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 2024-12-09.

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% 5% 7% 9% 40%	100587
	Night	12% 6% 2 5% 4 4 4 4 6% 8% 44%	99162
Transparency	Day	20% 49% 8% 10% 10% 4	104308
	Night	20% 48% 7% 10% 10% 5%	103580
Seeing	Day	13% 9% 21% 25% 22% 11%	14824
	Night	14% 7% 21% 30% 23% 6%	24480

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	7% 5% 2 8% 7% 7% 9% 7% 10% 14% 24%	4120
	11th to 20th	Day	5% 4 2 8% 6% 7% 8% 7% 11% 14% 28%	4066
	21st to end	Day	7% 7% 3 9% 8% 8% 8% 6% 9% 12% 23%	4118
August	1st to 10th	Day	3 3 1 4 4 4 5% 5% 7% 11% 53%	3785
	11th to 20th	Day	5% 4 2 6% 5% 6% 6% 6% 9% 13% 40%	3729
	21st to end	Day	9% 6% 3 8% 7% 6% 6% 5% 8% 9% 33%	4180
September	1st to 10th	Day	11% 5% 2 8% 5% 6% 7% 6% 8% 9% 33%	2280
	11th to 20th	Day	9% 6% 2 6% 5% 6% 6% 4 8% 8% 39%	2224
	21st to end	Day	7% 4 2 5% 4 5% 5% 4 7% 8% 50%	2090
October	1st to 10th	Day	7% 3 1 5% 4 4 4 3 7% 8% 55%	2004
	11th to 20th	Day	5% 4 2 5% 4 4 3 4 5% 8% 57%	1900
	21st to end	Day	9% 4 1 5% 3 3 4 3 4 5% 58%	2090
November	1st to 10th	Day	7% 5% 2 6% 4 3 4 4 5% 6% 53%	1958
	11th to 20th	Day	11% 5% 1 5% 3 3 3 3 4 6% 55%	1923
	21st to end	Day	13% 5% 2 7% 4 4 4 3 5% 7% 46%	1800
December	1st to 10th	Day	15% 7% 2 6% 4 3 3 4 5% 6% 44%	1782
	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	4 5% 2 7% 5% 6% 7% 7% 10% 13% 33%	2850
	11th to 20th	Night	3 3 2 5% 5% 6% 7% 6% 11% 13% 40%	2898
	21st to end	Night	5% 6% 3 8% 7% 7% 7% 6% 11% 14% 29%	3435
August	1st to 10th	Night	2 2 1 3 3 4 4 4 8% 13% 56%	3144
	11th to 20th	Night	3 2 1 5% 4 6% 6% 6% 9% 15% 43%	3100
	21st to end	Night	6% 5% 2 7% 5% 5% 6% 5% 8% 10% 40%	3476
September	1st to 10th	Night	8% 5% 2 7% 5% 5% 6% 5% 8% 11% 39%	1900
	11th to 20th	Night	9% 5% 2 6% 5% 5% 5% 5% 7% 9% 42%	1935
	21st to end	Night	7% 4 1 6% 4 4 4 3 6% 9% 52%	2090
October	1st to 10th	Night	7% 4 2 4 3 3 4 3 4 6% 60%	2171
	11th to 20th	Night	6% 4 2 5% 3 3 3 3 5% 7% 60%	2280
	21st to end	Night	11% 3 2 5% 3 3 4 3 4 7% 56%	2508
November	1st to 10th	Night	10% 6% 2 5% 3 3 3 3 4 7% 54%	2340
	11th to 20th	Night	12% 5% 1 4 4 3 3 3 4 6% 55%	2471
	21st to end	Night	11% 6% 2 6% 4 4 4 4 5% 7% 48%	2600
December	1st to 10th	Night	14% 7% 3 6% 4 4 4 3 5% 7% 44%	2581
	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	25% 43% 19% 11% 2	4056
	11th to 20th	Day	24% 44% 27% 5% 1	3997
	21st to end	Day	33% 42% 11% 11% 3	3987
August	1st to 10th	Day	8% 39% 8% 22% 22%	3773
	11th to 20th	Day	14% 43% 15% 21% 8% 1	3765
	21st to end	Day	28% 41% 8% 10% 11% 1	4179
September	1st to 10th	Day	17% 63% 8% 6% 5% 2	2280
	11th to 20th	Day	12% 62% 8% 8% 7% 3	2224
	21st to end	Day	10% 63% 6% 13% 6% 2	2090
October	1st to 10th	Day	16% 37% 5% 6% 13% 23%	3329
	11th to 20th	Day	6% 37% 3 14% 17% 24%	3140
	21st to end	Day	10% 37% 4 6% 31% 13%	3428
November	1st to 10th	Day	17% 58% 6% 9% 7% 4	1958
	11th to 20th	Day	17% 57% 4 7% 10% 5%	1923
	21st to end	Day	16% 58% 4 9% 8% 5%	1800
December	1st to 10th	Day	19% 58% 4 7% 9% 3	1782
	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	22% 44% 22% 11% 1	2805
	11th to 20th	Night	19% 46% 30% 5% 1	2844
	21st to end	Night	29% 46% 11% 13% 2	3325
August	1st to 10th	Night	9% 40% 11% 20% 20% 1	3132
	11th to 20th	Night	13% 43% 17% 21% 6%	3130
	21st to end	Night	24% 41% 10% 14% 8% 3	3476
September	1st to 10th	Night	15% 62% 10% 6% 4 2	1900
	11th to 20th	Night	11% 63% 9% 9% 5% 3	1935
	21st to end	Night	12% 62% 6% 12% 6% 2	2090
October	1st to 10th	Night	19% 37% 5% 7% 14% 18%	3626
	11th to 20th	Night	6% 37% 3 13% 19% 23%	3779
	21st to end	Night	10% 36% 4 5% 28% 17%	4120
November	1st to 10th	Night	19% 56% 6% 8% 7% 3	2340
	11th to 20th	Night	18% 57% 3 7% 9% 6%	2471
	21st to end	Night	15% 58% 4 8% 10% 5%	2600
December	1st to 10th	Night	19% 58% 3 9% 8% 2	2581
	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	8% 3 7% 24% 37% 21%	671
	11th to 20th	Day	7% 1 5% 20% 41% 26%	640
	21st to end	Day	9% 2 5% 17% 42% 25%	532
August	1st to 10th	Day	4 1 5% 21% 39% 29%	486
	11th to 20th	Day	7% 1 6% 19% 36% 31%	479
	21st to end	Day	12% 3 9% 22% 32% 23%	539
September	1st to 10th	Day	12% 1 8% 22% 39% 17%	490
	11th to 20th	Day	11% 3 11% 27% 32% 16%	490
	21st to end	Day	9% 3 11% 32% 33% 12%	490
October	1st to 10th	Day	8% 5% 19% 39% 22% 7%	404
	11th to 20th	Day	6% 6% 26% 34% 21% 6%	300
	21st to end	Day	16% 10% 20% 35% 15% 3	330
November	1st to 10th	Day	14% 8% 26% 36% 15% 2	300
	11th to 20th	Day	16% 16% 29% 27% 11% 1	300
	21st to end	Day	14% 16% 38% 22% 8% 2	300
December	1st to 10th	Day	20% 10% 37% 21% 10% 2	294
	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% 17% 51% 21%	555
	11th to 20th	Night	5% 1 3 14% 47% 30%	552
	21st to end	Night	5% 1 4 17% 52% 22%	624
August	1st to 10th	Night	5% 3 16% 50% 27%	567
	11th to 20th	Night	5% 1 3 14% 48% 30%	564
	21st to end	Night	9% 1 6% 20% 42% 21%	627
September	1st to 10th	Night	11% 1 6% 21% 43% 18%	570
	11th to 20th	Night	11% 3 7% 25% 44% 10%	605
	21st to end	Night	10% 2 10% 30% 41% 7%	760
October	1st to 10th	Night	8% 2 17% 37% 31% 5%	760
	11th to 20th	Night	7% 5% 20% 41% 24% 3	760
	21st to end	Night	13% 6% 20% 36% 22% 3	836
November	1st to 10th	Night	14% 6% 17% 41% 20% 2	780
	11th to 20th	Night	15% 8% 27% 35% 15% 1	800
	21st to end	Night	15% 9% 27% 34% 15% 1	800
December	1st to 10th	Night	17% 11% 28% 29% 14% 1	795
	11th to 20th	Night	18% 8% 32% 31% 9% 1	760
	21st to end	Night	26% 11% 28% 27% 7%	869

Page generated at 2024-12-06 02:54:50. Version ac07

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