Sarnia
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sarnia clear sky chart from 2005-11-05 to 2017-08-12.

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
37%
15246
14%
46423
10%
15208
43%
15208
20%
32285

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 15thNight
16%
897
9%
2506
3%
895
21%
895
12%
2007
January16th to endNight
20%
796
10%
2524
4%
796
27%
796
11%
1980
February1st to 15thNight
20%
701
10%
2287
3%
701
28%
701
11%
1768
February16th to endNight
25%
631
12%
1910
5%
631
31%
631
14%
1432
March1st to 15thNight
26%
720
13%
2046
8%
720
31%
720
16%
1523
March16th to endNight
36%
768
17%
2112
12%
768
41%
768
24%
1470
April1st to 15thNight
33%
632
14%
1818
8%
632
39%
632
21%
1293
April16th to endNight
39%
540
20%
1620
10%
540
48%
540
26%
1048
May1st to 15thNight
45%
540
14%
1620
10%
540
50%
540
23%
1097
May16th to endNight
51%
501
17%
1624
15%
501
56%
501
28%
985
June1st to 15thNight
56%
360
15%
1305
16%
360
63%
360
28%
773
June16th to endNight
62%
360
17%
1260
18%
360
67%
360
32%
712
July1st to 15thNight
67%
464
18%
1314
18%
464
69%
464
41%
762
July16th to endNight
71%
564
16%
1545
15%
531
72%
531
37%
904
August1st to 15thNight
67%
527
17%
1575
16%
524
67%
524
34%
942
August16th to endNight
65%
525
22%
1575
17%
525
68%
525
35%
922
September1st to 15thNight
55%
638
23%
1760
16%
638
59%
638
31%
1124
September16th to endNight
60%
657
21%
1815
17%
657
62%
657
33%
1135
October1st to 15thNight
46%
660
18%
1928
15%
660
51%
660
26%
1262
October16th to endNight
25%
704
13%
2170
7%
704
33%
704
15%
1601
November1st to 15thNight
34%
700
19%
2276
16%
700
40%
700
20%
1515
November16th to endNight
25%
720
12%
2493
8%
720
31%
720
14%
1791
December1st to 15thNight
15%
720
6%
2520
2%
720
21%
720
11%
1941
December16th to endNight
16%
921
7%
2820
1%
921
21%
921
9%
2298

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
13%8%36%6%35%45%7%34%
47537
Night
15%9%46%5%3445%6%34%
46605
Cloud CoverDay
14%8%36%5%35%45%7%34%
47547
Night
15%9%46%5%3445%6%34%
46609
TransparencyDay
48%6%13%20%10%1
47237
Night
49%5%12%21%10%1
46423
SeeingDay
17%5%24%26%18%7%
5623
Night
19%6%27%30%13%1
15254

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 15thDay
16%15%8%9%6%4345%5%20%
1432
16th to endDay
14%16%8%11%9%3445%5%15%
1698
February1st to 15thDay
16%16%5%10%8%35%445%18%
1575
16th to endDay
13%13%6%9%8%345%5%5%24%
1563
March1st to 15thDay
15%11%6%8%7%36%346%25%
1902
16th to endDay
16%9%5%7%6%35%446%29%
2112
April1st to 15thDay
19%10%36%434447%31%
2140
16th to endDay
17%8%24434447%38%
2340
May1st to 15thDay
18%5%35%5%35%45%7%35%
2331
16th to endDay
13%5%245%35%45%6%42%
2488
June1st to 15thDay
9%425%5%345%6%9%41%
2652
16th to endDay
9%435%5%35%6%6%9%39%
2700
July1st to 15thDay
7%4245%35%47%8%47%
2563
16th to endDay
9%424435%5%7%10%41%
2516
August1st to 15thDay
8%5%25%4347%6%9%41%
2288
16th to endDay
10%4245%35%5%7%8%42%
2275
September1st to 15thDay
13%6%25%5%345%5%8%39%
1858
16th to endDay
12%6%26%42446%9%40%
1815
October1st to 15thDay
13%6%26%6%445%5%6%38%
1702
16th to endDay
22%8%37%5%3434431%
1700
November1st to 15thDay
14%8%36%5%25%447%35%
1582
16th to endDay
16%10%5%9%7%45%46%6%24%
1467
December1st to 15thDay
16%15%5%8%6%44446%23%
1440
16th to endDay
18%18%6%8%7%34345%18%
1398
January1st to 15thNight
22%13%5%9%6%33345%22%
2506
16th to endNight
14%15%8%8%8%35%445%22%
2524
February1st to 15thNight
15%14%5%8%6%35%445%24%
2285
16th to endNight
16%12%49%7%3445%5%25%
1910
March1st to 15thNight
17%10%5%7%6%3445%5%29%
2034
16th to endNight
16%6%36%6%3445%6%35%
2112
April1st to 15thNight
19%9%45%43435%5%34%
1818
16th to endNight
15%7%3442445%7%40%
1620
May1st to 15thNight
16%5%37%5%3446%8%35%
1620
16th to endNight
12%425%4345%46%46%
1622
June1st to 15thNight
9%4245%35%6%6%9%42%
1305
16th to endNight
9%3245%245%5%9%47%
1260
July1st to 15thNight
6%425%424347%54%
1394
16th to endNight
6%4134345%6%9%50%
1652
August1st to 15thNight
6%415%4346%7%9%46%
1586
16th to endNight
8%433425%437%51%
1575
September1st to 15thNight
12%435%424446%46%
1760
16th to endNight
12%43442345%6%47%
1815
October1st to 15thNight
15%5%25%5%33347%41%
1928
16th to endNight
20%9%36%6%34446%29%
2170
November1st to 15thNight
15%8%35%5%3445%7%35%
2276
16th to endNight
20%11%47%5%34447%28%
2493
December1st to 15thNight
19%14%5%8%5%34446%23%
2520
16th to endNight
22%14%6%8%6%34445%18%
2820

Percentage Cloud Cover SE (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 15thDay
16%16%7%10%7%245%4420%
1432
16th to endDay
15%16%9%10%8%45%45%5%14%
1698
February1st to 15thDay
16%15%5%9%8%35%446%19%
1575
16th to endDay
13%13%6%10%7%46%35%5%23%
1563
March1st to 15thDay
16%12%5%8%8%45%346%25%
1913
16th to endDay
16%10%5%7%5%35%45%6%28%
2111
April1st to 15thDay
19%10%35%424447%31%
2140
16th to endDay
16%8%2442445%7%38%
2340
May1st to 15thDay
18%5%35%5%35%45%7%35%
2331
16th to endDay
13%5%35%5%35%446%42%
2488
June1st to 15thDay
9%5%35%5%25%5%6%9%41%
2652
16th to endDay
9%425%5%36%5%7%9%39%
2700
July1st to 15thDay
7%33443446%9%47%
2563
16th to endDay
9%424435%6%7%10%40%
2516
August1st to 15thDay
8%425%5%447%7%9%40%
2288
16th to endDay
10%5%24435%5%6%9%42%
2275
September1st to 15thDay
14%426%435%5%6%8%38%
1858
16th to endDay
13%5%25%42436%10%39%
1815
October1st to 15thDay
13%6%26%6%34447%37%
1702
16th to endDay
22%9%37%5%34335%31%
1700
November1st to 15thDay
14%9%36%5%34447%35%
1582
16th to endDay
16%10%5%9%7%45%5%5%5%24%
1467
December1st to 15thDay
17%15%48%7%44446%22%
1440
16th to endDay
19%17%7%8%6%34336%17%
1398
January1st to 15thNight
22%13%5%9%6%34335%22%
2506
16th to endNight
15%15%8%9%7%4444422%
2524
February1st to 15thNight
15%15%5%8%6%35%435%25%
2278
16th to endNight
17%11%410%6%4445%5%25%
1910
March1st to 15thNight
17%10%5%7%6%3445%429%
2046
16th to endNight
16%7%36%6%3445%6%35%
2112
April1st to 15thNight
19%9%35%43445%6%34%
1818
16th to endNight
14%8%3442445%7%39%
1620
May1st to 15thNight
15%7%36%5%3446%8%35%
1619
16th to endNight
12%325%4245%46%46%
1622
June1st to 15thNight
10%4245%36%5%6%7%42%
1305
16th to endNight
9%3244335%6%9%47%
1260
July1st to 15thNight
7%424424347%54%
1394
16th to endNight
6%2143245%6%9%50%
1652
August1st to 15thNight
6%425%4346%6%9%46%
1586
16th to endNight
9%4244235%37%52%
1575
September1st to 15thNight
12%436%434446%45%
1760
16th to endNight
11%434423446%48%
1815
October1st to 15thNight
15%6%26%5%23447%41%
1928
16th to endNight
21%9%46%6%34445%29%
2170
November1st to 15thNight
15%10%25%43436%7%35%
2276
16th to endNight
20%11%46%5%33446%28%
2493
December1st to 15thNight
19%13%6%8%5%24445%23%
2520
16th to endNight
22%13%7%9%5%3444419%
2820

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 15thDay
65%6%11%12%3
1433
16th to endDay
71%411%8%3
1698
February1st to 15thDay
66%411%13%4
1577
16th to endDay
61%412%14%6%1
1563
March1st to 15thDay
59%5%12%14%7%
1913
16th to endDay
54%5%10%19%8%1
2112
April1st to 15thDay
51%5%11%20%10%
2140
16th to endDay
44%5%14%18%13%2
2340
May1st to 15thDay
47%5%10%22%10%2
2331
16th to endDay
42%5%11%24%14%1
2492
June1st to 15thDay
37%6%15%25%14%1
2652
16th to endDay
38%7%15%23%15%
2700
July1st to 15thDay
32%5%10%29%18%1
2414
16th to endDay
36%8%15%23%14%2
2360
August1st to 15thDay
35%9%15%24%13%1
2275
16th to endDay
37%7%13%27%13%1
2275
September1st to 15thDay
41%6%15%25%10%
1858
16th to endDay
40%414%28%11%
1815
October1st to 15thDay
45%412%22%13%1
1702
16th to endDay
55%415%18%6%
1700
November1st to 15thDay
47%6%14%21%9%
1582
16th to endDay
58%6%15%14%4
1467
December1st to 15thDay
62%5%15%12%3
1440
16th to endDay
68%414%9%2
1398
January1st to 15thNight
65%311%12%6%
2506
16th to endNight
64%412%15%3
2524
February1st to 15thNight
61%6%9%15%6%
2287
16th to endNight
59%412%18%5%
1910
March1st to 15thNight
56%5%11%19%6%1
2046
16th to endNight
48%412%23%10%
2112
April1st to 15thNight
50%5%11%20%11%1
1818
16th to endNight
41%5%10%20%17%4
1620
May1st to 15thNight
46%5%10%22%12%3
1620
16th to endNight
36%6%11%25%16%3
1624
June1st to 15thNight
35%7%13%28%14%1
1305
16th to endNight
32%6%15%24%19%1
1260
July1st to 15thNight
29%48%32%22%2
1314
16th to endNight
29%7%16%26%18%3
1545
August1st to 15thNight
31%8%14%30%12%2
1575
16th to endNight
31%5%11%31%16%2
1575
September1st to 15thNight
37%6%12%27%13%2
1760
16th to endNight
35%5%11%31%13%1
1815
October1st to 15thNight
41%5%11%22%16%
1928
16th to endNight
55%5%11%19%6%
2170
November1st to 15thNight
46%5%13%23%10%1
2276
16th to endNight
55%5%16%17%4
2493
December1st to 15thNight
61%5%16%11%4
2520
16th to endNight
67%5%11%10%4
2820

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 15thDay
23%10%43%16%5%1
90
16th to endDay
36%10%32%19%1
96
February1st to 15thDay
23%12%45%18%
90
16th to endDay
16%11%43%22%7%
81
March1st to 15thDay
26%10%31%24%7%
203
16th to endDay
26%5%27%27%10%2
288
April1st to 15thDay
25%6%28%24%12%2
270
16th to endDay
22%6%26%21%16%7%
270
May1st to 15thDay
22%325%25%18%4
288
16th to endDay
15%424%24%20%9%
331
June1st to 15thDay
12%422%36%19%5%
447
16th to endDay
12%327%29%20%6%
495
July1st to 15thDay
12%121%29%23%11%
475
16th to endDay
7%217%33%27%11%
376
August1st to 15thDay
10%114%30%25%17%
297
16th to endDay
16%213%21%25%20%
268
September1st to 15thDay
14%315%20%32%14%
255
16th to endDay
15%216%25%29%10%
254
October1st to 15thDay
15%6%21%29%22%4
255
16th to endDay
27%9%31%22%8%
212
November1st to 15thDay
15%8%21%33%15%5%
90
16th to endDay
21%21%33%13%9%
65
December1st to 15thDay
26%18%35%18%1
60
16th to endDay
32%23%32%10%
67
January1st to 15thNight
29%11%34%19%5%
900
16th to endNight
22%9%34%26%6%
796
February1st to 15thNight
22%9%37%25%4
704
16th to endNight
22%10%32%27%6%
631
March1st to 15thNight
21%7%34%29%6%
720
16th to endNight
20%431%32%9%1
768
April1st to 15thNight
23%7%31%29%6%
632
16th to endNight
20%330%31%11%2
540
May1st to 15thNight
18%325%36%15%1
540
16th to endNight
12%224%38%19%2
503
June1st to 15thNight
10%224%43%19%
360
16th to endNight
10%116%46%22%1
360
July1st to 15thNight
11%13%40%29%4
464
16th to endNight
8%12%46%28%2
564
August1st to 15thNight
8%13%38%33%5%
527
16th to endNight
11%115%34%32%5%
525
September1st to 15thNight
13%319%31%25%6%
638
16th to endNight
14%314%35%25%5%
657
October1st to 15thNight
17%424%31%19%2
660
16th to endNight
25%10%32%25%5%
704
November1st to 15thNight
21%7%31%24%13%1
700
16th to endNight
25%14%27%22%9%
720
December1st to 15thNight
26%11%38%19%3
720
16th to endNight
29%11%33%21%3
921
Page generated at 2017-08-13 14:16:47. Version ac04

Copyright 2017 A. Danko


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