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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 2017-05-24.

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%
14517
14%
45902
10%
14481
44%
14481
19%
31812

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
18%
718
8%
2476
3%
716
24%
716
9%
1936
January16th to endNight
22%
768
10%
2496
5%
768
29%
768
12%
1925
February1st to 15thNight
19%
701
9%
2287
3%
701
27%
701
11%
1732
February16th to endNight
27%
631
12%
2012
6%
631
34%
631
15%
1472
March1st to 15thNight
25%
720
13%
1980
6%
720
31%
720
17%
1481
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%
360
17%
1441
17%
360
62%
360
26%
801
June1st to 15thNight
51%
330
13%
1320
14%
330
58%
330
22%
770
June16th to endNight
59%
330
12%
1320
18%
330
62%
330
25%
755
July1st to 15thNight
70%
310
17%
1240
26%
310
73%
310
34%
623
July16th to endNight
67%
450
15%
1399
15%
419
69%
419
32%
793
August1st to 15thNight
70%
494
18%
1474
14%
491
72%
491
35%
869
August16th to endNight
68%
574
22%
1624
16%
574
71%
574
36%
955
September1st to 15thNight
58%
660
21%
1655
10%
660
62%
660
34%
1084
September16th to endNight
58%
657
20%
1840
15%
657
61%
657
32%
1149
October1st to 15thNight
43%
660
17%
1980
16%
660
47%
660
22%
1361
October16th to endNight
28%
704
12%
2112
6%
704
35%
704
16%
1588
November1st to 15thNight
38%
700
18%
2373
16%
700
44%
700
20%
1590
November16th to endNight
30%
720
10%
2520
8%
720
34%
720
13%
1872
December1st to 15thNight
20%
720
7%
2520
4%
720
23%
720
10%
1996
December16th to endNight
17%
768
5%
2688
2%
768
22%
768
8%
2218

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%5%35%5%5%7%32%
46369
Night
15%8%36%5%3445%6%35%
46082
Cloud CoverDay
14%7%36%6%35%5%6%7%33%
46379
Night
15%8%36%5%3445%6%35%
46086
TransparencyDay
47%8%13%19%9%1
46067
Night
47%7%13%19%10%1
45902
SeeingDay
17%423%29%18%6%
4899
Night
19%6%28%30%14%1
14523

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%7%7%35%45%6%23%
1462
16th to endDay
14%13%6%11%8%36%5%6%5%17%
1728
February1st to 15thDay
13%13%6%12%8%35%44422%
1575
16th to endDay
17%12%5%8%6%245%37%27%
1458
March1st to 15thDay
16%8%5%7%7%35%5%5%5%28%
1969
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%41%
2517
June1st to 15thDay
14%6%25%5%35%5%7%9%36%
2310
16th to endDay
11%425%436%6%7%10%37%
2310
July1st to 15thDay
7%4245%37%6%6%9%41%
2310
16th to endDay
9%5%25%5%36%6%7%10%36%
2355
August1st to 15thDay
7%426%5%45%5%6%8%41%
2145
16th to endDay
10%5%245%25%5%6%9%41%
2214
September1st to 15thDay
15%5%25%4445%5%7%39%
1973
16th to endDay
13%5%35%6%3435%8%40%
1790
October1st to 15thDay
18%6%25%6%3446%6%34%
1650
16th to endDay
24%9%37%5%25%45%6%22%
1760
November1st to 15thDay
13%9%36%7%3446%7%33%
1480
16th to endDay
18%12%5%7%5%35%45%7%24%
1440
December1st to 15thDay
19%13%5%10%7%35%446%19%
1440
16th to endDay
21%12%5%8%6%3446%7%17%
1536
January1st to 15thNight
20%14%5%7%6%3445%5%22%
2476
16th to endNight
15%12%5%9%7%45%5%5%6%24%
2496
February1st to 15thNight
15%14%5%8%6%35%45%5%25%
2285
16th to endNight
15%9%39%6%35%445%30%
2012
March1st to 15thNight
18%8%47%7%35%345%31%
1968
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%1332446%7%48%
1439
June1st to 15thNight
13%5%245%345%5%10%40%
1320
16th to endNight
9%5%25%425%5%5%9%43%
1320
July1st to 15thNight
4223424448%56%
1320
16th to endNight
8%2134245%6%9%49%
1504
August1st to 15thNight
7%315%42446%9%49%
1485
16th to endNight
9%31433445%6%52%
1624
September1st to 15thNight
11%5%2432446%7%47%
1655
16th to endNight
13%424424347%48%
1840
October1st to 15thNight
17%6%25%5%2435%6%39%
1980
16th to endNight
21%9%46%5%3445%6%29%
2112
November1st to 15thNight
17%6%245%35%45%6%37%
2373
16th to endNight
21%10%46%5%35%5%5%7%26%
2520
December1st to 15thNight
21%13%5%6%5%35%45%5%23%
2520
16th to endNight
22%12%5%9%6%345%5%6%18%
2688

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%5%7%7%36%5%5%5%23%
1462
16th to endDay
13%14%6%11%9%46%6%5%5%17%
1728
February1st to 15thDay
13%13%6%12%8%45%445%21%
1575
16th to endDay
17%11%48%7%335%47%26%
1458
March1st to 15thDay
16%8%48%6%35%5%5%6%28%
1980
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
10%5%25%5%35%5%6%8%41%
2517
June1st to 15thDay
14%5%25%5%25%5%6%9%36%
2310
16th to endDay
11%424445%7%7%10%37%
2310
July1st to 15thDay
6%4245%36%7%7%9%41%
2310
16th to endDay
9%425%5%46%6%8%10%37%
2355
August1st to 15thDay
7%426%5%46%6%6%8%41%
2145
16th to endDay
9%5%245%35%5%6%9%41%
2214
September1st to 15thDay
15%425%5%345%5%7%39%
1973
16th to endDay
13%5%35%6%3435%8%40%
1790
October1st to 15thDay
18%7%25%5%35%45%6%34%
1650
16th to endDay
23%9%47%5%35%45%7%23%
1760
November1st to 15thDay
13%8%46%7%245%6%8%32%
1480
16th to endDay
17%11%5%7%6%345%5%7%24%
1440
December1st to 15thDay
19%12%5%10%8%35%45%6%19%
1440
16th to endDay
21%12%5%8%7%45%46%6%17%
1536
January1st to 15thNight
20%14%5%8%6%35%45%5%21%
2476
16th to endNight
15%11%5%9%7%45%5%46%23%
2496
February1st to 15thNight
14%14%5%8%6%35%5%5%5%25%
2278
16th to endNight
15%9%49%6%4445%5%30%
2012
March1st to 15thNight
18%8%47%7%34345%31%
1980
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%42332446%6%48%
1439
June1st to 15thNight
13%5%15%5%35%35%9%40%
1320
16th to endNight
9%5%25%425%5%6%9%43%
1320
July1st to 15thNight
432343435%8%56%
1320
16th to endNight
8%21442447%8%49%
1504
August1st to 15thNight
7%315%33446%9%49%
1485
16th to endNight
9%31433445%6%52%
1624
September1st to 15thNight
11%42432446%7%47%
1655
16th to endNight
12%42442435%7%48%
1840
October1st to 15thNight
16%7%26%5%23446%39%
1980
16th to endNight
21%9%37%5%3445%5%29%
2112
November1st to 15thNight
16%6%25%5%35%5%5%6%37%
2373
16th to endNight
21%9%46%425%5%5%7%26%
2520
December1st to 15thNight
21%12%46%5%35%45%5%23%
2520
16th to endNight
21%12%6%9%6%345%5%6%18%
2688

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
60%8%13%12%4
1463
16th to endDay
65%8%10%10%3
1728
February1st to 15thDay
64%6%12%14%1
1577
16th to endDay
56%8%13%14%6%
1458
March1st to 15thDay
55%7%12%16%7%
1980
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
37%8%14%22%14%2
2521
June1st to 15thDay
41%9%13%22%11%
2310
16th to endDay
37%9%16%21%13%
2310
July1st to 15thDay
33%8%14%24%16%1
2161
16th to endDay
39%10%15%21%10%1
2197
August1st to 15thDay
36%9%16%20%14%1
2132
16th to endDay
36%8%15%27%10%1
2214
September1st to 15thDay
41%9%15%23%9%
1973
16th to endDay
41%6%13%27%9%
1790
October1st to 15thDay
48%6%12%21%8%1
1650
16th to endDay
59%8%14%13%4
1760
November1st to 15thDay
47%10%15%18%7%1
1480
16th to endDay
57%10%14%13%4
1440
December1st to 15thDay
64%9%15%9%1
1440
16th to endDay
65%9%12%10%2
1536
January1st to 15thNight
61%7%13%12%4
2476
16th to endNight
59%7%15%13%3
2496
February1st to 15thNight
59%6%13%16%3
2287
16th to endNight
55%5%15%16%7%
2012
March1st to 15thNight
55%412%20%5%
1980
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
33%7%13%25%15%3
1441
June1st to 15thNight
39%5%13%24%15%1
1320
16th to endNight
36%6%13%24%18%1
1320
July1st to 15thNight
25%6%12%26%24%2
1240
16th to endNight
29%8%16%24%17%3
1399
August1st to 15thNight
29%8%18%27%14%1
1474
16th to endNight
30%7%12%33%15%1
1624
September1st to 15thNight
34%8%14%27%14%
1655
16th to endNight
34%7%13%31%12%
1840
October1st to 15thNight
45%7%12%22%12%
1980
16th to endNight
55%7%12%17%6%
2112
November1st to 15thNight
45%7%13%20%12%1
2373
16th to endNight
55%7%16%15%4
2520
December1st to 15thNight
61%9%13%12%3
2520
16th to endNight
65%9%12%9%2
2688

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
12%20%41%13%10%1
65
16th to endDay
31%13%31%22%1
96
February1st to 15thDay
25%6%50%16%1
90
16th to endDay
19%11%38%26%4
96
March1st to 15thDay
22%10%32%25%8%
270
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
11%221%35%22%5%
302
June1st to 15thDay
17%318%36%21%2
255
16th to endDay
13%114%34%28%6%
255
July1st to 15thDay
10%11%36%30%11%
245
16th to endDay
11%17%37%24%9%
270
August1st to 15thDay
7%15%30%32%14%
253
16th to endDay
14%210%22%29%20%
268
September1st to 15thDay
13%214%27%25%16%
255
16th to endDay
16%315%32%19%12%
254
October1st to 15thDay
19%324%27%18%6%
255
16th to endDay
26%6%30%26%9%
272
November1st to 15thDay
11%9%21%39%15%3
98
16th to endDay
23%13%26%25%10%1
60
December1st to 15thDay
16%11%43%20%6%1
60
16th to endDay
25%17%45%12%
64
January1st to 15thNight
27%12%34%19%5%
720
16th to endNight
19%8%36%28%6%
768
February1st to 15thNight
20%11%38%24%4
704
16th to endNight
19%9%35%29%7%
631
March1st to 15thNight
22%8%36%26%6%
720
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
361
June1st to 15thNight
16%123%36%20%1
330
16th to endNight
11%118%41%26%
330
July1st to 15thNight
414%46%30%3
310
16th to endNight
8%114%45%28%3
450
August1st to 15thNight
8%110%42%32%4
494
16th to endNight
10%212%36%33%4
574
September1st to 15thNight
14%220%29%26%6%
660
16th to endNight
15%215%31%29%4
657
October1st to 15thNight
19%6%23%28%19%2
660
16th to endNight
25%5%32%28%6%
704
November1st to 15thNight
18%6%29%29%14%1
700
16th to endNight
25%9%27%27%9%1
720
December1st to 15thNight
28%9%35%21%4
720
16th to endNight
26%8%38%22%3
768
Page generated at 2017-05-25 13:27:37. Version ac04

Copyright 2017 A. Danko


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