Cedar Glen Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cedar Glen Observatory clear sky chart from 2005-11-06 to 2025-01-07.

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	3 3 1 3 2 2 3 2 4 6% 71%	109604
	Night	2 4 1 4 3 3 3 2 4 5% 69%	108274
Transparency	Day	16% 4 5% 15% 28% 32%	109367
	Night	17% 5% 5% 15% 26% 32%	108101
Seeing	Day	7% 15% 34% 28% 11% 4	15879
	Night	5% 7% 20% 34% 27% 8%	25876

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	5% 5% 2 5% 2 3 3 2 4 7% 63%	2912
	11th to 20th	Day	6% 5% 2 4 2 2 3 2 5% 8% 60%	2960
	21st to end	Day	8% 9% 3 5% 4 4 4 3 4 6% 50%	3498
February	1st to 10th	Day	5% 8% 2 5% 3 2 3 2 4 5% 60%	1900
	11th to 20th	Day	4 6% 2 5% 4 3 3 2 5% 6% 59%	1850
	21st to end	Day	6% 9% 2 6% 4 4 3 3 5% 6% 54%	1570
March	1st to 10th	Day	6% 9% 2 5% 3 4 3 4 6% 8% 49%	3138
	11th to 20th	Day	3 5% 2 4 3 3 4 3 6% 8% 58%	3321
	21st to end	Day	5% 6% 2 5% 2 4 4 4 5% 7% 55%	4058
April	1st to 10th	Day	5% 6% 2 4 2 3 3 3 6% 6% 61%	2280
	11th to 20th	Day	3 4 1 4 2 3 3 2 4 5% 70%	2249
	21st to end	Day	2 4 1 2 2 4 3 3 5% 6% 68%	2280
May	1st to 10th	Day	1 2 1 2 1 2 2 2 4 5% 77%	4039
	11th to 20th	Day	1 2 1 2 1 2 2 2 4 5% 79%	4071
	21st to end	Day	1 2 1 2 1 1 1 1 2 5% 83%	4477
June	1st to 10th	Day	1 2 1 2 2 2 2 2 5% 6% 76%	2470
	11th to 20th	Day	1 1 1 2 1 2 4 87%	2485
	21st to end	Day	1 2 1 2 1 1 2 1 2 3 84%	2660
July	1st to 10th	Day	1 1 1 1 1 2 1 2 3 87%	4394
	11th to 20th	Day	1 1 1 2 1 2 3 2 3 5% 78%	4110
	21st to end	Day	1 1 1 2 2 2 3 2 4 5% 78%	4344
August	1st to 10th	Day	1 1 1 2 2 1 3 2 3 4 80%	3783
	11th to 20th	Day	1 1 1 1 1 1 2 2 4 87%	3724
	21st to end	Day	1 1 1 1 1 2 2 3 3 86%	4180
September	1st to 10th	Day	2 1 1 3 3 2 3 2 4 6% 74%	2277
	11th to 20th	Day	1 1 1 1 2 1 2 3 4 86%	2090
	21st to end	Day	1 1 2 2 2 3 2 3 4 81%	2090
October	1st to 10th	Day	1 2 1 2 2 2 2 2 5% 5% 77%	3490
	11th to 20th	Day	1 1 1 1 1 1 1 3 5% 83%	3412
	21st to end	Day	1 3 1 3 1 2 3 3 4 5% 74%	3259
November	1st to 10th	Day	2 4 1 3 3 3 2 3 4 6% 71%	1764
	11th to 20th	Day	3 3 1 4 2 3 3 2 4 6% 69%	1800
	21st to end	Day	4 5% 2 4 4 3 3 2 5% 7% 60%	1800
December	1st to 10th	Day	3 3 1 3 3 3 4 4 6% 7% 63%	2950
	11th to 20th	Day	4 6% 2 5% 2 4 6% 5% 6% 8% 52%	3409
	21st to end	Day	5% 7% 3 5% 4 5% 4 4 8% 9% 47%	4510
January	1st to 10th	Night	4 6% 2 5% 3 3 3 2 4 6% 62%	4175
	11th to 20th	Night	3 5% 2 6% 4 3 3 3 5% 8% 57%	4010
	21st to end	Night	9% 7% 3 5% 4 2 3 4 4 6% 52%	4180
February	1st to 10th	Night	5% 9% 2 6% 3 3 3 3 4 5% 58%	2280
	11th to 20th	Night	4 6% 2 4 4 3 3 3 4 5% 60%	2218
	21st to end	Night	5% 8% 4 7% 4 4 4 3 5% 6% 51%	1884
March	1st to 10th	Night	4 13% 2 10% 4 4 4 3 5% 6% 45%	3736
	11th to 20th	Night	2 6% 1 6% 4 3 4 3 5% 7% 57%	3659
	21st to end	Night	2 9% 2 8% 4 3 3 3 5% 7% 54%	3591
April	1st to 10th	Night	3 7% 1 5% 4 3 4 3 5% 6% 58%	1900
	11th to 20th	Night	2 4 1 4 3 3 3 3 4 6% 67%	1879
	21st to end	Night	2 4 2 4 3 4 4 3 4 5% 66%	1900
May	1st to 10th	Night	2 3 1 2 2 2 2 2 3 5% 77%	2929
	11th to 20th	Night	1 1 1 2 2 2 2 3 4 5% 79%	2834
	21st to end	Night	1 1 1 2 2 3 3 2 3 4 79%	3110
June	1st to 10th	Night	1 1 2 2 3 3 1 4 5% 78%	1710
	11th to 20th	Night	1 2 1 1 2 1 2 4 86%	1684
	21st to end	Night	1 1 1 1 1 2 1 3 3 86%	1520
July	1st to 10th	Night	1 1 1 1 2 2 92%	2558
	11th to 20th	Night	1 1 1 1 1 2 2 3 3 84%	2860
	21st to end	Night	1 2 1 2 2 1 1 1 3 4 82%	3219
August	1st to 10th	Night	1 1 1 1 1 1 1 2 4 85%	3166
	11th to 20th	Night	1 1 1 1 1 1 2 4 87%	3126
	21st to end	Night	1 1 1 1 1 1 1 1 2 91%	3498
September	1st to 10th	Night	2 1 1 2 2 2 2 2 2 4 80%	1900
	11th to 20th	Night	1 1 1 1 1 2 1 2 3 87%	2090
	21st to end	Night	1 1 2 1 2 2 2 3 3 84%	2090
October	1st to 10th	Night	1 2 1 2 1 1 1 2 2 3 84%	3490
	11th to 20th	Night	1 1 1 1 2 2 2 2 4 4 81%	3521
	21st to end	Night	1 3 2 3 3 2 2 2 3 4 75%	4303
November	1st to 10th	Night	2 4 1 4 3 2 3 2 4 6% 69%	2535
	11th to 20th	Night	2 4 2 4 3 3 3 3 4 6% 68%	2600
	21st to end	Night	3 5% 2 6% 4 3 4 3 5% 6% 58%	2600
December	1st to 10th	Night	3 4 1 4 3 2 4 3 4 6% 65%	4240
	11th to 20th	Night	4 5% 2 5% 4 4 4 4 6% 8% 53%	4811
	21st to end	Night	3 5% 2 7% 4 4 4 4 7% 11% 48%	6468

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	20% 4 4 22% 34% 15%	2913
	11th to 20th	Day	24% 4 13% 22% 24% 14%	2960
	21st to end	Day	33% 5% 7% 16% 23% 16%	3498
February	1st to 10th	Day	26% 2 5% 15% 26% 26%	1900
	11th to 20th	Day	26% 4 4 15% 29% 22%	1860
	21st to end	Day	32% 4 6% 16% 23% 18%	1570
March	1st to 10th	Day	30% 10% 5% 18% 24% 13%	3138
	11th to 20th	Day	21% 6% 11% 28% 19% 14%	3321
	21st to end	Day	23% 12% 9% 28% 21% 8%	4058
April	1st to 10th	Day	25% 5% 6% 23% 28% 13%	2280
	11th to 20th	Day	19% 6% 5% 19% 31% 21%	2252
	21st to end	Day	18% 5% 6% 20% 36% 14%	2280
May	1st to 10th	Day	12% 4 6% 19% 36% 22%	4039
	11th to 20th	Day	8% 5% 7% 17% 47% 16%	4074
	21st to end	Day	10% 7% 4 19% 45% 14%	4477
June	1st to 10th	Day	13% 3 5% 17% 37% 26%	2470
	11th to 20th	Day	5% 4 4 10% 28% 49%	2485
	21st to end	Day	9% 2 2 5% 22% 59%	2660
July	1st to 10th	Day	5% 1 2 5% 11% 76%	4325
	11th to 20th	Day	9% 2 4 10% 28% 45%	4041
	21st to end	Day	10% 2 5% 21% 20% 41%	4207
August	1st to 10th	Day	10% 2 4 15% 31% 37%	3770
	11th to 20th	Day	5% 1 3 13% 22% 56%	3760
	21st to end	Day	6% 1 2 5% 24% 61%	4179
September	1st to 10th	Day	11% 3 6% 7% 30% 43%	2277
	11th to 20th	Day	6% 1 3 9% 31% 49%	2090
	21st to end	Day	9% 2 3 11% 31% 44%	2090
October	1st to 10th	Day	11% 2 6% 9% 21% 50%	3490
	11th to 20th	Day	8% 2 3 8% 36% 44%	3412
	21st to end	Day	15% 3 2 7% 32% 41%	3259
November	1st to 10th	Day	17% 2 4 14% 32% 32%	1764
	11th to 20th	Day	19% 2 5% 12% 24% 38%	1800
	21st to end	Day	25% 3 5% 13% 24% 30%	1800
December	1st to 10th	Day	18% 3 6% 13% 28% 32%	2950
	11th to 20th	Day	27% 6% 7% 16% 28% 16%	3408
	21st to end	Day	30% 7% 9% 19% 22% 14%	4510
January	1st to 10th	Night	23% 5% 5% 15% 33% 20%	4175
	11th to 20th	Night	24% 6% 10% 25% 20% 14%	4010
	21st to end	Night	32% 6% 7% 15% 26% 15%	4180
February	1st to 10th	Night	29% 3 4 13% 21% 29%	2280
	11th to 20th	Night	26% 4 5% 15% 25% 25%	2219
	21st to end	Night	35% 4 4 16% 21% 21%	1884
March	1st to 10th	Night	32% 15% 4 17% 17% 15%	3736
	11th to 20th	Night	22% 5% 11% 25% 24% 13%	3659
	21st to end	Night	25% 12% 10% 24% 22% 7%	3591
April	1st to 10th	Night	26% 5% 8% 22% 22% 16%	1900
	11th to 20th	Night	19% 7% 5% 20% 28% 21%	1879
	21st to end	Night	20% 6% 5% 20% 34% 15%	1900
May	1st to 10th	Night	11% 6% 5% 24% 31% 23%	2929
	11th to 20th	Night	9% 5% 5% 21% 42% 18%	2835
	21st to end	Night	8% 9% 5% 19% 47% 12%	3110
June	1st to 10th	Night	9% 4 4 17% 37% 28%	1710
	11th to 20th	Night	6% 3 4 12% 28% 48%	1684
	21st to end	Night	6% 2 3 6% 22% 61%	1520
July	1st to 10th	Night	3 1 1 4 12% 79%	2518
	11th to 20th	Night	7% 1 4 11% 23% 53%	2806
	21st to end	Night	9% 1 4 22% 23% 40%	3118
August	1st to 10th	Night	6% 1 3 18% 33% 39%	3156
	11th to 20th	Night	4 1 3 12% 26% 53%	3156
	21st to end	Night	5% 1 1 5% 22% 66%	3498
September	1st to 10th	Night	8% 4 4 7% 28% 49%	1900
	11th to 20th	Night	5% 2 3 9% 32% 48%	2090
	21st to end	Night	7% 3 4 11% 29% 46%	2090
October	1st to 10th	Night	9% 2 3 8% 21% 58%	3490
	11th to 20th	Night	8% 2 2 7% 31% 49%	3521
	21st to end	Night	14% 3 3 5% 27% 48%	4303
November	1st to 10th	Night	18% 2 4 11% 30% 34%	2535
	11th to 20th	Night	18% 3 4 12% 26% 38%	2600
	21st to end	Night	25% 5% 5% 14% 20% 30%	2600
December	1st to 10th	Night	19% 3 3 11% 28% 35%	4240
	11th to 20th	Night	27% 6% 6% 17% 28% 17%	4811
	21st to end	Night	26% 7% 8% 23% 22% 14%	6468

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	15% 15% 31% 29% 8% 1	288
	11th to 20th	Day	15% 14% 28% 33% 10% 1	331
	21st to end	Day	14% 24% 29% 24% 7% 2	506
February	1st to 10th	Day	15% 22% 31% 21% 9% 2	460
	11th to 20th	Day	14% 21% 36% 23% 5% 1	455
	21st to end	Day	15% 27% 32% 21% 4	382
March	1st to 10th	Day	17% 26% 34% 15% 7% 1	460
	11th to 20th	Day	14% 22% 34% 23% 6% 2	460
	21st to end	Day	15% 27% 36% 16% 6%	506
April	1st to 10th	Day	11% 19% 36% 22% 10% 2	460
	11th to 20th	Day	7% 29% 36% 17% 8% 2	452
	21st to end	Day	7% 24% 33% 23% 10% 4	460
May	1st to 10th	Day	8% 20% 38% 23% 7% 4	463
	11th to 20th	Day	5% 15% 41% 25% 9% 5%	488
	21st to end	Day	7% 13% 39% 27% 8% 5%	529
June	1st to 10th	Day	2 12% 36% 29% 14% 6%	490
	11th to 20th	Day	1 11% 40% 30% 11% 7%	490
	21st to end	Day	3 8% 36% 32% 13% 8%	490
July	1st to 10th	Day	2 3 37% 36% 13% 8%	486
	11th to 20th	Day	1 1 31% 38% 17% 11%	484
	21st to end	Day	1 2 30% 38% 16% 12%	531
August	1st to 10th	Day	2 5% 39% 32% 14% 9%	487
	11th to 20th	Day	1 4 31% 36% 17% 11%	477
	21st to end	Day	2 3 32% 37% 17% 8%	539
September	1st to 10th	Day	2 5% 35% 36% 17% 5%	490
	11th to 20th	Day	3 9% 40% 31% 14% 2	490
	21st to end	Day	2 14% 32% 34% 15% 3	490
October	1st to 10th	Day	3 13% 37% 36% 11% 1	490
	11th to 20th	Day	4 11% 37% 34% 12% 2	490
	21st to end	Day	4 14% 32% 32% 16% 2	425
November	1st to 10th	Day	7% 15% 28% 35% 13% 2	300
	11th to 20th	Day	6% 18% 33% 26% 12% 4	300
	21st to end	Day	10% 17% 32% 25% 12% 3	300
December	1st to 10th	Day	10% 18% 31% 28% 12% 1	300
	11th to 20th	Day	8% 19% 27% 30% 14% 2	300
	21st to end	Day	14% 23% 31% 20% 9% 2	330
January	1st to 10th	Night	9% 12% 21% 33% 18% 7%	784
	11th to 20th	Night	9% 8% 26% 34% 18% 5%	760
	21st to end	Night	11% 12% 25% 31% 17% 4	836
February	1st to 10th	Night	10% 12% 23% 31% 18% 6%	760
	11th to 20th	Night	8% 11% 26% 32% 17% 5%	744
	21st to end	Night	11% 14% 26% 29% 16% 4	628
March	1st to 10th	Night	11% 13% 26% 31% 16% 3	760
	11th to 20th	Night	9% 9% 24% 31% 21% 7%	760
	21st to end	Night	7% 11% 28% 32% 19% 3	836
April	1st to 10th	Night	6% 9% 22% 38% 19% 4	760
	11th to 20th	Night	4 11% 27% 33% 21% 4	751
	21st to end	Night	3 8% 24% 35% 23% 7%	760
May	1st to 10th	Night	4 7% 26% 38% 22% 3	613
	11th to 20th	Night	4 4 22% 36% 28% 7%	561
	21st to end	Night	2 7% 23% 37% 24% 6%	617
June	1st to 10th	Night	1 4 18% 40% 33% 5%	570
	11th to 20th	Night	1 2 20% 42% 32% 4	544
	21st to end	Night	1 1 11% 36% 43% 9%	380
July	1st to 10th	Night	1 5% 31% 50% 13%	375
	11th to 20th	Night	2 10% 38% 42% 8%	552
	21st to end	Night	1 8% 36% 44% 10%	685
August	1st to 10th	Night	1 1 8% 34% 42% 14%	756
	11th to 20th	Night	2 1 5% 30% 45% 16%	752
	21st to end	Night	2 1 7% 30% 43% 17%	836
September	1st to 10th	Night	2 2 8% 30% 43% 16%	760
	11th to 20th	Night	1 1 14% 36% 35% 13%	760
	21st to end	Night	1 2 16% 36% 34% 11%	760
October	1st to 10th	Night	3 4 16% 45% 26% 6%	760
	11th to 20th	Night	3 3 18% 36% 30% 9%	760
	21st to end	Night	3 9% 20% 33% 23% 12%	836
November	1st to 10th	Night	5% 7% 17% 36% 27% 8%	780
	11th to 20th	Night	4 6% 25% 33% 25% 8%	800
	21st to end	Night	6% 9% 24% 33% 22% 6%	800
December	1st to 10th	Night	8% 10% 25% 31% 21% 5%	800
	11th to 20th	Night	10% 9% 25% 33% 19% 4	800
	21st to end	Night	10% 14% 26% 29% 16% 4	880

Page generated at 2025-01-04 00:24:03. Version ac07

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