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 2024-10-25.

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	9% 4 1 3 2 2 2 2 4 5% 65%	101140
	Night	12% 5% 1 4 3 2 3 2 4 5% 59%	97878
Transparency	Day	23% 4 8% 18% 23% 25%	100891
	Night	28% 5% 8% 18% 21% 21%	97716
Seeing	Day	11% 6% 21% 33% 22% 7%	15139
	Night	13% 2 10% 37% 31% 7%	24448

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	25% 10% 2 4 3 3 3 2 4 4 40%	2539
	11th to 20th	Day	25% 9% 3 8% 4 4 3 3 4 3 34%	2763
	21st to end	Day	25% 9% 3 6% 4 3 3 3 5% 7% 32%	3146
February	1st to 10th	Day	22% 6% 2 4 3 2 4 3 4 5% 46%	1710
	11th to 20th	Day	18% 7% 2 5% 3 3 3 3 4 6% 45%	1802
	21st to end	Day	21% 8% 2 4 3 3 2 3 4 4 46%	1570
March	1st to 10th	Day	20% 13% 3 8% 4 4 4 4 5% 5% 30%	3214
	11th to 20th	Day	15% 5% 1 3 2 3 3 2 4 6% 56%	3490
	21st to end	Day	17% 9% 3 6% 4 4 5% 4 6% 7% 33%	3996
April	1st to 10th	Day	15% 7% 2 5% 4 3 3 3 5% 7% 46%	2280
	11th to 20th	Day	13% 4 1 4 3 3 3 3 6% 7% 53%	2249
	21st to end	Day	10% 4 1 4 2 2 3 3 5% 7% 59%	2280
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	4 2 1 2 3 2 3 3 4 5% 69%	1900
	11th to 20th	Day	6% 3 1 2 2 2 3 3 4 4 69%	1900
	21st to end	Day	7% 3 1 4 3 2 3 2 3 5% 66%	2025
November	1st to 10th	Day	13% 4 1 3 3 4 3 2 5% 7% 54%	1697
	11th to 20th	Day	13% 4 1 3 4 3 4 4 5% 7% 52%	1710
	21st to end	Day	12% 4 2 4 3 3 4 3 4 6% 55%	1604
December	1st to 10th	Day	17% 5% 2 5% 4 3 4 4 4 6% 48%	1520
	11th to 20th	Day	29% 9% 3 6% 4 2 3 3 3 6% 32%	1928
	21st to end	Day	15% 6% 3 6% 4 5% 5% 4 6% 9% 37%	2794
January	1st to 10th	Night	18% 9% 2 5% 3 3 4 3 5% 7% 41%	4406
	11th to 20th	Night	23% 7% 2 7% 4 4 4 3 5% 5% 35%	4202
	21st to end	Night	25% 8% 3 7% 5% 4 4 3 5% 5% 33%	4521
February	1st to 10th	Night	20% 7% 1 3 3 3 3 2 4 5% 49%	2470
	11th to 20th	Night	16% 7% 2 5% 3 3 3 3 5% 7% 46%	2264
	21st to end	Night	18% 8% 2 4 3 2 4 3 4 5% 48%	1884
March	1st to 10th	Night	25% 13% 3 6% 3 3 3 3 4 4 32%	3657
	11th to 20th	Night	18% 5% 2 3 2 2 2 2 3 4 57%	3490
	21st to end	Night	23% 9% 2 5% 4 4 4 3 5% 6% 35%	3655
April	1st to 10th	Night	14% 6% 2 5% 5% 4 4 3 4 6% 48%	1900
	11th to 20th	Night	12% 5% 2 5% 4 3 3 2 4 7% 54%	1879
	21st to end	Night	9% 4 1 3 3 2 3 2 5% 6% 61%	1900
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	6% 2 1 3 3 2 2 2 4 4 72%	2280
	11th to 20th	Night	6% 3 1 2 1 2 3 2 4 5% 72%	2280
	21st to end	Night	7% 2 1 3 2 2 2 2 3 6% 70%	2436
November	1st to 10th	Night	13% 6% 1 3 2 2 2 3 4 6% 56%	2380
	11th to 20th	Night	12% 4 1 4 3 3 3 3 5% 7% 56%	2470
	21st to end	Night	13% 4 1 3 3 3 3 2 4 6% 57%	2574
December	1st to 10th	Night	19% 5% 2 3 3 3 3 3 3 6% 50%	2660
	11th to 20th	Night	30% 8% 2 5% 3 2 3 3 4 6% 33%	3276
	21st to end	Night	20% 7% 3 6% 5% 4 5% 4 5% 6% 34%	4862

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	47% 5% 9% 24% 13% 3	2539
	11th to 20th	Day	52% 7% 8% 13% 11% 8%	2763
	21st to end	Day	51% 7% 11% 16% 11% 5%	3146
February	1st to 10th	Day	42% 3 10% 18% 17% 10%	1710
	11th to 20th	Day	39% 5% 10% 19% 21% 7%	1812
	21st to end	Day	42% 4 10% 21% 17% 6%	1570
March	1st to 10th	Day	52% 11% 10% 13% 12% 3	3214
	11th to 20th	Day	30% 5% 9% 31% 14% 10%	3490
	21st to end	Day	43% 11% 17% 18% 9% 2	3996
April	1st to 10th	Day	37% 6% 13% 24% 15% 5%	2280
	11th to 20th	Day	30% 6% 14% 26% 18% 6%	2252
	21st to end	Day	24% 5% 15% 29% 24% 4	2280
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	16% 5% 5% 19% 26% 29%	1900
	11th to 20th	Day	18% 4 6% 20% 27% 26%	1900
	21st to end	Day	22% 5% 6% 19% 28% 21%	2025
November	1st to 10th	Day	31% 3 11% 20% 22% 14%	1697
	11th to 20th	Day	31% 5% 10% 20% 25% 10%	1710
	21st to end	Day	30% 5% 9% 21% 25% 11%	1604
December	1st to 10th	Day	38% 5% 8% 20% 19% 10%	1520
	11th to 20th	Day	54% 4 7% 15% 14% 6%	1928
	21st to end	Day	40% 9% 17% 19% 11% 4	2794
January	1st to 10th	Night	41% 7% 14% 23% 11% 4	4406
	11th to 20th	Night	49% 7% 12% 12% 11% 9%	4202
	21st to end	Night	52% 7% 10% 13% 13% 6%	4521
February	1st to 10th	Night	39% 4 8% 18% 20% 11%	2470
	11th to 20th	Night	38% 5% 8% 21% 20% 8%	2265
	21st to end	Night	38% 4 10% 24% 18% 7%	1884
March	1st to 10th	Night	53% 8% 9% 14% 11% 4	3657
	11th to 20th	Night	32% 5% 8% 25% 19% 11%	3490
	21st to end	Night	46% 10% 13% 19% 9% 3	3655
April	1st to 10th	Night	38% 6% 12% 20% 19% 6%	1900
	11th to 20th	Night	31% 6% 12% 26% 15% 9%	1879
	21st to end	Night	22% 6% 13% 32% 21% 6%	1900
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	18% 3 5% 17% 25% 31%	2280
	11th to 20th	Night	15% 4 6% 19% 28% 28%	2280
	21st to end	Night	18% 3 6% 19% 29% 24%	2436
November	1st to 10th	Night	29% 4 10% 21% 19% 17%	2380
	11th to 20th	Night	28% 4 10% 22% 25% 11%	2470
	21st to end	Night	31% 4 8% 20% 24% 14%	2574
December	1st to 10th	Night	37% 4 9% 19% 17% 14%	2660
	11th to 20th	Night	52% 3 7% 15% 16% 6%	3276
	21st to end	Night	46% 10% 12% 16% 11% 5%	4862

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	37% 9% 16% 22% 14% 3	180
	11th to 20th	Day	25% 6% 18% 29% 17% 5%	312
	21st to end	Day	25% 5% 20% 25% 20% 5%	407
February	1st to 10th	Day	26% 8% 19% 23% 20% 4	370
	11th to 20th	Day	22% 11% 26% 25% 14% 2	432
	21st to end	Day	20% 12% 24% 30% 12% 2	382
March	1st to 10th	Day	28% 13% 25% 23% 10% 1	460
	11th to 20th	Day	23% 13% 25% 22% 13% 4	460
	21st to end	Day	21% 11% 32% 23% 12% 1	506
April	1st to 10th	Day	18% 12% 28% 24% 15% 3	460
	11th to 20th	Day	16% 12% 29% 25% 15% 3	452
	21st to end	Day	10% 8% 25% 29% 22% 6%	460
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	11% 6% 18% 32% 26% 7%	514
November	1st to 10th	Day	15% 7% 13% 28% 28% 8%	293
	11th to 20th	Day	12% 3 16% 33% 24% 11%	270
	21st to end	Day	12% 5% 18% 32% 26% 7%	219
December	1st to 10th	Day	21% 4 16% 28% 21% 10%	180
	11th to 20th	Day	19% 7% 21% 26% 18% 9%	180
	21st to end	Day	22% 6% 22% 23% 20% 7%	198
January	1st to 10th	Night	25% 3 12% 30% 21% 9%	760
	11th to 20th	Night	17% 4 12% 38% 22% 6%	760
	21st to end	Night	23% 3 12% 34% 20% 8%	836
February	1st to 10th	Night	22% 3 14% 33% 22% 5%	760
	11th to 20th	Night	20% 3 15% 35% 21% 6%	744
	21st to end	Night	22% 3 14% 41% 16% 4	628
March	1st to 10th	Night	28% 4 13% 32% 18% 5%	760
	11th to 20th	Night	22% 3 14% 31% 25% 5%	760
	21st to end	Night	23% 3 15% 37% 19% 3	836
April	1st to 10th	Night	15% 3 13% 41% 24% 3	760
	11th to 20th	Night	13% 4 14% 36% 26% 7%	751
	21st to end	Night	9% 4 11% 39% 30% 7%	760
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 11% 36% 29% 14%	812
November	1st to 10th	Night	15% 2 9% 35% 28% 11%	740
	11th to 20th	Night	13% 2 11% 41% 25% 9%	760
	21st to end	Night	14% 3 13% 38% 23% 8%	760
December	1st to 10th	Night	20% 3 11% 37% 21% 8%	760
	11th to 20th	Night	29% 2 10% 34% 21% 4	760
	21st to end	Night	26% 4 14% 34% 18% 4	836

Page generated at 2024-10-22 17:21:00. Version ac07

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