Observatoire astronomique du bois de Belle-Rivière
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire astronomique du bois de Belle-Rivière clear sky chart from 2005-11-06 to 2024-03-08.

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% 9% 4 7% 6% 3 5% 5% 5% 7% 33%	78347
	Night	17% 10% 4 7% 6% 3 5% 4 5% 6% 33%	81207
Transparency	Day	49% 8% 13% 19% 10% 1	78052
	Night	51% 8% 12% 18% 9% 1	81036
Seeing	Day	20% 13% 29% 24% 11% 3	13599
	Night	22% 10% 31% 28% 9% 1	22762

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% 15% 6% 13% 7% 4 5% 4 4 5% 23%	2517
	11th to 20th	Day	15% 12% 6% 9% 7% 4 4 5% 6% 7% 27%	2520
	21st to end	Day	13% 18% 5% 8% 6% 3 6% 5% 5% 6% 23%	2772
February	1st to 10th	Day	14% 15% 5% 9% 6% 4 5% 5% 5% 6% 26%	1683
	11th to 20th	Day	14% 11% 6% 8% 7% 4 5% 6% 6% 6% 28%	1743
	21st to end	Day	18% 14% 5% 8% 6% 3 4 4 5% 5% 27%	1570
March	1st to 10th	Day	16% 11% 5% 9% 7% 4 6% 4 4 5% 30%	1867
	11th to 20th	Day	15% 12% 3 7% 7% 3 4 5% 5% 5% 33%	1883
	21st to end	Day	19% 8% 4 6% 5% 3 4 4 5% 5% 36%	2359
April	1st to 10th	Day	22% 9% 4 7% 6% 3 4 4 3 6% 33%	2160
	11th to 20th	Day	21% 7% 3 5% 5% 3 5% 4 5% 6% 36%	2134
	21st to end	Day	22% 9% 4 6% 6% 4 4 4 5% 5% 32%	2290
May	1st to 10th	Day	19% 8% 3 6% 6% 4 5% 4 5% 7% 34%	2506
	11th to 20th	Day	19% 7% 2 6% 6% 3 4 5% 5% 7% 37%	2478
	21st to end	Day	17% 6% 3 6% 6% 3 5% 5% 6% 7% 36%	2725
June	1st to 10th	Day	22% 7% 3 6% 5% 3 5% 6% 6% 7% 31%	2520
	11th to 20th	Day	15% 6% 3 6% 5% 3 5% 6% 6% 7% 38%	2520
	21st to end	Day	19% 8% 3 6% 6% 4 6% 6% 6% 8% 29%	2520
July	1st to 10th	Day	11% 5% 3 5% 6% 4 6% 5% 7% 7% 41%	2520
	11th to 20th	Day	13% 4 3 5% 6% 4 6% 6% 7% 9% 37%	2520
	21st to end	Day	12% 5% 2 5% 5% 3 6% 6% 7% 10% 37%	2744
August	1st to 10th	Day	12% 6% 2 6% 6% 4 5% 7% 7% 8% 38%	2506
	11th to 20th	Day	10% 5% 2 7% 6% 3 6% 6% 7% 8% 40%	2284
	21st to end	Day	13% 6% 2 5% 5% 3 4 5% 6% 9% 42%	2376
September	1st to 10th	Day	12% 5% 2 5% 5% 4 5% 5% 6% 9% 40%	2160
	11th to 20th	Day	13% 5% 3 4 4 3 5% 4 4 7% 49%	2098
	21st to end	Day	17% 5% 2 6% 5% 3 4 5% 5% 7% 43%	1980
October	1st to 10th	Day	20% 7% 3 5% 5% 3 4 5% 6% 6% 37%	1836
	11th to 20th	Day	20% 7% 3 7% 8% 4 5% 5% 5% 7% 28%	1774
	21st to end	Day	25% 9% 3 6% 6% 3 4 5% 5% 5% 28%	1782
November	1st to 10th	Day	16% 8% 4 6% 6% 4 5% 5% 5% 8% 34%	1671
	11th to 20th	Day	19% 8% 5% 7% 5% 3 5% 6% 5% 7% 30%	1611
	21st to end	Day	22% 10% 3 6% 5% 5% 6% 5% 5% 7% 25%	1520
December	1st to 10th	Day	24% 12% 6% 9% 6% 3 5% 5% 5% 5% 20%	1520
	11th to 20th	Day	21% 12% 5% 7% 6% 3 4 4 5% 5% 28%	1906
	21st to end	Day	27% 15% 5% 8% 5% 3 3 4 3 4 21%	2772
January	1st to 10th	Night	16% 14% 6% 10% 6% 4 5% 5% 5% 6% 23%	4429
	11th to 20th	Night	12% 12% 6% 11% 9% 4 6% 5% 5% 6% 25%	4440
	21st to end	Night	15% 16% 6% 9% 7% 4 5% 4 4 5% 25%	4884
February	1st to 10th	Night	14% 13% 6% 10% 7% 4 6% 5% 5% 7% 25%	2494
	11th to 20th	Night	13% 10% 5% 8% 7% 4 6% 4 6% 6% 30%	2323
	21st to end	Night	14% 14% 6% 8% 6% 2 4 4 4 5% 32%	1884
March	1st to 10th	Night	16% 13% 5% 7% 6% 3 4 4 5% 6% 30%	2241
	11th to 20th	Night	17% 12% 5% 6% 6% 4 4 4 4 6% 32%	2074
	21st to end	Night	17% 10% 3 7% 5% 3 4 3 5% 4 40%	1996
April	1st to 10th	Night	23% 9% 4 5% 5% 2 4 4 4 6% 32%	1800
	11th to 20th	Night	21% 7% 3 5% 6% 3 3 4 4 7% 37%	1775
	21st to end	Night	21% 8% 4 7% 5% 2 4 5% 4 6% 34%	1669
May	1st to 10th	Night	21% 7% 2 6% 5% 4 5% 4 4 6% 35%	1468
	11th to 20th	Night	19% 7% 3 5% 5% 3 4 4 5% 5% 40%	1415
	21st to end	Night	16% 6% 3 5% 6% 3 4 4 4 8% 41%	1550
June	1st to 10th	Night	21% 6% 3 6% 4 4 6% 4 8% 8% 32%	1440
	11th to 20th	Night	16% 8% 2 5% 5% 2 5% 5% 5% 8% 39%	1440
	21st to end	Night	18% 6% 3 4 6% 4 6% 5% 6% 7% 36%	1440
July	1st to 10th	Night	10% 4 2 5% 5% 4 5% 5% 7% 8% 45%	1440
	11th to 20th	Night	11% 6% 2 5% 5% 3 5% 6% 7% 10% 40%	1440
	21st to end	Night	11% 6% 3 5% 5% 3 4 5% 7% 10% 41%	1574
August	1st to 10th	Night	12% 5% 2 6% 4 3 4 5% 7% 8% 44%	1432
	11th to 20th	Night	12% 5% 2 6% 5% 3 5% 5% 5% 6% 45%	1595
	21st to end	Night	14% 5% 2 6% 5% 3 4 6% 6% 7% 44%	1980
September	1st to 10th	Night	10% 5% 3 6% 5% 3 5% 5% 5% 8% 44%	1800
	11th to 20th	Night	15% 6% 3 4 4 2 3 4 4 8% 48%	1862
	21st to end	Night	16% 5% 2 5% 4 3 4 5% 5% 7% 44%	1980
October	1st to 10th	Night	19% 7% 3 5% 4 3 5% 4 5% 5% 40%	2119
	11th to 20th	Night	21% 8% 3 6% 6% 3 4 4 4 6% 35%	2184
	21st to end	Night	22% 8% 4 7% 6% 4 4 5% 4 5% 31%	2574
November	1st to 10th	Night	19% 8% 3 6% 5% 3 5% 5% 5% 7% 33%	2407
	11th to 20th	Night	18% 10% 3 7% 6% 3 5% 4 5% 6% 34%	2566
	21st to end	Night	22% 12% 4 7% 6% 3 4 4 4 5% 29%	2660
December	1st to 10th	Night	20% 14% 6% 8% 7% 4 5% 4 5% 5% 23%	2660
	11th to 20th	Night	23% 14% 5% 7% 6% 3 4 4 4 4 27%	3288
	21st to end	Night	28% 16% 5% 8% 5% 2 3 3 3 4 23%	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	60% 11% 11% 12% 5% 1	2518
	11th to 20th	Day	54% 9% 15% 15% 7%	2520
	21st to end	Day	59% 9% 14% 12% 6%	2772
February	1st to 10th	Day	59% 6% 11% 18% 5% 2	1683
	11th to 20th	Day	56% 7% 13% 15% 9% 1	1752
	21st to end	Day	59% 5% 10% 15% 9% 2	1570
March	1st to 10th	Day	55% 6% 11% 16% 10% 2	1870
	11th to 20th	Day	51% 7% 12% 15% 12% 3	1883
	21st to end	Day	50% 5% 11% 16% 14% 4	2359
April	1st to 10th	Day	53% 6% 9% 18% 11% 2	2160
	11th to 20th	Day	47% 6% 9% 22% 14% 2	2134
	21st to end	Day	54% 5% 9% 16% 12% 4	2290
May	1st to 10th	Day	50% 6% 9% 18% 14% 2	2506
	11th to 20th	Day	46% 6% 11% 19% 15% 3	2482
	21st to end	Day	45% 8% 13% 18% 14% 2	2725
June	1st to 10th	Day	50% 9% 10% 18% 12% 1	2520
	11th to 20th	Day	43% 8% 13% 20% 13% 3	2520
	21st to end	Day	50% 9% 13% 17% 9% 1	2520
July	1st to 10th	Day	37% 10% 15% 25% 12% 1	2450
	11th to 20th	Day	38% 11% 17% 24% 10%	2445
	21st to end	Day	40% 10% 17% 24% 9%	2591
August	1st to 10th	Day	41% 11% 17% 24% 8%	2492
	11th to 20th	Day	37% 10% 18% 24% 10%	2284
	21st to end	Day	37% 8% 17% 25% 13% 1	2376
September	1st to 10th	Day	37% 8% 17% 25% 13%	2160
	11th to 20th	Day	34% 8% 13% 30% 13% 1	2098
	21st to end	Day	41% 7% 15% 27% 9% 1	1980
October	1st to 10th	Day	47% 7% 12% 21% 12%	1836
	11th to 20th	Day	54% 8% 14% 17% 6%	1774
	21st to end	Day	55% 7% 14% 16% 7% 1	1782
November	1st to 10th	Day	47% 8% 16% 21% 7% 1	1671
	11th to 20th	Day	52% 8% 13% 17% 10%	1611
	21st to end	Day	57% 11% 13% 14% 5% 1	1520
December	1st to 10th	Day	67% 8% 10% 12% 4	1520
	11th to 20th	Day	59% 7% 14% 15% 5%	1906
	21st to end	Day	67% 7% 10% 10% 5%	2772
January	1st to 10th	Night	60% 9% 15% 11% 4	4429
	11th to 20th	Night	55% 12% 16% 12% 4 1	4440
	21st to end	Night	61% 9% 13% 10% 6% 1	4884
February	1st to 10th	Night	58% 8% 12% 15% 6% 1	2494
	11th to 20th	Night	52% 8% 13% 20% 7% 1	2325
	21st to end	Night	54% 6% 10% 16% 13% 1	1884
March	1st to 10th	Night	55% 6% 10% 17% 10% 2	2251
	11th to 20th	Night	53% 5% 11% 17% 11% 3	2075
	21st to end	Night	48% 5% 8% 20% 14% 4	1996
April	1st to 10th	Night	52% 5% 10% 17% 13% 2	1800
	11th to 20th	Night	49% 5% 9% 20% 15% 2	1775
	21st to end	Night	51% 6% 8% 18% 13% 4	1669
May	1st to 10th	Night	50% 6% 8% 17% 15% 4	1468
	11th to 20th	Night	45% 7% 9% 16% 18% 4	1416
	21st to end	Night	43% 8% 12% 19% 17% 2	1551
June	1st to 10th	Night	48% 10% 11% 19% 11% 1	1440
	11th to 20th	Night	42% 8% 12% 22% 15% 2	1440
	21st to end	Night	45% 9% 12% 20% 13% 1	1440
July	1st to 10th	Night	34% 10% 14% 24% 17% 1	1400
	11th to 20th	Night	37% 9% 16% 27% 12%	1392
	21st to end	Night	37% 9% 17% 25% 11%	1486
August	1st to 10th	Night	36% 9% 18% 26% 11%	1422
	11th to 20th	Night	35% 10% 18% 24% 12%	1595
	21st to end	Night	37% 9% 16% 26% 12%	1980
September	1st to 10th	Night	38% 8% 14% 25% 15% 1	1800
	11th to 20th	Night	36% 6% 13% 33% 11% 1	1862
	21st to end	Night	39% 8% 12% 27% 13%	1980
October	1st to 10th	Night	46% 7% 11% 23% 12% 1	2119
	11th to 20th	Night	51% 7% 12% 22% 8%	2184
	21st to end	Night	55% 8% 14% 15% 8% 1	2574
November	1st to 10th	Night	50% 7% 14% 20% 8% 1	2407
	11th to 20th	Night	51% 7% 14% 16% 9% 2	2566
	21st to end	Night	58% 8% 12% 17% 6%	2660
December	1st to 10th	Night	63% 8% 12% 13% 4	2660
	11th to 20th	Night	61% 7% 9% 16% 6%	3288
	21st to end	Night	66% 6% 10% 14% 4	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	20% 17% 31% 26% 5% 1	180
	11th to 20th	Day	25% 21% 28% 19% 6% 1	180
	21st to end	Day	19% 17% 32% 23% 8% 1	198
February	1st to 10th	Day	29% 22% 33% 12% 2	258
	11th to 20th	Day	21% 18% 39% 19% 2	350
	21st to end	Day	28% 14% 33% 23% 2	382
March	1st to 10th	Day	23% 13% 33% 25% 5%	448
	11th to 20th	Day	19% 19% 35% 20% 6% 1	420
	21st to end	Day	26% 15% 31% 19% 10% 1	462
April	1st to 10th	Day	27% 15% 29% 20% 7% 2	420
	11th to 20th	Day	25% 18% 25% 20% 10% 2	412
	21st to end	Day	28% 16% 29% 19% 7% 1	420
May	1st to 10th	Day	23% 12% 33% 23% 7% 2	423
	11th to 20th	Day	19% 11% 34% 24% 10% 2	447
	21st to end	Day	17% 13% 35% 23% 10% 2	485
June	1st to 10th	Day	23% 12% 28% 26% 10% 2	450
	11th to 20th	Day	16% 13% 26% 30% 13% 2	450
	21st to end	Day	21% 9% 28% 25% 14% 3	450
July	1st to 10th	Day	11% 8% 28% 32% 17% 5%	445
	11th to 20th	Day	14% 7% 27% 34% 15% 4	444
	21st to end	Day	14% 7% 27% 33% 16% 3	488
August	1st to 10th	Day	14% 6% 24% 33% 20% 4	446
	11th to 20th	Day	10% 7% 24% 32% 17% 10%	439
	21st to end	Day	13% 8% 28% 25% 18% 7%	495
September	1st to 10th	Day	13% 7% 28% 29% 15% 8%	450
	11th to 20th	Day	12% 10% 25% 23% 20% 9%	450
	21st to end	Day	17% 11% 29% 21% 18% 5%	450
October	1st to 10th	Day	22% 13% 26% 22% 14% 3	450
	11th to 20th	Day	19% 16% 29% 23% 11% 1	437
	21st to end	Day	30% 15% 27% 21% 7%	396
November	1st to 10th	Day	25% 16% 26% 22% 9% 1	365
	11th to 20th	Day	24% 18% 36% 17% 5%	271
	21st to end	Day	23% 22% 28% 22% 4 1	180
December	1st to 10th	Day	31% 12% 27% 23% 7% 1	180
	11th to 20th	Day	28% 15% 36% 17% 3 1	180
	21st to end	Day	31% 20% 28% 15% 6% 1	198
January	1st to 10th	Night	24% 13% 33% 26% 4	760
	11th to 20th	Night	25% 14% 33% 23% 5%	760
	21st to end	Night	17% 11% 38% 26% 6% 1	836
February	1st to 10th	Night	20% 12% 39% 24% 5%	760
	11th to 20th	Night	19% 13% 41% 23% 4	743
	21st to end	Night	22% 11% 36% 28% 3	628
March	1st to 10th	Night	22% 13% 34% 27% 4	751
	11th to 20th	Night	23% 14% 33% 24% 6%	720
	21st to end	Night	23% 9% 32% 29% 7%	792
April	1st to 10th	Night	26% 12% 28% 28% 5%	720
	11th to 20th	Night	24% 12% 31% 28% 6%	711
	21st to end	Night	27% 10% 30% 24% 9%	589
May	1st to 10th	Night	24% 7% 34% 27% 7% 2	388
	11th to 20th	Night	23% 6% 31% 32% 8% 1	354
	21st to end	Night	16% 6% 39% 30% 9%	389
June	1st to 10th	Night	24% 6% 29% 32% 9% 1	360
	11th to 20th	Night	19% 6% 31% 33% 12% 1	360
	21st to end	Night	18% 6% 27% 31% 17% 1	360
July	1st to 10th	Night	9% 6% 30% 37% 17% 1	350
	11th to 20th	Night	12% 3 24% 44% 17%	348
	21st to end	Night	11% 3 26% 43% 15% 1	394
August	1st to 10th	Night	14% 4 17% 45% 19% 1	358
	11th to 20th	Night	14% 3 22% 35% 24% 2	531
	21st to end	Night	14% 5% 25% 34% 20% 2	792
September	1st to 10th	Night	13% 5% 25% 41% 16% 1	720
	11th to 20th	Night	17% 5% 21% 36% 19% 2	720
	21st to end	Night	17% 6% 27% 30% 18% 2	720
October	1st to 10th	Night	21% 8% 28% 30% 12% 1	720
	11th to 20th	Night	23% 9% 30% 28% 9% 1	720
	21st to end	Night	27% 10% 32% 26% 5%	792
November	1st to 10th	Night	24% 14% 29% 26% 7%	740
	11th to 20th	Night	23% 14% 34% 20% 10%	760
	21st to end	Night	28% 15% 31% 20% 6%	760
December	1st to 10th	Night	30% 12% 33% 21% 5%	760
	11th to 20th	Night	28% 15% 32% 20% 4 1	760
	21st to end	Night	33% 13% 31% 17% 5%	836

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