Las Dos Scopes
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Las Dos Scopes clear sky chart from 2005-11-06 to 2025-09-19.

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	2 3 1 4 3 3 4 4 6% 8% 61%	134415
	Night	3 4 2 5% 3 4 4 4 6% 7% 59%	132129
Transparency	Day	18% 6% 11% 24% 27% 15%	129415
	Night	21% 6% 11% 22% 27% 14%	128133
Seeing	Day	5% 9% 27% 31% 22% 6%	16354
	Night	5% 4 29% 42% 18% 1	26394

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 6% 3 6% 3 3 3 3 5% 6% 61%	3974
	11th to 20th	Day	2 4 2 4 2 2 2 2 4 6% 68%	4100
	21st to end	Day	3 4 2 5% 3 4 4 3 6% 6% 61%	4510
February	1st to 10th	Day	2 6% 2 5% 3 3 3 3 4 6% 61%	1824
	11th to 20th	Day	3 6% 2 5% 3 2 3 4 6% 7% 58%	1949
	21st to end	Day	2 8% 2 4 2 3 3 2 4 6% 61%	1650
March	1st to 10th	Day	2 5% 2 5% 3 3 3 3 4 7% 63%	4720
	11th to 20th	Day	3 6% 2 6% 4 4 5% 4 6% 8% 51%	5000
	21st to end	Day	2 5% 2 5% 3 4 3 3 5% 7% 61%	5678
April	1st to 10th	Day	3 4 2 3 4 3 3 3 5% 7% 63%	2400
	11th to 20th	Day	2 5% 2 4 3 3 4 4 5% 6% 61%	2371
	21st to end	Day	3 4 1 3 3 2 3 3 5% 8% 64%	2400
May	1st to 10th	Day	3 3 1 3 3 4 4 4 6% 8% 60%	5440
	11th to 20th	Day	3 2 1 3 2 3 3 4 5% 7% 66%	5707
	21st to end	Day	1 1 1 2 2 3 3 3 5% 8% 71%	6925
June	1st to 10th	Day	1 2 1 3 3 4 4 4 7% 10% 63%	2800
	11th to 20th	Day	2 2 1 2 3 2 3 3 5% 7% 71%	2800
	21st to end	Day	5% 3 1 4 4 4 5% 4 6% 7% 56%	2800
July	1st to 10th	Day	1 2 1 3 3 4 5% 5% 7% 9% 59%	6323
	11th to 20th	Day	1 1 1 3 3 4 7% 7% 11% 14% 48%	5880
	21st to end	Day	2 3 1 5% 5% 6% 7% 7% 10% 11% 42%	6401
August	1st to 10th	Day	2 2 1 4 4 5% 7% 6% 10% 13% 48%	5634
	11th to 20th	Day	2 2 1 3 3 4 5% 5% 9% 10% 58%	5366
	21st to end	Day	2 2 1 4 5% 5% 7% 6% 10% 12% 46%	5984
September	1st to 10th	Day	5% 4 1 4 4 4 4 6% 7% 8% 52%	2400
	11th to 20th	Day	5% 4 1 3 2 3 4 4 6% 7% 60%	2377
	21st to end	Day	3 2 1 3 2 2 3 2 5% 7% 69%	2068
October	1st to 10th	Day	4 2 1 3 2 3 2 2 4 4 73%	3170
	11th to 20th	Day	4 2 1 4 4 3 4 3 4 6% 64%	3150
	21st to end	Day	3 3 1 2 2 2 2 2 3 5% 77%	3438
November	1st to 10th	Day	3 4 1 3 1 1 3 3 4 7% 71%	1883
	11th to 20th	Day	3 3 1 2 2 2 3 3 5% 6% 72%	1800
	21st to end	Day	4 6% 1 3 2 3 2 3 4 6% 66%	1800
December	1st to 10th	Day	2 3 1 2 1 2 2 1 3 6% 78%	2663
	11th to 20th	Day	3 3 1 4 3 3 3 3 4 7% 66%	3026
	21st to end	Day	3 4 1 3 2 2 3 3 4 6% 70%	4004
January	1st to 10th	Night	1 6% 3 7% 4 4 4 3 5% 6% 58%	6033
	11th to 20th	Night	2 4 2 3 2 3 3 3 4 6% 68%	5880
	21st to end	Night	3 5% 2 6% 4 3 4 3 5% 7% 58%	6468
February	1st to 10th	Night	2 7% 3 5% 2 3 2 2 4 6% 63%	2575
	11th to 20th	Night	5% 7% 2 5% 3 2 4 3 5% 6% 59%	2338
	21st to end	Night	3 7% 2 5% 2 3 2 2 4 5% 65%	1980
March	1st to 10th	Night	2 7% 2 5% 3 3 3 3 4 5% 63%	5159
	11th to 20th	Night	7% 7% 2 5% 4 3 4 3 5% 5% 55%	5000
	21st to end	Night	3 6% 2 4 3 3 3 3 4 6% 63%	5288
April	1st to 10th	Night	4 4 2 4 3 3 4 3 5% 6% 63%	2000
	11th to 20th	Night	4 6% 1 3 3 3 4 3 6% 6% 60%	1977
	21st to end	Night	4 3 1 4 3 2 4 4 4 5% 65%	2000
May	1st to 10th	Night	5% 5% 2 6% 4 5% 4 4 5% 6% 53%	4540
	11th to 20th	Night	4 4 2 4 3 3 4 4 6% 7% 60%	4201
	21st to end	Night	3 2 1 3 3 3 4 3 6% 7% 66%	3972
June	1st to 10th	Night	2 2 1 5% 4 4 4 5% 6% 9% 59%	1600
	11th to 20th	Night	2 2 1 4 3 2 3 4 5% 6% 69%	1600
	21st to end	Night	5% 3 1 4 4 4 5% 4 7% 9% 53%	1600
July	1st to 10th	Night	2 2 1 5% 5% 5% 5% 5% 6% 7% 56%	3640
	11th to 20th	Night	2 2 1 5% 5% 6% 7% 7% 11% 13% 40%	4097
	21st to end	Night	6% 5% 2 6% 5% 6% 7% 6% 10% 11% 35%	4472
August	1st to 10th	Night	2 3 2 8% 6% 7% 7% 6% 9% 12% 39%	4175
	11th to 20th	Night	2 3 1 6% 4 6% 7% 6% 10% 13% 41%	4483
	21st to end	Night	3 4 2 9% 7% 7% 8% 6% 10% 13% 31%	4993
September	1st to 10th	Night	5% 3 1 4 4 5% 5% 5% 7% 10% 51%	2000
	11th to 20th	Night	6% 3 1 4 3 3 4 4 6% 8% 57%	1980
	21st to end	Night	5% 4 1 3 2 2 3 3 4 7% 66%	2108
October	1st to 10th	Night	3 2 1 3 2 2 2 2 3 5% 74%	3800
	11th to 20th	Night	4 2 1 3 3 3 4 3 6% 6% 63%	3778
	21st to end	Night	3 2 1 2 1 1 2 2 4 6% 76%	4120
November	1st to 10th	Night	3 2 1 2 1 2 3 2 3 5% 75%	2394
	11th to 20th	Night	2 2 1 2 2 2 2 2 4 5% 75%	2600
	21st to end	Night	6% 5% 2 3 3 3 3 3 4 5% 64%	2600
December	1st to 10th	Night	2 4 1 2 2 1 2 2 3 6% 75%	4523
	11th to 20th	Night	3 3 1 3 2 2 3 2 5% 8% 68%	5181
	21st to end	Night	3 5% 2 4 3 3 3 2 4 6% 67%	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	21% 6% 8% 33% 29% 3	3975
	11th to 20th	Day	14% 4 13% 28% 24% 17%	4100
	21st to end	Day	21% 6% 11% 19% 29% 14%	4510
February	1st to 10th	Day	22% 4 13% 27% 24% 10%	1824
	11th to 20th	Day	22% 4 9% 29% 27% 9%	1959
	21st to end	Day	22% 3 6% 20% 33% 16%	1650
March	1st to 10th	Day	17% 4 6% 18% 34% 21%	4720
	11th to 20th	Day	22% 8% 11% 23% 26% 10%	5000
	21st to end	Day	19% 5% 6% 32% 29% 8%	5678
April	1st to 10th	Day	18% 4 8% 22% 31% 17%	2400
	11th to 20th	Day	21% 5% 6% 19% 30% 18%	2374
	21st to end	Day	17% 4 9% 23% 31% 16%	2400
May	1st to 10th	Day	18% 7% 11% 21% 27% 17%	5440
	11th to 20th	Day	14% 7% 7% 19% 30% 22%	5710
	21st to end	Day	10% 4 10% 17% 25% 34%	6926
June	1st to 10th	Day	14% 5% 12% 21% 25% 22%	2800
	11th to 20th	Day	12% 3 6% 14% 25% 39%	2800
	21st to end	Day	24% 5% 9% 18% 23% 21%	2800
July	1st to 10th	Day	17% 9% 13% 17% 21% 24%	6255
	11th to 20th	Day	15% 10% 25% 32% 11% 5%	5811
	21st to end	Day	27% 11% 20% 27% 13% 3	6217
August	1st to 10th	Day	24% 12% 23% 24% 13% 5%	4096
	11th to 20th	Day	15% 7% 15% 30% 21% 11%	3882
	21st to end	Day	25% 10% 21% 26% 16% 3	4311
September	1st to 10th	Day	24% 7% 13% 26% 21% 9%	2400
	11th to 20th	Day	20% 6% 12% 20% 27% 15%	2377
	21st to end	Day	15% 3 7% 24% 35% 16%	2068
October	1st to 10th	Day	15% 4 5% 16% 34% 26%	3170
	11th to 20th	Day	19% 5% 7% 15% 36% 17%	3150
	21st to end	Day	12% 2 5% 20% 41% 19%	3438
November	1st to 10th	Day	14% 2 7% 25% 38% 14%	1883
	11th to 20th	Day	13% 4 8% 27% 38% 10%	1800
	21st to end	Day	20% 3 6% 25% 33% 13%	1800
December	1st to 10th	Day	11% 2 8% 31% 39% 9%	2663
	11th to 20th	Day	18% 3 8% 33% 34% 4	3024
	21st to end	Day	15% 4 9% 32% 33% 7%	4004
January	1st to 10th	Night	24% 5% 9% 29% 27% 6%	6033
	11th to 20th	Night	15% 4 14% 27% 27% 14%	5880
	21st to end	Night	22% 6% 11% 21% 32% 8%	6468
February	1st to 10th	Night	22% 3 12% 26% 27% 11%	2575
	11th to 20th	Night	24% 3 9% 28% 25% 10%	2338
	21st to end	Night	22% 2 6% 19% 34% 17%	1980
March	1st to 10th	Night	19% 5% 6% 16% 37% 17%	5159
	11th to 20th	Night	26% 7% 7% 19% 29% 12%	5000
	21st to end	Night	19% 6% 6% 30% 32% 8%	5288
April	1st to 10th	Night	19% 5% 7% 22% 30% 18%	2000
	11th to 20th	Night	22% 4 7% 19% 26% 22%	1977
	21st to end	Night	18% 5% 10% 20% 33% 14%	2000
May	1st to 10th	Night	24% 9% 10% 18% 20% 19%	4537
	11th to 20th	Night	19% 9% 10% 16% 23% 23%	4202
	21st to end	Night	14% 6% 10% 14% 17% 39%	3972
June	1st to 10th	Night	19% 7% 16% 18% 20% 20%	1600
	11th to 20th	Night	14% 4 8% 14% 22% 38%	1600
	21st to end	Night	25% 6% 13% 17% 18% 21%	1600
July	1st to 10th	Night	24% 9% 12% 15% 15% 25%	3600
	11th to 20th	Night	26% 12% 27% 21% 7% 7%	4044
	21st to end	Night	36% 11% 21% 20% 10% 1	4344
August	1st to 10th	Night	36% 13% 18% 17% 10% 6%	3037
	11th to 20th	Night	28% 10% 20% 17% 15% 11%	3243
	21st to end	Night	36% 12% 18% 21% 10% 4	3597
September	1st to 10th	Night	25% 8% 15% 24% 17% 10%	2000
	11th to 20th	Night	23% 6% 14% 15% 25% 18%	1980
	21st to end	Night	18% 5% 10% 19% 32% 17%	2108
October	1st to 10th	Night	14% 3 6% 14% 37% 25%	3800
	11th to 20th	Night	17% 6% 8% 17% 30% 23%	3778
	21st to end	Night	10% 2 6% 25% 36% 21%	4120
November	1st to 10th	Night	11% 3 7% 25% 40% 14%	2394
	11th to 20th	Night	12% 3 8% 25% 39% 13%	2600
	21st to end	Night	22% 3 6% 23% 32% 15%	2600
December	1st to 10th	Night	13% 2 6% 35% 32% 12%	4523
	11th to 20th	Night	15% 3 8% 30% 35% 8%	5182
	21st to end	Night	19% 4 9% 29% 35% 3	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	5% 9% 47% 30% 8% 1	300
	11th to 20th	Day	10% 6% 48% 28% 6% 1	300
	21st to end	Day	3 10% 40% 30% 13% 3	330
February	1st to 10th	Day	4 15% 40% 32% 9%	300
	11th to 20th	Day	8% 15% 42% 27% 7%	300
	21st to end	Day	8% 16% 47% 23% 6%	249
March	1st to 10th	Day	6% 21% 33% 31% 9% 1	390
	11th to 20th	Day	9% 17% 37% 25% 12% 1	500
	21st to end	Day	10% 25% 36% 20% 9%	550
April	1st to 10th	Day	7% 17% 41% 26% 8% 1	500
	11th to 20th	Day	9% 24% 38% 21% 8% 1	492
	21st to end	Day	7% 22% 37% 25% 8% 1	500
May	1st to 10th	Day	5% 14% 41% 27% 11% 1	503
	11th to 20th	Day	6% 14% 31% 30% 16% 3	585
	21st to end	Day	3 11% 31% 36% 17% 2	789
June	1st to 10th	Day	2 6% 22% 39% 28% 4	730
	11th to 20th	Day	2 6% 25% 37% 26% 4	730
	21st to end	Day	6% 4 18% 35% 29% 7%	730
July	1st to 10th	Day	3 1 12% 34% 39% 11%	718
	11th to 20th	Day	3 1 6% 24% 42% 23%	524
	21st to end	Day	3 2 6% 27% 40% 21%	575
August	1st to 10th	Day	4 2 8% 29% 40% 17%	527
	11th to 20th	Day	4 2 12% 31% 39% 13%	517
	21st to end	Day	3 2 10% 35% 36% 14%	583
September	1st to 10th	Day	5% 2 12% 36% 35% 11%	530
	11th to 20th	Day	4 2 22% 36% 30% 6%	523
	21st to end	Day	3 7% 18% 34% 29% 9%	319
October	1st to 10th	Day	6% 8% 23% 29% 28% 5%	300
	11th to 20th	Day	7% 8% 28% 28% 26% 4	300
	21st to end	Day	8% 8% 24% 35% 20% 4	330
November	1st to 10th	Day	7% 12% 33% 35% 13%	300
	11th to 20th	Day	3 7% 31% 42% 16% 2	300
	21st to end	Day	8% 11% 41% 26% 12% 2	300
December	1st to 10th	Day	4 6% 40% 32% 14% 2	300
	11th to 20th	Day	5% 13% 36% 35% 10% 1	300
	21st to end	Day	10% 11% 45% 27% 7%	330
January	1st to 10th	Night	4 3 38% 43% 11%	875
	11th to 20th	Night	6% 2 45% 36% 10% 1	800
	21st to end	Night	7% 3 37% 41% 11% 2	880
February	1st to 10th	Night	5% 4 43% 41% 7%	800
	11th to 20th	Night	7% 5% 45% 37% 5%	784
	21st to end	Night	6% 3 52% 37% 2	660
March	1st to 10th	Night	6% 5% 41% 41% 7%	800
	11th to 20th	Night	7% 6% 34% 42% 11%	800
	21st to end	Night	5% 6% 39% 43% 8%	795
April	1st to 10th	Night	6% 6% 45% 36% 7%	600
	11th to 20th	Night	7% 7% 41% 35% 9%	593
	21st to end	Night	5% 6% 42% 39% 8%	600
May	1st to 10th	Night	5% 6% 33% 45% 11%	600
	11th to 20th	Night	6% 5% 28% 41% 18% 2	591
	21st to end	Night	3 7% 30% 48% 12%	650
June	1st to 10th	Night	2 4 21% 49% 25% 1	600
	11th to 20th	Night	2 2 25% 51% 19% 1	600
	21st to end	Night	5% 3 13% 50% 28% 1	600
July	1st to 10th	Night	4 2 9% 43% 39% 2	585
	11th to 20th	Night	4 2 5% 36% 47% 5%	582
	21st to end	Night	5% 2 4 31% 49% 9%	657
August	1st to 10th	Night	4 2 5% 29% 52% 7%	597
	11th to 20th	Night	5% 3 5% 42% 41% 4	594
	21st to end	Night	3 3 5% 39% 45% 4	660
September	1st to 10th	Night	5% 1 8% 46% 38% 2	600
	11th to 20th	Night	6% 2 10% 48% 32% 2	594
	21st to end	Night	5% 2 18% 47% 27% 2	607
October	1st to 10th	Night	6% 4 21% 46% 22% 1	760
	11th to 20th	Night	5% 2 24% 49% 19% 2	760
	21st to end	Night	5% 3 26% 44% 19% 3	836
November	1st to 10th	Night	4 2 27% 47% 18% 1	834
	11th to 20th	Night	3 3 29% 49% 14% 2	1000
	21st to end	Night	8% 4 35% 36% 16% 1	1000
December	1st to 10th	Night	5% 3 37% 44% 10% 1	1000
	11th to 20th	Night	7% 4 40% 40% 9% 1	1000
	21st to end	Night	8% 4 44% 37% 7%	1100

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