Observatoire du Lac Rouge
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire du Lac Rouge clear sky chart from 2005-11-06 to 2026-04-17.

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	17% 10% 4 8% 5% 5% 5% 4 5% 6% 32%	131639
	Night	15% 11% 4 9% 5% 4 4 3 5% 6% 32%	130537
Transparency	Day	51% 6% 12% 20% 11% 1	135084
	Night	51% 5% 11% 20% 11% 1	135179
Seeing	Day	24% 15% 32% 20% 7% 2	16253
	Night	23% 12% 30% 27% 9% 1	25334

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% 16% 6% 14% 5% 4 4 4 4 5% 26%	4661
	11th to 20th	Day	10% 18% 8% 16% 6% 5% 4 3 4 4 23%	4650
	21st to end	Day	6% 11% 7% 14% 8% 6% 5% 3 5% 5% 28%	5124
February	1st to 10th	Day	9% 18% 5% 11% 7% 4 4 3 5% 5% 28%	1820
	11th to 20th	Day	10% 16% 6% 11% 5% 5% 4 3 4 6% 29%	1939
	21st to end	Day	14% 17% 5% 10% 6% 5% 5% 4 3 6% 27%	1730
March	1st to 10th	Day	18% 17% 5% 10% 8% 5% 4 3 3 3 24%	4576
	11th to 20th	Day	11% 14% 4 10% 6% 4 4 3 5% 6% 32%	4796
	21st to end	Day	17% 14% 3 8% 4 4 4 3 4 5% 33%	6102
April	1st to 10th	Day	19% 14% 3 8% 5% 4 4 3 4 5% 31%	2520
	11th to 20th	Day	23% 10% 2 7% 5% 4 3 4 4 6% 33%	2446
	21st to end	Day	21% 11% 3 7% 5% 5% 4 3 5% 4 32%	2576
May	1st to 10th	Day	27% 10% 3 8% 5% 5% 4 3 4 6% 26%	6316
	11th to 20th	Day	22% 9% 3 7% 5% 4 4 3 5% 7% 31%	6318
	21st to end	Day	23% 8% 3 7% 5% 4 5% 4 5% 7% 29%	6949
June	1st to 10th	Day	23% 7% 3 8% 5% 4 5% 5% 6% 6% 29%	2800
	11th to 20th	Day	15% 6% 3 7% 5% 6% 6% 4 7% 8% 34%	2800
	21st to end	Day	22% 8% 3 7% 5% 5% 5% 4 6% 7% 27%	2800
July	1st to 10th	Day	15% 6% 3 8% 6% 6% 6% 5% 6% 7% 31%	6360
	11th to 20th	Day	13% 5% 2 6% 4 5% 6% 6% 8% 9% 38%	6360
	21st to end	Day	10% 5% 2 6% 4 4 5% 4 7% 10% 43%	6926
August	1st to 10th	Day	14% 5% 2 7% 6% 6% 7% 5% 7% 10% 32%	4563
	11th to 20th	Day	15% 6% 2 7% 5% 5% 6% 4 7% 8% 35%	4189
	21st to end	Day	16% 5% 2 8% 4 4 5% 4 6% 8% 38%	4312
September	1st to 10th	Day	14% 5% 2 6% 4 4 4 4 6% 8% 43%	2400
	11th to 20th	Day	14% 5% 2 4 3 4 4 4 5% 6% 48%	2316
	21st to end	Day	20% 7% 2 6% 4 3 4 4 5% 6% 40%	2200
October	1st to 10th	Day	21% 7% 2 6% 4 4 4 3 6% 6% 37%	2060
	11th to 20th	Day	20% 10% 3 9% 6% 4 4 4 5% 7% 29%	1945
	21st to end	Day	24% 10% 3 8% 4 4 4 3 4 6% 30%	1980
November	1st to 10th	Day	16% 11% 3 7% 5% 5% 4 4 5% 6% 34%	1851
	11th to 20th	Day	18% 12% 4 9% 5% 3 4 4 6% 6% 29%	1780
	21st to end	Day	20% 15% 4 8% 5% 4 5% 3 4 6% 25%	1680
December	1st to 10th	Day	18% 18% 8% 12% 5% 4 4 3 3 4 22%	2680
	11th to 20th	Day	17% 15% 6% 10% 5% 3 4 3 4 5% 29%	3066
	21st to end	Day	20% 15% 5% 9% 4 5% 4 2 4 4 28%	4048
January	1st to 10th	Night	11% 17% 7% 14% 5% 4 4 3 4 5% 25%	8234
	11th to 20th	Night	9% 17% 8% 17% 8% 5% 4 3 4 5% 21%	8235
	21st to end	Night	6% 12% 5% 13% 8% 7% 6% 4 5% 6% 28%	9057
February	1st to 10th	Night	10% 13% 5% 11% 6% 6% 5% 3 5% 5% 30%	2798
	11th to 20th	Night	11% 13% 5% 11% 5% 5% 6% 3 5% 6% 31%	2566
	21st to end	Night	13% 13% 4 9% 5% 4 5% 3 5% 6% 32%	2076
March	1st to 10th	Night	20% 15% 4 10% 5% 4 4 3 3 4 28%	5484
	11th to 20th	Night	11% 14% 4 8% 5% 5% 5% 4 6% 7% 31%	5381
	21st to end	Night	15% 11% 5% 9% 6% 5% 5% 4 5% 6% 32%	5072
April	1st to 10th	Night	21% 11% 3 8% 5% 5% 3 3 4 6% 32%	2100
	11th to 20th	Night	19% 7% 2 6% 5% 4 5% 3 5% 6% 37%	2036
	21st to end	Night	21% 10% 4 5% 3 4 4 3 5% 6% 36%	1822
May	1st to 10th	Night	25% 10% 3 7% 4 5% 4 3 5% 6% 27%	3654
	11th to 20th	Night	22% 7% 2 6% 4 4 4 3 5% 7% 35%	3575
	21st to end	Night	23% 7% 3 7% 5% 5% 5% 3 5% 7% 29%	3926
June	1st to 10th	Night	18% 7% 3 6% 5% 4 4 4 6% 8% 34%	1600
	11th to 20th	Night	18% 7% 2 6% 4 5% 4 4 6% 7% 37%	1600
	21st to end	Night	20% 6% 3 6% 5% 5% 4 4 5% 7% 35%	1600
July	1st to 10th	Night	13% 5% 2 6% 5% 6% 6% 5% 9% 8% 35%	3600
	11th to 20th	Night	14% 4 2 6% 4 4 4 4 6% 7% 45%	3600
	21st to end	Night	9% 5% 2 5% 4 5% 5% 4 7% 7% 49%	3926
August	1st to 10th	Night	12% 5% 2 7% 4 5% 4 4 6% 8% 41%	2586
	11th to 20th	Night	16% 5% 2 6% 4 4 5% 3 5% 7% 44%	2825
	21st to end	Night	18% 6% 2 6% 4 4 4 4 5% 6% 42%	3586
September	1st to 10th	Night	11% 4 1 6% 4 3 5% 3 5% 7% 51%	2000
	11th to 20th	Night	14% 5% 2 5% 3 3 3 4 5% 6% 51%	2083
	21st to end	Night	17% 6% 2 5% 3 3 4 3 4 6% 46%	2200
October	1st to 10th	Night	17% 8% 3 6% 4 3 4 3 4 6% 43%	2336
	11th to 20th	Night	20% 8% 2 6% 4 3 4 3 5% 7% 38%	2455
	21st to end	Night	21% 9% 3 6% 5% 4 5% 3 5% 6% 32%	2860
November	1st to 10th	Night	16% 11% 3 7% 5% 5% 4 3 6% 7% 34%	2667
	11th to 20th	Night	17% 10% 3 8% 5% 5% 5% 3 5% 5% 33%	2839
	21st to end	Night	18% 16% 4 8% 5% 3 4 3 4 6% 28%	2940
December	1st to 10th	Night	16% 14% 5% 10% 6% 5% 5% 4 6% 7% 22%	4720
	11th to 20th	Night	21% 13% 4 9% 5% 4 4 3 4 4 28%	5348
	21st to end	Night	21% 18% 5% 9% 4 3 2 2 4 4 29%	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	60% 4 10% 19% 7% 1	4662
	11th to 20th	Day	64% 4 6% 14% 10% 2	4680
	21st to end	Day	56% 5% 7% 16% 14% 1	5124
February	1st to 10th	Day	59% 4 6% 19% 9% 2	1820
	11th to 20th	Day	57% 5% 9% 15% 13% 1	1948
	21st to end	Day	59% 4 6% 16% 11% 3	1730
March	1st to 10th	Day	65% 4 6% 11% 11% 4	4579
	11th to 20th	Day	52% 4 17% 12% 12% 3	4796
	21st to end	Day	53% 4 7% 15% 19% 3	6102
April	1st to 10th	Day	56% 4 9% 16% 12% 3	2520
	11th to 20th	Day	52% 3 9% 20% 13% 2	2446
	21st to end	Day	54% 5% 8% 18% 13% 3	2576
May	1st to 10th	Day	60% 5% 7% 18% 9% 1	6327
	11th to 20th	Day	51% 7% 14% 17% 8% 2	6322
	21st to end	Day	53% 6% 11% 17% 12% 1	6949
June	1st to 10th	Day	52% 7% 10% 18% 11% 2	2800
	11th to 20th	Day	45% 6% 12% 22% 12% 3	2800
	21st to end	Day	55% 7% 10% 17% 9% 1	2800
July	1st to 10th	Day	49% 7% 12% 24% 8%	6290
	11th to 20th	Day	39% 8% 15% 29% 9%	6285
	21st to end	Day	35% 6% 16% 32% 10%	6728
August	1st to 10th	Day	45% 8% 17% 21% 8%	4549
	11th to 20th	Day	43% 9% 16% 26% 6%	4231
	21st to end	Day	43% 7% 15% 21% 13% 1	4312
September	1st to 10th	Day	38% 6% 15% 28% 13%	2400
	11th to 20th	Day	35% 6% 13% 32% 13% 1	2316
	21st to end	Day	44% 6% 13% 25% 12%	2200
October	1st to 10th	Day	44% 6% 12% 28% 10%	3359
	11th to 20th	Day	45% 5% 14% 28% 8% 1	3148
	21st to end	Day	45% 4 21% 19% 10% 1	3180
November	1st to 10th	Day	50% 5% 13% 21% 10% 1	1851
	11th to 20th	Day	54% 5% 12% 17% 12% 1	1780
	21st to end	Day	59% 6% 11% 15% 7% 1	1680
December	1st to 10th	Day	67% 4 9% 15% 5%	2680
	11th to 20th	Day	58% 4 8% 18% 12%	3066
	21st to end	Day	60% 4 10% 15% 11%	4048
January	1st to 10th	Night	61% 5% 10% 17% 7% 1	8234
	11th to 20th	Night	64% 5% 8% 15% 6% 1	8280
	21st to end	Night	55% 6% 9% 14% 15% 1	9057
February	1st to 10th	Night	56% 5% 8% 20% 10% 1	2798
	11th to 20th	Night	54% 5% 9% 19% 12% 1	2568
	21st to end	Night	53% 5% 7% 20% 13% 2	2076
March	1st to 10th	Night	61% 3 8% 13% 12% 4	5494
	11th to 20th	Night	51% 6% 13% 15% 12% 3	5382
	21st to end	Night	53% 4 7% 21% 13% 3	5072
April	1st to 10th	Night	54% 4 8% 17% 15% 2	2100
	11th to 20th	Night	46% 6% 9% 22% 14% 2	2036
	21st to end	Night	49% 5% 9% 20% 14% 3	1822
May	1st to 10th	Night	57% 7% 10% 17% 8% 2	3660
	11th to 20th	Night	48% 8% 13% 19% 11% 2	3576
	21st to end	Night	54% 6% 11% 16% 12% 1	3927
June	1st to 10th	Night	47% 8% 11% 20% 13% 1	1600
	11th to 20th	Night	45% 6% 12% 21% 14% 3	1600
	21st to end	Night	48% 6% 12% 20% 13% 1	1600
July	1st to 10th	Night	42% 7% 21% 22% 8%	3560
	11th to 20th	Night	36% 8% 17% 31% 7%	3552
	21st to end	Night	33% 7% 17% 32% 11%	3809
August	1st to 10th	Night	41% 7% 15% 28% 9%	2576
	11th to 20th	Night	40% 6% 19% 27% 8%	2849
	21st to end	Night	43% 6% 14% 24% 13%	3586
September	1st to 10th	Night	33% 7% 15% 30% 15%	2000
	11th to 20th	Night	33% 5% 15% 34% 11% 1	2083
	21st to end	Night	40% 5% 11% 31% 14%	2200
October	1st to 10th	Night	44% 5% 13% 26% 12% 1	3817
	11th to 20th	Night	40% 5% 12% 30% 12%	3991
	21st to end	Night	44% 5% 17% 19% 12% 2	4610
November	1st to 10th	Night	49% 5% 14% 23% 8% 1	2667
	11th to 20th	Night	51% 6% 12% 19% 11% 1	2839
	21st to end	Night	57% 5% 10% 18% 9% 1	2940
December	1st to 10th	Night	59% 6% 12% 17% 5%	4720
	11th to 20th	Night	60% 4 7% 16% 12% 1	5348
	21st to end	Night	61% 3 6% 15% 14% 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% 19% 35% 22% 3	220
	11th to 20th	Day	29% 13% 38% 15% 5% 1	220
	21st to end	Day	17% 22% 36% 19% 5%	242
February	1st to 10th	Day	30% 19% 37% 12% 3	294
	11th to 20th	Day	22% 23% 39% 13% 3	426
	21st to end	Day	28% 18% 34% 17% 4	446
March	1st to 10th	Day	27% 19% 34% 16% 3 1	540
	11th to 20th	Day	28% 19% 33% 18% 2 1	540
	21st to end	Day	30% 22% 27% 14% 5% 1	594
April	1st to 10th	Day	35% 16% 28% 15% 6% 1	540
	11th to 20th	Day	37% 17% 25% 13% 8% 1	516
	21st to end	Day	32% 15% 35% 11% 5% 1	500
May	1st to 10th	Day	31% 16% 36% 13% 3 1	503
	11th to 20th	Day	24% 17% 34% 18% 6% 2	527
	21st to end	Day	24% 19% 34% 16% 5% 2	573
June	1st to 10th	Day	24% 13% 37% 18% 7% 1	530
	11th to 20th	Day	20% 18% 33% 18% 9% 2	530
	21st to end	Day	28% 12% 31% 20% 7% 2	530
July	1st to 10th	Day	15% 10% 38% 26% 8% 3	525
	11th to 20th	Day	15% 9% 40% 27% 8% 1	524
	21st to end	Day	14% 8% 36% 28% 11% 3	576
August	1st to 10th	Day	14% 8% 29% 35% 13% 2	526
	11th to 20th	Day	13% 9% 28% 31% 13% 6%	519
	21st to end	Day	17% 14% 26% 24% 14% 5%	583
September	1st to 10th	Day	17% 11% 32% 23% 11% 5%	530
	11th to 20th	Day	14% 9% 28% 28% 14% 7%	530
	21st to end	Day	21% 15% 25% 23% 12% 5%	530
October	1st to 10th	Day	26% 13% 26% 22% 10% 3	530
	11th to 20th	Day	25% 16% 30% 18% 9% 1	500
	21st to end	Day	32% 15% 27% 20% 5%	462
November	1st to 10th	Day	30% 15% 29% 19% 6% 1	425
	11th to 20th	Day	27% 16% 34% 17% 7% 1	320
	21st to end	Day	33% 20% 28% 15% 3 1	220
December	1st to 10th	Day	28% 12% 34% 17% 8% 1	220
	11th to 20th	Day	29% 18% 35% 15% 4	220
	21st to end	Day	29% 19% 29% 16% 5% 2	242
January	1st to 10th	Night	25% 12% 35% 23% 5%	840
	11th to 20th	Night	24% 15% 30% 25% 6%	840
	21st to end	Night	16% 14% 36% 28% 7%	924
February	1st to 10th	Night	18% 13% 39% 24% 6%	840
	11th to 20th	Night	19% 18% 36% 22% 4 1	823
	21st to end	Night	20% 16% 33% 26% 4	692
March	1st to 10th	Night	27% 15% 33% 21% 4	840
	11th to 20th	Night	25% 17% 31% 20% 5% 1	840
	21st to end	Night	23% 15% 33% 23% 6% 1	924
April	1st to 10th	Night	30% 14% 30% 22% 4	840
	11th to 20th	Night	26% 13% 33% 22% 5% 1	816
	21st to end	Night	27% 15% 31% 21% 6% 1	622
May	1st to 10th	Night	27% 15% 29% 22% 6% 1	434
	11th to 20th	Night	24% 11% 29% 28% 8%	394
	21st to end	Night	23% 10% 33% 24% 9%	433
June	1st to 10th	Night	24% 8% 28% 32% 8%	400
	11th to 20th	Night	23% 8% 24% 34% 11% 1	400
	21st to end	Night	20% 6% 26% 35% 12% 1	400
July	1st to 10th	Night	13% 7% 29% 39% 12% 1	390
	11th to 20th	Night	11% 5% 25% 44% 13% 1	388
	21st to end	Night	14% 6% 23% 42% 14% 1	438
August	1st to 10th	Night	12% 4 19% 47% 17% 1	398
	11th to 20th	Night	14% 4 22% 37% 20% 2	554
	21st to end	Night	17% 6% 25% 31% 18% 2	880
September	1st to 10th	Night	14% 6% 30% 35% 15% 1	800
	11th to 20th	Night	16% 6% 24% 33% 20% 2	800
	21st to end	Night	21% 8% 25% 29% 16% 2	800
October	1st to 10th	Night	22% 10% 27% 28% 12% 1	800
	11th to 20th	Night	26% 12% 27% 25% 10% 1	800
	21st to end	Night	29% 10% 30% 25% 6%	880
November	1st to 10th	Night	25% 14% 27% 25% 8% 1	820
	11th to 20th	Night	25% 13% 31% 20% 10% 1	840
	21st to end	Night	28% 18% 25% 23% 6% 1	840
December	1st to 10th	Night	26% 13% 30% 25% 6%	840
	11th to 20th	Night	28% 15% 29% 23% 5% 1	840
	21st to end	Night	31% 14% 30% 20% 4	924

Page generated at 2026-04-14 02:44:24. Version ac07

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