El Rito Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the El Rito Observatory clear sky chart from 2005-11-06 to 2025-03-27.

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 4 1 4 3 4 4 4 6% 8% 59%	112869
	Night	3 4 2 4 3 3 4 3 5% 7% 61%	115316
Transparency	Day	20% 6% 12% 24% 26% 12%	112625
	Night	21% 6% 11% 23% 27% 12%	115149
Seeing	Day	6% 9% 23% 32% 22% 8%	15653
	Night	5% 4 23% 46% 20% 2	25919

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	1 6% 3 6% 4 3 3 4 5% 7% 59%	3914
	11th to 20th	Day	1 3 2 3 2 3 3 2 5% 7% 70%	4100
	21st to end	Day	2 6% 2 5% 4 4 4 3 5% 7% 59%	4510
February	1st to 10th	Day	1 5% 2 4 4 3 5% 4 6% 7% 59%	1800
	11th to 20th	Day	2 6% 2 5% 4 3 5% 3 6% 7% 59%	1942
	21st to end	Day	2 6% 2 5% 3 3 3 3 6% 8% 59%	1650
March	1st to 10th	Day	1 5% 2 5% 3 4 3 3 4 7% 64%	3390
	11th to 20th	Day	5% 7% 3 6% 4 4 4 3 6% 9% 49%	3600
	21st to end	Day	2 6% 2 5% 4 4 5% 4 7% 7% 54%	4014
April	1st to 10th	Day	2 3 1 4 3 3 4 4 6% 8% 63%	2280
	11th to 20th	Day	2 4 1 4 3 3 5% 4 5% 8% 61%	2251
	21st to end	Day	3 5% 1 3 3 4 4 4 6% 7% 60%	2280
May	1st to 10th	Day	2 2 1 4 3 2 3 3 5% 7% 67%	3800
	11th to 20th	Day	5% 4 2 4 4 4 5% 5% 7% 8% 51%	4069
	21st to end	Day	2 2 1 3 2 3 4 4 5% 6% 69%	4825
June	1st to 10th	Day	2 2 1 3 3 4 5% 5% 7% 9% 61%	2660
	11th to 20th	Day	1 1 1 2 2 3 4 3 5% 7% 70%	2660
	21st to end	Day	4 3 1 4 3 4 5% 5% 7% 8% 57%	2660
July	1st to 10th	Day	2 2 1 4 4 4 6% 5% 7% 7% 57%	4430
	11th to 20th	Day	1 1 1 3 4 6% 9% 8% 10% 11% 45%	4148
	21st to end	Day	3 3 1 5% 5% 6% 7% 6% 11% 13% 41%	4454
August	1st to 10th	Day	2 3 1 6% 5% 7% 9% 8% 10% 12% 37%	4039
	11th to 20th	Day	2 3 1 3 3 4 5% 6% 7% 9% 57%	3726
	21st to end	Day	3 3 1 5% 5% 6% 7% 6% 9% 11% 43%	4180
September	1st to 10th	Day	5% 4 1 4 4 4 4 4 6% 8% 55%	2280
	11th to 20th	Day	4 4 1 4 3 4 3 4 6% 7% 59%	2280
	21st to end	Day	3 3 1 3 2 3 4 3 5% 6% 69%	2060
October	1st to 10th	Day	3 2 1 3 2 2 2 2 4 6% 72%	3170
	11th to 20th	Day	8% 4 2 4 3 3 4 3 5% 6% 59%	3150
	21st to end	Day	3 3 1 2 2 2 2 2 3 5% 76%	3438
November	1st to 10th	Day	2 3 1 3 2 3 3 3 5% 5% 72%	1874
	11th to 20th	Day	1 2 1 3 2 2 2 2 5% 6% 74%	1800
	21st to end	Day	4 5% 2 3 4 2 4 2 4 7% 63%	1785
December	1st to 10th	Day	1 3 1 2 2 2 2 1 3 7% 77%	2620
	11th to 20th	Day	1 3 1 4 3 3 3 2 4 8% 68%	3026
	21st to end	Day	3 5% 2 4 2 2 4 3 4 6% 66%	4004
January	1st to 10th	Night	1 5% 3 7% 4 4 3 3 5% 6% 60%	6079
	11th to 20th	Night	1 5% 2 4 2 3 4 3 4 6% 67%	5880
	21st to end	Night	2 6% 2 7% 4 3 4 3 5% 7% 59%	6468
February	1st to 10th	Night	1 6% 3 6% 3 2 3 2 4 6% 64%	2600
	11th to 20th	Night	3 7% 2 5% 3 3 3 3 5% 7% 59%	2343
	21st to end	Night	3 6% 1 3 2 2 3 3 5% 6% 65%	1980
March	1st to 10th	Night	2 6% 1 3 2 2 3 3 4 6% 67%	3694
	11th to 20th	Night	6% 9% 2 5% 4 4 3 3 5% 7% 51%	3600
	21st to end	Night	3 8% 3 6% 3 4 3 3 4 6% 56%	3772
April	1st to 10th	Night	2 4 2 4 3 3 4 3 5% 8% 62%	1900
	11th to 20th	Night	4 6% 2 3 3 3 4 4 4 6% 61%	1877
	21st to end	Night	3 5% 1 4 4 3 3 2 6% 6% 63%	1900
May	1st to 10th	Night	4 5% 2 4 4 3 3 3 4 5% 65%	3170
	11th to 20th	Night	6% 6% 2 5% 5% 5% 5% 4 6% 7% 49%	2815
	21st to end	Night	3 2 1 3 2 2 3 3 4 5% 70%	2762
June	1st to 10th	Night	2 2 1 3 3 4 5% 4 6% 10% 62%	1520
	11th to 20th	Night	3 3 1 2 3 3 3 3 4 6% 71%	1520
	21st to end	Night	3 3 2 5% 4 5% 6% 5% 6% 8% 53%	1520
July	1st to 10th	Night	2 3 1 6% 5% 6% 6% 5% 6% 7% 53%	2540
	11th to 20th	Night	2 2 1 4 4 6% 8% 7% 11% 13% 43%	2817
	21st to end	Night	5% 3 2 5% 4 5% 6% 6% 9% 12% 43%	3109
August	1st to 10th	Night	3 4 2 8% 7% 8% 8% 7% 11% 10% 32%	2898
	11th to 20th	Night	3 3 2 5% 5% 5% 6% 6% 9% 13% 43%	3113
	21st to end	Night	4 4 2 7% 7% 7% 8% 6% 11% 10% 34%	3487
September	1st to 10th	Night	5% 4 2 4 5% 4 5% 4 7% 9% 52%	1900
	11th to 20th	Night	5% 3 1 3 2 3 4 4 5% 8% 61%	1900
	21st to end	Night	5% 3 1 3 2 3 3 3 4 5% 68%	2115
October	1st to 10th	Night	4 3 1 2 2 2 2 2 4 6% 72%	3800
	11th to 20th	Night	9% 3 1 4 2 3 3 2 4 6% 63%	3778
	21st to end	Night	3 1 1 2 2 1 2 2 3 5% 79%	4120
November	1st to 10th	Night	2 2 1 2 2 2 2 3 4 6% 73%	2404
	11th to 20th	Night	1 2 1 2 2 1 2 2 4 6% 77%	2600
	21st to end	Night	4 6% 2 2 3 3 3 3 5% 5% 65%	2610
December	1st to 10th	Night	2 3 1 3 2 2 2 2 2 5% 77%	4570
	11th to 20th	Night	2 3 1 3 2 2 3 2 4 8% 69%	5181
	21st to end	Night	2 5% 2 5% 3 3 3 3 4 5% 65%	6974

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	24% 4 12% 32% 27% 1	3915
	11th to 20th	Day	15% 2 15% 28% 24% 15%	4100
	21st to end	Day	24% 5% 10% 23% 26% 10%	4510
February	1st to 10th	Day	23% 5% 14% 28% 22% 8%	1800
	11th to 20th	Day	24% 5% 11% 28% 27% 6%	1952
	21st to end	Day	22% 4 9% 22% 29% 15%	1650
March	1st to 10th	Day	18% 5% 7% 23% 40% 8%	3390
	11th to 20th	Day	26% 8% 10% 30% 21% 5%	3600
	21st to end	Day	23% 8% 10% 27% 25% 7%	4014
April	1st to 10th	Day	17% 5% 9% 23% 30% 16%	2280
	11th to 20th	Day	20% 4 10% 21% 29% 16%	2254
	21st to end	Day	20% 5% 9% 25% 29% 12%	2280
May	1st to 10th	Day	12% 6% 10% 17% 32% 23%	3800
	11th to 20th	Day	23% 10% 13% 22% 22% 10%	4072
	21st to end	Day	12% 5% 8% 15% 29% 31%	4825
June	1st to 10th	Day	16% 8% 13% 20% 24% 20%	2660
	11th to 20th	Day	12% 4 8% 15% 25% 37%	2660
	21st to end	Day	22% 6% 10% 19% 22% 21%	2660
July	1st to 10th	Day	22% 7% 11% 15% 18% 27%	4361
	11th to 20th	Day	22% 11% 19% 33% 11% 5%	4077
	21st to end	Day	27% 11% 21% 29% 9% 4	4314
August	1st to 10th	Day	31% 12% 22% 20% 10% 6%	4025
	11th to 20th	Day	20% 7% 17% 22% 21% 13%	3762
	21st to end	Day	29% 11% 19% 21% 16% 4	4179
September	1st to 10th	Day	25% 6% 11% 24% 22% 12%	2280
	11th to 20th	Day	21% 6% 11% 18% 28% 16%	2280
	21st to end	Day	15% 4 8% 23% 35% 15%	2060
October	1st to 10th	Day	13% 4 6% 17% 39% 22%	3170
	11th to 20th	Day	25% 4 7% 17% 33% 13%	3150
	21st to end	Day	12% 3 6% 25% 42% 11%	3438
November	1st to 10th	Day	15% 3 8% 25% 36% 12%	1874
	11th to 20th	Day	12% 3 9% 33% 37% 7%	1800
	21st to end	Day	21% 4 7% 28% 31% 9%	1785
December	1st to 10th	Day	11% 3 9% 37% 33% 7%	2620
	11th to 20th	Day	17% 4 9% 42% 25% 3	3024
	21st to end	Day	19% 4 13% 30% 31% 4	4004
January	1st to 10th	Night	25% 4 10% 33% 22% 5%	6079
	11th to 20th	Night	16% 7% 14% 28% 22% 14%	5880
	21st to end	Night	25% 5% 11% 24% 29% 7%	6468
February	1st to 10th	Night	21% 4 13% 29% 23% 8%	2600
	11th to 20th	Night	25% 5% 10% 27% 26% 6%	2343
	21st to end	Night	20% 4 7% 23% 34% 13%	1980
March	1st to 10th	Night	17% 4 7% 20% 43% 9%	3694
	11th to 20th	Night	29% 7% 10% 27% 21% 6%	3600
	21st to end	Night	23% 8% 10% 28% 26% 5%	3772
April	1st to 10th	Night	19% 4 11% 23% 28% 15%	1900
	11th to 20th	Night	22% 5% 7% 19% 27% 18%	1877
	21st to end	Night	19% 6% 11% 21% 30% 14%	1900
May	1st to 10th	Night	17% 8% 7% 13% 30% 24%	3170
	11th to 20th	Night	27% 12% 12% 21% 14% 13%	2816
	21st to end	Night	13% 5% 9% 13% 26% 34%	2762
June	1st to 10th	Night	16% 7% 14% 20% 22% 21%	1520
	11th to 20th	Night	15% 3 6% 12% 26% 37%	1520
	21st to end	Night	25% 6% 13% 15% 20% 21%	1520
July	1st to 10th	Night	27% 9% 12% 11% 13% 29%	2500
	11th to 20th	Night	24% 12% 26% 26% 6% 6%	2765
	21st to end	Night	29% 11% 22% 27% 10% 2	3011
August	1st to 10th	Night	38% 12% 22% 14% 7% 7%	2889
	11th to 20th	Night	27% 9% 22% 15% 12% 15%	3143
	21st to end	Night	36% 11% 21% 16% 12% 4	3487
September	1st to 10th	Night	27% 7% 14% 23% 17% 12%	1900
	11th to 20th	Night	19% 8% 12% 16% 24% 20%	1900
	21st to end	Night	19% 4 9% 18% 33% 17%	2115
October	1st to 10th	Night	15% 4 6% 15% 39% 22%	3800
	11th to 20th	Night	24% 3 7% 14% 34% 17%	3778
	21st to end	Night	10% 2 5% 26% 40% 16%	4120
November	1st to 10th	Night	12% 3 7% 26% 40% 12%	2404
	11th to 20th	Night	10% 3 8% 31% 39% 9%	2600
	21st to end	Night	20% 3 8% 24% 34% 10%	2610
December	1st to 10th	Night	13% 3 7% 36% 35% 6%	4570
	11th to 20th	Night	15% 3 9% 33% 35% 4	5182
	21st to end	Night	21% 5% 11% 27% 33% 3	6974

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	4 8% 30% 42% 12% 3	300
	11th to 20th	Day	8% 11% 28% 37% 13% 3	300
	21st to end	Day	5% 5% 25% 42% 17% 7%	330
February	1st to 10th	Day	3 13% 29% 40% 12% 2	300
	11th to 20th	Day	7% 9% 40% 29% 13% 1	300
	21st to end	Day	10% 16% 27% 38% 8% 2	249
March	1st to 10th	Day	6% 18% 32% 27% 15% 2	395
	11th to 20th	Day	11% 18% 28% 29% 10% 4	500
	21st to end	Day	12% 23% 34% 21% 9%	531
April	1st to 10th	Day	8% 20% 37% 23% 11% 2	460
	11th to 20th	Day	8% 23% 38% 22% 8% 1	452
	21st to end	Day	9% 20% 36% 26% 9% 1	460
May	1st to 10th	Day	7% 18% 38% 24% 11% 2	463
	11th to 20th	Day	6% 12% 26% 33% 18% 6%	558
	21st to end	Day	5% 11% 24% 38% 19% 3	734
June	1st to 10th	Day	2 4 18% 39% 30% 7%	680
	11th to 20th	Day	2 6% 23% 38% 24% 7%	680
	21st to end	Day	6% 5% 18% 34% 30% 8%	680
July	1st to 10th	Day	5% 2 14% 31% 37% 12%	671
	11th to 20th	Day	3 1 5% 28% 39% 23%	507
	21st to end	Day	5% 2 7% 24% 39% 24%	531
August	1st to 10th	Day	3 2 10% 32% 33% 19%	487
	11th to 20th	Day	6% 2 12% 34% 32% 14%	477
	21st to end	Day	5% 1 8% 37% 32% 16%	539
September	1st to 10th	Day	6% 2 13% 29% 36% 14%	490
	11th to 20th	Day	5% 3 16% 36% 31% 9%	490
	21st to end	Day	4 5% 18% 30% 32% 12%	329
October	1st to 10th	Day	4 8% 17% 31% 28% 12%	300
	11th to 20th	Day	8% 9% 21% 29% 21% 12%	300
	21st to end	Day	8% 8% 22% 30% 25% 8%	330
November	1st to 10th	Day	5% 11% 24% 34% 22% 4	300
	11th to 20th	Day	4 5% 20% 45% 21% 5%	300
	21st to end	Day	9% 10% 23% 35% 15% 8%	300
December	1st to 10th	Day	5% 9% 27% 35% 16% 8%	300
	11th to 20th	Day	6% 10% 25% 38% 20% 2	300
	21st to end	Day	10% 13% 30% 34% 12% 2	330
January	1st to 10th	Night	4 3 29% 46% 16% 1	895
	11th to 20th	Night	6% 3 30% 45% 15% 2	800
	21st to end	Night	6% 3 29% 45% 15% 1	880
February	1st to 10th	Night	5% 4 32% 48% 10%	800
	11th to 20th	Night	7% 6% 36% 41% 9%	784
	21st to end	Night	6% 6% 40% 44% 4	660
March	1st to 10th	Night	5% 7% 33% 47% 8% 1	800
	11th to 20th	Night	7% 6% 28% 45% 14%	800
	21st to end	Night	7% 9% 31% 45% 8%	786
April	1st to 10th	Night	5% 10% 38% 40% 7%	570
	11th to 20th	Night	8% 10% 30% 42% 9%	563
	21st to end	Night	4 7% 34% 46% 9%	570
May	1st to 10th	Night	4 6% 28% 50% 11%	570
	11th to 20th	Night	6% 4 23% 48% 18% 1	561
	21st to end	Night	4 6% 23% 51% 16%	617
June	1st to 10th	Night	3 2 17% 53% 24%	570
	11th to 20th	Night	4 2 19% 54% 20% 1	570
	21st to end	Night	4 2 12% 49% 32% 1	570
July	1st to 10th	Night	5% 1 7% 46% 38% 2	555
	11th to 20th	Night	3 1 3 38% 50% 5%	552
	21st to end	Night	5% 1 5% 28% 54% 7%	624
August	1st to 10th	Night	4 1 5% 31% 50% 8%	567
	11th to 20th	Night	5% 1 5% 42% 44% 3	564
	21st to end	Night	4 2 4 43% 44% 3	627
September	1st to 10th	Night	6% 1 7% 46% 38% 2	570
	11th to 20th	Night	5% 8% 51% 33% 2	570
	21st to end	Night	7% 2 13% 49% 28% 1	624
October	1st to 10th	Night	7% 3 15% 52% 21% 2	760
	11th to 20th	Night	6% 1 20% 50% 21% 3	760
	21st to end	Night	6% 2 23% 44% 21% 4	836
November	1st to 10th	Night	4 2 19% 55% 18% 2	844
	11th to 20th	Night	2 4 25% 49% 19% 2	1000
	21st to end	Night	7% 7% 25% 40% 20% 2	1000
December	1st to 10th	Night	6% 4 29% 46% 13% 1	1000
	11th to 20th	Night	7% 5% 30% 46% 12% 1	1000
	21st to end	Night	6% 5% 31% 48% 9% 1	1100

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