Eagle Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Eagle Observatory clear sky chart from 2005-11-06 to 2026-02-16.

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 5% 2 6% 4 4 5% 4 7% 9% 52%	139909
	Night	2 6% 3 7% 4 4 4 4 6% 8% 52%	138447
Transparency	Day	28% 6% 13% 25% 20% 8%	134815
	Night	28% 7% 14% 27% 18% 5%	134549
Seeing	Day	8% 14% 30% 29% 15% 3	17189
	Night	6% 7% 27% 41% 18% 1	27400

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 5% 4 10% 6% 6% 7% 6% 9% 10% 36%	4720
	11th to 20th	Day	6% 3 9% 5% 4 5% 4 5% 7% 52%	5296
	21st to end	Day	5% 4 9% 6% 5% 4 3 5% 9% 49%	5844
February	1st to 10th	Day	1 10% 3 10% 7% 6% 6% 4 5% 6% 42%	1890
	11th to 20th	Day	1 8% 4 9% 7% 6% 6% 5% 6% 8% 39%	1865
	21st to end	Day	1 8% 5% 11% 6% 5% 6% 5% 7% 7% 40%	1650
March	1st to 10th	Day	1 7% 3 8% 5% 5% 5% 4 7% 8% 48%	4748
	11th to 20th	Day	1 7% 3 8% 6% 5% 6% 5% 8% 8% 43%	5000
	21st to end	Day	1 8% 3 8% 5% 5% 6% 6% 9% 10% 39%	5617
April	1st to 10th	Day	3 7% 3 6% 5% 5% 5% 4 7% 8% 47%	2400
	11th to 20th	Day	3 9% 3 8% 6% 5% 6% 5% 7% 8% 41%	2371
	21st to end	Day	3 7% 4 7% 6% 5% 5% 5% 6% 9% 42%	2400
May	1st to 10th	Day	3 8% 3 7% 5% 5% 6% 5% 8% 8% 40%	5739
	11th to 20th	Day	4 5% 2 6% 4 5% 5% 5% 8% 10% 46%	6288
	21st to end	Day	2 3 1 4 4 4 5% 5% 8% 10% 53%	6925
June	1st to 10th	Day	3 3 1 4 4 4 5% 4 6% 10% 56%	2800
	11th to 20th	Day	3 2 1 3 2 3 4 4 6% 8% 65%	2800
	21st to end	Day	2 1 1 3 3 4 5% 4 7% 8% 64%	2800
July	1st to 10th	Day	2 2 1 3 3 3 3 3 5% 7% 68%	6339
	11th to 20th	Day	1 1 1 3 4 5% 6% 7% 10% 12% 50%	6326
	21st to end	Day	2 3 1 4 4 4 5% 5% 7% 9% 57%	6401
August	1st to 10th	Day	3 2 1 4 4 4 5% 4 8% 11% 54%	5779
	11th to 20th	Day	2 3 1 4 3 4 4 4 7% 9% 60%	5587
	21st to end	Day	3 3 1 5% 4 5% 5% 4 7% 10% 52%	5984
September	1st to 10th	Day	4 3 1 4 3 4 3 4 6% 8% 61%	2400
	11th to 20th	Day	4 3 1 4 4 5% 4 3 5% 8% 59%	2400
	21st to end	Day	5% 4 1 4 2 3 3 3 4 7% 63%	2132
October	1st to 10th	Day	3 3 1 3 3 2 2 2 4 5% 72%	3270
	11th to 20th	Day	3 3 1 3 3 4 5% 3 7% 10% 58%	3250
	21st to end	Day	3 5% 2 4 2 2 3 3 4 7% 64%	3548
November	1st to 10th	Day	2 5% 2 5% 3 2 4 3 6% 7% 60%	1898
	11th to 20th	Day	2 7% 2 5% 4 3 4 3 5% 7% 57%	1864
	21st to end	Day	2 7% 4 8% 4 3 3 3 5% 6% 56%	1680
December	1st to 10th	Day	1 6% 3 8% 4 4 4 3 4 6% 58%	2700
	11th to 20th	Day	1 4 3 7% 4 4 4 3 5% 9% 57%	3106
	21st to end	Day	1 7% 4 12% 6% 5% 6% 4 8% 9% 39%	4092
January	1st to 10th	Night	1 8% 5% 12% 6% 5% 5% 5% 7% 8% 37%	8201
	11th to 20th	Night	5% 3 10% 7% 4 4 3 4 6% 53%	7752
	21st to end	Night	1 8% 5% 10% 5% 5% 4 3 5% 6% 48%	8370
February	1st to 10th	Night	1 9% 4 10% 6% 4 6% 4 6% 7% 43%	2730
	11th to 20th	Night	1 9% 5% 11% 6% 5% 6% 5% 5% 8% 39%	2530
	21st to end	Night	1 11% 4 11% 6% 4 5% 4 5% 6% 43%	1980
March	1st to 10th	Night	1 9% 4 8% 5% 5% 5% 4 6% 7% 45%	5121
	11th to 20th	Night	1 8% 3 6% 4 4 4 3 5% 7% 55%	5000
	21st to end	Night	1 13% 4 8% 6% 5% 7% 4 7% 8% 37%	5337
April	1st to 10th	Night	4 9% 2 6% 5% 4 6% 4 7% 7% 46%	2000
	11th to 20th	Night	4 11% 3 7% 4 4 5% 4 6% 8% 45%	1977
	21st to end	Night	5% 9% 3 6% 4 4 4 4 5% 7% 49%	2000
May	1st to 10th	Night	5% 7% 2 6% 4 5% 6% 5% 6% 9% 45%	4237
	11th to 20th	Night	6% 6% 3 6% 5% 4 5% 5% 7% 9% 45%	3624
	21st to end	Night	3 3 1 4 3 4 4 4 6% 8% 59%	3972
June	1st to 10th	Night	2 2 1 3 2 4 4 3 6% 9% 63%	1600
	11th to 20th	Night	3 2 1 3 3 4 4 4 6% 7% 64%	1600
	21st to end	Night	2 1 1 2 2 2 3 4 7% 8% 68%	1600
July	1st to 10th	Night	3 2 1 4 3 4 4 4 6% 7% 61%	3640
	11th to 20th	Night	1 2 1 3 3 5% 6% 5% 8% 11% 55%	3640
	21st to end	Night	1 2 1 3 3 4 5% 5% 7% 9% 60%	4469
August	1st to 10th	Night	3 3 1 3 3 4 6% 6% 8% 10% 52%	4033
	11th to 20th	Night	2 2 1 3 3 3 4 4 7% 9% 61%	4260
	21st to end	Night	4 4 1 5% 4 5% 5% 5% 7% 10% 50%	4993
September	1st to 10th	Night	3 2 2 4 3 4 4 4 5% 7% 63%	2000
	11th to 20th	Night	3 3 1 3 3 3 3 3 5% 9% 63%	2000
	21st to end	Night	3 3 1 3 3 3 3 2 5% 7% 66%	2261
October	1st to 10th	Night	3 2 1 3 2 2 2 2 3 5% 75%	3920
	11th to 20th	Night	2 3 1 3 2 2 3 4 7% 11% 62%	3898
	21st to end	Night	4 6% 1 4 2 2 2 2 3 5% 69%	4252
November	1st to 10th	Night	3 5% 2 4 3 2 3 3 5% 6% 64%	2598
	11th to 20th	Night	2 8% 2 6% 3 3 3 3 4 6% 58%	2753
	21st to end	Night	2 9% 3 7% 4 4 3 2 5% 7% 54%	2940
December	1st to 10th	Night	1 6% 3 6% 4 3 3 3 4 4 62%	4710
	11th to 20th	Night	1 6% 3 7% 4 4 4 4 7% 8% 53%	5321
	21st to end	Night	1 10% 5% 11% 6% 5% 7% 5% 8% 7% 36%	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	38% 7% 21% 24% 9% 1	4723
	11th to 20th	Day	34% 6% 17% 25% 16% 1	5296
	21st to end	Day	31% 6% 15% 27% 19% 2	5844
February	1st to 10th	Day	43% 6% 17% 20% 11% 3	1890
	11th to 20th	Day	45% 6% 11% 23% 13% 2	1874
	21st to end	Day	42% 6% 12% 21% 16% 3	1650
March	1st to 10th	Day	36% 5% 8% 24% 21% 5%	4748
	11th to 20th	Day	34% 7% 14% 32% 12% 2	5000
	21st to end	Day	36% 8% 21% 27% 7% 1	5617
April	1st to 10th	Day	35% 6% 13% 23% 17% 5%	2400
	11th to 20th	Day	41% 8% 12% 19% 18% 2	2374
	21st to end	Day	38% 7% 11% 27% 15% 2	2400
May	1st to 10th	Day	34% 11% 14% 22% 17% 2	5739
	11th to 20th	Day	27% 9% 12% 27% 20% 5%	6292
	21st to end	Day	22% 7% 12% 27% 28% 3	6926
June	1st to 10th	Day	23% 6% 11% 25% 26% 9%	2800
	11th to 20th	Day	19% 5% 9% 17% 28% 22%	2800
	21st to end	Day	17% 5% 7% 23% 27% 21%	2800
July	1st to 10th	Day	15% 4 8% 13% 24% 35%	6271
	11th to 20th	Day	19% 6% 12% 31% 23% 9%	6251
	21st to end	Day	22% 5% 14% 20% 21% 19%	6217
August	1st to 10th	Day	27% 7% 19% 20% 15% 12%	4208
	11th to 20th	Day	24% 8% 16% 16% 26% 10%	4046
	21st to end	Day	22% 6% 17% 20% 25% 11%	4311
September	1st to 10th	Day	21% 5% 10% 22% 25% 17%	2400
	11th to 20th	Day	25% 5% 11% 22% 28% 11%	2400
	21st to end	Day	23% 4 8% 27% 29% 9%	2132
October	1st to 10th	Day	17% 3 6% 27% 33% 14%	3270
	11th to 20th	Day	19% 5% 11% 39% 22% 4	3250
	21st to end	Day	22% 4 8% 41% 24% 3	3548
November	1st to 10th	Day	24% 5% 13% 30% 26% 2	1898
	11th to 20th	Day	29% 5% 14% 32% 18% 3	1864
	21st to end	Day	31% 4 13% 34% 15% 4	1680
December	1st to 10th	Day	28% 7% 16% 37% 11% 1	2700
	11th to 20th	Day	27% 4 22% 35% 13%	3104
	21st to end	Day	39% 7% 14% 24% 14% 2	4092
January	1st to 10th	Night	40% 7% 19% 24% 10% 1	8202
	11th to 20th	Night	32% 8% 17% 26% 17% 1	7752
	21st to end	Night	36% 5% 13% 22% 22% 3	8370
February	1st to 10th	Night	38% 10% 15% 24% 11% 2	2730
	11th to 20th	Night	43% 8% 11% 25% 13% 1	2531
	21st to end	Night	41% 7% 9% 23% 18% 2	1980
March	1st to 10th	Night	36% 7% 8% 25% 22% 1	5121
	11th to 20th	Night	27% 6% 12% 36% 18% 2	5000
	21st to end	Night	39% 9% 18% 28% 5% 1	5337
April	1st to 10th	Night	35% 8% 11% 25% 18% 3	2000
	11th to 20th	Night	37% 6% 12% 24% 19% 2	1977
	21st to end	Night	34% 6% 11% 28% 20% 1	2000
May	1st to 10th	Night	30% 9% 16% 30% 13% 2	4234
	11th to 20th	Night	27% 10% 12% 33% 16% 3	3625
	21st to end	Night	19% 7% 15% 29% 26% 4	3972
June	1st to 10th	Night	17% 5% 14% 27% 27% 9%	1600
	11th to 20th	Night	19% 5% 9% 18% 24% 25%	1600
	21st to end	Night	13% 5% 9% 22% 27% 25%	1600
July	1st to 10th	Night	20% 7% 8% 15% 18% 33%	3600
	11th to 20th	Night	18% 7% 20% 29% 17% 9%	3592
	21st to end	Night	18% 6% 18% 27% 16% 15%	4342
August	1st to 10th	Night	25% 8% 23% 20% 15% 10%	2928
	11th to 20th	Night	21% 8% 20% 17% 21% 11%	3077
	21st to end	Night	23% 8% 15% 19% 26% 9%	3597
September	1st to 10th	Night	21% 5% 11% 19% 27% 18%	2000
	11th to 20th	Night	19% 5% 14% 22% 28% 12%	2000
	21st to end	Night	19% 4 9% 26% 33% 9%	2261
October	1st to 10th	Night	14% 3 6% 28% 37% 11%	3920
	11th to 20th	Night	16% 4 14% 41% 22% 4	3898
	21st to end	Night	20% 4 9% 41% 23% 3	4252
November	1st to 10th	Night	22% 5% 12% 33% 26% 3	2598
	11th to 20th	Night	29% 4 13% 32% 19% 2	2753
	21st to end	Night	30% 5% 12% 32% 19% 2	2940
December	1st to 10th	Night	26% 5% 20% 38% 12% 1	4710
	11th to 20th	Night	26% 7% 19% 37% 11%	5322
	21st to end	Night	38% 10% 14% 22% 15% 1	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	12% 15% 31% 26% 13% 3	330
	11th to 20th	Day	9% 9% 40% 33% 8% 1	330
	21st to end	Day	5% 7% 42% 34% 12%	363
February	1st to 10th	Day	13% 20% 36% 25% 5% 2	330
	11th to 20th	Day	11% 23% 34% 26% 4 1	315
	21st to end	Day	16% 21% 34% 22% 7%	249
March	1st to 10th	Day	12% 21% 35% 23% 8% 1	405
	11th to 20th	Day	9% 23% 36% 23% 8% 1	500
	21st to end	Day	12% 30% 36% 17% 5% 1	550
April	1st to 10th	Day	14% 25% 34% 19% 7% 2	500
	11th to 20th	Day	16% 31% 31% 16% 4 1	492
	21st to end	Day	13% 24% 36% 19% 7% 1	500
May	1st to 10th	Day	15% 24% 31% 21% 8% 1	503
	11th to 20th	Day	10% 15% 31% 28% 15% 1	715
	21st to end	Day	9% 15% 30% 30% 14% 2	789
June	1st to 10th	Day	5% 12% 27% 33% 20% 3	730
	11th to 20th	Day	6% 14% 31% 33% 15% 2	730
	21st to end	Day	3 11% 28% 34% 21% 2	730
July	1st to 10th	Day	4 5% 22% 34% 30% 5%	721
	11th to 20th	Day	3 5% 20% 36% 32% 5%	717
	21st to end	Day	5% 5% 22% 39% 24% 5%	575
August	1st to 10th	Day	6% 7% 29% 31% 21% 5%	527
	11th to 20th	Day	3 6% 22% 40% 21% 7%	517
	21st to end	Day	3 8% 25% 34% 23% 6%	583
September	1st to 10th	Day	5% 8% 26% 31% 23% 8%	530
	11th to 20th	Day	6% 11% 35% 27% 17% 4	530
	21st to end	Day	6% 13% 26% 28% 20% 7%	392
October	1st to 10th	Day	9% 12% 25% 25% 22% 7%	330
	11th to 20th	Day	9% 18% 28% 25% 17% 3	330
	21st to end	Day	10% 17% 31% 28% 13% 2	363
November	1st to 10th	Day	13% 16% 31% 28% 10% 1	330
	11th to 20th	Day	8% 16% 35% 32% 8% 2	330
	21st to end	Day	6% 14% 34% 36% 9%	330
December	1st to 10th	Day	11% 13% 34% 28% 12% 2	330
	11th to 20th	Day	7% 13% 38% 31% 9% 1	330
	21st to end	Day	13% 15% 36% 29% 7% 1	363
January	1st to 10th	Night	5% 13% 29% 38% 14% 1	1050
	11th to 20th	Night	5% 9% 33% 39% 13% 1	877
	21st to end	Night	6% 7% 31% 43% 12% 2	924
February	1st to 10th	Night	6% 11% 37% 37% 9% 1	840
	11th to 20th	Night	4 11% 39% 36% 9%	804
	21st to end	Night	7% 10% 40% 38% 5%	660
March	1st to 10th	Night	5% 10% 35% 41% 9%	800
	11th to 20th	Night	5% 8% 31% 44% 13%	800
	21st to end	Night	6% 10% 34% 39% 10%	818
April	1st to 10th	Night	8% 11% 35% 40% 7%	600
	11th to 20th	Night	10% 11% 34% 36% 9% 1	593
	21st to end	Night	9% 9% 31% 37% 13% 1	600
May	1st to 10th	Night	9% 8% 27% 43% 12% 1	600
	11th to 20th	Night	7% 5% 22% 47% 18% 1	591
	21st to end	Night	6% 9% 22% 39% 22% 2	650
June	1st to 10th	Night	3 5% 18% 49% 25% 1	600
	11th to 20th	Night	4 5% 23% 49% 18% 1	600
	21st to end	Night	2 3 18% 48% 28% 1	600
July	1st to 10th	Night	5% 1 9% 43% 39% 3	585
	11th to 20th	Night	1 2 7% 45% 42% 3	582
	21st to end	Night	3 1 6% 41% 47% 2	657
August	1st to 10th	Night	6% 2 9% 42% 40% 1	597
	11th to 20th	Night	3 2 8% 53% 32% 2	594
	21st to end	Night	4 2 9% 45% 36% 3	660
September	1st to 10th	Night	4 2 12% 51% 30% 3	600
	11th to 20th	Night	4 2 17% 48% 26% 3	600
	21st to end	Night	4 4 19% 41% 29% 3	725
October	1st to 10th	Night	5% 6% 22% 46% 18% 3	800
	11th to 20th	Night	4 7% 29% 42% 17% 1	800
	21st to end	Night	9% 6% 28% 41% 14% 2	880
November	1st to 10th	Night	6% 7% 34% 36% 16% 1	958
	11th to 20th	Night	6% 11% 33% 37% 11% 2	1050
	21st to end	Night	7% 9% 29% 42% 13% 1	1050
December	1st to 10th	Night	8% 9% 31% 40% 12%	1050
	11th to 20th	Night	7% 11% 34% 36% 12%	1050
	21st to end	Night	8% 11% 34% 38% 8% 1	1155

Page generated at 2026-02-12 23:42:15. Version ac07

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