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 2026-09-29.

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 3 1 4 3 3 4 4 6% 8% 59%	157693
	Night	4 4 2 4 3 3 3 3 5% 7% 61%	151303
Transparency	Day	20% 6% 11% 24% 25% 14%	152675
	Night	21% 6% 12% 25% 25% 10%	147331
Seeing	Day	7% 12% 35% 31% 13% 3	18100
	Night	6% 7% 40% 35% 11% 1	28030

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 5% 3 3 3 3 4 6% 64%	4720
	11th to 20th	Day	2 2 5% 4 4 2 2 3 6% 68%	5118
	21st to end	Day	1 5% 3 7% 2 3 3 2 4 6% 64%	5844
February	1st to 10th	Day	2 6% 2 4 3 3 3 2 5% 6% 63%	1890
	11th to 20th	Day	1 4 2 4 3 3 3 4 6% 8% 63%	2049
	21st to end	Day	2 5% 3 5% 3 3 3 3 4 6% 65%	1730
March	1st to 10th	Day	1 5% 1 4 3 3 4 3 4 7% 65%	4600
	11th to 20th	Day	4 6% 2 8% 4 4 4 4 6% 7% 51%	5105
	21st to end	Day	2 4 1 4 3 3 4 4 7% 10% 58%	5917
April	1st to 10th	Day	3 4 1 4 4 3 4 3 7% 8% 59%	2520
	11th to 20th	Day	5% 7% 2 5% 3 3 4 3 6% 7% 55%	2491
	21st to end	Day	7% 5% 1 4 3 4 5% 4 6% 8% 53%	2520
May	1st to 10th	Day	11% 6% 1 4 3 3 4 4 6% 8% 49%	7253
	11th to 20th	Day	5% 4 2 4 3 3 4 4 7% 10% 53%	8036
	21st to end	Day	5% 4 2 4 3 4 5% 4 7% 9% 52%	9026
June	1st to 10th	Day	5% 3 1 3 4 4 5% 5% 8% 10% 53%	2940
	11th to 20th	Day	4 2 1 3 2 4 4 4 7% 7% 62%	2940
	21st to end	Day	3 2 1 4 3 4 5% 5% 7% 10% 56%	2940
July	1st to 10th	Day	2 1 1 2 2 3 4 4 7% 9% 65%	8249
	11th to 20th	Day	2 1 1 3 3 4 5% 5% 8% 10% 59%	8250
	21st to end	Day	2 2 1 5% 4 6% 6% 5% 9% 11% 48%	8526
August	1st to 10th	Day	3 3 1 5% 4 4 6% 5% 9% 11% 51%	7461
	11th to 20th	Day	2 1 1 3 3 4 5% 5% 9% 12% 54%	7003
	21st to end	Day	3 3 2 5% 4 5% 6% 5% 8% 11% 48%	7751
September	1st to 10th	Day	5% 3 1 3 3 3 4 4 6% 8% 61%	2520
	11th to 20th	Day	4 2 1 3 3 3 5% 3 7% 7% 63%	2502
	21st to end	Day	6% 3 1 3 2 3 4 3 3 5% 67%	2288
October	1st to 10th	Day	4 2 1 2 2 2 2 2 3 4 77%	3282
	11th to 20th	Day	3 2 1 3 2 3 4 3 6% 7% 65%	3250
	21st to end	Day	3 3 1 2 1 2 2 2 3 6% 76%	3494
November	1st to 10th	Day	2 4 1 2 2 2 2 3 4 7% 72%	1853
	11th to 20th	Day	1 4 1 3 2 2 2 2 4 7% 72%	1890
	21st to end	Day	2 5% 1 3 2 2 2 3 5% 6% 67%	1837
December	1st to 10th	Day	1 5% 1 3 2 2 2 2 3 5% 74%	2700
	11th to 20th	Day	1 3 1 2 2 2 2 3 5% 8% 71%	3106
	21st to end	Day	1 3 2 4 3 3 4 3 5% 8% 64%	4092
January	1st to 10th	Night	1 6% 3 6% 3 3 3 3 4 7% 61%	8201
	11th to 20th	Night	1 3 1 5% 4 3 2 3 4 6% 69%	7916
	21st to end	Night	1 4 3 6% 3 3 3 3 4 5% 66%	8370
February	1st to 10th	Night	2 6% 2 5% 3 2 2 2 4 7% 65%	2727
	11th to 20th	Night	2 7% 2 5% 2 3 4 4 4 7% 59%	2458
	21st to end	Night	2 6% 2 4 2 2 2 2 3 6% 67%	2076
March	1st to 10th	Night	3 7% 2 4 2 2 3 2 4 6% 66%	5494
	11th to 20th	Night	6% 7% 1 4 3 3 3 2 4 6% 61%	5112
	21st to end	Night	2 6% 2 5% 3 3 3 3 4 6% 64%	5284
April	1st to 10th	Night	3 5% 1 3 3 3 3 3 5% 7% 65%	2100
	11th to 20th	Night	8% 7% 2 4 2 2 3 2 4 6% 59%	2077
	21st to end	Night	10% 6% 1 3 3 2 3 2 5% 7% 57%	2100
May	1st to 10th	Night	14% 6% 2 4 3 3 3 3 4 7% 52%	5694
	11th to 20th	Night	10% 4 1 3 2 2 3 3 5% 8% 58%	4840
	21st to end	Night	13% 6% 2 5% 3 3 3 3 4 6% 53%	5181
June	1st to 10th	Night	6% 3 1 2 3 3 4 3 6% 9% 60%	1680
	11th to 20th	Night	5% 2 3 2 3 3 3 6% 7% 67%	1680
	21st to end	Night	4 3 1 4 4 5% 4 4 7% 7% 57%	1680
July	1st to 10th	Night	4 2 1 4 3 4 4 4 7% 9% 59%	4740
	11th to 20th	Night	2 2 1 4 4 4 5% 5% 8% 11% 54%	4740
	21st to end	Night	3 3 1 6% 5% 6% 6% 6% 10% 11% 43%	5566
August	1st to 10th	Night	6% 3 1 4 4 4 5% 4 7% 9% 52%	5359
	11th to 20th	Night	4 2 1 5% 4 5% 6% 5% 9% 12% 48%	5853
	21st to end	Night	6% 4 2 6% 4 5% 6% 6% 9% 12% 40%	6465
September	1st to 10th	Night	5% 4 2 4 4 3 5% 4 6% 8% 55%	2100
	11th to 20th	Night	8% 3 1 2 2 2 3 3 6% 7% 63%	2117
	21st to end	Night	7% 3 1 3 3 3 3 3 5% 6% 64%	2288
October	1st to 10th	Night	4 3 1 3 2 2 2 2 3 5% 74%	3904
	11th to 20th	Night	5% 3 1 4 3 3 4 3 5% 7% 62%	3898
	21st to end	Night	3 3 1 2 2 2 2 2 3 6% 74%	4272
November	1st to 10th	Night	2 4 1 3 2 2 2 2 4 7% 73%	2665
	11th to 20th	Night	1 4 2 3 2 1 2 3 4 6% 74%	2730
	21st to end	Night	4 5% 2 3 2 2 2 2 4 7% 67%	2777
December	1st to 10th	Night	1 3 2 4 2 2 2 2 4 6% 74%	4710
	11th to 20th	Night	1 3 1 3 2 2 3 2 5% 8% 71%	5321
	21st to end	Night	2 5% 2 5% 3 3 4 4 5% 7% 61%	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	21% 3 7% 33% 29% 8%	4723
	11th to 20th	Day	18% 3 8% 25% 31% 14%	5118
	21st to end	Day	21% 4 7% 25% 30% 14%	5844
February	1st to 10th	Day	22% 3 11% 27% 26% 12%	1890
	11th to 20th	Day	19% 5% 10% 27% 31% 9%	2059
	21st to end	Day	21% 3 6% 20% 31% 18%	1730
March	1st to 10th	Day	18% 3 6% 17% 34% 22%	4600
	11th to 20th	Day	28% 6% 9% 22% 27% 9%	5105
	21st to end	Day	18% 5% 10% 38% 23% 6%	5917
April	1st to 10th	Day	20% 6% 11% 23% 26% 14%	2520
	11th to 20th	Day	27% 5% 9% 23% 21% 14%	2494
	21st to end	Day	26% 7% 11% 23% 23% 9%	2520
May	1st to 10th	Day	29% 6% 13% 28% 16% 8%	7253
	11th to 20th	Day	22% 7% 13% 20% 24% 13%	8040
	21st to end	Day	23% 8% 15% 23% 17% 15%	9027
June	1st to 10th	Day	22% 8% 16% 21% 21% 12%	2940
	11th to 20th	Day	18% 6% 10% 17% 26% 23%	2940
	21st to end	Day	20% 7% 11% 21% 23% 17%	2940
July	1st to 10th	Day	13% 6% 9% 16% 26% 29%	8181
	11th to 20th	Day	16% 8% 13% 25% 22% 16%	8175
	21st to end	Day	23% 9% 20% 21% 16% 10%	8338
August	1st to 10th	Day	23% 9% 17% 24% 18% 10%	5912
	11th to 20th	Day	19% 9% 22% 21% 18% 12%	5519
	21st to end	Day	22% 9% 19% 25% 20% 5%	6078
September	1st to 10th	Day	20% 5% 10% 24% 25% 16%	2520
	11th to 20th	Day	18% 6% 10% 18% 29% 19%	2502
	21st to end	Day	21% 3 6% 22% 32% 16%	2288
October	1st to 10th	Day	13% 3 6% 14% 37% 27%	3282
	11th to 20th	Day	15% 5% 8% 27% 31% 14%	3250
	21st to end	Day	12% 2 4 20% 44% 18%	3494
November	1st to 10th	Day	13% 3 7% 23% 38% 17%	1853
	11th to 20th	Day	14% 3 5% 30% 35% 12%	1890
	21st to end	Day	17% 4 8% 23% 32% 16%	1837
December	1st to 10th	Day	14% 3 8% 32% 33% 10%	2700
	11th to 20th	Day	11% 3 8% 32% 34% 12%	3104
	21st to end	Day	17% 4 9% 27% 31% 12%	4092
January	1st to 10th	Night	23% 3 6% 36% 27% 4	8202
	11th to 20th	Night	16% 4 11% 26% 28% 15%	7916
	21st to end	Night	19% 5% 11% 24% 29% 12%	8370
February	1st to 10th	Night	21% 3 9% 31% 27% 10%	2727
	11th to 20th	Night	24% 5% 9% 29% 25% 7%	2458
	21st to end	Night	20% 3 6% 26% 31% 15%	2076
March	1st to 10th	Night	20% 3 6% 18% 40% 13%	5494
	11th to 20th	Night	25% 4 9% 22% 31% 9%	5112
	21st to end	Night	21% 5% 10% 38% 22% 4	5284
April	1st to 10th	Night	19% 5% 11% 25% 26% 13%	2100
	11th to 20th	Night	26% 4 10% 24% 23% 13%	2077
	21st to end	Night	27% 5% 13% 24% 21% 9%	2100
May	1st to 10th	Night	31% 6% 14% 28% 12% 8%	5692
	11th to 20th	Night	22% 7% 15% 26% 17% 12%	4841
	21st to end	Night	30% 7% 15% 18% 17% 13%	5182
June	1st to 10th	Night	19% 8% 19% 25% 15% 13%	1680
	11th to 20th	Night	16% 6% 11% 23% 22% 23%	1680
	21st to end	Night	24% 7% 13% 20% 20% 17%	1680
July	1st to 10th	Night	17% 8% 12% 20% 24% 18%	4700
	11th to 20th	Night	18% 10% 19% 26% 19% 9%	4692
	21st to end	Night	28% 13% 22% 16% 13% 9%	5443
August	1st to 10th	Night	27% 12% 20% 23% 13% 5%	4232
	11th to 20th	Night	25% 13% 28% 15% 13% 5%	4613
	21st to end	Night	24% 12% 28% 20% 13% 3	5069
September	1st to 10th	Night	25% 7% 12% 24% 22% 10%	2100
	11th to 20th	Night	19% 5% 12% 21% 26% 16%	2117
	21st to end	Night	21% 4 8% 23% 31% 12%	2288
October	1st to 10th	Night	14% 5% 8% 22% 32% 20%	3904
	11th to 20th	Night	19% 6% 10% 26% 26% 12%	3898
	21st to end	Night	14% 3 6% 25% 38% 15%	4272
November	1st to 10th	Night	13% 3 8% 29% 33% 14%	2665
	11th to 20th	Night	14% 3 6% 31% 35% 11%	2730
	21st to end	Night	19% 3 8% 25% 33% 12%	2777
December	1st to 10th	Night	14% 3 7% 38% 30% 8%	4710
	11th to 20th	Night	13% 3 8% 29% 40% 7%	5322
	21st to end	Night	20% 5% 10% 26% 31% 8%	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	9% 18% 40% 26% 6% 2	330
	11th to 20th	Day	6% 18% 45% 27% 2 1	330
	21st to end	Day	4 14% 50% 23% 7% 1	363
February	1st to 10th	Day	6% 22% 49% 17% 5% 1	330
	11th to 20th	Day	5% 20% 50% 20% 4 1	330
	21st to end	Day	7% 23% 47% 21% 3	273
March	1st to 10th	Day	2 21% 49% 22% 5%	330
	11th to 20th	Day	9% 24% 37% 23% 6% 1	535
	21st to end	Day	9% 24% 43% 20% 4	594
April	1st to 10th	Day	8% 22% 41% 22% 6%	540
	11th to 20th	Day	10% 29% 37% 21% 3 1	532
	21st to end	Day	13% 19% 41% 21% 7% 1	540
May	1st to 10th	Day	15% 14% 38% 24% 8% 1	611
	11th to 20th	Day	11% 9% 32% 33% 12% 2	775
	21st to end	Day	8% 10% 32% 35% 13% 1	844
June	1st to 10th	Day	6% 8% 29% 38% 18% 2	780
	11th to 20th	Day	4 9% 34% 35% 15% 2	780
	21st to end	Day	4 9% 33% 35% 15% 3	780
July	1st to 10th	Day	6% 6% 23% 37% 23% 5%	771
	11th to 20th	Day	4 2 19% 42% 27% 6%	768
	21st to end	Day	4 2 18% 39% 29% 8%	701
August	1st to 10th	Day	4 6% 22% 37% 25% 6%	567
	11th to 20th	Day	4 2 26% 38% 24% 6%	557
	21st to end	Day	5% 4 26% 39% 22% 4	627
September	1st to 10th	Day	5% 4 28% 40% 19% 4	570
	11th to 20th	Day	5% 7% 35% 35% 15% 3	552
	21st to end	Day	9% 6% 27% 34% 20% 4	354
October	1st to 10th	Day	8% 8% 32% 28% 19% 5%	330
	11th to 20th	Day	5% 13% 38% 29% 12% 2	330
	21st to end	Day	7% 13% 37% 31% 9% 3	363
November	1st to 10th	Day	5% 11% 44% 27% 13% 1	330
	11th to 20th	Day	5% 12% 50% 23% 8% 2	330
	21st to end	Day	7% 14% 42% 28% 8% 1	330
December	1st to 10th	Day	4 20% 43% 25% 7% 1	330
	11th to 20th	Day	6% 20% 47% 20% 6% 1	330
	21st to end	Day	4 23% 46% 23% 4 1	363
January	1st to 10th	Night	4 14% 46% 30% 6%	1050
	11th to 20th	Night	3 12% 56% 22% 7%	937
	21st to end	Night	3 8% 57% 27% 5%	924
February	1st to 10th	Night	4 9% 62% 22% 2	840
	11th to 20th	Night	5% 11% 57% 24% 3	824
	21st to end	Night	5% 13% 59% 21% 2	692
March	1st to 10th	Night	4 9% 56% 26% 4	840
	11th to 20th	Night	8% 9% 42% 34% 7%	840
	21st to end	Night	6% 11% 46% 32% 4	779
April	1st to 10th	Night	5% 10% 49% 32% 3	630
	11th to 20th	Night	12% 9% 41% 32% 6%	623
	21st to end	Night	13% 9% 38% 33% 7%	630
May	1st to 10th	Night	12% 8% 33% 38% 9%	630
	11th to 20th	Night	14% 4 27% 42% 13% 1	621
	21st to end	Night	10% 6% 31% 39% 14% 1	683
June	1st to 10th	Night	7% 4 26% 45% 17% 1	630
	11th to 20th	Night	5% 4 29% 48% 14%	630
	21st to end	Night	5% 3 25% 48% 19%	630
July	1st to 10th	Night	8% 3 17% 42% 29% 2	615
	11th to 20th	Night	4 2 8% 52% 31% 3	612
	21st to end	Night	7% 2 8% 46% 35% 3	690
August	1st to 10th	Night	6% 2 13% 44% 34%	627
	11th to 20th	Night	6% 2 14% 51% 26% 1	624
	21st to end	Night	6% 2 14% 49% 28% 1	693
September	1st to 10th	Night	6% 3 16% 52% 22% 2	630
	11th to 20th	Night	9% 2 25% 42% 20% 2	630
	21st to end	Night	9% 3 26% 46% 15% 1	624
October	1st to 10th	Night	9% 4 35% 41% 10% 1	784
	11th to 20th	Night	4 4 43% 38% 10% 1	800
	21st to end	Night	6% 7% 43% 34% 10%	888
November	1st to 10th	Night	3 6% 49% 34% 8%	1025
	11th to 20th	Night	3 10% 50% 30% 6%	1050
	21st to end	Night	6% 9% 47% 33% 4	1050
December	1st to 10th	Night	2 10% 51% 33% 4	1050
	11th to 20th	Night	4 10% 55% 24% 6%	1050
	21st to end	Night	4 11% 57% 25% 3	1155

Page generated at 2026-09-26 02:18:44. Version ac07

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