Observatoire astronomique de Châteauguay
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire astronomique de Châteauguay clear sky chart from 2005-11-05 to 2017-09-24.

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
31%
14673
13%
46909
8%
14643
37%
14643
16%
33980

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%
720
8%
2506
4%
716
22%
716
8%
2008
January16th to endNight
21%
768
10%
2688
5%
768
28%
768
11%
2029
February1st to 15thNight
20%
703
7%
2303
4%
701
25%
701
10%
1847
February16th to endNight
24%
631
12%
1893
6%
631
33%
631
14%
1427
March1st to 15thNight
25%
720
13%
2160
9%
720
30%
720
14%
1650
March16th to endNight
31%
768
18%
1995
9%
768
37%
768
22%
1435
April1st to 15thNight
27%
718
15%
1796
5%
718
32%
718
19%
1368
April16th to endNight
29%
624
15%
1704
6%
624
35%
624
21%
1222
May1st to 15thNight
32%
399
16%
1479
13%
399
42%
399
17%
981
May16th to endNight
37%
374
12%
1497
12%
374
44%
374
17%
995
June1st to 15thNight
34%
360
8%
1440
8%
360
41%
360
13%
1018
June16th to endNight
45%
360
8%
1440
10%
360
50%
360
19%
924
July1st to 15thNight
53%
340
13%
1360
18%
340
58%
340
24%
803
July16th to endNight
54%
376
12%
1418
15%
354
57%
354
23%
840
August1st to 15thNight
56%
365
15%
1436
15%
363
59%
363
20%
889
August16th to endNight
54%
762
20%
1908
11%
762
57%
762
35%
1232
September1st to 15thNight
51%
720
14%
1800
8%
720
52%
720
29%
1249
September16th to endNight
49%
693
21%
1904
15%
693
53%
693
30%
1221
October1st to 15thNight
31%
660
18%
1941
9%
660
41%
660
20%
1376
October16th to endNight
27%
704
10%
2255
7%
704
32%
704
13%
1690
November1st to 15thNight
26%
700
15%
2277
11%
700
33%
700
15%
1653
November16th to endNight
24%
720
12%
2501
7%
720
30%
720
11%
1888
December1st to 15thNight
17%
720
7%
2520
3%
720
21%
720
8%
2055
December16th to endNight
13%
768
8%
2688
3%
768
20%
768
7%
2180

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%
48028
Night
19%9%36%5%34445%31%
47078
Cloud CoverDay
17%8%36%5%35%45%7%32%
48038
Night
19%10%46%5%34446%31%
47084
TransparencyDay
50%6%12%19%9%
47715
Night
53%5%11%18%9%1
46909
SeeingDay
21%8%26%24%13%4
5617
Night
23%8%28%27%10%
14675

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
21%14%5%9%7%3343421%
1432
16th to endDay
14%14%47%6%35%45%7%24%
1536
February1st to 15thDay
14%13%5%10%8%46%435%24%
1556
16th to endDay
18%12%47%7%34445%27%
1580
March1st to 15thDay
18%11%47%7%36%445%26%
1790
16th to endDay
18%8%26%42335%7%36%
2226
April1st to 15thDay
21%10%36%5%2434433%
2152
16th to endDay
19%6%345%24446%37%
2256
May1st to 15thDay
21%6%25%5%3445%6%33%
2481
16th to endDay
19%6%25%5%2445%7%35%
2618
June1st to 15thDay
23%6%235%25%448%31%
2520
16th to endDay
17%6%26%5%25%5%5%7%34%
2520
July1st to 15thDay
12%425%5%3446%8%39%
2520
16th to endDay
12%425%436%6%7%10%37%
2654
August1st to 15thDay
12%6%27%5%36%5%5%9%35%
2501
16th to endDay
10%32442446%9%47%
2292
September1st to 15thDay
15%5%235%2345%7%43%
2160
16th to endDay
13%5%2332435%7%48%
1915
October1st to 15thDay
20%7%25%5%2445%6%33%
1688
16th to endDay
26%9%45%5%33435%27%
1616
November1st to 15thDay
17%11%36%5%25%45%6%30%
1581
16th to endDay
22%11%5%7%6%3344426%
1458
December1st to 15thDay
25%14%47%6%245%6%6%15%
1440
16th to endDay
27%14%5%7%5%35%34417%
1536
January1st to 15thNight
18%15%6%9%7%3445%420%
2506
16th to endNight
13%14%6%8%6%45%44425%
2688
February1st to 15thNight
15%14%6%11%8%36%435%20%
2301
16th to endNight
17%11%48%6%44345%28%
1893
March1st to 15thNight
21%11%46%6%3443428%
2147
16th to endNight
18%9%36%5%2334437%
1995
April1st to 15thNight
26%9%345%24245%30%
1796
16th to endNight
23%8%24424335%36%
1704
May1st to 15thNight
22%6%36%423346%36%
1479
16th to endNight
19%7%3443445%6%35%
1495
June1st to 15thNight
26%6%35%33346%7%29%
1440
16th to endNight
17%425%5%35%6%6%8%35%
1440
July1st to 15thNight
11%3146%36%5%7%8%40%
1440
16th to endNight
11%5%245%35%5%5%10%40%
1514
August1st to 15thNight
13%5%25%435%46%10%39%
1446
16th to endNight
13%413434447%47%
1908
September1st to 15thNight
17%5%25%5%23445%42%
1800
16th to endNight
19%423324346%47%
1904
October1st to 15thNight
19%8%26%425%446%35%
1941
16th to endNight
26%8%36%5%34345%28%
2255
November1st to 15thNight
22%8%36%5%3445%430%
2277
16th to endNight
22%11%48%43443426%
2501
December1st to 15thNight
24%15%5%7%6%2434419%
2520
16th to endNight
25%18%5%7%5%2334419%
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
21%15%49%8%35%33321%
1432
16th to endDay
13%15%5%7%6%35%447%24%
1536
February1st to 15thDay
14%13%411%8%46%436%22%
1556
16th to endDay
17%13%47%7%34446%27%
1580
March1st to 15thDay
18%11%47%7%46%445%26%
1800
16th to endDay
19%7%35%42435%7%36%
2226
April1st to 15thDay
21%10%37%424345%32%
2152
16th to endDay
19%7%245%2345%6%37%
2256
May1st to 15thDay
20%6%35%5%35%45%6%33%
2481
16th to endDay
18%6%35%5%35%45%7%34%
2618
June1st to 15thDay
23%7%245%245%5%8%30%
2520
16th to endDay
18%5%26%5%36%45%8%33%
2520
July1st to 15thDay
12%425%5%35%5%6%8%38%
2520
16th to endDay
11%425%6%35%5%7%10%35%
2654
August1st to 15thDay
11%6%36%6%45%5%6%9%34%
2501
16th to endDay
9%41443446%9%46%
2292
September1st to 15thDay
16%5%2442345%7%43%
2160
16th to endDay
12%5%24324447%46%
1915
October1st to 15thDay
20%7%35%5%35%447%32%
1688
16th to endDay
25%9%46%5%34445%26%
1616
November1st to 15thDay
17%11%36%425%5%5%6%30%
1581
16th to endDay
22%11%5%8%5%3444426%
1458
December1st to 15thDay
24%14%5%6%6%35%5%5%5%15%
1440
16th to endDay
26%16%5%6%6%35%44416%
1536
January1st to 15thNight
17%16%6%9%6%35%5%4419%
2506
16th to endNight
13%14%5%9%6%35%5%45%25%
2688
February1st to 15thNight
15%13%6%11%8%46%435%20%
2294
16th to endNight
17%12%5%9%5%35%445%27%
1893
March1st to 15thNight
21%11%46%6%3344428%
2160
16th to endNight
18%10%36%5%23345%36%
1995
April1st to 15thNight
26%9%445%24345%30%
1796
16th to endNight
22%8%35%423335%36%
1704
May1st to 15thNight
21%6%35%5%33346%35%
1479
16th to endNight
19%6%35%43445%6%34%
1495
June1st to 15thNight
26%7%25%5%2435%7%28%
1440
16th to endNight
16%5%25%5%346%6%8%35%
1440
July1st to 15thNight
10%415%6%35%48%9%39%
1440
16th to endNight
11%5%24435%5%6%10%39%
1514
August1st to 15thNight
12%5%25%5%25%5%5%9%39%
1446
16th to endNight
12%424424447%47%
1908
September1st to 15thNight
16%5%25%5%23446%41%
1800
16th to endNight
18%42432335%5%47%
1904
October1st to 15thNight
18%8%35%5%24346%35%
1941
16th to endNight
26%8%37%5%34445%27%
2255
November1st to 15thNight
21%8%45%6%35%45%5%29%
2277
16th to endNight
21%12%48%5%3443426%
2501
December1st to 15thNight
24%14%6%7%5%35%435%18%
2520
16th to endNight
24%18%5%7%5%2333419%
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
67%49%12%5%
1433
16th to endDay
58%6%12%14%7%
1536
February1st to 15thDay
63%49%18%2
1558
16th to endDay
58%5%11%14%8%1
1580
March1st to 15thDay
59%6%10%15%6%1
1800
16th to endDay
47%5%11%18%13%3
2226
April1st to 15thDay
53%6%7%19%11%2
2152
16th to endDay
47%5%9%19%13%3
2256
May1st to 15thDay
50%5%9%18%14%1
2481
16th to endDay
47%7%12%19%11%1
2622
June1st to 15thDay
51%7%11%18%10%
2520
16th to endDay
48%7%11%22%8%1
2520
July1st to 15thDay
39%8%14%26%10%
2371
16th to endDay
40%9%17%23%8%
2487
August1st to 15thDay
43%9%16%22%7%
2487
16th to endDay
31%7%19%27%12%
2292
September1st to 15thDay
39%6%14%26%12%
2160
16th to endDay
35%6%12%32%11%
1915
October1st to 15thDay
50%6%13%21%8%
1688
16th to endDay
59%5%13%16%5%
1616
November1st to 15thDay
52%7%13%17%9%
1581
16th to endDay
59%6%9%15%7%
1458
December1st to 15thDay
67%8%11%10%1
1440
16th to endDay
69%6%11%7%5%
1536
January1st to 15thNight
65%6%10%13%4
2506
16th to endNight
59%6%10%15%7%
2688
February1st to 15thNight
66%5%10%13%3
2303
16th to endNight
58%411%15%9%
1893
March1st to 15thNight
58%5%8%17%8%1
2160
16th to endNight
50%49%17%14%3
1995
April1st to 15thNight
56%36%17%13%1
1796
16th to endNight
49%5%8%17%15%3
1704
May1st to 15thNight
49%48%16%16%4
1479
16th to endNight
48%6%10%19%13%2
1497
June1st to 15thNight
53%6%11%18%8%
1440
16th to endNight
43%7%15%18%13%1
1440
July1st to 15thNight
36%8%14%25%14%
1360
16th to endNight
37%7%18%22%13%
1418
August1st to 15thNight
39%8%18%21%11%
1436
16th to endNight
34%6%15%28%13%
1908
September1st to 15thNight
43%5%12%24%13%
1800
16th to endNight
38%5%11%29%14%
1904
October1st to 15thNight
49%6%9%23%10%
1941
16th to endNight
57%5%12%16%6%
2255
November1st to 15thNight
54%5%12%16%8%2
2277
16th to endNight
60%5%10%16%5%
2501
December1st to 15thNight
67%6%11%12%2
2520
16th to endNight
68%5%10%10%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
23%20%20%20%16%
60
16th to endDay
37%6%31%18%33
64
February1st to 15thDay
26%20%40%11%1
92
16th to endDay
28%10%28%26%4
239
March1st to 15thDay
23%14%34%21%6%
270
16th to endDay
26%9%28%20%11%2
288
April1st to 15thDay
30%12%30%18%7%2
270
16th to endDay
21%11%28%21%13%4
270
May1st to 15thDay
29%8%26%19%12%4
288
16th to endDay
20%10%30%21%14%2
331
June1st to 15thDay
28%7%24%27%9%2
315
16th to endDay
19%7%26%29%14%1
315
July1st to 15thDay
12%6%29%27%18%6%
305
16th to endDay
14%221%36%20%4
326
August1st to 15thDay
14%319%34%19%8%
313
16th to endDay
9%6%21%28%18%15%
332
September1st to 15thDay
16%420%25%19%13%
315
16th to endDay
12%7%25%17%23%12%
287
October1st to 15thDay
19%9%26%24%16%3
255
16th to endDay
31%11%25%21%9%
245
November1st to 15thDay
25%9%28%23%11%1
235
16th to endDay
33%10%28%20%7%
78
December1st to 15thDay
31%135%28%11
60
16th to endDay
40%14%31%14%
64
January1st to 15thNight
25%12%32%23%5%
720
16th to endNight
22%10%36%22%7%1
768
February1st to 15thNight
20%9%36%26%5%
704
16th to endNight
24%9%33%26%6%
631
March1st to 15thNight
26%10%30%26%4
720
16th to endNight
21%8%30%28%9%
768
April1st to 15thNight
28%10%28%28%4
718
16th to endNight
25%11%29%22%9%
624
May1st to 15thNight
23%5%31%25%11%1
399
16th to endNight
19%7%30%31%10%
375
June1st to 15thNight
29%5%21%32%10%
360
16th to endNight
16%328%37%12%
360
July1st to 15thNight
12%227%35%22%
340
16th to endNight
12%124%43%17%1
376
August1st to 15thNight
14%118%45%19%1
365
16th to endNight
15%221%35%23%1
762
September1st to 15thNight
19%220%39%17%1
720
16th to endNight
20%321%30%21%2
693
October1st to 15thNight
22%7%29%26%12%
660
16th to endNight
30%10%27%25%6%
704
November1st to 15thNight
26%9%30%22%11%
700
16th to endNight
26%13%27%19%11%
720
December1st to 15thNight
32%10%32%19%4
720
16th to endNight
33%12%31%17%31
768
Page generated at 2017-09-25 09:02:26. Version ac04

Copyright 2017 A. Danko


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