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RASC Toronto Centre
.

Toronto
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Toronto clear sky chart from 2005-11-05 to 2018-03-11.

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
39%
15524
14%
49157
10%
15488
44%
15488
20%
33939

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 15thNight
19%
778
8%
2683
4%
776
25%
776
10%
2080
January16th to endNight
21%
832
10%
2704
4%
832
28%
832
12%
2081
February1st to 15thNight
18%
761
9%
2482
3%
761
26%
761
12%
1877
February16th to endNight
26%
683
12%
2178
6%
683
33%
683
15%
1594
March1st to 15thNight
25%
764
13%
2101
6%
764
32%
764
18%
1560
March16th to endNight
34%
768
20%
2112
12%
768
42%
768
25%
1432
April1st to 15thNight
34%
718
15%
1817
6%
718
39%
718
23%
1320
April16th to endNight
45%
567
20%
1647
10%
567
52%
567
28%
1072
May1st to 15thNight
50%
489
17%
1569
12%
489
57%
489
24%
1018
May16th to endNight
55%
374
17%
1497
17%
374
61%
374
25%
840
June1st to 15thNight
53%
360
12%
1440
13%
360
59%
360
22%
837
June16th to endNight
58%
360
13%
1440
19%
360
61%
360
24%
836
July1st to 15thNight
70%
340
16%
1360
25%
340
73%
340
34%
687
July16th to endNight
67%
487
16%
1520
17%
456
68%
456
32%
865
August1st to 15thNight
71%
539
17%
1609
14%
536
73%
536
36%
943
August16th to endNight
69%
627
24%
1773
16%
627
72%
627
37%
1038
September1st to 15thNight
59%
720
20%
1806
10%
720
63%
720
35%
1167
September16th to endNight
59%
717
23%
2007
18%
717
62%
717
33%
1239
October1st to 15thNight
43%
720
16%
2160
15%
720
47%
720
23%
1483
October16th to endNight
30%
768
14%
2304
9%
768
37%
768
17%
1705
November1st to 15thNight
38%
760
17%
2576
15%
760
44%
760
19%
1743
November16th to endNight
29%
780
10%
2730
7%
780
35%
780
13%
2011
December1st to 15thNight
20%
780
7%
2730
4%
780
23%
780
10%
2144
December16th to endNight
16%
832
6%
2912
2%
832
22%
832
8%
2367

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
14%8%36%6%35%5%5%7%33%
49469
Night
15%8%36%5%3445%6%35%
49337
Cloud CoverDay
14%7%36%6%35%5%5%7%33%
49479
Night
15%8%36%5%3445%6%35%
49341
TransparencyDay
47%8%13%19%9%
49167
Night
47%7%13%20%10%1
49157
SeeingDay
17%423%28%17%6%
5869
Night
18%6%28%30%14%1
15530

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 15thDay
18%11%5%8%7%35%45%6%23%
1585
16th to endDay
14%13%5%11%8%35%5%6%6%18%
1872
February1st to 15thDay
14%14%6%12%7%35%44422%
1710
16th to endDay
18%11%5%8%6%245%36%26%
1578
March1st to 15thDay
16%8%5%7%7%35%5%5%5%29%
2085
16th to endDay
16%9%36%5%34446%34%
2112
April1st to 15thDay
20%10%36%5%2445%7%30%
2131
16th to endDay
17%7%25%425%445%38%
2322
May1st to 15thDay
14%6%36%5%35%45%7%35%
2382
16th to endDay
11%5%25%5%35%5%6%8%40%
2618
June1st to 15thDay
14%5%245%345%6%9%37%
2520
16th to endDay
12%425%435%6%7%9%37%
2520
July1st to 15thDay
7%4245%36%6%7%9%40%
2520
16th to endDay
9%5%25%5%46%6%7%9%36%
2542
August1st to 15thDay
7%5%26%5%45%5%6%8%40%
2340
16th to endDay
10%5%245%25%5%6%9%41%
2416
September1st to 15thDay
14%5%244345%5%7%41%
2152
16th to endDay
12%5%35%5%3445%8%41%
1953
October1st to 15thDay
19%7%25%6%3445%6%34%
1800
16th to endDay
23%9%37%6%25%46%7%23%
1920
November1st to 15thDay
14%9%46%7%3446%7%31%
1607
16th to endDay
17%12%47%6%35%45%8%24%
1560
December1st to 15thDay
18%13%5%9%7%35%446%20%
1560
16th to endDay
21%12%5%8%6%3446%7%18%
1664
January1st to 15thNight
20%13%47%6%34445%22%
2683
16th to endNight
15%11%5%8%7%35%5%5%6%24%
2704
February1st to 15thNight
15%13%5%8%6%35%45%5%25%
2480
16th to endNight
16%9%49%6%35%445%30%
2178
March1st to 15thNight
17%8%47%7%35%345%32%
2089
16th to endNight
15%8%46%42334442%
2112
April1st to 15thNight
18%7%35%6%34446%35%
1817
16th to endNight
13%5%35%425%446%44%
1647
May1st to 15thNight
15%4246%345%6%8%38%
1569
16th to endNight
12%5%2332446%6%47%
1495
June1st to 15thNight
13%5%25%435%45%9%40%
1440
16th to endNight
10%5%25%425%6%6%9%42%
1440
July1st to 15thNight
5%223425%448%55%
1440
16th to endNight
8%3144345%6%8%49%
1625
August1st to 15thNight
6%315%335%46%9%49%
1620
16th to endNight
9%3143345%5%6%53%
1773
September1st to 15thNight
11%5%1432446%7%48%
1806
16th to endNight
12%32442435%7%49%
2007
October1st to 15thNight
18%6%25%5%2435%6%39%
2160
16th to endNight
20%9%36%5%3445%6%30%
2304
November1st to 15thNight
18%7%245%35%45%6%36%
2576
16th to endNight
21%9%46%435%5%5%7%27%
2730
December1st to 15thNight
20%13%5%7%5%35%45%5%24%
2730
16th to endNight
21%12%5%9%7%345%5%6%19%
2912

Percentage Cloud Cover SE (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 15thDay
18%11%47%7%36%5%5%6%23%
1585
16th to endDay
13%13%5%11%8%45%6%5%6%18%
1872
February1st to 15thDay
14%14%5%12%8%35%445%21%
1710
16th to endDay
17%11%48%7%335%47%26%
1578
March1st to 15thDay
16%8%48%6%35%5%5%6%28%
2096
16th to endDay
16%8%46%5%34446%34%
2111
April1st to 15thDay
19%9%36%5%3345%7%30%
2131
16th to endDay
17%6%26%424446%37%
2322
May1st to 15thDay
14%6%27%5%35%5%5%8%35%
2382
16th to endDay
11%5%25%5%345%6%8%40%
2618
June1st to 15thDay
14%5%245%245%6%9%37%
2520
16th to endDay
11%5%24445%7%7%10%37%
2520
July1st to 15thDay
7%4245%36%7%7%9%41%
2520
16th to endDay
9%425%5%46%6%8%9%37%
2542
August1st to 15thDay
7%5%26%5%46%6%6%9%40%
2340
16th to endDay
9%5%245%35%5%6%9%42%
2416
September1st to 15thDay
14%4245%3445%7%41%
2152
16th to endDay
12%435%6%2435%8%41%
1953
October1st to 15thDay
18%7%35%5%35%45%6%34%
1800
16th to endDay
23%8%37%5%35%5%5%7%24%
1920
November1st to 15thDay
14%8%46%7%345%6%8%31%
1607
16th to endDay
17%11%47%6%345%5%7%25%
1560
December1st to 15thDay
18%12%5%9%8%35%35%6%20%
1560
16th to endDay
20%12%5%9%6%45%46%6%18%
1664
January1st to 15thNight
20%13%48%6%35%45%5%22%
2683
16th to endNight
15%11%5%8%7%35%5%5%6%23%
2704
February1st to 15thNight
14%14%5%8%6%35%5%5%5%25%
2473
16th to endNight
15%9%49%7%3445%5%29%
2178
March1st to 15thNight
18%8%37%6%34346%31%
2101
16th to endNight
15%8%46%5%2333442%
2112
April1st to 15thNight
18%7%25%5%44446%35%
1817
16th to endNight
12%5%35%43445%7%43%
1647
May1st to 15thNight
15%425%5%3446%8%38%
1568
16th to endNight
12%42342446%6%47%
1495
June1st to 15thNight
12%5%15%5%35%45%9%41%
1440
16th to endNight
10%5%25%425%5%6%8%42%
1440
July1st to 15thNight
5%32343435%8%55%
1440
16th to endNight
8%31442447%8%49%
1625
August1st to 15thNight
6%315%43445%9%50%
1620
16th to endNight
9%214335%45%6%52%
1773
September1st to 15thNight
11%4243245%6%7%48%
1806
16th to endNight
11%41442435%7%49%
2007
October1st to 15thNight
17%6%26%5%23446%39%
2160
16th to endNight
20%9%36%5%3445%5%30%
2304
November1st to 15thNight
17%7%25%5%25%5%5%6%36%
2576
16th to endNight
20%9%36%435%5%5%7%27%
2730
December1st to 15thNight
20%12%47%6%35%45%6%23%
2730
16th to endNight
20%12%5%9%6%345%5%6%19%
2912

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 15thDay
59%8%12%13%5%
1586
16th to endDay
64%8%11%10%4
1872
February1st to 15thDay
64%6%12%15%1
1712
16th to endDay
56%8%13%14%6%
1578
March1st to 15thDay
55%7%12%15%8%
2096
16th to endDay
48%6%10%18%13%1
2112
April1st to 15thDay
53%5%11%18%11%
2131
16th to endDay
46%5%11%19%14%2
2322
May1st to 15thDay
46%6%10%22%13%
2382
16th to endDay
38%8%14%21%14%2
2622
June1st to 15thDay
41%8%13%23%12%
2520
16th to endDay
38%9%16%22%12%
2520
July1st to 15thDay
34%9%14%24%16%1
2371
16th to endDay
40%9%15%22%10%1
2384
August1st to 15thDay
37%10%16%20%14%1
2327
16th to endDay
36%8%15%26%11%1
2416
September1st to 15thDay
39%9%15%23%11%
2152
16th to endDay
40%6%13%28%10%
1953
October1st to 15thDay
49%6%12%21%8%1
1800
16th to endDay
57%8%14%13%5%
1920
November1st to 15thDay
49%9%14%17%6%1
1607
16th to endDay
56%9%15%13%4
1560
December1st to 15thDay
63%8%15%10%2
1560
16th to endDay
64%8%12%10%3
1664
January1st to 15thNight
61%7%13%12%5%
2683
16th to endNight
58%7%15%13%3
2704
February1st to 15thNight
59%6%13%16%4
2482
16th to endNight
55%5%14%16%7%
2178
March1st to 15thNight
54%5%11%20%6%
2101
16th to endNight
45%410%21%16%2
2112
April1st to 15thNight
49%5%10%18%14%
1817
16th to endNight
39%6%11%22%16%3
1647
May1st to 15thNight
41%7%11%22%14%2
1569
16th to endNight
34%7%14%25%15%3
1497
June1st to 15thNight
39%6%13%24%15%1
1440
16th to endNight
37%6%12%24%18%
1440
July1st to 15thNight
26%6%12%27%24%2
1360
16th to endNight
30%7%15%25%17%3
1520
August1st to 15thNight
29%8%18%28%13%1
1609
16th to endNight
29%6%13%32%16%1
1773
September1st to 15thNight
33%8%14%27%15%1
1806
16th to endNight
33%6%12%32%13%
2007
October1st to 15thNight
45%7%11%22%12%
2160
16th to endNight
53%6%13%18%7%
2304
November1st to 15thNight
46%7%13%20%11%1
2576
16th to endNight
54%8%16%15%4
2730
December1st to 15thNight
60%8%13%12%3
2730
16th to endNight
64%8%12%9%3
2912

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 15thDay
13%16%39%20%9%1
98
16th to endDay
29%11%34%21%2
144
February1st to 15thDay
27%5%48%17%
135
16th to endDay
22%13%40%21%2
136
March1st to 15thDay
21%10%32%27%8%
312
16th to endDay
22%430%29%10%2
288
April1st to 15thDay
23%430%31%8%1
270
16th to endDay
19%6%29%25%13%5%
270
May1st to 15thDay
18%421%28%19%9%
288
16th to endDay
13%321%34%21%5%
331
June1st to 15thDay
19%216%35%23%2
315
16th to endDay
13%218%34%25%5%
315
July1st to 15thDay
11%11%35%30%10%
305
16th to endDay
11%16%35%26%10%
326
August1st to 15thDay
8%14%31%30%15%
313
16th to endDay
14%212%23%28%19%
332
September1st to 15thDay
12%213%28%25%17%
315
16th to endDay
13%315%28%21%17%
314
October1st to 15thDay
22%423%26%17%6%
315
16th to endDay
24%7%31%25%11%
336
November1st to 15thDay
18%7%25%32%14%2
135
16th to endDay
21%10%36%23%7%1
90
December1st to 15thDay
16%13%35%25%7%1
90
16th to endDay
25%14%44%15%
96
January1st to 15thNight
27%11%33%20%5%
780
16th to endNight
19%8%37%28%5%
832
February1st to 15thNight
20%10%39%23%4
764
16th to endNight
19%8%36%28%6%
683
March1st to 15thNight
21%8%36%26%7%
764
16th to endNight
19%6%31%29%12%1
768
April1st to 15thNight
20%6%32%32%7%
718
16th to endNight
14%5%29%35%12%2
567
May1st to 15thNight
17%222%33%20%2
489
16th to endNight
11%124%38%22%1
375
June1st to 15thNight
15%123%37%21%1
360
16th to endNight
12%118%42%24%
360
July1st to 15thNight
6%14%47%28%2
340
16th to endNight
8%113%45%28%3
487
August1st to 15thNight
8%10%43%33%4
539
16th to endNight
9%212%37%33%4
627
September1st to 15thNight
13%219%30%27%7%
720
16th to endNight
14%215%30%29%7%
717
October1st to 15thNight
19%6%23%28%19%2
720
16th to endNight
25%6%30%29%7%
768
November1st to 15thNight
20%6%28%29%14%1
760
16th to endNight
24%9%29%26%8%1
780
December1st to 15thNight
27%9%36%21%4
780
16th to endNight
25%9%39%22%2
832
Page generated at 2018-03-12 13:28:07. Version ac04

Copyright 2018 A. Danko


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