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 2024-12-06.

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% 34%	101713
	Night	16% 9% 3 7% 5% 4 4 4 5% 7% 35%	98010
Transparency	Day	45% 9% 14% 20% 11% 1	105317
	Night	45% 8% 14% 21% 11% 1	102494
Seeing	Day	19% 9% 29% 25% 13% 5%	14514
	Night	19% 7% 30% 30% 12% 1	23953

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% 12% 4 9% 5% 4 5% 4 5% 6% 29%	2517
	11th to 20th	Day	12% 16% 7% 15% 8% 6% 5% 3 5% 5% 19%	2753
	21st to end	Day	22% 18% 6% 11% 5% 4 4 3 4 5% 17%	3124
February	1st to 10th	Day	15% 14% 5% 14% 7% 5% 5% 4 5% 5% 23%	1710
	11th to 20th	Day	12% 14% 6% 12% 7% 5% 4 4 5% 6% 26%	1663
	21st to end	Day	17% 13% 4 10% 7% 4 5% 4 4 5% 26%	1470
March	1st to 10th	Day	19% 10% 4 8% 4 4 4 4 5% 6% 31%	3432
	11th to 20th	Day	10% 14% 4 10% 5% 6% 6% 5% 6% 6% 28%	3480
	21st to end	Day	16% 9% 3 7% 5% 5% 4 4 5% 6% 36%	3815
April	1st to 10th	Day	16% 12% 4 8% 6% 4 4 4 5% 6% 29%	2247
	11th to 20th	Day	20% 9% 2 7% 4 3 4 3 6% 6% 35%	2318
	21st to end	Day	20% 8% 3 8% 4 5% 5% 3 5% 6% 33%	2470
May	1st to 10th	Day	17% 8% 3 8% 4 4 5% 4 6% 8% 33%	4108
	11th to 20th	Day	15% 10% 3 8% 5% 5% 4 5% 6% 8% 32%	4383
	21st to end	Day	12% 5% 2 5% 4 5% 4 4 6% 8% 46%	4837
June	1st to 10th	Day	14% 6% 2 6% 6% 4 5% 4 7% 9% 37%	2660
	11th to 20th	Day	12% 5% 2 6% 4 5% 5% 5% 8% 10% 39%	2660
	21st to end	Day	13% 5% 2 6% 4 5% 5% 4 7% 9% 39%	2660
July	1st to 10th	Day	9% 5% 2 5% 4 5% 6% 5% 7% 11% 41%	4440
	11th to 20th	Day	9% 5% 2 5% 4 4 5% 4 7% 9% 46%	4440
	21st to end	Day	7% 5% 2 6% 5% 5% 6% 5% 8% 9% 41%	4507
August	1st to 10th	Day	16% 7% 2 6% 4 4 5% 3 6% 8% 39%	4104
	11th to 20th	Day	10% 7% 3 7% 5% 5% 5% 5% 8% 10% 36%	4044
	21st to end	Day	9% 6% 2 6% 4 4 5% 4 6% 9% 44%	4349
September	1st to 10th	Day	13% 5% 3 6% 4 4 4 4 6% 8% 43%	2280
	11th to 20th	Day	11% 6% 2 5% 4 4 5% 3 6% 7% 47%	2173
	21st to end	Day	13% 6% 2 7% 6% 6% 4 4 6% 9% 37%	2047
October	1st to 10th	Day	18% 8% 3 6% 5% 4 4 3 6% 7% 36%	1900
	11th to 20th	Day	19% 8% 3 8% 6% 5% 5% 4 5% 7% 30%	1900
	21st to end	Day	23% 10% 3 9% 5% 5% 5% 3 7% 7% 22%	2090
November	1st to 10th	Day	14% 9% 4 7% 6% 4 6% 3 7% 7% 33%	1694
	11th to 20th	Day	15% 12% 4 9% 6% 5% 5% 5% 7% 7% 26%	1600
	21st to end	Day	19% 13% 4 9% 5% 5% 5% 4 6% 7% 23%	1600
December	1st to 10th	Day	18% 15% 4 11% 6% 6% 5% 4 6% 6% 19%	1560
	11th to 20th	Day	19% 14% 4 9% 6% 5% 5% 5% 6% 6% 23%	1906
	21st to end	Day	29% 17% 5% 10% 6% 4 3 3 5% 4 13%	2772
January	1st to 10th	Night	18% 14% 5% 10% 7% 5% 5% 4 5% 6% 23%	4429
	11th to 20th	Night	15% 12% 5% 12% 9% 7% 6% 4 5% 6% 20%	4206
	21st to end	Night	22% 13% 5% 10% 7% 6% 5% 3 5% 5% 19%	4532
February	1st to 10th	Night	15% 14% 5% 9% 6% 6% 5% 4 5% 6% 25%	2470
	11th to 20th	Night	15% 13% 4 10% 6% 5% 5% 4 5% 5% 27%	2403
	21st to end	Night	15% 11% 4 10% 5% 5% 5% 4 5% 5% 30%	1979
March	1st to 10th	Night	19% 9% 4 8% 5% 5% 5% 3 5% 5% 32%	3408
	11th to 20th	Night	13% 10% 4 8% 5% 4 4 5% 5% 7% 35%	3479
	21st to end	Night	17% 7% 2 6% 3 3 3 3 5% 5% 44%	3817
April	1st to 10th	Night	19% 9% 3 7% 7% 4 4 4 5% 6% 33%	1933
	11th to 20th	Night	16% 8% 3 6% 5% 5% 5% 3 4 6% 38%	1826
	21st to end	Night	17% 7% 3 7% 4 5% 4 4 5% 8% 36%	1710
May	1st to 10th	Night	18% 8% 2 7% 4 4 4 4 6% 6% 39%	2833
	11th to 20th	Night	15% 7% 3 7% 5% 5% 4 4 6% 8% 36%	2509
	21st to end	Night	10% 5% 2 5% 4 4 3 4 6% 8% 51%	2738
June	1st to 10th	Night	13% 4 2 6% 5% 5% 5% 4 6% 8% 42%	1520
	11th to 20th	Night	9% 6% 3 6% 4 4 5% 5% 7% 10% 42%	1520
	21st to end	Night	11% 6% 3 7% 4 3 5% 5% 6% 8% 44%	1520
July	1st to 10th	Night	6% 4 2 5% 4 4 5% 3 6% 9% 51%	2520
	11th to 20th	Night	11% 4 2 4 3 4 3 3 6% 10% 50%	2520
	21st to end	Night	8% 4 1 5% 3 4 4 4 7% 8% 52%	3043
August	1st to 10th	Night	10% 5% 2 6% 4 5% 4 4 7% 8% 46%	2825
	11th to 20th	Night	11% 5% 2 6% 3 3 4 3 5% 8% 50%	2785
	21st to end	Night	11% 5% 2 5% 4 4 5% 4 7% 8% 47%	3274
September	1st to 10th	Night	9% 6% 1 6% 3 4 6% 4 7% 7% 47%	1900
	11th to 20th	Night	10% 4 2 4 4 3 3 3 4 7% 55%	2004
	21st to end	Night	15% 6% 2 6% 4 5% 5% 3 5% 7% 42%	2133
October	1st to 10th	Night	15% 7% 3 7% 4 4 5% 3 6% 6% 40%	2280
	11th to 20th	Night	18% 9% 3 7% 5% 4 4 3 5% 6% 36%	2280
	21st to end	Night	20% 10% 3 7% 4 5% 4 4 5% 6% 31%	2508
November	1st to 10th	Night	16% 8% 2 7% 5% 5% 4 3 6% 7% 38%	2597
	11th to 20th	Night	17% 10% 3 7% 5% 5% 5% 5% 6% 6% 31%	2800
	21st to end	Night	20% 11% 4 7% 5% 5% 5% 4 6% 7% 26%	2800
December	1st to 10th	Night	20% 14% 5% 8% 5% 4 5% 4 5% 5% 24%	2737
	11th to 20th	Night	15% 16% 5% 10% 6% 5% 5% 5% 5% 6% 23%	3288
	21st to end	Night	31% 14% 4 9% 5% 4 5% 4 5% 5% 14%	4884

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	52% 12% 18% 11% 7%	2518
	11th to 20th	Day	68% 8% 11% 9% 3	2753
	21st to end	Day	68% 9% 11% 9% 4	3124
February	1st to 10th	Day	61% 8% 13% 15% 2 1	1710
	11th to 20th	Day	56% 8% 14% 15% 6% 1	1672
	21st to end	Day	56% 9% 13% 15% 6% 1	1470
March	1st to 10th	Day	52% 9% 14% 17% 8%	3435
	11th to 20th	Day	49% 10% 14% 18% 8% 1	3480
	21st to end	Day	43% 9% 12% 21% 13% 2	3815
April	1st to 10th	Day	52% 7% 12% 17% 11% 1	2247
	11th to 20th	Day	47% 7% 11% 19% 14% 1	2318
	21st to end	Day	50% 7% 12% 17% 12% 3	2470
May	1st to 10th	Day	44% 9% 15% 17% 14% 1	4120
	11th to 20th	Day	46% 13% 14% 17% 8% 1	4387
	21st to end	Day	32% 10% 14% 24% 17% 3	4837
June	1st to 10th	Day	41% 10% 13% 21% 14% 1	2660
	11th to 20th	Day	36% 9% 14% 24% 16% 2	2660
	21st to end	Day	37% 10% 14% 24% 14% 1	2660
July	1st to 10th	Day	34% 7% 16% 26% 15% 2	4370
	11th to 20th	Day	31% 8% 14% 35% 11% 1	4365
	21st to end	Day	35% 10% 16% 21% 17% 1	4363
August	1st to 10th	Day	42% 8% 14% 20% 14% 1	4091
	11th to 20th	Day	39% 9% 17% 24% 11% 1	4083
	21st to end	Day	34% 8% 14% 33% 10% 1	4349
September	1st to 10th	Day	37% 10% 15% 27% 11% 1	2280
	11th to 20th	Day	34% 8% 15% 28% 14% 1	2173
	21st to end	Day	42% 10% 14% 25% 9%	2047
October	1st to 10th	Day	36% 7% 16% 27% 13% 1	3160
	11th to 20th	Day	38% 7% 16% 25% 14%	3140
	21st to end	Day	52% 7% 14% 21% 6%	3428
November	1st to 10th	Day	46% 10% 15% 20% 8% 1	1694
	11th to 20th	Day	53% 11% 14% 14% 7% 1	1600
	21st to end	Day	58% 9% 16% 15% 3	1600
December	1st to 10th	Day	63% 10% 13% 11% 3	1560
	11th to 20th	Day	58% 10% 17% 10% 5%	1906
	21st to end	Day	72% 9% 10% 8% 2	2772
January	1st to 10th	Night	57% 12% 14% 14% 3 1	4429
	11th to 20th	Night	62% 14% 12% 9% 3	4206
	21st to end	Night	63% 11% 13% 9% 3 1	4532
February	1st to 10th	Night	57% 8% 13% 18% 4 1	2470
	11th to 20th	Night	56% 7% 14% 15% 8%	2405
	21st to end	Night	53% 7% 15% 17% 7%	1979
March	1st to 10th	Night	51% 8% 12% 22% 6% 1	3418
	11th to 20th	Night	44% 9% 16% 19% 11% 2	3480
	21st to end	Night	38% 7% 11% 24% 18% 2	3817
April	1st to 10th	Night	50% 6% 11% 18% 13% 1	1933
	11th to 20th	Night	47% 7% 9% 20% 15% 2	1826
	21st to end	Night	44% 8% 11% 19% 15% 2	1710
May	1st to 10th	Night	43% 8% 13% 18% 16% 2	2840
	11th to 20th	Night	42% 14% 15% 18% 10% 2	2510
	21st to end	Night	28% 10% 14% 24% 21% 3	2739
June	1st to 10th	Night	38% 7% 12% 24% 16% 2	1520
	11th to 20th	Night	35% 7% 14% 21% 21% 2	1520
	21st to end	Night	36% 8% 13% 24% 18% 1	1520
July	1st to 10th	Night	29% 6% 15% 25% 21% 3	2480
	11th to 20th	Night	31% 6% 14% 33% 15% 1	2472
	21st to end	Night	29% 9% 15% 30% 17% 2	2946
August	1st to 10th	Night	36% 6% 13% 28% 15% 2	2814
	11th to 20th	Night	32% 7% 16% 33% 12% 1	2812
	21st to end	Night	33% 7% 14% 31% 14% 1	3274
September	1st to 10th	Night	32% 9% 16% 27% 15% 1	1900
	11th to 20th	Night	28% 7% 12% 34% 17% 1	2004
	21st to end	Night	40% 8% 13% 27% 11%	2133
October	1st to 10th	Night	33% 6% 11% 26% 23% 1	3800
	11th to 20th	Night	42% 6% 15% 26% 10%	3779
	21st to end	Night	40% 7% 17% 27% 10% 1	4120
November	1st to 10th	Night	44% 7% 14% 23% 11% 1	2597
	11th to 20th	Night	50% 9% 15% 17% 9% 1	2800
	21st to end	Night	54% 9% 18% 15% 3	2800
December	1st to 10th	Night	59% 9% 13% 13% 5%	2737
	11th to 20th	Night	59% 9% 15% 13% 3	3288
	21st to end	Night	69% 11% 11% 7% 2	4884

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	21% 16% 30% 26% 7% 2	180
	11th to 20th	Day	23% 18% 36% 14% 7% 2	247
	21st to end	Day	25% 13% 36% 20% 6% 1	297
February	1st to 10th	Day	24% 14% 44% 14% 3	270
	11th to 20th	Day	23% 16% 44% 14% 3	270
	21st to end	Day	31% 19% 31% 16% 2	249
March	1st to 10th	Day	21% 14% 37% 21% 8%	460
	11th to 20th	Day	21% 14% 36% 23% 6% 1	460
	21st to end	Day	27% 11% 33% 21% 7% 1	506
April	1st to 10th	Day	22% 14% 34% 21% 8% 1	460
	11th to 20th	Day	28% 12% 31% 18% 8% 4	452
	21st to end	Day	25% 11% 33% 20% 10% 3	460
May	1st to 10th	Day	23% 8% 29% 24% 10% 6%	463
	11th to 20th	Day	18% 5% 28% 29% 14% 6%	487
	21st to end	Day	15% 7% 26% 29% 16% 7%	529
June	1st to 10th	Day	15% 8% 30% 31% 13% 3	490
	11th to 20th	Day	14% 10% 24% 30% 18% 3	490
	21st to end	Day	17% 8% 25% 30% 15% 5%	490
July	1st to 10th	Day	10% 4 21% 32% 25% 8%	485
	11th to 20th	Day	14% 4 22% 30% 21% 9%	484
	21st to end	Day	9% 2 24% 37% 18% 9%	532
August	1st to 10th	Day	13% 4 21% 28% 22% 12%	486
	11th to 20th	Day	10% 5% 20% 28% 25% 13%	479
	21st to end	Day	11% 6% 22% 28% 21% 11%	539
September	1st to 10th	Day	14% 6% 23% 28% 17% 12%	490
	11th to 20th	Day	10% 4 20% 27% 21% 18%	490
	21st to end	Day	14% 8% 28% 27% 16% 8%	490
October	1st to 10th	Day	20% 9% 28% 22% 15% 6%	490
	11th to 20th	Day	19% 11% 37% 22% 9% 2	490
	21st to end	Day	28% 10% 31% 24% 6% 1	539
November	1st to 10th	Day	20% 16% 29% 24% 10% 1	292
	11th to 20th	Day	22% 17% 34% 21% 6% 2	200
	21st to end	Day	24% 15% 39% 20% 3	200
December	1st to 10th	Day	24% 12% 39% 18% 6% 1	190
	11th to 20th	Day	27% 20% 28% 20% 6%	180
	21st to end	Day	28% 14% 40% 16% 2	198
January	1st to 10th	Night	24% 11% 35% 24% 6% 1	760
	11th to 20th	Night	27% 11% 31% 25% 5%	760
	21st to end	Night	20% 7% 37% 28% 7%	836
February	1st to 10th	Night	20% 12% 41% 24% 3	760
	11th to 20th	Night	21% 12% 36% 25% 5%	743
	21st to end	Night	20% 11% 41% 23% 5%	628
March	1st to 10th	Night	20% 10% 36% 26% 7%	760
	11th to 20th	Night	22% 12% 36% 23% 6% 1	760
	21st to end	Night	21% 9% 33% 28% 9% 1	836
April	1st to 10th	Night	24% 10% 33% 28% 5%	760
	11th to 20th	Night	20% 9% 35% 26% 9% 1	702
	21st to end	Night	21% 6% 30% 31% 11%	570
May	1st to 10th	Night	18% 4 28% 33% 15% 2	570
	11th to 20th	Night	16% 3 30% 36% 15% 1	388
	21st to end	Night	11% 4 27% 37% 21%	411
June	1st to 10th	Night	14% 3 28% 39% 16% 1	380
	11th to 20th	Night	13% 4 27% 38% 17% 1	380
	21st to end	Night	11% 6% 20% 45% 18% 1	380
July	1st to 10th	Night	6% 2 23% 44% 22% 2	370
	11th to 20th	Night	11% 1 21% 43% 22% 2	368
	21st to end	Night	8% 2 18% 46% 25% 2	593
August	1st to 10th	Night	10% 2 14% 41% 31% 2	567
	11th to 20th	Night	8% 1 15% 42% 31% 3	564
	21st to end	Night	12% 3 20% 36% 26% 3	712
September	1st to 10th	Night	12% 4 22% 36% 21% 6%	760
	11th to 20th	Night	13% 2 18% 32% 29% 5%	760
	21st to end	Night	18% 4 21% 32% 21% 4	760
October	1st to 10th	Night	19% 5% 25% 29% 19% 2	760
	11th to 20th	Night	21% 7% 28% 32% 11% 1	760
	21st to end	Night	25% 8% 30% 31% 6%	836
November	1st to 10th	Night	21% 10% 26% 31% 11% 1	780
	11th to 20th	Night	22% 10% 33% 26% 8% 2	800
	21st to end	Night	27% 9% 32% 25% 7%	800
December	1st to 10th	Night	27% 8% 37% 22% 6% 1	783
	11th to 20th	Night	22% 11% 39% 24% 4	760
	21st to end	Night	32% 8% 34% 23% 3	836

Page generated at 2024-12-03 06:45:12. Version ac07

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