Ste-Thérèse
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ste-Thérèse clear sky chart from 2005-11-06 to 2025-09-04.

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% 9% 3 8% 5% 5% 5% 4 5% 7% 33%	126383
	Night	17% 11% 4 9% 5% 4 4 3 5% 6% 31%	122332
Transparency	Day	50% 4 12% 22% 10% 1	129828
	Night	53% 4 11% 20% 11% 1	126974
Seeing	Day	21% 10% 28% 25% 12% 4	15587
	Night	22% 8% 28% 31% 10% 1	24497

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	15% 17% 6% 14% 5% 5% 4 3 4 4 23%	3597
	11th to 20th	Day	13% 14% 6% 12% 6% 5% 4 3 4 6% 26%	3570
	21st to end	Day	11% 16% 5% 11% 5% 6% 6% 4 5% 5% 27%	3960
February	1st to 10th	Day	13% 16% 4 10% 5% 5% 4 4 5% 6% 27%	1760
	11th to 20th	Day	13% 13% 5% 10% 6% 6% 5% 4 5% 5% 28%	1847
	21st to end	Day	17% 16% 4 9% 4 5% 4 3 5% 5% 28%	1650
March	1st to 10th	Day	20% 13% 5% 10% 6% 4 4 3 4 4 26%	4476
	11th to 20th	Day	11% 13% 4 9% 5% 5% 5% 3 6% 7% 32%	4704
	21st to end	Day	19% 9% 4 8% 5% 5% 4 3 4 5% 35%	5960
April	1st to 10th	Day	21% 11% 3 7% 5% 4 4 3 4 5% 33%	2400
	11th to 20th	Day	21% 8% 2 8% 5% 4 3 3 4 5% 37%	2374
	21st to end	Day	22% 10% 3 7% 4 4 4 4 5% 5% 33%	2556
May	1st to 10th	Day	25% 10% 4 9% 5% 4 5% 4 5% 6% 23%	6294
	11th to 20th	Day	20% 8% 3 8% 5% 5% 5% 3 5% 7% 31%	6318
	21st to end	Day	22% 8% 2 6% 4 5% 4 4 6% 7% 31%	6949
June	1st to 10th	Day	21% 8% 3 6% 5% 6% 5% 4 5% 7% 31%	2800
	11th to 20th	Day	15% 6% 3 7% 5% 4 5% 4 6% 7% 38%	2800
	21st to end	Day	20% 7% 2 7% 6% 5% 5% 4 6% 7% 31%	2800
July	1st to 10th	Day	13% 6% 2 8% 6% 6% 6% 4 7% 8% 34%	6360
	11th to 20th	Day	11% 5% 2 6% 5% 5% 5% 4 7% 9% 41%	6360
	21st to end	Day	10% 5% 2 6% 3 4 4 4 6% 9% 47%	6926
August	1st to 10th	Day	13% 6% 2 7% 5% 5% 6% 4 7% 9% 34%	4563
	11th to 20th	Day	14% 6% 3 8% 5% 5% 4 4 6% 8% 39%	4128
	21st to end	Day	16% 5% 2 6% 5% 4 5% 4 6% 9% 40%	4312
September	1st to 10th	Day	11% 6% 2 5% 4 5% 5% 4 6% 9% 42%	2316
	11th to 20th	Day	13% 4 2 5% 4 4 4 3 5% 6% 50%	2206
	21st to end	Day	16% 6% 2 6% 4 4 4 3 5% 7% 42%	2090
October	1st to 10th	Day	20% 6% 3 7% 5% 4 4 3 5% 7% 36%	1952
	11th to 20th	Day	18% 9% 3 7% 6% 5% 5% 4 6% 6% 31%	1862
	21st to end	Day	23% 9% 4 7% 4 3 4 3 6% 6% 31%	1881
November	1st to 10th	Day	16% 10% 3 7% 5% 5% 4 3 6% 7% 35%	1761
	11th to 20th	Day	17% 11% 3 7% 4 5% 4 4 5% 6% 32%	1705
	21st to end	Day	22% 11% 3 6% 5% 5% 5% 4 6% 6% 26%	1600
December	1st to 10th	Day	21% 17% 6% 12% 5% 4 4 3 5% 4 19%	2600
	11th to 20th	Day	19% 13% 4 10% 5% 4 4 4 5% 5% 28%	2986
	21st to end	Day	24% 13% 4 9% 5% 4 4 4 5% 4 24%	3960
January	1st to 10th	Night	13% 19% 7% 15% 6% 4 4 3 4 4 21%	6349
	11th to 20th	Night	10% 15% 7% 15% 8% 5% 5% 3 5% 5% 22%	6315
	21st to end	Night	13% 14% 5% 12% 7% 5% 5% 3 5% 6% 26%	6996
February	1st to 10th	Night	14% 14% 5% 11% 6% 5% 6% 3 5% 6% 25%	2637
	11th to 20th	Night	14% 11% 4 9% 6% 4 5% 4 5% 6% 31%	2439
	21st to end	Night	15% 16% 4 9% 5% 4 4 3 5% 5% 32%	1980
March	1st to 10th	Night	22% 14% 4 7% 5% 4 3 3 4 4 30%	5364
	11th to 20th	Night	14% 13% 3 8% 5% 5% 5% 4 6% 7% 31%	5239
	21st to end	Night	15% 11% 4 9% 6% 5% 5% 4 4 5% 33%	4971
April	1st to 10th	Night	23% 10% 3 6% 4 4 4 4 4 6% 32%	2000
	11th to 20th	Night	22% 7% 3 7% 5% 4 3 3 4 6% 35%	1975
	21st to end	Night	22% 8% 3 7% 4 3 4 3 5% 5% 35%	1842
May	1st to 10th	Night	25% 10% 4 9% 5% 5% 4 4 4 6% 25%	3689
	11th to 20th	Night	22% 9% 3 7% 4 4 4 4 5% 7% 32%	3575
	21st to end	Night	19% 9% 3 8% 5% 4 4 4 5% 7% 31%	3926
June	1st to 10th	Night	20% 8% 3 7% 4 4 5% 4 6% 8% 32%	1600
	11th to 20th	Night	16% 8% 3 6% 4 4 5% 3 6% 7% 40%	1600
	21st to end	Night	20% 6% 3 6% 4 5% 5% 4 6% 6% 36%	1600
July	1st to 10th	Night	14% 6% 2 7% 5% 6% 6% 5% 7% 9% 34%	3600
	11th to 20th	Night	14% 6% 2 6% 5% 4 4 4 5% 8% 42%	3600
	21st to end	Night	10% 5% 2 6% 4 4 4 4 7% 8% 45%	3926
August	1st to 10th	Night	14% 7% 3 8% 5% 5% 5% 3 5% 7% 39%	2586
	11th to 20th	Night	15% 7% 3 8% 4 4 4 3 5% 7% 41%	2872
	21st to end	Night	17% 6% 2 8% 4 4 4 3 5% 7% 39%	3586
September	1st to 10th	Night	11% 5% 3 6% 5% 4 4 4 6% 7% 45%	1931
	11th to 20th	Night	14% 5% 2 5% 3 3 3 3 4 7% 50%	1973
	21st to end	Night	17% 4 2 6% 4 3 4 3 5% 7% 44%	2090
October	1st to 10th	Night	18% 7% 3 7% 4 3 4 3 5% 6% 40%	2226
	11th to 20th	Night	20% 7% 4 6% 5% 3 4 3 5% 6% 37%	2317
	21st to end	Night	22% 8% 4 8% 5% 4 4 3 4 6% 32%	2717
November	1st to 10th	Night	19% 10% 3 7% 5% 4 4 4 5% 7% 33%	2537
	11th to 20th	Night	19% 10% 3 8% 4 4 4 4 5% 6% 34%	2690
	21st to end	Night	22% 13% 3 8% 5% 4 4 3 5% 5% 28%	2800
December	1st to 10th	Night	18% 16% 5% 10% 6% 6% 6% 3 5% 5% 20%	4580
	11th to 20th	Night	24% 13% 4 9% 5% 3 4 3 4 6% 26%	5208
	21st to end	Night	25% 15% 4 9% 4 3 3 3 5% 5% 24%	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	66% 3 9% 17% 4 1	3598
	11th to 20th	Day	60% 3 10% 18% 7% 2	3600
	21st to end	Day	57% 4 12% 15% 11% 1	3960
February	1st to 10th	Day	58% 3 10% 19% 7% 2	1760
	11th to 20th	Day	58% 4 12% 16% 10% 1	1856
	21st to end	Day	59% 2 10% 17% 10% 2	1650
March	1st to 10th	Day	62% 3 7% 14% 11% 3	4479
	11th to 20th	Day	51% 5% 17% 13% 12% 2	4704
	21st to end	Day	53% 3 7% 16% 18% 2	5960
April	1st to 10th	Day	55% 4 7% 19% 13% 2	2400
	11th to 20th	Day	50% 3 7% 23% 15% 2	2374
	21st to end	Day	54% 4 8% 18% 13% 3	2556
May	1st to 10th	Day	61% 3 7% 20% 7% 1	6305
	11th to 20th	Day	53% 4 14% 19% 8% 2	6322
	21st to end	Day	51% 5% 11% 20% 12% 1	6949
June	1st to 10th	Day	52% 4 10% 19% 13% 2	2800
	11th to 20th	Day	43% 5% 11% 24% 14% 3	2800
	21st to end	Day	51% 4 13% 20% 10% 1	2800
July	1st to 10th	Day	46% 6% 14% 26% 8%	6290
	11th to 20th	Day	38% 6% 15% 30% 11%	6285
	21st to end	Day	34% 5% 15% 37% 9%	6728
August	1st to 10th	Day	45% 6% 18% 23% 9%	4549
	11th to 20th	Day	43% 5% 18% 27% 7%	4170
	21st to end	Day	41% 5% 16% 22% 15% 1	4312
September	1st to 10th	Day	37% 6% 14% 30% 13% 1	2316
	11th to 20th	Day	34% 4 13% 33% 14% 1	2206
	21st to end	Day	42% 4 14% 27% 12% 1	2090
October	1st to 10th	Day	46% 4 14% 27% 10%	3238
	11th to 20th	Day	44% 5% 18% 27% 7%	3078
	21st to end	Day	43% 4 20% 23% 9% 1	3081
November	1st to 10th	Day	48% 5% 14% 23% 9% 1	1761
	11th to 20th	Day	52% 5% 10% 20% 12% 1	1705
	21st to end	Day	59% 5% 14% 16% 6% 1	1600
December	1st to 10th	Day	70% 3 9% 15% 3	2600
	11th to 20th	Day	59% 4 10% 18% 10%	2986
	21st to end	Day	63% 4 11% 14% 7%	3960
January	1st to 10th	Night	68% 2 12% 14% 4	6349
	11th to 20th	Night	65% 4 10% 16% 4 1	6360
	21st to end	Night	60% 4 11% 11% 13% 1	6996
February	1st to 10th	Night	60% 4 9% 17% 9% 1	2637
	11th to 20th	Night	54% 3 10% 22% 9% 1	2441
	21st to end	Night	55% 4 9% 18% 13% 2	1980
March	1st to 10th	Night	59% 2 8% 15% 12% 4	5374
	11th to 20th	Night	53% 4 13% 16% 13% 2	5240
	21st to end	Night	54% 3 7% 21% 13% 2	4971
April	1st to 10th	Night	53% 4 7% 19% 15% 2	2000
	11th to 20th	Night	52% 4 6% 21% 15% 2	1975
	21st to end	Night	50% 4 8% 20% 14% 4	1842
May	1st to 10th	Night	61% 3 9% 18% 7% 2	3695
	11th to 20th	Night	53% 4 11% 20% 10% 2	3576
	21st to end	Night	54% 4 10% 17% 14% 1	3927
June	1st to 10th	Night	50% 5% 9% 21% 14% 1	1600
	11th to 20th	Night	43% 5% 12% 23% 15% 3	1600
	21st to end	Night	48% 6% 11% 20% 15% 1	1600
July	1st to 10th	Night	44% 6% 18% 22% 10%	3560
	11th to 20th	Night	40% 4 17% 29% 10%	3552
	21st to end	Night	36% 5% 16% 29% 13%	3809
August	1st to 10th	Night	45% 5% 13% 27% 10%	2576
	11th to 20th	Night	44% 5% 18% 25% 8%	2896
	21st to end	Night	44% 6% 13% 22% 13% 1	3586
September	1st to 10th	Night	37% 5% 14% 27% 16% 1	1931
	11th to 20th	Night	35% 4 14% 34% 13% 1	1973
	21st to end	Night	41% 5% 11% 29% 15%	2090
October	1st to 10th	Night	44% 5% 14% 26% 11% 1	3720
	11th to 20th	Night	44% 4 12% 31% 9%	3840
	21st to end	Night	46% 4 17% 19% 12% 2	4467
November	1st to 10th	Night	51% 4 11% 23% 9% 1	2537
	11th to 20th	Night	51% 4 12% 20% 11% 1	2690
	21st to end	Night	59% 4 11% 19% 8%	2800
December	1st to 10th	Night	67% 5% 11% 14% 4	4580
	11th to 20th	Night	61% 4 8% 16% 11%	5208
	21st to end	Night	63% 3 8% 15% 11%	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	25% 10% 30% 28% 8%	200
	11th to 20th	Day	25% 14% 34% 22% 5% 2	200
	21st to end	Day	20% 14% 31% 26% 6% 1	220
February	1st to 10th	Day	29% 18% 36% 14% 3	280
	11th to 20th	Day	21% 15% 38% 22% 3	394
	21st to end	Day	27% 13% 32% 24% 4	414
March	1st to 10th	Day	25% 13% 31% 23% 8%	500
	11th to 20th	Day	21% 13% 36% 23% 5% 1	500
	21st to end	Day	27% 12% 32% 19% 8% 2	550
April	1st to 10th	Day	28% 15% 26% 20% 8% 2	500
	11th to 20th	Day	30% 15% 23% 21% 10% 2	492
	21st to end	Day	27% 13% 31% 19% 7% 3	500
May	1st to 10th	Day	24% 11% 31% 24% 9% 2	503
	11th to 20th	Day	20% 6% 31% 26% 13% 4	527
	21st to end	Day	20% 10% 31% 25% 12% 3	573
June	1st to 10th	Day	23% 9% 27% 27% 11% 2	530
	11th to 20th	Day	15% 12% 26% 30% 15% 3	530
	21st to end	Day	22% 7% 28% 26% 14% 3	530
July	1st to 10th	Day	14% 6% 26% 32% 18% 5%	525
	11th to 20th	Day	14% 5% 27% 32% 18% 4	524
	21st to end	Day	12% 6% 24% 36% 17% 5%	576
August	1st to 10th	Day	13% 5% 22% 32% 22% 6%	526
	11th to 20th	Day	12% 4 19% 32% 21% 11%	519
	21st to end	Day	15% 7% 25% 24% 21% 8%	583
September	1st to 10th	Day	13% 5% 26% 27% 19% 9%	502
	11th to 20th	Day	14% 7% 21% 25% 20% 13%	490
	21st to end	Day	19% 8% 26% 24% 17% 7%	490
October	1st to 10th	Day	21% 9% 27% 22% 15% 5%	490
	11th to 20th	Day	21% 11% 31% 23% 11% 3	470
	21st to end	Day	32% 11% 25% 24% 8%	429
November	1st to 10th	Day	27% 13% 25% 23% 11% 1	395
	11th to 20th	Day	24% 13% 35% 19% 8% 1	305
	21st to end	Day	32% 13% 27% 20% 8% 1	200
December	1st to 10th	Day	28% 11% 25% 26% 9% 2	200
	11th to 20th	Day	26% 14% 37% 19% 4 1	200
	21st to end	Day	30% 15% 28% 18% 8% 1	220
January	1st to 10th	Night	24% 12% 32% 27% 6%	800
	11th to 20th	Night	24% 10% 31% 27% 7%	800
	21st to end	Night	18% 8% 35% 30% 8% 1	880
February	1st to 10th	Night	21% 8% 37% 29% 5% 1	800
	11th to 20th	Night	21% 11% 37% 26% 5%	783
	21st to end	Night	24% 9% 32% 32% 4	660
March	1st to 10th	Night	25% 10% 31% 29% 5%	800
	11th to 20th	Night	25% 9% 30% 27% 8%	800
	21st to end	Night	22% 9% 31% 31% 7%	880
April	1st to 10th	Night	27% 10% 28% 29% 6%	800
	11th to 20th	Night	26% 9% 30% 28% 6% 1	791
	21st to end	Night	27% 8% 31% 26% 7%	642
May	1st to 10th	Night	26% 6% 31% 29% 7% 2	443
	11th to 20th	Night	24% 3 28% 35% 9% 1	394
	21st to end	Night	19% 5% 36% 31% 8%	433
June	1st to 10th	Night	26% 4 24% 36% 11%	400
	11th to 20th	Night	19% 5% 28% 36% 13% 1	400
	21st to end	Night	21% 5% 24% 35% 15% 1	400
July	1st to 10th	Night	11% 4 27% 42% 16% 1	390
	11th to 20th	Night	13% 3 20% 46% 17%	388
	21st to end	Night	12% 3 19% 47% 18% 1	438
August	1st to 10th	Night	14% 5% 13% 44% 24% 1	398
	11th to 20th	Night	14% 2 18% 38% 24% 3	588
	21st to end	Night	16% 3 22% 37% 21% 2	880
September	1st to 10th	Night	14% 3 22% 42% 18% 1	773
	11th to 20th	Night	16% 5% 17% 37% 23% 3	760
	21st to end	Night	18% 4 26% 32% 18% 2	760
October	1st to 10th	Night	21% 6% 26% 34% 13% 1	760
	11th to 20th	Night	23% 6% 28% 30% 12% 1	760
	21st to end	Night	26% 8% 30% 28% 7%	836
November	1st to 10th	Night	23% 11% 28% 28% 9%	780
	11th to 20th	Night	24% 9% 32% 26% 10% 1	800
	21st to end	Night	29% 12% 28% 23% 8%	800
December	1st to 10th	Night	30% 9% 30% 25% 7%	800
	11th to 20th	Night	28% 11% 31% 24% 6% 1	800
	21st to end	Night	33% 10% 28% 21% 7%	880

Page generated at 2025-09-01 01:51:09. Version ac07

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