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 2005-11-06 to 2024-01-17.

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
27%
22957
18%
74865
8%
22913
39%
22913
19%
49403

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
20%
760
18%
2649
7%
757
34%
757
17%
1711
January11th to 20thNight
19%
748
15%
2616
5%
748
31%
748
11%
1826
January21st to endNight
17%
792
20%
2772
6%
792
35%
792
17%
1740
February1st to 10thNight
18%
720
15%
2376
6%
720
32%
720
14%
1646
February11th to 20thNight
15%
702
19%
2121
4%
700
33%
700
17%
1433
February21st to endNight
19%
592
22%
1776
7%
592
38%
592
19%
1188
March1st to 10thNight
17%
720
20%
2160
6%
720
34%
720
17%
1496
March11th to 20thNight
21%
720
17%
2012
5%
720
33%
720
18%
1400
March21st to endNight
22%
792
21%
2134
6%
792
34%
792
21%
1464
April1st to 10thNight
20%
720
18%
1800
4%
720
28%
720
19%
1320
April11th to 20thNight
23%
601
19%
1665
5%
601
34%
601
21%
1132
April21st to endNight
20%
540
15%
1620
5%
540
28%
540
17%
1141
May1st to 10thNight
24%
540
15%
1620
7%
540
31%
540
17%
1144
May11th to 20thNight
23%
502
16%
1564
8%
502
34%
502
18%
1084
May21st to endNight
31%
389
12%
1551
11%
388
41%
388
17%
1011
June1st to 10thNight
28%
360
13%
1329
11%
360
39%
360
16%
897
June11th to 20thNight
41%
360
14%
1260
14%
360
49%
360
23%
799
June21st to endNight
34%
360
10%
1342
9%
360
41%
360
18%
908
July1st to 10thNight
43%
350
12%
1400
13%
350
52%
350
22%
856
July11th to 20thNight
45%
348
14%
1392
17%
348
51%
348
23%
819
July21st to endNight
45%
394
16%
1486
15%
372
53%
372
24%
881
August1st to 10thNight
49%
494
14%
1558
10%
492
52%
492
26%
985
August11th to 20thNight
43%
532
18%
1596
10%
532
47%
532
26%
1026
August21st to endNight
46%
668
21%
1856
11%
668
51%
668
32%
1158
September1st to 10thNight
40%
720
20%
1845
7%
720
47%
720
36%
1161
September11th to 20thNight
40%
720
24%
1980
13%
720
49%
720
34%
1189
September21st to endNight
36%
720
25%
1980
13%
720
46%
720
28%
1258
October1st to 10thNight
36%
720
20%
1984
11%
720
44%
720
24%
1335
October11th to 20thNight
32%
720
20%
2230
10%
720
45%
720
23%
1441
October21st to endNight
23%
792
15%
2574
7%
792
34%
792
17%
1755
November1st to 10thNight
28%
740
22%
2407
11%
740
43%
740
22%
1535
November11th to 20thNight
25%
760
25%
2470
11%
760
44%
760
20%
1573
November21st to endNight
23%
807
19%
2569
6%
807
37%
807
17%
1663
December1st to 10thNight
19%
850
17%
2835
5%
850
32%
850
15%
1994
December11th to 20thNight
18%
850
17%
3431
5%
849
33%
849
13%
2271
December21st to endNight
18%
854
12%
4905
4%
841
33%
841
9%
3163

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%7%35%5%35%5%5%7%38%
74580
Night
18%8%36%5%3445%6%38%
75211
TransparencyDay
47%311%23%14%2
74285
Night
47%311%23%14%2
75041
SeeingDay
25%12%31%20%9%2
14201
Night
24%11%31%26%8%1
22967

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
16%8%36%6%35%6%47%36%
1517
11th to 20thDay
20%9%36%5%25%346%35%
1488
21st to endDay
14%10%46%5%35%5%5%5%39%
1584
February1st to 10thDay
17%10%36%5%35%5%5%6%34%
1582
11th to 20thDay
13%10%47%7%45%5%5%6%34%
1726
21st to endDay
15%11%46%5%45%46%6%34%
1480
March1st to 10thDay
16%9%36%6%26%46%5%36%
1797
11th to 20thDay
16%7%35%5%34446%42%
1947
21st to endDay
17%8%36%5%335%45%41%
2220
April1st to 10thDay
20%9%46%6%34446%35%
2160
11th to 20thDay
18%6%25%6%35%46%7%39%
2243
21st to endDay
22%8%46%7%35%445%32%
2340
May1st to 10thDay
23%8%36%5%35%45%6%34%
2340
11th to 20thDay
20%6%36%7%35%45%6%36%
2344
21st to endDay
16%6%35%5%346%6%8%38%
2725
June1st to 10thDay
23%7%35%5%35%6%6%8%30%
2623
11th to 20thDay
18%6%25%5%25%5%5%8%39%
2700
21st to endDay
24%6%35%5%35%5%5%8%32%
2610
July1st to 10thDay
15%6%25%6%35%7%5%8%39%
2520
11th to 20thDay
13%5%36%6%46%6%6%8%37%
2520
21st to endDay
14%5%36%6%46%5%7%9%37%
2744
August1st to 10thDay
14%425%6%35%5%7%9%40%
2350
11th to 20thDay
14%6%25%6%45%5%6%8%39%
2304
21st to endDay
12%5%25%5%345%5%8%46%
2498
September1st to 10thDay
12%5%25%435%45%7%47%
2114
11th to 20thDay
13%5%24434346%53%
1980
21st to endDay
17%5%2443446%7%45%
1980
October1st to 10thDay
19%6%26%435%447%39%
1976
11th to 20thDay
20%6%25%5%35%36%7%40%
1728
21st to endDay
24%8%37%5%33346%34%
1782
November1st to 10thDay
17%6%25%435%5%46%42%
1671
11th to 20thDay
21%5%244345%5%7%40%
1710
21st to endDay
21%7%24424346%43%
1606
December1st to 10thDay
22%11%36%434445%34%
1343
11th to 20thDay
23%9%35%423345%38%
1668
21st to endDay
25%13%245%3445%5%28%
2660
January1st to 10thNight
16%8%36%6%345%5%6%37%
2649
11th to 20thNight
16%13%49%5%445%5%5%31%
2616
21st to endNight
12%8%46%6%35%5%5%7%39%
2772
February1st to 10thNight
16%10%48%6%35%5%5%6%32%
2376
11th to 20thNight
13%10%47%6%35%446%38%
2119
21st to endNight
15%9%46%6%4445%6%38%
1776
March1st to 10thNight
15%11%46%6%35%5%5%5%36%
2150
11th to 20thNight
18%8%46%5%35%5%5%5%36%
2011
21st to endNight
19%8%36%5%24446%40%
2134
April1st to 10thNight
22%11%46%43443436%
1800
11th to 20thNight
18%6%36%5%36%45%6%38%
1665
21st to endNight
26%7%36%5%3345%6%32%
1620
May1st to 10thNight
22%9%45%5%35%45%7%31%
1620
11th to 20thNight
22%7%35%5%35%5%5%6%34%
1563
21st to endNight
18%7%36%6%25%5%5%7%34%
1550
June1st to 10thNight
23%8%35%6%35%35%9%31%
1329
11th to 20thNight
18%6%25%4345%6%8%38%
1260
21st to endNight
24%7%344246%6%7%32%
1342
July1st to 10thNight
16%6%345%25%6%6%10%37%
1440
11th to 20thNight
15%6%26%43445%10%40%
1440
21st to endNight
15%5%34435%6%6%9%39%
1574
August1st to 10thNight
14%5%26%5%36%5%6%8%41%
1568
11th to 20thNight
14%7%36%5%36%5%6%8%38%
1596
21st to endNight
14%5%25%5%2445%7%48%
1856
September1st to 10thNight
14%425%43445%7%49%
1845
11th to 20thNight
16%5%24323346%51%
1980
21st to endNight
16%5%25%435%447%46%
1980
October1st to 10thNight
19%6%25%5%4445%6%40%
1984
11th to 20thNight
18%6%25%5%35%5%5%6%40%
2230
21st to endNight
26%8%24434446%34%
2574
November1st to 10thNight
18%7%25%5%24446%42%
2407
11th to 20thNight
18%6%25%5%245%48%41%
2470
21st to endNight
18%7%26%5%3445%7%39%
2569
December1st to 10thNight
22%10%37%5%3445%5%33%
2835
11th to 20thNight
22%8%35%434445%38%
3531
21st to endNight
25%9%35%43445%6%33%
4980

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
48%310%23%15%1
1518
11th to 20thDay
51%312%19%12%3
1488
21st to endDay
47%210%21%17%2
1584
February1st to 10thDay
51%310%21%13%2
1582
11th to 20thDay
51%410%20%13%3
1735
21st to endDay
51%310%19%12%6%
1480
March1st to 10thDay
50%311%18%15%4
1800
11th to 20thDay
46%28%21%18%5%
1947
21st to endDay
46%39%19%18%6%
2220
April1st to 10thDay
53%37%18%15%5%
2160
11th to 20thDay
45%38%25%16%3
2243
21st to endDay
55%27%19%13%4
2340
May1st to 10thDay
52%26%23%14%3
2340
11th to 20thDay
49%36%22%16%3
2348
21st to endDay
45%414%23%13%2
2725
June1st to 10thDay
52%312%23%10%
2623
11th to 20thDay
45%311%23%17%2
2700
21st to endDay
52%412%20%11%1
2610
July1st to 10thDay
41%414%26%14%1
2450
11th to 20thDay
43%5%13%28%11%1
2445
21st to endDay
43%414%25%13%1
2591
August1st to 10thDay
41%415%29%11%
2336
11th to 20thDay
43%414%27%12%
2304
21st to endDay
36%313%25%20%2
2498
September1st to 10thDay
36%412%29%18%1
2114
11th to 20thDay
33%28%31%23%2
1980
21st to endDay
38%311%30%17%1
1980
October1st to 10thDay
46%39%25%15%1
1976
11th to 20thDay
45%312%29%10%1
1728
21st to endDay
53%210%20%13%2
1782
November1st to 10thDay
43%312%23%16%2
1671
11th to 20thDay
43%49%23%18%4
1710
21st to endDay
45%215%24%13%1
1606
December1st to 10thDay
53%39%22%12%1
1343
11th to 20thDay
50%47%22%15%3
1668
21st to endDay
60%29%19%8%3
2660
January1st to 10thNight
48%311%25%13%1
2649
11th to 20thNight
54%412%17%11%2
2616
21st to endNight
45%38%24%17%3
2772
February1st to 10thNight
53%311%18%13%3
2376
11th to 20thNight
48%39%22%16%3
2121
21st to endNight
48%28%21%16%4
1776
March1st to 10thNight
51%36%22%15%3
2160
11th to 20thNight
49%49%18%16%4
2012
21st to endNight
47%28%19%19%4
2134
April1st to 10thNight
53%26%18%16%4
1800
11th to 20thNight
47%47%24%18%1
1665
21st to endNight
53%311%17%13%3
1620
May1st to 10thNight
52%47%20%15%2
1620
11th to 20thNight
50%49%21%13%3
1564
21st to endNight
50%313%21%12%1
1551
June1st to 10thNight
53%310%24%10%1
1329
11th to 20thNight
45%314%23%13%2
1260
21st to endNight
50%5%13%21%9%2
1342
July1st to 10thNight
43%5%16%24%12%1
1400
11th to 20thNight
42%316%29%10%
1392
21st to endNight
40%417%25%12%1
1486
August1st to 10thNight
41%5%16%28%10%
1558
11th to 20thNight
42%5%17%22%14%
1596
21st to endNight
36%413%29%17%1
1856
September1st to 10thNight
36%314%30%17%
1845
11th to 20thNight
35%310%33%18%2
1980
21st to endNight
40%39%31%14%2
1980
October1st to 10thNight
45%410%25%14%1
1984
11th to 20thNight
44%413%27%12%1
2230
21st to endNight
51%311%20%13%1
2574
November1st to 10thNight
45%310%26%15%1
2407
11th to 20thNight
43%49%25%16%3
2470
21st to endNight
45%313%22%15%2
2569
December1st to 10thNight
54%38%22%12%1
2835
11th to 20thNight
50%39%19%18%1
3532
21st to endNight
54%211%20%11%1
4980

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
30%16%31%17%6%
180
11th to 20thDay
34%15%29%17%5%1
172
21st to endDay
24%18%34%21%21
176
February1st to 10thDay
31%16%31%18%3
302
11th to 20thDay
28%19%36%16%2
406
21st to endDay
25%18%34%19%4
346
March1st to 10thDay
28%16%36%16%4
420
11th to 20thDay
28%21%34%13%4
420
21st to endDay
27%19%30%14%8%2
462
April1st to 10thDay
34%15%31%13%6%1
420
11th to 20thDay
31%17%31%14%5%3
412
21st to endDay
33%16%28%16%5%3
420
May1st to 10thDay
33%16%27%20%32
423
11th to 20thDay
23%17%33%18%6%2
447
21st to endDay
22%15%36%20%8%1
485
June1st to 10thDay
24%11%31%22%10%2
553
11th to 20thDay
23%11%28%23%13%3
630
21st to endDay
24%9%29%26%11%2
540
July1st to 10thDay
20%8%31%27%11%3
445
11th to 20thDay
15%5%37%24%14%5%
444
21st to endDay
15%5%36%29%12%3
488
August1st to 10thDay
13%7%30%30%16%4
446
11th to 20thDay
17%6%29%26%16%6%
439
21st to endDay
16%8%31%27%14%5%
495
September1st to 10thDay
17%8%31%24%18%4
450
11th to 20thDay
20%11%27%21%14%8%
450
21st to endDay
19%10%30%23%12%5%
450
October1st to 10thDay
24%12%25%23%12%4
448
11th to 20thDay
28%10%32%17%11%3
360
21st to endDay
34%9%30%18%8%1
396
November1st to 10thDay
26%12%30%21%10%2
365
11th to 20thDay
30%12%30%21%6%1
370
21st to endDay
31%16%25%20%7%1
370
December1st to 10thDay
31%13%34%16%6%
193
11th to 20thDay
37%14%38%7%4
180
21st to endDay
35%15%28%16%7%1
198
January1st to 10thNight
24%14%35%25%3
760
11th to 20thNight
28%16%30%22%4
748
21st to endNight
18%18%37%22%4
792
February1st to 10thNight
24%15%33%24%4
720
11th to 20thNight
23%18%35%20%3
703
21st to endNight
23%12%36%24%4
592
March1st to 10thNight
26%14%38%20%2
720
11th to 20thNight
25%14%33%20%7%
720
21st to endNight
25%15%31%22%5%1
792
April1st to 10thNight
30%14%31%21%4
720
11th to 20thNight
23%14%34%22%5%
601
21st to endNight
32%11%32%21%5%
540
May1st to 10thNight
27%10%29%27%6%
540
11th to 20thNight
25%11%36%24%4
502
21st to endNight
22%7%31%34%5%1
389
June1st to 10thNight
27%431%30%7%1
360
11th to 20thNight
20%6%27%36%10%
360
21st to endNight
27%328%33%10%
360
July1st to 10thNight
19%230%36%13%1
350
11th to 20thNight
20%127%39%13%1
348
21st to endNight
16%327%37%16%1
394
August1st to 10thNight
15%326%41%14%1
494
11th to 20thNight
16%426%35%18%1
532
21st to endNight
17%7%21%37%16%2
668
September1st to 10thNight
17%433%29%15%1
720
11th to 20thNight
19%7%27%27%17%3
720
21st to endNight
21%8%29%28%12%2
720
October1st to 10thNight
22%8%26%28%14%1
720
11th to 20thNight
22%10%30%27%10%1
720
21st to endNight
32%11%29%22%6%
792
November1st to 10thNight
25%10%31%27%7%1
740
11th to 20thNight
23%12%33%23%9%1
760
21st to endNight
25%17%29%24%5%
807
December1st to 10thNight
29%12%33%19%6%
850
11th to 20thNight
26%16%32%21%5%
850
21st to endNight
30%13%32%22%3
863
Page generated at 2024-01-14 09:54:58. Version ac07

Copyright 2024 Attilla Danko


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