Eagle
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Eagle clear sky chart from 2005-11-06 to 2026-07-01.

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	7% 6% 2 5% 4 3 4 3 5% 6% 54%	146303
	Night	10% 7% 2 6% 4 4 4 3 5% 7% 49%	143376
Transparency	Day	29% 7% 11% 20% 20% 13%	141075
	Night	34% 7% 12% 19% 17% 10%	139604
Seeing	Day	9% 9% 22% 29% 23% 8%	16530
	Night	13% 5% 19% 38% 22% 3	25843

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	16% 18% 4 10% 6% 6% 5% 5% 7% 6% 18%	4722
	11th to 20th	Day	9% 8% 3 8% 4 4 4 3 6% 9% 41%	4740
	21st to end	Day	12% 10% 4 10% 5% 5% 4 4 4 6% 37%	5187
February	1st to 10th	Day	13% 13% 4 8% 6% 4 5% 3 5% 6% 33%	1848
	11th to 20th	Day	12% 13% 3 7% 5% 4 3 5% 6% 7% 34%	2050
	21st to end	Day	11% 12% 4 7% 7% 4 4 3 6% 6% 36%	1730
March	1st to 10th	Day	7% 10% 4 10% 7% 6% 5% 4 7% 8% 33%	4618
	11th to 20th	Day	8% 10% 3 6% 5% 4 4 3 5% 6% 47%	4902
	21st to end	Day	9% 11% 3 8% 6% 6% 6% 5% 7% 8% 32%	5876
April	1st to 10th	Day	10% 9% 2 6% 4 5% 4 4 7% 8% 42%	2520
	11th to 20th	Day	8% 8% 2 6% 5% 4 4 4 5% 8% 46%	2530
	21st to end	Day	9% 6% 2 5% 4 4 4 4 5% 7% 50%	2730
May	1st to 10th	Day	6% 5% 1 3 3 3 3 3 5% 6% 62%	7626
	11th to 20th	Day	6% 4 1 4 3 3 3 3 5% 7% 62%	7874
	21st to end	Day	4 3 1 3 3 3 3 3 6% 8% 62%	8992
June	1st to 10th	Day	9% 5% 2 5% 4 4 4 4 6% 8% 48%	2940
	11th to 20th	Day	7% 4 1 4 2 3 4 4 5% 7% 59%	2940
	21st to end	Day	3 3 1 3 2 3 3 3 4 5% 70%	2940
July	1st to 10th	Day	2 1 1 2 2 2 2 2 3 4 81%	6320
	11th to 20th	Day	1 1 1 2 1 1 2 1 2 4 83%	6320
	21st to end	Day	3 3 1 2 2 2 3 3 5% 7% 71%	6880
August	1st to 10th	Day	3 3 1 4 2 3 3 3 5% 7% 66%	5997
	11th to 20th	Day	2 1 1 2 2 2 2 2 3 4 82%	5798
	21st to end	Day	4 3 1 4 3 2 3 2 4 4 69%	5990
September	1st to 10th	Day	3 2 1 3 2 2 3 2 4 5% 74%	2400
	11th to 20th	Day	5% 4 1 3 3 3 3 3 4 6% 66%	2222
	21st to end	Day	6% 3 1 4 3 2 3 2 4 6% 67%	2200
October	1st to 10th	Day	5% 4 1 4 3 3 3 2 3 4 69%	3600
	11th to 20th	Day	8% 4 2 5% 4 3 4 4 5% 7% 55%	3124
	21st to end	Day	7% 7% 2 6% 4 4 4 3 5% 7% 50%	3200
November	1st to 10th	Day	14% 8% 2 6% 4 3 4 4 5% 7% 41%	1854
	11th to 20th	Day	16% 9% 3 6% 5% 5% 5% 4 6% 7% 34%	1890
	21st to end	Day	12% 8% 4 8% 6% 5% 5% 4 6% 9% 34%	1843
December	1st to 10th	Day	11% 6% 2 7% 4 3 4 3 6% 9% 45%	2700
	11th to 20th	Day	17% 14% 5% 11% 6% 5% 5% 4 5% 7% 20%	3108
	21st to end	Day	18% 12% 4 10% 6% 5% 4 4 6% 7% 24%	4092
January	1st to 10th	Night	19% 16% 4 11% 5% 5% 5% 4 6% 6% 19%	8172
	11th to 20th	Night	13% 9% 3 6% 3 4 3 2 5% 9% 43%	8220
	21st to end	Night	11% 8% 3 8% 4 4 4 4 5% 8% 41%	8994
February	1st to 10th	Night	18% 11% 4 7% 5% 5% 4 4 4 6% 33%	2766
	11th to 20th	Night	14% 11% 3 6% 5% 5% 4 4 6% 7% 35%	2458
	21st to end	Night	14% 11% 4 7% 6% 4 4 4 5% 7% 34%	2076
March	1st to 10th	Night	10% 11% 3 7% 4 4 4 4 6% 9% 37%	5496
	11th to 20th	Night	13% 12% 3 6% 4 3 3 3 4 5% 44%	5318
	21st to end	Night	11% 9% 3 8% 5% 5% 6% 5% 6% 9% 34%	5324
April	1st to 10th	Night	12% 7% 2 5% 3 4 5% 3 6% 7% 46%	2100
	11th to 20th	Night	11% 8% 2 5% 5% 5% 4 4 5% 5% 47%	2036
	21st to end	Night	8% 5% 2 6% 4 4 3 4 6% 7% 52%	1890
May	1st to 10th	Night	8% 3 1 3 2 2 3 3 5% 7% 62%	5321
	11th to 20th	Night	5% 4 2 5% 3 3 4 3 5% 7% 59%	4998
	21st to end	Night	4 4 1 4 3 4 3 3 6% 6% 61%	5181
June	1st to 10th	Night	10% 5% 2 5% 5% 4 3 3 7% 9% 47%	1680
	11th to 20th	Night	7% 4 1 4 3 3 4 3 4 6% 60%	1680
	21st to end	Night	3 3 1 3 3 4 4 3 4 6% 67%	1680
July	1st to 10th	Night	2 2 1 2 2 2 3 2 4 4 77%	3640
	11th to 20th	Night	1 1 1 1 2 2 2 3 4 83%	3640
	21st to end	Night	2 2 1 4 4 4 5% 4 6% 7% 61%	3970
August	1st to 10th	Night	2 3 1 4 3 4 4 3 5% 7% 64%	3802
	11th to 20th	Night	1 1 1 2 1 2 2 2 3 5% 80%	4051
	21st to end	Night	5% 3 1 4 2 3 3 2 4 5% 69%	5005
September	1st to 10th	Night	3 2 1 2 3 2 2 2 4 5% 75%	2000
	11th to 20th	Night	6% 3 1 4 3 3 2 3 4 7% 64%	2176
	21st to end	Night	7% 3 1 3 2 2 3 2 4 5% 67%	2200
October	1st to 10th	Night	4 3 1 3 3 3 3 2 4 4 70%	3600
	11th to 20th	Night	7% 4 2 4 3 3 3 3 5% 6% 61%	4013
	21st to end	Night	11% 6% 2 5% 3 4 3 4 6% 7% 48%	4600
November	1st to 10th	Night	15% 7% 3 6% 4 3 4 3 4 7% 44%	2665
	11th to 20th	Night	19% 7% 3 7% 4 4 3 4 5% 7% 37%	2730
	21st to end	Night	14% 9% 2 6% 4 4 4 3 5% 7% 42%	2772
December	1st to 10th	Night	12% 7% 2 5% 3 3 3 2 6% 10% 46%	4700
	11th to 20th	Night	19% 14% 4 10% 6% 5% 5% 4 7% 6% 21%	5316
	21st to end	Night	17% 11% 4 10% 6% 5% 5% 4 6% 8% 24%	7106

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	59% 15% 16% 9% 1	4723
	11th to 20th	Day	38% 12% 23% 23% 5%	4740
	21st to end	Day	47% 10% 15% 22% 6% 1	5187
February	1st to 10th	Day	51% 11% 19% 15% 4 1	1848
	11th to 20th	Day	46% 12% 17% 19% 6%	2060
	21st to end	Day	46% 9% 16% 19% 9% 1	1730
March	1st to 10th	Day	40% 11% 17% 22% 10% 1	4618
	11th to 20th	Day	35% 7% 12% 34% 12% 1	4902
	21st to end	Day	42% 12% 20% 18% 8% 1	5876
April	1st to 10th	Day	37% 8% 17% 23% 12% 2	2520
	11th to 20th	Day	33% 8% 13% 24% 17% 4	2533
	21st to end	Day	32% 7% 14% 27% 18% 3	2730
May	1st to 10th	Day	20% 5% 7% 24% 34% 9%	7626
	11th to 20th	Day	21% 5% 7% 26% 31% 10%	7877
	21st to end	Day	17% 6% 11% 28% 30% 8%	8994
June	1st to 10th	Day	31% 9% 12% 24% 21% 4	2940
	11th to 20th	Day	22% 5% 9% 23% 28% 12%	2940
	21st to end	Day	15% 4 8% 18% 31% 23%	2940
July	1st to 10th	Day	9% 2 4 10% 24% 52%	6252
	11th to 20th	Day	8% 2 2 6% 21% 60%	6245
	21st to end	Day	13% 3 3 15% 32% 33%	6681
August	1st to 10th	Day	19% 4 6% 12% 25% 33%	4366
	11th to 20th	Day	9% 2 3 16% 36% 33%	4197
	21st to end	Day	14% 3 4 18% 35% 27%	4317
September	1st to 10th	Day	13% 3 6% 18% 30% 30%	2400
	11th to 20th	Day	19% 5% 10% 23% 28% 15%	2222
	21st to end	Day	21% 3 8% 24% 33% 11%	2200
October	1st to 10th	Day	21% 4 7% 18% 40% 10%	3600
	11th to 20th	Day	28% 5% 11% 28% 24% 3	3124
	21st to end	Day	32% 6% 13% 29% 18% 1	3200
November	1st to 10th	Day	40% 9% 17% 25% 10%	1854
	11th to 20th	Day	46% 9% 20% 20% 4	1890
	21st to end	Day	45% 12% 21% 17% 5%	1843
December	1st to 10th	Day	35% 13% 24% 25% 3	2700
	11th to 20th	Day	59% 13% 18% 9% 1	3108
	21st to end	Day	55% 12% 17% 13% 3	4092
January	1st to 10th	Night	60% 13% 17% 9% 1	8172
	11th to 20th	Night	39% 10% 21% 24% 7%	8220
	21st to end	Night	41% 10% 16% 22% 9% 2	8994
February	1st to 10th	Night	50% 9% 18% 19% 3 1	2766
	11th to 20th	Night	45% 10% 17% 20% 8% 1	2459
	21st to end	Night	46% 9% 14% 19% 10% 1	2076
March	1st to 10th	Night	38% 9% 14% 26% 12% 1	5496
	11th to 20th	Night	41% 5% 7% 27% 19% 1	5318
	21st to end	Night	40% 12% 17% 22% 9%	5324
April	1st to 10th	Night	36% 6% 13% 26% 17% 3	2100
	11th to 20th	Night	35% 7% 11% 23% 21% 3	2036
	21st to end	Night	30% 6% 13% 26% 23% 3	1890
May	1st to 10th	Night	19% 5% 7% 21% 36% 12%	5319
	11th to 20th	Night	23% 5% 7% 24% 34% 8%	4998
	21st to end	Night	22% 6% 10% 25% 30% 8%	5182
June	1st to 10th	Night	33% 8% 11% 23% 22% 4	1680
	11th to 20th	Night	24% 5% 9% 20% 32% 11%	1680
	21st to end	Night	17% 5% 7% 17% 31% 24%	1680
July	1st to 10th	Night	12% 3 4 9% 18% 55%	3600
	11th to 20th	Night	7% 2 2 6% 20% 63%	3592
	21st to end	Night	18% 4 5% 12% 28% 33%	3857
August	1st to 10th	Night	21% 4 5% 11% 21% 37%	2761
	11th to 20th	Night	9% 3 4 11% 27% 46%	2928
	21st to end	Night	15% 3 3 12% 32% 35%	3598
September	1st to 10th	Night	14% 3 5% 13% 30% 35%	2000
	11th to 20th	Night	21% 4 7% 20% 25% 24%	2176
	21st to end	Night	20% 3 6% 19% 32% 19%	2200
October	1st to 10th	Night	18% 4 6% 19% 30% 23%	3600
	11th to 20th	Night	24% 4 11% 27% 29% 6%	4013
	21st to end	Night	33% 5% 11% 29% 20% 2	4600
November	1st to 10th	Night	39% 6% 14% 23% 17% 1	2665
	11th to 20th	Night	45% 7% 14% 25% 8%	2730
	21st to end	Night	41% 8% 19% 23% 8%	2772
December	1st to 10th	Night	34% 12% 28% 23% 4	4700
	11th to 20th	Night	59% 12% 17% 11% 2	5316
	21st to end	Night	52% 13% 18% 13% 4	7106

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	22% 13% 21% 24% 16% 4	220
	11th to 20th	Day	14% 10% 18% 32% 19% 7%	220
	21st to end	Day	14% 7% 17% 34% 22% 7%	242
February	1st to 10th	Day	19% 9% 29% 22% 17% 4	340
	11th to 20th	Day	17% 12% 28% 26% 15% 2	535
	21st to end	Day	17% 14% 27% 27% 13% 2	446
March	1st to 10th	Day	13% 16% 31% 26% 11% 2	540
	11th to 20th	Day	12% 13% 28% 28% 16% 2	540
	21st to end	Day	13% 16% 29% 26% 15% 2	594
April	1st to 10th	Day	13% 16% 21% 22% 21% 7%	540
	11th to 20th	Day	11% 15% 30% 23% 16% 4	532
	21st to end	Day	9% 14% 30% 27% 15% 4	540
May	1st to 10th	Day	5% 14% 29% 28% 17% 7%	543
	11th to 20th	Day	14% 9% 25% 27% 18% 6%	568
	21st to end	Day	7% 9% 17% 31% 23% 12%	617
June	1st to 10th	Day	7% 8% 23% 28% 23% 11%	570
	11th to 20th	Day	7% 10% 27% 32% 20% 5%	570
	21st to end	Day	5% 4 23% 32% 28% 8%	570
July	1st to 10th	Day	2 3 17% 39% 30% 8%	527
	11th to 20th	Day	1 3 21% 40% 29% 7%	524
	21st to end	Day	3 1 15% 36% 35% 10%	575
August	1st to 10th	Day	4 3 19% 36% 31% 8%	527
	11th to 20th	Day	3 1 15% 33% 36% 12%	517
	21st to end	Day	4 4 16% 31% 30% 15%	583
September	1st to 10th	Day	5% 3 12% 28% 34% 18%	530
	11th to 20th	Day	6% 4 15% 30% 30% 14%	530
	21st to end	Day	5% 5% 19% 29% 32% 10%	530
October	1st to 10th	Day	7% 8% 18% 23% 30% 13%	530
	11th to 20th	Day	10% 6% 22% 25% 26% 11%	420
	21st to end	Day	11% 10% 23% 28% 23% 6%	363
November	1st to 10th	Day	15% 8% 22% 28% 21% 5%	330
	11th to 20th	Day	15% 9% 20% 30% 20% 5%	330
	21st to end	Day	13% 5% 20% 34% 23% 5%	305
December	1st to 10th	Day	21% 4 17% 27% 18% 12%	220
	11th to 20th	Day	21% 10% 22% 28% 15% 5%	220
	21st to end	Day	19% 11% 24% 28% 14% 4	242
January	1st to 10th	Night	22% 8% 20% 28% 19% 2	840
	11th to 20th	Night	18% 6% 19% 32% 23% 3	840
	21st to end	Night	17% 4 16% 36% 24% 3	924
February	1st to 10th	Night	22% 6% 20% 33% 17% 2	840
	11th to 20th	Night	16% 5% 24% 36% 18% 2	824
	21st to end	Night	16% 8% 26% 35% 14% 2	692
March	1st to 10th	Night	15% 9% 27% 34% 14% 1	840
	11th to 20th	Night	15% 9% 21% 38% 15% 2	840
	21st to end	Night	15% 9% 26% 37% 12% 2	924
April	1st to 10th	Night	13% 8% 21% 38% 18% 2	840
	11th to 20th	Night	11% 9% 28% 33% 16% 2	788
	21st to end	Night	10% 9% 23% 42% 15% 2	630
May	1st to 10th	Night	8% 8% 24% 39% 19% 1	630
	11th to 20th	Night	10% 6% 23% 34% 24% 3	519
	21st to end	Night	8% 5% 18% 36% 27% 5%	455
June	1st to 10th	Night	11% 5% 17% 40% 25% 3	420
	11th to 20th	Night	7% 6% 24% 38% 24% 1	420
	21st to end	Night	3 1 19% 45% 30% 2	420
July	1st to 10th	Night	2 2 14% 49% 32% 2	390
	11th to 20th	Night	1 1 14% 57% 27%	388
	21st to end	Night	3 1 13% 47% 36% 1	438
August	1st to 10th	Night	4 1 13% 50% 31% 1	493
	11th to 20th	Night	1 2 10% 50% 36% 2	594
	21st to end	Night	4 2 13% 45% 31% 5%	870
September	1st to 10th	Night	3 1 11% 43% 38% 5%	800
	11th to 20th	Night	6% 2 11% 36% 39% 6%	800
	21st to end	Night	8% 3 15% 37% 29% 9%	800
October	1st to 10th	Night	8% 3 17% 40% 27% 5%	800
	11th to 20th	Night	9% 4 17% 38% 27% 6%	800
	21st to end	Night	11% 4 19% 39% 23% 4	880
November	1st to 10th	Night	15% 6% 19% 35% 24% 2	820
	11th to 20th	Night	19% 6% 19% 37% 16% 3	840
	21st to end	Night	18% 4 17% 36% 21% 5%	840
December	1st to 10th	Night	20% 5% 17% 36% 18% 4	840
	11th to 20th	Night	23% 7% 15% 37% 15% 2	840
	21st to end	Night	26% 7% 23% 31% 11% 2	924

Page generated at 2026-06-28 00:10:47. Version ac07

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