Saddleback Butte
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Saddleback Butte clear sky chart from 2005-11-06 to 2025-11-18.

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	1 1 1 2 2 2 2 2 4 5% 78%	135478
	Night	1 1 1 2 2 2 2 2 4 5% 77%	132408
Transparency	Day	10% 2 5% 14% 29% 41%	130561
	Night	10% 3 5% 17% 30% 35%	128297
Seeing	Day	3 8% 22% 30% 25% 12%	16935
	Night	2 3 22% 42% 27% 4	26748

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	1 3 1 3 2 2 2 2 4 5% 74%	3639
	11th to 20th	Day	3 3 1 2 2 2 3 2 4 6% 72%	3941
	21st to end	Day	4 5% 2 5% 3 3 3 3 5% 8% 59%	5016
February	1st to 10th	Day	3 3 1 4 3 3 2 3 4 5% 67%	2000
	11th to 20th	Day	3 1 1 3 2 2 3 2 5% 8% 69%	1950
	21st to end	Day	2 3 1 3 4 2 3 3 5% 6% 67%	1650
March	1st to 10th	Day	4 3 2 3 3 2 3 3 5% 8% 64%	4518
	11th to 20th	Day	2 3 1 4 2 3 4 4 5% 7% 65%	4678
	21st to end	Day	1 1 1 2 2 2 3 3 6% 9% 68%	5960
April	1st to 10th	Day	3 2 1 2 2 2 3 4 4 6% 71%	2400
	11th to 20th	Day	1 2 1 2 2 2 2 3 3 5% 79%	2369
	21st to end	Day	1 1 1 1 1 2 2 4 7% 80%	2400
May	1st to 10th	Day	1 1 1 1 1 1 2 1 3 5% 83%	5699
	11th to 20th	Day	1 1 1 1 1 2 2 3 5% 82%	5841
	21st to end	Day	1 1 1 1 1 1 2 3 88%	6423
June	1st to 10th	Day	1 1 1 1 2 2 4 6% 82%	2616
	11th to 20th	Day	1 1 2 3 91%	2800
	21st to end	Day	1 1 2 1 1 1 1 2 3 88%	2800
July	1st to 10th	Day	1 1 1 1 1 1 2 93%	6319
	11th to 20th	Day	1 1 1 2 1 1 2 1 3 4 84%	6237
	21st to end	Day	1 1 1 1 1 1 1 2 4 87%	6147
August	1st to 10th	Day	1 1 1 1 1 1 1 2 4 86%	5346
	11th to 20th	Day	1 1 1 1 1 2 94%	5364
	21st to end	Day	1 1 1 2 2 2 2 2 3 4 83%	5984
September	1st to 10th	Day	1 1 1 2 1 2 3 2 3 5% 79%	2400
	11th to 20th	Day	1 1 1 1 2 1 2 3 89%	2236
	21st to end	Day	1 1 1 2 2 2 2 4 86%	2200
October	1st to 10th	Day	1 1 1 1 1 1 1 3 4 85%	3600
	11th to 20th	Day	1 1 1 2 2 3 5% 86%	3401
	21st to end	Day	1 1 1 2 2 2 2 2 4 6% 78%	3411
November	1st to 10th	Day	1 1 2 2 2 2 1 3 6% 80%	1854
	11th to 20th	Day	2 2 1 3 2 2 3 3 4 5% 73%	1863
	21st to end	Day	3 1 1 2 3 3 3 3 5% 7% 69%	1800
December	1st to 10th	Day	2 2 1 2 2 3 4 3 6% 7% 66%	2950
	11th to 20th	Day	2 3 1 4 3 3 4 6% 7% 8% 59%	3409
	21st to end	Day	4 4 1 6% 4 5% 5% 4 6% 9% 53%	4257
January	1st to 10th	Night	2 3 1 4 2 2 3 2 4 6% 72%	6306
	11th to 20th	Night	2 2 1 3 2 2 2 2 4 6% 73%	5995
	21st to end	Night	3 4 2 3 3 3 4 4 5% 7% 62%	5984
February	1st to 10th	Night	3 4 1 4 3 3 4 3 4 5% 66%	2400
	11th to 20th	Night	3 2 1 3 2 3 3 3 6% 7% 68%	2338
	21st to end	Night	3 2 1 3 3 3 4 3 5% 6% 67%	1980
March	1st to 10th	Night	3 3 1 3 2 3 3 3 5% 7% 65%	5376
	11th to 20th	Night	3 3 1 4 3 4 4 3 5% 7% 62%	5320
	21st to end	Night	1 1 1 2 2 3 3 4 5% 7% 70%	5011
April	1st to 10th	Night	2 2 1 2 2 2 3 3 5% 6% 72%	2000
	11th to 20th	Night	1 2 2 2 2 2 3 4 5% 77%	1979
	21st to end	Night	1 1 1 1 2 2 2 4 5% 81%	2000
May	1st to 10th	Night	1 1 1 1 2 2 2 4 4 82%	4288
	11th to 20th	Night	1 1 1 1 2 3 4 87%	4074
	21st to end	Night	1 1 1 1 2 3 91%	4474
June	1st to 10th	Night	1 1 1 1 2 2 3 6% 84%	1777
	11th to 20th	Night	1 1 1 2 3 93%	1600
	21st to end	Night	1 1 1 2 1 3 91%	1600
July	1st to 10th	Night	1 1 1 1 95%	3640
	11th to 20th	Night	1 1 1 1 1 1 1 2 3 88%	3722
	21st to end	Night	1 1 1 1 1 1 1 3 91%	4735
August	1st to 10th	Night	1 1 1 1 2 1 2 4 87%	4486
	11th to 20th	Night	1 1 1 2 95%	4506
	21st to end	Night	1 1 1 2 1 1 3 3 85%	5015
September	1st to 10th	Night	1 1 1 1 1 1 1 3 3 87%	2000
	11th to 20th	Night	1 1 1 1 1 1 2 2 91%	2162
	21st to end	Night	1 1 1 1 1 2 3 89%	2200
October	1st to 10th	Night	1 1 1 1 1 2 1 2 2 89%	3600
	11th to 20th	Night	1 1 1 1 1 1 3 4 88%	3753
	21st to end	Night	1 1 2 2 2 2 2 3 4 83%	4392
November	1st to 10th	Night	1 1 2 1 2 2 3 4 6% 79%	2665
	11th to 20th	Night	1 2 1 2 2 3 2 2 4 6% 75%	2691
	21st to end	Night	2 2 1 3 3 2 3 4 4 6% 69%	2600
December	1st to 10th	Night	2 2 1 2 2 2 3 3 4 7% 71%	4240
	11th to 20th	Night	2 2 1 3 3 3 4 4 7% 9% 62%	4811
	21st to end	Night	2 2 1 5% 4 4 5% 4 7% 12% 53%	6688

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	13% 3 5% 29% 36% 14%	3639
	11th to 20th	Day	14% 3 12% 16% 23% 32%	3941
	21st to end	Day	23% 4 6% 21% 24% 22%	5016
February	1st to 10th	Day	19% 3 6% 21% 28% 23%	2000
	11th to 20th	Day	15% 3 6% 21% 35% 21%	1960
	21st to end	Day	16% 4 7% 21% 32% 20%	1650
March	1st to 10th	Day	16% 4 6% 22% 32% 20%	4518
	11th to 20th	Day	17% 4 9% 27% 32% 11%	4678
	21st to end	Day	12% 4 9% 31% 34% 10%	5960
April	1st to 10th	Day	14% 3 7% 22% 32% 22%	2400
	11th to 20th	Day	10% 2 5% 20% 38% 26%	2372
	21st to end	Day	7% 3 6% 21% 40% 23%	2400
May	1st to 10th	Day	7% 2 5% 18% 36% 32%	5699
	11th to 20th	Day	7% 2 3 12% 40% 36%	5844
	21st to end	Day	5% 1 2 9% 42% 41%	6424
June	1st to 10th	Day	6% 1 4 14% 30% 44%	2616
	11th to 20th	Day	2 1 2 10% 22% 63%	2800
	21st to end	Day	6% 1 2 3 17% 72%	2800
July	1st to 10th	Day	2 1 1 2 10% 84%	6251
	11th to 20th	Day	7% 2 2 5% 13% 71%	6162
	21st to end	Day	5% 1 2 6% 25% 61%	5970
August	1st to 10th	Day	6% 1 1 6% 29% 57%	3890
	11th to 20th	Day	3 1 1 4 18% 73%	3880
	21st to end	Day	5% 1 1 3 16% 73%	4311
September	1st to 10th	Day	9% 3 3 5% 19% 60%	2400
	11th to 20th	Day	4 2 2 5% 31% 57%	2236
	21st to end	Day	5% 2 2 7% 33% 50%	2200
October	1st to 10th	Day	6% 2 2 8% 20% 63%	3600
	11th to 20th	Day	4 1 2 9% 36% 47%	3401
	21st to end	Day	10% 2 3 9% 35% 42%	3411
November	1st to 10th	Day	8% 2 4 15% 39% 31%	1854
	11th to 20th	Day	14% 2 5% 17% 33% 29%	1863
	21st to end	Day	15% 5% 7% 17% 29% 27%	1800
December	1st to 10th	Day	17% 3 6% 16% 30% 29%	2950
	11th to 20th	Day	18% 6% 9% 23% 36% 9%	3408
	21st to end	Day	26% 4 11% 25% 27% 8%	4257
January	1st to 10th	Night	14% 3 5% 25% 35% 18%	6306
	11th to 20th	Night	13% 4 6% 20% 26% 31%	5995
	21st to end	Night	20% 4 8% 19% 26% 22%	5984
February	1st to 10th	Night	20% 4 7% 17% 27% 25%	2400
	11th to 20th	Night	16% 4 7% 20% 30% 23%	2339
	21st to end	Night	15% 5% 8% 22% 29% 22%	1980
March	1st to 10th	Night	15% 4 8% 26% 30% 18%	5376
	11th to 20th	Night	19% 6% 10% 32% 23% 10%	5320
	21st to end	Night	12% 5% 10% 34% 30% 9%	5011
April	1st to 10th	Night	13% 4 9% 27% 28% 19%	2000
	11th to 20th	Night	11% 2 5% 26% 33% 22%	1979
	21st to end	Night	7% 2 8% 24% 43% 17%	2000
May	1st to 10th	Night	6% 3 7% 21% 39% 24%	4285
	11th to 20th	Night	3 2 2 16% 49% 28%	4075
	21st to end	Night	3 1 2 14% 46% 33%	4474
June	1st to 10th	Night	5% 1 5% 19% 34% 36%	1777
	11th to 20th	Night	2 1 3 11% 28% 55%	1600
	21st to end	Night	4 1 2 4 22% 68%	1600
July	1st to 10th	Night	2 1 1 2 13% 82%	3600
	11th to 20th	Night	5% 1 1 6% 16% 70%	3674
	21st to end	Night	4 1 2 7% 31% 57%	4600
August	1st to 10th	Night	5% 2 2 6% 33% 53%	3256
	11th to 20th	Night	2 1 1 4 25% 68%	3256
	21st to end	Night	4 1 1 4 21% 70%	3608
September	1st to 10th	Night	5% 2 3 5% 26% 59%	2000
	11th to 20th	Night	3 2 2 6% 35% 52%	2162
	21st to end	Night	4 1 2 8% 35% 50%	2200
October	1st to 10th	Night	5% 1 2 8% 17% 67%	3600
	11th to 20th	Night	4 1 2 8% 40% 43%	3753
	21st to end	Night	8% 2 2 8% 34% 45%	4392
November	1st to 10th	Night	7% 2 4 17% 34% 35%	2665
	11th to 20th	Night	12% 2 5% 15% 33% 34%	2691
	21st to end	Night	16% 3 7% 19% 26% 29%	2600
December	1st to 10th	Night	14% 3 5% 12% 33% 34%	4240
	11th to 20th	Night	16% 5% 12% 23% 32% 13%	4811
	21st to end	Night	21% 6% 11% 30% 26% 7%	6688

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	5% 7% 26% 31% 27% 6%	200
	11th to 20th	Day	7% 12% 22% 25% 25% 9%	314
	21st to end	Day	7% 12% 23% 27% 24% 7%	550
February	1st to 10th	Day	4 14% 26% 29% 18% 9%	500
	11th to 20th	Day	7% 13% 27% 28% 17% 7%	495
	21st to end	Day	5% 13% 29% 32% 17% 5%	414
March	1st to 10th	Day	7% 18% 27% 28% 16% 5%	500
	11th to 20th	Day	5% 15% 27% 28% 20% 4	500
	21st to end	Day	3 20% 32% 26% 15% 4	550
April	1st to 10th	Day	7% 11% 29% 26% 20% 8%	500
	11th to 20th	Day	2 17% 31% 26% 16% 7%	492
	21st to end	Day	3 14% 29% 24% 17% 13%	500
May	1st to 10th	Day	4 11% 28% 29% 20% 8%	503
	11th to 20th	Day	3 12% 28% 29% 17% 12%	528
	21st to end	Day	3 10% 27% 28% 23% 10%	573
June	1st to 10th	Day	1 5% 24% 33% 24% 13%	530
	11th to 20th	Day	6% 24% 31% 24% 15%	530
	21st to end	Day	1 3 23% 33% 25% 14%	530
July	1st to 10th	Day	2 14% 38% 29% 17%	526
	11th to 20th	Day	1 10% 36% 31% 22%	524
	21st to end	Day	2 1 11% 35% 29% 23%	575
August	1st to 10th	Day	2 1 16% 40% 24% 18%	527
	11th to 20th	Day	1 1 11% 34% 31% 22%	517
	21st to end	Day	1 1 12% 33% 33% 19%	583
September	1st to 10th	Day	2 1 16% 27% 35% 19%	530
	11th to 20th	Day	1 4 18% 34% 31% 13%	530
	21st to end	Day	5% 16% 33% 31% 15%	530
October	1st to 10th	Day	2 5% 20% 27% 32% 13%	530
	11th to 20th	Day	1 5% 18% 29% 32% 14%	530
	21st to end	Day	2 4 20% 28% 33% 13%	498
November	1st to 10th	Day	1 6% 22% 24% 33% 13%	330
	11th to 20th	Day	4 5% 17% 33% 32% 10%	321
	21st to end	Day	3 8% 22% 28% 31% 8%	300
December	1st to 10th	Day	3 4 19% 36% 30% 9%	300
	11th to 20th	Day	3 6% 19% 31% 30% 10%	300
	21st to end	Day	8% 9% 23% 31% 25% 4	275
January	1st to 10th	Night	4 5% 24% 39% 23% 5%	800
	11th to 20th	Night	3 3 24% 44% 24% 3	800
	21st to end	Night	5% 3 25% 44% 21% 2	880
February	1st to 10th	Night	4 6% 24% 41% 22% 3	800
	11th to 20th	Night	3 4 29% 38% 21% 4	784
	21st to end	Night	3 5% 32% 42% 16% 2	660
March	1st to 10th	Night	3 8% 33% 37% 17% 2	800
	11th to 20th	Night	4 8% 27% 37% 21% 4	800
	21st to end	Night	2 8% 34% 38% 17% 1	880
April	1st to 10th	Night	3 6% 34% 35% 20% 2	800
	11th to 20th	Night	2 7% 35% 37% 17% 2	791
	21st to end	Night	1 7% 33% 36% 20% 4	800
May	1st to 10th	Night	1 5% 37% 41% 15% 1	684
	11th to 20th	Night	1 7% 30% 42% 19% 1	591
	21st to end	Night	7% 35% 40% 18%	650
June	1st to 10th	Night	3 28% 53% 15% 1	577
	11th to 20th	Night	23% 53% 23% 1	400
	21st to end	Night	1 1 16% 56% 27%	400
July	1st to 10th	Night	6% 51% 42% 1	390
	11th to 20th	Night	1 1 4 50% 43% 1	418
	21st to end	Night	1 7% 50% 39% 3	767
August	1st to 10th	Night	1 9% 50% 35% 4	796
	11th to 20th	Night	1 6% 45% 42% 6%	792
	21st to end	Night	1 7% 39% 44% 9%	880
September	1st to 10th	Night	1 9% 38% 46% 7%	800
	11th to 20th	Night	2 14% 42% 37% 6%	800
	21st to end	Night	1 15% 39% 38% 7%	800
October	1st to 10th	Night	2 2 18% 45% 30% 4	800
	11th to 20th	Night	1 2 18% 40% 34% 7%	800
	21st to end	Night	2 3 19% 36% 31% 9%	880
November	1st to 10th	Night	1 2 18% 39% 34% 6%	820
	11th to 20th	Night	2 2 16% 44% 29% 7%	828
	21st to end	Night	3 3 19% 41% 30% 3	800
December	1st to 10th	Night	4 3 23% 39% 27% 4	800
	11th to 20th	Night	5% 3 21% 44% 24% 3	800
	21st to end	Night	4 5% 29% 38% 20% 4	880

Page generated at 2025-11-14 21:56:01. Version ac07

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