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 2024-03-01.

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	4 4 2 3 4 2 4 5% 6% 8% 59%	78597
	Night	4 4 2 3 3 2 3 4 5% 8% 62%	80875
Transparency	Day	22% 6% 11% 24% 25% 12%	78309
	Night	22% 5% 12% 26% 26% 10%	80686
Seeing	Day	7% 11% 33% 31% 15% 3	14461
	Night	6% 7% 39% 36% 12% 1	24681

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	2 4 2 3 3 2 3 3 5% 7% 66%	2538
	11th to 20th	Day	1 3 2 5% 5% 4 3 4 4 8% 62%	2736
	21st to end	Day	2 6% 2 4 3 2 3 4 4 7% 61%	3146
February	1st to 10th	Day	3 6% 3 3 4 2 3 3 5% 6% 63%	1710
	11th to 20th	Day	1 3 2 3 3 2 3 4 6% 8% 64%	1849
	21st to end	Day	2 5% 3 5% 4 2 3 4 4 7% 62%	1570
March	1st to 10th	Day	2 4 2 4 4 2 3 4 5% 8% 63%	1800
	11th to 20th	Day	4 5% 2 4 4 2 4 4 6% 9% 55%	1975
	21st to end	Day	3 5% 2 3 3 3 3 5% 7% 9% 56%	2300
April	1st to 10th	Day	4 3 1 3 4 2 4 4 6% 9% 59%	2160
	11th to 20th	Day	6% 6% 2 4 4 3 4 4 6% 8% 53%	2131
	21st to end	Day	7% 5% 2 4 4 3 5% 6% 6% 8% 53%	2160
May	1st to 10th	Day	8% 5% 1 4 4 3 4 6% 7% 8% 50%	2218
	11th to 20th	Day	9% 5% 2 4 5% 3 5% 6% 8% 10% 44%	2425
	21st to end	Day	6% 3 1 3 4 2 5% 5% 6% 8% 55%	2724
June	1st to 10th	Day	5% 2 1 2 4 2 5% 6% 8% 11% 54%	2520
	11th to 20th	Day	4 2 1 3 3 2 5% 6% 7% 7% 61%	2520
	21st to end	Day	3 2 1 3 4 3 6% 6% 7% 10% 54%	2520
July	1st to 10th	Day	7% 2 1 3 4 3 5% 6% 8% 9% 52%	2520
	11th to 20th	Day	3 2 1 3 5% 4 5% 6% 9% 11% 53%	2520
	21st to end	Day	4 3 2 6% 6% 4 7% 7% 9% 11% 41%	2616
August	1st to 10th	Day	4 2 1 5% 5% 4 7% 7% 9% 11% 45%	2303
	11th to 20th	Day	5% 2 1 3 3 3 4 6% 8% 10% 55%	2123
	21st to end	Day	4 3 1 3 4 3 5% 5% 7% 9% 57%	2376
September	1st to 10th	Day	5% 3 1 3 3 3 3 5% 6% 8% 59%	2160
	11th to 20th	Day	5% 2 1 2 3 2 3 4 6% 6% 64%	2145
	21st to end	Day	6% 2 1 3 3 2 3 3 3 5% 69%	1980
October	1st to 10th	Day	6% 3 1 3 3 2 2 4 5% 7% 63%	1812
	11th to 20th	Day	2 2 1 2 2 1 3 2 4 6% 74%	1800
	21st to end	Day	5% 5% 1 3 2 1 2 3 4 5% 68%	1954
November	1st to 10th	Day	1 3 1 2 2 1 2 3 5% 7% 74%	1673
	11th to 20th	Day	1 4 1 3 2 2 2 2 4 7% 71%	1710
	21st to end	Day	2 4 2 3 2 2 3 3 5% 6% 68%	1663
December	1st to 10th	Day	1 4 2 3 3 2 3 3 4 7% 68%	1520
	11th to 20th	Day	2 5% 1 3 3 1 2 3 6% 10% 65%	1926
	21st to end	Day	1 3 3 3 4 2 4 4 5% 8% 62%	2794
January	1st to 10th	Night	2 6% 2 5% 4 3 3 3 4 8% 61%	4417
	11th to 20th	Night	1 3 2 4 5% 2 2 4 5% 8% 65%	4264
	21st to end	Night	2 5% 3 4 4 3 3 4 5% 7% 61%	4521
February	1st to 10th	Night	2 7% 3 5% 4 2 2 3 4 7% 64%	2468
	11th to 20th	Night	3 6% 3 5% 3 2 3 4 4 7% 60%	2218
	21st to end	Night	2 6% 2 4 3 1 3 3 3 6% 67%	1884
March	1st to 10th	Night	2 5% 2 3 3 1 3 3 4 6% 67%	2166
	11th to 20th	Night	5% 6% 2 3 2 2 3 3 4 7% 63%	1982
	21st to end	Night	4 6% 2 3 3 2 3 3 4 6% 64%	2054
April	1st to 10th	Night	3 5% 2 3 3 2 3 3 4 6% 66%	1800
	11th to 20th	Night	8% 7% 2 3 3 2 3 3 4 6% 58%	1777
	21st to end	Night	9% 5% 1 3 4 2 3 3 5% 7% 58%	1800
May	1st to 10th	Night	11% 5% 2 3 3 2 4 4 5% 7% 55%	1742
	11th to 20th	Night	14% 6% 2 3 4 2 4 4 6% 8% 47%	1467
	21st to end	Night	9% 4 1 3 3 2 3 4 5% 8% 57%	1552
June	1st to 10th	Night	6% 2 1 2 3 2 3 3 6% 9% 63%	1440
	11th to 20th	Night	5% 2 2 2 2 3 4 6% 8% 66%	1440
	21st to end	Night	5% 2 2 3 4 3 5% 5% 6% 8% 58%	1440
July	1st to 10th	Night	9% 3 2 4 3 4 5% 6% 8% 10% 46%	1440
	11th to 20th	Night	4 2 1 4 4 3 4 5% 7% 10% 56%	1440
	21st to end	Night	7% 4 2 5% 4 3 6% 6% 9% 12% 42%	1699
August	1st to 10th	Night	5% 3 2 4 6% 4 6% 5% 7% 11% 46%	1634
	11th to 20th	Night	6% 2 1 4 4 3 5% 6% 8% 10% 51%	1778
	21st to end	Night	5% 3 1 4 4 2 4 6% 8% 9% 54%	1980
September	1st to 10th	Night	5% 3 2 4 5% 2 5% 5% 6% 9% 54%	1800
	11th to 20th	Night	9% 3 1 2 2 1 2 4 5% 7% 64%	1814
	21st to end	Night	6% 3 1 2 2 2 3 3 4 5% 67%	1980
October	1st to 10th	Night	7% 4 1 3 2 2 3 3 4 6% 65%	2145
	11th to 20th	Night	3 3 1 2 2 1 2 3 4 5% 74%	2160
	21st to end	Night	5% 5% 2 3 2 1 2 3 3 6% 67%	2382
November	1st to 10th	Night	2 3 1 2 2 1 2 2 4 7% 74%	2405
	11th to 20th	Night	1 4 2 3 2 1 2 2 3 6% 73%	2470
	21st to end	Night	4 5% 2 3 2 1 2 2 3 7% 68%	2512
December	1st to 10th	Night	1 4 2 5% 3 2 3 3 5% 7% 66%	2660
	11th to 20th	Night	2 4 2 3 3 2 3 4 6% 9% 62%	3271
	21st to end	Night	2 6% 2 4 4 2 4 4 5% 7% 60%	4873

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	18% 4 9% 34% 27% 8%	2539
	11th to 20th	Day	21% 5% 10% 31% 25% 8%	2736
	21st to end	Day	23% 4 8% 34% 26% 5%	3146
February	1st to 10th	Day	23% 3 11% 28% 23% 11%	1710
	11th to 20th	Day	19% 4 10% 27% 32% 9%	1859
	21st to end	Day	23% 3 7% 21% 29% 17%	1570
March	1st to 10th	Day	20% 4 9% 25% 31% 12%	1800
	11th to 20th	Day	24% 4 10% 26% 28% 8%	1975
	21st to end	Day	24% 5% 11% 26% 23% 11%	2300
April	1st to 10th	Day	21% 5% 12% 23% 25% 14%	2160
	11th to 20th	Day	29% 5% 9% 24% 19% 13%	2134
	21st to end	Day	27% 7% 12% 22% 24% 8%	2160
May	1st to 10th	Day	28% 7% 14% 23% 20% 7%	2218
	11th to 20th	Day	32% 10% 18% 19% 16% 5%	2429
	21st to end	Day	25% 8% 16% 22% 18% 12%	2724
June	1st to 10th	Day	21% 8% 17% 22% 20% 12%	2520
	11th to 20th	Day	19% 6% 11% 16% 25% 22%	2520
	21st to end	Day	22% 7% 11% 22% 23% 15%	2520
July	1st to 10th	Day	27% 8% 13% 18% 21% 14%	2451
	11th to 20th	Day	22% 7% 14% 28% 20% 9%	2445
	21st to end	Day	32% 9% 20% 22% 12% 4	2471
August	1st to 10th	Day	28% 10% 19% 19% 15% 9%	2288
	11th to 20th	Day	22% 7% 13% 21% 24% 13%	2123
	21st to end	Day	23% 6% 13% 23% 26% 9%	2376
September	1st to 10th	Day	22% 5% 10% 22% 23% 17%	2160
	11th to 20th	Day	19% 5% 9% 18% 28% 20%	2145
	21st to end	Day	20% 3 5% 21% 34% 17%	1980
October	1st to 10th	Day	21% 5% 10% 18% 31% 14%	1812
	11th to 20th	Day	14% 3 7% 19% 36% 21%	1800
	21st to end	Day	20% 2 6% 26% 28% 17%	1954
November	1st to 10th	Day	11% 3 7% 23% 37% 18%	1673
	11th to 20th	Day	15% 4 5% 31% 34% 12%	1710
	21st to end	Day	17% 4 7% 22% 32% 17%	1663
December	1st to 10th	Day	18% 4 12% 28% 29% 9%	1520
	11th to 20th	Day	16% 3 11% 27% 33% 10%	1924
	21st to end	Day	19% 5% 10% 25% 29% 12%	2794
January	1st to 10th	Night	24% 3 8% 32% 29% 3	4417
	11th to 20th	Night	18% 4 11% 29% 29% 8%	4264
	21st to end	Night	22% 6% 13% 33% 21% 4	4521
February	1st to 10th	Night	23% 3 9% 31% 25% 8%	2468
	11th to 20th	Night	24% 5% 8% 30% 27% 7%	2218
	21st to end	Night	21% 3 6% 26% 30% 14%	1884
March	1st to 10th	Night	19% 4 8% 27% 30% 11%	2166
	11th to 20th	Night	23% 3 12% 27% 28% 6%	1982
	21st to end	Night	22% 5% 11% 26% 31% 6%	2054
April	1st to 10th	Night	20% 5% 11% 25% 27% 13%	1800
	11th to 20th	Night	28% 4 10% 26% 20% 12%	1777
	21st to end	Night	27% 5% 14% 24% 22% 8%	1800
May	1st to 10th	Night	29% 6% 11% 25% 23% 7%	1742
	11th to 20th	Night	34% 9% 18% 18% 15% 7%	1468
	21st to end	Night	25% 8% 16% 20% 18% 13%	1552
June	1st to 10th	Night	19% 8% 19% 26% 15% 14%	1440
	11th to 20th	Night	16% 6% 12% 22% 22% 22%	1440
	21st to end	Night	24% 7% 13% 21% 20% 15%	1440
July	1st to 10th	Night	31% 11% 15% 18% 17% 8%	1400
	11th to 20th	Night	20% 9% 16% 30% 18% 7%	1392
	21st to end	Night	30% 15% 24% 20% 10% 1	1605
August	1st to 10th	Night	29% 12% 22% 18% 11% 7%	1625
	11th to 20th	Night	25% 9% 16% 25% 18% 7%	1778
	21st to end	Night	23% 9% 16% 26% 19% 6%	1980
September	1st to 10th	Night	26% 7% 12% 23% 21% 11%	1800
	11th to 20th	Night	19% 5% 11% 20% 27% 18%	1814
	21st to end	Night	20% 4 8% 23% 33% 12%	1980
October	1st to 10th	Night	21% 7% 11% 21% 25% 15%	2145
	11th to 20th	Night	13% 4 8% 19% 36% 21%	2160
	21st to end	Night	20% 3 8% 24% 29% 15%	2382
November	1st to 10th	Night	12% 3 9% 28% 33% 15%	2405
	11th to 20th	Night	15% 3 6% 31% 35% 11%	2470
	21st to end	Night	18% 3 8% 25% 34% 12%	2512
December	1st to 10th	Night	19% 4 12% 29% 27% 8%	2660
	11th to 20th	Night	19% 4 11% 27% 34% 6%	3272
	21st to end	Night	22% 5% 12% 26% 28% 8%	4873

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	7% 16% 39% 29% 7% 2	270
	11th to 20th	Day	7% 16% 44% 29% 3 1	270
	21st to end	Day	4 10% 50% 27% 8% 2	297
February	1st to 10th	Day	6% 22% 48% 19% 4 1	270
	11th to 20th	Day	4 19% 51% 21% 4 1	270
	21st to end	Day	4 26% 45% 21% 4	225
March	1st to 10th	Day	1 22% 48% 25% 5%	240
	11th to 20th	Day	8% 21% 39% 25% 6% 1	415
	21st to end	Day	10% 25% 41% 21% 3	462
April	1st to 10th	Day	9% 23% 39% 22% 6%	420
	11th to 20th	Day	10% 28% 34% 23% 4 1	412
	21st to end	Day	11% 19% 40% 22% 7% 1	420
May	1st to 10th	Day	14% 13% 38% 26% 9% 1	481
	11th to 20th	Day	12% 7% 32% 34% 13% 3	625
	21st to end	Day	8% 9% 33% 34% 15% 1	679
June	1st to 10th	Day	5% 7% 28% 38% 19% 3	630
	11th to 20th	Day	4 7% 33% 37% 17% 3	630
	21st to end	Day	4 6% 31% 37% 18% 3	630
July	1st to 10th	Day	7% 4 19% 36% 28% 6%	621
	11th to 20th	Day	5% 1 17% 40% 29% 7%	618
	21st to end	Day	4 2 15% 36% 33% 9%	558
August	1st to 10th	Day	5% 6% 19% 36% 27% 7%	447
	11th to 20th	Day	6% 2 26% 35% 25% 7%	437
	21st to end	Day	6% 2 24% 39% 24% 5%	495
September	1st to 10th	Day	5% 4 25% 39% 22% 4	450
	11th to 20th	Day	6% 7% 30% 37% 17% 3	435
	21st to end	Day	9% 6% 24% 33% 23% 5%	270
October	1st to 10th	Day	9% 8% 28% 29% 21% 6%	270
	11th to 20th	Day	4 12% 34% 32% 15% 3	270
	21st to end	Day	8% 12% 33% 34% 10% 3	297
November	1st to 10th	Day	2 10% 41% 31% 15% 1	270
	11th to 20th	Day	4 13% 46% 26% 9% 3	270
	21st to end	Day	6% 12% 41% 30% 9% 1	270
December	1st to 10th	Day	3 19% 43% 26% 7% 1	270
	11th to 20th	Day	6% 17% 47% 22% 7% 1	270
	21st to end	Day	4 22% 44% 26% 3 1	297
January	1st to 10th	Night	4 12% 45% 32% 7% 1	950
	11th to 20th	Night	3 11% 56% 22% 7%	849
	21st to end	Night	3 7% 57% 28% 5%	836
February	1st to 10th	Night	4 9% 61% 24% 3	760
	11th to 20th	Night	5% 9% 57% 26% 3	744
	21st to end	Night	6% 11% 60% 22% 2	628
March	1st to 10th	Night	4 8% 56% 27% 5%	722
	11th to 20th	Night	7% 6% 41% 38% 8%	720
	21st to end	Night	6% 12% 44% 34% 4	668
April	1st to 10th	Night	5% 9% 48% 34% 4	540
	11th to 20th	Night	13% 9% 38% 34% 7%	533
	21st to end	Night	12% 8% 36% 35% 8% 1	540
May	1st to 10th	Night	11% 6% 33% 39% 10%	540
	11th to 20th	Night	15% 4 23% 43% 15% 1	531
	21st to end	Night	10% 5% 29% 40% 16% 1	584
June	1st to 10th	Night	7% 4 24% 45% 19% 1	540
	11th to 20th	Night	5% 3 27% 50% 16%	540
	21st to end	Night	5% 2 20% 51% 22%	540
July	1st to 10th	Night	9% 2 12% 41% 33% 2	525
	11th to 20th	Night	4 1 8% 50% 33% 3	522
	21st to end	Night	7% 2 5% 44% 39% 3	591
August	1st to 10th	Night	6% 2 12% 42% 39%	537
	11th to 20th	Night	6% 2 13% 50% 28% 1	534
	21st to end	Night	5% 2 12% 51% 29% 1	594
September	1st to 10th	Night	6% 2 15% 50% 25% 2	540
	11th to 20th	Night	10% 2 21% 43% 23% 2	540
	21st to end	Night	8% 3 24% 47% 17% 1	540
October	1st to 10th	Night	9% 4 34% 42% 11% 1	705
	11th to 20th	Night	3 4 40% 40% 11% 1	720
	21st to end	Night	7% 7% 39% 36% 11%	798
November	1st to 10th	Night	2 6% 47% 36% 9%	925
	11th to 20th	Night	3 9% 48% 32% 7%	950
	21st to end	Night	6% 8% 46% 35% 5%	950
December	1st to 10th	Night	2 9% 51% 34% 5%	950
	11th to 20th	Night	4 8% 56% 25% 7%	950
	21st to end	Night	4 10% 56% 26% 3	1045

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