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 2024-10-25.

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 3 5% 7% 54%	101523
	Night	5% 7% 2 7% 5% 5% 5% 4 5% 7% 48%	97483
Transparency	Day	28% 5% 10% 18% 21% 18%	101279
	Night	33% 5% 11% 19% 19% 13%	97316
Seeing	Day	6% 5% 16% 28% 29% 16%	14731
	Night	8% 3 17% 41% 26% 4	24370

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	5% 15% 5% 14% 7% 7% 5% 3 5% 6% 28%	2539
	11th to 20th	Day	6% 14% 6% 14% 7% 5% 4 4 5% 6% 28%	2855
	21st to end	Day	7% 13% 5% 15% 11% 10% 8% 4 5% 5% 17%	3146
February	1st to 10th	Day	6% 11% 3 11% 8% 6% 7% 5% 6% 7% 31%	1710
	11th to 20th	Day	6% 9% 3 8% 6% 6% 6% 4 8% 7% 39%	1816
	21st to end	Day	4 10% 3 9% 5% 5% 4 4 7% 7% 41%	1570
March	1st to 10th	Day	5% 9% 4 9% 5% 6% 5% 4 7% 9% 38%	3248
	11th to 20th	Day	3 8% 2 6% 5% 4 4 4 5% 7% 52%	3490
	21st to end	Day	9% 9% 3 8% 6% 5% 4 5% 6% 8% 36%	3825
April	1st to 10th	Day	6% 7% 2 6% 6% 4 4 6% 6% 7% 47%	2156
	11th to 20th	Day	6% 8% 3 6% 4 3 4 3 5% 7% 52%	2385
	21st to end	Day	8% 6% 2 4 4 4 4 3 5% 8% 53%	2470
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	6% 3 1 3 4 4 4 3 4 6% 61%	2066
	11th to 20th	Day	5% 5% 1 3 2 3 3 3 5% 7% 63%	1900
	21st to end	Day	4 4 2 5% 2 4 4 3 5% 7% 60%	1927
November	1st to 10th	Day	4 6% 2 6% 6% 5% 4 4 7% 8% 47%	1674
	11th to 20th	Day	7% 7% 1 6% 4 4 5% 4 7% 7% 49%	1710
	21st to end	Day	6% 9% 4 8% 5% 4 4 4 4 7% 45%	1710
December	1st to 10th	Day	7% 12% 3 9% 6% 5% 5% 5% 6% 6% 37%	1710
	11th to 20th	Day	8% 12% 4 12% 7% 8% 6% 5% 6% 7% 25%	2169
	21st to end	Day	5% 11% 5% 12% 8% 7% 6% 4 6% 7% 29%	3036
January	1st to 10th	Night	6% 11% 4 10% 6% 6% 6% 4 6% 9% 32%	4401
	11th to 20th	Night	10% 11% 5% 11% 6% 6% 5% 3 6% 8% 28%	4110
	21st to end	Night	7% 12% 5% 16% 11% 8% 6% 3 5% 6% 21%	4521
February	1st to 10th	Night	7% 10% 3 8% 6% 6% 5% 4 6% 9% 34%	2470
	11th to 20th	Night	6% 10% 3 8% 5% 5% 5% 3 6% 7% 41%	2249
	21st to end	Night	4 9% 3 8% 5% 5% 5% 5% 6% 8% 42%	1884
March	1st to 10th	Night	5% 10% 3 9% 7% 6% 6% 5% 6% 8% 36%	3626
	11th to 20th	Night	3 6% 2 6% 4 5% 6% 4 6% 8% 48%	3490
	21st to end	Night	7% 9% 3 8% 6% 6% 5% 5% 6% 7% 40%	3828
April	1st to 10th	Night	8% 7% 2 5% 6% 5% 5% 4 5% 7% 47%	2019
	11th to 20th	Night	7% 7% 2 6% 4 6% 4 3 5% 6% 50%	1743
	21st to end	Night	8% 6% 3 5% 4 3 4 4 5% 7% 52%	1710
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	4 3 1 5% 3 4 4 3 4 6% 62%	2114
	11th to 20th	Night	5% 4 2 4 3 3 3 3 4 6% 64%	2280
	21st to end	Night	4 3 1 4 2 3 4 2 5% 7% 65%	2530
November	1st to 10th	Night	5% 6% 2 6% 5% 3 4 4 6% 9% 51%	2405
	11th to 20th	Night	4 5% 3 5% 4 4 4 4 6% 8% 53%	2470
	21st to end	Night	5% 8% 3 6% 5% 5% 5% 3 5% 7% 50%	2470
December	1st to 10th	Night	7% 9% 3 8% 5% 4 5% 4 6% 7% 42%	2470
	11th to 20th	Night	7% 11% 3 11% 7% 7% 6% 4 7% 9% 28%	3041
	21st to end	Night	7% 11% 4 10% 7% 7% 8% 5% 7% 8% 26%	4614

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	56% 6% 18% 16% 3	2539
	11th to 20th	Day	56% 8% 16% 17% 4	2855
	21st to end	Day	57% 12% 15% 12% 3	3146
February	1st to 10th	Day	48% 10% 14% 18% 8% 2	1710
	11th to 20th	Day	39% 8% 20% 21% 11% 1	1826
	21st to end	Day	38% 5% 16% 27% 12% 1	1570
March	1st to 10th	Day	37% 6% 16% 24% 16% 1	3248
	11th to 20th	Day	30% 5% 13% 34% 16% 2	3490
	21st to end	Day	43% 7% 13% 23% 11% 2	3825
April	1st to 10th	Day	34% 7% 11% 24% 17% 7%	2156
	11th to 20th	Day	31% 4 10% 24% 26% 5%	2388
	21st to end	Day	29% 4 10% 27% 23% 6%	2470
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	25% 4 8% 18% 34% 11%	2066
	11th to 20th	Day	21% 4 8% 33% 28% 6%	1900
	21st to end	Day	23% 4 13% 35% 22% 3	1927
November	1st to 10th	Day	31% 7% 17% 24% 19% 2	1674
	11th to 20th	Day	31% 6% 15% 34% 13%	1710
	21st to end	Day	38% 6% 16% 26% 13% 1	1710
December	1st to 10th	Day	44% 8% 17% 21% 8% 1	1710
	11th to 20th	Day	54% 9% 18% 15% 4	2168
	21st to end	Day	50% 8% 16% 15% 11% 1	3036
January	1st to 10th	Night	45% 8% 19% 23% 6%	4401
	11th to 20th	Night	51% 8% 20% 15% 5%	4110
	21st to end	Night	61% 8% 13% 12% 5%	4521
February	1st to 10th	Night	43% 7% 17% 23% 7% 1	2470
	11th to 20th	Night	40% 5% 13% 24% 16% 1	2250
	21st to end	Night	36% 6% 13% 29% 14% 2	1884
March	1st to 10th	Night	42% 5% 13% 23% 15% 2	3626
	11th to 20th	Night	30% 6% 12% 32% 18% 2	3490
	21st to end	Night	39% 8% 10% 24% 16% 2	3828
April	1st to 10th	Night	35% 5% 10% 25% 16% 9%	2019
	11th to 20th	Night	34% 4 9% 25% 24% 5%	1743
	21st to end	Night	31% 4 11% 22% 26% 5%	1710
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	23% 4 9% 18% 33% 14%	2114
	11th to 20th	Night	22% 4 6% 24% 34% 10%	2280
	21st to end	Night	20% 4 8% 34% 28% 6%	2530
November	1st to 10th	Night	30% 5% 12% 29% 20% 5%	2405
	11th to 20th	Night	28% 5% 12% 35% 17% 2	2470
	21st to end	Night	34% 4 12% 34% 16% 1	2470
December	1st to 10th	Night	39% 7% 17% 23% 12% 2	2470
	11th to 20th	Night	48% 8% 19% 19% 6%	3041
	21st to end	Night	50% 7% 19% 15% 9%	4614

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	13% 4 18% 31% 22% 12%	180
	11th to 20th	Day	9% 5% 17% 33% 25% 10%	268
	21st to end	Day	11% 2 12% 34% 27% 14%	297
February	1st to 10th	Day	12% 4 20% 37% 19% 8%	270
	11th to 20th	Day	9% 5% 21% 35% 24% 6%	421
	21st to end	Day	6% 7% 25% 36% 21% 4	382
March	1st to 10th	Day	10% 8% 17% 33% 27% 4	460
	11th to 20th	Day	7% 6% 21% 33% 24% 9%	460
	21st to end	Day	15% 7% 28% 30% 17% 4	506
April	1st to 10th	Day	10% 11% 22% 25% 23% 9%	460
	11th to 20th	Day	8% 11% 27% 27% 19% 7%	452
	21st to end	Day	10% 10% 24% 25% 21% 10%	460
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	5% 4 14% 29% 35% 12%	311
November	1st to 10th	Day	6% 6% 17% 29% 25% 17%	270
	11th to 20th	Day	7% 3 15% 26% 35% 14%	270
	21st to end	Day	11% 5% 10% 28% 30% 16%	270
December	1st to 10th	Day	11% 1 12% 38% 25% 13%	270
	11th to 20th	Day	13% 3 13% 30% 33% 8%	270
	21st to end	Day	11% 8% 17% 32% 24% 8%	264
January	1st to 10th	Night	13% 3 15% 39% 24% 7%	760
	11th to 20th	Night	11% 3 15% 38% 26% 7%	760
	21st to end	Night	11% 3 15% 41% 24% 6%	836
February	1st to 10th	Night	10% 4 19% 44% 19% 4	760
	11th to 20th	Night	10% 3 17% 48% 20% 3	744
	21st to end	Night	8% 4 23% 45% 18% 2	628
March	1st to 10th	Night	11% 4 18% 45% 20% 2	760
	11th to 20th	Night	6% 3 21% 45% 22% 3	760
	21st to end	Night	12% 4 25% 42% 16% 1	836
April	1st to 10th	Night	11% 6% 22% 42% 17% 2	760
	11th to 20th	Night	8% 7% 30% 38% 16% 1	615
	21st to end	Night	8% 6% 27% 39% 19% 1	570
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	5% 3 18% 37% 31% 6%	812
November	1st to 10th	Night	8% 3 15% 40% 29% 5%	740
	11th to 20th	Night	8% 2 16% 45% 24% 5%	760
	21st to end	Night	8% 2 17% 40% 27% 7%	760
December	1st to 10th	Night	11% 2 15% 48% 21% 4	760
	11th to 20th	Night	12% 3 17% 39% 24% 4	760
	21st to end	Night	16% 4 18% 42% 18% 3	836

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