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 2026-07-01.

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% 8% 3 8% 5% 5% 5% 4 6% 8% 34%	138149
	Night	15% 9% 3 8% 5% 5% 5% 4 6% 7% 33%	134182
Transparency	Day	45% 8% 14% 20% 11% 1	141743
	Night	47% 8% 13% 19% 11% 1	138675
Seeing	Day	16% 8% 23% 31% 18% 5%	16499
	Night	18% 8% 27% 30% 15% 2	25918

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% 11% 4 10% 6% 6% 6% 5% 6% 7% 23%	4661
	11th to 20th	Day	10% 18% 7% 17% 8% 6% 5% 4 4 5% 13%	5103
	21st to end	Day	15% 14% 5% 13% 6% 6% 6% 4 5% 7% 20%	5780
February	1st to 10th	Day	15% 13% 4 11% 7% 5% 6% 5% 5% 6% 22%	1890
	11th to 20th	Day	12% 14% 5% 12% 7% 6% 5% 4 5% 6% 24%	1843
	21st to end	Day	17% 12% 4 10% 6% 5% 5% 4 5% 7% 25%	1621
March	1st to 10th	Day	18% 8% 3 8% 5% 4 5% 4 6% 5% 32%	5042
	11th to 20th	Day	11% 11% 4 9% 6% 5% 5% 4 6% 8% 30%	5090
	21st to end	Day	17% 8% 3 9% 6% 5% 4 3 5% 6% 33%	5586
April	1st to 10th	Day	17% 10% 4 9% 6% 4 4 4 5% 6% 31%	2483
	11th to 20th	Day	17% 10% 3 7% 4 5% 4 3 6% 6% 35%	2565
	21st to end	Day	18% 8% 3 8% 5% 5% 5% 4 6% 6% 34%	2730
May	1st to 10th	Day	17% 8% 3 8% 5% 4 5% 4 6% 8% 33%	7642
	11th to 20th	Day	13% 9% 3 8% 5% 5% 4 4 7% 8% 34%	8162
	21st to end	Day	17% 5% 2 6% 4 4 4 3 6% 7% 43%	9060
June	1st to 10th	Day	12% 6% 2 7% 5% 5% 5% 4 6% 9% 40%	2940
	11th to 20th	Day	10% 5% 2 6% 5% 5% 5% 5% 8% 10% 39%	2940
	21st to end	Day	11% 5% 2 6% 4 4 5% 5% 7% 9% 42%	2940
July	1st to 10th	Day	8% 4 2 6% 5% 5% 5% 5% 7% 11% 42%	6360
	11th to 20th	Day	7% 4 2 6% 4 4 5% 5% 6% 9% 48%	6360
	21st to end	Day	6% 4 2 5% 4 5% 5% 5% 7% 9% 48%	6476
August	1st to 10th	Day	14% 7% 2 6% 4 4 5% 4 5% 8% 40%	4234
	11th to 20th	Day	8% 6% 2 7% 6% 5% 5% 4 7% 10% 39%	4174
	21st to end	Day	7% 6% 2 6% 4 4 5% 4 7% 9% 46%	4485
September	1st to 10th	Day	12% 5% 2 6% 4 4 5% 4 6% 8% 44%	2400
	11th to 20th	Day	9% 5% 2 5% 4 5% 3 4 6% 8% 48%	2286
	21st to end	Day	13% 5% 2 7% 5% 5% 5% 4 6% 9% 38%	2155
October	1st to 10th	Day	16% 7% 2 6% 4 5% 5% 3 6% 8% 39%	2000
	11th to 20th	Day	18% 8% 3 8% 6% 5% 5% 4 5% 7% 31%	2000
	21st to end	Day	22% 10% 3 8% 5% 5% 5% 5% 6% 7% 23%	2200
November	1st to 10th	Day	14% 7% 3 8% 5% 5% 5% 4 7% 8% 33%	1787
	11th to 20th	Day	14% 10% 4 9% 6% 6% 6% 5% 6% 9% 26%	1680
	21st to end	Day	18% 14% 4 9% 5% 5% 5% 5% 6% 7% 22%	1680
December	1st to 10th	Day	20% 14% 4 10% 6% 6% 6% 4 7% 6% 17%	2680
	11th to 20th	Day	20% 14% 4 9% 6% 5% 4 5% 5% 5% 23%	3066
	21st to end	Day	27% 15% 5% 10% 6% 5% 4 4 5% 6% 14%	4048
January	1st to 10th	Night	15% 11% 4 10% 6% 6% 6% 5% 6% 7% 25%	8234
	11th to 20th	Night	12% 16% 5% 15% 9% 7% 6% 4 5% 6% 15%	7777
	21st to end	Night	14% 13% 5% 11% 7% 6% 6% 4 6% 7% 21%	8401
February	1st to 10th	Night	15% 14% 4 9% 6% 5% 5% 4 6% 6% 25%	2730
	11th to 20th	Night	16% 13% 4 10% 6% 5% 6% 4 5% 6% 26%	2663
	21st to end	Night	14% 11% 4 11% 6% 6% 6% 4 6% 6% 27%	2181
March	1st to 10th	Night	17% 8% 4 8% 6% 5% 5% 4 5% 6% 31%	5018
	11th to 20th	Night	10% 8% 3 8% 5% 5% 5% 4 6% 8% 36%	5089
	21st to end	Night	20% 8% 3 7% 4 3 3 3 4 5% 39%	5588
April	1st to 10th	Night	18% 10% 3 7% 6% 4 5% 4 5% 6% 32%	2137
	11th to 20th	Night	16% 9% 2 6% 5% 5% 4 4 5% 6% 37%	2021
	21st to end	Night	16% 7% 3 7% 5% 4 5% 4 5% 7% 37%	1890
May	1st to 10th	Night	20% 8% 3 7% 5% 4 4 3 5% 6% 34%	5257
	11th to 20th	Night	14% 8% 3 8% 5% 6% 5% 4 6% 8% 34%	4683
	21st to end	Night	17% 6% 2 6% 4 3 4 3 4 7% 44%	5114
June	1st to 10th	Night	12% 5% 3 6% 4 4 5% 4 6% 9% 42%	1680
	11th to 20th	Night	9% 6% 2 5% 5% 4 4 4 7% 9% 43%	1680
	21st to end	Night	10% 7% 3 6% 5% 4 5% 5% 6% 8% 43%	1680
July	1st to 10th	Night	6% 5% 3 6% 4 5% 4 4 6% 9% 47%	3600
	11th to 20th	Night	10% 5% 1 5% 4 4 4 3 6% 9% 49%	3600
	21st to end	Night	8% 4 2 5% 3 4 4 3 6% 7% 52%	4372
August	1st to 10th	Night	9% 6% 3 6% 5% 5% 5% 4 6% 8% 46%	2915
	11th to 20th	Night	11% 5% 2 5% 4 4 4 3 6% 8% 49%	2875
	21st to end	Night	9% 5% 3 6% 4 4 5% 4 7% 8% 46%	3378
September	1st to 10th	Night	10% 6% 2 5% 3 4 5% 4 6% 8% 48%	2000
	11th to 20th	Night	9% 4 2 4 4 4 4 3 4 6% 56%	2110
	21st to end	Night	15% 6% 2 6% 5% 4 4 4 5% 7% 42%	2244
October	1st to 10th	Night	15% 6% 3 6% 4 4 5% 4 6% 6% 42%	2400
	11th to 20th	Night	18% 9% 3 7% 5% 4 5% 4 5% 6% 35%	2400
	21st to end	Night	20% 8% 3 8% 4 5% 5% 4 6% 6% 31%	2640
November	1st to 10th	Night	16% 7% 3 8% 5% 4 4 3 6% 7% 38%	2727
	11th to 20th	Night	15% 10% 3 7% 6% 5% 5% 4 5% 7% 31%	2940
	21st to end	Night	19% 11% 3 7% 6% 5% 5% 4 6% 6% 26%	2940
December	1st to 10th	Night	18% 14% 4 10% 7% 5% 5% 4 5% 7% 19%	4720
	11th to 20th	Night	18% 15% 5% 9% 6% 5% 5% 3 5% 6% 23%	5348
	21st to end	Night	26% 14% 7% 10% 5% 5% 5% 3 4 5% 15%	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	52% 10% 16% 13% 9%	4662
	11th to 20th	Day	69% 6% 11% 9% 4	5137
	21st to end	Day	59% 7% 14% 11% 8%	5780
February	1st to 10th	Day	60% 8% 12% 15% 4 1	1890
	11th to 20th	Day	57% 8% 14% 14% 6% 1	1852
	21st to end	Day	54% 9% 16% 14% 6% 1	1621
March	1st to 10th	Day	49% 8% 15% 15% 13% 1	5045
	11th to 20th	Day	47% 8% 19% 17% 7% 2	5090
	21st to end	Day	46% 7% 13% 21% 12% 1	5586
April	1st to 10th	Day	51% 7% 13% 17% 11% 1	2483
	11th to 20th	Day	47% 7% 11% 20% 13% 1	2565
	21st to end	Day	48% 7% 12% 18% 11% 3	2730
May	1st to 10th	Day	46% 9% 14% 17% 11% 3	7651
	11th to 20th	Day	44% 11% 13% 18% 13% 1	8166
	21st to end	Day	38% 7% 11% 27% 14% 2	9061
June	1st to 10th	Day	39% 9% 13% 22% 16% 1	2940
	11th to 20th	Day	36% 10% 14% 24% 15% 1	2940
	21st to end	Day	36% 9% 16% 25% 14%	2940
July	1st to 10th	Day	33% 8% 17% 26% 15% 2	6290
	11th to 20th	Day	30% 6% 15% 32% 16% 1	6285
	21st to end	Day	30% 8% 15% 29% 18% 1	6290
August	1st to 10th	Day	40% 8% 15% 21% 15% 1	4221
	11th to 20th	Day	37% 9% 17% 26% 11%	4213
	21st to end	Day	33% 7% 15% 35% 10% 1	4485
September	1st to 10th	Day	35% 9% 16% 28% 11% 1	2400
	11th to 20th	Day	32% 8% 17% 29% 14% 1	2286
	21st to end	Day	40% 9% 16% 25% 9%	2155
October	1st to 10th	Day	34% 6% 18% 28% 14% 1	3260
	11th to 20th	Day	37% 7% 17% 24% 15%	3240
	21st to end	Day	49% 8% 16% 20% 6%	3538
November	1st to 10th	Day	45% 10% 15% 21% 8% 1	1787
	11th to 20th	Day	52% 11% 15% 14% 7%	1680
	21st to end	Day	58% 9% 16% 14% 2	1680
December	1st to 10th	Day	64% 9% 16% 9% 3	2680
	11th to 20th	Day	59% 9% 15% 9% 8%	3066
	21st to end	Day	70% 8% 11% 6% 4	4048
January	1st to 10th	Night	52% 10% 15% 18% 4	8234
	11th to 20th	Night	64% 11% 11% 9% 5%	7818
	21st to end	Night	57% 9% 13% 11% 10% 1	8401
February	1st to 10th	Night	57% 9% 13% 16% 5% 1	2730
	11th to 20th	Night	56% 8% 14% 15% 7%	2665
	21st to end	Night	54% 8% 15% 16% 7%	2181
March	1st to 10th	Night	50% 7% 13% 17% 11% 2	5028
	11th to 20th	Night	41% 8% 20% 21% 9% 2	5090
	21st to end	Night	44% 6% 10% 21% 16% 2	5588
April	1st to 10th	Night	50% 6% 12% 18% 13% 1	2137
	11th to 20th	Night	47% 7% 9% 21% 14% 2	2021
	21st to end	Night	43% 9% 11% 20% 15% 2	1890
May	1st to 10th	Night	49% 7% 11% 15% 14% 4	5264
	11th to 20th	Night	44% 11% 12% 18% 14% 2	4684
	21st to end	Night	39% 6% 11% 25% 16% 2	5115
June	1st to 10th	Night	37% 8% 12% 24% 17% 3	1680
	11th to 20th	Night	35% 7% 14% 21% 21% 2	1680
	21st to end	Night	38% 7% 13% 23% 18% 1	1680
July	1st to 10th	Night	33% 7% 14% 24% 20% 3	3560
	11th to 20th	Night	30% 7% 13% 30% 17% 1	3552
	21st to end	Night	30% 7% 12% 28% 22% 1	4243
August	1st to 10th	Night	35% 7% 14% 27% 15% 2	2904
	11th to 20th	Night	32% 6% 16% 33% 13% 1	2902
	21st to end	Night	33% 8% 14% 31% 13% 1	3378
September	1st to 10th	Night	31% 10% 14% 29% 14% 1	2000
	11th to 20th	Night	27% 8% 12% 35% 17%	2110
	21st to end	Night	41% 7% 13% 26% 12% 1	2244
October	1st to 10th	Night	33% 6% 11% 26% 23% 1	3920
	11th to 20th	Night	42% 7% 15% 26% 10%	3899
	21st to end	Night	39% 7% 16% 27% 10% 1	4252
November	1st to 10th	Night	44% 7% 14% 23% 12% 1	2727
	11th to 20th	Night	49% 9% 16% 16% 9% 1	2940
	21st to end	Night	56% 9% 16% 15% 3	2940
December	1st to 10th	Night	60% 8% 15% 13% 4	4720
	11th to 20th	Night	58% 8% 12% 12% 8%	5348
	21st to end	Night	68% 10% 12% 6% 4	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% 15% 30% 27% 6% 1	220
	11th to 20th	Day	21% 20% 34% 17% 7% 1	303
	21st to end	Day	22% 12% 33% 26% 7% 1	363
February	1st to 10th	Day	18% 16% 36% 22% 8%	330
	11th to 20th	Day	19% 16% 36% 25% 4	330
	21st to end	Day	22% 18% 29% 28% 4	299
March	1st to 10th	Day	19% 11% 34% 29% 8%	540
	11th to 20th	Day	17% 14% 33% 28% 7% 1	540
	21st to end	Day	24% 8% 30% 29% 8% 1	594
April	1st to 10th	Day	20% 11% 28% 33% 8% 1	540
	11th to 20th	Day	24% 9% 27% 27% 11% 2	532
	21st to end	Day	20% 8% 26% 34% 11% 2	540
May	1st to 10th	Day	17% 6% 24% 31% 17% 4	543
	11th to 20th	Day	13% 4 20% 36% 22% 5%	567
	21st to end	Day	14% 3 18% 33% 26% 6%	617
June	1st to 10th	Day	12% 4 19% 38% 24% 2	570
	11th to 20th	Day	11% 6% 20% 34% 26% 3	570
	21st to end	Day	14% 3 16% 38% 25% 4	570
July	1st to 10th	Day	7% 2 12% 36% 34% 9%	525
	11th to 20th	Day	13% 3 11% 34% 30% 9%	524
	21st to end	Day	8% 2 11% 42% 30% 7%	576
August	1st to 10th	Day	10% 4 11% 31% 33% 11%	526
	11th to 20th	Day	8% 3 13% 33% 31% 13%	519
	21st to end	Day	10% 3 15% 33% 30% 9%	583
September	1st to 10th	Day	10% 3 19% 29% 29% 11%	530
	11th to 20th	Day	7% 2 12% 32% 30% 17%	530
	21st to end	Day	14% 4 21% 32% 20% 9%	530
October	1st to 10th	Day	19% 6% 23% 26% 18% 8%	530
	11th to 20th	Day	19% 7% 32% 30% 10% 3	530
	21st to end	Day	24% 11% 28% 27% 10% 1	583
November	1st to 10th	Day	19% 10% 28% 29% 12% 2	323
	11th to 20th	Day	18% 14% 32% 28% 8% 1	220
	21st to end	Day	19% 17% 34% 24% 6%	220
December	1st to 10th	Day	24% 10% 35% 23% 7%	220
	11th to 20th	Day	23% 18% 34% 21% 4	220
	21st to end	Day	28% 13% 38% 18% 3	242
January	1st to 10th	Night	22% 13% 39% 19% 7%	840
	11th to 20th	Night	25% 15% 33% 23% 4	840
	21st to end	Night	18% 13% 37% 26% 6%	924
February	1st to 10th	Night	20% 13% 39% 23% 4	840
	11th to 20th	Night	21% 12% 37% 25% 5%	823
	21st to end	Night	20% 11% 39% 25% 5%	692
March	1st to 10th	Night	18% 10% 35% 29% 8%	840
	11th to 20th	Night	20% 11% 34% 26% 7% 1	840
	21st to end	Night	20% 8% 29% 33% 10% 1	924
April	1st to 10th	Night	23% 8% 29% 33% 7% 1	840
	11th to 20th	Night	18% 8% 29% 33% 10% 2	777
	21st to end	Night	20% 5% 25% 36% 14%	630
May	1st to 10th	Night	18% 3 20% 37% 20% 2	630
	11th to 20th	Night	14% 4 18% 42% 21% 1	433
	21st to end	Night	11% 4 15% 39% 27% 3	455
June	1st to 10th	Night	14% 2 17% 42% 22% 3	420
	11th to 20th	Night	11% 2 21% 38% 26% 1	420
	21st to end	Night	12% 3 15% 42% 27% 2	420
July	1st to 10th	Night	7% 2 9% 50% 27% 6%	390
	11th to 20th	Night	10% 4 13% 38% 31% 4	388
	21st to end	Night	9% 2 10% 44% 33% 3	627
August	1st to 10th	Night	9% 2 11% 36% 36% 6%	597
	11th to 20th	Night	9% 2 13% 34% 35% 7%	594
	21st to end	Night	10% 3 17% 33% 31% 5%	750
September	1st to 10th	Night	11% 4 18% 33% 26% 8%	800
	11th to 20th	Night	12% 3 14% 30% 33% 9%	800
	21st to end	Night	17% 4 19% 29% 25% 6%	800
October	1st to 10th	Night	18% 4 26% 26% 21% 5%	800
	11th to 20th	Night	20% 9% 29% 29% 12% 2	800
	21st to end	Night	25% 7% 30% 30% 7% 1	880
November	1st to 10th	Night	20% 9% 27% 30% 12% 2	820
	11th to 20th	Night	20% 10% 35% 25% 9% 2	840
	21st to end	Night	24% 11% 32% 26% 6%	840
December	1st to 10th	Night	26% 11% 35% 21% 6% 1	840
	11th to 20th	Night	21% 12% 42% 20% 4	840
	21st to end	Night	29% 11% 35% 22% 3	924

Page generated at 2026-06-28 02:10:44. Version ac07

Copyright © 2026 Attilla Danko.