Long Lake
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Long Lake 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 8% 4 9% 6% 6% 6% 5% 7% 8% 38%	137339
	Night	3 6% 3 8% 6% 5% 6% 5% 7% 8% 44%	131387
Transparency	Day	38% 7% 13% 23% 15% 4	132086
	Night	30% 7% 17% 26% 16% 4	127644
Seeing	Day	23% 29% 31% 13% 3	17378
	Night	19% 30% 30% 17% 5%	26956

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% 3 13% 8% 9% 7% 7% 10% 9% 29%	3539
	11th to 20th	Day	2 1 9% 7% 8% 9% 6% 9% 10% 38%	3848
	21st to end	Day	3 2 7% 6% 4 4 4 6% 9% 55%	4510
February	1st to 10th	Day	7% 5% 13% 9% 8% 8% 7% 10% 8% 27%	1800
	11th to 20th	Day	7% 4 14% 10% 8% 7% 5% 8% 6% 30%	1755
	21st to end	Day	8% 4 13% 9% 8% 7% 6% 9% 9% 27%	1495
March	1st to 10th	Day	6% 6% 15% 7% 6% 7% 5% 7% 6% 35%	4954
	11th to 20th	Day	1 9% 6% 21% 7% 5% 5% 3 5% 6% 31%	5000
	21st to end	Day	2 16% 9% 17% 9% 8% 8% 5% 6% 7% 14%	5486
April	1st to 10th	Day	4 17% 7% 12% 7% 6% 5% 4 5% 7% 26%	2370
	11th to 20th	Day	4 15% 5% 14% 8% 6% 5% 5% 6% 7% 24%	2458
	21st to end	Day	8% 21% 6% 12% 6% 5% 5% 4 5% 6% 23%	2600
May	1st to 10th	Day	6% 16% 6% 12% 6% 5% 4 4 5% 7% 30%	5964
	11th to 20th	Day	8% 14% 5% 11% 6% 5% 6% 5% 7% 8% 26%	6298
	21st to end	Day	8% 12% 5% 10% 6% 6% 6% 5% 6% 7% 30%	6925
June	1st to 10th	Day	12% 10% 3 8% 6% 6% 5% 5% 7% 8% 30%	2800
	11th to 20th	Day	11% 9% 3 7% 5% 5% 5% 4 8% 8% 34%	2982
	21st to end	Day	5% 5% 2 6% 4 5% 6% 4 7% 8% 48%	3000
July	1st to 10th	Day	5% 5% 3 7% 6% 6% 6% 6% 7% 8% 41%	6779
	11th to 20th	Day	4 4 2 5% 4 5% 6% 6% 8% 8% 46%	6411
	21st to end	Day	4 5% 2 6% 6% 6% 7% 5% 8% 9% 43%	6598
August	1st to 10th	Day	6% 8% 3 7% 5% 6% 6% 5% 8% 8% 40%	5779
	11th to 20th	Day	5% 5% 2 6% 5% 6% 6% 5% 6% 7% 47%	5798
	21st to end	Day	10% 6% 3 6% 4 4 4 4 5% 7% 48%	6304
September	1st to 10th	Day	8% 6% 2 4 3 3 4 4 5% 7% 52%	2400
	11th to 20th	Day	9% 8% 3 6% 4 4 4 4 6% 8% 45%	2286
	21st to end	Day	7% 8% 2 4 4 4 4 4 6% 6% 50%	2175
October	1st to 10th	Day	6% 9% 3 5% 3 3 3 2 3 5% 59%	3270
	11th to 20th	Day	4 10% 3 6% 3 3 3 3 4 6% 55%	3250
	21st to end	Day	2 10% 5% 8% 4 4 5% 5% 7% 8% 43%	3548
November	1st to 10th	Day	3 8% 4 8% 6% 7% 6% 5% 7% 9% 38%	1702
	11th to 20th	Day	2 7% 3 7% 6% 7% 5% 5% 8% 10% 41%	1680
	21st to end	Day	1 4 4 8% 5% 6% 6% 4 9% 10% 42%	1680
December	1st to 10th	Day	2 2 11% 7% 5% 5% 5% 7% 7% 47%	2700
	11th to 20th	Day	4 3 11% 6% 7% 9% 6% 11% 10% 32%	3106
	21st to end	Day	9% 4 14% 8% 6% 6% 5% 6% 8% 34%	4089
January	1st to 10th	Night	2 1 7% 10% 9% 8% 6% 11% 9% 38%	6342
	11th to 20th	Night	1 1 6% 8% 8% 8% 6% 9% 11% 41%	6174
	21st to end	Night	4 3 6% 5% 4 5% 5% 7% 9% 51%	6468
February	1st to 10th	Night	6% 3 10% 7% 8% 8% 6% 10% 10% 33%	2600
	11th to 20th	Night	1 5% 3 11% 8% 9% 7% 5% 11% 8% 32%	2532
	21st to end	Night	6% 4 11% 8% 7% 7% 6% 12% 9% 30%	2134
March	1st to 10th	Night	6% 6% 12% 5% 7% 7% 5% 7% 8% 37%	4940
	11th to 20th	Night	1 7% 4 13% 6% 5% 5% 5% 7% 10% 39%	5000
	21st to end	Night	1 8% 4 13% 7% 8% 8% 7% 9% 9% 24%	5489
April	1st to 10th	Night	3 10% 3 10% 7% 6% 5% 5% 6% 7% 38%	2029
	11th to 20th	Night	3 9% 4 10% 8% 5% 6% 6% 8% 7% 34%	1886
	21st to end	Night	5% 14% 3 9% 6% 5% 5% 5% 6% 8% 35%	1800
May	1st to 10th	Night	5% 10% 4 8% 5% 4 4 4 6% 7% 43%	4013
	11th to 20th	Night	6% 13% 3 8% 5% 5% 5% 4 7% 9% 36%	3617
	21st to end	Night	6% 9% 3 7% 5% 6% 5% 5% 8% 9% 38%	3972
June	1st to 10th	Night	9% 7% 2 6% 4 5% 5% 5% 8% 10% 38%	1600
	11th to 20th	Night	9% 6% 2 7% 4 5% 5% 4 6% 8% 45%	1411
	21st to end	Night	4 5% 2 4 3 4 4 4 6% 6% 58%	1400
July	1st to 10th	Night	4 2 1 3 3 4 6% 5% 7% 8% 56%	3180
	11th to 20th	Night	4 3 1 5% 4 3 5% 4 8% 9% 53%	3548
	21st to end	Night	3 2 2 5% 3 4 5% 4 6% 8% 58%	4258
August	1st to 10th	Night	6% 6% 2 5% 4 4 5% 4 7% 8% 48%	4033
	11th to 20th	Night	3 3 2 5% 4 5% 5% 4 5% 8% 57%	4051
	21st to end	Night	6% 7% 2 5% 3 3 3 3 4 5% 59%	4671
September	1st to 10th	Night	6% 5% 2 4 3 3 3 3 5% 7% 59%	2000
	11th to 20th	Night	6% 6% 2 6% 4 4 4 4 6% 7% 51%	2110
	21st to end	Night	8% 6% 2 5% 4 3 3 3 5% 6% 56%	2225
October	1st to 10th	Night	4 5% 2 6% 4 3 4 3 4 7% 58%	3920
	11th to 20th	Night	3 8% 3 6% 4 5% 4 4 4 6% 52%	3898
	21st to end	Night	3 7% 2 7% 5% 5% 5% 4 6% 7% 49%	4252
November	1st to 10th	Night	1 7% 3 7% 5% 5% 6% 6% 9% 10% 41%	2795
	11th to 20th	Night	1 5% 2 7% 6% 6% 6% 5% 9% 10% 42%	2940
	21st to end	Night	1 4 2 8% 5% 5% 7% 5% 9% 10% 43%	2940
December	1st to 10th	Night	2 2 6% 5% 6% 6% 6% 9% 8% 51%	4710
	11th to 20th	Night	4 3 10% 7% 7% 6% 6% 10% 13% 34%	5321
	21st to end	Night	5% 5% 14% 8% 7% 6% 5% 7% 8% 36%	7128

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	37% 9% 17% 23% 12% 2	3539
	11th to 20th	Day	31% 9% 21% 18% 15% 5%	3848
	21st to end	Day	22% 7% 19% 27% 20% 5%	4510
February	1st to 10th	Day	43% 9% 19% 20% 8% 1	1800
	11th to 20th	Day	45% 8% 17% 19% 8% 2	1764
	21st to end	Day	42% 7% 16% 18% 13% 3	1495
March	1st to 10th	Day	35% 9% 11% 24% 16% 5%	4954
	11th to 20th	Day	47% 6% 16% 23% 8% 1	5000
	21st to end	Day	57% 8% 18% 15% 2	5486
April	1st to 10th	Day	51% 7% 13% 20% 8% 1	2370
	11th to 20th	Day	53% 7% 16% 19% 4 1	2461
	21st to end	Day	58% 5% 15% 18% 5%	2600
May	1st to 10th	Day	50% 6% 9% 24% 9% 1	5964
	11th to 20th	Day	48% 7% 13% 22% 8% 2	6302
	21st to end	Day	44% 9% 13% 24% 10%	6926
June	1st to 10th	Day	44% 9% 16% 23% 8% 1	2800
	11th to 20th	Day	41% 7% 13% 19% 16% 3	2982
	21st to end	Day	29% 6% 12% 30% 17% 7%	3000
July	1st to 10th	Day	34% 7% 7% 22% 21% 9%	6706
	11th to 20th	Day	27% 7% 7% 24% 23% 12%	6334
	21st to end	Day	31% 7% 7% 20% 26% 9%	6409
August	1st to 10th	Day	38% 6% 8% 21% 21% 7%	4208
	11th to 20th	Day	33% 5% 8% 24% 22% 8%	4197
	21st to end	Day	30% 4 7% 23% 26% 10%	4547
September	1st to 10th	Day	30% 3 8% 22% 30% 7%	2400
	11th to 20th	Day	33% 5% 11% 22% 23% 5%	2286
	21st to end	Day	30% 5% 12% 27% 21% 5%	2175
October	1st to 10th	Day	29% 2 8% 24% 33% 4	3270
	11th to 20th	Day	29% 4 14% 33% 16% 4	3250
	21st to end	Day	35% 5% 18% 27% 14% 1	3548
November	1st to 10th	Day	36% 8% 18% 23% 13% 3	1702
	11th to 20th	Day	32% 8% 23% 25% 10% 2	1680
	21st to end	Day	30% 8% 23% 24% 14% 1	1680
December	1st to 10th	Day	29% 7% 25% 23% 13% 3	2700
	11th to 20th	Day	32% 10% 30% 22% 4 1	3104
	21st to end	Day	41% 6% 12% 21% 11% 8%	4089
January	1st to 10th	Night	28% 10% 18% 25% 17% 2	6342
	11th to 20th	Night	26% 10% 19% 26% 14% 5%	6174
	21st to end	Night	24% 7% 20% 25% 18% 6%	6468
February	1st to 10th	Night	36% 10% 20% 24% 10% 1	2600
	11th to 20th	Night	36% 8% 20% 23% 11% 2	2533
	21st to end	Night	35% 8% 16% 22% 16% 2	2134
March	1st to 10th	Night	33% 9% 11% 22% 19% 6%	4940
	11th to 20th	Night	34% 7% 19% 29% 10% 1	5000
	21st to end	Night	38% 10% 24% 24% 4 1	5489
April	1st to 10th	Night	39% 8% 20% 21% 11% 1	2029
	11th to 20th	Night	41% 9% 21% 22% 6% 1	1886
	21st to end	Night	42% 8% 21% 22% 7%	1800
May	1st to 10th	Night	37% 4 12% 29% 15% 2	4010
	11th to 20th	Night	40% 5% 17% 30% 7% 1	3618
	21st to end	Night	34% 8% 20% 29% 9%	3972
June	1st to 10th	Night	35% 9% 22% 24% 9% 2	1600
	11th to 20th	Night	32% 7% 17% 25% 16% 4	1411
	21st to end	Night	23% 5% 15% 31% 20% 6%	1400
July	1st to 10th	Night	20% 6% 7% 30% 32% 4	3145
	11th to 20th	Night	24% 5% 8% 28% 28% 7%	3502
	21st to end	Night	21% 5% 8% 26% 31% 8%	4136
August	1st to 10th	Night	34% 5% 10% 23% 19% 9%	2928
	11th to 20th	Night	31% 4 8% 27% 22% 8%	2928
	21st to end	Night	21% 4 7% 28% 32% 8%	3359
September	1st to 10th	Night	24% 4 9% 25% 31% 7%	2000
	11th to 20th	Night	29% 5% 14% 25% 22% 5%	2110
	21st to end	Night	27% 4 12% 30% 24% 3	2225
October	1st to 10th	Night	25% 3 9% 31% 29% 3	3920
	11th to 20th	Night	31% 3 13% 28% 21% 3	3898
	21st to end	Night	31% 5% 14% 30% 19% 1	4252
November	1st to 10th	Night	27% 11% 18% 26% 15% 2	2795
	11th to 20th	Night	29% 8% 25% 26% 11% 1	2940
	21st to end	Night	28% 10% 21% 24% 14% 3	2940
December	1st to 10th	Night	21% 8% 27% 27% 15% 1	4710
	11th to 20th	Night	31% 9% 30% 24% 6% 1	5322
	21st to end	Night	38% 7% 15% 23% 11% 7%	7128

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	29% 36% 23% 10% 2	278
	11th to 20th	Day	20% 46% 22% 8% 4	300
	21st to end	Day	18% 50% 23% 6% 2	330
February	1st to 10th	Day	34% 46% 16% 4	300
	11th to 20th	Day	38% 33% 19% 8% 2	300
	21st to end	Day	33% 40% 20% 6% 1	254
March	1st to 10th	Day	27% 38% 28% 5% 1	500
	11th to 20th	Day	24% 35% 34% 6% 1	500
	21st to end	Day	31% 31% 28% 9% 1	550
April	1st to 10th	Day	30% 38% 26% 5%	500
	11th to 20th	Day	28% 38% 30% 4	492
	21st to end	Day	32% 26% 29% 10% 2 1	500
May	1st to 10th	Day	24% 25% 30% 17% 3 1	535
	11th to 20th	Day	28% 19% 32% 16% 5% 1	725
	21st to end	Day	26% 22% 28% 19% 5% 1	789
June	1st to 10th	Day	18% 23% 32% 20% 6%	730
	11th to 20th	Day	25% 29% 32% 11% 3	730
	21st to end	Day	13% 22% 38% 20% 5% 1	730
July	1st to 10th	Day	9% 20% 39% 25% 7% 1	721
	11th to 20th	Day	9% 23% 43% 20% 5%	718
	21st to end	Day	9% 18% 44% 23% 5% 1	668
August	1st to 10th	Day	15% 22% 42% 16% 5%	527
	11th to 20th	Day	13% 16% 43% 24% 5%	517
	21st to end	Day	15% 23% 40% 15% 6%	583
September	1st to 10th	Day	12% 26% 44% 15% 2 1	530
	11th to 20th	Day	21% 26% 34% 15% 4	530
	21st to end	Day	19% 27% 37% 12% 5%	505
October	1st to 10th	Day	23% 28% 33% 14% 3	330
	11th to 20th	Day	27% 34% 26% 9% 3 1	330
	21st to end	Day	31% 39% 21% 7% 1	363
November	1st to 10th	Day	31% 41% 18% 7% 3	330
	11th to 20th	Day	31% 43% 21% 3 2	330
	21st to end	Day	30% 38% 28% 4 1	330
December	1st to 10th	Day	34% 41% 15% 8% 2	330
	11th to 20th	Day	41% 38% 16% 5% 1	330
	21st to end	Day	33% 36% 21% 8% 2	363
January	1st to 10th	Night	23% 39% 28% 9% 1	1006
	11th to 20th	Night	22% 41% 25% 9% 3	925
	21st to end	Night	16% 47% 27% 8% 2	880
February	1st to 10th	Night	24% 41% 23% 10% 2	800
	11th to 20th	Night	23% 37% 27% 10% 3 1	784
	21st to end	Night	24% 36% 28% 9% 3	660
March	1st to 10th	Night	21% 33% 30% 13% 3	800
	11th to 20th	Night	19% 33% 31% 14% 3	800
	21st to end	Night	16% 31% 35% 15% 2	880
April	1st to 10th	Night	20% 31% 31% 14% 3	629
	11th to 20th	Night	18% 30% 34% 14% 4	593
	21st to end	Night	17% 25% 34% 19% 6%	600
May	1st to 10th	Night	19% 21% 31% 21% 8% 1	600
	11th to 20th	Night	20% 15% 31% 24% 10% 1	591
	21st to end	Night	20% 17% 31% 25% 8%	650
June	1st to 10th	Night	17% 18% 29% 28% 8% 1	600
	11th to 20th	Night	18% 23% 34% 22% 3	411
	21st to end	Night	9% 12% 35% 35% 9%	400
July	1st to 10th	Night	4 8% 35% 39% 12% 1	390
	11th to 20th	Night	7% 14% 38% 35% 6%	544
	21st to end	Night	8% 13% 32% 36% 11% 1	657
August	1st to 10th	Night	8% 11% 36% 38% 8%	597
	11th to 20th	Night	8% 10% 34% 38% 11% 1	594
	21st to end	Night	10% 13% 33% 34% 10%	660
September	1st to 10th	Night	10% 14% 34% 31% 9% 2	600
	11th to 20th	Night	13% 16% 34% 27% 8% 2	710
	21st to end	Night	16% 21% 30% 25% 8% 1	800
October	1st to 10th	Night	16% 24% 36% 18% 6% 1	800
	11th to 20th	Night	21% 28% 28% 17% 6%	800
	21st to end	Night	21% 35% 32% 8% 4	880
November	1st to 10th	Night	24% 40% 28% 7% 1	960
	11th to 20th	Night	26% 43% 26% 5% 1	1050
	21st to end	Night	24% 37% 31% 8% 1	1050
December	1st to 10th	Night	24% 40% 24% 10% 2	1050
	11th to 20th	Night	25% 42% 24% 7% 2 1	1050
	21st to end	Night	26% 39% 23% 9% 3	1155

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