Kneeland School Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Kneeland School Observatory clear sky chart from 2005-11-06 to 2026-06-01.

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	14% 8% 2 4 3 3 3 3 4 6% 51%	141196
	Night	16% 9% 2 6% 4 3 3 3 4 5% 44%	139429
Transparency	Day	34% 6% 11% 20% 18% 11%	136019
	Night	39% 7% 11% 16% 15% 11%	135602
Seeing	Day	20% 12% 28% 25% 12% 4	17174
	Night	20% 6% 15% 29% 24% 5%	26332

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	28% 15% 3 7% 5% 4 4 3 3 5% 22%	4938
	11th to 20th	Day	19% 7% 1 4 2 3 2 2 3 4 54%	5340
	21st to end	Day	21% 8% 2 5% 4 3 4 3 4 5% 40%	5843
February	1st to 10th	Day	22% 11% 2 6% 4 3 4 4 4 6% 34%	1890
	11th to 20th	Day	23% 13% 3 6% 4 3 5% 3 4 7% 29%	1845
	21st to end	Day	26% 15% 3 6% 3 3 3 3 3 6% 31%	1693
March	1st to 10th	Day	26% 21% 2 5% 3 3 3 2 3 5% 27%	5062
	11th to 20th	Day	25% 14% 2 5% 3 2 3 2 4 5% 34%	5110
	21st to end	Day	31% 13% 2 7% 4 3 3 3 5% 5% 23%	5607
April	1st to 10th	Day	24% 13% 2 6% 4 4 4 3 5% 7% 27%	2483
	11th to 20th	Day	23% 12% 2 5% 4 3 3 3 4 5% 35%	2489
	21st to end	Day	19% 9% 2 5% 3 4 4 3 5% 8% 39%	2665
May	1st to 10th	Day	12% 10% 1 3 2 2 3 3 4 5% 54%	6010
	11th to 20th	Day	11% 7% 2 4 3 3 4 3 4 6% 54%	6137
	21st to end	Day	7% 6% 1 5% 3 3 4 3 5% 8% 54%	7056
June	1st to 10th	Day	14% 8% 2 5% 4 4 4 3 5% 8% 44%	2801
	11th to 20th	Day	8% 4 1 4 3 3 4 3 4 8% 57%	2800
	21st to end	Day	6% 3 1 3 2 2 3 2 3 5% 70%	2800
July	1st to 10th	Day	2 2 1 2 1 1 2 2 2 4 82%	6319
	11th to 20th	Day	2 1 1 2 1 1 2 1 1 3 84%	6013
	21st to end	Day	2 1 4 2 2 2 2 3 7% 72%	6402
August	1st to 10th	Day	1 2 1 3 2 2 3 2 4 8% 70%	5777
	11th to 20th	Day	5% 5% 1 3 2 2 3 2 3 5% 68%	5796
	21st to end	Day	4 2 2 1 2 2 2 3 6% 75%	6082
September	1st to 10th	Day	4 3 1 3 2 2 2 2 3 5% 74%	2400
	11th to 20th	Day	7% 5% 1 4 3 4 4 3 4 7% 57%	2296
	21st to end	Day	8% 4 1 3 2 2 2 2 5% 6% 65%	2161
October	1st to 10th	Day	6% 3 1 3 2 2 2 2 3 4 71%	3280
	11th to 20th	Day	10% 4 2 5% 3 4 5% 3 6% 8% 50%	3261
	21st to end	Day	17% 7% 2 5% 3 4 4 3 6% 6% 41%	3558
November	1st to 10th	Day	23% 8% 2 5% 4 3 4 4 4 9% 35%	2022
	11th to 20th	Day	25% 8% 2 6% 4 4 4 4 6% 8% 30%	1680
	21st to end	Day	21% 7% 2 7% 4 3 4 3 5% 7% 38%	1680
December	1st to 10th	Day	14% 6% 2 5% 3 3 4 4 5% 7% 47%	2700
	11th to 20th	Day	33% 11% 3 7% 4 5% 5% 3 5% 6% 18%	3108
	21st to end	Day	35% 15% 3 9% 5% 4 3 3 3 3 17%	4092
January	1st to 10th	Night	34% 14% 3 6% 4 4 4 3 4 5% 21%	7964
	11th to 20th	Night	17% 8% 2 5% 3 2 2 2 3 4 50%	7650
	21st to end	Night	24% 10% 2 6% 3 3 3 3 4 4 38%	8371
February	1st to 10th	Night	21% 11% 3 7% 4 3 4 3 5% 6% 33%	2730
	11th to 20th	Night	22% 14% 3 7% 4 4 3 3 3 5% 31%	2662
	21st to end	Night	22% 12% 3 6% 4 3 3 3 5% 7% 31%	2107
March	1st to 10th	Night	26% 21% 3 5% 2 2 3 2 4 6% 26%	5052
	11th to 20th	Night	19% 15% 3 6% 4 3 3 2 4 5% 35%	5110
	21st to end	Night	29% 19% 3 7% 3 3 3 2 4 5% 22%	5610
April	1st to 10th	Night	21% 14% 4 6% 4 4 4 3 5% 7% 28%	2137
	11th to 20th	Night	19% 12% 3 6% 4 4 4 3 5% 5% 35%	2079
	21st to end	Night	17% 11% 2 5% 4 4 4 3 5% 9% 36%	1951
May	1st to 10th	Night	11% 8% 2 5% 3 3 3 3 4 6% 53%	4190
	11th to 20th	Night	8% 15% 4 6% 3 3 3 2 3 4 50%	3987
	21st to end	Night	5% 8% 2 8% 6% 4 4 4 5% 6% 49%	4060
June	1st to 10th	Night	14% 7% 3 6% 4 5% 4 4 6% 6% 42%	1600
	11th to 20th	Night	6% 6% 2 5% 4 3 4 3 4 8% 56%	1600
	21st to end	Night	5% 3 2 3 3 2 3 4 4 7% 64%	1600
July	1st to 10th	Night	2 1 1 5% 3 4 4 2 3 5% 71%	3640
	11th to 20th	Night	1 1 1 2 2 3 2 1 2 5% 81%	3956
	21st to end	Night	1 2 3 12% 7% 4 4 2 3 5% 56%	4472
August	1st to 10th	Night	2 3 12% 5% 4 3 3 3 5% 58%	4035
	11th to 20th	Night	3 7% 2 6% 3 3 3 2 3 4 65%	4052
	21st to end	Night	4 2 1 3 2 2 3 2 4 6% 73%	4913
September	1st to 10th	Night	3 3 1 3 2 2 2 1 3 6% 75%	2000
	11th to 20th	Night	5% 5% 2 4 3 2 3 2 4 8% 61%	2100
	21st to end	Night	7% 5% 2 4 2 2 3 2 4 5% 64%	2237
October	1st to 10th	Night	5% 3 1 4 2 2 2 2 2 4 73%	3920
	11th to 20th	Night	12% 7% 3 6% 3 3 3 3 4 6% 50%	3897
	21st to end	Night	15% 7% 2 6% 4 4 5% 4 5% 7% 42%	4253
November	1st to 10th	Night	21% 9% 2 5% 4 4 4 4 4 6% 36%	2492
	11th to 20th	Night	22% 10% 3 7% 5% 4 4 3 5% 7% 29%	2940
	21st to end	Night	20% 8% 2 6% 4 3 4 3 4 6% 40%	2940
December	1st to 10th	Night	14% 7% 2 5% 3 3 4 3 5% 7% 47%	4700
	11th to 20th	Night	31% 11% 3 8% 5% 5% 4 3 4 5% 21%	5316
	21st to end	Night	33% 11% 2 6% 4 4 3 3 4 5% 24%	7106

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	64% 7% 8% 10% 8% 3	4939
	11th to 20th	Day	36% 4 4 11% 18% 27%	5340
	21st to end	Day	47% 4 8% 10% 16% 16%	5843
February	1st to 10th	Day	51% 6% 10% 16% 12% 6%	1890
	11th to 20th	Day	54% 7% 9% 17% 12% 1	1854
	21st to end	Day	57% 5% 10% 15% 10% 3	1693
March	1st to 10th	Day	60% 5% 7% 18% 8% 1	5062
	11th to 20th	Day	54% 5% 10% 14% 13% 4	5110
	21st to end	Day	62% 7% 13% 15% 3	5607
April	1st to 10th	Day	54% 9% 14% 14% 8% 1	2483
	11th to 20th	Day	50% 6% 14% 17% 10% 3	2492
	21st to end	Day	42% 8% 15% 21% 12% 1	2665
May	1st to 10th	Day	31% 7% 12% 24% 22% 4	6010
	11th to 20th	Day	27% 7% 16% 22% 26% 2	6140
	21st to end	Day	21% 11% 20% 42% 6%	7058
June	1st to 10th	Day	37% 9% 14% 24% 14% 2	2801
	11th to 20th	Day	23% 8% 14% 30% 21% 4	2800
	21st to end	Day	16% 6% 14% 28% 29% 8%	2800
July	1st to 10th	Day	6% 4 7% 22% 26% 35%	6251
	11th to 20th	Day	7% 2 5% 13% 31% 41%	5940
	21st to end	Day	3 4 13% 36% 26% 17%	6217
August	1st to 10th	Day	9% 4 10% 22% 32% 23%	4206
	11th to 20th	Day	11% 5% 12% 33% 27% 13%	4195
	21st to end	Day	13% 5% 11% 25% 37% 9%	4385
September	1st to 10th	Day	14% 4 8% 18% 34% 23%	2400
	11th to 20th	Day	23% 6% 13% 26% 27% 5%	2296
	21st to end	Day	19% 5% 12% 22% 25% 17%	2161
October	1st to 10th	Day	18% 4 9% 18% 18% 33%	3280
	11th to 20th	Day	28% 7% 13% 27% 18% 6%	3261
	21st to end	Day	41% 7% 9% 20% 15% 8%	3558
November	1st to 10th	Day	47% 7% 11% 18% 12% 6%	2022
	11th to 20th	Day	51% 7% 13% 13% 9% 7%	1680
	21st to end	Day	45% 6% 9% 13% 15% 11%	1680
December	1st to 10th	Day	36% 4 9% 17% 22% 12%	2700
	11th to 20th	Day	68% 7% 7% 8% 7% 3	3108
	21st to end	Day	72% 5% 5% 9% 7% 2	4092
January	1st to 10th	Night	66% 7% 9% 9% 8% 2	7964
	11th to 20th	Night	38% 5% 5% 10% 16% 26%	7650
	21st to end	Night	51% 4 5% 9% 12% 18%	8371
February	1st to 10th	Night	51% 7% 10% 15% 12% 6%	2730
	11th to 20th	Night	57% 7% 9% 14% 10% 3	2664
	21st to end	Night	54% 7% 12% 17% 8% 3	2107
March	1st to 10th	Night	60% 6% 8% 18% 6% 3	5052
	11th to 20th	Night	49% 10% 11% 15% 9% 6%	5110
	21st to end	Night	65% 8% 11% 12% 4 1	5610
April	1st to 10th	Night	53% 10% 14% 15% 7% 2	2137
	11th to 20th	Night	47% 10% 15% 16% 9% 3	2079
	21st to end	Night	42% 10% 18% 20% 8% 2	1951
May	1st to 10th	Night	28% 9% 14% 15% 26% 7%	4187
	11th to 20th	Night	30% 12% 16% 16% 23% 3	3988
	21st to end	Night	20% 19% 22% 32% 7%	4060
June	1st to 10th	Night	36% 11% 18% 21% 13% 1	1600
	11th to 20th	Night	20% 11% 18% 28% 19% 4	1600
	21st to end	Night	14% 7% 19% 26% 26% 8%	1600
July	1st to 10th	Night	7% 5% 12% 18% 21% 36%	3600
	11th to 20th	Night	7% 2 8% 13% 28% 43%	3906
	21st to end	Night	5% 9% 21% 25% 24% 15%	4345
August	1st to 10th	Night	9% 6% 12% 30% 21% 22%	2929
	11th to 20th	Night	10% 6% 15% 29% 29% 12%	2929
	21st to end	Night	13% 4 13% 25% 33% 13%	3532
September	1st to 10th	Night	12% 5% 10% 17% 30% 25%	2000
	11th to 20th	Night	20% 7% 16% 28% 22% 7%	2100
	21st to end	Night	23% 5% 12% 20% 21% 18%	2237
October	1st to 10th	Night	19% 3 8% 14% 21% 36%	3920
	11th to 20th	Night	31% 8% 11% 26% 18% 5%	3897
	21st to end	Night	39% 9% 11% 17% 16% 8%	4253
November	1st to 10th	Night	48% 8% 12% 14% 12% 6%	2492
	11th to 20th	Night	55% 8% 12% 12% 8% 5%	2940
	21st to end	Night	44% 7% 9% 15% 15% 10%	2940
December	1st to 10th	Night	36% 6% 10% 16% 21% 13%	4700
	11th to 20th	Night	67% 5% 7% 11% 8% 2	5316
	21st to end	Night	62% 8% 10% 11% 6% 2	7106

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	43% 16% 22% 15% 4	293
	11th to 20th	Day	31% 8% 24% 21% 12% 4	430
	21st to end	Day	29% 10% 24% 24% 10% 3	473
February	1st to 10th	Day	29% 16% 25% 20% 8% 2	430
	11th to 20th	Day	37% 16% 23% 18% 7%	425
	21st to end	Day	37% 17% 24% 16% 5% 1	405
March	1st to 10th	Day	37% 19% 25% 15% 4 1	540
	11th to 20th	Day	32% 14% 26% 19% 7% 2	540
	21st to end	Day	36% 16% 26% 17% 5% 1	594
April	1st to 10th	Day	32% 16% 27% 17% 6% 1	540
	11th to 20th	Day	32% 16% 25% 19% 6% 3	532
	21st to end	Day	25% 16% 31% 17% 9% 3	540
May	1st to 10th	Day	20% 18% 30% 20% 9% 3	543
	11th to 20th	Day	26% 16% 30% 18% 7% 3	568
	21st to end	Day	21% 16% 30% 22% 9% 3	617
June	1st to 10th	Day	17% 15% 31% 24% 10% 3	531
	11th to 20th	Day	13% 18% 37% 23% 7% 2	530
	21st to end	Day	4 12% 36% 30% 14% 4	530
July	1st to 10th	Day	6% 7% 35% 36% 12% 4	526
	11th to 20th	Day	2 5% 39% 35% 15% 5%	524
	21st to end	Day	1 6% 27% 40% 18% 7%	575
August	1st to 10th	Day	4 4 35% 33% 17% 6%	527
	11th to 20th	Day	4 7% 27% 37% 17% 8%	517
	21st to end	Day	5% 5% 27% 40% 15% 8%	583
September	1st to 10th	Day	8% 6% 33% 33% 14% 7%	530
	11th to 20th	Day	10% 11% 26% 33% 16% 4	530
	21st to end	Day	11% 9% 28% 30% 18% 4	530
October	1st to 10th	Day	12% 12% 25% 28% 19% 4	530
	11th to 20th	Day	17% 9% 21% 28% 20% 6%	530
	21st to end	Day	18% 12% 26% 26% 15% 3	583
November	1st to 10th	Day	24% 10% 22% 27% 12% 4	506
	11th to 20th	Day	28% 9% 22% 18% 16% 7%	220
	21st to end	Day	24% 9% 17% 29% 19% 3	220
December	1st to 10th	Day	24% 15% 21% 18% 15% 7%	220
	11th to 20th	Day	39% 9% 19% 18% 10% 5%	220
	21st to end	Day	39% 12% 18% 17% 12% 2	242
January	1st to 10th	Night	33% 9% 16% 25% 14% 3	840
	11th to 20th	Night	28% 6% 16% 29% 16% 5%	840
	21st to end	Night	29% 5% 16% 27% 19% 3	924
February	1st to 10th	Night	25% 10% 17% 33% 14% 1	840
	11th to 20th	Night	30% 9% 17% 24% 16% 3	824
	21st to end	Night	30% 10% 18% 28% 13% 1	692
March	1st to 10th	Night	37% 10% 15% 23% 12% 3	840
	11th to 20th	Night	29% 7% 16% 28% 19% 2	840
	21st to end	Night	31% 12% 17% 26% 12% 2	924
April	1st to 10th	Night	28% 10% 21% 24% 16% 2	840
	11th to 20th	Night	24% 10% 19% 26% 17% 4	831
	21st to end	Night	21% 6% 17% 31% 21% 4	691
May	1st to 10th	Night	15% 8% 19% 30% 24% 4	630
	11th to 20th	Night	18% 7% 14% 31% 23% 6%	549
	21st to end	Night	16% 8% 20% 29% 24% 3	455
June	1st to 10th	Night	14% 7% 18% 33% 26% 3	400
	11th to 20th	Night	8% 5% 23% 43% 21% 1	400
	21st to end	Night	7% 3 12% 43% 34% 3	400
July	1st to 10th	Night	3 3 10% 45% 36% 4	390
	11th to 20th	Night	3 2 8% 35% 43% 9%	520
	21st to end	Night	1 2 7% 29% 47% 15%	657
August	1st to 10th	Night	2 1 9% 34% 44% 11%	597
	11th to 20th	Night	4 1 7% 29% 48% 11%	594
	21st to end	Night	3 2 11% 31% 42% 11%	830
September	1st to 10th	Night	4 2 11% 34% 39% 11%	800
	11th to 20th	Night	7% 4 14% 30% 36% 10%	800
	21st to end	Night	9% 4 12% 30% 35% 11%	800
October	1st to 10th	Night	10% 5% 12% 30% 36% 8%	800
	11th to 20th	Night	15% 5% 13% 27% 32% 9%	800
	21st to end	Night	18% 5% 13% 30% 26% 8%	880
November	1st to 10th	Night	23% 6% 18% 29% 18% 6%	820
	11th to 20th	Night	28% 7% 14% 29% 19% 3	840
	21st to end	Night	23% 6% 17% 33% 18% 3	840
December	1st to 10th	Night	25% 7% 16% 29% 18% 4	840
	11th to 20th	Night	33% 9% 16% 27% 12% 3	840
	21st to end	Night	40% 8% 15% 23% 11% 2	924

Page generated at 2026-05-28 22:53:26. Version ac07

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