Observatoire de Ste-Christine
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire de Ste-Christine clear sky chart from 2005-11-06 to 2026-06-16.

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	19% 12% 4 9% 5% 5% 4 3 5% 6% 28%	137693
	Night	18% 14% 4 10% 6% 4 4 3 4 5% 27%	134361
Transparency	Day	56% 6% 11% 18% 8% 1	141150
	Night	59% 6% 10% 17% 8% 1	138993
Seeing	Day	26% 17% 30% 18% 7% 2	16616
	Night	26% 14% 29% 22% 8% 1	25544

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% 17% 6% 6% 3 2 3 3 16%	4661
	11th to 20th	Day	11% 18% 8% 20% 9% 5% 4 3 4 4 13%	4650
	21st to end	Day	9% 16% 7% 14% 11% 9% 5% 4 4 4 18%	5124
February	1st to 10th	Day	16% 17% 5% 12% 8% 5% 4 3 4 4 21%	1769
	11th to 20th	Day	15% 19% 6% 14% 6% 4 4 3 5% 5% 20%	2017
	21st to end	Day	15% 18% 5% 10% 6% 7% 4 3 4 5% 23%	1730
March	1st to 10th	Day	20% 14% 7% 13% 6% 5% 4 3 3 4 21%	4576
	11th to 20th	Day	15% 17% 4 9% 4 4 4 4 4 6% 29%	4750
	21st to end	Day	21% 14% 5% 9% 4 4 3 3 4 5% 29%	6097
April	1st to 10th	Day	23% 15% 4 8% 5% 4 4 3 3 4 26%	2520
	11th to 20th	Day	22% 12% 3 6% 4 4 3 3 4 4 34%	2519
	21st to end	Day	24% 11% 3 6% 5% 3 4 3 4 6% 30%	2730
May	1st to 10th	Day	27% 11% 3 8% 5% 5% 5% 4 5% 6% 22%	7891
	11th to 20th	Day	20% 8% 3 8% 5% 5% 5% 4 6% 8% 29%	8221
	21st to end	Day	21% 9% 3 7% 4 5% 5% 4 5% 6% 32%	9060
June	1st to 10th	Day	25% 8% 3 6% 4 4 5% 4 5% 7% 30%	2940
	11th to 20th	Day	18% 6% 2 7% 5% 4 4 4 6% 9% 35%	2870
	21st to end	Day	24% 7% 4 7% 5% 5% 5% 3 5% 7% 29%	2800
July	1st to 10th	Day	16% 8% 3 7% 5% 6% 6% 5% 7% 9% 28%	6360
	11th to 20th	Day	14% 6% 2 6% 4 5% 6% 5% 6% 9% 36%	6360
	21st to end	Day	14% 6% 2 5% 3 4 4 4 6% 9% 42%	6926
August	1st to 10th	Day	17% 7% 3 7% 4 5% 6% 5% 7% 9% 30%	4563
	11th to 20th	Day	18% 6% 2 6% 4 4 5% 4 6% 8% 34%	4161
	21st to end	Day	21% 5% 2 6% 4 4 4 3 5% 7% 39%	4312
September	1st to 10th	Day	15% 6% 2 5% 4 4 5% 4 5% 8% 42%	2400
	11th to 20th	Day	18% 5% 2 5% 3 3 3 3 5% 7% 45%	2264
	21st to end	Day	20% 8% 2 5% 3 3 4 3 6% 7% 38%	2200
October	1st to 10th	Day	22% 8% 3 6% 4 4 5% 4 6% 7% 33%	2142
	11th to 20th	Day	23% 11% 3 7% 5% 4 4 3 5% 6% 29%	1896
	21st to end	Day	27% 15% 3 7% 4 4 3 3 4 5% 25%	1980
November	1st to 10th	Day	21% 15% 3 8% 4 4 3 3 4 5% 30%	1851
	11th to 20th	Day	18% 18% 6% 9% 5% 4 3 3 4 5% 24%	1879
	21st to end	Day	23% 19% 5% 9% 5% 3 4 3 5% 5% 20%	1680
December	1st to 10th	Day	20% 22% 6% 13% 7% 4 3 3 4 4 15%	2680
	11th to 20th	Day	21% 18% 7% 11% 5% 4 4 2 3 4 22%	3066
	21st to end	Day	21% 17% 5% 12% 5% 4 4 3 4 5% 19%	4048
January	1st to 10th	Night	15% 22% 8% 15% 6% 4 4 3 3 4 18%	8234
	11th to 20th	Night	13% 21% 8% 19% 8% 5% 4 3 4 3 12%	8235
	21st to end	Night	10% 16% 6% 14% 11% 6% 4 3 4 4 21%	9057
February	1st to 10th	Night	13% 18% 5% 14% 7% 6% 4 3 4 5% 21%	2848
	11th to 20th	Night	13% 17% 5% 13% 7% 5% 4 3 4 5% 24%	2489
	21st to end	Night	14% 18% 5% 10% 5% 4 3 3 4 4 28%	2076
March	1st to 10th	Night	20% 15% 5% 9% 6% 4 4 3 3 4 27%	5484
	11th to 20th	Night	17% 17% 4 9% 5% 5% 4 3 4 6% 26%	5428
	21st to end	Night	17% 18% 5% 10% 5% 4 4 3 4 4 27%	5075
April	1st to 10th	Night	25% 13% 4 7% 5% 4 4 3 4 6% 27%	2100
	11th to 20th	Night	24% 10% 3 7% 4 4 4 3 4 5% 32%	2049
	21st to end	Night	22% 11% 3 7% 3 4 4 3 4 5% 33%	1890
May	1st to 10th	Night	27% 10% 3 8% 5% 4 5% 3 5% 6% 24%	5062
	11th to 20th	Night	23% 7% 3 7% 4 6% 5% 4 5% 7% 29%	4639
	21st to end	Night	20% 9% 2 7% 5% 4 4 4 5% 7% 31%	5114
June	1st to 10th	Night	24% 7% 3 5% 4 4 5% 4 5% 8% 31%	1680
	11th to 20th	Night	20% 6% 1 6% 5% 4 5% 4 6% 7% 36%	1640
	21st to end	Night	19% 8% 2 7% 5% 4 5% 5% 5% 7% 32%	1600
July	1st to 10th	Night	16% 8% 3 8% 5% 6% 6% 4 7% 8% 30%	3600
	11th to 20th	Night	19% 7% 2 6% 4 4 4 4 5% 7% 39%	3600
	21st to end	Night	14% 6% 2 6% 4 4 5% 4 6% 9% 40%	3926
August	1st to 10th	Night	22% 8% 2 7% 4 4 4 3 5% 6% 35%	2586
	11th to 20th	Night	17% 8% 3 7% 5% 5% 4 4 5% 7% 35%	2848
	21st to end	Night	20% 6% 2 6% 4 3 4 3 5% 6% 41%	3586
September	1st to 10th	Night	17% 7% 2 6% 5% 4 3 3 5% 6% 43%	2000
	11th to 20th	Night	16% 6% 1 5% 3 4 3 3 4 6% 49%	2135
	21st to end	Night	19% 6% 2 5% 5% 4 4 2 4 7% 42%	2200
October	1st to 10th	Night	19% 8% 2 6% 4 4 4 3 6% 6% 38%	2255
	11th to 20th	Night	22% 11% 3 7% 4 4 4 3 4 6% 32%	2503
	21st to end	Night	26% 11% 3 7% 5% 5% 4 3 4 5% 27%	2860
November	1st to 10th	Night	22% 13% 3 8% 4 4 4 4 4 5% 28%	2667
	11th to 20th	Night	21% 15% 5% 8% 4 3 3 3 4 5% 28%	2737
	21st to end	Night	22% 18% 6% 9% 4 3 4 2 4 5% 24%	2940
December	1st to 10th	Night	19% 24% 8% 13% 7% 4 3 2 3 3 13%	4720
	11th to 20th	Night	22% 18% 6% 12% 5% 5% 3 2 3 3 21%	5348
	21st to end	Night	22% 18% 5% 10% 4 4 3 2 4 5% 22%	7150

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	75% 5% 7% 11% 2	4662
	11th to 20th	Day	74% 7% 6% 9% 4	4680
	21st to end	Day	70% 7% 6% 9% 8%	5124
February	1st to 10th	Day	69% 5% 8% 13% 5% 1	1769
	11th to 20th	Day	69% 5% 9% 12% 5% 1	2026
	21st to end	Day	66% 5% 7% 14% 6% 2	1730
March	1st to 10th	Day	68% 5% 6% 10% 8% 2	4579
	11th to 20th	Day	57% 6% 14% 12% 11% 1	4750
	21st to end	Day	59% 5% 7% 14% 14% 1	6097
April	1st to 10th	Day	63% 5% 7% 16% 8% 1	2520
	11th to 20th	Day	55% 5% 8% 18% 13% 1	2519
	21st to end	Day	56% 5% 10% 17% 10% 2	2730
May	1st to 10th	Day	62% 6% 9% 17% 6% 1	7903
	11th to 20th	Day	52% 7% 15% 18% 7% 1	8225
	21st to end	Day	51% 7% 11% 22% 9%	9061
June	1st to 10th	Day	52% 7% 12% 19% 9% 1	2940
	11th to 20th	Day	45% 7% 13% 22% 11% 1	2870
	21st to end	Day	55% 6% 11% 19% 9%	2800
July	1st to 10th	Day	50% 7% 14% 22% 6%	6290
	11th to 20th	Day	42% 8% 14% 28% 7%	6285
	21st to end	Day	39% 7% 14% 33% 7%	6728
August	1st to 10th	Day	49% 7% 16% 21% 6%	4549
	11th to 20th	Day	47% 8% 20% 20% 6%	4200
	21st to end	Day	44% 6% 16% 20% 12% 1	4312
September	1st to 10th	Day	40% 7% 14% 28% 9% 1	2400
	11th to 20th	Day	39% 6% 12% 30% 13%	2264
	21st to end	Day	45% 6% 14% 25% 10%	2200
October	1st to 10th	Day	46% 6% 15% 26% 7%	3493
	11th to 20th	Day	51% 5% 14% 25% 4	3060
	21st to end	Day	53% 4 16% 20% 7% 1	3180
November	1st to 10th	Day	59% 5% 11% 18% 7%	1851
	11th to 20th	Day	63% 6% 9% 14% 8% 1	1879
	21st to end	Day	69% 6% 11% 12% 2	1680
December	1st to 10th	Day	76% 5% 7% 10% 2	2680
	11th to 20th	Day	68% 4 7% 15% 5%	3066
	21st to end	Day	69% 4 7% 12% 8%	4048
January	1st to 10th	Night	72% 5% 9% 10% 3	8234
	11th to 20th	Night	76% 6% 7% 7% 3	8280
	21st to end	Night	68% 4 7% 11% 10%	9057
February	1st to 10th	Night	67% 4 8% 14% 6% 1	2848
	11th to 20th	Night	65% 6% 8% 15% 6%	2491
	21st to end	Night	61% 4 9% 14% 10% 1	2076
March	1st to 10th	Night	61% 5% 7% 14% 10% 3	5494
	11th to 20th	Night	59% 5% 12% 13% 8% 1	5429
	21st to end	Night	61% 5% 6% 17% 9% 1	5075
April	1st to 10th	Night	61% 4 7% 16% 11% 1	2100
	11th to 20th	Night	56% 5% 7% 19% 12% 1	2049
	21st to end	Night	53% 6% 8% 19% 13% 2	1890
May	1st to 10th	Night	60% 6% 11% 16% 7% 1	5068
	11th to 20th	Night	53% 7% 13% 20% 7% 1	4640
	21st to end	Night	50% 7% 10% 18% 14% 1	5115
June	1st to 10th	Night	51% 6% 11% 22% 10% 1	1680
	11th to 20th	Night	46% 7% 11% 21% 12% 2	1640
	21st to end	Night	50% 7% 12% 19% 10% 1	1600
July	1st to 10th	Night	50% 7% 17% 19% 7%	3560
	11th to 20th	Night	44% 6% 15% 27% 8%	3552
	21st to end	Night	40% 7% 17% 27% 9%	3809
August	1st to 10th	Night	50% 6% 14% 25% 6%	2576
	11th to 20th	Night	47% 8% 17% 21% 7%	2875
	21st to end	Night	43% 6% 12% 25% 13% 1	3586
September	1st to 10th	Night	42% 7% 12% 26% 13%	2000
	11th to 20th	Night	38% 5% 15% 30% 12% 1	2135
	21st to end	Night	43% 6% 13% 25% 13% 1	2200
October	1st to 10th	Night	49% 5% 11% 24% 10%	3684
	11th to 20th	Night	50% 6% 10% 26% 7%	4078
	21st to end	Night	52% 5% 13% 18% 10% 2	4610
November	1st to 10th	Night	58% 6% 11% 18% 6% 1	2667
	11th to 20th	Night	58% 7% 10% 14% 9% 2	2737
	21st to end	Night	65% 5% 11% 14% 4	2940
December	1st to 10th	Night	79% 4 8% 7% 2	4720
	11th to 20th	Night	70% 5% 6% 12% 7%	5348
	21st to end	Night	66% 5% 7% 13% 8%	7150

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	35% 15% 32% 15% 3	220
	11th to 20th	Day	34% 22% 33% 10% 2	220
	21st to end	Day	24% 26% 32% 12% 6%	242
February	1st to 10th	Day	32% 27% 27% 12% 1 1	267
	11th to 20th	Day	28% 23% 36% 11% 2	505
	21st to end	Day	27% 26% 30% 15% 1	446
March	1st to 10th	Day	30% 22% 30% 15% 3	540
	11th to 20th	Day	30% 23% 31% 13% 2 1	540
	21st to end	Day	31% 25% 25% 14% 4 1	594
April	1st to 10th	Day	35% 18% 28% 13% 5% 1	540
	11th to 20th	Day	34% 20% 25% 14% 5% 2	532
	21st to end	Day	31% 20% 32% 10% 5% 2	540
May	1st to 10th	Day	34% 18% 28% 14% 5% 1	543
	11th to 20th	Day	23% 17% 29% 21% 9% 1	567
	21st to end	Day	24% 22% 31% 17% 6% 1	617
June	1st to 10th	Day	26% 15% 34% 17% 7% 1	570
	11th to 20th	Day	21% 15% 34% 20% 9% 1	550
	21st to end	Day	25% 14% 34% 17% 8% 2	530
July	1st to 10th	Day	18% 13% 33% 24% 11% 2	525
	11th to 20th	Day	15% 11% 38% 27% 7% 2	524
	21st to end	Day	17% 10% 36% 26% 9% 1	576
August	1st to 10th	Day	18% 10% 26% 29% 14% 2	526
	11th to 20th	Day	17% 8% 29% 26% 17% 2	519
	21st to end	Day	19% 13% 27% 24% 12% 6%	583
September	1st to 10th	Day	17% 13% 33% 21% 12% 4	530
	11th to 20th	Day	18% 9% 25% 23% 17% 8%	530
	21st to end	Day	19% 14% 28% 22% 12% 5%	530
October	1st to 10th	Day	23% 14% 28% 22% 10% 4	530
	11th to 20th	Day	28% 17% 25% 20% 8% 1	472
	21st to end	Day	37% 19% 24% 16% 4	462
November	1st to 10th	Day	36% 16% 27% 18% 2 1	425
	11th to 20th	Day	32% 20% 26% 14% 5% 1	419
	21st to end	Day	35% 24% 29% 9% 4	220
December	1st to 10th	Day	34% 18% 28% 15% 4 1	220
	11th to 20th	Day	28% 30% 27% 12% 2	220
	21st to end	Day	32% 24% 26% 12% 5% 1	242
January	1st to 10th	Night	32% 17% 31% 16% 3	840
	11th to 20th	Night	29% 20% 30% 18% 4	840
	21st to end	Night	22% 17% 35% 22% 4	924
February	1st to 10th	Night	24% 20% 33% 18% 5%	840
	11th to 20th	Night	24% 22% 34% 17% 3	823
	21st to end	Night	25% 17% 37% 19% 3	692
March	1st to 10th	Night	28% 18% 31% 20% 3	840
	11th to 20th	Night	30% 18% 29% 18% 5%	840
	21st to end	Night	28% 16% 28% 22% 5% 1	924
April	1st to 10th	Night	32% 15% 28% 21% 3	840
	11th to 20th	Night	29% 16% 29% 20% 5%	805
	21st to end	Night	30% 16% 27% 19% 7%	630
May	1st to 10th	Night	30% 12% 30% 21% 6% 1	562
	11th to 20th	Night	24% 11% 32% 25% 7% 1	414
	21st to end	Night	23% 11% 36% 24% 6%	455
June	1st to 10th	Night	26% 9% 31% 25% 9%	420
	11th to 20th	Night	23% 8% 28% 30% 11%	410
	21st to end	Night	20% 8% 31% 29% 11% 1	400
July	1st to 10th	Night	17% 7% 32% 32% 12% 1	390
	11th to 20th	Night	15% 5% 27% 37% 14% 2	388
	21st to end	Night	15% 6% 28% 39% 11%	438
August	1st to 10th	Night	19% 5% 22% 33% 20% 1	398
	11th to 20th	Night	17% 5% 22% 34% 20% 1	567
	21st to end	Night	17% 7% 25% 34% 15% 2	880
September	1st to 10th	Night	19% 8% 27% 32% 12% 2	800
	11th to 20th	Night	19% 5% 25% 28% 21% 2	800
	21st to end	Night	21% 9% 29% 26% 14% 2	800
October	1st to 10th	Night	22% 13% 28% 26% 10% 1	800
	11th to 20th	Night	28% 14% 26% 24% 8% 1	800
	21st to end	Night	33% 14% 29% 20% 4	880
November	1st to 10th	Night	32% 17% 29% 17% 5%	820
	11th to 20th	Night	28% 19% 27% 17% 8% 1	840
	21st to end	Night	32% 21% 25% 16% 5% 1	840
December	1st to 10th	Night	35% 18% 27% 16% 3	840
	11th to 20th	Night	31% 20% 30% 15% 5% 1	840
	21st to end	Night	37% 18% 25% 16% 4	924

Page generated at 2026-06-13 02:31:42. Version ac07

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