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 2024-08-30.

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% 32%	95791
	Night	19% 11% 4 9% 5% 4 4 3 5% 6% 30%	93276
Transparency	Day	51% 8% 12% 20% 9% 1	95510
	Night	55% 7% 10% 18% 9% 1	93111
Seeing	Day	22% 11% 27% 24% 13% 3	14372
	Night	24% 9% 28% 28% 10% 1	23278

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	18% 17% 6% 13% 6% 4 4 3 4 5% 21%	2517
	11th to 20th	Day	15% 15% 6% 11% 6% 6% 5% 3 5% 6% 22%	2520
	21st to end	Day	16% 17% 5% 11% 6% 5% 5% 4 5% 6% 22%	2772
February	1st to 10th	Day	17% 15% 5% 12% 6% 5% 5% 3 4 5% 22%	1651
	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	13% 6% 3 7% 5% 5% 5% 4 6% 9% 37%	2646
	11th to 20th	Day	11% 6% 2 6% 5% 4 4 4 6% 10% 40%	2408
	21st to end	Day	15% 5% 2 7% 4 4 4 4 6% 8% 42%	2486
September	1st to 10th	Day	13% 6% 2 6% 4 4 5% 4 6% 7% 43%	2160
	11th to 20th	Day	16% 6% 2 4 3 3 3 3 5% 7% 48%	2066
	21st to end	Day	15% 6% 2 7% 5% 4 4 4 7% 8% 40%	1980
October	1st to 10th	Day	22% 7% 2 7% 4 5% 5% 4 5% 7% 32%	1886
	11th to 20th	Day	20% 9% 3 8% 6% 6% 5% 4 7% 6% 28%	1745
	21st to end	Day	27% 10% 3 7% 5% 4 3 3 5% 6% 28%	1782
November	1st to 10th	Day	19% 11% 3 6% 6% 4 4 4 4 6% 33%	1671
	11th to 20th	Day	17% 12% 4 8% 6% 5% 5% 4 5% 6% 27%	1668
	21st to end	Day	23% 13% 4 8% 6% 5% 3 4 5% 5% 23%	1520
December	1st to 10th	Day	23% 18% 6% 9% 6% 4 4 3 4 5% 18%	1520
	11th to 20th	Day	23% 12% 4 10% 6% 4 3 5% 5% 5% 23%	1906
	21st to end	Day	28% 16% 4 11% 5% 4 4 3 3 3 19%	2772
January	1st to 10th	Night	17% 18% 6% 11% 6% 4 4 3 4 5% 20%	4429
	11th to 20th	Night	13% 15% 5% 14% 7% 7% 6% 4 6% 6% 19%	4440
	21st to end	Night	20% 17% 5% 10% 7% 5% 4 3 3 4 23%	4884
February	1st to 10th	Night	17% 16% 6% 13% 7% 5% 5% 3 5% 5% 19%	2527
	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	15% 5% 2 6% 4 4 4 4 6% 10% 40%	1512
	11th to 20th	Night	14% 6% 2 7% 4 4 5% 4 6% 7% 41%	1692
	21st to end	Night	14% 7% 3 6% 4 4 4 4 6% 7% 42%	2080
September	1st to 10th	Night	13% 6% 2 7% 4 4 4 4 6% 6% 43%	1800
	11th to 20th	Night	16% 5% 2 5% 3 4 3 3 4 7% 47%	1894
	21st to end	Night	18% 7% 2 5% 4 4 5% 3 5% 6% 42%	1980
October	1st to 10th	Night	19% 7% 3 7% 3 4 5% 3 6% 7% 37%	2070
	11th to 20th	Night	22% 9% 3 7% 5% 5% 4 3 5% 6% 31%	2214
	21st to end	Night	26% 9% 3 9% 5% 4 4 3 4 5% 29%	2574
November	1st to 10th	Night	21% 10% 3 7% 4 4 5% 4 6% 6% 31%	2407
	11th to 20th	Night	20% 11% 3 9% 4 4 4 4 5% 6% 31%	2508
	21st to end	Night	23% 13% 3 10% 5% 5% 4 3 4 5% 26%	2660
December	1st to 10th	Night	23% 19% 6% 10% 6% 4 4 3 4 5% 17%	2660
	11th to 20th	Night	24% 15% 5% 11% 5% 4 4 3 3 3 23%	3288
	21st to end	Night	27% 16% 6% 10% 5% 4 3 2 3 4 20%	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	66% 7% 11% 12% 3	2518
	11th to 20th	Day	61% 9% 12% 12% 5%	2520
	21st to end	Day	62% 10% 11% 12% 4	2772
February	1st to 10th	Day	64% 6% 9% 15% 5% 1	1651
	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	43% 10% 15% 25% 8%	2632
	11th to 20th	Day	38% 10% 17% 25% 10%	2408
	21st to end	Day	39% 8% 15% 25% 12%	2486
September	1st to 10th	Day	38% 10% 13% 27% 12% 1	2160
	11th to 20th	Day	36% 6% 11% 32% 14%	2066
	21st to end	Day	41% 8% 14% 26% 10% 1	1980
October	1st to 10th	Day	52% 8% 12% 20% 9%	1886
	11th to 20th	Day	53% 9% 13% 18% 6%	1745
	21st to end	Day	58% 6% 11% 17% 7% 1	1782
November	1st to 10th	Day	51% 7% 13% 19% 8% 1	1671
	11th to 20th	Day	57% 8% 12% 14% 9%	1668
	21st to end	Day	62% 9% 11% 13% 5%	1520
December	1st to 10th	Day	69% 7% 11% 10% 3	1520
	11th to 20th	Day	62% 8% 10% 15% 6%	1906
	21st to end	Day	71% 6% 11% 8% 4	2772
January	1st to 10th	Night	64% 9% 13% 10% 3	4429
	11th to 20th	Night	64% 9% 10% 11% 5%	4440
	21st to end	Night	66% 6% 10% 12% 6%	4884
February	1st to 10th	Night	67% 5% 8% 14% 5% 1	2527
	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	39% 8% 17% 25% 11%	1502
	11th to 20th	Night	40% 9% 15% 23% 12%	1692
	21st to end	Night	40% 9% 13% 25% 13% 1	2080
September	1st to 10th	Night	41% 8% 11% 25% 15% 1	1800
	11th to 20th	Night	37% 6% 14% 30% 13% 1	1894
	21st to end	Night	42% 8% 9% 25% 14% 1	1980
October	1st to 10th	Night	46% 7% 11% 23% 12%	2070
	11th to 20th	Night	53% 8% 9% 22% 7%	2214
	21st to end	Night	58% 6% 10% 15% 9% 1	2574
November	1st to 10th	Night	53% 6% 12% 20% 8% 1	2407
	11th to 20th	Night	55% 6% 11% 17% 10% 1	2508
	21st to end	Night	62% 6% 11% 15% 6%	2660
December	1st to 10th	Night	70% 6% 10% 11% 3	2660
	11th to 20th	Night	65% 6% 9% 15% 6%	3288
	21st to end	Night	69% 6% 9% 13% 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	29% 12% 29% 18% 10% 2	180
	11th to 20th	Day	28% 15% 33% 17% 7% 1	180
	21st to end	Day	19% 16% 32% 20% 12% 1	198
February	1st to 10th	Day	30% 21% 30% 16% 4	243
	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	15% 7% 24% 25% 20% 9%	532
September	1st to 10th	Day	13% 9% 24% 27% 18% 9%	450
	11th to 20th	Day	17% 8% 20% 26% 19% 11%	450
	21st to end	Day	16% 7% 29% 23% 19% 6%	450
October	1st to 10th	Day	22% 10% 29% 19% 16% 5%	450
	11th to 20th	Day	24% 15% 27% 20% 12% 2	422
	21st to end	Day	35% 13% 23% 22% 7%	396
November	1st to 10th	Day	29% 13% 27% 23% 8%	365
	11th to 20th	Day	24% 20% 28% 18% 9% 2	328
	21st to end	Day	32% 14% 28% 18% 7% 1	180
December	1st to 10th	Day	33% 15% 21% 21% 8% 2	180
	11th to 20th	Day	27% 18% 35% 13% 6%	180
	21st to end	Day	33% 17% 28% 17% 4 2	198
January	1st to 10th	Night	28% 11% 31% 25% 5% 1	760
	11th to 20th	Night	26% 12% 33% 23% 6%	760
	21st to end	Night	21% 11% 31% 29% 7% 1	836
February	1st to 10th	Night	25% 9% 34% 27% 5% 1	760
	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% 18% 38% 21% 2	832
September	1st to 10th	Night	16% 5% 21% 39% 17% 2	720
	11th to 20th	Night	18% 6% 19% 34% 21% 3	720
	21st to end	Night	20% 6% 28% 28% 15% 3	720
October	1st to 10th	Night	22% 6% 29% 28% 14% 1	720
	11th to 20th	Night	28% 8% 28% 28% 8% 1	720
	21st to end	Night	29% 9% 31% 25% 6%	792
November	1st to 10th	Night	26% 12% 31% 23% 8% 1	740
	11th to 20th	Night	26% 13% 30% 21% 9% 1	760
	21st to end	Night	30% 12% 30% 20% 7%	760
December	1st to 10th	Night	33% 13% 27% 22% 5%	760
	11th to 20th	Night	31% 12% 31% 19% 6% 1	760
	21st to end	Night	34% 11% 31% 19% 4	836

Page generated at 2024-08-27 09:49:39. Version ac07

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