SOLO Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the SOLO Observatory clear sky chart from 2005-11-06 to 2024-03-01.

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
38%
25145
11%
80774
8%
25056
41%
25056
16%
59571

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
24%
942
8%
4404
3%
926
28%
926
7%
3494
January11th to 20thNight
21%
941
2%
4439
2%
930
23%
930
4%
3869
January21st to endNight
20%
1032
5%
4779
2%
1023
24%
1023
6%
3819
February1st to 10thNight
28%
950
10%
2470
3%
950
32%
950
16%
1910
February11th to 20thNight
31%
928
14%
2404
5%
924
36%
924
21%
1781
February21st to endNight
35%
671
14%
1927
5%
671
42%
671
19%
1409
March1st to 10thNight
39%
720
15%
2165
9%
720
44%
720
20%
1521
March11th to 20thNight
36%
540
18%
1979
13%
540
44%
540
20%
1292
March21st to endNight
38%
594
16%
2076
14%
594
43%
594
17%
1440
April1st to 10thNight
35%
540
11%
1800
9%
540
40%
540
16%
1311
April11th to 20thNight
40%
533
14%
1775
13%
533
44%
533
16%
1268
April21st to endNight
41%
540
15%
1607
11%
540
44%
540
20%
1149
May1st to 10thNight
42%
540
12%
1440
8%
540
44%
540
20%
1070
May11th to 20thNight
50%
531
17%
1416
10%
531
53%
531
25%
993
May21st to endNight
54%
583
11%
1552
7%
582
56%
582
25%
1076
June1st to 10thNight
57%
540
10%
1440
5%
540
59%
540
29%
975
June11th to 20thNight
57%
540
11%
1440
7%
540
58%
540
29%
967
June21st to endNight
56%
540
12%
1440
8%
540
57%
540
27%
972
July1st to 10thNight
72%
525
14%
1400
9%
525
73%
525
41%
821
July11th to 20thNight
63%
522
15%
1392
8%
522
64%
522
37%
860
July21st to endNight
69%
591
19%
1487
11%
558
70%
558
42%
874
August1st to 10thNight
69%
537
21%
1435
17%
534
70%
534
39%
862
August11th to 20thNight
60%
534
20%
1600
19%
534
63%
534
31%
979
August21st to endNight
61%
594
17%
1938
18%
594
63%
594
30%
1153
September1st to 10thNight
58%
540
19%
1800
21%
540
62%
540
29%
1069
September11th to 20thNight
58%
540
21%
1800
21%
540
63%
540
30%
1074
September21st to endNight
43%
679
14%
2030
9%
679
47%
679
23%
1368
October1st to 10thNight
43%
720
16%
2160
11%
720
46%
720
23%
1461
October11th to 20thNight
30%
720
13%
2160
6%
720
36%
720
17%
1578
October21st to endNight
29%
792
12%
2524
7%
792
34%
792
13%
1923
November1st to 10thNight
31%
810
14%
2476
9%
810
36%
810
14%
1843
November11th to 20thNight
21%
950
9%
2660
4%
950
26%
950
10%
2175
November21st to endNight
24%
950
8%
2660
5%
950
28%
950
12%
2128
December1st to 10thNight
17%
950
4%
2660
2%
950
19%
950
8%
2257
December11th to 20thNight
16%
949
6%
3220
2%
948
19%
948
6%
2699
December21st to endNight
13%
1037
3%
4819
1%
1026
18%
1026
4%
4131

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
13%10%48%7%45%5%5%7%33%
78326
Night
13%12%5%9%7%45%5%5%6%30%
81128
TransparencyDay
50%8%14%20%8%1
78032
Night
53%8%12%18%8%1
80956
SeeingDay
16%6%23%34%17%4
15066
Night
18%7%26%32%15%2
25189

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
8%15%10%17%10%5%8%44415%
2527
11th to 20thDay
7%13%6%14%16%8%13%7%5%38%
2530
21st to endDay
6%17%8%16%11%5%6%5%5%5%16%
2856
February1st to 10thDay
8%12%410%8%6%7%7%6%7%24%
1710
11th to 20thDay
8%11%6%9%7%45%7%5%7%30%
1664
21st to endDay
10%10%5%9%9%45%5%5%8%30%
1527
March1st to 10thDay
10%10%5%7%6%36%6%6%7%34%
1816
11th to 20thDay
12%10%5%9%6%34446%37%
1980
21st to endDay
15%10%5%8%6%25%5%5%6%33%
2279
April1st to 10thDay
14%10%5%8%6%36%5%46%32%
2160
11th to 20thDay
20%11%36%5%35%5%5%6%31%
2134
21st to endDay
21%10%36%5%34446%35%
2349
May1st to 10thDay
16%7%47%5%35%5%5%7%36%
2520
11th to 20thDay
15%8%25%5%46%46%8%37%
2479
21st to endDay
13%7%36%5%35%5%6%8%39%
2725
June1st to 10thDay
10%6%25%5%35%5%6%9%45%
2520
11th to 20thDay
13%5%36%6%35%5%6%8%41%
2520
21st to endDay
12%5%25%5%36%5%6%10%40%
2520
July1st to 10thDay
7%314335%45%10%54%
2520
11th to 20thDay
8%5%25%5%35%5%7%8%47%
2520
21st to endDay
6%424435%5%5%9%52%
2743
August1st to 10thDay
9%5%25%5%35%5%6%8%47%
2492
11th to 20thDay
11%6%3443446%7%49%
2301
21st to endDay
11%6%3442445%8%50%
2417
September1st to 10thDay
11%6%25%5%3446%8%45%
2160
11th to 20thDay
12%7%36%6%35%45%8%41%
2160
21st to endDay
18%8%37%5%34346%37%
1908
October1st to 10thDay
18%10%35%6%35%5%5%6%34%
1800
11th to 20thDay
18%14%47%6%345%5%6%27%
1800
21st to endDay
21%14%5%7%6%44435%26%
1831
November1st to 10thDay
12%16%6%9%5%35%45%6%29%
1601
11th to 20thDay
15%16%10%14%8%45%34418%
1520
21st to endDay
15%13%7%11%9%5%5%5%6%5%21%
1520
December1st to 10thDay
10%16%7%14%14%6%8%345%13%
1520
11th to 20thDay
12%17%7%15%12%5%7%5%4312%
1914
21st to endDay
21%19%6%17%7%4443213%
2783
January1st to 10thNight
10%16%9%14%9%5%7%5%45%18%
4428
11th to 20thNight
7%12%8%14%13%13%12%7%338%
4440
21st to endNight
8%19%8%15%9%45%5%4418%
4806
February1st to 10thNight
7%12%6%11%8%6%7%6%6%6%25%
2470
11th to 20thNight
8%11%49%8%6%6%7%7%6%29%
2403
21st to endNight
10%13%6%8%6%45%35%7%31%
1927
March1st to 10thNight
11%10%49%7%35%5%5%6%35%
2156
11th to 20thNight
12%11%47%5%3445%6%39%
1979
21st to endNight
16%9%5%8%6%35%346%35%
2076
April1st to 10thNight
17%13%47%6%45%45%5%31%
1800
11th to 20thNight
20%11%37%5%35%45%6%32%
1775
21st to endNight
20%12%36%5%3445%5%33%
1607
May1st to 10thNight
15%9%5%9%7%345%5%7%33%
1440
11th to 20thNight
15%7%36%6%345%5%6%40%
1416
21st to endNight
12%7%35%6%45%7%6%8%36%
1551
June1st to 10thNight
14%5%25%6%36%5%5%8%40%
1440
11th to 20thNight
12%6%36%5%45%5%8%8%40%
1440
21st to endNight
12%5%36%6%5%45%6%8%40%
1440
July1st to 10thNight
6%4234345%5%10%53%
1440
11th to 20thNight
9%425%4245%6%9%49%
1440
21st to endNight
8%5%234246%7%8%52%
1575
August1st to 10thNight
7%5%244345%6%8%50%
1444
11th to 20thNight
11%5%26%434447%50%
1600
21st to endNight
14%5%2443345%6%50%
1938
September1st to 10thNight
11%5%26%4245%5%7%49%
1800
11th to 20thNight
11%6%25%5%346%5%7%47%
1800
21st to endNight
19%7%25%5%3445%8%38%
2030
October1st to 10thNight
17%11%35%42345%6%39%
2160
11th to 20thNight
18%14%47%6%2345%6%31%
2160
21st to endNight
22%14%48%6%2445%6%26%
2524
November1st to 10thNight
14%14%7%8%6%35%46%6%28%
2476
11th to 20thNight
14%17%8%12%7%44435%21%
2660
21st to endNight
14%12%5%14%9%445%6%5%23%
2660
December1st to 10thNight
12%17%9%14%12%5%5%45%415%
2660
11th to 20thNight
13%13%7%13%12%5%7%5%4416%
3283
21st to endNight
24%20%6%11%7%4443414%
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
69%7%9%12%2
2528
11th to 20thDay
72%9%11%7%1
2530
21st to endDay
67%10%11%10%2
2856
February1st to 10thDay
55%7%13%17%6%
1710
11th to 20thDay
51%8%13%22%6%
1673
21st to endDay
53%7%14%14%11%2
1527
March1st to 10thDay
49%8%15%19%9%
1818
11th to 20thDay
49%6%13%20%11%1
1980
21st to endDay
53%5%13%19%9%1
2279
April1st to 10thDay
54%7%11%17%11%1
2160
11th to 20thDay
55%6%11%16%10%2
2134
21st to endDay
52%5%11%20%10%1
2349
May1st to 10thDay
47%7%13%23%9%1
2520
11th to 20thDay
44%8%14%22%10%2
2483
21st to endDay
43%8%13%22%12%1
2725
June1st to 10thDay
35%9%19%24%12%1
2520
11th to 20thDay
39%9%15%21%14%1
2520
21st to endDay
38%10%19%24%8%1
2520
July1st to 10thDay
26%9%17%31%16%1
2451
11th to 20thDay
33%9%15%27%15%1
2445
21st to endDay
28%9%18%28%15%1
2591
August1st to 10thDay
34%8%18%29%9%2
2477
11th to 20thDay
35%8%19%28%11%
2301
21st to endDay
33%7%15%30%13%1
2417
September1st to 10thDay
36%7%18%29%10%
2160
11th to 20thDay
41%9%18%26%6%
2160
21st to endDay
48%7%14%24%6%
1908
October1st to 10thDay
49%8%14%23%6%
1800
11th to 20thDay
58%7%12%16%7%
1800
21st to endDay
60%8%10%16%6%
1831
November1st to 10thDay
56%6%11%18%8%1
1601
11th to 20thDay
70%6%10%10%4
1520
21st to endDay
62%9%12%13%41
1520
December1st to 10thDay
72%8%11%8%1
1520
11th to 20thDay
72%9%9%8%2
1915
21st to endDay
77%5%6%9%2
2783
January1st to 10thNight
65%8%12%11%3
4428
11th to 20thNight
69%13%11%5%1
4440
21st to endNight
66%8%11%13%2
4806
February1st to 10thNight
57%7%12%17%6%1
2470
11th to 20thNight
50%7%15%19%8%
2404
21st to endNight
52%6%12%20%8%2
1927
March1st to 10thNight
48%7%14%19%10%1
2167
11th to 20thNight
46%6%12%24%11%1
1980
21st to endNight
51%6%12%18%11%2
2076
April1st to 10thNight
55%6%10%15%14%1
1800
11th to 20thNight
53%6%10%18%11%2
1775
21st to endNight
51%5%8%23%12%1
1607
May1st to 10thNight
50%8%12%19%9%1
1440
11th to 20thNight
44%8%9%25%12%2
1417
21st to endNight
42%9%13%22%12%2
1552
June1st to 10thNight
40%8%15%24%11%2
1440
11th to 20thNight
38%9%15%19%17%2
1440
21st to endNight
40%9%12%27%12%1
1440
July1st to 10thNight
26%8%17%32%16%2
1400
11th to 20thNight
30%9%15%27%17%2
1392
21st to endNight
25%9%17%31%16%2
1487
August1st to 10thNight
29%7%16%32%11%4
1435
11th to 20thNight
34%7%16%27%14%2
1600
21st to endNight
34%8%15%26%16%1
1938
September1st to 10thNight
34%7%14%31%13%1
1800
11th to 20thNight
34%8%18%32%8%
1800
21st to endNight
44%7%15%26%7%
2030
October1st to 10thNight
44%7%14%25%9%1
2160
11th to 20thNight
53%7%13%19%7%1
2160
21st to endNight
58%7%10%19%6%
2524
November1st to 10thNight
55%8%12%18%7%
2476
11th to 20thNight
66%6%11%10%6%
2660
21st to endNight
61%8%15%11%4
2660
December1st to 10thNight
69%8%11%10%2
2660
11th to 20thNight
66%10%11%11%2
3281
21st to endNight
73%7%7%10%3
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
13%11%35%25%14%1
270
11th to 20thDay
18%9%30%31%11%
270
21st to endDay
15%9%28%34%12%1
297
February1st to 10thDay
11%11%35%34%8%1
270
11th to 20thDay
12%13%43%20%11%1
270
21st to endDay
14%9%40%33%4
225
March1st to 10thDay
14%7%29%36%13%
240
11th to 20thDay
17%6%31%33%11%2
240
21st to endDay
22%8%28%26%13%2
365
April1st to 10thDay
16%9%31%33%9%2
420
11th to 20thDay
24%7%21%33%12%3
412
21st to endDay
25%5%21%32%14%3
550
May1st to 10thDay
20%424%36%11%3
603
11th to 20thDay
19%420%34%18%5%
625
21st to endDay
17%6%17%34%22%4
679
June1st to 10thDay
11%422%40%20%4
630
11th to 20thDay
13%421%42%18%2
630
21st to endDay
15%418%37%22%5%
630
July1st to 10thDay
9%111%41%30%8%
621
11th to 20thDay
10%317%38%23%9%
618
21st to endDay
8%213%42%27%9%
684
August1st to 10thDay
12%315%36%28%8%
626
11th to 20thDay
12%5%12%32%33%6%
615
21st to endDay
15%5%15%34%25%6%
536
September1st to 10thDay
13%317%40%24%3
450
11th to 20thDay
14%7%18%35%22%4
450
21st to endDay
23%7%25%25%16%4
356
October1st to 10thDay
20%6%23%31%15%5%
270
11th to 20thDay
20%11%32%28%7%1
270
21st to endDay
27%10%33%25%6%
297
November1st to 10thDay
19%8%34%29%10%
270
11th to 20thDay
20%14%33%24%8%1
270
21st to endDay
20%10%33%31%6%1
270
December1st to 10thDay
17%13%36%26%8%2
270
11th to 20thDay
20%17%30%25%7%
270
21st to endDay
24%14%33%24%41
297
January1st to 10thNight
15%11%35%28%10%1
950
11th to 20thNight
16%9%36%28%9%1
950
21st to endNight
17%8%35%30%8%1
1045
February1st to 10thNight
14%10%32%33%9%1
950
11th to 20thNight
13%8%35%31%12%1
929
21st to endNight
17%6%30%37%10%
671
March1st to 10thNight
16%7%26%38%12%1
723
11th to 20thNight
18%433%33%11%1
540
21st to endNight
20%426%31%15%4
594
April1st to 10thNight
22%8%26%34%8%2
540
11th to 20thNight
26%5%19%35%13%2
533
21st to endNight
27%320%32%15%4
540
May1st to 10thNight
19%5%23%37%14%2
540
11th to 20thNight
18%319%38%18%4
531
21st to endNight
17%5%13%35%28%1
584
June1st to 10thNight
15%417%38%25%2
540
11th to 20thNight
16%314%44%22%1
540
21st to endNight
14%414%39%25%4
540
July1st to 10thNight
7%311%38%36%5%
525
11th to 20thNight
10%216%38%28%5%
522
21st to endNight
10%212%42%29%5%
591
August1st to 10thNight
10%310%41%32%3
537
11th to 20thNight
13%413%32%33%5%
534
21st to endNight
15%214%35%29%4
594
September1st to 10thNight
13%317%35%27%5%
540
11th to 20thNight
14%418%38%23%3
540
21st to endNight
20%6%25%26%21%2
679
October1st to 10thNight
23%5%23%29%17%3
720
11th to 20thNight
23%9%29%27%12%1
720
21st to endNight
30%7%26%28%9%
792
November1st to 10thNight
21%10%28%32%8%1
810
11th to 20thNight
22%13%32%22%10%1
950
21st to endNight
21%13%33%26%7%
950
December1st to 10thNight
20%13%35%24%8%
950
11th to 20thNight
22%14%31%24%8%1
950
21st to endNight
28%10%34%22%6%
1045
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