Sydney
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sydney clear sky chart from 2005-11-06 to 2024-01-11.

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
27%
23937
8%
74759
5%
23880
31%
23880
11%
59466

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%
849
3%
2649
1%
847
15%
847
4%
2367
January11th to 20thNight
15%
804
2%
2531
0%
804
17%
804
3%
2277
January21st to endNight
16%
874
5%
2758
2%
874
20%
874
7%
2333
February1st to 10thNight
16%
720
4%
2340
1%
720
20%
720
6%
1999
February11th to 20thNight
14%
701
6%
2258
1%
700
20%
700
8%
1857
February21st to endNight
20%
592
11%
1776
4%
592
26%
592
12%
1400
March1st to 10thNight
20%
718
11%
2160
5%
718
25%
718
12%
1707
March11th to 20thNight
29%
720
11%
2020
6%
720
33%
720
15%
1541
March21st to endNight
23%
649
11%
2035
5%
649
30%
649
12%
1582
April1st to 10thNight
24%
540
11%
1800
6%
540
33%
540
13%
1351
April11th to 20thNight
31%
534
12%
1776
9%
534
37%
534
15%
1290
April21st to endNight
29%
540
13%
1639
8%
540
34%
540
16%
1206
May1st to 10thNight
32%
540
12%
1440
7%
540
35%
540
17%
1107
May11th to 20thNight
39%
532
17%
1417
8%
532
43%
532
23%
1007
May21st to endNight
38%
583
10%
1551
5%
582
41%
582
20%
1144
June1st to 10thNight
30%
540
6%
1440
3%
540
31%
540
13%
1169
June11th to 20thNight
42%
540
9%
1440
4%
540
44%
540
19%
1067
June21st to endNight
40%
540
3%
1440
2%
540
40%
540
14%
1170
July1st to 10thNight
47%
526
7%
1401
4%
526
48%
526
19%
1056
July11th to 20thNight
50%
522
8%
1392
5%
522
51%
522
19%
1058
July21st to endNight
48%
590
8%
1486
5%
558
48%
558
18%
1127
August1st to 10thNight
53%
538
9%
1422
6%
534
55%
534
23%
1034
August11th to 20thNight
50%
532
10%
1601
8%
532
51%
532
17%
1189
August21st to endNight
53%
594
14%
1980
14%
594
55%
594
20%
1329
September1st to 10thNight
46%
540
12%
1800
10%
540
52%
540
19%
1235
September11th to 20thNight
37%
540
16%
1820
13%
540
42%
540
18%
1247
September21st to endNight
35%
562
14%
2002
11%
562
41%
562
16%
1407
October1st to 10thNight
34%
720
13%
2160
6%
720
39%
720
18%
1559
October11th to 20thNight
32%
720
9%
2160
6%
720
35%
720
16%
1651
October21st to endNight
20%
884
9%
2560
4%
884
24%
884
10%
2115
November1st to 10thNight
22%
830
8%
2408
4%
830
25%
830
11%
1972
November11th to 20thNight
16%
850
6%
2644
3%
850
20%
850
7%
2237
November21st to endNight
17%
850
4%
2660
1%
850
19%
850
6%
2278
December1st to 10thNight
14%
850
5%
2660
1%
850
18%
850
5%
2335
December11th to 20thNight
12%
850
3%
3281
1%
849
14%
849
3%
2958
December21st to endNight
10%
923
1%
4852
0%
907
12%
907
2%
4105

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
20%11%47%6%45%5%5%7%26%
74734
Night
20%11%48%6%45%5%5%6%25%
74973
TransparencyDay
57%9%13%15%6%1
74437
Night
61%8%12%13%6%
74805
SeeingDay
24%9%25%28%12%2
16516
Night
26%10%27%26%9%1
23954

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 10thDay
19%12%7%11%8%5%7%6%5%6%13%
1516
11th to 20thDay
18%13%7%12%9%47%5%5%7%14%
1441
21st to endDay
13%11%7%12%9%5%6%6%6%7%18%
1593
February1st to 10thDay
17%10%5%12%10%47%6%6%7%15%
1620
11th to 20thDay
15%13%6%9%7%47%6%5%7%21%
1591
21st to endDay
9%14%6%8%9%45%5%5%6%29%
1480
March1st to 10thDay
13%15%6%9%8%45%5%46%26%
1796
11th to 20thDay
13%11%6%8%9%46%6%6%7%24%
1938
21st to endDay
19%15%6%7%6%45%5%35%24%
2320
April1st to 10thDay
21%12%5%7%7%45%45%5%24%
2160
11th to 20thDay
21%12%36%5%24446%33%
2134
21st to endDay
25%12%36%5%35%45%5%26%
2317
May1st to 10thDay
26%12%37%5%3445%6%27%
2520
11th to 20thDay
23%10%35%6%3445%6%31%
2478
21st to endDay
21%9%35%5%45%5%5%8%30%
2724
June1st to 10thDay
30%11%46%5%3445%6%23%
2520
11th to 20thDay
20%8%46%6%3445%7%32%
2520
21st to endDay
26%10%46%6%35%45%6%24%
2520
July1st to 10thDay
17%6%37%6%45%5%6%9%34%
2520
11th to 20thDay
15%6%47%7%36%6%7%8%31%
2520
21st to endDay
21%8%47%6%36%5%6%7%27%
2745
August1st to 10thDay
18%6%27%5%45%6%7%9%31%
2506
11th to 20thDay
20%8%37%6%445%6%8%31%
2297
21st to endDay
18%6%35%6%45%5%7%9%33%
2376
September1st to 10thDay
19%6%35%5%35%5%6%7%36%
2160
11th to 20thDay
21%8%36%6%34446%34%
2139
21st to endDay
19%7%35%5%345%5%7%38%
1954
October1st to 10thDay
20%9%45%5%346%6%9%31%
1800
11th to 20thDay
21%10%5%7%7%35%6%5%6%25%
1800
21st to endDay
24%14%49%7%4445%6%19%
1795
November1st to 10thDay
22%13%5%9%6%45%5%6%6%21%
1670
11th to 20thDay
20%15%6%10%7%46%5%5%6%15%
1535
21st to endDay
16%17%5%9%8%47%6%5%7%16%
1520
December1st to 10thDay
21%16%7%9%8%5%7%6%5%5%12%
1520
11th to 20thDay
26%18%5%11%7%46%445%9%
1906
21st to endDay
21%15%7%10%7%46%5%45%14%
2783
January1st to 10thNight
17%15%6%12%9%6%6%5%5%5%14%
2649
11th to 20thNight
18%14%6%10%9%46%7%6%7%13%
2531
21st to endNight
13%12%7%12%8%45%5%6%7%19%
2758
February1st to 10thNight
18%12%411%8%46%6%6%6%18%
2340
11th to 20thNight
16%12%5%9%9%6%6%5%6%6%22%
2255
21st to endNight
11%12%7%11%9%35%45%6%26%
1776
March1st to 10thNight
16%14%6%10%6%45%445%26%
2151
11th to 20thNight
16%12%5%8%6%46%5%46%29%
2019
21st to endNight
21%13%6%7%7%34445%26%
2035
April1st to 10thNight
22%11%5%7%6%3446%6%27%
1800
11th to 20thNight
20%11%47%5%25%46%5%32%
1776
21st to endNight
25%10%37%6%33345%31%
1639
May1st to 10thNight
29%9%35%335%45%5%28%
1440
11th to 20thNight
22%10%25%5%24346%37%
1416
21st to endNight
19%8%36%5%35%5%5%8%33%
1550
June1st to 10thNight
31%10%45%5%4445%6%23%
1440
11th to 20thNight
23%7%25%43446%7%35%
1440
21st to endNight
26%8%47%6%3346%7%27%
1440
July1st to 10thNight
20%6%37%6%345%7%8%31%
1440
11th to 20thNight
17%7%36%6%35%5%8%8%31%
1440
21st to endNight
20%7%46%6%346%7%9%29%
1573
August1st to 10thNight
17%6%25%5%5%5%6%7%7%34%
1433
11th to 20thNight
19%8%25%7%35%5%6%7%32%
1601
21st to endNight
17%5%36%6%4446%8%39%
1980
September1st to 10thNight
15%7%35%5%45%5%5%7%38%
1800
11th to 20thNight
21%8%35%5%2345%5%38%
1820
21st to endNight
19%8%27%6%34447%37%
2002
October1st to 10thNight
18%6%37%5%35%5%7%8%34%
2160
11th to 20thNight
23%8%36%4245%6%7%31%
2160
21st to endNight
25%12%38%7%45%5%45%23%
2560
November1st to 10thNight
19%11%48%7%46%5%5%6%25%
2408
11th to 20thNight
22%13%5%9%7%5%5%5%5%6%18%
2644
21st to endNight
20%15%47%7%46%6%6%7%18%
2660
December1st to 10thNight
21%15%6%9%7%46%5%6%6%14%
2660
11th to 20thNight
24%18%6%11%7%345%4414%
3293
21st to endNight
26%15%6%12%6%3444416%
4884

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
75%8%7%6%3
1517
11th to 20thDay
72%9%11%6%1
1441
21st to endDay
67%10%10%8%4
1593
February1st to 10thDay
70%9%9%7%5%
1620
11th to 20thDay
62%10%12%11%41
1599
21st to endDay
54%10%13%13%9%2
1480
March1st to 10thDay
57%7%9%18%9%1
1800
11th to 20thDay
56%8%12%17%7%1
1938
21st to endDay
59%7%11%14%8%1
2320
April1st to 10thDay
57%8%11%15%8%2
2160
11th to 20thDay
52%6%11%18%12%1
2134
21st to endDay
57%7%13%14%9%1
2317
May1st to 10thDay
57%6%13%15%8%1
2520
11th to 20thDay
50%8%12%20%10%1
2482
21st to endDay
50%9%14%18%7%1
2724
June1st to 10thDay
61%8%10%15%5%
2520
11th to 20thDay
53%8%13%18%8%
2520
21st to endDay
59%11%11%13%6%
2520
July1st to 10thDay
44%14%17%18%7%
2450
11th to 20thDay
45%13%16%19%7%1
2444
21st to endDay
52%10%16%16%6%
2592
August1st to 10thDay
46%11%18%19%5%
2492
11th to 20thDay
48%11%17%19%5%1
2297
21st to endDay
44%10%18%21%6%
2376
September1st to 10thDay
46%9%14%21%8%1
2160
11th to 20thDay
50%7%13%21%9%1
2139
21st to endDay
44%8%15%24%8%1
1954
October1st to 10thDay
48%9%15%19%9%
1800
11th to 20thDay
57%9%14%16%4
1800
21st to endDay
65%9%11%10%4
1795
November1st to 10thDay
64%9%9%14%3
1670
11th to 20thDay
69%10%10%8%3
1535
21st to endDay
67%10%13%7%3
1520
December1st to 10thDay
76%10%8%42
1520
11th to 20thDay
78%8%7%6%1
1905
21st to endDay
72%10%12%42
2783
January1st to 10thNight
76%9%8%5%3
2649
11th to 20thNight
76%10%9%42
2531
21st to endNight
69%9%10%9%3
2758
February1st to 10thNight
71%8%10%8%3
2340
11th to 20thNight
65%9%11%11%31
2258
21st to endNight
59%9%11%12%8%1
1776
March1st to 10thNight
62%7%10%14%7%1
2160
11th to 20thNight
56%7%13%17%6%1
2020
21st to endNight
61%6%10%13%7%2
2035
April1st to 10thNight
58%6%9%16%10%1
1800
11th to 20thNight
53%8%9%17%11%1
1776
21st to endNight
56%411%17%11%1
1639
May1st to 10thNight
57%6%10%16%10%1
1440
11th to 20thNight
49%5%9%22%13%2
1417
21st to endNight
50%9%14%19%7%
1551
June1st to 10thNight
65%5%9%14%6%1
1440
11th to 20thNight
51%8%11%19%11%
1440
21st to endNight
59%10%11%12%7%
1440
July1st to 10thNight
49%11%17%16%7%
1401
11th to 20thNight
48%13%12%18%8%1
1392
21st to endNight
50%11%18%15%5%
1486
August1st to 10thNight
45%11%19%19%6%
1422
11th to 20thNight
50%12%16%17%6%
1601
21st to endNight
44%9%17%22%8%
1980
September1st to 10thNight
45%9%15%22%9%
1800
11th to 20thNight
48%7%13%21%10%1
1820
21st to endNight
50%8%11%22%8%1
2002
October1st to 10thNight
49%9%14%20%8%
2160
11th to 20thNight
55%9%16%17%4
2160
21st to endNight
66%7%10%13%5%
2560
November1st to 10thNight
62%9%13%12%4
2408
11th to 20thNight
67%10%11%8%3
2644
21st to endNight
68%11%12%7%2
2660
December1st to 10thNight
73%9%9%6%2
2660
11th to 20thNight
78%7%8%42
3295
21st to endNight
75%6%11%6%1
4884

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
25%19%35%18%4
370
11th to 20thDay
27%15%34%18%6%1
341
21st to endDay
21%13%39%23%4
374
February1st to 10thDay
25%19%36%16%3
340
11th to 20thDay
25%20%32%18%4
336
21st to endDay
14%11%42%24%8%1
280
March1st to 10thDay
17%14%38%24%6%
340
11th to 20thDay
15%13%32%26%12%1
402
21st to endDay
25%13%28%21%10%3
462
April1st to 10thDay
26%11%36%17%8%1
420
11th to 20thDay
26%10%26%28%10%
412
21st to endDay
28%8%22%28%12%2
514
May1st to 10thDay
30%8%26%25%8%3
603
11th to 20thDay
22%6%23%31%15%4
624
21st to endDay
25%6%22%35%11%1
680
June1st to 10thDay
35%6%18%28%11%2
630
11th to 20thDay
21%6%21%33%17%1
630
21st to endDay
27%417%33%16%3
630
July1st to 10thDay
20%414%41%20%2
620
11th to 20thDay
19%314%42%21%1
618
21st to endDay
23%216%37%19%2
685
August1st to 10thDay
17%414%40%24%2
625
11th to 20thDay
20%318%33%21%6%
468
21st to endDay
17%6%18%36%20%3
495
September1st to 10thDay
17%7%22%37%14%3
450
11th to 20thDay
26%9%23%28%13%2
439
21st to endDay
25%6%26%26%13%4
360
October1st to 10thDay
22%7%21%35%13%3
360
11th to 20thDay
24%11%28%18%16%3
360
21st to endDay
32%12%27%21%8%1
396
November1st to 10thDay
27%16%24%23%8%2
365
11th to 20thDay
33%16%28%18%41
370
21st to endDay
29%19%29%19%41
370
December1st to 10thDay
33%13%33%16%41
370
11th to 20thDay
29%23%30%15%31
370
21st to endDay
22%17%36%16%6%1
407
January1st to 10thNight
25%19%32%19%4
850
11th to 20thNight
26%16%35%19%4
804
21st to endNight
20%16%37%22%5%
874
February1st to 10thNight
26%15%33%23%3
720
11th to 20thNight
22%19%36%20%3
703
21st to endNight
18%12%38%24%8%1
592
March1st to 10thNight
23%10%37%23%6%
720
11th to 20thNight
21%11%29%28%10%1
720
21st to endNight
27%10%30%25%6%2
649
April1st to 10thNight
27%11%29%26%6%
540
11th to 20thNight
26%6%27%31%9%1
534
21st to endNight
32%5%25%25%12%1
540
May1st to 10thNight
33%424%25%10%4
540
11th to 20thNight
27%5%20%31%14%2
532
21st to endNight
23%425%36%11%1
583
June1st to 10thNight
33%422%30%11%1
540
11th to 20thNight
27%5%16%36%15%1
540
21st to endNight
27%316%40%14%1
540
July1st to 10thNight
23%415%39%17%2
526
11th to 20thNight
18%416%46%16%1
522
21st to endNight
24%314%38%21%1
590
August1st to 10thNight
19%314%41%21%2
538
11th to 20thNight
22%213%39%20%3
532
21st to endNight
18%5%16%39%22%
594
September1st to 10thNight
20%6%21%35%17%2
540
11th to 20thNight
27%5%25%29%13%1
540
21st to endNight
25%6%25%32%10%2
562
October1st to 10thNight
23%7%29%30%11%1
720
11th to 20thNight
31%8%22%26%12%2
720
21st to endNight
34%11%27%20%7%1
884
November1st to 10thNight
31%14%26%23%6%1
830
11th to 20thNight
33%16%27%16%6%1
850
21st to endNight
32%15%31%18%3
850
December1st to 10thNight
32%16%31%15%5%
850
11th to 20thNight
33%21%27%16%31
850
21st to endNight
28%16%33%17%5%1
935
Page generated at 2024-01-08 12:14:17. Version ac07

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