Toronto Islands
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Toronto Islands clear sky chart from 2005-11-06 to 2025-02-25.

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% 9% 3 8% 5% 5% 5% 4 6% 8% 33%	108802
	Night	15% 10% 3 8% 5% 5% 5% 4 6% 7% 33%	109847
Transparency	Day	45% 9% 15% 20% 10% 1	112440
	Night	47% 9% 14% 20% 10% 1	114372
Seeing	Day	16% 7% 23% 31% 19% 5%	14723
	Night	18% 7% 27% 30% 15% 2	24283

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	12% 11% 4 11% 6% 6% 6% 5% 6% 7% 26%	3597
	11th to 20th	Day	10% 17% 7% 18% 9% 6% 5% 4 4 5% 15%	3911
	21st to end	Day	18% 15% 6% 13% 5% 6% 5% 4 4 6% 18%	4466
February	1st to 10th	Day	15% 14% 4 11% 7% 6% 6% 5% 5% 6% 21%	1800
	11th to 20th	Day	12% 15% 5% 12% 7% 6% 5% 4 5% 6% 24%	1753
	21st to end	Day	17% 11% 4 10% 6% 5% 5% 4 5% 7% 25%	1507
March	1st to 10th	Day	19% 9% 4 9% 5% 5% 5% 4 6% 5% 31%	3432
	11th to 20th	Day	10% 13% 5% 10% 6% 5% 6% 4 6% 6% 29%	3480
	21st to end	Day	16% 7% 3 7% 5% 5% 5% 3 6% 7% 37%	3815
April	1st to 10th	Day	16% 10% 4 9% 7% 4 4 4 5% 6% 31%	2247
	11th to 20th	Day	17% 9% 3 7% 4 5% 4 3 6% 6% 36%	2318
	21st to end	Day	19% 8% 3 8% 5% 5% 5% 4 5% 6% 34%	2470
May	1st to 10th	Day	16% 7% 3 8% 5% 4 4 4 6% 8% 33%	4108
	11th to 20th	Day	14% 10% 4 9% 5% 5% 5% 4 7% 8% 30%	4366
	21st to end	Day	10% 5% 2 6% 4 4 4 4 6% 9% 46%	4837
June	1st to 10th	Day	13% 6% 2 7% 5% 5% 5% 5% 6% 9% 38%	2660
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 5% 8% 10% 40%	2660
	21st to end	Day	11% 5% 2 6% 4 4 5% 5% 7% 9% 41%	2660
July	1st to 10th	Day	8% 4 2 5% 4 5% 5% 5% 8% 11% 43%	4440
	11th to 20th	Day	8% 4 2 5% 4 4 5% 5% 6% 9% 47%	4440
	21st to end	Day	6% 5% 2 5% 5% 6% 6% 6% 8% 10% 43%	4504
August	1st to 10th	Day	14% 7% 2 6% 4 4 5% 4 5% 8% 40%	4104
	11th to 20th	Day	8% 6% 2 7% 6% 5% 5% 4 7% 10% 38%	4044
	21st to end	Day	7% 6% 2 6% 4 4 5% 4 7% 10% 46%	4348
September	1st to 10th	Day	12% 5% 2 6% 4 4 5% 5% 6% 8% 44%	2280
	11th to 20th	Day	9% 5% 2 5% 4 4 3 4 6% 8% 48%	2172
	21st to end	Day	13% 5% 2 8% 5% 6% 5% 4 6% 9% 38%	2047
October	1st to 10th	Day	17% 7% 2 6% 4 5% 5% 3 6% 8% 37%	1900
	11th to 20th	Day	18% 8% 3 8% 6% 5% 5% 4 5% 7% 31%	1900
	21st to end	Day	23% 11% 3 7% 5% 5% 5% 4 6% 7% 24%	2090
November	1st to 10th	Day	14% 7% 3 9% 6% 5% 5% 4 7% 8% 33%	1700
	11th to 20th	Day	14% 10% 4 9% 6% 6% 6% 5% 6% 9% 26%	1600
	21st to end	Day	18% 14% 4 9% 5% 5% 5% 5% 6% 7% 23%	1600
December	1st to 10th	Day	20% 14% 4 10% 6% 6% 6% 4 7% 7% 16%	2600
	11th to 20th	Day	21% 14% 4 9% 6% 5% 4 5% 5% 5% 23%	2986
	21st to end	Day	27% 15% 5% 10% 6% 5% 4 4 5% 6% 14%	3960
January	1st to 10th	Night	15% 11% 3 9% 6% 6% 6% 5% 6% 7% 26%	6349
	11th to 20th	Night	13% 14% 5% 16% 9% 7% 6% 4 6% 6% 14%	5969
	21st to end	Night	18% 14% 5% 10% 6% 5% 5% 4 6% 7% 20%	6490
February	1st to 10th	Night	15% 15% 4 9% 6% 5% 5% 4 6% 6% 24%	2600
	11th to 20th	Night	16% 14% 4 10% 7% 5% 6% 4 5% 6% 25%	2533
	21st to end	Night	15% 11% 4 10% 6% 6% 5% 4 6% 6% 28%	2038
March	1st to 10th	Night	20% 8% 3 8% 6% 5% 5% 3 5% 6% 31%	3408
	11th to 20th	Night	13% 10% 3 8% 5% 5% 4 4 5% 7% 35%	3479
	21st to end	Night	17% 7% 2 6% 3 3 3 3 5% 6% 44%	3817
April	1st to 10th	Night	18% 10% 3 7% 6% 4 4 3 5% 6% 33%	1933
	11th to 20th	Night	16% 8% 2 7% 5% 5% 4 4 5% 6% 38%	1827
	21st to end	Night	16% 8% 3 8% 5% 4 5% 4 5% 7% 37%	1710
May	1st to 10th	Night	18% 8% 2 7% 5% 4 4 3 5% 6% 37%	2833
	11th to 20th	Night	14% 9% 3 7% 5% 6% 5% 4 6% 9% 32%	2512
	21st to end	Night	10% 5% 2 5% 3 4 4 4 6% 8% 50%	2738
June	1st to 10th	Night	12% 5% 3 6% 5% 5% 6% 3 6% 9% 41%	1520
	11th to 20th	Night	9% 7% 2 5% 5% 4 4 4 7% 9% 43%	1520
	21st to end	Night	10% 6% 3 6% 5% 4 5% 5% 6% 8% 43%	1520
July	1st to 10th	Night	6% 5% 2 6% 4 4 4 4 6% 9% 50%	2520
	11th to 20th	Night	11% 4 1 5% 4 3 4 3 5% 10% 49%	2520
	21st to end	Night	7% 4 2 5% 3 4 4 4 8% 7% 52%	3045
August	1st to 10th	Night	9% 6% 3 6% 5% 5% 5% 4 6% 7% 46%	2825
	11th to 20th	Night	10% 5% 2 6% 4 4 4 4 6% 8% 49%	2785
	21st to end	Night	9% 5% 3 6% 4 4 5% 4 7% 7% 46%	3274
September	1st to 10th	Night	10% 6% 2 5% 3 4 5% 4 6% 8% 47%	1900
	11th to 20th	Night	9% 5% 2 4 4 4 4 3 4 6% 55%	2004
	21st to end	Night	15% 6% 2 6% 5% 4 4 4 6% 7% 41%	2132
October	1st to 10th	Night	15% 6% 3 7% 4 4 5% 4 6% 6% 40%	2280
	11th to 20th	Night	18% 8% 3 7% 5% 4 5% 4 5% 6% 35%	2280
	21st to end	Night	21% 8% 3 8% 4 5% 5% 4 6% 7% 30%	2508
November	1st to 10th	Night	16% 7% 2 8% 5% 4 4 3 6% 7% 38%	2594
	11th to 20th	Night	16% 10% 4 7% 5% 5% 6% 4 5% 7% 31%	2800
	21st to end	Night	19% 11% 3 7% 6% 5% 5% 4 6% 7% 26%	2800
December	1st to 10th	Night	18% 13% 5% 10% 7% 5% 5% 4 6% 7% 19%	4580
	11th to 20th	Night	18% 15% 5% 9% 6% 5% 5% 3 5% 6% 23%	5208
	21st to end	Night	26% 14% 7% 10% 5% 5% 5% 3 4 5% 15%	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	49% 12% 17% 14% 9%	3598
	11th to 20th	Day	69% 7% 12% 9% 3	3945
	21st to end	Day	64% 8% 12% 9% 7%	4466
February	1st to 10th	Day	61% 9% 12% 14% 3 1	1800
	11th to 20th	Day	57% 8% 15% 14% 6% 1	1762
	21st to end	Day	54% 10% 16% 13% 6% 1	1507
March	1st to 10th	Day	51% 10% 14% 17% 8%	3435
	11th to 20th	Day	48% 10% 15% 18% 8% 1	3480
	21st to end	Day	40% 9% 15% 22% 13% 2	3815
April	1st to 10th	Day	50% 7% 14% 17% 11% 1	2247
	11th to 20th	Day	46% 7% 11% 20% 14% 1	2318
	21st to end	Day	48% 7% 12% 18% 12% 3	2470
May	1st to 10th	Day	43% 10% 15% 16% 14% 2	4120
	11th to 20th	Day	46% 15% 13% 17% 8% 1	4370
	21st to end	Day	32% 9% 15% 25% 16% 3	4837
June	1st to 10th	Day	40% 10% 13% 21% 14% 1	2660
	11th to 20th	Day	35% 10% 14% 24% 16% 1	2660
	21st to end	Day	36% 9% 17% 24% 14%	2660
July	1st to 10th	Day	31% 8% 18% 26% 15% 2	4370
	11th to 20th	Day	30% 7% 16% 36% 11% 1	4365
	21st to end	Day	33% 10% 17% 21% 18% 1	4360
August	1st to 10th	Day	41% 8% 15% 20% 15% 1	4091
	11th to 20th	Day	37% 9% 18% 25% 11% 1	4083
	21st to end	Day	33% 7% 15% 34% 10% 1	4348
September	1st to 10th	Day	36% 9% 16% 27% 11% 1	2280
	11th to 20th	Day	33% 8% 16% 28% 14% 1	2172
	21st to end	Day	40% 9% 16% 25% 9%	2047
October	1st to 10th	Day	34% 6% 18% 27% 13% 1	3160
	11th to 20th	Day	37% 7% 17% 24% 15%	3140
	21st to end	Day	49% 8% 16% 21% 6%	3428
November	1st to 10th	Day	45% 10% 16% 20% 8% 1	1700
	11th to 20th	Day	52% 12% 15% 14% 7% 1	1600
	21st to end	Day	57% 10% 16% 15% 2	1600
December	1st to 10th	Day	64% 9% 16% 8% 3	2600
	11th to 20th	Day	60% 9% 15% 9% 7%	2986
	21st to end	Day	70% 8% 11% 6% 4	3960
January	1st to 10th	Night	51% 11% 14% 19% 4	6349
	11th to 20th	Night	63% 13% 12% 9% 3	6010
	21st to end	Night	59% 9% 13% 10% 8% 1	6490
February	1st to 10th	Night	58% 9% 13% 15% 4	2600
	11th to 20th	Night	57% 8% 13% 15% 7%	2535
	21st to end	Night	53% 8% 16% 16% 7%	2038
March	1st to 10th	Night	51% 8% 13% 22% 6% 1	3418
	11th to 20th	Night	44% 9% 16% 19% 10% 1	3480
	21st to end	Night	38% 7% 11% 25% 17% 2	3817
April	1st to 10th	Night	50% 6% 11% 18% 13% 1	1933
	11th to 20th	Night	46% 7% 9% 21% 14% 2	1827
	21st to end	Night	44% 9% 11% 19% 15% 2	1710
May	1st to 10th	Night	43% 9% 13% 17% 16% 2	2840
	11th to 20th	Night	42% 15% 14% 17% 10% 2	2513
	21st to end	Night	29% 9% 14% 25% 21% 3	2739
June	1st to 10th	Night	38% 8% 12% 23% 16% 2	1520
	11th to 20th	Night	35% 8% 14% 21% 21% 2	1520
	21st to end	Night	38% 7% 13% 23% 18% 1	1520
July	1st to 10th	Night	30% 6% 15% 24% 21% 4	2480
	11th to 20th	Night	30% 7% 14% 33% 15% 1	2472
	21st to end	Night	29% 8% 15% 28% 17% 2	2948
August	1st to 10th	Night	36% 7% 13% 28% 14% 2	2814
	11th to 20th	Night	32% 6% 16% 33% 12% 1	2812
	21st to end	Night	33% 8% 13% 31% 13% 1	3274
September	1st to 10th	Night	32% 10% 15% 28% 14% 1	1900
	11th to 20th	Night	28% 9% 12% 34% 17%	2004
	21st to end	Night	41% 8% 13% 26% 11%	2132
October	1st to 10th	Night	34% 6% 11% 25% 23% 1	3800
	11th to 20th	Night	42% 7% 15% 26% 10%	3779
	21st to end	Night	39% 7% 16% 27% 10% 1	4120
November	1st to 10th	Night	44% 7% 14% 23% 12% 1	2594
	11th to 20th	Night	49% 9% 16% 16% 9% 1	2800
	21st to end	Night	56% 10% 17% 15% 3	2800
December	1st to 10th	Night	60% 8% 15% 13% 3	4580
	11th to 20th	Night	59% 8% 12% 12% 8%	5208
	21st to end	Night	68% 10% 12% 6% 4	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	19% 14% 31% 29% 6% 2	200
	11th to 20th	Day	19% 19% 35% 18% 8% 1	275
	21st to end	Day	22% 11% 34% 26% 6% 1	330
February	1st to 10th	Day	18% 17% 37% 22% 6%	300
	11th to 20th	Day	19% 17% 36% 23% 4	300
	21st to end	Day	21% 19% 29% 27% 4	261
March	1st to 10th	Day	18% 10% 33% 30% 8%	460
	11th to 20th	Day	15% 13% 32% 30% 8% 1	460
	21st to end	Day	24% 5% 29% 31% 9% 1	506
April	1st to 10th	Day	19% 9% 27% 36% 9% 1	460
	11th to 20th	Day	23% 7% 28% 28% 11% 3	452
	21st to end	Day	20% 6% 25% 35% 12% 2	460
May	1st to 10th	Day	16% 6% 21% 33% 20% 4	463
	11th to 20th	Day	14% 3 16% 38% 24% 6%	487
	21st to end	Day	12% 2 15% 35% 29% 7%	529
June	1st to 10th	Day	13% 4 18% 37% 26% 3	490
	11th to 20th	Day	12% 4 17% 36% 29% 3	490
	21st to end	Day	14% 3 15% 36% 27% 5%	490
July	1st to 10th	Day	8% 2 11% 35% 35% 10%	485
	11th to 20th	Day	14% 2 11% 33% 31% 10%	484
	21st to end	Day	8% 2 10% 41% 31% 7%	532
August	1st to 10th	Day	11% 5% 10% 30% 33% 12%	486
	11th to 20th	Day	7% 3 13% 33% 31% 13%	479
	21st to end	Day	10% 3 15% 33% 29% 10%	539
September	1st to 10th	Day	10% 3 19% 30% 28% 11%	490
	11th to 20th	Day	8% 2 13% 31% 29% 17%	490
	21st to end	Day	14% 4 22% 32% 19% 9%	490
October	1st to 10th	Day	20% 7% 23% 26% 16% 8%	490
	11th to 20th	Day	18% 7% 31% 31% 10% 3	490
	21st to end	Day	25% 10% 28% 27% 10% 1	539
November	1st to 10th	Day	18% 10% 28% 29% 13% 2	296
	11th to 20th	Day	19% 13% 30% 30% 8% 1	200
	21st to end	Day	20% 15% 35% 24% 7% 1	200
December	1st to 10th	Day	24% 10% 36% 23% 8%	200
	11th to 20th	Day	24% 17% 35% 20% 5%	200
	21st to end	Day	26% 12% 38% 19% 4	220
January	1st to 10th	Night	22% 13% 39% 19% 7%	800
	11th to 20th	Night	25% 13% 34% 24% 4	800
	21st to end	Night	19% 11% 38% 26% 6%	880
February	1st to 10th	Night	21% 13% 39% 22% 4	800
	11th to 20th	Night	21% 12% 38% 24% 5%	783
	21st to end	Night	20% 11% 39% 25% 5%	647
March	1st to 10th	Night	19% 8% 36% 29% 8%	760
	11th to 20th	Night	20% 11% 34% 26% 8% 1	760
	21st to end	Night	19% 7% 28% 34% 11% 2	836
April	1st to 10th	Night	23% 6% 28% 35% 8% 1	760
	11th to 20th	Night	17% 8% 29% 33% 11% 2	703
	21st to end	Night	21% 4 25% 35% 15%	570
May	1st to 10th	Night	18% 3 19% 38% 21% 2	570
	11th to 20th	Night	14% 2 16% 43% 23% 1	391
	21st to end	Night	10% 3 14% 39% 29% 4	411
June	1st to 10th	Night	14% 2 17% 41% 24% 2	380
	11th to 20th	Night	12% 1 20% 38% 28% 2	380
	21st to end	Night	12% 2 16% 40% 28% 2	380
July	1st to 10th	Night	6% 2 9% 49% 28% 6%	370
	11th to 20th	Night	10% 3 13% 38% 31% 5%	368
	21st to end	Night	8% 2 10% 44% 33% 3	595
August	1st to 10th	Night	10% 2 11% 37% 35% 5%	567
	11th to 20th	Night	9% 2 13% 35% 35% 7%	564
	21st to end	Night	11% 2 17% 33% 32% 5%	712
September	1st to 10th	Night	11% 3 18% 34% 26% 9%	760
	11th to 20th	Night	12% 3 14% 30% 31% 9%	760
	21st to end	Night	17% 4 20% 29% 25% 6%	760
October	1st to 10th	Night	18% 5% 26% 27% 21% 4	760
	11th to 20th	Night	19% 9% 28% 29% 12% 2	760
	21st to end	Night	25% 7% 29% 31% 8% 1	836
November	1st to 10th	Night	21% 7% 27% 31% 13% 2	780
	11th to 20th	Night	20% 9% 35% 26% 9% 2	800
	21st to end	Night	24% 11% 31% 27% 7% 1	800
December	1st to 10th	Night	26% 11% 36% 20% 6% 1	800
	11th to 20th	Night	22% 11% 42% 21% 5%	800
	21st to end	Night	29% 10% 35% 23% 3	880

Page generated at 2025-02-22 06:51:36. Version ac07

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