Brockville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Brockville clear sky chart from 2005-11-06 to 2024-01-31.

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%
22725
13%
74994
8%
22683
33%
22683
15%
54305

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
14%
760
7%
2649
3%
757
19%
757
6%
2165
January11th to 20thNight
16%
760
7%
2660
4%
760
19%
760
6%
2185
January21st to endNight
17%
835
10%
2823
4%
835
25%
835
10%
2169
February1st to 10thNight
10%
720
7%
2340
2%
720
17%
720
7%
1920
February11th to 20thNight
13%
703
12%
2252
4%
700
23%
700
11%
1697
February21st to endNight
18%
592
13%
1776
5%
592
27%
592
11%
1379
March1st to 10thNight
20%
720
14%
2160
8%
720
27%
720
14%
1629
March11th to 20thNight
19%
720
14%
1980
4%
720
28%
720
15%
1480
March21st to endNight
22%
792
20%
2059
7%
792
30%
792
20%
1497
April1st to 10thNight
20%
720
16%
1800
4%
720
26%
720
19%
1322
April11th to 20thNight
22%
711
16%
1775
4%
711
28%
711
19%
1304
April21st to endNight
24%
653
15%
1733
6%
653
30%
653
19%
1280
May1st to 10thNight
32%
360
15%
1440
12%
360
40%
360
16%
945
May11th to 20thNight
31%
354
19%
1416
14%
354
45%
354
19%
869
May21st to endNight
36%
388
14%
1550
12%
388
46%
388
21%
914
June1st to 10thNight
36%
360
11%
1440
11%
360
46%
360
16%
949
June11th to 20thNight
38%
360
13%
1440
14%
360
47%
360
19%
878
June21st to endNight
41%
360
11%
1440
13%
360
48%
360
18%
935
July1st to 10thNight
47%
350
14%
1400
18%
350
55%
350
25%
792
July11th to 20thNight
47%
348
16%
1392
20%
348
55%
348
23%
813
July21st to endNight
49%
394
15%
1486
14%
372
55%
372
22%
874
August1st to 10thNight
51%
412
16%
1476
14%
410
57%
410
24%
902
August11th to 20thNight
50%
561
17%
1625
12%
561
54%
561
27%
1060
August21st to endNight
44%
792
18%
1980
8%
792
48%
792
31%
1321
September1st to 10thNight
43%
720
15%
1800
6%
720
46%
720
30%
1210
September11th to 20thNight
49%
720
22%
1804
13%
720
52%
720
33%
1174
September21st to endNight
41%
720
21%
2026
15%
720
46%
720
25%
1357
October1st to 10thNight
32%
720
14%
2160
10%
720
38%
720
18%
1539
October11th to 20thNight
26%
720
13%
2160
7%
720
34%
720
15%
1578
October21st to endNight
22%
792
11%
2510
5%
792
30%
792
12%
1899
November1st to 10thNight
25%
740
15%
2407
9%
740
33%
740
16%
1666
November11th to 20thNight
22%
760
15%
2615
9%
760
31%
760
13%
1849
November21st to endNight
18%
760
10%
2660
5%
760
25%
760
8%
2060
December1st to 10thNight
14%
760
6%
2660
2%
760
18%
760
6%
2206
December11th to 20thNight
14%
759
10%
3254
5%
759
21%
759
7%
2498
December21st to endNight
11%
829
4%
4846
1%
817
16%
817
3%
3990

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%10%47%6%35%45%6%33%
74886
Night
19%11%47%6%3445%6%31%
75239
TransparencyDay
52%6%12%19%10%1
74591
Night
54%6%12%18%9%1
75068
SeeingDay
25%15%29%19%8%2
13468
Night
25%13%29%23%8%1
22734

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
20%17%5%10%7%45%445%19%
1517
11th to 20thDay
20%17%6%10%7%35%34421%
1520
21st to endDay
15%15%6%10%10%5%6%5%5%419%
1758
February1st to 10thDay
18%16%6%11%8%35%446%20%
1620
11th to 20thDay
17%15%5%9%7%35%44426%
1595
21st to endDay
21%16%6%10%7%45%44421%
1480
March1st to 10thDay
16%14%5%10%7%45%44428%
1797
11th to 20thDay
19%12%5%8%6%44345%30%
1975
21st to endDay
22%10%46%5%34335%36%
2296
April1st to 10thDay
21%11%46%5%35%235%33%
2160
11th to 20thDay
22%8%36%434345%38%
2134
21st to endDay
23%10%36%435%446%32%
2240
May1st to 10thDay
19%7%36%6%35%5%5%6%35%
2520
11th to 20thDay
16%6%47%5%3445%8%39%
2478
21st to endDay
15%6%36%6%345%6%9%38%
2725
June1st to 10thDay
22%7%35%5%35%46%7%32%
2520
11th to 20thDay
17%6%245%45%5%6%8%38%
2520
21st to endDay
19%8%25%6%35%5%6%7%35%
2520
July1st to 10thDay
13%5%25%5%345%6%9%44%
2520
11th to 20thDay
14%5%35%5%45%6%7%9%38%
2520
21st to endDay
12%425%5%36%6%8%9%39%
2744
August1st to 10thDay
13%6%26%5%45%5%6%8%40%
2449
11th to 20thDay
13%6%346%46%5%6%9%40%
2257
21st to endDay
14%6%26%5%35%5%6%8%40%
2376
September1st to 10thDay
15%6%35%5%245%6%6%43%
2160
11th to 20thDay
14%6%25%5%2345%7%47%
2156
21st to endDay
19%7%25%5%35%5%5%8%38%
1931
October1st to 10thDay
22%8%36%5%3445%6%33%
1800
11th to 20thDay
21%11%38%7%3445%7%28%
1800
21st to endDay
28%9%27%6%35%446%26%
1846
November1st to 10thDay
17%8%47%7%45%46%7%32%
1671
11th to 20thDay
17%11%48%7%35%5%5%5%29%
1563
21st to endDay
21%16%5%8%6%35%45%6%21%
1520
December1st to 10thDay
25%18%6%10%8%34346%14%
1520
11th to 20thDay
22%18%5%9%6%34335%21%
1906
21st to endDay
27%18%5%10%5%3433319%
2772
January1st to 10thNight
20%19%6%10%7%4444418%
2649
11th to 20thNight
19%18%6%10%8%45%44419%
2660
21st to endNight
14%16%6%10%7%45%445%25%
2823
February1st to 10thNight
20%15%6%12%8%35%445%19%
2340
11th to 20thNight
16%14%6%10%8%35%445%26%
2250
21st to endNight
19%13%6%9%7%35%346%25%
1776
March1st to 10thNight
16%17%6%8%6%3434429%
2150
11th to 20thNight
20%14%5%6%6%24345%32%
1980
21st to endNight
21%11%46%5%2333437%
2059
April1st to 10thNight
23%9%5%7%5%2445%5%33%
1800
11th to 20thNight
22%8%26%6%34346%36%
1775
21st to endNight
23%9%36%5%3345%5%32%
1733
May1st to 10thNight
23%7%35%5%335%5%7%34%
1440
11th to 20thNight
14%7%37%5%44448%40%
1415
21st to endNight
14%5%35%4445%5%8%43%
1550
June1st to 10thNight
20%6%36%6%345%6%8%33%
1440
11th to 20thNight
16%5%35%5%35%5%5%8%41%
1440
21st to endNight
17%6%35%5%36%5%6%9%34%
1440
July1st to 10thNight
12%6%25%4345%5%8%47%
1440
11th to 20thNight
12%5%25%435%5%6%10%41%
1440
21st to endNight
12%6%25%5%35%6%6%8%44%
1574
August1st to 10thNight
12%6%25%435%6%7%10%40%
1486
11th to 20thNight
13%7%26%5%3445%8%42%
1625
21st to endNight
12%6%35%435%5%6%7%43%
1980
September1st to 10thNight
15%7%35%434447%45%
1800
11th to 20thNight
14%6%35%43235%7%48%
1804
21st to endNight
16%6%25%5%345%5%7%41%
2026
October1st to 10thNight
20%8%36%6%35%5%5%6%34%
2160
11th to 20thNight
20%9%37%6%3445%6%31%
2160
21st to endNight
28%8%36%6%34446%26%
2510
November1st to 10thNight
20%10%45%5%3445%7%34%
2407
11th to 20thNight
18%11%46%6%445%5%6%31%
2615
21st to endNight
22%14%48%6%4445%6%23%
2660
December1st to 10thNight
23%18%6%9%7%45%45%416%
2660
11th to 20thNight
23%15%5%8%7%34335%25%
3288
21st to endNight
31%14%6%10%6%3444415%
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
67%6%10%13%31
1518
11th to 20thDay
68%49%10%8%
1520
21st to endDay
67%5%11%10%6%1
1758
February1st to 10thDay
67%49%15%41
1620
11th to 20thDay
62%5%10%15%8%1
1604
21st to endDay
68%5%7%11%8%1
1480
March1st to 10thDay
61%411%15%8%1
1800
11th to 20thDay
57%5%10%13%13%2
1975
21st to endDay
53%47%17%14%5%
2296
April1st to 10thDay
55%47%18%13%3
2160
11th to 20thDay
49%48%20%15%3
2134
21st to endDay
54%5%8%15%13%4
2240
May1st to 10thDay
49%7%9%18%15%2
2520
11th to 20thDay
43%6%10%24%15%2
2482
21st to endDay
43%7%15%21%12%3
2725
June1st to 10thDay
51%6%11%19%12%1
2520
11th to 20thDay
43%7%12%25%13%2
2520
21st to endDay
47%8%13%20%11%1
2520
July1st to 10thDay
36%8%12%28%15%1
2450
11th to 20thDay
40%8%15%26%9%
2445
21st to endDay
38%9%18%23%11%
2591
August1st to 10thDay
40%9%16%25%10%
2435
11th to 20thDay
41%8%16%23%11%
2257
21st to endDay
40%7%14%27%11%
2376
September1st to 10thDay
40%7%14%25%13%1
2160
11th to 20thDay
38%6%12%30%15%
2156
21st to endDay
45%7%12%26%10%
1931
October1st to 10thDay
52%5%12%21%11%
1800
11th to 20thDay
56%6%15%17%6%1
1800
21st to endDay
61%6%11%15%7%1
1846
November1st to 10thDay
50%6%16%21%7%1
1671
11th to 20thDay
57%5%12%16%8%2
1563
21st to endDay
65%7%13%10%6%
1520
December1st to 10thDay
70%6%12%10%2
1520
11th to 20thDay
69%5%12%11%3
1906
21st to endDay
72%5%7%13%3
2772
January1st to 10thNight
70%5%10%10%4
2649
11th to 20thNight
70%5%10%9%5%1
2660
21st to endNight
62%5%10%15%8%1
2823
February1st to 10thNight
69%5%10%11%5%1
2340
11th to 20thNight
60%5%10%18%7%
2252
21st to endNight
62%5%9%16%8%1
1776
March1st to 10thNight
60%411%16%9%1
2160
11th to 20thNight
56%410%17%11%1
1981
21st to endNight
53%37%19%15%3
2059
April1st to 10thNight
53%39%20%13%2
1800
11th to 20thNight
50%5%10%18%16%2
1775
21st to endNight
54%49%16%13%3
1733
May1st to 10thNight
49%5%10%16%15%5%
1440
11th to 20thNight
43%6%10%23%15%3
1416
21st to endNight
40%5%16%20%16%3
1551
June1st to 10thNight
47%7%13%20%11%1
1440
11th to 20thNight
41%7%13%20%17%2
1440
21st to endNight
44%8%12%22%13%1
1440
July1st to 10thNight
34%8%12%27%17%2
1400
11th to 20thNight
38%6%14%29%12%
1392
21st to endNight
37%8%15%27%11%1
1486
August1st to 10thNight
37%9%17%24%13%1
1476
11th to 20thNight
40%7%14%25%14%1
1625
21st to endNight
38%7%14%28%12%
1980
September1st to 10thNight
40%6%13%27%13%1
1800
11th to 20thNight
37%6%13%30%13%1
1804
21st to endNight
42%6%11%28%12%1
2026
October1st to 10thNight
50%6%12%19%11%1
2160
11th to 20thNight
52%7%14%18%8%1
2160
21st to endNight
59%6%14%13%8%1
2510
November1st to 10thNight
50%6%15%18%10%1
2407
11th to 20thNight
52%6%14%17%8%2
2615
21st to endNight
63%6%12%14%5%
2660
December1st to 10thNight
71%5%11%11%2
2660
11th to 20thNight
64%5%11%15%5%
3288
21st to endNight
73%5%9%11%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
28%22%32%12%6%1
180
11th to 20thDay
37%18%28%14%21
180
21st to endDay
25%24%31%16%4
240
February1st to 10thDay
39%26%30%4
240
11th to 20thDay
34%24%35%6%
262
21st to endDay
38%19%29%12%2
346
March1st to 10thDay
27%20%32%16%4
420
11th to 20thDay
32%20%30%14%31
420
21st to endDay
35%18%25%14%6%1
462
April1st to 10thDay
35%14%30%16%5%
420
11th to 20thDay
33%17%25%14%8%3
412
21st to endDay
33%19%29%13%5%2
420
May1st to 10thDay
26%17%30%19%7%1
423
11th to 20thDay
21%16%36%18%8%2
447
21st to endDay
19%15%30%23%11%1
485
June1st to 10thDay
27%12%30%22%7%1
450
11th to 20thDay
18%12%32%24%11%2
450
21st to endDay
20%17%30%20%10%3
450
July1st to 10thDay
15%8%30%28%16%2
445
11th to 20thDay
16%10%29%29%14%3
444
21st to endDay
14%10%34%30%10%2
488
August1st to 10thDay
15%9%26%31%15%5%
446
11th to 20thDay
15%7%26%30%16%6%
439
21st to endDay
15%11%32%22%14%7%
495
September1st to 10thDay
17%11%30%23%11%7%
450
11th to 20thDay
15%10%25%25%15%10%
450
21st to endDay
21%11%27%23%16%3
450
October1st to 10thDay
26%16%24%18%11%5%
450
11th to 20thDay
28%19%28%17%6%2
450
21st to endDay
36%14%27%18%5%
428
November1st to 10thDay
27%20%28%18%7%1
365
11th to 20thDay
30%14%34%14%6%1
223
21st to endDay
31%19%35%13%2
180
December1st to 10thDay
37%20%24%15%31
180
11th to 20thDay
31%26%33%8%2
180
21st to endDay
36%21%28%13%21
198
January1st to 10thNight
33%18%27%18%4
760
11th to 20thNight
32%17%28%19%4
760
21st to endNight
25%16%32%21%6%
835
February1st to 10thNight
29%20%32%16%2
720
11th to 20thNight
24%19%37%17%3
703
21st to endNight
29%18%31%20%3
592
March1st to 10thNight
28%16%30%23%3
720
11th to 20thNight
28%18%31%18%41
720
21st to endNight
28%13%32%20%7%1
792
April1st to 10thNight
28%15%32%23%2
720
11th to 20thNight
27%17%29%19%7%
711
21st to endNight
28%11%31%21%8%
653
May1st to 10thNight
27%9%26%28%9%1
360
11th to 20thNight
16%10%36%30%8%
354
21st to endNight
15%9%34%30%10%1
389
June1st to 10thNight
21%7%28%35%8%1
360
11th to 20thNight
16%12%29%31%12%1
360
21st to endNight
17%8%28%33%14%1
360
July1st to 10thNight
11%6%31%37%15%
350
11th to 20thNight
13%428%36%18%1
348
21st to endNight
13%5%28%41%11%2
394
August1st to 10thNight
14%326%37%20%
412
11th to 20thNight
17%420%35%21%3
561
21st to endNight
14%7%27%34%15%3
792
September1st to 10thNight
17%8%27%31%16%2
720
11th to 20thNight
18%7%20%30%20%4
720
21st to endNight
18%11%27%25%18%2
720
October1st to 10thNight
25%12%26%20%15%1
720
11th to 20thNight
24%15%29%23%8%1
720
21st to endNight
32%13%28%22%4
792
November1st to 10thNight
27%14%30%21%8%
740
11th to 20thNight
25%20%29%17%9%
760
21st to endNight
35%16%26%17%6%
760
December1st to 10thNight
34%18%27%17%3
760
11th to 20thNight
31%17%32%17%31
760
21st to endNight
35%16%30%16%2
836
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