Sault Ste. Marie
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sault Ste. Marie clear sky chart from 2005-11-06 to 2025-11-03.

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	14% 10% 4 8% 5% 5% 4 4 5% 7% 34%	126595
	Night	15% 12% 4 10% 5% 5% 4 4 5% 6% 30%	123637
Transparency	Day	32% 39% 7% 14% 7% 1	130055
	Night	35% 38% 7% 12% 6% 1	128264
Seeing	Day	19% 14% 29% 24% 11% 3	16917
	Night	21% 10% 27% 31% 11% 1	26267

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	9% 17% 6% 15% 7% 6% 4 4 5% 5% 21%	3434
	11th to 20th	Day	12% 13% 6% 12% 8% 8% 6% 5% 5% 6% 19%	3589
	21st to end	Day	8% 20% 9% 16% 8% 6% 6% 4 4 4 14%	3982
February	1st to 10th	Day	9% 14% 5% 14% 9% 6% 6% 4 6% 6% 20%	1717
	11th to 20th	Day	11% 14% 6% 10% 7% 7% 6% 4 5% 6% 24%	1847
	21st to end	Day	10% 13% 6% 13% 7% 5% 4 4 5% 7% 25%	1650
March	1st to 10th	Day	14% 11% 4 9% 5% 4 5% 3 5% 7% 32%	4478
	11th to 20th	Day	14% 14% 4 9% 5% 5% 5% 4 5% 7% 29%	4934
	21st to end	Day	19% 12% 7% 10% 5% 4 5% 3 4 5% 26%	5546
April	1st to 10th	Day	16% 12% 4 8% 5% 5% 4 3 5% 6% 32%	2400
	11th to 20th	Day	19% 10% 3 7% 4 5% 4 3 5% 5% 35%	2552
	21st to end	Day	18% 10% 2 7% 4 4 4 4 6% 7% 34%	2600
May	1st to 10th	Day	16% 9% 3 7% 4 4 4 3 4 6% 42%	5888
	11th to 20th	Day	16% 8% 2 6% 4 3 3 3 5% 7% 43%	6089
	21st to end	Day	15% 8% 3 7% 4 4 4 3 5% 7% 41%	7399
June	1st to 10th	Day	15% 7% 2 5% 4 4 5% 4 7% 7% 40%	3000
	11th to 20th	Day	12% 7% 3 7% 5% 5% 5% 5% 7% 8% 38%	3000
	21st to end	Day	16% 7% 3 6% 4 4 5% 3 5% 8% 40%	3000
July	1st to 10th	Day	13% 7% 2 6% 4 4 5% 4 6% 8% 42%	6819
	11th to 20th	Day	10% 5% 2 6% 3 4 4 4 6% 9% 46%	6371
	21st to end	Day	11% 4 2 5% 3 3 4 4 6% 10% 49%	6926
August	1st to 10th	Day	8% 5% 3 6% 5% 5% 5% 5% 7% 8% 44%	4376
	11th to 20th	Day	14% 5% 2 6% 4 4 4 3 6% 7% 45%	4174
	21st to end	Day	14% 7% 2 6% 4 4 4 3 5% 7% 44%	4657
September	1st to 10th	Day	15% 6% 2 7% 5% 4 5% 4 5% 8% 40%	2340
	11th to 20th	Day	14% 6% 3 6% 4 4 4 4 5% 9% 41%	2200
	21st to end	Day	17% 9% 3 7% 5% 5% 3 3 5% 8% 35%	2200
October	1st to 10th	Day	18% 7% 3 7% 4 5% 5% 4 6% 7% 34%	2150
	11th to 20th	Day	22% 11% 4 10% 8% 6% 5% 4 5% 6% 20%	1913
	21st to end	Day	24% 9% 3 10% 6% 6% 6% 4 5% 5% 21%	1980
November	1st to 10th	Day	21% 13% 3 10% 7% 5% 5% 3 5% 6% 22%	1780
	11th to 20th	Day	16% 17% 4 11% 6% 6% 5% 3 7% 7% 19%	1692
	21st to end	Day	18% 19% 7% 13% 7% 5% 5% 3 4 6% 15%	1535
December	1st to 10th	Day	15% 18% 5% 11% 7% 6% 7% 4 6% 5% 17%	2280
	11th to 20th	Day	17% 15% 5% 18% 8% 7% 5% 3 4 4 13%	2621
	21st to end	Day	26% 21% 6% 11% 4 3 3 2 3 4 17%	3476
January	1st to 10th	Night	12% 15% 6% 13% 7% 5% 5% 4 5% 6% 23%	6514
	11th to 20th	Night	9% 17% 6% 14% 9% 9% 5% 3 5% 5% 17%	6316
	21st to end	Night	10% 15% 9% 18% 8% 8% 6% 4 4 5% 13%	6996
February	1st to 10th	Night	9% 16% 6% 14% 9% 7% 5% 5% 6% 6% 18%	2681
	11th to 20th	Night	11% 13% 5% 12% 8% 6% 6% 4 6% 5% 23%	2438
	21st to end	Night	10% 15% 5% 13% 7% 6% 5% 4 6% 6% 24%	1980
March	1st to 10th	Night	16% 11% 3 8% 4 4 4 3 5% 7% 34%	5362
	11th to 20th	Night	13% 12% 5% 9% 5% 5% 4 4 6% 7% 30%	5025
	21st to end	Night	18% 12% 5% 10% 5% 4 4 3 4 6% 29%	5427
April	1st to 10th	Night	18% 11% 3 9% 5% 4 4 4 6% 6% 31%	2000
	11th to 20th	Night	20% 8% 3 7% 4 3 4 3 5% 7% 37%	1797
	21st to end	Night	18% 9% 3 7% 5% 4 5% 4 5% 6% 36%	1800
May	1st to 10th	Night	16% 6% 3 6% 5% 4 4 3 4 6% 42%	4053
	11th to 20th	Night	18% 7% 3 8% 4 5% 4 3 5% 5% 39%	3801
	21st to end	Night	14% 10% 3 8% 4 4 4 3 5% 6% 39%	3496
June	1st to 10th	Night	12% 6% 2 6% 5% 4 5% 4 7% 9% 40%	1400
	11th to 20th	Night	13% 7% 3 5% 4 5% 4 4 6% 8% 40%	1400
	21st to end	Night	14% 7% 2 7% 5% 4 5% 4 6% 8% 41%	1400
July	1st to 10th	Night	14% 5% 2 5% 4 4 5% 4 6% 9% 41%	3160
	11th to 20th	Night	10% 5% 2 6% 4 4 4 4 5% 7% 49%	3591
	21st to end	Night	11% 4 2 4 3 3 4 3 6% 9% 51%	3948
August	1st to 10th	Night	10% 8% 3 7% 4 5% 5% 4 7% 8% 40%	2775
	11th to 20th	Night	12% 5% 2 6% 3 4 4 3 6% 8% 46%	2875
	21st to end	Night	12% 5% 2 6% 4 3 4 3 4 6% 51%	3238
September	1st to 10th	Night	12% 6% 3 6% 4 5% 4 4 5% 6% 45%	2040
	11th to 20th	Night	14% 6% 2 6% 4 3 5% 3 6% 8% 44%	2200
	21st to end	Night	19% 8% 2 7% 5% 4 4 4 5% 7% 37%	2200
October	1st to 10th	Night	18% 9% 2 6% 3 4 4 4 7% 7% 37%	2250
	11th to 20th	Night	23% 12% 3 8% 4 4 5% 4 6% 6% 26%	2485
	21st to end	Night	24% 12% 3 9% 5% 4 5% 4 5% 6% 24%	2860
November	1st to 10th	Night	20% 13% 4 7% 6% 4 4 4 5% 6% 27%	2563
	11th to 20th	Night	18% 16% 5% 10% 6% 5% 5% 4 5% 6% 19%	2705
	21st to end	Night	18% 16% 5% 11% 5% 5% 5% 4 5% 6% 18%	2863
December	1st to 10th	Night	12% 17% 6% 12% 7% 6% 5% 5% 6% 6% 18%	4910
	11th to 20th	Night	16% 16% 6% 13% 6% 5% 4 4 4 5% 21%	5586
	21st to end	Night	26% 22% 7% 11% 4 3 3 2 3 3 15%	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	46% 28% 9% 9% 5% 3	3435
	11th to 20th	Day	47% 28% 8% 11% 6%	3620
	21st to end	Day	53% 30% 6% 6% 6%	3982
February	1st to 10th	Day	24% 63% 5% 5% 2	1717
	11th to 20th	Day	24% 61% 5% 5% 5%	1856
	21st to end	Day	23% 62% 4 7% 4	1650
March	1st to 10th	Day	38% 30% 10% 9% 10% 2	4480
	11th to 20th	Day	44% 29% 8% 11% 7% 1	4934
	21st to end	Day	47% 29% 5% 11% 8% 1	5546
April	1st to 10th	Day	22% 62% 4 8% 4 1	2400
	11th to 20th	Day	21% 62% 2 8% 6% 1	2552
	21st to end	Day	19% 62% 5% 9% 5% 1	2600
May	1st to 10th	Day	34% 28% 4 17% 15% 2	5897
	11th to 20th	Day	31% 28% 7% 19% 13% 3	6093
	21st to end	Day	34% 29% 7% 15% 11% 4	7399
June	1st to 10th	Day	16% 62% 4 11% 6% 1	3000
	11th to 20th	Day	18% 62% 5% 9% 5% 1	3000
	21st to end	Day	17% 61% 5% 10% 6%	3000
July	1st to 10th	Day	30% 28% 11% 21% 9%	6746
	11th to 20th	Day	25% 29% 14% 26% 5%	6295
	21st to end	Day	21% 27% 11% 28% 13%	6728
August	1st to 10th	Day	21% 38% 9% 24% 8%	4361
	11th to 20th	Day	27% 37% 9% 21% 6%	4213
	21st to end	Day	27% 38% 11% 16% 7%	4656
September	1st to 10th	Day	20% 58% 7% 10% 5%	2340
	11th to 20th	Day	16% 58% 7% 16% 4	2200
	21st to end	Day	19% 58% 8% 11% 4	2200
October	1st to 10th	Day	21% 38% 10% 20% 11%	3501
	11th to 20th	Day	29% 37% 9% 23% 2	3090
	21st to end	Day	41% 38% 7% 10% 3	3180
November	1st to 10th	Day	29% 57% 5% 8% 2	1780
	11th to 20th	Day	28% 58% 5% 6% 2	1692
	21st to end	Day	33% 58% 3 3 3	1535
December	1st to 10th	Day	46% 40% 7% 6% 2	2280
	11th to 20th	Day	53% 34% 5% 5% 3	2621
	21st to end	Day	56% 27% 4 8% 5%	3476
January	1st to 10th	Night	45% 29% 7% 9% 6% 3	6514
	11th to 20th	Night	52% 27% 7% 10% 4	6360
	21st to end	Night	54% 30% 6% 5% 4 1	6996
February	1st to 10th	Night	25% 63% 5% 6% 2	2681
	11th to 20th	Night	23% 61% 5% 8% 3	2440
	21st to end	Night	23% 62% 5% 6% 4	1980
March	1st to 10th	Night	37% 30% 11% 12% 8% 2	5373
	11th to 20th	Night	41% 29% 12% 12% 6% 1	5026
	21st to end	Night	45% 28% 5% 11% 10% 1	5427
April	1st to 10th	Night	23% 62% 2 8% 5%	2000
	11th to 20th	Night	19% 62% 3 8% 6% 1	1797
	21st to end	Night	21% 62% 4 7% 6% 1	1800
May	1st to 10th	Night	33% 28% 5% 18% 13% 4	4060
	11th to 20th	Night	35% 29% 4 20% 10% 2	3802
	21st to end	Night	36% 28% 7% 15% 7% 5%	3497
June	1st to 10th	Night	16% 62% 4 9% 9% 1	1400
	11th to 20th	Night	19% 63% 4 8% 5% 1	1400
	21st to end	Night	16% 61% 4 11% 7% 1	1400
July	1st to 10th	Night	30% 29% 11% 18% 11%	3125
	11th to 20th	Night	25% 28% 12% 28% 8%	3544
	21st to end	Night	20% 28% 11% 26% 14% 1	3832
August	1st to 10th	Night	28% 38% 7% 19% 8%	2766
	11th to 20th	Night	26% 39% 9% 19% 7%	2902
	21st to end	Night	22% 37% 8% 24% 8%	3238
September	1st to 10th	Night	18% 58% 8% 11% 5%	2040
	11th to 20th	Night	15% 58% 7% 15% 4 1	2200
	21st to end	Night	20% 58% 7% 11% 5%	2200
October	1st to 10th	Night	23% 39% 9% 23% 6%	3679
	11th to 20th	Night	24% 38% 11% 22% 5%	4047
	21st to end	Night	36% 41% 12% 9% 2	4610
November	1st to 10th	Night	29% 56% 6% 7% 2	2563
	11th to 20th	Night	28% 58% 5% 7% 2	2705
	21st to end	Night	31% 59% 5% 3 2	2863
December	1st to 10th	Night	43% 39% 10% 6% 1	4910
	11th to 20th	Night	44% 34% 8% 7% 5% 1	5585
	21st to end	Night	58% 26% 4 9% 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	18% 15% 32% 23% 11% 1	260
	11th to 20th	Day	20% 11% 30% 29% 10% 1	300
	21st to end	Day	20% 13% 29% 29% 9% 1	330
February	1st to 10th	Day	20% 18% 34% 22% 6% 1	300
	11th to 20th	Day	18% 19% 39% 17% 5% 1	300
	21st to end	Day	18% 27% 35% 16% 5%	249
March	1st to 10th	Day	20% 18% 35% 19% 8%	300
	11th to 20th	Day	21% 16% 30% 24% 8% 2	480
	21st to end	Day	25% 14% 28% 21% 11% 1	550
April	1st to 10th	Day	21% 16% 28% 26% 7% 1	500
	11th to 20th	Day	25% 20% 24% 18% 10% 3	492
	21st to end	Day	25% 16% 28% 19% 9% 3	500
May	1st to 10th	Day	20% 17% 28% 19% 12% 4	503
	11th to 20th	Day	19% 12% 32% 23% 10% 4	625
	21st to end	Day	17% 13% 31% 25% 10% 3	789
June	1st to 10th	Day	17% 13% 34% 22% 11% 2	730
	11th to 20th	Day	16% 15% 32% 26% 9% 2	730
	21st to end	Day	20% 13% 29% 25% 10% 3	730
July	1st to 10th	Day	10% 10% 36% 27% 12% 4	721
	11th to 20th	Day	13% 10% 30% 27% 14% 5%	718
	21st to end	Day	12% 10% 30% 28% 15% 5%	794
August	1st to 10th	Day	12% 8% 24% 31% 19% 5%	617
	11th to 20th	Day	17% 6% 16% 30% 21% 10%	519
	21st to end	Day	17% 10% 24% 25% 18% 6%	583
September	1st to 10th	Day	19% 10% 23% 23% 18% 6%	530
	11th to 20th	Day	14% 9% 23% 31% 18% 4	530
	21st to end	Day	20% 12% 22% 28% 14% 3	530
October	1st to 10th	Day	21% 17% 24% 24% 12% 2	530
	11th to 20th	Day	23% 17% 31% 24% 4	443
	21st to end	Day	31% 17% 30% 17% 4 1	363
November	1st to 10th	Day	25% 23% 31% 14% 6% 1	306
	11th to 20th	Day	23% 21% 31% 18% 5% 1	245
	21st to end	Day	27% 18% 37% 15% 5%	200
December	1st to 10th	Day	25% 11% 33% 19% 11% 3	200
	11th to 20th	Day	24% 19% 36% 16% 5% 1	200
	21st to end	Day	32% 12% 30% 16% 9%	220
January	1st to 10th	Night	21% 13% 30% 29% 7%	1000
	11th to 20th	Night	21% 12% 29% 27% 10% 1	1000
	21st to end	Night	20% 10% 28% 31% 9% 1	1100
February	1st to 10th	Night	18% 13% 33% 30% 6% 1	881
	11th to 20th	Night	19% 13% 31% 29% 8% 1	783
	21st to end	Night	16% 14% 34% 30% 6%	660
March	1st to 10th	Night	18% 10% 34% 28% 9% 1	800
	11th to 20th	Night	18% 14% 32% 27% 8% 1	800
	21st to end	Night	19% 11% 30% 33% 7% 1	865
April	1st to 10th	Night	22% 10% 27% 34% 7% 1	600
	11th to 20th	Night	24% 10% 24% 32% 10% 1	593
	21st to end	Night	21% 9% 26% 32% 11% 1	600
May	1st to 10th	Night	18% 8% 24% 39% 11% 1	600
	11th to 20th	Night	20% 5% 26% 34% 13% 1	591
	21st to end	Night	14% 8% 27% 41% 10%	457
June	1st to 10th	Night	14% 5% 30% 41% 10%	400
	11th to 20th	Night	17% 5% 30% 36% 12%	400
	21st to end	Night	18% 5% 25% 36% 15% 1	400
July	1st to 10th	Night	12% 4 23% 48% 13% 1	390
	11th to 20th	Night	13% 5% 18% 40% 22% 2	567
	21st to end	Night	15% 3 19% 41% 20% 2	657
August	1st to 10th	Night	15% 4 17% 39% 24% 1	597
	11th to 20th	Night	10% 4 17% 36% 30% 3	594
	21st to end	Night	16% 5% 17% 38% 23% 1	660
September	1st to 10th	Night	15% 6% 23% 31% 21% 4	640
	11th to 20th	Night	16% 6% 23% 33% 20% 3	800
	21st to end	Night	22% 8% 20% 33% 15% 3	800
October	1st to 10th	Night	22% 11% 24% 28% 14% 1	800
	11th to 20th	Night	29% 13% 25% 27% 7% 1	800
	21st to end	Night	30% 11% 25% 29% 5% 1	880
November	1st to 10th	Night	29% 12% 27% 24% 8% 1	789
	11th to 20th	Night	26% 14% 29% 23% 7%	800
	21st to end	Night	26% 15% 31% 23% 5%	863
December	1st to 10th	Night	24% 13% 31% 23% 8% 1	1000
	11th to 20th	Night	26% 15% 32% 20% 6% 1	1000
	21st to end	Night	31% 12% 27% 23% 7% 1	1100

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