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 2005-11-05 to 2017-10-06.

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
32%
14713
13%
47046
9%
14682
38%
14682
17%
33652

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
20%
720
9%
2506
5%
716
25%
716
9%
1970
January16th to endNight
23%
768
11%
2688
6%
768
30%
768
11%
2012
February1st to 15thNight
20%
704
8%
2310
5%
701
25%
701
10%
1838
February16th to endNight
25%
631
12%
1893
6%
631
32%
631
14%
1422
March1st to 15thNight
26%
720
14%
2160
10%
720
32%
720
15%
1625
March16th to endNight
33%
768
19%
2000
9%
768
39%
768
23%
1428
April1st to 15thNight
27%
718
16%
1796
5%
718
32%
718
19%
1366
April16th to endNight
31%
612
17%
1692
6%
612
38%
612
21%
1191
May1st to 15thNight
32%
408
17%
1488
15%
408
40%
408
18%
985
May16th to endNight
34%
374
13%
1497
12%
374
43%
374
17%
995
June1st to 15thNight
34%
360
9%
1440
8%
360
42%
360
13%
1006
June16th to endNight
43%
360
9%
1440
12%
360
48%
360
19%
918
July1st to 15thNight
51%
340
12%
1360
18%
340
56%
340
24%
801
July16th to endNight
54%
376
12%
1418
16%
354
58%
354
23%
837
August1st to 15thNight
57%
374
15%
1445
17%
372
59%
372
21%
886
August16th to endNight
55%
747
20%
1893
12%
747
58%
747
35%
1222
September1st to 15thNight
51%
720
15%
1800
8%
720
52%
720
30%
1238
September16th to endNight
49%
717
22%
1979
15%
717
53%
717
31%
1241
October1st to 15thNight
34%
684
20%
1997
11%
684
44%
684
23%
1385
October16th to endNight
27%
704
11%
2266
7%
704
33%
704
15%
1680
November1st to 15thNight
26%
700
18%
2277
12%
700
36%
700
16%
1628
November16th to endNight
24%
720
13%
2493
8%
720
31%
720
12%
1863
December1st to 15thNight
18%
720
8%
2520
4%
720
23%
720
9%
1985
December16th to endNight
13%
768
10%
2688
3%
768
22%
768
9%
2130

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
18%8%36%5%3445%6%33%
48156
Night
19%9%46%5%34446%31%
47215
Cloud CoverDay
18%8%36%5%34446%32%
48166
Night
19%10%46%5%34445%31%
47220
TransparencyDay
51%412%20%9%1
47843
Night
54%410%19%10%1
47046
SeeingDay
22%7%26%24%14%4
5676
Night
24%7%27%28%10%
14714

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
22%14%6%10%5%35%33321%
1432
16th to endDay
14%13%48%6%45%5%46%25%
1536
February1st to 15thDay
14%14%5%10%7%36%435%23%
1549
16th to endDay
18%12%49%6%3344427%
1580
March1st to 15thDay
17%11%48%6%35%345%26%
1790
16th to endDay
18%9%35%424445%36%
2220
April1st to 15thDay
22%9%36%5%3344432%
2152
16th to endDay
19%7%26%5%24346%36%
2266
May1st to 15thDay
20%7%36%5%25%5%47%33%
2474
16th to endDay
20%6%25%43445%7%34%
2618
June1st to 15thDay
23%5%35%43445%7%31%
2520
16th to endDay
18%5%25%6%35%5%5%8%32%
2520
July1st to 15thDay
11%5%35%6%35%6%6%9%37%
2520
16th to endDay
12%5%245%35%6%6%10%37%
2654
August1st to 15thDay
11%5%26%6%46%6%6%8%34%
2493
16th to endDay
9%423425%5%6%8%46%
2307
September1st to 15thDay
15%5%245%3345%7%43%
2160
16th to endDay
12%5%14323448%48%
1980
October1st to 15thDay
20%6%26%5%34447%34%
1758
16th to endDay
24%9%36%6%34345%28%
1606
November1st to 15thDay
17%9%45%5%25%5%5%7%30%
1581
16th to endDay
23%9%45%434446%28%
1464
December1st to 15thDay
26%12%5%6%6%3445%5%18%
1440
16th to endDay
27%15%46%6%3334420%
1536
January1st to 15thNight
19%14%6%9%6%2444421%
2506
16th to endNight
14%13%6%8%6%45%5%45%25%
2688
February1st to 15thNight
15%13%6%11%8%45%44421%
2308
16th to endNight
17%12%48%5%45%335%27%
1893
March1st to 15thNight
20%12%47%6%24335%28%
2147
16th to endNight
17%9%35%6%2433438%
2000
April1st to 15thNight
26%8%45%434335%30%
1796
16th to endNight
21%8%35%424445%36%
1692
May1st to 15thNight
20%6%5%5%5%33346%36%
1488
16th to endNight
20%6%35%4345%5%6%34%
1495
June1st to 15thNight
26%7%26%3345%46%30%
1440
16th to endNight
16%445%426%5%5%9%35%
1440
July1st to 15thNight
12%4245%35%6%7%9%39%
1440
16th to endNight
11%4245%35%46%11%39%
1514
August1st to 15thNight
13%5%25%5%346%6%8%38%
1455
16th to endNight
12%5%24425%45%8%45%
1893
September1st to 15thNight
16%6%25%5%24446%41%
1800
16th to endNight
17%5%23212347%47%
1979
October1st to 15thNight
18%6%26%5%23445%38%
1997
16th to endNight
26%8%37%433335%29%
2266
November1st to 15thNight
20%9%36%5%35%446%31%
2277
16th to endNight
23%12%37%5%24345%27%
2493
December1st to 15thNight
24%14%5%8%5%2443421%
2520
16th to endNight
24%16%5%8%5%2333422%
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
23%14%6%9%7%2432321%
1432
16th to endDay
14%14%5%8%6%45%5%46%24%
1536
February1st to 15thDay
14%15%5%10%8%45%435%22%
1549
16th to endDay
18%11%5%9%6%3434426%
1580
March1st to 15thDay
18%11%48%6%35%445%26%
1800
16th to endDay
18%9%45%424446%35%
2220
April1st to 15thDay
23%8%36%6%24345%31%
2152
16th to endDay
21%7%25%424446%36%
2266
May1st to 15thDay
20%7%36%5%24446%33%
2474
16th to endDay
20%5%35%5%3445%7%33%
2618
June1st to 15thDay
24%6%25%425%448%31%
2520
16th to endDay
19%6%25%5%35%47%8%31%
2520
July1st to 15thDay
12%5%25%5%36%5%6%8%37%
2520
16th to endDay
12%5%245%36%6%5%10%36%
2654
August1st to 15thDay
12%5%26%6%35%6%6%8%34%
2493
16th to endDay
10%415%4245%6%9%45%
2307
September1st to 15thDay
15%5%25%424447%43%
2160
16th to endDay
13%424323447%48%
1980
October1st to 15thDay
20%7%25%5%445%46%33%
1758
16th to endDay
25%10%25%6%44345%27%
1606
November1st to 15thDay
18%11%25%5%34446%31%
1581
16th to endDay
22%11%46%6%23445%27%
1464
December1st to 15thDay
27%11%5%6%6%35%445%18%
1440
16th to endDay
27%16%5%7%6%3324419%
1536
January1st to 15thNight
19%15%6%9%6%34445%20%
2506
16th to endNight
14%14%6%8%6%45%44425%
2688
February1st to 15thNight
16%13%6%10%8%45%345%20%
2301
16th to endNight
17%13%47%6%45%34427%
1893
March1st to 15thNight
22%11%5%7%6%23335%28%
2160
16th to endNight
18%10%45%5%24335%37%
1999
April1st to 15thNight
26%9%36%33433430%
1796
16th to endNight
21%8%345%24346%36%
1692
May1st to 15thNight
19%7%36%5%23246%36%
1488
16th to endNight
20%7%26%43445%6%34%
1495
June1st to 15thNight
27%7%35%42445%6%29%
1440
16th to endNight
17%5%25%4245%6%7%36%
1440
July1st to 15thNight
11%425%5%25%6%7%8%39%
1440
16th to endNight
11%5%245%45%5%6%8%41%
1514
August1st to 15thNight
13%435%5%345%7%9%38%
1455
16th to endNight
12%4244235%5%7%45%
1893
September1st to 15thNight
16%6%25%5%2435%7%40%
1800
16th to endNight
17%5%24322346%48%
1979
October1st to 15thNight
18%6%36%5%24446%38%
1997
16th to endNight
27%8%27%423345%28%
2266
November1st to 15thNight
21%8%37%5%34445%31%
2277
16th to endNight
24%11%46%5%3334427%
2493
December1st to 15thNight
24%15%6%7%5%33335%20%
2520
16th to endNight
24%18%6%7%42332421%
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
68%38%13%5%
1433
16th to endDay
59%410%16%7%
1536
February1st to 15thDay
64%310%18%3
1551
16th to endDay
60%311%14%9%1
1580
March1st to 15thDay
59%310%16%7%1
1800
16th to endDay
50%310%20%13%2
2220
April1st to 15thDay
55%28%19%11%2
2152
16th to endDay
49%39%20%13%3
2266
May1st to 15thDay
51%49%19%14%1
2474
16th to endDay
48%5%12%19%11%2
2622
June1st to 15thDay
51%5%11%19%10%1
2520
16th to endDay
49%5%12%22%9%1
2520
July1st to 15thDay
41%6%12%27%11%
2371
16th to endDay
42%6%17%25%8%
2487
August1st to 15thDay
45%6%17%23%7%
2479
16th to endDay
34%417%29%13%
2307
September1st to 15thDay
40%413%28%12%
2160
16th to endDay
35%412%33%13%
1980
October1st to 15thDay
49%5%13%23%8%
1758
16th to endDay
58%412%17%6%
1606
November1st to 15thDay
53%411%19%10%
1581
16th to endDay
57%5%11%16%8%
1464
December1st to 15thDay
68%5%10%12%3
1440
16th to endDay
68%411%9%6%
1536
January1st to 15thNight
65%49%14%5%
2506
16th to endNight
60%49%16%8%
2688
February1st to 15thNight
66%39%15%4
2310
16th to endNight
60%211%15%10%
1893
March1st to 15thNight
59%39%17%9%1
2160
16th to endNight
51%28%18%15%3
2000
April1st to 15thNight
57%25%18%13%2
1796
16th to endNight
50%37%19%15%3
1692
May1st to 15thNight
50%26%19%15%5%
1488
16th to endNight
48%5%8%21%12%2
1497
June1st to 15thNight
55%48%20%9%1
1440
16th to endNight
44%6%12%20%14%1
1440
July1st to 15thNight
37%6%12%26%14%
1360
16th to endNight
38%6%17%23%12%
1418
August1st to 15thNight
41%6%16%24%10%
1445
16th to endNight
36%414%29%12%1
1893
September1st to 15thNight
43%411%25%13%1
1800
16th to endNight
36%5%11%30%15%
1979
October1st to 15thNight
47%5%9%26%10%
1997
16th to endNight
58%311%18%7%
2266
November1st to 15thNight
54%410%19%8%2
2277
16th to endNight
60%49%18%7%
2493
December1st to 15thNight
66%411%15%2
2520
16th to endNight
67%310%11%5%
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
26%13%18%28%13%
60
16th to endDay
39%6%25%18%9%1
64
February1st to 15thDay
32%14%32%16%4
96
16th to endDay
26%8%31%26%5%
239
March1st to 15thDay
27%9%29%27%5%
270
16th to endDay
22%5%32%25%11%2
288
April1st to 15thDay
27%14%27%19%8%3
270
16th to endDay
22%11%26%20%16%3
270
May1st to 15thDay
26%8%27%19%13%4
288
16th to endDay
22%9%29%20%14%3
331
June1st to 15thDay
28%9%20%27%10%3
315
16th to endDay
21%6%25%27%15%1
315
July1st to 15thDay
14%6%26%30%15%6%
305
16th to endDay
15%319%35%22%3
326
August1st to 15thDay
15%223%28%22%8%
313
16th to endDay
11%422%27%20%13%
332
September1st to 15thDay
15%223%26%18%13%
315
16th to endDay
13%6%26%21%20%11%
314
October1st to 15thDay
21%7%27%22%18%2
278
16th to endDay
35%9%21%24%9%
244
November1st to 15thDay
24%9%29%21%12%2
235
16th to endDay
33%10%26%21%7%1
84
December1st to 15thDay
31%6%30%25%33
60
16th to endDay
35%17%34%12%
64
January1st to 15thNight
26%11%30%24%6%
720
16th to endNight
23%9%32%25%7%
768
February1st to 15thNight
24%6%35%26%6%
704
16th to endNight
25%8%30%28%6%
631
March1st to 15thNight
28%7%30%26%7%
720
16th to endNight
22%5%31%29%9%
768
April1st to 15thNight
31%8%26%27%5%
718
16th to endNight
26%10%26%25%9%
612
May1st to 15thNight
22%5%32%28%9%1
408
16th to endNight
22%6%28%31%9%
375
June1st to 15thNight
29%423%30%11%
360
16th to endNight
18%228%36%13%
360
July1st to 15thNight
12%226%37%19%
340
16th to endNight
13%23%45%16%
376
August1st to 15thNight
14%115%44%21%2
374
16th to endNight
14%319%38%22%2
747
September1st to 15thNight
20%318%39%16%1
720
16th to endNight
19%421%31%19%3
717
October1st to 15thNight
22%6%28%27%13%
684
16th to endNight
32%8%26%24%7%
704
November1st to 15thNight
26%8%31%23%10%
700
16th to endNight
30%12%25%19%10%1
720
December1st to 15thNight
32%10%29%22%5%
720
16th to endNight
34%10%30%17%5%1
768
Page generated at 2017-10-07 14:07:47. Version ac04

Copyright 2017 A. Danko


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