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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 2017-09-10.

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%
14796
14%
46823
10%
14760
44%
14760
20%
32348

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%
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
58%
700
20%
1755
10%
700
62%
700
35%
1140
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%7%36%6%35%5%5%7%33%
47802
Night
15%8%36%5%3445%6%35%
47003
Cloud CoverDay
14%7%36%6%35%5%6%7%33%
47812
Night
15%8%36%5%3445%6%35%
47007
TransparencyDay
47%8%13%19%9%
47500
Night
47%7%13%20%10%1
46823
SeeingDay
17%422%29%18%6%
5327
Night
18%6%27%30%14%1
14802

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%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
15%5%244345%5%7%40%
2091
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%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%47%
1755
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
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
15%4245%345%5%7%40%
2091
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%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%47%
1755
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
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
40%9%15%23%10%
2091
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
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%14%
1755
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
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%314%30%24%14%
294
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
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
14%220%30%26%6%
700
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 2017-09-11 19:35:24. Version ac04

Copyright 2017 A. Danko


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