Kings Valley Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Kings Valley Observatory clear sky chart from 2005-11-06 to 2026-05-17.

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 5% 4 6% 8% 50%	140725
	Night	3 6% 2 5% 3 3 4 3 5% 7% 59%	139600
Transparency	Day	29% 7% 9% 23% 23% 10%	135680
	Night	24% 5% 9% 25% 26% 11%	135652
Seeing	Day	10% 13% 33% 29% 12% 3	17591
	Night	6% 10% 34% 36% 13% 2	27711

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	1 7% 3 9% 3 3 3 2 4 6% 60%	4720
	11th to 20th	Day	3 2 7% 5% 3 4 3 5% 7% 60%	4980
	21st to end	Day	4 3 8% 3 4 3 3 5% 7% 60%	5844
February	1st to 10th	Day	1 6% 2 9% 4 3 4 3 5% 7% 57%	1890
	11th to 20th	Day	4 3 6% 4 4 4 3 6% 10% 58%	2012
	21st to end	Day	1 6% 2 7% 3 3 4 4 4 7% 60%	1730
March	1st to 10th	Day	1 8% 4 7% 3 3 4 3 4 5% 57%	4600
	11th to 20th	Day	2 12% 6% 10% 5% 5% 4 3 4 6% 43%	5105
	21st to end	Day	2 9% 3 6% 4 4 5% 4 8% 9% 46%	5916
April	1st to 10th	Day	4 8% 2 6% 4 3 4 5% 6% 8% 50%	2520
	11th to 20th	Day	5% 11% 4 8% 5% 4 5% 4 5% 8% 42%	2491
	21st to end	Day	7% 11% 3 7% 5% 4 5% 4 6% 8% 40%	2520
May	1st to 10th	Day	8% 12% 3 8% 4 4 5% 4 6% 7% 39%	5804
	11th to 20th	Day	7% 8% 2 7% 5% 4 5% 5% 7% 8% 41%	6383
	21st to end	Day	6% 6% 1 5% 4 5% 6% 5% 8% 9% 44%	6925
June	1st to 10th	Day	5% 5% 2 5% 5% 5% 6% 6% 8% 9% 45%	2800
	11th to 20th	Day	5% 4 2 5% 4 6% 5% 5% 6% 9% 49%	2800
	21st to end	Day	4 5% 1 5% 5% 5% 8% 6% 8% 8% 44%	2800
July	1st to 10th	Day	5% 4 1 5% 4 5% 5% 5% 7% 8% 50%	6339
	11th to 20th	Day	5% 4 2 7% 6% 7% 7% 6% 9% 10% 37%	6340
	21st to end	Day	7% 5% 2 8% 6% 6% 6% 5% 7% 7% 41%	6686
August	1st to 10th	Day	8% 6% 3 7% 6% 7% 7% 6% 8% 9% 33%	5779
	11th to 20th	Day	5% 4 2 6% 6% 6% 7% 5% 7% 8% 44%	5375
	21st to end	Day	9% 7% 3 8% 5% 6% 6% 5% 7% 7% 39%	5984
September	1st to 10th	Day	5% 5% 3 5% 5% 4 5% 4 6% 7% 52%	2400
	11th to 20th	Day	6% 4 2 6% 4 3 5% 4 6% 7% 53%	2390
	21st to end	Day	6% 5% 1 4 3 3 3 3 5% 7% 61%	2195
October	1st to 10th	Day	5% 5% 2 4 3 3 3 3 3 4 66%	3270
	11th to 20th	Day	5% 4 2 5% 4 5% 5% 4 6% 7% 54%	3250
	21st to end	Day	3 6% 2 4 3 2 3 3 4 6% 65%	3462
November	1st to 10th	Day	1 4 2 5% 2 3 3 3 5% 7% 65%	1853
	11th to 20th	Day	1 4 3 5% 3 3 3 4 5% 7% 64%	1890
	21st to end	Day	1 5% 3 7% 3 3 3 3 5% 8% 58%	1774
December	1st to 10th	Day	1 4 2 6% 3 3 3 2 3 6% 68%	2700
	11th to 20th	Day	1 3 2 3 3 3 3 2 4 9% 68%	3106
	21st to end	Day	1 5% 2 8% 4 4 5% 3 6% 8% 54%	4092
January	1st to 10th	Night	5% 3 9% 4 3 4 2 4 7% 58%	8201
	11th to 20th	Night	3 2 6% 4 3 4 3 5% 7% 63%	8052
	21st to end	Night	1 5% 2 6% 4 4 4 3 5% 5% 63%	8370
February	1st to 10th	Night	1 6% 3 5% 3 3 4 3 4 8% 60%	2730
	11th to 20th	Night	1 4 2 6% 3 3 4 3 6% 8% 58%	2494
	21st to end	Night	1 5% 2 6% 3 3 3 3 5% 6% 63%	2076
March	1st to 10th	Night	1 8% 3 6% 4 3 4 3 5% 6% 58%	5494
	11th to 20th	Night	2 12% 3 6% 3 3 3 3 4 7% 54%	5114
	21st to end	Night	3 8% 3 6% 3 3 3 4 5% 8% 53%	5287
April	1st to 10th	Night	2 6% 2 5% 4 3 3 3 5% 8% 59%	2100
	11th to 20th	Night	5% 10% 3 6% 3 3 2 3 5% 7% 52%	2077
	21st to end	Night	7% 11% 2 5% 3 4 4 3 4 6% 50%	2100
May	1st to 10th	Night	8% 12% 3 5% 4 3 3 3 6% 7% 45%	4377
	11th to 20th	Night	7% 8% 2 4 4 3 4 4 5% 7% 52%	3665
	21st to end	Night	5% 6% 2 5% 3 3 3 3 5% 6% 60%	3972
June	1st to 10th	Night	4 4 1 4 2 3 4 3 5% 11% 59%	1600
	11th to 20th	Night	5% 3 1 3 3 3 3 4 6% 7% 63%	1600
	21st to end	Night	4 2 2 3 3 4 4 5% 8% 8% 58%	1600
July	1st to 10th	Night	4 3 1 4 3 3 3 4 5% 7% 62%	3640
	11th to 20th	Night	2 3 1 4 4 4 6% 5% 8% 11% 52%	3640
	21st to end	Night	3 3 1 5% 4 4 5% 6% 8% 11% 50%	4183
August	1st to 10th	Night	4 4 2 4 3 4 5% 5% 8% 10% 50%	4033
	11th to 20th	Night	4 3 1 4 3 4 5% 4 7% 9% 55%	4472
	21st to end	Night	7% 7% 3 8% 5% 4 4 4 6% 8% 46%	4993
September	1st to 10th	Night	6% 4 1 5% 3 3 3 3 6% 7% 59%	2000
	11th to 20th	Night	6% 3 1 3 3 3 4 4 5% 7% 62%	2010
	21st to end	Night	6% 4 2 4 2 3 3 3 5% 5% 63%	2200
October	1st to 10th	Night	4 4 2 3 2 2 3 2 3 5% 70%	3920
	11th to 20th	Night	3 5% 2 4 3 3 3 3 5% 7% 62%	3898
	21st to end	Night	3 6% 2 5% 2 2 2 2 4 5% 67%	4306
November	1st to 10th	Night	1 4 2 4 3 2 2 3 4 8% 67%	2665
	11th to 20th	Night	1 4 2 4 3 2 3 2 4 7% 67%	2730
	21st to end	Night	2 6% 2 5% 3 3 3 2 5% 7% 61%	2842
December	1st to 10th	Night	2 1 4 2 2 3 2 3 6% 73%	4710
	11th to 20th	Night	1 3 2 4 3 3 3 2 5% 8% 67%	5321
	21st to end	Night	1 7% 3 7% 4 4 4 4 5% 7% 54%	7128

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	26% 3 6% 27% 28% 9%	4723
	11th to 20th	Day	22% 6% 9% 25% 27% 11%	4980
	21st to end	Day	24% 5% 6% 25% 26% 14%	5844
February	1st to 10th	Day	27% 5% 10% 27% 22% 10%	1890
	11th to 20th	Day	23% 4 8% 29% 28% 8%	2022
	21st to end	Day	23% 3 8% 22% 29% 14%	1730
March	1st to 10th	Day	26% 6% 4 18% 31% 15%	4600
	11th to 20th	Day	36% 10% 7% 22% 21% 5%	5105
	21st to end	Day	28% 8% 9% 37% 15% 3	5916
April	1st to 10th	Day	30% 6% 9% 26% 20% 9%	2520
	11th to 20th	Day	38% 6% 9% 19% 20% 8%	2494
	21st to end	Day	39% 6% 10% 23% 18% 4	2520
May	1st to 10th	Day	39% 7% 9% 24% 15% 5%	5804
	11th to 20th	Day	34% 10% 10% 19% 18% 9%	6387
	21st to end	Day	30% 9% 13% 20% 23% 6%	6926
June	1st to 10th	Day	30% 9% 14% 22% 17% 8%	2800
	11th to 20th	Day	28% 7% 11% 17% 22% 15%	2800
	21st to end	Day	31% 8% 12% 19% 19% 11%	2800
July	1st to 10th	Day	25% 8% 8% 17% 25% 17%	6271
	11th to 20th	Day	33% 10% 13% 22% 15% 7%	6265
	21st to end	Day	36% 9% 11% 17% 17% 11%	6493
August	1st to 10th	Day	43% 10% 14% 17% 13% 4	4208
	11th to 20th	Day	34% 8% 12% 16% 19% 10%	3891
	21st to end	Day	34% 8% 10% 17% 23% 8%	4311
September	1st to 10th	Day	29% 5% 8% 22% 22% 14%	2400
	11th to 20th	Day	27% 6% 8% 21% 27% 12%	2390
	21st to end	Day	23% 5% 6% 22% 34% 11%	2195
October	1st to 10th	Day	20% 5% 6% 16% 34% 18%	3270
	11th to 20th	Day	26% 6% 7% 25% 27% 8%	3250
	21st to end	Day	21% 3 5% 25% 36% 10%	3462
November	1st to 10th	Day	19% 4 7% 24% 31% 15%	1853
	11th to 20th	Day	20% 4 5% 31% 30% 11%	1890
	21st to end	Day	24% 4 8% 24% 30% 11%	1774
December	1st to 10th	Day	19% 3 7% 32% 30% 9%	2700
	11th to 20th	Day	15% 3 8% 34% 30% 11%	3104
	21st to end	Day	25% 5% 8% 24% 28% 10%	4092
January	1st to 10th	Night	26% 4 6% 28% 30% 6%	8202
	11th to 20th	Night	19% 5% 8% 25% 25% 17%	8052
	21st to end	Night	23% 4 8% 22% 27% 17%	8370
February	1st to 10th	Night	23% 3 10% 29% 25% 10%	2730
	11th to 20th	Night	24% 4 8% 29% 26% 9%	2494
	21st to end	Night	22% 3 5% 25% 30% 15%	2076
March	1st to 10th	Night	26% 4 5% 16% 35% 13%	5494
	11th to 20th	Night	30% 4 7% 19% 27% 12%	5114
	21st to end	Night	28% 6% 8% 35% 20% 3	5287
April	1st to 10th	Night	25% 4 11% 27% 24% 9%	2100
	11th to 20th	Night	30% 6% 9% 26% 23% 7%	2077
	21st to end	Night	34% 5% 10% 26% 20% 5%	2100
May	1st to 10th	Night	36% 7% 11% 25% 13% 8%	4374
	11th to 20th	Night	29% 8% 12% 24% 21% 6%	3666
	21st to end	Night	24% 6% 14% 26% 24% 6%	3972
June	1st to 10th	Night	20% 7% 19% 30% 16% 9%	1600
	11th to 20th	Night	19% 6% 12% 20% 23% 20%	1600
	21st to end	Night	20% 5% 12% 24% 26% 12%	1600
July	1st to 10th	Night	21% 5% 9% 18% 32% 15%	3600
	11th to 20th	Night	21% 7% 20% 28% 18% 6%	3592
	21st to end	Night	24% 8% 18% 24% 14% 12%	4064
August	1st to 10th	Night	30% 8% 18% 24% 16% 3	2928
	11th to 20th	Night	22% 9% 18% 22% 19% 9%	3232
	21st to end	Night	30% 8% 14% 22% 22% 5%	3597
September	1st to 10th	Night	24% 5% 9% 24% 24% 14%	2000
	11th to 20th	Night	22% 4 10% 24% 26% 15%	2010
	21st to end	Night	23% 4 8% 23% 31% 11%	2200
October	1st to 10th	Night	17% 4 7% 21% 34% 17%	3920
	11th to 20th	Night	22% 5% 8% 29% 27% 10%	3898
	21st to end	Night	21% 3 4 25% 33% 14%	4306
November	1st to 10th	Night	17% 4 8% 24% 32% 15%	2665
	11th to 20th	Night	19% 3 6% 28% 33% 12%	2730
	21st to end	Night	23% 3 8% 24% 30% 12%	2842
December	1st to 10th	Night	14% 3 7% 31% 36% 9%	4710
	11th to 20th	Night	17% 3 6% 28% 35% 10%	5322
	21st to end	Night	28% 5% 8% 22% 27% 10%	7128

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	10% 13% 35% 31% 10% 2	330
	11th to 20th	Day	8% 16% 47% 23% 6% 1	330
	21st to end	Day	5% 17% 44% 27% 6% 2	363
February	1st to 10th	Day	7% 29% 39% 20% 3 2	330
	11th to 20th	Day	7% 23% 45% 20% 4	330
	21st to end	Day	10% 18% 42% 26% 4	273
March	1st to 10th	Day	8% 19% 41% 23% 7% 2	330
	11th to 20th	Day	13% 19% 39% 22% 6% 1	535
	21st to end	Day	17% 23% 34% 20% 6%	594
April	1st to 10th	Day	14% 25% 34% 20% 6% 1	540
	11th to 20th	Day	19% 26% 33% 16% 5% 1	532
	21st to end	Day	18% 19% 34% 21% 6% 1	540
May	1st to 10th	Day	18% 12% 38% 23% 6% 2	643
	11th to 20th	Day	16% 11% 29% 32% 10% 2	756
	21st to end	Day	12% 10% 29% 31% 15% 3	789
June	1st to 10th	Day	7% 9% 26% 35% 19% 4	730
	11th to 20th	Day	6% 10% 33% 32% 15% 4	730
	21st to end	Day	8% 8% 34% 30% 16% 5%	730
July	1st to 10th	Day	7% 6% 21% 35% 24% 7%	721
	11th to 20th	Day	5% 4 22% 36% 25% 8%	718
	21st to end	Day	8% 6% 17% 36% 25% 8%	704
August	1st to 10th	Day	9% 8% 26% 32% 20% 5%	527
	11th to 20th	Day	6% 5% 26% 39% 18% 6%	517
	21st to end	Day	9% 7% 26% 35% 18% 4	583
September	1st to 10th	Day	8% 8% 28% 35% 16% 4	530
	11th to 20th	Day	8% 12% 29% 34% 15% 3	520
	21st to end	Day	8% 9% 30% 33% 14% 5%	330
October	1st to 10th	Day	9% 11% 32% 25% 18% 5%	330
	11th to 20th	Day	6% 17% 38% 28% 8% 2	330
	21st to end	Day	9% 13% 42% 28% 7% 1	363
November	1st to 10th	Day	7% 14% 40% 27% 9% 3	330
	11th to 20th	Day	9% 15% 38% 29% 7% 2	330
	21st to end	Day	6% 15% 41% 30% 7% 1	330
December	1st to 10th	Day	8% 17% 38% 29% 7% 2	330
	11th to 20th	Day	7% 16% 44% 25% 7% 1	330
	21st to end	Day	9% 20% 43% 21% 6% 1	363
January	1st to 10th	Night	3 16% 38% 32% 8% 2	1050
	11th to 20th	Night	4 21% 42% 26% 6% 2	982
	21st to end	Night	3 14% 43% 34% 5% 1	924
February	1st to 10th	Night	4 16% 48% 26% 5%	840
	11th to 20th	Night	3 16% 47% 28% 5%	824
	21st to end	Night	5% 15% 46% 30% 3	692
March	1st to 10th	Night	3 14% 44% 32% 6% 1	840
	11th to 20th	Night	8% 10% 41% 32% 8% 1	840
	21st to end	Night	7% 10% 46% 32% 4 1	782
April	1st to 10th	Night	8% 13% 41% 34% 4	630
	11th to 20th	Night	12% 13% 37% 30% 7% 1	623
	21st to end	Night	14% 10% 36% 33% 7% 1	630
May	1st to 10th	Night	14% 7% 31% 36% 11% 1	630
	11th to 20th	Night	14% 5% 25% 42% 12% 2	609
	21st to end	Night	8% 7% 27% 40% 16% 3	650
June	1st to 10th	Night	6% 4 21% 47% 19% 3	600
	11th to 20th	Night	7% 4 26% 45% 16% 2	600
	21st to end	Night	4 2 20% 45% 26% 3	600
July	1st to 10th	Night	8% 2 14% 39% 33% 4	585
	11th to 20th	Night	2 2 14% 41% 37% 4	582
	21st to end	Night	7% 2 7% 44% 34% 5%	657
August	1st to 10th	Night	5% 2 14% 44% 31% 5%	597
	11th to 20th	Night	6% 1 15% 46% 27% 4	594
	21st to end	Night	6% 3 15% 43% 28% 5%	660
September	1st to 10th	Night	6% 3 16% 45% 25% 6%	600
	11th to 20th	Night	8% 3 21% 43% 20% 5%	600
	21st to end	Night	7% 5% 27% 40% 18% 4	600
October	1st to 10th	Night	7% 8% 30% 39% 13% 3	800
	11th to 20th	Night	4 8% 35% 39% 11% 4	800
	21st to end	Night	7% 8% 37% 35% 12% 1	910
November	1st to 10th	Night	4 10% 39% 35% 10% 2	1025
	11th to 20th	Night	4 14% 41% 32% 7% 1	1050
	21st to end	Night	5% 11% 39% 36% 8% 1	1050
December	1st to 10th	Night	4 14% 38% 36% 7% 1	1050
	11th to 20th	Night	5% 15% 43% 29% 7% 1	1050
	21st to end	Night	5% 16% 42% 31% 5% 1	1155

Page generated at 2026-05-13 23:58:57. Version ac07

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