Pictor Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Pictor Observatory clear sky chart from 2005-11-06 to 2024-01-17.

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
34%
23006
14%
74463
9%
22955
40%
22955
17%
52751

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
14%
758
10%
2555
4%
757
21%
757
8%
2037
January11th to 20thNight
12%
748
5%
2430
3%
748
16%
748
6%
2044
January21st to endNight
19%
792
10%
2574
4%
792
26%
792
10%
2014
February1st to 10thNight
15%
720
7%
2340
2%
720
21%
720
9%
1883
February11th to 20thNight
19%
701
10%
2274
3%
699
26%
699
11%
1729
February21st to endNight
17%
592
10%
1796
3%
592
25%
592
11%
1392
March1st to 10thNight
24%
720
16%
2016
8%
720
31%
720
18%
1450
March11th to 20thNight
26%
720
17%
1980
8%
720
34%
720
19%
1425
March21st to endNight
28%
792
18%
2178
9%
792
35%
792
19%
1573
April1st to 10thNight
28%
720
14%
1900
7%
720
33%
720
20%
1377
April11th to 20thNight
32%
587
19%
1651
8%
587
39%
587
23%
1130
April21st to endNight
35%
540
17%
1620
7%
540
42%
540
21%
1102
May1st to 10thNight
38%
540
16%
1620
10%
540
43%
540
23%
1088
May11th to 20thNight
43%
501
18%
1563
12%
501
50%
501
25%
1000
May21st to endNight
51%
388
18%
1551
18%
388
59%
388
29%
830
June1st to 10thNight
48%
360
14%
1440
15%
360
57%
360
24%
812
June11th to 20thNight
47%
360
17%
1326
16%
360
56%
360
25%
774
June21st to endNight
52%
360
19%
1260
18%
360
61%
360
27%
735
July1st to 10thNight
63%
350
19%
1225
22%
350
68%
350
35%
642
July11th to 20thNight
60%
476
17%
1519
18%
476
64%
476
33%
875
July21st to endNight
62%
591
15%
1672
13%
558
65%
558
33%
998
August1st to 10thNight
65%
537
18%
1600
16%
534
67%
534
33%
972
August11th to 20thNight
65%
534
23%
1598
17%
534
68%
534
35%
939
August21st to endNight
58%
620
22%
1808
15%
620
62%
620
34%
1086
September1st to 10thNight
52%
720
18%
1822
10%
720
56%
720
32%
1216
September11th to 20thNight
61%
720
26%
1980
19%
720
64%
720
37%
1177
September21st to endNight
48%
720
20%
1980
14%
720
52%
720
26%
1341
October1st to 10thNight
43%
720
17%
2137
16%
720
47%
720
24%
1417
October11th to 20thNight
32%
720
15%
2160
10%
720
40%
720
19%
1524
October21st to endNight
24%
792
16%
2386
11%
792
32%
792
15%
1798
November1st to 10thNight
37%
740
19%
2406
16%
740
44%
740
22%
1571
November11th to 20thNight
22%
760
13%
2648
8%
760
31%
760
14%
1892
November21st to endNight
22%
760
8%
2660
6%
760
26%
760
11%
2031
December1st to 10thNight
16%
760
6%
2660
3%
760
21%
760
7%
2163
December11th to 20thNight
15%
760
6%
3251
2%
758
22%
758
7%
2500
December21st to endNight
11%
827
3%
4877
1%
817
17%
817
3%
4214

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
15%10%47%6%45%5%5%7%31%
75123
Night
15%10%47%6%35%5%5%7%32%
74688
TransparencyDay
51%8%12%19%10%1
74839
Night
50%7%12%19%10%1
74508
SeeingDay
18%11%29%23%13%5%
13787
Night
19%10%29%29%11%1
23020

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
16%14%7%11%9%5%5%5%46%18%
1607
11th to 20thDay
16%18%8%14%7%5%445%5%15%
1674
21st to endDay
14%17%9%11%10%46%43416%
1782
February1st to 10thDay
16%17%6%10%10%5%6%5%45%17%
1620
11th to 20thDay
14%14%8%13%9%5%5%446%19%
1573
21st to endDay
18%15%6%11%6%35%5%46%21%
1458
March1st to 10thDay
16%12%5%9%8%45%5%6%5%26%
1941
11th to 20thDay
14%13%7%9%6%34447%30%
1980
21st to endDay
19%11%5%8%6%4435%6%29%
2178
April1st to 10thDay
16%12%6%7%6%3445%7%28%
2060
11th to 20thDay
18%10%36%6%3445%7%32%
2274
21st to endDay
21%10%37%5%3435%6%33%
2340
May1st to 10thDay
18%8%36%7%345%6%7%33%
2340
11th to 20thDay
17%7%45%6%345%6%8%35%
2330
21st to endDay
11%6%26%5%35%5%6%8%41%
2725
June1st to 10thDay
13%5%36%5%35%5%6%8%40%
2520
11th to 20thDay
12%6%35%5%46%5%6%9%40%
2628
21st to endDay
12%435%5%35%6%6%9%41%
2700
July1st to 10thDay
9%4245%36%5%6%10%45%
2696
11th to 20thDay
11%6%36%6%45%5%7%11%37%
2385
21st to endDay
9%5%35%6%5%7%6%6%10%39%
2547
August1st to 10thDay
9%5%26%6%5%6%6%8%9%39%
2327
11th to 20thDay
11%6%26%5%5%6%7%6%10%36%
2303
21st to endDay
12%7%35%6%35%5%6%9%40%
2530
September1st to 10thDay
12%6%37%6%45%6%7%8%38%
2135
11th to 20thDay
12%5%25%5%346%6%9%44%
1980
21st to endDay
15%6%27%7%35%5%7%8%36%
1980
October1st to 10thDay
18%7%46%6%345%5%7%35%
1823
11th to 20thDay
21%9%46%5%45%46%7%28%
1800
21st to endDay
24%11%48%7%36%5%5%6%22%
1967
November1st to 10thDay
15%11%46%6%35%6%5%7%33%
1672
11th to 20thDay
16%13%48%6%35%46%9%27%
1530
21st to endDay
20%15%7%8%7%35%46%6%19%
1520
December1st to 10thDay
17%17%7%11%6%445%5%7%18%
1520
11th to 20thDay
18%17%8%11%8%45%5%5%415%
1906
21st to endDay
29%17%9%11%7%334449%
2772
January1st to 10thNight
17%13%8%11%8%45%5%45%20%
2555
11th to 20thNight
20%17%7%11%7%35%5%45%16%
2430
21st to endNight
13%13%8%11%9%5%5%45%6%21%
2574
February1st to 10thNight
17%15%6%11%7%45%6%5%5%20%
2340
11th to 20thNight
16%13%6%8%8%46%5%6%7%23%
2273
21st to endNight
17%13%5%11%8%45%5%46%22%
1796
March1st to 10thNight
13%10%47%8%35%5%6%7%31%
2006
11th to 20thNight
15%10%47%6%35%45%7%33%
1979
21st to endNight
18%10%47%6%34445%35%
2178
April1st to 10thNight
18%8%46%5%45%46%7%33%
1900
11th to 20thNight
17%8%36%5%3445%7%37%
1651
21st to endNight
15%8%36%7%347%7%7%33%
1620
May1st to 10thNight
17%7%45%4346%5%8%36%
1620
11th to 20thNight
12%6%36%5%36%5%6%7%40%
1562
21st to endNight
9%5%244245%7%7%51%
1550
June1st to 10thNight
11%5%245%35%5%7%8%45%
1440
11th to 20thNight
10%5%25%5%35%7%6%10%43%
1326
21st to endNight
10%5%25%4345%6%9%47%
1260
July1st to 10thNight
5%325%5%3437%8%55%
1260
11th to 20thNight
9%5%15%5%2446%8%50%
1569
21st to endNight
7%5%26%436%6%6%9%48%
1771
August1st to 10thNight
7%425%5%45%5%6%8%48%
1611
11th to 20thNight
8%424425%5%7%9%49%
1598
21st to endNight
9%5%25%5%35%46%9%49%
1808
September1st to 10thNight
11%5%36%6%3445%7%46%
1822
11th to 20thNight
10%424425%45%7%53%
1980
21st to endNight
15%6%35%5%35%45%7%41%
1980
October1st to 10thNight
15%7%35%5%34447%42%
2137
11th to 20thNight
18%9%46%6%345%5%7%34%
2160
21st to endNight
23%9%46%6%35%46%6%27%
2386
November1st to 10thNight
15%8%36%5%345%6%8%38%
2406
11th to 20thNight
16%11%47%6%345%6%8%28%
2648
21st to endNight
20%14%5%7%6%45%5%5%7%23%
2660
December1st to 10thNight
19%15%6%9%7%36%5%5%5%19%
2660
11th to 20thNight
15%18%6%10%6%345%5%6%21%
3288
21st to endNight
27%20%7%10%7%3434412%
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
66%7%11%12%3
1608
11th to 20thDay
71%8%8%8%5%1
1674
21st to endDay
71%6%7%10%5%1
1782
February1st to 10thDay
70%6%9%11%31
1620
11th to 20thDay
65%7%8%13%6%
1582
21st to endDay
64%7%10%13%6%1
1458
March1st to 10thDay
58%7%13%15%6%1
1944
11th to 20thDay
56%5%10%18%9%2
1980
21st to endDay
56%5%10%17%11%1
2178
April1st to 10thDay
55%6%11%17%10%1
2060
11th to 20thDay
50%6%12%19%12%1
2274
21st to endDay
53%5%11%19%10%2
2340
May1st to 10thDay
49%7%12%20%11%1
2340
11th to 20thDay
45%7%13%20%12%2
2334
21st to endDay
38%9%14%22%14%2
2725
June1st to 10thDay
40%8%14%24%13%2
2520
11th to 20thDay
40%9%12%22%15%2
2628
21st to endDay
38%9%14%25%15%
2700
July1st to 10thDay
33%8%13%27%16%3
2622
11th to 20thDay
39%9%15%24%12%1
2313
21st to endDay
39%10%14%22%13%2
2405
August1st to 10thDay
37%11%16%25%11%1
2314
11th to 20thDay
40%10%16%22%10%1
2303
21st to endDay
39%9%14%25%12%2
2530
September1st to 10thDay
41%8%15%22%12%1
2135
11th to 20thDay
35%8%14%28%14%
1980
21st to endDay
43%9%14%23%10%1
1980
October1st to 10thDay
48%7%12%20%12%1
1823
11th to 20thDay
54%7%14%16%8%1
1800
21st to endDay
62%7%12%13%6%
1967
November1st to 10thDay
49%8%11%23%7%2
1672
11th to 20thDay
53%8%16%14%8%1
1530
21st to endDay
63%8%14%12%3
1520
December1st to 10thDay
65%10%11%11%3
1520
11th to 20thDay
69%8%10%10%3
1906
21st to endDay
78%8%8%6%1
2772
January1st to 10thNight
64%8%10%13%6%
2555
11th to 20thNight
70%7%10%9%4
2430
21st to endNight
63%6%11%13%5%1
2574
February1st to 10thNight
64%8%11%13%5%
2340
11th to 20thNight
59%7%13%14%6%
2275
21st to endNight
60%7%11%15%7%
1796
March1st to 10thNight
50%7%13%20%10%1
2016
11th to 20thNight
50%6%10%21%10%2
1980
21st to endNight
52%5%9%19%12%3
2178
April1st to 10thNight
50%6%10%20%13%1
1900
11th to 20thNight
46%5%11%19%17%2
1651
21st to endNight
46%7%11%18%14%3
1620
May1st to 10thNight
45%6%11%21%14%3
1620
11th to 20thNight
41%6%12%23%13%4
1563
21st to endNight
31%7%15%26%18%3
1551
June1st to 10thNight
35%7%13%27%15%3
1440
11th to 20thNight
34%9%13%24%18%2
1326
21st to endNight
34%8%14%24%19%1
1260
July1st to 10thNight
26%8%11%28%23%4
1225
11th to 20thNight
31%7%13%28%17%3
1519
21st to endNight
30%10%17%23%17%3
1672
August1st to 10thNight
31%9%15%31%13%1
1600
11th to 20thNight
29%9%16%30%14%2
1598
21st to endNight
32%7%14%29%16%2
1808
September1st to 10thNight
38%7%13%25%15%2
1822
11th to 20thNight
29%7%13%32%17%1
1980
21st to endNight
41%8%12%26%12%1
1980
October1st to 10thNight
42%7%11%23%15%1
2137
11th to 20thNight
48%7%13%21%10%
2160
21st to endNight
56%7%10%17%9%1
2386
November1st to 10thNight
42%7%14%23%12%1
2406
11th to 20thNight
51%9%14%17%8%1
2648
21st to endNight
60%7%17%12%41
2660
December1st to 10thNight
65%9%11%11%4
2660
11th to 20thNight
61%7%14%13%4
3288
21st to endNight
75%7%10%6%2
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
23%19%33%19%5%1
222
11th to 20thDay
19%21%43%12%31
258
21st to endDay
26%16%37%17%31
264
February1st to 10thDay
28%16%42%12%1
240
11th to 20thDay
25%22%40%13%1
240
21st to endDay
27%29%32%11%1
198
March1st to 10thDay
24%15%36%20%5%1
384
11th to 20thDay
23%13%37%19%5%1
420
21st to endDay
29%14%29%21%7%1
462
April1st to 10thDay
19%19%32%22%6%2
420
11th to 20thDay
26%15%25%19%10%4
412
21st to endDay
25%11%32%21%7%3
420
May1st to 10thDay
24%11%28%23%11%4
423
11th to 20thDay
16%11%31%21%17%4
447
21st to endDay
14%7%24%29%18%8%
485
June1st to 10thDay
14%7%30%32%12%4
450
11th to 20thDay
12%9%28%32%15%4
558
21st to endDay
13%7%31%31%15%3
630
July1st to 10thDay
9%5%23%29%26%8%
617
11th to 20thDay
14%5%22%29%19%11%
444
21st to endDay
9%325%33%22%7%
488
August1st to 10thDay
8%421%29%24%14%
446
11th to 20thDay
13%5%17%28%22%14%
439
21st to endDay
12%6%22%25%23%12%
495
September1st to 10thDay
13%7%22%27%20%11%
450
11th to 20thDay
9%5%19%27%28%12%
450
21st to endDay
15%10%26%26%14%8%
450
October1st to 10thDay
19%9%26%23%19%5%
450
11th to 20thDay
20%18%32%20%7%2
450
21st to endDay
29%13%33%20%5%1
482
November1st to 10thDay
20%22%33%16%7%2
270
11th to 20thDay
25%19%33%14%6%3
185
21st to endDay
26%16%41%16%3
180
December1st to 10thDay
28%22%32%13%5%1
180
11th to 20thDay
26%26%32%13%3
180
21st to endDay
31%20%34%12%3
198
January1st to 10thNight
21%18%37%17%5%1
760
11th to 20thNight
28%15%34%20%3
748
21st to endNight
19%11%36%27%6%
792
February1st to 10thNight
24%16%38%21%2
720
11th to 20thNight
22%16%34%23%5%
703
21st to endNight
25%16%35%22%3
592
March1st to 10thNight
19%14%36%26%6%
720
11th to 20thNight
19%14%36%23%6%1
720
21st to endNight
22%12%32%25%9%1
792
April1st to 10thNight
22%13%32%28%5%
720
11th to 20thNight
22%11%30%26%9%1
587
21st to endNight
18%9%34%31%8%
540
May1st to 10thNight
20%7%28%30%15%1
540
11th to 20thNight
17%427%37%14%1
501
21st to endNight
11%5%27%38%18%1
389
June1st to 10thNight
14%428%43%10%1
360
11th to 20thNight
10%432%41%12%
360
21st to endNight
13%424%44%14%
360
July1st to 10thNight
5%322%46%22%2
350
11th to 20thNight
10%220%41%24%2
476
21st to endNight
9%317%47%22%2
591
August1st to 10thNight
9%315%42%30%2
537
11th to 20thNight
8%216%38%31%5%
534
21st to endNight
10%320%38%26%3
620
September1st to 10thNight
12%6%22%32%23%5%
720
11th to 20thNight
11%416%38%27%4
720
21st to endNight
17%6%20%32%19%5%
720
October1st to 10thNight
18%8%26%30%17%2
720
11th to 20thNight
21%13%30%26%10%1
720
21st to endNight
27%10%33%25%5%
792
November1st to 10thNight
19%11%28%29%11%1
740
11th to 20thNight
21%15%34%21%8%1
760
21st to endNight
27%13%32%22%7%
760
December1st to 10thNight
27%17%33%18%4
760
11th to 20thNight
24%18%37%17%4
760
21st to endNight
29%14%35%20%2
836
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Copyright 2024 Attilla Danko


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