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 2026-08-30.

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 5% 2 6% 4 4 4 4 5% 7% 56%	153084
	Night	5% 6% 2 7% 5% 5% 5% 4 6% 7% 49%	146585
Transparency	Day	27% 5% 9% 19% 23% 18%	147834
	Night	32% 5% 11% 20% 20% 13%	142838
Seeing	Day	6% 5% 16% 28% 29% 16%	17161
	Night	8% 3 18% 42% 25% 4	26718

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% 11% 5% 12% 7% 6% 5% 4 6% 7% 34%	4722
	11th to 20th	Day	3 8% 4 10% 7% 6% 6% 4 6% 6% 39%	5335
	21st to end	Day	4 10% 4 11% 7% 8% 7% 4 7% 7% 31%	5844
February	1st to 10th	Day	6% 11% 3 10% 7% 6% 6% 5% 7% 7% 32%	1890
	11th to 20th	Day	6% 9% 3 9% 6% 6% 6% 4 8% 7% 38%	2013
	21st to end	Day	4 10% 3 9% 5% 5% 4 4 7% 8% 42%	1730
March	1st to 10th	Day	5% 10% 4 8% 5% 6% 5% 5% 7% 8% 39%	4770
	11th to 20th	Day	3 7% 2 6% 5% 5% 5% 4 6% 8% 49%	5110
	21st to end	Day	8% 9% 3 8% 5% 5% 5% 4 6% 8% 38%	5607
April	1st to 10th	Day	6% 6% 2 6% 5% 3 4 5% 6% 8% 49%	2383
	11th to 20th	Day	5% 7% 2 6% 4 3 4 4 5% 7% 52%	2639
	21st to end	Day	8% 5% 2 5% 4 4 4 3 6% 8% 52%	2730
May	1st to 10th	Day	3 4 2 5% 3 4 4 3 6% 6% 60%	7626
	11th to 20th	Day	5% 5% 2 5% 3 3 4 3 5% 6% 58%	7596
	21st to end	Day	3 3 2 5% 3 3 4 3 5% 7% 62%	8370
June	1st to 10th	Day	3 3 1 4 3 3 4 4 6% 9% 60%	2730
	11th to 20th	Day	4 3 1 3 3 3 3 3 5% 7% 66%	2935
	21st to end	Day	2 2 1 3 2 2 3 2 3 5% 74%	2940
July	1st to 10th	Day	1 2 1 3 2 3 4 3 5% 6% 70%	8219
	11th to 20th	Day	1 1 1 3 3 3 4 3 6% 8% 67%	7883
	21st to end	Day	1 2 1 3 2 2 3 3 6% 8% 70%	8304
August	1st to 10th	Day	1 2 1 2 2 2 3 2 4 6% 74%	5909
	11th to 20th	Day	1 1 1 2 3 3 4 3 4 6% 71%	5928
	21st to end	Day	3 3 1 4 3 4 5% 3 5% 6% 63%	6440
September	1st to 10th	Day	2 2 1 3 2 2 3 3 5% 6% 72%	2252
	11th to 20th	Day	2 3 1 3 3 3 3 2 5% 6% 70%	2200
	21st to end	Day	4 2 1 3 1 2 2 2 3 4 74%	2200
October	1st to 10th	Day	4 2 1 3 3 3 3 2 3 5% 70%	3548
	11th to 20th	Day	4 5% 1 4 2 3 3 3 5% 6% 64%	3250
	21st to end	Day	4 4 2 4 2 3 3 3 4 6% 64%	3369
November	1st to 10th	Day	4 6% 2 6% 6% 5% 4 4 6% 8% 49%	1854
	11th to 20th	Day	7% 7% 2 7% 4 3 5% 4 7% 8% 48%	1890
	21st to end	Day	6% 9% 3 8% 5% 4 4 3 4 7% 45%	1890
December	1st to 10th	Day	4 7% 2 5% 4 5% 5% 5% 7% 8% 48%	3040
	11th to 20th	Day	6% 9% 4 10% 6% 8% 7% 5% 7% 9% 30%	3499
	21st to end	Day	5% 11% 5% 13% 8% 7% 6% 4 5% 6% 29%	4439
January	1st to 10th	Night	6% 11% 4 10% 5% 6% 7% 4 6% 8% 33%	8141
	11th to 20th	Night	6% 7% 3 7% 5% 6% 5% 4 10% 9% 38%	7650
	21st to end	Night	4 8% 3 11% 7% 5% 5% 4 7% 8% 38%	8370
February	1st to 10th	Night	6% 10% 3 8% 6% 5% 5% 4 7% 10% 35%	2730
	11th to 20th	Night	6% 10% 3 9% 5% 5% 5% 3 5% 8% 40%	2491
	21st to end	Night	4 9% 3 7% 5% 5% 5% 5% 6% 9% 43%	2076
March	1st to 10th	Night	7% 11% 3 8% 6% 5% 7% 5% 7% 7% 35%	5344
	11th to 20th	Night	3 7% 3 8% 5% 5% 6% 4 7% 9% 44%	5110
	21st to end	Night	6% 7% 3 7% 5% 5% 5% 4 6% 7% 43%	5610
April	1st to 10th	Night	8% 7% 2 5% 6% 4 4 3 5% 7% 48%	2231
	11th to 20th	Night	6% 7% 2 5% 4 5% 5% 3 5% 6% 50%	1928
	21st to end	Night	8% 6% 2 6% 4 4 4 4 6% 7% 51%	1890
May	1st to 10th	Night	7% 5% 1 5% 4 4 4 3 5% 5% 56%	5321
	11th to 20th	Night	6% 3 1 5% 3 4 4 3 6% 7% 58%	5296
	21st to end	Night	5% 5% 2 6% 4 4 5% 4 6% 7% 52%	5837
June	1st to 10th	Night	5% 5% 2 5% 5% 4 4 4 5% 7% 56%	1888
	11th to 20th	Night	5% 3 1 5% 3 2 3 3 5% 6% 65%	1680
	21st to end	Night	3 3 1 3 3 3 4 3 5% 6% 66%	1680
July	1st to 10th	Night	2 3 1 6% 4 5% 4 4 5% 6% 61%	4740
	11th to 20th	Night	3 5% 2 7% 5% 5% 5% 4 7% 9% 48%	5076
	21st to end	Night	3 3 2 6% 5% 5% 5% 4 6% 8% 52%	5805
August	1st to 10th	Night	2 3 1 4 3 4 4 4 6% 7% 63%	4123
	11th to 20th	Night	2 4 2 5% 4 5% 4 4 5% 5% 60%	4141
	21st to end	Night	3 4 2 5% 3 5% 4 3 4 5% 61%	4726
September	1st to 10th	Night	2 2 1 4 3 3 4 3 5% 5% 67%	2146
	11th to 20th	Night	4 2 1 3 3 3 3 2 5% 6% 67%	2200
	21st to end	Night	5% 3 1 3 3 3 3 2 3 4 72%	2200
October	1st to 10th	Night	3 2 1 4 3 3 3 3 3 5% 70%	3649
	11th to 20th	Night	5% 4 2 4 3 3 3 3 4 6% 64%	3898
	21st to end	Night	4 4 1 4 3 3 4 3 6% 7% 60%	4426
November	1st to 10th	Night	5% 6% 2 6% 4 4 4 3 6% 8% 52%	2665
	11th to 20th	Night	4 5% 3 6% 4 4 4 4 6% 8% 52%	2730
	21st to end	Night	5% 8% 3 6% 5% 5% 5% 3 5% 8% 50%	2730
December	1st to 10th	Night	4 6% 2 5% 4 5% 5% 5% 9% 11% 45%	4370
	11th to 20th	Night	6% 10% 2 9% 6% 7% 8% 5% 8% 9% 31%	4941
	21st to end	Night	7% 10% 4 11% 7% 8% 8% 5% 7% 8% 25%	6746

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	49% 5% 24% 15% 7%	4723
	11th to 20th	Day	41% 8% 13% 25% 11% 2	5335
	21st to end	Day	44% 9% 14% 21% 12% 1	5844
February	1st to 10th	Day	47% 9% 14% 19% 9% 2	1890
	11th to 20th	Day	40% 8% 19% 21% 11% 2	2023
	21st to end	Day	37% 6% 15% 28% 12% 2	1730
March	1st to 10th	Day	36% 7% 12% 25% 17% 2	4770
	11th to 20th	Day	30% 6% 10% 32% 20% 2	5110
	21st to end	Day	42% 6% 14% 25% 12% 1	5607
April	1st to 10th	Day	33% 6% 10% 25% 20% 6%	2383
	11th to 20th	Day	31% 4 10% 23% 27% 5%	2642
	21st to end	Day	30% 4 10% 27% 24% 6%	2730
May	1st to 10th	Day	22% 4 8% 20% 32% 14%	7626
	11th to 20th	Day	25% 4 6% 14% 37% 14%	7599
	21st to end	Day	21% 4 6% 19% 37% 13%	8371
June	1st to 10th	Day	20% 5% 8% 17% 35% 15%	2730
	11th to 20th	Day	17% 4 7% 15% 29% 29%	2935
	21st to end	Day	13% 2 4 10% 29% 42%	2940
July	1st to 10th	Day	14% 3 3 7% 15% 58%	8151
	11th to 20th	Day	13% 4 4 12% 20% 46%	7809
	21st to end	Day	12% 3 5% 10% 26% 44%	8120
August	1st to 10th	Day	15% 3 4 11% 27% 39%	4338
	11th to 20th	Day	16% 4 5% 11% 31% 34%	4327
	21st to end	Day	15% 2 4 12% 27% 40%	4671
September	1st to 10th	Day	14% 3 7% 14% 29% 33%	2252
	11th to 20th	Day	16% 4 6% 18% 29% 26%	2200
	21st to end	Day	17% 2 5% 19% 36% 21%	2200
October	1st to 10th	Day	18% 3 5% 14% 39% 20%	3548
	11th to 20th	Day	21% 4 5% 27% 35% 8%	3250
	21st to end	Day	22% 3 9% 37% 25% 3	3369
November	1st to 10th	Day	30% 6% 17% 25% 20% 2	1854
	11th to 20th	Day	32% 6% 15% 33% 13%	1890
	21st to end	Day	38% 6% 15% 28% 12% 1	1890
December	1st to 10th	Day	30% 7% 18% 33% 10% 1	3040
	11th to 20th	Day	47% 8% 18% 23% 3	3498
	21st to end	Day	52% 6% 13% 18% 10%	4439
January	1st to 10th	Night	46% 6% 20% 21% 7%	8141
	11th to 20th	Night	36% 7% 17% 29% 10% 2	7650
	21st to end	Night	41% 6% 12% 25% 15% 1	8370
February	1st to 10th	Night	42% 7% 17% 25% 8% 2	2730
	11th to 20th	Night	41% 5% 13% 24% 16% 1	2492
	21st to end	Night	35% 6% 12% 30% 15% 2	2076
March	1st to 10th	Night	42% 7% 10% 22% 15% 4	5344
	11th to 20th	Night	34% 5% 10% 27% 21% 2	5110
	21st to end	Night	37% 7% 12% 26% 17% 2	5610
April	1st to 10th	Night	34% 5% 9% 24% 19% 9%	2231
	11th to 20th	Night	34% 4 9% 25% 24% 6%	1928
	21st to end	Night	32% 4 10% 22% 27% 5%	1890
May	1st to 10th	Night	28% 4 9% 16% 30% 14%	5319
	11th to 20th	Night	24% 5% 5% 17% 31% 18%	5297
	21st to end	Night	27% 5% 7% 14% 37% 10%	5838
June	1st to 10th	Night	26% 5% 8% 16% 30% 15%	1888
	11th to 20th	Night	20% 3 6% 15% 30% 25%	1680
	21st to end	Night	18% 3 5% 10% 27% 37%	1680
July	1st to 10th	Night	22% 5% 3 7% 14% 50%	4700
	11th to 20th	Night	28% 5% 5% 9% 18% 35%	5027
	21st to end	Night	25% 6% 6% 9% 19% 36%	5677
August	1st to 10th	Night	21% 5% 5% 11% 24% 35%	3018
	11th to 20th	Night	22% 4 6% 11% 26% 32%	3018
	21st to end	Night	16% 2 5% 10% 19% 48%	3423
September	1st to 10th	Night	18% 3 5% 13% 26% 35%	2146
	11th to 20th	Night	19% 3 6% 13% 28% 31%	2200
	21st to end	Night	18% 3 4 14% 31% 30%	2200
October	1st to 10th	Night	17% 3 6% 12% 32% 29%	3649
	11th to 20th	Night	23% 3 4 21% 35% 14%	3898
	21st to end	Night	23% 3 6% 33% 29% 5%	4426
November	1st to 10th	Night	29% 5% 12% 29% 21% 5%	2665
	11th to 20th	Night	30% 5% 12% 35% 16% 2	2730
	21st to end	Night	34% 4 12% 34% 15% 1	2730
December	1st to 10th	Night	29% 7% 20% 31% 12% 1	4370
	11th to 20th	Night	44% 8% 23% 20% 6%	4941
	21st to end	Night	51% 6% 18% 17% 8%	6746

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	11% 5% 20% 29% 23% 11%	220
	11th to 20th	Day	7% 4 17% 31% 28% 13%	328
	21st to end	Day	9% 2 12% 34% 29% 13%	363
February	1st to 10th	Day	10% 5% 20% 34% 21% 9%	330
	11th to 20th	Day	8% 5% 23% 35% 22% 6%	498
	21st to end	Day	6% 6% 24% 36% 22% 5%	446
March	1st to 10th	Day	10% 7% 18% 33% 26% 5%	540
	11th to 20th	Day	7% 7% 22% 32% 23% 9%	540
	21st to end	Day	14% 6% 26% 29% 20% 6%	594
April	1st to 10th	Day	9% 10% 20% 27% 22% 12%	540
	11th to 20th	Day	8% 11% 26% 26% 20% 8%	532
	21st to end	Day	10% 9% 24% 26% 21% 10%	540
May	1st to 10th	Day	5% 9% 24% 29% 22% 11%	543
	11th to 20th	Day	7% 6% 22% 26% 24% 15%	568
	21st to end	Day	8% 5% 18% 26% 26% 18%	617
June	1st to 10th	Day	3 6% 15% 28% 29% 19%	570
	11th to 20th	Day	4 6% 17% 32% 26% 16%	570
	21st to end	Day	2 2 16% 30% 36% 14%	570
July	1st to 10th	Day	1 1 10% 29% 40% 19%	566
	11th to 20th	Day	3 1 8% 26% 42% 21%	564
	21st to end	Day	3 1 5% 22% 42% 26%	619
August	1st to 10th	Day	3 1 9% 28% 34% 26%	567
	11th to 20th	Day	3 2 9% 27% 32% 27%	557
	21st to end	Day	4 3 10% 20% 38% 26%	620
September	1st to 10th	Day	2 2 9% 22% 30% 34%	530
	11th to 20th	Day	3 3 14% 25% 32% 23%	530
	21st to end	Day	6% 3 10% 23% 31% 26%	530
October	1st to 10th	Day	5% 5% 13% 25% 25% 27%	504
	11th to 20th	Day	5% 3 14% 25% 28% 25%	330
	21st to end	Day	6% 4 15% 27% 33% 15%	363
November	1st to 10th	Day	5% 6% 15% 29% 25% 18%	330
	11th to 20th	Day	7% 4 16% 27% 33% 13%	330
	21st to end	Day	11% 5% 9% 30% 30% 15%	330
December	1st to 10th	Day	10% 2 12% 35% 25% 16%	330
	11th to 20th	Day	12% 4 12% 30% 32% 10%	330
	21st to end	Day	10% 9% 20% 30% 23% 8%	322
January	1st to 10th	Night	13% 3 15% 40% 23% 6%	840
	11th to 20th	Night	10% 3 15% 38% 27% 7%	840
	21st to end	Night	10% 2 14% 44% 24% 5%	924
February	1st to 10th	Night	10% 4 20% 43% 20% 4	840
	11th to 20th	Night	10% 4 16% 49% 19% 3	824
	21st to end	Night	8% 4 22% 46% 18% 2	692
March	1st to 10th	Night	11% 4 18% 44% 19% 3	840
	11th to 20th	Night	6% 4 22% 44% 21% 2	840
	21st to end	Night	11% 4 25% 43% 16% 2	924
April	1st to 10th	Night	11% 6% 21% 43% 17% 3	840
	11th to 20th	Night	9% 6% 30% 38% 16% 1	680
	21st to end	Night	9% 6% 28% 38% 18% 1	630
May	1st to 10th	Night	8% 7% 26% 41% 17% 2	630
	11th to 20th	Night	9% 6% 19% 38% 25% 3	621
	21st to end	Night	9% 6% 20% 36% 25% 3	683
June	1st to 10th	Night	6% 5% 21% 42% 24% 3	628
	11th to 20th	Night	7% 4 20% 46% 23%	420
	21st to end	Night	4 2 19% 45% 30% 1	420
July	1st to 10th	Night	3 1 15% 46% 31% 3	410
	11th to 20th	Night	5% 2 15% 49% 27% 2	522
	21st to end	Night	4 1 10% 47% 36% 2	690
August	1st to 10th	Night	4 2 14% 45% 33% 1	627
	11th to 20th	Night	3 2 14% 48% 30% 2	624
	21st to end	Night	5% 1 13% 43% 32% 5%	745
September	1st to 10th	Night	2 2 11% 39% 39% 7%	800
	11th to 20th	Night	5% 2 14% 37% 35% 7%	800
	21st to end	Night	6% 3 13% 33% 36% 9%	800
October	1st to 10th	Night	6% 3 17% 39% 30% 6%	800
	11th to 20th	Night	6% 2 16% 38% 33% 6%	800
	21st to end	Night	6% 2 18% 37% 31% 6%	880
November	1st to 10th	Night	8% 3 16% 39% 30% 5%	820
	11th to 20th	Night	7% 2 17% 46% 24% 5%	840
	21st to end	Night	8% 2 16% 40% 27% 7%	840
December	1st to 10th	Night	10% 2 15% 46% 21% 5%	840
	11th to 20th	Night	12% 3 17% 39% 25% 4	840
	21st to end	Night	15% 5% 18% 41% 18% 3	924

Page generated at 2026-08-27 02:07:13. Version ac07

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