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Toronto
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Toronto clear sky chart from 2005-11-06 to 2026-03-18.

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%	131464
	Night	15% 9% 3 8% 5% 5% 5% 4 6% 7% 34%	130033
Transparency	Day	46% 8% 14% 20% 11% 1	135057
	Night	47% 7% 13% 20% 11% 1	134526
Seeing	Day	19% 10% 29% 24% 12% 5%	16075
	Night	19% 8% 30% 30% 12% 1	25617

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	17% 10% 4 12% 6% 6% 5% 4 6% 7% 23%	4661
	11th to 20th	Day	10% 17% 7% 17% 8% 6% 5% 4 5% 5% 16%	5103
	21st to end	Day	14% 14% 5% 13% 6% 5% 5% 4 6% 6% 21%	5780
February	1st to 10th	Day	15% 14% 4 13% 6% 5% 5% 4 5% 5% 24%	1890
	11th to 20th	Day	12% 14% 6% 12% 7% 5% 4 4 4 6% 25%	1843
	21st to end	Day	17% 13% 4 10% 6% 5% 5% 5% 4 6% 26%	1620
March	1st to 10th	Day	19% 9% 4 8% 5% 5% 4 4 5% 6% 32%	5042
	11th to 20th	Day	11% 12% 4 9% 5% 5% 5% 4 6% 8% 30%	5057
	21st to end	Day	18% 10% 4 8% 5% 5% 4 3 4 6% 33%	5465
April	1st to 10th	Day	17% 12% 4 8% 6% 4 4 3 5% 6% 30%	2365
	11th to 20th	Day	19% 10% 2 7% 4 4 4 3 5% 6% 35%	2442
	21st to end	Day	19% 8% 3 8% 4 5% 5% 3 5% 6% 33%	2600
May	1st to 10th	Day	20% 8% 3 8% 4 4 4 3 5% 7% 33%	5888
	11th to 20th	Day	16% 9% 3 7% 5% 4 4 4 6% 8% 34%	6289
	21st to end	Day	18% 6% 3 6% 4 4 4 4 6% 7% 39%	6949
June	1st to 10th	Day	14% 6% 2 6% 6% 4 5% 4 7% 9% 37%	2800
	11th to 20th	Day	11% 5% 2 6% 5% 5% 5% 5% 7% 10% 38%	2800
	21st to end	Day	13% 6% 2 6% 4 5% 5% 4 7% 9% 39%	2800
July	1st to 10th	Day	9% 5% 2 7% 5% 5% 6% 5% 6% 10% 40%	6360
	11th to 20th	Day	8% 5% 2 5% 4 4 5% 4 7% 9% 48%	6360
	21st to end	Day	7% 5% 2 5% 4 5% 5% 4 7% 9% 46%	6479
August	1st to 10th	Day	16% 7% 2 6% 4 4 5% 3 6% 8% 39%	4234
	11th to 20th	Day	10% 7% 3 7% 5% 5% 5% 5% 8% 10% 36%	4174
	21st to end	Day	9% 6% 2 6% 4 4 5% 4 6% 9% 44%	4486
September	1st to 10th	Day	13% 5% 3 6% 4 4 4 4 6% 8% 43%	2400
	11th to 20th	Day	10% 5% 2 5% 4 4 5% 3 6% 8% 47%	2287
	21st to end	Day	13% 6% 2 7% 6% 6% 4 4 6% 9% 37%	2155
October	1st to 10th	Day	17% 8% 3 6% 4 4 4 3 6% 7% 38%	2000
	11th to 20th	Day	19% 8% 3 8% 6% 5% 5% 4 5% 7% 31%	2000
	21st to end	Day	23% 10% 3 9% 5% 5% 5% 4 7% 7% 22%	2200
November	1st to 10th	Day	15% 9% 3 7% 6% 4 6% 3 7% 7% 33%	1781
	11th to 20th	Day	15% 12% 4 9% 6% 5% 5% 4 7% 8% 26%	1680
	21st to end	Day	19% 13% 4 9% 5% 5% 6% 4 6% 7% 22%	1680
December	1st to 10th	Day	19% 15% 5% 11% 7% 6% 6% 4 5% 7% 18%	2680
	11th to 20th	Day	20% 16% 4 9% 6% 4 4 4 5% 5% 22%	3066
	21st to end	Day	26% 16% 6% 11% 7% 4 3 3 4 4 15%	4048
January	1st to 10th	Night	15% 11% 4 10% 7% 5% 6% 5% 6% 7% 25%	8234
	11th to 20th	Night	12% 15% 5% 13% 10% 7% 6% 4 5% 6% 17%	7781
	21st to end	Night	14% 12% 5% 11% 7% 6% 6% 4 6% 6% 23%	8401
February	1st to 10th	Night	14% 14% 5% 9% 6% 6% 5% 4 6% 6% 27%	2730
	11th to 20th	Night	15% 13% 4 10% 7% 5% 5% 4 5% 6% 27%	2663
	21st to end	Night	14% 12% 4 10% 6% 5% 5% 4 5% 5% 29%	2181
March	1st to 10th	Night	16% 9% 5% 8% 5% 5% 6% 3 5% 6% 31%	5018
	11th to 20th	Night	11% 8% 3 8% 5% 4 5% 5% 7% 8% 36%	5057
	21st to end	Night	21% 8% 2 6% 3 3 3 3 4 5% 40%	5467
April	1st to 10th	Night	19% 9% 3 7% 7% 4 4 4 5% 6% 32%	2035
	11th to 20th	Night	16% 8% 3 6% 6% 5% 5% 3 5% 6% 38%	1923
	21st to end	Night	17% 7% 3 7% 4 5% 4 4 5% 8% 36%	1800
May	1st to 10th	Night	22% 8% 2 7% 4 4 4 3 5% 6% 35%	4053
	11th to 20th	Night	15% 7% 3 7% 5% 5% 4 4 6% 7% 38%	3603
	21st to end	Night	17% 6% 2 5% 4 3 3 4 5% 7% 44%	3926
June	1st to 10th	Night	12% 4 2 6% 5% 5% 5% 4 6% 8% 43%	1600
	11th to 20th	Night	9% 6% 3 6% 4 4 5% 4 7% 10% 42%	1600
	21st to end	Night	11% 6% 3 6% 4 4 5% 5% 6% 8% 44%	1600
July	1st to 10th	Night	7% 5% 2 6% 4 5% 5% 3 6% 9% 47%	3600
	11th to 20th	Night	10% 4 2 5% 3 4 4 3 6% 9% 49%	3600
	21st to end	Night	9% 4 1 5% 3 4 4 4 6% 7% 53%	4370
August	1st to 10th	Night	10% 5% 2 6% 4 5% 5% 4 7% 8% 46%	2915
	11th to 20th	Night	11% 5% 2 6% 3 3 4 3 5% 8% 50%	2875
	21st to end	Night	10% 5% 2 5% 4 4 5% 4 7% 8% 47%	3378
September	1st to 10th	Night	9% 6% 1 6% 3 4 6% 4 7% 7% 48%	2000
	11th to 20th	Night	10% 4 2 4 3 3 3 3 4 7% 56%	2110
	21st to end	Night	16% 6% 2 6% 4 5% 5% 3 5% 7% 42%	2245
October	1st to 10th	Night	15% 7% 3 6% 4 4 5% 3 6% 6% 42%	2400
	11th to 20th	Night	18% 9% 3 7% 5% 4 4 4 5% 6% 36%	2400
	21st to end	Night	20% 10% 3 8% 4 5% 4 4 5% 6% 32%	2640
November	1st to 10th	Night	16% 8% 3 7% 5% 5% 4 3 6% 7% 38%	2730
	11th to 20th	Night	16% 10% 3 8% 5% 5% 4 5% 5% 6% 31%	2940
	21st to end	Night	20% 12% 4 7% 5% 5% 5% 4 5% 7% 26%	2940
December	1st to 10th	Night	18% 13% 5% 10% 6% 5% 6% 4 6% 6% 20%	4720
	11th to 20th	Night	17% 16% 5% 10% 5% 5% 5% 4 5% 5% 23%	5348
	21st to end	Night	26% 13% 7% 10% 5% 4 4 3 5% 5% 16%	7150

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	54% 8% 15% 13% 9%	4662
	11th to 20th	Day	69% 5% 10% 11% 4	5137
	21st to end	Day	59% 6% 14% 12% 9%	5780
February	1st to 10th	Day	60% 7% 12% 16% 4 1	1890
	11th to 20th	Day	58% 7% 14% 15% 6% 1	1852
	21st to end	Day	56% 9% 13% 16% 6% 1	1620
March	1st to 10th	Day	50% 7% 15% 15% 13% 1	5045
	11th to 20th	Day	47% 9% 18% 17% 7% 2	5057
	21st to end	Day	49% 7% 11% 20% 12% 1	5465
April	1st to 10th	Day	53% 6% 12% 17% 11% 1	2365
	11th to 20th	Day	48% 7% 11% 20% 14% 1	2442
	21st to end	Day	49% 7% 12% 17% 12% 3	2600
May	1st to 10th	Day	48% 8% 14% 15% 12% 4	5897
	11th to 20th	Day	46% 11% 12% 15% 14% 2	6293
	21st to end	Day	42% 8% 12% 23% 13% 3	6949
June	1st to 10th	Day	41% 10% 13% 21% 15% 1	2800
	11th to 20th	Day	37% 9% 14% 24% 15% 1	2800
	21st to end	Day	37% 10% 14% 24% 14% 1	2800
July	1st to 10th	Day	36% 7% 15% 25% 15% 2	6290
	11th to 20th	Day	31% 7% 13% 32% 16% 1	6285
	21st to end	Day	32% 8% 14% 28% 17% 1	6293
August	1st to 10th	Day	42% 8% 14% 21% 15% 1	4221
	11th to 20th	Day	39% 8% 16% 25% 11%	4213
	21st to end	Day	34% 8% 14% 34% 10% 1	4486
September	1st to 10th	Day	36% 10% 15% 28% 11% 1	2400
	11th to 20th	Day	33% 7% 15% 29% 14%	2287
	21st to end	Day	42% 10% 14% 25% 9%	2155
October	1st to 10th	Day	35% 7% 16% 28% 14% 1	3260
	11th to 20th	Day	38% 7% 16% 25% 14%	3240
	21st to end	Day	52% 7% 14% 20% 6%	3538
November	1st to 10th	Day	47% 9% 15% 20% 8% 1	1781
	11th to 20th	Day	52% 11% 14% 14% 8% 1	1680
	21st to end	Day	58% 9% 15% 15% 3	1680
December	1st to 10th	Day	64% 8% 15% 10% 3	2680
	11th to 20th	Day	60% 8% 16% 9% 7%	3066
	21st to end	Day	71% 8% 8% 8% 5%	4048
January	1st to 10th	Night	54% 9% 14% 19% 4	8234
	11th to 20th	Night	63% 10% 10% 11% 5%	7822
	21st to end	Night	56% 7% 13% 12% 12% 1	8401
February	1st to 10th	Night	55% 7% 14% 18% 5% 1	2730
	11th to 20th	Night	56% 7% 13% 16% 8%	2665
	21st to end	Night	54% 6% 15% 17% 8%	2181
March	1st to 10th	Night	51% 7% 12% 18% 11% 2	5028
	11th to 20th	Night	41% 7% 20% 20% 10% 2	5058
	21st to end	Night	45% 5% 10% 21% 17% 2	5467
April	1st to 10th	Night	51% 6% 11% 18% 13% 1	2035
	11th to 20th	Night	47% 7% 9% 20% 15% 2	1923
	21st to end	Night	44% 8% 12% 19% 16% 2	1800
May	1st to 10th	Night	49% 6% 11% 14% 13% 5%	4060
	11th to 20th	Night	42% 11% 13% 18% 13% 3	3604
	21st to end	Night	38% 8% 14% 23% 16% 2	3927
June	1st to 10th	Night	37% 7% 12% 24% 17% 3	1600
	11th to 20th	Night	35% 7% 14% 22% 20% 2	1600
	21st to end	Night	36% 8% 13% 24% 18% 1	1600
July	1st to 10th	Night	33% 7% 14% 25% 20% 2	3560
	11th to 20th	Night	31% 6% 13% 30% 18% 1	3552
	21st to end	Night	29% 7% 12% 29% 22% 1	4241
August	1st to 10th	Night	35% 6% 13% 28% 15% 2	2904
	11th to 20th	Night	32% 6% 15% 33% 13% 1	2902
	21st to end	Night	33% 7% 14% 32% 13% 1	3378
September	1st to 10th	Night	32% 8% 16% 29% 14% 1	2000
	11th to 20th	Night	28% 7% 12% 36% 17% 1	2110
	21st to end	Night	41% 8% 13% 27% 11% 1	2245
October	1st to 10th	Night	33% 6% 11% 27% 23% 1	3920
	11th to 20th	Night	42% 6% 15% 27% 11%	3899
	21st to end	Night	39% 7% 16% 27% 10% 1	4252
November	1st to 10th	Night	44% 7% 14% 23% 12% 1	2730
	11th to 20th	Night	50% 8% 14% 18% 9% 1	2940
	21st to end	Night	55% 9% 18% 15% 3	2940
December	1st to 10th	Night	61% 8% 14% 13% 4	4720
	11th to 20th	Night	59% 8% 12% 13% 8%	5348
	21st to end	Night	67% 9% 11% 9% 5%	7150

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	20% 21% 29% 23% 6% 1	220
	11th to 20th	Day	24% 20% 34% 14% 6% 2	303
	21st to end	Day	25% 15% 36% 19% 5% 1	363
February	1st to 10th	Day	25% 15% 40% 16% 3 1	330
	11th to 20th	Day	25% 17% 41% 15% 2	330
	21st to end	Day	31% 17% 33% 17% 2	299
March	1st to 10th	Day	21% 15% 36% 21% 7%	540
	11th to 20th	Day	23% 16% 34% 21% 5% 1	528
	21st to end	Day	29% 11% 32% 20% 7% 1	550
April	1st to 10th	Day	24% 15% 33% 20% 7% 1	500
	11th to 20th	Day	28% 13% 31% 18% 7% 3	492
	21st to end	Day	25% 12% 33% 19% 9% 2	500
May	1st to 10th	Day	22% 10% 30% 23% 9% 5%	503
	11th to 20th	Day	17% 7% 28% 28% 13% 6%	527
	21st to end	Day	17% 8% 26% 28% 16% 7%	573
June	1st to 10th	Day	15% 8% 32% 30% 12% 3	530
	11th to 20th	Day	14% 10% 26% 30% 17% 3	530
	21st to end	Day	17% 8% 26% 30% 15% 5%	530
July	1st to 10th	Day	10% 5% 22% 32% 23% 7%	525
	11th to 20th	Day	13% 4 23% 30% 21% 8%	524
	21st to end	Day	9% 2 26% 37% 17% 9%	576
August	1st to 10th	Day	12% 4 22% 29% 21% 11%	526
	11th to 20th	Day	10% 6% 20% 28% 25% 12%	519
	21st to end	Day	11% 7% 22% 29% 20% 11%	583
September	1st to 10th	Day	14% 6% 23% 27% 18% 12%	530
	11th to 20th	Day	10% 4 19% 28% 22% 18%	530
	21st to end	Day	15% 8% 28% 28% 15% 7%	530
October	1st to 10th	Day	19% 9% 26% 24% 15% 6%	530
	11th to 20th	Day	19% 12% 38% 21% 8% 2	530
	21st to end	Day	28% 11% 31% 24% 6% 1	583
November	1st to 10th	Day	22% 16% 30% 22% 9% 1	319
	11th to 20th	Day	22% 19% 33% 20% 5% 2	220
	21st to end	Day	25% 15% 39% 18% 3	220
December	1st to 10th	Day	25% 15% 36% 18% 5%	220
	11th to 20th	Day	30% 20% 26% 20% 5%	220
	21st to end	Day	30% 15% 38% 14% 2	242
January	1st to 10th	Night	23% 12% 36% 23% 5% 1	840
	11th to 20th	Night	26% 13% 31% 25% 5%	840
	21st to end	Night	20% 9% 37% 27% 7%	924
February	1st to 10th	Night	20% 12% 40% 25% 3	840
	11th to 20th	Night	22% 12% 37% 25% 4	823
	21st to end	Night	19% 12% 41% 23% 4	692
March	1st to 10th	Night	20% 11% 36% 26% 7%	840
	11th to 20th	Night	22% 13% 35% 23% 6% 1	829
	21st to end	Night	21% 10% 32% 27% 9% 1	880
April	1st to 10th	Night	24% 10% 33% 27% 5%	800
	11th to 20th	Night	20% 10% 35% 26% 8% 1	739
	21st to end	Night	21% 7% 30% 31% 11%	600
May	1st to 10th	Night	19% 5% 28% 32% 14% 2	600
	11th to 20th	Night	16% 4 31% 35% 14%	409
	21st to end	Night	12% 4 27% 36% 20%	433
June	1st to 10th	Night	14% 3 28% 39% 16% 1	400
	11th to 20th	Night	13% 5% 28% 38% 16% 1	400
	21st to end	Night	11% 7% 21% 45% 17% 1	400
July	1st to 10th	Night	6% 3 23% 44% 22% 2	390
	11th to 20th	Night	11% 1 21% 43% 22% 2	388
	21st to end	Night	8% 2 19% 45% 24% 2	625
August	1st to 10th	Night	9% 2 13% 42% 31% 2	597
	11th to 20th	Night	8% 1 16% 42% 30% 3	594
	21st to end	Night	11% 3 20% 37% 26% 3	750
September	1st to 10th	Night	11% 4 23% 36% 21% 6%	800
	11th to 20th	Night	13% 2 17% 33% 30% 5%	800
	21st to end	Night	18% 4 21% 32% 21% 4	800
October	1st to 10th	Night	18% 5% 25% 30% 20% 3	800
	11th to 20th	Night	21% 7% 29% 32% 10% 1	800
	21st to end	Night	24% 8% 30% 32% 6%	880
November	1st to 10th	Night	20% 11% 26% 30% 10% 1	820
	11th to 20th	Night	22% 11% 33% 25% 8% 2	840
	21st to end	Night	27% 9% 32% 25% 7%	840
December	1st to 10th	Night	26% 9% 36% 23% 5%	840
	11th to 20th	Night	22% 12% 39% 23% 4	840
	21st to end	Night	31% 9% 35% 22% 3	924

Page generated at 2026-03-15 02:23:55. Version ac07

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