Observatoire de L’Avenir
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire de L’Avenir clear sky chart from 2005-11-05 to 2017-09-16.

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
26%
14620
11%
46823
7%
14588
32%
14588
14%
34946

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
13%
720
7%
2506
4%
716
17%
716
7%
2066
January16th to endNight
18%
768
8%
2688
5%
768
23%
768
7%
2156
February1st to 15thNight
15%
704
7%
2321
3%
701
21%
701
8%
1887
February16th to endNight
18%
631
9%
1893
4%
631
24%
631
10%
1514
March1st to 15thNight
19%
720
13%
2160
8%
720
26%
720
13%
1657
March16th to endNight
28%
768
18%
2013
7%
768
36%
768
19%
1477
April1st to 15thNight
22%
718
13%
1796
4%
718
27%
718
16%
1433
April16th to endNight
26%
582
16%
1662
5%
582
34%
582
19%
1167
May1st to 15thNight
29%
442
15%
1522
11%
442
37%
442
16%
1063
May16th to endNight
28%
375
11%
1497
10%
374
36%
374
13%
1031
June1st to 15thNight
32%
360
7%
1440
8%
360
38%
360
12%
1031
June16th to endNight
39%
360
8%
1440
10%
360
44%
360
16%
959
July1st to 15thNight
47%
340
10%
1360
15%
340
50%
340
20%
850
July16th to endNight
49%
376
11%
1418
14%
354
52%
354
21%
880
August1st to 15thNight
46%
401
12%
1472
12%
399
48%
399
19%
963
August16th to endNight
48%
702
17%
1848
10%
702
51%
702
30%
1221
September1st to 15thNight
42%
720
12%
1824
6%
720
44%
720
27%
1284
September16th to endNight
41%
661
19%
1825
13%
661
46%
661
29%
1198
October1st to 15thNight
28%
660
17%
1902
9%
660
36%
660
19%
1373
October16th to endNight
22%
704
9%
2288
5%
704
27%
704
11%
1764
November1st to 15thNight
22%
700
14%
2277
9%
700
30%
700
12%
1710
November16th to endNight
21%
720
12%
2463
8%
720
27%
720
9%
1901
December1st to 15thNight
13%
720
5%
2520
2%
720
17%
720
6%
2119
December16th to endNight
11%
768
8%
2688
3%
768
17%
768
5%
2242

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
21%10%36%5%34446%29%
47947
Night
20%11%47%5%34345%29%
46993
TransparencyDay
56%6%12%17%7%
47635
Night
57%5%10%17%8%
46823
SeeingDay
26%13%28%19%9%2
5641
Night
26%12%28%23%8%
14620

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%16%6%10%6%35%43316%
1432
16th to endDay
14%16%6%10%6%35%5%45%20%
1536
February1st to 15thDay
15%17%6%10%8%5%5%43417%
1537
16th to endDay
16%19%6%8%7%34435%20%
1580
March1st to 15thDay
19%13%5%7%6%3443425%
1790
16th to endDay
18%12%46%43333433%
2211
April1st to 15thDay
24%12%36%42433330%
2152
16th to endDay
24%8%25%433335%35%
2298
May1st to 15thDay
25%7%35%5%24446%30%
2439
16th to endDay
21%7%36%5%35%445%30%
2618
June1st to 15thDay
28%6%25%434446%28%
2520
16th to endDay
21%7%26%5%3446%8%29%
2520
July1st to 15thDay
16%5%25%6%45%6%5%9%33%
2520
16th to endDay
17%5%35%6%36%47%9%30%
2654
August1st to 15thDay
18%6%36%6%45%5%6%8%28%
2466
16th to endDay
15%5%245%2445%8%41%
2351
September1st to 15thDay
20%6%25%334346%39%
2136
16th to endDay
19%6%33323346%43%
1825
October1st to 15thDay
24%10%25%433345%30%
1726
16th to endDay
27%13%37%5%33435%22%
1584
November1st to 15thDay
21%11%37%424445%29%
1581
16th to endDay
23%15%5%7%42333427%
1495
December1st to 15thDay
28%16%48%5%3343417%
1440
16th to endDay
25%19%7%7%6%2433316%
1536
January1st to 15thNight
21%15%6%10%7%2433419%
2506
16th to endNight
13%17%6%9%9%45%44420%
2688
February1st to 15thNight
13%14%7%12%9%45%44419%
2320
16th to endNight
16%15%6%10%6%3433424%
1893
March1st to 15thNight
20%13%48%5%3434327%
2147
16th to endNight
18%11%45%5%2433436%
2013
April1st to 15thNight
25%11%36%6%23335%27%
1796
16th to endNight
23%7%25%324346%35%
1662
May1st to 15thNight
23%8%35%434336%33%
1522
16th to endNight
23%435%5%35%447%32%
1495
June1st to 15thNight
28%6%35%4245%47%28%
1440
16th to endNight
19%5%24425%6%48%34%
1440
July1st to 15thNight
15%5%346%25%46%9%35%
1440
16th to endNight
13%425%435%5%7%8%38%
1514
August1st to 15thNight
17%6%25%5%3445%9%36%
1482
16th to endNight
15%42442345%8%43%
1848
September1st to 15thNight
20%6%15%42335%6%39%
1824
16th to endNight
19%414324236%45%
1825
October1st to 15thNight
21%7%27%5%33345%35%
1902
16th to endNight
28%10%45%5%24335%26%
2288
November1st to 15thNight
22%11%36%5%2435%6%28%
2277
16th to endNight
24%14%48%42332426%
2463
December1st to 15thNight
25%16%7%9%6%2332418%
2520
16th to endNight
25%19%6%8%5%3433318%
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
72%5%7%10%3
1433
16th to endDay
64%7%11%12%3
1536
February1st to 15thDay
71%48%12%2
1540
16th to endDay
66%5%8%11%6%1
1580
March1st to 15thDay
62%411%12%7%
1800
16th to endDay
55%5%8%18%11%1
2211
April1st to 15thDay
59%47%17%9%2
2152
16th to endDay
52%49%17%12%3
2298
May1st to 15thDay
54%5%10%17%10%
2439
16th to endDay
54%7%10%18%8%
2622
June1st to 15thDay
55%6%11%16%8%
2520
16th to endDay
53%6%12%20%7%
2520
July1st to 15thDay
45%8%15%23%6%
2371
16th to endDay
49%8%17%18%6%
2487
August1st to 15thDay
50%9%17%18%3
2452
16th to endDay
39%6%18%25%9%
2351
September1st to 15thDay
45%5%14%23%10%
2136
16th to endDay
42%5%13%29%9%
1825
October1st to 15thDay
55%5%13%19%6%
1726
16th to endDay
63%5%12%13%4
1584
November1st to 15thDay
56%6%12%15%8%
1581
16th to endDay
61%5%11%15%6%
1495
December1st to 15thDay
71%5%10%10%1
1440
16th to endDay
73%48%6%6%
1536
January1st to 15thNight
69%5%9%10%3
2506
16th to endNight
67%49%12%4
2688
February1st to 15thNight
68%49%12%4
2321
16th to endNight
64%5%8%12%9%
1893
March1st to 15thNight
61%38%15%8%1
2160
16th to endNight
52%48%16%14%3
2013
April1st to 15thNight
60%45%16%11%1
1796
16th to endNight
48%5%9%18%14%3
1662
May1st to 15thNight
52%48%15%15%2
1522
16th to endNight
51%7%10%19%9%1
1497
June1st to 15thNight
55%6%11%18%7%
1440
16th to endNight
46%8%11%20%11%
1440
July1st to 15thNight
41%7%14%24%10%
1360
16th to endNight
39%8%18%21%11%
1418
August1st to 15thNight
44%8%17%23%6%
1472
16th to endNight
38%6%17%27%9%
1848
September1st to 15thNight
45%5%13%24%10%
1824
16th to endNight
40%5%12%30%11%
1825
October1st to 15thNight
51%6%11%22%8%
1902
16th to endNight
61%5%10%16%5%
2288
November1st to 15thNight
57%6%12%15%5%2
2277
16th to endNight
63%410%15%6%
2463
December1st to 15thNight
72%5%8%10%2
2520
16th to endNight
72%49%8%4
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%16%36%16%3
60
16th to endDay
37%15%32%9%31
64
February1st to 15thDay
31%23%26%13%5%
115
16th to endDay
28%18%32%15%3
239
March1st to 15thDay
26%23%26%18%4
270
16th to endDay
25%17%27%15%10%3
288
April1st to 15thDay
31%18%23%20%41
270
16th to endDay
28%15%28%12%10%3
270
May1st to 15thDay
36%10%30%10%10%1
288
16th to endDay
22%16%29%21%6%2
331
June1st to 15thDay
32%11%28%19%6%2
315
16th to endDay
25%8%36%20%8%
315
July1st to 15thDay
21%7%34%24%9%2
305
16th to endDay
17%435%29%11%1
326
August1st to 15thDay
25%7%23%25%15%2
313
16th to endDay
17%9%28%18%17%8%
332
September1st to 15thDay
21%7%23%25%13%8%
315
16th to endDay
21%11%28%18%12%7%
257
October1st to 15thDay
26%10%29%18%10%4
254
16th to endDay
36%14%22%17%9%
240
November1st to 15thDay
29%14%26%19%8%1
235
16th to endDay
32%19%21%16%7%2
115
December1st to 15thDay
43%13%26%13%3
60
16th to endDay
42%29%21%6%
64
January1st to 15thNight
29%18%30%16%4
720
16th to endNight
24%17%32%19%5%
768
February1st to 15thNight
21%16%34%22%3
704
16th to endNight
25%16%33%19%4
631
March1st to 15thNight
28%14%32%20%2
720
16th to endNight
24%14%27%24%7%1
768
April1st to 15thNight
31%14%26%22%5%
718
16th to endNight
29%14%26%21%7%
582
May1st to 15thNight
26%9%30%23%8%1
442
16th to endNight
23%10%31%25%8%
375
June1st to 15thNight
32%6%22%28%10%
360
16th to endNight
20%430%31%12%
360
July1st to 15thNight
16%327%34%16%1
340
16th to endNight
15%225%43%13%
376
August1st to 15thNight
22%320%32%21%
401
16th to endNight
18%323%36%15%2
702
September1st to 15thNight
23%5%23%30%14%1
720
16th to endNight
21%6%27%25%16%1
661
October1st to 15thNight
25%11%28%23%10%1
660
16th to endNight
35%11%27%20%4
704
November1st to 15thNight
27%14%30%19%8%
700
16th to endNight
32%17%23%15%9%1
720
December1st to 15thNight
33%17%30%14%4
720
16th to endNight
36%16%26%16%3
768
Page generated at 2017-09-17 12:05:47. Version ac04

Copyright 2017 A. Danko


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