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 2024-01-31.

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	19% 12% 5% 8% 6% 3 5% 4 5% 6% 27%	74918
	Night	18% 13% 5% 9% 7% 3 5% 4 4 5% 27%	75201
Transparency	Day	57% 6% 11% 17% 8% 1	74623
	Night	58% 6% 10% 16% 8% 1	75030
Seeing	Day	26% 17% 28% 18% 8% 2	13600
	Night	24% 15% 27% 24% 9% 1	22656

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% 20% 9% 15% 9% 5% 5% 3 3 3 12%	1517
	11th to 20th	Day	15% 17% 7% 15% 10% 3 5% 4 4 4 15%	1520
	21st to end	Day	10% 15% 8% 12% 9% 5% 7% 5% 5% 5% 19%	1664
February	1st to 10th	Day	13% 19% 7% 14% 9% 4 6% 4 4 4 15%	1525
	11th to 20th	Day	13% 18% 8% 14% 9% 3 5% 5% 4 4 16%	1732
	21st to end	Day	13% 16% 7% 13% 8% 5% 4 5% 4 4 20%	1480
March	1st to 10th	Day	14% 16% 7% 11% 7% 5% 4 4 4 4 24%	1797
	11th to 20th	Day	16% 16% 7% 8% 7% 4 4 3 4 4 27%	1847
	21st to end	Day	18% 15% 6% 9% 6% 4 3 3 3 4 28%	2366
April	1st to 10th	Day	21% 16% 5% 10% 6% 3 3 4 3 5% 25%	2160
	11th to 20th	Day	19% 14% 4 6% 5% 3 4 3 4 4 33%	2150
	21st to end	Day	23% 13% 4 7% 6% 3 5% 4 5% 6% 26%	2340
May	1st to 10th	Day	23% 10% 3 7% 5% 3 4 3 4 7% 31%	2394
	11th to 20th	Day	20% 8% 3 6% 6% 3 4 5% 5% 6% 33%	2478
	21st to end	Day	18% 8% 3 7% 6% 3 6% 5% 6% 7% 31%	2725
June	1st to 10th	Day	27% 8% 3 5% 5% 3 5% 6% 6% 6% 27%	2520
	11th to 20th	Day	19% 6% 3 6% 5% 4 4 4 6% 8% 34%	2520
	21st to end	Day	24% 8% 3 7% 5% 3 5% 5% 6% 7% 28%	2520
July	1st to 10th	Day	17% 7% 3 5% 6% 3 5% 4 7% 8% 35%	2520
	11th to 20th	Day	16% 6% 4 6% 5% 3 6% 6% 6% 9% 33%	2520
	21st to end	Day	17% 8% 3 6% 5% 3 6% 6% 6% 8% 31%	2744
August	1st to 10th	Day	17% 6% 3 6% 7% 4 5% 6% 6% 8% 30%	2503
	11th to 20th	Day	15% 7% 3 7% 5% 3 5% 6% 6% 9% 33%	2289
	21st to end	Day	18% 6% 3 6% 6% 3 5% 5% 6% 9% 35%	2376
September	1st to 10th	Day	17% 8% 2 5% 5% 3 5% 5% 6% 6% 39%	2160
	11th to 20th	Day	20% 7% 2 4 4 3 3 4 4 7% 43%	2034
	21st to end	Day	18% 9% 2 4 5% 3 5% 4 5% 8% 36%	1980
October	1st to 10th	Day	25% 10% 3 6% 5% 3 5% 3 6% 6% 28%	1936
	11th to 20th	Day	21% 12% 3 7% 6% 3 5% 4 6% 5% 28%	1710
	21st to end	Day	27% 20% 4 7% 5% 3 3 3 3 4 23%	1782
November	1st to 10th	Day	19% 17% 4 7% 5% 3 3 5% 5% 5% 27%	1671
	11th to 20th	Day	17% 18% 8% 10% 6% 4 3 5% 4 4 22%	1710
	21st to end	Day	18% 18% 7% 10% 7% 3 4 5% 5% 5% 18%	1530
December	1st to 10th	Day	20% 22% 9% 12% 7% 3 3 3 3 4 14%	1520
	11th to 20th	Day	18% 18% 9% 12% 5% 3 5% 3 3 4 19%	1906
	21st to end	Day	23% 17% 7% 13% 8% 3 4 4 3 4 15%	2772
January	1st to 10th	Night	16% 20% 9% 13% 9% 5% 5% 5% 5% 3 12%	2649
	11th to 20th	Night	15% 17% 7% 14% 9% 4 6% 3 3 4 16%	2660
	21st to end	Night	11% 14% 7% 14% 9% 6% 5% 5% 4 5% 19%	2919
February	1st to 10th	Night	14% 16% 7% 16% 10% 4 5% 4 4 4 17%	2434
	11th to 20th	Night	13% 13% 8% 14% 9% 5% 5% 5% 4 4 19%	2112
	21st to end	Night	13% 16% 7% 10% 9% 5% 6% 3 3 4 25%	1776
March	1st to 10th	Night	15% 16% 7% 9% 7% 4 5% 4 4 4 24%	2150
	11th to 20th	Night	17% 14% 5% 9% 7% 4 4 4 3 4 28%	2111
	21st to end	Night	18% 15% 6% 7% 5% 3 4 4 3 4 31%	1986
April	1st to 10th	Night	21% 13% 5% 8% 6% 3 4 3 4 5% 26%	1800
	11th to 20th	Night	20% 12% 4 5% 6% 3 5% 4 3 6% 32%	1757
	21st to end	Night	22% 11% 4 7% 6% 3 3 4 5% 5% 31%	1620
May	1st to 10th	Night	21% 10% 4 7% 6% 3 5% 5% 4 6% 30%	1580
	11th to 20th	Night	19% 8% 3 8% 6% 2 4 5% 4 5% 36%	1415
	21st to end	Night	18% 7% 3 6% 5% 4 6% 5% 5% 7% 35%	1550
June	1st to 10th	Night	26% 8% 3 5% 4 3 4 4 6% 7% 30%	1440
	11th to 20th	Night	19% 6% 2 6% 5% 2 5% 5% 6% 9% 36%	1440
	21st to end	Night	18% 8% 3 6% 5% 3 5% 6% 8% 7% 31%	1440
July	1st to 10th	Night	14% 7% 4 7% 5% 3 5% 6% 7% 8% 36%	1440
	11th to 20th	Night	11% 4 2 6% 5% 3 7% 7% 7% 9% 38%	1440
	21st to end	Night	13% 7% 2 6% 6% 3 5% 5% 6% 8% 38%	1574
August	1st to 10th	Night	16% 5% 2 6% 5% 3 4 6% 7% 9% 38%	1432
	11th to 20th	Night	14% 7% 3 6% 6% 3 5% 5% 6% 8% 38%	1592
	21st to end	Night	14% 7% 2 6% 5% 3 4 5% 6% 7% 39%	1980
September	1st to 10th	Night	16% 7% 3 5% 6% 3 4 4 5% 6% 41%	1800
	11th to 20th	Night	16% 7% 2 4 3 3 4 4 5% 6% 45%	1926
	21st to end	Night	20% 6% 2 4 4 3 4 4 5% 7% 41%	1980
October	1st to 10th	Night	21% 9% 3 5% 5% 3 4 4 5% 6% 34%	2020
	11th to 20th	Night	21% 12% 4 7% 6% 3 5% 4 4 5% 28%	2250
	21st to end	Night	25% 14% 4 7% 6% 3 4 4 4 5% 25%	2574
November	1st to 10th	Night	19% 14% 5% 7% 6% 4 5% 5% 4 6% 26%	2407
	11th to 20th	Night	17% 15% 6% 10% 6% 3 4 3 4 6% 26%	2470
	21st to end	Night	17% 17% 7% 11% 8% 3 3 3 4 5% 21%	2645
December	1st to 10th	Night	20% 22% 8% 11% 8% 3 4 4 3 4 13%	2660
	11th to 20th	Night	19% 20% 8% 14% 8% 3 4 3 3 3 15%	3288
	21st to end	Night	23% 18% 6% 13% 7% 3 4 3 3 4 16%	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	78% 4 7% 9% 2	1518
	11th to 20th	Day	73% 6% 7% 9% 5%	1520
	21st to end	Day	66% 5% 10% 12% 5% 1	1664
February	1st to 10th	Day	74% 4 6% 11% 4 1	1525
	11th to 20th	Day	72% 4 10% 10% 4 1	1741
	21st to end	Day	66% 5% 8% 12% 6% 2	1480
March	1st to 10th	Day	65% 5% 9% 14% 6% 2	1800
	11th to 20th	Day	60% 5% 11% 12% 10% 1	1847
	21st to end	Day	61% 3 7% 18% 9% 2	2366
April	1st to 10th	Day	63% 4 8% 16% 8% 1	2160
	11th to 20th	Day	55% 5% 7% 19% 13% 1	2150
	21st to end	Day	60% 5% 8% 15% 9% 3	2340
May	1st to 10th	Day	54% 4 7% 20% 13% 2	2394
	11th to 20th	Day	50% 6% 10% 19% 13% 1	2482
	21st to end	Day	50% 8% 13% 17% 11% 1	2725
June	1st to 10th	Day	54% 7% 11% 18% 8% 1	2520
	11th to 20th	Day	47% 6% 11% 23% 11% 2	2520
	21st to end	Day	55% 8% 11% 17% 8% 1	2520
July	1st to 10th	Day	44% 8% 14% 24% 10%	2450
	11th to 20th	Day	45% 9% 13% 27% 6%	2445
	21st to end	Day	48% 9% 14% 22% 6% 1	2591
August	1st to 10th	Day	48% 10% 16% 21% 5%	2489
	11th to 20th	Day	46% 8% 16% 20% 10%	2289
	21st to end	Day	45% 7% 13% 23% 11%	2376
September	1st to 10th	Day	43% 8% 13% 25% 11% 1	2160
	11th to 20th	Day	41% 6% 10% 29% 13%	2034
	21st to end	Day	45% 8% 13% 23% 10% 1	1980
October	1st to 10th	Day	57% 6% 11% 17% 8%	1936
	11th to 20th	Day	56% 6% 15% 17% 6%	1710
	21st to end	Day	68% 4 9% 13% 6% 1	1782
November	1st to 10th	Day	58% 6% 11% 17% 8%	1671
	11th to 20th	Day	66% 5% 9% 11% 7% 2	1710
	21st to end	Day	66% 6% 14% 11% 3	1530
December	1st to 10th	Day	76% 4 9% 8% 3	1520
	11th to 20th	Day	68% 5% 8% 13% 5%	1906
	21st to end	Day	74% 6% 8% 9% 4	2772
January	1st to 10th	Night	75% 6% 8% 8% 3	2649
	11th to 20th	Night	73% 5% 8% 10% 4	2660
	21st to end	Night	66% 6% 9% 11% 7% 1	2919
February	1st to 10th	Night	72% 5% 7% 11% 5%	2434
	11th to 20th	Night	68% 5% 8% 13% 6%	2114
	21st to end	Night	64% 4 9% 13% 10% 1	1776
March	1st to 10th	Night	64% 4 9% 15% 7% 1	2160
	11th to 20th	Night	59% 6% 9% 14% 10% 2	2112
	21st to end	Night	58% 4 7% 18% 11% 3	1986
April	1st to 10th	Night	61% 4 9% 15% 11% 1	1800
	11th to 20th	Night	53% 4 9% 20% 13% 1	1757
	21st to end	Night	55% 6% 9% 17% 12% 2	1620
May	1st to 10th	Night	55% 5% 7% 18% 14% 2	1580
	11th to 20th	Night	49% 7% 10% 16% 16% 2	1416
	21st to end	Night	48% 8% 11% 21% 12% 1	1551
June	1st to 10th	Night	51% 6% 11% 22% 8% 1	1440
	11th to 20th	Night	44% 7% 12% 23% 11% 3	1440
	21st to end	Night	49% 9% 14% 19% 9%	1440
July	1st to 10th	Night	42% 9% 13% 22% 13% 1	1400
	11th to 20th	Night	37% 10% 15% 29% 8%	1392
	21st to end	Night	42% 9% 15% 25% 8%	1486
August	1st to 10th	Night	38% 9% 20% 25% 7%	1422
	11th to 20th	Night	41% 10% 16% 22% 10%	1592
	21st to end	Night	41% 9% 15% 24% 11%	1980
September	1st to 10th	Night	41% 9% 13% 25% 12% 1	1800
	11th to 20th	Night	38% 8% 15% 28% 11% 1	1926
	21st to end	Night	42% 7% 13% 25% 11% 1	1980
October	1st to 10th	Night	51% 7% 11% 21% 11%	2020
	11th to 20th	Night	56% 7% 11% 19% 6%	2250
	21st to end	Night	61% 6% 10% 13% 8% 1	2574
November	1st to 10th	Night	58% 6% 11% 17% 7% 1	2407
	11th to 20th	Night	60% 6% 10% 14% 8% 2	2470
	21st to end	Night	66% 6% 11% 14% 4	2645
December	1st to 10th	Night	76% 5% 8% 8% 2	2660
	11th to 20th	Night	75% 4 7% 8% 5%	3288
	21st to end	Night	73% 5% 7% 12% 3	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	27% 19% 34% 16% 4	180
	11th to 20th	Day	28% 25% 32% 10% 4 1	180
	21st to end	Day	26% 20% 34% 13% 7% 1	196
February	1st to 10th	Day	40% 31% 21% 8% 1	198
	11th to 20th	Day	30% 27% 30% 10% 3	400
	21st to end	Day	29% 22% 30% 17% 1	346
March	1st to 10th	Day	30% 18% 31% 16% 4	420
	11th to 20th	Day	29% 24% 27% 14% 4 1	420
	21st to end	Day	32% 22% 24% 14% 7% 1	462
April	1st to 10th	Day	35% 17% 28% 14% 6% 1	420
	11th to 20th	Day	35% 17% 25% 14% 6% 3	412
	21st to end	Day	34% 17% 29% 13% 5% 2	420
May	1st to 10th	Day	33% 17% 28% 15% 6% 2	423
	11th to 20th	Day	22% 18% 30% 19% 7% 3	447
	21st to end	Day	20% 19% 32% 21% 6% 2	485
June	1st to 10th	Day	32% 15% 30% 16% 6% 1	450
	11th to 20th	Day	21% 15% 30% 22% 11% 2	450
	21st to end	Day	25% 12% 33% 19% 8% 2	450
July	1st to 10th	Day	19% 11% 31% 25% 12% 2	445
	11th to 20th	Day	15% 11% 37% 26% 9% 3	444
	21st to end	Day	20% 9% 34% 26% 10% 1	488
August	1st to 10th	Day	17% 12% 26% 28% 15% 2	446
	11th to 20th	Day	18% 9% 28% 26% 16% 5%	439
	21st to end	Day	18% 14% 26% 23% 12% 6%	495
September	1st to 10th	Day	19% 11% 29% 22% 13% 6%	450
	11th to 20th	Day	19% 12% 24% 20% 18% 7%	450
	21st to end	Day	18% 14% 26% 24% 14% 5%	450
October	1st to 10th	Day	26% 16% 25% 16% 12% 5%	450
	11th to 20th	Day	29% 20% 22% 18% 10% 1	405
	21st to end	Day	37% 19% 22% 17% 5%	396
November	1st to 10th	Day	31% 18% 29% 16% 5% 1	365
	11th to 20th	Day	29% 23% 29% 12% 6% 2	370
	21st to end	Day	32% 18% 35% 13% 3	190
December	1st to 10th	Day	32% 23% 24% 14% 6% 2	180
	11th to 20th	Day	32% 26% 29% 12% 1 1	180
	21st to end	Day	35% 24% 27% 11% 4	198
January	1st to 10th	Night	28% 21% 29% 19% 3 1	760
	11th to 20th	Night	26% 22% 30% 17% 4	760
	21st to end	Night	20% 20% 33% 22% 5% 1	835
February	1st to 10th	Night	24% 20% 32% 20% 4	720
	11th to 20th	Night	21% 23% 34% 19% 4	703
	21st to end	Night	26% 18% 31% 23% 3	592
March	1st to 10th	Night	28% 16% 30% 21% 4	720
	11th to 20th	Night	28% 19% 27% 20% 6%	720
	21st to end	Night	27% 18% 26% 21% 8% 1	792
April	1st to 10th	Night	30% 16% 28% 20% 6%	720
	11th to 20th	Night	27% 17% 27% 21% 8%	693
	21st to end	Night	29% 15% 29% 20% 7%	540
May	1st to 10th	Night	25% 12% 29% 25% 8% 1	500
	11th to 20th	Night	23% 10% 32% 26% 8% 1	354
	21st to end	Night	19% 12% 27% 32% 9% 1	389
June	1st to 10th	Night	27% 9% 27% 27% 9% 1	360
	11th to 20th	Night	21% 6% 27% 33% 14%	360
	21st to end	Night	18% 8% 24% 37% 12% 1	360
July	1st to 10th	Night	15% 5% 29% 36% 14%	350
	11th to 20th	Night	12% 3 26% 39% 20% 1	348
	21st to end	Night	12% 6% 23% 42% 16%	394
August	1st to 10th	Night	17% 5% 18% 39% 21%	358
	11th to 20th	Night	14% 6% 22% 36% 21% 2	528
	21st to end	Night	16% 7% 23% 33% 19% 2	792
September	1st to 10th	Night	18% 8% 23% 35% 14% 1	720
	11th to 20th	Night	20% 8% 21% 30% 19% 2	720
	21st to end	Night	23% 8% 28% 24% 16% 2	720
October	1st to 10th	Night	26% 13% 22% 25% 13% 1	720
	11th to 20th	Night	28% 13% 26% 21% 10% 1	720
	21st to end	Night	30% 17% 28% 21% 4	792
November	1st to 10th	Night	27% 17% 30% 20% 5% 1	740
	11th to 20th	Night	25% 20% 28% 16% 9% 1	760
	21st to end	Night	28% 23% 26% 17% 5% 1	760
December	1st to 10th	Night	31% 24% 26% 15% 4	760
	11th to 20th	Night	28% 22% 28% 17% 5% 1	760
	21st to end	Night	33% 21% 25% 18% 3	836

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