Lakeside Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lakeside Site clear sky chart from 2005-11-06 to 2025-10-04.

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 5% 2 6% 4 4 4 3 6% 7% 54%	136134
	Night	5% 6% 2 7% 5% 5% 5% 4 6% 7% 50%	130593
Transparency	Day	30% 3 8% 20% 22% 16%	130873
	Night	34% 3 9% 22% 20% 13%	126868
Seeing	Day	7% 8% 22% 33% 22% 8%	16073
	Night	8% 5% 15% 39% 27% 5%	25624

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% 14% 5% 13% 8% 7% 6% 4 5% 6% 27%	4086
	11th to 20th	Day	4 9% 4 13% 10% 8% 5% 4 7% 6% 29%	4100
	21st to end	Day	5% 12% 5% 16% 10% 7% 5% 3 9% 8% 19%	4510
February	1st to 10th	Day	6% 9% 4 13% 8% 7% 6% 5% 6% 8% 28%	1800
	11th to 20th	Day	6% 10% 4 9% 6% 5% 5% 4 6% 10% 36%	1885
	21st to end	Day	4 10% 4 8% 7% 5% 5% 4 7% 9% 36%	1650
March	1st to 10th	Day	4 9% 4 9% 6% 5% 5% 4 6% 9% 40%	4707
	11th to 20th	Day	3 6% 3 6% 5% 5% 6% 4 6% 8% 48%	5000
	21st to end	Day	6% 9% 3 9% 5% 5% 6% 5% 6% 9% 37%	5486
April	1st to 10th	Day	6% 7% 2 6% 5% 5% 5% 4 7% 8% 45%	2245
	11th to 20th	Day	5% 8% 3 6% 5% 4 3 4 5% 7% 49%	2534
	21st to end	Day	7% 7% 2 6% 4 4 4 4 5% 8% 50%	2600
May	1st to 10th	Day	5% 5% 2 5% 4 4 4 3 5% 7% 57%	5880
	11th to 20th	Day	5% 4 2 6% 4 3 4 3 5% 7% 56%	5841
	21st to end	Day	3 4 1 4 3 3 4 3 5% 8% 61%	6423
June	1st to 10th	Day	3 3 1 3 4 3 5% 4 7% 8% 59%	2600
	11th to 20th	Day	4 3 1 3 3 3 4 3 5% 7% 63%	2759
	21st to end	Day	2 2 1 3 2 2 2 2 5% 5% 74%	2800
July	1st to 10th	Day	1 2 1 3 2 2 3 3 4 5% 74%	6319
	11th to 20th	Day	2 2 1 2 2 3 4 3 5% 7% 69%	5978
	21st to end	Day	2 2 1 2 2 2 3 3 4 7% 72%	6401
August	1st to 10th	Day	2 2 1 3 2 2 3 3 4 6% 72%	5779
	11th to 20th	Day	2 2 1 3 3 3 3 3 4 6% 71%	5798
	21st to end	Day	2 2 1 5% 3 4 4 3 5% 6% 63%	6393
September	1st to 10th	Day	2 2 1 3 3 2 3 3 4 6% 71%	2236
	11th to 20th	Day	3 3 1 3 3 3 3 3 5% 5% 68%	2200
	21st to end	Day	5% 3 1 3 2 3 2 2 4 5% 70%	2200
October	1st to 10th	Day	4 2 1 4 3 3 3 2 4 5% 69%	3442
	11th to 20th	Day	4 4 2 4 3 3 3 3 5% 6% 62%	3150
	21st to end	Day	4 5% 2 5% 3 3 4 3 5% 6% 61%	3296
November	1st to 10th	Day	5% 6% 2 7% 6% 5% 4 4 7% 8% 47%	1764
	11th to 20th	Day	6% 8% 2 5% 4 5% 4 3 7% 7% 49%	1800
	21st to end	Day	6% 9% 2 9% 5% 4 4 4 5% 7% 45%	1800
December	1st to 10th	Day	4 7% 2 6% 8% 5% 5% 6% 14% 7% 35%	2757
	11th to 20th	Day	5% 9% 4 10% 7% 6% 7% 5% 8% 11% 27%	3405
	21st to end	Day	7% 11% 5% 13% 9% 7% 6% 4 6% 7% 26%	4510
January	1st to 10th	Night	4 10% 4 9% 7% 5% 6% 4 7% 8% 35%	5867
	11th to 20th	Night	7% 10% 4 11% 6% 7% 7% 5% 7% 9% 27%	5880
	21st to end	Night	5% 11% 4 10% 9% 7% 5% 4 4 7% 34%	6468
February	1st to 10th	Night	4 11% 4 9% 6% 5% 5% 5% 6% 7% 37%	2600
	11th to 20th	Night	6% 9% 3 9% 6% 5% 4 4 5% 7% 44%	2397
	21st to end	Night	3 8% 4 8% 6% 5% 4 5% 6% 8% 43%	1980
March	1st to 10th	Night	5% 11% 3 8% 6% 6% 5% 4 6% 7% 40%	5186
	11th to 20th	Night	3 7% 2 7% 4 6% 6% 5% 7% 9% 44%	5000
	21st to end	Night	5% 7% 3 7% 5% 5% 6% 4 7% 8% 43%	5489
April	1st to 10th	Night	6% 7% 2 6% 4 5% 5% 3 6% 6% 48%	2150
	11th to 20th	Night	6% 8% 2 7% 4 4 4 4 5% 7% 49%	1813
	21st to end	Night	8% 7% 2 7% 5% 4 4 4 5% 6% 49%	1800
May	1st to 10th	Night	7% 5% 2 6% 4 3 4 3 6% 7% 53%	4100
	11th to 20th	Night	7% 3 1 4 3 4 4 4 6% 7% 57%	4074
	21st to end	Night	6% 4 1 5% 4 5% 4 4 6% 7% 55%	4474
June	1st to 10th	Night	5% 4 1 5% 5% 3 4 4 7% 8% 53%	1800
	11th to 20th	Night	4 3 1 4 4 3 3 3 5% 7% 63%	1634
	21st to end	Night	3 2 1 3 3 4 3 3 6% 6% 67%	1600
July	1st to 10th	Night	2 3 1 4 3 3 3 3 4 5% 68%	3640
	11th to 20th	Night	2 4 2 5% 5% 4 5% 4 7% 8% 54%	3980
	21st to end	Night	3 3 1 5% 3 4 4 4 5% 7% 61%	4472
August	1st to 10th	Night	2 2 1 4 2 3 5% 5% 5% 8% 63%	4033
	11th to 20th	Night	2 3 1 5% 3 4 5% 3 5% 6% 62%	4051
	21st to end	Night	3 4 1 5% 4 4 4 3 5% 5% 62%	4571
September	1st to 10th	Night	3 2 1 3 4 3 4 3 5% 6% 67%	2162
	11th to 20th	Night	4 3 1 4 4 3 3 2 4 6% 68%	2200
	21st to end	Night	5% 4 1 3 3 3 3 2 3 4 70%	2200
October	1st to 10th	Night	3 3 1 4 3 3 3 2 4 5% 70%	3602
	11th to 20th	Night	5% 5% 2 6% 3 3 3 3 4 5% 60%	3778
	21st to end	Night	5% 5% 1 5% 3 4 5% 4 5% 7% 56%	4258
November	1st to 10th	Night	5% 6% 2 7% 4 4 4 3 5% 8% 51%	2535
	11th to 20th	Night	4 6% 3 8% 4 4 4 3 6% 8% 51%	2600
	21st to end	Night	5% 8% 3 6% 5% 3 5% 3 5% 8% 49%	2600
December	1st to 10th	Night	3 6% 2 6% 4 4 4 4 6% 9% 52%	4320
	11th to 20th	Night	7% 10% 3 8% 6% 5% 5% 4 7% 9% 36%	4811
	21st to end	Night	7% 11% 4 10% 7% 6% 6% 5% 7% 8% 29%	6468

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	57% 4 18% 14% 7%	4086
	11th to 20th	Day	52% 5% 17% 16% 8% 3	4100
	21st to end	Day	60% 3 12% 19% 5%	4510
February	1st to 10th	Day	52% 5% 13% 21% 8% 2	1800
	11th to 20th	Day	44% 3 17% 23% 12% 1	1895
	21st to end	Day	43% 3 13% 27% 11% 2	1650
March	1st to 10th	Day	42% 2 8% 31% 14% 3	4707
	11th to 20th	Day	33% 3 8% 38% 17% 1	5000
	21st to end	Day	44% 3 16% 27% 9% 1	5486
April	1st to 10th	Day	37% 4 11% 26% 17% 5%	2245
	11th to 20th	Day	35% 2 7% 25% 27% 4	2537
	21st to end	Day	33% 3 8% 29% 23% 4	2600
May	1st to 10th	Day	27% 2 7% 25% 30% 9%	5880
	11th to 20th	Day	27% 3 4 19% 36% 10%	5844
	21st to end	Day	22% 2 4 25% 37% 9%	6424
June	1st to 10th	Day	22% 3 7% 22% 35% 12%	2600
	11th to 20th	Day	21% 2 4 18% 30% 24%	2759
	21st to end	Day	14% 2 1 11% 33% 39%	2800
July	1st to 10th	Day	13% 3 2 8% 16% 59%	6251
	11th to 20th	Day	14% 3 2 7% 24% 49%	5906
	21st to end	Day	12% 2 2 8% 26% 49%	6217
August	1st to 10th	Day	17% 3 3 14% 29% 35%	4208
	11th to 20th	Day	18% 3 3 11% 35% 29%	4197
	21st to end	Day	15% 2 2 13% 31% 37%	4612
September	1st to 10th	Day	16% 2 3 17% 32% 30%	2236
	11th to 20th	Day	19% 2 5% 20% 30% 24%	2200
	21st to end	Day	19% 2 5% 21% 36% 18%	2200
October	1st to 10th	Day	20% 2 5% 15% 40% 18%	3442
	11th to 20th	Day	23% 2 5% 32% 31% 8%	3150
	21st to end	Day	25% 2 8% 37% 24% 3	3296
November	1st to 10th	Day	35% 2 16% 25% 20% 2	1764
	11th to 20th	Day	33% 3 14% 36% 13% 1	1800
	21st to end	Day	40% 3 14% 29% 13% 1	1800
December	1st to 10th	Day	35% 11% 21% 24% 8% 1	2757
	11th to 20th	Day	49% 4 21% 24% 3	3404
	21st to end	Day	57% 3 13% 18% 9% 1	4510
January	1st to 10th	Night	46% 4 17% 25% 8%	5867
	11th to 20th	Night	50% 6% 16% 18% 8% 2	5880
	21st to end	Night	51% 3 10% 24% 12% 1	6468
February	1st to 10th	Night	44% 4 16% 25% 9% 2	2600
	11th to 20th	Night	41% 3 12% 26% 18% 1	2398
	21st to end	Night	38% 3 10% 30% 16% 2	1980
March	1st to 10th	Night	44% 2 7% 25% 18% 4	5186
	11th to 20th	Night	36% 3 8% 30% 23% 1	5000
	21st to end	Night	39% 3 12% 30% 15% 2	5489
April	1st to 10th	Night	36% 3 10% 25% 19% 8%	2150
	11th to 20th	Night	35% 3 6% 27% 25% 5%	1813
	21st to end	Night	36% 3 8% 23% 27% 4	1800
May	1st to 10th	Night	32% 3 7% 20% 29% 10%	4097
	11th to 20th	Night	26% 3 5% 24% 34% 9%	4075
	21st to end	Night	29% 3 4 20% 36% 8%	4474
June	1st to 10th	Night	28% 3 6% 21% 30% 13%	1800
	11th to 20th	Night	22% 2 5% 19% 32% 21%	1634
	21st to end	Night	19% 3 1 14% 27% 37%	1600
July	1st to 10th	Night	20% 2 2 6% 15% 55%	3600
	11th to 20th	Night	25% 4 2 7% 21% 41%	3929
	21st to end	Night	21% 3 3 6% 23% 43%	4344
August	1st to 10th	Night	21% 4 4 11% 27% 33%	2928
	11th to 20th	Night	23% 4 3 11% 28% 31%	2928
	21st to end	Night	16% 3 2 11% 22% 47%	3294
September	1st to 10th	Night	19% 2 2 15% 25% 36%	2162
	11th to 20th	Night	20% 1 5% 15% 31% 28%	2200
	21st to end	Night	20% 2 2 15% 34% 27%	2200
October	1st to 10th	Night	19% 2 5% 13% 35% 27%	3602
	11th to 20th	Night	27% 2 3 23% 34% 11%	3778
	21st to end	Night	27% 3 5% 33% 27% 5%	4258
November	1st to 10th	Night	33% 2 10% 29% 20% 5%	2535
	11th to 20th	Night	32% 3 11% 36% 16% 2	2600
	21st to end	Night	35% 2 11% 35% 16% 1	2600
December	1st to 10th	Night	28% 5% 18% 37% 12% 1	4320
	11th to 20th	Night	44% 3 22% 24% 6%	4811
	21st to end	Night	51% 3 15% 20% 10%	6468

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% 6% 24% 32% 18% 6%	300
	11th to 20th	Day	9% 6% 19% 37% 23% 6%	300
	21st to end	Day	10% 5% 13% 39% 25% 9%	330
February	1st to 10th	Day	8% 9% 28% 33% 18% 4	300
	11th to 20th	Day	9% 9% 20% 41% 18% 4	431
	21st to end	Day	6% 10% 26% 34% 21% 4	414
March	1st to 10th	Day	11% 8% 19% 37% 20% 5%	500
	11th to 20th	Day	8% 9% 23% 36% 21% 4	500
	21st to end	Day	14% 9% 25% 34% 16% 2	550
April	1st to 10th	Day	12% 10% 24% 28% 22% 4	500
	11th to 20th	Day	11% 18% 25% 29% 15% 3	492
	21st to end	Day	11% 15% 26% 22% 21% 5%	500
May	1st to 10th	Day	6% 16% 31% 28% 12% 7%	503
	11th to 20th	Day	9% 12% 29% 28% 17% 5%	528
	21st to end	Day	9% 9% 25% 29% 21% 8%	573
June	1st to 10th	Day	5% 9% 26% 33% 19% 8%	530
	11th to 20th	Day	7% 10% 32% 28% 18% 6%	530
	21st to end	Day	2 6% 31% 35% 21% 5%	530
July	1st to 10th	Day	2 4 23% 40% 25% 6%	526
	11th to 20th	Day	2 3 22% 43% 18% 11%	524
	21st to end	Day	2 3 17% 39% 30% 9%	575
August	1st to 10th	Day	4 3 23% 34% 25% 10%	527
	11th to 20th	Day	4 3 17% 35% 29% 12%	517
	21st to end	Day	3 6% 15% 33% 29% 14%	583
September	1st to 10th	Day	2 5% 19% 28% 24% 23%	530
	11th to 20th	Day	4 6% 19% 31% 27% 12%	530
	21st to end	Day	6% 6% 19% 25% 31% 13%	530
October	1st to 10th	Day	6% 8% 18% 28% 25% 15%	460
	11th to 20th	Day	5% 10% 19% 22% 26% 18%	300
	21st to end	Day	7% 7% 23% 29% 28% 6%	330
November	1st to 10th	Day	10% 11% 19% 29% 22% 9%	300
	11th to 20th	Day	7% 8% 20% 36% 19% 9%	300
	21st to end	Day	10% 7% 15% 29% 30% 8%	300
December	1st to 10th	Day	9% 7% 13% 35% 23% 13%	300
	11th to 20th	Day	13% 4 15% 41% 24% 4	300
	21st to end	Day	13% 8% 20% 35% 20% 4	330
January	1st to 10th	Night	12% 5% 15% 37% 25% 7%	800
	11th to 20th	Night	12% 6% 14% 35% 27% 7%	800
	21st to end	Night	12% 4 12% 40% 26% 5%	880
February	1st to 10th	Night	10% 6% 18% 42% 21% 4	800
	11th to 20th	Night	10% 3 16% 46% 22% 3	784
	21st to end	Night	7% 5% 18% 46% 21% 3	660
March	1st to 10th	Night	10% 7% 14% 45% 21% 4	800
	11th to 20th	Night	7% 6% 16% 43% 27% 2	800
	21st to end	Night	12% 5% 21% 40% 18% 3	880
April	1st to 10th	Night	10% 9% 18% 41% 19% 4	800
	11th to 20th	Night	10% 9% 23% 41% 15% 2	625
	21st to end	Night	11% 7% 20% 38% 21% 3	600
May	1st to 10th	Night	10% 7% 22% 39% 20% 3	600
	11th to 20th	Night	9% 7% 17% 37% 26% 4	591
	21st to end	Night	11% 7% 17% 34% 26% 5%	650
June	1st to 10th	Night	7% 7% 15% 38% 29% 5%	600
	11th to 20th	Night	5% 8% 17% 41% 27% 1	434
	21st to end	Night	3 4 17% 40% 33% 4	400
July	1st to 10th	Night	4 2 15% 41% 34% 4	390
	11th to 20th	Night	4 3 15% 46% 31% 1	530
	21st to end	Night	5% 2 10% 40% 40% 3	657
August	1st to 10th	Night	4 2 12% 43% 36% 2	597
	11th to 20th	Night	4 2 12% 44% 35% 3	594
	21st to end	Night	5% 3 13% 37% 35% 8%	683
September	1st to 10th	Night	3 3 10% 36% 38% 10%	800
	11th to 20th	Night	4 4 12% 36% 35% 9%	800
	21st to end	Night	6% 4 13% 31% 35% 11%	800
October	1st to 10th	Night	5% 3 16% 37% 31% 8%	772
	11th to 20th	Night	6% 4 13% 35% 36% 6%	760
	21st to end	Night	7% 5% 14% 36% 31% 7%	836
November	1st to 10th	Night	9% 5% 16% 35% 30% 6%	780
	11th to 20th	Night	6% 4 17% 44% 24% 5%	800
	21st to end	Night	8% 4 15% 39% 27% 7%	800
December	1st to 10th	Night	10% 4 14% 44% 25% 4	841
	11th to 20th	Night	14% 4 14% 40% 25% 4	800
	21st to end	Night	17% 6% 16% 39% 19% 3	880

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