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 2024-01-16.

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	15% 9% 4 7% 6% 3 5% 5% 5% 7% 34%	74607
	Night	16% 11% 4 8% 6% 3 5% 5% 5% 6% 30%	75191
Transparency	Day	34% 35% 9% 15% 7% 1	74306
	Night	38% 35% 8% 13% 5% 1	75027
Seeing	Day	19% 13% 29% 24% 12% 3	14399
	Night	21% 9% 27% 31% 11% 1	23974

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	11% 18% 8% 14% 9% 5% 6% 4 5% 5% 17%	1442
	11th to 20th	Day	15% 14% 7% 10% 10% 4 4 5% 3 6% 21%	1480
	21st to end	Day	13% 15% 7% 11% 9% 5% 5% 6% 5% 6% 18%	1584
February	1st to 10th	Day	9% 13% 5% 13% 11% 4 7% 6% 7% 7% 19%	1545
	11th to 20th	Day	12% 13% 6% 8% 9% 5% 6% 5% 4 6% 25%	1658
	21st to end	Day	10% 13% 7% 12% 8% 4 5% 5% 5% 7% 26%	1480
March	1st to 10th	Day	13% 10% 6% 8% 6% 3 4 4 4 7% 36%	1798
	11th to 20th	Day	13% 10% 4 7% 6% 3 5% 4 5% 7% 36%	1962
	21st to end	Day	16% 9% 4 6% 5% 3 5% 4 5% 6% 36%	2205
April	1st to 10th	Day	17% 11% 4 7% 6% 4 5% 4 5% 6% 31%	2160
	11th to 20th	Day	20% 9% 4 6% 4 4 4 4 4 6% 35%	2294
	21st to end	Day	18% 10% 3 7% 5% 3 5% 5% 6% 7% 34%	2340
May	1st to 10th	Day	17% 8% 2 5% 5% 3 4 4 5% 7% 40%	2340
	11th to 20th	Day	17% 7% 3 5% 5% 3 4 4 5% 6% 42%	2389
	21st to end	Day	14% 5% 2 4 4 3 5% 5% 7% 8% 43%	2895
June	1st to 10th	Day	15% 6% 2 4 4 3 5% 5% 7% 8% 41%	2700
	11th to 20th	Day	12% 6% 3 6% 5% 3 5% 5% 7% 9% 38%	2700
	21st to end	Day	14% 6% 2 5% 5% 3 4 5% 5% 8% 41%	2700
July	1st to 10th	Day	8% 4 2 4 4 2 5% 5% 6% 9% 49%	2700
	11th to 20th	Day	12% 5% 2 5% 5% 3 5% 5% 5% 8% 45%	2531
	21st to end	Day	12% 6% 2 5% 4 2 4 4 6% 10% 46%	2743
August	1st to 10th	Day	11% 4 2 5% 5% 3 5% 6% 6% 8% 45%	2410
	11th to 20th	Day	13% 5% 2 5% 5% 3 4 5% 7% 8% 44%	2303
	21st to end	Day	14% 7% 3 5% 5% 3 4 4 5% 8% 42%	2570
September	1st to 10th	Day	15% 6% 2 6% 6% 3 4 4 5% 7% 40%	2106
	11th to 20th	Day	15% 6% 3 6% 5% 3 4 5% 5% 8% 40%	1980
	21st to end	Day	17% 8% 3 6% 7% 4 4 4 6% 9% 32%	1980
October	1st to 10th	Day	19% 7% 4 6% 6% 4 5% 4 5% 7% 33%	1936
	11th to 20th	Day	23% 11% 4 8% 9% 4 5% 5% 4 6% 19%	1723
	21st to end	Day	25% 9% 4 9% 7% 5% 6% 5% 5% 5% 20%	1782
November	1st to 10th	Day	21% 13% 3 8% 8% 4 5% 4 4 7% 22%	1672
	11th to 20th	Day	15% 15% 5% 9% 8% 5% 6% 4 7% 7% 19%	1608
	21st to end	Day	18% 17% 7% 11% 8% 4 4 4 4 6% 15%	1459
December	1st to 10th	Day	14% 16% 7% 9% 8% 5% 7% 5% 5% 5% 18%	1330
	11th to 20th	Day	17% 16% 6% 12% 8% 4 5% 4 4 5% 18%	1671
	21st to end	Day	26% 22% 6% 9% 6% 3 4 3 3 4 15%	2431
January	1st to 10th	Night	15% 15% 8% 11% 9% 4 5% 4 5% 6% 18%	2720
	11th to 20th	Night	14% 18% 7% 10% 9% 5% 5% 4 4 5% 19%	2591
	21st to end	Night	16% 13% 6% 13% 9% 5% 7% 5% 4 5% 17%	2772
February	1st to 10th	Night	9% 15% 7% 12% 11% 5% 6% 6% 7% 7% 17%	2413
	11th to 20th	Night	13% 12% 5% 10% 9% 5% 6% 6% 5% 6% 24%	2188
	21st to end	Night	11% 14% 7% 13% 8% 4 5% 5% 5% 6% 23%	1776
March	1st to 10th	Night	12% 9% 4 8% 7% 4 4 5% 5% 6% 37%	2149
	11th to 20th	Night	13% 10% 4 7% 6% 4 5% 5% 6% 6% 36%	1997
	21st to end	Night	14% 8% 4 6% 5% 3 5% 5% 5% 6% 40%	2165
April	1st to 10th	Night	18% 10% 4 9% 5% 3 5% 5% 6% 7% 30%	1800
	11th to 20th	Night	19% 8% 3 6% 5% 2 4 4 4 8% 37%	1615
	21st to end	Night	17% 8% 3 6% 6% 3 4 5% 4 6% 36%	1620
May	1st to 10th	Night	15% 6% 4 7% 6% 4 4 5% 6% 6% 38%	1620
	11th to 20th	Night	16% 8% 3 6% 5% 3 5% 5% 6% 6% 36%	1504
	21st to end	Night	13% 7% 3 5% 4 3 5% 4 6% 7% 44%	1378
June	1st to 10th	Night	13% 6% 2 4 5% 3 4 5% 7% 9% 41%	1260
	11th to 20th	Night	13% 6% 3 4 5% 4 5% 5% 5% 9% 42%	1260
	21st to end	Night	13% 6% 2 6% 5% 3 4 5% 5% 8% 42%	1260
July	1st to 10th	Night	10% 4 2 3 4 3 5% 6% 6% 8% 49%	1260
	11th to 20th	Night	10% 6% 3 6% 5% 4 4 6% 5% 8% 44%	1425
	21st to end	Night	12% 6% 2 4 5% 3 4 4 6% 10% 44%	1575
August	1st to 10th	Night	10% 5% 2 5% 3 3 5% 5% 6% 9% 47%	1526
	11th to 20th	Night	8% 4 3 6% 4 4 5% 4 6% 7% 49%	1598
	21st to end	Night	13% 4 2 6% 6% 3 5% 5% 5% 7% 45%	1783
September	1st to 10th	Night	13% 5% 3 5% 5% 4 4 5% 5% 5% 46%	1836
	11th to 20th	Night	16% 6% 2 5% 5% 2 4 4 6% 7% 43%	1980
	21st to end	Night	19% 7% 3 6% 6% 3 5% 5% 5% 7% 35%	1980
October	1st to 10th	Night	20% 9% 2 5% 4 3 4 5% 6% 7% 34%	2024
	11th to 20th	Night	24% 11% 3 7% 5% 3 5% 5% 5% 6% 25%	2236
	21st to end	Night	25% 12% 3 8% 5% 3 5% 5% 5% 6% 23%	2574
November	1st to 10th	Night	19% 13% 5% 6% 7% 3 5% 4 5% 6% 27%	2406
	11th to 20th	Night	19% 14% 6% 10% 7% 4 5% 5% 5% 6% 19%	2569
	21st to end	Night	19% 15% 6% 10% 6% 4 5% 5% 5% 6% 19%	2719
December	1st to 10th	Night	14% 16% 7% 10% 8% 3 5% 5% 5% 7% 20%	2850
	11th to 20th	Night	18% 16% 6% 8% 7% 3 4 4 3 5% 27%	3526
	21st to end	Night	24% 24% 6% 9% 6% 3 3 3 3 4 15%	5236

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	45% 38% 8% 7% 1	1443
	11th to 20th	Day	44% 39% 6% 9% 2	1480
	21st to end	Day	47% 35% 5% 9% 4	1584
February	1st to 10th	Day	43% 36% 7% 10% 4	1545
	11th to 20th	Day	39% 36% 9% 11% 4 1	1667
	21st to end	Day	39% 35% 7% 14% 5%	1480
March	1st to 10th	Day	33% 35% 9% 13% 10% 1	1800
	11th to 20th	Day	31% 35% 11% 16% 6% 1	1962
	21st to end	Day	35% 35% 7% 15% 5% 2	2205
April	1st to 10th	Day	35% 35% 6% 15% 7% 1	2160
	11th to 20th	Day	35% 34% 7% 16% 8%	2294
	21st to end	Day	33% 35% 6% 11% 11% 4	2340
May	1st to 10th	Day	28% 35% 6% 19% 11% 1	2340
	11th to 20th	Day	30% 36% 6% 15% 12% 1	2393
	21st to end	Day	24% 36% 10% 17% 10% 3	2895
June	1st to 10th	Day	28% 35% 9% 19% 9% 1	2700
	11th to 20th	Day	26% 36% 9% 19% 10%	2700
	21st to end	Day	29% 35% 10% 18% 7% 1	2700
July	1st to 10th	Day	22% 36% 11% 20% 11%	2626
	11th to 20th	Day	24% 36% 8% 21% 10% 1	2455
	21st to end	Day	26% 36% 12% 19% 7%	2591
August	1st to 10th	Day	27% 35% 12% 18% 7% 1	2395
	11th to 20th	Day	23% 35% 11% 22% 9% 1	2303
	21st to end	Day	26% 35% 9% 21% 8% 1	2570
September	1st to 10th	Day	27% 35% 10% 19% 9%	2106
	11th to 20th	Day	29% 35% 13% 20% 3	1980
	21st to end	Day	34% 36% 10% 16% 4	1980
October	1st to 10th	Day	34% 35% 9% 17% 5% 1	1936
	11th to 20th	Day	46% 35% 7% 10% 2	1723
	21st to end	Day	44% 36% 8% 9% 3 1	1782
November	1st to 10th	Day	40% 39% 7% 11% 4	1672
	11th to 20th	Day	40% 40% 8% 9% 3	1608
	21st to end	Day	45% 39% 9% 6% 1	1459
December	1st to 10th	Day	43% 38% 9% 9% 1 1	1330
	11th to 20th	Day	52% 31% 8% 7% 2	1671
	21st to end	Day	60% 23% 6% 7% 4	2431
January	1st to 10th	Night	43% 39% 8% 8% 2	2720
	11th to 20th	Night	45% 39% 6% 7% 3	2591
	21st to end	Night	46% 36% 4 9% 4	2772
February	1st to 10th	Night	45% 35% 6% 8% 4 1	2413
	11th to 20th	Night	43% 36% 10% 8% 3	2190
	21st to end	Night	43% 35% 8% 11% 3	1776
March	1st to 10th	Night	34% 34% 8% 14% 9% 1	2160
	11th to 20th	Night	34% 34% 10% 16% 6% 1	1998
	21st to end	Night	33% 35% 8% 14% 8% 2	2165
April	1st to 10th	Night	35% 35% 8% 12% 9% 1	1800
	11th to 20th	Night	33% 34% 5% 18% 9% 1	1615
	21st to end	Night	33% 35% 6% 13% 10% 3	1620
May	1st to 10th	Night	32% 35% 6% 15% 10% 2	1620
	11th to 20th	Night	34% 35% 4 17% 9% 1	1505
	21st to end	Night	26% 36% 8% 16% 12% 3	1379
June	1st to 10th	Night	27% 35% 10% 17% 10% 1	1260
	11th to 20th	Night	25% 35% 8% 19% 11% 2	1260
	21st to end	Night	29% 36% 9% 18% 8%	1260
July	1st to 10th	Night	22% 36% 9% 20% 11% 1	1225
	11th to 20th	Night	25% 37% 7% 20% 10% 1	1378
	21st to end	Night	27% 37% 10% 19% 7%	1487
August	1st to 10th	Night	25% 35% 12% 21% 6% 2	1517
	11th to 20th	Night	22% 34% 12% 22% 10% 1	1598
	21st to end	Night	26% 35% 10% 19% 9% 1	1783
September	1st to 10th	Night	25% 35% 9% 22% 8% 1	1836
	11th to 20th	Night	29% 35% 12% 20% 4	1980
	21st to end	Night	33% 35% 11% 16% 5%	1980
October	1st to 10th	Night	32% 35% 10% 16% 6% 1	2024
	11th to 20th	Night	42% 35% 8% 13% 2	2236
	21st to end	Night	43% 36% 7% 10% 3	2574
November	1st to 10th	Night	36% 40% 7% 13% 4	2406
	11th to 20th	Night	44% 38% 6% 8% 4	2569
	21st to end	Night	44% 38% 10% 7% 1	2719
December	1st to 10th	Night	43% 39% 8% 9% 2	2850
	11th to 20th	Night	45% 31% 10% 8% 4 2	3525
	21st to end	Night	62% 23% 6% 8% 1	5236

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% 15% 29% 24% 12% 1	234
	11th to 20th	Day	20% 12% 28% 29% 11% 1	255
	21st to end	Day	21% 11% 27% 31% 10% 1	264
February	1st to 10th	Day	20% 16% 36% 23% 4 1	240
	11th to 20th	Day	17% 20% 39% 17% 5% 1	240
	21st to end	Day	18% 27% 35% 16% 4	198
March	1st to 10th	Day	20% 18% 33% 19% 9%	240
	11th to 20th	Day	19% 14% 29% 27% 9% 2	402
	21st to end	Day	24% 12% 28% 22% 13% 1	462
April	1st to 10th	Day	20% 16% 27% 28% 7% 1	420
	11th to 20th	Day	25% 16% 25% 19% 11% 3	412
	21st to end	Day	24% 15% 28% 19% 10% 4	420
May	1st to 10th	Day	22% 16% 26% 19% 12% 4	423
	11th to 20th	Day	19% 12% 31% 22% 11% 4	535
	21st to end	Day	16% 12% 30% 27% 11% 4	679
June	1st to 10th	Day	17% 11% 34% 23% 12% 3	630
	11th to 20th	Day	15% 14% 30% 28% 10% 3	630
	21st to end	Day	17% 11% 29% 28% 12% 3	630
July	1st to 10th	Day	8% 9% 36% 29% 14% 5%	621
	11th to 20th	Day	14% 9% 28% 28% 16% 6%	618
	21st to end	Day	13% 10% 29% 28% 16% 5%	684
August	1st to 10th	Day	12% 7% 22% 31% 21% 6%	529
	11th to 20th	Day	16% 6% 14% 31% 23% 11%	439
	21st to end	Day	18% 9% 23% 24% 19% 6%	495
September	1st to 10th	Day	19% 8% 22% 25% 20% 6%	450
	11th to 20th	Day	16% 10% 24% 31% 15% 4	450
	21st to end	Day	21% 12% 23% 26% 14% 3	450
October	1st to 10th	Day	21% 15% 24% 23% 14% 2	450
	11th to 20th	Day	26% 16% 29% 23% 5% 1	373
	21st to end	Day	31% 17% 31% 17% 3 1	297
November	1st to 10th	Day	24% 21% 33% 16% 6% 1	270
	11th to 20th	Day	22% 20% 33% 18% 5% 1	221
	21st to end	Day	28% 17% 35% 15% 6%	180
December	1st to 10th	Day	26% 9% 33% 19% 11% 2	180
	11th to 20th	Day	24% 17% 37% 15% 6% 1	180
	21st to end	Day	33% 13% 31% 16% 8% 1	198
January	1st to 10th	Night	22% 13% 30% 29% 7%	950
	11th to 20th	Night	22% 11% 29% 27% 10% 1	926
	21st to end	Night	21% 9% 28% 31% 9% 1	990
February	1st to 10th	Night	18% 11% 34% 31% 6%	793
	11th to 20th	Night	19% 12% 31% 29% 8% 1	703
	21st to end	Night	17% 13% 33% 30% 6%	592
March	1st to 10th	Night	16% 9% 34% 29% 10% 1	720
	11th to 20th	Night	18% 12% 32% 28% 9% 1	720
	21st to end	Night	18% 10% 30% 33% 7% 1	779
April	1st to 10th	Night	21% 10% 26% 35% 7% 1	540
	11th to 20th	Night	22% 9% 25% 33% 10% 1	533
	21st to end	Night	20% 9% 25% 33% 12% 1	540
May	1st to 10th	Night	18% 8% 25% 38% 11% 1	540
	11th to 20th	Night	21% 4 26% 34% 14% 1	531
	21st to end	Night	14% 6% 27% 42% 11%	411
June	1st to 10th	Night	15% 5% 27% 43% 11%	360
	11th to 20th	Night	16% 6% 28% 36% 13%	360
	21st to end	Night	18% 3 24% 37% 16% 1	360
July	1st to 10th	Night	12% 4 23% 48% 13% 1	350
	11th to 20th	Night	14% 5% 16% 40% 23% 2	508
	21st to end	Night	15% 3 18% 41% 21% 2	591
August	1st to 10th	Night	14% 3 18% 38% 25% 1	537
	11th to 20th	Night	10% 3 17% 36% 31% 3	534
	21st to end	Night	16% 5% 17% 37% 23% 1	594
September	1st to 10th	Night	16% 5% 23% 32% 21% 4	576
	11th to 20th	Night	18% 6% 23% 32% 17% 3	720
	21st to end	Night	22% 8% 21% 32% 15% 3	720
October	1st to 10th	Night	24% 10% 23% 27% 15% 1	720
	11th to 20th	Night	29% 12% 24% 26% 7% 1	720
	21st to end	Night	32% 10% 25% 28% 5% 1	792
November	1st to 10th	Night	28% 12% 27% 24% 8% 1	740
	11th to 20th	Night	25% 14% 30% 23% 7%	760
	21st to end	Night	26% 14% 31% 25% 5%	819
December	1st to 10th	Night	24% 13% 32% 23% 7% 1	950
	11th to 20th	Night	26% 14% 32% 20% 6% 1	950
	21st to end	Night	31% 12% 28% 23% 7%	1045

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