Lac Gagnon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lac Gagnon clear sky chart from 2005-11-06 to 2026-09-29.

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	16% 11% 4 9% 6% 5% 5% 4 5% 7% 29%	149855
	Night	15% 12% 4 10% 6% 5% 4 4 5% 6% 28%	141544
Transparency	Day	53% 6% 12% 19% 9% 1	153298
	Night	55% 6% 12% 18% 9% 1	146190
Seeing	Day	24% 18% 30% 18% 8% 2	16836
	Night	23% 14% 28% 25% 9% 1	25784

By Month

Percentage Cloud Cover NE (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	12% 17% 8% 18% 8% 6% 5% 3 4 4 15%	4661
	11th to 20th	Day	9% 22% 8% 19% 8% 4 3 2 4 5% 16%	4650
	21st to end	Day	6% 13% 8% 16% 9% 8% 6% 4 4 5% 19%	5161
February	1st to 10th	Day	11% 16% 7% 13% 10% 5% 5% 3 4 6% 21%	1890
	11th to 20th	Day	11% 19% 5% 14% 6% 5% 4 2 4 6% 24%	1868
	21st to end	Day	15% 18% 4 12% 7% 6% 4 3 4 5% 23%	1730
March	1st to 10th	Day	16% 17% 5% 12% 7% 4 4 3 4 5% 22%	4576
	11th to 20th	Day	11% 15% 6% 12% 6% 5% 5% 3 5% 6% 26%	4987
	21st to end	Day	16% 14% 4 8% 5% 4 4 3 5% 5% 33%	5961
April	1st to 10th	Day	21% 15% 4 8% 4 3 3 3 4 6% 30%	2520
	11th to 20th	Day	22% 12% 3 8% 5% 4 3 3 4 5% 32%	2494
	21st to end	Day	20% 11% 3 9% 4 5% 4 4 5% 4 30%	2704
May	1st to 10th	Day	20% 11% 3 8% 5% 5% 5% 4 6% 8% 23%	8237
	11th to 20th	Day	17% 8% 3 8% 5% 5% 5% 4 6% 8% 30%	8221
	21st to end	Day	21% 9% 3 8% 5% 4 4 3 5% 6% 32%	9060
June	1st to 10th	Day	22% 9% 3 7% 6% 5% 4 4 5% 6% 29%	2940
	11th to 20th	Day	15% 6% 2 7% 6% 5% 6% 4 6% 9% 33%	2940
	21st to end	Day	20% 7% 3 7% 6% 5% 5% 4 6% 7% 29%	2940
July	1st to 10th	Day	14% 6% 2 7% 5% 5% 6% 4 6% 10% 35%	8280
	11th to 20th	Day	11% 5% 2 6% 5% 5% 5% 4 6% 10% 42%	8280
	21st to end	Day	12% 6% 3 6% 5% 4 5% 4 7% 10% 38%	8993
August	1st to 10th	Day	16% 8% 3 8% 6% 5% 6% 4 6% 7% 31%	6483
	11th to 20th	Day	15% 7% 3 7% 4 5% 5% 5% 7% 9% 34%	5912
	21st to end	Day	14% 7% 2 7% 5% 5% 5% 4 7% 10% 35%	6080
September	1st to 10th	Day	15% 7% 2 6% 4 4 4 4 6% 8% 40%	2520
	11th to 20th	Day	13% 6% 2 6% 4 3 4 4 6% 8% 44%	2494
	21st to end	Day	19% 7% 3 5% 3 4 4 3 6% 7% 39%	2261
October	1st to 10th	Day	21% 10% 3 6% 5% 4 4 3 4 7% 34%	2000
	11th to 20th	Day	24% 13% 3 8% 5% 4 4 3 5% 6% 25%	2000
	21st to end	Day	25% 14% 3 9% 4 5% 4 3 5% 6% 23%	1990
November	1st to 10th	Day	17% 14% 5% 8% 5% 4 4 3 4 6% 31%	1851
	11th to 20th	Day	19% 15% 5% 11% 5% 5% 5% 3 5% 4 22%	1697
	21st to end	Day	21% 19% 7% 11% 6% 4 3 3 4 4 17%	1680
December	1st to 10th	Day	19% 21% 9% 12% 8% 4 5% 3 4 4 11%	2680
	11th to 20th	Day	17% 17% 7% 15% 7% 4 4 3 3 3 20%	3066
	21st to end	Day	19% 18% 5% 11% 5% 6% 5% 3 4 4 20%	4048
January	1st to 10th	Night	11% 19% 8% 15% 7% 5% 4 3 4 5% 18%	8234
	11th to 20th	Night	10% 19% 8% 18% 10% 6% 4 3 4 5% 15%	8235
	21st to end	Night	7% 15% 7% 16% 8% 8% 7% 4 6% 6% 18%	9015
February	1st to 10th	Night	12% 14% 5% 14% 7% 6% 5% 4 5% 5% 24%	2730
	11th to 20th	Night	11% 15% 5% 14% 7% 5% 4 3 5% 5% 26%	2637
	21st to end	Night	12% 16% 5% 11% 5% 5% 4 4 5% 6% 26%	2076
March	1st to 10th	Night	18% 17% 4 10% 5% 4 4 3 4 4 26%	5484
	11th to 20th	Night	12% 14% 4 10% 6% 5% 5% 4 6% 7% 28%	5188
	21st to end	Night	16% 12% 4 11% 7% 5% 4 3 5% 5% 29%	5213
April	1st to 10th	Night	21% 12% 4 7% 4 4 4 3 5% 7% 30%	2100
	11th to 20th	Night	19% 9% 3 7% 4 4 4 4 5% 5% 35%	2075
	21st to end	Night	21% 9% 3 7% 4 4 4 3 5% 4 35%	1932
May	1st to 10th	Night	17% 11% 3 9% 5% 5% 5% 5% 6% 8% 25%	4660
	11th to 20th	Night	16% 9% 3 8% 5% 5% 5% 4 5% 7% 34%	4639
	21st to end	Night	20% 10% 3 8% 5% 5% 5% 4 5% 6% 31%	5114
June	1st to 10th	Night	16% 8% 3 7% 5% 5% 4 4 6% 8% 34%	1680
	11th to 20th	Night	16% 6% 3 6% 5% 4 5% 5% 7% 8% 37%	1680
	21st to end	Night	18% 6% 3 7% 4 5% 5% 4 6% 7% 35%	1680
July	1st to 10th	Night	13% 6% 2 6% 5% 5% 5% 4 7% 10% 36%	4680
	11th to 20th	Night	10% 6% 3 6% 4 4 4 4 6% 8% 45%	4680
	21st to end	Night	12% 6% 2 6% 5% 5% 5% 4 6% 7% 42%	5084
August	1st to 10th	Night	14% 7% 3 8% 5% 5% 5% 4 6% 8% 36%	3666
	11th to 20th	Night	15% 7% 2 6% 4 4 4 4 5% 7% 41%	4084
	21st to end	Night	16% 8% 3 7% 4 4 4 3 6% 6% 39%	5045
September	1st to 10th	Night	13% 7% 2 7% 4 4 3 3 4 6% 46%	2100
	11th to 20th	Night	14% 5% 2 5% 3 4 4 3 5% 7% 49%	2126
	21st to end	Night	16% 7% 2 6% 4 4 3 3 5% 7% 42%	2314
October	1st to 10th	Night	18% 9% 2 6% 4 4 4 4 5% 5% 39%	2400
	11th to 20th	Night	21% 12% 3 7% 5% 4 5% 3 5% 5% 31%	2400
	21st to end	Night	22% 11% 4 8% 5% 5% 4 4 4 7% 27%	2849
November	1st to 10th	Night	18% 13% 4 8% 5% 5% 4 4 5% 6% 28%	2667
	11th to 20th	Night	17% 14% 5% 10% 6% 5% 5% 4 5% 5% 24%	2919
	21st to end	Night	20% 18% 6% 14% 5% 4 4 3 5% 4 17%	2940
December	1st to 10th	Night	17% 18% 6% 14% 7% 6% 5% 4 5% 5% 13%	4720
	11th to 20th	Night	21% 14% 5% 12% 6% 4 4 3 4 6% 22%	5348
	21st to end	Night	21% 21% 5% 10% 6% 4 3 3 4 6% 19%	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	72% 5% 8% 12% 3	4662
	11th to 20th	Day	73% 4 4 10% 9%	4680
	21st to end	Day	65% 7% 8% 10% 10% 1	5161
February	1st to 10th	Day	65% 5% 7% 15% 7% 2	1890
	11th to 20th	Day	62% 6% 9% 14% 9% 1	1877
	21st to end	Day	64% 4 7% 14% 9% 1	1730
March	1st to 10th	Day	65% 5% 7% 10% 11% 2	4579
	11th to 20th	Day	58% 6% 14% 12% 9% 1	4987
	21st to end	Day	52% 5% 8% 17% 16% 2	5961
April	1st to 10th	Day	57% 4 9% 17% 11% 3	2520
	11th to 20th	Day	55% 5% 7% 19% 11% 2	2494
	21st to end	Day	56% 5% 8% 16% 12% 3	2704
May	1st to 10th	Day	55% 8% 10% 18% 8% 1	8249
	11th to 20th	Day	50% 8% 14% 20% 8% 1	8225
	21st to end	Day	51% 6% 10% 19% 13% 1	9061
June	1st to 10th	Day	55% 5% 10% 18% 10% 1	2940
	11th to 20th	Day	45% 8% 13% 23% 10% 2	2940
	21st to end	Day	51% 9% 13% 18% 9%	2940
July	1st to 10th	Day	43% 7% 15% 25% 10%	8210
	11th to 20th	Day	36% 7% 16% 30% 10%	8205
	21st to end	Day	39% 7% 17% 30% 7%	8795
August	1st to 10th	Day	50% 8% 14% 19% 8%	6469
	11th to 20th	Day	43% 8% 18% 25% 6%	5952
	21st to end	Day	43% 8% 18% 22% 9% 1	6080
September	1st to 10th	Day	41% 7% 14% 25% 13%	2520
	11th to 20th	Day	38% 7% 14% 30% 11%	2494
	21st to end	Day	44% 6% 13% 23% 13%	2261
October	1st to 10th	Day	50% 6% 11% 26% 6%	3260
	11th to 20th	Day	54% 7% 12% 20% 6%	3240
	21st to end	Day	54% 7% 19% 14% 5% 1	3190
November	1st to 10th	Day	55% 6% 13% 19% 6% 1	1851
	11th to 20th	Day	65% 7% 9% 10% 8%	1697
	21st to end	Day	71% 6% 10% 9% 4 1	1680
December	1st to 10th	Day	76% 6% 7% 9% 2	2680
	11th to 20th	Day	69% 5% 7% 14% 6%	3066
	21st to end	Day	68% 6% 7% 15% 4	4048
January	1st to 10th	Night	68% 6% 10% 12% 3	8234
	11th to 20th	Night	72% 6% 9% 9% 4	8280
	21st to end	Night	66% 5% 7% 10% 11%	9015
February	1st to 10th	Night	62% 6% 9% 15% 7% 1	2730
	11th to 20th	Night	61% 5% 9% 17% 7% 1	2639
	21st to end	Night	58% 6% 10% 16% 9% 1	2076
March	1st to 10th	Night	62% 5% 9% 11% 11% 3	5494
	11th to 20th	Night	54% 7% 13% 16% 7% 3	5189
	21st to end	Night	54% 5% 8% 20% 9% 2	5213
April	1st to 10th	Night	53% 6% 10% 16% 12% 2	2100
	11th to 20th	Night	49% 6% 9% 21% 13% 2	2075
	21st to end	Night	51% 6% 9% 18% 14% 2	1932
May	1st to 10th	Night	53% 8% 11% 19% 7% 1	4666
	11th to 20th	Night	48% 9% 13% 20% 9% 1	4640
	21st to end	Night	52% 6% 9% 19% 13% 1	5115
June	1st to 10th	Night	47% 7% 13% 21% 11% 1	1680
	11th to 20th	Night	41% 9% 13% 22% 12% 2	1680
	21st to end	Night	47% 7% 14% 20% 11% 1	1680
July	1st to 10th	Night	42% 7% 18% 22% 11%	4640
	11th to 20th	Night	35% 8% 19% 30% 9%	4632
	21st to end	Night	41% 8% 15% 28% 9%	4967
August	1st to 10th	Night	45% 8% 15% 23% 9% 1	3656
	11th to 20th	Night	42% 7% 17% 27% 6%	4110
	21st to end	Night	44% 7% 16% 22% 9% 1	5045
September	1st to 10th	Night	38% 6% 15% 28% 12% 1	2100
	11th to 20th	Night	35% 6% 16% 33% 10%	2126
	21st to end	Night	42% 5% 14% 26% 12%	2314
October	1st to 10th	Night	42% 7% 15% 25% 11%	3920
	11th to 20th	Night	47% 8% 15% 21% 8%	3899
	21st to end	Night	51% 7% 18% 14% 9% 1	4599
November	1st to 10th	Night	55% 7% 14% 17% 6%	2667
	11th to 20th	Night	61% 6% 10% 14% 7% 1	2919
	21st to end	Night	69% 6% 11% 11% 3	2940
December	1st to 10th	Night	71% 7% 10% 8% 3	4720
	11th to 20th	Night	65% 5% 6% 14% 9%	5348
	21st to end	Night	67% 4 5% 13% 10%	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	18% 20% 41% 17% 4	220
	11th to 20th	Day	29% 20% 33% 14% 4	220
	21st to end	Day	21% 19% 34% 22% 4	248
February	1st to 10th	Day	28% 26% 34% 9% 3	330
	11th to 20th	Day	24% 30% 35% 10% 1	355
	21st to end	Day	29% 22% 33% 13% 2	446
March	1st to 10th	Day	27% 23% 32% 13% 5%	540
	11th to 20th	Day	27% 23% 33% 14% 3 1	540
	21st to end	Day	31% 25% 25% 14% 5% 1	594
April	1st to 10th	Day	34% 20% 26% 14% 6% 1	540
	11th to 20th	Day	35% 20% 22% 13% 8% 2	532
	21st to end	Day	30% 22% 30% 12% 5% 1	540
May	1st to 10th	Day	27% 21% 30% 16% 5% 1	543
	11th to 20th	Day	23% 20% 30% 19% 7% 2	567
	21st to end	Day	25% 20% 29% 19% 6% 1	617
June	1st to 10th	Day	25% 17% 31% 19% 6% 1	570
	11th to 20th	Day	19% 19% 32% 19% 9% 2	570
	21st to end	Day	22% 16% 30% 21% 8% 2	570
July	1st to 10th	Day	13% 13% 36% 28% 8% 2	565
	11th to 20th	Day	15% 14% 33% 27% 9% 1	564
	21st to end	Day	13% 12% 35% 26% 12% 3	620
August	1st to 10th	Day	16% 9% 28% 34% 11% 2	566
	11th to 20th	Day	15% 10% 29% 26% 14% 6%	559
	21st to end	Day	17% 16% 30% 18% 12% 6%	627
September	1st to 10th	Day	19% 12% 32% 20% 11% 6%	570
	11th to 20th	Day	13% 12% 28% 19% 18% 9%	570
	21st to end	Day	20% 14% 25% 20% 13% 7%	562
October	1st to 10th	Day	28% 14% 23% 19% 12% 3	530
	11th to 20th	Day	30% 21% 28% 13% 6% 2	530
	21st to end	Day	33% 15% 27% 19% 5%	467
November	1st to 10th	Day	32% 16% 29% 18% 4 1	425
	11th to 20th	Day	28% 22% 32% 10% 7% 1	237
	21st to end	Day	35% 21% 30% 13% 1	220
December	1st to 10th	Day	32% 17% 31% 15% 4	220
	11th to 20th	Day	32% 22% 34% 9% 2 1	220
	21st to end	Day	29% 19% 33% 14% 4 1	242
January	1st to 10th	Night	26% 15% 36% 18% 4	840
	11th to 20th	Night	30% 17% 27% 20% 6%	840
	21st to end	Night	18% 15% 35% 24% 7% 1	924
February	1st to 10th	Night	18% 19% 34% 23% 6% 1	840
	11th to 20th	Night	21% 21% 36% 19% 4	823
	21st to end	Night	22% 20% 29% 25% 4	692
March	1st to 10th	Night	25% 17% 32% 21% 5%	840
	11th to 20th	Night	24% 20% 31% 21% 4 1	840
	21st to end	Night	25% 15% 32% 22% 6%	924
April	1st to 10th	Night	29% 15% 28% 22% 6%	840
	11th to 20th	Night	24% 17% 29% 23% 7%	831
	21st to end	Night	26% 17% 25% 22% 8%	672
May	1st to 10th	Night	22% 14% 27% 26% 10% 1	420
	11th to 20th	Night	21% 10% 30% 30% 9%	414
	21st to end	Night	18% 12% 34% 27% 9%	455
June	1st to 10th	Night	18% 8% 33% 32% 9%	420
	11th to 20th	Night	18% 10% 28% 31% 13% 1	420
	21st to end	Night	19% 7% 24% 34% 15%	420
July	1st to 10th	Night	12% 4 28% 44% 13%	410
	11th to 20th	Night	14% 5% 23% 39% 18%	408
	21st to end	Night	12% 5% 25% 38% 17% 2	460
August	1st to 10th	Night	11% 6% 21% 40% 21% 1	418
	11th to 20th	Night	12% 4 21% 36% 24% 3	612
	21st to end	Night	17% 7% 24% 32% 17% 2	924
September	1st to 10th	Night	18% 5% 27% 31% 17% 1	840
	11th to 20th	Night	18% 7% 21% 30% 21% 3	840
	21st to end	Night	20% 9% 23% 28% 18% 2	833
October	1st to 10th	Night	22% 12% 28% 23% 14% 1	800
	11th to 20th	Night	28% 14% 27% 23% 7% 1	800
	21st to end	Night	28% 14% 29% 25% 4	880
November	1st to 10th	Night	28% 14% 29% 22% 7% 1	820
	11th to 20th	Night	26% 18% 30% 16% 10% 1	840
	21st to end	Night	30% 20% 24% 20% 5% 1	840
December	1st to 10th	Night	29% 18% 28% 18% 6%	840
	11th to 20th	Night	28% 18% 30% 18% 4 1	840
	21st to end	Night	33% 18% 27% 18% 5%	924

Page generated at 2026-09-26 04:18:43. Version ac07

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