Oakville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Oakville clear sky chart from 2005-11-05 to

2017-09-12
.

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
38%
14828
14%
46839
10%
14792
43%
14792
20%
32200

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
15%
716
9%
2455
3%
716
22%
716
9%
1918
January16th to endNight
18%
768
10%
2496
3%
768
26%
768
11%
1909
February1st to 15thNight
16%
701
7%
2287
2%
701
23%
701
11%
1769
February16th to endNight
24%
631
12%
2006
5%
631
33%
631
15%
1455
March1st to 15thNight
27%
720
12%
1980
6%
720
32%
720
18%
1481
March16th to endNight
35%
768
20%
2112
11%
768
43%
768
24%
1461
April1st to 15thNight
32%
718
15%
1826
6%
718
37%
718
23%
1327
April16th to endNight
44%
560
21%
1640
10%
560
51%
560
27%
1058
May1st to 15thNight
50%
507
17%
1587
13%
507
55%
507
25%
1034
May16th to endNight
53%
374
17%
1497
17%
374
60%
374
25%
854
June1st to 15thNight
51%
360
13%
1440
14%
360
59%
360
22%
853
June16th to endNight
61%
360
13%
1440
18%
360
66%
360
24%
832
July1st to 15thNight
67%
340
16%
1360
23%
340
71%
340
34%
683
July16th to endNight
68%
508
16%
1539
16%
475
70%
475
34%
868
August1st to 15thNight
72%
539
16%
1609
15%
536
74%
536
37%
954
August16th to endNight
64%
622
23%
1768
16%
622
67%
622
36%
1051
September1st to 15thNight
58%
707
21%
1784
11%
707
62%
707
35%
1144
September16th to endNight
58%
657
21%
1831
15%
657
60%
657
32%
1150
October1st to 15thNight
44%
660
18%
1980
16%
660
48%
660
24%
1310
October16th to endNight
26%
704
13%
2112
7%
704
32%
704
16%
1548
November1st to 15thNight
37%
700
18%
2362
14%
700
44%
700
21%
1552
November16th to endNight
27%
720
11%
2520
7%
720
33%
720
13%
1825
December1st to 15thNight
17%
720
6%
2520
3%
720
22%
720
9%
1958
December16th to endNight
14%
768
5%
2688
1%
768
19%
768
7%
2206

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%7%36%6%35%5%6%8%35%
47811
Night
15%8%36%5%3445%7%35%
47021
Cloud CoverDay
13%7%36%6%35%5%6%7%35%
47821
Night
15%8%36%5%3445%7%35%
47025
TransparencyDay
46%7%14%20%10%1
47511
Night
47%6%13%20%10%1
46839
SeeingDay
16%5%23%28%18%8%
5326
Night
18%7%28%29%14%1
14836

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
18%11%49%7%37%5%5%7%19%
1480
16th to endDay
12%14%7%10%8%5%7%5%5%7%15%
1728
February1st to 15thDay
13%13%6%10%7%5%5%5%5%6%18%
1575
16th to endDay
17%10%47%7%35%5%7%7%24%
1462
March1st to 15thDay
14%8%6%8%7%35%446%28%
1969
16th to endDay
14%7%36%6%3445%7%35%
2112
April1st to 15thDay
18%7%45%5%35%446%32%
2122
16th to endDay
15%7%25%5%34345%41%
2331
May1st to 15thDay
13%5%36%6%25%5%6%7%37%
2362
16th to endDay
9%5%245%45%45%8%43%
2618
June1st to 15thDay
12%425%5%35%5%5%8%41%
2520
16th to endDay
11%3145%35%6%7%9%41%
2520
July1st to 15thDay
6%324436%6%8%10%44%
2520
16th to endDay
8%3235%46%6%7%10%41%
2519
August1st to 15thDay
5%5%146%346%7%9%43%
2340
16th to endDay
9%4145%35%45%8%47%
2421
September1st to 15thDay
12%4245%35%5%5%7%42%
2093
16th to endDay
13%5%245%3445%8%42%
1799
October1st to 15thDay
15%7%36%5%3445%7%36%
1650
16th to endDay
22%9%37%6%35%45%5%25%
1760
November1st to 15thDay
11%7%38%5%35%5%6%9%34%
1494
16th to endDay
17%10%38%5%36%5%5%7%25%
1440
December1st to 15thDay
17%13%48%7%45%5%5%7%19%
1440
16th to endDay
20%11%5%9%9%46%46%6%15%
1536
January1st to 15thNight
18%13%6%9%7%3445%5%21%
2455
16th to endNight
14%11%6%8%7%46%5%5%7%21%
2496
February1st to 15thNight
14%13%7%8%6%35%5%6%7%22%
2285
16th to endNight
14%12%48%6%3445%6%29%
2006
March1st to 15thNight
19%7%37%5%346%47%29%
1968
16th to endNight
15%9%36%5%23335%41%
2112
April1st to 15thNight
18%7%35%5%335%5%6%35%
1826
16th to endNight
12%7%25%5%24347%44%
1640
May1st to 15thNight
15%5%245%4447%7%39%
1587
16th to endNight
11%5%2442445%7%46%
1495
June1st to 15thNight
13%425%5%25%46%8%42%
1440
16th to endNight
9%315%5%35%5%6%7%45%
1440
July1st to 15thNight
5%3144235%48%55%
1440
16th to endNight
7%3234335%6%8%50%
1646
August1st to 15thNight
7%213425%6%6%9%49%
1620
16th to endNight
7%424424447%51%
1768
September1st to 15thNight
11%424434447%47%
1784
16th to endNight
11%5%245%3445%7%46%
1831
October1st to 15thNight
17%5%25%42445%7%40%
1980
16th to endNight
21%8%35%5%36%5%46%29%
2112
November1st to 15thNight
15%5%24435%45%7%38%
2362
16th to endNight
19%9%45%5%25%5%6%7%28%
2520
December1st to 15thNight
20%13%5%7%6%3445%6%22%
2520
16th to endNight
20%13%7%9%7%36%45%6%16%
2688

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
18%13%48%6%36%5%5%6%20%
1480
16th to endDay
12%14%7%9%8%5%7%5%5%7%16%
1728
February1st to 15thDay
14%12%7%9%8%45%5%5%6%19%
1575
16th to endDay
17%11%46%6%36%45%8%24%
1462
March1st to 15thDay
14%9%48%7%35%5%5%6%29%
1980
16th to endDay
14%7%36%6%35%35%6%35%
2111
April1st to 15thDay
18%7%35%5%36%45%6%33%
2122
16th to endDay
16%6%25%5%34445%41%
2331
May1st to 15thDay
13%6%36%5%345%6%7%38%
2362
16th to endDay
10%5%25%5%345%6%8%43%
2618
June1st to 15thDay
12%425%5%3446%8%41%
2520
16th to endDay
11%3145%35%5%7%10%40%
2520
July1st to 15thDay
6%3145%46%6%8%9%45%
2520
16th to endDay
8%4245%36%6%6%10%42%
2519
August1st to 15thDay
6%4146%46%6%7%9%43%
2340
16th to endDay
9%3245%3445%8%47%
2421
September1st to 15thDay
12%425%5%35%5%5%8%42%
2093
16th to endDay
14%425%5%3435%7%43%
1799
October1st to 15thDay
16%6%35%5%345%5%6%36%
1650
16th to endDay
23%8%37%5%35%46%5%25%
1760
November1st to 15thDay
11%7%37%5%35%5%6%9%34%
1494
16th to endDay
19%9%47%6%35%45%7%25%
1440
December1st to 15thDay
18%13%48%8%46%46%6%19%
1440
16th to endDay
20%11%5%9%9%45%5%5%6%15%
1536
January1st to 15thNight
19%13%5%9%6%35%35%5%21%
2455
16th to endNight
15%11%6%9%7%45%5%5%6%22%
2496
February1st to 15thNight
14%13%6%9%7%35%45%7%22%
2278
16th to endNight
14%12%47%7%3445%7%28%
2006
March1st to 15thNight
20%7%37%5%3445%7%29%
1980
16th to endNight
15%9%46%43333441%
2112
April1st to 15thNight
18%8%35%6%2445%6%35%
1826
16th to endNight
12%7%245%24347%44%
1640
May1st to 15thNight
15%4345%3436%8%39%
1586
16th to endNight
12%424424446%47%
1495
June1st to 15thNight
13%4245%25%35%9%41%
1440
16th to endNight
10%325%5%26%5%6%7%44%
1440
July1st to 15thNight
5%323433448%55%
1440
16th to endNight
7%3135%2446%8%50%
1646
August1st to 15thNight
7%313435%6%7%8%49%
1620
16th to endNight
7%415%425%447%51%
1768
September1st to 15thNight
11%42442445%7%47%
1784
16th to endNight
12%5%245%24447%47%
1831
October1st to 15thNight
17%5%25%42445%6%40%
1980
16th to endNight
21%8%26%5%35%446%29%
2112
November1st to 15thNight
15%5%245%35%5%5%7%38%
2362
16th to endNight
20%9%45%5%25%5%5%7%28%
2520
December1st to 15thNight
21%13%5%7%5%3445%5%22%
2520
16th to endNight
21%13%7%8%7%46%445%17%
2688

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
63%6%13%12%3
1481
16th to endDay
67%6%11%10%3
1728
February1st to 15thDay
63%6%12%14%2
1577
16th to endDay
56%8%15%14%5%
1462
March1st to 15thDay
56%7%13%15%6%
1980
16th to endDay
47%6%12%21%11%1
2112
April1st to 15thDay
51%5%11%18%11%
2122
16th to endDay
44%5%11%20%15%2
2331
May1st to 15thDay
43%7%12%23%11%
2362
16th to endDay
37%7%15%23%14%2
2622
June1st to 15thDay
40%6%14%25%12%1
2520
16th to endDay
35%8%16%24%13%
2520
July1st to 15thDay
29%9%14%25%18%1
2371
16th to endDay
34%10%16%23%12%2
2363
August1st to 15thDay
32%11%17%23%14%2
2327
16th to endDay
33%9%14%28%13%1
2421
September1st to 15thDay
37%9%16%23%11%
2093
16th to endDay
40%6%15%27%9%
1799
October1st to 15thDay
45%6%14%21%9%1
1650
16th to endDay
58%6%16%14%3
1760
November1st to 15thDay
44%8%18%19%7%
1494
16th to endDay
56%7%16%14%4
1440
December1st to 15thDay
62%8%16%11%1
1440
16th to endDay
68%8%11%9%1
1536
January1st to 15thNight
63%5%12%13%3
2455
16th to endNight
60%5%15%13%4
2496
February1st to 15thNight
60%6%14%15%3
2287
16th to endNight
54%5%15%17%6%
2006
March1st to 15thNight
54%5%14%19%5%
1980
16th to endNight
47%48%23%14%2
2112
April1st to 15thNight
49%5%9%20%13%1
1826
16th to endNight
40%6%9%22%17%3
1640
May1st to 15thNight
42%5%11%24%14%2
1587
16th to endNight
36%6%13%25%15%3
1497
June1st to 15thNight
39%6%12%23%16%1
1440
16th to endNight
35%8%13%25%16%1
1440
July1st to 15thNight
26%5%12%25%25%3
1360
16th to endNight
29%7%16%25%17%3
1539
August1st to 15thNight
29%7%19%28%12%2
1609
16th to endNight
32%5%12%31%16%1
1768
September1st to 15thNight
34%5%14%28%14%1
1784
16th to endNight
37%413%30%12%
1831
October1st to 15thNight
43%5%13%24%12%
1980
16th to endNight
54%5%15%17%7%
2112
November1st to 15thNight
43%7%14%21%12%
2362
16th to endNight
53%7%16%17%4
2520
December1st to 15thNight
61%6%15%12%3
2520
16th to endNight
68%6%13%9%2
2688

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
20%16%38%13%10%1
68
16th to endDay
30%12%39%15%2
96
February1st to 15thDay
14%7%55%18%3
90
16th to endDay
22%12%29%30%4
88
March1st to 15thDay
20%9%33%28%8%
270
16th to endDay
23%5%28%31%9%2
288
April1st to 15thDay
20%9%28%31%7%2
270
16th to endDay
19%5%26%25%16%5%
270
May1st to 15thDay
17%323%27%20%8%
288
16th to endDay
12%224%32%20%8%
331
June1st to 15thDay
13%421%35%21%4
315
16th to endDay
14%121%32%23%7%
315
July1st to 15thDay
8%213%34%27%13%
305
16th to endDay
8%18%33%25%12%
326
August1st to 15thDay
8%15%29%26%18%
313
16th to endDay
11%118%21%26%20%
332
September1st to 15thDay
12%215%29%26%14%
299
16th to endDay
18%314%28%21%12%
254
October1st to 15thDay
17%5%23%26%18%7%
255
16th to endDay
26%8%28%26%8%
272
November1st to 15thDay
9%12%27%31%13%5%
97
16th to endDay
20%16%20%25%18%
60
December1st to 15thDay
18%21%31%20%8%
60
16th to endDay
23%21%43%10%
64
January1st to 15thNight
24%15%36%18%5%
720
16th to endNight
20%10%40%22%7%
768
February1st to 15thNight
21%13%39%21%4
704
16th to endNight
20%10%35%28%5%
631
March1st to 15thNight
25%8%32%26%7%
720
16th to endNight
20%5%30%30%11%1
768
April1st to 15thNight
21%6%32%30%7%
718
16th to endNight
14%5%28%35%14%1
560
May1st to 15thNight
17%122%34%20%2
507
16th to endNight
14%224%33%24%1
375
June1st to 15thNight
15%123%37%21%1
360
16th to endNight
9%119%43%24%
360
July1st to 15thNight
5%19%44%25%3
340
16th to endNight
8%113%45%27%3
508
August1st to 15thNight
8%10%41%33%4
539
16th to endNight
9%114%35%34%4
622
September1st to 15thNight
13%318%29%27%7%
707
16th to endNight
13%318%28%30%6%
657
October1st to 15thNight
19%5%24%25%21%3
660
16th to endNight
25%8%32%27%5%
704
November1st to 15thNight
18%7%32%27%13%2
700
16th to endNight
23%11%31%23%8%1
720
December1st to 15thNight
28%13%33%19%5%
720
16th to endNight
26%11%37%20%3
768
Page generated at 2017-09-13 07:39:20. Version ac04

Copyright 2017 A. Danko


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