Observatoire Plourde
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire Plourde clear sky chart from 2005-11-06 to 2024-01-12.

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
24%
23144
9%
74818
6%
23102
28%
23102
11%
59054

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
16%
950
7%
2838
4%
946
18%
946
6%
2469
January11th to 20thNight
17%
906
6%
2716
2%
906
22%
906
8%
2265
January21st to endNight
28%
877
9%
2763
6%
877
32%
877
9%
2269
February1st to 10thNight
25%
720
9%
2340
6%
720
30%
720
10%
1882
February11th to 20thNight
20%
703
9%
2275
4%
700
27%
700
10%
1833
February21st to endNight
19%
592
11%
1924
5%
592
26%
592
10%
1533
March1st to 10thNight
24%
720
12%
2058
8%
720
28%
720
12%
1641
March11th to 20thNight
21%
720
11%
1980
6%
720
25%
720
12%
1607
March21st to endNight
24%
792
17%
2165
8%
792
31%
792
18%
1614
April1st to 10thNight
21%
720
12%
1800
5%
720
25%
720
16%
1423
April11th to 20thNight
28%
569
14%
1633
8%
569
32%
569
16%
1233
April21st to endNight
28%
540
14%
1620
8%
540
35%
540
19%
1163
May1st to 10thNight
35%
360
14%
1440
16%
360
40%
360
15%
970
May11th to 20thNight
33%
354
14%
1415
16%
354
43%
354
15%
958
May21st to endNight
29%
389
10%
1437
6%
388
37%
388
16%
977
June1st to 10thNight
27%
360
8%
1260
3%
360
31%
360
16%
875
June11th to 20thNight
33%
360
8%
1260
4%
360
36%
360
20%
802
June21st to endNight
41%
360
7%
1260
4%
360
42%
360
21%
819
July1st to 10thNight
40%
350
8%
1225
5%
350
43%
350
20%
812
July11th to 20thNight
42%
348
9%
1218
9%
348
45%
348
22%
790
July21st to endNight
45%
394
9%
1379
11%
372
47%
372
16%
946
August1st to 10thNight
38%
437
9%
1501
8%
435
43%
435
16%
1046
August11th to 20thNight
43%
534
13%
1598
8%
534
49%
534
25%
1070
August21st to endNight
37%
608
14%
1796
10%
608
39%
608
20%
1291
September1st to 10thNight
32%
720
12%
1800
5%
720
35%
720
22%
1330
September11th to 20thNight
30%
720
13%
1854
5%
720
34%
720
21%
1372
September21st to endNight
34%
720
14%
2042
9%
720
38%
720
19%
1480
October1st to 10thNight
28%
720
13%
2160
11%
720
32%
720
15%
1622
October11th to 20thNight
15%
720
7%
2160
4%
720
19%
720
8%
1853
October21st to endNight
17%
792
6%
2532
4%
792
21%
792
7%
2163
November1st to 10thNight
13%
740
7%
2592
3%
740
19%
740
6%
2168
November11th to 20thNight
13%
760
6%
2660
4%
760
17%
760
5%
2285
November21st to endNight
7%
760
4%
2660
1%
760
10%
760
4%
2366
December1st to 10thNight
15%
844
4%
2744
2%
844
16%
844
4%
2446
December11th to 20thNight
18%
950
5%
3510
2%
949
20%
949
5%
3045
December21st to endNight
15%
1035
4%
5203
3%
1026
17%
1026
3%
4636

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%13%5%9%7%45%5%5%6%24%
74692
Night
17%14%6%9%8%45%5%5%5%22%
75021
TransparencyDay
60%6%9%17%8%1
74381
Night
63%6%9%15%7%1
74867
SeeingDay
25%15%32%19%7%2
14060
Night
24%12%31%24%8%1
23154

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
15%19%7%13%7%47%7%5%410%
1328
11th to 20thDay
13%18%6%11%8%47%8%9%6%11%
1267
21st to endDay
11%16%6%10%10%6%8%7%7%7%13%
1592
February1st to 10thDay
7%13%7%11%10%7%8%7%7%7%16%
1620
11th to 20thDay
10%19%7%10%9%5%5%7%6%7%16%
1573
21st to endDay
9%17%7%11%9%37%5%5%7%19%
1332
March1st to 10thDay
12%12%6%12%10%6%6%5%5%5%23%
1898
11th to 20thDay
14%15%6%9%9%35%435%28%
1980
21st to endDay
14%14%5%9%6%4445%6%28%
2191
April1st to 10thDay
18%16%7%10%7%3445%5%21%
2160
11th to 20thDay
18%13%5%9%6%34445%30%
2292
21st to endDay
19%12%5%7%5%3444431%
2340
May1st to 10thDay
15%12%49%7%36%6%5%6%28%
2519
11th to 20thDay
24%10%36%5%35%447%29%
2478
21st to endDay
20%9%37%5%3445%7%33%
2835
June1st to 10thDay
22%8%36%5%45%46%7%30%
2700
11th to 20thDay
17%8%36%6%35%5%5%7%35%
2700
21st to endDay
20%7%36%6%35%5%6%7%32%
2700
July1st to 10thDay
18%7%47%6%45%5%6%8%30%
2700
11th to 20thDay
16%8%37%6%47%6%7%8%30%
2700
21st to endDay
18%8%37%7%46%6%7%7%27%
2855
August1st to 10thDay
20%9%38%7%45%5%6%8%25%
2425
11th to 20thDay
18%9%37%6%45%5%6%6%30%
2303
21st to endDay
17%9%47%6%45%5%5%8%30%
2541
September1st to 10thDay
21%8%47%5%35%447%32%
2160
11th to 20thDay
24%10%36%6%3445%7%26%
2102
21st to endDay
24%11%38%5%34445%29%
1918
October1st to 10thDay
26%13%36%5%32246%30%
1800
11th to 20thDay
31%20%5%7%5%3343316%
1800
21st to endDay
28%22%6%7%5%3433314%
1820
November1st to 10thDay
22%25%7%8%6%44335%13%
1486
11th to 20thDay
23%20%7%14%8%4433311%
1520
21st to endDay
21%24%10%11%8%443239%
1520
December1st to 10thDay
15%24%8%14%7%3434412%
1435
11th to 20thDay
13%21%7%11%8%46%5%5%6%15%
1671
21st to endDay
15%21%9%18%12%35%2338%
2431
January1st to 10thNight
14%16%9%14%10%5%6%6%4411%
2838
11th to 20thNight
15%18%7%9%8%47%9%7%6%10%
2716
21st to endNight
9%15%6%12%10%6%9%7%6%6%13%
2763
February1st to 10thNight
8%13%5%10%11%6%10%7%7%7%15%
2340
11th to 20thNight
10%17%7%12%10%46%6%5%6%17%
2273
21st to endNight
9%17%5%12%9%47%6%6%6%18%
1924
March1st to 10thNight
10%12%6%12%9%5%8%6%45%22%
2048
11th to 20thNight
14%15%6%10%9%5%6%45%422%
1979
21st to endNight
13%13%49%6%35%5%5%6%30%
2165
April1st to 10thNight
19%16%5%10%5%3343428%
1800
11th to 20thNight
18%10%49%6%4445%5%30%
1633
21st to endNight
20%11%6%7%5%24346%32%
1620
May1st to 10thNight
13%12%46%6%346%5%7%33%
1440
11th to 20thNight
20%10%35%5%345%6%6%35%
1415
21st to endNight
18%7%46%6%45%5%5%8%33%
1436
June1st to 10thNight
21%9%36%7%24347%33%
1260
11th to 20thNight
15%8%36%5%3445%7%40%
1260
21st to endNight
17%5%25%6%35%45%8%38%
1260
July1st to 10thNight
16%6%35%6%45%5%7%9%35%
1260
11th to 20thNight
15%6%45%5%445%7%9%35%
1260
21st to endNight
15%7%36%6%46%5%6%8%33%
1460
August1st to 10thNight
14%10%47%7%346%5%6%34%
1511
11th to 20thNight
14%7%36%5%345%7%8%39%
1598
21st to endNight
18%8%37%6%35%6%6%6%34%
1796
September1st to 10thNight
20%8%36%6%345%5%6%34%
1800
11th to 20thNight
20%10%46%5%34447%34%
1854
21st to endNight
23%10%35%432345%36%
2042
October1st to 10thNight
23%12%36%5%3445%6%29%
2160
11th to 20thNight
28%19%6%7%7%33345%16%
2160
21st to endNight
22%23%6%9%6%35%43415%
2532
November1st to 10thNight
21%21%7%10%5%3444417%
2592
11th to 20thNight
21%19%9%11%8%4343414%
2660
21st to endNight
21%21%8%13%9%4433311%
2660
December1st to 10thNight
15%23%8%13%10%46%5%3310%
2744
11th to 20thNight
16%19%7%12%12%5%6%6%4411%
3526
21st to endNight
18%19%11%16%11%444338%
5236

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
74%5%7%12%2
1329
11th to 20thDay
68%7%6%12%8%
1267
21st to endDay
68%5%6%13%8%
1592
February1st to 10thDay
66%5%7%15%8%
1620
11th to 20thDay
66%5%8%14%6%
1582
21st to endDay
64%6%7%16%6%1
1332
March1st to 10thDay
63%46%13%13%1
1901
11th to 20thDay
61%47%16%12%1
1980
21st to endDay
57%5%7%19%10%2
2191
April1st to 10thDay
65%5%7%13%9%1
2160
11th to 20thDay
56%5%8%18%12%1
2292
21st to endDay
56%5%9%15%14%2
2340
May1st to 10thDay
55%7%9%18%11%1
2519
11th to 20thDay
55%6%7%19%12%1
2482
21st to endDay
52%7%9%19%13%1
2835
June1st to 10thDay
53%6%10%21%10%1
2700
11th to 20thDay
48%6%9%22%13%2
2700
21st to endDay
49%7%10%23%10%1
2700
July1st to 10thDay
50%8%12%23%8%
2626
11th to 20thDay
47%8%15%23%7%
2619
21st to endDay
54%8%14%20%4
2696
August1st to 10thDay
56%9%13%19%2
2411
11th to 20thDay
52%9%15%17%7%1
2303
21st to endDay
51%7%14%22%6%
2541
September1st to 10thDay
51%7%14%20%8%
2160
11th to 20thDay
58%7%14%17%4
2102
21st to endDay
58%6%9%21%6%
1918
October1st to 10thDay
57%412%18%8%
1800
11th to 20thDay
74%5%7%11%4
1800
21st to endDay
76%38%10%2
1820
November1st to 10thDay
75%6%9%6%4
1486
11th to 20thDay
81%36%8%2
1520
21st to endDay
83%46%6%1
1520
December1st to 10thDay
76%5%6%9%3
1435
11th to 20thDay
70%5%5%15%4
1671
21st to endDay
84%36%6%2
2431
January1st to 10thNight
75%5%6%11%2
2838
11th to 20thNight
69%7%7%11%6%
2716
21st to endNight
68%6%6%12%7%1
2763
February1st to 10thNight
65%7%8%11%9%
2340
11th to 20thNight
67%5%8%14%6%
2275
21st to endNight
64%6%7%15%7%1
1924
March1st to 10thNight
63%5%8%12%10%1
2058
11th to 20thNight
65%5%7%13%9%2
1980
21st to endNight
55%5%7%17%14%2
2165
April1st to 10thNight
61%46%16%12%2
1800
11th to 20thNight
56%6%7%18%12%1
1633
21st to endNight
53%47%16%16%3
1620
May1st to 10thNight
49%7%8%20%13%3
1440
11th to 20thNight
49%7%6%21%16%
1416
21st to endNight
48%8%10%19%14%1
1437
June1st to 10thNight
52%6%9%21%12%1
1260
11th to 20thNight
44%5%10%22%18%1
1260
21st to endNight
44%7%12%24%11%2
1260
July1st to 10thNight
44%8%12%26%10%
1225
11th to 20thNight
41%9%16%24%10%
1218
21st to endNight
48%9%14%25%4
1379
August1st to 10thNight
49%8%15%24%4
1501
11th to 20thNight
41%9%19%24%7%1
1598
21st to endNight
49%8%13%22%7%
1796
September1st to 10thNight
50%7%13%21%8%1
1800
11th to 20thNight
50%7%16%21%6%
1854
21st to endNight
51%6%13%23%6%
2042
October1st to 10thNight
56%7%12%18%7%
2160
11th to 20thNight
73%5%8%12%2
2160
21st to endNight
73%5%8%9%5%
2532
November1st to 10thNight
72%5%10%10%2
2592
11th to 20thNight
76%5%8%9%3
2660
21st to endNight
80%5%7%7%1
2660
December1st to 10thNight
80%5%6%6%3
2744
11th to 20thNight
76%5%6%10%2
3525
21st to endNight
82%46%6%3
5236

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
24%19%37%16%31
180
11th to 20thDay
14%19%37%22%7%1
162
21st to endDay
17%14%39%25%5%1
218
February1st to 10thDay
13%28%38%18%11
240
11th to 20thDay
20%20%38%18%31
240
21st to endDay
23%24%41%12%1
198
March1st to 10thDay
19%17%42%15%5%1
392
11th to 20thDay
24%17%39%16%4
420
21st to endDay
19%23%35%16%5%1
462
April1st to 10thDay
22%21%30%19%7%1
420
11th to 20thDay
25%17%32%17%6%2
412
21st to endDay
25%15%33%19%7%1
420
May1st to 10thDay
23%14%33%22%7%2
423
11th to 20thDay
26%17%31%17%7%2
447
21st to endDay
26%16%33%19%7%
595
June1st to 10thDay
27%14%31%21%7%
630
11th to 20thDay
24%18%30%21%6%1
630
21st to endDay
21%10%34%25%9%2
630
July1st to 10thDay
18%15%34%23%8%2
621
11th to 20thDay
17%13%33%26%11%1
618
21st to endDay
20%11%29%27%9%3
599
August1st to 10thDay
26%8%27%26%9%3
446
11th to 20thDay
20%7%28%27%13%6%
439
21st to endDay
25%12%27%20%12%4
495
September1st to 10thDay
24%15%27%21%11%3
450
11th to 20thDay
29%11%31%21%7%1
450
21st to endDay
32%13%28%16%8%3
450
October1st to 10thDay
32%13%29%18%8%1
450
11th to 20thDay
39%20%25%12%31
450
21st to endDay
35%19%29%13%31
375
November1st to 10thDay
39%18%31%11%1
180
11th to 20thDay
32%23%29%12%31
180
21st to endDay
37%23%28%8%4
180
December1st to 10thDay
31%13%31%14%8%2
180
11th to 20thDay
24%22%37%11%7%1
180
21st to endDay
28%17%31%18%5%2
198
January1st to 10thNight
23%13%36%21%6%1
950
11th to 20thNight
25%11%36%23%5%
906
21st to endNight
16%10%32%28%12%1
877
February1st to 10thNight
15%12%39%25%9%1
720
11th to 20thNight
20%13%35%24%8%
703
21st to endNight
17%15%39%22%6%1
592
March1st to 10thNight
16%16%35%25%7%1
720
11th to 20thNight
24%15%32%22%6%
720
21st to endNight
20%14%36%23%6%1
792
April1st to 10thNight
29%13%32%21%5%1
720
11th to 20thNight
24%14%29%24%7%1
569
21st to endNight
24%10%32%25%8%1
540
May1st to 10thNight
19%9%31%30%11%
360
11th to 20thNight
27%11%25%30%6%1
354
21st to endNight
21%11%34%29%5%
389
June1st to 10thNight
25%10%31%25%8%1
360
11th to 20thNight
16%14%31%28%9%1
360
21st to endNight
19%5%27%36%11%1
360
July1st to 10thNight
17%7%31%33%11%1
350
11th to 20thNight
18%7%27%36%12%
348
21st to endNight
15%6%25%39%14%2
394
August1st to 10thNight
18%7%26%29%18%2
437
11th to 20thNight
19%5%23%34%18%1
534
21st to endNight
24%8%25%28%14%1
608
September1st to 10thNight
24%11%28%23%13%1
720
11th to 20thNight
26%11%27%24%11%2
720
21st to endNight
28%9%23%27%11%2
720
October1st to 10thNight
29%11%27%23%9%1
720
11th to 20thNight
37%13%25%17%6%2
720
21st to endNight
34%12%28%19%5%1
792
November1st to 10thNight
31%16%32%16%41
740
11th to 20thNight
30%17%28%19%5%
760
21st to endNight
33%13%34%15%41
760
December1st to 10thNight
28%15%30%20%7%
844
11th to 20thNight
27%12%34%20%7%1
950
21st to endNight
28%13%29%21%7%3
1045
Page generated at 2024-01-08 22:31:30. Version ac07

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