Double AA Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Double AA 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	9% 5% 2 4 4 3 4 4 5% 7% 54%	78909
	Night	9% 4 2 4 3 2 3 4 4 7% 58%	80560
Transparency	Day	30% 6% 10% 23% 23% 7%	78634
	Night	27% 5% 10% 22% 26% 11%	80355
Seeing	Day	11% 7% 25% 30% 21% 7%	14227
	Night	10% 8% 33% 35% 13% 1	24315

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	9% 6% 3 4 4 3 3 3 4 6% 55%	2847
	11th to 20th	Day	9% 4 1 2 3 2 2 3 3 6% 65%	2850
	21st to end	Day	18% 10% 3 5% 3 2 2 3 3 4 48%	3135
February	1st to 10th	Day	11% 6% 2 6% 4 3 3 3 4 7% 51%	1852
	11th to 20th	Day	12% 5% 3 6% 4 2 3 3 5% 5% 52%	1849
	21st to end	Day	17% 8% 2 4 2 1 2 3 3 4 53%	1570
March	1st to 10th	Day	13% 5% 2 5% 3 3 4 4 6% 7% 48%	1948
	11th to 20th	Day	13% 6% 2 5% 4 2 4 4 3 5% 51%	1980
	21st to end	Day	10% 6% 2 5% 4 3 5% 4 5% 6% 50%	2178
April	1st to 10th	Day	10% 5% 2 4 3 2 4 3 4 6% 56%	1980
	11th to 20th	Day	11% 5% 3 5% 4 3 3 4 5% 6% 51%	2062
	21st to end	Day	10% 4 3 5% 4 2 5% 4 5% 7% 51%	2340
May	1st to 10th	Day	11% 6% 2 5% 4 3 4 3 6% 6% 51%	2340
	11th to 20th	Day	12% 5% 3 5% 4 3 4 5% 6% 7% 47%	2302
	21st to end	Day	9% 5% 3 6% 6% 4 5% 5% 6% 9% 42%	2531
June	1st to 10th	Day	6% 4 2 4 5% 4 5% 5% 6% 8% 51%	2340
	11th to 20th	Day	5% 3 2 3 5% 2 5% 5% 6% 8% 56%	2340
	21st to end	Day	4 3 2 3 3 2 4 4 5% 8% 61%	2340
July	1st to 10th	Day	6% 4 2 5% 5% 5% 6% 7% 7% 10% 45%	2340
	11th to 20th	Day	4 2 1 3 4 2 4 5% 5% 10% 60%	2340
	21st to end	Day	4 2 1 3 4 3 7% 6% 7% 11% 53%	2546
August	1st to 10th	Day	2 3 2 3 4 3 5% 5% 6% 8% 58%	2328
	11th to 20th	Day	6% 4 1 5% 4 3 5% 6% 7% 9% 50%	2301
	21st to end	Day	4 3 1 3 5% 2 5% 6% 6% 10% 56%	2327
September	1st to 10th	Day	10% 3 2 3 4 2 3 3 5% 8% 57%	1980
	11th to 20th	Day	12% 5% 3 5% 5% 4 6% 4 5% 7% 46%	1980
	21st to end	Day	8% 2 2 3 4 2 4 4 4 6% 61%	1980
October	1st to 10th	Day	6% 2 2 4 3 3 5% 4 5% 7% 61%	1967
	11th to 20th	Day	10% 3 2 3 2 1 2 3 4 5% 65%	1800
	21st to end	Day	12% 5% 2 3 3 2 3 2 3 4 61%	1980
November	1st to 10th	Day	10% 4 1 4 3 2 3 3 3 6% 61%	1830
	11th to 20th	Day	6% 3 1 3 2 2 3 3 3 5% 67%	1710
	21st to end	Day	12% 5% 2 3 3 2 3 3 3 5% 58%	1710
December	1st to 10th	Day	10% 6% 2 4 4 2 3 4 4 6% 53%	1710
	11th to 20th	Day	12% 5% 2 5% 4 3 3 4 5% 5% 51%	2161
	21st to end	Day	12% 6% 3 5% 5% 2 3 4 4 6% 49%	3135
January	1st to 10th	Night	11% 6% 2 4 4 2 3 4 5% 6% 54%	4108
	11th to 20th	Night	7% 5% 1 3 3 1 2 2 3 5% 67%	4120
	21st to end	Night	17% 8% 3 4 3 2 3 3 3 5% 50%	4532
February	1st to 10th	Night	11% 5% 2 5% 4 2 3 4 4 5% 54%	2343
	11th to 20th	Night	13% 5% 3 4 3 2 3 3 4 6% 53%	2218
	21st to end	Night	11% 7% 2 4 4 2 3 3 3 5% 55%	1884
March	1st to 10th	Night	11% 5% 3 5% 4 2 4 4 5% 6% 50%	2017
	11th to 20th	Night	12% 6% 2 4 4 2 3 4 3 7% 54%	1980
	21st to end	Night	7% 5% 2 4 4 2 4 4 5% 7% 55%	2178
April	1st to 10th	Night	7% 4 3 4 3 3 4 4 5% 8% 55%	1980
	11th to 20th	Night	9% 4 2 4 4 2 4 4 5% 6% 56%	1841
	21st to end	Night	10% 4 1 4 3 2 4 4 5% 8% 55%	1620
May	1st to 10th	Night	8% 4 3 4 4 3 3 5% 6% 7% 55%	1620
	11th to 20th	Night	10% 4 2 4 5% 2 4 4 6% 8% 51%	1593
	21st to end	Night	6% 3 1 4 4 3 4 5% 7% 10% 54%	1745
June	1st to 10th	Night	4 2 1 2 4 2 4 4 6% 12% 59%	1620
	11th to 20th	Night	3 2 1 3 3 2 3 4 7% 12% 60%	1620
	21st to end	Night	2 2 1 3 3 2 4 3 4 9% 68%	1620
July	1st to 10th	Night	4 3 2 4 4 2 5% 4 7% 10% 55%	1620
	11th to 20th	Night	2 1 1 2 3 2 3 4 5% 9% 68%	1620
	21st to end	Night	1 1 1 3 3 2 3 4 6% 11% 64%	1772
August	1st to 10th	Night	2 2 1 3 2 1 3 4 6% 12% 65%	1611
	11th to 20th	Night	5% 3 1 4 4 2 4 4 6% 9% 57%	1600
	21st to end	Night	3 2 1 3 3 2 3 5% 6% 11% 60%	2024
September	1st to 10th	Night	8% 3 2 4 4 2 3 3 4 6% 60%	1980
	11th to 20th	Night	9% 5% 3 5% 5% 3 4 4 5% 6% 51%	1980
	21st to end	Night	7% 2 1 3 2 2 3 3 4 7% 65%	1980
October	1st to 10th	Night	6% 2 1 3 3 2 3 4 5% 7% 64%	1980
	11th to 20th	Night	9% 3 2 3 3 2 2 3 3 5% 66%	2155
	21st to end	Night	12% 3 2 3 2 2 2 2 3 5% 63%	2376
November	1st to 10th	Night	9% 3 2 3 3 2 3 2 4 4 66%	2245
	11th to 20th	Night	5% 3 1 3 3 2 4 3 4 6% 66%	2470
	21st to end	Night	12% 4 1 4 3 2 3 4 4 6% 56%	2470
December	1st to 10th	Night	10% 5% 2 3 4 2 3 3 4 6% 59%	2470
	11th to 20th	Night	10% 6% 2 6% 4 2 4 4 4 5% 55%	3036
	21st to end	Night	11% 6% 2 4 3 2 3 3 4 5% 55%	4532

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	29% 5% 8% 21% 30% 6%	2848
	11th to 20th	Day	22% 3 9% 23% 37% 6%	2850
	21st to end	Day	42% 3 5% 21% 22% 7%	3135
February	1st to 10th	Day	35% 5% 7% 22% 24% 8%	1852
	11th to 20th	Day	36% 5% 8% 21% 22% 9%	1859
	21st to end	Day	36% 3 5% 14% 29% 13%	1570
March	1st to 10th	Day	35% 6% 8% 17% 21% 13%	1948
	11th to 20th	Day	36% 6% 9% 20% 22% 7%	1980
	21st to end	Day	35% 6% 10% 21% 21% 7%	2178
April	1st to 10th	Day	30% 6% 10% 25% 18% 12%	1980
	11th to 20th	Day	34% 6% 9% 21% 19% 11%	2062
	21st to end	Day	33% 6% 10% 23% 22% 5%	2340
May	1st to 10th	Day	34% 6% 11% 23% 19% 7%	2340
	11th to 20th	Day	35% 8% 13% 23% 18% 2	2306
	21st to end	Day	37% 9% 15% 21% 16% 2	2531
June	1st to 10th	Day	29% 7% 16% 27% 17% 3	2340
	11th to 20th	Day	25% 7% 14% 27% 22% 5%	2340
	21st to end	Day	22% 7% 13% 26% 26% 6%	2340
July	1st to 10th	Day	30% 10% 19% 25% 14% 2	2276
	11th to 20th	Day	19% 7% 13% 31% 26% 4	2271
	21st to end	Day	22% 9% 17% 30% 22%	2405
August	1st to 10th	Day	21% 7% 14% 29% 25% 4	2314
	11th to 20th	Day	28% 10% 14% 26% 20% 3	2301
	21st to end	Day	23% 7% 14% 29% 21% 6%	2327
September	1st to 10th	Day	27% 5% 11% 23% 24% 11%	1980
	11th to 20th	Day	38% 6% 8% 20% 19% 9%	1980
	21st to end	Day	24% 6% 8% 23% 29% 11%	1980
October	1st to 10th	Day	23% 6% 11% 21% 24% 15%	1967
	11th to 20th	Day	23% 4 7% 18% 31% 17%	1800
	21st to end	Day	29% 3 7% 22% 26% 14%	1980
November	1st to 10th	Day	26% 4 8% 23% 28% 11%	1830
	11th to 20th	Day	21% 4 9% 24% 31% 12%	1710
	21st to end	Day	31% 3 6% 20% 28% 12%	1710
December	1st to 10th	Day	32% 4 7% 26% 24% 6%	1710
	11th to 20th	Day	35% 5% 8% 16% 27% 9%	2159
	21st to end	Day	35% 5% 7% 24% 24% 6%	3135
January	1st to 10th	Night	28% 6% 7% 21% 31% 8%	4108
	11th to 20th	Night	22% 3 11% 21% 34% 8%	4120
	21st to end	Night	38% 4 6% 16% 26% 9%	4532
February	1st to 10th	Night	33% 4 9% 20% 23% 11%	2343
	11th to 20th	Night	33% 4 7% 20% 25% 11%	2218
	21st to end	Night	33% 3 6% 16% 23% 18%	1884
March	1st to 10th	Night	35% 5% 7% 15% 21% 17%	2017
	11th to 20th	Night	32% 5% 8% 21% 24% 10%	1980
	21st to end	Night	29% 7% 12% 22% 24% 7%	2178
April	1st to 10th	Night	27% 6% 10% 22% 20% 14%	1980
	11th to 20th	Night	29% 7% 9% 19% 22% 14%	1841
	21st to end	Night	28% 6% 11% 24% 25% 6%	1620
May	1st to 10th	Night	29% 6% 11% 21% 24% 9%	1620
	11th to 20th	Night	30% 8% 16% 23% 19% 3	1594
	21st to end	Night	26% 8% 16% 28% 19% 3	1746
June	1st to 10th	Night	19% 8% 16% 34% 19% 5%	1620
	11th to 20th	Night	17% 7% 15% 31% 23% 7%	1620
	21st to end	Night	15% 6% 13% 26% 31% 9%	1620
July	1st to 10th	Night	23% 8% 16% 31% 20% 2	1575
	11th to 20th	Night	13% 5% 11% 32% 32% 6%	1566
	21st to end	Night	15% 6% 15% 33% 29% 3	1673
August	1st to 10th	Night	13% 4 11% 34% 30% 7%	1601
	11th to 20th	Night	21% 7% 11% 29% 26% 6%	1600
	21st to end	Night	18% 6% 13% 30% 27% 7%	2024
September	1st to 10th	Night	25% 5% 11% 21% 29% 9%	1980
	11th to 20th	Night	32% 8% 9% 19% 21% 11%	1980
	21st to end	Night	19% 5% 8% 22% 30% 16%	1980
October	1st to 10th	Night	20% 6% 11% 23% 24% 17%	1980
	11th to 20th	Night	24% 3 8% 14% 30% 21%	2155
	21st to end	Night	28% 3 5% 20% 27% 18%	2376
November	1st to 10th	Night	23% 4 7% 22% 28% 16%	2245
	11th to 20th	Night	20% 4 9% 22% 30% 14%	2470
	21st to end	Night	31% 4 7% 17% 29% 12%	2470
December	1st to 10th	Night	28% 4 7% 23% 25% 12%	2470
	11th to 20th	Night	32% 5% 6% 16% 30% 12%	3037
	21st to end	Night	32% 4 7% 20% 27% 10%	4532

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	14% 14% 36% 28% 7%	270
	11th to 20th	Day	17% 14% 37% 24% 6% 2	270
	21st to end	Day	19% 9% 39% 24% 8% 1	297
February	1st to 10th	Day	16% 12% 43% 21% 7%	270
	11th to 20th	Day	17% 13% 49% 17% 3	270
	21st to end	Day	24% 19% 40% 15% 2	225
March	1st to 10th	Day	18% 21% 33% 21% 8%	240
	11th to 20th	Day	20% 20% 36% 17% 5% 2	240
	21st to end	Day	14% 16% 47% 18% 5% 1	264
April	1st to 10th	Day	16% 19% 33% 25% 7%	240
	11th to 20th	Day	16% 14% 43% 22% 4 1	340
	21st to end	Day	14% 15% 40% 22% 7% 2	600
May	1st to 10th	Day	11% 11% 38% 31% 8% 1	603
	11th to 20th	Day	15% 7% 35% 27% 13% 3	625
	21st to end	Day	11% 7% 31% 29% 16% 5%	679
June	1st to 10th	Day	5% 4 16% 41% 27% 7%	630
	11th to 20th	Day	5% 3 21% 43% 21% 6%	630
	21st to end	Day	4 2 14% 39% 30% 10%	630
July	1st to 10th	Day	6% 2 9% 34% 35% 15%	621
	11th to 20th	Day	3 2 7% 32% 41% 14%	618
	21st to end	Day	4 1 4 32% 43% 16%	684
August	1st to 10th	Day	3 1 7% 39% 38% 12%	626
	11th to 20th	Day	7% 2 11% 35% 35% 10%	615
	21st to end	Day	6% 1 5% 30% 39% 20%	446
September	1st to 10th	Day	6% 1 7% 25% 42% 19%	270
	11th to 20th	Day	6% 2 9% 27% 38% 18%	270
	21st to end	Day	12% 3 7% 33% 33% 11%	270
October	1st to 10th	Day	5% 4 20% 36% 26% 9%	270
	11th to 20th	Day	11% 8% 29% 34% 16% 3	270
	21st to end	Day	23% 10% 27% 26% 12% 3	297
November	1st to 10th	Day	14% 7% 33% 31% 12% 4	270
	11th to 20th	Day	13% 9% 35% 29% 10% 4	270
	21st to end	Day	17% 13% 41% 20% 7% 1	270
December	1st to 10th	Day	13% 8% 39% 27% 11% 1	270
	11th to 20th	Day	14% 12% 39% 28% 7%	270
	21st to end	Day	21% 10% 37% 25% 6%	297
January	1st to 10th	Night	11% 11% 41% 29% 8%	950
	11th to 20th	Night	13% 14% 36% 30% 6%	950
	21st to end	Night	13% 10% 36% 35% 6%	1045
February	1st to 10th	Night	13% 12% 42% 29% 4	823
	11th to 20th	Night	16% 14% 41% 26% 4	744
	21st to end	Night	17% 16% 46% 20% 1	628
March	1st to 10th	Night	13% 14% 41% 28% 4	573
	11th to 20th	Night	14% 12% 42% 26% 6%	540
	21st to end	Night	10% 12% 47% 27% 4	594
April	1st to 10th	Night	9% 13% 50% 23% 4	540
	11th to 20th	Night	11% 14% 44% 26% 4	533
	21st to end	Night	11% 12% 45% 23% 8% 1	540
May	1st to 10th	Night	10% 9% 46% 29% 6% 1	540
	11th to 20th	Night	11% 6% 40% 30% 13% 1	531
	21st to end	Night	6% 3 39% 36% 14% 2	584
June	1st to 10th	Night	4 2 24% 46% 22% 2	540
	11th to 20th	Night	4 2 31% 53% 11%	540
	21st to end	Night	2 1 22% 50% 23% 3	540
July	1st to 10th	Night	4 13% 46% 34% 3	525
	11th to 20th	Night	3 12% 48% 34% 2	522
	21st to end	Night	2 1 9% 53% 33% 3	591
August	1st to 10th	Night	2 1 8% 59% 27% 2	537
	11th to 20th	Night	6% 1 9% 48% 33% 3	534
	21st to end	Night	4 1 7% 47% 37% 4	594
September	1st to 10th	Night	7% 3 11% 44% 31% 3	540
	11th to 20th	Night	12% 1 13% 40% 30% 3	540
	21st to end	Night	8% 1 19% 46% 25% 2	540
October	1st to 10th	Night	6% 2 29% 39% 22% 1	540
	11th to 20th	Night	11% 6% 32% 39% 11% 1	715
	21st to end	Night	14% 9% 32% 33% 11% 1	792
November	1st to 10th	Night	9% 6% 36% 35% 12% 1	765
	11th to 20th	Night	7% 11% 37% 36% 9% 1	950
	21st to end	Night	14% 11% 39% 26% 9% 1	950
December	1st to 10th	Night	13% 10% 37% 33% 7%	950
	11th to 20th	Night	15% 10% 40% 29% 6%	950
	21st to end	Night	13% 13% 40% 27% 7%	1045

Page generated at 2024-02-27 05:30:18. Version ac07

Copyright © 2024 Attilla Danko.