Lac de la Montagne noire
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lac de la Montagne noire clear sky chart from 2005-11-06 to 2024-01-14.

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
25%
22479
13%
74739
7%
22437
33%
22437
15%
53310

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
10%
760
9%
2649
1%
757
18%
757
7%
2122
January11th to 20thNight
16%
735
10%
2569
3%
735
24%
735
9%
1957
January21st to endNight
19%
792
14%
2772
7%
792
29%
792
12%
1975
February1st to 10thNight
13%
720
12%
2372
4%
720
23%
720
10%
1794
February11th to 20thNight
13%
703
12%
2217
3%
700
24%
700
11%
1640
February21st to endNight
18%
592
14%
1776
6%
592
29%
592
14%
1297
March1st to 10thNight
17%
720
14%
2160
7%
720
26%
720
13%
1619
March11th to 20thNight
18%
720
14%
2066
5%
720
27%
720
14%
1530
March21st to endNight
24%
792
20%
2003
7%
792
33%
792
19%
1426
April1st to 10thNight
22%
720
14%
1800
4%
720
27%
720
18%
1350
April11th to 20thNight
26%
711
17%
1775
6%
711
32%
711
22%
1237
April21st to endNight
23%
585
15%
1665
7%
585
29%
585
16%
1182
May1st to 10thNight
28%
360
16%
1440
12%
360
40%
360
17%
945
May11th to 20thNight
29%
354
19%
1416
15%
354
46%
354
17%
897
May21st to endNight
28%
389
11%
1551
8%
388
40%
388
17%
993
June1st to 10thNight
29%
360
9%
1440
8%
360
39%
360
15%
952
June11th to 20thNight
38%
360
10%
1440
11%
360
44%
360
18%
903
June21st to endNight
43%
360
9%
1440
13%
360
48%
360
17%
959
July1st to 10thNight
45%
350
11%
1400
14%
350
52%
350
24%
810
July11th to 20thNight
47%
348
12%
1392
16%
348
52%
348
23%
825
July21st to endNight
48%
394
13%
1486
15%
372
52%
372
22%
897
August1st to 10thNight
54%
358
14%
1422
14%
356
59%
356
23%
851
August11th to 20thNight
49%
505
16%
1569
11%
505
54%
505
27%
995
August21st to endNight
41%
792
16%
1980
7%
792
45%
792
29%
1328
September1st to 10thNight
40%
720
15%
1800
6%
720
44%
720
31%
1193
September11th to 20thNight
43%
720
19%
1854
10%
720
47%
720
32%
1201
September21st to endNight
38%
720
20%
1980
13%
720
44%
720
27%
1303
October1st to 10thNight
31%
720
19%
2133
11%
720
40%
720
18%
1479
October11th to 20thNight
23%
720
13%
2186
6%
720
31%
720
15%
1600
October21st to endNight
19%
792
10%
2574
5%
792
26%
792
12%
1925
November1st to 10thNight
21%
740
14%
2407
6%
740
31%
740
13%
1731
November11th to 20thNight
20%
760
15%
2598
10%
760
27%
760
11%
1920
November21st to endNight
16%
760
10%
2660
5%
760
23%
760
8%
2036
December1st to 10thNight
13%
760
7%
2660
3%
760
19%
760
7%
2174
December11th to 20thNight
13%
760
11%
3246
4%
759
20%
759
6%
2505
December21st to endNight
12%
827
7%
4841
3%
817
19%
817
4%
3759

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%11%5%8%6%35%5%5%6%29%
74757
Night
16%12%5%8%6%35%45%6%29%
74995
TransparencyDay
56%411%19%9%1
74462
Night
54%412%19%9%1
74824
SeeingDay
26%17%31%18%6%2
13380
Night
23%15%29%23%9%1
22488

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
14%17%10%12%9%45%43417%
1517
11th to 20thDay
15%18%7%11%7%44345%22%
1464
21st to endDay
10%13%7%12%7%35%5%5%5%26%
1584
February1st to 10thDay
9%19%6%10%11%5%4446%21%
1586
11th to 20thDay
12%17%6%12%8%35%435%25%
1630
21st to endDay
14%18%7%11%7%35%445%23%
1480
March1st to 10thDay
13%13%6%10%8%5%4446%26%
1797
11th to 20thDay
14%15%5%9%8%36%446%27%
1890
21st to endDay
18%11%48%6%34446%33%
2353
April1st to 10thDay
19%15%5%8%6%33446%28%
2160
11th to 20thDay
21%9%47%5%35%345%33%
2134
21st to endDay
20%12%48%5%44446%29%
2311
May1st to 10thDay
20%11%47%6%3445%7%30%
2520
11th to 20thDay
20%8%47%7%4445%6%32%
2478
21st to endDay
20%8%36%5%35%5%5%7%32%
2725
June1st to 10thDay
24%9%37%5%36%6%6%6%26%
2520
11th to 20thDay
17%7%37%7%45%6%5%8%32%
2520
21st to endDay
23%8%36%8%45%5%6%6%26%
2520
July1st to 10thDay
15%6%46%6%35%6%6%8%35%
2520
11th to 20thDay
15%6%36%6%47%5%7%9%32%
2520
21st to endDay
14%8%36%7%36%6%7%9%31%
2744
August1st to 10thDay
15%8%37%7%45%7%7%7%29%
2506
11th to 20thDay
16%6%36%7%36%7%7%8%33%
2311
21st to endDay
14%8%37%5%445%6%9%36%
2376
September1st to 10thDay
17%6%36%6%3445%7%38%
2160
11th to 20thDay
16%5%36%5%35%45%7%40%
2106
21st to endDay
20%9%35%43445%6%38%
1980
October1st to 10thDay
24%9%35%6%345%5%6%31%
1823
11th to 20thDay
25%12%48%7%3445%5%23%
1774
21st to endDay
26%14%5%8%6%24435%23%
1782
November1st to 10thDay
17%13%5%7%5%35%446%30%
1671
11th to 20thDay
20%15%6%9%7%3445%5%21%
1577
21st to endDay
18%18%6%11%7%44435%20%
1520
December1st to 10thDay
21%19%7%11%7%3343418%
1520
11th to 20thDay
18%17%7%11%7%34445%19%
1906
21st to endDay
20%19%7%10%6%33345%19%
2772
January1st to 10thNight
14%18%9%13%8%45%5%45%16%
2649
11th to 20thNight
14%17%7%11%8%44447%20%
2569
21st to endNight
9%12%6%10%8%5%6%46%7%26%
2772
February1st to 10thNight
11%15%6%12%9%5%6%5%46%23%
2372
11th to 20thNight
11%14%6%12%8%45%5%5%5%25%
2215
21st to endNight
13%14%6%10%7%45%5%6%6%25%
1776
March1st to 10thNight
14%13%411%7%46%5%46%26%
2150
11th to 20thNight
15%14%5%8%7%4445%5%28%
2065
21st to endNight
15%10%47%5%35%5%46%36%
2003
April1st to 10thNight
22%11%47%6%3345%6%29%
1800
11th to 20thNight
17%8%37%5%35%5%5%6%37%
1775
21st to endNight
20%9%47%6%35%45%6%32%
1665
May1st to 10thNight
19%10%45%5%35%447%35%
1440
11th to 20thNight
19%8%35%434447%38%
1415
21st to endNight
16%7%36%5%35%46%7%37%
1550
June1st to 10thNight
18%9%36%5%35%6%6%8%31%
1440
11th to 20thNight
19%6%35%5%4445%8%37%
1440
21st to endNight
20%7%26%5%35%5%6%7%35%
1440
July1st to 10thNight
12%6%25%6%245%48%44%
1440
11th to 20thNight
13%5%36%5%36%5%6%9%40%
1440
21st to endNight
12%6%246%446%7%8%41%
1574
August1st to 10thNight
11%7%25%5%346%7%8%40%
1432
11th to 20thNight
11%7%27%5%35%6%5%7%42%
1569
21st to endNight
15%6%245%35%5%6%8%41%
1980
September1st to 10thNight
14%7%35%435%45%7%44%
1800
11th to 20thNight
17%6%2442445%7%45%
1854
21st to endNight
18%7%25%5%3345%7%43%
1980
October1st to 10thNight
17%10%35%6%35%45%5%37%
2133
11th to 20thNight
22%12%47%5%44446%29%
2186
21st to endNight
23%13%47%7%34347%24%
2574
November1st to 10thNight
18%12%47%7%35%46%5%28%
2407
11th to 20thNight
16%12%5%10%7%45%5%6%7%22%
2598
21st to endNight
18%18%6%9%7%3445%6%21%
2660
December1st to 10thNight
18%15%8%15%9%34345%15%
2660
11th to 20thNight
19%16%6%11%8%34345%21%
3288
21st to endNight
20%20%6%9%8%3434418%
4884

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
70%28%14%5%
1518
11th to 20thDay
65%37%14%10%2
1464
21st to endDay
58%5%7%17%10%3
1584
February1st to 10thDay
64%37%16%8%2
1586
11th to 20thDay
62%39%13%11%1
1639
21st to endDay
64%28%14%9%3
1480
March1st to 10thDay
60%47%17%9%3
1800
11th to 20thDay
59%39%15%11%3
1890
21st to endDay
53%49%17%13%4
2353
April1st to 10thDay
58%39%16%11%3
2160
11th to 20thDay
55%38%21%11%2
2134
21st to endDay
58%38%16%11%4
2311
May1st to 10thDay
55%47%21%12%2
2520
11th to 20thDay
53%38%19%14%2
2482
21st to endDay
52%411%19%12%1
2725
June1st to 10thDay
57%6%9%18%9%1
2520
11th to 20thDay
50%5%12%20%10%3
2520
21st to endDay
58%6%10%17%9%
2520
July1st to 10thDay
45%6%15%25%9%
2450
11th to 20thDay
45%6%16%23%9%
2445
21st to endDay
49%6%15%23%8%
2591
August1st to 10thDay
50%7%17%22%4
2492
11th to 20thDay
46%7%17%22%7%
2311
21st to endDay
44%5%15%24%11%1
2376
September1st to 10thDay
45%5%14%24%13%
2160
11th to 20thDay
43%6%13%27%10%1
2106
21st to endDay
47%5%13%25%10%
1980
October1st to 10thDay
54%411%21%10%1
1823
11th to 20thDay
63%5%10%17%41
1774
21st to endDay
65%311%13%7%1
1782
November1st to 10thDay
55%413%19%8%1
1671
11th to 20thDay
64%311%14%7%1
1577
21st to endDay
68%410%13%5%1
1520
December1st to 10thDay
70%310%12%5%
1520
11th to 20thDay
67%310%14%6%1
1906
21st to endDay
68%28%15%7%
2772
January1st to 10thNight
70%38%14%4
2649
11th to 20thNight
64%311%12%7%3
2569
21st to endNight
56%39%17%12%2
2772
February1st to 10thNight
61%49%19%6%2
2372
11th to 20thNight
59%311%17%8%1
2217
21st to endNight
57%310%18%10%2
1776
March1st to 10thNight
59%39%17%9%2
2160
11th to 20thNight
57%310%15%13%1
2066
21st to endNight
49%49%20%14%4
2003
April1st to 10thNight
55%39%19%12%2
1800
11th to 20thNight
46%412%23%13%2
1775
21st to endNight
52%49%20%13%2
1665
May1st to 10thNight
50%39%21%13%3
1440
11th to 20thNight
47%410%20%16%3
1416
21st to endNight
45%6%13%22%12%3
1551
June1st to 10thNight
50%5%13%23%9%
1440
11th to 20thNight
46%413%23%12%3
1440
21st to endNight
48%6%13%21%11%
1440
July1st to 10thNight
37%6%19%26%11%1
1400
11th to 20thNight
40%5%18%28%9%1
1392
21st to endNight
38%8%19%26%9%
1486
August1st to 10thNight
38%7%21%27%7%
1422
11th to 20thNight
40%5%20%25%10%
1569
21st to endNight
41%5%18%26%9%
1980
September1st to 10thNight
40%416%27%13%1
1800
11th to 20thNight
38%5%16%32%9%1
1854
21st to endNight
41%5%15%28%11%
1980
October1st to 10thNight
49%5%10%23%12%1
2133
11th to 20thNight
56%313%20%7%
2186
21st to endNight
60%412%17%7%1
2574
November1st to 10thNight
55%414%19%6%1
2407
11th to 20thNight
58%5%11%17%7%2
2598
21st to endNight
63%412%15%5%1
2660
December1st to 10thNight
72%310%11%4
2660
11th to 20thNight
66%38%15%7%1
3288
21st to endNight
70%37%14%6%1
4884

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
19%21%38%18%3
180
11th to 20thDay
27%17%36%14%5%1
166
21st to endDay
22%20%37%16%5%1
176
February1st to 10thDay
35%29%31%41
226
11th to 20thDay
28%25%38%8%
297
21st to endDay
31%23%31%14%2
346
March1st to 10thDay
26%20%32%18%3
420
11th to 20thDay
29%21%32%13%31
420
21st to endDay
33%19%26%14%5%2
462
April1st to 10thDay
33%15%31%13%6%1
420
11th to 20thDay
36%16%24%15%8%1
412
21st to endDay
32%19%32%12%41
420
May1st to 10thDay
30%19%31%16%22
423
11th to 20thDay
26%20%29%17%6%2
447
21st to endDay
26%19%31%18%5%1
485
June1st to 10thDay
28%15%35%15%6%1
450
11th to 20thDay
23%18%29%19%9%2
450
21st to endDay
27%12%32%19%8%1
450
July1st to 10thDay
17%9%39%25%7%2
445
11th to 20thDay
18%9%40%27%6%
444
21st to endDay
17%12%34%27%8%2
488
August1st to 10thDay
16%12%30%28%12%1
446
11th to 20thDay
18%8%32%26%10%6%
439
21st to endDay
19%15%31%17%11%7%
495
September1st to 10thDay
19%14%31%21%10%5%
450
11th to 20thDay
16%14%28%23%12%6%
450
21st to endDay
24%14%26%19%11%6%
450
October1st to 10thDay
29%16%25%17%9%3
450
11th to 20thDay
35%18%24%16%6%1
437
21st to endDay
36%14%28%16%5%
396
November1st to 10thDay
33%17%28%17%41
365
11th to 20thDay
30%22%30%12%7%
237
21st to endDay
31%26%30%11%3
180
December1st to 10thDay
33%16%29%17%41
180
11th to 20thDay
28%29%31%10%21
180
21st to endDay
37%22%24%11%33
198
January1st to 10thNight
25%22%33%15%5%
760
11th to 20thNight
26%18%29%21%6%
735
21st to endNight
16%16%37%22%7%1
792
February1st to 10thNight
20%23%34%19%4
720
11th to 20thNight
22%21%37%16%3
703
21st to endNight
24%18%33%22%3
592
March1st to 10thNight
26%18%33%19%4
720
11th to 20thNight
25%20%32%16%5%1
720
21st to endNight
24%15%31%22%7%1
792
April1st to 10thNight
30%16%27%22%5%
720
11th to 20thNight
24%17%29%22%6%1
711
21st to endNight
28%13%30%20%8%1
585
May1st to 10thNight
24%12%29%23%9%2
360
11th to 20thNight
21%15%28%27%8%1
354
21st to endNight
18%12%37%24%9%
389
June1st to 10thNight
22%10%32%27%8%
360
11th to 20thNight
21%9%26%29%14%1
360
21st to endNight
22%423%35%16%1
360
July1st to 10thNight
14%5%30%34%17%
350
11th to 20thNight
14%5%26%38%16%1
348
21st to endNight
13%6%28%37%15%1
394
August1st to 10thNight
13%6%19%44%17%1
358
11th to 20thNight
13%5%23%34%23%2
505
21st to endNight
17%8%28%27%16%3
792
September1st to 10thNight
18%8%29%30%14%1
720
11th to 20thNight
20%8%24%30%18%2
720
21st to endNight
21%12%25%24%16%2
720
October1st to 10thNight
23%15%24%23%13%1
720
11th to 20thNight
28%14%28%19%9%1
720
21st to endNight
29%17%28%20%6%
792
November1st to 10thNight
26%18%29%19%6%1
740
11th to 20thNight
25%19%29%17%9%1
760
21st to endNight
30%21%25%17%5%1
760
December1st to 10thNight
29%19%27%17%7%1
760
11th to 20thNight
29%20%28%17%5%1
760
21st to endNight
33%18%27%17%5%
836
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