Observatoire de Sainte-Sophie
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire de Sainte-Sophie clear sky chart from 2005-11-06 to 2025-09-19.

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	16% 10% 3 8% 5% 5% 5% 4 5% 7% 32%	126615
	Night	16% 11% 4 9% 5% 5% 4 3 5% 6% 33%	122443
Transparency	Day	49% 6% 13% 20% 10% 1	130060
	Night	51% 6% 12% 19% 10% 1	127085
Seeing	Day	21% 16% 32% 21% 8% 2	15626
	Night	21% 11% 33% 26% 8% 1	24533

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	14% 20% 7% 13% 5% 4 3 3 5% 4 23%	3597
	11th to 20th	Day	12% 15% 6% 13% 6% 5% 4 4 4 5% 26%	3570
	21st to end	Day	9% 16% 6% 11% 6% 5% 5% 4 5% 5% 28%	3960
February	1st to 10th	Day	13% 15% 4 10% 8% 6% 4 3 4 5% 27%	1759
	11th to 20th	Day	11% 13% 5% 12% 7% 5% 5% 4 5% 7% 26%	1838
	21st to end	Day	17% 15% 4 10% 6% 4 5% 3 4 5% 27%	1650
March	1st to 10th	Day	18% 15% 5% 10% 6% 5% 4 3 4 4 25%	4476
	11th to 20th	Day	10% 13% 4 10% 5% 5% 5% 3 5% 7% 33%	4722
	21st to end	Day	18% 10% 4 9% 5% 5% 4 3 4 5% 34%	5958
April	1st to 10th	Day	20% 13% 3 7% 4 5% 4 3 4 5% 33%	2400
	11th to 20th	Day	21% 8% 2 6% 5% 4 4 3 5% 6% 35%	2374
	21st to end	Day	20% 10% 4 7% 5% 4 4 3 5% 5% 33%	2556
May	1st to 10th	Day	26% 10% 3 8% 5% 5% 5% 4 5% 6% 23%	6333
	11th to 20th	Day	21% 8% 3 7% 4 4 5% 3 6% 8% 30%	6318
	21st to end	Day	22% 8% 2 7% 4 5% 5% 4 6% 7% 31%	6949
June	1st to 10th	Day	21% 7% 3 6% 6% 5% 5% 4 6% 7% 30%	2800
	11th to 20th	Day	14% 6% 3 7% 5% 5% 5% 5% 7% 7% 35%	2800
	21st to end	Day	19% 8% 4 7% 5% 6% 5% 5% 6% 7% 29%	2800
July	1st to 10th	Day	14% 6% 2 8% 6% 6% 6% 5% 7% 8% 32%	6360
	11th to 20th	Day	12% 5% 2 6% 4 5% 6% 5% 7% 9% 39%	6360
	21st to end	Day	10% 5% 2 5% 4 4 5% 4 6% 9% 46%	6926
August	1st to 10th	Day	13% 5% 3 7% 5% 6% 6% 5% 7% 8% 34%	4563
	11th to 20th	Day	14% 6% 3 7% 4 5% 5% 4 7% 8% 37%	4151
	21st to end	Day	16% 4 2 6% 5% 4 5% 4 6% 8% 40%	4312
September	1st to 10th	Day	13% 5% 2 5% 4 4 4 4 6% 10% 43%	2400
	11th to 20th	Day	12% 4 2 6% 4 3 4 3 6% 7% 50%	2304
	21st to end	Day	17% 7% 1 6% 4 3 4 4 6% 7% 42%	2090
October	1st to 10th	Day	20% 7% 2 6% 4 4 4 3 5% 7% 36%	1944
	11th to 20th	Day	19% 9% 3 8% 6% 5% 5% 3 6% 6% 30%	1864
	21st to end	Day	22% 11% 3 7% 5% 4 4 3 5% 5% 31%	1881
November	1st to 10th	Day	14% 9% 3 7% 5% 6% 5% 4 5% 8% 34%	1761
	11th to 20th	Day	17% 11% 3 8% 5% 5% 4 4 5% 7% 31%	1693
	21st to end	Day	20% 13% 3 7% 6% 5% 5% 4 5% 7% 25%	1600
December	1st to 10th	Day	18% 17% 6% 13% 6% 5% 4 3 4 4 20%	2600
	11th to 20th	Day	17% 16% 4 9% 5% 4 3 3 5% 4 29%	2986
	21st to end	Day	22% 14% 4 9% 4 4 5% 3 4 4 26%	3960
January	1st to 10th	Night	12% 21% 7% 13% 6% 4 4 3 4 4 22%	6349
	11th to 20th	Night	9% 14% 7% 16% 7% 6% 4 3 5% 5% 24%	6315
	21st to end	Night	10% 13% 5% 13% 7% 6% 5% 4 5% 5% 27%	6996
February	1st to 10th	Night	12% 13% 4 12% 7% 4 6% 3 6% 6% 27%	2640
	11th to 20th	Night	12% 11% 4 11% 5% 5% 5% 4 5% 5% 31%	2447
	21st to end	Night	14% 13% 4 9% 6% 5% 5% 3 4 5% 32%	1980
March	1st to 10th	Night	21% 14% 4 9% 5% 4 4 3 4 4 29%	5364
	11th to 20th	Night	11% 14% 4 7% 5% 4 5% 4 6% 8% 32%	5220
	21st to end	Night	15% 10% 4 9% 6% 5% 5% 3 5% 5% 34%	4973
April	1st to 10th	Night	23% 9% 3 7% 4 4 4 3 5% 6% 32%	2000
	11th to 20th	Night	19% 8% 2 7% 5% 4 4 4 5% 6% 37%	1975
	21st to end	Night	21% 8% 3 6% 3 4 5% 3 5% 6% 36%	1842
May	1st to 10th	Night	25% 9% 3 8% 5% 5% 4 3 5% 5% 26%	3650
	11th to 20th	Night	21% 8% 3 7% 4 4 4 3 6% 7% 33%	3575
	21st to end	Night	20% 9% 3 8% 5% 4 5% 3 6% 6% 31%	3926
June	1st to 10th	Night	20% 6% 3 7% 5% 4 4 4 6% 8% 34%	1600
	11th to 20th	Night	16% 8% 2 7% 3 5% 4 4 6% 7% 39%	1600
	21st to end	Night	19% 6% 2 6% 5% 4 5% 4 5% 7% 37%	1600
July	1st to 10th	Night	13% 7% 3 7% 5% 5% 6% 5% 7% 8% 35%	3600
	11th to 20th	Night	13% 6% 2 6% 4 4 4 4 5% 7% 44%	3600
	21st to end	Night	9% 5% 2 6% 4 5% 5% 4 6% 7% 47%	3926
August	1st to 10th	Night	13% 6% 3 7% 5% 5% 5% 4 6% 8% 40%	2586
	11th to 20th	Night	15% 7% 2 6% 4 4 4 3 5% 7% 43%	2861
	21st to end	Night	18% 5% 2 5% 4 4 4 3 5% 7% 42%	3586
September	1st to 10th	Night	10% 4 2 6% 5% 5% 4 4 6% 7% 47%	2000
	11th to 20th	Night	13% 5% 2 5% 4 3 4 3 4 8% 51%	2052
	21st to end	Night	17% 5% 2 5% 3 4 3 3 6% 7% 46%	2090
October	1st to 10th	Night	18% 7% 3 6% 5% 4 4 3 4 5% 41%	2232
	11th to 20th	Night	19% 8% 3 6% 4 4 4 3 5% 6% 37%	2315
	21st to end	Night	21% 9% 3 8% 5% 4 4 3 5% 6% 32%	2717
November	1st to 10th	Night	17% 9% 3 8% 5% 5% 4 4 5% 7% 33%	2537
	11th to 20th	Night	17% 9% 3 8% 5% 4 5% 4 5% 5% 35%	2705
	21st to end	Night	20% 13% 4 8% 5% 4 3 3 4 6% 29%	2800
December	1st to 10th	Night	16% 14% 5% 9% 7% 6% 5% 4 6% 6% 21%	4580
	11th to 20th	Night	23% 13% 4 8% 5% 4 4 3 4 4 28%	5208
	21st to end	Night	23% 17% 5% 8% 4 3 3 2 4 4 28%	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	63% 6% 10% 17% 4 1	3598
	11th to 20th	Day	58% 7% 10% 17% 6% 3	3600
	21st to end	Day	56% 6% 10% 15% 11% 1	3960
February	1st to 10th	Day	59% 5% 8% 17% 8% 2	1759
	11th to 20th	Day	58% 5% 12% 15% 10% 1	1847
	21st to end	Day	59% 4 9% 15% 10% 3	1650
March	1st to 10th	Day	63% 4 8% 11% 10% 3	4479
	11th to 20th	Day	49% 6% 18% 14% 11% 2	4722
	21st to end	Day	52% 5% 7% 16% 18% 2	5958
April	1st to 10th	Day	55% 4 8% 18% 12% 3	2400
	11th to 20th	Day	48% 6% 9% 22% 14% 2	2374
	21st to end	Day	53% 6% 9% 17% 13% 3	2556
May	1st to 10th	Day	60% 6% 8% 18% 7% 1	6344
	11th to 20th	Day	51% 7% 16% 16% 8% 2	6322
	21st to end	Day	50% 7% 12% 17% 12% 1	6949
June	1st to 10th	Day	51% 7% 11% 18% 12% 2	2800
	11th to 20th	Day	43% 8% 12% 22% 12% 3	2800
	21st to end	Day	53% 8% 12% 17% 9% 1	2800
July	1st to 10th	Day	46% 7% 14% 24% 8%	6290
	11th to 20th	Day	38% 8% 15% 29% 11%	6285
	21st to end	Day	33% 6% 17% 34% 10%	6728
August	1st to 10th	Day	44% 8% 19% 21% 8%	4549
	11th to 20th	Day	41% 9% 17% 26% 6%	4193
	21st to end	Day	41% 7% 17% 21% 13% 1	4312
September	1st to 10th	Day	36% 8% 16% 29% 13%	2400
	11th to 20th	Day	33% 6% 15% 32% 12% 1	2304
	21st to end	Day	42% 6% 15% 25% 11%	2090
October	1st to 10th	Day	44% 7% 14% 25% 9%	3230
	11th to 20th	Day	44% 6% 16% 27% 7%	3080
	21st to end	Day	42% 6% 21% 20% 10% 1	3081
November	1st to 10th	Day	47% 8% 14% 21% 9% 1	1761
	11th to 20th	Day	51% 7% 13% 18% 11% 1	1693
	21st to end	Day	57% 8% 15% 14% 6% 1	1600
December	1st to 10th	Day	68% 5% 9% 14% 4	2600
	11th to 20th	Day	58% 5% 10% 17% 10%	2986
	21st to end	Day	61% 5% 10% 15% 9%	3960
January	1st to 10th	Night	65% 6% 12% 14% 4	6349
	11th to 20th	Night	61% 6% 12% 15% 5% 1	6360
	21st to end	Night	57% 7% 11% 11% 14% 1	6996
February	1st to 10th	Night	57% 5% 10% 18% 8% 1	2640
	11th to 20th	Night	53% 6% 11% 20% 10% 1	2449
	21st to end	Night	53% 5% 10% 18% 13% 2	1980
March	1st to 10th	Night	58% 5% 8% 13% 12% 4	5374
	11th to 20th	Night	48% 7% 15% 16% 11% 3	5221
	21st to end	Night	52% 5% 7% 21% 12% 3	4973
April	1st to 10th	Night	52% 5% 8% 19% 14% 2	2000
	11th to 20th	Night	48% 5% 9% 21% 15% 2	1975
	21st to end	Night	49% 5% 8% 20% 14% 3	1842
May	1st to 10th	Night	58% 6% 10% 17% 7% 2	3656
	11th to 20th	Night	49% 7% 14% 18% 10% 2	3576
	21st to end	Night	51% 7% 11% 16% 13% 1	3927
June	1st to 10th	Night	48% 7% 12% 19% 14% 1	1600
	11th to 20th	Night	44% 7% 12% 21% 14% 3	1600
	21st to end	Night	47% 8% 12% 19% 14% 1	1600
July	1st to 10th	Night	44% 7% 18% 22% 9%	3560
	11th to 20th	Night	37% 6% 18% 31% 8%	3552
	21st to end	Night	34% 6% 17% 30% 13%	3809
August	1st to 10th	Night	42% 8% 14% 27% 9%	2576
	11th to 20th	Night	41% 5% 19% 26% 8%	2885
	21st to end	Night	41% 7% 15% 23% 13% 1	3586
September	1st to 10th	Night	33% 8% 16% 27% 15% 1	2000
	11th to 20th	Night	33% 6% 15% 34% 12% 1	2052
	21st to end	Night	38% 6% 13% 29% 14%	2090
October	1st to 10th	Night	44% 5% 14% 25% 11% 1	3726
	11th to 20th	Night	41% 6% 13% 29% 11%	3838
	21st to end	Night	43% 5% 20% 18% 13% 2	4467
November	1st to 10th	Night	49% 7% 13% 22% 8% 1	2537
	11th to 20th	Night	50% 6% 13% 19% 10% 2	2705
	21st to end	Night	57% 5% 12% 18% 7% 1	2800
December	1st to 10th	Night	63% 6% 13% 14% 4	4580
	11th to 20th	Night	59% 5% 9% 16% 11% 1	5208
	21st to end	Night	61% 4 8% 15% 13%	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	19% 20% 38% 20% 4	200
	11th to 20th	Day	24% 18% 38% 15% 5% 1	200
	21st to end	Day	17% 21% 38% 20% 4	220
February	1st to 10th	Day	26% 26% 37% 9% 1	280
	11th to 20th	Day	21% 24% 41% 12% 2	385
	21st to end	Day	27% 19% 34% 18% 2	414
March	1st to 10th	Day	27% 18% 33% 18% 4	500
	11th to 20th	Day	21% 23% 35% 17% 3 1	500
	21st to end	Day	28% 20% 30% 15% 7% 1	550
April	1st to 10th	Day	27% 19% 32% 16% 6% 1	500
	11th to 20th	Day	31% 20% 26% 15% 7% 1	492
	21st to end	Day	27% 21% 31% 16% 4 1	500
May	1st to 10th	Day	25% 16% 36% 16% 5% 1	503
	11th to 20th	Day	21% 16% 34% 21% 7% 1	527
	21st to end	Day	22% 19% 30% 22% 6% 1	573
June	1st to 10th	Day	22% 17% 32% 21% 7% 1	530
	11th to 20th	Day	18% 15% 32% 25% 9% 2	530
	21st to end	Day	26% 11% 32% 21% 8% 2	530
July	1st to 10th	Day	12% 11% 35% 27% 12% 3	525
	11th to 20th	Day	14% 11% 34% 28% 11% 2	524
	21st to end	Day	13% 10% 33% 30% 13% 2	576
August	1st to 10th	Day	13% 9% 28% 33% 15% 2	526
	11th to 20th	Day	12% 7% 27% 31% 16% 7%	519
	21st to end	Day	17% 11% 26% 26% 14% 6%	583
September	1st to 10th	Day	16% 7% 35% 23% 13% 6%	530
	11th to 20th	Day	11% 9% 25% 28% 20% 7%	522
	21st to end	Day	20% 12% 26% 24% 12% 5%	490
October	1st to 10th	Day	24% 14% 29% 20% 12% 1	490
	11th to 20th	Day	21% 17% 33% 20% 8% 1	470
	21st to end	Day	28% 16% 31% 20% 5%	429
November	1st to 10th	Day	25% 19% 30% 19% 6% 1	395
	11th to 20th	Day	22% 20% 34% 17% 5%	293
	21st to end	Day	28% 21% 32% 15% 4 1	200
December	1st to 10th	Day	27% 17% 27% 24% 6% 1	200
	11th to 20th	Day	26% 24% 36% 13% 1 1	200
	21st to end	Day	30% 23% 25% 14% 7% 1	220
January	1st to 10th	Night	23% 15% 36% 23% 5%	800
	11th to 20th	Night	21% 15% 35% 24% 5%	800
	21st to end	Night	14% 13% 41% 25% 6%	880
February	1st to 10th	Night	18% 13% 43% 22% 4 1	800
	11th to 20th	Night	20% 15% 42% 19% 4	783
	21st to end	Night	22% 13% 35% 27% 3	660
March	1st to 10th	Night	24% 15% 34% 23% 4	800
	11th to 20th	Night	22% 16% 36% 21% 6%	800
	21st to end	Night	20% 14% 36% 24% 5%	880
April	1st to 10th	Night	27% 14% 33% 22% 4	800
	11th to 20th	Night	24% 13% 35% 24% 4 1	791
	21st to end	Night	28% 12% 33% 20% 6%	642
May	1st to 10th	Night	23% 13% 33% 24% 5% 2	430
	11th to 20th	Night	22% 11% 29% 29% 8%	394
	21st to end	Night	20% 8% 40% 24% 8%	433
June	1st to 10th	Night	24% 9% 32% 28% 8%	400
	11th to 20th	Night	21% 7% 31% 31% 11%	400
	21st to end	Night	22% 7% 27% 31% 13% 1	400
July	1st to 10th	Night	10% 6% 36% 35% 12% 1	390
	11th to 20th	Night	11% 5% 25% 44% 14%	388
	21st to end	Night	13% 4 27% 43% 12% 1	438
August	1st to 10th	Night	15% 4 19% 44% 17% 1	398
	11th to 20th	Night	14% 4 25% 32% 23% 2	577
	21st to end	Night	16% 5% 26% 34% 17% 2	880
September	1st to 10th	Night	13% 6% 28% 38% 14% 1	800
	11th to 20th	Night	15% 5% 24% 34% 21% 2	793
	21st to end	Night	19% 7% 27% 31% 15% 2	760
October	1st to 10th	Night	21% 10% 29% 29% 10% 1	760
	11th to 20th	Night	23% 9% 33% 26% 8% 1	760
	21st to end	Night	26% 11% 33% 25% 5%	836
November	1st to 10th	Night	22% 14% 32% 24% 7% 1	780
	11th to 20th	Night	23% 12% 35% 22% 8% 1	800
	21st to end	Night	28% 16% 32% 19% 6% 1	800
December	1st to 10th	Night	26% 13% 35% 21% 6%	800
	11th to 20th	Night	27% 16% 32% 20% 4 1	800
	21st to end	Night	31% 14% 31% 19% 5%	880

Page generated at 2025-09-16 01:49:10. Version ac07

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