Magdalena Ridge Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Magdalena Ridge Observatory clear sky chart from 2005-11-06 to 2026-01-02.

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	2 4 2 5% 4 4 5% 4 6% 7% 58%	134729
	Night	3 4 2 4 3 4 4 4 5% 7% 61%	134159
Transparency	Day	20% 7% 8% 16% 28% 22%	129723
	Night	20% 6% 7% 16% 29% 22%	130168
Seeing	Day	9% 19% 28% 27% 14% 3	15805
	Night	6% 15% 28% 32% 18% 2	26504

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 7% 4 3 3 2 4 5% 62%	4107
	11th to 20th	Day	1 2 1 5% 3 3 4 3 4 5% 69%	4100
	21st to end	Day	2 8% 3 6% 4 3 3 3 4 6% 59%	4510
February	1st to 10th	Day	1 5% 2 5% 3 3 4 3 5% 6% 65%	1800
	11th to 20th	Day	3 5% 2 5% 3 4 4 2 4 5% 62%	1934
	21st to end	Day	2 5% 2 4 2 2 3 3 5% 6% 67%	1675
March	1st to 10th	Day	1 5% 2 5% 4 3 4 3 5% 6% 63%	4954
	11th to 20th	Day	4 7% 2 5% 3 4 4 3 5% 6% 56%	5000
	21st to end	Day	1 4 2 6% 4 4 5% 3 5% 7% 58%	5519
April	1st to 10th	Day	2 4 1 4 3 3 3 4 5% 7% 65%	2400
	11th to 20th	Day	3 4 2 5% 3 3 3 3 4 6% 64%	2371
	21st to end	Day	2 3 1 4 2 4 4 3 4 6% 67%	2400
May	1st to 10th	Day	2 3 1 4 3 4 4 3 5% 6% 65%	5440
	11th to 20th	Day	2 3 1 4 4 4 5% 4 5% 6% 62%	5615
	21st to end	Day	1 2 1 3 3 3 4 3 5% 6% 69%	6423
June	1st to 10th	Day	2 3 1 4 4 3 5% 4 7% 9% 56%	2600
	11th to 20th	Day	2 3 2 4 3 3 4 3 5% 6% 66%	2600
	21st to end	Day	6% 5% 3 6% 5% 5% 5% 5% 8% 7% 46%	2600
July	1st to 10th	Day	3 4 2 6% 5% 5% 6% 5% 8% 9% 47%	5879
	11th to 20th	Day	2 2 2 5% 5% 7% 8% 7% 10% 12% 42%	5880
	21st to end	Day	4 6% 2 9% 7% 8% 8% 7% 9% 11% 29%	6401
August	1st to 10th	Day	2 3 2 5% 4 6% 7% 6% 10% 11% 44%	5699
	11th to 20th	Day	3 2 2 6% 6% 7% 7% 6% 9% 12% 41%	5366
	21st to end	Day	3 4 2 6% 6% 6% 7% 6% 8% 11% 40%	5984
September	1st to 10th	Day	7% 5% 2 6% 5% 5% 5% 4 6% 7% 48%	2400
	11th to 20th	Day	6% 3 2 5% 4 5% 5% 5% 6% 8% 52%	2400
	21st to end	Day	3 2 1 4 3 3 4 3 6% 7% 64%	2122
October	1st to 10th	Day	3 2 1 3 2 3 3 3 4 6% 69%	3270
	11th to 20th	Day	4 3 1 3 3 2 3 2 4 6% 67%	3250
	21st to end	Day	1 1 1 2 1 1 2 2 2 4 82%	3548
November	1st to 10th	Day	2 3 1 3 2 2 2 2 4 7% 72%	2059
	11th to 20th	Day	2 2 1 3 3 3 4 3 3 5% 71%	2058
	21st to end	Day	3 5% 2 4 4 3 4 3 4 6% 63%	1890
December	1st to 10th	Day	2 2 1 3 2 1 2 3 4 5% 75%	2742
	11th to 20th	Day	2 4 1 4 3 3 3 2 4 6% 67%	3124
	21st to end	Day	1 3 1 3 2 3 3 3 4 6% 69%	4609
January	1st to 10th	Night	2 5% 3 6% 4 3 3 3 5% 6% 59%	5880
	11th to 20th	Night	1 2 1 3 2 2 3 2 4 5% 75%	5880
	21st to end	Night	2 5% 2 4 3 4 4 4 5% 6% 60%	6468
February	1st to 10th	Night	1 3 2 5% 3 3 4 3 5% 7% 64%	2600
	11th to 20th	Night	3 5% 2 5% 3 3 3 3 4 5% 63%	2352
	21st to end	Night	2 4 2 3 2 3 3 3 5% 6% 66%	1950
March	1st to 10th	Night	1 4 2 4 3 4 3 2 4 6% 67%	4940
	11th to 20th	Night	5% 7% 2 4 3 3 3 3 4 6% 59%	5000
	21st to end	Night	1 3 1 3 3 4 4 4 6% 5% 66%	5454
April	1st to 10th	Night	2 3 1 4 3 4 3 3 5% 7% 65%	2000
	11th to 20th	Night	3 4 1 4 2 4 3 2 3 5% 68%	1977
	21st to end	Night	2 3 1 4 4 3 3 3 4 6% 67%	2000
May	1st to 10th	Night	3 4 2 6% 4 3 3 3 5% 5% 63%	4540
	11th to 20th	Night	2 3 1 3 3 3 4 3 4 6% 67%	4295
	21st to end	Night	1 2 1 3 3 3 3 2 3 5% 74%	4474
June	1st to 10th	Night	2 5% 2 5% 4 4 4 4 6% 7% 57%	1800
	11th to 20th	Night	3 2 1 4 3 4 4 3 4 6% 66%	1800
	21st to end	Night	5% 5% 2 6% 6% 5% 5% 5% 6% 8% 47%	1800
July	1st to 10th	Night	3 4 2 6% 5% 5% 6% 4 7% 9% 48%	4100
	11th to 20th	Night	2 4 2 7% 5% 5% 7% 6% 10% 13% 41%	4100
	21st to end	Night	4 6% 2 8% 7% 6% 7% 6% 10% 12% 32%	4472
August	1st to 10th	Night	4 5% 2 6% 5% 6% 7% 6% 9% 12% 38%	4113
	11th to 20th	Night	3 4 2 6% 5% 6% 7% 6% 9% 12% 40%	4483
	21st to end	Night	4 5% 2 7% 6% 6% 8% 7% 10% 13% 31%	4993
September	1st to 10th	Night	5% 5% 2 6% 5% 6% 6% 5% 5% 8% 47%	2000
	11th to 20th	Night	6% 3 1 5% 4 3 5% 4 5% 8% 56%	2000
	21st to end	Night	5% 3 1 4 3 3 3 3 4 5% 64%	2272
October	1st to 10th	Night	3 3 1 3 2 2 3 2 4 6% 72%	3920
	11th to 20th	Night	3 3 1 3 2 2 3 2 5% 7% 67%	3898
	21st to end	Night	2 1 1 2 2 2 2 2 3 5% 78%	4252
November	1st to 10th	Night	2 3 1 3 1 2 3 3 4 6% 73%	2460
	11th to 20th	Night	1 2 1 3 2 2 3 2 4 6% 73%	2536
	21st to end	Night	3 5% 2 4 3 3 4 3 4 6% 64%	2730
December	1st to 10th	Night	2 3 1 3 2 2 3 3 4 6% 72%	4665
	11th to 20th	Night	2 2 1 4 3 4 4 3 5% 7% 64%	5321
	21st to end	Night	2 3 1 3 3 3 3 3 4 5% 69%	6634

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% 5% 4 16% 39% 13%	4108
	11th to 20th	Day	13% 7% 6% 18% 33% 23%	4100
	21st to end	Day	22% 8% 4 12% 30% 24%	4510
February	1st to 10th	Day	19% 5% 6% 16% 29% 26%	1800
	11th to 20th	Day	23% 4 6% 15% 30% 22%	1944
	21st to end	Day	16% 5% 4 10% 33% 32%	1675
March	1st to 10th	Day	18% 6% 4 7% 30% 36%	4954
	11th to 20th	Day	22% 8% 5% 13% 30% 22%	5000
	21st to end	Day	20% 7% 5% 13% 40% 15%	5519
April	1st to 10th	Day	17% 5% 5% 12% 37% 25%	2400
	11th to 20th	Day	19% 4 4 10% 28% 34%	2374
	21st to end	Day	15% 5% 5% 14% 35% 26%	2400
May	1st to 10th	Day	16% 5% 5% 16% 34% 24%	5440
	11th to 20th	Day	17% 7% 6% 10% 33% 27%	5618
	21st to end	Day	11% 5% 6% 9% 19% 50%	6424
June	1st to 10th	Day	20% 6% 7% 16% 23% 28%	2600
	11th to 20th	Day	16% 5% 5% 9% 20% 45%	2600
	21st to end	Day	29% 7% 10% 14% 18% 23%	2600
July	1st to 10th	Day	26% 11% 11% 13% 19% 20%	5816
	11th to 20th	Day	25% 11% 22% 22% 14% 6%	5811
	21st to end	Day	39% 13% 17% 20% 9% 2	6217
August	1st to 10th	Day	24% 11% 17% 29% 15% 4	4150
	11th to 20th	Day	23% 13% 13% 25% 21% 5%	3882
	21st to end	Day	33% 11% 16% 19% 17% 3	4311
September	1st to 10th	Day	30% 9% 9% 19% 20% 13%	2400
	11th to 20th	Day	25% 9% 9% 16% 25% 16%	2400
	21st to end	Day	16% 6% 7% 17% 31% 22%	2122
October	1st to 10th	Day	14% 6% 4 12% 30% 34%	3270
	11th to 20th	Day	17% 5% 5% 15% 37% 22%	3250
	21st to end	Day	8% 2 2 17% 33% 37%	3548
November	1st to 10th	Day	12% 4 3 20% 37% 24%	2059
	11th to 20th	Day	15% 4 3 17% 37% 24%	2058
	21st to end	Day	21% 5% 4 15% 34% 21%	1890
December	1st to 10th	Day	12% 3 4 20% 41% 20%	2742
	11th to 20th	Day	19% 5% 4 15% 40% 18%	3122
	21st to end	Day	14% 5% 5% 21% 32% 21%	4609
January	1st to 10th	Night	23% 6% 5% 16% 38% 12%	5880
	11th to 20th	Night	12% 4 5% 17% 40% 22%	5880
	21st to end	Night	22% 7% 5% 13% 29% 26%	6468
February	1st to 10th	Night	19% 4 6% 19% 27% 25%	2600
	11th to 20th	Night	21% 5% 4 21% 27% 23%	2352
	21st to end	Night	18% 4 4 13% 32% 30%	1950
March	1st to 10th	Night	18% 4 3 9% 38% 27%	4940
	11th to 20th	Night	23% 6% 5% 16% 30% 21%	5000
	21st to end	Night	17% 4 6% 19% 40% 14%	5454
April	1st to 10th	Night	18% 4 5% 13% 35% 25%	2000
	11th to 20th	Night	17% 4 5% 12% 29% 34%	1977
	21st to end	Night	17% 5% 5% 12% 37% 24%	2000
May	1st to 10th	Night	20% 6% 7% 14% 32% 21%	4537
	11th to 20th	Night	15% 6% 6% 13% 34% 27%	4296
	21st to end	Night	13% 4 3 8% 18% 55%	4474
June	1st to 10th	Night	21% 7% 8% 14% 20% 30%	1800
	11th to 20th	Night	17% 5% 5% 10% 20% 44%	1800
	21st to end	Night	31% 7% 11% 12% 13% 25%	1800
July	1st to 10th	Night	28% 8% 13% 14% 18% 19%	4055
	11th to 20th	Night	29% 8% 23% 20% 15% 6%	4046
	21st to end	Night	39% 9% 23% 18% 10% 1	4344
August	1st to 10th	Night	33% 10% 18% 24% 13% 3	2986
	11th to 20th	Night	30% 9% 14% 25% 18% 5%	3243
	21st to end	Night	37% 11% 18% 19% 12% 3	3597
September	1st to 10th	Night	31% 9% 12% 18% 17% 12%	2000
	11th to 20th	Night	24% 6% 9% 18% 22% 20%	2000
	21st to end	Night	20% 5% 7% 14% 32% 22%	2272
October	1st to 10th	Night	14% 4 5% 12% 32% 32%	3920
	11th to 20th	Night	16% 3 8% 18% 29% 26%	3898
	21st to end	Night	10% 3 2 14% 36% 34%	4252
November	1st to 10th	Night	12% 4 4 18% 37% 25%	2460
	11th to 20th	Night	13% 3 4 18% 34% 28%	2536
	21st to end	Night	20% 5% 5% 17% 33% 20%	2730
December	1st to 10th	Night	14% 4 4 22% 33% 22%	4665
	11th to 20th	Night	18% 5% 4 14% 38% 21%	5322
	21st to end	Night	16% 4 5% 21% 34% 20%	6634

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	9% 27% 35% 24% 5%	303
	11th to 20th	Day	14% 25% 30% 21% 8% 1	300
	21st to end	Day	9% 28% 33% 18% 11% 1	330
February	1st to 10th	Day	11% 27% 33% 19% 8% 2	300
	11th to 20th	Day	16% 25% 41% 16% 2	300
	21st to end	Day	20% 36% 24% 15% 3 1	274
March	1st to 10th	Day	15% 36% 29% 15% 5% 1	500
	11th to 20th	Day	19% 30% 31% 14% 5% 1	500
	21st to end	Day	15% 40% 30% 12% 3 1	550
April	1st to 10th	Day	13% 28% 38% 16% 5% 1	500
	11th to 20th	Day	15% 34% 33% 13% 4	492
	21st to end	Day	13% 32% 33% 18% 4	500
May	1st to 10th	Day	8% 28% 40% 20% 4 1	503
	11th to 20th	Day	8% 21% 36% 26% 8% 2	528
	21st to end	Day	6% 23% 41% 22% 6% 1	573
June	1st to 10th	Day	6% 14% 32% 33% 13% 1	530
	11th to 20th	Day	5% 14% 33% 35% 12% 1	530
	21st to end	Day	7% 8% 27% 38% 17% 3	530
July	1st to 10th	Day	5% 4 21% 37% 29% 5%	526
	11th to 20th	Day	4 2 14% 36% 35% 9%	524
	21st to end	Day	5% 2 11% 37% 33% 11%	575
August	1st to 10th	Day	4 3 14% 36% 35% 8%	527
	11th to 20th	Day	5% 4 15% 42% 27% 7%	517
	21st to end	Day	7% 2 16% 39% 28% 8%	583
September	1st to 10th	Day	9% 4 22% 38% 22% 5%	530
	11th to 20th	Day	5% 8% 26% 39% 19% 3	530
	21st to end	Day	5% 11% 32% 31% 19% 2	414
October	1st to 10th	Day	9% 12% 29% 27% 18% 5%	330
	11th to 20th	Day	12% 13% 29% 30% 15% 2	330
	21st to end	Day	10% 19% 25% 28% 15% 3	363
November	1st to 10th	Day	9% 21% 32% 27% 9% 2	330
	11th to 20th	Day	8% 15% 30% 32% 14% 2	330
	21st to end	Day	7% 31% 30% 22% 9% 1	330
December	1st to 10th	Day	9% 24% 35% 24% 8% 1	330
	11th to 20th	Day	5% 31% 30% 23% 10% 1	330
	21st to end	Day	15% 28% 32% 20% 6%	363
January	1st to 10th	Night	7% 16% 34% 28% 14% 2	804
	11th to 20th	Night	6% 22% 34% 24% 12% 2	800
	21st to end	Night	5% 22% 30% 28% 13% 2	880
February	1st to 10th	Night	4 24% 34% 25% 12% 1	800
	11th to 20th	Night	8% 21% 39% 23% 7% 1	784
	21st to end	Night	8% 27% 36% 25% 3 1	660
March	1st to 10th	Night	9% 23% 32% 27% 9% 1	800
	11th to 20th	Night	8% 21% 32% 28% 11% 1	800
	21st to end	Night	7% 24% 36% 25% 7%	870
April	1st to 10th	Night	6% 24% 40% 25% 5% 1	600
	11th to 20th	Night	7% 30% 34% 24% 6%	593
	21st to end	Night	4 26% 41% 22% 7%	600
May	1st to 10th	Night	5% 17% 42% 31% 6%	600
	11th to 20th	Night	8% 12% 33% 34% 14% 1	591
	21st to end	Night	3 12% 40% 35% 9%	650
June	1st to 10th	Night	5% 8% 32% 38% 16% 1	600
	11th to 20th	Night	5% 10% 31% 40% 13%	600
	21st to end	Night	7% 5% 22% 40% 23% 3	600
July	1st to 10th	Night	7% 3 16% 38% 31% 5%	585
	11th to 20th	Night	5% 1 9% 37% 41% 7%	582
	21st to end	Night	6% 3 11% 26% 43% 11%	657
August	1st to 10th	Night	4 4 8% 27% 47% 10%	597
	11th to 20th	Night	4 3 11% 36% 41% 5%	594
	21st to end	Night	5% 2 10% 35% 42% 7%	660
September	1st to 10th	Night	7% 3 12% 39% 35% 4	600
	11th to 20th	Night	7% 4 16% 42% 28% 4	600
	21st to end	Night	5% 5% 20% 41% 25% 3	757
October	1st to 10th	Night	6% 7% 30% 37% 17% 3	800
	11th to 20th	Night	7% 8% 31% 36% 17% 2	800
	21st to end	Night	6% 13% 24% 32% 20% 4	880
November	1st to 10th	Night	5% 12% 25% 36% 20% 2	820
	11th to 20th	Night	4 13% 26% 36% 18% 3	856
	21st to end	Night	8% 19% 25% 29% 17% 2	1050
December	1st to 10th	Night	7% 17% 30% 32% 13% 1	1050
	11th to 20th	Night	6% 20% 31% 31% 11% 1	1050
	21st to end	Night	6% 22% 31% 31% 8% 1	934

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