Knoll
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Knoll clear sky chart from 2005-11-06 to 2025-04-26.

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	4 6% 2 6% 4 4 4 4 5% 7% 54%	118414
	Night	5% 7% 2 7% 5% 5% 5% 4 6% 7% 48%	119050
Transparency	Day	28% 5% 10% 20% 22% 16%	118170
	Night	33% 5% 11% 20% 19% 12%	118883
Seeing	Day	7% 5% 16% 28% 28% 16%	15338
	Night	8% 3 18% 41% 25% 4	25087

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	4 12% 5% 13% 7% 6% 5% 4 6% 7% 31%	3639
	11th to 20th	Day	4 10% 5% 13% 8% 6% 5% 4 5% 5% 35%	4095
	21st to end	Day	5% 11% 4 12% 8% 8% 7% 4 6% 6% 28%	4510
February	1st to 10th	Day	6% 11% 3 10% 8% 6% 7% 5% 7% 7% 31%	1800
	11th to 20th	Day	6% 9% 3 8% 6% 6% 6% 4 7% 7% 38%	1915
	21st to end	Day	3 10% 3 9% 5% 5% 4 4 6% 8% 42%	1650
March	1st to 10th	Day	5% 11% 4 8% 5% 6% 5% 5% 7% 8% 39%	4667
	11th to 20th	Day	3 7% 2 6% 5% 5% 5% 4 6% 8% 48%	5000
	21st to end	Day	8% 9% 3 9% 5% 5% 5% 4 6% 8% 38%	5486
April	1st to 10th	Day	6% 7% 2 6% 5% 3 4 5% 6% 8% 48%	2270
	11th to 20th	Day	5% 7% 2 6% 4 3 4 3 5% 7% 52%	2512
	21st to end	Day	8% 6% 2 5% 4 4 4 3 5% 8% 53%	2537
May	1st to 10th	Day	5% 6% 2 6% 4 4 4 3 6% 7% 53%	4110
	11th to 20th	Day	4 3 1 4 3 3 3 4 5% 6% 64%	4071
	21st to end	Day	4 4 2 4 4 4 5% 4 5% 6% 58%	4477
June	1st to 10th	Day	3 3 1 4 3 3 4 4 6% 9% 59%	2470
	11th to 20th	Day	4 3 1 3 3 3 3 3 5% 7% 65%	2655
	21st to end	Day	2 2 1 3 2 2 3 2 3 5% 74%	2660
July	1st to 10th	Day	1 2 1 2 2 2 3 3 4 5% 77%	4420
	11th to 20th	Day	2 1 1 3 3 3 3 3 6% 8% 67%	4239
	21st to end	Day	2 2 1 3 2 2 3 3 5% 8% 69%	4454
August	1st to 10th	Day	2 2 1 3 2 3 4 3 5% 7% 68%	4092
	11th to 20th	Day	2 1 1 3 3 4 5% 3 5% 6% 68%	4028
	21st to end	Day	3 2 1 2 2 2 3 2 3 4 75%	4415
September	1st to 10th	Day	2 2 1 2 2 2 3 2 5% 6% 73%	2140
	11th to 20th	Day	2 2 1 2 3 3 3 2 5% 6% 70%	2090
	21st to end	Day	4 2 1 3 1 2 2 2 3 5% 74%	2090
October	1st to 10th	Day	4 2 1 3 3 3 3 2 3 5% 70%	3440
	11th to 20th	Day	4 5% 1 4 2 3 3 3 5% 6% 64%	3150
	21st to end	Day	4 4 2 4 2 3 3 3 4 6% 64%	3265
November	1st to 10th	Day	4 6% 2 6% 6% 5% 4 4 7% 8% 48%	1764
	11th to 20th	Day	7% 7% 1 6% 4 3 5% 4 7% 8% 49%	1800
	21st to end	Day	6% 9% 3 8% 5% 4 4 4 4 8% 45%	1800
December	1st to 10th	Day	4 7% 2 5% 4 5% 5% 5% 7% 8% 47%	2950
	11th to 20th	Day	6% 9% 4 10% 6% 8% 7% 5% 7% 9% 29%	3409
	21st to end	Day	5% 11% 5% 13% 8% 7% 6% 4 5% 6% 29%	4344
January	1st to 10th	Night	5% 11% 4 10% 5% 6% 7% 4 6% 9% 33%	6288
	11th to 20th	Night	7% 9% 4 9% 6% 7% 6% 5% 8% 8% 31%	5880
	21st to end	Night	6% 11% 4 12% 8% 6% 5% 3 5% 7% 33%	6468
February	1st to 10th	Night	7% 10% 3 8% 6% 5% 5% 4 6% 9% 35%	2600
	11th to 20th	Night	6% 10% 3 8% 5% 5% 5% 3 6% 8% 41%	2370
	21st to end	Night	4 9% 3 8% 5% 5% 6% 5% 6% 8% 42%	1980
March	1st to 10th	Night	7% 11% 3 8% 6% 5% 7% 5% 7% 7% 34%	5227
	11th to 20th	Night	3 7% 3 8% 5% 5% 7% 4 7% 9% 43%	5000
	21st to end	Night	7% 7% 3 7% 5% 5% 5% 4 6% 7% 43%	5489
April	1st to 10th	Night	7% 7% 2 5% 6% 4 4 3 5% 7% 47%	2125
	11th to 20th	Night	6% 7% 2 6% 4 6% 5% 3 5% 6% 50%	1835
	21st to end	Night	8% 6% 3 5% 4 3 4 4 6% 7% 51%	1759
May	1st to 10th	Night	11% 8% 2 6% 4 4 3 3 6% 6% 48%	2860
	11th to 20th	Night	6% 3 1 4 3 3 3 3 6% 6% 61%	2834
	21st to end	Night	8% 5% 2 5% 3 4 4 4 6% 7% 52%	3110
June	1st to 10th	Night	5% 5% 1 5% 5% 4 4 4 5% 7% 55%	1708
	11th to 20th	Night	5% 3 1 5% 3 2 3 3 5% 7% 63%	1520
	21st to end	Night	2 2 1 3 2 3 4 3 5% 6% 68%	1520
July	1st to 10th	Night	2 2 1 4 3 3 3 3 4 5% 71%	2540
	11th to 20th	Night	3 5% 2 6% 5% 5% 5% 4 8% 9% 47%	2722
	21st to end	Night	4 3 2 6% 4 4 4 4 6% 7% 56%	3109
August	1st to 10th	Night	2 3 1 5% 4 5% 5% 4 6% 7% 58%	2847
	11th to 20th	Night	2 3 1 5% 3 4 4 3 5% 6% 64%	2811
	21st to end	Night	3 2 1 3 2 3 2 2 3 5% 74%	3239
September	1st to 10th	Night	2 2 1 4 3 3 4 3 5% 5% 68%	2038
	11th to 20th	Night	4 2 1 3 3 3 3 3 5% 6% 67%	2090
	21st to end	Night	5% 3 1 2 3 2 3 2 3 4 73%	2090
October	1st to 10th	Night	3 2 1 4 3 3 3 3 3 5% 70%	3538
	11th to 20th	Night	5% 4 2 4 3 3 3 3 4 6% 64%	3778
	21st to end	Night	4 4 1 4 3 3 4 3 6% 7% 60%	4289
November	1st to 10th	Night	5% 6% 2 6% 4 3 4 4 5% 9% 51%	2535
	11th to 20th	Night	4 5% 3 5% 4 4 4 4 6% 8% 53%	2600
	21st to end	Night	5% 8% 3 6% 5% 5% 5% 3 5% 7% 49%	2600
December	1st to 10th	Night	4 5% 2 5% 4 5% 5% 5% 9% 11% 45%	4240
	11th to 20th	Night	6% 10% 3 9% 6% 7% 8% 5% 8% 9% 31%	4811
	21st to end	Night	7% 10% 4 11% 7% 8% 8% 5% 7% 8% 24%	6600

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	51% 5% 21% 15% 7%	3639
	11th to 20th	Day	49% 7% 13% 20% 9% 3	4095
	21st to end	Day	48% 10% 12% 19% 10% 1	4510
February	1st to 10th	Day	48% 10% 14% 18% 9% 2	1800
	11th to 20th	Day	40% 8% 19% 21% 11% 2	1925
	21st to end	Day	37% 6% 15% 27% 13% 2	1650
March	1st to 10th	Day	36% 7% 12% 25% 17% 2	4667
	11th to 20th	Day	31% 6% 10% 32% 19% 2	5000
	21st to end	Day	42% 6% 14% 25% 11% 1	5486
April	1st to 10th	Day	33% 6% 10% 24% 19% 7%	2270
	11th to 20th	Day	31% 4 10% 23% 27% 5%	2515
	21st to end	Day	29% 4 10% 27% 24% 6%	2537
May	1st to 10th	Day	27% 4 9% 22% 27% 11%	4110
	11th to 20th	Day	19% 4 9% 18% 38% 13%	4074
	21st to end	Day	24% 5% 9% 22% 31% 9%	4477
June	1st to 10th	Day	20% 6% 9% 18% 34% 13%	2470
	11th to 20th	Day	18% 4 7% 16% 29% 26%	2655
	21st to end	Day	13% 2 5% 10% 28% 43%	2660
July	1st to 10th	Day	11% 2 4 6% 13% 64%	4351
	11th to 20th	Day	13% 3 4 8% 21% 50%	4165
	21st to end	Day	13% 3 6% 9% 31% 39%	4314
August	1st to 10th	Day	15% 3 5% 12% 27% 38%	4078
	11th to 20th	Day	16% 4 5% 10% 31% 34%	4067
	21st to end	Day	13% 2 4 11% 28% 42%	4414
September	1st to 10th	Day	13% 2 7% 14% 29% 34%	2140
	11th to 20th	Day	16% 4 7% 19% 29% 26%	2090
	21st to end	Day	16% 2 5% 18% 36% 21%	2090
October	1st to 10th	Day	18% 3 5% 14% 39% 21%	3440
	11th to 20th	Day	21% 4 5% 27% 35% 8%	3150
	21st to end	Day	22% 3 9% 37% 26% 3	3265
November	1st to 10th	Day	31% 7% 17% 24% 20% 2	1764
	11th to 20th	Day	31% 6% 15% 34% 14%	1800
	21st to end	Day	38% 6% 15% 27% 13% 1	1800
December	1st to 10th	Day	31% 7% 18% 33% 11% 1	2950
	11th to 20th	Day	47% 8% 19% 23% 3	3408
	21st to end	Day	53% 6% 13% 17% 10%	4344
January	1st to 10th	Night	44% 7% 19% 21% 8%	6288
	11th to 20th	Night	46% 8% 17% 21% 7% 2	5880
	21st to end	Night	47% 6% 10% 23% 13%	6468
February	1st to 10th	Night	43% 7% 17% 23% 8% 2	2600
	11th to 20th	Night	40% 5% 13% 24% 16% 1	2371
	21st to end	Night	36% 6% 12% 28% 15% 3	1980
March	1st to 10th	Night	42% 7% 11% 22% 15% 4	5227
	11th to 20th	Night	35% 5% 10% 27% 21% 1	5000
	21st to end	Night	37% 7% 12% 26% 17% 2	5489
April	1st to 10th	Night	35% 5% 9% 24% 18% 9%	2125
	11th to 20th	Night	34% 4 9% 24% 24% 5%	1835
	21st to end	Night	32% 4 11% 22% 26% 5%	1759
May	1st to 10th	Night	35% 4 9% 18% 28% 7%	2860
	11th to 20th	Night	21% 4 8% 22% 32% 13%	2835
	21st to end	Night	29% 6% 10% 16% 34% 6%	3110
June	1st to 10th	Night	27% 5% 9% 17% 29% 13%	1708
	11th to 20th	Night	22% 3 6% 16% 31% 21%	1520
	21st to end	Night	16% 3 6% 11% 25% 39%	1520
July	1st to 10th	Night	15% 3 4 7% 12% 59%	2500
	11th to 20th	Night	28% 5% 5% 7% 22% 34%	2673
	21st to end	Night	24% 4 6% 8% 25% 34%	3011
August	1st to 10th	Night	21% 5% 5% 11% 24% 34%	2838
	11th to 20th	Night	21% 3 5% 11% 26% 33%	2838
	21st to end	Night	14% 2 4 10% 19% 51%	3239
September	1st to 10th	Night	17% 3 5% 13% 25% 36%	2038
	11th to 20th	Night	18% 3 6% 13% 28% 31%	2090
	21st to end	Night	17% 3 4 13% 32% 30%	2090
October	1st to 10th	Night	17% 3 6% 12% 32% 30%	3538
	11th to 20th	Night	23% 3 4 21% 36% 14%	3778
	21st to end	Night	23% 3 6% 34% 29% 5%	4289
November	1st to 10th	Night	30% 5% 11% 29% 21% 5%	2535
	11th to 20th	Night	29% 5% 12% 35% 17% 2	2600
	21st to end	Night	34% 4 12% 34% 16% 1	2600
December	1st to 10th	Night	29% 7% 20% 31% 12% 1	4240
	11th to 20th	Night	44% 8% 23% 19% 5%	4811
	21st to end	Night	52% 7% 18% 17% 7%	6600

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% 5% 20% 31% 22% 12%	200
	11th to 20th	Day	8% 4 18% 32% 26% 12%	298
	21st to end	Day	10% 2 12% 35% 27% 13%	330
February	1st to 10th	Day	11% 6% 22% 35% 19% 7%	300
	11th to 20th	Day	9% 5% 23% 35% 23% 6%	460
	21st to end	Day	6% 6% 25% 36% 22% 5%	414
March	1st to 10th	Day	10% 7% 17% 33% 27% 5%	500
	11th to 20th	Day	8% 7% 21% 33% 23% 9%	500
	21st to end	Day	14% 6% 27% 29% 18% 5%	550
April	1st to 10th	Day	9% 10% 21% 26% 23% 10%	500
	11th to 20th	Day	9% 11% 27% 26% 20% 8%	492
	21st to end	Day	10% 9% 23% 26% 21% 10%	481
May	1st to 10th	Day	6% 9% 27% 29% 21% 8%	463
	11th to 20th	Day	6% 6% 21% 27% 25% 14%	488
	21st to end	Day	9% 5% 17% 27% 27% 16%	529
June	1st to 10th	Day	3 6% 14% 28% 29% 19%	490
	11th to 20th	Day	5% 6% 18% 31% 26% 14%	490
	21st to end	Day	2 2 15% 31% 36% 14%	490
July	1st to 10th	Day	1 1 10% 30% 39% 19%	486
	11th to 20th	Day	3 1 9% 27% 41% 20%	484
	21st to end	Day	2 1 6% 21% 41% 28%	531
August	1st to 10th	Day	3 1 8% 28% 34% 25%	487
	11th to 20th	Day	3 1 9% 26% 34% 26%	477
	21st to end	Day	4 2 10% 20% 38% 25%	539
September	1st to 10th	Day	2 3 9% 21% 31% 34%	490
	11th to 20th	Day	3 3 14% 23% 32% 23%	490
	21st to end	Day	6% 3 11% 23% 31% 26%	490
October	1st to 10th	Day	5% 5% 13% 26% 24% 27%	466
	11th to 20th	Day	5% 3 12% 25% 27% 28%	300
	21st to end	Day	6% 4 15% 29% 33% 12%	330
November	1st to 10th	Day	6% 6% 17% 29% 25% 17%	300
	11th to 20th	Day	7% 3 16% 28% 33% 13%	300
	21st to end	Day	11% 5% 9% 30% 30% 15%	300
December	1st to 10th	Day	10% 1 11% 36% 24% 17%	300
	11th to 20th	Day	13% 3 12% 31% 33% 8%	300
	21st to end	Day	11% 7% 19% 32% 24% 8%	293
January	1st to 10th	Night	12% 3 15% 40% 23% 6%	800
	11th to 20th	Night	10% 3 16% 38% 26% 7%	800
	21st to end	Night	11% 3 15% 42% 24% 5%	880
February	1st to 10th	Night	10% 4 20% 43% 19% 4	800
	11th to 20th	Night	9% 3 17% 49% 20% 3	784
	21st to end	Night	8% 4 22% 45% 18% 2	660
March	1st to 10th	Night	11% 4 18% 45% 20% 3	800
	11th to 20th	Night	6% 4 22% 45% 21% 2	800
	21st to end	Night	12% 4 25% 42% 16% 2	880
April	1st to 10th	Night	11% 6% 21% 43% 17% 3	800
	11th to 20th	Night	8% 6% 30% 38% 16% 1	647
	21st to end	Night	8% 6% 27% 39% 19% 1	587
May	1st to 10th	Night	9% 7% 27% 40% 15% 2	570
	11th to 20th	Night	9% 6% 18% 38% 26% 4	561
	21st to end	Night	10% 7% 19% 36% 26% 3	617
June	1st to 10th	Night	6% 6% 19% 42% 25% 3	568
	11th to 20th	Night	7% 3 21% 45% 23%	380
	21st to end	Night	2 1 19% 46% 30% 1	380
July	1st to 10th	Night	4 1 15% 44% 33% 4	370
	11th to 20th	Night	4 2 16% 49% 28% 2	471
	21st to end	Night	4 1 9% 46% 38% 2	624
August	1st to 10th	Night	5% 2 12% 44% 35% 1	567
	11th to 20th	Night	3 2 14% 47% 31% 2	564
	21st to end	Night	5% 2 14% 42% 33% 5%	681
September	1st to 10th	Night	3 2 11% 38% 39% 8%	760
	11th to 20th	Night	5% 2 14% 36% 35% 7%	760
	21st to end	Night	6% 3 13% 33% 36% 10%	760
October	1st to 10th	Night	6% 2 16% 39% 30% 6%	760
	11th to 20th	Night	6% 2 15% 38% 34% 6%	760
	21st to end	Night	6% 3 18% 37% 31% 6%	836
November	1st to 10th	Night	8% 3 16% 39% 29% 5%	780
	11th to 20th	Night	8% 2 16% 47% 23% 5%	800
	21st to end	Night	8% 2 17% 40% 27% 7%	800
December	1st to 10th	Night	10% 2 15% 46% 21% 5%	800
	11th to 20th	Night	12% 3 17% 39% 24% 4	800
	21st to end	Night	16% 3 18% 42% 18% 3	880

Page generated at 2025-04-23 07:25:06. Version ac07

Copyright © 2025 Attilla Danko.