Hume Cronyn Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Hume Cronyn Observatory clear sky chart from 2005-11-05 to 2017-12-20.

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
35%
15388
14%
47815
10%
15349
40%
15349
18%
34040

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
12%
779
8%
2429
3%
777
18%
777
8%
2024
January16th to endNight
16%
768
9%
2496
3%
768
22%
768
7%
2069
February1st to 15thNight
17%
702
6%
2287
2%
701
22%
701
8%
1828
February16th to endNight
22%
631
10%
1951
4%
631
29%
631
12%
1521
March1st to 15thNight
24%
720
14%
2016
8%
720
30%
720
16%
1546
March16th to endNight
33%
768
19%
2112
11%
768
39%
768
21%
1494
April1st to 15thNight
28%
677
15%
1831
7%
677
34%
677
20%
1323
April16th to endNight
37%
540
20%
1620
9%
540
45%
540
24%
1062
May1st to 15thNight
40%
540
16%
1620
10%
540
46%
540
23%
1087
May16th to endNight
48%
431
17%
1554
15%
431
54%
431
26%
917
June1st to 15thNight
50%
360
14%
1388
15%
360
57%
360
24%
805
June16th to endNight
56%
360
17%
1260
16%
360
63%
360
29%
725
July1st to 15thNight
66%
390
19%
1262
23%
390
69%
390
36%
687
July16th to endNight
65%
564
15%
1595
15%
531
68%
531
34%
951
August1st to 15thNight
69%
539
17%
1609
15%
536
71%
536
33%
974
August16th to endNight
63%
580
25%
1726
17%
580
68%
580
36%
1002
September1st to 15thNight
56%
720
22%
1893
13%
720
60%
720
33%
1207
September16th to endNight
58%
717
22%
1980
18%
717
61%
717
32%
1248
October1st to 15thNight
44%
720
17%
2133
15%
720
48%
720
24%
1431
October16th to endNight
24%
768
14%
2325
9%
768
31%
768
14%
1747
November1st to 15thNight
35%
760
17%
2507
15%
760
40%
760
18%
1714
November16th to endNight
23%
780
10%
2730
6%
780
28%
780
11%
2083
December1st to 15thNight
15%
780
5%
2730
2%
780
19%
780
8%
2222
December16th to endNight
12%
794
6%
2761
1%
794
17%
794
5%
2373

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%9%47%6%3445%7%31%
48990
Night
15%9%46%5%3445%6%32%
47994
Cloud CoverDay
15%9%47%6%35%45%7%30%
49000
Night
15%9%47%5%3445%6%32%
47998
TransparencyDay
51%6%11%18%9%
48687
Night
50%6%11%19%10%1
47815
SeeingDay
18%7%26%24%15%7%
5944
Night
20%8%28%28%12%1
15394

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
19%15%6%12%8%35%43415%
1496
16th to endDay
14%18%8%12%8%44335%14%
1728
February1st to 15thDay
16%16%7%10%8%45%445%17%
1575
16th to endDay
15%14%8%11%7%46%445%18%
1521
March1st to 15thDay
17%12%6%10%6%34446%24%
1933
16th to endDay
17%9%5%8%5%2445%5%29%
2112
April1st to 15thDay
19%11%45%42445%7%28%
2126
16th to endDay
18%9%25%5%23347%37%
2340
May1st to 15thDay
19%6%25%5%2445%7%35%
2331
16th to endDay
14%425%5%346%6%6%40%
2559
June1st to 15thDay
14%5%25%5%345%5%8%39%
2568
16th to endDay
14%4245%36%5%6%9%38%
2700
July1st to 15thDay
11%3245%35%5%5%9%41%
2617
16th to endDay
11%425%5%35%5%7%9%38%
2465
August1st to 15thDay
11%5%25%6%35%6%6%8%37%
2340
16th to endDay
12%5%25%5%346%5%9%38%
2463
September1st to 15thDay
14%6%35%5%4445%7%38%
2065
16th to endDay
16%41442446%8%40%
1980
October1st to 15thDay
20%6%26%5%34446%33%
1826
16th to endDay
27%10%37%6%24445%23%
1896
November1st to 15thDay
16%10%35%5%4445%7%32%
1680
16th to endDay
19%16%5%8%6%35%5%47%18%
1560
December1st to 15thDay
17%18%7%10%6%3435%5%17%
1560
16th to endDay
21%18%9%11%7%3434410%
1549
January1st to 15thNight
21%14%7%10%6%35%435%17%
2429
16th to endNight
16%16%7%11%7%36%445%15%
2496
February1st to 15thNight
15%14%6%9%8%45%5%5%5%19%
2285
16th to endNight
17%11%5%9%7%35%45%6%22%
1951
March1st to 15thNight
17%10%5%8%7%345%45%27%
2004
16th to endNight
17%8%45%6%24336%36%
2112
April1st to 15thNight
20%9%34424346%34%
1831
16th to endNight
12%7%25%6%25%5%5%8%39%
1620
May1st to 15thNight
16%6%25%5%2446%7%36%
1620
16th to endNight
10%4344345%6%6%47%
1552
June1st to 15thNight
12%5%14425%5%6%10%41%
1388
16th to endNight
10%325%425%5%5%10%45%
1260
July1st to 15thNight
5%31442335%8%55%
1338
16th to endNight
8%323425%46%9%48%
1703
August1st to 15thNight
7%314435%6%7%8%47%
1620
16th to endNight
9%423423445%54%
1726
September1st to 15thNight
12%5%135%2446%7%46%
1893
16th to endNight
12%41443345%6%47%
1980
October1st to 15thNight
17%6%25%5%23347%39%
2133
16th to endNight
23%8%36%5%34446%28%
2325
November1st to 15thNight
16%8%35%6%2445%7%34%
2507
16th to endNight
21%14%5%6%5%2445%6%22%
2730
December1st to 15thNight
20%16%7%9%5%35%445%17%
2730
16th to endNight
21%15%9%11%7%3444413%
2761

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
19%15%7%11%8%36%34415%
1496
16th to endDay
14%18%8%12%9%45%335%14%
1728
February1st to 15thDay
16%16%7%10%7%5%5%345%17%
1575
16th to endDay
15%13%7%11%8%46%445%17%
1521
March1st to 15thDay
17%12%5%10%6%34446%23%
1944
16th to endDay
17%9%5%7%6%2445%5%29%
2111
April1st to 15thDay
19%11%46%5%24448%27%
2126
16th to endDay
17%9%35%42335%7%36%
2340
May1st to 15thDay
18%7%26%434448%34%
2331
16th to endDay
13%5%25%4345%6%6%39%
2559
June1st to 15thDay
14%5%25%5%35%45%8%39%
2568
16th to endDay
12%5%245%35%6%6%10%37%
2700
July1st to 15thDay
10%425%6%35%5%5%9%41%
2617
16th to endDay
9%5%35%6%35%5%6%9%38%
2465
August1st to 15thDay
10%5%35%6%36%6%6%8%37%
2340
16th to endDay
11%5%25%6%35%5%6%9%38%
2463
September1st to 15thDay
13%6%26%6%345%6%7%37%
2065
16th to endDay
15%5%245%2346%9%40%
1980
October1st to 15thDay
19%6%36%5%35%45%6%33%
1826
16th to endDay
26%10%36%7%34445%23%
1896
November1st to 15thDay
16%9%35%6%345%5%7%32%
1680
16th to endDay
19%15%5%8%7%346%46%19%
1560
December1st to 15thDay
17%17%7%10%7%34446%16%
1560
16th to endDay
20%19%8%11%7%35%35%410%
1549
January1st to 15thNight
21%14%6%11%6%36%33418%
2429
16th to endNight
15%16%7%10%7%35%5%45%15%
2496
February1st to 15thNight
14%15%6%9%7%36%5%5%5%19%
2278
16th to endNight
16%11%5%10%7%45%446%23%
1951
March1st to 15thNight
17%10%5%8%7%345%5%5%27%
2016
16th to endNight
16%8%46%6%24336%36%
2112
April1st to 15thNight
19%10%35%43335%6%33%
1831
16th to endNight
12%7%25%6%35%45%8%39%
1620
May1st to 15thNight
16%6%25%5%345%6%7%36%
1619
16th to endNight
9%4344245%6%6%46%
1552
June1st to 15thNight
11%4244346%6%9%42%
1388
16th to endNight
9%424426%5%6%9%45%
1260
July1st to 15thNight
5%31442345%8%55%
1338
16th to endNight
7%32343447%9%47%
1703
August1st to 15thNight
6%414435%6%8%8%46%
1620
16th to endNight
8%4244245%46%53%
1726
September1st to 15thNight
11%5%2442446%7%45%
1893
16th to endNight
12%41443346%6%46%
1980
October1st to 15thNight
17%6%35%5%24347%39%
2133
16th to endNight
22%9%36%6%3445%6%27%
2325
November1st to 15thNight
15%7%36%5%2446%7%34%
2507
16th to endNight
21%13%47%5%3445%6%23%
2730
December1st to 15thNight
20%14%6%9%6%345%46%17%
2730
16th to endNight
20%15%8%13%7%3444413%
2761

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
72%6%8%9%3
1497
16th to endDay
72%6%7%10%3
1728
February1st to 15thDay
69%5%8%12%4
1577
16th to endDay
68%410%11%4
1521
March1st to 15thDay
62%5%11%13%6%
1944
16th to endDay
55%6%10%17%9%1
2112
April1st to 15thDay
55%5%11%18%9%
2126
16th to endDay
47%5%11%19%14%1
2340
May1st to 15thDay
47%6%11%21%11%
2331
16th to endDay
42%7%12%22%13%1
2563
June1st to 15thDay
42%5%13%24%12%1
2568
16th to endDay
40%8%12%22%14%
2700
July1st to 15thDay
36%6%11%26%16%2
2464
16th to endDay
40%8%13%22%13%2
2310
August1st to 15thDay
41%8%14%21%12%1
2327
16th to endDay
40%8%13%22%13%1
2463
September1st to 15thDay
43%6%13%23%12%
2065
16th to endDay
40%6%13%27%10%
1980
October1st to 15thDay
50%6%11%17%12%
1826
16th to endDay
62%6%13%12%5%
1896
November1st to 15thDay
51%6%12%19%8%1
1680
16th to endDay
64%6%13%11%3
1560
December1st to 15thDay
68%6%12%9%2
1560
16th to endDay
76%5%8%7%1
1549
January1st to 15thNight
69%6%8%9%6%
2429
16th to endNight
68%6%8%13%2
2496
February1st to 15thNight
64%6%10%12%4
2287
16th to endNight
61%6%10%16%5%
1951
March1st to 15thNight
57%5%9%19%6%
2016
16th to endNight
49%49%21%12%2
2112
April1st to 15thNight
50%49%21%12%1
1831
16th to endNight
42%5%8%20%18%3
1620
May1st to 15thNight
44%6%10%23%12%2
1620
16th to endNight
35%7%12%25%14%3
1554
June1st to 15thNight
36%7%12%26%15%1
1388
16th to endNight
33%6%15%24%17%1
1260
July1st to 15thNight
27%6%8%31%22%3
1262
16th to endNight
30%8%15%23%19%2
1595
August1st to 15thNight
30%9%13%30%14%2
1609
16th to endNight
31%5%11%31%17%2
1726
September1st to 15thNight
35%6%13%26%16%2
1893
16th to endNight
35%6%12%29%15%
1980
October1st to 15thNight
44%5%10%22%16%
2133
16th to endNight
56%6%11%17%7%
2325
November1st to 15thNight
47%7%12%20%10%1
2507
16th to endNight
60%6%14%14%3
2730
December1st to 15thNight
67%6%12%9%3
2730
16th to endNight
74%5%8%8%2
2761

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
21%22%37%8%8%1
83
16th to endDay
35%11%39%13%
96
February1st to 15thDay
23%17%47%11%
90
16th to endDay
18%18%50%9%2
81
March1st to 15thDay
28%9%33%20%6%
234
16th to endDay
26%6%35%21%7%2
288
April1st to 15thDay
25%12%26%21%12%1
270
16th to endDay
21%9%30%21%10%7%
270
May1st to 15thDay
21%8%27%24%12%5%
288
16th to endDay
15%6%29%26%15%6%
331
June1st to 15thDay
16%325%33%16%4
363
16th to endDay
13%7%28%30%15%4
495
July1st to 15thDay
13%421%31%20%8%
450
16th to endDay
9%418%28%27%11%
326
August1st to 15thDay
11%215%28%27%15%
313
16th to endDay
12%318%19%26%18%
332
September1st to 15thDay
11%220%21%28%16%
315
16th to endDay
15%5%15%25%21%16%
314
October1st to 15thDay
23%6%24%24%16%5%
315
16th to endDay
29%11%32%21%41
312
November1st to 15thDay
22%12%32%18%10%3
126
16th to endDay
24%17%38%12%6%
90
December1st to 15thDay
26%26%23%18%4
90
16th to endDay
34%25%31%8%
72
January1st to 15thNight
27%15%36%15%4
782
16th to endNight
23%10%35%24%5%
768
February1st to 15thNight
24%14%34%22%4
704
16th to endNight
22%11%32%26%5%
631
March1st to 15thNight
23%10%32%24%7%
720
16th to endNight
21%8%30%27%10%1
768
April1st to 15thNight
25%10%31%25%6%
677
16th to endNight
15%8%32%32%9%1
540
May1st to 15thNight
18%5%26%34%14%
540
16th to endNight
13%230%36%15%2
432
June1st to 15thNight
14%226%42%13%
360
16th to endNight
11%222%46%16%
360
July1st to 15thNight
7%117%49%21%2
390
16th to endNight
9%16%46%25%1
564
August1st to 15thNight
8%112%45%29%3
539
16th to endNight
10%216%35%31%3
580
September1st to 15thNight
13%419%32%24%6%
720
16th to endNight
14%316%32%26%6%
717
October1st to 15thNight
20%5%23%31%17%2
720
16th to endNight
28%9%32%23%6%
768
November1st to 15thNight
19%9%29%28%10%1
760
16th to endNight
27%12%29%21%7%
780
December1st to 15thNight
30%14%34%16%4
780
16th to endNight
27%12%38%16%4
794
Page generated at 2017-12-21 07:04:44. Version ac04

Copyright 2017 A. Danko


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