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 2026-06-16.

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% 12% 5% 10% 6% 5% 5% 4 5% 6% 25%	137645
	Night	16% 14% 5% 12% 6% 5% 4 3 4 5% 25%	134406
Transparency	Day	57% 7% 11% 18% 8% 1	141115
	Night	59% 7% 10% 16% 8% 1	139025
Seeing	Day	26% 18% 29% 17% 7% 2	16658
	Night	25% 16% 27% 23% 8% 1	25592

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% 17% 10% 20% 9% 9% 4 2 3 3 12%	4661
	11th to 20th	Day	7% 17% 9% 22% 14% 7% 6% 3 4 3 8%	4650
	21st to end	Day	8% 15% 8% 14% 9% 15% 6% 3 5% 4 12%	5124
February	1st to 10th	Day	12% 18% 6% 17% 8% 7% 5% 3 4 4 17%	1779
	11th to 20th	Day	11% 18% 8% 17% 9% 5% 4 4 5% 4 15%	2030
	21st to end	Day	12% 18% 6% 14% 8% 7% 3 4 4 5% 20%	1730
March	1st to 10th	Day	18% 15% 7% 15% 6% 5% 5% 3 3 4 18%	4576
	11th to 20th	Day	12% 17% 6% 11% 6% 4 4 3 5% 5% 26%	4754
	21st to end	Day	19% 14% 6% 13% 5% 4 3 2 3 4 26%	6091
April	1st to 10th	Day	20% 18% 4 10% 5% 4 3 3 3 5% 24%	2520
	11th to 20th	Day	19% 16% 5% 8% 4 4 4 2 4 4 31%	2513
	21st to end	Day	22% 13% 3 8% 4 4 5% 3 5% 6% 27%	2730
May	1st to 10th	Day	25% 13% 3 8% 5% 5% 5% 4 5% 7% 20%	7831
	11th to 20th	Day	18% 9% 3 8% 6% 6% 6% 4 6% 7% 26%	8221
	21st to end	Day	21% 10% 3 7% 5% 4 5% 4 5% 6% 30%	9060
June	1st to 10th	Day	25% 9% 3 6% 4 4 5% 5% 5% 6% 28%	2940
	11th to 20th	Day	18% 7% 2 7% 5% 5% 4 4 6% 8% 33%	2870
	21st to end	Day	24% 8% 3 7% 5% 4 5% 4 6% 6% 28%	2800
July	1st to 10th	Day	15% 8% 3 8% 6% 6% 7% 5% 8% 9% 26%	6360
	11th to 20th	Day	13% 7% 3 7% 5% 5% 6% 5% 7% 9% 34%	6360
	21st to end	Day	14% 7% 3 6% 4 4 5% 4 6% 9% 39%	6926
August	1st to 10th	Day	18% 8% 3 8% 5% 5% 6% 5% 7% 8% 28%	4547
	11th to 20th	Day	17% 8% 3 8% 5% 4 6% 4 7% 9% 29%	4145
	21st to end	Day	19% 6% 3 6% 4 4 4 4 6% 8% 36%	4312
September	1st to 10th	Day	15% 7% 2 6% 4 4 5% 4 6% 6% 41%	2400
	11th to 20th	Day	17% 7% 2 5% 3 3 3 3 4 7% 44%	2260
	21st to end	Day	18% 9% 2 5% 4 4 5% 3 5% 8% 36%	2200
October	1st to 10th	Day	22% 10% 3 7% 4 4 5% 2 6% 6% 31%	2150
	11th to 20th	Day	20% 13% 3 8% 5% 4 5% 3 5% 5% 28%	1900
	21st to end	Day	25% 20% 4 8% 4 3 3 2 3 4 24%	1980
November	1st to 10th	Day	18% 19% 4 7% 5% 4 3 3 4 5% 26%	1851
	11th to 20th	Day	15% 21% 7% 11% 5% 4 4 3 4 4 22%	1890
	21st to end	Day	18% 19% 8% 13% 5% 4 4 4 5% 5% 16%	1690
December	1st to 10th	Day	14% 24% 8% 20% 9% 4 4 2 3 4 10%	2680
	11th to 20th	Day	17% 19% 7% 16% 4 5% 4 2 4 4 19%	3066
	21st to end	Day	18% 17% 6% 14% 7% 4 5% 3 3 5% 18%	4048
January	1st to 10th	Night	10% 18% 9% 20% 11% 6% 4 3 4 3 13%	8234
	11th to 20th	Night	9% 18% 9% 22% 12% 7% 5% 3 3 3 10%	8235
	21st to end	Night	8% 14% 6% 16% 10% 11% 6% 4 4 4 16%	9057
February	1st to 10th	Night	12% 17% 6% 17% 8% 6% 4 3 4 4 18%	2840
	11th to 20th	Night	11% 15% 7% 16% 9% 6% 4 4 4 4 19%	2474
	21st to end	Night	12% 18% 6% 11% 8% 7% 4 2 3 4 25%	2076
March	1st to 10th	Night	18% 16% 6% 11% 6% 6% 4 3 4 4 23%	5484
	11th to 20th	Night	13% 16% 5% 12% 6% 5% 5% 4 5% 5% 24%	5424
	21st to end	Night	14% 18% 6% 13% 7% 5% 4 3 3 3 25%	5078
April	1st to 10th	Night	21% 14% 5% 9% 5% 4 4 3 5% 6% 26%	2100
	11th to 20th	Night	21% 14% 4 6% 5% 4 5% 2 3 6% 30%	2054
	21st to end	Night	21% 11% 3 8% 5% 4 3 3 6% 5% 32%	1890
May	1st to 10th	Night	24% 13% 4 8% 5% 4 4 4 5% 7% 23%	5122
	11th to 20th	Night	21% 9% 3 8% 5% 5% 5% 4 6% 6% 29%	4639
	21st to end	Night	20% 10% 3 7% 4 5% 4 3 5% 6% 33%	5114
June	1st to 10th	Night	25% 8% 2 6% 4 4 4 3 6% 7% 31%	1680
	11th to 20th	Night	19% 7% 2 6% 4 4 4 4 6% 8% 35%	1640
	21st to end	Night	19% 9% 2 7% 5% 5% 4 5% 8% 6% 31%	1600
July	1st to 10th	Night	14% 8% 3 9% 6% 6% 5% 5% 7% 9% 29%	3600
	11th to 20th	Night	18% 7% 3 6% 4 4 4 4 5% 7% 38%	3600
	21st to end	Night	12% 7% 2 7% 5% 4 5% 4 7% 8% 38%	3926
August	1st to 10th	Night	22% 8% 3 8% 4 4 3 4 5% 6% 34%	2586
	11th to 20th	Night	14% 8% 3 9% 5% 6% 5% 4 6% 8% 33%	2882
	21st to end	Night	16% 6% 2 7% 4 4 4 4 5% 6% 40%	3586
September	1st to 10th	Night	16% 7% 3 6% 5% 4 4 3 5% 6% 42%	2000
	11th to 20th	Night	15% 7% 1 5% 3 4 4 3 5% 6% 47%	2140
	21st to end	Night	20% 7% 3 5% 4 4 4 3 5% 6% 41%	2200
October	1st to 10th	Night	20% 9% 3 6% 4 4 4 3 5% 6% 35%	2246
	11th to 20th	Night	20% 12% 4 8% 4 4 5% 3 4 5% 30%	2500
	21st to end	Night	24% 15% 4 8% 5% 4 4 3 4 5% 25%	2860
November	1st to 10th	Night	19% 15% 5% 8% 5% 4 5% 3 4 6% 26%	2667
	11th to 20th	Night	16% 17% 6% 12% 5% 4 3 3 4 5% 26%	2730
	21st to end	Night	16% 19% 7% 13% 6% 4 3 3 4 5% 20%	2924
December	1st to 10th	Night	15% 23% 10% 21% 7% 4 3 2 3 3 9%	4720
	11th to 20th	Night	17% 21% 7% 17% 6% 5% 3 2 3 3 15%	5348
	21st to end	Night	18% 18% 5% 13% 6% 5% 5% 2 3 5% 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	78% 4 8% 8% 1	4662
	11th to 20th	Day	77% 7% 6% 7% 3	4680
	21st to end	Day	71% 7% 7% 8% 7%	5124
February	1st to 10th	Day	71% 5% 6% 12% 5% 1	1779
	11th to 20th	Day	71% 4 9% 11% 4 1	2039
	21st to end	Day	66% 5% 8% 13% 6% 2	1730
March	1st to 10th	Day	68% 7% 6% 8% 7% 3	4579
	11th to 20th	Day	59% 6% 13% 12% 9% 1	4754
	21st to end	Day	62% 5% 6% 13% 14% 1	6091
April	1st to 10th	Day	63% 4 8% 16% 8% 1	2520
	11th to 20th	Day	57% 5% 7% 18% 13% 1	2513
	21st to end	Day	58% 5% 8% 17% 9% 2	2730
May	1st to 10th	Day	61% 7% 9% 16% 6%	7843
	11th to 20th	Day	52% 10% 13% 18% 6% 1	8225
	21st to end	Day	51% 7% 10% 23% 8%	9061
June	1st to 10th	Day	53% 7% 11% 19% 9% 1	2940
	11th to 20th	Day	46% 7% 12% 23% 11% 1	2870
	21st to end	Day	55% 8% 11% 18% 8% 1	2800
July	1st to 10th	Day	48% 9% 15% 21% 7%	6290
	11th to 20th	Day	41% 10% 13% 29% 7%	6285
	21st to end	Day	40% 8% 12% 33% 7%	6728
August	1st to 10th	Day	50% 9% 14% 20% 6%	4533
	11th to 20th	Day	48% 9% 17% 20% 5%	4184
	21st to end	Day	44% 7% 15% 19% 13% 1	4312
September	1st to 10th	Day	40% 8% 12% 29% 10% 1	2400
	11th to 20th	Day	39% 6% 11% 30% 14%	2260
	21st to end	Day	44% 8% 13% 23% 11% 1	2200
October	1st to 10th	Day	47% 7% 13% 25% 8%	3501
	11th to 20th	Day	50% 7% 13% 22% 7%	3077
	21st to end	Day	54% 4 14% 20% 8% 1	3180
November	1st to 10th	Day	60% 6% 10% 16% 7%	1851
	11th to 20th	Day	66% 5% 9% 12% 7% 1	1890
	21st to end	Day	69% 6% 13% 10% 2	1690
December	1st to 10th	Day	80% 4 8% 7% 2	2680
	11th to 20th	Day	67% 6% 7% 14% 5%	3066
	21st to end	Day	70% 5% 7% 10% 8% 1	4048
January	1st to 10th	Night	74% 6% 8% 8% 2	8234
	11th to 20th	Night	76% 7% 7% 6% 3	8280
	21st to end	Night	67% 8% 7% 10% 8%	9057
February	1st to 10th	Night	69% 5% 7% 13% 5%	2840
	11th to 20th	Night	68% 6% 8% 13% 6%	2476
	21st to end	Night	63% 4 9% 13% 9% 1	2076
March	1st to 10th	Night	63% 6% 8% 12% 9% 2	5494
	11th to 20th	Night	60% 7% 13% 12% 8% 1	5425
	21st to end	Night	63% 5% 5% 16% 10% 1	5078
April	1st to 10th	Night	59% 4 9% 16% 11% 1	2100
	11th to 20th	Night	56% 4 8% 19% 12% 1	2054
	21st to end	Night	53% 6% 9% 17% 13% 2	1890
May	1st to 10th	Night	58% 7% 10% 16% 8% 1	5128
	11th to 20th	Night	51% 9% 11% 21% 7% 1	4640
	21st to end	Night	50% 7% 9% 20% 13%	5115
June	1st to 10th	Night	51% 6% 10% 22% 10% 1	1680
	11th to 20th	Night	45% 7% 12% 22% 11% 3	1640
	21st to end	Night	50% 8% 13% 19% 9% 1	1600
July	1st to 10th	Night	47% 9% 17% 20% 8%	3560
	11th to 20th	Night	43% 8% 13% 28% 8%	3552
	21st to end	Night	41% 8% 15% 27% 9%	3809
August	1st to 10th	Night	49% 7% 14% 24% 6%	2576
	11th to 20th	Night	45% 11% 17% 19% 7%	2909
	21st to end	Night	41% 9% 13% 23% 13% 1	3586
September	1st to 10th	Night	40% 9% 12% 27% 12% 1	2000
	11th to 20th	Night	36% 7% 15% 29% 13% 1	2140
	21st to end	Night	43% 7% 12% 24% 13% 1	2200
October	1st to 10th	Night	49% 7% 11% 24% 10%	3675
	11th to 20th	Night	49% 7% 11% 23% 10%	4062
	21st to end	Night	52% 6% 14% 18% 9% 1	4610
November	1st to 10th	Night	58% 6% 11% 17% 6% 1	2667
	11th to 20th	Night	60% 6% 10% 14% 8% 2	2730
	21st to end	Night	67% 6% 10% 13% 4	2924
December	1st to 10th	Night	81% 5% 6% 6% 1	4720
	11th to 20th	Night	74% 6% 5% 10% 6%	5348
	21st to end	Night	69% 4 6% 13% 7%	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	28% 22% 33% 14% 4	220
	11th to 20th	Day	29% 25% 32% 9% 4 1	220
	21st to end	Day	28% 19% 36% 10% 5% 1	242
February	1st to 10th	Day	33% 31% 24% 9% 2	272
	11th to 20th	Day	29% 26% 31% 12% 2	518
	21st to end	Day	30% 23% 31% 15% 1	446
March	1st to 10th	Day	32% 19% 30% 15% 3	540
	11th to 20th	Day	32% 24% 27% 14% 3 1	540
	21st to end	Day	35% 23% 23% 13% 6% 1	594
April	1st to 10th	Day	36% 18% 27% 13% 5% 1	540
	11th to 20th	Day	36% 19% 25% 13% 5% 2	532
	21st to end	Day	34% 19% 28% 12% 6% 2	540
May	1st to 10th	Day	34% 18% 27% 15% 6% 1	543
	11th to 20th	Day	24% 19% 29% 19% 7% 2	567
	21st to end	Day	21% 21% 31% 20% 5% 1	617
June	1st to 10th	Day	29% 15% 31% 17% 8% 1	570
	11th to 20th	Day	22% 15% 32% 20% 9% 1	550
	21st to end	Day	27% 13% 33% 17% 7% 2	530
July	1st to 10th	Day	17% 13% 33% 24% 11% 2	525
	11th to 20th	Day	15% 12% 39% 25% 7% 2	524
	21st to end	Day	19% 10% 35% 26% 9% 1	576
August	1st to 10th	Day	17% 12% 27% 29% 14% 2	526
	11th to 20th	Day	18% 9% 28% 25% 15% 5%	519
	21st to end	Day	18% 16% 26% 23% 11% 5%	583
September	1st to 10th	Day	19% 11% 29% 22% 13% 5%	530
	11th to 20th	Day	17% 12% 23% 22% 21% 7%	530
	21st to end	Day	19% 15% 26% 23% 13% 4	530
October	1st to 10th	Day	24% 16% 27% 17% 12% 5%	530
	11th to 20th	Day	28% 21% 23% 19% 9% 1	475
	21st to end	Day	35% 20% 23% 16% 5%	462
November	1st to 10th	Day	34% 19% 28% 15% 4	425
	11th to 20th	Day	28% 23% 30% 13% 6% 1	430
	21st to end	Day	35% 21% 31% 10% 2	230
December	1st to 10th	Day	30% 22% 27% 14% 5% 1	220
	11th to 20th	Day	34% 25% 30% 10%	220
	21st to end	Day	34% 23% 27% 10% 4 1	242
January	1st to 10th	Night	27% 23% 30% 18% 2	840
	11th to 20th	Night	27% 22% 30% 17% 4	840
	21st to end	Night	20% 20% 33% 20% 5% 1	924
February	1st to 10th	Night	23% 20% 31% 21% 4	840
	11th to 20th	Night	22% 23% 34% 19% 3	823
	21st to end	Night	25% 18% 31% 23% 2	692
March	1st to 10th	Night	29% 17% 30% 20% 3	840
	11th to 20th	Night	28% 20% 27% 20% 6%	840
	21st to end	Night	27% 19% 27% 20% 7% 1	924
April	1st to 10th	Night	31% 16% 28% 20% 5%	840
	11th to 20th	Night	29% 18% 26% 20% 7%	810
	21st to end	Night	29% 15% 29% 20% 7%	630
May	1st to 10th	Night	26% 13% 29% 24% 7% 1	583
	11th to 20th	Night	23% 10% 31% 26% 8% 1	414
	21st to end	Night	19% 14% 27% 31% 9%	455
June	1st to 10th	Night	26% 9% 26% 27% 10% 1	420
	11th to 20th	Night	21% 9% 26% 31% 13%	410
	21st to end	Night	19% 9% 26% 35% 11% 1	400
July	1st to 10th	Night	15% 5% 29% 36% 14%	390
	11th to 20th	Night	13% 4 24% 39% 19% 1	388
	21st to end	Night	13% 6% 24% 43% 15%	438
August	1st to 10th	Night	18% 5% 17% 39% 21%	398
	11th to 20th	Night	13% 7% 22% 35% 22% 2	589
	21st to end	Night	16% 8% 23% 33% 19% 2	880
September	1st to 10th	Night	18% 8% 24% 34% 15% 1	800
	11th to 20th	Night	18% 8% 19% 30% 23% 2	800
	21st to end	Night	23% 8% 28% 25% 15% 2	800
October	1st to 10th	Night	25% 13% 22% 25% 13% 1	800
	11th to 20th	Night	27% 13% 27% 22% 10% 1	800
	21st to end	Night	30% 17% 28% 22% 4	880
November	1st to 10th	Night	29% 18% 28% 20% 5% 1	820
	11th to 20th	Night	26% 20% 28% 16% 9% 1	840
	21st to end	Night	28% 23% 27% 16% 5% 1	840
December	1st to 10th	Night	30% 25% 27% 15% 4	840
	11th to 20th	Night	29% 22% 28% 16% 4	840
	21st to end	Night	33% 21% 24% 18% 3	924

Page generated at 2026-06-13 02:31:43. Version ac07

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