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 2025-04-26.

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	10% 4 1 3 2 2 2 2 4 5% 64%	117666
	Night	12% 5% 1 4 3 2 3 2 4 5% 59%	119817
Transparency	Day	24% 4 8% 18% 23% 24%	117417
	Night	28% 4 8% 17% 22% 21%	119655
Seeing	Day	11% 6% 21% 33% 22% 7%	15716
	Night	13% 2 11% 37% 30% 7%	25178

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	20% 7% 2 3 3 2 3 2 4 6% 47%	3639
	11th to 20th	Day	18% 6% 2 5% 3 3 2 2 3 3 54%	3961
	21st to end	Day	20% 7% 2 4 3 3 3 3 4 6% 45%	4510
February	1st to 10th	Day	23% 6% 2 4 3 2 3 2 4 5% 45%	1800
	11th to 20th	Day	18% 7% 2 5% 3 3 3 4 4 7% 44%	1900
	21st to end	Day	20% 8% 2 4 3 3 2 3 4 4 47%	1650
March	1st to 10th	Day	19% 11% 3 7% 4 3 4 4 5% 6% 34%	4620
	11th to 20th	Day	18% 7% 2 4 3 3 3 2 4 6% 48%	5000
	21st to end	Day	19% 8% 3 6% 4 4 4 4 6% 6% 36%	5735
April	1st to 10th	Day	15% 7% 2 5% 4 3 3 3 5% 7% 47%	2400
	11th to 20th	Day	13% 4 1 4 3 3 3 3 6% 7% 53%	2369
	21st to end	Day	10% 4 1 4 2 2 3 3 5% 7% 59%	2342
May	1st to 10th	Day	8% 3 1 2 2 2 2 2 3 5% 71%	3871
	11th to 20th	Day	3 2 1 2 2 1 2 2 2 4 79%	4377
	21st to end	Day	4 2 1 2 2 2 2 2 4 6% 73%	4813
June	1st to 10th	Day	5% 4 1 3 3 2 2 3 4 7% 65%	2660
	11th to 20th	Day	1 2 1 2 2 2 1 2 4 4 81%	2660
	21st to end	Day	2 2 1 2 1 1 1 1 3 3 84%	2660
July	1st to 10th	Day	1 1 1 1 2 2 93%	4420
	11th to 20th	Day	1 1 1 2 1 1 2 1 3 3 84%	4420
	21st to end	Day	1 1 1 1 1 1 2 2 88%	4497
August	1st to 10th	Day	2 2 1 2 2 2 1 2 3 4 79%	4091
	11th to 20th	Day	1 1 1 1 1 1 2 3 89%	3753
	21st to end	Day	2 1 1 1 1 1 1 1 2 89%	4180
September	1st to 10th	Day	2 1 1 1 2 1 2 2 88%	2280
	11th to 20th	Day	3 2 1 3 1 2 2 2 4 4 76%	2280
	21st to end	Day	3 2 1 2 1 2 2 2 2 4 79%	2061
October	1st to 10th	Day	3 2 1 3 2 2 3 3 4 5% 73%	3180
	11th to 20th	Day	5% 3 1 2 2 2 2 2 4 4 74%	3161
	21st to end	Day	5% 3 1 4 3 3 3 2 4 7% 65%	3448
November	1st to 10th	Day	12% 4 1 3 3 4 3 2 5% 7% 55%	1788
	11th to 20th	Day	14% 4 1 3 4 3 4 3 5% 7% 51%	1800
	21st to end	Day	14% 4 2 4 3 3 4 3 4 6% 55%	1688
December	1st to 10th	Day	10% 3 1 4 3 3 3 3 4 7% 59%	2620
	11th to 20th	Day	28% 7% 3 5% 3 2 3 3 4 6% 35%	3028
	21st to end	Day	26% 6% 2 5% 3 4 4 4 6% 8% 30%	4004
January	1st to 10th	Night	13% 7% 2 5% 3 3 4 3 5% 9% 45%	6306
	11th to 20th	Night	16% 5% 2 5% 3 3 3 2 3 4 54%	5998
	21st to end	Night	18% 6% 2 6% 4 3 3 3 4 4 47%	6468
February	1st to 10th	Night	22% 7% 1 3 3 3 3 2 4 5% 48%	2600
	11th to 20th	Night	16% 7% 2 5% 4 3 3 3 5% 7% 45%	2386
	21st to end	Night	17% 8% 2 4 3 3 4 3 4 5% 48%	1980
March	1st to 10th	Night	22% 11% 3 6% 3 3 3 3 4 6% 36%	5271
	11th to 20th	Night	24% 8% 2 4 2 2 2 2 3 4 48%	5000
	21st to end	Night	23% 9% 2 5% 3 3 4 3 5% 7% 37%	5238
April	1st to 10th	Night	13% 6% 2 5% 5% 4 4 3 4 6% 48%	2000
	11th to 20th	Night	12% 5% 2 5% 4 3 3 2 4 7% 54%	1979
	21st to end	Night	8% 4 2 3 3 2 3 2 5% 6% 62%	1954
May	1st to 10th	Night	6% 5% 1 3 2 2 2 2 3 5% 69%	3099
	11th to 20th	Night	4 2 1 1 1 2 2 3 5% 79%	2516
	21st to end	Night	4 1 1 2 2 1 2 2 3 5% 77%	2762
June	1st to 10th	Night	5% 3 1 3 3 3 2 3 5% 6% 66%	1520
	11th to 20th	Night	1 2 1 2 1 2 2 2 3 4 81%	1520
	21st to end	Night	2 1 2 2 2 1 1 3 2 83%	1520
July	1st to 10th	Night	1 1 1 1 1 1 93%	2540
	11th to 20th	Night	2 2 2 2 1 2 2 2 3 80%	2540
	21st to end	Night	1 1 2 1 1 1 1 3 4 84%	3061
August	1st to 10th	Night	2 2 1 2 2 2 1 2 4 4 77%	2848
	11th to 20th	Night	1 1 1 1 1 1 3 2 87%	3094
	21st to end	Night	3 1 1 2 1 1 1 1 1 2 88%	3498
September	1st to 10th	Night	2 1 1 1 1 1 1 2 3 88%	1900
	11th to 20th	Night	3 3 1 1 2 2 2 2 3 4 78%	1900
	21st to end	Night	3 1 1 1 2 2 2 2 3 5% 80%	2114
October	1st to 10th	Night	3 2 1 3 2 2 2 2 3 3 77%	3800
	11th to 20th	Night	4 2 1 2 1 1 2 2 3 5% 79%	3777
	21st to end	Night	8% 2 1 3 3 3 3 3 3 5% 65%	4121
November	1st to 10th	Night	13% 6% 1 3 2 2 2 3 5% 6% 57%	2509
	11th to 20th	Night	12% 5% 1 4 3 3 3 3 5% 7% 55%	2600
	21st to end	Night	14% 4 1 3 3 3 3 2 4 6% 56%	2710
December	1st to 10th	Night	11% 3 1 2 2 3 3 3 4 6% 61%	4560
	11th to 20th	Night	27% 7% 2 5% 3 3 4 4 6% 9% 31%	5176
	21st to end	Night	27% 8% 3 6% 4 4 4 3 4 6% 30%	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	38% 4 14% 21% 14% 8%	3639
	11th to 20th	Day	36% 5% 6% 14% 23% 16%	3961
	21st to end	Day	41% 5% 8% 12% 21% 13%	4510
February	1st to 10th	Day	43% 3 10% 17% 17% 10%	1800
	11th to 20th	Day	40% 5% 9% 20% 20% 7%	1910
	21st to end	Day	41% 3 10% 21% 17% 8%	1650
March	1st to 10th	Day	48% 9% 8% 16% 17% 3	4620
	11th to 20th	Day	38% 5% 12% 28% 11% 7%	5000
	21st to end	Day	44% 9% 16% 20% 10% 1	5735
April	1st to 10th	Day	37% 6% 13% 25% 16% 5%	2400
	11th to 20th	Day	30% 6% 14% 26% 19% 6%	2372
	21st to end	Day	24% 5% 14% 29% 24% 4	2342
May	1st to 10th	Day	17% 4 11% 29% 24% 16%	3871
	11th to 20th	Day	12% 2 6% 26% 42% 11%	4380
	21st to end	Day	14% 4 13% 34% 30% 5%	4814
June	1st to 10th	Day	20% 4 11% 25% 29% 11%	2660
	11th to 20th	Day	9% 3 8% 21% 35% 24%	2660
	21st to end	Day	8% 2 3 13% 34% 40%	2660
July	1st to 10th	Day	3 1 1 5% 14% 75%	4351
	11th to 20th	Day	7% 2 2 8% 15% 66%	4345
	21st to end	Day	5% 1 2 5% 23% 64%	4355
August	1st to 10th	Day	10% 2 3 7% 19% 59%	4076
	11th to 20th	Day	4 1 2 6% 34% 53%	3789
	21st to end	Day	6% 1 2 8% 37% 46%	4179
September	1st to 10th	Day	5% 1 3 7% 28% 56%	2280
	11th to 20th	Day	13% 3 6% 20% 36% 23%	2280
	21st to end	Day	11% 2 5% 18% 34% 30%	2061
October	1st to 10th	Day	13% 3 3 12% 23% 45%	3180
	11th to 20th	Day	15% 3 4 18% 40% 20%	3161
	21st to end	Day	21% 4 6% 19% 36% 15%	3448
November	1st to 10th	Day	29% 3 11% 21% 22% 14%	1788
	11th to 20th	Day	32% 5% 11% 20% 24% 9%	1800
	21st to end	Day	31% 5% 8% 20% 24% 13%	1688
December	1st to 10th	Day	26% 4 8% 23% 27% 13%	2620
	11th to 20th	Day	51% 3 8% 16% 15% 7%	3028
	21st to end	Day	48% 8% 15% 17% 9% 4	4004
January	1st to 10th	Night	35% 6% 18% 21% 12% 9%	6306
	11th to 20th	Night	35% 5% 8% 13% 23% 16%	5998
	21st to end	Night	40% 5% 7% 11% 21% 16%	6468
February	1st to 10th	Night	40% 3 8% 18% 20% 11%	2600
	11th to 20th	Night	38% 5% 8% 21% 20% 8%	2387
	21st to end	Night	37% 4 10% 24% 18% 8%	1980
March	1st to 10th	Night	48% 6% 8% 18% 13% 6%	5271
	11th to 20th	Night	41% 4 9% 23% 15% 8%	5000
	21st to end	Night	45% 8% 13% 20% 11% 3	5238
April	1st to 10th	Night	38% 6% 12% 20% 20% 6%	2000
	11th to 20th	Night	31% 6% 12% 26% 15% 10%	1979
	21st to end	Night	22% 6% 13% 32% 22% 6%	1954
May	1st to 10th	Night	17% 6% 15% 22% 24% 17%	3099
	11th to 20th	Night	11% 2 8% 25% 42% 12%	2516
	21st to end	Night	11% 4 13% 37% 30% 5%	2762
June	1st to 10th	Night	18% 7% 11% 26% 27% 11%	1520
	11th to 20th	Night	10% 3 6% 22% 34% 26%	1520
	21st to end	Night	9% 2 4 11% 34% 39%	1520
July	1st to 10th	Night	2 1 2 6% 15% 74%	2500
	11th to 20th	Night	10% 3 2 7% 13% 64%	2492
	21st to end	Night	7% 1 2 5% 23% 62%	2965
August	1st to 10th	Night	12% 2 2 9% 22% 53%	2839
	11th to 20th	Night	4 1 2 8% 35% 49%	3124
	21st to end	Night	8% 1 2 11% 33% 45%	3498
September	1st to 10th	Night	5% 1 2 8% 30% 54%	1900
	11th to 20th	Night	12% 3 6% 18% 40% 22%	1900
	21st to end	Night	10% 2 5% 18% 32% 33%	2114
October	1st to 10th	Night	14% 2 3 11% 20% 49%	3800
	11th to 20th	Night	11% 2 5% 24% 34% 23%	3777
	21st to end	Night	22% 3 5% 17% 34% 20%	4121
November	1st to 10th	Night	28% 4 10% 22% 19% 17%	2509
	11th to 20th	Night	29% 4 10% 22% 24% 11%	2600
	21st to end	Night	31% 4 8% 20% 23% 14%	2710
December	1st to 10th	Night	25% 3 8% 23% 25% 17%	4560
	11th to 20th	Night	50% 4 8% 14% 17% 6%	5176
	21st to end	Night	53% 8% 11% 15% 8% 5%	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	35% 9% 17% 24% 14% 3	200
	11th to 20th	Day	23% 7% 19% 29% 17% 5%	339
	21st to end	Day	24% 5% 21% 26% 20% 5%	440
February	1st to 10th	Day	28% 8% 20% 23% 19% 4	400
	11th to 20th	Day	23% 11% 27% 24% 13% 2	470
	21st to end	Day	18% 12% 24% 31% 13% 2	414
March	1st to 10th	Day	27% 12% 26% 24% 10% 1	500
	11th to 20th	Day	24% 13% 26% 21% 13% 4	500
	21st to end	Day	22% 10% 31% 22% 13% 2	550
April	1st to 10th	Day	18% 12% 27% 25% 15% 3	500
	11th to 20th	Day	15% 12% 29% 27% 15% 3	492
	21st to end	Day	9% 8% 26% 29% 21% 6%	481
May	1st to 10th	Day	8% 10% 32% 29% 17% 5%	463
	11th to 20th	Day	9% 8% 23% 28% 23% 9%	488
	21st to end	Day	8% 8% 19% 31% 25% 10%	529
June	1st to 10th	Day	6% 6% 22% 34% 22% 10%	490
	11th to 20th	Day	3 6% 27% 35% 22% 7%	490
	21st to end	Day	1 3 20% 42% 23% 11%	490
July	1st to 10th	Day	1 13% 50% 26% 9%	486
	11th to 20th	Day	1 14% 44% 33% 8%	484
	21st to end	Day	1 1 13% 45% 29% 12%	531
August	1st to 10th	Day	4 2 16% 43% 24% 10%	487
	11th to 20th	Day	1 2 22% 38% 26% 11%	477
	21st to end	Day	1 1 14% 44% 28% 11%	539
September	1st to 10th	Day	2 2 17% 47% 24% 7%	490
	11th to 20th	Day	6% 4 22% 38% 26% 4	490
	21st to end	Day	3 5% 22% 40% 26% 4	490
October	1st to 10th	Day	4 7% 23% 32% 28% 7%	490
	11th to 20th	Day	7% 5% 18% 32% 31% 8%	490
	21st to end	Day	10% 6% 19% 32% 25% 6%	539
November	1st to 10th	Day	14% 7% 16% 28% 27% 7%	324
	11th to 20th	Day	13% 4 17% 33% 23% 10%	300
	21st to end	Day	16% 5% 17% 31% 24% 7%	243
December	1st to 10th	Day	19% 4 17% 29% 22% 12%	200
	11th to 20th	Day	21% 7% 20% 26% 18% 9%	200
	21st to end	Day	25% 5% 21% 23% 20% 6%	220
January	1st to 10th	Night	24% 3 14% 30% 21% 9%	800
	11th to 20th	Night	16% 4 14% 39% 21% 6%	800
	21st to end	Night	22% 3 13% 35% 20% 8%	880
February	1st to 10th	Night	24% 3 14% 33% 21% 5%	800
	11th to 20th	Night	20% 3 16% 35% 20% 5%	784
	21st to end	Night	21% 3 14% 42% 16% 4	660
March	1st to 10th	Night	27% 4 13% 33% 18% 5%	800
	11th to 20th	Night	23% 4 14% 30% 24% 5%	800
	21st to end	Night	23% 3 15% 36% 19% 3	880
April	1st to 10th	Night	15% 3 14% 41% 24% 3	800
	11th to 20th	Night	13% 4 14% 37% 26% 6%	791
	21st to end	Night	9% 4 11% 40% 30% 7%	782
May	1st to 10th	Night	10% 3 16% 39% 26% 6%	718
	11th to 20th	Night	8% 2 9% 37% 39% 6%	374
	21st to end	Night	6% 2 10% 39% 38% 6%	411
June	1st to 10th	Night	6% 2 10% 39% 37% 7%	380
	11th to 20th	Night	1 1 12% 40% 42% 4	380
	21st to end	Night	3 1 5% 41% 46% 5%	380
July	1st to 10th	Night	1 3 36% 56% 5%	370
	11th to 20th	Night	2 2 42% 49% 5%	368
	21st to end	Night	2 2 30% 56% 11%	589
August	1st to 10th	Night	3 4 34% 53% 7%	567
	11th to 20th	Night	1 1 4 42% 44% 9%	732
	21st to end	Night	2 3 34% 55% 6%	836
September	1st to 10th	Night	1 1 5% 36% 50% 8%	760
	11th to 20th	Night	3 1 6% 37% 42% 10%	760
	21st to end	Night	3 1 8% 40% 37% 11%	760
October	1st to 10th	Night	6% 1 8% 43% 32% 10%	760
	11th to 20th	Night	8% 1 9% 36% 39% 7%	760
	21st to end	Night	7% 2 12% 37% 28% 14%	836
November	1st to 10th	Night	15% 2 9% 35% 28% 10%	780
	11th to 20th	Night	14% 2 12% 40% 24% 9%	800
	21st to end	Night	15% 2 14% 38% 22% 8%	800
December	1st to 10th	Night	19% 3 11% 38% 22% 8%	800
	11th to 20th	Night	30% 2 10% 34% 20% 4	800
	21st to end	Night	27% 4 14% 34% 17% 4	880

Page generated at 2025-04-23 06:25:08. Version ac07

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