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 2025-05-26.

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% 12% 4 9% 6% 5% 5% 4 5% 6% 29%	114022
	Night	16% 13% 4 10% 6% 5% 4 3 5% 6% 28%	115243
Transparency	Day	54% 7% 11% 18% 9% 1	117511
	Night	56% 6% 12% 17% 9% 1	119918
Seeing	Day	24% 18% 30% 18% 8% 2	15074
	Night	23% 14% 29% 24% 9% 1	24209

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% 19% 8% 19% 8% 6% 5% 2 3 3 13%	3597
	11th to 20th	Day	11% 17% 6% 20% 9% 4 4 2 4 5% 18%	3570
	21st to end	Day	8% 16% 9% 16% 7% 6% 5% 4 4 6% 21%	3983
February	1st to 10th	Day	11% 16% 7% 13% 10% 5% 5% 3 4 6% 20%	1800
	11th to 20th	Day	11% 19% 5% 14% 5% 5% 4 2 4 6% 24%	1777
	21st to end	Day	16% 18% 4 11% 7% 6% 4 3 3 5% 24%	1650
March	1st to 10th	Day	17% 17% 5% 12% 7% 4 4 3 4 4 22%	4476
	11th to 20th	Day	11% 15% 6% 11% 6% 5% 5% 3 5% 6% 26%	4879
	21st to end	Day	16% 14% 4 8% 5% 4 4 3 5% 5% 33%	5832
April	1st to 10th	Day	21% 15% 3 7% 4 3 4 3 4 6% 30%	2400
	11th to 20th	Day	22% 12% 3 8% 5% 4 3 3 4 5% 33%	2374
	21st to end	Day	20% 11% 3 9% 5% 5% 4 4 5% 4 30%	2576
May	1st to 10th	Day	20% 10% 3 8% 5% 4 4 4 6% 7% 27%	4566
	11th to 20th	Day	18% 8% 3 8% 5% 5% 5% 4 6% 7% 32%	4538
	21st to end	Day	17% 8% 3 8% 5% 5% 5% 4 5% 7% 34%	4907
June	1st to 10th	Day	22% 9% 3 7% 6% 5% 4 4 5% 6% 28%	2660
	11th to 20th	Day	15% 5% 2 7% 6% 5% 6% 4 6% 9% 34%	2660
	21st to end	Day	21% 7% 3 7% 6% 5% 5% 4 6% 7% 29%	2660
July	1st to 10th	Day	14% 7% 3 7% 6% 5% 6% 4 7% 9% 31%	4440
	11th to 20th	Day	15% 6% 2 7% 5% 5% 5% 4 6% 9% 35%	4440
	21st to end	Day	12% 7% 3 5% 4 4 5% 4 6% 8% 44%	4814
August	1st to 10th	Day	14% 7% 3 8% 6% 5% 6% 4 7% 8% 30%	4423
	11th to 20th	Day	16% 8% 2 7% 4 5% 5% 4 6% 8% 35%	4005
	21st to end	Day	14% 6% 2 7% 5% 4 5% 3 7% 9% 37%	4180
September	1st to 10th	Day	15% 7% 2 7% 4 4 4 3 5% 7% 41%	2280
	11th to 20th	Day	14% 7% 2 6% 4 3 4 4 6% 7% 42%	2256
	21st to end	Day	20% 8% 3 5% 4 4 4 3 6% 7% 37%	2065
October	1st to 10th	Day	22% 10% 3 6% 5% 4 4 3 4 7% 32%	1900
	11th to 20th	Day	24% 13% 4 8% 5% 4 4 3 5% 6% 24%	1900
	21st to end	Day	25% 14% 3 8% 4 4 4 3 5% 6% 23%	1891
November	1st to 10th	Day	16% 13% 4 7% 5% 4 4 3 4 6% 33%	1761
	11th to 20th	Day	19% 15% 5% 10% 5% 6% 5% 4 5% 4 22%	1616
	21st to end	Day	21% 18% 7% 10% 6% 5% 3 4 4 4 18%	1600
December	1st to 10th	Day	19% 22% 9% 11% 8% 4 5% 3 4 4 11%	2600
	11th to 20th	Day	17% 17% 7% 14% 7% 4 4 3 3 3 20%	2986
	21st to end	Day	19% 18% 5% 11% 5% 6% 5% 3 4 4 20%	3960
January	1st to 10th	Night	12% 21% 9% 16% 6% 5% 4 3 4 4 17%	6349
	11th to 20th	Night	10% 15% 7% 17% 10% 6% 4 3 4 5% 18%	6315
	21st to end	Night	8% 17% 8% 15% 7% 7% 5% 3 5% 5% 19%	6968
February	1st to 10th	Night	12% 14% 5% 14% 7% 6% 5% 4 5% 5% 23%	2600
	11th to 20th	Night	12% 15% 5% 14% 7% 5% 4 3 5% 5% 25%	2508
	21st to end	Night	12% 16% 5% 11% 6% 5% 4 4 5% 6% 26%	1980
March	1st to 10th	Night	19% 17% 4 10% 5% 4 4 3 4 4 26%	5364
	11th to 20th	Night	11% 14% 4 10% 6% 5% 5% 4 6% 7% 28%	5076
	21st to end	Night	16% 11% 4 11% 6% 5% 4 3 5% 5% 30%	5100
April	1st to 10th	Night	21% 12% 4 7% 4 4 4 3 5% 7% 31%	2000
	11th to 20th	Night	19% 9% 3 7% 4 4 4 4 5% 5% 36%	1975
	21st to end	Night	21% 10% 3 7% 4 5% 4 3 5% 4 35%	1840
May	1st to 10th	Night	19% 11% 3 10% 5% 4 4 4 5% 7% 28%	2594
	11th to 20th	Night	18% 8% 2 7% 4 4 5% 3 5% 7% 37%	2575
	21st to end	Night	17% 8% 2 7% 5% 5% 5% 4 5% 7% 34%	2784
June	1st to 10th	Night	16% 8% 3 7% 5% 5% 4 4 6% 8% 33%	1520
	11th to 20th	Night	15% 6% 3 6% 5% 3 4 5% 7% 8% 37%	1520
	21st to end	Night	18% 6% 3 7% 4 4 5% 4 6% 7% 35%	1520
July	1st to 10th	Night	13% 7% 3 8% 6% 5% 5% 4 5% 9% 34%	2520
	11th to 20th	Night	13% 6% 3 8% 4 4 5% 3 6% 8% 39%	2520
	21st to end	Night	10% 5% 2 5% 5% 4 4 5% 7% 7% 47%	2739
August	1st to 10th	Night	12% 7% 3 9% 5% 5% 5% 4 6% 8% 38%	2506
	11th to 20th	Night	16% 7% 2 6% 4 4 4 4 5% 7% 41%	2789
	21st to end	Night	17% 6% 2 7% 5% 4 4 3 6% 6% 39%	3476
September	1st to 10th	Night	14% 7% 2 7% 4 4 3 3 4 6% 47%	1900
	11th to 20th	Night	14% 6% 2 5% 3 3 4 3 5% 7% 48%	1924
	21st to end	Night	17% 7% 2 6% 4 3 3 3 5% 7% 42%	2114
October	1st to 10th	Night	19% 9% 2 6% 5% 4 4 4 5% 5% 37%	2280
	11th to 20th	Night	22% 12% 3 7% 5% 4 5% 3 5% 5% 30%	2280
	21st to end	Night	22% 11% 4 8% 5% 5% 4 4 4 7% 26%	2706
November	1st to 10th	Night	17% 13% 4 8% 5% 5% 4 4 5% 6% 28%	2537
	11th to 20th	Night	17% 14% 5% 10% 6% 5% 5% 4 5% 5% 25%	2780
	21st to end	Night	21% 17% 5% 13% 5% 4 4 3 5% 4 18%	2800
December	1st to 10th	Night	18% 18% 5% 14% 7% 6% 5% 3 5% 5% 13%	4580
	11th to 20th	Night	22% 14% 5% 12% 6% 4 3 3 4 6% 23%	5208
	21st to end	Night	21% 21% 5% 10% 6% 3 3 3 4 6% 19%	6996

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	76% 5% 6% 10% 3	3598
	11th to 20th	Day	70% 4 5% 12% 8%	3600
	21st to end	Day	63% 7% 8% 12% 10% 1	3983
February	1st to 10th	Day	66% 5% 7% 14% 7% 2	1800
	11th to 20th	Day	63% 6% 10% 12% 9% 1	1786
	21st to end	Day	64% 4 7% 14% 9% 1	1650
March	1st to 10th	Day	65% 5% 6% 10% 11% 2	4479
	11th to 20th	Day	57% 6% 14% 12% 9% 1	4879
	21st to end	Day	51% 6% 8% 18% 16% 2	5832
April	1st to 10th	Day	56% 4 9% 18% 11% 3	2400
	11th to 20th	Day	54% 4 7% 20% 12% 2	2374
	21st to end	Day	57% 5% 8% 15% 12% 3	2576
May	1st to 10th	Day	53% 8% 10% 18% 8% 1	4580
	11th to 20th	Day	48% 8% 15% 18% 9% 1	4542
	21st to end	Day	48% 8% 11% 18% 14% 1	4907
June	1st to 10th	Day	56% 6% 11% 17% 9% 1	2660
	11th to 20th	Day	45% 8% 13% 22% 10% 2	2660
	21st to end	Day	52% 9% 13% 17% 9%	2660
July	1st to 10th	Day	45% 8% 14% 25% 7%	4370
	11th to 20th	Day	43% 8% 17% 24% 7%	4365
	21st to end	Day	38% 7% 15% 31% 9%	4661
August	1st to 10th	Day	49% 9% 15% 21% 6%	4409
	11th to 20th	Day	44% 8% 17% 26% 5%	4045
	21st to end	Day	42% 7% 16% 22% 12% 1	4180
September	1st to 10th	Day	42% 7% 14% 25% 13%	2280
	11th to 20th	Day	39% 7% 14% 29% 10% 1	2256
	21st to end	Day	46% 6% 14% 24% 10%	2065
October	1st to 10th	Day	51% 6% 11% 26% 5%	3160
	11th to 20th	Day	55% 7% 12% 20% 6%	3140
	21st to end	Day	54% 7% 20% 13% 5% 1	3091
November	1st to 10th	Day	53% 6% 14% 20% 6% 1	1761
	11th to 20th	Day	64% 7% 9% 10% 8%	1616
	21st to end	Day	70% 6% 10% 10% 4 1	1600
December	1st to 10th	Day	76% 6% 7% 9% 2	2600
	11th to 20th	Day	69% 5% 7% 14% 6%	2986
	21st to end	Day	68% 6% 7% 15% 5%	3960
January	1st to 10th	Night	70% 6% 11% 10% 2	6349
	11th to 20th	Night	68% 7% 11% 10% 4	6360
	21st to end	Night	67% 5% 8% 8% 11%	6968
February	1st to 10th	Night	62% 6% 9% 15% 7% 1	2600
	11th to 20th	Night	62% 5% 10% 17% 7% 1	2510
	21st to end	Night	58% 6% 10% 16% 9% 1	1980
March	1st to 10th	Night	62% 5% 8% 11% 11% 3	5374
	11th to 20th	Night	53% 7% 13% 16% 7% 3	5077
	21st to end	Night	54% 5% 8% 21% 9% 2	5100
April	1st to 10th	Night	53% 6% 10% 16% 13% 2	2000
	11th to 20th	Night	48% 6% 9% 21% 14% 2	1975
	21st to end	Night	51% 6% 9% 18% 13% 3	1840
May	1st to 10th	Night	52% 9% 10% 18% 9% 2	2600
	11th to 20th	Night	45% 10% 15% 18% 11% 2	2576
	21st to end	Night	48% 7% 10% 20% 13% 2	2785
June	1st to 10th	Night	47% 8% 14% 21% 10%	1520
	11th to 20th	Night	41% 9% 14% 22% 12% 2	1520
	21st to end	Night	48% 7% 13% 19% 12% 1	1520
July	1st to 10th	Night	47% 7% 17% 19% 10%	2480
	11th to 20th	Night	42% 7% 19% 25% 6%	2472
	21st to end	Night	34% 8% 18% 29% 11%	2651
August	1st to 10th	Night	43% 9% 15% 26% 7%	2496
	11th to 20th	Night	42% 7% 18% 27% 6%	2815
	21st to end	Night	44% 7% 15% 22% 11% 2	3476
September	1st to 10th	Night	39% 6% 14% 28% 13% 1	1900
	11th to 20th	Night	36% 6% 16% 32% 9% 1	1924
	21st to end	Night	42% 5% 15% 28% 10%	2114
October	1st to 10th	Night	42% 7% 15% 25% 10%	3800
	11th to 20th	Night	48% 8% 15% 21% 8%	3779
	21st to end	Night	51% 7% 18% 13% 9% 1	4456
November	1st to 10th	Night	55% 7% 15% 17% 6%	2537
	11th to 20th	Night	61% 6% 10% 14% 7% 1	2780
	21st to end	Night	68% 6% 11% 11% 3	2800
December	1st to 10th	Night	72% 8% 11% 8% 2	4580
	11th to 20th	Night	65% 5% 6% 14% 9%	5208
	21st to end	Night	67% 4 5% 13% 10%	6996

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	19% 21% 41% 17% 3	200
	11th to 20th	Day	27% 19% 34% 16% 5% 1	200
	21st to end	Day	22% 19% 35% 20% 4	225
February	1st to 10th	Day	30% 28% 31% 8% 3	300
	11th to 20th	Day	26% 29% 36% 9%	324
	21st to end	Day	31% 23% 31% 13% 2	414
March	1st to 10th	Day	27% 22% 31% 13% 5%	500
	11th to 20th	Day	25% 24% 33% 14% 3 1	500
	21st to end	Day	31% 24% 24% 15% 5% 1	550
April	1st to 10th	Day	33% 20% 25% 14% 6% 1	500
	11th to 20th	Day	34% 20% 23% 13% 9% 2	492
	21st to end	Day	29% 22% 30% 12% 5% 1	500
May	1st to 10th	Day	27% 21% 30% 15% 5% 1	503
	11th to 20th	Day	22% 20% 30% 20% 7% 2	527
	21st to end	Day	23% 19% 30% 19% 7% 1	549
June	1st to 10th	Day	24% 17% 32% 21% 6%	490
	11th to 20th	Day	18% 18% 33% 19% 10% 2	490
	21st to end	Day	23% 16% 28% 22% 8% 2	490
July	1st to 10th	Day	14% 11% 35% 29% 9% 2	485
	11th to 20th	Day	15% 13% 32% 28% 10% 1	484
	21st to end	Day	13% 11% 34% 28% 11% 3	532
August	1st to 10th	Day	16% 10% 28% 33% 11% 2	486
	11th to 20th	Day	15% 10% 26% 27% 14% 7%	479
	21st to end	Day	18% 16% 29% 19% 12% 6%	539
September	1st to 10th	Day	19% 11% 30% 21% 12% 7%	490
	11th to 20th	Day	14% 12% 28% 19% 18% 9%	490
	21st to end	Day	21% 14% 25% 20% 12% 7%	490
October	1st to 10th	Day	29% 14% 22% 20% 12% 3	490
	11th to 20th	Day	31% 21% 27% 13% 6% 2	490
	21st to end	Day	33% 16% 28% 19% 4	434
November	1st to 10th	Day	31% 16% 29% 19% 4 1	395
	11th to 20th	Day	27% 22% 34% 9% 6% 1	216
	21st to end	Day	34% 21% 30% 14% 2 1	200
December	1st to 10th	Day	33% 18% 30% 16% 4	200
	11th to 20th	Day	33% 23% 32% 10% 3 1	200
	21st to end	Day	29% 20% 32% 13% 5% 1	220
January	1st to 10th	Night	27% 16% 37% 16% 4	800
	11th to 20th	Night	28% 17% 28% 21% 6%	800
	21st to end	Night	19% 15% 35% 24% 7% 1	880
February	1st to 10th	Night	19% 19% 34% 22% 5%	800
	11th to 20th	Night	22% 21% 36% 18% 4	783
	21st to end	Night	23% 19% 30% 25% 3	660
March	1st to 10th	Night	25% 17% 31% 22% 5%	800
	11th to 20th	Night	23% 19% 31% 21% 5% 1	800
	21st to end	Night	25% 15% 31% 22% 6%	880
April	1st to 10th	Night	29% 15% 27% 22% 6%	800
	11th to 20th	Night	24% 17% 29% 23% 7%	791
	21st to end	Night	27% 17% 25% 22% 8%	640
May	1st to 10th	Night	23% 14% 28% 26% 9% 1	400
	11th to 20th	Night	21% 10% 29% 31% 9%	394
	21st to end	Night	17% 11% 35% 27% 9%	423
June	1st to 10th	Night	18% 8% 34% 31% 8% 1	380
	11th to 20th	Night	17% 9% 29% 31% 13% 1	380
	21st to end	Night	20% 7% 24% 33% 16%	380
July	1st to 10th	Night	12% 4 28% 42% 14%	370
	11th to 20th	Night	14% 4 24% 39% 19%	368
	21st to end	Night	12% 5% 25% 38% 18% 2	416
August	1st to 10th	Night	11% 6% 21% 39% 21% 1	378
	11th to 20th	Night	12% 4 21% 34% 25% 3	554
	21st to end	Night	17% 7% 25% 32% 17% 2	836
September	1st to 10th	Night	19% 5% 28% 30% 17% 1	760
	11th to 20th	Night	19% 7% 21% 29% 22% 2	760
	21st to end	Night	21% 10% 23% 27% 18% 1	760
October	1st to 10th	Night	23% 12% 28% 23% 14% 1	760
	11th to 20th	Night	29% 14% 26% 22% 8% 1	760
	21st to end	Night	28% 15% 28% 24% 4	836
November	1st to 10th	Night	27% 14% 28% 22% 7% 1	780
	11th to 20th	Night	26% 19% 30% 16% 10% 1	800
	21st to end	Night	32% 19% 24% 19% 6% 1	800
December	1st to 10th	Night	30% 18% 28% 18% 6%	800
	11th to 20th	Night	29% 18% 30% 18% 4 1	800
	21st to end	Night	33% 17% 27% 18% 5%	880

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