Long Lake Conservation Center
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Long Lake Conservation Center clear sky chart from 2005-11-06 to 2026-08-30.

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% 9% 3 8% 5% 5% 5% 4 6% 7% 36%	145118
	Night	11% 10% 4 10% 5% 5% 5% 4 5% 6% 35%	137431
Transparency	Day	46% 5% 12% 25% 11% 1	148659
	Night	48% 4 12% 23% 12% 1	141968
Seeing	Day	16% 10% 31% 26% 13% 3	18688
	Night	16% 8% 33% 31% 11% 1	28478

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	7% 14% 5% 19% 9% 6% 5% 4 5% 4 23%	4124
	11th to 20th	Day	5% 12% 7% 15% 8% 8% 9% 6% 8% 6% 15%	4669
	21st to end	Day	3 13% 8% 13% 7% 5% 7% 5% 7% 8% 24%	5669
February	1st to 10th	Day	7% 14% 5% 12% 7% 6% 5% 5% 6% 6% 27%	1890
	11th to 20th	Day	7% 11% 4 11% 6% 5% 5% 4 6% 6% 35%	1844
	21st to end	Day	9% 11% 5% 12% 7% 4 4 4 6% 7% 32%	1587
March	1st to 10th	Day	11% 9% 3 8% 5% 4 5% 3 6% 8% 39%	4909
	11th to 20th	Day	9% 9% 4 11% 6% 5% 4 4 6% 7% 35%	5090
	21st to end	Day	21% 12% 4 9% 5% 4 4 3 4 6% 31%	5661
April	1st to 10th	Day	17% 12% 4 9% 6% 4 4 3 5% 5% 32%	2520
	11th to 20th	Day	16% 13% 3 8% 5% 5% 5% 4 4 6% 30%	2561
	21st to end	Day	22% 9% 4 7% 5% 5% 4 3 4 5% 33%	2730
May	1st to 10th	Day	12% 6% 2 6% 4 4 4 3 5% 6% 47%	8088
	11th to 20th	Day	16% 10% 3 6% 4 3 4 3 5% 6% 42%	8222
	21st to end	Day	13% 7% 3 6% 4 4 4 4 6% 8% 40%	9047
June	1st to 10th	Day	11% 6% 2 6% 4 5% 5% 5% 7% 9% 40%	3003
	11th to 20th	Day	16% 7% 3 7% 4 4 5% 4 6% 7% 37%	3150
	21st to end	Day	12% 6% 2 6% 5% 5% 6% 4 8% 9% 37%	3150
July	1st to 10th	Day	8% 5% 2 6% 4 5% 6% 5% 8% 11% 40%	8850
	11th to 20th	Day	9% 4 2 5% 3 4 4 4 6% 10% 49%	8550
	21st to end	Day	9% 4 2 5% 4 4 4 4 6% 9% 48%	8990
August	1st to 10th	Day	11% 5% 2 5% 4 5% 5% 4 7% 9% 43%	4417
	11th to 20th	Day	12% 5% 2 6% 5% 4 5% 4 6% 9% 42%	4301
	21st to end	Day	14% 6% 3 6% 4 4 5% 4 6% 7% 42%	4640
September	1st to 10th	Day	10% 6% 2 7% 5% 4 4 4 5% 9% 44%	2400
	11th to 20th	Day	12% 7% 2 6% 5% 4 4 4 6% 7% 42%	2365
	21st to end	Day	15% 6% 3 6% 4 4 4 3 5% 7% 43%	2109
October	1st to 10th	Day	17% 10% 2 6% 5% 4 4 4 5% 7% 37%	2000
	11th to 20th	Day	17% 12% 3 8% 4 4 4 4 4 6% 34%	2000
	21st to end	Day	20% 13% 3 8% 5% 4 4 4 5% 6% 29%	2140
November	1st to 10th	Day	13% 14% 4 9% 6% 6% 5% 3 4 6% 31%	1662
	11th to 20th	Day	14% 15% 6% 12% 5% 5% 4 3 4 5% 26%	1680
	21st to end	Day	13% 12% 5% 13% 7% 5% 5% 4 6% 6% 26%	1680
December	1st to 10th	Day	10% 14% 6% 16% 15% 6% 4 3 4 5% 18%	2690
	11th to 20th	Day	9% 17% 8% 12% 6% 5% 5% 4 5% 5% 26%	3088
	21st to end	Day	18% 18% 6% 22% 6% 4 4 2 3 4 13%	3642
January	1st to 10th	Night	7% 11% 5% 18% 9% 6% 5% 3 5% 5% 25%	8799
	11th to 20th	Night	5% 13% 5% 13% 8% 7% 9% 8% 8% 5% 19%	8303
	21st to end	Night	4 13% 7% 12% 6% 6% 5% 5% 6% 7% 29%	8540
February	1st to 10th	Night	7% 12% 5% 10% 6% 6% 5% 4 6% 6% 34%	2730
	11th to 20th	Night	6% 9% 4 9% 7% 5% 6% 4 7% 7% 36%	2663
	21st to end	Night	11% 11% 4 10% 7% 5% 5% 5% 6% 7% 31%	2218
March	1st to 10th	Night	10% 8% 3 7% 4 4 4 3 5% 7% 46%	5198
	11th to 20th	Night	10% 10% 4 11% 6% 6% 5% 4 6% 6% 32%	5090
	21st to end	Night	20% 13% 5% 10% 4 4 4 3 4 5% 28%	5509
April	1st to 10th	Night	17% 10% 4 9% 4 5% 4 3 5% 5% 35%	2100
	11th to 20th	Night	17% 12% 4 7% 5% 4 4 3 4 6% 35%	2005
	21st to end	Night	19% 9% 3 7% 5% 3 4 4 4 6% 35%	1890
May	1st to 10th	Night	11% 7% 2 6% 4 4 4 3 5% 6% 48%	4795
	11th to 20th	Night	16% 7% 2 6% 3 3 3 3 4 5% 49%	4670
	21st to end	Night	14% 7% 3 6% 4 4 4 4 6% 7% 41%	5139
June	1st to 10th	Night	12% 6% 2 6% 4 5% 4 5% 5% 10% 41%	1611
	11th to 20th	Night	11% 6% 2 6% 5% 4 5% 4 5% 7% 44%	1470
	21st to end	Night	9% 5% 3 7% 4 4 4 4 7% 8% 44%	1470
July	1st to 10th	Night	9% 4 2 5% 3 4 4 4 6% 9% 49%	4138
	11th to 20th	Night	8% 3 1 4 4 3 4 3 6% 9% 55%	4422
	21st to end	Night	9% 5% 2 6% 3 4 4 4 6% 9% 49%	5117
August	1st to 10th	Night	10% 5% 2 5% 4 3 3 4 6% 7% 50%	2947
	11th to 20th	Night	14% 5% 2 4 3 3 4 4 5% 6% 49%	2978
	21st to end	Night	12% 5% 2 6% 4 4 4 3 6% 8% 45%	3462
September	1st to 10th	Night	9% 4 2 5% 3 4 5% 4 5% 7% 52%	2000
	11th to 20th	Night	9% 6% 2 6% 3 4 4 3 5% 8% 50%	2033
	21st to end	Night	15% 5% 2 5% 4 3 3 3 5% 7% 47%	2270
October	1st to 10th	Night	14% 7% 3 6% 4 3 4 3 4 6% 44%	2400
	11th to 20th	Night	15% 11% 4 7% 4 4 5% 3 4 6% 38%	2400
	21st to end	Night	18% 11% 4 8% 5% 4 4 4 5% 6% 31%	2700
November	1st to 10th	Night	14% 12% 4 8% 5% 4 5% 4 5% 6% 34%	2853
	11th to 20th	Night	15% 12% 5% 10% 6% 4 5% 3 5% 6% 30%	2940
	21st to end	Night	12% 10% 4 11% 7% 5% 4 4 6% 7% 30%	2940
December	1st to 10th	Night	7% 11% 6% 19% 11% 8% 6% 4 5% 6% 18%	4720
	11th to 20th	Night	10% 15% 5% 15% 7% 6% 5% 5% 6% 6% 21%	5339
	21st to end	Night	20% 20% 6% 16% 5% 4 3 2 4 4 16%	7572

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	64% 3 8% 14% 11%	4125
	11th to 20th	Day	66% 4 8% 15% 8%	4669
	21st to end	Day	57% 4 9% 20% 9%	5669
February	1st to 10th	Day	57% 4 9% 19% 10% 1	1890
	11th to 20th	Day	49% 4 13% 22% 10% 1	1853
	21st to end	Day	53% 4 12% 19% 12% 1	1587
March	1st to 10th	Day	43% 5% 14% 23% 11% 4	4909
	11th to 20th	Day	48% 4 14% 24% 10% 1	5090
	21st to end	Day	56% 4 9% 21% 9%	5663
April	1st to 10th	Day	55% 4 9% 18% 13% 2	2520
	11th to 20th	Day	55% 4 11% 17% 11% 1	2561
	21st to end	Day	54% 4 9% 21% 11%	2730
May	1st to 10th	Day	37% 4 11% 27% 20% 1	8127
	11th to 20th	Day	44% 4 9% 24% 15% 5%	8226
	21st to end	Day	40% 5% 9% 30% 15% 1	9061
June	1st to 10th	Day	39% 6% 16% 28% 10% 1	3003
	11th to 20th	Day	45% 6% 13% 22% 12% 1	3150
	21st to end	Day	41% 8% 14% 26% 10% 1	3150
July	1st to 10th	Day	37% 5% 20% 28% 9%	8776
	11th to 20th	Day	31% 5% 15% 35% 15% 1	8470
	21st to end	Day	33% 5% 16% 31% 15% 1	8794
August	1st to 10th	Day	37% 5% 15% 29% 12% 1	4402
	11th to 20th	Day	38% 6% 17% 32% 7%	4340
	21st to end	Day	42% 5% 16% 26% 10% 1	4639
September	1st to 10th	Day	37% 6% 16% 32% 9%	2400
	11th to 20th	Day	41% 6% 19% 27% 7%	2365
	21st to end	Day	42% 5% 12% 33% 8% 1	2109
October	1st to 10th	Day	38% 3 12% 33% 14% 1	3260
	11th to 20th	Day	44% 4 11% 23% 17% 1	3240
	21st to end	Day	53% 4 15% 22% 6%	3442
November	1st to 10th	Day	55% 5% 10% 18% 11% 1	1662
	11th to 20th	Day	61% 5% 12% 15% 7% 1	1680
	21st to end	Day	59% 5% 13% 17% 5% 2	1680
December	1st to 10th	Day	70% 4 9% 14% 3 1	2690
	11th to 20th	Day	61% 4 7% 17% 11%	3085
	21st to end	Day	77% 4 5% 9% 5%	3642
January	1st to 10th	Night	61% 3 11% 14% 11%	8800
	11th to 20th	Night	63% 5% 8% 15% 9%	8303
	21st to end	Night	54% 3 9% 23% 10%	8540
February	1st to 10th	Night	52% 3 10% 22% 12% 1	2730
	11th to 20th	Night	46% 5% 12% 24% 12% 1	2664
	21st to end	Night	52% 4 11% 21% 11% 1	2218
March	1st to 10th	Night	39% 3 16% 21% 17% 3	5198
	11th to 20th	Night	52% 4 10% 21% 12%	5090
	21st to end	Night	59% 3 9% 16% 11% 1	5509
April	1st to 10th	Night	52% 4 9% 18% 16% 1	2100
	11th to 20th	Night	52% 4 8% 21% 14% 1	2005
	21st to end	Night	50% 4 8% 23% 13% 1	1890
May	1st to 10th	Night	36% 5% 11% 30% 17% 1	4820
	11th to 20th	Night	38% 4 9% 24% 19% 6%	4671
	21st to end	Night	42% 5% 9% 28% 15% 1	5149
June	1st to 10th	Night	39% 6% 17% 26% 11% 2	1611
	11th to 20th	Night	39% 6% 12% 24% 17% 2	1470
	21st to end	Night	37% 7% 14% 29% 12% 1	1470
July	1st to 10th	Night	32% 5% 19% 32% 12% 1	4105
	11th to 20th	Night	27% 4 15% 37% 16% 1	4382
	21st to end	Night	33% 4 16% 33% 13% 1	5002
August	1st to 10th	Night	33% 5% 18% 26% 16% 2	2938
	11th to 20th	Night	35% 5% 14% 36% 10% 1	3005
	21st to end	Night	37% 5% 17% 29% 10% 1	3462
September	1st to 10th	Night	31% 7% 16% 34% 12%	2000
	11th to 20th	Night	33% 5% 18% 32% 11%	2033
	21st to end	Night	39% 5% 11% 34% 12%	2270
October	1st to 10th	Night	29% 3 7% 37% 19% 4	3920
	11th to 20th	Night	43% 3 10% 26% 17%	3899
	21st to end	Night	51% 4 13% 22% 10%	4348
November	1st to 10th	Night	49% 5% 12% 23% 9% 1	2853
	11th to 20th	Night	55% 5% 13% 18% 8% 1	2940
	21st to end	Night	53% 6% 15% 20% 5% 1	2940
December	1st to 10th	Night	68% 5% 11% 13% 3 1	4720
	11th to 20th	Night	63% 4 10% 14% 8% 1	5341
	21st to end	Night	73% 3 7% 13% 5%	7572

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	11% 12% 34% 29% 11% 2	330
	11th to 20th	Day	16% 10% 32% 34% 8% 1	330
	21st to end	Day	12% 9% 38% 25% 14% 2	363
February	1st to 10th	Day	17% 13% 43% 20% 6% 1	330
	11th to 20th	Day	12% 14% 37% 25% 10% 2	330
	21st to end	Day	14% 14% 42% 25% 4	273
March	1st to 10th	Day	18% 10% 40% 23% 8% 1	330
	11th to 20th	Day	18% 10% 37% 25% 8% 2	330
	21st to end	Day	23% 14% 31% 19% 11% 1	390
April	1st to 10th	Day	23% 13% 33% 22% 7% 1	540
	11th to 20th	Day	26% 11% 29% 23% 10% 1	599
	21st to end	Day	25% 11% 30% 22% 11% 1	750
May	1st to 10th	Day	18% 14% 30% 24% 12% 3	753
	11th to 20th	Day	20% 12% 29% 24% 11% 3	775
	21st to end	Day	18% 8% 28% 30% 13% 3	844
June	1st to 10th	Day	13% 8% 32% 30% 14% 4	780
	11th to 20th	Day	17% 11% 35% 25% 10% 2	780
	21st to end	Day	15% 9% 31% 26% 14% 5%	780
July	1st to 10th	Day	8% 5% 24% 30% 24% 9%	771
	11th to 20th	Day	9% 6% 32% 25% 19% 9%	768
	21st to end	Day	7% 4 29% 33% 20% 8%	849
August	1st to 10th	Day	11% 5% 26% 30% 22% 6%	776
	11th to 20th	Day	14% 5% 22% 32% 22% 5%	765
	21st to end	Day	14% 5% 25% 29% 22% 5%	761
September	1st to 10th	Day	12% 7% 27% 31% 18% 4	530
	11th to 20th	Day	13% 8% 27% 31% 17% 4	495
	21st to end	Day	18% 11% 30% 21% 13% 6%	330
October	1st to 10th	Day	21% 8% 33% 22% 11% 4	330
	11th to 20th	Day	18% 16% 35% 25% 6% 1	330
	21st to end	Day	27% 12% 37% 17% 6% 1	363
November	1st to 10th	Day	21% 14% 35% 22% 8% 1	330
	11th to 20th	Day	22% 15% 38% 19% 5% 1	330
	21st to end	Day	18% 11% 42% 24% 5%	330
December	1st to 10th	Day	17% 13% 37% 25% 7% 1	330
	11th to 20th	Day	19% 15% 35% 24% 7%	330
	21st to end	Day	27% 10% 37% 20% 5% 1	363
January	1st to 10th	Night	14% 9% 36% 31% 10% 1	1050
	11th to 20th	Night	15% 9% 39% 28% 8% 1	1050
	21st to end	Night	16% 9% 38% 28% 8% 1	1155
February	1st to 10th	Night	14% 9% 37% 30% 9% 1	1050
	11th to 20th	Night	10% 10% 42% 27% 10% 1	1029
	21st to end	Night	16% 9% 35% 30% 9% 1	834
March	1st to 10th	Night	14% 11% 39% 27% 8% 1	713
	11th to 20th	Night	16% 10% 41% 28% 5% 1	630
	21st to end	Night	21% 9% 29% 28% 10% 3	693
April	1st to 10th	Night	20% 11% 34% 28% 6% 1	630
	11th to 20th	Night	23% 7% 33% 29% 7%	623
	21st to end	Night	24% 8% 28% 29% 10% 1	630
May	1st to 10th	Night	17% 10% 33% 30% 9% 1	630
	11th to 20th	Night	19% 7% 31% 33% 9% 1	621
	21st to end	Night	15% 6% 29% 36% 12%	683
June	1st to 10th	Night	14% 6% 29% 38% 13% 1	630
	11th to 20th	Night	14% 5% 33% 39% 9%	630
	21st to end	Night	11% 4 28% 39% 17% 1	630
July	1st to 10th	Night	7% 2 24% 40% 25% 1	615
	11th to 20th	Night	9% 3 27% 37% 22% 2	612
	21st to end	Night	7% 2 22% 46% 20% 2	690
August	1st to 10th	Night	8% 2 20% 48% 21% 1	627
	11th to 20th	Night	14% 3 21% 37% 23% 2	624
	21st to end	Night	10% 5% 24% 39% 20% 2	687
September	1st to 10th	Night	11% 4 24% 40% 19% 3	600
	11th to 20th	Night	12% 5% 31% 34% 17% 2	600
	21st to end	Night	16% 6% 31% 28% 15% 3	670
October	1st to 10th	Night	20% 9% 30% 29% 11% 1	800
	11th to 20th	Night	21% 11% 35% 27% 6%	800
	21st to end	Night	26% 9% 34% 25% 6%	880
November	1st to 10th	Night	19% 9% 34% 29% 9%	1007
	11th to 20th	Night	21% 12% 33% 25% 8% 1	1050
	21st to end	Night	18% 12% 39% 25% 6%	1050
December	1st to 10th	Night	15% 11% 35% 29% 9% 1	1050
	11th to 20th	Night	19% 10% 38% 24% 7% 1	1050
	21st to end	Night	26% 9% 34% 23% 7% 1	1155

Page generated at 2026-08-27 03:07:11. Version ac07

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