Sydney
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sydney 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
23%
15171
7%
46796
4%
15131
27%
15131
10%
37599

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
13%
748
3%
2506
1%
746
16%
746
4%
2215
January16th to endNight
11%
799
3%
2679
0%
799
15%
799
4%
2341
February1st to 15thNight
14%
701
5%
2286
1%
701
17%
701
5%
1924
February16th to endNight
15%
631
7%
1940
2%
631
20%
631
8%
1592
March1st to 15thNight
20%
720
9%
2127
4%
720
25%
720
10%
1696
March16th to endNight
20%
672
10%
2016
5%
672
26%
672
11%
1565
April1st to 15thNight
24%
539
11%
1796
7%
539
32%
539
11%
1341
April16th to endNight
24%
540
13%
1692
7%
540
32%
540
13%
1232
May1st to 15thNight
27%
540
11%
1440
5%
540
31%
540
13%
1113
May16th to endNight
30%
561
10%
1496
4%
560
33%
560
15%
1121
June1st to 15thNight
26%
540
5%
1440
2%
540
27%
540
12%
1165
June16th to endNight
34%
540
5%
1440
2%
540
35%
540
13%
1148
July1st to 15thNight
45%
510
7%
1360
4%
510
46%
510
20%
988
July16th to endNight
38%
565
9%
1419
4%
532
42%
532
16%
1091
August1st to 15thNight
46%
539
9%
1468
6%
535
48%
535
17%
1106
August16th to endNight
47%
573
12%
1875
10%
573
50%
573
17%
1308
September1st to 15thNight
36%
531
11%
1768
9%
531
42%
531
15%
1270
September16th to endNight
33%
507
15%
1787
11%
507
40%
507
16%
1235
October1st to 15thNight
26%
660
11%
1980
5%
660
31%
660
14%
1500
October16th to endNight
16%
725
6%
2225
2%
725
20%
725
9%
1849
November1st to 15thNight
20%
730
6%
2328
4%
730
22%
730
9%
1917
November16th to endNight
12%
750
4%
2520
1%
750
15%
750
4%
2159
December1st to 15thNight
13%
750
4%
2520
1%
750
17%
750
4%
2229
December16th to endNight
6%
800
2%
2688
0%
800
8%
800
2%
2494

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
21%10%47%6%35%5%5%6%24%
47874
Night
21%10%47%6%35%5%5%6%24%
46967
TransparencyDay
58%8%12%14%5%
47563
Night
62%8%11%12%5%
46796
SeeingDay
24%17%22%23%11%1
7798
Night
24%21%23%21%7%1
15176

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
15%11%6%9%8%5%7%7%6%7%14%
1432
16th to endDay
15%11%7%9%8%37%6%6%7%16%
1542
February1st to 15thDay
15%11%5%10%8%36%5%5%7%18%
1575
16th to endDay
11%14%7%7%6%35%5%5%6%24%
1533
March1st to 15thDay
14%12%6%8%7%46%5%5%6%23%
1823
16th to endDay
18%14%6%7%7%35%435%24%
2207
April1st to 15thDay
19%11%36%6%4435%6%27%
2153
16th to endDay
27%10%35%423445%28%
2265
May1st to 15thDay
27%9%35%5%3434428%
2512
16th to endDay
23%9%35%5%345%5%8%26%
2618
June1st to 15thDay
31%9%45%5%2435%6%22%
2520
16th to endDay
23%8%46%6%3445%6%27%
2520
July1st to 15thDay
15%5%26%5%35%5%6%9%34%
2520
16th to endDay
19%8%46%6%36%5%6%7%26%
2653
August1st to 15thDay
23%6%27%5%345%6%7%27%
2480
16th to endDay
19%7%245%345%5%8%33%
2327
September1st to 15thDay
22%6%36%5%35%446%32%
2112
16th to endDay
18%6%35%5%33447%37%
1840
October1st to 15thDay
20%10%46%6%2445%7%27%
1650
16th to endDay
27%11%48%6%345%4417%
1647
November1st to 15thDay
25%13%5%8%6%34445%16%
1529
16th to endDay
16%17%49%6%36%6%5%7%17%
1440
December1st to 15thDay
22%14%6%9%7%5%6%6%5%5%10%
1440
16th to endDay
20%17%7%11%8%47%4448%
1536
January1st to 15thNight
16%13%5%10%9%5%6%6%5%6%14%
2506
16th to endNight
17%12%7%10%7%35%5%6%7%16%
2679
February1st to 15thNight
18%10%410%7%36%5%5%6%20%
2285
16th to endNight
14%14%7%8%7%45%5%5%6%20%
1940
March1st to 15thNight
17%12%6%7%6%45%445%26%
2114
16th to endNight
21%12%5%6%6%3443427%
2016
April1st to 15thNight
22%9%45%5%3445%5%29%
1796
16th to endNight
24%8%35%41335%433%
1692
May1st to 15thNight
29%7%25%424445%28%
1440
16th to endNight
21%8%34434448%31%
1494
June1st to 15thNight
31%7%26%444445%23%
1440
16th to endNight
25%7%35%42346%7%28%
1440
July1st to 15thNight
17%425%4345%6%8%36%
1440
16th to endNight
20%6%35%6%35%6%7%8%27%
1515
August1st to 15thNight
21%6%146%45%5%5%6%32%
1479
16th to endNight
17%5%245%345%6%8%37%
1875
September1st to 15thNight
18%7%35%5%3445%5%36%
1768
16th to endNight
20%6%16%424446%38%
1787
October1st to 15thNight
21%6%27%5%25%36%8%31%
1980
16th to endNight
26%11%37%5%3445%5%21%
2225
November1st to 15thNight
22%10%47%6%35%45%6%22%
2328
16th to endNight
20%15%47%6%35%5%5%6%18%
2520
December1st to 15thNight
22%12%5%7%6%36%6%6%7%15%
2520
16th to endNight
22%17%6%9%6%36%5%4411%
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
71%10%8%7%2
1433
16th to endDay
70%10%9%5%2
1542
February1st to 15thDay
68%9%9%8%3
1578
16th to endDay
59%8%12%11%7%
1533
March1st to 15thDay
59%7%9%16%6%
1833
16th to endDay
60%6%11%15%5%
2207
April1st to 15thDay
55%7%10%14%10%1
2153
16th to endDay
57%5%12%13%10%1
2265
May1st to 15thDay
56%7%11%17%6%
2512
16th to endDay
54%8%12%17%5%
2622
June1st to 15thDay
63%7%10%13%4
2520
16th to endDay
56%9%12%13%7%
2520
July1st to 15thDay
41%14%16%19%7%
2372
16th to endDay
53%9%15%15%5%
2486
August1st to 15thDay
51%9%15%17%5%
2466
16th to endDay
45%10%19%20%5%
2327
September1st to 15thDay
52%7%12%19%6%
2112
16th to endDay
45%7%15%22%8%
1840
October1st to 15thDay
55%7%13%15%8%
1650
16th to endDay
67%9%10%9%3
1647
November1st to 15thDay
70%8%8%10%2
1529
16th to endDay
68%8%11%7%3
1440
December1st to 15thDay
80%7%7%4
1440
16th to endDay
81%7%5%31
1536
January1st to 15thNight
74%8%8%5%2
2506
16th to endNight
73%9%9%6%1
2679
February1st to 15thNight
69%7%10%9%3
2286
16th to endNight
64%8%11%10%4
1940
March1st to 15thNight
63%6%10%13%5%
2127
16th to endNight
61%411%13%6%1
2016
April1st to 15thNight
56%6%8%16%10%
1796
16th to endNight
54%5%10%15%12%1
1692
May1st to 15thNight
58%5%9%16%8%1
1440
16th to endNight
52%7%12%18%7%
1496
June1st to 15thNight
64%5%10%15%4
1440
16th to endNight
57%9%10%13%8%
1440
July1st to 15thNight
44%11%16%18%10%
1360
16th to endNight
51%11%14%16%5%
1419
August1st to 15thNight
51%8%16%16%6%
1468
16th to endNight
45%10%16%21%6%
1875
September1st to 15thNight
50%9%12%19%8%
1768
16th to endNight
49%7%13%22%7%
1787
October1st to 15thNight
55%8%12%16%6%
1980
16th to endNight
67%6%10%11%4
2225
November1st to 15thNight
65%8%12%10%3
2328
16th to endNight
70%9%11%6%2
2520
December1st to 15thNight
73%9%9%5%1
2520
16th to endNight
82%7%5%31
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
16%27%34%16%4
240
16th to endDay
24%23%33%14%3
256
February1st to 15thDay
21%25%32%16%2
236
16th to endDay
21%20%33%14%8%1
212
March1st to 15thDay
15%25%31%15%9%2
246
16th to endDay
25%23%23%17%7%2
288
April1st to 15thDay
24%19%25%19%9%1
270
16th to endDay
24%17%21%24%11%
333
May1st to 15thDay
30%17%18%18%10%4
468
16th to endDay
22%15%19%28%11%2
519
June1st to 15thDay
31%14%19%23%8%1
495
16th to endDay
23%15%15%30%12%1
495
July1st to 15thDay
16%10%13%38%20%1
475
16th to endDay
22%14%17%28%16%
514
August1st to 15thDay
22%8%14%30%21%2
453
16th to endDay
23%7%17%29%18%3
332
September1st to 15thDay
25%10%21%32%8%1
299
16th to endDay
20%11%25%25%16%1
231
October1st to 15thDay
26%12%24%21%13%2
225
16th to endDay
28%17%33%15%5%
240
November1st to 15thDay
26%22%25%14%7%3
235
16th to endDay
31%24%25%13%5%
240
December1st to 15thDay
30%26%26%12%4
240
16th to endDay
28%28%26%12%21
256
January1st to 15thNight
21%28%30%17%2
750
16th to endNight
21%27%32%15%3
799
February1st to 15thNight
21%28%28%19%2
704
16th to endNight
19%25%29%18%6%
631
March1st to 15thNight
20%24%26%20%6%
720
16th to endNight
24%25%24%18%6%1
672
April1st to 15thNight
23%22%21%24%5%
539
16th to endNight
24%21%23%20%8%1
540
May1st to 15thNight
28%19%19%18%9%4
540
16th to endNight
22%19%19%25%11%
561
June1st to 15thNight
26%20%20%25%6%
540
16th to endNight
25%18%13%28%11%1
540
July1st to 15thNight
18%13%14%37%15%
510
16th to endNight
20%17%15%26%17%1
565
August1st to 15thNight
23%10%10%32%20%2
539
16th to endNight
19%9%17%37%15%
573
September1st to 15thNight
25%10%21%28%13%
531
16th to endNight
25%13%23%26%10%1
507
October1st to 15thNight
24%16%25%22%10%1
660
16th to endNight
33%17%26%16%4
725
November1st to 15thNight
28%24%22%17%5%2
730
16th to endNight
30%29%23%12%4
750
December1st to 15thNight
28%30%24%12%4
750
16th to endNight
31%29%24%10%21
800
Page generated at 2017-09-13 08:39:25. Version ac04

Copyright 2017 A. Danko


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