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Kopernik Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Kopernik Observatory clear sky chart from 2005-11-06 to 2025-11-03.

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	16% 11% 4 9% 5% 5% 5% 4 5% 7% 30%	127099
	Night	16% 11% 4 10% 6% 4 4 3 5% 6% 31%	122947
Transparency	Day	52% 6% 11% 20% 10% 1	130629
	Night	53% 5% 12% 18% 10% 1	127503
Seeing	Day	26% 17% 28% 18% 9% 3	16040
	Night	23% 15% 28% 24% 9% 1	25237

By Month

Percentage Cloud Cover NE (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	12% 15% 10% 23% 6% 3 3 2 3 5% 17%	3597
	11th to 20th	Day	13% 16% 9% 20% 7% 5% 4 3 4 4 15%	3593
	21st to end	Day	15% 14% 8% 11% 7% 4 4 4 4 5% 24%	4466
February	1st to 10th	Day	16% 14% 6% 13% 8% 5% 5% 3 4 5% 21%	1800
	11th to 20th	Day	12% 15% 7% 13% 8% 6% 5% 3 5% 6% 22%	1813
	21st to end	Day	17% 13% 4 13% 8% 4 4 3 5% 5% 24%	1650
March	1st to 10th	Day	19% 15% 6% 10% 6% 4 3 2 3 4 28%	4568
	11th to 20th	Day	12% 14% 5% 9% 5% 4 4 3 4 6% 35%	4980
	21st to end	Day	14% 12% 4 11% 6% 6% 5% 4 5% 5% 29%	5729
April	1st to 10th	Day	17% 15% 4 8% 5% 4 4 3 5% 6% 30%	2400
	11th to 20th	Day	16% 11% 3 8% 5% 5% 4 4 5% 6% 33%	2374
	21st to end	Day	18% 12% 3 7% 5% 4 4 3 5% 7% 34%	2400
May	1st to 10th	Day	29% 10% 3 7% 4 4 4 3 5% 6% 25%	6174
	11th to 20th	Day	19% 10% 3 9% 5% 5% 5% 3 6% 7% 28%	6318
	21st to end	Day	20% 9% 3 6% 4 4 4 5% 6% 8% 30%	6949
June	1st to 10th	Day	18% 7% 2 6% 5% 5% 5% 4 6% 9% 32%	2800
	11th to 20th	Day	16% 7% 3 7% 5% 5% 6% 5% 6% 8% 33%	2800
	21st to end	Day	13% 8% 3 6% 5% 5% 5% 4 7% 8% 35%	2800
July	1st to 10th	Day	8% 6% 2 7% 5% 6% 6% 5% 7% 10% 37%	6360
	11th to 20th	Day	8% 6% 3 8% 6% 6% 6% 6% 8% 11% 32%	6360
	21st to end	Day	12% 7% 2 6% 5% 5% 5% 4 6% 8% 39%	6888
August	1st to 10th	Day	18% 8% 3 7% 5% 5% 6% 4 5% 8% 32%	4234
	11th to 20th	Day	16% 8% 3 7% 5% 6% 5% 4 7% 9% 31%	4013
	21st to end	Day	14% 8% 3 7% 4 4 5% 4 6% 7% 38%	4312
September	1st to 10th	Day	16% 7% 3 7% 3 4 5% 4 5% 8% 40%	2400
	11th to 20th	Day	13% 6% 2 6% 4 4 4 4 5% 8% 43%	2400
	21st to end	Day	20% 8% 3 6% 4 4 5% 4 6% 6% 34%	2138
October	1st to 10th	Day	15% 9% 3 8% 4 5% 4 3 5% 7% 36%	2000
	11th to 20th	Day	16% 10% 3 7% 5% 4 5% 3 5% 7% 33%	2000
	21st to end	Day	21% 13% 3 7% 5% 5% 4 3 5% 6% 28%	2129
November	1st to 10th	Day	14% 11% 2 8% 5% 4 4 3 5% 7% 38%	1779
	11th to 20th	Day	15% 16% 4 9% 5% 4 4 3 5% 5% 31%	1729
	21st to end	Day	18% 16% 5% 9% 6% 4 5% 3 5% 7% 23%	1600
December	1st to 10th	Day	14% 15% 7% 15% 8% 6% 5% 3 5% 5% 17%	2600
	11th to 20th	Day	19% 14% 8% 11% 5% 4 3 2 3 5% 26%	2986
	21st to end	Day	17% 17% 6% 13% 7% 5% 5% 3 4 5% 18%	3960
January	1st to 10th	Night	13% 13% 7% 24% 8% 4 4 3 4 4 16%	6349
	11th to 20th	Night	10% 14% 8% 18% 7% 5% 4 3 5% 6% 19%	6288
	21st to end	Night	16% 13% 5% 14% 9% 6% 4 3 4 5% 20%	6490
February	1st to 10th	Night	15% 13% 5% 12% 7% 5% 6% 4 5% 5% 24%	2600
	11th to 20th	Night	13% 14% 6% 14% 8% 6% 5% 4 4 4 21%	2472
	21st to end	Night	18% 12% 3 13% 6% 5% 4 4 5% 6% 25%	1980
March	1st to 10th	Night	16% 11% 6% 10% 7% 4 4 3 4 4 29%	5255
	11th to 20th	Night	14% 14% 5% 9% 4 4 3 3 4 6% 35%	4979
	21st to end	Night	16% 13% 5% 11% 5% 5% 4 4 5% 5% 28%	5202
April	1st to 10th	Night	19% 12% 5% 8% 5% 4 4 3 4 7% 28%	2000
	11th to 20th	Night	20% 12% 3 7% 4 3 4 3 5% 6% 34%	1975
	21st to end	Night	18% 10% 3 6% 4 5% 4 3 5% 6% 37%	2000
May	1st to 10th	Night	30% 11% 3 7% 4 3 4 3 4 5% 26%	3806
	11th to 20th	Night	18% 9% 3 7% 4 4 4 4 6% 6% 34%	3575
	21st to end	Night	21% 10% 3 8% 4 5% 4 4 5% 6% 30%	3926
June	1st to 10th	Night	17% 8% 2 6% 5% 4 3 3 6% 9% 38%	1600
	11th to 20th	Night	15% 7% 2 5% 5% 5% 4 3 6% 9% 39%	1600
	21st to end	Night	11% 6% 2 6% 4 4 5% 4 5% 8% 44%	1600
July	1st to 10th	Night	10% 7% 3 8% 6% 5% 4 4 5% 10% 39%	3600
	11th to 20th	Night	11% 6% 2 6% 4 5% 6% 4 7% 9% 39%	3600
	21st to end	Night	12% 6% 2 6% 4 4 4 3 5% 7% 45%	3961
August	1st to 10th	Night	18% 7% 3 8% 5% 4 4 3 5% 7% 35%	2915
	11th to 20th	Night	15% 7% 3 8% 4 5% 4 3 4 6% 41%	3002
	21st to end	Night	12% 8% 2 6% 4 4 4 4 5% 7% 44%	3586
September	1st to 10th	Night	14% 7% 2 6% 4 4 4 4 5% 6% 45%	2000
	11th to 20th	Night	12% 5% 2 5% 4 3 4 3 4 7% 51%	2000
	21st to end	Night	16% 8% 2 6% 4 5% 5% 3 6% 7% 38%	2258
October	1st to 10th	Night	16% 8% 3 7% 5% 4 4 4 5% 6% 39%	2400
	11th to 20th	Night	18% 8% 3 6% 4 4 4 3 6% 7% 37%	2400
	21st to end	Night	21% 13% 3 8% 5% 3 3 3 5% 6% 30%	2710
November	1st to 10th	Night	12% 11% 3 8% 5% 4 4 3 5% 6% 39%	2564
	11th to 20th	Night	17% 11% 4 7% 5% 5% 4 4 5% 5% 32%	2670
	21st to end	Night	14% 14% 5% 8% 5% 4 5% 5% 6% 8% 27%	2800
December	1st to 10th	Night	12% 15% 7% 13% 7% 5% 4 4 6% 6% 21%	4580
	11th to 20th	Night	20% 15% 6% 9% 5% 3 3 3 4 4 28%	5208
	21st to end	Night	19% 17% 6% 11% 7% 4 4 3 4 4 20%	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	71% 3 9% 14% 3 1	3598
	11th to 20th	Day	72% 4 7% 10% 6% 1	3623
	21st to end	Day	61% 4 10% 16% 8%	4466
February	1st to 10th	Day	65% 6% 8% 14% 6% 1	1800
	11th to 20th	Day	64% 5% 8% 17% 7%	1822
	21st to end	Day	62% 4 10% 16% 7% 1	1650
March	1st to 10th	Day	61% 4 10% 15% 9% 1	4571
	11th to 20th	Day	50% 5% 15% 19% 8% 3	4980
	21st to end	Day	56% 5% 7% 14% 15% 2	5729
April	1st to 10th	Day	55% 5% 7% 21% 10% 2	2400
	11th to 20th	Day	52% 5% 10% 19% 13% 1	2374
	21st to end	Day	51% 5% 8% 20% 13% 3	2400
May	1st to 10th	Day	60% 6% 9% 15% 9% 1	6184
	11th to 20th	Day	55% 7% 8% 20% 10% 1	6322
	21st to end	Day	51% 8% 10% 20% 11% 1	6949
June	1st to 10th	Day	47% 7% 11% 21% 13% 1	2800
	11th to 20th	Day	47% 8% 12% 22% 11% 1	2800
	21st to end	Day	44% 7% 13% 24% 11% 1	2800
July	1st to 10th	Day	41% 8% 15% 25% 11% 1	6290
	11th to 20th	Day	42% 9% 16% 23% 10%	6285
	21st to end	Day	41% 7% 12% 25% 15% 1	6690
August	1st to 10th	Day	51% 6% 14% 18% 11% 1	4221
	11th to 20th	Day	47% 8% 14% 24% 7%	4052
	21st to end	Day	43% 5% 11% 32% 8% 1	4312
September	1st to 10th	Day	43% 6% 11% 26% 13% 1	2400
	11th to 20th	Day	39% 6% 11% 24% 20% 1	2400
	21st to end	Day	49% 6% 11% 21% 13% 1	2138
October	1st to 10th	Day	45% 6% 11% 23% 15% 1	3260
	11th to 20th	Day	45% 5% 10% 23% 15% 3	3240
	21st to end	Day	41% 5% 16% 26% 12% 1	3419
November	1st to 10th	Day	47% 5% 13% 21% 13% 2	1779
	11th to 20th	Day	55% 4 11% 18% 9% 2	1729
	21st to end	Day	60% 5% 13% 16% 5% 1	1600
December	1st to 10th	Day	68% 5% 11% 12% 3	2600
	11th to 20th	Day	63% 4 11% 14% 9%	2986
	21st to end	Day	68% 4 11% 11% 6%	3960
January	1st to 10th	Night	69% 4 11% 11% 5%	6349
	11th to 20th	Night	64% 5% 12% 12% 5% 1	6333
	21st to end	Night	65% 4 9% 10% 12% 1	6490
February	1st to 10th	Night	61% 5% 11% 15% 7%	2600
	11th to 20th	Night	64% 4 10% 14% 7% 1	2474
	21st to end	Night	59% 4 11% 16% 9% 1	1980
March	1st to 10th	Night	58% 4 12% 15% 10%	5265
	11th to 20th	Night	51% 5% 17% 18% 6% 4	4980
	21st to end	Night	55% 5% 8% 18% 12% 2	5202
April	1st to 10th	Night	58% 5% 8% 18% 10% 2	2000
	11th to 20th	Night	51% 4 10% 18% 15% 1	1975
	21st to end	Night	48% 5% 10% 20% 14% 3	2000
May	1st to 10th	Night	61% 5% 8% 16% 8% 2	3812
	11th to 20th	Night	49% 8% 14% 18% 10% 1	3576
	21st to end	Night	53% 8% 9% 18% 11% 1	3927
June	1st to 10th	Night	44% 6% 11% 24% 15% 1	1600
	11th to 20th	Night	42% 8% 14% 25% 11% 1	1600
	21st to end	Night	38% 7% 13% 28% 13% 1	1600
July	1st to 10th	Night	42% 7% 14% 22% 14% 1	3560
	11th to 20th	Night	39% 9% 15% 23% 14%	3552
	21st to end	Night	38% 6% 11% 26% 18% 1	3844
August	1st to 10th	Night	49% 6% 15% 21% 8%	2904
	11th to 20th	Night	44% 6% 14% 25% 10%	3029
	21st to end	Night	39% 5% 12% 31% 12% 1	3586
September	1st to 10th	Night	40% 6% 12% 25% 16% 2	2000
	11th to 20th	Night	34% 5% 11% 30% 18% 1	2000
	21st to end	Night	45% 6% 11% 22% 15% 1	2258
October	1st to 10th	Night	50% 6% 10% 22% 12% 1	3920
	11th to 20th	Night	40% 5% 13% 22% 14% 5%	3899
	21st to end	Night	42% 5% 16% 26% 11% 1	4370
November	1st to 10th	Night	45% 6% 12% 20% 15% 2	2564
	11th to 20th	Night	53% 5% 11% 19% 11% 2	2670
	21st to end	Night	53% 8% 15% 19% 6%	2800
December	1st to 10th	Night	61% 7% 12% 17% 3	4580
	11th to 20th	Night	59% 4 11% 14% 10%	5208
	21st to end	Night	67% 5% 8% 12% 7% 1	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	32% 27% 30% 8% 4 1	200
	11th to 20th	Day	40% 28% 24% 5% 1	205
	21st to end	Day	29% 29% 29% 10% 2	330
February	1st to 10th	Day	36% 29% 28% 6%	300
	11th to 20th	Day	40% 29% 27% 4	360
	21st to end	Day	36% 23% 30% 10% 1	414
March	1st to 10th	Day	35% 20% 31% 11% 4	500
	11th to 20th	Day	37% 20% 27% 12% 3 1	500
	21st to end	Day	34% 26% 25% 10% 3 2	550
April	1st to 10th	Day	37% 22% 25% 11% 4	500
	11th to 20th	Day	32% 25% 25% 10% 6% 2	492
	21st to end	Day	30% 23% 28% 12% 6% 1	500
May	1st to 10th	Day	34% 17% 28% 11% 8% 2	503
	11th to 20th	Day	24% 17% 31% 17% 8% 3	527
	21st to end	Day	23% 11% 31% 20% 11% 4	573
June	1st to 10th	Day	20% 16% 31% 20% 12% 1	530
	11th to 20th	Day	20% 14% 27% 26% 12% 1	530
	21st to end	Day	19% 13% 34% 24% 8% 2	530
July	1st to 10th	Day	13% 8% 32% 29% 13% 5%	525
	11th to 20th	Day	12% 8% 27% 31% 18% 4	524
	21st to end	Day	15% 9% 35% 27% 11% 3	576
August	1st to 10th	Day	14% 10% 27% 23% 20% 7%	526
	11th to 20th	Day	18% 7% 24% 30% 15% 7%	519
	21st to end	Day	13% 12% 27% 26% 13% 9%	583
September	1st to 10th	Day	18% 12% 25% 21% 17% 7%	530
	11th to 20th	Day	14% 9% 25% 22% 20% 11%	530
	21st to end	Day	23% 13% 29% 20% 11% 5%	530
October	1st to 10th	Day	24% 13% 24% 20% 14% 5%	530
	11th to 20th	Day	25% 20% 28% 19% 6% 2	530
	21st to end	Day	31% 17% 27% 17% 6%	543
November	1st to 10th	Day	27% 17% 25% 21% 8% 1	401
	11th to 20th	Day	30% 22% 25% 15% 7%	329
	21st to end	Day	40% 21% 32% 7% 1 1	200
December	1st to 10th	Day	36% 20% 33% 9% 3 1	200
	11th to 20th	Day	37% 24% 27% 12% 2	200
	21st to end	Day	32% 27% 30% 11% 1	220
January	1st to 10th	Night	26% 26% 32% 14% 2	800
	11th to 20th	Night	27% 21% 30% 20% 3	800
	21st to end	Night	20% 25% 36% 17% 2	880
February	1st to 10th	Night	29% 20% 32% 17% 1	800
	11th to 20th	Night	28% 23% 35% 13% 1	783
	21st to end	Night	34% 18% 32% 14% 2	660
March	1st to 10th	Night	28% 24% 28% 18% 3	800
	11th to 20th	Night	28% 22% 31% 16% 3	800
	21st to end	Night	27% 21% 30% 17% 5% 1	880
April	1st to 10th	Night	29% 21% 30% 17% 3	800
	11th to 20th	Night	28% 20% 28% 17% 6%	791
	21st to end	Night	25% 15% 32% 22% 6%	800
May	1st to 10th	Night	29% 11% 24% 28% 7%	495
	11th to 20th	Night	18% 12% 34% 27% 8% 1	394
	21st to end	Night	14% 9% 30% 34% 11% 1	433
June	1st to 10th	Night	19% 8% 24% 36% 13%	400
	11th to 20th	Night	19% 8% 25% 34% 14% 1	400
	21st to end	Night	13% 7% 28% 42% 10%	400
July	1st to 10th	Night	9% 5% 22% 44% 16% 2	390
	11th to 20th	Night	12% 5% 20% 43% 19% 1	388
	21st to end	Night	15% 4 21% 44% 14% 1	448
August	1st to 10th	Night	11% 4 22% 38% 24% 2	597
	11th to 20th	Night	17% 4 15% 33% 28% 3	669
	21st to end	Night	15% 6% 19% 35% 23% 2	880
September	1st to 10th	Night	17% 7% 23% 32% 18% 3	800
	11th to 20th	Night	16% 6% 18% 32% 24% 5%	800
	21st to end	Night	20% 9% 26% 27% 16% 2	800
October	1st to 10th	Night	21% 10% 26% 24% 18% 2	800
	11th to 20th	Night	24% 15% 29% 25% 7% 1	800
	21st to end	Night	29% 15% 28% 21% 6%	880
November	1st to 10th	Night	20% 17% 30% 25% 7%	789
	11th to 20th	Night	27% 18% 32% 17% 5% 1	800
	21st to end	Night	25% 19% 31% 20% 4	800
December	1st to 10th	Night	28% 23% 29% 17% 3	800
	11th to 20th	Night	28% 22% 29% 19% 3	800
	21st to end	Night	29% 20% 33% 16% 3	880

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