	1954
	11th to 20th	Day	6% 6% 2 6% 3 2 4 3 4 6% 59%	2050
	21st to end	Day	4 4 2 4 3 2 3 3 4 6% 65%	1893
March	1st to 10th	Day	3 5% 2 4 3 3 4 3 5% 6% 62%	5064
	11th to 20th	Day	3 3 1 3 3 3 3 3 5% 6% 68%	5110
	21st to end	Day	1 4 1 6% 4 4 5% 4 6% 6% 60%	5607
April	1st to 10th	Day	2 3 1 4 3 3 3 3 5% 7% 68%	2310
	11th to 20th	Day	2 2 1 3 2 2 2 2 2 4 78%	2446
	21st to end	Day	1 2 1 2 2 2 2 2 3 4 79%	2520
May	1st to 10th	Day	1 1 1 1 2 1 2 3 87%	5704
	11th to 20th	Day	1 1 1 2 2 2 2 2 3 4 80%	5841
	21st to end	Day	1 2 1 2 1 1 2 2 2 3 84%	6423
June	1st to 10th	Day	2 2 1 2 3 2 2 3 5% 6% 72%	2600
	11th to 20th	Day	2 2 1 2 2 3 3 3 3 4 77%	2600
	21st to end	Day	4 3 1 4 4 4 5% 4 7% 6% 57%	2600
July	1st to 10th	Day	3 2 1 6% 6% 7% 8% 6% 9% 9% 42%	5879
	11th to 20th	Day	4 4 2 7% 7% 7% 8% 7% 9% 10% 34%	5880
	21st to end	Day	6% 5% 2 7% 7% 8% 8% 6% 8% 9% 33%	6401
August	1st to 10th	Day	3 3 2 5% 5% 7% 8% 7% 9% 12% 38%	5779
	11th to 20th	Day	4 3 2 6% 6% 8% 9% 7% 10% 13% 33%	5649
	21st to end	Day	3 4 2 7% 6% 7% 7% 6% 9% 9% 41%	5881
September	1st to 10th	Day	9% 6% 3 7% 6% 5% 7% 5% 6% 7% 41%	2200
	11th to 20th	Day	4 3 2 5% 4 5% 5% 4 5% 7% 56%	2200
	21st to end	Day	4 2 1 3 3 3 3 3 6% 6% 66%	2200
October	1st to 10th	Day	2 2 1 2 3 3 3 2 3 4 75%	3437
	11th to 20th	Day	2 2 1 2 2 2 2 1 2 3 80%	3250
	21st to end	Day	1 1 1 2 1 2 2 2 3 4 82%	3548
November	1st to 10th	Day	1 2 1 3 2 2 2 2 4 6% 74%	2059
	11th to 20th	Day	3 4 1 4 2 2 3 3 5% 5% 68%	2100
	21st to end	Day	5% 5% 2 4 3 3 3 3 6% 6% 59%	1978
December	1st to 10th	Day	2 2 1 3 3 2 3 3 3 4 75%	3040
	11th to 20th	Day	3 4 2 5% 3 2 3 3 5% 6% 65%	3499
	21st to end	Day	3 3 1 3 2 2 3 3 4 6% 68%	4609
January	1st to 10th	Night	4 5% 2 5% 3 4 4 3 5% 6% 58%	7605
	11th to 20th	Night	1 1 2 2 2 2 2 3 5% 80%	7650
	21st to end	Night	8% 7% 2 5% 4 3 4 3 4 7% 53%	8370
February	1st to 10th	Night	4 4 1 4 4 4 3 3 4 5% 64%	2662
	11th to 20th	Night	5% 6% 2 4 4 3 3 3 5% 6% 59%	2458
	21st to end	Night	3 4 2 4 3 4 3 3 4 5% 65%	1911
March	1st to 10th	Night	2 3 2 4 3 3 3 3 4 5% 68%	5050
	11th to 20th	Night	3 4 2 3 2 2 3 3 4 4 70%	5110
	21st to end	Night	2 6% 2 5% 3 3 3 3 4 7% 62%	5610
April	1st to 10th	Night	2 3 1 3 3 2 3 3 4 7% 71%	2310
	11th to 20th	Night	1 2 1 3 2 2 3 2 4 4 75%	2119
	21st to end	Night	1 2 1 2 2 2 2 2 3 5% 79%	2100
May	1st to 10th	Night	1 1 1 1 1 1 2 2 89%	4295
	11th to 20th	Night	1 1 1 2 2 3 4 5% 80%	4074
	21st to end	Night	1 2 1 1 1 1 1 2 3 86%	4474
June	1st to 10th	Night	2 2 1 2 2 3 2 2 4 7% 74%	1800
	11th to 20th	Night	2 1 1 2 2 1 2 2 3 4 80%	1800
	21st to end	Night	3 3 1 5% 4 4 4 5% 6% 6% 59%	1800
July	1st to 10th	Night	3 4 2 8% 6% 6% 6% 7% 8% 10% 40%	4100
	11th to 20th	Night	4 6% 3 8% 7% 6% 8% 7% 10% 12% 31%	4100
	21st to end	Night	4 5% 2 8% 6% 6% 7% 6% 11% 15% 30%	4472
August	1st to 10th	Night	3 4 2 6% 5% 6% 6% 7% 12% 16% 33%	4033
	11th to 20th	Night	4 5% 2 9% 7% 8% 9% 7% 10% 12% 27%	4200
	21st to end	Night	4 4 2 7% 5% 5% 6% 5% 9% 11% 42%	5082
September	1st to 10th	Night	9% 6% 2 6% 5% 5% 5% 4 6% 8% 44%	2200
	11th to 20th	Night	5% 3 1 4 3 4 3 3 5% 7% 62%	2200
	21st to end	Night	3 2 1 3 3 2 2 2 4 5% 71%	2200
October	1st to 10th	Night	2 1 1 2 2 2 2 2 3 5% 78%	3755
	11th to 20th	Night	2 3 1 3 2 2 2 2 3 4 78%	3898
	21st to end	Night	1 2 1 1 1 1 2 4 86%	4252
November	1st to 10th	Night	1 2 1 2 2 2 2 3 4 5% 77%	2460
	11th to 20th	Night	3 3 1 3 3 2 3 3 5% 6% 69%	2520
	21st to end	Night	6% 4 2 5% 4 3 3 3 5% 6% 59%	2638
December	1st to 10th	Night	4 2 1 3 2 2 2 2 3 5% 73%	4370
	11th to 20th	Night	2 4 2 5% 3 3 3 3 4 5% 65%	4941
	21st to end	Night	4 3 1 3 3 3 3 3 3 5% 67%	6611

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	22% 2 3 11% 28% 33%	5321
	11th to 20th	Day	12% 2 3 5% 28% 50%	5340
	21st to end	Day	29% 3 2 9% 24% 33%	5844
February	1st to 10th	Day	23% 2 3 10% 24% 38%	1954
	11th to 20th	Day	27% 2 4 12% 27% 28%	2060
	21st to end	Day	22% 2 2 6% 28% 41%	1893
March	1st to 10th	Day	20% 3 4 6% 21% 46%	5064
	11th to 20th	Day	16% 3 4 14% 30% 34%	5110
	21st to end	Day	21% 4 4 6% 32% 32%	5607
April	1st to 10th	Day	16% 2 2 7% 32% 40%	2310
	11th to 20th	Day	13% 1 2 5% 26% 53%	2449
	21st to end	Day	11% 2 2 6% 28% 52%	2520
May	1st to 10th	Day	6% 1 1 5% 21% 65%	5704
	11th to 20th	Day	9% 2 2 7% 22% 58%	5844
	21st to end	Day	8% 1 1 2 16% 72%	6424
June	1st to 10th	Day	13% 2 4 5% 28% 48%	2600
	11th to 20th	Day	11% 3 3 4 22% 57%	2600
	21st to end	Day	23% 5% 7% 9% 27% 29%	2600
July	1st to 10th	Day	28% 11% 16% 21% 13% 12%	5816
	11th to 20th	Day	36% 13% 17% 24% 10% 1	5811
	21st to end	Day	39% 12% 16% 13% 13% 6%	6217
August	1st to 10th	Day	36% 13% 19% 18% 12% 2	4208
	11th to 20th	Day	33% 12% 18% 25% 9% 3	4084
	21st to end	Day	30% 11% 18% 16% 17% 8%	4232
September	1st to 10th	Day	40% 8% 9% 14% 19% 12%	2200
	11th to 20th	Day	25% 5% 7% 14% 28% 21%	2200
	21st to end	Day	18% 4 6% 16% 33% 23%	2200
October	1st to 10th	Day	13% 2 4 10% 19% 51%	3437
	11th to 20th	Day	11% 2 2 8% 35% 42%	3250
	21st to end	Day	8% 1 2 7% 29% 53%	3548
November	1st to 10th	Day	13% 2 2 11% 33% 39%	2059
	11th to 20th	Day	18% 2 3 12% 29% 36%	2100
	21st to end	Day	24% 2 3 15% 28% 27%	1978
December	1st to 10th	Day	15% 2 3 9% 30% 42%	3040
	11th to 20th	Day	20% 2 4 7% 22% 45%	3498
	21st to end	Day	16% 2 3 10% 38% 30%	4609
January	1st to 10th	Night	25% 3 4 10% 31% 27%	7605
	11th to 20th	Night	9% 1 2 8% 27% 52%	7650
	21st to end	Night	32% 3 3 9% 26% 28%	8370
February	1st to 10th	Night	23% 2 3 8% 26% 37%	2662
	11th to 20th	Night	26% 2 4 12% 28% 27%	2459
	21st to end	Night	21% 2 3 8% 24% 41%	1911
March	1st to 10th	Night	18% 2 3 7% 24% 46%	5050
	11th to 20th	Night	17% 3 3 12% 34% 31%	5110
	21st to end	Night	22% 3 5% 9% 31% 31%	5610
April	1st to 10th	Night	15% 1 3 10% 36% 35%	2310
	11th to 20th	Night	13% 2 3 8% 29% 46%	2119
	21st to end	Night	11% 1 3 6% 30% 49%	2100
May	1st to 10th	Night	5% 1 1 5% 33% 55%	4292
	11th to 20th	Night	7% 2 3 9% 22% 57%	4075
	21st to end	Night	7% 1 1 3 20% 69%	4474
June	1st to 10th	Night	13% 2 2 7% 33% 43%	1800
	11th to 20th	Night	9% 1 3 5% 25% 57%	1800
	21st to end	Night	21% 7% 7% 10% 22% 33%	1800
July	1st to 10th	Night	33% 10% 16% 20% 9% 12%	4055
	11th to 20th	Night	39% 11% 21% 19% 8% 1	4046
	21st to end	Night	35% 12% 20% 15% 10% 7%	4344
August	1st to 10th	Night	33% 11% 22% 21% 10% 4	2928
	11th to 20th	Night	36% 11% 20% 21% 9% 3	3041
	21st to end	Night	30% 11% 15% 20% 15% 9%	3660
September	1st to 10th	Night	35% 9% 12% 16% 17% 11%	2200
	11th to 20th	Night	20% 5% 7% 19% 28% 20%	2200
	21st to end	Night	16% 4 7% 18% 32% 23%	2200
October	1st to 10th	Night	10% 3 4 10% 21% 51%	3755
	11th to 20th	Night	13% 2 3 13% 33% 37%	3898
	21st to end	Night	6% 1 2 9% 29% 52%	4252
November	1st to 10th	Night	11% 2 4 12% 36% 36%	2460
	11th to 20th	Night	17% 2 3 16% 29% 34%	2520
	21st to end	Night	25% 3 4 13% 28% 26%	2638
December	1st to 10th	Night	15% 1 4 9% 30% 41%	4370
	11th to 20th	Night	21% 3 3 9% 22% 42%	4941
	21st to end	Night	20% 2 4 9% 33% 32%	6611

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	18% 12% 25% 33% 10% 2	330
	11th to 20th	Day	13% 7% 30% 34% 14% 2	330
	21st to end	Day	15% 14% 31% 28% 10% 1	363
February	1st to 10th	Day	13% 14% 30% 28% 12% 3	394
	11th to 20th	Day	23% 19% 31% 22% 6%	535
	21st to end	Day	17% 26% 33% 19% 5% 1	446
March	1st to 10th	Day	18% 24% 31% 19% 9%	540
	11th to 20th	Day	17% 20% 27% 24% 9% 3	540
	21st to end	Day	14% 24% 34% 17% 8% 2	594
April	1st to 10th	Day	10% 22% 35% 21% 10% 3	540
	11th to 20th	Day	11% 25% 37% 15% 10% 2	532
	21st to end	Day	10% 22% 38% 17% 9% 3	540
May	1st to 10th	Day	11% 17% 39% 22% 8% 3	508
	11th to 20th	Day	6% 16% 39% 24% 12% 3	528
	21st to end	Day	6% 16% 46% 23% 7% 2	573
June	1st to 10th	Day	6% 8% 43% 28% 11% 3	530
	11th to 20th	Day	3 8% 40% 33% 13% 3	530
	21st to end	Day	4 4 31% 36% 19% 5%	530
July	1st to 10th	Day	7% 2 16% 41% 25% 9%	526
	11th to 20th	Day	8% 1 10% 37% 33% 10%	524
	21st to end	Day	11% 2 11% 33% 31% 12%	575
August	1st to 10th	Day	6% 1 12% 33% 33% 15%	527
	11th to 20th	Day	7% 2 11% 37% 33% 10%	517
	21st to end	Day	8% 2 11% 32% 30% 17%	583
September	1st to 10th	Day	12% 4 15% 39% 23% 7%	530
	11th to 20th	Day	6% 3 20% 39% 25% 7%	530
	21st to end	Day	6% 7% 19% 39% 23% 6%	530
October	1st to 10th	Day	5% 7% 26% 34% 21% 7%	432
	11th to 20th	Day	8% 8% 25% 28% 22% 8%	330
	21st to end	Day	5% 8% 26% 30% 22% 9%	363
November	1st to 10th	Day	7% 12% 23% 37% 18% 5%	330
	11th to 20th	Day	8% 11% 24% 32% 22% 4	330
	21st to end	Day	13% 18% 27% 28% 13% 1	330
December	1st to 10th	Day	10% 12% 27% 33% 18% 1	330
	11th to 20th	Day	7% 12% 31% 36% 12% 2	330
	21st to end	Day	21% 15% 23% 26% 13% 2	363
January	1st to 10th	Night	8% 3 17% 44% 23% 4	840
	11th to 20th	Night	6% 4 22% 42% 22% 4	840
	21st to end	Night	12% 6% 23% 38% 18% 2	924
February	1st to 10th	Night	7% 5% 20% 41% 22% 4	840
	11th to 20th	Night	11% 5% 24% 42% 16% 1	824
	21st to end	Night	7% 7% 26% 44% 14% 2	692
March	1st to 10th	Night	7% 9% 26% 40% 16% 2	840
	11th to 20th	Night	7% 8% 20% 39% 23% 4	840
	21st to end	Night	5% 8% 23% 42% 20% 2	924
April	1st to 10th	Night	4 6% 23% 45% 22% 2	840
	11th to 20th	Night	4 9% 28% 41% 17% 1	665
	21st to end	Night	3 6% 29% 44% 17% 1	630
May	1st to 10th	Night	2 7% 23% 48% 18% 2	603
	11th to 20th	Night	1 5% 20% 46% 25% 2	591
	21st to end	Night	2 4 20% 45% 28% 1	650
June	1st to 10th	Night	4 1 16% 47% 29% 3	600
	11th to 20th	Night	2 2 18% 43% 34% 1	600
	21st to end	Night	3 2 15% 33% 43% 4	600
July	1st to 10th	Night	5% 2 8% 27% 50% 8%	585
	11th to 20th	Night	7% 2 7% 24% 47% 13%	582
	21st to end	Night	10% 1 7% 21% 46% 14%	657
August	1st to 10th	Night	7% 1 6% 18% 53% 16%	597
	11th to 20th	Night	6% 2 8% 18% 50% 17%	594
	21st to end	Night	7% 1 6% 20% 50% 16%	697
September	1st to 10th	Night	12% 2 8% 20% 45% 12%	800
	11th to 20th	Night	6% 1 5% 29% 51% 8%	800
	21st to end	Night	4 2 7% 40% 42% 6%	800
October	1st to 10th	Night	3 2 10% 40% 39% 6%	800
	11th to 20th	Night	6% 2 10% 44% 32% 6%	800
	21st to end	Night	1 4 11% 39% 38% 7%	880
November	1st to 10th	Night	3 5% 11% 39% 37% 6%	820
	11th to 20th	Night	5% 4 13% 40% 35% 4	840
	21st to end	Night	9% 6% 18% 41% 23% 4	840
December	1st to 10th	Night	8% 3 15% 44% 25% 4	840
	11th to 20th	Night	7% 4 18% 46% 22% 2	840
	21st to end	Night	10% 6% 20% 38% 22% 5%	924

Page generated at 2026-04-28 23:21:47. Version ac07

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