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 2024-01-16.

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 TypeMinimum conditions for hour to be usableOut of hours
Clear of CloudsTransparencySeeingSky Brightness
Planetary:50%(no limit)Average(no limit)Nighttime Hours
Deep Sky:70%Average(no limit)5.9Nighttime Hours
CCD Imaging:70%Below AveragePoor(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

PlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
Night
36%
22838
14%
74874
9%
22792
42%
22792
18%
52110

By Month

MonthDays of MonthPlanetaryData
Pts
Deep Sky
Max 60%
Data
Pts
Both Planetary and Deep Sky
Max 60%
Data
Pts
Either Planetary or Deep SkyData
Pts
CCD ImagingData
Pts
January1st to 10thNight
18%
758
10%
2649
5%
757
25%
757
10%
2041
January11th to 20thNight
19%
741
6%
2453
2%
741
23%
741
8%
1978
January21st to endNight
24%
792
11%
2574
6%
792
31%
792
14%
1926
February1st to 10thNight
17%
720
8%
2340
3%
720
24%
720
11%
1784
February11th to 20thNight
20%
700
11%
2275
4%
700
29%
700
12%
1715
February21st to endNight
21%
592
12%
1866
4%
592
30%
592
15%
1356
March1st to 10thNight
25%
720
16%
1980
6%
720
34%
720
19%
1413
March11th to 20thNight
22%
720
17%
1980
8%
720
30%
720
18%
1433
March21st to endNight
32%
792
19%
2178
10%
792
39%
792
23%
1501
April1st to 10thNight
26%
720
14%
1832
5%
720
32%
720
21%
1337
April11th to 20thNight
32%
665
17%
1729
7%
665
38%
665
23%
1231
April21st to endNight
36%
540
17%
1620
7%
540
44%
540
21%
1110
May1st to 10thNight
43%
540
16%
1620
9%
540
49%
540
24%
1071
May11th to 20thNight
44%
368
22%
1430
16%
368
58%
368
24%
831
May21st to endNight
52%
388
17%
1551
18%
388
60%
388
28%
835
June1st to 10thNight
48%
360
14%
1440
15%
360
57%
360
22%
839
June11th to 20thNight
45%
360
15%
1440
15%
360
55%
360
24%
824
June21st to endNight
55%
360
15%
1440
20%
360
61%
360
23%
835
July1st to 10thNight
63%
350
17%
1400
23%
350
70%
350
33%
704
July11th to 20thNight
59%
348
19%
1392
25%
348
64%
348
29%
744
July21st to endNight
64%
561
18%
1644
15%
530
67%
530
35%
944
August1st to 10thNight
67%
537
17%
1600
14%
534
70%
534
34%
961
August11th to 20thNight
68%
534
24%
1598
16%
534
73%
534
38%
927
August21st to endNight
58%
674
21%
1862
12%
674
62%
674
33%
1145
September1st to 10thNight
57%
720
17%
1800
8%
720
59%
720
34%
1180
September11th to 20thNight
57%
720
27%
1898
16%
720
63%
720
38%
1145
September21st to endNight
50%
720
20%
2020
16%
720
54%
720
28%
1333
October1st to 10thNight
42%
720
16%
2160
14%
720
47%
720
23%
1473
October11th to 20thNight
35%
720
14%
2160
10%
720
41%
720
19%
1542
October21st to endNight
28%
792
15%
2376
10%
792
35%
792
16%
1776
November1st to 10thNight
38%
740
19%
2464
15%
740
45%
740
21%
1611
November11th to 20thNight
27%
760
14%
2660
8%
760
37%
760
15%
1882
November21st to endNight
26%
760
9%
2660
6%
760
31%
760
13%
1974
December1st to 10thNight
19%
760
8%
2660
5%
760
24%
760
10%
2072
December11th to 20thNight
20%
759
6%
3250
2%
758
26%
758
8%
2513
December21st to endNight
16%
827
3%
4873
1%
817
21%
817
4%
4124

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 ForecastData
Points
Cloud CoverDay
15%8%47%6%35%5%6%8%33%
74683
Night
16%9%47%6%35%5%5%7%35%
75104
TransparencyDay
47%9%14%19%10%1
74398
Night
48%8%13%20%10%1
74923
SeeingDay
19%9%29%25%13%5%
13321
Night
19%7%30%30%12%1
22854

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
16%11%6%9%7%46%6%6%6%23%
1517
11th to 20thDay
17%13%5%10%8%45%46%6%21%
1617
21st to endDay
13%13%6%12%8%36%5%5%6%21%
1782
February1st to 10thDay
16%14%5%13%8%35%5%5%5%21%
1620
11th to 20thDay
12%13%7%10%8%45%5%46%27%
1573
21st to endDay
18%12%5%9%8%35%5%46%26%
1385
March1st to 10thDay
14%9%5%7%7%45%6%6%7%31%
1977
11th to 20thDay
14%11%5%8%6%45%5%5%5%31%
1980
21st to endDay
18%10%47%6%35%446%32%
2178
April1st to 10thDay
16%11%5%7%7%35%45%6%29%
2128
11th to 20thDay
19%9%36%5%2445%6%36%
2194
21st to endDay
20%7%37%5%45%5%5%6%33%
2340
May1st to 10thDay
16%8%48%6%35%46%8%34%
2340
11th to 20thDay
14%7%35%5%35%5%5%7%40%
2463
21st to endDay
12%425%5%45%5%6%9%44%
2725
June1st to 10thDay
14%6%35%6%35%5%7%9%38%
2520
11th to 20thDay
12%5%25%5%45%6%7%10%40%
2520
21st to endDay
13%425%5%45%6%7%9%40%
2520
July1st to 10thDay
7%425%5%46%6%7%9%45%
2520
11th to 20thDay
11%5%25%5%36%5%7%10%40%
2520
21st to endDay
9%6%25%6%47%7%9%10%36%
2574
August1st to 10thDay
8%5%26%6%46%5%7%9%41%
2327
11th to 20thDay
8%5%36%6%45%7%7%10%40%
2303
21st to endDay
11%6%35%5%35%5%7%10%41%
2475
September1st to 10thDay
14%435%5%446%6%8%42%
2160
11th to 20thDay
11%5%245%35%46%8%46%
2059
21st to endDay
13%5%36%7%45%5%6%9%38%
1940
October1st to 10thDay
19%8%35%6%3446%7%35%
1800
11th to 20thDay
20%9%37%7%36%5%5%7%29%
1800
21st to endDay
24%10%48%7%35%46%7%22%
1980
November1st to 10thDay
14%9%46%7%36%46%8%34%
1608
11th to 20thDay
15%11%47%7%45%5%7%8%26%
1520
21st to endDay
20%12%5%7%6%45%5%5%8%23%
1520
December1st to 10thDay
18%13%5%10%8%5%6%5%5%6%19%
1520
11th to 20thDay
19%13%48%7%446%5%7%23%
1906
21st to endDay
29%16%6%9%8%3435%413%
2772
January1st to 10thNight
18%13%5%9%8%45%5%5%5%24%
2649
11th to 20thNight
20%14%5%9%8%46%445%21%
2453
21st to endNight
14%11%5%9%7%46%5%5%7%27%
2574
February1st to 10thNight
16%14%5%9%7%5%5%5%5%6%24%
2340
11th to 20thNight
16%12%5%9%7%35%5%5%5%27%
2273
21st to endNight
16%11%49%7%35%5%5%5%30%
1866
March1st to 10thNight
13%8%5%7%7%46%5%5%5%35%
1970
11th to 20thNight
16%11%5%8%7%34446%34%
1979
21st to endNight
16%9%37%43445%5%39%
2178
April1st to 10thNight
19%8%36%7%445%5%6%33%
1832
11th to 20thNight
16%8%35%6%35%446%39%
1729
21st to endNight
17%7%46%5%35%5%5%8%36%
1620
May1st to 10thNight
16%7%25%5%445%7%6%39%
1620
11th to 20thNight
15%4345%3445%8%46%
1429
21st to endNight
10%5%244245%6%7%51%
1550
June1st to 10thNight
12%435%6%45%5%6%9%43%
1440
11th to 20thNight
10%6%35%5%25%5%6%10%43%
1440
21st to endNight
11%5%26%425%5%6%8%45%
1440
July1st to 10thNight
5%424435%448%57%
1440
11th to 20thNight
10%42443446%10%49%
1440
21st to endNight
8%3244345%7%8%51%
1741
August1st to 10thNight
7%415%5%35%5%6%8%49%
1611
11th to 20thNight
7%425%4345%6%9%52%
1598
21st to endNight
11%424435%46%7%49%
1862
September1st to 10thNight
10%5%25%435%5%7%7%46%
1800
11th to 20thNight
11%424423447%55%
1898
21st to endNight
14%5%25%5%35%45%7%43%
2020
October1st to 10thNight
16%7%36%6%3446%6%39%
2160
11th to 20thNight
19%9%36%5%3445%6%35%
2160
21st to endNight
22%10%46%5%445%5%6%29%
2376
November1st to 10thNight
17%7%36%5%45%46%7%38%
2464
11th to 20thNight
17%9%36%6%45%6%6%6%31%
2660
21st to endNight
21%10%46%6%45%5%5%7%27%
2660
December1st to 10thNight
21%13%6%7%6%35%5%5%5%24%
2660
11th to 20thNight
16%16%5%9%6%45%6%5%6%23%
3288
21st to endNight
31%13%5%8%6%345%5%5%14%
4884

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
58%9%15%12%5%
1518
11th to 20thDay
63%10%11%11%5%
1617
21st to endDay
63%7%11%12%6%1
1782
February1st to 10thDay
64%7%12%14%21
1620
11th to 20thDay
57%7%14%15%7%1
1582
21st to endDay
57%8%12%16%6%1
1385
March1st to 10thDay
51%9%14%17%9%1
1980
11th to 20thDay
52%8%10%17%11%2
1980
21st to endDay
51%7%10%17%13%2
2178
April1st to 10thDay
53%7%12%17%11%1
2128
11th to 20thDay
47%7%11%20%14%1
2194
21st to endDay
50%7%12%17%12%3
2340
May1st to 10thDay
47%7%11%20%14%1
2340
11th to 20thDay
42%8%12%24%13%2
2467
21st to endDay
36%9%16%24%14%2
2725
June1st to 10thDay
40%10%13%21%15%1
2520
11th to 20thDay
36%9%13%24%15%2
2520
21st to endDay
36%10%14%24%14%1
2520
July1st to 10thDay
31%9%14%25%18%3
2450
11th to 20thDay
35%9%16%27%12%1
2445
21st to endDay
38%12%16%21%12%1
2430
August1st to 10thDay
35%11%17%22%13%1
2314
11th to 20thDay
35%11%17%25%12%
2303
21st to endDay
36%10%15%26%12%1
2475
September1st to 10thDay
37%10%15%26%11%1
2160
11th to 20thDay
34%8%16%27%14%1
2059
21st to endDay
41%10%15%26%8%
1940
October1st to 10thDay
47%8%15%18%11%1
1800
11th to 20thDay
52%9%13%19%6%1
1800
21st to endDay
59%8%13%14%5%1
1980
November1st to 10thDay
46%10%15%20%8%1
1608
11th to 20thDay
53%11%15%14%7%1
1520
21st to endDay
57%10%16%14%3
1520
December1st to 10thDay
63%10%13%11%3
1520
11th to 20thDay
58%10%17%10%5%
1906
21st to endDay
72%9%10%8%2
2772
January1st to 10thNight
59%8%12%15%4
2649
11th to 20thNight
64%9%13%10%41
2453
21st to endNight
55%8%15%14%6%1
2574
February1st to 10thNight
59%7%13%16%41
2340
11th to 20thNight
58%7%12%15%8%
2275
21st to endNight
54%6%15%17%7%
1866
March1st to 10thNight
49%7%13%21%8%1
1980
11th to 20thNight
53%410%19%12%2
1980
21st to endNight
46%6%10%21%15%3
2178
April1st to 10thNight
49%6%11%19%13%1
1832
11th to 20thNight
46%7%9%20%15%2
1729
21st to endNight
45%7%11%20%14%2
1620
May1st to 10thNight
42%7%11%21%16%3
1620
11th to 20thNight
37%6%10%26%16%4
1430
21st to endNight
29%9%15%24%18%4
1551
June1st to 10thNight
38%7%12%24%17%2
1440
11th to 20thNight
36%7%13%21%21%2
1440
21st to endNight
35%8%13%24%18%1
1440
July1st to 10thNight
26%7%12%27%25%4
1400
11th to 20thNight
31%7%14%28%18%2
1392
21st to endNight
28%9%16%28%16%3
1644
August1st to 10thNight
31%8%18%28%14%2
1600
11th to 20thNight
27%9%16%34%14%1
1598
21st to endNight
32%8%14%29%16%1
1862
September1st to 10thNight
33%9%17%26%14%1
1800
11th to 20thNight
29%7%12%35%16%1
1898
21st to endNight
39%8%13%28%11%
2020
October1st to 10thNight
43%9%13%20%14%1
2160
11th to 20thNight
49%8%14%22%7%
2160
21st to endNight
55%7%11%17%9%1
2376
November1st to 10thNight
43%7%14%23%12%1
2464
11th to 20thNight
50%9%15%17%9%1
2660
21st to endNight
54%9%18%15%3
2660
December1st to 10thNight
59%9%13%13%5%
2660
11th to 20thNight
59%9%15%13%3
3288
21st to endNight
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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 10thDay
21%16%30%26%7%2
180
11th to 20thDay
23%19%36%13%8%2
232
21st to endDay
22%14%37%21%5%1
264
February1st to 10thDay
25%15%45%13%3
240
11th to 20thDay
25%15%44%14%3
240
21st to endDay
32%20%30%17%1
220
March1st to 10thDay
20%14%37%20%8%
420
11th to 20thDay
21%12%36%23%6%1
420
21st to endDay
27%10%32%21%8%1
462
April1st to 10thDay
21%14%35%22%8%1
420
11th to 20thDay
26%11%32%18%8%4
412
21st to endDay
24%10%32%20%10%3
420
May1st to 10thDay
23%8%29%24%10%6%
423
11th to 20thDay
18%5%29%29%13%6%
447
21st to endDay
15%6%24%30%16%8%
485
June1st to 10thDay
14%7%30%33%13%3
450
11th to 20thDay
16%9%22%30%19%4
450
21st to endDay
16%6%24%32%17%6%
450
July1st to 10thDay
10%220%33%26%8%
445
11th to 20thDay
14%321%30%22%9%
444
21st to endDay
10%224%37%18%9%
488
August1st to 10thDay
11%320%29%23%13%
446
11th to 20thDay
10%318%29%26%13%
439
21st to endDay
12%6%22%27%21%12%
495
September1st to 10thDay
15%5%22%28%18%12%
450
11th to 20thDay
11%5%22%27%19%17%
450
21st to endDay
13%8%28%27%16%8%
450
October1st to 10thDay
21%8%26%22%15%7%
450
11th to 20thDay
20%11%37%22%8%2
450
21st to endDay
29%10%31%24%6%1
495
November1st to 10thDay
18%16%29%24%11%1
266
11th to 20thDay
23%14%34%22%6%2
180
21st to endDay
24%10%41%22%3
180
December1st to 10thDay
26%12%39%18%6%1
180
11th to 20thDay
27%20%28%20%6%
180
21st to endDay
28%14%40%16%2
198
January1st to 10thNight
24%11%35%24%6%1
760
11th to 20thNight
28%11%31%25%5%
741
21st to endNight
19%7%38%29%8%
792
February1st to 10thNight
21%12%41%23%3
720
11th to 20thNight
22%12%36%25%5%
703
21st to endNight
20%11%41%23%4
592
March1st to 10thNight
19%10%37%26%8%
720
11th to 20thNight
22%12%35%23%7%1
720
21st to endNight
21%9%32%28%10%1
792
April1st to 10thNight
23%10%33%28%5%
720
11th to 20thNight
19%9%34%27%9%1
665
21st to endNight
22%6%29%31%11%
540
May1st to 10thNight
18%427%33%16%2
540
11th to 20thNight
16%232%35%14%1
368
21st to endNight
11%426%37%22%1
389
June1st to 10thNight
13%328%39%17%1
360
11th to 20thNight
14%428%37%17%1
360
21st to endNight
11%5%20%45%18%1
360
July1st to 10thNight
6%321%45%23%2
350
11th to 20thNight
11%121%43%22%2
348
21st to endNight
8%218%46%24%2
561
August1st to 10thNight
10%113%42%31%3
537
11th to 20thNight
7%114%43%31%3
534
21st to endNight
12%319%36%26%3
674
September1st to 10thNight
12%322%36%21%6%
720
11th to 20thNight
14%219%33%27%5%
720
21st to endNight
17%421%33%22%4
720
October1st to 10thNight
19%5%24%29%19%2
720
11th to 20thNight
21%6%29%32%10%2
720
21st to endNight
27%7%29%31%6%
792
November1st to 10thNight
20%10%26%31%11%1
740
11th to 20thNight
22%9%33%26%9%2
760
21st to endNight
26%8%32%26%8%
760
December1st to 10thNight
28%8%36%22%6%
760
11th to 20thNight
22%11%39%24%4
760
21st to endNight
32%8%34%23%3
836
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