Ballreich Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ballreich Observatory clear sky chart from 2005-11-06 to 2024-01-27.

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
36%
24200
16%
74560
10%
24146
42%
24146
20%
51942

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
15%
950
12%
2648
3%
946
23%
946
12%
2080
January11th to 20thNight
13%
810
8%
2520
3%
810
18%
810
9%
2063
January21st to endNight
17%
820
11%
2664
5%
820
24%
820
11%
2100
February1st to 10thNight
16%
720
8%
2340
4%
720
22%
720
11%
1845
February11th to 20thNight
20%
701
12%
2131
7%
700
27%
700
13%
1611
February21st to endNight
16%
592
14%
1776
4%
592
26%
592
13%
1342
March1st to 10thNight
25%
720
15%
2102
8%
720
32%
720
17%
1541
March11th to 20thNight
27%
720
20%
1980
9%
720
35%
720
22%
1360
March21st to endNight
30%
792
17%
2178
9%
792
37%
792
21%
1568
April1st to 10thNight
26%
658
14%
1918
6%
658
34%
658
21%
1333
April11th to 20thNight
30%
533
20%
1635
9%
533
39%
533
21%
1094
April21st to endNight
32%
540
18%
1620
6%
540
42%
540
23%
1101
May1st to 10thNight
33%
540
11%
1620
5%
540
38%
540
17%
1178
May11th to 20thNight
41%
531
17%
1592
11%
531
47%
531
24%
1078
May21st to endNight
56%
583
16%
1745
12%
582
60%
582
31%
1064
June1st to 10thNight
53%
540
15%
1589
12%
540
57%
540
31%
978
June11th to 20thNight
58%
540
18%
1440
13%
540
62%
540
34%
915
June21st to endNight
57%
540
20%
1440
14%
540
62%
540
35%
898
July1st to 10thNight
64%
525
17%
1400
15%
525
65%
525
36%
886
July11th to 20thNight
64%
522
20%
1464
18%
522
67%
522
39%
866
July21st to endNight
67%
591
19%
1672
17%
558
70%
558
38%
978
August1st to 10thNight
69%
537
21%
1600
19%
534
70%
534
35%
926
August11th to 20thNight
65%
534
22%
1598
18%
534
68%
534
34%
952
August21st to endNight
68%
594
23%
1812
19%
594
71%
594
36%
1042
September1st to 10thNight
58%
670
22%
1930
17%
670
62%
670
33%
1186
September11th to 20thNight
63%
720
28%
1980
22%
720
66%
720
38%
1180
September21st to endNight
52%
720
24%
1980
19%
720
56%
720
31%
1260
October1st to 10thNight
49%
720
21%
2029
18%
720
53%
720
29%
1296
October11th to 20thNight
33%
720
18%
2160
12%
720
42%
720
22%
1458
October21st to endNight
28%
792
19%
2473
13%
792
36%
792
18%
1711
November1st to 10thNight
35%
740
21%
2406
16%
740
42%
740
24%
1507
November11th to 20thNight
26%
760
19%
2470
10%
760
38%
760
18%
1696
November21st to endNight
24%
760
14%
2470
9%
760
31%
760
14%
1824
December1st to 10thNight
18%
760
10%
2470
5%
760
24%
760
12%
1897
December11th to 20thNight
19%
759
11%
3000
4%
758
28%
758
11%
2185
December21st to endNight
14%
946
4%
4708
2%
935
19%
935
5%
3943

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%10%47%6%45%5%5%7%32%
75139
Night
15%10%47%6%35%45%7%34%
74818
TransparencyDay
50%5%12%20%11%2
74852
Night
49%5%11%20%12%2
74625
SeeingDay
19%10%27%24%15%7%
14305
Night
19%9%28%29%13%2
24212

By Month

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 10thDay
17%16%7%11%9%5%45%5%5%16%
1517
11th to 20thDay
18%18%9%13%7%45%44315%
1654
21st to endDay
17%17%8%12%9%45%5%45%16%
1836
February1st to 10thDay
17%16%7%11%8%45%44420%
1620
11th to 20thDay
15%12%6%11%8%5%6%5%45%23%
1713
21st to endDay
17%13%5%12%6%34446%25%
1480
March1st to 10thDay
19%11%7%9%7%3445%6%25%
1858
11th to 20thDay
16%14%5%10%5%4445%6%29%
1980
21st to endDay
23%12%5%8%6%34446%25%
2178
April1st to 10thDay
14%11%48%7%45%5%6%6%30%
2057
11th to 20thDay
17%10%36%5%45%5%5%7%33%
2272
21st to endDay
20%9%45%6%2445%7%33%
2340
May1st to 10thDay
17%8%48%7%35%6%5%7%31%
2340
11th to 20thDay
18%8%36%6%45%5%6%6%33%
2301
21st to endDay
9%5%36%7%46%6%6%9%39%
2531
June1st to 10thDay
13%6%36%5%45%5%6%8%38%
2366
11th to 20thDay
11%5%36%6%35%5%6%9%39%
2520
21st to endDay
11%5%26%6%45%7%7%9%38%
2520
July1st to 10thDay
9%5%35%6%45%5%6%9%42%
2520
11th to 20thDay
8%4246%35%5%7%11%44%
2444
21st to endDay
8%5%26%6%37%6%6%10%41%
2547
August1st to 10thDay
8%4246%45%7%7%10%43%
2327
11th to 20thDay
9%5%35%6%45%6%8%11%38%
2303
21st to endDay
10%5%26%445%5%7%9%43%
2540
September1st to 10thDay
14%6%245%35%5%6%7%43%
2012
11th to 20thDay
10%5%26%5%35%6%7%8%44%
1980
21st to endDay
16%7%26%43445%7%42%
1980
October1st to 10thDay
13%8%37%6%2446%7%40%
1931
11th to 20thDay
16%8%36%6%35%6%5%6%37%
1800
21st to endDay
19%10%46%7%446%5%6%29%
1882
November1st to 10thDay
12%8%45%6%4446%8%40%
1672
11th to 20thDay
17%12%47%5%34447%34%
1710
21st to endDay
18%13%5%8%6%35%447%27%
1710
December1st to 10thDay
16%18%8%11%7%35%435%19%
1621
11th to 20thDay
16%15%7%11%7%35%45%7%21%
2153
21st to endDay
21%22%8%11%7%4443411%
2924
January1st to 10thNight
18%15%6%10%7%345%5%423%
2648
11th to 20thNight
17%18%6%11%8%44435%19%
2520
21st to endNight
16%16%7%11%7%45%435%22%
2664
February1st to 10thNight
20%13%5%10%8%45%445%22%
2340
11th to 20thNight
16%14%6%8%8%45%5%45%27%
2130
21st to endNight
19%13%5%8%6%45%446%26%
1776
March1st to 10thNight
16%11%6%7%8%34445%32%
2102
11th to 20thNight
14%9%25%7%35%5%5%7%38%
1980
21st to endNight
19%10%46%5%34437%33%
2178
April1st to 10thNight
14%11%46%6%35%45%6%35%
1918
11th to 20thNight
16%7%27%6%445%6%7%37%
1635
21st to endNight
18%8%36%6%35%45%7%36%
1620
May1st to 10thNight
18%8%38%7%45%5%47%30%
1620
11th to 20thNight
17%8%35%44445%8%38%
1592
21st to endNight
10%5%25%435%6%6%11%43%
1744
June1st to 10thNight
10%6%345%445%6%7%46%
1589
11th to 20thNight
9%5%35%435%6%8%9%44%
1440
21st to endNight
9%425%5%35%5%7%10%45%
1440
July1st to 10thNight
8%4246%445%7%8%47%
1440
11th to 20thNight
8%4245%35%5%7%10%48%
1512
21st to endNight
7%425%5%26%6%6%10%48%
1771
August1st to 10thNight
6%325%5%46%5%7%10%47%
1611
11th to 20thNight
7%5%36%5%345%6%9%47%
1598
21st to endNight
7%425%435%5%5%8%51%
1812
September1st to 10thNight
11%6%35%5%2445%8%48%
1930
11th to 20thNight
10%5%24435%447%53%
1980
21st to endNight
11%6%36%5%3445%6%47%
1980
October1st to 10thNight
12%6%35%6%3445%7%45%
2029
11th to 20thNight
18%10%27%5%2445%7%37%
2160
21st to endNight
21%8%36%5%3445%6%33%
2473
November1st to 10thNight
13%8%35%5%2445%6%42%
2406
11th to 20thNight
16%11%46%6%345%5%7%33%
2470
21st to endNight
19%13%48%6%35%45%5%27%
2470
December1st to 10thNight
17%15%6%9%7%345%5%6%23%
2470
11th to 20thNight
19%13%6%8%6%35%45%6%26%
3042
21st to endNight
24%19%8%9%6%35%45%5%12%
4728

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
71%410%13%3
1518
11th to 20thDay
74%410%9%3
1654
21st to endDay
71%38%12%5%1
1836
February1st to 10thDay
68%410%12%5%1
1620
11th to 20thDay
63%49%16%7%1
1723
21st to endDay
61%312%15%7%2
1480
March1st to 10thDay
60%411%19%6%
1858
11th to 20thDay
57%411%17%9%2
1980
21st to endDay
62%49%19%6%1
2178
April1st to 10thDay
53%6%11%17%11%1
2057
11th to 20thDay
49%6%12%19%12%2
2272
21st to endDay
50%5%11%21%11%2
2340
May1st to 10thDay
51%7%11%19%11%1
2340
11th to 20thDay
50%6%10%18%13%2
2305
21st to endDay
40%7%13%25%13%2
2531
June1st to 10thDay
42%6%11%25%12%3
2366
11th to 20thDay
40%6%14%22%15%2
2520
21st to endDay
39%8%15%20%14%4
2520
July1st to 10thDay
38%6%11%24%18%4
2451
11th to 20thDay
33%7%14%28%16%2
2369
21st to endDay
36%7%14%25%16%2
2405
August1st to 10thDay
32%8%17%28%14%1
2314
11th to 20thDay
36%8%16%26%11%2
2303
21st to endDay
36%7%13%23%18%3
2540
September1st to 10thDay
39%6%13%23%16%4
2012
11th to 20thDay
36%6%12%26%18%2
1980
21st to endDay
42%5%11%24%19%
1980
October1st to 10thDay
44%6%11%22%16%1
1931
11th to 20thDay
46%5%11%23%13%1
1800
21st to endDay
53%5%13%18%10%1
1882
November1st to 10thDay
42%412%24%16%1
1672
11th to 20thDay
52%412%20%12%1
1710
21st to endDay
58%412%18%8%
1710
December1st to 10thDay
68%410%14%4
1621
11th to 20thDay
62%411%18%5%
2150
21st to endDay
78%39%8%3
2924
January1st to 10thNight
63%39%17%7%
2648
11th to 20thNight
69%411%12%4
2520
21st to endNight
66%310%14%6%1
2664
February1st to 10thNight
65%411%14%5%1
2340
11th to 20thNight
60%49%18%8%1
2131
21st to endNight
60%410%16%9%2
1776
March1st to 10thNight
55%411%20%10%1
2102
11th to 20thNight
45%5%11%21%14%2
1980
21st to endNight
52%49%24%10%2
2178
April1st to 10thNight
49%412%18%14%2
1918
11th to 20thNight
46%6%11%18%18%2
1635
21st to endNight
47%410%22%13%3
1620
May1st to 10thNight
54%5%10%17%11%3
1620
11th to 20thNight
45%6%11%18%18%2
1593
21st to endNight
35%7%14%27%15%3
1745
June1st to 10thNight
36%6%11%27%16%4
1589
11th to 20thNight
34%8%14%25%17%3
1440
21st to endNight
33%7%14%27%16%3
1440
July1st to 10thNight
34%7%11%24%20%4
1400
11th to 20thNight
29%7%15%27%19%2
1464
21st to endNight
29%7%17%25%18%4
1672
August1st to 10thNight
30%7%14%30%17%2
1600
11th to 20thNight
32%7%15%30%14%2
1598
21st to endNight
29%7%14%24%22%4
1812
September1st to 10thNight
34%6%13%24%17%5%
1930
11th to 20thNight
31%6%10%27%24%1
1980
21st to endNight
38%5%11%24%20%2
1980
October1st to 10thNight
40%5%11%24%19%2
2029
11th to 20thNight
47%5%9%23%15%1
2160
21st to endNight
51%410%23%11%2
2473
November1st to 10thNight
42%412%24%16%2
2406
11th to 20thNight
51%410%22%12%1
2470
21st to endNight
59%412%18%7%1
2470
December1st to 10thNight
62%411%15%7%
2470
11th to 20thNight
58%5%13%18%6%
3044
21st to endNight
74%5%10%8%3
4728

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
22%23%27%20%7%1
270
11th to 20thDay
27%16%39%12%41
270
21st to endDay
30%15%28%21%6%
282
February1st to 10thDay
33%16%39%13%
240
11th to 20thDay
25%18%37%17%4
240
21st to endDay
25%21%41%11%2
198
March1st to 10thDay
23%16%35%18%6%
298
11th to 20thDay
23%13%36%20%6%1
420
21st to endDay
32%12%31%18%6%1
462
April1st to 10thDay
20%14%31%23%11%1
420
11th to 20thDay
22%14%31%18%10%4
412
21st to endDay
26%11%31%22%9%2
420
May1st to 10thDay
26%8%32%22%9%3
423
11th to 20thDay
22%6%28%24%12%7%
447
21st to endDay
11%7%24%28%19%11%
485
June1st to 10thDay
15%427%31%18%5%
476
11th to 20thDay
13%5%28%27%21%6%
630
21st to endDay
14%7%26%28%19%5%
630
July1st to 10thDay
13%318%31%21%14%
621
11th to 20thDay
9%321%30%23%13%
542
21st to endDay
10%420%26%28%13%
488
August1st to 10thDay
12%413%29%24%18%
446
11th to 20thDay
13%215%31%26%14%
439
21st to endDay
9%418%28%24%16%
495
September1st to 10thDay
17%5%15%26%24%14%
450
11th to 20thDay
8%317%24%30%18%
450
21st to endDay
17%10%21%25%18%9%
450
October1st to 10thDay
14%8%24%24%21%8%
450
11th to 20thDay
18%16%31%24%9%2
450
21st to endDay
25%13%36%20%5%2
397
November1st to 10thDay
17%12%35%20%12%4
270
11th to 20thDay
27%18%28%16%10%1
270
21st to endDay
25%16%36%21%3
270
December1st to 10thDay
22%19%34%15%8%1
227
11th to 20thDay
23%20%36%18%3
270
21st to endDay
31%16%33%15%4
297
January1st to 10thNight
25%15%35%20%5%1
950
11th to 20thNight
28%14%36%17%4
810
21st to endNight
22%15%35%24%4
820
February1st to 10thNight
28%13%33%24%3
720
11th to 20thNight
25%12%36%25%3
703
21st to endNight
28%13%38%19%3
592
March1st to 10thNight
21%11%34%27%7%
720
11th to 20thNight
19%15%35%24%6%1
720
21st to endNight
23%10%30%27%9%
792
April1st to 10thNight
21%12%36%26%5%
658
11th to 20thNight
20%10%36%23%10%1
533
21st to endNight
22%6%34%29%8%1
540
May1st to 10thNight
23%7%28%32%9%1
540
11th to 20thNight
21%6%25%33%13%2
531
21st to endNight
11%321%41%21%4
584
June1st to 10thNight
11%323%43%19%
540
11th to 20thNight
11%320%44%21%1
540
21st to endNight
11%322%39%23%2
540
July1st to 10thNight
10%214%38%32%4
525
11th to 20thNight
10%316%41%26%5%
522
21st to endNight
8%215%43%29%2
591
August1st to 10thNight
8%211%45%31%4
537
11th to 20thNight
10%311%40%31%5%
534
21st to endNight
8%312%37%35%4
594
September1st to 10thNight
13%415%34%30%5%
670
11th to 20thNight
10%314%35%33%5%
720
21st to endNight
13%7%20%35%23%2
720
October1st to 10thNight
15%7%23%33%20%3
720
11th to 20thNight
23%11%28%29%8%1
720
21st to endNight
25%11%31%26%6%1
792
November1st to 10thNight
17%10%32%29%11%1
740
11th to 20thNight
21%14%33%23%8%2
760
21st to endNight
27%10%33%23%6%
760
December1st to 10thNight
26%13%34%21%5%
760
11th to 20thNight
25%12%37%22%4
760
21st to endNight
30%13%34%20%3
954
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