Centre écologique de Port-au-Saumon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Centre écologique de Port-au-Saumon clear sky chart from 2005-11-06 to 2025-08-05.

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	15% 9% 3 8% 5% 5% 5% 4 6% 7% 33%	125828
	Night	15% 11% 4 9% 5% 5% 5% 4 5% 6% 31%	122332
Transparency	Day	50% 8% 16% 18% 8% 1	129260
	Night	54% 8% 13% 17% 7% 1	126975
Seeing	Day	21% 13% 30% 24% 10% 2	16592
	Night	22% 10% 30% 28% 9% 1	24712

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% 23% 5% 10% 5% 4 4 3 4 5% 22%	3316
	11th to 20th	Day	9% 14% 6% 12% 8% 7% 6% 4 6% 7% 22%	3570
	21st to end	Day	5% 8% 4 11% 6% 6% 8% 6% 7% 7% 33%	3960
February	1st to 10th	Day	6% 13% 5% 9% 9% 8% 6% 6% 7% 6% 25%	1640
	11th to 20th	Day	10% 13% 5% 12% 7% 6% 5% 4 5% 5% 26%	1847
	21st to end	Day	11% 10% 4 9% 6% 7% 5% 5% 5% 7% 31%	1650
March	1st to 10th	Day	18% 13% 4 10% 5% 5% 4 3 5% 5% 27%	4476
	11th to 20th	Day	13% 13% 4 10% 6% 6% 6% 4 5% 7% 27%	4876
	21st to end	Day	15% 15% 4 9% 5% 4 4 3 4 5% 32%	5644
April	1st to 10th	Day	18% 13% 4 9% 6% 4 4 3 5% 5% 28%	2400
	11th to 20th	Day	17% 8% 3 8% 5% 5% 4 3 4 6% 37%	2542
	21st to end	Day	20% 11% 3 6% 4 4 4 3 4 6% 34%	2600
May	1st to 10th	Day	18% 9% 4 8% 5% 4 4 4 5% 6% 32%	5932
	11th to 20th	Day	22% 7% 2 7% 5% 4 4 4 4 6% 34%	6354
	21st to end	Day	17% 7% 3 8% 6% 5% 5% 4 6% 9% 31%	7451
June	1st to 10th	Day	18% 8% 3 7% 5% 5% 5% 4 6% 7% 31%	3000
	11th to 20th	Day	18% 6% 3 7% 5% 4 5% 4 7% 7% 36%	3000
	21st to end	Day	20% 8% 3 7% 5% 5% 5% 4 7% 7% 30%	3000
July	1st to 10th	Day	14% 6% 2 7% 5% 5% 5% 5% 7% 10% 33%	6820
	11th to 20th	Day	13% 6% 2 6% 5% 6% 6% 5% 7% 9% 35%	6504
	21st to end	Day	10% 4 2 6% 4 5% 5% 4 7% 9% 44%	6926
August	1st to 10th	Day	12% 5% 2 7% 5% 6% 7% 6% 8% 10% 31%	4395
	11th to 20th	Day	14% 7% 3 8% 5% 5% 5% 5% 7% 9% 33%	4045
	21st to end	Day	15% 5% 2 6% 4 4 5% 4 5% 8% 42%	4505
September	1st to 10th	Day	13% 7% 2 6% 5% 4 5% 3 6% 8% 41%	2256
	11th to 20th	Day	13% 5% 2 6% 4 4 4 3 6% 7% 47%	2090
	21st to end	Day	16% 6% 3 6% 4 4 4 3 6% 8% 40%	2090
October	1st to 10th	Day	18% 7% 2 7% 4 5% 4 4 6% 7% 37%	2056
	11th to 20th	Day	22% 8% 3 6% 4 5% 5% 4 7% 7% 31%	1764
	21st to end	Day	23% 12% 3 7% 5% 5% 5% 3 4 5% 28%	1881
November	1st to 10th	Day	16% 11% 3 9% 5% 6% 4 4 6% 6% 30%	1761
	11th to 20th	Day	18% 12% 4 9% 5% 5% 4 4 5% 6% 26%	1668
	21st to end	Day	19% 16% 4 8% 6% 4 4 2 4 6% 26%	1435
December	1st to 10th	Day	16% 14% 6% 11% 4 4 4 3 3 5% 30%	2280
	11th to 20th	Day	18% 10% 3 8% 6% 4 4 3 4 8% 33%	2618
	21st to end	Day	17% 11% 3 10% 6% 5% 4 3 4 7% 30%	3476
January	1st to 10th	Night	16% 20% 5% 11% 7% 4 4 3 4 5% 20%	6625
	11th to 20th	Night	9% 15% 7% 18% 7% 6% 5% 3 5% 5% 20%	6315
	21st to end	Night	5% 9% 5% 10% 7% 7% 7% 4 7% 8% 32%	6996
February	1st to 10th	Night	8% 13% 4 9% 6% 6% 5% 5% 6% 6% 31%	2759
	11th to 20th	Night	10% 15% 5% 12% 8% 6% 4 4 5% 5% 26%	2439
	21st to end	Night	12% 13% 5% 10% 6% 4 4 3 5% 7% 32%	1980
March	1st to 10th	Night	19% 14% 4 9% 5% 4 5% 3 5% 6% 27%	5364
	11th to 20th	Night	12% 16% 4 10% 6% 6% 6% 4 5% 6% 26%	5082
	21st to end	Night	18% 17% 4 8% 3 4 3 3 4 5% 32%	5284
April	1st to 10th	Night	19% 13% 5% 9% 5% 4 4 3 4 4 31%	2000
	11th to 20th	Night	17% 10% 3 9% 5% 4 5% 3 5% 6% 33%	1807
	21st to end	Night	23% 10% 3 6% 4 4 2 3 5% 5% 34%	1800
May	1st to 10th	Night	18% 9% 3 7% 4 4 4 4 5% 6% 34%	4039
	11th to 20th	Night	24% 8% 3 6% 4 4 5% 4 6% 6% 31%	3539
	21st to end	Night	16% 8% 3 6% 5% 4 5% 5% 6% 7% 35%	3446
June	1st to 10th	Night	18% 8% 3 8% 5% 5% 5% 4 7% 7% 31%	1400
	11th to 20th	Night	15% 6% 2 6% 5% 4 4 5% 7% 7% 39%	1400
	21st to end	Night	22% 8% 3 7% 5% 4 4 5% 5% 7% 30%	1400
July	1st to 10th	Night	11% 6% 2 7% 5% 6% 5% 5% 7% 9% 36%	3160
	11th to 20th	Night	17% 6% 2 6% 4 4 5% 4 6% 8% 38%	3458
	21st to end	Night	10% 5% 2 6% 5% 5% 5% 4 6% 8% 46%	3926
August	1st to 10th	Night	16% 5% 2 8% 5% 6% 5% 4 6% 7% 36%	2591
	11th to 20th	Night	15% 5% 2 10% 7% 6% 7% 5% 7% 8% 28%	2782
	21st to end	Night	15% 6% 3 7% 5% 4 4 3 4 7% 43%	3149
September	1st to 10th	Night	15% 5% 2 6% 5% 4 4 4 6% 7% 43%	1923
	11th to 20th	Night	17% 7% 2 5% 4 4 5% 3 4 6% 42%	2090
	21st to end	Night	15% 7% 3 7% 4 4 3 3 6% 5% 44%	2090
October	1st to 10th	Night	17% 7% 3 6% 4 4 4 3 5% 5% 42%	2123
	11th to 20th	Night	23% 7% 2 5% 4 5% 4 4 5% 6% 34%	2413
	21st to end	Night	22% 9% 3 6% 4 4 4 4 5% 7% 33%	2717
November	1st to 10th	Night	16% 11% 3 8% 4 4 4 4 5% 8% 33%	2537
	11th to 20th	Night	19% 10% 3 7% 5% 4 5% 4 6% 6% 31%	2730
	21st to end	Night	18% 14% 4 8% 5% 5% 5% 3 5% 5% 27%	2965
December	1st to 10th	Night	12% 16% 7% 11% 6% 5% 4 4 4 5% 26%	4910
	11th to 20th	Night	19% 11% 3 7% 5% 5% 5% 4 5% 7% 29%	5591
	21st to end	Night	15% 13% 4 9% 6% 5% 5% 3 4 8% 26%	7502

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	68% 8% 13% 9% 2	3317
	11th to 20th	Day	62% 7% 13% 15% 3 1	3600
	21st to end	Day	46% 11% 13% 15% 14%	3960
February	1st to 10th	Day	56% 8% 13% 14% 8% 2	1640
	11th to 20th	Day	59% 7% 12% 14% 8% 1	1855
	21st to end	Day	51% 7% 11% 19% 9% 2	1650
March	1st to 10th	Day	57% 8% 10% 10% 11% 3	4479
	11th to 20th	Day	56% 9% 16% 11% 7% 1	4876
	21st to end	Day	55% 5% 8% 18% 10% 4	5644
April	1st to 10th	Day	55% 6% 12% 15% 9% 2	2400
	11th to 20th	Day	47% 7% 12% 23% 9% 2	2542
	21st to end	Day	51% 7% 10% 18% 13% 2	2600
May	1st to 10th	Day	51% 8% 13% 17% 11% 1	5943
	11th to 20th	Day	49% 8% 15% 19% 6% 2	6358
	21st to end	Day	46% 9% 17% 18% 10%	7451
June	1st to 10th	Day	49% 9% 11% 20% 10% 1	3000
	11th to 20th	Day	44% 8% 16% 20% 11% 1	3000
	21st to end	Day	51% 9% 14% 16% 9% 1	3000
July	1st to 10th	Day	46% 7% 18% 22% 7%	6745
	11th to 20th	Day	45% 7% 24% 19% 4	6425
	21st to end	Day	36% 7% 22% 28% 8%	6728
August	1st to 10th	Day	44% 11% 21% 18% 7%	4381
	11th to 20th	Day	46% 8% 22% 20% 4	4084
	21st to end	Day	41% 7% 21% 19% 12%	4505
September	1st to 10th	Day	38% 8% 18% 25% 11%	2256
	11th to 20th	Day	37% 7% 18% 27% 10% 1	2090
	21st to end	Day	41% 8% 16% 25% 9%	2090
October	1st to 10th	Day	52% 7% 16% 19% 5%	3420
	11th to 20th	Day	49% 7% 19% 22% 2	2902
	21st to end	Day	48% 7% 18% 20% 7%	3081
November	1st to 10th	Day	52% 10% 15% 19% 4 1	1761
	11th to 20th	Day	57% 10% 12% 16% 5%	1668
	21st to end	Day	62% 9% 13% 13% 4	1435
December	1st to 10th	Day	59% 6% 15% 10% 9%	2280
	11th to 20th	Day	55% 6% 13% 14% 11%	2618
	21st to end	Day	59% 9% 13% 12% 6% 1	3476
January	1st to 10th	Night	68% 9% 11% 9% 3	6625
	11th to 20th	Night	66% 7% 13% 9% 5% 1	6360
	21st to end	Night	47% 10% 11% 20% 12%	6996
February	1st to 10th	Night	53% 8% 11% 17% 10% 1	2759
	11th to 20th	Night	61% 7% 11% 14% 7%	2442
	21st to end	Night	55% 7% 10% 18% 9% 1	1980
March	1st to 10th	Night	60% 6% 10% 13% 11% 1	5374
	11th to 20th	Night	59% 9% 14% 12% 5% 2	5083
	21st to end	Night	55% 5% 8% 20% 10% 1	5284
April	1st to 10th	Night	58% 5% 7% 15% 12% 3	2000
	11th to 20th	Night	51% 7% 10% 18% 12% 1	1807
	21st to end	Night	53% 7% 9% 18% 12% 2	1800
May	1st to 10th	Night	49% 8% 12% 16% 13% 1	4045
	11th to 20th	Night	51% 10% 11% 19% 8% 1	3540
	21st to end	Night	44% 11% 14% 19% 11% 1	3447
June	1st to 10th	Night	51% 8% 14% 19% 8% 1	1400
	11th to 20th	Night	43% 7% 15% 19% 14% 2	1400
	21st to end	Night	54% 8% 13% 16% 9%	1400
July	1st to 10th	Night	46% 7% 20% 23% 4	3125
	11th to 20th	Night	45% 7% 24% 21% 3	3414
	21st to end	Night	38% 8% 23% 24% 8%	3809
August	1st to 10th	Night	47% 9% 17% 22% 5%	2581
	11th to 20th	Night	53% 10% 19% 11% 6%	2809
	21st to end	Night	44% 7% 14% 24% 10%	3149
September	1st to 10th	Night	41% 11% 14% 23% 10% 1	1923
	11th to 20th	Night	44% 7% 17% 22% 9% 1	2090
	21st to end	Night	42% 8% 13% 25% 11%	2090
October	1st to 10th	Night	50% 5% 13% 25% 6%	3539
	11th to 20th	Night	48% 7% 17% 24% 4	4001
	21st to end	Night	47% 8% 19% 19% 7%	4467
November	1st to 10th	Night	52% 9% 16% 17% 6%	2537
	11th to 20th	Night	55% 10% 13% 15% 6%	2730
	21st to end	Night	63% 9% 12% 12% 5%	2965
December	1st to 10th	Night	65% 6% 11% 13% 4	4910
	11th to 20th	Night	59% 8% 10% 18% 4	5592
	21st to end	Night	61% 9% 13% 12% 4	7502

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	24% 16% 37% 17% 5% 3	200
	11th to 20th	Day	21% 18% 40% 14% 8% 1	200
	21st to end	Day	14% 16% 35% 24% 10% 1	220
February	1st to 10th	Day	20% 20% 34% 19% 6% 2	240
	11th to 20th	Day	19% 16% 40% 21% 4	443
	21st to end	Day	18% 17% 38% 20% 7% 1	414
March	1st to 10th	Day	25% 15% 30% 23% 6% 1	500
	11th to 20th	Day	22% 14% 34% 20% 8% 1	500
	21st to end	Day	24% 17% 30% 20% 7% 2	550
April	1st to 10th	Day	28% 16% 30% 20% 5% 1	500
	11th to 20th	Day	25% 18% 29% 21% 6% 2	492
	21st to end	Day	26% 16% 32% 19% 6% 2	500
May	1st to 10th	Day	23% 16% 29% 21% 9% 2	503
	11th to 20th	Day	19% 14% 31% 25% 10% 1	537
	21st to end	Day	21% 15% 34% 20% 8% 2	790
June	1st to 10th	Day	24% 12% 30% 23% 10% 1	730
	11th to 20th	Day	21% 9% 28% 27% 14% 2	730
	21st to end	Day	21% 6% 27% 33% 11% 1	730
July	1st to 10th	Day	17% 10% 29% 27% 15% 2	720
	11th to 20th	Day	15% 9% 26% 33% 14% 3	586
	21st to end	Day	13% 9% 26% 35% 16% 2	576
August	1st to 10th	Day	15% 10% 26% 30% 16% 3	502
	11th to 20th	Day	17% 6% 30% 26% 18% 3	479
	21st to end	Day	15% 12% 27% 25% 15% 7%	539
September	1st to 10th	Day	16% 10% 28% 27% 14% 5%	490
	11th to 20th	Day	20% 12% 25% 25% 15% 4	490
	21st to end	Day	19% 12% 26% 25% 13% 5%	490
October	1st to 10th	Day	18% 13% 29% 25% 11% 3	472
	11th to 20th	Day	28% 17% 25% 20% 9% 1	390
	21st to end	Day	30% 14% 31% 18% 6% 1	429
November	1st to 10th	Day	28% 14% 31% 21% 4 1	395
	11th to 20th	Day	26% 16% 28% 22% 8% 1	400
	21st to end	Day	32% 18% 32% 17%	235
December	1st to 10th	Day	24% 18% 32% 17% 10% 1	200
	11th to 20th	Day	26% 19% 36% 14% 6% 1	200
	21st to end	Day	25% 18% 31% 20% 5%	220
January	1st to 10th	Night	23% 11% 37% 22% 7% 1	860
	11th to 20th	Night	21% 13% 35% 24% 7%	800
	21st to end	Night	14% 8% 35% 34% 8% 1	880
February	1st to 10th	Night	16% 11% 42% 24% 7% 1	800
	11th to 20th	Night	21% 11% 38% 23% 6% 1	783
	21st to end	Night	21% 12% 32% 27% 7% 1	660
March	1st to 10th	Night	21% 10% 37% 27% 5% 1	800
	11th to 20th	Night	23% 12% 36% 22% 7%	800
	21st to end	Night	23% 13% 30% 26% 7%	880
April	1st to 10th	Night	29% 10% 30% 25% 5% 1	800
	11th to 20th	Night	24% 11% 30% 27% 8%	623
	21st to end	Night	31% 11% 25% 26% 6% 1	600
May	1st to 10th	Night	26% 8% 28% 30% 7% 1	598
	11th to 20th	Night	26% 8% 24% 31% 11% 1	394
	21st to end	Night	24% 11% 31% 23% 10%	433
June	1st to 10th	Night	20% 8% 28% 35% 9% 1	400
	11th to 20th	Night	19% 4 26% 37% 14% 1	400
	21st to end	Night	24% 7% 26% 34% 9%	400
July	1st to 10th	Night	18% 4 30% 35% 13% 1	390
	11th to 20th	Night	14% 5% 21% 44% 14% 1	388
	21st to end	Night	15% 4 19% 46% 16% 1	438
August	1st to 10th	Night	15% 5% 17% 45% 17% 1	413
	11th to 20th	Night	16% 4 22% 39% 18% 1	562
	21st to end	Night	15% 7% 23% 37% 16% 2	639
September	1st to 10th	Night	17% 7% 28% 34% 13% 1	760
	11th to 20th	Night	21% 8% 26% 28% 14% 3	760
	21st to end	Night	20% 7% 27% 32% 12% 2	760
October	1st to 10th	Night	22% 11% 27% 28% 10% 2	760
	11th to 20th	Night	28% 9% 28% 25% 9% 1	760
	21st to end	Night	26% 11% 32% 23% 7%	836
November	1st to 10th	Night	25% 15% 30% 24% 5%	780
	11th to 20th	Night	25% 15% 32% 19% 7% 1	865
	21st to end	Night	26% 15% 31% 23% 5% 1	900
December	1st to 10th	Night	28% 12% 31% 22% 6% 1	900
	11th to 20th	Night	26% 13% 35% 21% 5%	900
	21st to end	Night	26% 14% 29% 22% 8% 1	990

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