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 2025-02-06.

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%	108453
	Night	18% 12% 4 9% 5% 4 4 3 5% 6% 29%	109806
Transparency	Day	51% 7% 12% 20% 9% 1	111945
	Night	56% 6% 10% 18% 10% 1	114465
Seeing	Day	22% 11% 27% 23% 13% 3	14821
	Night	24% 9% 28% 28% 10% 1	23915

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	17% 21% 7% 13% 5% 5% 3 2 3 4 18%	3597
	11th to 20th	Day	13% 17% 7% 13% 7% 6% 6% 3 4 5% 19%	3570
	21st to end	Day	13% 16% 5% 11% 5% 5% 5% 4 5% 6% 25%	3960
February	1st to 10th	Day	17% 15% 5% 13% 6% 5% 5% 3 4 5% 23%	1693
	11th to 20th	Day	14% 15% 5% 11% 6% 5% 5% 3 5% 5% 26%	1787
	21st to end	Day	16% 16% 4 7% 6% 5% 5% 4 4 6% 26%	1570
March	1st to 10th	Day	19% 12% 4 9% 6% 4 5% 3 4 6% 27%	3116
	11th to 20th	Day	15% 17% 5% 10% 6% 5% 4 3 5% 6% 26%	3269
	21st to end	Day	15% 10% 3 9% 5% 4 4 3 4 5% 37%	4166
April	1st to 10th	Day	23% 11% 3 8% 6% 4 4 3 5% 5% 30%	2280
	11th to 20th	Day	21% 9% 2 6% 4 4 3 3 5% 6% 36%	2254
	21st to end	Day	23% 9% 3 7% 5% 4 4 3 4 6% 32%	2451
May	1st to 10th	Day	22% 9% 3 8% 4 4 5% 3 6% 6% 29%	4313
	11th to 20th	Day	18% 8% 3 8% 5% 5% 5% 4 5% 8% 31%	4398
	21st to end	Day	14% 7% 2 7% 5% 5% 5% 4 7% 9% 35%	4837
June	1st to 10th	Day	21% 7% 2 7% 6% 4 5% 4 6% 8% 30%	2660
	11th to 20th	Day	15% 6% 3 6% 5% 4 5% 4 7% 8% 38%	2660
	21st to end	Day	22% 7% 3 6% 5% 4 5% 4 5% 7% 32%	2660
July	1st to 10th	Day	12% 6% 2 7% 5% 5% 5% 4 7% 10% 37%	4440
	11th to 20th	Day	12% 6% 3 6% 4 5% 6% 5% 7% 9% 38%	4440
	21st to end	Day	13% 6% 2 5% 4 4 5% 4 6% 8% 43%	4814
August	1st to 10th	Day	15% 7% 3 8% 5% 5% 5% 4 7% 9% 32%	4423
	11th to 20th	Day	13% 7% 2 6% 5% 5% 4 4 6% 10% 38%	3991
	21st to end	Day	15% 5% 2 6% 4 4 4 4 7% 8% 41%	4180
September	1st to 10th	Day	13% 5% 2 6% 4 4 5% 4 6% 8% 44%	2280
	11th to 20th	Day	15% 6% 2 5% 3 3 3 3 5% 7% 48%	2180
	21st to end	Day	15% 6% 2 7% 5% 4 4 4 6% 7% 40%	2090
October	1st to 10th	Day	21% 7% 2 7% 4 5% 5% 4 5% 7% 32%	1990
	11th to 20th	Day	19% 9% 3 7% 5% 5% 5% 4 7% 6% 29%	1841
	21st to end	Day	26% 10% 2 7% 5% 5% 3 3 5% 6% 29%	1881
November	1st to 10th	Day	19% 11% 3 6% 6% 4 4 4 4 6% 33%	1761
	11th to 20th	Day	17% 11% 4 8% 6% 5% 5% 4 5% 6% 28%	1755
	21st to end	Day	23% 13% 4 8% 6% 5% 3 4 5% 5% 23%	1600
December	1st to 10th	Day	18% 22% 7% 12% 6% 4 5% 3 4 4 16%	2600
	11th to 20th	Day	20% 13% 4 11% 5% 5% 4 4 5% 6% 24%	2986
	21st to end	Day	23% 14% 5% 10% 5% 5% 5% 6% 6% 3 18%	3960
January	1st to 10th	Night	15% 24% 8% 12% 5% 4 3 3 3 4 18%	6349
	11th to 20th	Night	10% 17% 7% 16% 7% 6% 6% 3 5% 5% 16%	6315
	21st to end	Night	15% 16% 6% 12% 7% 5% 5% 3 4 5% 23%	6996
February	1st to 10th	Night	17% 17% 6% 12% 6% 5% 5% 3 5% 5% 20%	2596
	11th to 20th	Night	15% 12% 4 11% 7% 6% 4 4 5% 5% 26%	2279
	21st to end	Night	18% 13% 3 10% 5% 5% 4 3 4 5% 30%	1884
March	1st to 10th	Night	21% 11% 4 7% 5% 4 4 3 4 5% 32%	3724
	11th to 20th	Night	19% 19% 4 9% 5% 4 3 2 3 4 28%	3688
	21st to end	Night	14% 12% 4 9% 5% 5% 5% 3 4 5% 36%	3466
April	1st to 10th	Night	24% 10% 3 7% 5% 4 4 3 5% 6% 29%	1900
	11th to 20th	Night	23% 9% 2 7% 4 4 4 3 5% 5% 33%	1875
	21st to end	Night	21% 11% 2 6% 5% 4 3 3 4 5% 35%	1729
May	1st to 10th	Night	22% 10% 3 8% 5% 4 4 3 5% 7% 29%	2656
	11th to 20th	Night	23% 9% 3 7% 4 3 4 3 4 6% 34%	2495
	21st to end	Night	17% 7% 2 7% 4 4 5% 4 5% 8% 38%	2738
June	1st to 10th	Night	23% 8% 3 5% 4 4 4 4 5% 7% 31%	1520
	11th to 20th	Night	17% 5% 2 7% 5% 4 4 4 7% 8% 37%	1520
	21st to end	Night	19% 6% 3 8% 6% 4 5% 4 5% 7% 33%	1520
July	1st to 10th	Night	14% 7% 3 9% 6% 5% 5% 4 6% 8% 35%	2520
	11th to 20th	Night	13% 6% 2 6% 4 4 5% 4 5% 8% 41%	2520
	21st to end	Night	13% 6% 3 7% 5% 5% 5% 4 6% 6% 41%	2739
August	1st to 10th	Night	18% 7% 4 7% 5% 4 4 3 5% 7% 35%	2506
	11th to 20th	Night	15% 7% 2 9% 4 5% 4 4 6% 6% 37%	2804
	21st to end	Night	17% 6% 2 6% 5% 4 4 4 5% 6% 40%	3476
September	1st to 10th	Night	13% 6% 2 7% 4 4 5% 4 6% 6% 44%	1900
	11th to 20th	Night	15% 5% 2 5% 3 4 3 3 4 7% 48%	2000
	21st to end	Night	18% 6% 2 6% 4 4 5% 3 5% 6% 42%	2090
October	1st to 10th	Night	19% 7% 3 7% 3 4 5% 3 6% 7% 37%	2186
	11th to 20th	Night	21% 8% 3 7% 5% 4 4 4 5% 6% 33%	2337
	21st to end	Night	25% 9% 3 8% 4 4 4 3 4 5% 30%	2717
November	1st to 10th	Night	21% 10% 3 7% 4 4 5% 4 6% 6% 31%	2537
	11th to 20th	Night	20% 11% 3 9% 4 4 4 4 4 6% 31%	2640
	21st to end	Night	23% 13% 3 10% 6% 5% 4 3 4 5% 26%	2800
December	1st to 10th	Night	18% 21% 7% 13% 7% 5% 4 3 4 4 14%	4580
	11th to 20th	Night	23% 14% 5% 10% 5% 4 4 3 4 4 23%	5208
	21st to end	Night	24% 15% 5% 9% 4 4 4 4 6% 4 19%	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	71% 5% 9% 13% 2	3598
	11th to 20th	Day	67% 7% 9% 11% 6%	3600
	21st to end	Day	59% 8% 10% 14% 9% 1	3960
February	1st to 10th	Day	64% 6% 8% 16% 5% 1	1693
	11th to 20th	Day	60% 5% 11% 16% 7% 1	1796
	21st to end	Day	59% 5% 13% 14% 8% 1	1570
March	1st to 10th	Day	59% 6% 9% 18% 7% 1	3119
	11th to 20th	Day	58% 7% 12% 12% 10% 2	3269
	21st to end	Day	49% 4 9% 19% 17% 1	4166
April	1st to 10th	Day	56% 6% 8% 18% 11% 2	2280
	11th to 20th	Day	49% 5% 9% 21% 14% 1	2254
	21st to end	Day	53% 6% 10% 18% 11% 3	2451
May	1st to 10th	Day	53% 8% 9% 20% 9% 1	4327
	11th to 20th	Day	49% 10% 14% 17% 8% 1	4402
	21st to end	Day	43% 8% 12% 24% 12% 1	4837
June	1st to 10th	Day	51% 7% 11% 19% 11% 1	2660
	11th to 20th	Day	42% 7% 12% 23% 13% 2	2660
	21st to end	Day	51% 8% 11% 20% 9% 1	2660
July	1st to 10th	Day	41% 8% 13% 28% 9%	4370
	11th to 20th	Day	40% 8% 15% 31% 6%	4365
	21st to end	Day	38% 8% 13% 33% 8%	4661
August	1st to 10th	Day	47% 8% 15% 22% 8%	4409
	11th to 20th	Day	41% 8% 18% 26% 6%	4032
	21st to end	Day	40% 7% 17% 21% 14%	4180
September	1st to 10th	Day	37% 10% 13% 28% 11%	2280
	11th to 20th	Day	36% 6% 11% 32% 14%	2180
	21st to end	Day	42% 8% 13% 26% 10% 1	2090
October	1st to 10th	Day	45% 6% 14% 28% 8%	3302
	11th to 20th	Day	45% 7% 18% 25% 6%	3031
	21st to end	Day	47% 5% 17% 23% 7% 1	3081
November	1st to 10th	Day	52% 7% 13% 20% 9% 1	1761
	11th to 20th	Day	55% 7% 11% 16% 10%	1755
	21st to end	Day	62% 8% 11% 13% 5%	1600
December	1st to 10th	Day	72% 6% 8% 12% 2	2600
	11th to 20th	Day	61% 7% 8% 16% 8%	2986
	21st to end	Day	68% 6% 11% 10% 5%	3960
January	1st to 10th	Night	70% 6% 9% 11% 3	6349
	11th to 20th	Night	69% 7% 9% 10% 4	6360
	21st to end	Night	64% 5% 8% 11% 11%	6996
February	1st to 10th	Night	66% 5% 8% 14% 5% 1	2596
	11th to 20th	Night	59% 7% 9% 16% 8%	2281
	21st to end	Night	58% 5% 9% 16% 12% 1	1884
March	1st to 10th	Night	54% 7% 9% 18% 9% 3	3734
	11th to 20th	Night	61% 4 9% 13% 12% 1	3689
	21st to end	Night	50% 5% 8% 21% 14% 2	3466
April	1st to 10th	Night	56% 5% 8% 17% 13% 1	1900
	11th to 20th	Night	53% 5% 7% 20% 13% 2	1875
	21st to end	Night	51% 5% 8% 18% 14% 3	1729
May	1st to 10th	Night	53% 8% 10% 18% 8% 3	2662
	11th to 20th	Night	50% 7% 10% 21% 10% 2	2496
	21st to end	Night	45% 7% 10% 19% 18% 1	2739
June	1st to 10th	Night	51% 7% 9% 21% 11% 1	1520
	11th to 20th	Night	44% 6% 13% 20% 14% 3	1520
	21st to end	Night	49% 8% 11% 19% 12% 1	1520
July	1st to 10th	Night	46% 8% 12% 22% 12%	2480
	11th to 20th	Night	39% 7% 14% 30% 9%	2472
	21st to end	Night	42% 7% 15% 23% 13%	2651
August	1st to 10th	Night	48% 7% 12% 25% 8%	2496
	11th to 20th	Night	46% 8% 17% 21% 8%	2829
	21st to end	Night	43% 7% 12% 22% 14% 1	3476
September	1st to 10th	Night	40% 8% 11% 25% 15% 1	1900
	11th to 20th	Night	36% 6% 14% 30% 13% 1	2000
	21st to end	Night	42% 8% 9% 25% 15% 1	2090
October	1st to 10th	Night	46% 6% 12% 27% 9%	3654
	11th to 20th	Night	46% 6% 10% 29% 9%	3873
	21st to end	Night	50% 5% 13% 19% 12% 1	4467
November	1st to 10th	Night	53% 6% 12% 20% 8% 1	2537
	11th to 20th	Night	55% 5% 11% 17% 10% 1	2640
	21st to end	Night	62% 6% 11% 15% 6%	2800
December	1st to 10th	Night	74% 5% 10% 9% 3	4580
	11th to 20th	Night	65% 4 8% 14% 10%	5208
	21st to end	Night	65% 6% 8% 13% 8%	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	29% 15% 29% 17% 9% 2	200
	11th to 20th	Day	26% 16% 34% 18% 6% 1	200
	21st to end	Day	19% 17% 34% 20% 10% 1	220
February	1st to 10th	Day	29% 22% 30% 16% 4	255
	11th to 20th	Day	25% 16% 35% 19% 5% 1	395
	21st to end	Day	27% 13% 30% 26% 4	382
March	1st to 10th	Day	26% 10% 30% 27% 7%	460
	11th to 20th	Day	23% 13% 36% 19% 8% 1	460
	21st to end	Day	27% 16% 25% 22% 8% 1	506
April	1st to 10th	Day	31% 13% 25% 20% 9% 2	460
	11th to 20th	Day	28% 18% 26% 15% 9% 4	452
	21st to end	Day	28% 12% 30% 16% 12% 3	460
May	1st to 10th	Day	24% 11% 31% 19% 13% 2	463
	11th to 20th	Day	18% 10% 31% 26% 13% 3	487
	21st to end	Day	18% 9% 33% 25% 12% 2	529
June	1st to 10th	Day	23% 9% 25% 29% 10% 2	490
	11th to 20th	Day	16% 10% 26% 29% 17% 2	490
	21st to end	Day	22% 10% 27% 23% 15% 2	490
July	1st to 10th	Day	14% 5% 25% 33% 19% 5%	485
	11th to 20th	Day	14% 8% 29% 29% 15% 5%	484
	21st to end	Day	16% 6% 23% 32% 21% 2	532
August	1st to 10th	Day	14% 6% 22% 30% 21% 5%	486
	11th to 20th	Day	12% 7% 23% 33% 19% 7%	479
	21st to end	Day	16% 7% 24% 25% 19% 9%	539
September	1st to 10th	Day	13% 10% 25% 26% 18% 8%	490
	11th to 20th	Day	16% 7% 18% 25% 22% 12%	490
	21st to end	Day	16% 7% 28% 23% 20% 6%	490
October	1st to 10th	Day	21% 10% 30% 19% 15% 5%	490
	11th to 20th	Day	24% 14% 28% 19% 12% 2	458
	21st to end	Day	34% 14% 23% 22% 8%	429
November	1st to 10th	Day	29% 15% 27% 22% 7%	395
	11th to 20th	Day	23% 19% 29% 18% 9% 1	355
	21st to end	Day	34% 16% 27% 17% 7% 1	200
December	1st to 10th	Day	33% 16% 21% 22% 8% 2	200
	11th to 20th	Day	27% 19% 35% 14% 6%	200
	21st to end	Day	30% 16% 29% 17% 4 3	220
January	1st to 10th	Night	28% 12% 31% 24% 4 1	800
	11th to 20th	Night	25% 13% 33% 22% 6%	800
	21st to end	Night	21% 11% 32% 29% 7% 1	880
February	1st to 10th	Night	25% 9% 34% 27% 5% 1	781
	11th to 20th	Night	22% 12% 36% 26% 4	743
	21st to end	Night	25% 11% 29% 30% 5%	628
March	1st to 10th	Night	25% 12% 30% 28% 6%	760
	11th to 20th	Night	28% 11% 29% 24% 7%	760
	21st to end	Night	25% 11% 29% 27% 7% 1	836
April	1st to 10th	Night	28% 9% 29% 28% 6%	760
	11th to 20th	Night	27% 13% 29% 23% 8% 1	751
	21st to end	Night	27% 11% 28% 25% 8% 1	589
May	1st to 10th	Night	25% 6% 31% 26% 11% 1	470
	11th to 20th	Night	22% 6% 31% 32% 9% 1	374
	21st to end	Night	18% 7% 31% 34% 9% 1	411
June	1st to 10th	Night	27% 6% 26% 31% 10% 1	380
	11th to 20th	Night	20% 4 28% 35% 14%	380
	21st to end	Night	19% 8% 23% 35% 14% 1	380
July	1st to 10th	Night	14% 3 27% 41% 15% 1	370
	11th to 20th	Night	11% 4 21% 47% 16% 1	368
	21st to end	Night	14% 2 20% 46% 16% 1	416
August	1st to 10th	Night	15% 3 17% 44% 20% 1	378
	11th to 20th	Night	14% 5% 20% 35% 24% 2	568
	21st to end	Night	16% 5% 19% 38% 20% 2	836
September	1st to 10th	Night	16% 6% 22% 38% 17% 1	760
	11th to 20th	Night	17% 6% 18% 34% 23% 3	760
	21st to end	Night	20% 6% 28% 28% 16% 3	760
October	1st to 10th	Night	22% 6% 28% 29% 14% 1	760
	11th to 20th	Night	27% 8% 28% 28% 8% 1	760
	21st to end	Night	28% 10% 31% 24% 6%	836
November	1st to 10th	Night	26% 13% 30% 23% 8% 1	780
	11th to 20th	Night	26% 13% 30% 22% 9% 1	800
	21st to end	Night	30% 13% 31% 20% 7%	800
December	1st to 10th	Night	33% 13% 27% 22% 5%	800
	11th to 20th	Night	31% 13% 30% 19% 6% 1	800
	21st to end	Night	34% 11% 31% 19% 5%	880

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