Saddleback Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Saddleback Observatory clear sky chart from 2005-11-06 to 2024-01-13.

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% 7% 2 3 3 2 3 3 4 5% 59%	74755
	Night	10% 8% 2 3 3 2 3 3 4 6% 56%	74991
Transparency	Day	29% 3 7% 20% 24% 17%	74465
	Night	31% 4 7% 19% 23% 16%	74802
Seeing	Day	16% 18% 31% 21% 11% 3	13933
	Night	16% 10% 17% 30% 23% 4	23323

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	16% 15% 2 5% 4 3 3 4 5% 7% 36%	1519
	11th to 20th	Day	13% 11% 2 4 3 3 4 4 4 7% 46%	1538
	21st to end	Day	12% 15% 3 4 3 2 3 4 4 7% 42%	1782
February	1st to 10th	Day	16% 12% 3 3 2 2 3 4 4 7% 45%	1620
	11th to 20th	Day	12% 14% 4 3 4 2 3 3 4 5% 46%	1687
	21st to end	Day	12% 18% 4 4 3 2 3 3 3 5% 43%	1480
March	1st to 10th	Day	14% 18% 6% 6% 4 3 3 3 3 7% 33%	1828
	11th to 20th	Day	16% 15% 3 4 4 2 3 4 5% 7% 37%	1980
	21st to end	Day	15% 18% 3 3 4 2 3 4 4 7% 38%	2276
April	1st to 10th	Day	13% 15% 3 3 4 2 4 4 5% 7% 39%	2160
	11th to 20th	Day	11% 13% 2 4 4 2 3 4 4 6% 47%	2129
	21st to end	Day	11% 8% 1 3 3 2 4 4 5% 7% 52%	2160
May	1st to 10th	Day	9% 8% 2 3 4 2 3 4 4 6% 57%	2264
	11th to 20th	Day	8% 7% 2 4 4 2 3 4 5% 7% 55%	2477
	21st to end	Day	12% 7% 1 5% 4 2 4 5% 4 6% 50%	2723
June	1st to 10th	Day	8% 4 2 4 4 2 3 4 5% 7% 57%	2520
	11th to 20th	Day	4 3 1 2 2 1 2 3 3 5% 74%	2520
	21st to end	Day	3 1 1 2 2 1 1 2 3 4 81%	2520
July	1st to 10th	Day	1 1 1 1 1 1 2 2 2 3 85%	2520
	11th to 20th	Day	2 1 1 1 1 1 1 1 2 3 86%	2520
	21st to end	Day	2 1 1 2 2 1 2 2 3 3 81%	2626
August	1st to 10th	Day	3 2 1 2 1 1 2 2 3 3 80%	2328
	11th to 20th	Day	1 1 1 1 1 2 2 2 4 85%	2163
	21st to end	Day	1 1 1 1 1 1 2 2 2 88%	2376
September	1st to 10th	Day	2 1 1 1 1 1 2 2 3 86%	2160
	11th to 20th	Day	4 2 1 2 2 1 2 3 3 5% 73%	2160
	21st to end	Day	5% 4 1 1 1 1 2 3 4 5% 74%	1950
October	1st to 10th	Day	8% 3 1 3 2 1 2 3 3 5% 69%	1800
	11th to 20th	Day	8% 4 1 2 3 2 3 3 3 6% 65%	1800
	21st to end	Day	9% 5% 1 3 3 2 2 2 4 6% 63%	1980
November	1st to 10th	Day	13% 9% 2 3 3 2 3 5% 4 6% 51%	1674
	11th to 20th	Day	13% 6% 2 4 4 3 4 4 5% 7% 50%	1710
	21st to end	Day	10% 9% 3 3 3 2 5% 4 5% 6% 51%	1563
December	1st to 10th	Day	17% 9% 2 4 3 2 3 5% 5% 7% 45%	1520
	11th to 20th	Day	22% 14% 4 5% 4 3 4 3 3 5% 31%	1928
	21st to end	Day	12% 10% 3 4 4 3 4 6% 6% 9% 39%	2794
January	1st to 10th	Night	14% 14% 3 5% 3 2 4 5% 4 6% 40%	2646
	11th to 20th	Night	12% 11% 4 5% 3 2 4 4 5% 7% 43%	2462
	21st to end	Night	13% 15% 3 4 3 3 4 4 4 6% 43%	2574
February	1st to 10th	Night	15% 8% 2 3 4 2 3 4 5% 7% 49%	2340
	11th to 20th	Night	10% 13% 2 3 3 3 4 5% 5% 7% 45%	2160
	21st to end	Night	15% 13% 3 5% 3 2 3 4 4 5% 43%	1776
March	1st to 10th	Night	15% 19% 4 5% 4 2 3 4 5% 5% 35%	2129
	11th to 20th	Night	13% 14% 3 3 3 3 4 4 6% 8% 40%	1980
	21st to end	Night	14% 18% 3 3 3 2 4 4 3 6% 41%	2080
April	1st to 10th	Night	13% 13% 2 6% 4 2 4 4 4 6% 43%	1800
	11th to 20th	Night	11% 11% 2 3 3 2 3 4 4 7% 48%	1779
	21st to end	Night	9% 8% 1 3 2 2 3 3 5% 7% 57%	1800
May	1st to 10th	Night	10% 6% 2 3 3 2 3 2 3 4 61%	1691
	11th to 20th	Night	8% 5% 3 3 3 3 4 5% 5% 6% 55%	1416
	21st to end	Night	11% 6% 2 4 4 2 3 4 3 7% 55%	1552
June	1st to 10th	Night	7% 5% 2 3 4 2 3 3 3 7% 62%	1440
	11th to 20th	Night	3 3 1 2 2 1 2 3 4 6% 73%	1440
	21st to end	Night	3 2 2 2 2 1 2 2 3 4 77%	1440
July	1st to 10th	Night	1 2 1 1 1 1 1 1 2 3 84%	1440
	11th to 20th	Night	1 1 1 2 1 1 1 1 2 3 87%	1440
	21st to end	Night	2 2 1 2 2 2 2 2 3 3 79%	1689
August	1st to 10th	Night	4 2 2 2 2 2 2 3 4 76%	1611
	11th to 20th	Night	1 1 1 2 1 3 3 4 4 80%	1736
	21st to end	Night	1 1 1 2 1 1 2 2 2 3 85%	1980
September	1st to 10th	Night	2 1 2 1 1 1 2 2 4 84%	1800
	11th to 20th	Night	4 1 1 2 2 1 2 2 3 4 77%	1800
	21st to end	Night	4 2 1 2 2 1 2 3 3 5% 75%	2006
October	1st to 10th	Night	7% 3 2 3 2 1 2 2 2 4 72%	2160
	11th to 20th	Night	7% 3 1 2 3 1 2 3 4 5% 68%	2160
	21st to end	Night	9% 4 1 1 2 1 2 3 5% 6% 66%	2376
November	1st to 10th	Night	13% 9% 2 4 2 2 3 4 5% 6% 51%	2405
	11th to 20th	Night	11% 5% 2 3 3 2 4 4 6% 8% 52%	2470
	21st to end	Night	10% 7% 3 4 3 2 4 3 4 7% 53%	2615
December	1st to 10th	Night	17% 9% 2 3 3 1 3 3 4 7% 48%	2660
	11th to 20th	Night	23% 15% 3 4 3 2 3 4 5% 7% 31%	3276
	21st to end	Night	14% 14% 4 5% 5% 3 4 5% 5% 6% 36%	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	49% 6% 8% 21% 13% 3	1519
	11th to 20th	Day	40% 3 8% 20% 17% 11%	1538
	21st to end	Day	44% 4 7% 16% 23% 6%	1782
February	1st to 10th	Day	40% 3 10% 20% 17% 9%	1620
	11th to 20th	Day	41% 4 8% 20% 21% 6%	1696
	21st to end	Day	45% 3 8% 23% 15% 6%	1480
March	1st to 10th	Day	54% 4 7% 18% 13% 5%	1828
	11th to 20th	Day	48% 3 10% 18% 17% 5%	1980
	21st to end	Day	49% 4 12% 20% 12% 3	2276
April	1st to 10th	Day	45% 4 12% 20% 16% 3	2160
	11th to 20th	Day	39% 4 11% 23% 17% 5%	2132
	21st to end	Day	32% 4 14% 28% 19% 3	2160
May	1st to 10th	Day	30% 3 10% 26% 26% 5%	2264
	11th to 20th	Day	30% 4 10% 30% 21% 6%	2480
	21st to end	Day	36% 5% 11% 27% 18% 3	2724
June	1st to 10th	Day	28% 4 10% 24% 27% 9%	2520
	11th to 20th	Day	15% 3 7% 23% 34% 17%	2520
	21st to end	Day	11% 1 3 17% 39% 29%	2520
July	1st to 10th	Day	7% 2 2 12% 28% 50%	2451
	11th to 20th	Day	8% 1 2 14% 29% 46%	2445
	21st to end	Day	11% 2 2 11% 26% 48%	2480
August	1st to 10th	Day	12% 2 2 15% 29% 40%	2312
	11th to 20th	Day	7% 2 1 13% 35% 41%	2163
	21st to end	Day	6% 1 1 13% 37% 41%	2376
September	1st to 10th	Day	8% 2 1 11% 33% 46%	2160
	11th to 20th	Day	15% 2 4 22% 35% 21%	2160
	21st to end	Day	15% 3 4 22% 33% 22%	1950
October	1st to 10th	Day	21% 3 5% 21% 32% 18%	1800
	11th to 20th	Day	22% 3 6% 21% 28% 20%	1800
	21st to end	Day	25% 2 8% 21% 27% 18%	1980
November	1st to 10th	Day	36% 4 7% 21% 20% 12%	1674
	11th to 20th	Day	36% 4 9% 20% 23% 8%	1710
	21st to end	Day	36% 3 7% 22% 22% 11%	1563
December	1st to 10th	Day	40% 4 8% 21% 20% 7%	1520
	11th to 20th	Day	58% 3 6% 14% 14% 4	1928
	21st to end	Day	41% 6% 12% 21% 16% 4	2794
January	1st to 10th	Night	45% 4 10% 21% 14% 4	2646
	11th to 20th	Night	41% 4 9% 17% 19% 10%	2462
	21st to end	Night	44% 4 6% 16% 22% 8%	2574
February	1st to 10th	Night	37% 4 7% 20% 22% 9%	2340
	11th to 20th	Night	40% 4 8% 21% 20% 7%	2162
	21st to end	Night	44% 4 8% 22% 16% 6%	1776
March	1st to 10th	Night	53% 3 8% 19% 12% 5%	2129
	11th to 20th	Night	43% 5% 9% 19% 18% 6%	1980
	21st to end	Night	46% 7% 11% 19% 14% 3	2080
April	1st to 10th	Night	43% 6% 11% 21% 16% 3	1800
	11th to 20th	Night	36% 5% 12% 23% 18% 6%	1779
	21st to end	Night	29% 4 15% 32% 17% 3	1800
May	1st to 10th	Night	30% 3 10% 25% 27% 5%	1691
	11th to 20th	Night	30% 5% 11% 27% 20% 6%	1416
	21st to end	Night	32% 4 14% 29% 18% 3	1552
June	1st to 10th	Night	24% 6% 12% 24% 24% 9%	1440
	11th to 20th	Night	14% 3 8% 25% 33% 16%	1440
	21st to end	Night	15% 2 3 17% 33% 30%	1440
July	1st to 10th	Night	9% 1 2 10% 28% 49%	1400
	11th to 20th	Night	6% 2 2 14% 24% 52%	1392
	21st to end	Night	12% 2 2 9% 24% 52%	1595
August	1st to 10th	Night	15% 2 3 12% 27% 41%	1602
	11th to 20th	Night	9% 2 2 12% 32% 43%	1736
	21st to end	Night	8% 1 3 12% 30% 46%	1980
September	1st to 10th	Night	9% 2 1 9% 31% 49%	1800
	11th to 20th	Night	13% 2 5% 20% 38% 23%	1800
	21st to end	Night	14% 3 4 22% 34% 23%	2006
October	1st to 10th	Night	21% 2 6% 19% 32% 21%	2160
	11th to 20th	Night	19% 3 5% 21% 30% 22%	2160
	21st to end	Night	20% 3 8% 23% 27% 18%	2376
November	1st to 10th	Night	35% 5% 7% 19% 21% 13%	2405
	11th to 20th	Night	31% 5% 10% 22% 22% 10%	2470
	21st to end	Night	33% 3 7% 22% 23% 11%	2615
December	1st to 10th	Night	38% 4 8% 17% 22% 10%	2660
	11th to 20th	Night	55% 3 4 13% 20% 5%	3276
	21st to end	Night	49% 5% 10% 17% 15% 4	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	46% 14% 24% 13% 3 1	180
	11th to 20th	Day	30% 17% 25% 22% 5%	246
	21st to end	Day	27% 17% 24% 20% 11% 1	374
February	1st to 10th	Day	30% 17% 27% 18% 7% 1	340
	11th to 20th	Day	28% 25% 28% 14% 5%	387
	21st to end	Day	28% 24% 28% 16% 5%	346
March	1st to 10th	Day	39% 26% 20% 10% 5%	420
	11th to 20th	Day	31% 22% 24% 15% 8% 1	420
	21st to end	Day	31% 29% 23% 12% 4	462
April	1st to 10th	Day	27% 26% 28% 11% 7% 1	420
	11th to 20th	Day	30% 23% 25% 17% 4 1	412
	21st to end	Day	18% 25% 29% 17% 10% 2	420
May	1st to 10th	Day	18% 26% 31% 18% 5% 2	423
	11th to 20th	Day	20% 20% 31% 18% 7% 4	448
	21st to end	Day	16% 19% 28% 24% 9% 4	485
June	1st to 10th	Day	12% 18% 33% 22% 10% 4	450
	11th to 20th	Day	10% 20% 40% 19% 8% 3	450
	21st to end	Day	5% 14% 37% 28% 12% 5%	450
July	1st to 10th	Day	2 11% 47% 24% 12% 5%	446
	11th to 20th	Day	2 9% 45% 26% 14% 4	444
	21st to end	Day	2 6% 43% 27% 16% 6%	487
August	1st to 10th	Day	4 10% 39% 26% 15% 6%	447
	11th to 20th	Day	2 10% 37% 29% 16% 6%	437
	21st to end	Day	2 11% 41% 28% 16% 2	495
September	1st to 10th	Day	3 10% 40% 26% 17% 2	450
	11th to 20th	Day	8% 16% 33% 28% 13% 2	450
	21st to end	Day	8% 17% 39% 24% 10% 2	450
October	1st to 10th	Day	7% 23% 29% 26% 14% 2	450
	11th to 20th	Day	11% 15% 28% 29% 14% 2	450
	21st to end	Day	17% 17% 26% 24% 13% 2	495
November	1st to 10th	Day	22% 17% 19% 24% 16% 3	270
	11th to 20th	Day	17% 13% 27% 23% 18% 1	270
	21st to end	Day	16% 19% 28% 22% 11% 3	201
December	1st to 10th	Day	28% 17% 24% 14% 12% 4	180
	11th to 20th	Day	28% 24% 15% 19% 12% 2	180
	21st to end	Day	27% 21% 21% 18% 12% 1	198
January	1st to 10th	Night	27% 11% 23% 24% 11% 4	760
	11th to 20th	Night	22% 14% 28% 27% 9% 1	728
	21st to end	Night	26% 15% 20% 24% 15% 1	792
February	1st to 10th	Night	24% 14% 21% 29% 11% 1	720
	11th to 20th	Night	24% 13% 20% 27% 15% 2	704
	21st to end	Night	27% 12% 21% 31% 8% 2	592
March	1st to 10th	Night	31% 14% 19% 22% 13% 2	720
	11th to 20th	Night	25% 13% 16% 24% 19% 2	720
	21st to end	Night	29% 14% 18% 24% 13% 1	792
April	1st to 10th	Night	22% 12% 20% 29% 16% 1	720
	11th to 20th	Night	20% 12% 20% 29% 15% 4	711
	21st to end	Night	15% 9% 19% 33% 20% 4	720
May	1st to 10th	Night	14% 14% 22% 26% 21% 3	611
	11th to 20th	Night	14% 6% 14% 33% 29% 4	354
	21st to end	Night	14% 6% 15% 28% 32% 5%	389
June	1st to 10th	Night	9% 6% 15% 29% 36% 5%	360
	11th to 20th	Night	5% 6% 15% 37% 33% 3	360
	21st to end	Night	4 3 12% 38% 39% 5%	360
July	1st to 10th	Night	2 1 6% 41% 49% 3	350
	11th to 20th	Night	1 1 7% 43% 44% 4	348
	21st to end	Night	2 1 5% 31% 53% 8%	507
August	1st to 10th	Night	4 1 5% 35% 47% 7%	537
	11th to 20th	Night	2 1 7% 40% 41% 9%	668
	21st to end	Night	1 1 7% 47% 40% 5%	792
September	1st to 10th	Night	2 2 11% 40% 40% 4	720
	11th to 20th	Night	4 4 13% 35% 35% 9%	720
	21st to end	Night	6% 6% 22% 29% 27% 9%	720
October	1st to 10th	Night	10% 8% 19% 31% 29% 4	720
	11th to 20th	Night	11% 8% 19% 31% 27% 5%	720
	21st to end	Night	12% 12% 20% 27% 24% 5%	792
November	1st to 10th	Night	19% 10% 16% 29% 23% 3	740
	11th to 20th	Night	15% 14% 21% 33% 15% 3	760
	21st to end	Night	17% 12% 26% 26% 17% 3	760
December	1st to 10th	Night	25% 14% 20% 29% 11% 1	760
	11th to 20th	Night	30% 12% 20% 26% 11% 1	760
	21st to end	Night	28% 17% 21% 27% 7% 1	836

Page generated at 2024-01-09 22:25:04. Version ac07

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