Observatoire de Clarenceville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire de Clarenceville 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 9% 5% 5% 5% 4 5% 7% 30%	131503
	Night	17% 12% 4 10% 6% 5% 4 3 5% 5% 28%	130679
Transparency	Day	53% 5% 12% 21% 9% 1	134972
	Night	57% 4 11% 18% 10% 1	135297
Seeing	Day	22% 14% 30% 22% 10% 3	16384
	Night	24% 12% 29% 26% 9% 1	25471

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	16% 19% 7% 14% 7% 6% 4 3 3 4 16%	4661
	11th to 20th	Day	12% 17% 8% 17% 8% 7% 5% 3 4 4 16%	4650
	21st to end	Day	11% 13% 5% 13% 8% 8% 6% 4 5% 6% 21%	5124
February	1st to 10th	Day	15% 15% 5% 13% 8% 5% 5% 4 4 6% 21%	1832
	11th to 20th	Day	13% 17% 5% 11% 6% 4 4 4 4 6% 24%	1988
	21st to end	Day	16% 16% 4 8% 7% 6% 5% 4 4 6% 24%	1730
March	1st to 10th	Day	19% 13% 4 11% 6% 5% 5% 3 4 6% 24%	4576
	11th to 20th	Day	15% 15% 4 9% 5% 4 4 3 5% 6% 29%	4773
	21st to end	Day	20% 12% 4 7% 5% 4 4 3 3 5% 33%	6102
April	1st to 10th	Day	21% 12% 3 7% 5% 5% 4 4 4 6% 29%	2520
	11th to 20th	Day	21% 8% 3 9% 4 4 3 3 5% 5% 35%	2446
	21st to end	Day	22% 9% 3 7% 5% 4 4 3 4 5% 32%	2575
May	1st to 10th	Day	28% 11% 3 8% 5% 4 5% 3 5% 5% 23%	6152
	11th to 20th	Day	20% 7% 3 8% 5% 5% 5% 3 5% 7% 32%	6318
	21st to end	Day	20% 9% 3 7% 5% 4 5% 4 6% 6% 31%	6949
June	1st to 10th	Day	21% 8% 2 6% 5% 5% 5% 4 5% 8% 30%	2800
	11th to 20th	Day	15% 6% 2 6% 5% 5% 5% 5% 6% 8% 37%	2800
	21st to end	Day	21% 7% 3 7% 5% 4 4 4 6% 7% 32%	2800
July	1st to 10th	Day	12% 6% 3 8% 6% 6% 6% 4 7% 9% 33%	6360
	11th to 20th	Day	11% 5% 2 6% 4 5% 6% 5% 7% 9% 40%	6360
	21st to end	Day	12% 6% 2 6% 4 4 4 4 6% 9% 43%	6926
August	1st to 10th	Day	15% 7% 3 7% 5% 5% 6% 5% 7% 9% 32%	4563
	11th to 20th	Day	14% 6% 2 7% 4 5% 5% 4 7% 8% 38%	4088
	21st to end	Day	14% 6% 2 6% 4 4 4 3 6% 9% 41%	4312
September	1st to 10th	Day	13% 6% 2 6% 4 4 4 4 6% 7% 45%	2400
	11th to 20th	Day	15% 4 2 5% 4 3 4 3 4 7% 48%	2294
	21st to end	Day	15% 5% 3 6% 5% 4 5% 4 5% 8% 41%	2200
October	1st to 10th	Day	20% 7% 3 7% 4 4 5% 4 5% 7% 34%	2100
	11th to 20th	Day	18% 8% 3 8% 5% 5% 5% 5% 6% 6% 31%	1941
	21st to end	Day	24% 12% 3 8% 5% 5% 4 2 4 5% 28%	1980
November	1st to 10th	Day	18% 13% 3 7% 4 5% 5% 4 6% 5% 31%	1851
	11th to 20th	Day	18% 13% 4 9% 6% 5% 4 4 5% 6% 27%	1858
	21st to end	Day	21% 15% 4 8% 6% 5% 5% 4 6% 6% 20%	1680
December	1st to 10th	Day	18% 19% 6% 14% 6% 5% 4 4 4 4 16%	2680
	11th to 20th	Day	20% 13% 5% 10% 5% 5% 4 3 5% 6% 23%	3066
	21st to end	Day	21% 15% 5% 12% 6% 6% 4 5% 5% 5% 17%	4048
January	1st to 10th	Night	15% 22% 8% 14% 5% 4 3 2 4 4 19%	8234
	11th to 20th	Night	12% 19% 7% 17% 8% 6% 5% 3 5% 4 13%	8235
	21st to end	Night	12% 14% 5% 13% 9% 7% 5% 3 4 5% 22%	9057
February	1st to 10th	Night	15% 16% 6% 13% 8% 5% 4 3 4 5% 20%	2783
	11th to 20th	Night	13% 14% 4 12% 7% 6% 5% 4 6% 5% 24%	2517
	21st to end	Night	16% 14% 5% 10% 6% 4 4 3 5% 4 29%	2076
March	1st to 10th	Night	21% 13% 4 9% 6% 5% 4 3 4 5% 28%	5484
	11th to 20th	Night	16% 14% 4 8% 5% 5% 5% 4 5% 6% 29%	5401
	21st to end	Night	16% 13% 5% 11% 6% 5% 5% 3 4 4 30%	5072
April	1st to 10th	Night	22% 12% 3 8% 5% 4 5% 4 4 5% 29%	2100
	11th to 20th	Night	24% 11% 3 8% 5% 4 4 3 4 5% 30%	2036
	21st to end	Night	20% 10% 3 7% 5% 5% 4 3 4 5% 34%	1825
May	1st to 10th	Night	25% 12% 3 8% 5% 4 4 4 5% 6% 24%	3831
	11th to 20th	Night	22% 9% 3 8% 5% 4 3 3 5% 6% 31%	3575
	21st to end	Night	18% 9% 3 8% 5% 4 4 3 5% 7% 32%	3926
June	1st to 10th	Night	24% 8% 2 6% 4 5% 4 4 6% 8% 30%	1600
	11th to 20th	Night	17% 6% 2 7% 5% 4 4 4 6% 8% 36%	1600
	21st to end	Night	19% 7% 3 6% 5% 4 4 4 6% 7% 34%	1600
July	1st to 10th	Night	12% 6% 3 7% 6% 5% 6% 5% 6% 9% 35%	3600
	11th to 20th	Night	13% 6% 3 7% 5% 5% 4 4 6% 8% 40%	3600
	21st to end	Night	11% 6% 2 8% 5% 5% 5% 4 6% 8% 40%	3926
August	1st to 10th	Night	16% 8% 4 7% 5% 4 4 3 5% 7% 36%	2586
	11th to 20th	Night	14% 7% 3 7% 5% 5% 5% 3 6% 7% 38%	2923
	21st to end	Night	16% 6% 2 6% 4 4 4 4 5% 7% 42%	3586
September	1st to 10th	Night	13% 6% 2 7% 4 4 4 4 5% 8% 45%	2000
	11th to 20th	Night	13% 6% 2 5% 4 4 3 3 5% 6% 48%	2105
	21st to end	Night	18% 6% 2 6% 4 4 4 3 5% 5% 43%	2200
October	1st to 10th	Night	18% 7% 3 7% 4 4 4 3 5% 6% 38%	2297
	11th to 20th	Night	20% 8% 3 7% 5% 4 5% 4 5% 6% 33%	2458
	21st to end	Night	25% 9% 3 8% 5% 5% 3 3 5% 5% 28%	2860
November	1st to 10th	Night	20% 11% 3 7% 4 5% 4 3 5% 6% 30%	2667
	11th to 20th	Night	18% 12% 3 9% 5% 4 4 4 4 5% 32%	2761
	21st to end	Night	21% 14% 4 9% 5% 4 5% 4 5% 5% 23%	2940
December	1st to 10th	Night	18% 23% 6% 12% 7% 5% 5% 3 4 4 14%	4720
	11th to 20th	Night	22% 14% 5% 10% 6% 5% 5% 3 5% 4 21%	5348
	21st to end	Night	23% 15% 5% 10% 5% 4 4 4 6% 4 18%	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	71% 3 10% 13% 2	4662
	11th to 20th	Day	71% 4 8% 10% 7% 1	4680
	21st to end	Day	62% 5% 11% 10% 11% 1	5124
February	1st to 10th	Day	64% 4 9% 16% 5% 1	1832
	11th to 20th	Day	61% 4 11% 17% 6% 1	1997
	21st to end	Day	60% 5% 10% 16% 8% 1	1730
March	1st to 10th	Day	61% 3 9% 14% 9% 3	4579
	11th to 20th	Day	56% 4 14% 15% 10% 1	4773
	21st to end	Day	55% 3 6% 17% 17% 1	6102
April	1st to 10th	Day	56% 4 7% 20% 11% 1	2520
	11th to 20th	Day	52% 4 7% 20% 15% 2	2446
	21st to end	Day	54% 4 9% 19% 11% 3	2575
May	1st to 10th	Day	64% 4 8% 17% 8% 1	6163
	11th to 20th	Day	53% 4 14% 20% 8% 1	6322
	21st to end	Day	52% 4 11% 22% 10% 1	6949
June	1st to 10th	Day	52% 5% 10% 20% 12% 1	2800
	11th to 20th	Day	44% 5% 11% 24% 14% 2	2800
	21st to end	Day	51% 5% 11% 22% 9% 2	2800
July	1st to 10th	Day	45% 6% 14% 24% 10%	6290
	11th to 20th	Day	38% 7% 13% 31% 11%	6285
	21st to end	Day	36% 6% 13% 36% 9%	6728
August	1st to 10th	Day	47% 6% 16% 23% 8%	4549
	11th to 20th	Day	41% 6% 17% 28% 7%	4128
	21st to end	Day	40% 5% 18% 22% 14%	4312
September	1st to 10th	Day	37% 5% 13% 31% 13% 1	2400
	11th to 20th	Day	36% 4 11% 35% 14%	2294
	21st to end	Day	42% 5% 15% 27% 11% 1	2200
October	1st to 10th	Day	42% 5% 14% 30% 9%	3425
	11th to 20th	Day	43% 5% 19% 26% 7%	3144
	21st to end	Day	48% 4 18% 23% 7%	3180
November	1st to 10th	Day	53% 5% 12% 21% 8% 1	1851
	11th to 20th	Day	56% 6% 12% 16% 10% 1	1858
	21st to end	Day	63% 6% 12% 14% 5%	1680
December	1st to 10th	Day	70% 5% 10% 13% 2	2680
	11th to 20th	Day	61% 4 12% 16% 7% 1	3066
	21st to end	Day	69% 4 10% 12% 5%	4048
January	1st to 10th	Night	70% 2 11% 12% 4	8234
	11th to 20th	Night	72% 4 8% 10% 5%	8280
	21st to end	Night	64% 2 9% 13% 12%	9057
February	1st to 10th	Night	66% 4 8% 15% 6% 1	2783
	11th to 20th	Night	59% 4 10% 19% 8%	2519
	21st to end	Night	58% 4 9% 18% 11% 1	2076
March	1st to 10th	Night	60% 2 8% 15% 12% 3	5494
	11th to 20th	Night	56% 4 13% 16% 10% 1	5402
	21st to end	Night	57% 4 4 21% 12% 2	5072
April	1st to 10th	Night	57% 3 7% 19% 12% 1	2100
	11th to 20th	Night	57% 3 6% 20% 12% 1	2036
	21st to end	Night	52% 3 8% 19% 14% 4	1825
May	1st to 10th	Night	62% 3 10% 16% 7% 2	3837
	11th to 20th	Night	55% 4 9% 21% 9% 1	3576
	21st to end	Night	51% 5% 9% 20% 13% 1	3927
June	1st to 10th	Night	53% 4 10% 20% 11% 1	1600
	11th to 20th	Night	45% 5% 12% 21% 15% 2	1600
	21st to end	Night	48% 5% 13% 20% 12% 1	1600
July	1st to 10th	Night	44% 6% 17% 23% 10%	3560
	11th to 20th	Night	40% 6% 14% 29% 12%	3552
	21st to end	Night	41% 6% 13% 27% 12%	3809
August	1st to 10th	Night	47% 5% 14% 26% 9%	2576
	11th to 20th	Night	45% 6% 18% 22% 9%	2949
	21st to end	Night	41% 4 14% 24% 15% 1	3586
September	1st to 10th	Night	39% 5% 12% 30% 13% 1	2000
	11th to 20th	Night	37% 3 14% 33% 13%	2105
	21st to end	Night	43% 3 13% 26% 14% 1	2200
October	1st to 10th	Night	46% 4 12% 27% 10%	3752
	11th to 20th	Night	45% 4 10% 29% 12%	3994
	21st to end	Night	50% 3 14% 21% 11% 1	4610
November	1st to 10th	Night	54% 4 11% 21% 8% 1	2667
	11th to 20th	Night	54% 4 11% 20% 10% 1	2761
	21st to end	Night	62% 5% 12% 16% 6%	2940
December	1st to 10th	Night	74% 5% 10% 10% 2	4720
	11th to 20th	Night	64% 5% 9% 13% 9%	5348
	21st to end	Night	67% 3 9% 13% 8%	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	26% 19% 28% 20% 6% 1	220
	11th to 20th	Day	27% 22% 32% 15% 3 1	220
	21st to end	Day	19% 19% 38% 17% 7%	242
February	1st to 10th	Day	30% 19% 39% 9% 3	300
	11th to 20th	Day	25% 21% 37% 14% 3	476
	21st to end	Day	26% 19% 33% 19% 3	446
March	1st to 10th	Day	27% 17% 31% 20% 5%	540
	11th to 20th	Day	27% 20% 31% 17% 4 1	540
	21st to end	Day	33% 18% 26% 15% 7%	594
April	1st to 10th	Day	30% 19% 26% 18% 6%	540
	11th to 20th	Day	29% 21% 28% 12% 7% 3	516
	21st to end	Day	28% 15% 33% 13% 9% 1	500
May	1st to 10th	Day	27% 16% 30% 16% 9% 1	503
	11th to 20th	Day	18% 15% 31% 25% 10% 1	527
	21st to end	Day	18% 14% 32% 26% 9% 1	573
June	1st to 10th	Day	22% 13% 30% 25% 8% 2	530
	11th to 20th	Day	16% 12% 31% 28% 11% 2	530
	21st to end	Day	22% 10% 34% 24% 8% 2	530
July	1st to 10th	Day	14% 6% 28% 34% 15% 3	525
	11th to 20th	Day	14% 5% 32% 31% 14% 3	524
	21st to end	Day	14% 6% 27% 36% 16% 2	576
August	1st to 10th	Day	14% 5% 27% 30% 20% 4	526
	11th to 20th	Day	14% 5% 27% 29% 18% 7%	519
	21st to end	Day	16% 10% 27% 25% 16% 7%	583
September	1st to 10th	Day	14% 8% 30% 26% 15% 7%	530
	11th to 20th	Day	14% 8% 19% 24% 21% 13%	530
	21st to end	Day	15% 12% 28% 22% 17% 7%	530
October	1st to 10th	Day	19% 12% 28% 21% 14% 5%	530
	11th to 20th	Day	23% 16% 29% 22% 8% 2	497
	21st to end	Day	32% 15% 26% 21% 5% 1	462
November	1st to 10th	Day	29% 17% 29% 19% 5%	425
	11th to 20th	Day	24% 22% 29% 16% 8% 2	398
	21st to end	Day	32% 21% 25% 16% 5%	220
December	1st to 10th	Day	30% 14% 30% 18% 7%	220
	11th to 20th	Day	24% 24% 36% 13% 3	220
	21st to end	Day	26% 24% 29% 15% 4 2	242
January	1st to 10th	Night	27% 17% 33% 19% 4	840
	11th to 20th	Night	26% 16% 33% 20% 5%	840
	21st to end	Night	20% 14% 35% 24% 6% 1	924
February	1st to 10th	Night	24% 13% 33% 25% 5%	840
	11th to 20th	Night	23% 15% 36% 23% 3	823
	21st to end	Night	26% 15% 31% 25% 4	692
March	1st to 10th	Night	26% 14% 31% 24% 4	840
	11th to 20th	Night	30% 15% 29% 21% 6%	840
	21st to end	Night	26% 16% 27% 24% 6%	924
April	1st to 10th	Night	30% 15% 26% 25% 5%	840
	11th to 20th	Night	30% 16% 25% 22% 6%	816
	21st to end	Night	26% 15% 29% 23% 7%	625
May	1st to 10th	Night	25% 9% 32% 24% 9% 1	507
	11th to 20th	Night	21% 10% 34% 26% 8% 1	394
	21st to end	Night	17% 9% 33% 32% 9%	433
June	1st to 10th	Night	27% 8% 24% 30% 11% 1	400
	11th to 20th	Night	19% 7% 30% 32% 13%	400
	21st to end	Night	20% 7% 26% 34% 14% 1	400
July	1st to 10th	Night	12% 4 31% 36% 18%	390
	11th to 20th	Night	10% 4 24% 46% 15% 1	388
	21st to end	Night	13% 4 20% 46% 16% 1	438
August	1st to 10th	Night	14% 4 16% 45% 20% 1	398
	11th to 20th	Night	14% 4 21% 35% 24% 2	615
	21st to end	Night	17% 5% 22% 35% 19% 2	880
September	1st to 10th	Night	15% 7% 26% 35% 16% 1	800
	11th to 20th	Night	16% 7% 18% 32% 24% 4	800
	21st to end	Night	19% 7% 28% 26% 18% 3	800
October	1st to 10th	Night	21% 10% 25% 28% 15% 2	800
	11th to 20th	Night	24% 11% 30% 26% 8% 1	800
	21st to end	Night	28% 10% 32% 24% 6%	880
November	1st to 10th	Night	26% 15% 32% 21% 6% 1	820
	11th to 20th	Night	24% 17% 30% 20% 8% 1	840
	21st to end	Night	29% 17% 30% 18% 6% 1	840
December	1st to 10th	Night	31% 16% 30% 20% 5%	840
	11th to 20th	Night	30% 15% 30% 18% 5% 1	840
	21st to end	Night	32% 16% 31% 18% 4	924

Page generated at 2026-04-14 02:44:25. Version ac07

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