Vanier
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vanier clear sky chart from 2005-11-06 to 2024-01-16.

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
28%
22747
12%
74900
7%
22698
35%
22698
15%
54756

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
13%
760
9%
2649
2%
757
21%
757
7%
2135
January11th to 20thNight
18%
744
11%
2602
4%
744
27%
744
9%
1999
January21st to endNight
23%
792
13%
2772
6%
792
33%
792
12%
2009
February1st to 10thNight
22%
720
12%
2520
6%
720
32%
720
11%
1886
February11th to 20thNight
15%
702
10%
2110
2%
700
24%
700
12%
1635
February21st to endNight
22%
592
15%
1776
7%
592
33%
592
15%
1311
March1st to 10thNight
22%
720
14%
2160
8%
720
31%
720
15%
1618
March11th to 20thNight
23%
720
14%
2071
5%
720
31%
720
14%
1549
March21st to endNight
31%
792
17%
2044
7%
792
38%
792
21%
1521
April1st to 10thNight
25%
720
13%
1800
5%
720
29%
720
17%
1398
April11th to 20thNight
27%
623
16%
1687
6%
623
33%
623
22%
1199
April21st to endNight
25%
540
15%
1620
8%
540
32%
540
17%
1180
May1st to 10thNight
28%
504
13%
1584
8%
504
36%
504
16%
1141
May11th to 20thNight
33%
354
17%
1416
16%
354
43%
354
15%
942
May21st to endNight
30%
389
11%
1520
9%
388
41%
388
16%
1016
June1st to 10thNight
34%
360
8%
1260
6%
360
39%
360
15%
894
June11th to 20thNight
41%
360
10%
1260
11%
360
46%
360
19%
845
June21st to endNight
38%
360
8%
1260
8%
360
41%
360
15%
899
July1st to 10thNight
39%
350
9%
1356
11%
350
46%
350
19%
887
July11th to 20thNight
45%
348
10%
1392
14%
348
49%
348
18%
908
July21st to endNight
50%
394
9%
1486
12%
372
51%
372
17%
1009
August1st to 10thNight
55%
358
13%
1422
14%
356
58%
356
20%
894
August11th to 20thNight
45%
524
10%
1588
7%
524
47%
524
20%
1110
August21st to endNight
44%
697
18%
1885
9%
697
48%
697
26%
1270
September1st to 10thNight
42%
720
12%
1800
5%
720
45%
720
27%
1258
September11th to 20thNight
42%
720
15%
1960
8%
720
47%
720
28%
1317
September21st to endNight
40%
720
19%
1980
12%
720
45%
720
26%
1364
October1st to 10thNight
35%
720
20%
1980
12%
720
43%
720
23%
1402
October11th to 20thNight
30%
720
11%
2312
6%
720
37%
720
15%
1724
October21st to endNight
22%
792
10%
2574
5%
792
29%
792
14%
1900
November1st to 10thNight
27%
740
13%
2407
7%
740
35%
740
14%
1748
November11th to 20thNight
27%
760
16%
2470
10%
760
35%
760
14%
1805
November21st to endNight
20%
834
10%
2810
4%
834
28%
834
11%
2187
December1st to 10thNight
19%
850
7%
2850
3%
850
23%
850
8%
2307
December11th to 20thNight
17%
850
11%
3451
4%
848
25%
848
8%
2645
December21st to endNight
12%
898
7%
5066
2%
881
20%
881
5%
3844

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
19%9%47%6%35%5%5%7%31%
74573
Night
19%11%47%6%34446%31%
75225
TransparencyDay
52%7%13%19%9%1
74278
Night
55%6%11%18%9%1
75055
SeeingDay
23%14%29%22%10%2
14109
Night
24%11%29%28%8%1
22758

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
19%15%7%10%6%35%45%6%21%
1517
11th to 20thDay
16%17%8%8%7%5%4445%24%
1480
21st to endDay
10%12%5%9%6%45%6%5%7%31%
1584
February1st to 10thDay
11%14%7%11%7%45%5%5%6%25%
1440
11th to 20thDay
15%13%7%9%6%45%5%46%27%
1734
21st to endDay
13%13%6%9%8%345%47%28%
1480
March1st to 10thDay
15%12%5%8%6%3445%7%32%
1797
11th to 20thDay
17%12%5%6%6%345%5%6%32%
1888
21st to endDay
16%11%47%5%445%6%6%33%
2308
April1st to 10thDay
22%11%47%6%4445%5%28%
2160
11th to 20thDay
21%6%35%6%44446%39%
2222
21st to endDay
24%8%36%6%34446%31%
2340
May1st to 10thDay
22%7%36%5%3445%7%34%
2392
11th to 20thDay
19%6%36%6%46%5%5%7%33%
2478
21st to endDay
21%6%26%6%45%5%5%7%33%
2751
June1st to 10thDay
20%6%46%6%47%6%7%7%28%
2700
11th to 20thDay
20%6%35%5%36%46%8%34%
2700
21st to endDay
23%7%37%6%45%5%5%7%28%
2700
July1st to 10thDay
15%6%36%6%46%5%7%10%31%
2558
11th to 20thDay
15%5%36%6%45%6%8%10%32%
2520
21st to endDay
15%6%37%6%46%5%7%9%32%
2744
August1st to 10thDay
17%6%36%7%47%7%6%10%29%
2495
11th to 20thDay
15%6%26%6%45%46%9%36%
2304
21st to endDay
17%5%26%5%445%6%7%38%
2468
September1st to 10thDay
18%7%26%5%345%6%8%37%
2160
11th to 20thDay
19%5%2342335%9%45%
1999
21st to endDay
21%6%36%43445%6%38%
1980
October1st to 10thDay
20%7%35%5%35%5%5%7%33%
1978
11th to 20thDay
25%8%37%7%45%6%5%7%24%
1647
21st to endDay
28%10%47%4345%5%5%24%
1782
November1st to 10thDay
20%10%37%6%45%346%32%
1671
11th to 20thDay
23%11%5%7%5%35%45%5%26%
1710
21st to endDay
23%15%5%6%6%345%45%23%
1368
December1st to 10thDay
23%17%5%6%6%35%45%5%21%
1330
11th to 20thDay
22%13%5%8%7%44435%27%
1668
21st to endDay
22%18%5%6%6%33445%26%
2520
January1st to 10thNight
16%20%6%11%8%35%335%21%
2649
11th to 20thNight
17%16%6%9%6%35%445%24%
2602
21st to endNight
10%14%5%9%8%5%5%5%5%6%28%
2772
February1st to 10thNight
12%12%6%10%9%45%5%5%5%27%
2520
11th to 20thNight
14%16%6%9%7%35%446%26%
2108
21st to endNight
15%13%5%9%6%35%45%6%29%
1776
March1st to 10thNight
15%13%5%8%6%36%5%45%30%
2150
11th to 20thNight
18%13%47%6%4445%5%29%
2070
21st to endNight
18%11%36%5%445%36%35%
2044
April1st to 10thNight
23%12%5%6%6%34446%28%
1800
11th to 20thNight
20%7%36%5%335%6%7%35%
1687
21st to endNight
24%10%36%5%23445%34%
1620
May1st to 10thNight
23%8%35%6%35%5%45%33%
1584
11th to 20thNight
23%7%35%6%3435%6%35%
1415
21st to endNight
23%5%345%35%447%37%
1519
June1st to 10thNight
22%7%36%6%35%6%5%8%28%
1260
11th to 20thNight
20%5%35%5%445%6%7%37%
1260
21st to endNight
22%8%46%6%35%447%31%
1260
July1st to 10thNight
17%7%36%435%5%5%9%36%
1396
11th to 20thNight
18%6%36%6%35%5%5%9%36%
1440
21st to endNight
16%6%37%5%35%5%6%8%35%
1574
August1st to 10thNight
16%5%246%35%6%6%10%38%
1432
11th to 20thNight
16%7%36%6%45%5%6%8%34%
1588
21st to endNight
17%435%5%45%45%7%41%
1885
September1st to 10thNight
19%6%26%6%34447%40%
1800
11th to 20thNight
19%6%3442435%6%43%
1960
21st to endNight
20%6%34425%35%6%41%
1980
October1st to 10thNight
19%7%26%5%35%5%5%6%37%
1980
11th to 20thNight
26%8%35%6%4444431%
2312
21st to endNight
25%10%36%5%335%5%7%29%
2574
November1st to 10thNight
20%10%36%6%4446%6%31%
2407
11th to 20thNight
21%10%47%6%34446%31%
2470
21st to endNight
23%13%5%7%5%35%345%25%
2810
December1st to 10thNight
24%15%5%9%7%35%445%19%
2850
11th to 20thNight
21%13%5%9%7%34446%25%
3531
21st to endNight
24%19%48%5%2333325%
5140

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
65%6%9%13%6%
1518
11th to 20thDay
65%410%14%6%1
1480
21st to endDay
53%6%10%19%12%1
1584
February1st to 10thDay
60%5%11%14%8%2
1440
11th to 20thDay
59%5%13%12%9%1
1743
21st to endDay
56%5%9%19%8%2
1480
March1st to 10thDay
53%6%10%17%12%2
1800
11th to 20thDay
53%6%10%17%13%1
1888
21st to endDay
51%6%12%18%11%3
2308
April1st to 10thDay
58%411%13%10%3
2160
11th to 20thDay
47%411%24%12%2
2222
21st to endDay
55%5%10%16%11%2
2340
May1st to 10thDay
49%6%12%17%14%2
2392
11th to 20thDay
49%7%11%20%12%1
2482
21st to endDay
51%7%11%19%11%1
2751
June1st to 10thDay
50%10%12%18%8%1
2700
11th to 20thDay
47%7%13%20%11%2
2700
21st to endDay
56%8%11%16%9%
2700
July1st to 10thDay
44%11%16%23%6%
2488
11th to 20thDay
43%10%17%22%7%
2445
21st to endDay
48%9%17%20%7%
2591
August1st to 10thDay
48%11%19%20%3
2481
11th to 20thDay
43%8%18%21%9%
2304
21st to endDay
43%9%13%25%9%
2468
September1st to 10thDay
43%8%16%23%10%
2160
11th to 20thDay
38%6%18%29%10%
1999
21st to endDay
46%6%14%26%9%
1980
October1st to 10thDay
49%7%13%24%8%
1978
11th to 20thDay
57%8%16%16%2
1647
21st to endDay
62%7%9%17%5%1
1782
November1st to 10thDay
55%6%12%19%8%
1671
11th to 20thDay
60%5%10%18%6%1
1710
21st to endDay
64%5%12%13%5%1
1368
December1st to 10thDay
67%5%11%13%4
1330
11th to 20thDay
61%5%8%18%7%
1668
21st to endDay
63%6%11%12%6%2
2520
January1st to 10thNight
69%48%14%5%1
2649
11th to 20thNight
64%410%15%6%1
2602
21st to endNight
57%5%9%18%10%1
2772
February1st to 10thNight
59%5%9%17%8%1
2520
11th to 20thNight
61%5%11%14%9%1
2110
21st to endNight
56%5%8%16%13%1
1776
March1st to 10thNight
56%6%9%16%11%2
2160
11th to 20thNight
56%6%8%15%12%2
2071
21st to endNight
52%5%10%18%11%4
2044
April1st to 10thNight
58%49%15%11%3
1800
11th to 20thNight
48%6%10%21%12%2
1687
21st to endNight
54%5%8%17%14%2
1620
May1st to 10thNight
53%6%9%15%14%2
1584
11th to 20thNight
50%6%10%17%16%2
1416
21st to endNight
48%7%10%18%15%1
1520
June1st to 10thNight
52%7%13%18%9%1
1260
11th to 20thNight
47%7%12%20%11%3
1260
21st to endNight
53%7%12%17%11%
1260
July1st to 10thNight
44%9%18%21%9%
1356
11th to 20thNight
45%8%16%23%7%1
1392
21st to endNight
47%9%17%19%8%
1486
August1st to 10thNight
39%10%19%27%5%
1422
11th to 20thNight
46%9%20%19%6%
1588
21st to endNight
43%7%14%28%9%
1885
September1st to 10thNight
44%6%14%23%11%1
1800
11th to 20thNight
41%6%17%27%8%1
1960
21st to endNight
44%6%11%27%12%
1980
October1st to 10thNight
46%7%10%24%11%1
1980
11th to 20thNight
56%7%13%20%5%
2312
21st to endNight
57%5%13%17%7%
2574
November1st to 10thNight
54%6%13%20%6%1
2407
11th to 20thNight
54%7%13%17%9%
2470
21st to endNight
62%6%11%14%6%1
2810
December1st to 10thNight
68%5%11%12%4
2850
11th to 20thNight
62%5%9%15%8%
3532
21st to endNight
65%5%8%15%6%1
5140

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
27%19%31%17%41
180
11th to 20thDay
28%23%30%14%5%
170
21st to endDay
15%22%36%22%31
176
February1st to 10thDay
25%27%34%11%31
160
11th to 20thDay
23%19%37%16%4
410
21st to endDay
22%21%30%23%4
346
March1st to 10thDay
23%19%30%20%6%1
420
11th to 20thDay
23%18%33%18%7%1
420
21st to endDay
22%16%26%23%11%2
462
April1st to 10thDay
27%15%29%20%9%
420
11th to 20thDay
25%12%30%22%9%1
412
21st to endDay
29%14%32%17%6%2
420
May1st to 10thDay
27%17%32%18%5%1
423
11th to 20thDay
20%13%33%23%8%2
447
21st to endDay
23%18%32%19%7%1
511
June1st to 10thDay
23%13%30%25%9%1
630
11th to 20thDay
22%11%27%27%13%1
630
21st to endDay
26%9%27%25%12%2
630
July1st to 10thDay
18%12%29%26%13%2
483
11th to 20thDay
15%10%32%29%12%2
444
21st to endDay
15%9%34%28%13%2
488
August1st to 10thDay
18%7%27%27%16%4
446
11th to 20thDay
18%5%28%27%18%3
439
21st to endDay
22%10%26%19%15%8%
495
September1st to 10thDay
18%12%26%27%14%4
450
11th to 20thDay
20%12%28%18%18%5%
450
21st to endDay
20%13%23%23%14%6%
450
October1st to 10thDay
22%13%26%25%10%3
450
11th to 20thDay
30%14%26%18%10%1
373
21st to endDay
34%14%29%17%6%
396
November1st to 10thDay
30%15%24%22%8%1
365
11th to 20thDay
28%16%29%17%9%
370
21st to endDay
31%17%30%18%31
185
December1st to 10thDay
33%12%27%19%6%3
180
11th to 20thDay
31%18%29%17%32
180
21st to endDay
34%17%32%13%41
198
January1st to 10thNight
26%16%32%22%4
760
11th to 20thNight
25%15%31%25%4
744
21st to endNight
17%12%34%30%6%1
792
February1st to 10thNight
19%13%35%27%6%
720
11th to 20thNight
22%15%38%20%41
703
21st to endNight
23%12%33%27%4
592
March1st to 10thNight
22%11%36%26%6%
720
11th to 20thNight
25%14%32%22%6%1
720
21st to endNight
23%9%29%30%7%1
792
April1st to 10thNight
29%13%26%26%6%
720
11th to 20thNight
25%9%34%25%6%
623
21st to endNight
29%11%29%24%6%
540
May1st to 10thNight
24%10%31%28%6%
504
11th to 20thNight
25%9%28%31%6%
354
21st to endNight
28%5%31%28%8%
389
June1st to 10thNight
25%7%27%36%5%
360
11th to 20thNight
19%6%26%37%12%
360
21st to endNight
23%6%24%37%10%
360
July1st to 10thNight
18%5%30%37%10%1
350
11th to 20thNight
19%322%41%14%1
348
21st to endNight
16%5%18%46%14%
394
August1st to 10thNight
19%413%48%16%1
358
11th to 20thNight
16%5%22%40%16%2
524
21st to endNight
19%5%25%32%18%2
697
September1st to 10thNight
20%5%25%34%15%1
720
11th to 20thNight
21%7%24%31%17%2
720
21st to endNight
22%7%25%30%15%1
720
October1st to 10thNight
22%9%26%33%8%1
720
11th to 20thNight
29%10%24%27%9%1
720
21st to endNight
30%11%30%24%4
792
November1st to 10thNight
26%13%26%26%9%
740
11th to 20thNight
26%14%27%25%8%1
760
21st to endNight
30%13%31%20%7%
834
December1st to 10thNight
31%12%28%22%8%1
850
11th to 20thNight
25%18%28%22%6%1
850
21st to endNight
33%16%29%18%41
908
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