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 2026-07-31.

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% 8% 60%	146483
	Night	3 4 2 4 3 3 4 3 5% 7% 61%	144080
Transparency	Day	19% 6% 12% 24% 27% 13%	141472
	Night	21% 5% 11% 23% 27% 12%	140099
Seeing	Day	6% 9% 23% 32% 22% 8%	17564
	Night	5% 4 23% 46% 20% 1	27631

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% 3 3 3 3 4 7% 60%	5080
	11th to 20th	Day	1 2 1 2 2 2 2 1 4 5% 77%	5340
	21st to end	Day	2 6% 2 4 4 4 3 3 5% 7% 60%	5844
February	1st to 10th	Day	1 5% 2 4 3 3 4 4 6% 7% 60%	1890
	11th to 20th	Day	2 6% 2 5% 4 3 5% 3 6% 7% 58%	2042
	21st to end	Day	2 5% 2 4 3 3 3 3 5% 7% 61%	1730
March	1st to 10th	Day	1 4 2 5% 3 3 3 3 4 6% 64%	4830
	11th to 20th	Day	4 5% 2 6% 4 4 4 3 6% 9% 53%	5110
	21st to end	Day	2 4 2 4 3 4 4 4 7% 8% 58%	5785
April	1st to 10th	Day	2 4 1 4 3 3 4 4 6% 8% 62%	2520
	11th to 20th	Day	2 4 1 4 3 3 5% 4 5% 7% 61%	2491
	21st to end	Day	3 5% 1 3 3 3 4 4 6% 8% 61%	2520
May	1st to 10th	Day	4 3 1 4 4 3 5% 4 6% 9% 58%	7057
	11th to 20th	Day	3 3 1 3 3 3 4 4 6% 7% 64%	7604
	21st to end	Day	2 2 1 3 2 3 3 4 6% 7% 67%	9026
June	1st to 10th	Day	1 2 1 3 3 4 5% 5% 7% 9% 60%	2940
	11th to 20th	Day	1 1 1 2 2 3 4 3 5% 7% 71%	2940
	21st to end	Day	4 3 1 4 3 4 5% 5% 7% 7% 59%	2940
July	1st to 10th	Day	2 2 1 3 3 4 5% 5% 6% 6% 63%	6479
	11th to 20th	Day	1 1 1 3 4 6% 8% 8% 11% 12% 46%	6063
	21st to end	Day	2 3 1 5% 5% 6% 7% 7% 11% 12% 41%	6532
August	1st to 10th	Day	2 2 1 4 4 6% 8% 6% 9% 11% 46%	5702
	11th to 20th	Day	2 2 1 2 3 4 6% 6% 8% 10% 56%	5366
	21st to end	Day	3 3 1 4 4 6% 7% 6% 10% 12% 44%	5984
September	1st to 10th	Day	5% 4 1 4 4 4 4 4 6% 8% 55%	2400
	11th to 20th	Day	4 4 1 4 3 4 3 4 6% 7% 60%	2400
	21st to end	Day	3 3 1 3 2 3 4 3 5% 6% 68%	2168
October	1st to 10th	Day	3 2 1 3 2 2 2 2 4 6% 72%	3270
	11th to 20th	Day	8% 4 2 4 3 3 4 3 5% 6% 59%	3250
	21st to end	Day	3 3 1 2 2 2 2 2 4 5% 75%	3548
November	1st to 10th	Day	2 3 1 3 2 2 3 3 5% 5% 72%	1970
	11th to 20th	Day	1 2 1 3 2 2 2 3 5% 6% 73%	1890
	21st to end	Day	4 5% 2 3 3 2 4 3 4 7% 63%	1874
December	1st to 10th	Day	1 3 1 2 2 2 2 1 3 7% 77%	2700
	11th to 20th	Day	1 3 1 4 2 3 3 2 4 8% 68%	3106
	21st to end	Day	3 5% 2 3 2 2 4 3 4 6% 66%	4092
January	1st to 10th	Night	1 5% 3 7% 4 4 4 3 6% 7% 57%	7883
	11th to 20th	Night	1 3 1 3 2 2 3 2 4 5% 73%	7650
	21st to end	Night	2 6% 2 6% 3 2 3 2 4 7% 62%	8370
February	1st to 10th	Night	1 6% 2 6% 2 2 2 2 4 6% 65%	2730
	11th to 20th	Night	3 7% 2 5% 3 3 3 3 5% 7% 58%	2463
	21st to end	Night	3 6% 1 3 2 2 3 3 5% 6% 66%	2076
March	1st to 10th	Night	2 7% 2 4 3 2 3 3 4 6% 65%	5269
	11th to 20th	Night	5% 7% 2 5% 3 3 3 3 5% 6% 58%	5110
	21st to end	Night	2 6% 2 4 3 3 3 3 4 7% 63%	5423
April	1st to 10th	Night	2 5% 2 4 3 3 4 3 5% 7% 62%	2100
	11th to 20th	Night	4 6% 2 4 3 3 4 4 4 6% 60%	2077
	21st to end	Night	2 5% 1 4 4 3 3 3 6% 6% 63%	2100
May	1st to 10th	Night	7% 6% 2 5% 4 4 4 3 5% 7% 54%	5890
	11th to 20th	Night	4 4 1 4 3 3 4 3 5% 6% 62%	5267
	21st to end	Night	3 3 1 5% 3 3 4 3 5% 6% 65%	5181
June	1st to 10th	Night	2 2 1 3 3 4 4 4 6% 9% 61%	1680
	11th to 20th	Night	3 3 1 3 3 3 3 3 4 6% 71%	1680
	21st to end	Night	4 3 2 5% 4 4 6% 5% 6% 7% 55%	1680
July	1st to 10th	Night	2 3 1 5% 4 5% 5% 4 6% 6% 59%	3720
	11th to 20th	Night	2 2 1 4 4 5% 7% 7% 10% 13% 45%	4131
	21st to end	Night	4 4 2 7% 5% 6% 7% 7% 9% 11% 38%	4562
August	1st to 10th	Night	3 3 1 6% 5% 6% 7% 6% 9% 9% 43%	4108
	11th to 20th	Night	2 3 2 5% 4 5% 7% 6% 9% 13% 44%	4483
	21st to end	Night	5% 4 2 7% 6% 7% 8% 6% 11% 10% 35%	4993
September	1st to 10th	Night	5% 4 2 4 5% 4 5% 4 7% 9% 51%	2000
	11th to 20th	Night	5% 3 1 4 3 3 4 4 5% 8% 61%	2000
	21st to end	Night	5% 3 1 4 2 3 3 3 4 5% 67%	2227
October	1st to 10th	Night	4 3 1 2 2 2 2 2 4 6% 72%	3920
	11th to 20th	Night	9% 3 1 4 2 3 3 2 4 6% 62%	3898
	21st to end	Night	3 1 1 2 1 1 2 2 3 5% 79%	4252
November	1st to 10th	Night	2 2 1 2 2 2 2 3 4 6% 75%	2527
	11th to 20th	Night	1 2 1 2 2 1 2 2 4 6% 77%	2730
	21st to end	Night	4 5% 2 2 3 3 3 3 5% 5% 65%	2741
December	1st to 10th	Night	2 3 1 3 2 2 2 2 2 5% 77%	4710
	11th to 20th	Night	2 3 1 2 2 2 2 2 4 8% 70%	5321
	21st to end	Night	2 4 2 5% 3 3 3 3 4 5% 66%	7128

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	23% 4 13% 36% 23% 1	5083
	11th to 20th	Day	12% 2 13% 30% 31% 12%	5340
	21st to end	Day	23% 4 9% 24% 31% 9%	5844
February	1st to 10th	Day	22% 5% 14% 28% 24% 7%	1890
	11th to 20th	Day	24% 5% 11% 28% 27% 5%	2052
	21st to end	Day	21% 4 8% 24% 29% 14%	1730
March	1st to 10th	Day	18% 3 6% 17% 41% 14%	4830
	11th to 20th	Day	23% 6% 9% 26% 29% 7%	5110
	21st to end	Day	20% 6% 9% 35% 24% 6%	5785
April	1st to 10th	Day	18% 5% 9% 24% 29% 15%	2520
	11th to 20th	Day	20% 4 9% 21% 29% 16%	2494
	21st to end	Day	19% 5% 9% 24% 31% 13%	2520
May	1st to 10th	Day	19% 6% 12% 21% 29% 13%	7057
	11th to 20th	Day	16% 6% 9% 17% 34% 19%	7607
	21st to end	Day	14% 4 10% 19% 30% 24%	9027
June	1st to 10th	Day	17% 7% 12% 20% 24% 20%	2940
	11th to 20th	Day	11% 4 8% 15% 25% 37%	2940
	21st to end	Day	21% 5% 10% 19% 23% 23%	2940
July	1st to 10th	Day	19% 6% 11% 15% 20% 29%	6411
	11th to 20th	Day	21% 11% 23% 29% 9% 7%	5992
	21st to end	Day	28% 11% 22% 26% 11% 3	6348
August	1st to 10th	Day	31% 11% 21% 20% 10% 6%	4153
	11th to 20th	Day	20% 7% 17% 22% 21% 13%	3882
	21st to end	Day	28% 11% 19% 21% 15% 4	4311
September	1st to 10th	Day	25% 7% 12% 24% 22% 11%	2400
	11th to 20th	Day	21% 6% 11% 18% 28% 15%	2400
	21st to end	Day	16% 4 8% 22% 35% 15%	2168
October	1st to 10th	Day	14% 3 6% 17% 39% 21%	3270
	11th to 20th	Day	25% 4 7% 17% 34% 13%	3250
	21st to end	Day	13% 3 6% 25% 42% 11%	3548
November	1st to 10th	Day	14% 3 8% 26% 37% 12%	1970
	11th to 20th	Day	12% 3 9% 33% 36% 7%	1890
	21st to end	Day	21% 4 8% 29% 30% 8%	1874
December	1st to 10th	Day	11% 3 9% 37% 33% 6%	2700
	11th to 20th	Day	16% 4 9% 42% 26% 3	3104
	21st to end	Day	19% 4 13% 30% 31% 4	4092
January	1st to 10th	Night	26% 4 12% 34% 19% 4	7884
	11th to 20th	Night	13% 5% 12% 31% 27% 12%	7650
	21st to end	Night	23% 4 9% 24% 32% 8%	8370
February	1st to 10th	Night	20% 4 13% 29% 25% 8%	2730
	11th to 20th	Night	26% 5% 10% 28% 26% 6%	2463
	21st to end	Night	19% 4 7% 24% 34% 13%	2076
March	1st to 10th	Night	20% 3 6% 16% 41% 14%	5269
	11th to 20th	Night	26% 5% 8% 22% 29% 10%	5110
	21st to end	Night	18% 6% 8% 33% 27% 7%	5423
April	1st to 10th	Night	20% 4 10% 23% 28% 15%	2100
	11th to 20th	Night	22% 5% 7% 18% 28% 19%	2077
	21st to end	Night	20% 5% 11% 20% 30% 14%	2100
May	1st to 10th	Night	26% 7% 10% 19% 24% 13%	5888
	11th to 20th	Night	20% 7% 9% 18% 23% 24%	5268
	21st to end	Night	19% 5% 10% 14% 22% 31%	5182
June	1st to 10th	Night	17% 7% 13% 20% 21% 22%	1680
	11th to 20th	Night	16% 3 6% 13% 25% 37%	1680
	21st to end	Night	24% 6% 12% 14% 20% 24%	1680
July	1st to 10th	Night	23% 8% 13% 10% 15% 31%	3680
	11th to 20th	Night	24% 11% 30% 21% 6% 9%	4079
	21st to end	Night	35% 11% 21% 22% 10% 1	4434
August	1st to 10th	Night	37% 12% 21% 14% 8% 7%	2981
	11th to 20th	Night	27% 9% 21% 16% 12% 15%	3243
	21st to end	Night	37% 10% 21% 17% 11% 4	3597
September	1st to 10th	Night	27% 7% 14% 22% 17% 11%	2000
	11th to 20th	Night	19% 8% 12% 17% 24% 20%	2000
	21st to end	Night	19% 5% 9% 18% 33% 17%	2227
October	1st to 10th	Night	15% 4 6% 15% 39% 22%	3920
	11th to 20th	Night	25% 3 7% 14% 33% 17%	3898
	21st to end	Night	10% 2 5% 27% 40% 16%	4252
November	1st to 10th	Night	11% 2 7% 26% 41% 12%	2527
	11th to 20th	Night	10% 3 8% 31% 39% 8%	2730
	21st to end	Night	20% 3 9% 25% 33% 10%	2741
December	1st to 10th	Night	13% 3 7% 36% 35% 6%	4710
	11th to 20th	Night	15% 3 9% 33% 36% 5%	5322
	21st to end	Night	21% 5% 11% 27% 33% 3	7128

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	5% 8% 30% 43% 11% 3	330
	11th to 20th	Day	7% 10% 29% 38% 14% 3	330
	21st to end	Day	5% 5% 26% 41% 17% 6%	363
February	1st to 10th	Day	3 12% 29% 39% 13% 3	330
	11th to 20th	Day	8% 10% 40% 29% 12% 1	330
	21st to end	Day	9% 16% 26% 37% 10% 1	273
March	1st to 10th	Day	6% 18% 33% 26% 15% 2	430
	11th to 20th	Day	11% 18% 28% 28% 10% 4	540
	21st to end	Day	11% 22% 34% 22% 10% 1	594
April	1st to 10th	Day	9% 19% 35% 24% 11% 2	540
	11th to 20th	Day	8% 24% 38% 22% 7% 1	532
	21st to end	Day	9% 22% 36% 23% 9% 1	540
May	1st to 10th	Day	7% 18% 36% 24% 12% 2	543
	11th to 20th	Day	7% 15% 26% 31% 16% 5%	646
	21st to end	Day	5% 11% 25% 38% 19% 3	844
June	1st to 10th	Day	2 5% 20% 39% 28% 7%	780
	11th to 20th	Day	2 6% 25% 38% 23% 6%	780
	21st to end	Day	6% 6% 21% 33% 28% 7%	780
July	1st to 10th	Day	5% 2 14% 32% 36% 11%	771
	11th to 20th	Day	3 1 6% 30% 38% 23%	589
	21st to end	Day	4 1 8% 24% 39% 23%	616
August	1st to 10th	Day	2 2 13% 33% 32% 18%	527
	11th to 20th	Day	5% 2 12% 34% 32% 15%	517
	21st to end	Day	5% 1 8% 38% 31% 16%	583
September	1st to 10th	Day	5% 2 13% 30% 35% 14%	530
	11th to 20th	Day	5% 3 18% 35% 29% 9%	530
	21st to end	Day	4 5% 19% 31% 31% 11%	360
October	1st to 10th	Day	5% 8% 18% 30% 28% 12%	330
	11th to 20th	Day	8% 10% 23% 28% 20% 11%	330
	21st to end	Day	7% 8% 23% 30% 25% 8%	363
November	1st to 10th	Day	5% 10% 24% 34% 22% 5%	330
	11th to 20th	Day	5% 6% 19% 44% 22% 5%	330
	21st to end	Day	8% 9% 24% 36% 15% 7%	330
December	1st to 10th	Day	5% 10% 28% 35% 14% 7%	330
	11th to 20th	Day	5% 10% 25% 37% 20% 3	330
	21st to end	Day	9% 13% 29% 36% 11% 2	363
January	1st to 10th	Night	4 3 30% 46% 16% 1	940
	11th to 20th	Night	5% 3 30% 45% 15% 2	840
	21st to end	Night	6% 3 29% 45% 15% 1	924
February	1st to 10th	Night	5% 4 31% 49% 11%	840
	11th to 20th	Night	7% 7% 36% 41% 9%	824
	21st to end	Night	6% 6% 40% 44% 4	692
March	1st to 10th	Night	5% 7% 33% 47% 8%	840
	11th to 20th	Night	7% 6% 28% 45% 14%	840
	21st to end	Night	6% 9% 32% 44% 8%	840
April	1st to 10th	Night	5% 11% 37% 40% 7%	630
	11th to 20th	Night	7% 10% 31% 42% 9%	623
	21st to end	Night	4 7% 36% 44% 8%	630
May	1st to 10th	Night	5% 7% 27% 49% 12%	630
	11th to 20th	Night	6% 4 24% 47% 17% 1	621
	21st to end	Night	4 6% 24% 51% 15%	683
June	1st to 10th	Night	3 3 17% 54% 23%	630
	11th to 20th	Night	3 2 19% 55% 19% 1	630
	21st to end	Night	4 2 14% 48% 30% 1	630
July	1st to 10th	Night	5% 1 8% 47% 37% 2	615
	11th to 20th	Night	3 1 4 39% 49% 4	612
	21st to end	Night	5% 1 5% 29% 53% 6%	687
August	1st to 10th	Night	4 1 5% 33% 50% 8%	597
	11th to 20th	Night	5% 1 5% 42% 44% 3	594
	21st to end	Night	4 2 4 43% 43% 3	660
September	1st to 10th	Night	6% 1 7% 47% 37% 2	600
	11th to 20th	Night	6% 8% 53% 32% 2	600
	21st to end	Night	7% 2 13% 50% 27% 1	657
October	1st to 10th	Night	8% 3 16% 52% 21% 2	800
	11th to 20th	Night	6% 2 20% 50% 20% 2	800
	21st to end	Night	6% 2 23% 45% 20% 4	880
November	1st to 10th	Night	3 2 21% 54% 18% 2	887
	11th to 20th	Night	2 4 25% 49% 18% 2	1050
	21st to end	Night	7% 6% 26% 40% 19% 1	1050
December	1st to 10th	Night	6% 4 30% 46% 13% 1	1050
	11th to 20th	Night	7% 5% 29% 45% 13% 1	1050
	21st to end	Night	6% 5% 31% 48% 9% 1	1155

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