Sonrisa Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sonrisa Observatory clear sky chart from 2005-11-06 to 2025-08-05.

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	5% 4 1 4 3 3 3 3 4 6% 64%	129601
	Night	7% 7% 2 5% 3 3 4 3 4 6% 56%	127568
Transparency	Day	20% 3 5% 17% 27% 27%	129333
	Night	28% 3 5% 16% 23% 25%	127351
Seeing	Day	7% 5% 21% 38% 22% 7%	16783
	Night	9% 2 10% 32% 36% 10%	27128

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	6% 2 1 3 2 2 3 2 3 4 70%	4098
	11th to 20th	Day	5% 4 2 3 2 2 2 2 4 5% 67%	4358
	21st to end	Day	10% 4 2 5% 3 4 5% 4 7% 9% 48%	5016
February	1st to 10th	Day	9% 5% 2 5% 4 3 4 3 4 4 58%	2000
	11th to 20th	Day	10% 6% 1 4 3 3 4 3 6% 7% 54%	1950
	21st to end	Day	9% 6% 2 5% 5% 4 5% 3 5% 6% 50%	1650
March	1st to 10th	Day	9% 6% 2 6% 4 4 4 4 7% 9% 44%	4518
	11th to 20th	Day	11% 4 2 5% 3 3 3 3 5% 7% 55%	4770
	21st to end	Day	10% 6% 2 4 4 3 3 3 5% 7% 54%	5788
April	1st to 10th	Day	7% 5% 2 5% 3 3 4 3 4 8% 56%	2400
	11th to 20th	Day	4 5% 1 4 3 3 4 3 4 6% 62%	2369
	21st to end	Day	6% 5% 1 3 3 3 3 3 4 8% 62%	2400
May	1st to 10th	Day	5% 5% 2 5% 2 3 3 2 3 5% 65%	5699
	11th to 20th	Day	3 6% 3 5% 3 4 4 4 6% 7% 55%	5841
	21st to end	Day	3 6% 3 5% 3 3 3 3 4 7% 61%	6423
June	1st to 10th	Day	5% 8% 2 5% 3 3 2 2 4 7% 59%	2600
	11th to 20th	Day	3 5% 2 3 2 2 3 2 3 5% 70%	2600
	21st to end	Day	2 5% 1 4 2 2 3 3 4 5% 71%	2600
July	1st to 10th	Day	1 2 1 2 1 1 2 2 3 4 82%	5879
	11th to 20th	Day	1 4 2 4 2 2 3 2 4 6% 70%	5880
	21st to end	Day	1 2 1 2 1 2 2 2 4 5% 78%	6105
August	1st to 10th	Day	1 2 1 2 1 2 2 2 4 5% 77%	3832
	11th to 20th	Day	1 1 1 1 1 1 2 2 3 5% 81%	3724
	21st to end	Day	1 2 1 2 1 2 3 2 3 4 79%	4180
September	1st to 10th	Day	3 2 1 3 2 2 3 3 5% 5% 71%	2266
	11th to 20th	Day	3 3 3 1 2 2 2 5% 5% 74%	2090
	21st to end	Day	2 3 1 3 2 2 3 2 4 5% 73%	2090
October	1st to 10th	Day	2 2 1 3 2 2 2 2 3 4 77%	3490
	11th to 20th	Day	3 4 1 3 2 2 3 2 3 5% 71%	3457
	21st to end	Day	2 3 1 3 2 2 3 3 5% 7% 70%	3295
November	1st to 10th	Day	5% 3 1 2 3 2 3 3 5% 7% 66%	1764
	11th to 20th	Day	4 3 1 4 2 3 2 2 5% 5% 68%	1800
	21st to end	Day	7% 5% 1 4 2 3 4 4 4 8% 58%	1800
December	1st to 10th	Day	4 3 1 2 2 2 3 2 5% 9% 67%	2950
	11th to 20th	Day	8% 4 1 4 4 4 5% 5% 6% 7% 52%	3409
	21st to end	Day	8% 5% 2 6% 5% 6% 5% 4 7% 9% 44%	4510
January	1st to 10th	Night	5% 4 1 4 2 3 4 2 4 7% 65%	5867
	11th to 20th	Night	6% 5% 2 5% 3 3 4 2 4 5% 60%	5616
	21st to end	Night	14% 7% 2 4 3 3 4 3 5% 6% 49%	5984
February	1st to 10th	Night	10% 5% 2 5% 3 2 3 3 5% 5% 56%	2400
	11th to 20th	Night	11% 7% 2 5% 4 3 3 3 3 5% 53%	2338
	21st to end	Night	12% 7% 2 6% 3 3 4 3 4 6% 51%	1980
March	1st to 10th	Night	20% 9% 2 5% 3 4 3 2 4 6% 40%	5376
	11th to 20th	Night	13% 9% 2 5% 3 4 4 3 5% 6% 47%	5230
	21st to end	Night	12% 14% 3 6% 3 3 4 2 4 5% 44%	5182
April	1st to 10th	Night	9% 9% 2 5% 4 3 4 3 5% 7% 49%	2000
	11th to 20th	Night	8% 10% 3 6% 3 2 2 3 3 6% 52%	1979
	21st to end	Night	8% 10% 2 6% 4 3 3 4 4 5% 50%	2000
May	1st to 10th	Night	9% 12% 3 5% 3 3 3 2 3 5% 53%	4288
	11th to 20th	Night	7% 18% 5% 8% 3 3 4 3 4 6% 40%	4074
	21st to end	Night	8% 14% 4 7% 3 4 4 2 4 5% 47%	4474
June	1st to 10th	Night	6% 14% 5% 7% 4 4 3 4 5% 7% 39%	1800
	11th to 20th	Night	3 10% 3 5% 3 3 4 2 6% 9% 52%	1800
	21st to end	Night	3 7% 3 5% 3 3 3 4 6% 8% 55%	1800
July	1st to 10th	Night	1 4 2 3 1 2 3 3 3 5% 73%	4100
	11th to 20th	Night	1 6% 4 6% 4 3 5% 3 4 7% 58%	4100
	21st to end	Night	2 6% 2 4 2 3 6% 2 4 5% 65%	4779
August	1st to 10th	Night	2 3 1 2 1 2 3 3 4 8% 71%	3206
	11th to 20th	Night	1 4 2 2 1 2 3 3 5% 8% 69%	3126
	21st to end	Night	2 5% 2 3 2 2 4 3 3 4 71%	3498
September	1st to 10th	Night	3 6% 3 4 3 4 4 2 4 7% 60%	1913
	11th to 20th	Night	5% 6% 1 3 2 2 2 2 4 7% 67%	2090
	21st to end	Night	3 4 2 3 2 2 4 2 5% 5% 67%	2090
October	1st to 10th	Night	2 3 1 3 2 2 2 2 3 4 75%	3490
	11th to 20th	Night	6% 12% 2 4 3 2 3 2 3 5% 58%	3469
	21st to end	Night	4 4 2 3 2 3 2 3 4 6% 67%	4265
November	1st to 10th	Night	5% 4 2 4 3 2 4 3 4 6% 64%	2535
	11th to 20th	Night	4 4 2 5% 3 3 3 3 4 5% 65%	2600
	21st to end	Night	7% 5% 2 5% 4 4 5% 4 5% 7% 54%	2600
December	1st to 10th	Night	5% 3 1 3 3 3 5% 3 5% 5% 65%	4240
	11th to 20th	Night	10% 6% 2 5% 3 3 5% 4 6% 7% 49%	4811
	21st to end	Night	8% 6% 2 6% 4 4 5% 4 6% 10% 44%	6468

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	19% 3 3 18% 25% 32%	4099
	11th to 20th	Day	21% 2 7% 19% 22% 30%	4358
	21st to end	Day	31% 5% 5% 11% 26% 23%	5016
February	1st to 10th	Day	31% 3 4 14% 20% 28%	2000
	11th to 20th	Day	30% 4 6% 14% 26% 20%	1960
	21st to end	Day	35% 6% 5% 14% 20% 21%	1650
March	1st to 10th	Day	32% 9% 5% 20% 21% 13%	4518
	11th to 20th	Day	28% 5% 8% 26% 22% 11%	4770
	21st to end	Day	29% 5% 9% 31% 16% 10%	5788
April	1st to 10th	Day	27% 4 8% 23% 24% 13%	2400
	11th to 20th	Day	23% 4 6% 20% 27% 20%	2372
	21st to end	Day	21% 4 7% 26% 31% 11%	2400
May	1st to 10th	Day	23% 3 6% 22% 34% 13%	5699
	11th to 20th	Day	23% 3 5% 25% 34% 10%	5844
	21st to end	Day	23% 3 5% 21% 37% 12%	6424
June	1st to 10th	Day	24% 2 6% 24% 30% 14%	2600
	11th to 20th	Day	17% 2 3 13% 33% 33%	2600
	21st to end	Day	16% 1 2 9% 28% 45%	2600
July	1st to 10th	Day	8% 1 1 7% 19% 64%	5816
	11th to 20th	Day	15% 2 4 12% 43% 23%	5811
	21st to end	Day	9% 2 5% 20% 28% 35%	5930
August	1st to 10th	Day	10% 2 4 20% 39% 25%	3819
	11th to 20th	Day	8% 2 4 15% 26% 46%	3760
	21st to end	Day	10% 2 2 9% 28% 51%	4179
September	1st to 10th	Day	14% 3 3 11% 33% 35%	2266
	11th to 20th	Day	11% 3 2 12% 34% 38%	2090
	21st to end	Day	13% 2 3 13% 32% 37%	2090
October	1st to 10th	Day	13% 2 3 10% 15% 58%	3490
	11th to 20th	Day	16% 3 2 13% 27% 39%	3457
	21st to end	Day	15% 2 2 10% 32% 39%	3295
November	1st to 10th	Day	18% 3 5% 17% 21% 36%	1764
	11th to 20th	Day	19% 3 5% 13% 21% 40%	1800
	21st to end	Day	24% 4 5% 15% 19% 32%	1800
December	1st to 10th	Day	16% 2 5% 14% 25% 38%	2950
	11th to 20th	Day	30% 4 7% 14% 23% 22%	3408
	21st to end	Day	34% 5% 7% 24% 22% 8%	4510
January	1st to 10th	Night	21% 4 3 14% 29% 29%	5867
	11th to 20th	Night	25% 3 8% 18% 16% 30%	5616
	21st to end	Night	36% 4 4 10% 23% 23%	5984
February	1st to 10th	Night	30% 3 6% 14% 21% 27%	2400
	11th to 20th	Night	34% 4 4 15% 21% 22%	2339
	21st to end	Night	35% 4 4 14% 21% 21%	1980
March	1st to 10th	Night	44% 7% 7% 13% 17% 13%	5376
	11th to 20th	Night	38% 4 8% 23% 19% 8%	5230
	21st to end	Night	41% 6% 10% 16% 17% 10%	5182
April	1st to 10th	Night	33% 4 8% 22% 20% 14%	2000
	11th to 20th	Night	33% 3 6% 17% 23% 17%	1979
	21st to end	Night	35% 3 7% 23% 20% 12%	2000
May	1st to 10th	Night	33% 4 7% 22% 24% 10%	4285
	11th to 20th	Night	42% 3 5% 20% 23% 7%	4075
	21st to end	Night	40% 3 4 21% 21% 11%	4474
June	1st to 10th	Night	38% 2 9% 21% 19% 11%	1800
	11th to 20th	Night	27% 3 2 16% 27% 26%	1800
	21st to end	Night	23% 1 2 12% 28% 33%	1800
July	1st to 10th	Night	12% 1 10% 18% 59%	4055
	11th to 20th	Night	23% 2 4 15% 40% 16%	4046
	21st to end	Night	19% 2 4 20% 28% 27%	4642
August	1st to 10th	Night	11% 1 4 22% 41% 20%	3196
	11th to 20th	Night	12% 2 5% 16% 26% 39%	3156
	21st to end	Night	14% 2 3 10% 25% 46%	3498
September	1st to 10th	Night	22% 3 3 12% 28% 32%	1913
	11th to 20th	Night	19% 2 3 9% 33% 34%	2090
	21st to end	Night	17% 3 2 15% 35% 29%	2090
October	1st to 10th	Night	14% 2 3 10% 17% 54%	3490
	11th to 20th	Night	28% 3 3 10% 19% 38%	3469
	21st to end	Night	20% 3 2 10% 27% 39%	4265
November	1st to 10th	Night	21% 3 5% 17% 17% 37%	2535
	11th to 20th	Night	21% 3 4 14% 18% 40%	2600
	21st to end	Night	29% 4 6% 15% 15% 30%	2600
December	1st to 10th	Night	20% 2 4 14% 23% 36%	4240
	11th to 20th	Night	32% 4 6% 12% 20% 26%	4811
	21st to end	Night	32% 6% 9% 23% 19% 10%	6468

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	13% 9% 13% 39% 23% 3	300
	11th to 20th	Day	12% 4 23% 39% 18% 5%	415
	21st to end	Day	11% 7% 26% 37% 14% 4	550
February	1st to 10th	Day	11% 7% 28% 32% 17% 4	500
	11th to 20th	Day	10% 8% 32% 34% 14% 2	495
	21st to end	Day	11% 9% 35% 34% 10% 1	414
March	1st to 10th	Day	12% 10% 34% 31% 11% 2	500
	11th to 20th	Day	14% 7% 28% 34% 13% 4	500
	21st to end	Day	7% 13% 35% 32% 11% 2	550
April	1st to 10th	Day	9% 8% 29% 34% 16% 4	500
	11th to 20th	Day	4 10% 34% 34% 13% 4	492
	21st to end	Day	7% 9% 25% 35% 16% 7%	500
May	1st to 10th	Day	11% 9% 28% 32% 16% 5%	503
	11th to 20th	Day	8% 6% 27% 38% 18% 3	528
	21st to end	Day	6% 9% 26% 38% 18% 3	573
June	1st to 10th	Day	6% 3 21% 36% 28% 6%	530
	11th to 20th	Day	5% 2 19% 40% 27% 8%	530
	21st to end	Day	4 2 16% 42% 28% 9%	530
July	1st to 10th	Day	4 1 8% 43% 34% 11%	526
	11th to 20th	Day	2 4 41% 35% 17%	524
	21st to end	Day	3 1 6% 38% 37% 14%	575
August	1st to 10th	Day	3 8% 43% 33% 13%	504
	11th to 20th	Day	3 1 6% 45% 31% 14%	477
	21st to end	Day	4 10% 42% 34% 11%	539
September	1st to 10th	Day	5% 13% 46% 29% 8%	490
	11th to 20th	Day	5% 2 19% 45% 23% 5%	490
	21st to end	Day	4 3 22% 39% 24% 7%	490
October	1st to 10th	Day	4 5% 23% 40% 23% 6%	490
	11th to 20th	Day	7% 3 23% 42% 20% 5%	490
	21st to end	Day	5% 4 20% 36% 27% 8%	448
November	1st to 10th	Day	7% 4 18% 36% 27% 8%	300
	11th to 20th	Day	6% 3 22% 35% 28% 6%	300
	21st to end	Day	7% 8% 20% 40% 20% 5%	300
December	1st to 10th	Day	9% 3 21% 37% 25% 5%	300
	11th to 20th	Day	6% 4 18% 39% 26% 9%	300
	21st to end	Day	11% 8% 21% 38% 17% 5%	330
January	1st to 10th	Night	8% 4 16% 39% 26% 8%	800
	11th to 20th	Night	8% 3 13% 42% 28% 7%	800
	21st to end	Night	13% 2 15% 41% 25% 4	880
February	1st to 10th	Night	11% 4 11% 39% 28% 7%	800
	11th to 20th	Night	12% 4 15% 37% 26% 5%	784
	21st to end	Night	13% 4 15% 41% 23% 4	660
March	1st to 10th	Night	12% 5% 16% 40% 24% 3	800
	11th to 20th	Night	14% 4 10% 37% 26% 8%	800
	21st to end	Night	12% 3 12% 38% 30% 4	880
April	1st to 10th	Night	11% 3 12% 40% 29% 5%	800
	11th to 20th	Night	11% 4 13% 36% 30% 6%	791
	21st to end	Night	11% 4 12% 33% 33% 8%	800
May	1st to 10th	Night	12% 4 12% 33% 34% 5%	684
	11th to 20th	Night	13% 3 13% 28% 35% 7%	591
	21st to end	Night	14% 3 15% 30% 35% 4	650
June	1st to 10th	Night	12% 2 15% 29% 36% 7%	600
	11th to 20th	Night	7% 1 10% 31% 46% 5%	600
	21st to end	Night	6% 2 7% 30% 49% 7%	600
July	1st to 10th	Night	6% 5% 18% 55% 15%	585
	11th to 20th	Night	3 3 14% 61% 20%	582
	21st to end	Night	5% 1 3 14% 53% 24%	785
August	1st to 10th	Night	5% 1 3 16% 54% 22%	772
	11th to 20th	Night	4 5% 12% 54% 24%	752
	21st to end	Night	5% 3 12% 53% 27%	836
September	1st to 10th	Night	6% 1 4 17% 54% 18%	760
	11th to 20th	Night	9% 1 5% 24% 50% 11%	760
	21st to end	Night	4 2 6% 30% 43% 15%	760
October	1st to 10th	Night	5% 1 7% 35% 43% 8%	760
	11th to 20th	Night	9% 2 8% 35% 36% 10%	760
	21st to end	Night	8% 2 9% 33% 34% 14%	836
November	1st to 10th	Night	6% 1 10% 37% 36% 11%	780
	11th to 20th	Night	5% 2 9% 36% 35% 13%	800
	21st to end	Night	8% 2 10% 42% 29% 10%	800
December	1st to 10th	Night	10% 2 11% 42% 28% 7%	800
	11th to 20th	Night	14% 3 14% 39% 25% 6%	800
	21st to end	Night	11% 4 16% 38% 24% 8%	880

Page generated at 2025-08-01 22:32:29. Version ac07

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