Ranchito de las Estrellas Observator
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ranchito de las Estrellas Observator clear sky chart from 2005-11-06 to 2026-06-01.

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	11% 5% 2 5% 4 4 4 3 5% 7% 51%	132469
	Night	11% 5% 2 4 3 3 3 3 4 7% 55%	131034
Transparency	Day	32% 5% 10% 21% 22% 11%	136238
	Night	30% 5% 10% 21% 22% 13%	135329
Seeing	Day	12% 7% 22% 30% 22% 7%	17005
	Night	13% 6% 27% 37% 15% 1	26970

By Month

Percentage Cloud Cover SE (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	11% 6% 3 5% 3 3 3 3 4 5% 54%	5289
	11th to 20th	Day	11% 5% 1 4 3 2 3 2 5% 5% 59%	5310
	21st to end	Day	21% 7% 2 6% 3 3 3 2 3 5% 43%	6084
February	1st to 10th	Day	16% 7% 2 6% 3 2 3 2 3 5% 52%	2100
	11th to 20th	Day	15% 8% 2 5% 3 3 4 3 4 5% 48%	2049
	21st to end	Day	17% 6% 1 4 3 2 2 2 4 5% 54%	1730
March	1st to 10th	Day	12% 8% 2 6% 4 4 4 3 5% 5% 50%	4975
	11th to 20th	Day	14% 5% 1 4 3 3 3 3 4 6% 53%	5090
	21st to end	Day	11% 6% 2 5% 4 3 4 4 6% 7% 49%	5583
April	1st to 10th	Day	13% 8% 2 4 5% 4 4 4 5% 6% 46%	2310
	11th to 20th	Day	15% 7% 2 6% 4 3 4 3 5% 6% 44%	2311
	21st to end	Day	14% 6% 2 6% 4 3 4 3 5% 5% 49%	2714
May	1st to 10th	Day	17% 6% 2 5% 4 4 4 4 6% 7% 39%	5992
	11th to 20th	Day	12% 6% 3 7% 4 4 4 3 5% 7% 45%	5992
	21st to end	Day	12% 7% 2 7% 5% 5% 6% 4 7% 8% 37%	6577
June	1st to 10th	Day	5% 3 1 4 4 5% 4 4 6% 9% 54%	2601
	11th to 20th	Day	5% 4 1 4 4 5% 4 4 7% 8% 54%	2600
	21st to end	Day	6% 4 1 4 4 4 5% 5% 8% 9% 50%	2600
July	1st to 10th	Day	10% 5% 3 7% 5% 6% 5% 4 7% 8% 40%	5900
	11th to 20th	Day	3 2 1 4 4 4 5% 4 7% 10% 56%	5900
	21st to end	Day	4 4 1 6% 4 4 5% 5% 7% 11% 48%	6422
August	1st to 10th	Day	1 1 2 3 3 3 3 4 7% 72%	4234
	11th to 20th	Day	4 2 1 4 2 3 3 3 6% 9% 63%	3942
	21st to end	Day	4 3 1 4 3 4 5% 5% 7% 10% 55%	4152
September	1st to 10th	Day	10% 5% 2 4 5% 4 5% 4 5% 5% 51%	2200
	11th to 20th	Day	10% 5% 2 6% 4 4 4 3 5% 7% 50%	2200
	21st to end	Day	8% 3 1 5% 3 4 5% 3 5% 6% 57%	2200
October	1st to 10th	Day	6% 3 2 4 3 3 3 3 6% 6% 63%	2200
	11th to 20th	Day	10% 4 2 4 3 3 3 2 4 6% 61%	2045
	21st to end	Day	11% 4 1 4 2 2 3 2 3 5% 63%	2200
November	1st to 10th	Day	13% 6% 2 4 3 3 3 3 3 5% 54%	2058
	11th to 20th	Day	8% 5% 1 5% 3 3 3 4 4 6% 58%	1921
	21st to end	Day	15% 6% 2 5% 3 3 3 2 4 5% 51%	1890
December	1st to 10th	Day	17% 6% 2 6% 4 3 4 3 4 5% 47%	3030
	11th to 20th	Day	14% 8% 2 6% 4 3 4 3 5% 5% 46%	3481
	21st to end	Day	13% 5% 2 4 2 2 3 3 3 5% 59%	4587
January	1st to 10th	Night	13% 5% 2 4 3 3 2 2 3 4 59%	7634
	11th to 20th	Night	8% 4 1 3 2 2 2 2 3 6% 68%	7680
	21st to end	Night	25% 6% 3 5% 3 3 3 2 3 5% 42%	8186
February	1st to 10th	Night	13% 8% 2 5% 3 3 3 2 3 5% 54%	2520
	11th to 20th	Night	17% 5% 2 5% 2 2 2 2 4 6% 52%	2458
	21st to end	Night	17% 5% 1 4 3 2 2 2 4 5% 53%	2076
March	1st to 10th	Night	11% 6% 2 5% 4 4 4 3 5% 6% 50%	5103
	11th to 20th	Night	13% 4 2 5% 3 3 3 3 5% 6% 53%	5090
	21st to end	Night	11% 7% 2 5% 4 4 3 2 4 6% 52%	5588
April	1st to 10th	Night	10% 5% 2 5% 4 4 4 3 5% 6% 52%	2310
	11th to 20th	Night	15% 5% 2 6% 4 3 3 3 5% 5% 48%	2253
	21st to end	Night	14% 7% 2 3 4 3 3 3 4 7% 50%	1903
May	1st to 10th	Night	21% 7% 2 4 3 3 3 3 4 7% 44%	4143
	11th to 20th	Night	9% 6% 2 6% 4 5% 5% 4 5% 7% 48%	4143
	21st to end	Night	12% 6% 2 5% 4 4 5% 3 6% 9% 44%	4542
June	1st to 10th	Night	3 3 1 4 3 3 3 3 7% 10% 60%	1800
	11th to 20th	Night	4 3 1 4 2 3 3 3 6% 9% 61%	1800
	21st to end	Night	6% 3 1 3 3 3 4 4 6% 9% 58%	1800
July	1st to 10th	Night	9% 4 2 6% 4 4 4 4 6% 10% 49%	4078
	11th to 20th	Night	2 2 1 3 3 3 3 3 7% 11% 63%	4077
	21st to end	Night	3 4 2 5% 4 3 4 4 7% 10% 55%	4449
August	1st to 10th	Night	1 1 1 1 1 2 2 4 6% 79%	2926
	11th to 20th	Night	3 2 1 3 2 2 3 3 6% 10% 64%	3111
	21st to end	Night	3 2 1 4 3 3 4 4 7% 11% 59%	3749
September	1st to 10th	Night	8% 4 1 4 3 4 5% 4 6% 7% 53%	2200
	11th to 20th	Night	10% 6% 2 6% 4 4 3 3 5% 9% 50%	2200
	21st to end	Night	8% 3 1 3 3 3 4 3 5% 7% 61%	2200
October	1st to 10th	Night	5% 3 1 3 2 2 3 3 5% 5% 69%	2200
	11th to 20th	Night	10% 3 1 3 2 3 3 3 4 5% 63%	2333
	21st to end	Night	12% 4 1 4 2 2 2 1 3 4 63%	2640
November	1st to 10th	Night	11% 5% 2 4 2 2 2 2 3 5% 60%	2460
	11th to 20th	Night	7% 5% 2 5% 3 3 3 3 3 6% 61%	2693
	21st to end	Night	16% 5% 2 4 3 3 3 2 4 6% 51%	2730
December	1st to 10th	Night	18% 5% 2 5% 3 3 3 2 5% 6% 48%	4380
	11th to 20th	Night	17% 9% 2 5% 3 2 3 2 3 5% 49%	4946
	21st to end	Night	15% 6% 1 4 2 2 2 2 3 4 59%	6633

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	34% 3 5% 24% 26% 9%	5290
	11th to 20th	Day	28% 2 4 17% 31% 17%	5310
	21st to end	Day	46% 3 4 14% 22% 12%	6084
February	1st to 10th	Day	38% 3 6% 14% 22% 17%	2100
	11th to 20th	Day	39% 4 6% 19% 20% 13%	2059
	21st to end	Day	35% 3 5% 16% 25% 17%	1730
March	1st to 10th	Day	36% 5% 5% 14% 20% 20%	4975
	11th to 20th	Day	32% 6% 8% 9% 15% 30%	5090
	21st to end	Day	33% 6% 9% 21% 22% 9%	5585
April	1st to 10th	Day	40% 5% 8% 17% 16% 14%	2310
	11th to 20th	Day	40% 6% 9% 16% 18% 11%	2311
	21st to end	Day	37% 5% 9% 19% 22% 8%	2714
May	1st to 10th	Day	42% 7% 11% 18% 18% 4	6030
	11th to 20th	Day	38% 6% 8% 15% 25% 8%	5996
	21st to end	Day	41% 9% 12% 21% 13% 5%	6590
June	1st to 10th	Day	25% 8% 13% 28% 21% 4	2601
	11th to 20th	Day	26% 7% 14% 28% 19% 7%	2600
	21st to end	Day	28% 8% 14% 23% 22% 5%	2600
July	1st to 10th	Day	39% 7% 18% 27% 8% 1	5836
	11th to 20th	Day	23% 6% 16% 34% 18% 3	5831
	21st to end	Day	27% 8% 16% 28% 19% 2	6240
August	1st to 10th	Day	12% 4 11% 33% 37% 1	4220
	11th to 20th	Day	18% 6% 18% 39% 18% 3	3981
	21st to end	Day	22% 10% 19% 27% 20% 3	4151
September	1st to 10th	Day	33% 6% 11% 20% 19% 11%	2200
	11th to 20th	Day	34% 7% 11% 21% 22% 5%	2200
	21st to end	Day	26% 6% 9% 22% 22% 15%	2200
October	1st to 10th	Day	14% 3 6% 13% 26% 37%	3590
	11th to 20th	Day	18% 3 7% 18% 33% 22%	3311
	21st to end	Day	22% 3 4 19% 38% 13%	3538
November	1st to 10th	Day	33% 4 8% 18% 26% 11%	2058
	11th to 20th	Day	27% 5% 9% 18% 24% 17%	1921
	21st to end	Day	37% 3 6% 18% 21% 14%	1890
December	1st to 10th	Day	41% 4 6% 17% 22% 11%	3030
	11th to 20th	Day	40% 5% 6% 11% 24% 13%	3479
	21st to end	Day	31% 3 5% 17% 29% 16%	4587
January	1st to 10th	Night	31% 2 5% 20% 29% 13%	7635
	11th to 20th	Night	22% 1 3 18% 31% 24%	7680
	21st to end	Night	47% 3 3 11% 22% 14%	8186
February	1st to 10th	Night	35% 3 6% 13% 24% 19%	2520
	11th to 20th	Night	36% 3 7% 18% 22% 14%	2458
	21st to end	Night	34% 4 6% 15% 23% 19%	2076
March	1st to 10th	Night	34% 5% 7% 15% 23% 16%	5103
	11th to 20th	Night	31% 6% 8% 13% 16% 26%	5090
	21st to end	Night	34% 5% 8% 18% 24% 11%	5588
April	1st to 10th	Night	33% 6% 10% 19% 17% 16%	2310
	11th to 20th	Night	38% 5% 11% 14% 18% 14%	2253
	21st to end	Night	35% 5% 11% 19% 21% 9%	1903
May	1st to 10th	Night	41% 5% 9% 22% 16% 7%	4170
	11th to 20th	Night	34% 7% 12% 17% 18% 12%	4144
	21st to end	Night	37% 7% 13% 27% 11% 5%	4551
June	1st to 10th	Night	18% 8% 17% 31% 22% 4	1800
	11th to 20th	Night	20% 6% 16% 31% 21% 7%	1800
	21st to end	Night	22% 8% 13% 30% 23% 5%	1800
July	1st to 10th	Night	32% 7% 20% 33% 7% 1	4035
	11th to 20th	Night	15% 6% 21% 39% 17% 2	4026
	21st to end	Night	24% 7% 20% 29% 16% 4	4320
August	1st to 10th	Night	7% 4 12% 38% 36% 2	2916
	11th to 20th	Night	17% 5% 24% 36% 17% 2	3138
	21st to end	Night	19% 9% 21% 30% 17% 3	3749
September	1st to 10th	Night	29% 7% 13% 23% 19% 11%	2200
	11th to 20th	Night	32% 7% 13% 23% 18% 7%	2200
	21st to end	Night	22% 5% 12% 25% 21% 15%	2200
October	1st to 10th	Night	11% 3 7% 15% 23% 42%	3590
	11th to 20th	Night	16% 3 8% 17% 31% 23%	3793
	21st to end	Night	22% 3 5% 20% 35% 16%	4252
November	1st to 10th	Night	29% 4 7% 20% 26% 14%	2460
	11th to 20th	Night	25% 5% 8% 20% 24% 18%	2693
	21st to end	Night	35% 4 8% 16% 22% 15%	2730
December	1st to 10th	Night	39% 3 6% 19% 22% 11%	4380
	11th to 20th	Night	40% 3 5% 10% 24% 17%	4947
	21st to end	Night	32% 2 4 17% 26% 18%	6633

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	17% 15% 36% 25% 5% 1	330
	11th to 20th	Day	20% 12% 34% 25% 8% 2	330
	21st to end	Day	20% 12% 38% 23% 7%	363
February	1st to 10th	Day	22% 13% 35% 22% 7%	330
	11th to 20th	Day	22% 15% 38% 22% 3	330
	21st to end	Day	21% 16% 38% 21% 4	273
March	1st to 10th	Day	21% 17% 33% 25% 3	330
	11th to 20th	Day	18% 17% 38% 20% 6%	330
	21st to end	Day	14% 14% 38% 26% 8%	363
April	1st to 10th	Day	18% 15% 41% 20% 6% 1	330
	11th to 20th	Day	19% 11% 44% 21% 6% 1	349
	21st to end	Day	18% 14% 38% 22% 7% 1	734
May	1st to 10th	Day	15% 9% 36% 30% 10%	753
	11th to 20th	Day	16% 9% 29% 31% 12% 3	775
	21st to end	Day	14% 5% 25% 36% 16% 4	844
June	1st to 10th	Day	6% 1 16% 43% 27% 6%	731
	11th to 20th	Day	6% 2 17% 48% 23% 5%	730
	21st to end	Day	6% 1 11% 35% 36% 11%	730
July	1st to 10th	Day	8% 2 8% 34% 35% 13%	721
	11th to 20th	Day	2 1 6% 34% 45% 12%	718
	21st to end	Day	4 2 4 32% 44% 15%	794
August	1st to 10th	Day	2 4 32% 44% 17%	726
	11th to 20th	Day	6% 1 3 32% 41% 17%	577
	21st to end	Day	5% 6% 25% 39% 25%	488
September	1st to 10th	Day	10% 2 5% 21% 40% 22%	330
	11th to 20th	Day	6% 1 4 23% 44% 22%	330
	21st to end	Day	12% 2 5% 30% 35% 16%	330
October	1st to 10th	Day	5% 1 10% 33% 38% 13%	330
	11th to 20th	Day	10% 4 25% 32% 25% 5%	330
	21st to end	Day	19% 9% 22% 25% 21% 4	363
November	1st to 10th	Day	18% 8% 27% 27% 15% 5%	330
	11th to 20th	Day	12% 12% 22% 34% 16% 4	330
	21st to end	Day	20% 12% 34% 20% 13% 2	330
December	1st to 10th	Day	18% 8% 32% 26% 12% 3	330
	11th to 20th	Day	18% 11% 36% 22% 10% 3	330
	21st to end	Day	17% 9% 36% 25% 10% 2	363
January	1st to 10th	Night	17% 8% 36% 31% 7%	1050
	11th to 20th	Night	16% 11% 33% 33% 6%	1050
	21st to end	Night	20% 10% 35% 30% 6%	1081
February	1st to 10th	Night	19% 10% 34% 31% 5%	840
	11th to 20th	Night	21% 12% 39% 25% 3	824
	21st to end	Night	22% 10% 42% 23% 3	692
March	1st to 10th	Night	18% 13% 38% 29% 3	667
	11th to 20th	Night	16% 12% 38% 29% 5%	630
	21st to end	Night	11% 11% 45% 29% 4	693
April	1st to 10th	Night	12% 10% 46% 28% 3	630
	11th to 20th	Night	16% 11% 42% 27% 4	623
	21st to end	Night	16% 8% 42% 26% 8%	630
May	1st to 10th	Night	15% 8% 43% 30% 5%	630
	11th to 20th	Night	13% 6% 34% 35% 12%	621
	21st to end	Night	11% 5% 32% 38% 15%	683
June	1st to 10th	Night	4 2 22% 50% 21% 3	600
	11th to 20th	Night	5% 1 26% 52% 16%	600
	21st to end	Night	5% 1 15% 50% 27% 2	600
July	1st to 10th	Night	7% 1 10% 49% 30% 4	585
	11th to 20th	Night	4 1 7% 53% 33% 2	582
	21st to end	Night	2 1 6% 50% 37% 4	657
August	1st to 10th	Night	1 4 51% 39% 4	597
	11th to 20th	Night	7% 1 4 47% 38% 4	594
	21st to end	Night	4 3 42% 44% 7%	660
September	1st to 10th	Night	9% 2 9% 41% 35% 6%	600
	11th to 20th	Night	12% 1 4 42% 37% 4	600
	21st to end	Night	9% 1 11% 41% 36% 3	600
October	1st to 10th	Night	7% 13% 47% 31% 3	600
	11th to 20th	Night	11% 3 25% 41% 19% 1	733
	21st to end	Night	14% 8% 27% 34% 16% 1	880
November	1st to 10th	Night	13% 4 24% 44% 14% 1	820
	11th to 20th	Night	10% 7% 28% 39% 15% 1	1013
	21st to end	Night	18% 8% 31% 32% 11%	1050
December	1st to 10th	Night	14% 9% 30% 37% 10% 1	1050
	11th to 20th	Night	20% 9% 30% 34% 7%	1050
	21st to end	Night	17% 8% 32% 34% 9%	1155

Page generated at 2026-05-29 00:53:30. Version ac07

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