L'Observatoire des Lacs
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the L'Observatoire des Lacs clear sky chart from 2005-11-05 to 2017-10-31.

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
28%
14964
17%
47412
8%
14933
38%
14933
20%
31467

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
23%
720
18%
2506
8%
716
37%
716
18%
1601
January16th to endNight
17%
768
18%
2688
5%
768
34%
768
14%
1756
February1st to 15thNight
19%
703
14%
2270
5%
701
31%
701
14%
1591
February16th to endNight
19%
631
19%
1893
6%
631
35%
631
18%
1291
March1st to 15thNight
17%
720
16%
2121
4%
720
30%
720
16%
1519
March16th to endNight
26%
768
20%
2082
7%
768
36%
768
23%
1385
April1st to 15thNight
21%
703
17%
1781
4%
703
29%
703
19%
1298
April16th to endNight
23%
540
16%
1620
5%
540
32%
540
19%
1110
May1st to 15thNight
26%
540
14%
1620
8%
540
34%
540
17%
1154
May16th to endNight
26%
411
11%
1533
9%
410
35%
410
14%
1065
June1st to 15thNight
30%
360
10%
1305
8%
360
37%
360
15%
927
June16th to endNight
38%
360
10%
1314
10%
360
45%
360
22%
846
July1st to 15thNight
44%
340
10%
1360
13%
340
49%
340
21%
831
July16th to endNight
43%
376
13%
1418
12%
354
50%
354
23%
854
August1st to 15thNight
45%
511
13%
1582
8%
509
49%
509
24%
1027
August16th to endNight
47%
623
21%
1769
12%
623
51%
623
33%
1075
September1st to 15thNight
39%
720
19%
1890
9%
720
45%
720
34%
1190
September16th to endNight
41%
717
28%
1980
16%
717
51%
717
33%
1187
October1st to 15thNight
35%
720
21%
2043
10%
720
45%
720
26%
1324
October16th to endNight
23%
768
16%
2482
7%
768
36%
768
19%
1664
November1st to 15thNight
30%
700
21%
2277
11%
700
44%
700
22%
1466
November16th to endNight
26%
731
20%
2403
9%
731
39%
731
17%
1567
December1st to 15thNight
19%
750
16%
2691
6%
750
33%
750
14%
1843
December16th to endNight
18%
784
17%
2784
5%
784
33%
784
14%
1896

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%6%25%5%34446%37%
48331
Night
18%7%35%424446%37%
47582
TransparencyDay
46%310%23%14%1
48019
Night
47%311%23%13%1
47412
SeeingDay
24%11%29%21%10%3
6276
Night
23%10%30%25%8%
14965

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
17%6%35%5%245%47%36%
1432
16th to endDay
15%10%25%5%25%5%46%37%
1536
February1st to 15thDay
15%9%37%6%35%45%5%32%
1589
16th to endDay
14%11%36%5%45%45%6%33%
1580
March1st to 15thDay
19%9%36%5%3434434%
1829
16th to endDay
16%7%34423445%42%
2142
April1st to 15thDay
19%6%35%5%24446%36%
2167
16th to endDay
19%6%35%5%24345%38%
2340
May1st to 15thDay
25%7%25%5%24445%30%
2332
16th to endDay
21%5%25%5%345%5%6%33%
2590
June1st to 15thDay
27%7%244245%47%28%
2649
16th to endDay
21%5%25%5%35%5%47%33%
2640
July1st to 15thDay
13%5%246%36%6%5%8%36%
2520
16th to endDay
13%5%36%5%46%6%6%7%34%
2654
August1st to 15thDay
14%425%5%345%6%8%38%
2355
16th to endDay
12%414434448%46%
2432
September1st to 15thDay
13%5%24434345%46%
2068
16th to endDay
14%413323347%51%
1980
October1st to 15thDay
19%5%14335%347%40%
1917
16th to endDay
21%6%26%5%33335%38%
1740
November1st to 15thDay
20%5%24425%5%47%37%
1581
16th to endDay
21%6%25%5%2223442%
1554
December1st to 15thDay
23%9%24323445%34%
1269
16th to endDay
23%12%35%5%2234431%
1435
January1st to 15thNight
14%9%35%5%2445%6%38%
2506
16th to endNight
14%9%47%5%2445%6%35%
2688
February1st to 15thNight
12%9%48%7%35%45%6%31%
2269
16th to endNight
16%9%45%5%2344437%
1893
March1st to 15thNight
19%10%35%5%2444334%
2108
16th to endNight
17%6%35%423335%42%
2082
April1st to 15thNight
20%8%36%5%2433436%
1781
16th to endNight
23%5%35%43435%6%34%
1620
May1st to 15thNight
23%8%345%2445%6%32%
1620
16th to endNight
23%7%36%5%2445%7%28%
1531
June1st to 15thNight
25%7%35%5%34447%28%
1305
16th to endNight
20%5%243235%6%8%36%
1314
July1st to 15thNight
15%6%35%5%245%5%9%35%
1440
16th to endNight
14%5%25%435%5%5%10%38%
1514
August1st to 15thNight
13%6%25%5%36%5%5%7%38%
1592
16th to endNight
12%42442435%7%48%
1769
September1st to 15thNight
15%424323346%48%
1890
16th to endNight
13%414324337%51%
1980
October1st to 15thNight
18%5%25%32445%5%42%
2043
16th to endNight
22%7%245%24445%36%
2482
November1st to 15thNight
19%6%25%424447%38%
2277
16th to endNight
18%6%16%433345%39%
2403
December1st to 15thNight
21%10%35%5%2443434%
2691
16th to endNight
22%11%34333345%32%
2784

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
46%311%22%13%2
1433
16th to endDay
46%211%23%13%1
1536
February1st to 15thDay
53%210%20%11%1
1592
16th to endDay
50%310%18%13%3
1580
March1st to 15thDay
52%210%18%13%2
1839
16th to endDay
43%29%20%19%4
2142
April1st to 15thDay
49%26%21%17%3
2167
16th to endDay
46%38%21%14%3
2340
May1st to 15thDay
54%27%20%12%2
2332
16th to endDay
50%411%21%11%1
2594
June1st to 15thDay
55%310%20%9%
2649
16th to endDay
50%310%20%13%
2640
July1st to 15thDay
41%5%13%27%11%
2371
16th to endDay
45%5%13%23%11%
2487
August1st to 15thDay
42%414%28%9%
2341
16th to endDay
35%314%26%19%1
2432
September1st to 15thDay
38%39%27%18%1
2068
16th to endDay
33%28%31%22%1
1980
October1st to 15thDay
44%29%26%14%1
1917
16th to endDay
48%29%26%12%1
1740
November1st to 15thDay
45%412%21%14%1
1581
16th to endDay
46%311%21%15%1
1554
December1st to 15thDay
51%312%21%10%
1269
16th to endDay
56%28%18%12%1
1435
January1st to 15thNight
45%312%24%11%1
2506
16th to endNight
48%39%22%14%2
2688
February1st to 15thNight
53%311%19%11%1
2270
16th to endNight
49%210%21%14%2
1893
March1st to 15thNight
53%37%20%12%2
2121
16th to endNight
43%29%19%19%4
2082
April1st to 15thNight
51%35%19%17%2
1781
16th to endNight
50%310%18%14%3
1620
May1st to 15thNight
52%46%19%14%2
1620
16th to endNight
54%311%18%9%1
1533
June1st to 15thNight
56%311%19%8%1
1305
16th to endNight
44%414%23%11%1
1314
July1st to 15thNight
43%416%24%11%
1360
16th to endNight
41%417%24%10%
1418
August1st to 15thNight
43%416%24%10%
1582
16th to endNight
34%414%29%15%
1769
September1st to 15thNight
37%211%31%15%1
1890
16th to endNight
33%38%34%17%1
1980
October1st to 15thNight
42%311%26%14%1
2043
16th to endNight
48%312%24%11%
2482
November1st to 15thNight
45%211%23%14%1
2277
16th to endNight
46%310%23%14%1
2403
December1st to 15thNight
53%28%24%11%
2691
16th to endNight
53%210%21%12%
2784

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
25%15%28%20%11%
60
16th to endDay
21%20%34%18%4
64
February1st to 15thDay
27%14%32%20%4
217
16th to endDay
20%17%32%22%6%
239
March1st to 15thDay
31%15%33%15%4
270
16th to endDay
25%20%29%12%8%3
288
April1st to 15thDay
28%13%33%15%5%3
270
16th to endDay
25%16%28%16%6%5%
270
May1st to 15thDay
37%10%22%20%6%2
288
16th to endDay
27%10%33%20%6%1
331
June1st to 15thDay
29%9%26%22%11%
444
16th to endDay
20%7%31%27%10%2
435
July1st to 15thDay
16%6%32%24%14%4
305
16th to endDay
14%433%28%15%4
326
August1st to 15thDay
15%8%25%29%17%3
313
16th to endDay
15%8%24%25%18%7%
332
September1st to 15thDay
20%5%28%24%15%4
315
16th to endDay
18%7%26%19%15%12%
314
October1st to 15thDay
22%11%23%23%13%5%
299
16th to endDay
28%8%33%20%8%
288
November1st to 15thDay
24%12%28%21%10%2
235
16th to endDay
31%14%22%21%9%1
240
December1st to 15thDay
31%7%39%15%5%
69
16th to endDay
35%15%31%15%1
64
January1st to 15thNight
21%14%33%27%3
720
16th to endNight
23%17%32%22%3
768
February1st to 15thNight
19%16%34%25%3
704
16th to endNight
22%14%33%23%5%
631
March1st to 15thNight
29%12%36%17%3
720
16th to endNight
22%16%29%24%7%
768
April1st to 15thNight
25%15%33%20%5%
703
16th to endNight
27%12%30%22%5%
540
May1st to 15thNight
27%9%29%26%7%
540
16th to endNight
26%8%30%29%4
411
June1st to 15thNight
28%5%27%31%7%
360
16th to endNight
22%427%35%10%
360
July1st to 15thNight
17%29%34%16%
340
16th to endNight
16%227%36%16%1
376
August1st to 15thNight
14%426%37%16%
511
16th to endNight
15%424%34%18%2
623
September1st to 15thNight
17%432%29%13%2
720
16th to endNight
17%7%28%26%16%3
717
October1st to 15thNight
22%8%28%26%13%1
720
16th to endNight
28%12%31%20%7%
768
November1st to 15thNight
24%8%30%26%8%1
700
16th to endNight
22%15%28%23%9%
731
December1st to 15thNight
29%12%32%21%5%
750
16th to endNight
30%11%32%21%3
784
Page generated at 2017-11-01 17:23:42. Version ac04

Copyright 2017 A. Danko


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