Lac Georges
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lac Georges clear sky chart from 2005-11-06 to 2026-04-02.

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	15% 11% 4 9% 6% 5% 5% 4 5% 6% 31%	131612
	Night	15% 12% 4 10% 6% 5% 5% 3 5% 6% 29%	130206
Transparency	Day	54% 4 11% 21% 10% 1	135090
	Night	56% 4 10% 20% 10% 1	134815
Seeing	Day	24% 17% 31% 19% 7% 2	16088
	Night	23% 14% 30% 24% 9% 1	25326

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	11% 17% 7% 17% 8% 5% 4 3 5% 5% 19%	4661
	11th to 20th	Day	9% 19% 8% 17% 8% 6% 5% 3 4 5% 17%	4650
	21st to end	Day	7% 13% 8% 16% 10% 7% 5% 4 5% 5% 20%	5364
February	1st to 10th	Day	11% 16% 5% 14% 8% 5% 5% 3 5% 5% 22%	1890
	11th to 20th	Day	10% 17% 6% 13% 5% 6% 4 3 5% 5% 25%	1843
	21st to end	Day	16% 15% 5% 12% 7% 5% 5% 3 4 4 25%	1708
March	1st to 10th	Day	16% 15% 5% 13% 6% 4 5% 3 4 6% 23%	4619
	11th to 20th	Day	11% 15% 6% 9% 7% 5% 4 4 5% 7% 28%	5090
	21st to end	Day	15% 12% 3 9% 6% 4 4 3 4 5% 35%	5862
April	1st to 10th	Day	21% 13% 4 8% 5% 4 3 3 4 6% 30%	2412
	11th to 20th	Day	21% 10% 3 7% 4 3 4 2 5% 5% 35%	2374
	21st to end	Day	21% 11% 4 8% 5% 4 4 3 4 5% 31%	2572
May	1st to 10th	Day	22% 10% 3 8% 5% 5% 5% 4 5% 6% 28%	6346
	11th to 20th	Day	15% 9% 3 8% 5% 5% 5% 4 6% 8% 33%	6318
	21st to end	Day	21% 9% 2 8% 5% 4 4 3 5% 6% 32%	6949
June	1st to 10th	Day	21% 9% 3 7% 6% 4 4 4 5% 7% 30%	2800
	11th to 20th	Day	15% 6% 3 6% 5% 5% 5% 4 6% 8% 39%	2800
	21st to end	Day	18% 7% 2 7% 6% 5% 5% 4 5% 7% 32%	2800
July	1st to 10th	Day	14% 6% 2 7% 6% 5% 6% 5% 7% 9% 33%	6360
	11th to 20th	Day	11% 6% 2 7% 5% 5% 5% 4 6% 8% 42%	6360
	21st to end	Day	10% 5% 2 5% 4 4 4 4 7% 10% 45%	6926
August	1st to 10th	Day	13% 6% 3 8% 5% 5% 6% 5% 7% 8% 35%	4477
	11th to 20th	Day	16% 7% 2 7% 5% 5% 5% 4 6% 7% 36%	4174
	21st to end	Day	12% 6% 2 6% 4 4 5% 4 7% 10% 38%	4312
September	1st to 10th	Day	14% 6% 2 7% 4 3 4 4 5% 8% 43%	2400
	11th to 20th	Day	12% 6% 3 6% 4 4 4 3 5% 7% 44%	2400
	21st to end	Day	19% 7% 2 6% 4 4 3 4 6% 8% 37%	2125
October	1st to 10th	Day	19% 10% 2 6% 4 4 4 4 4 6% 36%	2000
	11th to 20th	Day	22% 11% 3 8% 6% 4 4 4 5% 6% 27%	2000
	21st to end	Day	25% 11% 3 8% 5% 4 4 3 4 5% 27%	2048
November	1st to 10th	Day	15% 12% 3 7% 5% 5% 4 4 6% 6% 32%	1818
	11th to 20th	Day	18% 14% 5% 11% 6% 4 4 3 5% 5% 23%	1680
	21st to end	Day	20% 18% 6% 13% 6% 4 5% 3 4 5% 18%	1680
December	1st to 10th	Day	18% 23% 6% 12% 6% 5% 5% 3 5% 5% 12%	2680
	11th to 20th	Day	16% 15% 7% 13% 6% 5% 4 3 4 4 23%	3066
	21st to end	Day	19% 19% 6% 13% 5% 5% 5% 3 3 4 18%	4048
January	1st to 10th	Night	11% 18% 9% 17% 7% 5% 4 3 4 4 18%	8234
	11th to 20th	Night	9% 17% 7% 17% 9% 5% 5% 4 4 5% 18%	8235
	21st to end	Night	8% 14% 6% 14% 9% 8% 6% 4 5% 5% 21%	8801
February	1st to 10th	Night	10% 14% 6% 13% 9% 6% 5% 5% 4 6% 23%	2730
	11th to 20th	Night	11% 14% 5% 12% 8% 5% 5% 3 4 5% 26%	2663
	21st to end	Night	11% 15% 5% 11% 6% 6% 4 3 5% 6% 26%	2097
March	1st to 10th	Night	18% 17% 4 9% 5% 4 4 3 3 5% 28%	5437
	11th to 20th	Night	11% 14% 5% 9% 6% 5% 6% 4 7% 8% 26%	5089
	21st to end	Night	15% 12% 4 11% 5% 4 4 3 5% 6% 32%	5312
April	1st to 10th	Night	20% 12% 3 9% 5% 4 4 3 4 7% 29%	2011
	11th to 20th	Night	17% 11% 3 6% 5% 4 4 4 5% 6% 35%	1975
	21st to end	Night	21% 11% 3 8% 4 4 4 3 4 5% 33%	1844
May	1st to 10th	Night	20% 10% 4 7% 5% 5% 5% 4 6% 7% 26%	3594
	11th to 20th	Night	15% 7% 2 6% 5% 5% 5% 3 6% 7% 38%	3575
	21st to end	Night	18% 9% 3 8% 6% 4 5% 4 5% 6% 32%	3926
June	1st to 10th	Night	18% 6% 2 6% 5% 5% 5% 4 6% 9% 34%	1600
	11th to 20th	Night	13% 6% 3 6% 4 4 4 4 6% 7% 43%	1600
	21st to end	Night	17% 6% 3 5% 6% 5% 6% 4 6% 8% 35%	1600
July	1st to 10th	Night	14% 7% 3 7% 5% 5% 5% 5% 6% 8% 35%	3600
	11th to 20th	Night	12% 6% 2 6% 4 4 4 4 6% 8% 44%	3600
	21st to end	Night	8% 5% 2 6% 5% 4 4 3 6% 9% 48%	3926
August	1st to 10th	Night	11% 7% 3 8% 5% 5% 6% 4 5% 7% 39%	2669
	11th to 20th	Night	15% 7% 3 6% 4 4 4 4 5% 7% 41%	2875
	21st to end	Night	15% 6% 2 6% 4 5% 4 4 5% 7% 41%	3553
September	1st to 10th	Night	11% 6% 2 6% 5% 4 4 4 5% 6% 47%	2000
	11th to 20th	Night	14% 5% 2 5% 3 3 3 3 6% 8% 50%	2000
	21st to end	Night	17% 8% 2 6% 4 3 4 2 4 6% 43%	2272
October	1st to 10th	Night	18% 8% 3 6% 4 3 4 3 5% 6% 41%	2400
	11th to 20th	Night	19% 10% 3 8% 6% 5% 4 3 4 7% 30%	2400
	21st to end	Night	21% 11% 3 9% 5% 5% 5% 3 4 5% 28%	2791
November	1st to 10th	Night	16% 12% 4 8% 5% 5% 4 4 5% 6% 31%	2699
	11th to 20th	Night	17% 14% 4 10% 5% 5% 5% 4 4 5% 27%	2940
	21st to end	Night	19% 16% 5% 12% 6% 4 5% 3 4 6% 20%	2940
December	1st to 10th	Night	17% 19% 6% 13% 7% 6% 5% 4 5% 6% 14%	4720
	11th to 20th	Night	20% 15% 4 11% 6% 4 4 3 3 4 25%	5348
	21st to end	Night	21% 21% 5% 11% 6% 3 3 2 4 4 20%	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	68% 3 9% 15% 5%	4662
	11th to 20th	Day	71% 3 7% 10% 9%	4680
	21st to end	Day	67% 3 8% 12% 9% 1	5364
February	1st to 10th	Day	64% 3 8% 18% 6% 1	1890
	11th to 20th	Day	61% 3 11% 15% 10% 1	1852
	21st to end	Day	63% 2 10% 13% 11% 1	1708
March	1st to 10th	Day	63% 2 7% 13% 12% 2	4622
	11th to 20th	Day	57% 3 15% 14% 9% 2	5090
	21st to end	Day	54% 2 5% 21% 17% 2	5862
April	1st to 10th	Day	58% 2 6% 18% 13% 3	2412
	11th to 20th	Day	54% 2 6% 21% 16% 2	2374
	21st to end	Day	57% 2 7% 17% 13% 3	2572
May	1st to 10th	Day	58% 2 6% 21% 9% 3	6357
	11th to 20th	Day	50% 3 12% 23% 11% 1	6322
	21st to end	Day	53% 4 10% 19% 13% 1	6949
June	1st to 10th	Day	54% 3 10% 21% 12% 1	2800
	11th to 20th	Day	44% 4 11% 27% 12% 2	2800
	21st to end	Day	50% 5% 13% 21% 10% 1	2800
July	1st to 10th	Day	44% 6% 14% 27% 8%	6290
	11th to 20th	Day	38% 5% 14% 33% 10%	6285
	21st to end	Day	34% 5% 16% 35% 9%	6728
August	1st to 10th	Day	45% 6% 16% 25% 8%	4463
	11th to 20th	Day	45% 5% 15% 28% 6% 1	4213
	21st to end	Day	40% 6% 16% 26% 12% 1	4312
September	1st to 10th	Day	40% 4 14% 31% 11%	2400
	11th to 20th	Day	39% 4 12% 33% 12% 1	2400
	21st to end	Day	45% 4 14% 26% 10%	2125
October	1st to 10th	Day	49% 4 10% 29% 7%	3260
	11th to 20th	Day	52% 5% 13% 22% 8% 1	3240
	21st to end	Day	53% 5% 18% 18% 6%	3286
November	1st to 10th	Day	52% 4 13% 24% 7% 1	1818
	11th to 20th	Day	62% 4 12% 14% 8% 1	1680
	21st to end	Day	70% 4 11% 9% 6% 1	1680
December	1st to 10th	Day	74% 5% 9% 10% 2	2680
	11th to 20th	Day	65% 4 8% 15% 8%	3066
	21st to end	Day	71% 3 7% 15% 4	4048
January	1st to 10th	Night	70% 3 10% 13% 4	8234
	11th to 20th	Night	69% 3 9% 13% 5%	8280
	21st to end	Night	65% 4 7% 13% 11%	8801
February	1st to 10th	Night	62% 3 8% 18% 8% 1	2730
	11th to 20th	Night	61% 3 8% 21% 7% 1	2665
	21st to end	Night	59% 3 9% 20% 9% 1	2097
March	1st to 10th	Night	62% 2 8% 15% 11% 3	5447
	11th to 20th	Night	54% 5% 14% 17% 7% 2	5090
	21st to end	Night	54% 2 6% 21% 13% 3	5312
April	1st to 10th	Night	56% 3 7% 18% 13% 2	2011
	11th to 20th	Night	50% 3 6% 24% 15% 2	1975
	21st to end	Night	55% 3 7% 18% 15% 3	1844
May	1st to 10th	Night	56% 3 8% 21% 9% 2	3600
	11th to 20th	Night	46% 4 12% 22% 14% 2	3576
	21st to end	Night	53% 3 11% 20% 13% 1	3927
June	1st to 10th	Night	47% 4 13% 27% 9% 1	1600
	11th to 20th	Night	41% 4 11% 29% 14% 2	1600
	21st to end	Night	46% 6% 13% 22% 12% 1	1600
July	1st to 10th	Night	45% 6% 16% 23% 10%	3560
	11th to 20th	Night	37% 6% 14% 32% 11%	3552
	21st to end	Night	33% 5% 14% 37% 12%	3809
August	1st to 10th	Night	42% 6% 15% 26% 11%	2659
	11th to 20th	Night	43% 5% 15% 29% 8%	2902
	21st to end	Night	41% 5% 15% 26% 11% 2	3553
September	1st to 10th	Night	38% 4 12% 32% 14% 1	2000
	11th to 20th	Night	34% 3 14% 37% 11% 1	2000
	21st to end	Night	44% 3 12% 30% 11%	2272
October	1st to 10th	Night	41% 3 13% 30% 13%	3920
	11th to 20th	Night	48% 4 15% 24% 9% 1	3899
	21st to end	Night	50% 5% 17% 18% 9%	4503
November	1st to 10th	Night	54% 3 13% 21% 9%	2699
	11th to 20th	Night	60% 3 10% 17% 8% 1	2940
	21st to end	Night	67% 3 11% 15% 4	2940
December	1st to 10th	Night	70% 6% 10% 11% 3	4720
	11th to 20th	Night	64% 3 7% 15% 11%	5348
	21st to end	Night	70% 2 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	21% 22% 37% 16% 3	220
	11th to 20th	Day	24% 18% 38% 15% 4 1	220
	21st to end	Day	20% 21% 36% 19% 5%	286
February	1st to 10th	Day	30% 22% 32% 13% 3	330
	11th to 20th	Day	26% 31% 33% 10%	330
	21st to end	Day	28% 24% 32% 14% 1	424
March	1st to 10th	Day	26% 23% 35% 12% 4	540
	11th to 20th	Day	30% 21% 30% 15% 3 1	540
	21st to end	Day	31% 23% 29% 13% 4 1	594
April	1st to 10th	Day	34% 21% 25% 15% 5% 1	504
	11th to 20th	Day	35% 21% 21% 13% 9% 2	492
	21st to end	Day	32% 20% 30% 12% 5% 1	500
May	1st to 10th	Day	29% 16% 32% 15% 6% 2	503
	11th to 20th	Day	21% 17% 32% 21% 6% 3	527
	21st to end	Day	24% 17% 31% 19% 7% 2	573
June	1st to 10th	Day	27% 12% 34% 19% 6% 2	530
	11th to 20th	Day	18% 14% 33% 23% 9% 2	530
	21st to end	Day	20% 14% 35% 21% 8% 2	530
July	1st to 10th	Day	13% 8% 36% 32% 10% 2	525
	11th to 20th	Day	13% 11% 37% 25% 11% 2	524
	21st to end	Day	13% 9% 36% 28% 11% 3	576
August	1st to 10th	Day	15% 8% 30% 29% 14% 4	526
	11th to 20th	Day	16% 7% 26% 32% 13% 7%	519
	21st to end	Day	18% 11% 30% 24% 11% 6%	583
September	1st to 10th	Day	17% 11% 31% 21% 13% 6%	530
	11th to 20th	Day	14% 11% 23% 24% 19% 10%	530
	21st to end	Day	22% 13% 29% 18% 12% 6%	530
October	1st to 10th	Day	24% 16% 24% 22% 11% 3	530
	11th to 20th	Day	27% 22% 30% 14% 6% 1	530
	21st to end	Day	31% 15% 31% 18% 4	498
November	1st to 10th	Day	29% 19% 29% 18% 3 1	392
	11th to 20th	Day	27% 22% 31% 11% 7% 1	220
	21st to end	Day	32% 24% 30% 11% 3 1	220
December	1st to 10th	Day	30% 14% 39% 15% 2	220
	11th to 20th	Day	28% 27% 34% 8% 2	220
	21st to end	Day	29% 20% 35% 11% 4	242
January	1st to 10th	Night	27% 15% 37% 18% 4	840
	11th to 20th	Night	29% 18% 28% 21% 5%	840
	21st to end	Night	18% 14% 39% 23% 6%	924
February	1st to 10th	Night	19% 18% 37% 21% 4	840
	11th to 20th	Night	22% 19% 38% 17% 3	823
	21st to end	Night	23% 21% 30% 23% 4	692
March	1st to 10th	Night	26% 17% 33% 19% 4	840
	11th to 20th	Night	25% 17% 35% 18% 5% 1	840
	21st to end	Night	24% 17% 33% 19% 7%	924
April	1st to 10th	Night	27% 16% 29% 23% 5%	805
	11th to 20th	Night	26% 16% 30% 20% 7% 1	791
	21st to end	Night	28% 14% 30% 22% 6%	644
May	1st to 10th	Night	25% 11% 27% 27% 9% 1	400
	11th to 20th	Night	23% 11% 29% 29% 8%	394
	21st to end	Night	17% 9% 36% 28% 10%	433
June	1st to 10th	Night	21% 8% 32% 32% 7% 1	400
	11th to 20th	Night	17% 9% 28% 31% 14% 1	400
	21st to end	Night	19% 7% 30% 33% 12% 1	400
July	1st to 10th	Night	11% 5% 29% 39% 15% 1	390
	11th to 20th	Night	14% 5% 26% 39% 16% 1	388
	21st to end	Night	10% 4 27% 43% 14% 1	438
August	1st to 10th	Night	11% 4 22% 39% 22% 1	442
	11th to 20th	Night	11% 4 22% 38% 22% 3	594
	21st to end	Night	14% 7% 27% 33% 17% 2	860
September	1st to 10th	Night	16% 5% 30% 31% 17% 1	800
	11th to 20th	Night	16% 6% 24% 31% 20% 4	800
	21st to end	Night	21% 10% 26% 25% 17% 2	800
October	1st to 10th	Night	23% 12% 27% 23% 14% 1	800
	11th to 20th	Night	25% 13% 33% 21% 7% 1	800
	21st to end	Night	28% 15% 29% 23% 5%	880
November	1st to 10th	Night	26% 17% 28% 22% 6% 1	820
	11th to 20th	Night	27% 18% 30% 17% 9%	840
	21st to end	Night	31% 19% 25% 20% 4	840
December	1st to 10th	Night	29% 19% 30% 19% 3	840
	11th to 20th	Night	28% 19% 29% 19% 5% 1	840
	21st to end	Night	34% 16% 28% 17% 4	924

Page generated at 2026-03-30 02:18:44. Version ac07

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