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 2017-03-15.

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%
14911
14%
45167
9%
14874
40%
14874
19%
31898

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
27%
867
12%
2041
February1st to 15thNight
16%
701
9%
2287
3%
701
24%
701
11%
1749
February16th to endNight
26%
631
13%
1901
6%
631
34%
631
13%
1428
March1st to 15thNight
26%
720
14%
2064
8%
720
31%
720
16%
1511
March16th to endNight
37%
704
17%
1936
10%
704
43%
704
22%
1351
April1st to 15thNight
29%
553
16%
1648
8%
553
36%
553
21%
1148
April16th to endNight
36%
495
19%
1485
11%
495
43%
495
24%
986
May1st to 15thNight
43%
495
17%
1485
12%
495
49%
495
24%
983
May16th to endNight
47%
455
16%
1460
12%
455
54%
455
27%
893
June1st to 15thNight
47%
330
16%
1155
16%
330
53%
330
25%
710
June16th to endNight
53%
330
15%
1155
16%
330
57%
330
29%
680
July1st to 15thNight
66%
413
17%
1188
17%
413
68%
413
40%
678
July16th to endNight
63%
522
13%
1373
10%
489
65%
489
34%
841
August1st to 15thNight
66%
494
19%
1474
17%
491
67%
491
30%
904
August16th to endNight
60%
525
21%
1575
16%
525
64%
525
33%
941
September1st to 15thNight
56%
620
20%
1755
15%
620
59%
620
31%
1100
September16th to endNight
56%
657
20%
1815
15%
657
59%
657
31%
1158
October1st to 15thNight
42%
660
17%
1917
14%
660
48%
660
25%
1292
October16th to endNight
24%
704
11%
2200
7%
704
31%
704
14%
1641
November1st to 15thNight
30%
700
17%
2276
14%
700
35%
700
17%
1600
November16th to endNight
23%
720
11%
2493
7%
720
30%
720
11%
1880
December1st to 15thNight
14%
759
7%
2559
2%
759
20%
759
9%
2014
December16th to endNight
14%
960
8%
2865
2%
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%32%
45559
Night
14%9%46%5%3445%6%33%
45344
Cloud CoverDay
13%9%47%5%35%45%7%32%
45569
Night
14%9%46%5%3445%6%33%
45348
TransparencyDay
50%6%12%19%10%1
45254
Night
49%6%11%20%10%1
45167
SeeingDay
17%6%27%25%14%7%
5058
Night
19%8%29%28%11%1
14920

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%
1881
16th to endDay
14%11%5%9%6%2445%5%28%
1936
April1st to 15thDay
18%11%5%6%5%24446%30%
1979
16th to endDay
16%8%2443445%7%37%
2145
May1st to 15thDay
18%6%35%6%25%446%37%
2136
16th to endDay
12%5%26%5%2435%7%43%
2300
June1st to 15thDay
11%6%26%43445%8%40%
2475
16th to endDay
11%6%34435%47%8%40%
2475
July1st to 15thDay
8%4245%35%5%6%9%44%
2360
16th to endDay
9%5%25%5%3447%10%39%
2384
August1st to 15thDay
9%5%26%6%35%6%7%8%38%
2145
16th to endDay
11%5%36%42445%9%42%
2275
September1st to 15thDay
14%5%25%43447%8%38%
1862
16th to endDay
14%6%24435%5%6%9%38%
1815
October1st to 15thDay
17%8%37%5%2345%5%35%
1711
16th to endDay
25%9%47%5%3445%5%25%
1672
November1st to 15thDay
15%13%5%7%5%34445%29%
1582
16th to endDay
15%14%7%10%6%35%5%45%20%
1467
December1st to 15thDay
15%15%5%8%6%46%45%5%20%
1398
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
12%8%5%5%5%245%5%6%36%
1936
April1st to 15thNight
17%9%46%42345%7%34%
1648
16th to endNight
17%8%24424435%40%
1485
May1st to 15thNight
12%7%26%5%35%5%6%6%38%
1485
16th to endNight
12%5%2443435%6%46%
1458
June1st to 15thNight
12%5%235%26%5%5%7%42%
1155
16th to endNight
8%424435%6%6%9%44%
1155
July1st to 15thNight
7%42332347%7%52%
1268
16th to endNight
7%314435%47%9%46%
1475
August1st to 15thNight
8%314436%6%6%8%45%
1485
16th to endNight
9%5%25%423446%51%
1575
September1st to 15thNight
12%5%245%23448%46%
1755
16th to endNight
11%6%3442345%8%44%
1815
October1st to 15thNight
14%6%25%5%35%35%7%40%
1917
16th to endNight
22%10%46%5%3345%6%28%
2200
November1st to 15thNight
13%9%47%7%345%5%6%33%
2276
16th to endNight
19%12%46%6%35%46%6%23%
2493
December1st to 15thNight
20%14%5%8%5%34446%21%
2559
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%
1892
16th to endDay
13%11%5%10%6%25%35%5%28%
1935
April1st to 15thDay
17%11%5%7%5%34446%30%
1979
16th to endDay
16%8%2443435%8%37%
2145
May1st to 15thDay
17%7%35%5%25%446%37%
2136
16th to endDay
11%6%36%5%2435%7%42%
2300
June1st to 15thDay
10%7%26%425%45%8%40%
2475
16th to endDay
11%6%345%35%47%8%40%
2475
July1st to 15thDay
7%4245%35%5%6%9%44%
2360
16th to endDay
9%5%25%5%35%5%7%10%39%
2384
August1st to 15thDay
9%416%6%35%6%7%8%38%
2145
16th to endDay
11%5%35%42446%9%42%
2275
September1st to 15thDay
14%5%35%435%47%8%37%
1862
16th to endDay
14%6%24435%5%6%9%37%
1815
October1st to 15thDay
17%8%37%5%34346%35%
1711
16th to endDay
24%10%37%5%2445%5%26%
1672
November1st to 15thDay
15%13%47%5%34446%28%
1582
16th to endDay
14%13%7%9%7%35%5%5%5%20%
1467
December1st to 15thDay
15%15%6%8%6%36%5%5%6%21%
1398
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
12%8%5%5%5%245%46%36%
1936
April1st to 15thNight
17%8%46%42345%7%34%
1648
16th to endNight
17%8%24434445%40%
1485
May1st to 15thNight
11%8%36%5%35%5%5%6%38%
1484
16th to endNight
11%5%24435%346%46%
1458
June1st to 15thNight
12%5%335%26%5%5%8%42%
1155
16th to endNight
7%424435%6%5%9%44%
1155
July1st to 15thNight
7%4143235%6%8%52%
1268
16th to endNight
7%315%4345%7%10%46%
1475
August1st to 15thNight
8%3145%36%6%7%8%45%
1485
16th to endNight
9%5%25%423346%51%
1575
September1st to 15thNight
11%4245%2345%8%45%
1755
16th to endNight
11%6%3442345%8%44%
1815
October1st to 15thNight
14%6%25%5%25%448%39%
1917
16th to endNight
22%10%46%6%3335%5%28%
2200
November1st to 15thNight
13%8%47%7%35%45%6%33%
2276
16th to endNight
20%12%36%6%25%5%6%7%24%
2493
December1st to 15thNight
20%14%5%8%5%35%446%21%
2559
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%
1892
16th to endDay
56%5%11%18%6%1
1936
April1st to 15thDay
55%49%18%11%
1979
16th to endDay
44%5%15%16%14%2
2145
May1st to 15thDay
48%5%10%23%11%1
2136
16th to endDay
40%6%12%22%16%2
2304
June1st to 15thDay
41%6%11%24%15%
2475
16th to endDay
39%6%13%23%15%
2475
July1st to 15thDay
35%7%11%27%15%3
2211
16th to endDay
39%7%15%21%13%2
2223
August1st to 15thDay
38%9%13%23%13%1
2132
16th to endDay
37%7%13%26%12%1
2275
September1st to 15thDay
41%8%14%25%9%
1862
16th to endDay
42%7%13%25%10%
1815
October1st to 15thDay
49%5%11%20%12%1
1711
16th to endDay
58%6%15%14%4
1672
November1st to 15thDay
55%6%12%16%8%
1582
16th to endDay
64%5%12%11%4
1467
December1st to 15thDay
64%6%13%11%3
1398
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
46%6%11%22%11%1
1936
April1st to 15thNight
49%49%20%14%1
1648
16th to endNight
45%39%17%20%3
1485
May1st to 15thNight
43%5%10%23%13%2
1485
16th to endNight
37%5%10%25%15%5%
1460
June1st to 15thNight
38%7%11%24%17%1
1155
16th to endNight
33%7%15%22%18%1
1155
July1st to 15thNight
27%6%11%31%21%2
1188
16th to endNight
31%8%16%24%16%2
1373
August1st to 15thNight
33%9%11%28%15%1
1474
16th to endNight
32%6%11%28%18%2
1575
September1st to 15thNight
36%5%13%29%14%
1755
16th to endNight
36%6%12%31%11%
1815
October1st to 15thNight
42%6%12%23%13%
1917
16th to endNight
56%5%13%18%5%
2200
November1st to 15thNight
50%6%13%20%8%
2276
16th to endNight
58%7%13%16%4
2493
December1st to 15thNight
63%6%13%11%5%
2559
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%27%25%41
183
16th to endDay
22%430%24%12%4
224
April1st to 15thDay
21%10%30%24%10%2
210
16th to endDay
21%5%28%22%15%6%
210
May1st to 15thDay
22%333%22%12%6%
228
16th to endDay
16%5%25%27%17%8%
286
June1st to 15thDay
13%6%34%30%12%3
420
16th to endDay
12%6%30%27%18%5%
420
July1st to 15thDay
11%424%32%18%8%
400
16th to endDay
11%226%32%17%10%
370
August1st to 15thDay
8%18%28%23%20%
253
16th to endDay
16%414%22%25%17%
268
September1st to 15thDay
13%219%26%23%14%
255
16th to endDay
16%5%16%28%20%13%
254
October1st to 15thDay
20%7%27%23%17%3
255
16th to endDay
28%13%29%22%4
184
November1st to 15thDay
17%11%31%26%11%2
90
16th to endDay
13%24%36%16%6%1
65
December1st to 15thDay
26%18%36%16%1
60
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
17%7%30%30%12%1
704
April1st to 15thNight
22%10%33%25%7%
553
16th to endNight
22%5%28%31%9%2
495
May1st to 15thNight
16%427%36%12%2
495
16th to endNight
15%226%35%17%2
457
June1st to 15thNight
14%428%36%16%
330
16th to endNight
9%227%40%20%
330
July1st to 15thNight
10%116%45%22%3
413
16th to endNight
7%121%41%25%2
522
August1st to 15thNight
10%14%43%27%4
494
16th to endNight
13%117%32%29%5%
525
September1st to 15thNight
16%419%34%18%7%
620
16th to endNight
14%5%18%34%20%7%
657
October1st to 15thNight
17%5%29%30%15%1
660
16th to endNight
28%10%30%24%4
704
November1st to 15thNight
18%12%32%22%12%1
700
16th to endNight
26%13%32%20%6%
720
December1st to 15thNight
27%14%34%19%3
759
16th to endNight
28%12%36%18%3
960
Page generated at 2017-03-16 11:05:27. Version ac04

Copyright 2017 A. Danko


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