Observatoire de l'Agence Spatiale Canadienne
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire de l'Agence Spatiale Canadienne clear sky chart from 2005-11-06 to 2024-01-27.

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
30%
22601
14%
74903
9%
22559
37%
22559
16%
53419

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%
760
9%
2649
4%
757
24%
757
8%
2105
January11th to 20thNight
17%
760
10%
2660
4%
760
24%
760
9%
2064
January21st to endNight
23%
820
12%
2868
7%
820
31%
820
13%
2100
February1st to 10thNight
17%
720
9%
2394
4%
720
25%
720
10%
1894
February11th to 20thNight
20%
703
12%
2166
4%
700
30%
700
14%
1604
February21st to endNight
24%
592
16%
1776
7%
592
35%
592
16%
1295
March1st to 10thNight
25%
720
15%
2160
10%
720
33%
720
15%
1597
March11th to 20thNight
24%
720
15%
2101
6%
720
32%
720
16%
1541
March21st to endNight
29%
792
22%
1980
9%
792
37%
792
23%
1441
April1st to 10thNight
25%
720
16%
1800
4%
720
30%
720
18%
1358
April11th to 20thNight
27%
711
16%
1775
4%
711
34%
711
21%
1297
April21st to endNight
29%
560
18%
1640
8%
560
36%
560
19%
1170
May1st to 10thNight
28%
432
16%
1512
11%
432
37%
432
17%
1040
May11th to 20thNight
31%
354
19%
1416
18%
354
42%
354
18%
907
May21st to endNight
34%
388
13%
1551
10%
388
46%
388
19%
975
June1st to 10thNight
33%
360
11%
1440
10%
360
43%
360
15%
979
June11th to 20thNight
40%
360
11%
1440
12%
360
48%
360
19%
894
June21st to endNight
40%
360
10%
1440
13%
360
47%
360
16%
959
July1st to 10thNight
47%
350
13%
1400
17%
350
54%
350
22%
829
July11th to 20thNight
52%
348
13%
1392
18%
348
57%
348
24%
829
July21st to endNight
50%
394
14%
1486
15%
372
56%
372
21%
892
August1st to 10thNight
57%
358
17%
1422
21%
356
59%
356
22%
845
August11th to 20thNight
52%
527
17%
1591
12%
527
56%
527
27%
1019
August21st to endNight
51%
792
19%
1980
10%
792
54%
792
31%
1335
September1st to 10thNight
48%
720
16%
1800
8%
720
51%
720
32%
1205
September11th to 20thNight
51%
720
20%
1888
13%
720
54%
720
33%
1195
September21st to endNight
42%
720
21%
1980
15%
720
47%
720
27%
1318
October1st to 10thNight
35%
720
20%
2078
13%
720
44%
720
23%
1423
October11th to 20thNight
30%
720
16%
2213
9%
720
39%
720
17%
1596
October21st to endNight
24%
792
12%
2574
6%
792
32%
792
14%
1902
November1st to 10thNight
23%
740
17%
2407
9%
740
34%
740
16%
1687
November11th to 20thNight
25%
760
18%
2524
11%
760
34%
760
15%
1793
November21st to endNight
20%
760
12%
2660
6%
760
28%
760
10%
2015
December1st to 10thNight
18%
760
8%
2660
4%
760
23%
760
8%
2135
December11th to 20thNight
15%
760
11%
3241
4%
759
24%
759
8%
2459
December21st to endNight
13%
828
6%
4839
2%
817
21%
817
5%
3722

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
17%9%37%6%35%5%5%7%33%
74870
Night
19%10%47%6%3445%6%32%
75167
TransparencyDay
51%5%12%21%10%1
74575
Night
54%410%20%10%1
74996
SeeingDay
22%12%28%23%11%3
13509
Night
24%9%29%27%10%1
22610

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
20%17%6%11%6%45%33321%
1517
11th to 20thDay
19%14%6%11%7%34445%24%
1520
21st to endDay
14%13%48%7%5%5%6%5%6%27%
1632
February1st to 10thDay
17%16%5%9%6%45%435%25%
1565
11th to 20thDay
16%11%5%10%7%45%5%5%6%27%
1680
21st to endDay
18%15%5%8%7%43445%28%
1480
March1st to 10thDay
16%11%5%9%7%46%446%28%
1797
11th to 20thDay
16%11%48%6%35%45%6%32%
1853
21st to endDay
19%10%47%5%245%45%34%
2376
April1st to 10thDay
22%9%47%5%435%45%30%
2160
11th to 20thDay
21%8%35%5%34346%38%
2134
21st to endDay
21%10%38%5%3445%6%31%
2319
May1st to 10thDay
19%7%36%5%35%5%47%35%
2463
11th to 20thDay
17%7%36%5%35%5%5%6%38%
2478
21st to endDay
17%6%36%5%45%5%6%8%36%
2725
June1st to 10thDay
21%6%45%5%45%5%6%8%31%
2520
11th to 20thDay
15%6%26%5%3446%8%40%
2520
21st to endDay
20%7%36%6%36%5%5%7%32%
2520
July1st to 10thDay
11%6%35%6%35%6%6%9%40%
2520
11th to 20thDay
12%5%35%5%45%6%7%10%37%
2520
21st to endDay
12%6%25%6%35%7%7%10%38%
2744
August1st to 10thDay
12%5%36%6%45%7%6%9%37%
2506
11th to 20thDay
9%5%25%6%46%5%7%9%41%
2287
21st to endDay
12%6%35%435%6%6%8%42%
2376
September1st to 10thDay
11%5%35%6%346%6%8%42%
2160
11th to 20thDay
15%6%2442345%8%48%
2071
21st to endDay
15%6%25%5%346%6%8%41%
1980
October1st to 10thDay
20%6%36%6%45%5%5%7%33%
1877
11th to 20thDay
17%9%37%8%46%5%7%7%28%
1746
21st to endDay
27%9%36%5%3435%5%29%
1782
November1st to 10thDay
18%9%46%5%35%5%5%8%32%
1671
11th to 20thDay
18%10%46%6%36%6%5%6%28%
1653
21st to endDay
23%10%46%6%46%5%5%7%24%
1520
December1st to 10thDay
24%14%6%8%7%35%44419%
1520
11th to 20thDay
22%14%5%7%5%3446%6%25%
1906
21st to endDay
27%14%5%9%7%3444320%
2772
January1st to 10thNight
19%16%6%10%7%35%5%4421%
2649
11th to 20thNight
17%15%6%9%7%4445%5%23%
2660
21st to endNight
15%12%6%8%7%45%45%5%28%
2868
February1st to 10thNight
16%15%6%12%8%45%5%45%21%
2394
11th to 20thNight
16%10%5%10%6%46%45%5%29%
2164
21st to endNight
17%13%48%6%34445%31%
1776
March1st to 10thNight
17%14%48%7%35%445%30%
2150
11th to 20thNight
18%12%5%6%6%44446%31%
2101
21st to endNight
19%10%47%5%3444438%
1980
April1st to 10thNight
24%9%46%5%35%447%30%
1800
11th to 20thNight
23%7%46%5%34446%35%
1775
21st to endNight
21%10%36%5%345%45%34%
1640
May1st to 10thNight
20%8%46%6%44446%34%
1512
11th to 20thNight
19%7%46%5%3446%6%37%
1415
21st to endNight
16%7%25%5%35%6%5%7%39%
1550
June1st to 10thNight
22%8%37%5%336%5%7%32%
1440
11th to 20thNight
17%5%36%445%5%5%8%38%
1440
21st to endNight
17%5%47%6%37%45%8%34%
1440
July1st to 10thNight
12%5%25%6%446%7%8%40%
1440
11th to 20thNight
10%5%35%5%45%6%7%9%39%
1440
21st to endNight
12%5%36%6%36%47%10%39%
1574
August1st to 10thNight
13%6%25%5%445%6%9%41%
1432
11th to 20thNight
13%5%26%5%35%6%6%7%42%
1591
21st to endNight
13%6%25%5%35%5%5%8%42%
1980
September1st to 10thNight
12%6%27%6%345%6%7%43%
1800
11th to 20thNight
16%6%25%323347%49%
1888
21st to endNight
16%6%35%5%2445%8%42%
1980
October1st to 10thNight
17%7%35%6%245%5%6%38%
2078
11th to 20thNight
21%8%37%6%4445%6%32%
2213
21st to endNight
25%8%47%5%45%5%45%30%
2574
November1st to 10thNight
19%9%47%5%45%45%6%32%
2407
11th to 20thNight
20%10%47%6%35%45%7%31%
2524
21st to endNight
23%13%47%6%34445%26%
2660
December1st to 10thNight
22%16%6%9%6%35%5%45%19%
2660
11th to 20thNight
23%14%48%6%3443425%
3288
21st to endNight
27%15%6%9%5%23345%21%
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
69%48%14%4
1518
11th to 20thDay
65%49%13%9%
1520
21st to endDay
57%5%10%18%9%1
1632
February1st to 10thDay
63%48%18%6%1
1565
11th to 20thDay
59%412%16%8%1
1689
21st to endDay
61%310%15%9%2
1480
March1st to 10thDay
58%49%17%10%2
1800
11th to 20thDay
53%312%16%13%2
1853
21st to endDay
53%39%20%12%2
2376
April1st to 10thDay
57%38%18%11%2
2160
11th to 20thDay
49%39%23%15%2
2134
21st to endDay
54%49%18%11%3
2319
May1st to 10thDay
50%5%8%21%15%2
2463
11th to 20thDay
46%5%10%21%16%3
2482
21st to endDay
46%6%13%19%13%3
2725
June1st to 10thDay
52%6%11%19%11%1
2520
11th to 20thDay
42%5%12%24%14%3
2520
21st to endDay
51%5%13%20%10%1
2520
July1st to 10thDay
39%6%14%28%12%1
2450
11th to 20thDay
41%6%15%29%9%
2445
21st to endDay
42%7%16%26%9%
2591
August1st to 10thDay
42%6%17%26%8%
2492
11th to 20thDay
38%6%18%26%11%
2287
21st to endDay
39%5%15%27%13%
2376
September1st to 10thDay
38%6%15%28%12%
2160
11th to 20thDay
36%412%34%14%1
2071
21st to endDay
42%5%15%27%11%1
1980
October1st to 10thDay
50%6%12%22%10%
1877
11th to 20thDay
54%5%14%19%7%
1746
21st to endDay
58%411%18%8%1
1782
November1st to 10thDay
51%5%13%21%9%1
1671
11th to 20thDay
56%6%10%16%11%
1653
21st to endDay
60%7%12%14%6%
1520
December1st to 10thDay
70%5%9%12%4
1520
11th to 20thDay
60%5%11%17%6%
1906
21st to endDay
70%412%9%5%
2772
January1st to 10thNight
68%49%14%5%
2649
11th to 20thNight
64%5%10%13%7%1
2660
21st to endNight
58%410%16%11%1
2868
February1st to 10thNight
66%48%15%6%1
2394
11th to 20thNight
58%311%19%8%1
2166
21st to endNight
56%39%17%13%1
1776
March1st to 10thNight
58%39%17%10%2
2160
11th to 20thNight
57%39%16%13%3
2102
21st to endNight
52%37%20%14%4
1980
April1st to 10thNight
56%48%18%13%2
1800
11th to 20thNight
51%47%22%14%2
1775
21st to endNight
53%47%20%13%4
1640
May1st to 10thNight
52%45%19%15%5%
1512
11th to 20thNight
48%48%18%17%4
1416
21st to endNight
44%6%11%21%15%3
1551
June1st to 10thNight
52%5%8%22%11%1
1440
11th to 20thNight
44%6%11%22%14%3
1440
21st to endNight
50%5%11%19%14%1
1440
July1st to 10thNight
39%6%12%25%16%1
1400
11th to 20thNight
38%7%14%28%13%
1392
21st to endNight
40%7%17%25%10%1
1486
August1st to 10thNight
40%6%17%27%11%
1422
11th to 20thNight
40%6%16%25%13%
1591
21st to endNight
40%6%13%28%12%1
1980
September1st to 10thNight
40%5%12%26%15%1
1800
11th to 20thNight
37%413%32%13%1
1888
21st to endNight
42%6%10%26%15%
1980
October1st to 10thNight
46%5%10%25%13%1
2078
11th to 20thNight
54%410%24%7%
2213
21st to endNight
58%412%16%9%1
2574
November1st to 10thNight
53%5%11%22%8%1
2407
11th to 20thNight
54%5%11%18%10%1
2524
21st to endNight
61%5%11%17%6%
2660
December1st to 10thNight
68%5%11%13%4
2660
11th to 20thNight
63%49%16%7%
3288
21st to endNight
68%310%14%4
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
31%14%26%20%8%1
180
11th to 20thDay
28%17%32%17%6%1
180
21st to endDay
23%16%32%19%10%1
188
February1st to 10thDay
34%19%37%11%
216
11th to 20thDay
24%15%38%19%31
348
21st to endDay
28%14%28%26%3
346
March1st to 10thDay
25%12%33%23%6%
420
11th to 20thDay
22%16%32%21%7%1
420
21st to endDay
27%13%29%21%8%2
462
April1st to 10thDay
30%13%29%18%8%2
420
11th to 20thDay
30%18%22%16%11%3
412
21st to endDay
29%11%29%19%10%2
420
May1st to 10thDay
25%13%30%20%10%2
423
11th to 20thDay
18%11%32%24%11%4
447
21st to endDay
19%13%33%22%11%2
485
June1st to 10thDay
24%12%26%26%9%2
450
11th to 20thDay
17%11%26%29%15%2
450
21st to endDay
21%9%27%24%15%3
450
July1st to 10thDay
12%9%24%31%19%5%
445
11th to 20thDay
14%7%28%32%15%4
444
21st to endDay
15%6%27%32%18%2
488
August1st to 10thDay
14%5%25%30%21%6%
446
11th to 20thDay
12%5%24%33%18%9%
439
21st to endDay
16%9%23%25%17%10%
495
September1st to 10thDay
13%5%30%27%16%9%
450
11th to 20thDay
17%8%22%27%16%10%
450
21st to endDay
17%9%27%23%17%7%
450
October1st to 10thDay
22%11%27%22%14%4
450
11th to 20thDay
23%14%29%21%11%2
423
21st to endDay
35%13%24%22%6%
396
November1st to 10thDay
27%14%27%24%8%1
365
11th to 20thDay
26%19%31%16%7%2
313
21st to endDay
31%9%36%20%41
180
December1st to 10thDay
36%10%22%24%7%2
180
11th to 20thDay
28%21%36%11%5%
180
21st to endDay
30%21%27%17%42
198
January1st to 10thNight
29%12%31%24%5%
760
11th to 20thNight
26%11%34%22%7%
760
21st to endNight
23%10%33%26%7%1
820
February1st to 10thNight
25%9%36%25%5%1
720
11th to 20thNight
23%11%36%23%5%1
703
21st to endNight
25%11%31%29%4
592
March1st to 10thNight
25%10%32%27%6%
720
11th to 20thNight
27%10%34%23%7%
720
21st to endNight
25%8%31%27%8%1
792
April1st to 10thNight
30%11%27%27%5%
720
11th to 20thNight
27%12%28%25%7%1
711
21st to endNight
28%10%28%26%8%
560
May1st to 10thNight
25%7%34%25%7%2
432
11th to 20thNight
22%7%32%30%8%1
354
21st to endNight
20%9%32%30%10%
389
June1st to 10thNight
25%5%28%30%11%1
360
11th to 20thNight
19%5%29%33%13%
360
21st to endNight
18%5%30%33%14%1
360
July1st to 10thNight
13%5%28%37%17%
350
11th to 20thNight
12%225%45%14%2
348
21st to endNight
12%324%43%16%1
394
August1st to 10thNight
15%316%45%19%2
358
11th to 20thNight
13%421%37%22%2
527
21st to endNight
16%422%37%20%2
792
September1st to 10thNight
15%425%38%16%1
720
11th to 20thNight
18%6%20%35%19%3
720
21st to endNight
20%7%26%30%15%3
720
October1st to 10thNight
21%9%29%28%13%1
720
11th to 20thNight
27%8%29%27%9%
720
21st to endNight
29%11%30%25%5%
792
November1st to 10thNight
25%12%32%22%8%1
740
11th to 20thNight
27%13%30%21%9%1
760
21st to endNight
30%15%27%20%8%1
760
December1st to 10thNight
31%13%29%22%5%
760
11th to 20thNight
31%13%31%18%6%1
760
21st to endNight
33%14%30%17%5%
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