Abraas Stargate Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Abraas Stargate Observatory clear sky chart from 2005-11-06 to 2025-05-11.

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	3 4 1 4 3 3 4 4 6% 8% 60%	117777
	Night	4 4 2 4 3 3 3 3 5% 7% 62%	120063
Transparency	Day	20% 6% 11% 24% 26% 14%	117526
	Night	21% 5% 11% 26% 27% 11%	119905
Seeing	Day	7% 12% 34% 31% 14% 3	16105
	Night	6% 7% 39% 36% 12% 1	26264

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	1 5% 3 4 3 3 3 2 4 7% 65%	3638
	11th to 20th	Day	1 3 2 6% 5% 5% 3 3 4 7% 62%	3934
	21st to end	Day	2 5% 3 6% 2 3 3 2 4 6% 65%	4510
February	1st to 10th	Day	3 6% 2 4 3 3 3 2 5% 6% 63%	1800
	11th to 20th	Day	1 4 2 4 3 3 3 4 6% 8% 63%	1949
	21st to end	Day	2 5% 3 5% 3 3 3 3 4 6% 63%	1650
March	1st to 10th	Day	1 5% 1 4 3 3 4 3 4 7% 65%	4500
	11th to 20th	Day	4 6% 3 8% 4 4 4 4 6% 7% 51%	4995
	21st to end	Day	2 4 1 4 3 3 4 4 7% 10% 59%	5789
April	1st to 10th	Day	3 4 1 4 4 3 4 4 7% 8% 59%	2400
	11th to 20th	Day	5% 7% 2 5% 3 4 4 3 6% 7% 53%	2371
	21st to end	Day	7% 5% 1 4 3 4 5% 4 6% 8% 53%	2400
May	1st to 10th	Day	7% 6% 1 4 4 3 4 4 6% 8% 52%	4037
	11th to 20th	Day	7% 5% 2 4 3 3 5% 5% 8% 10% 47%	4310
	21st to end	Day	4 2 1 3 3 4 5% 4 7% 9% 56%	4825
June	1st to 10th	Day	5% 3 1 3 3 4 5% 5% 8% 11% 53%	2660
	11th to 20th	Day	4 2 1 3 2 4 4 5% 7% 7% 61%	2660
	21st to end	Day	3 3 1 4 4 5% 5% 6% 7% 10% 53%	2660
July	1st to 10th	Day	4 2 1 3 3 4 5% 4 7% 9% 58%	4430
	11th to 20th	Day	3 2 1 4 4 5% 6% 6% 9% 11% 50%	4430
	21st to end	Day	3 3 1 5% 3 5% 5% 4 8% 9% 54%	4567
August	1st to 10th	Day	4 4 2 6% 5% 5% 6% 5% 9% 11% 43%	4041
	11th to 20th	Day	3 2 1 3 3 4 5% 5% 9% 11% 55%	3726
	21st to end	Day	3 3 2 4 4 5% 6% 5% 8% 10% 51%	4180
September	1st to 10th	Day	5% 3 1 3 3 3 4 4 6% 8% 60%	2280
	11th to 20th	Day	5% 2 1 3 3 2 4 3 6% 6% 65%	2264
	21st to end	Day	6% 2 1 3 2 3 3 2 3 5% 69%	2090
October	1st to 10th	Day	4 2 1 2 2 2 2 2 3 5% 77%	3182
	11th to 20th	Day	3 2 1 3 2 3 4 3 6% 7% 65%	3150
	21st to end	Day	3 3 1 2 1 2 2 2 3 6% 76%	3386
November	1st to 10th	Day	2 4 1 2 2 1 2 3 4 7% 72%	1763
	11th to 20th	Day	1 4 1 3 1 2 3 2 4 7% 72%	1800
	21st to end	Day	2 5% 1 3 2 2 2 3 5% 6% 68%	1750
December	1st to 10th	Day	1 5% 1 3 2 2 2 2 3 5% 74%	2620
	11th to 20th	Day	1 3 1 2 2 2 2 3 5% 8% 71%	3026
	21st to end	Day	1 3 2 4 3 3 4 3 5% 8% 64%	4004
January	1st to 10th	Night	1 6% 3 6% 3 3 3 3 4 7% 60%	6327
	11th to 20th	Night	1 4 2 6% 4 3 3 3 5% 7% 64%	6090
	21st to end	Night	1 4 3 5% 3 3 3 3 4 6% 65%	6468
February	1st to 10th	Night	2 7% 3 5% 3 2 2 2 4 7% 64%	2597
	11th to 20th	Night	3 7% 2 5% 2 3 4 4 5% 7% 59%	2338
	21st to end	Night	2 6% 2 4 3 2 2 2 3 6% 67%	1980
March	1st to 10th	Night	3 7% 2 4 2 2 3 2 4 6% 66%	5374
	11th to 20th	Night	6% 7% 1 4 3 3 3 2 4 6% 61%	5002
	21st to end	Night	3 6% 2 5% 3 3 3 3 4 6% 63%	5170
April	1st to 10th	Night	3 5% 2 3 3 3 3 3 5% 6% 65%	2000
	11th to 20th	Night	8% 8% 2 4 2 2 3 2 4 6% 58%	1977
	21st to end	Night	10% 6% 1 4 3 2 3 2 5% 7% 57%	2000
May	1st to 10th	Night	11% 6% 2 4 2 2 3 3 4 6% 58%	3153
	11th to 20th	Night	14% 5% 1 3 3 2 3 3 6% 8% 52%	2598
	21st to end	Night	8% 3 1 3 2 2 3 3 5% 7% 62%	2762
June	1st to 10th	Night	6% 2 1 2 3 3 3 3 7% 9% 62%	1520
	11th to 20th	Night	5% 2 2 2 3 3 3 6% 8% 66%	1520
	21st to end	Night	5% 3 1 4 4 5% 4 4 7% 7% 56%	1520
July	1st to 10th	Night	6% 3 1 5% 3 4 4 4 7% 9% 53%	2540
	11th to 20th	Night	3 2 1 4 3 4 5% 5% 9% 14% 50%	2540
	21st to end	Night	5% 3 1 4 3 3 4 4 8% 10% 54%	2979
August	1st to 10th	Night	8% 4 2 6% 6% 6% 6% 5% 8% 10% 38%	2896
	11th to 20th	Night	4 2 1 4 4 5% 6% 5% 9% 12% 48%	3113
	21st to end	Night	4 4 1 5% 4 5% 5% 5% 8% 11% 47%	3487
September	1st to 10th	Night	5% 3 2 4 4 3 5% 4 7% 8% 54%	1900
	11th to 20th	Night	8% 3 1 2 2 1 3 3 5% 7% 65%	1915
	21st to end	Night	6% 3 1 3 2 3 3 3 4 5% 67%	2090
October	1st to 10th	Night	4 3 1 3 2 2 2 2 3 5% 74%	3785
	11th to 20th	Night	6% 4 1 4 2 3 4 3 5% 7% 62%	3778
	21st to end	Night	3 3 1 2 2 2 2 2 3 6% 74%	4139
November	1st to 10th	Night	2 4 1 3 2 2 2 2 4 7% 72%	2535
	11th to 20th	Night	1 4 2 3 2 1 1 2 4 5% 74%	2600
	21st to end	Night	4 5% 1 3 2 2 2 2 4 7% 68%	2645
December	1st to 10th	Night	3 2 4 2 2 2 2 4 6% 75%	4570
	11th to 20th	Night	1 3 1 3 2 2 3 2 5% 8% 71%	5181
	21st to end	Night	2 5% 2 5% 3 3 4 4 5% 7% 60%	6974

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	20% 3 7% 33% 27% 10%	3639
	11th to 20th	Day	22% 4 8% 22% 28% 15%	3934
	21st to end	Day	21% 4 7% 28% 30% 11%	4510
February	1st to 10th	Day	22% 3 11% 27% 24% 12%	1800
	11th to 20th	Day	19% 5% 11% 27% 31% 8%	1959
	21st to end	Day	22% 3 6% 20% 30% 18%	1650
March	1st to 10th	Day	18% 3 6% 17% 34% 22%	4500
	11th to 20th	Day	28% 6% 9% 22% 27% 9%	4995
	21st to end	Day	18% 5% 10% 38% 23% 5%	5789
April	1st to 10th	Day	20% 6% 12% 23% 25% 14%	2400
	11th to 20th	Day	28% 5% 9% 23% 19% 14%	2374
	21st to end	Day	26% 7% 12% 24% 23% 8%	2400
May	1st to 10th	Day	26% 6% 12% 22% 18% 15%	4037
	11th to 20th	Day	27% 9% 16% 22% 18% 7%	4314
	21st to end	Day	19% 7% 15% 21% 20% 18%	4825
June	1st to 10th	Day	21% 8% 16% 22% 20% 12%	2660
	11th to 20th	Day	18% 6% 11% 16% 25% 23%	2660
	21st to end	Day	22% 7% 11% 22% 23% 15%	2660
July	1st to 10th	Day	19% 7% 12% 18% 26% 18%	4361
	11th to 20th	Day	20% 9% 15% 27% 19% 9%	4355
	21st to end	Day	24% 6% 15% 21% 18% 16%	4423
August	1st to 10th	Day	30% 10% 20% 24% 12% 5%	4027
	11th to 20th	Day	19% 9% 16% 18% 21% 16%	3762
	21st to end	Day	23% 8% 15% 21% 27% 7%	4179
September	1st to 10th	Day	21% 5% 10% 23% 24% 17%	2280
	11th to 20th	Day	19% 5% 9% 18% 29% 20%	2264
	21st to end	Day	20% 3 5% 21% 34% 18%	2090
October	1st to 10th	Day	13% 3 6% 14% 36% 27%	3182
	11th to 20th	Day	15% 5% 8% 27% 31% 13%	3150
	21st to end	Day	12% 2 4 20% 43% 19%	3386
November	1st to 10th	Day	13% 3 7% 22% 37% 17%	1763
	11th to 20th	Day	14% 4 5% 30% 35% 13%	1800
	21st to end	Day	17% 4 7% 22% 33% 17%	1750
December	1st to 10th	Day	14% 3 8% 32% 33% 10%	2620
	11th to 20th	Day	12% 3 8% 33% 33% 11%	3024
	21st to end	Day	17% 4 9% 27% 31% 11%	4004
January	1st to 10th	Night	24% 3 7% 34% 27% 5%	6327
	11th to 20th	Night	20% 4 9% 24% 28% 16%	6090
	21st to end	Night	19% 5% 11% 27% 26% 11%	6468
February	1st to 10th	Night	22% 3 9% 31% 25% 10%	2597
	11th to 20th	Night	25% 5% 8% 30% 26% 6%	2338
	21st to end	Night	21% 3 6% 25% 30% 15%	1980
March	1st to 10th	Night	20% 3 6% 18% 40% 13%	5374
	11th to 20th	Night	26% 4 9% 21% 32% 9%	5002
	21st to end	Night	21% 5% 10% 39% 22% 3	5170
April	1st to 10th	Night	20% 5% 11% 25% 27% 13%	2000
	11th to 20th	Night	27% 4 10% 25% 21% 13%	1977
	21st to end	Night	27% 5% 14% 25% 21% 8%	2000
May	1st to 10th	Night	26% 6% 12% 23% 20% 14%	3153
	11th to 20th	Night	30% 8% 18% 25% 9% 11%	2599
	21st to end	Night	20% 7% 15% 19% 25% 14%	2762
June	1st to 10th	Night	19% 8% 19% 25% 15% 14%	1520
	11th to 20th	Night	16% 6% 12% 22% 22% 22%	1520
	21st to end	Night	24% 7% 13% 20% 20% 15%	1520
July	1st to 10th	Night	24% 9% 12% 21% 21% 13%	2500
	11th to 20th	Night	19% 9% 21% 33% 13% 5%	2492
	21st to end	Night	22% 10% 19% 22% 13% 13%	2886
August	1st to 10th	Night	36% 12% 22% 16% 8% 6%	2887
	11th to 20th	Night	24% 11% 22% 17% 18% 8%	3143
	21st to end	Night	25% 11% 18% 24% 19% 4	3487
September	1st to 10th	Night	25% 7% 12% 24% 21% 11%	1900
	11th to 20th	Night	19% 5% 11% 20% 28% 18%	1915
	21st to end	Night	19% 4 8% 23% 33% 13%	2090
October	1st to 10th	Night	14% 5% 8% 22% 31% 20%	3785
	11th to 20th	Night	19% 6% 10% 26% 27% 12%	3778
	21st to end	Night	14% 3 6% 25% 37% 15%	4139
November	1st to 10th	Night	14% 3 8% 28% 32% 14%	2535
	11th to 20th	Night	14% 3 6% 30% 35% 12%	2600
	21st to end	Night	18% 3 8% 25% 34% 12%	2645
December	1st to 10th	Night	13% 3 8% 38% 31% 8%	4570
	11th to 20th	Night	13% 3 8% 29% 40% 6%	5182
	21st to end	Night	21% 5% 10% 26% 30% 8%	6974

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	8% 15% 41% 28% 6% 2	300
	11th to 20th	Day	7% 17% 45% 28% 2 1	300
	21st to end	Day	5% 12% 49% 25% 7% 2	330
February	1st to 10th	Day	6% 24% 48% 17% 4 1	300
	11th to 20th	Day	4 19% 51% 21% 4 1	300
	21st to end	Day	5% 24% 46% 22% 3	249
March	1st to 10th	Day	2 22% 47% 24% 6%	300
	11th to 20th	Day	9% 21% 38% 25% 6% 1	495
	21st to end	Day	9% 25% 41% 21% 4	550
April	1st to 10th	Day	9% 23% 40% 22% 6%	500
	11th to 20th	Day	10% 28% 37% 22% 3 1	492
	21st to end	Day	12% 17% 41% 22% 7% 1	500
May	1st to 10th	Day	15% 14% 37% 25% 8% 1	568
	11th to 20th	Day	12% 7% 31% 36% 12% 3	676
	21st to end	Day	7% 10% 32% 36% 14% 1	734
June	1st to 10th	Day	5% 7% 27% 39% 19% 3	680
	11th to 20th	Day	5% 7% 33% 37% 16% 3	680
	21st to end	Day	4 7% 32% 37% 17% 3	680
July	1st to 10th	Day	7% 5% 20% 36% 26% 6%	671
	11th to 20th	Day	4 1 18% 41% 29% 6%	668
	21st to end	Day	4 2 17% 37% 31% 9%	605
August	1st to 10th	Day	5% 6% 20% 37% 26% 6%	487
	11th to 20th	Day	5% 2 27% 36% 24% 6%	477
	21st to end	Day	6% 3 25% 39% 23% 5%	539
September	1st to 10th	Day	5% 4 24% 41% 22% 4	490
	11th to 20th	Day	5% 7% 32% 35% 17% 3	474
	21st to end	Day	9% 6% 25% 33% 22% 5%	300
October	1st to 10th	Day	8% 7% 29% 30% 21% 6%	300
	11th to 20th	Day	4 12% 36% 32% 14% 3	300
	21st to end	Day	8% 12% 35% 32% 9% 3	330
November	1st to 10th	Day	5% 11% 42% 28% 14% 1	300
	11th to 20th	Day	5% 13% 48% 24% 8% 2	300
	21st to end	Day	7% 13% 42% 28% 8% 1	300
December	1st to 10th	Day	3 19% 42% 27% 8% 1	300
	11th to 20th	Day	5% 18% 48% 22% 6% 1	300
	21st to end	Day	4 22% 44% 25% 4 1	330
January	1st to 10th	Night	4 12% 46% 31% 6% 1	1000
	11th to 20th	Night	3 12% 56% 22% 7%	893
	21st to end	Night	3 8% 57% 27% 5%	880
February	1st to 10th	Night	4 9% 61% 23% 2	800
	11th to 20th	Night	5% 9% 57% 26% 3	784
	21st to end	Night	6% 12% 59% 21% 2	660
March	1st to 10th	Night	4 9% 56% 27% 5%	800
	11th to 20th	Night	8% 8% 41% 36% 7%	800
	21st to end	Night	6% 11% 45% 33% 5%	742
April	1st to 10th	Night	5% 10% 48% 33% 4	600
	11th to 20th	Night	13% 9% 39% 33% 6%	593
	21st to end	Night	13% 8% 37% 34% 7% 1	600
May	1st to 10th	Night	12% 7% 33% 38% 10%	600
	11th to 20th	Night	14% 4 24% 43% 14% 1	563
	21st to end	Night	9% 6% 30% 39% 15% 1	617
June	1st to 10th	Night	6% 4 24% 46% 19% 1	570
	11th to 20th	Night	5% 3 28% 49% 15%	570
	21st to end	Night	5% 3 21% 50% 21%	570
July	1st to 10th	Night	8% 3 15% 40% 32% 2	555
	11th to 20th	Night	4 1 8% 51% 32% 3	552
	21st to end	Night	7% 2 7% 44% 38% 3	624
August	1st to 10th	Night	7% 2 12% 42% 37%	567
	11th to 20th	Night	6% 2 14% 50% 27% 1	564
	21st to end	Night	5% 2 13% 50% 28% 1	627
September	1st to 10th	Night	6% 2 14% 52% 24% 2	570
	11th to 20th	Night	10% 2 24% 41% 22% 2	570
	21st to end	Night	8% 3 25% 47% 16% 1	570
October	1st to 10th	Night	8% 3 34% 42% 11% 1	745
	11th to 20th	Night	3 4 41% 39% 11% 1	760
	21st to end	Night	6% 7% 41% 35% 10%	843
November	1st to 10th	Night	4 6% 47% 35% 8%	975
	11th to 20th	Night	3 10% 49% 31% 7%	1000
	21st to end	Night	6% 9% 47% 34% 5%	1000
December	1st to 10th	Night	2 9% 51% 34% 5%	1000
	11th to 20th	Night	4 10% 56% 24% 7%	1000
	21st to end	Night	4 11% 56% 26% 3	1100

Page generated at 2025-05-08 07:33:57. Version ac07

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