Lac Chantier
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lac Chantier clear sky chart from 2005-11-06 to 2026-01-17.

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% 13% 5% 11% 6% 5% 5% 4 5% 6% 25%	127706
	Night	15% 14% 6% 12% 7% 5% 5% 3 4 5% 24%	123966
Transparency	Day	59% 4 10% 18% 8% 1	131112
	Night	62% 4 10% 16% 8% 1	128634
Seeing	Day	27% 17% 32% 16% 6% 1	15829
	Night	25% 15% 31% 21% 7% 1	24878

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	9% 20% 9% 21% 10% 7% 7% 3 3 3 8%	3677
	11th to 20th	Day	8% 15% 8% 20% 12% 8% 4 3 4 4 14%	3618
	21st to end	Day	6% 11% 8% 21% 7% 5% 5% 5% 7% 7% 19%	3960
February	1st to 10th	Day	8% 17% 7% 16% 8% 8% 5% 4 5% 6% 16%	1739
	11th to 20th	Day	10% 18% 7% 17% 7% 6% 5% 3 4 5% 18%	1796
	21st to end	Day	12% 18% 7% 12% 8% 6% 5% 3 5% 3 20%	1650
March	1st to 10th	Day	13% 21% 6% 14% 7% 5% 4 2 3 4 21%	4476
	11th to 20th	Day	11% 17% 7% 12% 7% 5% 4 3 4 5% 24%	4766
	21st to end	Day	13% 17% 6% 9% 5% 4 4 3 5% 5% 31%	5918
April	1st to 10th	Day	19% 19% 5% 10% 6% 4 3 3 4 5% 24%	2400
	11th to 20th	Day	21% 13% 5% 9% 4 3 3 3 4 5% 30%	2374
	21st to end	Day	19% 14% 4 8% 6% 4 4 3 4 4 29%	2617
May	1st to 10th	Day	22% 14% 5% 8% 6% 5% 4 3 5% 6% 23%	6346
	11th to 20th	Day	22% 10% 3 7% 6% 5% 5% 4 6% 6% 27%	6318
	21st to end	Day	22% 11% 3 9% 5% 5% 4 3 4 6% 28%	6949
June	1st to 10th	Day	23% 11% 3 8% 6% 4 4 3 6% 6% 25%	2800
	11th to 20th	Day	16% 9% 2 7% 6% 5% 5% 4 6% 9% 31%	2800
	21st to end	Day	23% 9% 3 9% 6% 6% 4 4 6% 6% 24%	2800
July	1st to 10th	Day	19% 10% 4 8% 6% 5% 5% 5% 7% 7% 24%	6360
	11th to 20th	Day	12% 9% 3 8% 5% 5% 5% 5% 6% 9% 32%	6360
	21st to end	Day	11% 7% 3 7% 4 5% 5% 5% 7% 9% 38%	6926
August	1st to 10th	Day	16% 8% 4 9% 5% 6% 6% 5% 6% 9% 27%	4563
	11th to 20th	Day	17% 9% 3 8% 5% 5% 5% 4 6% 7% 30%	4251
	21st to end	Day	15% 8% 4 8% 6% 5% 6% 4 6% 8% 31%	4312
September	1st to 10th	Day	18% 9% 2 7% 4 4 4 3 7% 6% 36%	2400
	11th to 20th	Day	16% 9% 3 7% 4 4 4 3 5% 6% 38%	2345
	21st to end	Day	23% 9% 3 7% 4 4 4 3 5% 6% 34%	2200
October	1st to 10th	Day	21% 14% 4 8% 4 3 4 3 5% 6% 27%	2015
	11th to 20th	Day	23% 17% 5% 10% 4 3 4 4 4 4 21%	1959
	21st to end	Day	25% 20% 6% 8% 4 4 3 2 4 5% 18%	1980
November	1st to 10th	Day	17% 21% 7% 9% 4 4 4 2 3 5% 24%	1851
	11th to 20th	Day	16% 20% 7% 16% 6% 4 3 3 4 4 17%	1706
	21st to end	Day	18% 23% 8% 16% 6% 4 3 2 3 4 13%	1680
December	1st to 10th	Day	15% 19% 9% 19% 8% 8% 4 2 3 3 9%	2680
	11th to 20th	Day	15% 19% 6% 14% 11% 7% 4 2 4 3 14%	3066
	21st to end	Day	15% 15% 9% 16% 9% 6% 4 3 4 3 17%	4048
January	1st to 10th	Night	10% 20% 10% 20% 9% 6% 5% 3 3 3 11%	6489
	11th to 20th	Night	7% 15% 7% 20% 14% 11% 6% 4 3 3 10%	6400
	21st to end	Night	5% 11% 7% 20% 10% 8% 8% 4 6% 5% 16%	6996
February	1st to 10th	Night	9% 14% 6% 14% 12% 7% 7% 4 5% 5% 18%	2660
	11th to 20th	Night	9% 17% 7% 16% 8% 7% 6% 4 4 5% 17%	2488
	21st to end	Night	9% 16% 6% 13% 9% 6% 5% 3 5% 5% 23%	1980
March	1st to 10th	Night	16% 18% 5% 12% 8% 5% 5% 3 4 4 19%	5364
	11th to 20th	Night	10% 17% 6% 13% 7% 6% 5% 4 5% 6% 23%	5191
	21st to end	Night	13% 13% 6% 11% 6% 6% 5% 4 5% 6% 25%	5013
April	1st to 10th	Night	20% 16% 5% 10% 4 4 3 3 4 5% 25%	2000
	11th to 20th	Night	16% 13% 4 8% 4 5% 3 4 4 6% 33%	1975
	21st to end	Night	20% 13% 4 8% 4 4 3 3 4 6% 33%	1798
May	1st to 10th	Night	20% 13% 4 8% 4 4 4 3 5% 6% 28%	3594
	11th to 20th	Night	20% 11% 3 8% 5% 4 4 3 5% 7% 30%	3575
	21st to end	Night	24% 9% 3 8% 5% 5% 5% 4 5% 6% 27%	3926
June	1st to 10th	Night	21% 11% 3 6% 5% 5% 5% 4 7% 6% 30%	1600
	11th to 20th	Night	16% 10% 3 7% 5% 4 4 3 5% 8% 34%	1600
	21st to end	Night	20% 7% 3 7% 5% 4 5% 4 6% 7% 32%	1600
July	1st to 10th	Night	14% 9% 4 9% 7% 6% 6% 5% 6% 7% 26%	3600
	11th to 20th	Night	12% 9% 3 8% 5% 5% 5% 4 6% 8% 36%	3600
	21st to end	Night	11% 6% 2 6% 4 4 4 4 6% 8% 44%	3926
August	1st to 10th	Night	12% 9% 4 8% 4 5% 5% 4 6% 9% 36%	2586
	11th to 20th	Night	18% 9% 3 8% 5% 3 4 3 5% 6% 36%	2748
	21st to end	Night	19% 9% 3 8% 5% 4 4 3 5% 7% 34%	3586
September	1st to 10th	Night	17% 9% 3 6% 4 5% 4 3 4 7% 39%	2000
	11th to 20th	Night	17% 9% 3 6% 4 4 4 2 4 6% 42%	2055
	21st to end	Night	18% 11% 3 7% 4 4 3 3 4 5% 38%	2200
October	1st to 10th	Night	19% 10% 3 7% 5% 3 4 2 4 5% 36%	2381
	11th to 20th	Night	21% 18% 4 8% 5% 4 4 3 5% 5% 24%	2440
	21st to end	Night	24% 18% 5% 10% 5% 4 3 2 3 5% 20%	2860
November	1st to 10th	Night	16% 18% 7% 11% 5% 4 4 3 4 5% 23%	2667
	11th to 20th	Night	15% 16% 8% 15% 7% 6% 4 3 3 4 19%	2910
	21st to end	Night	18% 20% 9% 16% 8% 4 4 3 3 3 12%	2940
December	1st to 10th	Night	12% 18% 8% 20% 12% 8% 4 2 3 3 9%	4720
	11th to 20th	Night	19% 18% 6% 14% 8% 6% 4 3 3 3 16%	5348
	21st to end	Night	14% 20% 8% 15% 7% 4 3 4 3 4 17%	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	82% 2 5% 8% 3	3678
	11th to 20th	Day	74% 2 3 12% 7% 1	3648
	21st to end	Day	63% 2 5% 14% 15% 1	3960
February	1st to 10th	Day	69% 2 5% 13% 9% 2	1739
	11th to 20th	Day	69% 3 6% 12% 10% 1	1805
	21st to end	Day	68% 2 6% 13% 9% 2	1650
March	1st to 10th	Day	69% 2 5% 9% 13% 3	4479
	11th to 20th	Day	63% 3 10% 11% 11% 2	4766
	21st to end	Day	56% 2 6% 18% 17% 2	5918
April	1st to 10th	Day	63% 3 8% 14% 11% 2	2400
	11th to 20th	Day	58% 3 6% 20% 11% 2	2374
	21st to end	Day	60% 3 8% 14% 13% 2	2617
May	1st to 10th	Day	61% 3 7% 17% 10% 1	6357
	11th to 20th	Day	57% 3 11% 21% 7% 1	6322
	21st to end	Day	58% 3 7% 17% 13% 2	6949
June	1st to 10th	Day	59% 4 7% 19% 10% 1	2800
	11th to 20th	Day	49% 4 12% 23% 11% 1	2800
	21st to end	Day	59% 4 12% 18% 8%	2800
July	1st to 10th	Day	55% 6% 12% 23% 5%	6290
	11th to 20th	Day	46% 6% 19% 25% 4	6285
	21st to end	Day	40% 6% 18% 28% 8%	6728
August	1st to 10th	Day	52% 5% 16% 22% 6%	4549
	11th to 20th	Day	50% 5% 16% 24% 5%	4293
	21st to end	Day	49% 5% 12% 21% 11% 1	4312
September	1st to 10th	Day	47% 3 15% 25% 9% 1	2400
	11th to 20th	Day	46% 3 14% 27% 9%	2345
	21st to end	Day	52% 4 11% 23% 10%	2200
October	1st to 10th	Day	56% 5% 10% 23% 6%	3275
	11th to 20th	Day	60% 4 13% 18% 5%	3162
	21st to end	Day	64% 4 15% 12% 4 1	3180
November	1st to 10th	Day	64% 3 9% 18% 7%	1851
	11th to 20th	Day	71% 3 7% 12% 6%	1706
	21st to end	Day	77% 3 6% 9% 5%	1680
December	1st to 10th	Day	81% 2 4 10% 3	2680
	11th to 20th	Day	74% 2 4 14% 5%	3066
	21st to end	Day	73% 2 4 14% 7%	4048
January	1st to 10th	Night	80% 2 7% 9% 2	6489
	11th to 20th	Night	79% 3 5% 9% 3 1	6445
	21st to end	Night	68% 3 5% 12% 11% 1	6996
February	1st to 10th	Night	67% 3 5% 15% 8% 1	2660
	11th to 20th	Night	69% 3 5% 14% 7% 1	2490
	21st to end	Night	63% 3 6% 16% 11% 2	1980
March	1st to 10th	Night	69% 2 8% 8% 10% 2	5374
	11th to 20th	Night	62% 3 9% 13% 10% 3	5192
	21st to end	Night	59% 3 7% 19% 9% 2	5013
April	1st to 10th	Night	62% 2 7% 16% 12% 2	2000
	11th to 20th	Night	52% 4 8% 21% 12% 2	1975
	21st to end	Night	54% 2 8% 21% 12% 2	1798
May	1st to 10th	Night	57% 3 10% 18% 10% 2	3600
	11th to 20th	Night	56% 4 11% 19% 9% 1	3576
	21st to end	Night	57% 3 10% 18% 11% 1	3927
June	1st to 10th	Night	53% 4 11% 22% 11% 1	1600
	11th to 20th	Night	48% 4 14% 22% 10% 3	1600
	21st to end	Night	50% 4 14% 22% 10% 1	1600
July	1st to 10th	Night	53% 7% 15% 19% 5%	3560
	11th to 20th	Night	45% 5% 21% 25% 4	3552
	21st to end	Night	36% 6% 19% 30% 10%	3809
August	1st to 10th	Night	44% 5% 21% 22% 8%	2576
	11th to 20th	Night	48% 5% 20% 23% 5%	2772
	21st to end	Night	49% 4 15% 22% 7% 2	3586
September	1st to 10th	Night	45% 4 17% 24% 10%	2000
	11th to 20th	Night	44% 4 15% 29% 7% 1	2055
	21st to end	Night	48% 4 11% 27% 9%	2200
October	1st to 10th	Night	49% 4 14% 21% 10% 1	3901
	11th to 20th	Night	59% 3 12% 18% 7%	3963
	21st to end	Night	60% 4 14% 14% 7% 1	4610
November	1st to 10th	Night	65% 3 10% 17% 5%	2667
	11th to 20th	Night	68% 4 7% 14% 6% 1	2910
	21st to end	Night	76% 4 6% 11% 4	2940
December	1st to 10th	Night	79% 5% 7% 7% 3	4720
	11th to 20th	Night	73% 3 3 14% 6% 1	5348
	21st to end	Night	71% 2 5% 10% 10% 1	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	22% 23% 44% 10% 2	220
	11th to 20th	Day	25% 20% 35% 16% 2 1	212
	21st to end	Day	21% 22% 35% 19% 4	220
February	1st to 10th	Day	32% 29% 33% 4 1	270
	11th to 20th	Day	27% 32% 34% 7% 1	343
	21st to end	Day	28% 26% 34% 11% 1	414
March	1st to 10th	Day	25% 21% 36% 14% 3	500
	11th to 20th	Day	28% 23% 32% 13% 3	500
	21st to end	Day	29% 23% 31% 13% 4 1	550
April	1st to 10th	Day	34% 16% 33% 12% 5% 1	500
	11th to 20th	Day	36% 18% 24% 14% 6% 1	492
	21st to end	Day	34% 18% 33% 11% 3	500
May	1st to 10th	Day	28% 18% 32% 15% 5% 1	503
	11th to 20th	Day	30% 14% 31% 18% 5% 2	527
	21st to end	Day	29% 18% 30% 17% 5% 1	573
June	1st to 10th	Day	30% 12% 39% 14% 4 1	530
	11th to 20th	Day	25% 16% 34% 17% 8% 1	530
	21st to end	Day	28% 13% 34% 17% 7% 1	530
July	1st to 10th	Day	22% 10% 37% 23% 8% 2	525
	11th to 20th	Day	19% 13% 38% 23% 7% 1	524
	21st to end	Day	17% 13% 34% 26% 9% 1	576
August	1st to 10th	Day	20% 7% 32% 29% 9% 2	526
	11th to 20th	Day	20% 8% 30% 27% 10% 5%	519
	21st to end	Day	22% 14% 28% 21% 9% 6%	583
September	1st to 10th	Day	25% 14% 30% 19% 9% 3	530
	11th to 20th	Day	20% 8% 30% 23% 14% 5%	530
	21st to end	Day	26% 15% 26% 20% 11% 3	530
October	1st to 10th	Day	28% 14% 32% 16% 9% 2	530
	11th to 20th	Day	31% 17% 31% 14% 6% 1	507
	21st to end	Day	35% 15% 32% 16% 3	462
November	1st to 10th	Day	35% 21% 30% 10% 4	425
	11th to 20th	Day	31% 21% 35% 10% 4	246
	21st to end	Day	34% 24% 32% 7% 4	220
December	1st to 10th	Day	31% 20% 30% 15% 5%	220
	11th to 20th	Day	33% 24% 33% 7% 3	220
	21st to end	Day	31% 18% 36% 10% 4 2	242
January	1st to 10th	Night	26% 19% 39% 13% 3	840
	11th to 20th	Night	23% 23% 33% 16% 5%	825
	21st to end	Night	15% 19% 40% 21% 5% 1	880
February	1st to 10th	Night	18% 23% 37% 17% 5%	800
	11th to 20th	Night	21% 22% 39% 14% 3 1	783
	21st to end	Night	22% 20% 35% 19% 3	660
March	1st to 10th	Night	26% 20% 31% 19% 4	800
	11th to 20th	Night	26% 20% 31% 17% 5% 1	800
	21st to end	Night	24% 15% 34% 22% 5% 1	880
April	1st to 10th	Night	31% 15% 28% 23% 4	800
	11th to 20th	Night	27% 16% 29% 19% 8% 1	791
	21st to end	Night	29% 16% 30% 19% 6%	598
May	1st to 10th	Night	26% 10% 30% 24% 9% 1	400
	11th to 20th	Night	27% 8% 30% 27% 7% 1	394
	21st to end	Night	23% 11% 36% 23% 6% 1	433
June	1st to 10th	Night	26% 8% 33% 27% 7%	400
	11th to 20th	Night	21% 9% 28% 29% 13% 1	400
	21st to end	Night	24% 6% 26% 30% 11% 2	400
July	1st to 10th	Night	16% 7% 33% 36% 7% 1	390
	11th to 20th	Night	14% 5% 32% 32% 15% 1	388
	21st to end	Night	16% 6% 29% 38% 10% 2	438
August	1st to 10th	Night	14% 6% 25% 38% 16% 1	398
	11th to 20th	Night	16% 4 26% 35% 17% 2	516
	21st to end	Night	22% 9% 26% 27% 14% 3	880
September	1st to 10th	Night	23% 7% 28% 31% 11% 1	800
	11th to 20th	Night	21% 7% 25% 29% 16% 1	800
	21st to end	Night	24% 11% 27% 23% 13% 2	800
October	1st to 10th	Night	24% 13% 30% 23% 9% 2	800
	11th to 20th	Night	32% 14% 31% 17% 6% 1	800
	21st to end	Night	33% 16% 28% 18% 5%	880
November	1st to 10th	Night	28% 20% 31% 16% 4 1	820
	11th to 20th	Night	26% 19% 31% 15% 8% 1	840
	21st to end	Night	31% 22% 27% 17% 3 1	840
December	1st to 10th	Night	27% 19% 33% 16% 5% 1	840
	11th to 20th	Night	28% 20% 33% 13% 5% 1	840
	21st to end	Night	32% 21% 28% 14% 4 1	924

Page generated at 2026-01-14 01:14:29. Version ac07

Copyright © 2026 Attilla Danko.