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 2025-02-06.

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	15% 8% 2 4 3 3 3 3 4 6% 50%	112642
	Night	17% 9% 2 5% 3 3 3 3 4 5% 44%	114440
Transparency	Day	35% 6% 11% 19% 18% 11%	112399
	Night	40% 7% 11% 16% 15% 11%	114273
Seeing	Day	20% 12% 28% 25% 12% 4	15437
	Night	20% 6% 15% 29% 24% 5%	24643

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	31% 16% 2 6% 4 3 4 3 3 5% 23%	3799
	11th to 20th	Day	25% 9% 2 4 2 2 2 2 3 3 46%	4100
	21st to end	Day	25% 7% 2 4 3 3 3 2 4 4 42%	4510
February	1st to 10th	Day	23% 11% 2 6% 4 3 4 4 5% 6% 34%	1756
	11th to 20th	Day	24% 11% 3 6% 3 3 5% 3 4 7% 32%	1665
	21st to end	Day	26% 15% 2 6% 3 3 3 3 2 6% 31%	1536
March	1st to 10th	Day	30% 24% 2 5% 3 2 2 2 2 3 23%	3442
	11th to 20th	Day	20% 10% 2 4 3 2 2 2 4 5% 45%	3490
	21st to end	Day	31% 13% 3 8% 5% 4 4 3 4 5% 20%	3825
April	1st to 10th	Day	24% 13% 3 7% 4 4 4 3 5% 6% 26%	2247
	11th to 20th	Day	24% 13% 2 5% 4 3 3 3 4 5% 34%	2249
	21st to end	Day	19% 9% 2 5% 3 4 4 3 5% 8% 37%	2411
May	1st to 10th	Day	16% 11% 1 3 2 3 3 3 3 4 50%	4110
	11th to 20th	Day	10% 4 1 3 2 2 2 2 3 6% 64%	4182
	21st to end	Day	10% 7% 1 4 3 3 4 3 5% 7% 53%	4813
June	1st to 10th	Day	15% 8% 2 5% 4 4 4 3 5% 8% 42%	2660
	11th to 20th	Day	8% 4 1 3 3 3 4 3 4 7% 58%	2660
	21st to end	Day	6% 3 1 3 2 2 2 2 3 5% 70%	2660
July	1st to 10th	Day	2 2 1 1 1 2 1 2 4 83%	4420
	11th to 20th	Day	3 2 1 2 2 2 2 2 2 4 79%	4204
	21st to end	Day	1 1 1 4 2 2 2 3 3 6% 75%	4455
August	1st to 10th	Day	1 2 1 3 2 2 3 3 5% 9% 70%	4091
	11th to 20th	Day	2 3 1 4 3 3 4 3 4 6% 69%	4026
	21st to end	Day	5% 3 1 2 2 2 2 2 3 5% 73%	4252
September	1st to 10th	Day	4 3 1 2 1 2 2 2 3 5% 76%	2280
	11th to 20th	Day	7% 4 1 4 3 4 3 3 4 7% 58%	2181
	21st to end	Day	8% 4 1 3 2 2 3 2 5% 6% 65%	2053
October	1st to 10th	Day	6% 3 1 2 2 2 2 2 3 4 72%	3180
	11th to 20th	Day	10% 4 1 5% 3 4 5% 3 6% 8% 50%	3161
	21st to end	Day	17% 7% 2 6% 3 4 4 3 6% 6% 41%	3448
November	1st to 10th	Day	23% 8% 2 5% 4 4 4 3 4 9% 36%	1924
	11th to 20th	Day	25% 8% 2 6% 4 4 4 4 6% 8% 31%	1600
	21st to end	Day	22% 7% 2 7% 4 3 4 3 5% 7% 37%	1600
December	1st to 10th	Day	15% 6% 2 5% 3 3 4 4 5% 7% 47%	2620
	11th to 20th	Day	33% 11% 3 7% 4 5% 4 3 5% 6% 18%	3028
	21st to end	Day	35% 15% 3 9% 5% 4 3 3 3 3 17%	4004
January	1st to 10th	Night	33% 14% 3 6% 4 3 4 3 4 5% 22%	6150
	11th to 20th	Night	22% 10% 3 6% 3 3 2 2 3 3 44%	5880
	21st to end	Night	30% 10% 2 4 2 2 2 1 3 3 40%	6468
February	1st to 10th	Night	22% 11% 3 7% 4 4 4 3 5% 7% 32%	2535
	11th to 20th	Night	23% 13% 3 7% 5% 4 3 3 3 5% 32%	2402
	21st to end	Night	21% 13% 3 6% 4 3 4 3 5% 7% 32%	1913
March	1st to 10th	Night	29% 21% 3 5% 3 2 3 2 4 4 23%	3432
	11th to 20th	Night	18% 11% 3 5% 3 2 2 2 4 5% 45%	3490
	21st to end	Night	26% 21% 3 7% 4 4 4 2 3 4 22%	3828
April	1st to 10th	Night	22% 14% 4 6% 4 4 4 3 5% 7% 28%	1933
	11th to 20th	Night	19% 13% 3 5% 4 4 4 4 5% 6% 33%	1879
	21st to end	Night	17% 11% 2 5% 4 4 4 3 6% 9% 36%	1765
May	1st to 10th	Night	12% 10% 3 5% 3 3 3 2 4 5% 50%	2860
	11th to 20th	Night	6% 7% 2 4 3 3 3 2 3 5% 61%	2716
	21st to end	Night	6% 10% 2 5% 4 4 4 4 5% 6% 49%	2762
June	1st to 10th	Night	14% 8% 3 6% 4 5% 4 4 5% 6% 41%	1520
	11th to 20th	Night	6% 6% 2 5% 3 3 4 3 4 8% 56%	1520
	21st to end	Night	6% 3 2 3 3 3 3 3 4 7% 64%	1520
July	1st to 10th	Night	2 1 1 2 2 2 3 1 2 5% 79%	2540
	11th to 20th	Night	2 2 1 3 2 3 2 2 3 6% 75%	2758
	21st to end	Night	2 3 8% 5% 3 4 3 3 5% 65%	3109
August	1st to 10th	Night	2 1 9% 5% 5% 4 4 4 7% 60%	2848
	11th to 20th	Night	2 4 2 7% 3 3 3 2 3 6% 65%	2812
	21st to end	Night	5% 2 1 3 2 2 3 2 3 5% 73%	3424
September	1st to 10th	Night	3 3 1 2 2 1 2 1 3 6% 77%	1900
	11th to 20th	Night	5% 5% 2 4 3 2 3 3 4 8% 62%	1995
	21st to end	Night	7% 5% 2 4 2 2 3 2 4 5% 64%	2125
October	1st to 10th	Night	5% 3 1 4 2 2 2 2 2 4 73%	3800
	11th to 20th	Night	12% 7% 3 6% 3 3 3 3 4 6% 50%	3777
	21st to end	Night	15% 7% 2 6% 4 4 5% 4 5% 6% 41%	4121
November	1st to 10th	Night	21% 9% 2 5% 4 4 4 4 4 6% 37%	2370
	11th to 20th	Night	22% 10% 3 7% 5% 4 4 3 5% 7% 29%	2800
	21st to end	Night	21% 8% 2 6% 4 3 4 4 4 6% 40%	2800
December	1st to 10th	Night	15% 7% 2 5% 3 3 4 3 5% 7% 47%	4560
	11th to 20th	Night	31% 11% 3 8% 5% 5% 4 3 4 5% 21%	5176
	21st to end	Night	33% 11% 2 6% 4 4 3 3 4 5% 24%	6952

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% 7% 11% 8% 4	3799
	11th to 20th	Day	45% 5% 4 14% 19% 13%	4100
	21st to end	Day	46% 4 8% 9% 16% 17%	4510
February	1st to 10th	Day	51% 6% 11% 16% 12% 5%	1756
	11th to 20th	Day	52% 7% 9% 18% 13% 2	1674
	21st to end	Day	56% 6% 10% 16% 10% 2	1536
March	1st to 10th	Day	68% 4 6% 15% 6% 1	3442
	11th to 20th	Day	42% 5% 12% 19% 17% 5%	3490
	21st to end	Day	64% 7% 14% 11% 3	3825
April	1st to 10th	Day	56% 9% 13% 13% 8% 1	2247
	11th to 20th	Day	52% 6% 15% 16% 9% 3	2252
	21st to end	Day	43% 9% 15% 20% 11% 2	2411
May	1st to 10th	Day	35% 8% 14% 23% 14% 6%	4110
	11th to 20th	Day	23% 5% 10% 22% 37% 3	4185
	21st to end	Day	26% 13% 21% 34% 6%	4814
June	1st to 10th	Day	39% 9% 15% 23% 13% 2	2660
	11th to 20th	Day	24% 8% 15% 30% 20% 4	2660
	21st to end	Day	16% 5% 14% 28% 29% 8%	2660
July	1st to 10th	Day	7% 4 7% 14% 17% 51%	4351
	11th to 20th	Day	10% 3 7% 15% 26% 38%	4131
	21st to end	Day	4 2 10% 24% 34% 25%	4315
August	1st to 10th	Day	9% 4 9% 21% 33% 23%	4076
	11th to 20th	Day	10% 5% 12% 33% 27% 13%	4065
	21st to end	Day	13% 5% 11% 25% 36% 10%	4251
September	1st to 10th	Day	13% 3 8% 17% 35% 24%	2280
	11th to 20th	Day	23% 6% 12% 26% 27% 5%	2181
	21st to end	Day	19% 5% 12% 23% 24% 17%	2053
October	1st to 10th	Day	17% 4 9% 18% 18% 34%	3180
	11th to 20th	Day	28% 7% 13% 28% 18% 6%	3161
	21st to end	Day	41% 7% 9% 19% 15% 8%	3448
November	1st to 10th	Day	47% 6% 11% 17% 12% 6%	1924
	11th to 20th	Day	50% 7% 14% 13% 9% 8%	1600
	21st to end	Day	47% 6% 9% 13% 14% 11%	1600
December	1st to 10th	Day	36% 4 8% 17% 22% 12%	2620
	11th to 20th	Day	68% 7% 7% 8% 7% 2	3028
	21st to end	Day	73% 5% 5% 9% 7% 2	4004
January	1st to 10th	Night	64% 7% 9% 9% 8% 3	6150
	11th to 20th	Night	46% 6% 6% 12% 19% 11%	5880
	21st to end	Night	51% 3 4 8% 11% 22%	6468
February	1st to 10th	Night	52% 7% 11% 15% 11% 5%	2535
	11th to 20th	Night	55% 7% 9% 14% 11% 3	2404
	21st to end	Night	52% 7% 13% 18% 7% 3	1913
March	1st to 10th	Night	65% 6% 9% 15% 5%	3432
	11th to 20th	Night	40% 12% 12% 17% 12% 8%	3490
	21st to end	Night	66% 9% 10% 11% 4 1	3828
April	1st to 10th	Night	54% 10% 14% 15% 6% 2	1933
	11th to 20th	Night	49% 10% 16% 15% 8% 3	1879
	21st to end	Night	43% 10% 18% 20% 7% 2	1765
May	1st to 10th	Night	32% 11% 19% 17% 14% 7%	2860
	11th to 20th	Night	23% 8% 16% 15% 33% 5%	2717
	21st to end	Night	24% 22% 21% 29% 4	2762
June	1st to 10th	Night	37% 12% 18% 20% 11% 1	1520
	11th to 20th	Night	21% 10% 18% 28% 18% 4	1520
	21st to end	Night	14% 7% 20% 25% 26% 8%	1520
July	1st to 10th	Night	8% 4 11% 13% 15% 50%	2500
	11th to 20th	Night	10% 3 11% 14% 23% 40%	2708
	21st to end	Night	5% 6% 16% 20% 31% 22%	3011
August	1st to 10th	Night	10% 6% 12% 29% 22% 22%	2839
	11th to 20th	Night	9% 6% 15% 29% 28% 11%	2839
	21st to end	Night	13% 4 13% 25% 32% 13%	3424
September	1st to 10th	Night	11% 5% 10% 17% 31% 27%	1900
	11th to 20th	Night	19% 7% 16% 28% 22% 7%	1995
	21st to end	Night	23% 5% 13% 20% 21% 18%	2125
October	1st to 10th	Night	18% 3 8% 14% 20% 37%	3800
	11th to 20th	Night	32% 8% 11% 26% 18% 5%	3777
	21st to end	Night	40% 9% 11% 17% 16% 8%	4121
November	1st to 10th	Night	48% 8% 12% 13% 12% 6%	2370
	11th to 20th	Night	55% 8% 12% 11% 9% 6%	2800
	21st to end	Night	44% 7% 9% 15% 14% 11%	2800
December	1st to 10th	Night	36% 5% 9% 15% 21% 13%	4560
	11th to 20th	Night	67% 5% 7% 11% 8% 1	5176
	21st to end	Night	62% 8% 11% 11% 6% 2	6952

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% 15% 22% 15% 4	269
	11th to 20th	Day	34% 9% 25% 19% 10% 4	400
	21st to end	Day	30% 11% 22% 24% 10% 3	440
February	1st to 10th	Day	28% 17% 24% 20% 7% 2	386
	11th to 20th	Day	36% 14% 23% 19% 7% 1	365
	21st to end	Day	35% 18% 24% 16% 6% 1	348
March	1st to 10th	Day	39% 17% 24% 15% 5% 1	460
	11th to 20th	Day	33% 13% 26% 18% 8% 2	460
	21st to end	Day	36% 17% 25% 17% 5%	506
April	1st to 10th	Day	33% 17% 27% 16% 5% 1	460
	11th to 20th	Day	34% 16% 23% 19% 6% 2	452
	21st to end	Day	25% 17% 30% 17% 8% 3	460
May	1st to 10th	Day	21% 18% 30% 20% 9% 2	463
	11th to 20th	Day	27% 14% 29% 19% 8% 3	488
	21st to end	Day	21% 17% 30% 21% 9% 2	529
June	1st to 10th	Day	18% 16% 29% 24% 10% 3	490
	11th to 20th	Day	13% 17% 37% 24% 7% 2	490
	21st to end	Day	4 11% 37% 30% 14% 3	490
July	1st to 10th	Day	7% 7% 34% 36% 13% 4	486
	11th to 20th	Day	2 5% 40% 34% 14% 5%	484
	21st to end	Day	1 6% 29% 39% 18% 6%	531
August	1st to 10th	Day	4 3 36% 33% 17% 6%	487
	11th to 20th	Day	3 8% 27% 38% 17% 7%	477
	21st to end	Day	6% 5% 28% 39% 16% 7%	539
September	1st to 10th	Day	7% 6% 32% 34% 14% 7%	490
	11th to 20th	Day	10% 10% 27% 34% 15% 4	490
	21st to end	Day	11% 9% 28% 30% 19% 4	490
October	1st to 10th	Day	10% 11% 27% 29% 19% 4	490
	11th to 20th	Day	17% 9% 19% 29% 21% 6%	490
	21st to end	Day	17% 13% 27% 26% 15% 3	539
November	1st to 10th	Day	23% 11% 23% 27% 12% 4	468
	11th to 20th	Day	27% 9% 22% 19% 17% 8%	200
	21st to end	Day	26% 10% 16% 27% 19% 3	200
December	1st to 10th	Day	27% 15% 19% 17% 16% 8%	200
	11th to 20th	Day	40% 8% 21% 18% 11% 4	200
	21st to end	Day	39% 11% 18% 18% 12% 1	220
January	1st to 10th	Night	32% 8% 16% 26% 15% 3	800
	11th to 20th	Night	29% 6% 17% 27% 16% 5%	800
	21st to end	Night	30% 5% 15% 27% 20% 4	880
February	1st to 10th	Night	26% 10% 15% 33% 15% 1	780
	11th to 20th	Night	29% 8% 16% 25% 17% 4	744
	21st to end	Night	29% 11% 18% 28% 14% 1	628
March	1st to 10th	Night	37% 11% 15% 23% 12% 3	760
	11th to 20th	Night	30% 6% 15% 26% 21% 2	760
	21st to end	Night	31% 12% 16% 26% 12% 2	836
April	1st to 10th	Night	28% 10% 21% 22% 16% 3	760
	11th to 20th	Night	24% 10% 20% 25% 17% 5%	751
	21st to end	Night	22% 6% 17% 30% 20% 4	625
May	1st to 10th	Night	15% 8% 20% 29% 24% 4	570
	11th to 20th	Night	18% 6% 13% 31% 24% 7%	496
	21st to end	Night	17% 8% 20% 29% 23% 3	411
June	1st to 10th	Night	15% 7% 18% 32% 26% 2	380
	11th to 20th	Night	7% 5% 22% 42% 22% 1	380
	21st to end	Night	7% 3 12% 42% 34% 2	380
July	1st to 10th	Night	3 3 10% 44% 36% 4	370
	11th to 20th	Night	3 2 9% 36% 42% 8%	493
	21st to end	Night	1 2 7% 30% 46% 15%	624
August	1st to 10th	Night	2 1 8% 34% 43% 12%	567
	11th to 20th	Night	3 1 7% 29% 49% 11%	564
	21st to end	Night	4 2 11% 32% 41% 11%	788
September	1st to 10th	Night	4 2 11% 34% 39% 11%	760
	11th to 20th	Night	6% 4 13% 31% 35% 10%	760
	21st to end	Night	9% 4 12% 30% 34% 11%	760
October	1st to 10th	Night	9% 4 12% 29% 37% 9%	760
	11th to 20th	Night	16% 5% 12% 26% 33% 9%	760
	21st to end	Night	18% 5% 13% 30% 27% 8%	836
November	1st to 10th	Night	22% 6% 18% 29% 19% 6%	780
	11th to 20th	Night	27% 7% 14% 29% 20% 3	800
	21st to end	Night	24% 6% 16% 33% 18% 4	800
December	1st to 10th	Night	26% 7% 15% 29% 18% 4	800
	11th to 20th	Night	33% 9% 16% 27% 12% 3	800
	21st to end	Night	40% 8% 14% 24% 11% 2	880

Page generated at 2025-02-03 00:05:49. Version ac07

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