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 2018-03-21.

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%
16015
8%
49245
4%
15975
27%
15975
10%
39550

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%
823
3%
2716
1%
821
15%
821
4%
2389
January16th to endNight
11%
878
3%
2902
0%
878
15%
878
4%
2542
February1st to 15thNight
13%
761
5%
2481
1%
761
17%
761
5%
2088
February16th to endNight
15%
683
8%
2100
2%
683
21%
683
9%
1701
March1st to 15thNight
20%
780
9%
2304
4%
780
25%
780
10%
1844
March16th to endNight
20%
696
10%
2081
5%
696
26%
696
11%
1618
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
37%
540
12%
1800
10%
540
42%
540
16%
1287
September16th to endNight
33%
553
16%
1949
12%
553
39%
553
16%
1356
October1st to 15thNight
28%
720
10%
2160
5%
720
32%
720
14%
1627
October16th to endNight
19%
799
9%
2427
4%
799
23%
799
11%
1968
November1st to 15thNight
20%
805
6%
2527
4%
805
22%
805
9%
2085
November16th to endNight
13%
825
4%
2730
1%
825
16%
825
5%
2331
December1st to 15thNight
13%
825
4%
2730
1%
825
17%
825
4%
2406
December16th to endNight
7%
880
2%
2912
0%
880
9%
880
2%
2695

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%10%47%6%35%5%5%6%24%
49613
Night
20%10%47%6%35%5%5%6%25%
49416
TransparencyDay
58%8%12%14%5%
49302
Night
62%8%11%12%5%
49245
SeeingDay
24%17%22%22%10%1
8387
Night
24%21%23%21%7%
16020

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%15%
1552
16th to endDay
15%11%7%9%8%47%6%6%6%16%
1671
February1st to 15thDay
16%11%5%10%8%36%5%5%7%17%
1710
16th to endDay
11%14%7%7%6%35%5%5%6%25%
1659
March1st to 15thDay
14%13%5%8%7%36%5%5%6%22%
1976
16th to endDay
17%14%6%7%7%34435%24%
2270
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%434446%33%
2160
16th to endDay
18%6%345%3345%7%36%
2007
October1st to 15thDay
19%10%46%6%235%5%7%28%
1800
16th to endDay
26%11%48%6%345%45%19%
1796
November1st to 15thDay
24%13%5%8%6%34445%17%
1660
16th to endDay
16%17%49%6%36%6%5%7%17%
1560
December1st to 15thDay
22%15%5%8%7%5%6%5%5%5%11%
1560
16th to endDay
19%16%6%11%8%5%8%5%448%
1664
January1st to 15thNight
16%13%5%9%9%5%6%6%5%6%15%
2716
16th to endNight
17%11%6%10%7%46%5%6%7%16%
2902
February1st to 15thNight
17%10%410%7%46%5%5%5%21%
2480
16th to endNight
14%13%7%8%7%45%45%6%22%
2100
March1st to 15thNight
17%13%5%7%5%35%445%25%
2291
16th to endNight
20%12%5%7%6%3443427%
2081
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%
1800
16th to endNight
20%6%16%5%24346%38%
1949
October1st to 15thNight
21%5%27%5%25%36%8%31%
2160
16th to endNight
25%10%36%5%3445%5%25%
2427
November1st to 15thNight
21%10%48%6%45%45%6%22%
2527
16th to endNight
19%15%47%6%35%5%5%6%18%
2730
December1st to 15thNight
22%13%5%7%6%45%5%6%6%15%
2730
16th to endNight
21%17%6%9%7%36%5%5%5%10%
2912

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%9%8%7%3
1553
16th to endDay
71%10%9%5%2
1671
February1st to 15thDay
69%9%9%8%3
1713
16th to endDay
57%8%12%11%7%1
1659
March1st to 15thDay
59%6%9%16%6%
1986
16th to endDay
60%6%11%15%5%
2270
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%20%6%
2160
16th to endDay
45%7%15%21%8%
2007
October1st to 15thDay
54%7%14%15%7%
1800
16th to endDay
65%8%10%11%3
1796
November1st to 15thDay
69%8%8%10%2
1660
16th to endDay
67%8%11%8%3
1560
December1st to 15thDay
79%7%6%41
1560
16th to endDay
81%7%5%31
1664
January1st to 15thNight
74%8%8%5%2
2716
16th to endNight
73%9%9%6%1
2902
February1st to 15thNight
69%7%9%9%3
2481
16th to endNight
63%7%11%10%5%1
2100
March1st to 15thNight
63%6%9%13%5%
2304
16th to endNight
61%411%13%6%1
2081
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%
1800
16th to endNight
49%7%12%22%7%
1949
October1st to 15thNight
54%8%13%16%6%
2160
16th to endNight
64%6%10%14%4
2427
November1st to 15thNight
65%8%12%10%2
2527
16th to endNight
69%9%11%6%2
2730
December1st to 15thNight
73%9%10%5%1
2730
16th to endNight
81%7%5%31
2912

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
17%29%35%13%3
285
16th to endDay
24%22%33%16%3
304
February1st to 15thDay
24%23%32%16%3
281
16th to endDay
21%20%33%15%7%1
251
March1st to 15thDay
18%23%29%17%9%2
294
16th to endDay
24%22%23%18%8%2
311
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%9%20%33%7%1
315
16th to endDay
22%10%23%26%16%1
280
October1st to 15thDay
24%11%23%23%14%1
270
16th to endDay
28%15%31%14%9%
288
November1st to 15thDay
26%22%25%14%8%2
280
16th to endDay
29%24%26%13%5%
285
December1st to 15thDay
30%24%27%12%4
285
16th to endDay
26%27%29%12%21
304
January1st to 15thNight
21%28%31%16%2
825
16th to endNight
22%25%33%15%2
878
February1st to 15thNight
22%28%28%18%2
764
16th to endNight
20%24%29%19%5%
683
March1st to 15thNight
22%23%26%19%7%
780
16th to endNight
23%24%25%19%6%1
696
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%
540
16th to endNight
24%12%25%25%10%1
553
October1st to 15thNight
23%15%25%23%9%1
720
16th to endNight
32%16%26%17%5%
799
November1st to 15thNight
27%22%22%17%6%1
805
16th to endNight
29%27%24%13%4
825
December1st to 15thNight
29%29%24%12%4
825
16th to endNight
30%28%26%11%21
880
Page generated at 2018-03-22 12:34:22. Version ac04

Copyright 2018 A. Danko


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