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 2024-11-04.

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 6% 7% 34%	101531
	Night	18% 10% 4 8% 5% 4 4 3 5% 6% 33%	97476
Transparency	Day	49% 4 13% 22% 10% 1	104994
	Night	52% 4 12% 21% 10% 1	102102
Seeing	Day	21% 10% 28% 25% 12% 4	14554
	Night	22% 7% 28% 31% 10% 1	23503

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% 14% 5% 13% 6% 5% 5% 3 5% 4 24%	2517
	11th to 20th	Day	15% 12% 6% 10% 6% 4 4 3 5% 7% 28%	2520
	21st to end	Day	14% 16% 4 10% 5% 6% 6% 4 5% 5% 24%	2772
February	1st to 10th	Day	14% 16% 4 10% 5% 5% 4 4 5% 6% 27%	1672
	11th to 20th	Day	13% 13% 4 10% 5% 6% 5% 4 5% 5% 29%	1752
	21st to end	Day	18% 16% 4 9% 5% 5% 4 3 5% 5% 28%	1570
March	1st to 10th	Day	20% 13% 4 10% 6% 5% 4 3 5% 5% 26%	3116
	11th to 20th	Day	13% 17% 5% 10% 6% 5% 5% 3 5% 5% 28%	3288
	21st to end	Day	15% 7% 3 8% 5% 5% 4 3 5% 5% 39%	4156
April	1st to 10th	Day	21% 11% 3 7% 5% 4 4 3 4 5% 33%	2280
	11th to 20th	Day	21% 8% 2 7% 5% 4 3 4 4 5% 36%	2254
	21st to end	Day	22% 10% 3 7% 4 4 3 4 4 5% 33%	2428
May	1st to 10th	Day	19% 9% 3 8% 5% 5% 5% 4 6% 7% 30%	4388
	11th to 20th	Day	18% 7% 3 8% 5% 5% 5% 4 6% 7% 32%	4398
	21st to end	Day	16% 6% 2 6% 5% 5% 5% 4 6% 8% 37%	4837
June	1st to 10th	Day	21% 8% 3 6% 5% 6% 5% 4 5% 7% 31%	2660
	11th to 20th	Day	15% 6% 3 7% 5% 4 5% 4 6% 7% 38%	2660
	21st to end	Day	20% 7% 2 7% 6% 5% 5% 4 6% 7% 30%	2660
July	1st to 10th	Day	12% 6% 2 7% 6% 6% 6% 5% 7% 9% 36%	4440
	11th to 20th	Day	13% 5% 2 6% 5% 5% 5% 5% 7% 9% 37%	4440
	21st to end	Day	11% 5% 2 6% 3 4 4 4 6% 8% 46%	4814
August	1st to 10th	Day	14% 6% 2 8% 6% 5% 6% 4 7% 9% 33%	4423
	11th to 20th	Day	14% 6% 3 8% 4 5% 4 4 6% 9% 38%	3999
	21st to end	Day	16% 5% 2 6% 5% 4 5% 4 6% 9% 40%	4180
September	1st to 10th	Day	11% 6% 2 5% 4 5% 5% 4 6% 9% 42%	2280
	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 6% 5% 4 4 3 6% 7% 35%	1698
	11th to 20th	Day	18% 12% 4 8% 4 5% 4 4 5% 6% 31%	1620
	21st to end	Day	22% 11% 3 6% 5% 5% 5% 4 6% 6% 27%	1520
December	1st to 10th	Day	24% 13% 5% 10% 5% 4 4 3 4 5% 22%	1520
	11th to 20th	Day	22% 13% 4 9% 5% 3 4 3 5% 5% 28%	1906
	21st to end	Day	28% 16% 4 9% 5% 4 3 2 4 4 21%	2772
January	1st to 10th	Night	17% 15% 6% 11% 6% 4 4 3 5% 5% 24%	4429
	11th to 20th	Night	12% 14% 5% 11% 7% 5% 6% 4 6% 6% 26%	4440
	21st to end	Night	15% 16% 5% 11% 6% 4 4 3 5% 5% 25%	4884
February	1st to 10th	Night	14% 14% 5% 11% 6% 5% 6% 3 5% 6% 24%	2506
	11th to 20th	Night	14% 11% 4 9% 6% 4 5% 4 5% 6% 31%	2314
	21st to end	Night	15% 16% 4 9% 5% 4 4 2 6% 5% 32%	1884
March	1st to 10th	Night	20% 12% 4 7% 5% 4 3 3 4 5% 34%	3724
	11th to 20th	Night	17% 18% 4 9% 5% 4 3 3 4 4 28%	3655
	21st to end	Night	12% 10% 4 9% 6% 4 4 4 4 5% 39%	3475
April	1st to 10th	Night	23% 10% 3 6% 4 4 4 4 4 6% 32%	1900
	11th to 20th	Night	22% 7% 3 7% 5% 4 3 3 4 6% 35%	1875
	21st to end	Night	22% 8% 3 7% 4 3 4 4 5% 5% 35%	1750
May	1st to 10th	Night	22% 9% 3 8% 4 4 4 4 5% 6% 31%	2581
	11th to 20th	Night	22% 8% 2 6% 4 4 4 4 4 6% 36%	2495
	21st to end	Night	16% 8% 3 8% 4 4 4 4 5% 8% 37%	2738
June	1st to 10th	Night	20% 8% 3 6% 4 4 5% 4 6% 8% 32%	1520
	11th to 20th	Night	16% 8% 3 6% 3 3 5% 3 6% 7% 40%	1520
	21st to end	Night	20% 6% 3 6% 5% 5% 5% 3 6% 6% 35%	1520
July	1st to 10th	Night	13% 6% 2 8% 5% 6% 5% 5% 7% 8% 35%	2520
	11th to 20th	Night	14% 6% 2 5% 5% 4 4 4 5% 8% 42%	2520
	21st to end	Night	11% 6% 2 6% 4 4 4 4 6% 8% 44%	2739
August	1st to 10th	Night	15% 7% 3 8% 5% 5% 5% 3 5% 7% 38%	2506
	11th to 20th	Night	15% 7% 3 8% 4 4 4 3 5% 7% 40%	2782
	21st to end	Night	17% 6% 2 8% 4 4 4 3 5% 7% 39%	3476
September	1st to 10th	Night	11% 5% 3 6% 5% 4 4 4 6% 7% 45%	1900
	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%	2453
	11th to 20th	Night	19% 10% 3 8% 4 4 4 3 5% 6% 33%	2555
	21st to end	Night	22% 13% 3 7% 5% 4 4 3 5% 5% 29%	2660
December	1st to 10th	Night	21% 14% 5% 9% 5% 5% 4 4 5% 5% 23%	2660
	11th to 20th	Night	23% 14% 5% 8% 5% 3 4 3 4 5% 27%	3288
	21st to end	Night	29% 15% 5% 9% 4 3 3 2 4 4 23%	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	64% 3 13% 14% 5% 1	2518
	11th to 20th	Day	57% 3 14% 19% 7%	2520
	21st to end	Day	60% 4 15% 14% 6% 1	2772
February	1st to 10th	Day	58% 3 10% 20% 7% 2	1672
	11th to 20th	Day	57% 4 12% 16% 10% 1	1761
	21st to end	Day	59% 2 10% 16% 10% 2	1570
March	1st to 10th	Day	61% 3 9% 18% 8% 1	3119
	11th to 20th	Day	58% 4 11% 13% 12% 3	3288
	21st to end	Day	46% 4 8% 20% 19% 2	4156
April	1st to 10th	Day	55% 4 7% 19% 12% 2	2280
	11th to 20th	Day	50% 4 7% 23% 15% 2	2254
	21st to end	Day	55% 3 8% 18% 13% 4	2428
May	1st to 10th	Day	53% 3 9% 24% 10% 1	4402
	11th to 20th	Day	51% 4 16% 19% 8% 2	4402
	21st to end	Day	44% 4 12% 24% 15% 2	4837
June	1st to 10th	Day	52% 5% 10% 20% 12% 2	2660
	11th to 20th	Day	43% 5% 11% 24% 13% 3	2660
	21st to end	Day	52% 5% 13% 20% 10% 1	2660
July	1st to 10th	Day	43% 6% 14% 27% 10% 1	4370
	11th to 20th	Day	40% 6% 17% 30% 8%	4365
	21st to end	Day	36% 5% 15% 34% 10%	4661
August	1st to 10th	Day	46% 6% 18% 22% 9%	4409
	11th to 20th	Day	43% 5% 18% 27% 6%	4041
	21st to end	Day	41% 5% 16% 22% 15% 1	4180
September	1st to 10th	Day	37% 6% 14% 30% 13% 1	2280
	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	1698
	11th to 20th	Day	53% 5% 11% 19% 11%	1620
	21st to end	Day	57% 5% 15% 16% 6% 1	1520
December	1st to 10th	Day	67% 3 11% 14% 5%	1520
	11th to 20th	Day	59% 4 11% 19% 7%	1906
	21st to end	Day	69% 3 12% 11% 6%	2772
January	1st to 10th	Night	63% 3 16% 14% 5%	4429
	11th to 20th	Night	59% 4 13% 18% 5% 1	4440
	21st to end	Night	62% 5% 14% 12% 7% 1	4884
February	1st to 10th	Night	61% 4 9% 17% 8% 1	2506
	11th to 20th	Night	54% 3 10% 22% 10% 1	2316
	21st to end	Night	55% 4 9% 17% 13% 2	1884
March	1st to 10th	Night	55% 2 10% 19% 10% 3	3734
	11th to 20th	Night	60% 3 9% 14% 13% 2	3656
	21st to end	Night	49% 3 7% 22% 16% 3	3475
April	1st to 10th	Night	53% 4 7% 19% 15% 2	1900
	11th to 20th	Night	51% 4 6% 22% 15% 2	1875
	21st to end	Night	50% 4 8% 20% 14% 4	1750
May	1st to 10th	Night	54% 2 11% 21% 9% 3	2587
	11th to 20th	Night	50% 4 12% 20% 12% 2	2496
	21st to end	Night	47% 3 10% 20% 18% 1	2739
June	1st to 10th	Night	50% 5% 10% 22% 13% 1	1520
	11th to 20th	Night	43% 5% 12% 23% 15% 3	1520
	21st to end	Night	49% 6% 11% 19% 14% 1	1520
July	1st to 10th	Night	45% 6% 15% 21% 13% 1	2480
	11th to 20th	Night	39% 5% 20% 28% 8%	2472
	21st to end	Night	37% 6% 18% 25% 13%	2651
August	1st to 10th	Night	46% 5% 12% 26% 10%	2496
	11th to 20th	Night	44% 5% 18% 25% 7%	2806
	21st to end	Night	44% 6% 13% 22% 14% 1	3476
September	1st to 10th	Night	37% 5% 14% 27% 16% 1	1900
	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 12% 23% 9% 1	2453
	11th to 20th	Night	51% 4 12% 20% 10% 1	2555
	21st to end	Night	59% 4 11% 19% 8%	2660
December	1st to 10th	Night	64% 5% 11% 16% 4	2660
	11th to 20th	Night	61% 3 8% 19% 7% 1	3288
	21st to end	Night	67% 3 9% 15% 5%	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	23% 10% 28% 30% 8%	180
	11th to 20th	Day	26% 12% 33% 23% 4 2	180
	21st to end	Day	21% 12% 31% 27% 7% 2	198
February	1st to 10th	Day	31% 17% 35% 14% 4	252
	11th to 20th	Day	21% 13% 39% 23% 4	359
	21st to end	Day	28% 12% 32% 24% 4	382
March	1st to 10th	Day	25% 12% 31% 24% 8%	460
	11th to 20th	Day	22% 13% 35% 24% 5% 1	460
	21st to end	Day	27% 11% 32% 19% 9% 2	506
April	1st to 10th	Day	28% 13% 26% 21% 8% 3	460
	11th to 20th	Day	30% 14% 23% 21% 9% 2	452
	21st to end	Day	27% 13% 30% 19% 8% 3	460
May	1st to 10th	Day	22% 10% 32% 25% 9% 2	463
	11th to 20th	Day	20% 6% 31% 26% 13% 3	487
	21st to end	Day	17% 11% 32% 25% 12% 3	529
June	1st to 10th	Day	24% 9% 26% 26% 12% 3	490
	11th to 20th	Day	15% 11% 24% 31% 15% 3	490
	21st to end	Day	23% 7% 26% 26% 14% 4	490
July	1st to 10th	Day	13% 5% 24% 33% 19% 5%	485
	11th to 20th	Day	15% 5% 26% 32% 18% 4	484
	21st to end	Day	12% 6% 22% 37% 17% 5%	532
August	1st to 10th	Day	15% 5% 22% 31% 21% 6%	486
	11th to 20th	Day	12% 4 20% 31% 21% 12%	479
	21st to end	Day	15% 6% 24% 25% 21% 8%	539
September	1st to 10th	Day	14% 5% 27% 28% 18% 9%	490
	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	26% 13% 25% 24% 11% 1	374
	11th to 20th	Day	25% 12% 35% 19% 8% 1	280
	21st to end	Day	31% 12% 26% 22% 8% 1	180
December	1st to 10th	Day	29% 11% 24% 27% 8% 2	180
	11th to 20th	Day	26% 12% 37% 19% 4 1	180
	21st to end	Day	32% 16% 28% 16% 8% 1	198
January	1st to 10th	Night	25% 11% 30% 28% 6%	760
	11th to 20th	Night	25% 10% 32% 27% 7%	760
	21st to end	Night	18% 8% 35% 30% 8% 1	836
February	1st to 10th	Night	22% 8% 36% 29% 5% 1	760
	11th to 20th	Night	21% 11% 36% 27% 5%	743
	21st to end	Night	24% 8% 32% 32% 4	628
March	1st to 10th	Night	25% 9% 31% 31% 5%	760
	11th to 20th	Night	26% 10% 30% 26% 8%	760
	21st to end	Night	22% 9% 31% 31% 7%	836
April	1st to 10th	Night	26% 10% 28% 30% 6%	760
	11th to 20th	Night	26% 9% 30% 28% 6% 1	751
	21st to end	Night	27% 8% 31% 26% 8%	610
May	1st to 10th	Night	24% 5% 32% 29% 8% 2	421
	11th to 20th	Night	24% 3 28% 35% 9% 1	374
	21st to end	Night	18% 5% 37% 31% 8%	411
June	1st to 10th	Night	26% 4 23% 36% 12%	380
	11th to 20th	Night	19% 4 28% 35% 13% 1	380
	21st to end	Night	21% 4 24% 35% 15% 1	380
July	1st to 10th	Night	11% 4 27% 43% 15% 1	370
	11th to 20th	Night	13% 3 21% 46% 18%	368
	21st to end	Night	12% 3 18% 46% 19% 1	416
August	1st to 10th	Night	15% 4 12% 44% 23% 1	378
	11th to 20th	Night	15% 2 18% 37% 24% 3	558
	21st to end	Night	15% 2 22% 37% 21% 2	836
September	1st to 10th	Night	14% 3 23% 42% 18% 1	760
	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	24% 10% 29% 28% 9%	755
	11th to 20th	Night	24% 8% 32% 25% 10% 1	760
	21st to end	Night	29% 11% 28% 24% 8%	760
December	1st to 10th	Night	30% 9% 29% 24% 7%	760
	11th to 20th	Night	27% 11% 31% 24% 6% 1	760
	21st to end	Night	34% 10% 29% 20% 6%	836

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