Strathroy
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Strathroy clear sky chart from 2005-11-06 to 2024-02-05.

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
34%
23447
13%
80206
10%
23341
39%
23341
16%
58090

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%
945
6%
4472
3%
926
19%
926
5%
3604
January11th to 20thNight
15%
770
3%
4140
3%
752
18%
752
3%
3614
January21st to endNight
17%
833
5%
4525
4%
814
22%
814
5%
3765
February1st to 10thNight
16%
739
7%
2399
3%
739
21%
739
9%
1950
February11th to 20thNight
20%
700
9%
2253
4%
700
27%
700
11%
1714
February21st to endNight
16%
592
10%
1776
2%
592
25%
592
12%
1390
March1st to 10thNight
25%
720
15%
2048
8%
720
31%
720
16%
1507
March11th to 20thNight
27%
720
18%
1980
9%
720
34%
720
20%
1414
March21st to endNight
30%
792
16%
2178
10%
792
34%
792
18%
1600
April1st to 10thNight
27%
720
14%
1931
6%
720
33%
720
20%
1401
April11th to 20thNight
33%
543
19%
1607
9%
543
41%
543
23%
1087
April21st to endNight
33%
540
16%
1620
7%
540
40%
540
21%
1115
May1st to 10thNight
38%
540
15%
1620
9%
540
43%
540
22%
1104
May11th to 20thNight
45%
531
17%
1592
12%
531
51%
531
26%
1030
May21st to endNight
54%
422
18%
1585
19%
422
61%
422
28%
890
June1st to 10thNight
48%
360
15%
1414
16%
360
57%
360
25%
806
June11th to 20thNight
53%
360
18%
1260
19%
360
61%
360
27%
750
June21st to endNight
55%
360
20%
1260
20%
360
62%
360
28%
724
July1st to 10thNight
65%
375
20%
1250
23%
375
69%
375
37%
676
July11th to 20thNight
63%
522
18%
1481
17%
522
66%
522
35%
888
July21st to endNight
66%
591
15%
1672
12%
558
69%
558
34%
988
August1st to 10thNight
69%
537
18%
1600
16%
534
70%
534
32%
970
August11th to 20thNight
66%
534
22%
1598
18%
534
68%
534
34%
948
August21st to endNight
61%
594
24%
1782
17%
594
65%
594
34%
1047
September1st to 10thNight
56%
716
18%
1868
11%
716
59%
716
33%
1200
September11th to 20thNight
61%
720
26%
1980
19%
720
63%
720
37%
1176
September21st to endNight
47%
720
19%
1980
15%
720
50%
720
27%
1336
October1st to 10thNight
42%
720
18%
2106
15%
720
47%
720
25%
1394
October11th to 20thNight
31%
720
14%
2160
10%
720
38%
720
19%
1538
October21st to endNight
25%
792
13%
2426
9%
792
31%
792
13%
1840
November1st to 10thNight
35%
740
20%
2406
17%
740
42%
740
21%
1582
November11th to 20thNight
22%
760
12%
2588
7%
760
29%
760
13%
1860
November21st to endNight
23%
760
8%
2660
6%
760
27%
760
11%
2049
December1st to 10thNight
15%
760
5%
2660
2%
760
18%
760
8%
2161
December11th to 20thNight
15%
760
6%
3273
3%
759
21%
759
6%
2582
December21st to endNight
13%
939
3%
5056
1%
926
18%
926
3%
4390

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
16%10%47%6%45%5%5%7%31%
78405
Night
16%11%5%7%6%35%5%5%7%31%
80440
TransparencyDay
52%7%12%18%10%1
78113
Night
53%7%12%17%9%1
80252
SeeingDay
18%11%28%24%13%5%
14008
Night
20%10%28%29%12%1
23468

By Month

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 10thDay
18%20%7%12%6%4443417%
2463
11th to 20thDay
14%19%10%16%10%6%6%4339%
2810
21st to endDay
26%19%10%10%6%3432413%
3124
February1st to 10thDay
18%15%5%11%10%45%5%45%19%
1656
11th to 20thDay
16%13%7%12%9%5%5%446%19%
1592
21st to endDay
19%14%6%11%7%35%45%5%22%
1480
March1st to 10thDay
16%12%5%10%7%45%445%27%
1912
11th to 20thDay
14%12%6%9%5%3445%6%31%
1980
21st to endDay
20%11%5%8%6%345%4429%
2178
April1st to 10thDay
16%13%5%6%6%3445%7%31%
2035
11th to 20thDay
19%11%35%5%35%46%7%33%
2312
21st to endDay
21%9%46%5%2445%6%33%
2340
May1st to 10thDay
17%8%36%6%345%6%6%35%
2340
11th to 20thDay
17%8%36%6%3445%7%37%
2301
21st to endDay
12%5%35%5%36%5%5%9%42%
2691
June1st to 10thDay
12%6%36%5%35%6%6%8%40%
2541
11th to 20thDay
11%6%35%6%36%6%6%9%41%
2700
21st to endDay
13%435%6%35%5%6%9%41%
2700
July1st to 10thDay
10%4245%35%5%6%10%46%
2668
11th to 20thDay
11%5%25%6%35%6%6%10%42%
2426
21st to endDay
9%6%26%6%36%6%7%10%39%
2547
August1st to 10thDay
9%425%6%5%6%6%7%10%39%
2327
11th to 20thDay
9%6%36%8%46%6%7%10%36%
2303
21st to endDay
11%6%36%5%45%46%9%42%
2559
September1st to 10thDay
11%6%36%5%45%6%5%8%39%
2084
11th to 20thDay
12%5%245%346%6%8%45%
1980
21st to endDay
17%7%26%5%35%5%5%9%36%
1980
October1st to 10thDay
16%7%26%6%45%5%5%7%37%
1854
11th to 20thDay
20%10%47%5%345%5%8%28%
1800
21st to endDay
25%11%47%7%445%5%5%24%
1926
November1st to 10thDay
15%11%37%7%45%45%6%33%
1672
11th to 20thDay
16%14%46%7%46%6%5%7%26%
1592
21st to endDay
21%16%6%8%7%5%46%5%6%18%
1520
December1st to 10thDay
16%17%7%11%7%345%6%7%17%
1520
11th to 20thDay
19%17%8%10%7%445%5%5%16%
1910
21st to endDay
30%20%7%8%6%3444410%
2582
January1st to 10thNight
17%18%8%11%6%44445%19%
4488
11th to 20thNight
15%19%8%12%8%5%7%6%4411%
4145
21st to endNight
24%16%8%10%7%3445%5%14%
4532
February1st to 10thNight
18%15%6%10%8%35%6%45%20%
2399
11th to 20thNight
17%13%6%8%6%36%5%6%6%23%
2251
21st to endNight
18%13%410%7%36%45%5%24%
1776
March1st to 10thNight
15%11%48%6%45%5%5%7%30%
2048
11th to 20thNight
15%10%5%7%6%44447%35%
1980
21st to endNight
20%9%47%6%45%445%32%
2178
April1st to 10thNight
18%10%45%5%35%5%5%6%34%
1931
11th to 20thNight
18%8%35%5%3445%8%37%
1607
21st to endNight
16%9%47%5%45%45%8%35%
1620
May1st to 10thNight
16%8%37%5%345%5%8%35%
1620
11th to 20thNight
13%6%36%6%25%5%6%8%40%
1592
21st to endNight
11%423436%5%5%7%50%
1584
June1st to 10thNight
13%425%435%5%6%9%44%
1414
11th to 20thNight
10%425%5%25%6%7%10%43%
1260
21st to endNight
10%4246%345%5%8%48%
1260
July1st to 10thNight
7%4245%33448%56%
1286
11th to 20thNight
10%425%42446%9%50%
1530
21st to endNight
8%5%23435%6%8%9%48%
1771
August1st to 10thNight
8%426%5%35%6%5%9%47%
1611
11th to 20thNight
7%5%25%5%36%5%6%9%48%
1598
21st to endNight
9%5%14435%46%8%51%
1782
September1st to 10thNight
9%6%45%6%25%5%5%8%46%
1868
11th to 20thNight
11%5%243345%48%51%
1980
21st to endNight
16%6%26%6%3435%7%42%
1980
October1st to 10thNight
14%7%37%6%3445%6%42%
2106
11th to 20thNight
21%8%36%5%2445%6%35%
2160
21st to endNight
25%10%47%6%45%45%6%26%
2426
November1st to 10thNight
15%9%35%5%3346%7%39%
2406
11th to 20thNight
16%11%5%7%6%45%5%7%7%27%
2588
21st to endNight
21%16%5%7%6%345%6%5%23%
2660
December1st to 10thNight
20%16%7%9%6%35%5%5%7%19%
2660
11th to 20thNight
16%17%8%9%7%44445%21%
3285
21st to endNight
28%20%7%8%6%3433413%
5058

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
70%9%9%10%2
2464
11th to 20thDay
79%7%7%42
2810
21st to endDay
78%5%9%5%3
3124
February1st to 10thDay
68%6%11%10%5%
1656
11th to 20thDay
66%5%10%12%5%
1601
21st to endDay
64%6%10%12%6%1
1480
March1st to 10thDay
59%5%13%15%7%1
1912
11th to 20thDay
54%6%10%18%10%2
1980
21st to endDay
58%5%8%17%10%1
2178
April1st to 10thDay
54%6%11%19%10%1
2035
11th to 20thDay
49%6%13%18%13%1
2312
21st to endDay
51%6%14%16%12%2
2340
May1st to 10thDay
47%7%12%20%12%2
2340
11th to 20thDay
47%6%12%20%13%2
2305
21st to endDay
39%8%14%23%15%2
2691
June1st to 10thDay
39%8%13%25%13%2
2541
11th to 20thDay
38%9%13%22%17%2
2700
21st to endDay
39%8%12%25%16%1
2700
July1st to 10thDay
33%7%12%27%18%3
2595
11th to 20thDay
36%7%15%26%14%1
2352
21st to endDay
37%9%15%22%15%2
2405
August1st to 10thDay
37%9%16%27%11%1
2314
11th to 20thDay
40%9%16%22%11%1
2303
21st to endDay
39%7%14%25%14%1
2559
September1st to 10thDay
41%8%15%21%13%1
2084
11th to 20thDay
35%8%13%30%14%
1980
21st to endDay
44%7%14%24%11%1
1980
October1st to 10thDay
45%7%13%20%13%1
1854
11th to 20thDay
54%8%14%17%7%1
1800
21st to endDay
62%6%12%13%6%
1926
November1st to 10thDay
51%6%13%20%8%1
1672
11th to 20thDay
56%8%16%12%7%1
1592
21st to endDay
66%6%14%12%2
1520
December1st to 10thDay
65%10%12%10%3
1520
11th to 20thDay
70%7%12%9%2
1906
21st to endDay
79%7%10%4
2582
January1st to 10thNight
67%8%13%9%3
4488
11th to 20thNight
74%9%9%5%2
4145
21st to endNight
71%7%11%8%2
4532
February1st to 10thNight
65%8%9%12%5%1
2399
11th to 20thNight
60%6%13%15%6%
2253
21st to endNight
61%6%11%15%6%
1776
March1st to 10thNight
54%6%11%20%8%1
2048
11th to 20thNight
49%6%11%21%11%1
1980
21st to endNight
54%5%8%19%11%2
2178
April1st to 10thNight
50%7%10%20%12%1
1931
11th to 20thNight
46%5%11%20%17%2
1607
21st to endNight
48%6%11%17%15%3
1620
May1st to 10thNight
46%6%10%21%13%4
1620
11th to 20thNight
41%6%12%21%15%4
1593
21st to endNight
33%7%12%27%17%3
1585
June1st to 10thNight
36%6%12%27%16%3
1414
11th to 20thNight
33%10%14%22%19%2
1260
21st to endNight
33%7%14%26%18%1
1260
July1st to 10thNight
28%6%10%30%21%5%
1250
11th to 20thNight
31%7%12%29%17%3
1481
21st to endNight
29%9%19%22%17%3
1672
August1st to 10thNight
32%9%15%30%14%1
1600
11th to 20thNight
31%7%14%32%13%2
1598
21st to endNight
32%7%13%30%17%1
1782
September1st to 10thNight
36%6%16%25%15%2
1868
11th to 20thNight
31%6%14%31%18%1
1980
21st to endNight
42%7%14%23%14%1
1980
October1st to 10thNight
42%6%12%22%17%1
2106
11th to 20thNight
51%5%13%20%9%1
2160
21st to endNight
58%7%11%14%9%1
2426
November1st to 10thNight
44%6%13%24%11%1
2406
11th to 20thNight
54%7%15%16%7%1
2588
21st to endNight
61%7%17%12%3
2660
December1st to 10thNight
65%8%14%10%3
2660
11th to 20thNight
65%7%13%12%3
3288
21st to endNight
76%7%11%5%1
5058

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
23%23%29%19%5%1
252
11th to 20thDay
22%19%43%11%41
270
21st to endDay
29%15%33%20%21
297
February1st to 10thDay
26%20%39%11%31
252
11th to 20thDay
27%20%40%12%1
240
21st to endDay
27%28%33%11%1
198
March1st to 10thDay
27%14%38%16%5%1
352
11th to 20thDay
21%15%33%24%5%1
420
21st to endDay
29%13%32%20%5%1
462
April1st to 10thDay
18%19%34%20%8%1
420
11th to 20thDay
27%12%27%21%8%5%
412
21st to endDay
24%11%32%21%9%3
420
May1st to 10thDay
22%11%28%26%10%4
423
11th to 20thDay
19%8%28%24%16%5%
447
21st to endDay
13%8%21%32%19%8%
485
June1st to 10thDay
13%7%30%31%14%4
471
11th to 20thDay
13%8%28%32%15%4
630
21st to endDay
13%7%28%31%17%4
630
July1st to 10thDay
10%6%21%29%25%9%
621
11th to 20thDay
15%426%27%20%8%
525
21st to endDay
9%5%21%32%24%10%
488
August1st to 10thDay
9%418%28%24%16%
446
11th to 20thDay
11%5%18%28%23%16%
439
21st to endDay
11%6%19%26%27%10%
495
September1st to 10thDay
12%5%22%28%22%11%
450
11th to 20thDay
9%422%23%28%14%
450
21st to endDay
17%11%22%26%15%9%
450
October1st to 10thDay
20%9%25%23%17%6%
450
11th to 20thDay
20%16%33%22%7%1
450
21st to endDay
28%15%33%20%4
441
November1st to 10thDay
19%18%33%19%9%3
270
11th to 20thDay
23%22%30%16%6%2
214
21st to endDay
29%16%35%17%3
180
December1st to 10thDay
28%19%31%16%6%1
180
11th to 20thDay
28%22%27%19%3
180
21st to endDay
29%23%31%15%2
198
January1st to 10thNight
24%16%37%16%5%1
950
11th to 20thNight
29%15%31%21%4
772
21st to endNight
23%11%35%25%6%
836
February1st to 10thNight
25%12%38%22%3
739
11th to 20thNight
25%14%30%25%6%
703
21st to endNight
26%15%37%19%3
592
March1st to 10thNight
19%13%35%27%6%
720
11th to 20thNight
19%15%34%24%7%1
720
21st to endNight
24%11%29%27%8%1
792
April1st to 10thNight
22%15%30%28%5%
720
11th to 20thNight
21%12%31%25%11%1
543
21st to endNight
21%8%33%30%8%1
540
May1st to 10thNight
19%7%29%32%11%1
540
11th to 20thNight
14%429%41%11%2
531
21st to endNight
12%327%41%17%1
424
June1st to 10thNight
14%428%40%14%
360
11th to 20thNight
13%325%44%14%
360
21st to endNight
10%5%21%47%16%1
360
July1st to 10thNight
7%118%46%26%2
375
11th to 20thNight
12%317%41%25%2
522
21st to endNight
9%216%49%22%2
591
August1st to 10thNight
9%211%45%30%4
537
11th to 20thNight
9%214%38%32%5%
534
21st to endNight
12%217%37%30%3
594
September1st to 10thNight
10%5%22%35%24%5%
716
11th to 20thNight
11%5%17%37%27%4
720
21st to endNight
17%7%21%33%16%5%
720
October1st to 10thNight
18%6%26%31%17%3
720
11th to 20thNight
24%12%27%27%10%1
720
21st to endNight
28%11%31%25%4
792
November1st to 10thNight
20%11%29%30%9%1
740
11th to 20thNight
22%13%36%21%6%1
760
21st to endNight
28%13%29%24%6%
760
December1st to 10thNight
29%15%33%18%5%
760
11th to 20thNight
24%17%36%19%4
760
21st to endNight
29%12%35%21%3
945
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