Seti DS Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Seti DS Observatory clear sky chart from 2005-11-06 to 2026-04-02.

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	11% 6% 2 6% 5% 5% 5% 4 7% 9% 41%	130672
	Night	12% 6% 2 6% 4 4 4 4 6% 8% 44%	131209
Transparency	Day	24% 39% 9% 12% 11% 5%	134357
	Night	24% 38% 9% 12% 11% 6%	135599
Seeing	Day	13% 9% 21% 25% 21% 10%	16498
	Night	14% 7% 21% 30% 22% 6%	26213

By Month

Percentage Cloud Cover SE (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	17% 6% 2 6% 4 4 4 3 6% 7% 42%	5289
	11th to 20th	Day	11% 6% 2 6% 4 3 4 3 4 6% 51%	5324
	21st to end	Day	21% 8% 2 6% 4 4 4 4 5% 5% 36%	6436
February	1st to 10th	Day	17% 8% 2 7% 4 3 4 4 5% 5% 40%	2100
	11th to 20th	Day	17% 7% 2 6% 3 3 4 3 5% 7% 42%	2048
	21st to end	Day	16% 9% 3 8% 5% 4 4 3 4 7% 39%	1730
March	1st to 10th	Day	18% 9% 3 7% 4 3 4 3 6% 7% 36%	4815
	11th to 20th	Day	12% 6% 3 6% 4 4 4 4 6% 7% 45%	5090
	21st to end	Day	13% 8% 3 7% 5% 4 4 3 5% 6% 42%	5857
April	1st to 10th	Day	11% 5% 2 7% 5% 5% 5% 4 7% 8% 40%	2412
	11th to 20th	Day	13% 6% 3 7% 4 4 4 4 6% 8% 41%	2374
	21st to end	Day	8% 5% 2 5% 4 5% 5% 4 7% 7% 47%	2400
May	1st to 10th	Day	16% 6% 3 7% 5% 4 5% 5% 7% 8% 34%	5405
	11th to 20th	Day	9% 4 2 5% 4 4 5% 4 7% 10% 46%	5404
	21st to end	Day	5% 4 2 6% 4 5% 5% 5% 8% 12% 42%	5932
June	1st to 10th	Day	8% 6% 2 7% 6% 7% 7% 5% 8% 11% 35%	2400
	11th to 20th	Day	4 5% 2 8% 7% 7% 6% 7% 9% 12% 34%	2563
	21st to end	Day	7% 5% 3 7% 6% 6% 8% 8% 10% 12% 28%	2600
July	1st to 10th	Day	5% 5% 2 7% 6% 7% 8% 6% 10% 14% 30%	5900
	11th to 20th	Day	4 4 2 7% 6% 7% 7% 7% 11% 14% 33%	5818
	21st to end	Day	6% 5% 2 7% 7% 7% 8% 6% 9% 13% 29%	5922
August	1st to 10th	Day	3 2 1 5% 4 5% 5% 5% 8% 11% 52%	3905
	11th to 20th	Day	5% 4 1 5% 5% 6% 6% 6% 9% 13% 40%	3849
	21st to end	Day	9% 6% 3 8% 7% 6% 6% 5% 8% 9% 34%	4312
September	1st to 10th	Day	10% 5% 2 8% 5% 6% 6% 5% 8% 10% 35%	2400
	11th to 20th	Day	9% 6% 2 6% 5% 5% 6% 4 8% 8% 41%	2341
	21st to end	Day	7% 4 2 5% 4 5% 5% 4 7% 8% 50%	2200
October	1st to 10th	Day	7% 3 2 5% 4 4 4 3 7% 8% 54%	2109
	11th to 20th	Day	5% 4 2 5% 4 4 3 4 5% 7% 58%	2000
	21st to end	Day	9% 4 1 5% 3 3 4 3 4 6% 58%	2200
November	1st to 10th	Day	7% 5% 2 6% 4 3 4 4 5% 7% 54%	2058
	11th to 20th	Day	10% 5% 1 5% 3 3 3 3 4 6% 55%	2019
	21st to end	Day	12% 5% 2 7% 4 4 4 3 5% 7% 46%	1890
December	1st to 10th	Day	17% 8% 3 7% 4 3 4 3 4 5% 41%	3020
	11th to 20th	Day	10% 6% 2 6% 4 4 4 4 7% 7% 46%	3575
	21st to end	Day	17% 9% 3 6% 4 4 4 3 4 5% 42%	4975
January	1st to 10th	Night	19% 7% 2 5% 3 3 4 3 5% 7% 44%	7634
	11th to 20th	Night	16% 7% 2 5% 3 3 3 3 4 6% 47%	7644
	21st to end	Night	22% 8% 3 6% 4 4 4 3 4 7% 35%	7745
February	1st to 10th	Night	16% 7% 3 6% 4 4 4 4 4 6% 43%	2520
	11th to 20th	Night	19% 8% 2 5% 4 3 3 3 6% 6% 40%	2458
	21st to end	Night	19% 8% 3 7% 3 3 4 3 5% 6% 39%	2076
March	1st to 10th	Night	19% 9% 3 7% 3 3 4 3 5% 6% 38%	5287
	11th to 20th	Night	14% 6% 2 5% 4 4 3 3 5% 6% 49%	5090
	21st to end	Night	15% 6% 2 5% 4 4 4 3 5% 6% 46%	5312
April	1st to 10th	Night	15% 6% 3 6% 4 4 4 3 5% 6% 46%	2010
	11th to 20th	Night	12% 6% 2 6% 4 4 4 4 5% 7% 46%	1975
	21st to end	Night	7% 5% 1 5% 4 3 4 3 5% 8% 56%	2000
May	1st to 10th	Night	15% 7% 2 7% 5% 4 4 3 6% 8% 38%	4490
	11th to 20th	Night	13% 7% 2 6% 4 3 4 3 6% 8% 45%	4489
	21st to end	Night	7% 5% 2 6% 4 5% 5% 4 7% 12% 43%	4922
June	1st to 10th	Night	7% 6% 3 6% 4 4 5% 5% 9% 10% 42%	2000
	11th to 20th	Night	3 4 2 5% 5% 6% 6% 5% 8% 11% 46%	1829
	21st to end	Night	5% 5% 3 6% 6% 6% 5% 6% 7% 10% 40%	1800
July	1st to 10th	Night	3 5% 2 6% 5% 6% 7% 6% 10% 13% 37%	4078
	11th to 20th	Night	3 3 2 5% 5% 5% 6% 6% 10% 13% 43%	4138
	21st to end	Night	4 5% 2 7% 6% 6% 7% 5% 10% 13% 34%	4929
August	1st to 10th	Night	2 2 1 3 3 4 5% 5% 8% 13% 55%	3244
	11th to 20th	Night	3 2 1 5% 4 6% 6% 6% 9% 15% 43%	3200
	21st to end	Night	6% 6% 2 7% 5% 5% 6% 5% 7% 10% 40%	3586
September	1st to 10th	Night	8% 5% 2 7% 5% 5% 6% 5% 8% 11% 40%	2000
	11th to 20th	Night	8% 4 2 6% 5% 5% 5% 5% 7% 10% 44%	2037
	21st to end	Night	7% 4 1 6% 4 4 4 3 6% 9% 51%	2200
October	1st to 10th	Night	7% 4 2 4 3 3 4 3 4 6% 59%	2285
	11th to 20th	Night	6% 4 2 5% 3 3 3 3 5% 6% 62%	2400
	21st to end	Night	11% 3 2 5% 3 3 4 3 4 7% 56%	2640
November	1st to 10th	Night	10% 5% 2 5% 3 3 3 2 4 7% 55%	2460
	11th to 20th	Night	11% 5% 2 4 4 3 3 3 4 6% 56%	2595
	21st to end	Night	11% 6% 2 6% 4 4 4 4 5% 7% 48%	2730
December	1st to 10th	Night	16% 7% 3 7% 4 4 4 3 4 5% 42%	4380
	11th to 20th	Night	10% 7% 2 6% 5% 4 4 4 6% 6% 46%	4834
	21st to end	Night	18% 10% 3 6% 4 4 3 2 3 5% 43%	6192

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	34% 22% 6% 15% 19% 3	5290
	11th to 20th	Day	28% 21% 3 14% 24% 10%	5324
	21st to end	Day	40% 24% 5% 8% 12% 11%	6436
February	1st to 10th	Day	19% 59% 3 5% 9% 5%	2100
	11th to 20th	Day	19% 60% 4 7% 8% 2	2058
	21st to end	Day	19% 59% 4 4 9% 4	1730
March	1st to 10th	Day	37% 30% 6% 10% 9% 8%	4815
	11th to 20th	Day	25% 30% 7% 11% 14% 14%	5090
	21st to end	Day	32% 31% 7% 11% 11% 7%	5859
April	1st to 10th	Day	17% 63% 2 6% 8% 4	2412
	11th to 20th	Day	16% 63% 4 6% 6% 4	2374
	21st to end	Day	14% 63% 5% 8% 7% 3	2400
May	1st to 10th	Day	34% 33% 11% 14% 6% 2	5440
	11th to 20th	Day	22% 31% 14% 19% 13% 1	5408
	21st to end	Day	21% 33% 13% 23% 8% 1	5945
June	1st to 10th	Day	15% 64% 6% 9% 5% 1	2400
	11th to 20th	Day	17% 66% 6% 6% 5%	2563
	21st to end	Day	16% 65% 8% 7% 3	2600
July	1st to 10th	Day	25% 34% 24% 14% 3	5836
	11th to 20th	Day	24% 35% 32% 8%	5749
	21st to end	Day	31% 33% 15% 19% 2	5752
August	1st to 10th	Day	10% 39% 8% 22% 21%	3893
	11th to 20th	Day	14% 42% 15% 21% 8%	3885
	21st to end	Day	28% 41% 9% 10% 11% 1	4311
September	1st to 10th	Day	16% 60% 9% 8% 5% 2	2400
	11th to 20th	Day	12% 60% 8% 9% 8% 2	2341
	21st to end	Day	11% 60% 7% 13% 7% 2	2200
October	1st to 10th	Day	17% 36% 5% 6% 14% 23%	3434
	11th to 20th	Day	6% 36% 3 14% 18% 24%	3240
	21st to end	Day	10% 36% 4 7% 31% 13%	3538
November	1st to 10th	Day	17% 55% 6% 9% 8% 5%	2058
	11th to 20th	Day	17% 55% 4 8% 11% 5%	2019
	21st to end	Day	16% 55% 5% 9% 9% 5%	1890
December	1st to 10th	Day	33% 35% 4 8% 17% 3	3020
	11th to 20th	Day	20% 32% 7% 13% 18% 9%	3572
	21st to end	Day	32% 28% 6% 11% 19% 4	4975
January	1st to 10th	Night	33% 22% 8% 14% 16% 6%	7635
	11th to 20th	Night	31% 21% 4 13% 21% 11%	7644
	21st to end	Night	40% 23% 5% 11% 14% 7%	7745
February	1st to 10th	Night	17% 59% 4 6% 9% 4	2520
	11th to 20th	Night	20% 58% 3 7% 8% 3	2459
	21st to end	Night	19% 59% 4 6% 7% 5%	2076
March	1st to 10th	Night	39% 30% 7% 7% 11% 6%	5287
	11th to 20th	Night	26% 30% 6% 11% 14% 13%	5090
	21st to end	Night	29% 31% 7% 17% 11% 6%	5312
April	1st to 10th	Night	18% 62% 3 5% 7% 5%	2010
	11th to 20th	Night	16% 63% 4 7% 6% 4	1975
	21st to end	Night	12% 62% 5% 10% 9% 3	2000
May	1st to 10th	Night	33% 33% 11% 12% 9% 2	4520
	11th to 20th	Night	27% 30% 13% 19% 10%	4490
	21st to end	Night	23% 31% 16% 23% 6% 1	4931
June	1st to 10th	Night	13% 63% 7% 11% 5%	2000
	11th to 20th	Night	14% 65% 7% 11% 3	1829
	21st to end	Night	15% 63% 10% 8% 4	1800
July	1st to 10th	Night	23% 34% 24% 15% 3	4035
	11th to 20th	Night	21% 36% 36% 6% 1	4087
	21st to end	Night	29% 36% 13% 21% 2	4785
August	1st to 10th	Night	10% 39% 11% 20% 19% 1	3232
	11th to 20th	Night	13% 42% 18% 21% 6%	3230
	21st to end	Night	25% 40% 10% 14% 8% 3	3586
September	1st to 10th	Night	15% 60% 10% 8% 5% 2	2000
	11th to 20th	Night	11% 60% 9% 10% 6% 3	2037
	21st to end	Night	13% 59% 7% 13% 6% 2	2200
October	1st to 10th	Night	19% 36% 5% 8% 14% 18%	3740
	11th to 20th	Night	6% 36% 3 13% 19% 23%	3899
	21st to end	Night	10% 35% 4 5% 28% 17%	4252
November	1st to 10th	Night	19% 53% 6% 8% 9% 4	2460
	11th to 20th	Night	17% 54% 3 9% 10% 6%	2595
	21st to end	Night	16% 55% 5% 9% 10% 5%	2730
December	1st to 10th	Night	32% 35% 3 10% 17% 4	4380
	11th to 20th	Night	23% 32% 7% 13% 15% 9%	4836
	21st to end	Night	35% 27% 4 11% 17% 6%	6192

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	24% 15% 39% 15% 5% 1	330
	11th to 20th	Day	21% 22% 34% 18% 4 1	330
	21st to end	Day	27% 21% 37% 12% 3	363
February	1st to 10th	Day	24% 18% 38% 15% 4 1	330
	11th to 20th	Day	28% 20% 34% 12% 5%	330
	21st to end	Day	18% 30% 38% 11% 2	273
March	1st to 10th	Day	18% 21% 38% 20% 3	330
	11th to 20th	Day	22% 25% 33% 17% 3	330
	21st to end	Day	17% 18% 34% 22% 9% 1	482
April	1st to 10th	Day	19% 17% 32% 22% 9% 1	504
	11th to 20th	Day	16% 18% 32% 22% 10% 2	492
	21st to end	Day	10% 10% 32% 30% 15% 4	500
May	1st to 10th	Day	16% 11% 29% 25% 17% 3	503
	11th to 20th	Day	12% 6% 24% 30% 20% 7%	527
	21st to end	Day	6% 5% 19% 35% 23% 12%	573
June	1st to 10th	Day	12% 2 13% 31% 27% 15%	530
	11th to 20th	Day	9% 3 11% 33% 31% 13%	693
	21st to end	Day	8% 2 12% 29% 30% 19%	730
July	1st to 10th	Day	8% 3 8% 24% 37% 20%	721
	11th to 20th	Day	7% 1 5% 21% 41% 26%	688
	21st to end	Day	9% 2 5% 18% 42% 24%	576
August	1st to 10th	Day	4 1 5% 21% 40% 28%	526
	11th to 20th	Day	7% 1 6% 19% 36% 32%	519
	21st to end	Day	11% 3 9% 23% 31% 23%	583
September	1st to 10th	Day	11% 1 9% 24% 37% 17%	530
	11th to 20th	Day	11% 3 10% 27% 33% 16%	530
	21st to end	Day	8% 4 11% 33% 33% 12%	530
October	1st to 10th	Day	8% 5% 20% 38% 22% 7%	439
	11th to 20th	Day	5% 7% 27% 33% 22% 6%	330
	21st to end	Day	17% 10% 21% 36% 13% 3	363
November	1st to 10th	Day	13% 9% 26% 34% 16% 2	330
	11th to 20th	Day	15% 15% 30% 27% 12% 2	330
	21st to end	Day	13% 18% 38% 22% 8% 2	330
December	1st to 10th	Day	22% 11% 36% 20% 9% 2	330
	11th to 20th	Day	20% 15% 40% 20% 5% 1	330
	21st to end	Day	24% 14% 31% 22% 8% 1	363
January	1st to 10th	Night	21% 11% 32% 30% 6% 1	1050
	11th to 20th	Night	20% 13% 28% 31% 8%	1040
	21st to end	Night	23% 13% 32% 28% 4	924
February	1st to 10th	Night	19% 12% 36% 28% 6%	840
	11th to 20th	Night	25% 13% 29% 27% 6%	823
	21st to end	Night	23% 16% 35% 22% 3	692
March	1st to 10th	Night	17% 14% 34% 29% 7%	751
	11th to 20th	Night	17% 7% 32% 33% 10%	630
	21st to end	Night	15% 10% 31% 34% 10%	693
April	1st to 10th	Night	19% 9% 28% 31% 12%	603
	11th to 20th	Night	15% 9% 31% 31% 13% 1	593
	21st to end	Night	10% 6% 27% 40% 17% 1	600
May	1st to 10th	Night	11% 5% 24% 40% 19% 1	600
	11th to 20th	Night	8% 4 19% 41% 24% 3	591
	21st to end	Night	8% 2 16% 35% 33% 6%	650
June	1st to 10th	Night	9% 1 9% 38% 36% 9%	600
	11th to 20th	Night	3 2 8% 30% 47% 11%	600
	21st to end	Night	7% 1 7% 28% 38% 18%	600
July	1st to 10th	Night	5% 1 5% 17% 52% 21%	585
	11th to 20th	Night	5% 1 3 13% 47% 31%	582
	21st to end	Night	5% 1 4 17% 51% 22%	657
August	1st to 10th	Night	5% 3 16% 51% 26%	597
	11th to 20th	Night	5% 1 3 13% 48% 30%	594
	21st to end	Night	9% 2 6% 20% 42% 21%	660
September	1st to 10th	Night	10% 1 7% 23% 42% 17%	600
	11th to 20th	Night	11% 3 7% 25% 45% 10%	637
	21st to end	Night	10% 2 11% 31% 40% 6%	800
October	1st to 10th	Night	8% 2 18% 37% 31% 5%	800
	11th to 20th	Night	7% 5% 19% 41% 25% 3	800
	21st to end	Night	13% 6% 20% 37% 21% 2	880
November	1st to 10th	Night	13% 6% 17% 42% 20% 2	820
	11th to 20th	Night	14% 8% 26% 36% 15% 1	840
	21st to end	Night	15% 9% 28% 33% 14% 1	840
December	1st to 10th	Night	18% 11% 28% 28% 14%	840
	11th to 20th	Night	18% 9% 31% 32% 10%	840
	21st to end	Night	26% 11% 28% 28% 7%	961

Page generated at 2026-03-30 01:18:40. Version ac07

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