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 2018-02-22.

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%
16034
14%
48846
10%
15996
42%
15996
20%
33959

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%
972
9%
2716
3%
970
22%
970
13%
2154
January16th to endNight
19%
862
10%
2734
4%
862
25%
862
11%
2144
February1st to 15thNight
20%
761
9%
2482
3%
761
27%
761
11%
1927
February16th to endNight
24%
659
12%
1995
5%
659
30%
659
13%
1502
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
47%
540
26%
1048
May1st to 15thNight
45%
540
14%
1620
10%
540
49%
540
23%
1097
May16th to endNight
51%
501
17%
1624
15%
501
56%
501
28%
985
June1st to 15thNight
55%
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
70%
464
41%
762
July16th to endNight
69%
564
16%
1545
15%
531
71%
531
37%
904
August1st to 15thNight
66%
539
18%
1609
16%
536
67%
536
34%
959
August16th to endNight
65%
573
24%
1719
18%
573
68%
573
36%
1002
September1st to 15thNight
56%
696
22%
1920
15%
696
60%
696
32%
1212
September16th to endNight
60%
717
23%
1980
18%
717
63%
717
33%
1230
October1st to 15thNight
46%
720
18%
2103
15%
720
51%
720
25%
1388
October16th to endNight
27%
768
15%
2367
8%
768
36%
768
16%
1727
November1st to 15thNight
34%
760
17%
2471
15%
760
39%
760
20%
1663
November16th to endNight
25%
780
12%
2701
7%
780
32%
780
15%
1918
December1st to 15thNight
16%
780
7%
2730
2%
780
22%
780
11%
2088
December16th to endNight
15%
998
7%
3055
1%
998
22%
998
9%
2478

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%3445%7%34%
49393
Night
15%9%46%5%3445%6%34%
49028
Cloud CoverDay
14%8%36%5%35%45%7%34%
49403
Night
15%9%46%5%3445%6%34%
49032
TransparencyDay
48%5%13%20%10%1
49093
Night
49%5%12%20%10%1
48846
SeeingDay
18%5%24%25%18%7%
6239
Night
19%6%27%29%13%1
16042

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%3445%5%20%
1552
16th to endDay
15%16%8%10%9%34445%16%
1840
February1st to 15thDay
16%16%5%9%8%35%445%19%
1710
16th to endDay
14%13%6%9%8%3445%5%23%
1625
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%5%347%6%9%41%
2340
16th to endDay
10%425%5%35%46%8%42%
2483
September1st to 15thDay
12%5%15%5%345%6%8%40%
2027
16th to endDay
12%6%25%42446%8%42%
1980
October1st to 15thDay
14%6%36%6%445%5%6%38%
1857
16th to endDay
21%8%37%6%3434431%
1854
November1st to 15thDay
14%9%37%5%25%5%5%6%34%
1717
16th to endDay
15%10%5%9%7%45%45%6%25%
1589
December1st to 15thDay
16%14%5%8%6%44446%24%
1560
16th to endDay
19%17%6%8%7%34445%18%
1515
January1st to 15thNight
21%13%5%9%6%34345%23%
2716
16th to endNight
14%15%8%9%7%35%445%22%
2734
February1st to 15thNight
15%15%5%8%6%35%445%23%
2480
16th to endNight
17%12%49%6%3445%5%25%
1995
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%
1620
16th to endNight
8%424425%437%51%
1719
September1st to 15thNight
11%435%42445%7%46%
1920
16th to endNight
11%43442345%7%47%
1980
October1st to 15thNight
16%5%25%5%33347%40%
2103
16th to endNight
20%9%36%6%35%446%30%
2367
November1st to 15thNight
16%9%36%5%3445%7%34%
2471
16th to endNight
19%10%47%5%24447%29%
2701
December1st to 15thNight
18%13%5%8%6%24446%23%
2730
16th to endNight
21%14%7%8%6%34445%19%
3055

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%6%10%7%245%4420%
1552
16th to endDay
15%15%9%10%8%45%45%5%16%
1840
February1st to 15thDay
17%16%5%9%8%35%435%19%
1710
16th to endDay
14%13%6%10%7%45%35%5%23%
1625
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%
2340
16th to endDay
10%5%25%5%35%5%5%8%42%
2483
September1st to 15thDay
13%426%435%5%6%8%39%
2027
16th to endDay
13%5%25%42436%9%41%
1980
October1st to 15thDay
14%6%26%6%345%47%38%
1857
16th to endDay
21%8%37%6%34345%31%
1854
November1st to 15thDay
14%8%37%5%34447%34%
1717
16th to endDay
16%10%5%9%7%45%5%5%5%25%
1589
December1st to 15thDay
16%15%48%7%44446%23%
1560
16th to endDay
19%16%7%8%6%34346%17%
1515
January1st to 15thNight
22%13%5%9%6%34335%23%
2716
16th to endNight
15%15%8%9%7%4444422%
2734
February1st to 15thNight
16%15%5%9%6%35%435%24%
2473
16th to endNight
17%12%410%6%4435%5%25%
1995
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%
1620
16th to endNight
8%3244245%47%52%
1719
September1st to 15thNight
11%425%43445%6%46%
1920
16th to endNight
11%5%34423447%48%
1980
October1st to 15thNight
16%6%26%5%23446%40%
2103
16th to endNight
20%9%36%6%44445%30%
2367
November1st to 15thNight
16%10%35%43436%7%34%
2471
16th to endNight
20%10%46%5%3345%6%29%
2701
December1st to 15thNight
18%13%6%8%5%24446%23%
2730
16th to endNight
21%14%7%9%5%3434420%
3055

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
64%6%11%12%4
1553
16th to endDay
70%412%9%3
1840
February1st to 15thDay
67%410%13%4
1712
16th to endDay
62%412%14%5%1
1625
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
2327
16th to endDay
38%7%12%27%12%1
2483
September1st to 15thDay
40%6%15%25%11%
2027
16th to endDay
38%5%14%29%12%
1980
October1st to 15thDay
45%412%22%13%1
1857
16th to endDay
54%414%18%7%
1854
November1st to 15thDay
48%6%14%20%9%
1717
16th to endDay
57%6%15%15%4
1589
December1st to 15thDay
61%5%14%13%4
1560
16th to endDay
68%414%9%3
1515
January1st to 15thNight
64%311%12%7%
2716
16th to endNight
64%412%15%3
2734
February1st to 15thNight
61%6%9%15%6%
2482
16th to endNight
59%411%17%5%
1995
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
30%7%14%30%12%2
1609
16th to endNight
31%5%11%31%17%2
1719
September1st to 15thNight
36%5%12%28%14%1
1920
16th to endNight
35%5%11%32%14%1
1980
October1st to 15thNight
43%5%11%22%16%
2103
16th to endNight
54%5%11%20%7%
2367
November1st to 15thNight
47%5%13%22%9%1
2471
16th to endNight
54%5%17%17%5%
2701
December1st to 15thNight
61%5%16%12%4
2730
16th to endNight
66%5%11%11%5%
3055

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
24%10%42%15%5%
135
16th to endDay
31%9%39%18%1
144
February1st to 15thDay
29%10%42%17%
135
16th to endDay
23%12%38%21%6%
100
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%31%25%17%
313
16th to endDay
18%214%21%25%18%
332
September1st to 15thDay
11%316%22%31%14%
315
16th to endDay
14%216%22%27%15%
314
October1st to 15thDay
18%6%20%27%21%5%
315
16th to endDay
25%9%32%21%9%
270
November1st to 15thDay
20%7%27%25%12%6%
135
16th to endDay
21%16%40%14%7%
97
December1st to 15thDay
23%22%32%18%3
90
16th to endDay
31%20%34%10%1
101
January1st to 15thNight
28%10%35%19%5%
975
16th to endNight
22%9%35%26%6%
862
February1st to 15thNight
22%9%38%25%4
764
16th to endNight
23%9%33%26%5%
659
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%
539
16th to endNight
10%115%35%32%4
573
September1st to 15thNight
12%319%32%26%6%
696
16th to endNight
13%314%34%27%6%
717
October1st to 15thNight
18%423%31%19%2
720
16th to endNight
25%10%32%25%6%
768
November1st to 15thNight
22%8%29%25%13%
760
16th to endNight
25%13%30%21%9%
780
December1st to 15thNight
26%11%38%19%4
780
16th to endNight
29%11%35%20%3
998
Page generated at 2018-02-23 11:21:36. Version ac04

Copyright 2018 A. Danko


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