Concordia
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Concordia clear sky chart from 2005-11-06 to 2025-06-10.

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% 6% 2 6% 4 4 4 3 5% 7% 50%	119987
	Night	9% 6% 2 5% 4 3 4 3 5% 7% 53%	118511
Transparency	Day	33% 6% 12% 26% 20% 4	123698
	Night	30% 5% 12% 26% 22% 5%	122932
Seeing	Day	12% 9% 31% 30% 15% 3	16464
	Night	11% 8% 34% 36% 10% 1	26423

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	10% 9% 3 9% 5% 5% 5% 4 6% 7% 38%	4077
	11th to 20th	Day	6% 11% 5% 9% 6% 4 4 3 4 5% 44%	4080
	21st to end	Day	6% 11% 5% 9% 4 4 3 2 4 5% 47%	4488
February	1st to 10th	Day	9% 11% 3 7% 4 3 5% 3 5% 7% 43%	1800
	11th to 20th	Day	7% 9% 3 6% 4 4 5% 4 6% 6% 46%	1924
	21st to end	Day	6% 7% 2 6% 5% 4 4 3 6% 6% 52%	1650
March	1st to 10th	Day	9% 7% 2 5% 3 3 3 3 4 5% 56%	4737
	11th to 20th	Day	9% 6% 1 4 3 3 3 3 5% 6% 57%	4980
	21st to end	Day	11% 8% 3 6% 4 4 4 4 5% 7% 44%	5462
April	1st to 10th	Day	12% 7% 3 5% 3 3 4 3 6% 6% 50%	2200
	11th to 20th	Day	11% 7% 3 7% 4 4 5% 4 6% 6% 44%	2532
	21st to end	Day	18% 7% 2 6% 4 3 3 4 5% 6% 42%	2600
May	1st to 10th	Day	13% 6% 2 5% 4 4 4 4 5% 6% 48%	5862
	11th to 20th	Day	11% 5% 2 6% 4 3 3 2 4 6% 54%	5862
	21st to end	Day	17% 6% 2 7% 4 4 4 4 6% 7% 39%	6434
June	1st to 10th	Day	6% 4 2 4 4 3 4 4 5% 8% 56%	2588
	11th to 20th	Day	6% 4 1 3 4 4 5% 5% 6% 9% 52%	2470
	21st to end	Day	4 4 1 5% 4 4 4 4 5% 8% 55%	2470
July	1st to 10th	Day	9% 6% 2 6% 4 4 5% 4 6% 8% 46%	4120
	11th to 20th	Day	5% 3 2 5% 4 5% 5% 4 7% 9% 52%	4120
	21st to end	Day	5% 3 2 5% 3 4 5% 4 7% 8% 54%	4465
August	1st to 10th	Day	8% 4 2 6% 4 4 4 4 5% 8% 51%	4104
	11th to 20th	Day	11% 5% 2 5% 4 4 5% 3 5% 7% 48%	4041
	21st to end	Day	4 3 1 4 3 4 4 4 6% 8% 59%	4472
September	1st to 10th	Day	12% 5% 2 4 3 2 3 3 5% 5% 56%	2099
	11th to 20th	Day	9% 4 2 4 3 4 4 3 6% 7% 55%	2090
	21st to end	Day	9% 4 1 5% 3 3 3 3 5% 6% 58%	2090
October	1st to 10th	Day	13% 5% 2 4 3 3 3 3 4 5% 54%	2028
	11th to 20th	Day	10% 4 1 4 3 2 4 2 4 4 62%	1900
	21st to end	Day	10% 7% 1 5% 3 3 3 3 4 5% 55%	2060
November	1st to 10th	Day	8% 4 1 4 3 3 4 3 5% 7% 58%	1763
	11th to 20th	Day	8% 7% 2 4 4 3 3 3 3 6% 58%	1800
	21st to end	Day	11% 8% 1 4 3 3 3 2 4 7% 53%	1800
December	1st to 10th	Day	5% 5% 2 5% 3 3 3 3 5% 6% 60%	2940
	11th to 20th	Day	6% 7% 3 5% 5% 4 3 2 4 6% 56%	3391
	21st to end	Day	13% 10% 5% 11% 4 4 4 3 4 6% 35%	4488
January	1st to 10th	Night	9% 9% 4 12% 5% 4 4 4 5% 6% 39%	5888
	11th to 20th	Night	5% 7% 3 7% 4 5% 4 3 5% 5% 52%	5900
	21st to end	Night	9% 9% 4 9% 4 3 3 3 4 4 49%	6490
February	1st to 10th	Night	10% 10% 3 5% 5% 4 4 4 6% 6% 44%	2600
	11th to 20th	Night	7% 8% 3 6% 5% 4 4 5% 5% 6% 45%	2378
	21st to end	Night	7% 6% 2 6% 5% 3 3 3 4 5% 55%	1980
March	1st to 10th	Night	9% 5% 1 4 3 2 3 2 4 6% 62%	5126
	11th to 20th	Night	7% 5% 1 3 3 2 3 3 5% 8% 59%	4980
	21st to end	Night	12% 7% 2 5% 4 4 5% 4 6% 7% 44%	5467
April	1st to 10th	Night	10% 5% 2 5% 4 4 4 4 4 7% 52%	2195
	11th to 20th	Night	12% 6% 2 5% 4 4 4 3 5% 6% 49%	1819
	21st to end	Night	12% 7% 2 6% 3 3 4 3 6% 7% 46%	1800
May	1st to 10th	Night	17% 6% 2 5% 3 2 3 3 5% 7% 49%	4053
	11th to 20th	Night	12% 4 2 3 3 3 3 3 4 7% 56%	4053
	21st to end	Night	17% 5% 2 5% 3 3 3 3 5% 8% 45%	4443
June	1st to 10th	Night	5% 3 1 4 3 3 3 4 5% 10% 59%	1796
	11th to 20th	Night	5% 4 1 5% 4 4 3 4 7% 8% 55%	1710
	21st to end	Night	3 3 2 3 3 3 3 5% 7% 11% 57%	1710
July	1st to 10th	Night	8% 5% 2 5% 4 4 4 3 5% 9% 51%	2850
	11th to 20th	Night	3 2 1 4 4 4 4 5% 7% 10% 56%	2850
	21st to end	Night	5% 3 1 4 3 3 3 3 7% 9% 58%	3098
August	1st to 10th	Night	3 4 1 4 4 4 4 4 6% 9% 56%	2836
	11th to 20th	Night	10% 5% 2 5% 3 4 5% 3 5% 8% 50%	2798
	21st to end	Night	5% 3 1 4 3 3 3 3 5% 9% 61%	3191
September	1st to 10th	Night	8% 3 1 4 3 2 3 3 5% 6% 63%	2080
	11th to 20th	Night	9% 3 2 4 3 3 4 4 4 6% 59%	2090
	21st to end	Night	6% 3 1 4 3 3 3 3 5% 6% 61%	2090
October	1st to 10th	Night	12% 4 1 4 3 3 3 3 5% 6% 56%	2133
	11th to 20th	Night	10% 5% 2 4 2 3 3 2 3 5% 61%	2280
	21st to end	Night	11% 5% 2 4 3 3 3 2 4 5% 59%	2536
November	1st to 10th	Night	7% 4 1 3 3 3 3 3 4 7% 62%	2535
	11th to 20th	Night	7% 5% 2 5% 3 3 3 3 5% 6% 60%	2600
	21st to end	Night	10% 6% 2 4 3 3 3 3 4 6% 56%	2600
December	1st to 10th	Night	4 5% 1 3 3 3 3 3 4 6% 65%	4250
	11th to 20th	Night	8% 5% 2 5% 3 4 4 4 6% 7% 53%	4816
	21st to end	Night	14% 10% 4 8% 4 4 4 3 4 6% 38%	6490

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	43% 7% 12% 23% 14% 2	4078
	11th to 20th	Day	42% 6% 11% 21% 17% 2	4080
	21st to end	Day	41% 3 12% 24% 17% 2	4488
February	1st to 10th	Day	41% 7% 16% 22% 11% 4	1800
	11th to 20th	Day	37% 6% 14% 26% 14% 4	1934
	21st to end	Day	31% 6% 10% 25% 22% 5%	1650
March	1st to 10th	Day	31% 4 7% 22% 25% 10%	4737
	11th to 20th	Day	29% 4 8% 23% 28% 8%	4980
	21st to end	Day	38% 6% 19% 29% 8% 1	5464
April	1st to 10th	Day	35% 5% 13% 24% 20% 3	2200
	11th to 20th	Day	38% 8% 11% 25% 16% 2	2532
	21st to end	Day	42% 6% 12% 25% 15% 1	2600
May	1st to 10th	Day	35% 6% 11% 27% 17% 4	5900
	11th to 20th	Day	32% 5% 9% 22% 26% 6%	5866
	21st to end	Day	42% 7% 11% 25% 14% 1	6447
June	1st to 10th	Day	25% 7% 18% 33% 15% 3	2588
	11th to 20th	Day	26% 9% 14% 28% 20% 3	2470
	21st to end	Day	25% 7% 13% 30% 20% 4	2470
July	1st to 10th	Day	34% 6% 13% 24% 19% 4	4056
	11th to 20th	Day	27% 7% 14% 28% 20% 3	4051
	21st to end	Day	24% 7% 13% 25% 26% 5%	4325
August	1st to 10th	Day	31% 6% 13% 25% 20% 4	4090
	11th to 20th	Day	36% 5% 15% 24% 18% 2	4080
	21st to end	Day	22% 6% 17% 27% 21% 7%	4471
September	1st to 10th	Day	30% 5% 10% 25% 22% 8%	2099
	11th to 20th	Day	28% 6% 11% 26% 26% 3	2090
	21st to end	Day	27% 5% 9% 30% 25% 4	2090
October	1st to 10th	Day	22% 4 5% 18% 44% 6%	3366
	11th to 20th	Day	18% 3 10% 31% 28% 10%	3140
	21st to end	Day	27% 3 10% 25% 31% 4	3376
November	1st to 10th	Day	27% 4 11% 30% 24% 4	1763
	11th to 20th	Day	29% 4 9% 26% 28% 4	1800
	21st to end	Day	33% 3 11% 28% 21% 3	1800
December	1st to 10th	Day	25% 4 11% 37% 21% 2	2940
	11th to 20th	Day	31% 4 14% 37% 13% 1	3389
	21st to end	Day	50% 5% 10% 24% 10% 1	4488
January	1st to 10th	Night	46% 5% 10% 24% 14% 1	5888
	11th to 20th	Night	33% 5% 11% 26% 22% 3	5900
	21st to end	Night	40% 4 10% 20% 18% 8%	6490
February	1st to 10th	Night	40% 6% 12% 22% 15% 4	2600
	11th to 20th	Night	37% 6% 12% 26% 16% 3	2378
	21st to end	Night	31% 4 10% 24% 23% 9%	1980
March	1st to 10th	Night	25% 3 8% 27% 29% 8%	5126
	11th to 20th	Night	23% 4 7% 20% 33% 12%	4980
	21st to end	Night	37% 6% 21% 26% 8% 2	5467
April	1st to 10th	Night	33% 6% 11% 24% 23% 3	2195
	11th to 20th	Night	35% 5% 13% 24% 19% 3	1819
	21st to end	Night	36% 6% 14% 25% 17% 2	1800
May	1st to 10th	Night	36% 5% 11% 25% 19% 4	4080
	11th to 20th	Night	28% 6% 11% 24% 22% 9%	4054
	21st to end	Night	37% 7% 15% 24% 16% 1	4452
June	1st to 10th	Night	22% 7% 17% 32% 19% 3	1796
	11th to 20th	Night	25% 6% 14% 31% 18% 5%	1710
	21st to end	Night	21% 5% 17% 30% 21% 6%	1710
July	1st to 10th	Night	31% 7% 13% 23% 23% 5%	2805
	11th to 20th	Night	21% 6% 15% 28% 26% 4	2796
	21st to end	Night	20% 5% 15% 28% 27% 5%	2999
August	1st to 10th	Night	23% 6% 17% 26% 22% 6%	2826
	11th to 20th	Night	34% 6% 16% 24% 18% 2	2825
	21st to end	Night	21% 4 17% 29% 21% 8%	3191
September	1st to 10th	Night	22% 5% 12% 27% 25% 10%	2080
	11th to 20th	Night	26% 5% 10% 27% 27% 6%	2090
	21st to end	Night	24% 5% 11% 24% 31% 6%	2090
October	1st to 10th	Night	18% 4 6% 18% 48% 6%	3562
	11th to 20th	Night	19% 3 8% 29% 29% 11%	3779
	21st to end	Night	23% 3 8% 29% 32% 4	4172
November	1st to 10th	Night	23% 4 10% 29% 26% 8%	2535
	11th to 20th	Night	26% 4 10% 29% 26% 4	2600
	21st to end	Night	31% 4 10% 28% 23% 4	2600
December	1st to 10th	Night	21% 5% 15% 37% 22% 2	4250
	11th to 20th	Night	29% 5% 13% 33% 18% 2	4817
	21st to end	Night	47% 5% 10% 26% 11% 1	6490

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	12% 11% 39% 25% 12% 1	300
	11th to 20th	Day	16% 18% 33% 27% 6%	300
	21st to end	Day	11% 10% 49% 22% 8%	330
February	1st to 10th	Day	14% 17% 43% 22% 5%	300
	11th to 20th	Day	12% 15% 43% 23% 6% 1	300
	21st to end	Day	10% 16% 51% 19% 3	249
March	1st to 10th	Day	14% 15% 42% 22% 6%	300
	11th to 20th	Day	22% 13% 31% 25% 7% 1	300
	21st to end	Day	22% 15% 45% 13% 4	330
April	1st to 10th	Day	17% 17% 41% 21% 4	300
	11th to 20th	Day	15% 16% 41% 24% 4	650
	21st to end	Day	21% 16% 36% 17% 8% 2	700
May	1st to 10th	Day	16% 11% 33% 29% 10% 1	703
	11th to 20th	Day	17% 10% 29% 26% 14% 3	725
	21st to end	Day	16% 8% 30% 30% 12% 3	789
June	1st to 10th	Day	6% 4 26% 34% 24% 6%	726
	11th to 20th	Day	6% 5% 34% 33% 19% 2	680
	21st to end	Day	6% 6% 35% 36% 15% 1	680
July	1st to 10th	Day	8% 3 18% 36% 28% 6%	671
	11th to 20th	Day	5% 2 18% 43% 26% 6%	668
	21st to end	Day	7% 3 15% 40% 31% 5%	739
August	1st to 10th	Day	8% 2 15% 40% 31% 3	676
	11th to 20th	Day	7% 3 21% 42% 24% 3	665
	21st to end	Day	9% 2 18% 36% 28% 7%	714
September	1st to 10th	Day	12% 3 20% 40% 22% 3	309
	11th to 20th	Day	6% 3 25% 41% 18% 6%	300
	21st to end	Day	14% 7% 27% 30% 18% 4	300
October	1st to 10th	Day	20% 11% 20% 28% 19% 3	300
	11th to 20th	Day	8% 13% 42% 25% 12%	300
	21st to end	Day	16% 14% 35% 25% 8% 2	330
November	1st to 10th	Day	14% 13% 40% 23% 8% 2	300
	11th to 20th	Day	13% 16% 37% 23% 10% 2	300
	21st to end	Day	19% 12% 34% 23% 10% 2	300
December	1st to 10th	Day	9% 10% 41% 29% 10% 1	300
	11th to 20th	Day	13% 10% 42% 28% 7%	300
	21st to end	Day	18% 15% 38% 24% 5%	330
January	1st to 10th	Night	12% 9% 36% 36% 6%	1000
	11th to 20th	Night	12% 11% 35% 36% 5% 1	1000
	21st to end	Night	11% 9% 41% 34% 6%	1100
February	1st to 10th	Night	15% 9% 42% 31% 4	1000
	11th to 20th	Night	12% 13% 40% 31% 4	824
	21st to end	Night	11% 12% 45% 27% 4 1	660
March	1st to 10th	Night	12% 13% 41% 30% 4	695
	11th to 20th	Night	16% 12% 35% 30% 7% 1	600
	21st to end	Night	19% 13% 41% 22% 5%	660
April	1st to 10th	Night	12% 14% 44% 27% 5%	600
	11th to 20th	Night	17% 14% 37% 29% 4	593
	21st to end	Night	13% 11% 40% 28% 7% 1	600
May	1st to 10th	Night	19% 8% 35% 30% 7% 1	600
	11th to 20th	Night	15% 8% 31% 35% 9% 1	591
	21st to end	Night	14% 8% 31% 35% 12% 1	650
June	1st to 10th	Night	7% 4 29% 42% 18% 1	599
	11th to 20th	Night	7% 3 37% 39% 14%	570
	21st to end	Night	4 4 38% 42% 10%	570
July	1st to 10th	Night	6% 3 22% 44% 25%	555
	11th to 20th	Night	3 2 21% 52% 20% 2	552
	21st to end	Night	6% 1 17% 50% 25% 1	624
August	1st to 10th	Night	5% 1 19% 52% 22%	567
	11th to 20th	Night	8% 1 18% 52% 20%	564
	21st to end	Night	6% 1 22% 46% 23% 2	627
September	1st to 10th	Night	8% 2 25% 44% 19% 2	570
	11th to 20th	Night	9% 3 32% 37% 18% 1	570
	21st to end	Night	8% 4 31% 42% 14% 1	570
October	1st to 10th	Night	14% 7% 28% 35% 16% 1	613
	11th to 20th	Night	12% 10% 36% 34% 8%	760
	21st to end	Night	14% 10% 34% 32% 10%	864
November	1st to 10th	Night	9% 10% 32% 39% 10%	975
	11th to 20th	Night	10% 11% 40% 32% 7%	1000
	21st to end	Night	13% 10% 32% 36% 9% 1	1000
December	1st to 10th	Night	9% 9% 38% 38% 5% 1	1000
	11th to 20th	Night	15% 11% 33% 35% 6%	1000
	21st to end	Night	17% 10% 34% 32% 6%	1100

Page generated at 2025-06-07 09:28:18. Version ac07

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