Out Back Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Out Back Observatory clear sky chart from 2005-11-05 to 2017-12-02.

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%
15761
14%
47751
9%
15724
41%
15724
19%
33628

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%
896
9%
2506
2%
895
21%
895
12%
2011
January16th to endNight
21%
867
10%
2595
4%
867
28%
867
12%
2041
February1st to 15thNight
16%
701
9%
2287
3%
701
24%
701
11%
1749
February16th to endNight
27%
631
13%
1901
6%
631
35%
631
13%
1428
March1st to 15thNight
26%
720
14%
2064
8%
720
31%
720
16%
1511
March16th to endNight
36%
768
17%
2112
10%
768
41%
768
22%
1489
April1st to 15thNight
29%
603
15%
1798
8%
603
36%
603
21%
1252
April16th to endNight
35%
540
19%
1620
10%
540
42%
540
24%
1078
May1st to 15thNight
42%
540
16%
1620
11%
540
48%
540
23%
1077
May16th to endNight
45%
497
16%
1596
12%
497
53%
497
26%
988
June1st to 15thNight
46%
360
14%
1260
15%
360
51%
360
24%
784
June16th to endNight
53%
360
16%
1260
16%
360
58%
360
29%
740
July1st to 15thNight
67%
453
16%
1303
16%
453
69%
453
39%
748
July16th to endNight
63%
564
15%
1492
12%
531
65%
531
34%
913
August1st to 15thNight
66%
539
18%
1609
16%
536
67%
536
30%
995
August16th to endNight
59%
573
22%
1719
16%
573
64%
573
32%
1032
September1st to 15thNight
57%
677
20%
1915
15%
677
60%
677
32%
1189
September16th to endNight
57%
717
23%
1980
17%
717
60%
717
32%
1247
October1st to 15thNight
41%
720
16%
2092
13%
720
46%
720
25%
1424
October16th to endNight
26%
768
13%
2400
8%
768
33%
768
15%
1766
November1st to 15thNight
30%
760
16%
2471
13%
760
36%
760
16%
1760
November16th to endNight
23%
780
12%
2701
6%
780
30%
780
12%
2012
December1st to 15thNight
14%
767
7%
2585
2%
767
21%
767
9%
2036
December16th to endNight
14%
960
8%
2865
1%
960
20%
960
9%
2358

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
14%9%47%5%35%45%7%33%
48688
Night
14%9%46%5%3445%6%33%
47928
Cloud CoverDay
14%9%47%5%35%45%7%32%
48698
Night
14%9%46%5%3445%6%33%
47932
TransparencyDay
49%6%12%19%10%1
48383
Night
49%6%11%20%10%1
47751
SeeingDay
17%6%28%25%14%6%
6097
Night
19%8%29%28%11%1
15770

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%17%7%9%7%35%44419%
1432
16th to endDay
14%15%8%11%9%45%5%5%5%14%
1628
February1st to 15thDay
13%17%5%9%8%36%5%46%20%
1575
16th to endDay
14%12%5%8%8%45%5%5%6%24%
1570
March1st to 15thDay
14%12%5%10%6%45%446%25%
1883
16th to endDay
15%12%6%9%6%24445%28%
2112
April1st to 15thDay
18%11%46%5%24346%31%
2160
16th to endDay
16%7%25%43445%7%37%
2340
May1st to 15thDay
18%6%25%5%24446%38%
2331
16th to endDay
12%6%26%5%2445%7%41%
2515
June1st to 15thDay
11%6%25%435%45%8%41%
2700
16th to endDay
11%5%34435%47%8%39%
2700
July1st to 15thDay
8%4245%25%5%6%9%44%
2574
16th to endDay
9%5%25%5%345%7%9%40%
2573
August1st to 15thDay
9%5%26%6%35%6%7%8%37%
2340
16th to endDay
11%5%36%32445%8%42%
2483
September1st to 15thDay
13%5%25%435%5%7%7%39%
2031
16th to endDay
14%6%24436%5%6%8%39%
1980
October1st to 15thDay
18%8%37%5%2345%5%35%
1866
16th to endDay
24%9%47%5%3445%6%26%
1824
November1st to 15thDay
16%13%5%7%5%34445%28%
1717
16th to endDay
14%14%6%9%6%35%5%5%6%21%
1589
December1st to 15thDay
15%15%5%8%6%46%45%5%21%
1409
16th to endDay
19%17%7%9%6%335%5%5%15%
1356
January1st to 15thNight
21%11%6%8%6%44445%21%
2506
16th to endNight
13%11%7%9%6%35%5%5%6%23%
2595
February1st to 15thNight
14%15%5%9%5%45%45%5%25%
2285
16th to endNight
15%10%49%6%35%5%5%6%25%
1901
March1st to 15thNight
13%11%5%7%6%35%435%32%
2052
16th to endNight
14%8%5%5%5%245%5%5%36%
2112
April1st to 15thNight
18%9%45%42345%7%34%
1798
16th to endNight
16%8%35%424446%40%
1620
May1st to 15thNight
12%8%26%5%35%5%6%6%37%
1620
16th to endNight
12%5%25%435%347%45%
1594
June1st to 15thNight
11%5%245%36%6%5%7%41%
1260
16th to endNight
8%424435%5%6%9%45%
1260
July1st to 15thNight
7%42332447%7%52%
1383
16th to endNight
7%314435%47%9%47%
1594
August1st to 15thNight
8%324436%7%6%8%45%
1620
16th to endNight
9%425%5%2345%5%51%
1719
September1st to 15thNight
11%4245%235%5%8%47%
1915
16th to endNight
11%5%2442345%8%45%
1980
October1st to 15thNight
14%6%25%5%35%45%7%39%
2092
16th to endNight
21%10%46%5%33446%30%
2400
November1st to 15thNight
14%9%47%6%345%5%5%31%
2471
16th to endNight
19%12%36%5%345%6%7%24%
2701
December1st to 15thNight
19%14%5%8%5%34446%21%
2585
16th to endNight
19%15%7%9%6%2445%417%
2865

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
15%17%6%9%7%44445%19%
1432
16th to endDay
14%16%8%12%8%5%5%45%5%14%
1628
February1st to 15thDay
13%17%5%9%8%35%5%45%19%
1575
16th to endDay
14%12%5%7%8%45%45%6%24%
1570
March1st to 15thDay
14%12%5%10%6%46%446%25%
1894
16th to endDay
15%11%5%10%6%25%345%27%
2111
April1st to 15thDay
18%11%46%5%24446%30%
2160
16th to endDay
16%8%25%43445%8%36%
2340
May1st to 15thDay
18%7%35%5%24446%38%
2331
16th to endDay
12%6%35%5%2445%7%41%
2515
June1st to 15thDay
10%6%26%435%45%8%41%
2700
16th to endDay
11%6%245%35%5%7%8%39%
2700
July1st to 15thDay
7%425%5%35%5%6%9%44%
2574
16th to endDay
9%5%25%5%35%5%6%10%40%
2573
August1st to 15thDay
9%5%26%6%36%6%7%8%37%
2340
16th to endDay
11%6%35%42446%8%42%
2483
September1st to 15thDay
13%5%25%435%46%8%38%
2031
16th to endDay
14%5%24436%5%6%9%38%
1980
October1st to 15thDay
18%8%37%5%34346%35%
1866
16th to endDay
23%10%37%5%3445%5%26%
1824
November1st to 15thDay
16%13%48%5%34445%28%
1717
16th to endDay
14%13%7%9%7%35%5%5%6%21%
1589
December1st to 15thDay
15%15%6%8%6%36%5%5%6%21%
1409
16th to endDay
19%17%7%9%7%335%5%5%15%
1356
January1st to 15thNight
21%11%5%8%6%35%446%21%
2506
16th to endNight
13%11%7%9%7%35%5%5%6%22%
2595
February1st to 15thNight
13%14%5%9%5%35%445%25%
2278
16th to endNight
16%10%49%6%35%5%5%6%25%
1901
March1st to 15thNight
14%11%5%7%5%35%435%32%
2064
16th to endNight
14%8%5%5%5%245%46%36%
2112
April1st to 15thNight
18%8%46%42345%7%34%
1798
16th to endNight
16%8%35%434446%39%
1620
May1st to 15thNight
12%8%35%5%35%5%5%6%37%
1619
16th to endNight
12%5%25%435%346%45%
1594
June1st to 15thNight
11%5%345%26%6%5%7%41%
1260
16th to endNight
8%424435%6%5%9%45%
1260
July1st to 15thNight
7%4143245%6%8%51%
1383
16th to endNight
7%315%43447%10%46%
1594
August1st to 15thNight
8%3145%36%6%6%8%45%
1620
16th to endNight
9%5%25%42335%6%51%
1719
September1st to 15thNight
11%42442445%8%46%
1915
16th to endNight
11%5%3442345%8%45%
1980
October1st to 15thNight
14%6%26%5%25%448%39%
2092
16th to endNight
21%10%45%6%3335%6%30%
2400
November1st to 15thNight
14%8%47%7%35%45%5%31%
2471
16th to endNight
19%12%36%6%245%6%7%24%
2701
December1st to 15thNight
19%14%5%8%5%35%446%21%
2585
16th to endNight
19%15%7%9%6%3445%5%17%
2865

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
67%5%10%13%3
1433
16th to endDay
70%5%10%9%3
1628
February1st to 15thDay
65%5%11%12%4
1577
16th to endDay
58%6%11%15%6%1
1570
March1st to 15thDay
60%6%10%15%7%
1894
16th to endDay
57%411%17%7%1
2112
April1st to 15thDay
54%410%19%10%
2160
16th to endDay
45%6%15%16%14%2
2340
May1st to 15thDay
47%5%9%23%11%2
2331
16th to endDay
41%6%12%21%15%1
2519
June1st to 15thDay
40%6%12%25%14%
2700
16th to endDay
39%7%13%23%14%
2700
July1st to 15thDay
34%7%11%26%16%2
2425
16th to endDay
39%7%14%22%14%2
2412
August1st to 15thDay
39%9%13%24%12%1
2327
16th to endDay
38%7%13%26%12%1
2483
September1st to 15thDay
40%8%13%25%11%
2031
16th to endDay
41%7%13%26%11%
1980
October1st to 15thDay
49%5%10%20%11%1
1866
16th to endDay
58%5%15%15%5%
1824
November1st to 15thDay
56%6%12%16%8%
1717
16th to endDay
63%6%13%11%4
1589
December1st to 15thDay
64%6%14%11%3
1409
16th to endDay
68%6%10%11%1
1356
January1st to 15thNight
63%5%10%14%6%
2506
16th to endNight
61%6%12%16%3
2595
February1st to 15thNight
60%5%10%16%6%
2287
16th to endNight
56%6%11%18%7%
1901
March1st to 15thNight
54%5%11%20%7%1
2064
16th to endNight
48%5%10%22%11%1
2112
April1st to 15thNight
49%410%20%14%1
1798
16th to endNight
45%49%17%19%3
1620
May1st to 15thNight
44%5%10%22%13%3
1620
16th to endNight
38%5%10%25%14%4
1596
June1st to 15thNight
38%8%11%24%16%
1260
16th to endNight
33%7%15%24%18%1
1260
July1st to 15thNight
27%6%11%30%20%2
1303
16th to endNight
31%8%15%24%17%2
1492
August1st to 15thNight
33%9%12%28%14%1
1609
16th to endNight
33%6%10%28%18%1
1719
September1st to 15thNight
35%6%13%29%14%
1915
16th to endNight
35%6%12%32%12%
1980
October1st to 15thNight
43%6%11%23%13%
2092
16th to endNight
55%5%12%19%6%
2400
November1st to 15thNight
51%6%12%20%7%
2471
16th to endNight
57%7%14%16%4
2701
December1st to 15thNight
63%6%13%11%4
2585
16th to endNight
67%5%10%11%3
2865

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
24%13%42%14%5%
90
16th to endDay
34%7%35%19%21
96
February1st to 15thDay
23%15%43%16%1
90
16th to endDay
14%20%38%19%6%
81
March1st to 15thDay
25%15%28%25%41
184
16th to endDay
25%430%23%11%3
288
April1st to 15thDay
24%10%29%24%9%2
270
16th to endDay
20%8%31%21%13%4
270
May1st to 15thDay
23%334%20%12%5%
288
16th to endDay
17%6%28%24%15%6%
352
June1st to 15thDay
12%5%33%32%12%4
495
16th to endDay
12%7%32%26%15%4
495
July1st to 15thDay
10%325%32%19%8%
475
16th to endDay
11%226%32%17%9%
433
August1st to 15thDay
10%117%30%22%17%
313
16th to endDay
15%417%22%24%15%
332
September1st to 15thDay
12%120%25%22%16%
315
16th to endDay
15%416%26%21%15%
314
October1st to 15thDay
23%7%26%22%16%3
315
16th to endDay
27%12%32%22%4
240
November1st to 15thDay
23%10%31%22%10%1
135
16th to endDay
16%24%38%15%41
97
December1st to 15thDay
25%17%38%15%3
63
16th to endDay
30%24%37%7%
66
January1st to 15thNight
27%12%36%18%41
900
16th to endNight
18%11%38%24%7%
867
February1st to 15thNight
21%13%38%21%4
704
16th to endNight
20%13%29%29%6%
631
March1st to 15thNight
20%13%32%27%6%
720
16th to endNight
19%8%29%29%11%1
768
April1st to 15thNight
22%10%32%26%7%
603
16th to endNight
21%6%30%30%9%2
540
May1st to 15thNight
17%5%27%36%12%1
540
16th to endNight
16%328%33%16%2
499
June1st to 15thNight
14%429%35%16%
360
16th to endNight
10%226%40%19%
360
July1st to 15thNight
10%115%46%22%3
453
16th to endNight
8%120%42%25%2
564
August1st to 15thNight
10%14%42%27%4
539
16th to endNight
12%118%32%28%5%
573
September1st to 15thNight
15%318%33%20%7%
677
16th to endNight
13%5%17%33%22%6%
717
October1st to 15thNight
17%5%29%29%15%1
720
16th to endNight
27%10%30%25%4
768
November1st to 15thNight
19%11%32%23%11%1
760
16th to endNight
25%14%32%20%6%
780
December1st to 15thNight
27%14%34%20%3
767
16th to endNight
28%12%36%18%3
960
Page generated at 2017-12-03 11:16:45. Version ac04

Copyright 2017 A. Danko


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