Singing Mountain Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Singing Mountain Observatory clear sky chart from 2005-11-06 to 2026-03-18.

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	4 6% 2 5% 4 4 4 4 6% 8% 54%	140151
	Night	4 8% 3 6% 4 4 4 3 5% 6% 53%	138873
Transparency	Day	26% 8% 10% 22% 23% 10%	135036
	Night	29% 7% 10% 24% 22% 8%	134994
Seeing	Day	7% 9% 25% 34% 21% 4	17131
	Night	8% 4 23% 43% 21% 1	27406

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	4 10% 4 11% 6% 5% 6% 4 6% 6% 39%	5057
	11th to 20th	Day	4 8% 2 8% 3 3 3 3 5% 5% 55%	5340
	21st to end	Day	3 9% 3 6% 4 4 3 3 4 6% 56%	5844
February	1st to 10th	Day	7% 11% 3 7% 5% 4 4 3 6% 5% 44%	1890
	11th to 20th	Day	6% 14% 4 9% 4 4 3 3 5% 9% 38%	1879
	21st to end	Day	6% 14% 5% 8% 4 3 4 3 4 5% 43%	1730
March	1st to 10th	Day	3 12% 3 8% 4 4 4 4 5% 7% 46%	5035
	11th to 20th	Day	3 9% 3 9% 5% 4 5% 5% 6% 8% 42%	5078
	21st to end	Day	5% 12% 4 9% 6% 5% 5% 4 6% 6% 39%	5519
April	1st to 10th	Day	7% 8% 3 6% 4 4 5% 4 5% 7% 47%	2400
	11th to 20th	Day	6% 10% 2 7% 5% 5% 5% 4 5% 7% 44%	2371
	21st to end	Day	5% 8% 3 6% 4 5% 4 4 6% 8% 48%	2400
May	1st to 10th	Day	5% 8% 3 7% 5% 4 5% 4 6% 9% 44%	5822
	11th to 20th	Day	3 4 2 5% 4 5% 6% 5% 7% 8% 51%	5978
	21st to end	Day	4 4 1 3 3 3 4 4 6% 7% 61%	6925
June	1st to 10th	Day	3 3 2 3 3 4 4 4 6% 9% 60%	2800
	11th to 20th	Day	3 3 1 3 2 4 4 3 5% 6% 66%	2800
	21st to end	Day	2 2 1 3 3 3 4 3 6% 7% 65%	2800
July	1st to 10th	Day	2 1 1 3 3 3 4 3 4 5% 70%	6339
	11th to 20th	Day	1 1 1 3 3 3 5% 5% 10% 13% 54%	5940
	21st to end	Day	2 3 1 3 3 4 5% 5% 8% 10% 57%	6401
August	1st to 10th	Day	2 2 1 3 4 4 5% 4 9% 13% 54%	5779
	11th to 20th	Day	2 2 1 4 3 4 5% 4 7% 9% 61%	5649
	21st to end	Day	3 3 1 5% 4 4 4 5% 8% 13% 49%	5984
September	1st to 10th	Day	5% 3 1 4 3 3 4 3 6% 7% 61%	2400
	11th to 20th	Day	4 3 1 3 3 4 4 4 6% 7% 61%	2392
	21st to end	Day	4 3 1 4 3 4 3 3 4 5% 66%	2106
October	1st to 10th	Day	4 2 1 2 2 2 2 2 3 4 76%	3270
	11th to 20th	Day	4 3 1 4 3 4 5% 4 7% 9% 55%	3250
	21st to end	Day	5% 5% 1 4 3 3 3 2 4 6% 65%	3548
November	1st to 10th	Day	4 4 2 4 2 3 4 3 5% 5% 63%	2005
	11th to 20th	Day	7% 6% 2 5% 2 3 3 3 4 6% 59%	1842
	21st to end	Day	5% 10% 3 6% 4 3 3 2 4 5% 57%	1680
December	1st to 10th	Day	5% 9% 2 4 2 2 2 2 3 5% 63%	2700
	11th to 20th	Day	5% 8% 3 7% 3 3 3 2 5% 8% 53%	3106
	21st to end	Day	4 10% 3 7% 4 5% 5% 4 6% 8% 44%	4092
January	1st to 10th	Night	4 11% 6% 12% 6% 5% 5% 4 4 6% 37%	7919
	11th to 20th	Night	4 12% 3 5% 2 2 3 2 3 4 59%	7650
	21st to end	Night	3 12% 4 7% 3 3 3 2 3 4 55%	8370
February	1st to 10th	Night	6% 12% 3 7% 4 3 3 3 5% 5% 46%	2730
	11th to 20th	Night	7% 13% 4 9% 5% 4 2 4 5% 6% 42%	2626
	21st to end	Night	6% 13% 5% 7% 3 3 3 3 4 5% 47%	2076
March	1st to 10th	Night	4 12% 4 8% 5% 4 4 3 4 5% 45%	5061
	11th to 20th	Night	3 11% 4 7% 5% 4 4 3 5% 6% 48%	5077
	21st to end	Night	6% 15% 4 9% 4 4 4 3 5% 5% 39%	5453
April	1st to 10th	Night	8% 12% 3 6% 5% 4 4 3 4 6% 46%	2000
	11th to 20th	Night	8% 9% 3 8% 4 5% 4 4 5% 5% 44%	1977
	21st to end	Night	10% 8% 2 6% 4 3 4 3 5% 6% 50%	2000
May	1st to 10th	Night	8% 8% 2 6% 5% 4 5% 4 6% 8% 43%	4154
	11th to 20th	Night	5% 5% 2 5% 4 5% 5% 5% 6% 7% 51%	3919
	21st to end	Night	5% 3 1 4 3 3 3 3 5% 7% 62%	3972
June	1st to 10th	Night	2 3 1 4 3 3 4 4 6% 8% 62%	1600
	11th to 20th	Night	4 3 1 3 3 3 3 3 4 6% 68%	1600
	21st to end	Night	2 2 1 3 3 4 4 4 6% 7% 65%	1600
July	1st to 10th	Night	1 2 1 4 4 4 5% 4 5% 5% 65%	3640
	11th to 20th	Night	1 2 1 4 4 4 6% 5% 10% 13% 51%	4022
	21st to end	Night	2 3 1 5% 4 4 5% 5% 7% 10% 55%	4472
August	1st to 10th	Night	2 2 1 5% 4 5% 6% 5% 8% 11% 50%	4033
	11th to 20th	Night	2 2 1 4 3 4 4 4 7% 9% 60%	4197
	21st to end	Night	3 3 2 6% 6% 6% 6% 6% 8% 9% 45%	4993
September	1st to 10th	Night	3 3 1 4 4 3 4 3 6% 7% 62%	2000
	11th to 20th	Night	5% 3 1 4 4 3 4 3 6% 7% 61%	2003
	21st to end	Night	5% 2 1 4 2 3 2 2 4 6% 67%	2292
October	1st to 10th	Night	4 3 1 2 2 2 2 2 3 5% 75%	3920
	11th to 20th	Night	4 3 1 4 3 4 5% 4 6% 8% 58%	3898
	21st to end	Night	6% 6% 2 4 3 3 3 2 3 4 65%	4252
November	1st to 10th	Night	4 6% 1 4 3 2 3 3 4 5% 64%	2492
	11th to 20th	Night	7% 6% 2 5% 2 2 3 2 4 5% 62%	2776
	21st to end	Night	7% 10% 3 5% 2 2 3 3 4 6% 56%	2940
December	1st to 10th	Night	5% 7% 2 4 2 2 2 2 5% 5% 65%	4710
	11th to 20th	Night	5% 9% 3 6% 4 4 3 4 5% 7% 52%	5321
	21st to end	Night	5% 12% 4 9% 5% 5% 4 3 4 6% 43%	7128

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	39% 13% 16% 21% 10%	5060
	11th to 20th	Day	29% 7% 15% 26% 21% 2	5340
	21st to end	Day	30% 6% 11% 28% 21% 4	5844
February	1st to 10th	Day	41% 8% 14% 20% 12% 4	1890
	11th to 20th	Day	44% 7% 9% 22% 15% 3	1888
	21st to end	Day	42% 7% 8% 22% 18% 4	1730
March	1st to 10th	Day	31% 11% 8% 21% 20% 8%	5035
	11th to 20th	Day	34% 8% 12% 32% 13% 2	5078
	21st to end	Day	39% 13% 11% 26% 11% 1	5519
April	1st to 10th	Day	35% 7% 9% 24% 20% 6%	2400
	11th to 20th	Day	38% 8% 10% 19% 21% 4	2374
	21st to end	Day	33% 9% 9% 24% 23% 3	2400
May	1st to 10th	Day	29% 14% 11% 23% 20% 4	5822
	11th to 20th	Day	24% 11% 8% 25% 26% 6%	5981
	21st to end	Day	18% 8% 8% 22% 36% 7%	6926
June	1st to 10th	Day	20% 6% 8% 22% 29% 14%	2800
	11th to 20th	Day	18% 5% 7% 11% 28% 31%	2800
	21st to end	Day	16% 7% 7% 15% 26% 30%	2800
July	1st to 10th	Day	16% 5% 5% 9% 18% 47%	6271
	11th to 20th	Day	16% 8% 12% 25% 27% 13%	5869
	21st to end	Day	18% 9% 13% 17% 25% 18%	6217
August	1st to 10th	Day	24% 10% 20% 20% 15% 11%	4208
	11th to 20th	Day	24% 9% 11% 16% 26% 14%	4084
	21st to end	Day	22% 11% 11% 20% 23% 14%	4311
September	1st to 10th	Day	22% 8% 8% 15% 29% 18%	2400
	11th to 20th	Day	21% 7% 10% 19% 28% 15%	2392
	21st to end	Day	21% 5% 7% 18% 38% 12%	2106
October	1st to 10th	Day	15% 4 5% 16% 38% 22%	3270
	11th to 20th	Day	21% 8% 7% 30% 29% 5%	3250
	21st to end	Day	21% 6% 7% 31% 32% 4	3548
November	1st to 10th	Day	22% 7% 9% 27% 32% 4	2005
	11th to 20th	Day	27% 5% 10% 32% 22% 4	1842
	21st to end	Day	32% 5% 10% 27% 22% 4	1680
December	1st to 10th	Day	26% 4 11% 38% 18% 2	2700
	11th to 20th	Day	31% 6% 12% 29% 21% 1	3104
	21st to end	Day	35% 9% 13% 20% 20% 2	4092
January	1st to 10th	Night	45% 9% 13% 22% 11% 1	7920
	11th to 20th	Night	29% 5% 13% 26% 23% 3	7650
	21st to end	Night	32% 5% 11% 23% 23% 5%	8370
February	1st to 10th	Night	38% 7% 14% 23% 15% 2	2730
	11th to 20th	Night	42% 7% 11% 23% 15% 2	2627
	21st to end	Night	39% 5% 9% 26% 18% 4	2076
March	1st to 10th	Night	36% 10% 6% 21% 22% 5%	5061
	11th to 20th	Night	33% 8% 10% 26% 19% 3	5077
	21st to end	Night	42% 10% 10% 26% 11% 1	5453
April	1st to 10th	Night	38% 7% 7% 21% 20% 6%	2000
	11th to 20th	Night	40% 8% 8% 18% 20% 7%	1977
	21st to end	Night	34% 6% 9% 23% 25% 3	2000
May	1st to 10th	Night	31% 11% 12% 23% 20% 3	4151
	11th to 20th	Night	26% 8% 9% 29% 24% 3	3920
	21st to end	Night	19% 7% 7% 20% 37% 10%	3972
June	1st to 10th	Night	19% 7% 10% 19% 28% 17%	1600
	11th to 20th	Night	17% 5% 7% 14% 21% 35%	1600
	21st to end	Night	16% 5% 7% 16% 23% 32%	1600
July	1st to 10th	Night	18% 7% 7% 9% 14% 45%	3600
	11th to 20th	Night	18% 9% 13% 29% 16% 16%	3970
	21st to end	Night	20% 9% 14% 19% 21% 17%	4344
August	1st to 10th	Night	29% 11% 21% 14% 13% 12%	2928
	11th to 20th	Night	23% 8% 18% 13% 18% 19%	3038
	21st to end	Night	27% 9% 12% 16% 22% 15%	3597
September	1st to 10th	Night	21% 7% 10% 17% 24% 21%	2000
	11th to 20th	Night	21% 7% 11% 16% 27% 17%	2003
	21st to end	Night	19% 4 6% 19% 37% 14%	2292
October	1st to 10th	Night	14% 4 5% 16% 41% 21%	3920
	11th to 20th	Night	21% 8% 8% 29% 27% 7%	3898
	21st to end	Night	23% 5% 6% 31% 30% 4	4252
November	1st to 10th	Night	23% 5% 9% 29% 29% 5%	2492
	11th to 20th	Night	26% 4 10% 32% 24% 4	2776
	21st to end	Night	31% 5% 9% 26% 25% 4	2940
December	1st to 10th	Night	23% 4 10% 44% 19% 1	4710
	11th to 20th	Night	31% 6% 10% 33% 18%	5322
	21st to end	Night	40% 9% 10% 21% 19% 1	7128

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	12% 6% 25% 37% 16% 3	330
	11th to 20th	Day	9% 9% 28% 38% 15% 1	330
	21st to end	Day	8% 4 26% 45% 14% 2	363
February	1st to 10th	Day	11% 11% 33% 34% 9% 2	330
	11th to 20th	Day	14% 15% 32% 30% 8% 1	330
	21st to end	Day	10% 15% 30% 35% 10% 1	273
March	1st to 10th	Day	12% 17% 28% 29% 11% 2	524
	11th to 20th	Day	9% 17% 29% 30% 14% 1	529
	21st to end	Day	16% 19% 33% 23% 8% 1	550
April	1st to 10th	Day	13% 15% 31% 27% 12% 2	500
	11th to 20th	Day	15% 19% 35% 21% 8% 2	492
	21st to end	Day	11% 19% 34% 23% 13%	500
May	1st to 10th	Day	12% 18% 32% 26% 11% 1	503
	11th to 20th	Day	9% 10% 29% 29% 19% 3	587
	21st to end	Day	6% 12% 25% 34% 19% 3	789
June	1st to 10th	Day	4 7% 25% 35% 25% 4	730
	11th to 20th	Day	5% 8% 27% 37% 21% 3	730
	21st to end	Day	2 7% 24% 40% 24% 2	730
July	1st to 10th	Day	1 3 16% 42% 33% 5%	721
	11th to 20th	Day	3 1 11% 41% 35% 8%	556
	21st to end	Day	5% 3 13% 37% 34% 8%	575
August	1st to 10th	Day	4 4 20% 36% 29% 7%	527
	11th to 20th	Day	3 3 17% 38% 31% 9%	517
	21st to end	Day	4 1 15% 42% 31% 7%	583
September	1st to 10th	Day	5% 3 20% 34% 29% 9%	530
	11th to 20th	Day	5% 6% 27% 37% 22% 3	530
	21st to end	Day	5% 10% 19% 29% 28% 7%	436
October	1st to 10th	Day	7% 9% 22% 25% 27% 10%	330
	11th to 20th	Day	5% 10% 26% 32% 23% 5%	330
	21st to end	Day	7% 8% 24% 32% 24% 5%	363
November	1st to 10th	Day	5% 12% 26% 33% 20% 3	330
	11th to 20th	Day	6% 6% 28% 35% 21% 4	330
	21st to end	Day	12% 5% 26% 33% 19% 5%	330
December	1st to 10th	Day	9% 10% 28% 34% 15% 5%	330
	11th to 20th	Day	9% 3 28% 36% 21% 3	330
	21st to end	Day	12% 10% 30% 36% 11% 2	363
January	1st to 10th	Night	10% 5% 24% 42% 17% 1	950
	11th to 20th	Night	10% 4 25% 43% 16% 1	840
	21st to end	Night	11% 3 25% 46% 13% 2	924
February	1st to 10th	Night	11% 5% 31% 42% 10%	840
	11th to 20th	Night	10% 7% 33% 38% 12%	824
	21st to end	Night	12% 5% 34% 42% 7%	692
March	1st to 10th	Night	11% 6% 31% 41% 11% 1	840
	11th to 20th	Night	6% 5% 29% 43% 17%	828
	21st to end	Night	12% 8% 27% 41% 12%	869
April	1st to 10th	Night	10% 7% 33% 41% 9%	600
	11th to 20th	Night	12% 8% 29% 38% 12% 2	593
	21st to end	Night	10% 6% 29% 38% 16% 1	600
May	1st to 10th	Night	10% 8% 27% 42% 13%	600
	11th to 20th	Night	8% 4 24% 41% 20% 2	591
	21st to end	Night	7% 7% 25% 38% 21% 2	650
June	1st to 10th	Night	2 3 20% 46% 27% 1	600
	11th to 20th	Night	4 5% 21% 49% 21% 1	600
	21st to end	Night	2 2 17% 48% 30% 1	600
July	1st to 10th	Night	3 1 10% 49% 37% 2	585
	11th to 20th	Night	2 6% 44% 44% 3	582
	21st to end	Night	4 1 7% 43% 43% 2	657
August	1st to 10th	Night	5% 1 11% 42% 40% 2	597
	11th to 20th	Night	3 2 9% 46% 38% 2	594
	21st to end	Night	4 1 10% 45% 36% 2	660
September	1st to 10th	Night	4 2 11% 47% 36% 1	600
	11th to 20th	Night	4 2 15% 47% 31% 1	603
	21st to end	Night	6% 2 17% 41% 31% 4	800
October	1st to 10th	Night	7% 4 18% 46% 24% 1	800
	11th to 20th	Night	6% 2 23% 43% 23% 2	800
	21st to end	Night	10% 4 20% 42% 21% 3	880
November	1st to 10th	Night	5% 3 24% 46% 21% 1	852
	11th to 20th	Night	9% 4 24% 44% 18% 2	1050
	21st to end	Night	9% 6% 23% 44% 17% 2	1050
December	1st to 10th	Night	12% 5% 23% 45% 16% 1	1050
	11th to 20th	Night	12% 5% 27% 39% 16% 1	1050
	21st to end	Night	13% 6% 27% 42% 11% 1	1155

Page generated at 2026-03-15 00:23:53. Version ac07

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