Site d'observation de Charles Desjardins
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Site d'observation de Charles Desjardins clear sky chart from 2005-11-06 to 2025-02-21.

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% 13% 4 10% 6% 5% 5% 3 5% 6% 26%	108555
	Night	16% 14% 5% 12% 6% 5% 4 3 4 5% 25%	110026
Transparency	Day	56% 7% 11% 18% 8% 1	112071
	Night	59% 7% 10% 15% 8% 1	114674
Seeing	Day	26% 17% 29% 18% 8% 2	14934
	Night	24% 15% 27% 24% 9% 1	23985

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	13% 20% 9% 20% 9% 9% 3 2 2 2 11%	3597
	11th to 20th	Day	8% 17% 8% 24% 14% 4 5% 3 4 4 9%	3570
	21st to end	Day	10% 17% 9% 14% 6% 11% 6% 3 4 4 15%	3960
February	1st to 10th	Day	12% 19% 6% 17% 8% 6% 5% 3 4 4 16%	1694
	11th to 20th	Day	12% 18% 8% 16% 9% 6% 5% 4 4 4 15%	1931
	21st to end	Day	12% 18% 6% 13% 7% 7% 3 4 4 5% 20%	1570
March	1st to 10th	Day	21% 16% 5% 10% 6% 5% 4 3 4 5% 21%	3116
	11th to 20th	Day	13% 21% 8% 13% 6% 4 4 2 4 3 22%	3249
	21st to end	Day	16% 14% 6% 12% 5% 4 3 2 3 4 32%	4156
April	1st to 10th	Day	20% 18% 4 10% 5% 4 3 3 3 4 25%	2280
	11th to 20th	Day	19% 15% 4 8% 5% 4 4 3 4 4 32%	2271
	21st to end	Day	23% 14% 3 8% 4 4 4 3 4 6% 26%	2470
May	1st to 10th	Day	24% 12% 3 7% 4 4 5% 3 5% 7% 26%	4216
	11th to 20th	Day	19% 9% 3 8% 6% 5% 6% 4 6% 6% 28%	4398
	21st to end	Day	14% 8% 3 7% 5% 5% 5% 5% 7% 8% 33%	4837
June	1st to 10th	Day	26% 9% 3 6% 4 4 5% 5% 5% 6% 27%	2660
	11th to 20th	Day	18% 7% 2 7% 5% 4 4 4 6% 8% 34%	2660
	21st to end	Day	24% 9% 3 7% 5% 4 4 4 6% 6% 27%	2660
July	1st to 10th	Day	14% 8% 3 7% 5% 5% 6% 4 8% 9% 32%	4440
	11th to 20th	Day	14% 7% 3 7% 5% 5% 6% 5% 7% 9% 31%	4440
	21st to end	Day	15% 8% 3 6% 5% 4 5% 4 6% 7% 38%	4814
August	1st to 10th	Day	19% 8% 3 8% 5% 5% 6% 5% 7% 8% 27%	4407
	11th to 20th	Day	18% 8% 3 8% 5% 4 6% 5% 7% 9% 28%	4016
	21st to end	Day	19% 6% 2 6% 4 4 4 4 6% 8% 36%	4180
September	1st to 10th	Day	16% 8% 2 6% 4 4 5% 4 6% 6% 40%	2280
	11th to 20th	Day	18% 7% 2 5% 3 3 3 3 4 7% 43%	2147
	21st to end	Day	18% 9% 2 5% 4 4 5% 3 5% 8% 36%	2090
October	1st to 10th	Day	23% 10% 3 8% 4 4 5% 2 6% 6% 28%	2043
	11th to 20th	Day	20% 13% 3 8% 5% 4 5% 3 5% 5% 28%	1805
	21st to end	Day	25% 20% 4 8% 4 3 3 2 3 4 24%	1881
November	1st to 10th	Day	18% 18% 4 7% 5% 4 3 4 5% 5% 28%	1761
	11th to 20th	Day	16% 21% 6% 11% 5% 5% 4 3 4 4 23%	1800
	21st to end	Day	18% 19% 7% 12% 5% 4 3 4 5% 5% 17%	1610
December	1st to 10th	Day	14% 24% 8% 20% 9% 4 3 2 3 3 10%	2600
	11th to 20th	Day	17% 19% 7% 16% 4 4 4 2 4 4 19%	2986
	21st to end	Day	18% 18% 6% 14% 7% 4 6% 3 3 4 18%	3960
January	1st to 10th	Night	11% 19% 9% 22% 11% 6% 3 2 4 2 11%	6349
	11th to 20th	Night	8% 19% 8% 22% 12% 6% 5% 3 3 3 10%	6315
	21st to end	Night	10% 16% 7% 15% 9% 8% 5% 4 4 4 18%	6996
February	1st to 10th	Night	13% 18% 6% 16% 9% 6% 4 3 4 4 17%	2705
	11th to 20th	Night	12% 15% 7% 16% 9% 7% 4 3 4 4 19%	2353
	21st to end	Night	12% 18% 6% 11% 7% 7% 4 2 4 4 25%	1885
March	1st to 10th	Night	21% 15% 4 8% 5% 4 4 3 4 5% 27%	3724
	11th to 20th	Night	15% 19% 6% 13% 6% 4 4 3 3 3 24%	3709
	21st to end	Night	13% 18% 6% 12% 6% 4 3 3 3 3 29%	3472
April	1st to 10th	Night	21% 14% 4 9% 5% 4 4 3 5% 5% 26%	1900
	11th to 20th	Night	21% 13% 4 6% 5% 4 5% 3 4 6% 31%	1856
	21st to end	Night	21% 11% 3 8% 5% 4 3 3 5% 5% 32%	1710
May	1st to 10th	Night	23% 12% 3 8% 5% 4 4 4 5% 6% 26%	2752
	11th to 20th	Night	21% 9% 3 8% 5% 4 5% 4 5% 5% 32%	2495
	21st to end	Night	17% 7% 2 6% 4 5% 5% 4 6% 8% 37%	2738
June	1st to 10th	Night	26% 8% 2 6% 4 4 4 4 6% 7% 30%	1520
	11th to 20th	Night	19% 7% 2 6% 4 4 4 4 6% 8% 36%	1520
	21st to end	Night	19% 9% 2 7% 5% 4 4 5% 8% 6% 30%	1520
July	1st to 10th	Night	14% 9% 3 9% 6% 5% 5% 4 6% 7% 32%	2520
	11th to 20th	Night	17% 7% 3 6% 4 4 5% 5% 6% 7% 36%	2520
	21st to end	Night	14% 7% 3 7% 5% 4 5% 4 6% 6% 37%	2739
August	1st to 10th	Night	23% 8% 3 8% 4 4 4 4 5% 6% 32%	2506
	11th to 20th	Night	15% 8% 3 9% 5% 6% 6% 4 6% 8% 31%	2792
	21st to end	Night	16% 6% 2 7% 4 4 4 4 5% 6% 41%	3476
September	1st to 10th	Night	16% 7% 2 6% 5% 4 4 3 5% 6% 41%	1900
	11th to 20th	Night	15% 7% 2 5% 3 4 4 3 5% 6% 46%	2033
	21st to end	Night	20% 6% 2 5% 4 4 4 3 5% 6% 41%	2090
October	1st to 10th	Night	21% 10% 3 6% 4 4 4 3 5% 6% 33%	2133
	11th to 20th	Night	21% 13% 4 8% 4 4 5% 3 4 5% 29%	2375
	21st to end	Night	24% 15% 4 8% 5% 3 4 3 4 5% 25%	2717
November	1st to 10th	Night	18% 15% 5% 8% 5% 5% 5% 3 5% 6% 26%	2537
	11th to 20th	Night	16% 16% 5% 11% 5% 4 3 3 4 5% 27%	2600
	21st to end	Night	17% 19% 7% 13% 6% 4 3 3 4 5% 21%	2785
December	1st to 10th	Night	15% 23% 10% 21% 7% 4 3 2 3 3 9%	4580
	11th to 20th	Night	18% 21% 7% 17% 6% 4 3 2 3 3 16%	5208
	21st to end	Night	18% 18% 5% 13% 6% 5% 5% 2 3 5% 20%	6996

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	81% 4 7% 8% 1	3598
	11th to 20th	Day	76% 7% 7% 7% 3 1	3600
	21st to end	Day	71% 6% 7% 9% 6% 1	3960
February	1st to 10th	Day	72% 5% 6% 11% 5% 1	1694
	11th to 20th	Day	72% 4 9% 9% 4 1	1940
	21st to end	Day	65% 5% 9% 13% 6% 2	1570
March	1st to 10th	Day	64% 8% 8% 11% 8% 1	3119
	11th to 20th	Day	66% 5% 9% 9% 9% 1	3249
	21st to end	Day	57% 3 7% 16% 15% 1	4156
April	1st to 10th	Day	63% 4 8% 16% 8% 1	2280
	11th to 20th	Day	55% 5% 7% 19% 12% 1	2271
	21st to end	Day	59% 5% 8% 16% 9% 2	2470
May	1st to 10th	Day	56% 7% 11% 18% 8% 1	4230
	11th to 20th	Day	51% 11% 15% 15% 7% 1	4402
	21st to end	Day	44% 9% 12% 23% 10% 1	4837
June	1st to 10th	Day	54% 8% 11% 18% 9% 1	2660
	11th to 20th	Day	46% 7% 12% 22% 11% 2	2660
	21st to end	Day	55% 8% 11% 18% 8% 1	2660
July	1st to 10th	Day	44% 9% 15% 24% 8%	4370
	11th to 20th	Day	44% 10% 13% 29% 4	4365
	21st to end	Day	43% 8% 12% 30% 7%	4661
August	1st to 10th	Day	52% 9% 15% 19% 6%	4393
	11th to 20th	Day	49% 9% 17% 20% 5%	4055
	21st to end	Day	44% 7% 15% 19% 13% 1	4180
September	1st to 10th	Day	41% 8% 12% 27% 11% 1	2280
	11th to 20th	Day	40% 6% 11% 30% 13%	2147
	21st to end	Day	45% 8% 13% 23% 10% 1	2090
October	1st to 10th	Day	48% 7% 13% 24% 7%	3394
	11th to 20th	Day	50% 8% 13% 22% 7%	2982
	21st to end	Day	53% 4 15% 20% 7% 1	3081
November	1st to 10th	Day	58% 6% 11% 17% 8%	1761
	11th to 20th	Day	65% 5% 9% 12% 8% 2	1800
	21st to end	Day	68% 6% 13% 10% 3	1610
December	1st to 10th	Day	81% 4 8% 6% 2	2600
	11th to 20th	Day	67% 6% 7% 15% 5%	2986
	21st to end	Day	70% 5% 7% 10% 8% 1	3960
January	1st to 10th	Night	77% 7% 7% 6% 2	6349
	11th to 20th	Night	77% 7% 8% 6% 2	6360
	21st to end	Night	67% 7% 8% 8% 9% 1	6996
February	1st to 10th	Night	70% 5% 7% 12% 5%	2705
	11th to 20th	Night	68% 6% 8% 13% 6%	2355
	21st to end	Night	63% 4 10% 13% 9% 1	1885
March	1st to 10th	Night	58% 7% 10% 15% 8% 2	3734
	11th to 20th	Night	64% 7% 8% 12% 10% 1	3710
	21st to end	Night	61% 4 6% 16% 11% 1	3472
April	1st to 10th	Night	59% 4 9% 15% 11% 1	1900
	11th to 20th	Night	54% 4 9% 20% 12% 1	1856
	21st to end	Night	54% 6% 9% 17% 12% 2	1710
May	1st to 10th	Night	56% 7% 10% 17% 8% 1	2758
	11th to 20th	Night	50% 10% 14% 16% 9% 1	2496
	21st to end	Night	44% 9% 12% 19% 15% 1	2739
June	1st to 10th	Night	51% 6% 11% 22% 9% 1	1520
	11th to 20th	Night	44% 7% 13% 23% 11% 3	1520
	21st to end	Night	50% 8% 14% 18% 9% 1	1520
July	1st to 10th	Night	48% 8% 13% 20% 11%	2480
	11th to 20th	Night	42% 9% 14% 28% 7%	2472
	21st to end	Night	44% 9% 13% 24% 9%	2651
August	1st to 10th	Night	50% 8% 14% 23% 5%	2496
	11th to 20th	Night	46% 11% 17% 19% 7%	2819
	21st to end	Night	41% 8% 13% 23% 14% 1	3476
September	1st to 10th	Night	41% 9% 12% 26% 12% 1	1900
	11th to 20th	Night	37% 8% 15% 28% 12% 1	2033
	21st to end	Night	42% 7% 13% 24% 12% 1	2090
October	1st to 10th	Night	51% 7% 11% 23% 9%	3562
	11th to 20th	Night	50% 7% 11% 23% 10%	3937
	21st to end	Night	52% 7% 14% 18% 9% 1	4467
November	1st to 10th	Night	58% 6% 11% 17% 7% 1	2537
	11th to 20th	Night	59% 6% 10% 14% 9% 2	2600
	21st to end	Night	66% 6% 11% 13% 4	2785
December	1st to 10th	Night	82% 5% 6% 6% 1	4580
	11th to 20th	Night	73% 6% 5% 10% 6%	5208
	21st to end	Night	69% 4 7% 13% 7%	6996

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	28% 22% 32% 14% 4	200
	11th to 20th	Day	28% 24% 34% 10% 4 1	200
	21st to end	Day	27% 20% 35% 10% 6% 1	220
February	1st to 10th	Day	36% 32% 22% 8% 2	247
	11th to 20th	Day	30% 27% 31% 10% 2	479
	21st to end	Day	30% 22% 31% 16% 1	382
March	1st to 10th	Day	31% 18% 31% 17% 3	460
	11th to 20th	Day	29% 24% 27% 15% 4 1	460
	21st to end	Day	31% 24% 24% 14% 7% 1	506
April	1st to 10th	Day	35% 18% 27% 14% 5% 1	460
	11th to 20th	Day	36% 18% 25% 13% 5% 3	452
	21st to end	Day	34% 17% 29% 12% 6% 2	460
May	1st to 10th	Day	32% 17% 27% 16% 6% 2	463
	11th to 20th	Day	22% 18% 30% 20% 8% 3	487
	21st to end	Day	19% 20% 32% 22% 6% 2	529
June	1st to 10th	Day	30% 15% 30% 17% 8% 1	490
	11th to 20th	Day	21% 15% 31% 21% 11% 1	490
	21st to end	Day	28% 13% 32% 18% 8% 2	490
July	1st to 10th	Day	18% 12% 32% 25% 12% 2	485
	11th to 20th	Day	15% 12% 37% 25% 8% 2	484
	21st to end	Day	20% 9% 35% 26% 9% 1	532
August	1st to 10th	Day	18% 12% 27% 28% 13% 2	486
	11th to 20th	Day	19% 9% 28% 25% 15% 4	479
	21st to end	Day	18% 15% 25% 24% 12% 6%	539
September	1st to 10th	Day	20% 11% 29% 22% 13% 5%	490
	11th to 20th	Day	18% 11% 22% 21% 21% 7%	490
	21st to end	Day	18% 14% 26% 23% 14% 4	490
October	1st to 10th	Day	25% 16% 27% 16% 11% 5%	490
	11th to 20th	Day	28% 20% 22% 18% 10% 1	440
	21st to end	Day	35% 20% 22% 17% 5%	429
November	1st to 10th	Day	33% 18% 28% 16% 4 1	395
	11th to 20th	Day	29% 23% 29% 13% 6% 2	400
	21st to end	Day	33% 21% 32% 11% 2	210
December	1st to 10th	Day	31% 23% 27% 14% 5% 2	200
	11th to 20th	Day	34% 25% 30% 11% 1 1	200
	21st to end	Day	34% 23% 27% 11% 4 1	220
January	1st to 10th	Night	27% 22% 30% 18% 2 1	800
	11th to 20th	Night	26% 23% 31% 17% 4	800
	21st to end	Night	19% 20% 34% 21% 5% 1	880
February	1st to 10th	Night	24% 21% 31% 20% 4	800
	11th to 20th	Night	22% 23% 34% 18% 3	783
	21st to end	Night	26% 18% 31% 23% 3	629
March	1st to 10th	Night	29% 16% 30% 21% 4	760
	11th to 20th	Night	27% 19% 27% 21% 6%	760
	21st to end	Night	27% 18% 26% 21% 8% 1	836
April	1st to 10th	Night	30% 15% 29% 21% 6%	760
	11th to 20th	Night	28% 17% 27% 21% 7%	732
	21st to end	Night	29% 15% 29% 20% 7%	570
May	1st to 10th	Night	26% 12% 29% 25% 8% 1	527
	11th to 20th	Night	23% 10% 31% 26% 9% 1	374
	21st to end	Night	19% 12% 27% 32% 9%	411
June	1st to 10th	Night	27% 8% 26% 27% 10% 1	380
	11th to 20th	Night	20% 7% 26% 32% 14%	380
	21st to end	Night	19% 9% 25% 35% 11% 1	380
July	1st to 10th	Night	15% 5% 28% 37% 14%	370
	11th to 20th	Night	13% 4 25% 38% 19% 1	368
	21st to end	Night	13% 6% 23% 42% 16%	416
August	1st to 10th	Night	19% 5% 17% 38% 20%	378
	11th to 20th	Night	14% 6% 23% 35% 20% 2	559
	21st to end	Night	16% 7% 23% 33% 19% 2	836
September	1st to 10th	Night	18% 8% 24% 34% 14% 1	760
	11th to 20th	Night	19% 8% 20% 30% 22% 2	760
	21st to end	Night	22% 8% 28% 25% 16% 2	760
October	1st to 10th	Night	26% 13% 22% 24% 13% 1	760
	11th to 20th	Night	28% 13% 26% 22% 10% 1	760
	21st to end	Night	30% 17% 28% 21% 4	836
November	1st to 10th	Night	28% 18% 29% 20% 5% 1	780
	11th to 20th	Night	25% 20% 28% 16% 9% 1	800
	21st to end	Night	29% 23% 26% 16% 5% 1	800
December	1st to 10th	Night	30% 24% 27% 15% 4	800
	11th to 20th	Night	29% 22% 28% 17% 5% 1	800
	21st to end	Night	32% 21% 25% 18% 3	880

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