Onion Valley Campground
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Onion Valley Campground 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 6% 2 6% 4 4 4 3 5% 6% 55%	152674
	Night	4 8% 3 6% 4 4 4 3 5% 6% 52%	146877
Transparency	Day	28% 5% 9% 18% 23% 18%	147553
	Night	31% 5% 10% 18% 22% 14%	143001
Seeing	Day	10% 11% 24% 30% 20% 6%	17071
	Night	9% 7% 21% 37% 22% 4	26273

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	6% 15% 5% 14% 8% 6% 6% 5% 6% 7% 24%	4722
	11th to 20th	Day	5% 8% 2 6% 5% 3 4 3 6% 7% 52%	4740
	21st to end	Day	5% 8% 4 8% 5% 5% 5% 4 6% 8% 42%	5426
February	1st to 10th	Day	5% 8% 5% 9% 5% 4 5% 5% 8% 9% 37%	1898
	11th to 20th	Day	4 11% 4 9% 6% 5% 5% 4 6% 9% 36%	2050
	21st to end	Day	3 9% 4 10% 6% 5% 5% 5% 7% 9% 37%	1730
March	1st to 10th	Day	5% 16% 5% 8% 5% 4 5% 4 8% 8% 33%	4618
	11th to 20th	Day	2 8% 3 8% 5% 4 4 5% 6% 7% 47%	4811
	21st to end	Day	3 11% 4 10% 6% 5% 5% 4 5% 7% 39%	6097
April	1st to 10th	Day	5% 11% 4 9% 5% 5% 6% 5% 7% 6% 38%	2520
	11th to 20th	Day	5% 10% 3 7% 4 6% 4 3 6% 7% 45%	2489
	21st to end	Day	7% 8% 3 7% 4 4 4 4 5% 8% 47%	2593
May	1st to 10th	Day	4 7% 2 5% 3 3 3 3 4 6% 60%	7626
	11th to 20th	Day	4 6% 2 4 3 3 3 3 4 5% 62%	8102
	21st to end	Day	5% 4 2 5% 4 4 4 3 5% 7% 58%	8992
June	1st to 10th	Day	6% 5% 2 6% 5% 4 4 4 6% 8% 49%	2940
	11th to 20th	Day	5% 4 1 4 3 2 3 3 5% 6% 62%	2940
	21st to end	Day	2 3 1 3 3 3 3 3 4 5% 69%	2940
July	1st to 10th	Day	1 2 1 3 2 2 2 2 3 4 78%	8219
	11th to 20th	Day	3 3 1 4 3 3 3 3 4 5% 70%	8220
	21st to end	Day	3 2 1 4 3 4 5% 4 5% 6% 62%	8922
August	1st to 10th	Day	2 3 1 3 2 3 3 3 5% 8% 66%	6189
	11th to 20th	Day	2 1 1 2 2 2 2 2 3 4 80%	5484
	21st to end	Day	4 3 1 4 3 3 3 2 3 5% 69%	6093
September	1st to 10th	Day	3 1 1 2 2 2 3 2 4 5% 75%	2400
	11th to 20th	Day	4 3 2 4 3 3 2 3 4 6% 66%	2320
	21st to end	Day	5% 4 2 4 2 2 3 3 4 6% 68%	2200
October	1st to 10th	Day	4 4 1 4 3 3 2 3 4 5% 67%	3440
	11th to 20th	Day	8% 6% 2 4 3 2 3 3 4 6% 60%	3261
	21st to end	Day	4 5% 3 8% 5% 4 4 4 5% 8% 50%	3268
November	1st to 10th	Day	7% 8% 3 8% 5% 4 5% 4 5% 8% 44%	1854
	11th to 20th	Day	8% 7% 3 7% 5% 5% 5% 5% 7% 8% 41%	1890
	21st to end	Day	3 7% 5% 7% 4 5% 4 4 6% 8% 45%	1780
December	1st to 10th	Day	5% 5% 3 6% 4 3 4 3 6% 7% 54%	2700
	11th to 20th	Day	7% 14% 5% 10% 7% 6% 6% 5% 7% 9% 25%	3108
	21st to end	Day	7% 12% 4 11% 6% 5% 6% 5% 7% 8% 29%	4092
January	1st to 10th	Night	5% 14% 6% 12% 7% 5% 6% 5% 6% 7% 28%	8172
	11th to 20th	Night	5% 9% 3 5% 3 4 4 3 4 6% 54%	8220
	21st to end	Night	5% 10% 3 8% 5% 5% 5% 4 5% 8% 42%	8752
February	1st to 10th	Night	4 9% 3 10% 6% 4 4 5% 7% 7% 41%	2720
	11th to 20th	Night	4 11% 3 9% 6% 6% 6% 4 7% 8% 37%	2458
	21st to end	Night	3 9% 4 10% 6% 6% 6% 5% 7% 7% 37%	2076
March	1st to 10th	Night	5% 13% 5% 9% 5% 5% 4 4 5% 7% 37%	5496
	11th to 20th	Night	3 9% 4 10% 6% 5% 5% 4 6% 7% 43%	5394
	21st to end	Night	3 11% 4 9% 6% 5% 5% 5% 6% 9% 37%	5118
April	1st to 10th	Night	6% 11% 3 7% 6% 4 4 4 6% 7% 42%	2100
	11th to 20th	Night	5% 9% 3 7% 3 5% 4 3 5% 7% 49%	2079
	21st to end	Night	5% 8% 3 5% 4 4 4 4 5% 6% 52%	2027
May	1st to 10th	Night	4 6% 2 5% 3 3 3 3 4 7% 60%	5321
	11th to 20th	Night	4 8% 2 3 3 2 3 2 3 5% 65%	4745
	21st to end	Night	4 4 2 5% 3 3 3 3 4 6% 62%	5181
June	1st to 10th	Night	5% 6% 2 6% 4 5% 5% 3 5% 7% 52%	1680
	11th to 20th	Night	4 5% 2 4 3 3 3 2 4 5% 66%	1680
	21st to end	Night	2 3 2 4 2 3 2 3 3 6% 70%	1680
July	1st to 10th	Night	2 2 1 3 2 3 3 2 3 4 76%	4740
	11th to 20th	Night	3 3 1 4 4 4 3 2 3 4 69%	4740
	21st to end	Night	3 3 2 5% 3 4 4 4 5% 7% 61%	5153
August	1st to 10th	Night	2 3 1 4 2 3 3 3 5% 8% 65%	3815
	11th to 20th	Night	2 2 1 3 2 2 3 2 3 5% 77%	4606
	21st to end	Night	5% 4 2 4 2 3 3 2 4 4 66%	5105
September	1st to 10th	Night	3 2 3 2 2 2 2 3 4 76%	2000
	11th to 20th	Night	4 4 1 4 3 2 2 3 3 4 69%	2080
	21st to end	Night	3 3 1 3 2 3 3 3 3 6% 70%	2200
October	1st to 10th	Night	3 4 1 3 2 3 3 2 3 4 73%	3755
	11th to 20th	Night	3 4 2 4 3 3 3 2 4 4 68%	3897
	21st to end	Night	5% 6% 3 5% 4 5% 5% 4 5% 6% 50%	4533
November	1st to 10th	Night	8% 9% 3 6% 5% 5% 4 5% 7% 7% 42%	2665
	11th to 20th	Night	7% 8% 3 6% 5% 5% 4 4 6% 9% 43%	2730
	21st to end	Night	4 8% 4 8% 5% 5% 4 4 6% 7% 45%	2837
December	1st to 10th	Night	4 7% 2 6% 3 3 4 3 5% 7% 55%	4700
	11th to 20th	Night	6% 13% 4 10% 6% 5% 6% 5% 8% 9% 29%	5316
	21st to end	Night	7% 13% 4 11% 7% 6% 6% 5% 6% 7% 29%	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	54% 8% 14% 15% 9%	4723
	11th to 20th	Day	31% 8% 9% 16% 20% 17%	4740
	21st to end	Day	39% 10% 9% 11% 18% 13%	5426
February	1st to 10th	Day	38% 13% 15% 21% 11% 2	1898
	11th to 20th	Day	41% 9% 19% 20% 10% 2	2060
	21st to end	Day	40% 10% 17% 20% 11% 3	1730
March	1st to 10th	Day	45% 8% 11% 17% 16% 4	4618
	11th to 20th	Day	31% 7% 16% 30% 15% 1	4811
	21st to end	Day	39% 8% 17% 21% 14% 2	6097
April	1st to 10th	Day	41% 7% 15% 21% 14% 3	2520
	11th to 20th	Day	34% 5% 12% 27% 19% 4	2492
	21st to end	Day	33% 6% 13% 28% 18% 3	2593
May	1st to 10th	Day	24% 3 7% 23% 38% 5%	7626
	11th to 20th	Day	23% 3 7% 20% 34% 13%	8105
	21st to end	Day	24% 4 7% 26% 34% 5%	8994
June	1st to 10th	Day	31% 5% 10% 23% 26% 6%	2940
	11th to 20th	Day	21% 3 7% 20% 30% 18%	2940
	21st to end	Day	17% 2 5% 16% 31% 28%	2940
July	1st to 10th	Day	11% 1 3 9% 21% 55%	8151
	11th to 20th	Day	18% 2 3 7% 18% 53%	8145
	21st to end	Day	21% 3 5% 11% 21% 39%	8723
August	1st to 10th	Day	19% 2 4 8% 22% 46%	4548
	11th to 20th	Day	11% 1 3 8% 30% 46%	4000
	21st to end	Day	14% 1 3 12% 35% 35%	4420
September	1st to 10th	Day	12% 2 4 11% 28% 43%	2400
	11th to 20th	Day	20% 2 6% 18% 29% 26%	2320
	21st to end	Day	18% 2 7% 20% 32% 22%	2200
October	1st to 10th	Day	19% 2 5% 15% 33% 26%	3440
	11th to 20th	Day	25% 2 7% 25% 31% 9%	3261
	21st to end	Day	30% 5% 11% 26% 22% 6%	3268
November	1st to 10th	Day	37% 6% 12% 24% 18% 4	1854
	11th to 20th	Day	38% 6% 16% 26% 14% 1	1890
	21st to end	Day	34% 4 17% 25% 18% 2	1780
December	1st to 10th	Day	29% 6% 9% 17% 33% 6%	2700
	11th to 20th	Day	54% 9% 13% 16% 8% 1	3108
	21st to end	Day	50% 8% 17% 18% 7%	4092
January	1st to 10th	Night	50% 9% 15% 20% 7%	8172
	11th to 20th	Night	30% 7% 8% 15% 22% 17%	8220
	21st to end	Night	39% 8% 9% 12% 20% 11%	8752
February	1st to 10th	Night	37% 8% 17% 24% 13% 3	2720
	11th to 20th	Night	39% 8% 17% 21% 14% 2	2459
	21st to end	Night	40% 8% 16% 21% 10% 5%	2076
March	1st to 10th	Night	44% 5% 12% 17% 17% 6%	5496
	11th to 20th	Night	37% 5% 10% 30% 16% 1	5394
	21st to end	Night	39% 8% 19% 22% 11% 1	5118
April	1st to 10th	Night	37% 6% 15% 24% 16% 2	2100
	11th to 20th	Night	33% 4 14% 25% 19% 5%	2079
	21st to end	Night	30% 6% 15% 27% 20% 3	2027
May	1st to 10th	Night	23% 3 6% 23% 36% 8%	5319
	11th to 20th	Night	23% 3 5% 22% 38% 9%	4745
	21st to end	Night	22% 4 7% 26% 39% 2	5182
June	1st to 10th	Night	29% 5% 10% 25% 26% 4	1680
	11th to 20th	Night	19% 4 7% 19% 36% 14%	1680
	21st to end	Night	17% 2 5% 16% 30% 29%	1680
July	1st to 10th	Night	13% 2 3 8% 21% 52%	4700
	11th to 20th	Night	21% 1 3 6% 19% 50%	4692
	21st to end	Night	21% 3 4 14% 20% 38%	5040
August	1st to 10th	Night	20% 3 4 10% 17% 47%	2797
	11th to 20th	Night	13% 2 4 7% 29% 45%	3356
	21st to end	Night	15% 1 2 13% 33% 34%	3698
September	1st to 10th	Night	14% 2 3 10% 25% 46%	2000
	11th to 20th	Night	19% 2 5% 17% 27% 30%	2080
	21st to end	Night	15% 2 7% 18% 32% 27%	2200
October	1st to 10th	Night	17% 2 5% 14% 34% 28%	3755
	11th to 20th	Night	19% 2 6% 27% 34% 11%	3897
	21st to end	Night	32% 4 8% 21% 26% 8%	4533
November	1st to 10th	Night	37% 6% 13% 20% 19% 5%	2665
	11th to 20th	Night	36% 5% 17% 24% 17% 1	2730
	21st to end	Night	35% 5% 14% 21% 22% 3	2837
December	1st to 10th	Night	28% 5% 9% 19% 31% 8%	4700
	11th to 20th	Night	48% 10% 12% 18% 10% 1	5316
	21st to end	Night	51% 8% 16% 15% 10%	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	22% 14% 20% 25% 14% 5%	220
	11th to 20th	Day	10% 10% 20% 27% 26% 7%	220
	21st to end	Day	8% 9% 24% 31% 20% 9%	326
February	1st to 10th	Day	12% 10% 22% 33% 17% 5%	436
	11th to 20th	Day	13% 15% 24% 29% 17% 2	535
	21st to end	Day	11% 16% 23% 28% 17% 4	446
March	1st to 10th	Day	15% 14% 26% 29% 15% 1	540
	11th to 20th	Day	14% 14% 22% 27% 17% 6%	540
	21st to end	Day	13% 16% 27% 28% 14% 3	594
April	1st to 10th	Day	11% 14% 29% 26% 16% 4	540
	11th to 20th	Day	14% 14% 27% 25% 14% 6%	532
	21st to end	Day	11% 15% 25% 27% 18% 4	540
May	1st to 10th	Day	7% 17% 28% 26% 17% 5%	543
	11th to 20th	Day	20% 12% 24% 21% 16% 7%	568
	21st to end	Day	11% 11% 21% 27% 21% 8%	617
June	1st to 10th	Day	7% 15% 26% 23% 22% 6%	570
	11th to 20th	Day	11% 16% 26% 28% 15% 4	570
	21st to end	Day	6% 11% 21% 32% 23% 6%	570
July	1st to 10th	Day	3 6% 26% 37% 23% 4	566
	11th to 20th	Day	4 8% 24% 39% 21% 4	564
	21st to end	Day	5% 6% 19% 40% 24% 6%	619
August	1st to 10th	Day	5% 6% 22% 35% 25% 7%	567
	11th to 20th	Day	4 8% 22% 31% 24% 11%	557
	21st to end	Day	5% 7% 26% 33% 21% 8%	620
September	1st to 10th	Day	6% 5% 19% 35% 24% 11%	530
	11th to 20th	Day	8% 8% 25% 28% 24% 8%	530
	21st to end	Day	6% 8% 25% 31% 23% 7%	530
October	1st to 10th	Day	11% 12% 22% 28% 20% 7%	530
	11th to 20th	Day	10% 12% 23% 24% 25% 5%	530
	21st to end	Day	11% 13% 25% 27% 18% 6%	407
November	1st to 10th	Day	15% 13% 22% 27% 17% 5%	330
	11th to 20th	Day	12% 11% 23% 27% 23% 5%	330
	21st to end	Day	11% 11% 20% 34% 19% 5%	272
December	1st to 10th	Day	13% 11% 19% 30% 18% 10%	220
	11th to 20th	Day	18% 7% 20% 32% 18% 5%	220
	21st to end	Day	18% 10% 21% 29% 18% 4	242
January	1st to 10th	Night	14% 8% 23% 31% 19% 5%	840
	11th to 20th	Night	9% 6% 21% 38% 20% 6%	840
	21st to end	Night	11% 6% 21% 37% 20% 5%	924
February	1st to 10th	Night	10% 7% 25% 35% 20% 3	840
	11th to 20th	Night	9% 9% 24% 37% 18% 3	824
	21st to end	Night	9% 9% 24% 40% 16% 2	692
March	1st to 10th	Night	10% 10% 25% 36% 15% 3	840
	11th to 20th	Night	11% 10% 22% 32% 22% 3	840
	21st to end	Night	11% 11% 28% 34% 13% 2	924
April	1st to 10th	Night	10% 9% 25% 33% 20% 2	840
	11th to 20th	Night	10% 10% 25% 33% 18% 4	831
	21st to end	Night	11% 5% 26% 34% 20% 3	767
May	1st to 10th	Night	9% 9% 28% 34% 18% 2	630
	11th to 20th	Night	12% 9% 19% 33% 24% 4	434
	21st to end	Night	9% 7% 22% 32% 26% 5%	455
June	1st to 10th	Night	7% 6% 24% 37% 25% 1	420
	11th to 20th	Night	7% 9% 24% 38% 19% 3	420
	21st to end	Night	3 4 23% 48% 21% 2	420
July	1st to 10th	Night	4 3 20% 46% 26% 2	410
	11th to 20th	Night	2 2 20% 55% 20% 1	408
	21st to end	Night	3 2 15% 49% 29% 1	460
August	1st to 10th	Night	4 2 17% 44% 29% 3	482
	11th to 20th	Night	3 3 17% 43% 30% 4	832
	21st to end	Night	5% 3 13% 44% 32% 3	916
September	1st to 10th	Night	5% 2 13% 40% 35% 6%	800
	11th to 20th	Night	6% 3 13% 36% 32% 9%	800
	21st to end	Night	6% 5% 15% 35% 28% 12%	800
October	1st to 10th	Night	8% 4 21% 35% 25% 6%	800
	11th to 20th	Night	6% 7% 18% 34% 28% 7%	800
	21st to end	Night	9% 6% 18% 36% 23% 8%	880
November	1st to 10th	Night	13% 7% 18% 33% 24% 5%	820
	11th to 20th	Night	13% 8% 20% 38% 19% 3	840
	21st to end	Night	9% 7% 23% 34% 22% 5%	840
December	1st to 10th	Night	12% 6% 23% 33% 22% 4	840
	11th to 20th	Night	13% 9% 21% 36% 18% 3	840
	21st to end	Night	17% 9% 26% 33% 13% 2	924

Page generated at 2026-08-27 01:07:09. Version ac07

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