Etscorn Campus Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Etscorn Campus Observatory clear sky chart from 2005-11-06 to 2025-10-19.

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 2 1 3 3 3 4 3 5% 7% 66%	134222
	Night	3 3 1 4 3 3 4 3 5% 7% 63%	132966
Transparency	Day	17% 3 7% 19% 30% 24%	129227
	Night	20% 3 6% 17% 29% 24%	128964
Seeing	Day	5% 9% 23% 32% 23% 8%	15916
	Night	5% 4 25% 43% 22% 2	26226

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	3 7% 2 4 3 3 3 2 4 6% 63%	4098
	11th to 20th	Day	1 3 1 2 2 2 2 3 4 5% 75%	4100
	21st to end	Day	3 4 2 5% 3 3 3 3 5% 6% 64%	4510
February	1st to 10th	Day	2 4 1 4 2 3 3 2 5% 7% 67%	1805
	11th to 20th	Day	3 4 2 4 3 3 4 3 3 5% 64%	1949
	21st to end	Day	1 4 1 3 2 2 2 3 4 6% 72%	1650
March	1st to 10th	Day	2 2 1 3 2 3 4 3 5% 7% 68%	4951
	11th to 20th	Day	3 4 2 4 3 3 3 3 5% 7% 62%	5000
	21st to end	Day	1 3 2 4 3 3 4 3 6% 7% 65%	5546
April	1st to 10th	Day	2 3 1 3 2 2 3 3 5% 7% 70%	2400
	11th to 20th	Day	3 3 1 2 2 3 2 3 4 6% 71%	2371
	21st to end	Day	2 2 1 2 2 2 3 2 4 5% 75%	2400
May	1st to 10th	Day	1 1 1 2 2 2 3 3 5% 7% 74%	5440
	11th to 20th	Day	2 2 1 2 3 3 3 3 5% 6% 70%	5569
	21st to end	Day	1 1 2 1 2 2 3 4 6% 77%	6423
June	1st to 10th	Day	1 2 1 3 3 3 4 4 6% 9% 64%	2760
	11th to 20th	Day	2 2 1 2 2 2 3 2 5% 6% 74%	2800
	21st to end	Day	4 4 1 4 4 4 5% 5% 7% 7% 55%	2620
July	1st to 10th	Day	2 2 1 3 4 4 5% 5% 7% 8% 60%	5879
	11th to 20th	Day	1 1 1 3 3 4 5% 4 8% 12% 58%	5880
	21st to end	Day	2 3 2 5% 5% 6% 7% 6% 9% 11% 43%	6401
August	1st to 10th	Day	2 1 1 2 3 5% 5% 5% 8% 11% 56%	5656
	11th to 20th	Day	2 2 1 3 3 3 5% 5% 9% 11% 56%	5366
	21st to end	Day	3 2 1 4 4 5% 6% 5% 9% 10% 51%	5984
September	1st to 10th	Day	5% 3 2 5% 4 4 6% 4 6% 8% 54%	2400
	11th to 20th	Day	5% 3 1 4 3 3 4 4 7% 8% 59%	2400
	21st to end	Day	3 2 1 2 3 2 3 3 4 6% 72%	2138
October	1st to 10th	Day	2 1 1 2 2 2 2 2 3 4 79%	3270
	11th to 20th	Day	3 2 1 3 2 3 2 2 4 7% 73%	3230
	21st to end	Day	2 1 1 1 1 1 1 2 4 86%	3438
November	1st to 10th	Day	3 1 1 2 1 2 2 2 4 7% 75%	1959
	11th to 20th	Day	2 2 1 2 2 2 3 2 4 5% 76%	1912
	21st to end	Day	5% 2 1 3 3 3 4 3 5% 6% 65%	1800
December	1st to 10th	Day	2 2 1 2 1 1 1 2 4 7% 77%	2693
	11th to 20th	Day	2 2 1 3 3 3 3 2 4 6% 71%	3026
	21st to end	Day	2 3 1 3 2 2 3 2 5% 7% 71%	4398
January	1st to 10th	Night	2 7% 2 5% 3 3 3 3 4 6% 60%	5867
	11th to 20th	Night	2 2 1 2 2 2 3 3 4 6% 74%	5880
	21st to end	Night	4 5% 2 4 3 3 3 3 4 6% 61%	6468
February	1st to 10th	Night	2 4 2 3 3 2 3 2 4 6% 69%	2595
	11th to 20th	Night	4 4 2 4 3 3 3 3 5% 6% 63%	2338
	21st to end	Night	2 3 1 3 3 2 3 3 4 8% 68%	1980
March	1st to 10th	Night	4 4 1 3 3 3 2 2 3 5% 70%	4940
	11th to 20th	Night	6% 5% 2 5% 2 3 3 2 4 6% 62%	5000
	21st to end	Night	2 3 1 4 2 3 3 3 5% 6% 67%	5412
April	1st to 10th	Night	2 2 1 3 3 3 3 4 4 6% 69%	2000
	11th to 20th	Night	3 3 1 3 3 3 3 2 4 5% 70%	1977
	21st to end	Night	3 3 1 3 3 3 3 3 4 6% 70%	2000
May	1st to 10th	Night	3 4 1 4 3 3 4 3 5% 5% 64%	4540
	11th to 20th	Night	3 2 1 2 3 2 4 3 5% 6% 70%	4341
	21st to end	Night	1 1 2 2 2 3 3 4 6% 77%	4474
June	1st to 10th	Night	3 3 1 4 3 3 4 4 6% 8% 61%	1630
	11th to 20th	Night	3 3 1 3 3 2 3 3 6% 6% 68%	1600
	21st to end	Night	4 4 2 6% 4 4 5% 4 7% 9% 51%	1767
July	1st to 10th	Night	3 3 1 5% 5% 5% 5% 5% 6% 9% 52%	4100
	11th to 20th	Night	2 2 1 5% 5% 5% 6% 6% 9% 13% 46%	4100
	21st to end	Night	4 4 2 6% 7% 7% 7% 8% 10% 12% 33%	4472
August	1st to 10th	Night	3 4 2 6% 6% 7% 7% 6% 9% 11% 41%	4153
	11th to 20th	Night	2 3 1 5% 5% 6% 7% 6% 10% 12% 42%	4483
	21st to end	Night	2 4 2 7% 6% 7% 8% 7% 10% 14% 33%	4993
September	1st to 10th	Night	4 3 1 5% 5% 5% 4 5% 7% 8% 51%	2000
	11th to 20th	Night	5% 3 2 4 3 4 5% 4 5% 8% 58%	2000
	21st to end	Night	4 2 1 3 3 2 3 3 5% 6% 66%	2256
October	1st to 10th	Night	2 2 1 2 2 2 3 2 4 6% 74%	3920
	11th to 20th	Night	3 2 1 3 2 3 3 2 4 6% 70%	3874
	21st to end	Night	2 2 2 1 1 2 1 3 5% 80%	4120
November	1st to 10th	Night	3 1 1 2 1 1 2 2 4 6% 75%	2340
	11th to 20th	Night	1 2 1 2 2 2 2 2 3 6% 78%	2465
	21st to end	Night	5% 4 1 3 3 2 3 2 3 5% 69%	2600
December	1st to 10th	Night	3 2 1 2 2 2 2 2 4 5% 75%	4494
	11th to 20th	Night	2 2 1 2 2 2 3 3 5% 8% 68%	5181
	21st to end	Night	3 3 1 3 2 2 2 2 4 6% 71%	6606

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% 2 3 20% 45% 6%	4099
	11th to 20th	Day	12% 3 6% 18% 43% 17%	4100
	21st to end	Day	20% 4 6% 18% 32% 19%	4510
February	1st to 10th	Day	18% 2 5% 19% 33% 24%	1805
	11th to 20th	Day	23% 3 4 18% 31% 21%	1959
	21st to end	Day	15% 3 2 12% 38% 30%	1650
March	1st to 10th	Day	17% 4 2 9% 33% 35%	4951
	11th to 20th	Day	20% 6% 3 17% 28% 25%	5000
	21st to end	Day	18% 4 3 15% 40% 21%	5546
April	1st to 10th	Day	14% 3 3 14% 34% 32%	2400
	11th to 20th	Day	16% 3 2 12% 28% 40%	2374
	21st to end	Day	13% 3 3 14% 35% 33%	2400
May	1st to 10th	Day	11% 2 5% 19% 29% 34%	5440
	11th to 20th	Day	14% 4 4 9% 29% 39%	5572
	21st to end	Day	9% 2 4 11% 17% 57%	6424
June	1st to 10th	Day	16% 4 6% 18% 24% 33%	2760
	11th to 20th	Day	12% 3 3 10% 22% 51%	2800
	21st to end	Day	25% 5% 7% 15% 22% 27%	2620
July	1st to 10th	Day	20% 4 11% 16% 21% 28%	5816
	11th to 20th	Day	17% 4 17% 31% 21% 10%	5811
	21st to end	Day	32% 5% 16% 26% 16% 5%	6217
August	1st to 10th	Day	19% 6% 13% 31% 23% 8%	4118
	11th to 20th	Day	20% 4 10% 22% 29% 15%	3882
	21st to end	Day	28% 6% 15% 27% 19% 5%	4311
September	1st to 10th	Day	26% 5% 9% 20% 22% 17%	2400
	11th to 20th	Day	21% 6% 9% 18% 24% 22%	2400
	21st to end	Day	15% 3 5% 18% 33% 26%	2138
October	1st to 10th	Day	12% 2 5% 11% 29% 40%	3270
	11th to 20th	Day	15% 2 4 14% 37% 29%	3230
	21st to end	Day	7% 1 2 15% 41% 33%	3438
November	1st to 10th	Day	11% 2 3 20% 40% 24%	1959
	11th to 20th	Day	13% 2 4 22% 38% 22%	1912
	21st to end	Day	20% 3 5% 18% 35% 19%	1800
December	1st to 10th	Day	12% 1 3 31% 38% 15%	2693
	11th to 20th	Day	17% 2 6% 28% 39% 8%	3024
	21st to end	Day	14% 2 6% 28% 35% 15%	4398
January	1st to 10th	Night	25% 4 4 18% 40% 9%	5867
	11th to 20th	Night	13% 3 6% 18% 44% 17%	5880
	21st to end	Night	24% 3 5% 16% 31% 21%	6468
February	1st to 10th	Night	18% 2 5% 20% 30% 25%	2595
	11th to 20th	Night	22% 3 5% 20% 28% 23%	2338
	21st to end	Night	17% 2 4 12% 34% 31%	1980
March	1st to 10th	Night	19% 3 2 9% 36% 31%	4940
	11th to 20th	Night	23% 5% 3 14% 31% 24%	5000
	21st to end	Night	17% 4 3 16% 36% 25%	5412
April	1st to 10th	Night	16% 3 3 11% 37% 31%	2000
	11th to 20th	Night	16% 3 3 12% 25% 40%	1977
	21st to end	Night	16% 3 4 12% 32% 33%	2000
May	1st to 10th	Night	20% 3 6% 13% 24% 34%	4537
	11th to 20th	Night	16% 3 6% 10% 25% 40%	4342
	21st to end	Night	11% 2 4 9% 14% 61%	4474
June	1st to 10th	Night	21% 3 8% 16% 20% 33%	1630
	11th to 20th	Night	17% 3 3 10% 18% 48%	1600
	21st to end	Night	29% 4 11% 15% 15% 26%	1767
July	1st to 10th	Night	27% 5% 13% 16% 16% 22%	4055
	11th to 20th	Night	27% 4 18% 26% 17% 7%	4046
	21st to end	Night	39% 5% 17% 24% 12% 2	4344
August	1st to 10th	Night	33% 5% 16% 23% 16% 7%	3015
	11th to 20th	Night	30% 6% 12% 18% 24% 10%	3243
	21st to end	Night	37% 6% 18% 20% 14% 5%	3597
September	1st to 10th	Night	27% 7% 13% 19% 19% 15%	2000
	11th to 20th	Night	24% 5% 10% 17% 19% 24%	2000
	21st to end	Night	19% 4 6% 15% 29% 27%	2256
October	1st to 10th	Night	13% 3 5% 10% 29% 39%	3920
	11th to 20th	Night	17% 2 4 16% 29% 32%	3874
	21st to end	Night	10% 2 2 14% 36% 36%	4120
November	1st to 10th	Night	11% 3 3 20% 39% 26%	2340
	11th to 20th	Night	11% 1 4 19% 36% 29%	2465
	21st to end	Night	20% 2 4 18% 35% 20%	2600
December	1st to 10th	Night	14% 2 3 28% 34% 19%	4494
	11th to 20th	Night	16% 2 5% 24% 40% 13%	5182
	21st to end	Night	16% 2 4 26% 37% 15%	6606

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	6% 7% 31% 46% 9% 1	300
	11th to 20th	Day	6% 8% 32% 40% 13% 1	300
	21st to end	Day	5% 8% 40% 28% 18% 2	330
February	1st to 10th	Day	6% 10% 27% 41% 12% 3	300
	11th to 20th	Day	9% 12% 35% 38% 6%	300
	21st to end	Day	10% 17% 37% 29% 5% 2	249
March	1st to 10th	Day	7% 21% 36% 26% 9% 1	497
	11th to 20th	Day	9% 20% 30% 29% 10% 2	500
	21st to end	Day	9% 23% 36% 23% 9% 1	550
April	1st to 10th	Day	6% 17% 38% 25% 11% 3	500
	11th to 20th	Day	7% 22% 35% 25% 10% 1	492
	21st to end	Day	6% 17% 35% 29% 11% 1	500
May	1st to 10th	Day	4 16% 34% 30% 14% 3	503
	11th to 20th	Day	3 11% 34% 30% 17% 5%	528
	21st to end	Day	2 12% 35% 32% 18% 1	573
June	1st to 10th	Day	2 6% 21% 39% 28% 5%	690
	11th to 20th	Day	2 4 18% 41% 28% 5%	730
	21st to end	Day	6% 2 15% 36% 31% 9%	550
July	1st to 10th	Day	3 1 11% 33% 36% 17%	526
	11th to 20th	Day	3 1 3 26% 39% 28%	524
	21st to end	Day	2 1 3 26% 40% 28%	575
August	1st to 10th	Day	2 1 5% 25% 43% 23%	527
	11th to 20th	Day	4 2 6% 28% 42% 19%	517
	21st to end	Day	5% 1 5% 28% 44% 18%	583
September	1st to 10th	Day	5% 2 8% 32% 40% 14%	530
	11th to 20th	Day	4 1 15% 36% 36% 8%	530
	21st to end	Day	4 5% 17% 34% 31% 10%	398
October	1st to 10th	Day	3 5% 22% 30% 32% 9%	330
	11th to 20th	Day	8% 5% 19% 37% 25% 6%	324
	21st to end	Day	8% 6% 17% 37% 24% 8%	330
November	1st to 10th	Day	7% 9% 25% 40% 17% 3	300
	11th to 20th	Day	3 8% 19% 43% 23% 4	300
	21st to end	Day	5% 10% 35% 33% 15% 2	300
December	1st to 10th	Day	5% 6% 38% 39% 11% 1	300
	11th to 20th	Day	4 11% 33% 39% 12% 1	300
	21st to end	Day	9% 8% 37% 36% 10% 1	330
January	1st to 10th	Night	5% 4 29% 47% 15% 1	800
	11th to 20th	Night	5% 4 36% 40% 14% 1	800
	21st to end	Night	5% 6% 33% 41% 14% 1	880
February	1st to 10th	Night	4 5% 34% 43% 13% 1	800
	11th to 20th	Night	6% 5% 38% 42% 8% 1	784
	21st to end	Night	4 8% 45% 39% 4	660
March	1st to 10th	Night	5% 8% 38% 41% 9%	800
	11th to 20th	Night	5% 8% 32% 42% 13% 1	800
	21st to end	Night	5% 8% 35% 41% 9%	854
April	1st to 10th	Night	3 6% 41% 43% 7%	600
	11th to 20th	Night	4 9% 42% 37% 8%	593
	21st to end	Night	3 8% 41% 40% 8%	600
May	1st to 10th	Night	4 3 36% 48% 9%	600
	11th to 20th	Night	5% 4 28% 44% 19%	591
	21st to end	Night	2 2 29% 53% 13%	650
June	1st to 10th	Night	3 3 20% 54% 21%	600
	11th to 20th	Night	3 2 21% 52% 22%	600
	21st to end	Night	6% 2 11% 50% 31% 1	600
July	1st to 10th	Night	5% 1 8% 41% 41% 3	585
	11th to 20th	Night	3 1 3 35% 52% 6%	582
	21st to end	Night	4 2 4 26% 55% 9%	657
August	1st to 10th	Night	4 1 3 28% 55% 9%	597
	11th to 20th	Night	4 2 5% 30% 56% 4	594
	21st to end	Night	3 1 5% 33% 52% 6%	660
September	1st to 10th	Night	5% 1 7% 43% 41% 3	600
	11th to 20th	Night	7% 1 10% 47% 34% 2	600
	21st to end	Night	4 2 14% 49% 29% 2	726
October	1st to 10th	Night	5% 2 18% 50% 24% 1	800
	11th to 20th	Night	4 3 20% 52% 19% 2	792
	21st to end	Night	5% 3 21% 41% 26% 3	836
November	1st to 10th	Night	4 2 23% 48% 22% 1	780
	11th to 20th	Night	3 3 23% 48% 21% 2	865
	21st to end	Night	7% 6% 27% 39% 20% 2	1000
December	1st to 10th	Night	6% 3 29% 46% 15%	1000
	11th to 20th	Night	6% 5% 32% 45% 12%	1000
	21st to end	Night	5% 4 33% 47% 10% 1	940

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