Lagoon Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lagoon Observatory clear sky chart from 2005-11-06 to 2026-01-02.

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 3 1 4 2 3 3 3 5% 8% 64%	135338
	Night	5% 4 1 4 2 2 3 3 5% 6% 65%	133517
Transparency	Day	20% 4 9% 19% 27% 23%	130423
	Night	20% 3 7% 18% 27% 25%	129404
Seeing	Day	7% 7% 21% 36% 23% 6%	17160
	Night	7% 4 11% 31% 36% 12%	27000

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	5% 2 1 2 2 2 3 2 3 4 73%	3736
	11th to 20th	Day	7% 3 1 3 2 2 3 2 3 7% 65%	4100
	21st to end	Day	10% 4 2 4 3 3 3 3 7% 10% 52%	4740
February	1st to 10th	Day	10% 5% 1 3 3 3 2 3 4 5% 61%	2000
	11th to 20th	Day	9% 4 1 3 2 3 3 3 6% 7% 60%	1950
	21st to end	Day	7% 4 2 4 3 3 3 3 5% 6% 61%	1650
March	1st to 10th	Day	10% 5% 2 5% 3 3 3 3 5% 6% 56%	4518
	11th to 20th	Day	8% 4 2 4 3 3 3 3 5% 8% 58%	4824
	21st to end	Day	6% 5% 2 5% 4 4 5% 4 6% 9% 51%	5918
April	1st to 10th	Day	6% 5% 2 4 3 2 3 3 5% 8% 61%	2400
	11th to 20th	Day	4 4 2 3 2 2 3 3 5% 7% 64%	2369
	21st to end	Day	4 4 1 4 3 2 2 2 5% 8% 65%	2400
May	1st to 10th	Day	3 4 1 4 2 3 3 2 5% 7% 66%	5440
	11th to 20th	Day	3 6% 3 6% 4 3 3 3 5% 7% 57%	5792
	21st to end	Day	2 4 2 6% 4 3 3 3 5% 9% 60%	6423
June	1st to 10th	Day	4 8% 2 5% 3 3 3 4 6% 8% 53%	2750
	11th to 20th	Day	3 4 2 4 3 2 4 2 5% 8% 63%	2800
	21st to end	Day	2 4 1 3 2 2 2 3 5% 8% 67%	2800
July	1st to 10th	Day	1 1 1 2 2 2 2 2 5% 9% 74%	6319
	11th to 20th	Day	1 2 1 4 3 3 3 3 6% 9% 65%	6128
	21st to end	Day	1 2 1 3 2 2 3 3 6% 8% 68%	6107
August	1st to 10th	Day	1 2 1 2 1 2 2 2 6% 9% 73%	5346
	11th to 20th	Day	1 2 1 2 1 1 2 3 4 8% 75%	5364
	21st to end	Day	1 1 2 2 2 2 2 5% 7% 76%	5984
September	1st to 10th	Day	1 2 1 3 2 2 3 2 4 7% 73%	2400
	11th to 20th	Day	3 3 1 4 2 2 2 2 5% 9% 67%	2305
	21st to end	Day	1 3 1 4 3 2 3 3 6% 7% 68%	2200
October	1st to 10th	Day	2 2 1 1 1 2 2 2 5% 10% 71%	3554
	11th to 20th	Day	3 7% 2 4 2 2 3 3 6% 8% 60%	3261
	21st to end	Day	3 2 1 3 2 3 3 3 5% 5% 68%	3558
November	1st to 10th	Day	3 2 2 4 2 2 3 3 5% 7% 67%	1885
	11th to 20th	Day	6% 3 1 3 2 3 3 3 4 7% 66%	1890
	21st to end	Day	4 3 2 5% 3 2 3 3 5% 8% 62%	1890
December	1st to 10th	Day	4 2 2 3 3 4 4 4 7% 8% 60%	3040
	11th to 20th	Day	9% 4 2 5% 2 3 5% 4 5% 7% 53%	3405
	21st to end	Day	10% 5% 2 6% 4 4 4 5% 7% 9% 44%	4092
January	1st to 10th	Night	5% 3 1 3 2 3 3 2 4 6% 68%	6219
	11th to 20th	Night	7% 4 2 3 2 2 2 2 3 5% 67%	5880
	21st to end	Night	10% 4 1 4 3 3 3 3 5% 6% 57%	6232
February	1st to 10th	Night	9% 6% 2 5% 3 2 2 3 4 5% 61%	2400
	11th to 20th	Night	9% 5% 2 4 2 3 3 2 4 6% 61%	2338
	21st to end	Night	11% 4 2 4 3 3 3 2 4 5% 60%	1980
March	1st to 10th	Night	7% 5% 2 4 3 2 4 4 6% 8% 55%	5376
	11th to 20th	Night	6% 6% 2 5% 4 3 4 3 4 5% 59%	5159
	21st to end	Night	9% 7% 2 4 2 2 3 3 4 6% 57%	5055
April	1st to 10th	Night	6% 5% 1 4 3 3 3 3 4 7% 62%	2000
	11th to 20th	Night	4 5% 2 3 3 2 3 2 4 6% 65%	1979
	21st to end	Night	4 5% 1 3 3 3 3 3 5% 6% 65%	2000
May	1st to 10th	Night	2 4 1 3 2 2 3 2 4 6% 71%	4560
	11th to 20th	Night	2 7% 2 5% 3 2 2 2 3 5% 66%	4123
	21st to end	Night	1 2 1 2 2 2 1 1 3 4 81%	4474
June	1st to 10th	Night	3 6% 2 6% 5% 3 3 3 6% 7% 57%	1644
	11th to 20th	Night	1 6% 2 3 3 2 3 2 5% 7% 68%	1600
	21st to end	Night	2 4 2 4 3 3 4 3 5% 8% 63%	1600
July	1st to 10th	Night	1 1 1 2 1 1 2 1 6% 6% 77%	3640
	11th to 20th	Night	1 3 1 5% 4 3 3 3 5% 8% 63%	3822
	21st to end	Night	1 2 1 3 2 2 2 2 4 6% 75%	4779
August	1st to 10th	Night	1 1 1 2 2 2 2 2 4 8% 74%	4486
	11th to 20th	Night	1 2 1 2 1 1 2 1 3 5% 81%	4506
	21st to end	Night	1 1 1 3 2 2 3 2 5% 6% 75%	5015
September	1st to 10th	Night	2 4 1 4 2 3 3 3 5% 9% 65%	2000
	11th to 20th	Night	3 3 2 4 2 2 2 2 5% 7% 68%	2095
	21st to end	Night	1 4 2 3 2 2 2 3 5% 6% 71%	2200
October	1st to 10th	Night	2 2 1 2 2 1 2 2 5% 8% 73%	3629
	11th to 20th	Night	3 4 3 4 2 3 3 3 6% 7% 63%	3897
	21st to end	Night	3 3 2 3 1 2 2 2 2 6% 76%	4253
November	1st to 10th	Night	3 3 1 3 3 2 2 2 6% 7% 68%	2631
	11th to 20th	Night	4 3 2 4 2 2 2 3 4 6% 67%	2730
	21st to end	Night	5% 3 1 4 3 3 4 3 5% 7% 62%	2730
December	1st to 10th	Night	4 3 1 4 3 3 3 2 5% 6% 65%	4370
	11th to 20th	Night	10% 5% 1 4 3 3 4 4 6% 8% 52%	5009
	21st to end	Night	10% 5% 2 6% 4 5% 5% 5% 7% 8% 43%	7106

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	16% 1 5% 22% 30% 25%	3736
	11th to 20th	Day	21% 4 10% 16% 17% 32%	4100
	21st to end	Day	27% 4 6% 18% 26% 19%	4740
February	1st to 10th	Day	27% 4 5% 17% 25% 23%	2000
	11th to 20th	Day	24% 4 8% 17% 26% 21%	1960
	21st to end	Day	25% 3 8% 21% 22% 21%	1650
March	1st to 10th	Day	28% 5% 9% 19% 22% 17%	4518
	11th to 20th	Day	24% 4 14% 25% 21% 11%	4824
	21st to end	Day	26% 7% 14% 29% 18% 5%	5918
April	1st to 10th	Day	23% 4 13% 25% 24% 11%	2400
	11th to 20th	Day	20% 3 10% 25% 27% 14%	2372
	21st to end	Day	19% 5% 13% 25% 29% 10%	2400
May	1st to 10th	Day	17% 7% 13% 19% 29% 15%	5440
	11th to 20th	Day	26% 4 14% 20% 28% 7%	5795
	21st to end	Day	20% 5% 16% 29% 23% 7%	6424
June	1st to 10th	Day	26% 6% 14% 19% 25% 9%	2750
	11th to 20th	Day	21% 4 10% 15% 31% 19%	2800
	21st to end	Day	17% 2 8% 12% 31% 30%	2800
July	1st to 10th	Day	9% 1 3 14% 20% 53%	6251
	11th to 20th	Day	15% 2 4 15% 33% 32%	6053
	21st to end	Day	14% 2 6% 19% 35% 24%	5932
August	1st to 10th	Day	12% 1 5% 14% 42% 26%	3890
	11th to 20th	Day	10% 1 5% 10% 35% 40%	3880
	21st to end	Day	11% 1 5% 14% 32% 37%	4311
September	1st to 10th	Day	15% 2 7% 13% 30% 33%	2400
	11th to 20th	Day	18% 3 7% 15% 31% 26%	2305
	21st to end	Day	17% 3 7% 19% 29% 26%	2200
October	1st to 10th	Day	10% 2 5% 18% 22% 43%	3554
	11th to 20th	Day	22% 2 5% 15% 32% 24%	3261
	21st to end	Day	18% 3 4 11% 33% 31%	3558
November	1st to 10th	Day	19% 2 7% 17% 24% 31%	1885
	11th to 20th	Day	20% 3 8% 14% 20% 35%	1890
	21st to end	Day	21% 3 8% 14% 23% 30%	1890
December	1st to 10th	Day	21% 4 5% 17% 23% 31%	3040
	11th to 20th	Day	30% 4 7% 16% 24% 19%	3404
	21st to end	Day	33% 6% 11% 23% 18% 9%	4092
January	1st to 10th	Night	19% 3 5% 13% 34% 25%	6219
	11th to 20th	Night	22% 3 7% 18% 21% 30%	5880
	21st to end	Night	27% 3 5% 16% 27% 22%	6232
February	1st to 10th	Night	27% 3 6% 15% 24% 26%	2400
	11th to 20th	Night	27% 3 5% 19% 23% 23%	2339
	21st to end	Night	28% 3 7% 17% 22% 24%	1980
March	1st to 10th	Night	23% 7% 9% 20% 28% 14%	5376
	11th to 20th	Night	26% 5% 12% 25% 19% 13%	5159
	21st to end	Night	27% 5% 12% 28% 22% 7%	5055
April	1st to 10th	Night	24% 3 12% 25% 23% 12%	2000
	11th to 20th	Night	21% 4 9% 23% 28% 15%	1979
	21st to end	Night	21% 3 12% 24% 28% 12%	2000
May	1st to 10th	Night	15% 5% 12% 23% 31% 14%	4557
	11th to 20th	Night	21% 5% 10% 25% 30% 9%	4124
	21st to end	Night	9% 3 8% 39% 33% 9%	4474
June	1st to 10th	Night	27% 5% 13% 21% 26% 7%	1644
	11th to 20th	Night	17% 3 9% 18% 33% 19%	1600
	21st to end	Night	19% 2 7% 11% 32% 30%	1600
July	1st to 10th	Night	8% 1 3 7% 22% 59%	3600
	11th to 20th	Night	17% 3 3 12% 33% 31%	3774
	21st to end	Night	10% 3 4 20% 38% 25%	4642
August	1st to 10th	Night	13% 2 3 15% 38% 30%	3256
	11th to 20th	Night	10% 2 4 11% 35% 39%	3256
	21st to end	Night	11% 2 4 9% 37% 38%	3608
September	1st to 10th	Night	17% 2 7% 9% 27% 37%	2000
	11th to 20th	Night	17% 2 5% 13% 36% 28%	2095
	21st to end	Night	15% 1 6% 13% 34% 30%	2200
October	1st to 10th	Night	11% 1 3 14% 24% 47%	3629
	11th to 20th	Night	19% 2 5% 17% 28% 28%	3897
	21st to end	Night	14% 1 3 9% 31% 42%	4253
November	1st to 10th	Night	17% 3 6% 15% 25% 34%	2631
	11th to 20th	Night	19% 2 6% 14% 22% 36%	2730
	21st to end	Night	24% 3 6% 17% 20% 31%	2730
December	1st to 10th	Night	20% 2 4 14% 24% 35%	4370
	11th to 20th	Night	31% 3 8% 14% 20% 23%	5009
	21st to end	Night	34% 6% 9% 25% 17% 8%	7106

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	15% 7% 31% 34% 12%	239
	11th to 20th	Day	12% 11% 28% 37% 11% 2	400
	21st to end	Day	13% 12% 32% 30% 11% 2	490
February	1st to 10th	Day	13% 13% 30% 28% 12% 3	500
	11th to 20th	Day	12% 11% 31% 33% 10% 2	495
	21st to end	Day	12% 13% 31% 32% 11% 1	414
March	1st to 10th	Day	15% 16% 31% 28% 9% 1	500
	11th to 20th	Day	13% 11% 31% 28% 14% 2	500
	21st to end	Day	10% 14% 30% 31% 13% 2	550
April	1st to 10th	Day	9% 10% 26% 34% 17% 3	500
	11th to 20th	Day	7% 13% 27% 36% 13% 4	492
	21st to end	Day	5% 9% 27% 36% 18% 5%	500
May	1st to 10th	Day	6% 9% 27% 36% 18% 4	503
	11th to 20th	Day	5% 7% 23% 38% 22% 4	528
	21st to end	Day	6% 8% 25% 36% 20% 5%	573
June	1st to 10th	Day	6% 6% 20% 35% 26% 7%	530
	11th to 20th	Day	3 3 17% 40% 29% 8%	530
	21st to end	Day	3 2 12% 39% 35% 8%	530
July	1st to 10th	Day	3 1 6% 40% 36% 13%	526
	11th to 20th	Day	2 1 4 33% 44% 16%	524
	21st to end	Day	2 1 5% 37% 40% 16%	575
August	1st to 10th	Day	3 8% 40% 35% 13%	527
	11th to 20th	Day	3 1 7% 37% 40% 13%	517
	21st to end	Day	1 2 9% 42% 36% 10%	583
September	1st to 10th	Day	3 1 13% 42% 30% 11%	530
	11th to 20th	Day	5% 4 20% 42% 23% 6%	530
	21st to end	Day	2 5% 18% 39% 30% 7%	530
October	1st to 10th	Day	3 4 20% 45% 23% 4	530
	11th to 20th	Day	5% 5% 22% 43% 20% 5%	530
	21st to end	Day	4 7% 23% 36% 23% 7%	583
November	1st to 10th	Day	5% 7% 20% 35% 22% 9%	361
	11th to 20th	Day	8% 7% 31% 33% 17% 4	330
	21st to end	Day	6% 12% 28% 34% 16% 4	330
December	1st to 10th	Day	8% 10% 26% 37% 16% 2	330
	11th to 20th	Day	6% 9% 28% 34% 19% 3	308
	21st to end	Day	15% 11% 32% 27% 13% 2	242
January	1st to 10th	Night	12% 5% 18% 39% 19% 6%	804
	11th to 20th	Night	9% 7% 21% 40% 21% 2	800
	21st to end	Night	13% 9% 18% 36% 21% 3	880
February	1st to 10th	Night	12% 6% 16% 36% 24% 6%	800
	11th to 20th	Night	10% 5% 17% 40% 23% 6%	784
	21st to end	Night	12% 7% 19% 36% 23% 3	660
March	1st to 10th	Night	11% 6% 18% 39% 23% 3	800
	11th to 20th	Night	9% 4 15% 36% 29% 8%	800
	21st to end	Night	9% 4 15% 36% 31% 4	880
April	1st to 10th	Night	9% 3 12% 37% 34% 5%	800
	11th to 20th	Night	5% 5% 13% 35% 35% 7%	791
	21st to end	Night	6% 4 10% 34% 37% 10%	800
May	1st to 10th	Night	7% 3 10% 34% 36% 9%	800
	11th to 20th	Night	6% 4 8% 30% 40% 12%	614
	21st to end	Night	2 3 10% 31% 43% 11%	650
June	1st to 10th	Night	4 2 5% 31% 43% 15%	444
	11th to 20th	Night	2 1 3 22% 53% 18%	400
	21st to end	Night	4 1 1 20% 56% 18%	400
July	1st to 10th	Night	4 1 5% 59% 31%	390
	11th to 20th	Night	4 5% 45% 45%	466
	21st to end	Night	3 2 10% 49% 35%	785
August	1st to 10th	Night	3 1 1 14% 54% 27%	796
	11th to 20th	Night	3 1 1 12% 50% 33%	792
	21st to end	Night	2 1 1 14% 53% 29%	880
September	1st to 10th	Night	4 1 3 19% 48% 25%	800
	11th to 20th	Night	4 1 3 23% 53% 17%	800
	21st to end	Night	3 1 4 26% 49% 17%	800
October	1st to 10th	Night	4 1 7% 35% 46% 9%	800
	11th to 20th	Night	6% 2 8% 33% 41% 10%	800
	21st to end	Night	5% 3 10% 36% 35% 11%	880
November	1st to 10th	Night	4 5% 10% 38% 33% 10%	820
	11th to 20th	Night	5% 3 15% 39% 29% 9%	840
	21st to end	Night	6% 5% 19% 38% 27% 4	840
December	1st to 10th	Night	8% 7% 18% 38% 24% 5%	840
	11th to 20th	Night	12% 5% 18% 41% 21% 3	840
	21st to end	Night	12% 8% 19% 38% 20% 3	924

Page generated at 2025-12-29 22:14:05. Version ac07

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