Canadian Lakes
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Canadian Lakes 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	13% 10% 4 9% 6% 5% 5% 4 5% 7% 33%	126153
	Night	14% 11% 4 9% 5% 5% 4 3 5% 6% 32%	123133
Transparency	Day	48% 6% 12% 20% 12% 1	129679
	Night	50% 5% 12% 20% 12% 1	127681
Seeing	Day	18% 13% 30% 23% 11% 4	17076
	Night	19% 10% 30% 29% 10% 1	26881

By Month

Percentage Cloud Cover SE (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% 21% 7% 6% 4 3 3 5% 13%	3617
	11th to 20th	Day	11% 15% 8% 19% 15% 9% 7% 3 4 3 6%	3620
	21st to end	Day	15% 19% 10% 14% 7% 4 5% 3 4 3 15%	3982
February	1st to 10th	Day	11% 14% 6% 12% 10% 7% 7% 3 5% 6% 18%	1794
	11th to 20th	Day	12% 14% 6% 14% 10% 6% 5% 3 4 6% 20%	1948
	21st to end	Day	12% 16% 7% 12% 6% 5% 5% 3 5% 7% 22%	1650
March	1st to 10th	Day	12% 10% 3 11% 6% 6% 5% 4 5% 6% 32%	4480
	11th to 20th	Day	12% 8% 5% 9% 6% 6% 5% 4 5% 8% 33%	4878
	21st to end	Day	20% 12% 5% 9% 5% 4 4 3 4 5% 28%	5634
April	1st to 10th	Day	18% 13% 3 7% 5% 5% 4 4 5% 6% 29%	2400
	11th to 20th	Day	17% 10% 3 7% 5% 5% 4 3 5% 6% 35%	2462
	21st to end	Day	15% 10% 3 8% 5% 6% 4 3 5% 7% 33%	2600
May	1st to 10th	Day	18% 8% 2 6% 4 4 4 3 5% 7% 38%	5862
	11th to 20th	Day	13% 8% 2 8% 4 4 5% 4 6% 8% 38%	5895
	21st to end	Day	13% 7% 3 7% 5% 4 5% 3 5% 7% 41%	6935
June	1st to 10th	Day	11% 6% 3 5% 5% 4 5% 5% 5% 8% 43%	2800
	11th to 20th	Day	12% 6% 2 6% 4 4 5% 4 6% 8% 42%	2800
	21st to end	Day	11% 6% 2 6% 4 6% 5% 5% 6% 7% 41%	2800
July	1st to 10th	Day	11% 6% 3 7% 4 5% 5% 4 7% 10% 38%	6360
	11th to 20th	Day	7% 5% 2 6% 4 4 5% 4 6% 9% 47%	6360
	21st to end	Day	8% 4 2 6% 4 5% 4 4 7% 9% 46%	6924
August	1st to 10th	Day	11% 5% 2 7% 5% 5% 6% 5% 7% 8% 40%	4276
	11th to 20th	Day	12% 5% 2 6% 4 4 5% 4 6% 7% 46%	4174
	21st to end	Day	8% 6% 2 7% 5% 5% 5% 5% 6% 8% 44%	4444
September	1st to 10th	Day	11% 5% 2 6% 5% 5% 5% 3 6% 7% 43%	2356
	11th to 20th	Day	11% 4 2 5% 4 5% 5% 3 6% 8% 47%	2178
	21st to end	Day	13% 7% 2 8% 5% 5% 4 3 6% 7% 40%	2090
October	1st to 10th	Day	17% 7% 3 6% 5% 4 3 3 5% 5% 42%	2090
	11th to 20th	Day	19% 10% 4 9% 5% 6% 5% 4 4 7% 26%	1837
	21st to end	Day	20% 11% 3 9% 7% 7% 5% 3 5% 7% 23%	1881
November	1st to 10th	Day	14% 12% 4 8% 5% 4 4 3 6% 6% 35%	1762
	11th to 20th	Day	13% 18% 6% 12% 6% 5% 4 3 6% 5% 23%	1800
	21st to end	Day	21% 16% 6% 10% 5% 4 4 3 5% 6% 21%	1800
December	1st to 10th	Day	10% 21% 10% 14% 6% 6% 5% 4 5% 5% 13%	2674
	11th to 20th	Day	15% 19% 11% 13% 8% 5% 4 3 4 4 14%	3008
	21st to end	Day	24% 22% 6% 11% 6% 5% 4 3 3 4 13%	3982
January	1st to 10th	Night	11% 15% 8% 21% 7% 5% 4 3 4 5% 16%	6348
	11th to 20th	Night	11% 16% 8% 19% 10% 12% 5% 3 4 4 9%	6360
	21st to end	Night	13% 18% 8% 15% 6% 5% 6% 3 5% 6% 15%	6996
February	1st to 10th	Night	12% 15% 5% 12% 10% 6% 5% 5% 5% 5% 20%	2601
	11th to 20th	Night	12% 13% 5% 11% 8% 5% 5% 4 6% 6% 24%	2338
	21st to end	Night	15% 14% 5% 12% 6% 5% 4 4 5% 6% 25%	1980
March	1st to 10th	Night	15% 8% 3 8% 4 4 5% 3 5% 7% 37%	5373
	11th to 20th	Night	12% 9% 3 6% 4 4 4 4 5% 9% 40%	5082
	21st to end	Night	17% 13% 4 8% 5% 4 4 3 5% 6% 32%	5340
April	1st to 10th	Night	16% 12% 3 6% 5% 4 4 3 4 6% 36%	2000
	11th to 20th	Night	19% 9% 3 7% 4 3 4 3 5% 6% 36%	1887
	21st to end	Night	17% 8% 2 7% 4 4 4 4 6% 7% 37%	1800
May	1st to 10th	Night	14% 9% 3 8% 4 4 5% 3 6% 7% 37%	4033
	11th to 20th	Night	15% 9% 3 7% 4 4 4 2 5% 7% 40%	3997
	21st to end	Night	18% 6% 2 5% 3 3 3 3 4 5% 47%	3942
June	1st to 10th	Night	10% 7% 2 6% 5% 4 4 4 6% 9% 43%	1600
	11th to 20th	Night	11% 6% 2 7% 5% 4 3 4 6% 9% 43%	1600
	21st to end	Night	8% 5% 2 6% 5% 4 5% 4 6% 8% 47%	1600
July	1st to 10th	Night	9% 6% 2 6% 5% 4 5% 5% 6% 8% 44%	3618
	11th to 20th	Night	6% 5% 2 5% 4 4 4 4 5% 7% 53%	3617
	21st to end	Night	9% 6% 2 5% 4 4 4 3 5% 7% 50%	3947
August	1st to 10th	Night	11% 5% 2 6% 4 3 3 3 5% 8% 50%	2871
	11th to 20th	Night	11% 4 2 5% 3 4 4 3 6% 8% 51%	2875
	21st to end	Night	9% 5% 2 6% 4 4 4 4 5% 7% 50%	3450
September	1st to 10th	Night	8% 5% 2 5% 4 4 4 4 5% 8% 52%	2023
	11th to 20th	Night	10% 4 1 4 3 3 3 3 5% 7% 55%	2179
	21st to end	Night	14% 6% 3 6% 4 4 5% 3 5% 9% 41%	2090
October	1st to 10th	Night	17% 7% 2 4 3 3 3 3 4 7% 47%	2090
	11th to 20th	Night	18% 9% 4 7% 5% 4 4 4 4 7% 34%	2337
	21st to end	Night	21% 11% 3 8% 5% 4 4 3 4 7% 31%	2717
November	1st to 10th	Night	13% 11% 3 7% 5% 4 4 3 6% 6% 38%	2536
	11th to 20th	Night	15% 14% 4 10% 5% 5% 5% 4 7% 6% 25%	2600
	21st to end	Night	17% 15% 5% 10% 5% 5% 5% 4 5% 6% 24%	2600
December	1st to 10th	Night	11% 16% 6% 13% 7% 6% 5% 5% 6% 7% 19%	4511
	11th to 20th	Night	16% 22% 6% 12% 8% 5% 4 3 4 5% 14%	5199
	21st to end	Night	25% 22% 6% 10% 5% 3 3 2 4 4 16%	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	73% 6% 9% 10% 2	3618
	11th to 20th	Day	82% 4 6% 5% 2	3620
	21st to end	Day	73% 5% 10% 8% 4	3982
February	1st to 10th	Day	65% 7% 10% 13% 5%	1794
	11th to 20th	Day	65% 5% 9% 12% 8%	1958
	21st to end	Day	62% 6% 11% 14% 6%	1650
March	1st to 10th	Day	51% 4 15% 17% 10% 2	4480
	11th to 20th	Day	48% 6% 16% 18% 11% 1	4878
	21st to end	Day	58% 5% 10% 16% 11% 1	5636
April	1st to 10th	Day	55% 5% 10% 18% 11% 1	2400
	11th to 20th	Day	50% 5% 10% 19% 13% 2	2462
	21st to end	Day	49% 6% 11% 18% 13% 2	2600
May	1st to 10th	Day	44% 6% 11% 20% 17% 2	5897
	11th to 20th	Day	42% 8% 12% 22% 14% 2	5899
	21st to end	Day	41% 5% 10% 22% 19% 2	6949
June	1st to 10th	Day	37% 7% 11% 29% 15% 2	2800
	11th to 20th	Day	38% 7% 13% 23% 18% 1	2800
	21st to end	Day	39% 9% 12% 23% 16% 2	2800
July	1st to 10th	Day	39% 6% 13% 24% 15% 2	6291
	11th to 20th	Day	32% 7% 13% 31% 17% 1	6285
	21st to end	Day	31% 7% 14% 28% 19% 1	6728
August	1st to 10th	Day	39% 7% 11% 27% 15% 1	4261
	11th to 20th	Day	36% 7% 12% 28% 16% 1	4213
	21st to end	Day	36% 7% 14% 27% 15% 1	4443
September	1st to 10th	Day	37% 7% 14% 28% 12% 2	2356
	11th to 20th	Day	33% 7% 14% 30% 15% 1	2178
	21st to end	Day	42% 6% 13% 25% 13%	2090
October	1st to 10th	Day	31% 4 9% 33% 20% 3	3480
	11th to 20th	Day	44% 5% 12% 25% 14%	3027
	21st to end	Day	54% 5% 14% 20% 7%	3081
November	1st to 10th	Day	48% 6% 13% 21% 11%	1762
	11th to 20th	Day	61% 6% 13% 14% 6%	1800
	21st to end	Day	64% 7% 12% 12% 4	1800
December	1st to 10th	Day	70% 8% 11% 9% 2	2674
	11th to 20th	Day	73% 5% 10% 11% 1	3005
	21st to end	Day	76% 5% 6% 9% 4	3982
January	1st to 10th	Night	69% 6% 9% 11% 5% 1	6348
	11th to 20th	Night	77% 5% 8% 5% 4	6360
	21st to end	Night	68% 6% 11% 10% 4	6996
February	1st to 10th	Night	63% 6% 11% 13% 6% 1	2601
	11th to 20th	Night	60% 7% 9% 16% 8% 1	2339
	21st to end	Night	58% 6% 13% 15% 8% 1	1980
March	1st to 10th	Night	45% 5% 16% 23% 10% 1	5373
	11th to 20th	Night	41% 5% 18% 23% 12% 1	5082
	21st to end	Night	52% 6% 11% 19% 11% 1	5340
April	1st to 10th	Night	49% 4 9% 21% 15% 1	2000
	11th to 20th	Night	47% 5% 10% 20% 16% 2	1887
	21st to end	Night	44% 6% 12% 21% 14% 3	1800
May	1st to 10th	Night	45% 6% 13% 16% 17% 3	4060
	11th to 20th	Night	43% 6% 10% 24% 16% 2	3998
	21st to end	Night	41% 4 8% 24% 20% 3	3950
June	1st to 10th	Night	36% 6% 11% 27% 18% 2	1600
	11th to 20th	Night	37% 7% 13% 23% 21% 1	1600
	21st to end	Night	34% 7% 14% 27% 16% 2	1600
July	1st to 10th	Night	36% 6% 12% 26% 14% 5%	3580
	11th to 20th	Night	29% 6% 13% 29% 22% 1	3572
	21st to end	Night	33% 6% 15% 25% 20% 2	3832
August	1st to 10th	Night	32% 6% 13% 30% 18% 1	2862
	11th to 20th	Night	32% 6% 11% 36% 16% 1	2902
	21st to end	Night	33% 6% 12% 29% 18% 1	3450
September	1st to 10th	Night	31% 7% 11% 32% 17% 1	2023
	11th to 20th	Night	28% 5% 12% 36% 17% 1	2179
	21st to end	Night	40% 6% 14% 26% 13% 1	2090
October	1st to 10th	Night	29% 4 10% 38% 18% 2	3480
	11th to 20th	Night	42% 5% 11% 24% 17% 1	3886
	21st to end	Night	46% 4 10% 29% 11%	4467
November	1st to 10th	Night	45% 6% 13% 22% 13% 1	2536
	11th to 20th	Night	56% 6% 15% 16% 6% 1	2600
	21st to end	Night	60% 5% 15% 15% 4	2600
December	1st to 10th	Night	62% 8% 17% 11% 3	4511
	11th to 20th	Night	71% 5% 11% 10% 3	5201
	21st to end	Night	72% 4 8% 8% 7%	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	22% 15% 35% 21% 5% 1	300
	11th to 20th	Day	23% 20% 37% 14% 5%	300
	21st to end	Day	26% 17% 35% 18% 4	330
February	1st to 10th	Day	19% 24% 35% 17% 4 1	300
	11th to 20th	Day	22% 28% 34% 13% 3	300
	21st to end	Day	29% 25% 35% 10% 2	249
March	1st to 10th	Day	22% 25% 37% 12% 3	300
	11th to 20th	Day	26% 14% 30% 21% 7% 1	450
	21st to end	Day	27% 16% 30% 20% 6% 1	550
April	1st to 10th	Day	26% 18% 31% 19% 5% 1	500
	11th to 20th	Day	27% 20% 31% 14% 6% 3	492
	21st to end	Day	22% 15% 32% 21% 9% 2	500
May	1st to 10th	Day	22% 17% 33% 18% 7% 3	503
	11th to 20th	Day	19% 12% 31% 23% 11% 4	535
	21st to end	Day	15% 13% 30% 26% 13% 4	789
June	1st to 10th	Day	12% 11% 36% 27% 10% 3	730
	11th to 20th	Day	16% 11% 31% 28% 10% 4	730
	21st to end	Day	14% 8% 33% 28% 13% 3	730
July	1st to 10th	Day	9% 6% 26% 32% 19% 7%	721
	11th to 20th	Day	8% 10% 27% 29% 19% 7%	718
	21st to end	Day	9% 6% 30% 30% 17% 8%	794
August	1st to 10th	Day	10% 6% 23% 27% 23% 11%	556
	11th to 20th	Day	13% 6% 19% 28% 23% 12%	519
	21st to end	Day	13% 6% 22% 29% 21% 9%	583
September	1st to 10th	Day	13% 9% 23% 26% 20% 10%	530
	11th to 20th	Day	10% 7% 17% 29% 24% 14%	522
	21st to end	Day	18% 11% 22% 26% 17% 6%	490
October	1st to 10th	Day	22% 12% 27% 22% 15% 3	490
	11th to 20th	Day	26% 15% 29% 24% 5%	405
	21st to end	Day	29% 18% 32% 15% 4 2	330
November	1st to 10th	Day	25% 19% 32% 18% 5% 1	300
	11th to 20th	Day	23% 23% 36% 14% 3 1	300
	21st to end	Day	32% 17% 33% 14% 5%	300
December	1st to 10th	Day	25% 24% 28% 16% 5% 1	300
	11th to 20th	Day	22% 20% 41% 13% 3	300
	21st to end	Day	28% 21% 32% 14% 3 2	330
January	1st to 10th	Night	21% 17% 34% 22% 6% 1	1000
	11th to 20th	Night	22% 16% 34% 22% 5% 1	1000
	21st to end	Night	20% 12% 33% 29% 6%	1100
February	1st to 10th	Night	19% 14% 37% 26% 3	830
	11th to 20th	Night	21% 14% 38% 23% 4	783
	21st to end	Night	23% 18% 37% 20% 3	660
March	1st to 10th	Night	19% 14% 35% 24% 8%	800
	11th to 20th	Night	18% 14% 36% 25% 7% 1	800
	21st to end	Night	22% 12% 34% 26% 6%	830
April	1st to 10th	Night	21% 13% 34% 27% 5% 1	600
	11th to 20th	Night	26% 10% 33% 24% 6% 1	593
	21st to end	Night	20% 14% 33% 26% 7% 1	600
May	1st to 10th	Night	17% 10% 32% 33% 7% 1	600
	11th to 20th	Night	18% 9% 32% 29% 12% 1	591
	21st to end	Night	14% 7% 30% 30% 18% 1	650
June	1st to 10th	Night	13% 9% 30% 35% 14% 1	600
	11th to 20th	Night	14% 6% 28% 38% 15% 1	600
	21st to end	Night	10% 5% 28% 41% 15% 2	600
July	1st to 10th	Night	8% 2 21% 42% 24% 3	585
	11th to 20th	Night	8% 4 21% 43% 22% 2	582
	21st to end	Night	9% 3 24% 41% 22% 1	657
August	1st to 10th	Night	9% 3 18% 45% 23% 2	597
	11th to 20th	Night	10% 3 18% 41% 23% 4	594
	21st to end	Night	12% 3 19% 40% 23% 2	660
September	1st to 10th	Night	9% 4 23% 36% 23% 4	623
	11th to 20th	Night	11% 4 20% 36% 24% 4	793
	21st to end	Night	16% 7% 24% 32% 17% 4	760
October	1st to 10th	Night	21% 7% 23% 34% 15% 1	760
	11th to 20th	Night	21% 13% 29% 27% 9% 1	760
	21st to end	Night	27% 11% 32% 23% 6%	836
November	1st to 10th	Night	19% 11% 34% 27% 8% 1	780
	11th to 20th	Night	24% 14% 35% 22% 5% 1	800
	21st to end	Night	24% 14% 33% 26% 4 1	800
December	1st to 10th	Night	22% 15% 33% 25% 5%	957
	11th to 20th	Night	25% 13% 37% 20% 4 1	1000
	21st to end	Night	31% 13% 33% 20% 2	1100

Page generated at 2025-09-16 01:49:17. Version ac07

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