Cameron Park Rotary Club Community Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cameron Park Rotary Club Community Observatory 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	8% 4 1 3 2 2 2 2 4 5% 67%	152587
	Night	11% 4 1 3 2 2 3 2 4 5% 61%	147090
Transparency	Day	22% 4 7% 17% 25% 25%	147536
	Night	27% 4 7% 18% 23% 22%	143127
Seeing	Day	11% 6% 21% 33% 22% 7%	17527
	Night	13% 2 11% 37% 30% 7%	26803

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	23% 7% 2 3 2 2 3 2 4 6% 44%	4722
	11th to 20th	Day	14% 5% 2 4 3 2 2 2 3 4 59%	5159
	21st to end	Day	15% 6% 3 5% 4 3 4 3 5% 7% 44%	5843
February	1st to 10th	Day	22% 6% 2 4 3 2 3 2 4 5% 46%	1890
	11th to 20th	Day	18% 8% 2 5% 3 3 4 4 4 7% 43%	1998
	21st to end	Day	20% 8% 2 4 3 3 2 3 4 5% 46%	1730
March	1st to 10th	Day	18% 11% 3 7% 4 3 4 4 5% 6% 34%	4722
	11th to 20th	Day	18% 7% 2 4 3 3 3 2 4 6% 48%	5110
	21st to end	Day	19% 8% 3 6% 4 4 4 4 6% 7% 36%	5861
April	1st to 10th	Day	15% 7% 1 5% 4 3 3 3 5% 7% 47%	2520
	11th to 20th	Day	13% 4 1 4 3 3 3 3 6% 6% 53%	2489
	21st to end	Day	10% 4 1 4 2 3 3 3 5% 7% 58%	2520
May	1st to 10th	Day	6% 4 1 3 2 2 2 2 3 5% 70%	7192
	11th to 20th	Day	3 1 1 2 1 1 2 2 3 4 80%	8160
	21st to end	Day	3 2 1 2 2 2 2 2 3 5% 76%	8992
June	1st to 10th	Day	5% 4 1 3 3 2 2 3 4 6% 67%	2940
	11th to 20th	Day	1 2 1 2 2 1 1 2 4 4 81%	2940
	21st to end	Day	2 2 1 2 1 1 1 1 3 3 85%	2940
July	1st to 10th	Day	1 1 1 1 1 1 2 92%	8219
	11th to 20th	Day	3 2 1 2 1 1 1 1 3 3 82%	8220
	21st to end	Day	1 1 1 1 1 1 3 3 86%	8384
August	1st to 10th	Day	1 1 1 2 1 1 1 1 3 3 85%	5907
	11th to 20th	Day	1 1 1 1 1 1 2 2 91%	5527
	21st to end	Day	2 1 1 1 1 2 2 2 2 3 83%	6093
September	1st to 10th	Day	2 1 1 1 1 2 1 2 3 87%	2400
	11th to 20th	Day	3 2 1 3 1 2 2 2 4 4 76%	2400
	21st to end	Day	4 2 1 2 1 2 2 2 2 4 79%	2169
October	1st to 10th	Day	3 2 1 2 2 2 3 3 4 5% 73%	3280
	11th to 20th	Day	5% 3 1 2 2 2 2 2 4 4 74%	3261
	21st to end	Day	5% 3 1 4 3 3 3 2 4 6% 65%	3558
November	1st to 10th	Day	12% 4 1 3 3 4 3 2 5% 7% 56%	1879
	11th to 20th	Day	15% 5% 1 4 4 3 4 3 5% 7% 49%	1890
	21st to end	Day	13% 4 1 3 3 3 4 3 4 6% 56%	1772
December	1st to 10th	Day	9% 3 1 4 3 3 3 3 4 7% 60%	2700
	11th to 20th	Day	28% 7% 3 5% 3 3 3 3 4 6% 35%	3108
	21st to end	Day	26% 6% 2 5% 3 4 4 4 6% 8% 30%	4092
January	1st to 10th	Night	20% 8% 2 5% 3 3 4 3 5% 8% 41%	8172
	11th to 20th	Night	12% 4 1 4 2 3 3 2 4 5% 60%	7807
	21st to end	Night	16% 6% 2 7% 4 4 3 3 5% 5% 46%	8371
February	1st to 10th	Night	21% 6% 1 3 3 3 3 2 4 5% 49%	2730
	11th to 20th	Night	17% 7% 2 6% 4 3 3 3 5% 7% 44%	2508
	21st to end	Night	18% 7% 2 4 3 3 4 3 4 5% 48%	2076
March	1st to 10th	Night	22% 11% 3 6% 3 3 3 3 4 5% 37%	5389
	11th to 20th	Night	23% 8% 2 4 2 2 2 2 3 4 48%	5110
	21st to end	Night	22% 9% 2 5% 3 3 4 3 5% 7% 37%	5354
April	1st to 10th	Night	14% 6% 2 5% 4 4 4 3 4 6% 48%	2100
	11th to 20th	Night	12% 5% 2 5% 4 3 3 2 4 7% 53%	2079
	21st to end	Night	9% 4 2 3 3 2 3 2 5% 6% 60%	2100
May	1st to 10th	Night	5% 4 1 4 2 3 2 2 3 5% 68%	5770
	11th to 20th	Night	3 2 1 2 2 2 2 2 3 4 79%	4700
	21st to end	Night	3 1 1 2 2 2 2 2 3 5% 77%	5181
June	1st to 10th	Night	5% 3 1 3 3 3 2 3 5% 5% 67%	1680
	11th to 20th	Night	1 1 1 2 1 2 2 2 3 4 82%	1680
	21st to end	Night	2 1 2 2 1 1 1 2 2 84%	1680
July	1st to 10th	Night	1 1 1 1 2 2 92%	4740
	11th to 20th	Night	4 4 1 3 2 1 2 2 2 2 79%	4740
	21st to end	Night	1 1 1 2 1 2 2 2 3 4 82%	5703
August	1st to 10th	Night	2 2 2 1 1 1 2 3 3 83%	4125
	11th to 20th	Night	1 1 1 1 1 2 2 90%	4559
	21st to end	Night	2 2 1 2 1 1 1 1 2 3 82%	5105
September	1st to 10th	Night	2 1 1 1 1 1 1 2 3 87%	2000
	11th to 20th	Night	3 3 1 2 2 2 2 2 3 4 78%	2000
	21st to end	Night	3 2 1 1 2 2 2 2 3 5% 79%	2225
October	1st to 10th	Night	3 2 1 3 2 2 2 2 3 3 77%	3920
	11th to 20th	Night	4 2 1 2 1 1 2 2 3 4 78%	3897
	21st to end	Night	8% 2 1 3 3 3 3 3 3 5% 65%	4253
November	1st to 10th	Night	13% 6% 1 3 2 2 2 3 5% 6% 57%	2638
	11th to 20th	Night	13% 5% 1 4 3 3 3 3 5% 8% 53%	2730
	21st to end	Night	13% 4 1 3 3 3 3 2 4 6% 57%	2846
December	1st to 10th	Night	11% 3 1 2 2 2 3 3 4 6% 62%	4700
	11th to 20th	Night	27% 7% 2 5% 3 3 4 4 6% 8% 31%	5316
	21st to end	Night	27% 9% 3 6% 4 4 4 3 4 5% 30%	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	41% 4 13% 22% 13% 6%	4723
	11th to 20th	Day	29% 4 5% 13% 25% 24%	5159
	21st to end	Day	38% 5% 7% 17% 21% 12%	5843
February	1st to 10th	Day	42% 3 9% 18% 17% 11%	1890
	11th to 20th	Day	41% 5% 9% 20% 19% 6%	2008
	21st to end	Day	41% 3 11% 21% 16% 7%	1730
March	1st to 10th	Day	47% 9% 8% 16% 17% 3	4722
	11th to 20th	Day	37% 5% 11% 28% 11% 7%	5110
	21st to end	Day	43% 9% 15% 21% 10% 2	5861
April	1st to 10th	Day	37% 6% 12% 24% 16% 5%	2520
	11th to 20th	Day	30% 6% 14% 26% 18% 6%	2492
	21st to end	Day	25% 5% 14% 29% 23% 3	2520
May	1st to 10th	Day	19% 3 8% 25% 32% 13%	7192
	11th to 20th	Day	10% 2 5% 26% 44% 13%	8163
	21st to end	Day	12% 4 8% 24% 44% 7%	8994
June	1st to 10th	Day	19% 4 10% 24% 31% 12%	2940
	11th to 20th	Day	9% 3 7% 19% 35% 27%	2940
	21st to end	Day	8% 1 3 12% 37% 39%	2940
July	1st to 10th	Day	4 1 1 6% 20% 68%	8151
	11th to 20th	Day	10% 2 1 6% 10% 70%	8145
	21st to end	Day	6% 2 2 11% 23% 56%	8197
August	1st to 10th	Day	10% 2 2 7% 20% 59%	4336
	11th to 20th	Day	4 1 2 7% 34% 51%	4031
	21st to end	Day	7% 1 2 8% 37% 44%	4420
September	1st to 10th	Day	5% 1 3 9% 28% 53%	2400
	11th to 20th	Day	13% 3 6% 20% 36% 22%	2400
	21st to end	Day	12% 2 5% 18% 34% 29%	2169
October	1st to 10th	Day	14% 3 3 13% 23% 44%	3280
	11th to 20th	Day	15% 3 4 18% 40% 20%	3261
	21st to end	Day	21% 4 6% 19% 36% 15%	3558
November	1st to 10th	Day	29% 3 11% 21% 23% 13%	1879
	11th to 20th	Day	35% 5% 10% 19% 23% 9%	1890
	21st to end	Day	30% 4 8% 21% 25% 13%	1772
December	1st to 10th	Day	25% 3 8% 24% 27% 12%	2700
	11th to 20th	Day	51% 3 8% 16% 15% 7%	3108
	21st to end	Day	49% 7% 15% 16% 9% 4	4092
January	1st to 10th	Night	42% 5% 15% 19% 12% 7%	8172
	11th to 20th	Night	28% 4 7% 12% 26% 23%	7807
	21st to end	Night	40% 4 6% 15% 20% 15%	8371
February	1st to 10th	Night	39% 3 8% 18% 20% 12%	2730
	11th to 20th	Night	40% 5% 8% 20% 19% 8%	2509
	21st to end	Night	38% 4 10% 24% 17% 7%	2076
March	1st to 10th	Night	48% 6% 8% 18% 14% 6%	5389
	11th to 20th	Night	41% 4 9% 22% 16% 8%	5110
	21st to end	Night	44% 8% 13% 21% 11% 3	5354
April	1st to 10th	Night	37% 6% 12% 20% 20% 6%	2100
	11th to 20th	Night	31% 6% 13% 25% 15% 10%	2079
	21st to end	Night	24% 6% 13% 33% 20% 5%	2100
May	1st to 10th	Night	20% 5% 11% 24% 25% 15%	5768
	11th to 20th	Night	11% 3 5% 26% 42% 13%	4700
	21st to end	Night	11% 3 8% 29% 44% 5%	5182
June	1st to 10th	Night	18% 7% 10% 26% 27% 12%	1680
	11th to 20th	Night	9% 2 5% 20% 35% 28%	1680
	21st to end	Night	9% 2 4 11% 36% 38%	1680
July	1st to 10th	Night	3 1 1 6% 26% 63%	4700
	11th to 20th	Night	14% 2 2 5% 9% 68%	4692
	21st to end	Night	8% 2 2 12% 22% 54%	5578
August	1st to 10th	Night	11% 2 2 8% 23% 53%	3019
	11th to 20th	Night	5% 2 2 10% 34% 48%	3322
	21st to end	Night	9% 1 2 12% 34% 43%	3698
September	1st to 10th	Night	5% 1 2 9% 30% 52%	2000
	11th to 20th	Night	12% 3 6% 18% 39% 21%	2000
	21st to end	Night	11% 2 6% 18% 32% 32%	2225
October	1st to 10th	Night	14% 2 3 11% 21% 48%	3920
	11th to 20th	Night	12% 2 5% 25% 34% 22%	3897
	21st to end	Night	22% 3 5% 17% 34% 19%	4253
November	1st to 10th	Night	27% 4 10% 22% 20% 16%	2638
	11th to 20th	Night	30% 4 10% 22% 23% 10%	2730
	21st to end	Night	30% 3 8% 21% 24% 14%	2846
December	1st to 10th	Night	24% 3 8% 24% 25% 16%	4700
	11th to 20th	Night	50% 4 8% 14% 17% 7%	5316
	21st to end	Night	53% 8% 11% 15% 8% 4	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	35% 10% 17% 22% 14% 3	220
	11th to 20th	Day	21% 6% 17% 30% 19% 7%	366
	21st to end	Day	22% 5% 22% 27% 19% 4	473
February	1st to 10th	Day	26% 7% 20% 23% 19% 5%	430
	11th to 20th	Day	24% 12% 26% 24% 13% 2	508
	21st to end	Day	18% 12% 24% 31% 12% 2	446
March	1st to 10th	Day	26% 12% 27% 23% 11% 1	540
	11th to 20th	Day	22% 12% 25% 22% 15% 4	540
	21st to end	Day	21% 10% 31% 23% 13% 2	594
April	1st to 10th	Day	18% 11% 26% 25% 16% 4	540
	11th to 20th	Day	15% 12% 28% 27% 15% 3	532
	21st to end	Day	10% 8% 26% 30% 20% 6%	540
May	1st to 10th	Day	8% 9% 31% 29% 17% 6%	543
	11th to 20th	Day	9% 9% 23% 28% 22% 8%	568
	21st to end	Day	7% 7% 20% 32% 24% 10%	617
June	1st to 10th	Day	5% 6% 22% 36% 22% 10%	570
	11th to 20th	Day	2 7% 26% 36% 22% 6%	570
	21st to end	Day	1 5% 20% 40% 24% 10%	570
July	1st to 10th	Day	1 1 17% 48% 24% 9%	566
	11th to 20th	Day	2 14% 44% 32% 8%	564
	21st to end	Day	1 1 13% 46% 27% 11%	619
August	1st to 10th	Day	3 2 16% 43% 26% 10%	567
	11th to 20th	Day	1 1 21% 39% 27% 11%	557
	21st to end	Day	2 1 14% 44% 28% 10%	620
September	1st to 10th	Day	3 2 19% 46% 24% 7%	530
	11th to 20th	Day	6% 4 21% 38% 26% 5%	530
	21st to end	Day	4 5% 22% 39% 26% 5%	530
October	1st to 10th	Day	4 8% 22% 32% 26% 8%	530
	11th to 20th	Day	7% 5% 18% 31% 31% 8%	530
	21st to end	Day	11% 6% 19% 31% 27% 6%	583
November	1st to 10th	Day	14% 7% 15% 28% 28% 9%	355
	11th to 20th	Day	17% 5% 16% 32% 21% 9%	330
	21st to end	Day	14% 5% 17% 31% 25% 8%	267
December	1st to 10th	Day	17% 4 17% 30% 22% 11%	220
	11th to 20th	Day	20% 7% 19% 25% 18% 10%	220
	21st to end	Day	27% 6% 21% 22% 19% 6%	242
January	1st to 10th	Night	25% 3 14% 30% 20% 8%	840
	11th to 20th	Night	16% 4 13% 39% 23% 6%	840
	21st to end	Night	21% 3 12% 37% 20% 7%	924
February	1st to 10th	Night	23% 3 14% 35% 21% 4	840
	11th to 20th	Night	21% 4 16% 35% 19% 5%	824
	21st to end	Night	21% 3 15% 42% 15% 3	692
March	1st to 10th	Night	26% 4 14% 34% 18% 4	840
	11th to 20th	Night	22% 3 14% 32% 25% 4	840
	21st to end	Night	22% 3 15% 38% 19% 3	924
April	1st to 10th	Night	15% 3 13% 41% 24% 3	840
	11th to 20th	Night	13% 4 15% 36% 26% 6%	831
	21st to end	Night	10% 3 11% 40% 30% 6%	840
May	1st to 10th	Night	10% 3 16% 39% 28% 5%	793
	11th to 20th	Night	8% 2 11% 38% 36% 5%	414
	21st to end	Night	6% 2 10% 40% 37% 5%	455
June	1st to 10th	Night	6% 2 9% 41% 37% 6%	420
	11th to 20th	Night	1 1 12% 41% 41% 3	420
	21st to end	Night	3 1 6% 41% 45% 4	420
July	1st to 10th	Night	4 37% 54% 4	410
	11th to 20th	Night	2 2 43% 48% 4	408
	21st to end	Night	2 2 30% 56% 10%	651
August	1st to 10th	Night	3 4 33% 54% 6%	627
	11th to 20th	Night	3 43% 44% 9%	810
	21st to end	Night	2 1 3 36% 53% 5%	916
September	1st to 10th	Night	2 1 5% 37% 49% 8%	800
	11th to 20th	Night	3 1 6% 38% 42% 9%	800
	21st to end	Night	3 2 8% 41% 36% 11%	800
October	1st to 10th	Night	6% 1 8% 43% 32% 10%	800
	11th to 20th	Night	8% 1 9% 36% 38% 7%	800
	21st to end	Night	8% 2 12% 37% 28% 13%	880
November	1st to 10th	Night	15% 2 9% 35% 29% 10%	820
	11th to 20th	Night	15% 2 13% 39% 23% 8%	840
	21st to end	Night	15% 2 14% 38% 23% 8%	840
December	1st to 10th	Night	18% 3 12% 38% 23% 8%	840
	11th to 20th	Night	29% 2 10% 34% 20% 5%	840
	21st to end	Night	28% 4 14% 33% 17% 4	924

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

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