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 2024-04-03.

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 6% 6% 3 5% 5% 5% 7% 34%	78641
	Night	18% 10% 4 7% 6% 3 4 4 5% 6% 33%	81482
Transparency	Day	50% 4 12% 21% 11% 1	78346
	Night	53% 4 11% 20% 10% 1	81311
Seeing	Day	21% 10% 28% 25% 12% 4	13710
	Night	22% 7% 28% 31% 10% 1	22861

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% 12% 7% 4 5% 4 5% 4 24%	2517
	11th to 20th	Day	15% 12% 6% 9% 7% 3 4 4 5% 7% 28%	2520
	21st to end	Day	14% 16% 4 9% 7% 4 6% 5% 5% 5% 24%	2772
February	1st to 10th	Day	14% 16% 4 9% 6% 4 4 5% 5% 6% 27%	1672
	11th to 20th	Day	13% 12% 5% 8% 7% 4 6% 5% 6% 5% 29%	1752
	21st to end	Day	18% 14% 6% 8% 5% 3 5% 4 5% 5% 28%	1570
March	1st to 10th	Day	16% 12% 4 9% 6% 4 5% 4 5% 5% 30%	1897
	11th to 20th	Day	16% 12% 4 6% 6% 3 5% 4 5% 6% 33%	1976
	21st to end	Day	19% 9% 3 6% 6% 3 4 4 4 5% 36%	2498
April	1st to 10th	Day	21% 10% 4 7% 6% 3 4 4 4 5% 33%	2184
	11th to 20th	Day	21% 7% 3 6% 5% 3 4 4 4 5% 37%	2134
	21st to end	Day	22% 9% 4 6% 5% 3 4 4 4 5% 32%	2300
May	1st to 10th	Day	20% 7% 3 6% 6% 3 5% 5% 5% 6% 34%	2496
	11th to 20th	Day	20% 6% 3 5% 5% 3 5% 4 6% 7% 37%	2478
	21st to end	Day	17% 6% 3 5% 5% 3 5% 5% 5% 8% 36%	2725
June	1st to 10th	Day	22% 8% 2 5% 5% 4 5% 5% 5% 8% 31%	2520
	11th to 20th	Day	15% 5% 3 6% 5% 3 6% 5% 5% 7% 39%	2520
	21st to end	Day	20% 7% 3 7% 7% 3 5% 5% 6% 8% 30%	2520
July	1st to 10th	Day	12% 4 2 5% 5% 4 6% 6% 7% 8% 41%	2520
	11th to 20th	Day	13% 5% 2 4 6% 4 6% 7% 7% 10% 37%	2520
	21st to end	Day	12% 5% 2 6% 5% 3 6% 7% 7% 9% 38%	2744
August	1st to 10th	Day	12% 6% 2 6% 6% 4 5% 6% 6% 9% 38%	2506
	11th to 20th	Day	10% 5% 2 6% 6% 4 6% 5% 6% 9% 41%	2289
	21st to end	Day	13% 5% 2 4 5% 3 4 5% 6% 8% 43%	2376
September	1st to 10th	Day	12% 6% 2 4 5% 3 5% 5% 6% 9% 41%	2160
	11th to 20th	Day	14% 4 2 4 4 2 4 4 5% 6% 50%	2090
	21st to end	Day	16% 6% 2 5% 5% 3 4 3 5% 7% 42%	1980
October	1st to 10th	Day	21% 6% 3 6% 5% 3 4 5% 5% 7% 36%	1850
	11th to 20th	Day	19% 9% 3 6% 7% 4 6% 5% 5% 6% 29%	1764
	21st to end	Day	25% 8% 4 6% 6% 2 4 4 5% 6% 30%	1782
November	1st to 10th	Day	16% 9% 3 6% 5% 3 4 4 6% 7% 35%	1671
	11th to 20th	Day	18% 11% 4 7% 5% 4 4 5% 5% 7% 31%	1620
	21st to end	Day	22% 10% 4 5% 6% 4 5% 5% 6% 6% 27%	1520
December	1st to 10th	Day	25% 12% 6% 9% 7% 3 4 4 4 5% 22%	1520
	11th to 20th	Day	22% 12% 5% 8% 6% 2 4 4 5% 5% 28%	1906
	21st to end	Day	28% 15% 5% 8% 5% 3 4 3 3 4 21%	2772
January	1st to 10th	Night	17% 14% 6% 10% 7% 4 4 4 5% 5% 24%	4429
	11th to 20th	Night	12% 13% 6% 9% 9% 4 6% 5% 5% 6% 26%	4440
	21st to end	Night	15% 15% 6% 10% 7% 4 4 4 5% 5% 25%	4884
February	1st to 10th	Night	14% 13% 6% 10% 7% 3 6% 4 5% 6% 25%	2506
	11th to 20th	Night	14% 10% 4 8% 7% 3 5% 5% 5% 6% 31%	2314
	21st to end	Night	15% 14% 5% 8% 6% 2 4 4 5% 5% 32%	1884
March	1st to 10th	Night	18% 13% 5% 7% 6% 3 4 4 4 5% 32%	2270
	11th to 20th	Night	18% 13% 4 6% 5% 3 5% 4 4 6% 32%	2200
	21st to end	Night	16% 9% 4 7% 6% 2 4 4 4 5% 39%	2099
April	1st to 10th	Night	24% 8% 4 6% 5% 3 4 5% 4 6% 32%	1821
	11th to 20th	Night	22% 6% 3 6% 5% 3 3 3 4 7% 37%	1775
	21st to end	Night	22% 8% 3 6% 5% 3 4 4 4 6% 35%	1658
May	1st to 10th	Night	21% 8% 2 7% 5% 3 4 5% 4 6% 35%	1479
	11th to 20th	Night	20% 6% 2 5% 5% 3 4 5% 5% 5% 39%	1415
	21st to end	Night	17% 6% 2 6% 5% 3 5% 5% 5% 7% 41%	1550
June	1st to 10th	Night	20% 7% 3 6% 5% 3 5% 5% 6% 9% 32%	1440
	11th to 20th	Night	17% 7% 3 5% 4 3 4 5% 6% 7% 39%	1440
	21st to end	Night	19% 5% 3 6% 5% 4 5% 4 6% 6% 36%	1440
July	1st to 10th	Night	11% 4 2 5% 5% 3 5% 6% 7% 9% 43%	1440
	11th to 20th	Night	11% 5% 2 4 6% 3 5% 6% 6% 10% 41%	1440
	21st to end	Night	12% 5% 3 5% 5% 3 5% 4 7% 9% 42%	1574
August	1st to 10th	Night	12% 5% 2 5% 5% 3 5% 4 6% 9% 43%	1432
	11th to 20th	Night	12% 6% 2 5% 5% 3 5% 5% 5% 7% 44%	1592
	21st to end	Night	14% 5% 2 6% 5% 3 4 4 6% 8% 43%	1980
September	1st to 10th	Night	12% 5% 3 5% 6% 3 4 5% 6% 7% 45%	1800
	11th to 20th	Night	15% 5% 2 4 4 3 3 3 4 7% 49%	1869
	21st to end	Night	17% 4 2 6% 5% 2 4 4 5% 7% 44%	1980
October	1st to 10th	Night	19% 6% 3 6% 5% 2 5% 4 5% 6% 40%	2108
	11th to 20th	Night	21% 7% 4 6% 6% 3 4 3 5% 6% 36%	2195
	21st to end	Night	23% 8% 4 7% 6% 3 4 4 4 6% 32%	2574
November	1st to 10th	Night	19% 9% 3 6% 5% 3 4 5% 5% 7% 33%	2407
	11th to 20th	Night	19% 9% 3 7% 5% 3 4 4 5% 6% 34%	2555
	21st to end	Night	22% 12% 4 6% 6% 3 4 3 4 6% 29%	2660
December	1st to 10th	Night	21% 13% 5% 8% 6% 4 5% 5% 4 6% 23%	2660
	11th to 20th	Night	23% 14% 5% 7% 5% 2 4 4 4 5% 27%	3288
	21st to end	Night	29% 15% 5% 8% 5% 2 3 3 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	57% 3 10% 18% 10% 2	1900
	11th to 20th	Day	53% 3 12% 15% 14% 3	1976
	21st to end	Day	51% 4 9% 18% 15% 4	2498
April	1st to 10th	Day	55% 4 7% 19% 12% 2	2184
	11th to 20th	Day	49% 3 7% 23% 15% 2	2134
	21st to end	Day	55% 3 8% 18% 12% 4	2300
May	1st to 10th	Day	50% 3 7% 22% 15% 2	2496
	11th to 20th	Day	46% 4 10% 21% 15% 3	2482
	21st to end	Day	46% 5% 13% 19% 15% 2	2725
June	1st to 10th	Day	52% 5% 10% 20% 12% 2	2520
	11th to 20th	Day	44% 5% 10% 24% 14% 3	2520
	21st to end	Day	52% 5% 13% 19% 10% 1	2520
July	1st to 10th	Day	39% 6% 14% 28% 12% 1	2450
	11th to 20th	Day	40% 5% 17% 27% 10%	2445
	21st to end	Day	40% 6% 18% 27% 9%	2591
August	1st to 10th	Day	43% 5% 18% 25% 9%	2492
	11th to 20th	Day	39% 5% 19% 26% 10%	2289
	21st to end	Day	37% 5% 16% 27% 14% 1	2376
September	1st to 10th	Day	38% 6% 14% 28% 13% 1	2160
	11th to 20th	Day	35% 5% 12% 32% 15% 1	2090
	21st to end	Day	42% 4 14% 27% 11% 1	1980
October	1st to 10th	Day	49% 4 12% 23% 12%	1850
	11th to 20th	Day	54% 5% 14% 20% 7%	1764
	21st to end	Day	56% 3 13% 19% 8% 1	1782
November	1st to 10th	Day	48% 5% 14% 23% 9% 1	1671
	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	56% 3 9% 18% 11% 3	2280
	11th to 20th	Night	55% 3 9% 16% 13% 3	2201
	21st to end	Night	50% 3 7% 20% 15% 4	2099
April	1st to 10th	Night	53% 5% 7% 19% 15% 2	1821
	11th to 20th	Night	50% 4 6% 22% 15% 2	1775
	21st to end	Night	51% 4 7% 20% 13% 4	1658
May	1st to 10th	Night	51% 2 7% 19% 15% 5%	1479
	11th to 20th	Night	47% 4 8% 19% 18% 4	1416
	21st to end	Night	44% 5% 11% 20% 17% 2	1551
June	1st to 10th	Night	50% 5% 10% 22% 13% 1	1440
	11th to 20th	Night	43% 5% 11% 23% 15% 3	1440
	21st to end	Night	47% 6% 12% 20% 14%	1440
July	1st to 10th	Night	36% 6% 14% 27% 17% 1	1400
	11th to 20th	Night	38% 5% 15% 29% 12%	1392
	21st to end	Night	38% 6% 18% 26% 12%	1486
August	1st to 10th	Night	39% 5% 17% 26% 12%	1422
	11th to 20th	Night	38% 5% 17% 27% 12%	1592
	21st to end	Night	39% 5% 15% 28% 13% 1	1980
September	1st to 10th	Night	38% 5% 14% 27% 15% 1	1800
	11th to 20th	Night	36% 4 13% 34% 12% 1	1869
	21st to end	Night	41% 5% 11% 29% 14%	1980
October	1st to 10th	Night	46% 5% 10% 25% 13% 1	2108
	11th to 20th	Night	51% 4 12% 25% 9%	2195
	21st to end	Night	56% 3 12% 19% 9% 1	2574
November	1st to 10th	Night	51% 4 12% 23% 9% 1	2407
	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% 31% 19% 9% 2	506
April	1st to 10th	Day	27% 13% 28% 21% 8% 3	428
	11th to 20th	Day	29% 13% 23% 23% 10% 2	412
	21st to end	Day	27% 12% 30% 20% 8% 3	420
May	1st to 10th	Day	23% 10% 32% 24% 9% 2	423
	11th to 20th	Day	21% 6% 32% 25% 12% 3	447
	21st to end	Day	17% 11% 33% 24% 12% 3	485
June	1st to 10th	Day	24% 10% 26% 26% 11% 3	450
	11th to 20th	Day	16% 11% 24% 30% 15% 3	450
	21st to end	Day	22% 6% 25% 28% 16% 4	450
July	1st to 10th	Day	13% 5% 22% 34% 20% 6%	445
	11th to 20th	Day	15% 5% 26% 32% 19% 4	444
	21st to end	Day	13% 6% 22% 37% 18% 5%	488
August	1st to 10th	Day	14% 4 22% 31% 22% 6%	446
	11th to 20th	Day	11% 4 20% 33% 19% 13%	439
	21st to end	Day	15% 7% 24% 25% 21% 8%	495
September	1st to 10th	Day	13% 4 26% 28% 19% 9%	450
	11th to 20th	Day	16% 7% 22% 25% 18% 12%	450
	21st to end	Day	18% 7% 26% 24% 17% 7%	450
October	1st to 10th	Day	22% 9% 26% 22% 15% 5%	450
	11th to 20th	Day	22% 11% 30% 22% 12% 3	432
	21st to end	Day	33% 11% 24% 24% 8% 1	396
November	1st to 10th	Day	27% 13% 24% 24% 11% 1	365
	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%	729
	11th to 20th	Night	25% 9% 29% 29% 7% 1	711
	21st to end	Night	28% 8% 30% 26% 8%	578
May	1st to 10th	Night	24% 6% 31% 30% 8% 2	399
	11th to 20th	Night	24% 3 30% 35% 8% 1	354
	21st to end	Night	18% 5% 37% 31% 9% 1	389
June	1st to 10th	Night	27% 3 23% 35% 12%	360
	11th to 20th	Night	19% 4 29% 34% 14% 1	360
	21st to end	Night	19% 4 24% 35% 16% 1	360
July	1st to 10th	Night	10% 4 27% 42% 15% 1	350
	11th to 20th	Night	12% 3 21% 46% 18%	348
	21st to end	Night	12% 3 19% 46% 19% 1	394
August	1st to 10th	Night	15% 4 12% 44% 24% 1	358
	11th to 20th	Night	14% 2 18% 38% 24% 3	528
	21st to end	Night	16% 2 22% 36% 22% 2	792
September	1st to 10th	Night	14% 3 22% 42% 18% 1	720
	11th to 20th	Night	17% 5% 18% 38% 21% 2	720
	21st to end	Night	18% 4 27% 32% 18% 3	720
October	1st to 10th	Night	21% 6% 26% 34% 12% 1	720
	11th to 20th	Night	24% 7% 27% 30% 12% 1	720
	21st to end	Night	28% 7% 30% 28% 7%	792
November	1st to 10th	Night	24% 10% 29% 28% 9%	740
	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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