Lake Stars Observatory
Clear Sky Chart
History

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

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	12% 8% 3 6% 4 4 4 3 5% 7% 44%	127330
	Night	12% 8% 3 6% 4 4 3 3 5% 6% 46%	124921
Transparency	Day	39% 5% 11% 25% 17% 3	130939
	Night	38% 4 10% 25% 18% 4	129388
Seeing	Day	18% 13% 30% 25% 12% 2	17256
	Night	18% 13% 30% 27% 11% 1	27189

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	16% 11% 3 8% 5% 4 3 3 4 5% 38%	4097
	11th to 20th	Day	9% 11% 3 9% 5% 5% 4 3 4 6% 41%	4170
	21st to end	Day	16% 11% 4 7% 3 3 4 3 4 5% 39%	4587
February	1st to 10th	Day	16% 12% 4 10% 5% 4 4 2 4 5% 34%	1800
	11th to 20th	Day	14% 12% 3 7% 4 4 4 3 4 5% 40%	1774
	21st to end	Day	16% 10% 3 6% 3 5% 3 3 5% 5% 40%	1686
March	1st to 10th	Day	14% 10% 3 5% 3 2 3 2 4 5% 49%	4936
	11th to 20th	Day	11% 6% 2 5% 3 3 4 3 4 6% 53%	4980
	21st to end	Day	14% 11% 3 8% 5% 5% 4 4 6% 7% 34%	5462
April	1st to 10th	Day	13% 8% 3 7% 5% 4 4 3 5% 6% 43%	2390
	11th to 20th	Day	16% 9% 2 6% 4 4 4 4 5% 5% 41%	2374
	21st to end	Day	21% 9% 2 7% 5% 4 4 3 4 7% 34%	2400
May	1st to 10th	Day	16% 8% 3 6% 5% 4 5% 4 6% 8% 34%	5810
	11th to 20th	Day	13% 7% 3 7% 4 4 5% 4 6% 8% 40%	5862
	21st to end	Day	20% 6% 2 5% 4 4 4 3 5% 6% 40%	6931
June	1st to 10th	Day	8% 5% 2 5% 4 5% 5% 4 6% 9% 46%	2800
	11th to 20th	Day	7% 5% 2 7% 4 4 5% 4 6% 10% 45%	2800
	21st to end	Day	5% 3 1 5% 5% 4 5% 4 7% 9% 51%	2800
July	1st to 10th	Day	10% 6% 2 6% 4 4 5% 4 6% 8% 45%	6236
	11th to 20th	Day	7% 6% 2 7% 5% 4 6% 4 6% 11% 42%	5900
	21st to end	Day	6% 4 2 6% 4 5% 6% 5% 9% 11% 41%	6422
August	1st to 10th	Day	4 4 2 5% 4 4 4 4 7% 11% 52%	4234
	11th to 20th	Day	9% 6% 2 6% 4 4 5% 4 5% 8% 47%	4077
	21st to end	Day	6% 5% 2 4 3 4 4 3 6% 9% 55%	4312
September	1st to 10th	Day	10% 5% 2 5% 4 3 4 4 5% 7% 50%	2400
	11th to 20th	Day	11% 6% 2 6% 3 3 4 3 4 7% 50%	2363
	21st to end	Day	8% 6% 2 5% 4 4 4 3 6% 7% 53%	2105
October	1st to 10th	Day	10% 4 2 5% 3 3 3 2 5% 5% 56%	2000
	11th to 20th	Day	14% 6% 2 5% 2 3 3 2 3 5% 55%	2000
	21st to end	Day	20% 7% 3 6% 3 2 3 2 3 5% 46%	2200
November	1st to 10th	Day	11% 7% 2 5% 3 3 3 2 4 5% 55%	2057
	11th to 20th	Day	15% 7% 2 5% 3 3 3 3 5% 6% 49%	1837
	21st to end	Day	17% 9% 3 6% 2 2 3 3 5% 6% 44%	1680
December	1st to 10th	Day	9% 9% 4 6% 4 3 3 3 4 5% 51%	2690
	11th to 20th	Day	12% 9% 4 5% 4 3 3 3 4 6% 48%	3088
	21st to end	Day	19% 21% 5% 10% 4 3 3 2 3 5% 24%	4070
January	1st to 10th	Night	14% 11% 5% 13% 6% 5% 4 2 3 4 33%	6083
	11th to 20th	Night	11% 8% 3 12% 6% 6% 4 3 3 4 39%	6030
	21st to end	Night	16% 11% 4 7% 4 3 3 2 4 5% 41%	6633
February	1st to 10th	Night	14% 12% 4 7% 5% 3 3 4 5% 6% 36%	2601
	11th to 20th	Night	15% 10% 3 7% 5% 3 3 3 5% 5% 42%	2511
	21st to end	Night	15% 9% 3 8% 4 3 4 3 4 5% 43%	1960
March	1st to 10th	Night	16% 12% 3 5% 3 3 3 3 4 4 44%	4919
	11th to 20th	Night	12% 8% 2 4 3 3 3 3 5% 6% 52%	4980
	21st to end	Night	15% 10% 3 7% 4 4 4 4 5% 7% 36%	5467
April	1st to 10th	Night	11% 6% 2 5% 3 4 3 3 4 8% 50%	2010
	11th to 20th	Night	14% 8% 2 4 4 3 3 3 5% 8% 46%	1975
	21st to end	Night	17% 8% 3 6% 5% 4 4 3 5% 7% 39%	2000
May	1st to 10th	Night	17% 9% 3 6% 4 3 3 3 5% 8% 39%	4099
	11th to 20th	Night	13% 7% 2 6% 4 3 3 3 6% 9% 43%	4053
	21st to end	Night	17% 7% 2 5% 4 3 3 3 4 7% 44%	3942
June	1st to 10th	Night	7% 4 2 5% 4 3 5% 4 8% 9% 50%	1600
	11th to 20th	Night	5% 5% 1 5% 3 3 4 4 9% 11% 49%	1600
	21st to end	Night	3 3 1 3 3 3 3 4 7% 9% 61%	1600
July	1st to 10th	Night	8% 5% 3 6% 4 4 4 3 6% 9% 47%	3710
	11th to 20th	Night	4 4 2 6% 4 4 5% 4 6% 10% 51%	4077
	21st to end	Night	5% 4 1 4 3 4 4 5% 7% 11% 50%	4449
August	1st to 10th	Night	3 2 1 4 4 3 3 4 6% 9% 63%	2926
	11th to 20th	Night	9% 6% 2 6% 4 4 4 3 5% 7% 51%	2977
	21st to end	Night	4 4 1 4 3 4 4 3 6% 9% 61%	3586
September	1st to 10th	Night	10% 5% 2 4 3 3 3 4 4 7% 57%	2000
	11th to 20th	Night	9% 4 2 4 3 3 5% 3 6% 8% 53%	2033
	21st to end	Night	8% 4 1 5% 3 3 3 3 5% 6% 58%	2275
October	1st to 10th	Night	7% 4 1 4 3 3 3 3 5% 6% 61%	2400
	11th to 20th	Night	13% 6% 2 5% 3 3 3 3 4 5% 53%	2400
	21st to end	Night	17% 7% 2 4 3 3 3 3 3 4 50%	2640
November	1st to 10th	Night	12% 5% 2 4 3 2 3 3 4 5% 57%	2460
	11th to 20th	Night	12% 8% 2 5% 3 3 3 2 3 5% 52%	2776
	21st to end	Night	16% 9% 3 5% 3 3 3 2 4 5% 46%	2940
December	1st to 10th	Night	10% 9% 3 6% 4 3 4 3 4 5% 49%	4720
	11th to 20th	Night	15% 10% 3 6% 4 3 3 2 4 5% 44%	5339
	21st to end	Night	24% 18% 5% 8% 4 3 3 2 3 4 26%	7150

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	49% 4 10% 24% 13% 1	4098
	11th to 20th	Day	44% 3 9% 25% 15% 4	4170
	21st to end	Day	47% 3 9% 17% 17% 7%	4587
February	1st to 10th	Day	53% 4 9% 20% 12% 1	1800
	11th to 20th	Day	48% 4 11% 20% 15% 3	1783
	21st to end	Day	45% 4 8% 24% 14% 5%	1686
March	1st to 10th	Day	40% 2 7% 23% 22% 6%	4936
	11th to 20th	Day	33% 3 8% 24% 24% 8%	4980
	21st to end	Day	48% 5% 15% 25% 6%	5464
April	1st to 10th	Day	42% 5% 10% 23% 17% 3	2390
	11th to 20th	Day	44% 5% 12% 22% 15% 2	2374
	21st to end	Day	51% 4 11% 21% 12% 1	2400
May	1st to 10th	Day	46% 7% 12% 21% 14% 1	5848
	11th to 20th	Day	41% 7% 13% 23% 14% 2	5866
	21st to end	Day	44% 6% 8% 26% 15% 1	6945
June	1st to 10th	Day	33% 8% 15% 27% 16% 2	2800
	11th to 20th	Day	33% 7% 14% 28% 15% 3	2800
	21st to end	Day	27% 7% 17% 30% 16% 4	2800
July	1st to 10th	Day	36% 6% 11% 24% 20% 2	6169
	11th to 20th	Day	35% 7% 13% 30% 13% 1	5831
	21st to end	Day	31% 9% 19% 31% 9% 1	6240
August	1st to 10th	Day	26% 7% 18% 28% 21%	4220
	11th to 20th	Day	35% 6% 14% 29% 15% 1	4116
	21st to end	Day	27% 6% 13% 36% 15% 4	4311
September	1st to 10th	Day	33% 6% 12% 25% 19% 6%	2400
	11th to 20th	Day	34% 4 8% 26% 25% 2	2363
	21st to end	Day	31% 5% 10% 26% 24% 4	2105
October	1st to 10th	Day	19% 2 6% 20% 40% 13%	3260
	11th to 20th	Day	23% 2 4 24% 38% 9%	3240
	21st to end	Day	35% 3 7% 26% 26% 3	3538
November	1st to 10th	Day	33% 3 12% 27% 22% 4	2057
	11th to 20th	Day	37% 3 9% 23% 23% 4	1837
	21st to end	Day	43% 4 8% 29% 15% 2	1680
December	1st to 10th	Day	37% 3 9% 35% 15% 1	2690
	11th to 20th	Day	39% 3 9% 30% 17% 1	3085
	21st to end	Day	65% 3 10% 15% 6% 1	4070
January	1st to 10th	Night	57% 3 10% 20% 11% 1	6083
	11th to 20th	Night	50% 3 8% 23% 13% 3	6030
	21st to end	Night	48% 3 9% 19% 17% 4	6633
February	1st to 10th	Night	48% 5% 11% 22% 13% 2	2601
	11th to 20th	Night	45% 4 11% 22% 16% 3	2512
	21st to end	Night	44% 4 8% 22% 17% 5%	1960
March	1st to 10th	Night	45% 3 7% 19% 23% 4	4919
	11th to 20th	Night	34% 4 8% 22% 26% 7%	4980
	21st to end	Night	47% 6% 13% 22% 11% 1	5467
April	1st to 10th	Night	35% 4 11% 25% 20% 4	2010
	11th to 20th	Night	38% 5% 9% 25% 18% 5%	1975
	21st to end	Night	45% 5% 10% 24% 14% 1	2000
May	1st to 10th	Night	44% 6% 14% 21% 14% 2	4126
	11th to 20th	Night	38% 7% 11% 23% 16% 5%	4054
	21st to end	Night	39% 6% 10% 26% 16% 2	3950
June	1st to 10th	Night	28% 7% 17% 29% 16% 4	1600
	11th to 20th	Night	26% 9% 13% 27% 22% 5%	1600
	21st to end	Night	18% 6% 18% 31% 22% 6%	1600
July	1st to 10th	Night	33% 5% 13% 25% 21% 2	3670
	11th to 20th	Night	28% 7% 13% 36% 16% 1	4026
	21st to end	Night	25% 7% 19% 39% 10% 1	4320
August	1st to 10th	Night	18% 6% 19% 31% 23% 2	2916
	11th to 20th	Night	34% 5% 12% 30% 18% 2	3004
	21st to end	Night	21% 5% 13% 39% 17% 4	3586
September	1st to 10th	Night	30% 4 10% 26% 23% 7%	2000
	11th to 20th	Night	29% 6% 11% 24% 25% 5%	2033
	21st to end	Night	27% 4 9% 28% 28% 4	2275
October	1st to 10th	Night	15% 2 6% 22% 43% 12%	3920
	11th to 20th	Night	23% 3 7% 21% 29% 16%	3899
	21st to end	Night	33% 3 6% 30% 25% 3	4252
November	1st to 10th	Night	30% 3 11% 28% 21% 6%	2460
	11th to 20th	Night	35% 3 8% 25% 23% 5%	2776
	21st to end	Night	42% 3 9% 26% 17% 2	2940
December	1st to 10th	Night	38% 4 9% 34% 14% 1	4720
	11th to 20th	Night	44% 3 10% 25% 17% 1	5341
	21st to end	Night	63% 3 11% 16% 6% 1	7150

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	25% 22% 38% 13% 2	330
	11th to 20th	Day	31% 22% 39% 8% 1	330
	21st to end	Day	20% 25% 41% 13% 1	363
February	1st to 10th	Day	30% 23% 35% 12%	300
	11th to 20th	Day	30% 24% 34% 10% 2	300
	21st to end	Day	33% 23% 33% 8% 3	249
March	1st to 10th	Day	23% 28% 36% 12% 1	300
	11th to 20th	Day	37% 15% 34% 12% 2	300
	21st to end	Day	35% 25% 30% 9% 1	330
April	1st to 10th	Day	29% 18% 33% 15% 5%	490
	11th to 20th	Day	30% 20% 30% 16% 3	492
	21st to end	Day	29% 16% 31% 19% 5%	500
May	1st to 10th	Day	22% 18% 35% 19% 5%	677
	11th to 20th	Day	21% 14% 30% 24% 9% 2	725
	21st to end	Day	18% 12% 35% 22% 11% 2	789
June	1st to 10th	Day	10% 6% 28% 32% 21% 3	730
	11th to 20th	Day	11% 6% 29% 37% 16% 2	730
	21st to end	Day	7% 8% 36% 33% 13% 2	730
July	1st to 10th	Day	11% 5% 19% 31% 28% 7%	721
	11th to 20th	Day	6% 3 27% 37% 24% 3	718
	21st to end	Day	8% 3 21% 38% 26% 5%	794
August	1st to 10th	Day	9% 3 22% 42% 20% 4	726
	11th to 20th	Day	11% 3 22% 35% 25% 4	660
	21st to end	Day	11% 3 16% 34% 28% 8%	583
September	1st to 10th	Day	13% 3 17% 37% 25% 5%	530
	11th to 20th	Day	10% 5% 22% 35% 19% 9%	493
	21st to end	Day	13% 9% 28% 32% 14% 4	330
October	1st to 10th	Day	14% 10% 30% 29% 14% 3	330
	11th to 20th	Day	18% 19% 32% 22% 6% 1	330
	21st to end	Day	32% 19% 32% 15% 2 1	363
November	1st to 10th	Day	17% 16% 45% 16% 5% 1	330
	11th to 20th	Day	25% 19% 33% 17% 5% 1	330
	21st to end	Day	34% 14% 29% 19% 3	330
December	1st to 10th	Day	18% 25% 34% 17% 4 1	330
	11th to 20th	Day	24% 22% 36% 15% 3	330
	21st to end	Day	28% 27% 33% 11% 1	363
January	1st to 10th	Night	22% 19% 34% 20% 4	1050
	11th to 20th	Night	21% 24% 34% 17% 3	1050
	21st to end	Night	19% 23% 38% 19% 2	1155
February	1st to 10th	Night	23% 20% 37% 17% 2	1001
	11th to 20th	Night	23% 21% 37% 17% 2	957
	21st to end	Night	28% 19% 34% 16% 3	640
March	1st to 10th	Night	21% 19% 37% 21% 2	600
	11th to 20th	Night	26% 14% 34% 23% 3	600
	21st to end	Night	31% 15% 33% 18% 3	660
April	1st to 10th	Night	18% 18% 37% 23% 4	600
	11th to 20th	Night	24% 13% 34% 24% 5%	593
	21st to end	Night	21% 13% 37% 22% 7%	600
May	1st to 10th	Night	18% 10% 33% 31% 7%	600
	11th to 20th	Night	15% 9% 30% 31% 13% 1	591
	21st to end	Night	14% 9% 28% 29% 17% 2	650
June	1st to 10th	Night	9% 3 22% 38% 26% 2	600
	11th to 20th	Night	8% 4 29% 38% 20% 2	600
	21st to end	Night	4 4 31% 42% 18% 2	600
July	1st to 10th	Night	10% 2 13% 43% 27% 5%	585
	11th to 20th	Night	5% 1 21% 42% 29% 3	582
	21st to end	Night	7% 3 16% 39% 34% 2	657
August	1st to 10th	Night	5% 1 19% 45% 29% 2	597
	11th to 20th	Night	6% 2 17% 42% 29% 3	594
	21st to end	Night	6% 1 17% 38% 34% 4	660
September	1st to 10th	Night	12% 3 19% 38% 27% 3	600
	11th to 20th	Night	12% 2 18% 34% 30% 5%	600
	21st to end	Night	10% 5% 25% 36% 21% 3	675
October	1st to 10th	Night	9% 8% 27% 33% 21% 3	800
	11th to 20th	Night	18% 12% 34% 28% 9%	800
	21st to end	Night	24% 13% 34% 23% 7%	880
November	1st to 10th	Night	14% 14% 36% 27% 9%	820
	11th to 20th	Night	19% 18% 32% 24% 7%	887
	21st to end	Night	25% 16% 33% 21% 5%	1050
December	1st to 10th	Night	20% 18% 35% 22% 4	1050
	11th to 20th	Night	25% 14% 35% 22% 3	1050
	21st to end	Night	27% 19% 34% 19% 2	1155

Page generated at 2026-01-29 00:21:42. Version ac07

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