Rutenbeck Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Rutenbeck Observatory clear sky chart from 2005-11-06 to 2025-12-18.

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	12% 8% 3 8% 5% 4 4 4 6% 7% 38%	127490
	Night	13% 9% 3 8% 5% 4 4 3 5% 6% 39%	123793
Transparency	Day	43% 6% 12% 24% 13% 2	130998
	Night	44% 6% 11% 23% 15% 2	128358
Seeing	Day	16% 10% 28% 26% 15% 5%	17357
	Night	17% 9% 31% 31% 12% 1	27223

By Month

Percentage Cloud Cover SE (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	8% 12% 7% 16% 7% 6% 5% 4 4 5% 25%	3617
	11th to 20th	Day	8% 10% 5% 11% 7% 6% 6% 6% 8% 6% 27%	3620
	21st to end	Day	13% 14% 7% 9% 5% 4 4 3 5% 6% 29%	4396
February	1st to 10th	Day	12% 14% 5% 9% 6% 5% 5% 4 4 6% 28%	1800
	11th to 20th	Day	14% 10% 2 7% 6% 6% 5% 3 5% 7% 35%	1866
	21st to end	Day	12% 13% 4 10% 5% 3 4 3 5% 8% 33%	1650
March	1st to 10th	Day	18% 9% 3 6% 4 3 2 2 4 5% 44%	4480
	11th to 20th	Day	10% 6% 2 6% 4 4 5% 4 6% 7% 46%	4934
	21st to end	Day	20% 12% 5% 11% 5% 4 4 4 5% 6% 25%	5819
April	1st to 10th	Day	16% 11% 3 8% 5% 4 4 4 4 7% 33%	2400
	11th to 20th	Day	16% 9% 3 8% 5% 5% 5% 3 5% 7% 35%	2374
	21st to end	Day	21% 9% 3 7% 4 4 4 4 5% 6% 34%	2400
May	1st to 10th	Day	14% 8% 3 8% 4 4 5% 4 6% 7% 37%	6073
	11th to 20th	Day	15% 6% 2 6% 4 4 4 4 6% 7% 42%	6319
	21st to end	Day	12% 6% 3 7% 5% 4 5% 4 7% 9% 38%	6935
June	1st to 10th	Day	9% 5% 2 5% 5% 4 5% 5% 7% 8% 45%	2800
	11th to 20th	Day	10% 5% 2 6% 4 4 5% 4 6% 9% 45%	2800
	21st to end	Day	10% 6% 3 6% 6% 4 5% 4 6% 8% 41%	2800
July	1st to 10th	Day	8% 7% 3 7% 5% 5% 5% 4 7% 10% 37%	6360
	11th to 20th	Day	8% 6% 2 6% 4 4 4 4 6% 9% 45%	6360
	21st to end	Day	10% 6% 3 8% 5% 5% 5% 5% 7% 10% 37%	6924
August	1st to 10th	Day	7% 5% 2 6% 4 4 5% 5% 8% 10% 43%	4310
	11th to 20th	Day	10% 5% 2 6% 4 4 5% 4 6% 10% 43%	3952
	21st to end	Day	7% 6% 2 6% 4 4 5% 3 6% 9% 50%	4312
September	1st to 10th	Day	12% 4 2 5% 4 3 4 4 6% 8% 48%	2400
	11th to 20th	Day	10% 4 2 3 3 4 3 3 5% 7% 55%	2367
	21st to end	Day	9% 5% 2 6% 4 3 4 3 6% 7% 49%	2195
October	1st to 10th	Day	12% 6% 3 5% 3 4 3 4 5% 6% 49%	2000
	11th to 20th	Day	16% 8% 3 6% 4 4 4 3 4 7% 40%	2000
	21st to end	Day	19% 8% 3 6% 4 3 4 2 5% 6% 41%	2080
November	1st to 10th	Day	12% 8% 3 5% 4 4 3 4 5% 7% 44%	1852
	11th to 20th	Day	14% 13% 4 9% 5% 4 4 3 5% 7% 33%	1879
	21st to end	Day	16% 13% 4 9% 5% 3 4 3 5% 5% 35%	1680
December	1st to 10th	Day	9% 9% 3 9% 4 4 4 3 6% 7% 42%	2690
	11th to 20th	Day	15% 14% 6% 13% 6% 6% 5% 4 5% 5% 22%	3064
	21st to end	Day	21% 22% 8% 14% 6% 4 3 2 3 5% 13%	3982
January	1st to 10th	Night	10% 12% 6% 15% 5% 5% 4 3 4 5% 31%	6348
	11th to 20th	Night	11% 14% 5% 12% 8% 6% 5% 5% 6% 4 23%	6360
	21st to end	Night	14% 15% 6% 9% 5% 4 3 3 4 5% 32%	6564
February	1st to 10th	Night	14% 13% 4 7% 6% 5% 4 3 4 5% 34%	2600
	11th to 20th	Night	13% 10% 3 8% 5% 4 5% 3 5% 5% 40%	2421
	21st to end	Night	15% 12% 4 7% 4 4 3 2 4 6% 39%	1980
March	1st to 10th	Night	18% 9% 3 5% 3 3 4 3 4 5% 43%	5373
	11th to 20th	Night	9% 6% 2 6% 4 4 3 3 5% 7% 50%	5054
	21st to end	Night	18% 12% 5% 11% 5% 5% 4 3 4 5% 26%	5110
April	1st to 10th	Night	17% 10% 2 6% 4 4 3 3 5% 6% 40%	2000
	11th to 20th	Night	17% 8% 3 6% 5% 3 3 3 4 6% 40%	1975
	21st to end	Night	16% 9% 3 7% 5% 5% 4 3 5% 7% 35%	2000
May	1st to 10th	Night	18% 7% 2 8% 5% 5% 4 4 5% 6% 37%	3828
	11th to 20th	Night	12% 5% 2 6% 5% 5% 5% 4 5% 7% 43%	3596
	21st to end	Night	12% 7% 2 6% 3 4 5% 3 6% 8% 43%	3942
June	1st to 10th	Night	7% 5% 2 5% 5% 4 5% 4 6% 8% 49%	1600
	11th to 20th	Night	8% 6% 2 6% 5% 4 4 4 8% 9% 44%	1600
	21st to end	Night	10% 5% 2 6% 5% 6% 5% 4 6% 8% 44%	1600
July	1st to 10th	Night	12% 5% 3 7% 5% 4 5% 3 7% 8% 41%	3618
	11th to 20th	Night	7% 5% 2 6% 3 3 4 4 6% 8% 52%	3617
	21st to end	Night	8% 6% 3 6% 5% 4 5% 5% 6% 9% 44%	3947
August	1st to 10th	Night	4 4 2 5% 5% 4 5% 4 7% 8% 53%	2847
	11th to 20th	Night	6% 5% 2 6% 4 3 4 4 6% 8% 53%	3100
	21st to end	Night	8% 4 2 5% 4 4 4 3 5% 8% 53%	3586
September	1st to 10th	Night	9% 5% 2 4 3 3 4 2 4 7% 57%	2000
	11th to 20th	Night	9% 4 1 5% 4 4 4 3 6% 8% 52%	2012
	21st to end	Night	8% 5% 2 6% 4 4 4 3 5% 7% 52%	2201
October	1st to 10th	Night	11% 5% 2 5% 4 3 3 2 4 7% 54%	2400
	11th to 20th	Night	15% 8% 3 6% 4 3 3 3 4 6% 46%	2400
	21st to end	Night	19% 8% 3 7% 4 3 4 3 4 6% 38%	2759
November	1st to 10th	Night	11% 7% 2 6% 3 3 3 3 5% 6% 51%	2666
	11th to 20th	Night	15% 10% 4 7% 4 4 3 3 5% 5% 38%	2735
	21st to end	Night	17% 10% 4 8% 5% 3 4 3 4 5% 37%	2940
December	1st to 10th	Night	10% 8% 3 8% 5% 4 5% 3 5% 6% 42%	4720
	11th to 20th	Night	16% 14% 5% 9% 4 3 4 3 4 5% 31%	5298
	21st to end	Night	22% 19% 5% 12% 6% 5% 4 4 4 4 15%	6996

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	60% 5% 10% 17% 7%	3618
	11th to 20th	Day	53% 5% 12% 11% 16% 2	3620
	21st to end	Day	55% 5% 15% 17% 7%	4396
February	1st to 10th	Day	56% 5% 13% 17% 8% 1	1800
	11th to 20th	Day	48% 6% 12% 23% 10% 2	1875
	21st to end	Day	49% 7% 12% 22% 9% 2	1650
March	1st to 10th	Day	43% 5% 11% 28% 10% 3	4480
	11th to 20th	Day	36% 6% 12% 33% 13%	4934
	21st to end	Day	58% 8% 12% 16% 6% 1	5821
April	1st to 10th	Day	51% 7% 12% 21% 9%	2400
	11th to 20th	Day	48% 6% 11% 22% 12% 2	2374
	21st to end	Day	48% 8% 12% 19% 12% 2	2400
May	1st to 10th	Day	43% 7% 10% 21% 17% 1	6108
	11th to 20th	Day	39% 7% 11% 27% 14% 2	6323
	21st to end	Day	40% 8% 12% 26% 11% 3	6949
June	1st to 10th	Day	33% 9% 14% 25% 16% 2	2800
	11th to 20th	Day	35% 6% 13% 23% 20% 3	2800
	21st to end	Day	39% 9% 13% 25% 13% 2	2800
July	1st to 10th	Day	40% 7% 13% 27% 11% 1	6291
	11th to 20th	Day	35% 7% 15% 28% 15% 1	6285
	21st to end	Day	39% 9% 17% 19% 14% 1	6728
August	1st to 10th	Day	32% 9% 18% 27% 13% 1	4295
	11th to 20th	Day	35% 7% 15% 28% 14% 1	3990
	21st to end	Day	31% 6% 12% 32% 17% 2	4311
September	1st to 10th	Day	33% 7% 11% 27% 19% 3	2400
	11th to 20th	Day	28% 6% 13% 30% 20% 3	2367
	21st to end	Day	33% 6% 11% 29% 19% 2	2195
October	1st to 10th	Day	23% 4 6% 32% 34% 1	3260
	11th to 20th	Day	29% 4 11% 24% 28% 3	3240
	21st to end	Day	40% 4 10% 29% 14% 3	3344
November	1st to 10th	Day	39% 6% 14% 26% 12% 2	1852
	11th to 20th	Day	51% 5% 13% 21% 10% 1	1879
	21st to end	Day	53% 5% 14% 20% 8%	1680
December	1st to 10th	Day	41% 5% 16% 30% 7% 1	2690
	11th to 20th	Day	62% 6% 12% 14% 6% 1	3061
	21st to end	Day	76% 4 7% 8% 4	3982
January	1st to 10th	Night	54% 5% 12% 20% 8%	6348
	11th to 20th	Night	60% 5% 12% 10% 13%	6360
	21st to end	Night	54% 5% 11% 18% 11% 1	6564
February	1st to 10th	Night	52% 5% 12% 19% 12% 1	2600
	11th to 20th	Night	46% 5% 11% 24% 13% 1	2422
	21st to end	Night	47% 5% 13% 21% 13% 2	1980
March	1st to 10th	Night	44% 5% 10% 23% 14% 4	5373
	11th to 20th	Night	34% 5% 10% 31% 17% 3	5054
	21st to end	Night	59% 6% 9% 16% 8% 1	5110
April	1st to 10th	Night	44% 6% 11% 24% 14% 2	2000
	11th to 20th	Night	45% 5% 9% 21% 16% 4	1975
	21st to end	Night	47% 7% 11% 21% 12% 2	2000
May	1st to 10th	Night	46% 8% 10% 16% 18% 3	3855
	11th to 20th	Night	37% 9% 12% 23% 16% 3	3597
	21st to end	Night	37% 8% 11% 27% 14% 2	3950
June	1st to 10th	Night	29% 9% 15% 25% 19% 3	1600
	11th to 20th	Night	33% 7% 11% 23% 23% 3	1600
	21st to end	Night	36% 10% 12% 21% 17% 4	1600
July	1st to 10th	Night	39% 6% 13% 24% 15% 2	3580
	11th to 20th	Night	31% 6% 13% 31% 18% 1	3572
	21st to end	Night	35% 9% 18% 21% 15% 3	3832
August	1st to 10th	Night	26% 9% 16% 31% 18% 2	2838
	11th to 20th	Night	29% 8% 15% 31% 17% 1	3128
	21st to end	Night	29% 7% 11% 30% 19% 4	3586
September	1st to 10th	Night	27% 6% 11% 26% 27% 3	2000
	11th to 20th	Night	29% 6% 10% 30% 20% 4	2012
	21st to end	Night	32% 6% 10% 28% 21% 3	2201
October	1st to 10th	Night	23% 4 7% 34% 31% 2	3920
	11th to 20th	Night	30% 4 9% 22% 31% 4	3899
	21st to end	Night	44% 4 8% 24% 17% 3	4445
November	1st to 10th	Night	35% 6% 11% 27% 18% 3	2666
	11th to 20th	Night	47% 4 12% 23% 13% 1	2735
	21st to end	Night	49% 5% 11% 24% 10% 1	2940
December	1st to 10th	Night	42% 4 15% 30% 8% 1	4720
	11th to 20th	Night	54% 5% 13% 20% 7%	5300
	21st to end	Night	71% 6% 8% 11% 4	6996

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	18% 12% 34% 26% 10% 1	300
	11th to 20th	Day	20% 15% 43% 17% 5%	300
	21st to end	Day	19% 12% 38% 24% 6% 1	330
February	1st to 10th	Day	20% 16% 37% 22% 5%	300
	11th to 20th	Day	22% 21% 31% 21% 6%	300
	21st to end	Day	20% 16% 44% 15% 5%	249
March	1st to 10th	Day	17% 19% 41% 18% 6%	300
	11th to 20th	Day	23% 19% 32% 20% 6% 1	300
	21st to end	Day	27% 16% 34% 17% 5% 2	480
April	1st to 10th	Day	24% 14% 34% 22% 6%	500
	11th to 20th	Day	22% 17% 28% 20% 10% 2	492
	21st to end	Day	25% 13% 31% 21% 9% 1	500
May	1st to 10th	Day	19% 11% 32% 27% 9% 3	595
	11th to 20th	Day	21% 11% 28% 24% 14% 3	725
	21st to end	Day	15% 12% 26% 25% 15% 6%	789
June	1st to 10th	Day	9% 7% 26% 33% 19% 6%	730
	11th to 20th	Day	10% 5% 31% 33% 18% 4	730
	21st to end	Day	12% 8% 28% 31% 16% 5%	730
July	1st to 10th	Day	10% 4 16% 31% 25% 14%	721
	11th to 20th	Day	10% 5% 22% 32% 22% 10%	718
	21st to end	Day	7% 2 21% 38% 26% 5%	794
August	1st to 10th	Day	6% 3 21% 33% 28% 9%	726
	11th to 20th	Day	12% 4 18% 29% 24% 12%	586
	21st to end	Day	8% 4 17% 35% 26% 10%	583
September	1st to 10th	Day	13% 7% 20% 28% 23% 9%	530
	11th to 20th	Day	7% 3 18% 37% 25% 10%	530
	21st to end	Day	10% 9% 28% 25% 20% 7%	525
October	1st to 10th	Day	14% 8% 28% 27% 19% 4	330
	11th to 20th	Day	20% 20% 33% 19% 7% 1	330
	21st to end	Day	26% 15% 29% 23% 4 1	363
November	1st to 10th	Day	18% 15% 35% 20% 9% 4	330
	11th to 20th	Day	25% 18% 33% 15% 7% 2	330
	21st to end	Day	26% 14% 33% 22% 5%	330
December	1st to 10th	Day	15% 15% 42% 20% 7% 2	330
	11th to 20th	Day	19% 12% 40% 22% 8%	321
	21st to end	Day	29% 10% 40% 18% 3	330
January	1st to 10th	Night	18% 12% 39% 26% 6%	1000
	11th to 20th	Night	18% 13% 37% 27% 5% 1	1000
	21st to end	Night	20% 13% 35% 28% 4	1100
February	1st to 10th	Night	22% 10% 39% 25% 4	1000
	11th to 20th	Night	19% 11% 38% 27% 4	866
	21st to end	Night	21% 11% 41% 23% 3 1	660
March	1st to 10th	Night	23% 10% 38% 24% 5%	800
	11th to 20th	Night	17% 10% 36% 31% 6%	635
	21st to end	Night	26% 10% 35% 24% 5%	660
April	1st to 10th	Night	23% 11% 37% 24% 4	600
	11th to 20th	Night	21% 13% 32% 27% 7% 1	593
	21st to end	Night	22% 10% 31% 30% 7% 1	600
May	1st to 10th	Night	17% 8% 35% 32% 8% 1	600
	11th to 20th	Night	17% 6% 31% 32% 13%	591
	21st to end	Night	13% 5% 29% 35% 16% 2	650
June	1st to 10th	Night	7% 5% 23% 48% 16% 1	600
	11th to 20th	Night	11% 3 29% 43% 14% 1	600
	21st to end	Night	10% 6% 28% 39% 16% 1	600
July	1st to 10th	Night	10% 3 13% 41% 30% 4	585
	11th to 20th	Night	8% 3 18% 41% 27% 3	582
	21st to end	Night	7% 1 15% 45% 29% 2	657
August	1st to 10th	Night	5% 2 15% 43% 31% 4	597
	11th to 20th	Night	6% 2 13% 42% 32% 5%	594
	21st to end	Night	9% 1 15% 45% 28% 3	660
September	1st to 10th	Night	10% 4 18% 38% 27% 4	600
	11th to 20th	Night	9% 3 21% 35% 28% 4	612
	21st to end	Night	10% 9% 26% 32% 23% 1	800
October	1st to 10th	Night	12% 7% 28% 34% 19% 1	800
	11th to 20th	Night	20% 12% 29% 27% 11%	800
	21st to end	Night	24% 11% 32% 25% 7%	880
November	1st to 10th	Night	17% 8% 39% 27% 9% 1	820
	11th to 20th	Night	20% 15% 36% 23% 6%	845
	21st to end	Night	22% 14% 33% 25% 7%	1050
December	1st to 10th	Night	21% 13% 37% 23% 6%	1050
	11th to 20th	Night	22% 12% 33% 27% 6%	1036
	21st to end	Night	28% 11% 34% 24% 3	1100

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