St-Jean-Sur-Richelieu
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the St-Jean-Sur-Richelieu clear sky chart from 2005-11-06 to 2026-06-01.

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% 3 8% 5% 5% 5% 4 5% 7% 31%	132136
	Night	18% 12% 4 9% 5% 5% 4 3 5% 6% 29%	131027
Transparency	Day	52% 7% 12% 20% 9% 1	135580
	Night	56% 6% 10% 18% 10% 1	135657
Seeing	Day	22% 12% 28% 23% 12% 3	16537
	Night	24% 10% 28% 28% 10% 1	25551

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% 6% 15% 6% 5% 4 3 3 5% 18%	4661
	11th to 20th	Day	12% 17% 7% 15% 7% 6% 5% 4 4 5% 19%	4650
	21st to end	Day	11% 14% 5% 12% 8% 6% 6% 5% 5% 6% 23%	5124
February	1st to 10th	Day	16% 14% 5% 13% 7% 6% 5% 3 4 5% 24%	1825
	11th to 20th	Day	14% 14% 5% 11% 6% 5% 5% 3 5% 6% 26%	1981
	21st to end	Day	16% 16% 4 8% 7% 5% 5% 4 4 7% 25%	1730
March	1st to 10th	Day	18% 12% 5% 10% 7% 5% 6% 4 5% 5% 25%	4576
	11th to 20th	Day	14% 14% 4 9% 5% 4 4 4 5% 7% 30%	4774
	21st to end	Day	18% 11% 4 9% 5% 5% 4 3 4 5% 32%	6102
April	1st to 10th	Day	22% 11% 3 8% 6% 4 4 3 5% 6% 30%	2520
	11th to 20th	Day	21% 10% 3 6% 4 4 3 3 5% 6% 35%	2494
	21st to end	Day	22% 9% 3 7% 5% 4 5% 3 4 6% 32%	2709
May	1st to 10th	Day	27% 11% 4 9% 4 4 4 3 5% 5% 23%	6313
	11th to 20th	Day	20% 7% 3 7% 5% 5% 5% 4 6% 7% 31%	6458
	21st to end	Day	20% 9% 2 7% 5% 4 5% 4 6% 7% 31%	7103
June	1st to 10th	Day	21% 7% 2 7% 6% 4 5% 4 6% 7% 31%	2800
	11th to 20th	Day	15% 6% 3 6% 5% 4 5% 4 7% 8% 38%	2800
	21st to end	Day	22% 7% 3 6% 5% 4 5% 4 5% 7% 33%	2800
July	1st to 10th	Day	13% 7% 3 8% 5% 6% 6% 5% 7% 9% 32%	6360
	11th to 20th	Day	11% 6% 2 6% 4 5% 6% 4 7% 9% 41%	6360
	21st to end	Day	12% 6% 2 5% 4 4 4 4 6% 9% 44%	6926
August	1st to 10th	Day	14% 7% 3 8% 5% 5% 5% 4 7% 9% 33%	4563
	11th to 20th	Day	13% 7% 3 6% 5% 5% 4 4 6% 9% 39%	4119
	21st to end	Day	15% 5% 2 7% 4 4 4 4 7% 8% 41%	4312
September	1st to 10th	Day	12% 5% 2 6% 4 4 5% 4 6% 8% 45%	2400
	11th to 20th	Day	14% 6% 2 5% 3 3 3 3 5% 7% 49%	2295
	21st to end	Day	15% 6% 2 7% 5% 4 4 4 6% 7% 40%	2200
October	1st to 10th	Day	20% 6% 2 7% 4 5% 4 4 5% 7% 35%	2095
	11th to 20th	Day	19% 8% 3 7% 5% 5% 5% 4 7% 6% 30%	1938
	21st to end	Day	26% 10% 3 7% 5% 4 3 3 5% 6% 29%	1980
November	1st to 10th	Day	19% 12% 3 6% 6% 4 4 4 4 6% 32%	1851
	11th to 20th	Day	17% 12% 4 8% 6% 5% 5% 4 5% 6% 27%	1843
	21st to end	Day	23% 14% 4 9% 6% 5% 3 4 5% 5% 23%	1680
December	1st to 10th	Day	18% 22% 6% 11% 6% 4 5% 3 4 4 16%	2680
	11th to 20th	Day	20% 13% 4 11% 5% 5% 4 4 5% 6% 24%	3066
	21st to end	Day	23% 14% 5% 10% 5% 5% 5% 6% 6% 3 18%	4048
January	1st to 10th	Night	14% 22% 8% 13% 6% 4 4 3 4 4 20%	8234
	11th to 20th	Night	12% 18% 7% 16% 8% 7% 5% 3 5% 5% 15%	8235
	21st to end	Night	12% 14% 5% 12% 9% 6% 5% 3 4 5% 24%	9057
February	1st to 10th	Night	16% 16% 6% 13% 6% 5% 5% 3 5% 5% 21%	2793
	11th to 20th	Night	15% 12% 5% 11% 7% 6% 4 4 5% 5% 26%	2525
	21st to end	Night	17% 13% 4 10% 5% 5% 4 3 4 5% 30%	2076
March	1st to 10th	Night	20% 13% 5% 8% 6% 4 4 3 4 5% 30%	5484
	11th to 20th	Night	16% 14% 4 8% 5% 5% 5% 3 5% 7% 29%	5389
	21st to end	Night	16% 13% 4 10% 5% 5% 5% 3 4 5% 30%	5072
April	1st to 10th	Night	24% 10% 3 7% 5% 4 4 3 5% 6% 29%	2100
	11th to 20th	Night	23% 10% 2 8% 4 4 4 3 5% 5% 32%	2075
	21st to end	Night	20% 10% 2 7% 5% 4 3 3 5% 5% 36%	1911
May	1st to 10th	Night	25% 11% 4 8% 5% 4 4 3 5% 6% 24%	3891
	11th to 20th	Night	24% 9% 3 8% 4 4 4 3 5% 6% 30%	3655
	21st to end	Night	19% 8% 4 8% 5% 4 4 3 5% 7% 32%	4014
June	1st to 10th	Night	23% 8% 3 6% 4 4 4 4 5% 7% 32%	1600
	11th to 20th	Night	17% 5% 2 7% 5% 4 4 4 7% 7% 37%	1600
	21st to end	Night	19% 6% 3 7% 6% 4 5% 4 5% 7% 34%	1600
July	1st to 10th	Night	13% 7% 3 8% 6% 5% 5% 4 7% 9% 34%	3600
	11th to 20th	Night	14% 7% 2 7% 4 4 5% 4 5% 7% 41%	3600
	21st to end	Night	10% 5% 3 7% 5% 5% 5% 4 6% 8% 42%	3926
August	1st to 10th	Night	17% 7% 3 7% 5% 4 4 3 5% 7% 37%	2586
	11th to 20th	Night	15% 7% 2 9% 4 5% 4 4 6% 6% 38%	2895
	21st to end	Night	17% 6% 2 6% 5% 4 4 4 5% 6% 40%	3586
September	1st to 10th	Night	13% 6% 2 7% 4 4 5% 4 5% 6% 44%	2000
	11th to 20th	Night	14% 5% 2 5% 3 4 3 3 4 7% 48%	2105
	21st to end	Night	18% 7% 3 6% 4 4 5% 3 5% 5% 42%	2200
October	1st to 10th	Night	18% 7% 3 6% 3 4 5% 3 6% 7% 39%	2301
	11th to 20th	Night	21% 8% 3 7% 5% 4 4 4 5% 6% 33%	2460
	21st to end	Night	24% 9% 3 8% 4 4 4 3 4 5% 29%	2860
November	1st to 10th	Night	21% 10% 3 7% 4 4 5% 4 6% 6% 31%	2667
	11th to 20th	Night	20% 11% 3 9% 5% 4 4 4 5% 6% 31%	2772
	21st to end	Night	22% 13% 4 10% 6% 5% 4 3 4 5% 25%	2940
December	1st to 10th	Night	18% 21% 7% 13% 7% 5% 4 3 4 4 15%	4720
	11th to 20th	Night	23% 14% 5% 11% 5% 4 4 3 4 4 23%	5348
	21st to end	Night	24% 15% 5% 9% 4 4 4 4 6% 5% 19%	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	69% 5% 10% 14% 2	4662
	11th to 20th	Day	67% 6% 8% 11% 8% 1	4680
	21st to end	Day	61% 7% 8% 13% 10%	5124
February	1st to 10th	Day	63% 6% 8% 16% 6% 1	1825
	11th to 20th	Day	60% 5% 11% 17% 6% 1	1990
	21st to end	Day	59% 5% 12% 15% 8% 1	1730
March	1st to 10th	Day	61% 5% 8% 15% 9% 2	4579
	11th to 20th	Day	53% 6% 16% 14% 10% 1	4774
	21st to end	Day	55% 4 7% 17% 16% 1	6102
April	1st to 10th	Day	56% 5% 9% 18% 11% 1	2520
	11th to 20th	Day	51% 5% 8% 21% 14% 1	2494
	21st to end	Day	53% 6% 9% 19% 11% 2	2709
May	1st to 10th	Day	62% 6% 7% 17% 7% 1	6324
	11th to 20th	Day	50% 8% 14% 18% 8% 1	6462
	21st to end	Day	51% 6% 11% 20% 10% 1	7103
June	1st to 10th	Day	51% 7% 10% 19% 11% 1	2800
	11th to 20th	Day	42% 7% 11% 24% 13% 2	2800
	21st to end	Day	50% 8% 11% 21% 9% 1	2800
July	1st to 10th	Day	46% 8% 13% 25% 9%	6290
	11th to 20th	Day	38% 7% 13% 30% 11%	6285
	21st to end	Day	35% 7% 13% 37% 8%	6728
August	1st to 10th	Day	45% 8% 16% 23% 8%	4549
	11th to 20th	Day	41% 8% 18% 26% 7%	4160
	21st to end	Day	40% 7% 17% 21% 14%	4312
September	1st to 10th	Day	36% 9% 13% 31% 11%	2400
	11th to 20th	Day	35% 6% 11% 33% 14%	2295
	21st to end	Day	42% 8% 13% 26% 11% 1	2200
October	1st to 10th	Day	44% 6% 14% 28% 8%	3407
	11th to 20th	Day	44% 7% 17% 25% 6%	3128
	21st to end	Day	48% 5% 17% 22% 7% 1	3180
November	1st to 10th	Day	53% 7% 12% 19% 8% 1	1851
	11th to 20th	Day	56% 7% 11% 16% 9%	1843
	21st to end	Day	63% 8% 11% 13% 5%	1680
December	1st to 10th	Day	71% 6% 8% 12% 2	2680
	11th to 20th	Day	61% 6% 9% 16% 8%	3066
	21st to end	Day	68% 6% 10% 10% 6%	4048
January	1st to 10th	Night	68% 5% 10% 12% 4	8234
	11th to 20th	Night	71% 6% 7% 10% 5%	8280
	21st to end	Night	63% 5% 8% 13% 11%	9057
February	1st to 10th	Night	65% 5% 8% 15% 6% 1	2793
	11th to 20th	Night	59% 7% 9% 17% 8%	2527
	21st to end	Night	58% 5% 8% 16% 12% 1	2076
March	1st to 10th	Night	58% 5% 7% 14% 11% 4	5494
	11th to 20th	Night	55% 5% 13% 15% 11% 1	5390
	21st to end	Night	56% 5% 7% 20% 11% 2	5072
April	1st to 10th	Night	56% 5% 8% 17% 12% 1	2100
	11th to 20th	Night	54% 5% 7% 20% 13% 1	2075
	21st to end	Night	51% 5% 8% 19% 15% 3	1911
May	1st to 10th	Night	60% 6% 9% 16% 7% 2	3897
	11th to 20th	Night	54% 6% 9% 20% 9% 1	3656
	21st to end	Night	52% 6% 9% 18% 14% 1	4015
June	1st to 10th	Night	52% 6% 8% 21% 12% 1	1600
	11th to 20th	Night	44% 6% 12% 20% 14% 3	1600
	21st to end	Night	48% 8% 10% 20% 13% 1	1600
July	1st to 10th	Night	45% 8% 16% 21% 9%	3560
	11th to 20th	Night	41% 6% 13% 28% 11%	3552
	21st to end	Night	39% 7% 13% 28% 13%	3809
August	1st to 10th	Night	47% 7% 12% 26% 8%	2576
	11th to 20th	Night	45% 8% 17% 22% 9%	2920
	21st to end	Night	43% 7% 12% 23% 14% 1	3586
September	1st to 10th	Night	40% 8% 11% 27% 15% 1	2000
	11th to 20th	Night	36% 6% 13% 31% 13% 1	2105
	21st to end	Night	43% 8% 9% 24% 15% 1	2200
October	1st to 10th	Night	45% 6% 12% 27% 10%	3769
	11th to 20th	Night	46% 6% 10% 29% 9%	3996
	21st to end	Night	50% 5% 13% 19% 12% 1	4610
November	1st to 10th	Night	53% 6% 12% 20% 8% 1	2667
	11th to 20th	Night	55% 6% 11% 17% 10% 1	2772
	21st to end	Night	62% 6% 11% 15% 6%	2940
December	1st to 10th	Night	74% 5% 10% 9% 3	4720
	11th to 20th	Night	65% 5% 8% 14% 9%	5348
	21st to end	Night	65% 6% 8% 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	29% 15% 28% 19% 9% 1	220
	11th to 20th	Day	26% 17% 35% 16% 5%	220
	21st to end	Day	17% 18% 33% 20% 10% 1	242
February	1st to 10th	Day	26% 20% 32% 17% 4	297
	11th to 20th	Day	25% 15% 35% 21% 4	469
	21st to end	Day	26% 14% 33% 24% 4	446
March	1st to 10th	Day	25% 12% 31% 25% 6%	540
	11th to 20th	Day	26% 14% 34% 19% 7% 1	540
	21st to end	Day	28% 16% 27% 21% 7% 1	594
April	1st to 10th	Day	31% 15% 27% 19% 8% 1	540
	11th to 20th	Day	30% 18% 26% 16% 8% 3	532
	21st to end	Day	26% 13% 32% 16% 11% 3	540
May	1st to 10th	Day	25% 14% 29% 18% 11% 2	543
	11th to 20th	Day	20% 10% 31% 25% 12% 3	567
	21st to end	Day	20% 10% 33% 25% 11% 2	617
June	1st to 10th	Day	22% 10% 26% 29% 10% 2	530
	11th to 20th	Day	16% 10% 27% 28% 16% 2	530
	21st to end	Day	22% 10% 30% 23% 14% 2	530
July	1st to 10th	Day	14% 6% 26% 32% 18% 5%	525
	11th to 20th	Day	13% 8% 29% 31% 14% 5%	524
	21st to end	Day	15% 7% 24% 32% 20% 2	576
August	1st to 10th	Day	13% 6% 22% 31% 21% 6%	526
	11th to 20th	Day	12% 7% 23% 32% 19% 7%	519
	21st to end	Day	16% 8% 25% 24% 19% 8%	583
September	1st to 10th	Day	13% 10% 25% 26% 18% 8%	530
	11th to 20th	Day	15% 7% 18% 26% 23% 12%	530
	21st to end	Day	16% 8% 28% 23% 19% 6%	530
October	1st to 10th	Day	19% 10% 30% 20% 16% 5%	530
	11th to 20th	Day	23% 14% 30% 20% 12% 2	495
	21st to end	Day	34% 13% 23% 23% 7%	462
November	1st to 10th	Day	31% 15% 26% 20% 7%	425
	11th to 20th	Day	25% 18% 28% 18% 9% 2	383
	21st to end	Day	34% 15% 29% 15% 6%	220
December	1st to 10th	Day	31% 16% 22% 21% 7% 2	220
	11th to 20th	Day	26% 19% 36% 14% 5%	220
	21st to end	Day	30% 17% 30% 17% 4 3	242
January	1st to 10th	Night	28% 11% 31% 24% 4 1	840
	11th to 20th	Night	26% 14% 33% 22% 6%	840
	21st to end	Night	20% 12% 32% 28% 7% 1	924
February	1st to 10th	Night	24% 10% 33% 28% 5%	840
	11th to 20th	Night	22% 12% 36% 26% 4	823
	21st to end	Night	25% 12% 30% 29% 5%	692
March	1st to 10th	Night	25% 13% 31% 26% 5%	840
	11th to 20th	Night	28% 13% 29% 24% 7%	840
	21st to end	Night	26% 12% 29% 26% 6% 1	924
April	1st to 10th	Night	28% 10% 30% 27% 5%	840
	11th to 20th	Night	28% 13% 29% 23% 7%	831
	21st to end	Night	26% 11% 29% 25% 8% 1	651
May	1st to 10th	Night	24% 8% 31% 26% 10% 1	520
	11th to 20th	Night	22% 7% 32% 30% 8% 1	414
	21st to end	Night	19% 7% 32% 33% 9% 1	455
June	1st to 10th	Night	27% 6% 27% 30% 10% 1	400
	11th to 20th	Night	20% 5% 29% 34% 13%	400
	21st to end	Night	18% 9% 24% 35% 14% 1	400
July	1st to 10th	Night	14% 3 28% 40% 14% 1	390
	11th to 20th	Night	11% 4 22% 47% 16% 1	388
	21st to end	Night	14% 3 21% 46% 15% 1	438
August	1st to 10th	Night	14% 3 17% 45% 20% 1	398
	11th to 20th	Night	14% 5% 21% 36% 24% 2	599
	21st to end	Night	16% 6% 19% 38% 20% 2	880
September	1st to 10th	Night	15% 6% 22% 38% 17% 2	800
	11th to 20th	Night	16% 6% 17% 34% 24% 3	800
	21st to end	Night	20% 6% 28% 28% 16% 3	800
October	1st to 10th	Night	22% 6% 28% 29% 15% 1	800
	11th to 20th	Night	27% 8% 28% 28% 8% 1	800
	21st to end	Night	28% 10% 32% 25% 6%	880
November	1st to 10th	Night	26% 13% 30% 23% 7% 1	820
	11th to 20th	Night	26% 13% 30% 23% 8% 1	840
	21st to end	Night	30% 13% 31% 19% 7%	840
December	1st to 10th	Night	32% 14% 28% 22% 5%	840
	11th to 20th	Night	30% 13% 31% 19% 5% 1	840
	21st to end	Night	34% 11% 31% 19% 5%	924

Page generated at 2026-05-29 01:53:28. Version ac07

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