Brampton BrightSkies Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Brampton BrightSkies Observatory clear sky chart from 2005-11-06 to 2024-03-01.

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
33%
23011
14%
80444
9%
22917
41%
22917
17%
56010

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
16%
753
10%
4399
3%
737
26%
737
6%
3290
January11th to 20thNight
16%
755
8%
4161
2%
740
23%
740
5%
3257
January21st to endNight
19%
830
7%
4523
5%
814
28%
814
7%
3559
February1st to 10thNight
16%
760
11%
2470
3%
760
26%
760
12%
1838
February11th to 20thNight
18%
740
13%
2405
3%
740
29%
740
13%
1775
February21st to endNight
20%
628
12%
1979
4%
628
29%
628
15%
1417
March1st to 10thNight
23%
723
17%
1987
6%
723
32%
723
19%
1400
March11th to 20thNight
23%
720
17%
1980
8%
720
32%
720
18%
1423
March21st to endNight
31%
792
20%
2178
9%
792
39%
792
22%
1508
April1st to 10thNight
24%
720
15%
1845
5%
720
30%
720
20%
1333
April11th to 20thNight
30%
646
18%
1710
7%
646
37%
646
24%
1199
April21st to endNight
32%
540
17%
1620
5%
540
41%
540
21%
1110
May1st to 10thNight
42%
540
16%
1620
9%
540
48%
540
25%
1069
May11th to 20thNight
44%
386
23%
1448
16%
386
57%
386
25%
840
May21st to endNight
53%
388
18%
1551
17%
388
62%
388
29%
816
June1st to 10thNight
48%
360
15%
1440
13%
360
60%
360
23%
829
June11th to 20thNight
47%
360
17%
1440
17%
360
58%
360
24%
814
June21st to endNight
55%
360
17%
1262
18%
360
63%
360
27%
737
July1st to 10thNight
64%
350
18%
1336
23%
350
70%
350
36%
667
July11th to 20thNight
60%
348
20%
1392
26%
348
65%
348
30%
741
July21st to endNight
62%
581
18%
1663
15%
549
66%
549
35%
951
August1st to 10thNight
64%
537
17%
1600
13%
534
67%
534
34%
963
August11th to 20thNight
65%
534
24%
1598
18%
534
69%
534
38%
908
August21st to endNight
54%
661
21%
1849
12%
661
58%
661
32%
1145
September1st to 10thNight
55%
720
18%
1800
9%
720
59%
720
35%
1159
September11th to 20thNight
56%
720
27%
1917
16%
720
62%
720
38%
1138
September21st to endNight
47%
720
20%
2006
15%
720
52%
720
27%
1333
October1st to 10thNight
40%
720
17%
2160
13%
720
45%
720
24%
1451
October11th to 20thNight
32%
720
16%
2160
10%
720
40%
720
19%
1526
October21st to endNight
24%
792
15%
2376
10%
792
32%
792
15%
1762
November1st to 10thNight
35%
740
19%
2465
14%
740
43%
740
20%
1613
November11th to 20thNight
23%
760
14%
2660
7%
760
33%
760
15%
1860
November21st to endNight
24%
760
11%
2660
6%
760
31%
760
13%
1925
December1st to 10thNight
17%
760
10%
2660
4%
760
24%
760
10%
2026
December11th to 20thNight
16%
760
7%
3258
2%
758
23%
758
8%
2502
December21st to endNight
12%
827
4%
4866
1%
817
18%
817
4%
4126

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
14%9%47%7%45%5%6%7%32%
78652
Night
15%9%47%6%45%5%5%7%33%
80727
TransparencyDay
49%7%13%20%10%1
78368
Night
49%7%12%20%11%1
80545
SeeingDay
18%12%29%25%12%4
13661
Night
19%10%31%28%11%1
23042

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
15%14%5%9%6%45%5%5%6%26%
2517
11th to 20thDay
11%18%7%13%11%5%5%5%45%18%
2782
21st to endDay
21%19%6%10%7%35%445%17%
3124
February1st to 10thDay
14%14%5%10%9%46%5%5%6%22%
1710
11th to 20thDay
12%13%6%11%9%45%5%5%7%25%
1663
21st to endDay
17%13%411%6%45%446%26%
1473
March1st to 10thDay
13%10%5%8%8%36%5%6%5%31%
1977
11th to 20thDay
13%11%5%8%8%35%5%5%5%33%
1980
21st to endDay
17%9%48%7%35%45%6%32%
2178
April1st to 10thDay
15%10%5%8%7%35%45%7%30%
2114
11th to 20thDay
18%7%46%5%35%45%6%37%
2214
21st to endDay
19%9%36%6%35%45%6%34%
2340
May1st to 10thDay
16%8%37%6%35%46%8%34%
2340
11th to 20thDay
14%7%35%6%345%6%6%40%
2445
21st to endDay
11%5%26%5%35%5%6%8%44%
2725
June1st to 10thDay
13%6%36%6%445%6%8%39%
2520
11th to 20thDay
12%6%25%6%35%5%7%9%41%
2520
21st to endDay
12%5%25%5%45%6%6%10%40%
2685
July1st to 10thDay
7%425%6%5%6%5%7%9%45%
2574
11th to 20thDay
11%5%25%5%46%6%7%9%40%
2520
21st to endDay
9%6%36%7%46%6%7%10%36%
2553
August1st to 10thDay
8%5%36%5%46%6%8%10%39%
2327
11th to 20thDay
7%6%37%7%46%7%7%9%38%
2303
21st to endDay
11%5%26%6%35%6%7%9%40%
2488
September1st to 10thDay
12%6%35%6%35%6%6%9%40%
2160
11th to 20thDay
10%6%36%5%3446%9%45%
2039
21st to endDay
13%5%37%7%45%5%6%8%36%
1954
October1st to 10thDay
19%9%36%5%346%46%35%
1800
11th to 20thDay
19%8%47%7%45%45%8%29%
1800
21st to endDay
24%11%37%7%45%5%5%6%23%
1980
November1st to 10thDay
14%10%46%6%36%5%6%9%33%
1609
11th to 20thDay
13%11%5%8%7%46%7%7%7%26%
1520
21st to endDay
16%15%5%7%6%46%46%7%22%
1520
December1st to 10thDay
16%14%7%12%8%46%5%5%7%17%
1520
11th to 20thDay
19%13%6%9%7%45%6%5%6%21%
1906
21st to endDay
29%17%6%11%6%33445%12%
2772
January1st to 10thNight
17%14%6%9%8%45%45%5%23%
4429
11th to 20thNight
14%13%5%11%11%6%6%5%5%6%18%
4175
21st to endNight
20%12%6%8%9%5%6%5%5%6%18%
4532
February1st to 10thNight
13%13%5%9%8%46%6%5%6%26%
2470
11th to 20thNight
12%12%5%8%8%5%6%6%5%6%27%
2403
21st to endNight
13%10%5%9%7%5%6%5%47%29%
1979
March1st to 10thNight
13%7%47%7%45%5%6%7%35%
1977
11th to 20thNight
14%11%47%6%35%447%34%
1979
21st to endNight
15%9%46%6%45%445%39%
2178
April1st to 10thNight
17%9%37%6%35%6%5%6%33%
1845
11th to 20thNight
15%7%36%5%45%5%6%6%39%
1710
21st to endNight
16%7%37%5%25%5%5%7%37%
1620
May1st to 10thNight
16%6%35%5%36%5%6%7%40%
1620
11th to 20thNight
14%5%25%4245%5%8%46%
1447
21st to endNight
10%42442445%9%52%
1550
June1st to 10thNight
12%425%6%35%5%6%9%43%
1440
11th to 20thNight
9%5%35%435%6%6%9%45%
1440
21st to endNight
11%425%5%3447%8%48%
1262
July1st to 10thNight
6%42343445%8%58%
1376
11th to 20thNight
9%425%5%35%5%6%7%51%
1440
21st to endNight
7%324435%6%6%8%51%
1761
August1st to 10thNight
7%425%6%35%5%6%7%51%
1611
11th to 20thNight
7%4244245%6%9%53%
1598
21st to endNight
10%435%435%5%5%7%48%
1849
September1st to 10thNight
9%425%6%45%5%7%7%47%
1800
11th to 20thNight
11%42432445%7%54%
1917
21st to endNight
14%6%36%5%3445%7%42%
2006
October1st to 10thNight
17%7%26%5%3446%6%39%
2160
11th to 20thNight
17%9%36%5%45%45%7%35%
2160
21st to endNight
20%10%38%6%35%5%6%7%28%
2376
November1st to 10thNight
16%7%26%6%35%5%6%7%38%
2465
11th to 20thNight
15%9%48%7%36%6%6%8%30%
2660
21st to endNight
18%10%48%6%35%5%6%8%27%
2660
December1st to 10thNight
20%12%48%8%35%5%5%7%23%
2660
11th to 20thNight
15%16%6%10%7%35%5%6%7%21%
3288
21st to endNight
29%15%6%9%6%445%45%13%
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
57%10%14%12%7%
2518
11th to 20thDay
68%5%11%11%4
2782
21st to endDay
70%6%9%9%5%1
3124
February1st to 10thDay
62%6%12%16%31
1710
11th to 20thDay
58%6%12%15%8%1
1672
21st to endDay
58%6%11%16%8%1
1473
March1st to 10thDay
53%5%14%17%9%1
1980
11th to 20thDay
54%5%9%19%11%2
1980
21st to endDay
53%410%19%13%2
2178
April1st to 10thDay
54%5%11%18%11%1
2114
11th to 20thDay
47%5%11%21%15%1
2214
21st to endDay
51%5%11%19%12%3
2340
May1st to 10thDay
48%5%12%20%14%1
2340
11th to 20thDay
43%6%12%24%13%2
2449
21st to endDay
37%7%16%24%14%2
2725
June1st to 10thDay
40%8%12%23%15%2
2520
11th to 20thDay
38%7%13%25%16%1
2520
21st to endDay
37%8%15%25%15%1
2685
July1st to 10thDay
33%7%14%25%18%3
2504
11th to 20thDay
36%7%16%28%11%1
2445
21st to endDay
39%9%15%21%14%2
2410
August1st to 10thDay
35%9%18%24%12%2
2314
11th to 20thDay
37%8%19%25%12%
2303
21st to endDay
38%8%15%27%12%1
2488
September1st to 10thDay
39%9%14%26%11%1
2160
11th to 20thDay
35%6%15%30%14%1
2039
21st to endDay
43%8%15%25%9%
1954
October1st to 10thDay
47%7%15%19%11%1
1800
11th to 20thDay
53%8%13%20%7%1
1800
21st to endDay
60%7%13%15%5%1
1980
November1st to 10thDay
47%7%16%21%8%1
1609
11th to 20thDay
53%7%15%15%8%
1520
21st to endDay
59%7%15%16%3
1520
December1st to 10thDay
65%7%12%12%3
1520
11th to 20thDay
61%9%13%12%5%
1906
21st to endDay
74%6%9%9%2
2772
January1st to 10thNight
60%9%11%15%5%
4429
11th to 20thNight
64%9%12%11%31
4175
21st to endNight
64%8%11%11%5%1
4532
February1st to 10thNight
57%6%11%20%5%1
2470
11th to 20thNight
57%6%11%17%9%
2405
21st to endNight
54%5%14%19%8%1
1979
March1st to 10thNight
48%7%14%20%11%2
1987
11th to 20thNight
51%5%9%20%12%2
1980
21st to endNight
47%48%21%16%3
2178
April1st to 10thNight
51%5%10%18%14%1
1845
11th to 20thNight
45%6%10%20%16%2
1710
21st to endNight
46%6%10%19%16%3
1620
May1st to 10thNight
43%6%10%22%17%3
1620
11th to 20thNight
37%6%10%26%17%4
1448
21st to endNight
31%6%15%25%19%4
1551
June1st to 10thNight
37%7%11%25%18%2
1440
11th to 20thNight
36%6%11%24%22%2
1440
21st to endNight
35%6%14%26%17%1
1262
July1st to 10thNight
25%7%11%27%27%4
1336
11th to 20thNight
31%6%12%30%19%2
1392
21st to endNight
29%7%14%28%18%3
1663
August1st to 10thNight
32%8%16%29%14%2
1600
11th to 20thNight
27%8%14%35%14%2
1598
21st to endNight
34%7%12%27%18%1
1849
September1st to 10thNight
34%7%15%28%15%1
1800
11th to 20thNight
29%7%12%34%18%
1917
21st to endNight
40%7%13%28%11%1
2006
October1st to 10thNight
44%7%12%22%15%1
2160
11th to 20thNight
48%7%12%24%8%
2160
21st to endNight
55%7%11%17%10%1
2376
November1st to 10thNight
44%6%13%23%12%1
2465
11th to 20thNight
50%7%15%18%9%1
2660
21st to endNight
55%6%17%18%4
2660
December1st to 10thNight
60%7%12%16%5%
2660
11th to 20thNight
60%8%14%14%4
3288
21st to endNight
72%8%10%8%2
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
22%18%29%23%7%1
180
11th to 20thDay
22%27%30%13%7%1
256
21st to endDay
25%19%31%21%4
297
February1st to 10thDay
23%23%39%10%5%
270
11th to 20thDay
21%23%39%15%2
270
21st to endDay
28%26%35%10%1
233
March1st to 10thDay
21%17%35%22%6%
420
11th to 20thDay
22%18%34%19%6%1
420
21st to endDay
27%15%31%20%6%1
462
April1st to 10thDay
18%19%35%21%8%
420
11th to 20thDay
24%17%29%18%9%3
412
21st to endDay
22%14%33%21%8%2
420
May1st to 10thDay
21%10%30%23%11%5%
423
11th to 20thDay
17%8%31%26%12%6%
447
21st to endDay
15%6%27%29%17%6%
485
June1st to 10thDay
12%9%31%33%12%3
450
11th to 20thDay
14%9%26%30%19%2
450
21st to endDay
14%8%29%33%13%4
615
July1st to 10thDay
7%5%24%35%21%8%
499
11th to 20thDay
13%5%22%34%18%9%
444
21st to endDay
7%427%39%17%6%
488
August1st to 10thDay
9%6%22%28%24%11%
446
11th to 20thDay
7%5%22%32%20%13%
439
21st to endDay
12%7%23%29%19%10%
495
September1st to 10thDay
13%6%23%30%17%11%
450
11th to 20thDay
10%5%23%25%23%13%
450
21st to endDay
14%10%30%23%17%7%
450
October1st to 10thDay
23%11%25%21%13%6%
450
11th to 20thDay
20%15%35%19%8%2
450
21st to endDay
30%13%26%23%6%1
495
November1st to 10thDay
21%21%26%21%10%1
257
11th to 20thDay
26%18%30%20%42
180
21st to endDay
25%15%39%17%3
180
December1st to 10thDay
26%17%37%16%3
180
11th to 20thDay
26%23%32%15%4
180
21st to endDay
26%21%37%13%3
198
January1st to 10thNight
23%17%36%19%5%
760
11th to 20thNight
26%17%31%22%4
760
21st to endNight
19%11%39%24%7%
836
February1st to 10thNight
20%18%38%21%3
760
11th to 20thNight
22%14%39%21%4
743
21st to endNight
19%17%38%23%4
628
March1st to 10thNight
19%13%38%24%5%
723
11th to 20thNight
20%15%36%23%6%
720
21st to endNight
20%11%32%28%8%1
792
April1st to 10thNight
22%10%35%28%4
720
11th to 20thNight
18%12%36%24%9%2
646
21st to endNight
20%8%31%31%10%
540
May1st to 10thNight
17%6%29%31%15%2
540
11th to 20thNight
16%429%38%12%1
386
21st to endNight
11%326%37%22%1
389
June1st to 10thNight
13%5%27%38%17%1
360
11th to 20thNight
9%7%29%38%17%
360
21st to endNight
11%5%22%45%17%
360
July1st to 10thNight
6%321%46%23%2
350
11th to 20thNight
11%322%41%21%2
348
21st to endNight
8%320%45%23%2
581
August1st to 10thNight
9%216%42%28%2
537
11th to 20thNight
7%315%43%28%4
534
21st to endNight
10%324%35%25%3
661
September1st to 10thNight
11%7%22%34%21%5%
720
11th to 20thNight
13%5%20%31%27%5%
720
21st to endNight
16%7%21%32%20%4
720
October1st to 10thNight
19%6%28%27%18%3
720
11th to 20thNight
21%12%29%28%9%1
720
21st to endNight
27%10%31%27%5%
792
November1st to 10thNight
20%11%29%29%10%1
740
11th to 20thNight
19%14%36%23%7%2
760
21st to endNight
24%12%33%25%5%
760
December1st to 10thNight
29%13%36%17%5%
760
11th to 20thNight
23%14%41%19%3
760
21st to endNight
30%14%33%20%3
836
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