Lac Lasalle
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lac Lasalle clear sky chart from 2005-11-06 to 2024-02-10.

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%
22586
13%
80560
7%
22496
34%
22496
14%
57857

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
11%
755
8%
4391
2%
737
20%
737
4%
3320
January11th to 20thNight
15%
757
8%
4424
2%
740
23%
740
5%
3292
January21st to endNight
18%
830
8%
4875
6%
814
29%
814
7%
3815
February1st to 10thNight
14%
759
12%
2498
3%
759
25%
759
11%
1882
February11th to 20thNight
13%
703
12%
2209
3%
700
26%
700
11%
1624
February21st to endNight
18%
592
15%
1776
5%
592
30%
592
13%
1301
March1st to 10thNight
17%
720
15%
2160
8%
720
26%
720
12%
1625
March11th to 20thNight
17%
720
14%
2071
4%
720
28%
720
14%
1515
March21st to endNight
23%
792
20%
1998
6%
792
33%
792
19%
1426
April1st to 10thNight
21%
720
14%
1800
4%
720
26%
720
18%
1357
April11th to 20thNight
25%
711
17%
1775
5%
711
32%
711
22%
1253
April21st to endNight
22%
583
15%
1663
6%
583
29%
583
17%
1188
May1st to 10thNight
24%
370
15%
1450
10%
370
36%
370
16%
966
May11th to 20thNight
27%
354
18%
1416
14%
354
42%
354
17%
906
May21st to endNight
25%
389
12%
1551
7%
388
39%
388
17%
991
June1st to 10thNight
27%
360
9%
1440
6%
360
38%
360
15%
959
June11th to 20thNight
37%
360
10%
1440
11%
360
44%
360
16%
937
June21st to endNight
40%
360
10%
1440
11%
360
46%
360
16%
966
July1st to 10thNight
44%
350
12%
1400
14%
350
53%
350
23%
813
July11th to 20thNight
47%
348
13%
1392
17%
348
53%
348
20%
851
July21st to endNight
47%
394
12%
1486
14%
372
52%
372
21%
915
August1st to 10thNight
54%
358
14%
1422
13%
356
61%
356
21%
861
August11th to 20thNight
49%
510
16%
1574
10%
510
54%
510
27%
1015
August21st to endNight
41%
792
17%
1980
7%
792
46%
792
30%
1330
September1st to 10thNight
42%
720
16%
1800
5%
720
46%
720
32%
1198
September11th to 20thNight
45%
720
19%
1858
10%
720
50%
720
33%
1207
September21st to endNight
39%
720
21%
1980
13%
720
45%
720
27%
1312
October1st to 10thNight
31%
720
19%
2127
11%
720
41%
720
19%
1474
October11th to 20thNight
24%
720
14%
2187
6%
720
34%
720
15%
1604
October21st to endNight
20%
792
11%
2574
4%
792
29%
792
13%
1918
November1st to 10thNight
23%
740
14%
2407
6%
740
32%
740
13%
1728
November11th to 20thNight
21%
760
15%
2587
10%
760
28%
760
12%
1892
November21st to endNight
16%
760
11%
2660
5%
760
24%
760
9%
2017
December1st to 10thNight
13%
760
8%
2660
3%
760
19%
760
7%
2166
December11th to 20thNight
14%
760
11%
3248
4%
759
22%
759
7%
2487
December21st to endNight
11%
827
7%
4841
2%
817
20%
817
4%
3746

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
17%11%48%6%35%5%5%6%30%
78086
Night
15%11%5%8%7%35%45%6%31%
80877
TransparencyDay
53%8%11%17%9%1
77791
Night
51%9%12%18%9%1
80706
SeeingDay
24%19%32%18%6%2
13461
Night
21%16%31%23%8%1
22609

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
13%17%6%13%9%44445%21%
2517
11th to 20thDay
12%14%7%15%13%4433422%
2520
21st to endDay
10%15%9%13%7%46%6%5%5%22%
2772
February1st to 10thDay
11%18%6%9%9%445%47%23%
1664
11th to 20thDay
11%16%7%10%6%45%45%5%27%
1638
21st to endDay
15%16%7%9%8%35%435%25%
1480
March1st to 10thDay
13%13%7%9%9%44436%28%
1797
11th to 20thDay
15%13%48%8%45%5%5%6%28%
1885
21st to endDay
18%11%47%6%24445%34%
2358
April1st to 10thDay
19%13%38%6%34345%30%
2160
11th to 20thDay
21%9%36%5%3445%5%34%
2134
21st to endDay
20%11%48%6%345%45%30%
2299
May1st to 10thDay
20%10%47%5%4445%7%31%
2520
11th to 20thDay
21%8%37%6%335%5%6%33%
2478
21st to endDay
20%8%35%6%35%5%5%7%33%
2725
June1st to 10thDay
23%8%36%6%35%5%6%8%27%
2520
11th to 20thDay
16%6%37%7%36%5%6%7%33%
2520
21st to endDay
22%8%47%6%35%6%6%6%26%
2520
July1st to 10thDay
14%6%36%5%5%6%5%6%8%36%
2520
11th to 20thDay
15%6%36%7%36%6%7%9%32%
2520
21st to endDay
13%7%37%7%47%6%6%9%33%
2744
August1st to 10thDay
14%7%37%6%5%6%7%6%8%31%
2506
11th to 20thDay
13%6%37%6%46%6%7%8%33%
2305
21st to endDay
14%7%27%6%35%5%6%8%38%
2376
September1st to 10thDay
16%6%36%5%345%6%8%40%
2160
11th to 20thDay
15%5%35%5%35%45%7%43%
2102
21st to endDay
19%8%35%5%3445%7%39%
1980
October1st to 10thDay
22%8%36%5%345%6%7%33%
1831
11th to 20thDay
23%10%47%6%35%5%5%426%
1772
21st to endDay
25%11%37%6%35%45%5%25%
1782
November1st to 10thDay
15%11%47%5%5%5%45%8%31%
1671
11th to 20thDay
19%12%5%10%6%445%6%6%24%
1592
21st to endDay
19%15%6%8%6%445%6%5%22%
1520
December1st to 10thDay
21%17%7%9%7%345%45%19%
1520
11th to 20thDay
18%15%6%10%6%34446%23%
1906
21st to endDay
21%18%7%10%5%33445%21%
2772
January1st to 10thNight
13%16%7%11%8%35%5%5%6%22%
4429
11th to 20thNight
10%12%6%13%11%6%6%45%5%23%
4440
21st to endNight
10%13%7%13%10%5%5%446%22%
4884
February1st to 10thNight
10%14%5%10%9%45%5%6%5%26%
2498
11th to 20thNight
10%13%6%10%7%35%45%7%28%
2207
21st to endNight
12%14%6%9%5%45%5%5%7%29%
1776
March1st to 10thNight
13%13%5%9%7%45%5%5%5%29%
2150
11th to 20thNight
15%12%6%8%6%35%45%7%30%
2070
21st to endNight
15%9%47%6%35%445%38%
1998
April1st to 10thNight
20%11%46%7%3445%6%30%
1800
11th to 20thNight
17%6%36%6%445%5%6%37%
1775
21st to endNight
20%9%47%5%345%5%6%34%
1663
May1st to 10thNight
19%8%36%6%33447%35%
1450
11th to 20thNight
19%6%45%5%2435%7%39%
1415
21st to endNight
17%6%36%5%3445%8%38%
1550
June1st to 10thNight
19%6%45%5%45%5%6%8%32%
1440
11th to 20thNight
18%7%35%5%35%5%5%7%38%
1440
21st to endNight
19%6%35%435%5%5%7%36%
1440
July1st to 10thNight
11%5%25%5%445%5%8%45%
1440
11th to 20thNight
12%5%26%5%36%5%6%8%41%
1440
21st to endNight
11%6%35%5%45%5%5%8%43%
1574
August1st to 10thNight
11%435%5%35%6%7%9%41%
1432
11th to 20thNight
11%7%25%6%3446%7%46%
1574
21st to endNight
14%6%26%43445%8%45%
1980
September1st to 10thNight
11%6%35%5%345%6%6%46%
1800
11th to 20thNight
14%5%25%42345%8%47%
1858
21st to endNight
18%5%2443445%7%44%
1980
October1st to 10thNight
17%7%36%6%35%446%39%
2127
11th to 20thNight
21%9%36%6%35%5%5%6%33%
2187
21st to endNight
22%9%47%7%3445%7%29%
2574
November1st to 10thNight
17%9%48%6%35%47%7%30%
2407
11th to 20thNight
16%10%48%6%45%5%5%7%28%
2587
21st to endNight
18%14%5%9%6%3445%5%26%
2660
December1st to 10thNight
17%14%6%12%8%35%5%5%7%18%
2660
11th to 20thNight
18%15%6%10%8%345%45%25%
3288
21st to endNight
21%20%6%8%6%33445%21%
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
64%8%11%12%4
2518
11th to 20thDay
62%10%5%13%8%1
2520
21st to endDay
61%9%10%12%6%1
2772
February1st to 10thDay
61%5%8%16%7%2
1664
11th to 20thDay
59%6%10%14%10%1
1647
21st to endDay
62%48%15%9%3
1480
March1st to 10thDay
58%6%8%17%10%2
1800
11th to 20thDay
55%7%10%14%12%3
1885
21st to endDay
51%6%10%17%13%4
2358
April1st to 10thDay
56%6%9%16%11%3
2160
11th to 20thDay
50%7%9%20%12%2
2134
21st to endDay
55%6%8%15%11%4
2299
May1st to 10thDay
53%6%8%19%12%2
2520
11th to 20thDay
50%6%10%17%15%3
2482
21st to endDay
50%7%11%18%13%1
2725
June1st to 10thDay
54%8%11%16%10%1
2520
11th to 20thDay
48%9%12%18%11%3
2520
21st to endDay
56%8%11%16%9%1
2520
July1st to 10thDay
43%9%14%24%9%
2450
11th to 20thDay
44%9%15%22%9%
2445
21st to endDay
46%9%16%21%8%
2591
August1st to 10thDay
47%11%16%21%5%
2492
11th to 20thDay
43%12%17%20%8%
2305
21st to endDay
42%8%15%23%12%1
2376
September1st to 10thDay
41%8%14%24%13%
2160
11th to 20thDay
39%8%14%27%11%1
2102
21st to endDay
45%8%12%25%10%
1980
October1st to 10thDay
49%8%12%20%11%1
1831
11th to 20thDay
58%10%11%17%41
1772
21st to endDay
60%7%12%13%7%1
1782
November1st to 10thDay
50%8%14%18%9%1
1671
11th to 20thDay
57%9%12%13%9%
1592
21st to endDay
61%10%11%13%5%1
1520
December1st to 10thDay
66%7%10%11%6%
1520
11th to 20thDay
61%8%11%13%7%
1906
21st to endDay
65%7%8%13%7%
2772
January1st to 10thNight
59%11%13%13%4
4429
11th to 20thNight
56%13%13%12%5%1
4440
21st to endNight
61%11%10%11%7%1
4884
February1st to 10thNight
58%7%10%17%7%1
2498
11th to 20thNight
54%8%11%18%9%1
2209
21st to endNight
54%6%10%16%11%2
1776
March1st to 10thNight
56%8%8%17%10%2
2160
11th to 20thNight
53%6%11%15%12%2
2071
21st to endNight
47%6%10%19%15%4
1998
April1st to 10thNight
54%5%9%17%13%2
1800
11th to 20thNight
44%7%11%21%14%2
1775
21st to endNight
50%7%10%18%12%3
1663
May1st to 10thNight
49%5%10%18%13%4
1450
11th to 20thNight
43%8%12%17%17%3
1416
21st to endNight
43%8%12%21%13%3
1551
June1st to 10thNight
47%9%13%21%10%
1440
11th to 20thNight
45%8%10%22%12%3
1440
21st to endNight
46%9%13%20%12%
1440
July1st to 10thNight
35%9%18%25%13%1
1400
11th to 20thNight
39%9%16%27%9%
1392
21st to endNight
37%10%18%25%10%
1486
August1st to 10thNight
36%11%20%25%8%
1422
11th to 20thNight
36%10%18%25%11%
1574
21st to endNight
38%8%17%26%11%
1980
September1st to 10thNight
35%9%16%26%13%1
1800
11th to 20thNight
34%8%16%31%10%1
1858
21st to endNight
38%8%13%28%12%
1980
October1st to 10thNight
46%8%10%23%12%1
2127
11th to 20thNight
51%9%13%20%7%
2187
21st to endNight
55%8%13%16%8%1
2574
November1st to 10thNight
50%9%15%19%6%1
2407
11th to 20thNight
52%9%13%16%8%2
2587
21st to endNight
58%9%12%16%6%1
2660
December1st to 10thNight
65%9%10%11%4
2660
11th to 20thNight
61%8%9%15%7%1
3288
21st to endNight
64%7%8%14%6%
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
17%26%39%17%2
180
11th to 20thDay
27%21%34%13%5%1
180
21st to endDay
18%22%40%14%41
198
February1st to 10thDay
34%30%29%6%2
250
11th to 20thDay
26%28%37%8%1
305
21st to endDay
29%25%29%14%2
346
March1st to 10thDay
26%23%34%14%3
420
11th to 20thDay
26%25%32%14%3
420
21st to endDay
30%22%26%15%5%1
462
April1st to 10thDay
31%18%34%13%4
420
11th to 20thDay
33%20%24%14%8%1
412
21st to endDay
29%20%34%13%31
420
May1st to 10thDay
26%22%33%14%31
423
11th to 20thDay
26%20%31%17%5%1
447
21st to endDay
24%21%32%18%4
485
June1st to 10thDay
26%18%35%15%6%1
450
11th to 20thDay
19%20%33%17%10%1
450
21st to endDay
22%17%32%21%7%1
450
July1st to 10thDay
14%11%38%26%8%2
445
11th to 20thDay
16%13%37%27%6%1
444
21st to endDay
15%11%36%27%9%1
488
August1st to 10thDay
17%11%30%30%10%2
446
11th to 20thDay
13%11%31%27%12%6%
439
21st to endDay
17%17%30%19%11%6%
495
September1st to 10thDay
18%12%35%20%10%5%
450
11th to 20thDay
14%16%29%24%12%6%
450
21st to endDay
21%16%25%21%12%5%
450
October1st to 10thDay
27%18%26%18%10%2
450
11th to 20thDay
27%22%27%17%6%1
435
21st to endDay
32%16%33%16%4
396
November1st to 10thDay
29%20%29%17%41
365
11th to 20thDay
25%26%31%13%6%
252
21st to endDay
28%28%29%12%2
180
December1st to 10thDay
30%21%28%16%5%
180
11th to 20thDay
25%29%36%8%2
180
21st to endDay
34%26%24%11%41
198
January1st to 10thNight
23%20%35%17%4
760
11th to 20thNight
22%22%31%21%4
760
21st to endNight
15%17%40%22%5%1
836
February1st to 10thNight
18%22%38%19%4
759
11th to 20thNight
20%21%40%15%4
703
21st to endNight
22%19%35%22%2
592
March1st to 10thNight
23%19%35%18%3
720
11th to 20thNight
23%21%33%17%5%1
720
21st to endNight
21%18%32%23%5%1
792
April1st to 10thNight
27%19%29%21%5%
720
11th to 20thNight
23%17%31%23%5%1
711
21st to endNight
25%17%31%19%7%
583
May1st to 10thNight
22%13%35%22%6%2
370
11th to 20thNight
21%15%29%28%6%1
354
21st to endNight
19%11%41%21%8%
389
June1st to 10thNight
23%7%38%25%7%
360
11th to 20thNight
22%9%27%31%11%1
360
21st to endNight
20%7%28%31%14%1
360
July1st to 10thNight
14%7%31%33%14%1
350
11th to 20thNight
12%7%27%40%14%1
348
21st to endNight
13%6%28%40%12%1
394
August1st to 10thNight
13%5%22%43%16%
358
11th to 20thNight
12%6%25%34%22%1
510
21st to endNight
15%9%30%28%16%2
792
September1st to 10thNight
15%7%32%33%12%1
720
11th to 20thNight
15%10%26%31%16%1
720
21st to endNight
20%12%26%26%15%2
720
October1st to 10thNight
21%15%28%24%12%1
720
11th to 20thNight
25%15%29%22%8%1
720
21st to endNight
28%14%32%21%5%
792
November1st to 10thNight
23%19%29%22%6%1
740
11th to 20thNight
23%19%31%19%8%1
760
21st to endNight
26%24%28%17%41
760
December1st to 10thNight
26%20%31%17%5%
760
11th to 20thNight
27%21%30%18%41
760
21st to endNight
31%20%30%15%4
836
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