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 2025-01-22.

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%	108980
	Night	3 6% 2 5% 3 3 4 3 5% 7% 59%	109147
Transparency	Day	29% 7% 9% 23% 23% 9%	108726
	Night	23% 5% 10% 26% 26% 10%	108991
Seeing	Day	9% 12% 32% 29% 13% 3	15797
	Night	6% 10% 33% 36% 13% 2	25954

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	4 2 8% 4 3 4 3 5% 8% 57%	2618
	11th to 20th	Day	1 5% 3 9% 4 4 5% 5% 6% 8% 51%	2752
	21st to end	Day	1 6% 4 8% 3 4 3 3 5% 8% 55%	3155
February	1st to 10th	Day	1 7% 2 9% 4 3 4 3 5% 6% 56%	1710
	11th to 20th	Day	4 3 6% 3 3 4 3 5% 10% 59%	1815
	21st to end	Day	1 7% 2 8% 4 3 4 4 4 7% 58%	1570
March	1st to 10th	Day	1 8% 4 7% 4 3 4 3 5% 6% 54%	3130
	11th to 20th	Day	2 14% 5% 9% 4 5% 4 3 4 6% 42%	3485
	21st to end	Day	2 10% 3 6% 4 3 5% 5% 7% 8% 47%	4036
April	1st to 10th	Day	4 7% 2 5% 4 3 4 5% 6% 8% 50%	2280
	11th to 20th	Day	6% 11% 4 8% 5% 4 5% 4 5% 7% 41%	2251
	21st to end	Day	7% 11% 3 7% 5% 4 6% 4 6% 8% 40%	2280
May	1st to 10th	Day	7% 12% 3 9% 5% 5% 5% 4 7% 7% 36%	3969
	11th to 20th	Day	9% 8% 3 7% 5% 5% 5% 5% 8% 10% 37%	4388
	21st to end	Day	5% 5% 1 5% 5% 4 6% 5% 8% 10% 46%	4825
June	1st to 10th	Day	5% 5% 2 5% 5% 5% 6% 6% 8% 10% 46%	2660
	11th to 20th	Day	5% 4 2 5% 4 5% 5% 5% 6% 9% 49%	2660
	21st to end	Day	4 5% 1 5% 5% 5% 8% 7% 9% 8% 43%	2660
July	1st to 10th	Day	5% 4 1 4 4 5% 5% 6% 6% 7% 52%	4430
	11th to 20th	Day	4 4 2 6% 6% 6% 7% 6% 8% 11% 39%	4430
	21st to end	Day	7% 5% 2 6% 5% 5% 6% 5% 7% 8% 45%	4655
August	1st to 10th	Day	10% 7% 3 8% 7% 6% 7% 5% 8% 8% 32%	4092
	11th to 20th	Day	5% 4 2 7% 6% 6% 7% 5% 7% 8% 42%	3735
	21st to end	Day	6% 6% 2 7% 4 5% 6% 5% 7% 8% 43%	4180
September	1st to 10th	Day	5% 5% 2 5% 5% 4 5% 4 6% 7% 53%	2280
	11th to 20th	Day	6% 4 2 5% 4 3 5% 4 6% 7% 54%	2271
	21st to end	Day	5% 5% 1 4 3 3 3 3 5% 7% 61%	2085
October	1st to 10th	Day	5% 5% 1 4 3 3 3 3 3 4 66%	3170
	11th to 20th	Day	5% 4 2 5% 4 5% 5% 4 6% 7% 53%	3150
	21st to end	Day	3 6% 2 4 3 2 3 3 4 6% 65%	3355
November	1st to 10th	Day	1 4 2 5% 2 3 3 3 5% 7% 65%	1763
	11th to 20th	Day	1 4 3 5% 3 3 3 4 5% 7% 64%	1800
	21st to end	Day	1 5% 3 7% 3 3 3 3 5% 8% 59%	1690
December	1st to 10th	Day	1 4 2 5% 3 3 3 2 3 7% 68%	2620
	11th to 20th	Day	1 3 2 3 3 3 3 2 4 8% 69%	3026
	21st to end	Day	1 5% 2 8% 4 4 5% 3 6% 8% 54%	4004
January	1st to 10th	Night	5% 3 9% 5% 3 4 3 5% 7% 55%	4557
	11th to 20th	Night	3 1 4 3 3 5% 5% 7% 9% 61%	4466
	21st to end	Night	1 7% 2 6% 4 3 4 3 5% 6% 58%	4534
February	1st to 10th	Night	1 6% 3 5% 4 3 4 3 4 8% 60%	2470
	11th to 20th	Night	1 5% 2 6% 3 3 3 3 6% 7% 59%	2252
	21st to end	Night	1 5% 2 6% 4 3 3 4 4 6% 62%	1884
March	1st to 10th	Night	1 7% 3 6% 4 3 4 3 5% 6% 58%	3734
	11th to 20th	Night	3 16% 3 6% 3 3 3 3 4 6% 52%	3494
	21st to end	Night	2 8% 3 5% 3 3 3 4 5% 8% 56%	3610
April	1st to 10th	Night	3 7% 2 5% 4 3 3 3 5% 7% 59%	1900
	11th to 20th	Night	5% 11% 3 6% 3 3 3 3 5% 7% 52%	1877
	21st to end	Night	7% 11% 2 5% 3 3 4 3 4 7% 50%	1900
May	1st to 10th	Night	7% 10% 3 5% 4 4 3 4 6% 7% 49%	2995
	11th to 20th	Night	9% 7% 2 4 4 3 4 4 5% 7% 49%	2517
	21st to end	Night	4 5% 1 4 3 3 4 3 6% 6% 60%	2762
June	1st to 10th	Night	4 4 1 4 2 3 4 4 5% 11% 59%	1520
	11th to 20th	Night	5% 3 1 3 3 3 3 4 6% 7% 62%	1520
	21st to end	Night	4 2 2 3 3 4 4 5% 8% 8% 58%	1520
July	1st to 10th	Night	5% 4 1 4 2 3 3 4 5% 6% 62%	2540
	11th to 20th	Night	1 2 1 3 3 4 5% 5% 7% 11% 56%	2540
	21st to end	Night	3 3 1 4 3 4 4 5% 8% 10% 56%	2904
August	1st to 10th	Night	5% 5% 2 5% 4 4 5% 5% 8% 9% 46%	2847
	11th to 20th	Night	4 3 1 4 4 4 5% 5% 8% 11% 52%	3102
	21st to end	Night	3 6% 2 7% 4 5% 4 4 6% 9% 49%	3487
September	1st to 10th	Night	6% 4 1 5% 3 3 3 3 6% 7% 58%	1900
	11th to 20th	Night	6% 3 1 3 3 3 3 4 5% 6% 63%	1909
	21st to end	Night	6% 4 1 4 2 3 3 3 4 5% 64%	2090
October	1st to 10th	Night	4 4 2 3 2 2 3 2 3 5% 71%	3800
	11th to 20th	Night	3 5% 2 4 3 3 3 3 5% 7% 61%	3778
	21st to end	Night	3 6% 2 5% 2 2 2 2 4 5% 67%	4172
November	1st to 10th	Night	1 4 2 4 3 2 3 3 4 8% 66%	2535
	11th to 20th	Night	1 5% 2 4 3 2 3 2 4 7% 67%	2600
	21st to end	Night	1 6% 2 5% 3 3 3 2 5% 8% 62%	2706
December	1st to 10th	Night	1 2 1 4 2 2 3 2 3 6% 74%	4570
	11th to 20th	Night	1 3 2 4 3 3 3 3 5% 8% 67%	5181
	21st to end	Night	1 7% 3 7% 4 4 4 4 5% 7% 53%	6974

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	23% 5% 10% 29% 23% 9%	2619
	11th to 20th	Day	27% 7% 11% 26% 21% 8%	2752
	21st to end	Day	27% 5% 9% 31% 22% 5%	3155
February	1st to 10th	Day	28% 5% 11% 27% 21% 9%	1710
	11th to 20th	Day	22% 4 8% 28% 29% 9%	1825
	21st to end	Day	25% 3 8% 24% 27% 13%	1570
March	1st to 10th	Day	27% 7% 6% 20% 32% 9%	3130
	11th to 20th	Day	37% 10% 8% 28% 14% 3	3485
	21st to end	Day	29% 9% 10% 32% 17% 4	4036
April	1st to 10th	Day	29% 6% 10% 25% 20% 10%	2280
	11th to 20th	Day	39% 6% 9% 19% 19% 8%	2254
	21st to end	Day	39% 6% 10% 23% 18% 3	2280
May	1st to 10th	Day	40% 8% 9% 20% 16% 8%	3969
	11th to 20th	Day	36% 10% 13% 22% 17% 2	4392
	21st to end	Day	25% 9% 13% 21% 23% 7%	4825
June	1st to 10th	Day	29% 9% 15% 22% 17% 8%	2660
	11th to 20th	Day	28% 7% 11% 18% 21% 15%	2660
	21st to end	Day	31% 8% 12% 19% 20% 11%	2660
July	1st to 10th	Day	26% 8% 8% 16% 28% 15%	4361
	11th to 20th	Day	31% 10% 11% 21% 19% 9%	4355
	21st to end	Day	31% 8% 11% 18% 17% 13%	4508
August	1st to 10th	Day	43% 10% 14% 17% 13% 4	4078
	11th to 20th	Day	34% 9% 12% 16% 19% 11%	3771
	21st to end	Day	34% 8% 10% 17% 23% 9%	4179
September	1st to 10th	Day	29% 5% 8% 21% 22% 15%	2280
	11th to 20th	Day	26% 5% 8% 20% 28% 12%	2271
	21st to end	Day	22% 5% 6% 22% 34% 11%	2085
October	1st to 10th	Day	20% 5% 6% 16% 34% 19%	3170
	11th to 20th	Day	27% 6% 7% 26% 27% 7%	3150
	21st to end	Day	21% 3 5% 25% 35% 10%	3355
November	1st to 10th	Day	19% 4 7% 24% 30% 15%	1763
	11th to 20th	Day	20% 4 5% 31% 29% 11%	1800
	21st to end	Day	23% 4 7% 23% 31% 12%	1690
December	1st to 10th	Day	19% 3 7% 32% 31% 9%	2620
	11th to 20th	Day	15% 3 8% 34% 29% 10%	3024
	21st to end	Day	25% 5% 8% 24% 28% 10%	4004
January	1st to 10th	Night	27% 4 8% 26% 28% 6%	4557
	11th to 20th	Night	17% 7% 10% 29% 26% 11%	4466
	21st to end	Night	26% 5% 10% 30% 21% 7%	4534
February	1st to 10th	Night	24% 3 11% 29% 24% 9%	2470
	11th to 20th	Night	24% 4 8% 29% 27% 8%	2252
	21st to end	Night	23% 3 6% 26% 29% 14%	1884
March	1st to 10th	Night	25% 4 7% 19% 37% 9%	3734
	11th to 20th	Night	34% 5% 8% 26% 22% 4	3494
	21st to end	Night	24% 7% 8% 35% 22% 3	3610
April	1st to 10th	Night	25% 5% 10% 26% 25% 9%	1900
	11th to 20th	Night	31% 6% 9% 25% 22% 7%	1877
	21st to end	Night	34% 5% 10% 26% 20% 4	1900
May	1st to 10th	Night	32% 7% 10% 23% 17% 11%	2995
	11th to 20th	Night	30% 11% 14% 24% 19% 2	2518
	21st to end	Night	21% 7% 15% 25% 24% 8%	2762
June	1st to 10th	Night	19% 7% 19% 30% 16% 10%	1520
	11th to 20th	Night	19% 6% 12% 20% 23% 20%	1520
	21st to end	Night	20% 5% 13% 25% 26% 11%	1520
July	1st to 10th	Night	22% 6% 11% 18% 29% 14%	2500
	11th to 20th	Night	18% 7% 14% 32% 20% 8%	2492
	21st to end	Night	19% 8% 16% 28% 13% 16%	2813
August	1st to 10th	Night	31% 8% 18% 25% 15% 3	2838
	11th to 20th	Night	23% 9% 18% 21% 19% 10%	3132
	21st to end	Night	29% 7% 14% 22% 22% 5%	3487
September	1st to 10th	Night	25% 5% 9% 24% 23% 14%	1900
	11th to 20th	Night	21% 4 10% 24% 26% 16%	1909
	21st to end	Night	22% 4 8% 23% 32% 10%	2090
October	1st to 10th	Night	16% 4 7% 21% 34% 18%	3800
	11th to 20th	Night	22% 5% 8% 29% 27% 9%	3778
	21st to end	Night	21% 3 4 24% 33% 14%	4172
November	1st to 10th	Night	18% 4 8% 24% 32% 15%	2535
	11th to 20th	Night	19% 3 6% 27% 33% 12%	2600
	21st to end	Night	23% 3 8% 23% 31% 13%	2706
December	1st to 10th	Night	14% 3 7% 31% 36% 9%	4570
	11th to 20th	Night	18% 3 7% 28% 35% 10%	5182
	21st to end	Night	28% 5% 8% 21% 27% 10%	6974

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	9% 11% 35% 32% 11% 2	300
	11th to 20th	Day	6% 15% 48% 24% 6% 1	300
	21st to end	Day	2 16% 43% 29% 7% 2	300
February	1st to 10th	Day	3 30% 42% 20% 3 1	270
	11th to 20th	Day	6% 21% 47% 21% 5%	270
	21st to end	Day	8% 20% 44% 24% 4	225
March	1st to 10th	Day	8% 16% 42% 23% 8% 3	270
	11th to 20th	Day	11% 17% 41% 24% 6% 1	455
	21st to end	Day	17% 24% 33% 20% 6%	506
April	1st to 10th	Day	15% 24% 33% 21% 7% 1	460
	11th to 20th	Day	20% 26% 31% 17% 5% 1	452
	21st to end	Day	17% 18% 35% 22% 7% 1	460
May	1st to 10th	Day	19% 12% 37% 24% 5% 2	553
	11th to 20th	Day	17% 10% 27% 33% 10% 2	675
	21st to end	Day	12% 9% 29% 31% 16% 3	734
June	1st to 10th	Day	6% 9% 25% 36% 20% 5%	680
	11th to 20th	Day	6% 10% 34% 32% 15% 4	680
	21st to end	Day	7% 7% 34% 30% 17% 5%	680
July	1st to 10th	Day	7% 6% 21% 34% 24% 8%	671
	11th to 20th	Day	5% 4 21% 36% 26% 8%	668
	21st to end	Day	9% 5% 16% 36% 26% 8%	654
August	1st to 10th	Day	10% 7% 23% 33% 22% 5%	487
	11th to 20th	Day	6% 5% 26% 40% 18% 6%	477
	21st to end	Day	9% 6% 27% 35% 19% 4	539
September	1st to 10th	Day	8% 8% 27% 36% 17% 4	490
	11th to 20th	Day	9% 11% 28% 35% 15% 3	481
	21st to end	Day	8% 10% 29% 33% 14% 6%	300
October	1st to 10th	Day	8% 10% 31% 26% 18% 6%	300
	11th to 20th	Day	4 15% 40% 30% 8% 3	300
	21st to end	Day	9% 13% 42% 28% 7% 1	330
November	1st to 10th	Day	7% 14% 39% 28% 9% 3	300
	11th to 20th	Day	9% 16% 38% 29% 7% 2	300
	21st to end	Day	6% 15% 40% 31% 7% 1	300
December	1st to 10th	Day	9% 16% 37% 29% 8% 2	300
	11th to 20th	Day	6% 14% 46% 26% 8% 1	300
	21st to end	Day	8% 19% 43% 22% 7% 1	330
January	1st to 10th	Night	3 16% 37% 33% 8% 2	1000
	11th to 20th	Night	4 20% 42% 26% 6% 2	935
	21st to end	Night	3 15% 40% 35% 6% 1	840
February	1st to 10th	Night	4 17% 47% 27% 6%	760
	11th to 20th	Night	3 16% 45% 30% 6%	744
	21st to end	Night	4 15% 45% 32% 4	628
March	1st to 10th	Night	3 15% 41% 33% 7% 1	760
	11th to 20th	Night	8% 9% 39% 34% 9% 1	760
	21st to end	Night	6% 11% 45% 32% 5% 1	708
April	1st to 10th	Night	9% 13% 40% 34% 5%	570
	11th to 20th	Night	13% 13% 35% 31% 7% 1	563
	21st to end	Night	13% 10% 35% 34% 7% 1	570
May	1st to 10th	Night	13% 7% 31% 36% 12% 2	570
	11th to 20th	Night	15% 4 23% 42% 13% 2	561
	21st to end	Night	8% 7% 26% 40% 16% 3	617
June	1st to 10th	Night	6% 4 20% 48% 19% 4	570
	11th to 20th	Night	8% 4 25% 45% 16% 2	570
	21st to end	Night	3 2 19% 46% 27% 3	570
July	1st to 10th	Night	8% 3 13% 38% 34% 5%	555
	11th to 20th	Night	2 2 14% 41% 38% 4	552
	21st to end	Night	7% 2 6% 43% 36% 6%	624
August	1st to 10th	Night	5% 2 12% 44% 32% 5%	567
	11th to 20th	Night	6% 1 15% 46% 27% 4	564
	21st to end	Night	6% 3 15% 42% 29% 6%	627
September	1st to 10th	Night	6% 3 16% 43% 25% 6%	570
	11th to 20th	Night	8% 2 21% 43% 21% 5%	570
	21st to end	Night	7% 5% 26% 39% 19% 4	570
October	1st to 10th	Night	7% 8% 29% 39% 13% 4	760
	11th to 20th	Night	4 7% 34% 40% 11% 4	760
	21st to end	Night	7% 8% 37% 34% 12% 2	864
November	1st to 10th	Night	4 9% 37% 36% 11% 2	975
	11th to 20th	Night	4 15% 40% 32% 8% 1	1000
	21st to end	Night	5% 11% 38% 37% 9% 1	1000
December	1st to 10th	Night	4 14% 37% 37% 7% 1	1000
	11th to 20th	Night	4 15% 43% 29% 8% 1	1000
	21st to end	Night	5% 16% 41% 32% 6% 1	1100

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