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 2024-11-02.

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	17% 11% 4 9% 6% 5% 5% 4 5% 6% 30%	101525
	Night	16% 12% 4 9% 5% 5% 4 3 5% 6% 30%	97446
Transparency	Day	53% 7% 12% 19% 9% 1	101284
	Night	54% 7% 12% 18% 8% 1	97307
Seeing	Day	24% 17% 30% 19% 8% 2	14444
	Night	23% 14% 29% 24% 9% 1	23447

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	15% 19% 8% 15% 8% 5% 4 2 3 4 16%	2517
	11th to 20th	Day	13% 16% 6% 20% 8% 4 3 3 4 5% 19%	2520
	21st to end	Day	11% 16% 8% 14% 8% 7% 5% 4 4 5% 18%	2781
February	1st to 10th	Day	12% 17% 7% 13% 10% 5% 5% 3 4 6% 20%	1710
	11th to 20th	Day	12% 19% 5% 13% 5% 5% 4 2 4 6% 25%	1685
	21st to end	Day	16% 17% 4 11% 7% 6% 4 3 3 5% 24%	1570
March	1st to 10th	Day	16% 19% 5% 9% 6% 4 4 3 4 5% 25%	3116
	11th to 20th	Day	11% 19% 7% 13% 6% 5% 4 3 4 4 24%	3407
	21st to end	Day	12% 10% 3 8% 6% 4 4 4 6% 6% 37%	4070
April	1st to 10th	Day	21% 15% 3 7% 4 3 4 3 4 6% 30%	2280
	11th to 20th	Day	22% 11% 2 8% 5% 4 4 3 4 5% 33%	2254
	21st to end	Day	20% 11% 3 9% 4 5% 4 4 5% 4 30%	2446
May	1st to 10th	Day	20% 10% 3 8% 5% 4 4 4 5% 7% 28%	4426
	11th to 20th	Day	18% 8% 3 8% 5% 5% 5% 4 6% 7% 32%	4398
	21st to end	Day	17% 7% 3 9% 5% 5% 5% 4 5% 7% 34%	4837
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% 3 7% 5% 5% 4 3 4 6% 33%	1680
	11th to 20th	Day	20% 15% 5% 10% 6% 5% 5% 4 5% 4 21%	1536
	21st to end	Day	21% 17% 7% 10% 6% 5% 3 4 4 4 18%	1520
December	1st to 10th	Day	22% 21% 6% 11% 6% 5% 4 3 4 4 15%	1520
	11th to 20th	Day	19% 17% 7% 13% 6% 4 5% 3 4 5% 19%	1906
	21st to end	Day	23% 20% 6% 12% 5% 4 3 2 3 4 18%	2772
January	1st to 10th	Night	15% 19% 7% 11% 6% 5% 4 4 4 5% 21%	4429
	11th to 20th	Night	12% 14% 6% 15% 10% 6% 4 3 5% 6% 20%	4440
	21st to end	Night	11% 18% 8% 15% 6% 7% 4 3 4 5% 18%	4870
February	1st to 10th	Night	12% 14% 6% 14% 7% 6% 5% 4 5% 5% 23%	2470
	11th to 20th	Night	12% 15% 5% 13% 7% 5% 4 3 5% 5% 26%	2380
	21st to end	Night	13% 16% 5% 10% 5% 5% 4 4 5% 6% 27%	1884
March	1st to 10th	Night	18% 15% 4 9% 5% 4 4 3 4 5% 29%	3724
	11th to 20th	Night	15% 18% 5% 11% 5% 4 4 3 5% 5% 26%	3548
	21st to end	Night	13% 10% 3 10% 6% 4 4 3 4 5% 36%	3562
April	1st to 10th	Night	21% 12% 3 7% 4 4 4 3 5% 7% 31%	1900
	11th to 20th	Night	19% 9% 3 7% 4 4 4 4 5% 5% 36%	1875
	21st to end	Night	21% 10% 3 8% 4 5% 4 3 4 4 35%	1749
May	1st to 10th	Night	19% 11% 3 10% 5% 4 4 4 5% 7% 28%	2514
	11th to 20th	Night	18% 8% 2 7% 4 4 5% 3 5% 7% 37%	2495
	21st to end	Night	17% 8% 2 7% 5% 5% 5% 4 5% 7% 35%	2738
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	18% 13% 4 7% 5% 5% 4 4 5% 6% 28%	2421
	11th to 20th	Night	17% 14% 5% 10% 6% 5% 4 4 5% 5% 25%	2641
	21st to end	Night	21% 17% 5% 13% 5% 4 4 3 5% 4 18%	2660
December	1st to 10th	Night	19% 20% 6% 11% 6% 5% 4 3 4 5% 16%	2660
	11th to 20th	Night	21% 16% 6% 11% 5% 4 3 3 3 4 23%	3288
	21st to end	Night	24% 22% 5% 11% 5% 3 3 3 3 4 18%	4884

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% 6% 8% 9% 3	2518
	11th to 20th	Day	69% 5% 6% 13% 6% 1	2520
	21st to end	Day	67% 8% 8% 10% 5% 1	2781
February	1st to 10th	Day	66% 5% 7% 15% 6% 1	1710
	11th to 20th	Day	61% 6% 10% 12% 9% 1	1694
	21st to end	Day	64% 5% 7% 14% 9% 1	1570
March	1st to 10th	Day	62% 6% 8% 14% 10% 1	3119
	11th to 20th	Day	63% 6% 10% 13% 8% 2	3407
	21st to end	Day	44% 7% 10% 22% 15% 2	4070
April	1st to 10th	Day	57% 4 9% 17% 10% 3	2280
	11th to 20th	Day	54% 4 8% 20% 12% 2	2254
	21st to end	Day	57% 5% 8% 15% 12% 3	2446
May	1st to 10th	Day	53% 8% 10% 19% 8% 2	4440
	11th to 20th	Day	48% 8% 15% 18% 9% 1	4402
	21st to end	Day	47% 8% 11% 18% 14% 1	4837
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	52% 7% 12% 21% 8%	1900
	11th to 20th	Day	61% 6% 12% 16% 5% 1	1900
	21st to end	Day	61% 6% 13% 13% 6% 1	1891
November	1st to 10th	Day	52% 6% 14% 20% 6% 1	1680
	11th to 20th	Day	65% 7% 10% 10% 8%	1536
	21st to end	Day	69% 6% 10% 10% 4 1	1520
December	1st to 10th	Day	73% 6% 9% 9% 3	1520
	11th to 20th	Day	68% 6% 9% 12% 5%	1906
	21st to end	Day	72% 5% 5% 13% 5%	2772
January	1st to 10th	Night	65% 7% 15% 11% 3	4429
	11th to 20th	Night	64% 8% 13% 11% 4 1	4440
	21st to end	Night	69% 5% 10% 8% 7%	4870
February	1st to 10th	Night	62% 6% 9% 15% 6% 1	2470
	11th to 20th	Night	61% 5% 10% 17% 7% 1	2382
	21st to end	Night	57% 6% 11% 16% 10% 1	1884
March	1st to 10th	Night	57% 6% 11% 13% 10% 2	3734
	11th to 20th	Night	59% 7% 10% 15% 8% 1	3549
	21st to end	Night	48% 6% 10% 21% 12% 3	3562
April	1st to 10th	Night	53% 6% 10% 16% 13% 2	1900
	11th to 20th	Night	48% 6% 9% 22% 13% 2	1875
	21st to end	Night	52% 6% 9% 17% 13% 3	1749
May	1st to 10th	Night	52% 9% 11% 18% 9% 2	2520
	11th to 20th	Night	44% 10% 15% 18% 11% 2	2496
	21st to end	Night	48% 7% 10% 20% 13% 2	2739
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	47% 7% 11% 23% 11%	2280
	11th to 20th	Night	55% 7% 13% 18% 6%	2280
	21st to end	Night	58% 7% 13% 15% 7% 1	2706
November	1st to 10th	Night	54% 7% 15% 17% 6%	2421
	11th to 20th	Night	61% 6% 11% 14% 6% 2	2641
	21st to end	Night	67% 6% 11% 12% 3	2660
December	1st to 10th	Night	71% 6% 10% 10% 4	2660
	11th to 20th	Night	65% 5% 8% 14% 6% 1	3288
	21st to end	Night	72% 5% 6% 13% 5%	4884

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% 39% 18% 3	180
	11th to 20th	Day	28% 18% 33% 16% 5% 1	180
	21st to end	Day	22% 19% 33% 21% 4	202
February	1st to 10th	Day	30% 28% 31% 8% 4	270
	11th to 20th	Day	26% 29% 36% 9%	292
	21st to end	Day	32% 23% 30% 13% 2	382
March	1st to 10th	Day	27% 22% 32% 14% 6%	460
	11th to 20th	Day	24% 23% 33% 15% 3 1	460
	21st to end	Day	30% 24% 25% 15% 6% 1	506
April	1st to 10th	Day	32% 19% 27% 15% 7% 1	460
	11th to 20th	Day	34% 19% 23% 13% 9% 2	452
	21st to end	Day	28% 23% 30% 13% 5% 1	460
May	1st to 10th	Day	28% 19% 30% 15% 6% 2	463
	11th to 20th	Day	21% 19% 30% 21% 7% 2	487
	21st to end	Day	22% 19% 31% 19% 7% 1	529
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% 27% 19% 4	434
November	1st to 10th	Day	30% 16% 29% 20% 4 1	368
	11th to 20th	Day	28% 21% 36% 8% 6% 2	196
	21st to end	Day	33% 21% 28% 15% 2 1	180
December	1st to 10th	Day	33% 18% 30% 14% 4	180
	11th to 20th	Day	31% 23% 33% 9% 2 1	180
	21st to end	Day	31% 21% 31% 13% 3 1	198
January	1st to 10th	Night	28% 15% 36% 17% 4	760
	11th to 20th	Night	29% 17% 28% 21% 6%	760
	21st to end	Night	19% 15% 35% 24% 7% 1	836
February	1st to 10th	Night	19% 19% 34% 22% 5%	760
	11th to 20th	Night	21% 21% 36% 18% 4	743
	21st to end	Night	23% 20% 30% 24% 4	628
March	1st to 10th	Night	24% 17% 32% 22% 5%	760
	11th to 20th	Night	24% 20% 31% 20% 5% 1	760
	21st to end	Night	24% 15% 32% 22% 7%	836
April	1st to 10th	Night	29% 15% 27% 23% 6%	760
	11th to 20th	Night	24% 17% 29% 23% 7%	751
	21st to end	Night	26% 17% 25% 22% 9%	609
May	1st to 10th	Night	23% 13% 28% 26% 9% 1	380
	11th to 20th	Night	22% 9% 29% 32% 9%	374
	21st to end	Night	17% 11% 36% 28% 9%	411
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% 8% 1	745
	11th to 20th	Night	26% 19% 30% 15% 10% 1	760
	21st to end	Night	32% 19% 24% 20% 5% 1	760
December	1st to 10th	Night	30% 18% 28% 18% 5%	760
	11th to 20th	Night	28% 18% 30% 18% 4 1	760
	21st to end	Night	33% 17% 27% 17% 4	836

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