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 2024-07-08.

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	12% 6% 2 6% 5% 5% 5% 4 7% 8% 40%	89315
	Night	13% 6% 2 5% 4 4 4 4 6% 8% 45%	89943
Transparency	Day	19% 56% 6% 9% 8% 3	89098
	Night	19% 54% 6% 9% 8% 3	89765
Seeing	Day	13% 9% 21% 24% 22% 11%	14263
	Night	14% 7% 21% 30% 23% 6%	23937

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 5% 4 4 4 3 6% 8% 41%	2847
	11th to 20th	Day	13% 6% 2 5% 3 3 4 2 4 5% 54%	2851
	21st to end	Day	24% 7% 2 5% 4 4 4 3 4 5% 37%	3476
February	1st to 10th	Day	17% 8% 2 8% 4 4 4 4 5% 5% 39%	1900
	11th to 20th	Day	18% 7% 2 6% 3 3 4 3 5% 6% 43%	1848
	21st to end	Day	17% 9% 2 8% 5% 4 4 3 5% 6% 38%	1570
March	1st to 10th	Day	22% 10% 3 8% 4 3 4 4 6% 7% 30%	3280
	11th to 20th	Day	14% 7% 3 7% 5% 5% 5% 4 7% 9% 34%	3480
	21st to end	Day	12% 7% 3 6% 5% 5% 5% 4 6% 7% 43%	3998
April	1st to 10th	Day	11% 5% 2 7% 5% 5% 5% 4 7% 8% 40%	2280
	11th to 20th	Day	14% 6% 3 7% 5% 4 4 4 6% 8% 39%	2254
	21st to end	Day	9% 5% 2 5% 4 5% 4 4 7% 8% 48%	2280
May	1st to 10th	Day	12% 5% 3 7% 5% 5% 6% 5% 7% 9% 36%	3765
	11th to 20th	Day	13% 6% 2 6% 5% 4 4 4 6% 8% 43%	3764
	21st to end	Day	5% 3 2 5% 4 6% 5% 5% 8% 11% 46%	4129
June	1st to 10th	Day	8% 6% 2 7% 6% 7% 7% 5% 7% 11% 34%	2280
	11th to 20th	Day	4 5% 2 8% 7% 7% 6% 7% 9% 12% 34%	2435
	21st to end	Day	7% 6% 3 8% 6% 7% 8% 7% 9% 11% 28%	2470
July	1st to 10th	Day	10% 6% 3 7% 7% 7% 7% 7% 10% 12% 25%	2433
	11th to 20th	Day	6% 5% 3 9% 7% 8% 8% 7% 10% 12% 24%	2314
	21st to end	Day	7% 6% 3 7% 8% 7% 7% 7% 9% 11% 28%	2350
August	1st to 10th	Day	6% 4 2 7% 6% 7% 7% 6% 10% 12% 33%	2148
	11th to 20th	Day	8% 6% 2 8% 7% 8% 7% 7% 9% 10% 28%	2125
	21st to end	Day	11% 6% 2 7% 7% 7% 5% 6% 9% 10% 32%	2376
September	1st to 10th	Day	9% 5% 2 8% 5% 6% 7% 6% 8% 9% 35%	2160
	11th to 20th	Day	9% 6% 2 6% 5% 6% 6% 4 8% 8% 40%	2107
	21st to end	Day	8% 5% 2 5% 4 5% 5% 4 7% 8% 48%	1980
October	1st to 10th	Day	6% 3 1 5% 4 4 4 3 7% 8% 54%	1899
	11th to 20th	Day	6% 4 2 5% 4 4 4 4 5% 8% 55%	1800
	21st to end	Day	10% 4 1 5% 3 3 4 3 4 5% 57%	1980
November	1st to 10th	Day	7% 5% 2 5% 4 3 4 4 5% 7% 55%	1858
	11th to 20th	Day	11% 5% 1 5% 3 4 4 3 5% 6% 55%	1827
	21st to end	Day	13% 5% 2 7% 4 4 4 3 5% 7% 45%	1710
December	1st to 10th	Day	15% 7% 2 6% 5% 3 4 4 6% 6% 44%	1710
	11th to 20th	Day	15% 9% 3 7% 4 4 4 4 5% 6% 39%	2221
	21st to end	Day	18% 9% 2 6% 5% 5% 4 3 5% 6% 37%	3410
January	1st to 10th	Night	16% 8% 2 4 3 3 4 4 5% 6% 46%	4108
	11th to 20th	Night	15% 6% 1 5% 3 2 3 3 4 6% 53%	4112
	21st to end	Night	27% 7% 2 4 2 3 3 2 4 7% 40%	4180
February	1st to 10th	Night	17% 7% 2 6% 4 4 4 4 4 6% 42%	2280
	11th to 20th	Night	19% 7% 2 5% 4 3 3 3 6% 6% 42%	2218
	21st to end	Night	20% 8% 3 7% 3 3 4 3 5% 6% 38%	1884
March	1st to 10th	Night	24% 11% 3 7% 3 4 4 3 4 5% 31%	3587
	11th to 20th	Night	15% 8% 3 6% 5% 5% 4 4 6% 8% 37%	3480
	21st to end	Night	14% 6% 2 5% 4 4 5% 4 6% 6% 44%	3631
April	1st to 10th	Night	14% 6% 3 5% 4 4 4 3 5% 6% 46%	1900
	11th to 20th	Night	13% 6% 2 7% 4 4 4 4 5% 7% 45%	1875
	21st to end	Night	7% 4 1 5% 4 3 4 3 5% 8% 57%	1900
May	1st to 10th	Night	13% 6% 2 6% 5% 4 3 3 5% 8% 45%	3130
	11th to 20th	Night	15% 7% 3 6% 4 4 4 3 6% 6% 43%	3129
	21st to end	Night	7% 4 1 4 4 4 5% 4 8% 13% 46%	3426
June	1st to 10th	Night	7% 6% 3 6% 4 4 5% 5% 9% 10% 42%	1900
	11th to 20th	Night	3 4 2 5% 4 5% 6% 5% 8% 12% 47%	1738
	21st to end	Night	6% 5% 3 5% 6% 6% 5% 6% 7% 10% 40%	1710
July	1st to 10th	Night	5% 6% 2 5% 5% 6% 6% 5% 9% 12% 38%	1692
	11th to 20th	Night	4 4 2 5% 5% 5% 6% 7% 12% 12% 37%	1642
	21st to end	Night	4 5% 2 6% 6% 5% 5% 5% 10% 13% 39%	1968
August	1st to 10th	Night	4 3 1 4 3 4 5% 5% 10% 14% 46%	1790
	11th to 20th	Night	5% 3 1 6% 6% 6% 6% 6% 10% 15% 36%	1776
	21st to end	Night	8% 5% 2 6% 5% 4 6% 5% 8% 12% 39%	1980
September	1st to 10th	Night	7% 5% 2 7% 4 5% 5% 5% 8% 12% 41%	1800
	11th to 20th	Night	8% 4 2 6% 5% 5% 5% 5% 7% 10% 43%	1833
	21st to end	Night	7% 4 1 6% 5% 4 4 4 6% 9% 50%	1980
October	1st to 10th	Night	6% 4 2 4 3 3 4 3 4 6% 60%	2056
	11th to 20th	Night	6% 4 2 5% 3 3 3 3 5% 7% 59%	2160
	21st to end	Night	11% 3 2 5% 3 3 4 3 5% 7% 55%	2376
November	1st to 10th	Night	9% 5% 2 5% 2 3 3 3 4 7% 56%	2220
	11th to 20th	Night	11% 5% 1 4 4 3 3 3 4 6% 55%	2347
	21st to end	Night	12% 6% 2 6% 4 4 4 4 5% 7% 47%	2470
December	1st to 10th	Night	15% 7% 3 6% 4 4 4 3 5% 7% 44%	2470
	11th to 20th	Night	14% 8% 2 6% 5% 4 5% 4 5% 6% 42%	2969
	21st to end	Night	18% 10% 3 6% 5% 4 3 3 4 5% 40%	4226

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	27% 38% 4 10% 15% 6%	2848
	11th to 20th	Day	19% 38% 3 11% 23% 6%	2851
	21st to end	Day	32% 41% 3 7% 13% 4	3476
February	1st to 10th	Day	18% 65% 3 4 6% 4	1900
	11th to 20th	Day	16% 65% 3 6% 7% 2	1858
	21st to end	Day	17% 65% 3 3 8% 3	1570
March	1st to 10th	Day	38% 43% 7% 8% 3 1	3280
	11th to 20th	Day	28% 43% 6% 12% 9% 1	3480
	21st to end	Day	25% 44% 7% 7% 11% 6%	3998
April	1st to 10th	Day	15% 66% 2 6% 8% 4	2280
	11th to 20th	Day	16% 67% 4 6% 5% 3	2254
	21st to end	Day	13% 65% 4 7% 7% 3	2280
May	1st to 10th	Day	25% 45% 11% 10% 6% 3	3800
	11th to 20th	Day	24% 42% 8% 11% 15% 1	3768
	21st to end	Day	14% 44% 12% 24% 5% 1	4141
June	1st to 10th	Day	15% 67% 6% 8% 4 1	2280
	11th to 20th	Day	16% 69% 6% 5% 5%	2435
	21st to end	Day	16% 68% 7% 7% 3	2470
July	1st to 10th	Day	12% 65% 11% 8% 2	2369
	11th to 20th	Day	16% 67% 9% 7% 1	2245
	21st to end	Day	13% 64% 7% 11% 4 1	2219
August	1st to 10th	Day	11% 68% 10% 8% 3	2136
	11th to 20th	Day	13% 70% 7% 7% 2 1	2125
	21st to end	Day	13% 67% 8% 7% 3 1	2376
September	1st to 10th	Day	13% 67% 8% 6% 4 2	2160
	11th to 20th	Day	10% 65% 8% 7% 7% 3	2107
	21st to end	Day	11% 66% 6% 12% 5% 1	1980
October	1st to 10th	Day	9% 65% 7% 9% 7% 2	1899
	11th to 20th	Day	9% 64% 3 7% 11% 5%	1800
	21st to end	Day	13% 62% 3 5% 10% 8%	1980
November	1st to 10th	Day	15% 60% 5% 8% 7% 4	1858
	11th to 20th	Day	17% 60% 4 7% 9% 4	1827
	21st to end	Day	15% 61% 4 8% 7% 5%	1710
December	1st to 10th	Day	19% 60% 4 7% 7% 3	1710
	11th to 20th	Day	21% 49% 3 6% 15% 6%	2218
	21st to end	Day	30% 40% 7% 7% 14% 2	3410
January	1st to 10th	Night	25% 38% 6% 9% 15% 7%	4108
	11th to 20th	Night	20% 37% 4 13% 18% 8%	4112
	21st to end	Night	29% 39% 4 11% 13% 4	4180
February	1st to 10th	Night	15% 66% 3 6% 6% 3	2280
	11th to 20th	Night	16% 64% 2 7% 8% 3	2219
	21st to end	Night	18% 65% 4 5% 5% 5%	1884
March	1st to 10th	Night	41% 43% 6% 6% 3 1	3587
	11th to 20th	Night	29% 43% 7% 10% 8% 3	3480
	21st to end	Night	24% 44% 6% 13% 10% 4	3631
April	1st to 10th	Night	15% 65% 3 5% 7% 5%	1900
	11th to 20th	Night	16% 67% 4 6% 5% 3	1875
	21st to end	Night	11% 65% 3 8% 9% 3	1900
May	1st to 10th	Night	23% 45% 10% 10% 9% 3	3160
	11th to 20th	Night	27% 42% 7% 12% 11% 1	3130
	21st to end	Night	16% 43% 16% 18% 6% 1	3435
June	1st to 10th	Night	13% 66% 6% 11% 4	1900
	11th to 20th	Night	13% 68% 6% 11% 3	1738
	21st to end	Night	14% 66% 8% 8% 4	1710
July	1st to 10th	Night	10% 63% 12% 13% 2	1647
	11th to 20th	Night	10% 69% 12% 8% 2	1588
	21st to end	Night	8% 64% 11% 13% 3	1858
August	1st to 10th	Night	9% 67% 13% 9% 1	1778
	11th to 20th	Night	10% 70% 11% 7% 2	1776
	21st to end	Night	12% 67% 8% 9% 3 2	1980
September	1st to 10th	Night	12% 65% 10% 7% 4 3	1800
	11th to 20th	Night	9% 67% 9% 8% 5% 3	1833
	21st to end	Night	12% 65% 6% 11% 5% 1	1980
October	1st to 10th	Night	8% 65% 6% 10% 8% 2	2056
	11th to 20th	Night	8% 64% 4 10% 11% 4	2160
	21st to end	Night	14% 62% 2 5% 10% 6%	2376
November	1st to 10th	Night	17% 58% 6% 8% 7% 3	2220
	11th to 20th	Night	16% 59% 3 8% 9% 5%	2347
	21st to end	Night	14% 60% 4 8% 9% 5%	2470
December	1st to 10th	Night	18% 60% 3 9% 6% 2	2470
	11th to 20th	Night	20% 50% 3 6% 10% 11%	2971
	21st to end	Night	32% 38% 5% 9% 12% 4	4226

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% 14% 39% 16% 6% 1	270
	11th to 20th	Day	21% 20% 34% 20% 5% 1	270
	21st to end	Day	25% 23% 37% 12% 3	297
February	1st to 10th	Day	27% 20% 33% 16% 3 1	270
	11th to 20th	Day	30% 17% 34% 13% 5%	270
	21st to end	Day	17% 32% 39% 11% 1	225
March	1st to 10th	Day	19% 23% 37% 19% 3	270
	11th to 20th	Day	22% 24% 34% 17% 3	270
	21st to end	Day	17% 19% 36% 19% 8% 1	404
April	1st to 10th	Day	18% 16% 33% 23% 10% 1	460
	11th to 20th	Day	17% 18% 31% 22% 11% 2	452
	21st to end	Day	10% 10% 32% 30% 15% 3	460
May	1st to 10th	Day	14% 11% 29% 25% 18% 4	463
	11th to 20th	Day	13% 6% 21% 31% 22% 8%	487
	21st to end	Day	6% 4 18% 35% 25% 12%	529
June	1st to 10th	Day	13% 2 11% 31% 28% 16%	490
	11th to 20th	Day	9% 3 11% 33% 32% 13%	645
	21st to end	Day	9% 2 12% 29% 29% 19%	680
July	1st to 10th	Day	9% 2 7% 23% 38% 21%	658
	11th to 20th	Day	7% 1 5% 20% 42% 26%	592
	21st to end	Day	10% 2 5% 17% 41% 26%	488
August	1st to 10th	Day	5% 1 5% 19% 38% 31%	446
	11th to 20th	Day	8% 1 5% 19% 36% 31%	439
	21st to end	Day	12% 2 8% 20% 33% 25%	495
September	1st to 10th	Day	8% 2 7% 24% 40% 19%	450
	11th to 20th	Day	11% 2 10% 26% 34% 16%	450
	21st to end	Day	9% 3 9% 32% 34% 13%	450
October	1st to 10th	Day	6% 5% 18% 40% 23% 8%	369
	11th to 20th	Day	6% 7% 24% 34% 23% 7%	270
	21st to end	Day	18% 11% 20% 34% 13% 3	297
November	1st to 10th	Day	14% 6% 25% 37% 17% 2	270
	11th to 20th	Day	16% 16% 29% 26% 12% 1	270
	21st to end	Day	14% 17% 37% 22% 8% 2	270
December	1st to 10th	Day	21% 9% 35% 22% 10% 2	270
	11th to 20th	Day	23% 16% 39% 18% 4 1	270
	21st to end	Day	26% 13% 32% 21% 7%	297
January	1st to 10th	Night	21% 10% 32% 30% 6% 1	950
	11th to 20th	Night	20% 12% 29% 31% 8%	942
	21st to end	Night	23% 13% 31% 28% 4	836
February	1st to 10th	Night	20% 12% 36% 28% 6%	760
	11th to 20th	Night	24% 13% 29% 28% 7%	743
	21st to end	Night	23% 16% 34% 23% 3	628
March	1st to 10th	Night	16% 13% 34% 29% 7%	679
	11th to 20th	Night	16% 7% 33% 34% 10%	570
	21st to end	Night	15% 11% 31% 32% 11%	627
April	1st to 10th	Night	19% 9% 29% 31% 13%	570
	11th to 20th	Night	16% 9% 30% 31% 14% 1	563
	21st to end	Night	9% 6% 28% 39% 16% 1	570
May	1st to 10th	Night	9% 5% 25% 40% 20% 1	570
	11th to 20th	Night	8% 4 17% 42% 25% 3	561
	21st to end	Night	7% 2 15% 36% 33% 6%	617
June	1st to 10th	Night	9% 1 8% 37% 36% 9%	570
	11th to 20th	Night	4 1 8% 30% 46% 11%	570
	21st to end	Night	8% 1 7% 29% 37% 18%	570
July	1st to 10th	Night	5% 1 5% 16% 51% 22%	549
	11th to 20th	Night	5% 1 2 14% 47% 30%	522
	21st to end	Night	5% 1 4 16% 52% 23%	591
August	1st to 10th	Night	5% 3 15% 49% 28%	537
	11th to 20th	Night	5% 1 3 13% 48% 30%	534
	21st to end	Night	9% 2 6% 19% 43% 21%	594
September	1st to 10th	Night	9% 1 5% 22% 44% 19%	540
	11th to 20th	Night	11% 3 7% 25% 44% 11%	573
	21st to end	Night	11% 2 10% 30% 41% 7%	720
October	1st to 10th	Night	7% 2 16% 38% 33% 5%	720
	11th to 20th	Night	7% 5% 20% 40% 25% 4	720
	21st to end	Night	14% 7% 21% 35% 21% 3	792
November	1st to 10th	Night	13% 6% 15% 42% 21% 3	740
	11th to 20th	Night	14% 7% 27% 35% 15% 1	760
	21st to end	Night	15% 8% 27% 34% 15% 1	760
December	1st to 10th	Night	17% 11% 28% 29% 15% 1	760
	11th to 20th	Night	18% 8% 32% 31% 9% 1	760
	21st to end	Night	26% 11% 28% 27% 7%	869

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