Selu Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Selu Observatory clear sky chart from 2005-11-05 to 2019-06-10.

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
42%
18087
19%
53873
12%
18049
50%
18049
23%
35198

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
21%
838
19%
2717
8%
836
35%
836
14%
1831
January16th to endNight
19%
896
21%
2912
7%
896
36%
896
16%
1882
February1st to 15thNight
19%
821
18%
2677
7%
821
34%
821
17%
1743
February16th to endNight
18%
735
20%
2175
7%
735
32%
735
15%
1509
March1st to 15thNight
25%
840
20%
2310
9%
840
35%
840
21%
1576
March16th to endNight
28%
896
16%
2464
8%
896
35%
896
21%
1708
April1st to 15thNight
31%
838
19%
2206
6%
838
40%
838
25%
1455
April16th to endNight
39%
717
19%
1963
9%
717
45%
717
26%
1299
May1st to 15thNight
44%
630
16%
1890
8%
630
49%
630
24%
1238
May16th to endNight
56%
657
13%
1972
9%
657
59%
657
26%
1296
June1st to 15thNight
64%
612
15%
1836
13%
612
67%
612
29%
1183
June16th to endNight
69%
585
17%
1755
13%
585
72%
585
32%
1076
July1st to 15thNight
70%
555
13%
1665
12%
555
71%
555
28%
1075
July16th to endNight
75%
612
14%
1739
12%
579
76%
579
31%
1094
August1st to 15thNight
69%
575
18%
1715
15%
572
69%
572
29%
1130
August16th to endNight
71%
715
18%
1957
14%
715
72%
715
31%
1278
September1st to 15thNight
62%
780
22%
2072
17%
780
64%
780
30%
1364
September16th to endNight
52%
777
20%
2145
16%
777
55%
777
26%
1431
October1st to 15thNight
50%
780
24%
2311
22%
780
56%
780
28%
1451
October16th to endNight
41%
832
28%
2496
19%
832
54%
832
29%
1491
November1st to 15thNight
43%
820
25%
2524
18%
820
52%
820
26%
1574
November16th to endNight
35%
840
26%
2730
17%
840
48%
840
24%
1625
December1st to 15thNight
26%
840
19%
2730
8%
840
39%
840
15%
1845
December16th to endNight
23%
896
18%
2912
7%
896
36%
896
14%
2044

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%6%26%5%35%5%5%7%36%
54622
Night
11%6%25%5%35%5%5%8%41%
54066
Cloud CoverDay
13%6%25%5%35%5%5%7%36%
54632
Night
11%6%25%5%345%5%8%41%
54070
TransparencyDay
44%7%12%19%13%2
54333
Night
40%7%12%22%14%2
53873
SeeingDay
19%11%21%21%16%9%
7874
Night
17%11%22%28%17%2
18094

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%7%26%5%35%45%7%35%
1881
16th to endDay
13%7%36%5%35%5%45%39%
2016
February1st to 15thDay
12%7%47%6%36%6%46%35%
1845
16th to endDay
16%6%38%6%3445%6%33%
1866
March1st to 15thDay
15%6%25%5%35%447%40%
2299
16th to endDay
16%7%36%5%34446%37%
2464
April1st to 15thDay
11%5%35%5%2345%8%44%
2400
16th to endDay
14%6%36%5%25%5%5%7%37%
2614
May1st to 15thDay
15%6%36%6%36%6%5%7%31%
2721
16th to endDay
12%5%35%6%36%5%6%9%33%
2847
June1st to 15thDay
9%426%5%46%6%7%10%35%
2652
16th to endDay
7%5%25%7%46%6%7%10%36%
2535
July1st to 15thDay
9%5%36%6%5%7%6%7%8%31%
2535
16th to endDay
9%5%26%7%49%7%8%9%29%
2673
August1st to 15thDay
13%6%26%7%47%7%8%9%28%
2487
16th to endDay
11%5%26%6%46%7%6%9%35%
2584
September1st to 15thDay
13%6%25%6%345%5%7%38%
2215
16th to endDay
20%5%25%5%35%5%5%6%33%
2145
October1st to 15thDay
16%5%24424347%45%
1977
16th to endDay
12%6%25%423446%47%
2080
November1st to 15thDay
13%5%24424447%45%
1990
16th to endDay
11%7%25%5%34446%45%
1890
December1st to 15thDay
14%7%26%5%3446%7%38%
1890
16th to endDay
17%9%35%4245%6%6%34%
2016
January1st to 15thNight
13%6%36%5%45%5%5%7%36%
2717
16th to endNight
13%8%25%5%35%5%5%7%37%
2912
February1st to 15thNight
14%7%35%5%3446%7%38%
2675
16th to endNight
13%6%36%5%35%6%6%6%35%
2175
March1st to 15thNight
13%6%26%5%345%6%7%39%
2298
16th to endNight
14%6%35%425%5%47%39%
2464
April1st to 15thNight
11%6%236%25%5%5%9%41%
2206
16th to endNight
13%5%145%3445%6%43%
1963
May1st to 15thNight
13%5%35%5%3445%8%42%
1890
16th to endNight
9%5%26%6%3446%9%40%
1970
June1st to 15thNight
7%424426%5%6%11%44%
1836
16th to endNight
5%324435%47%11%47%
1755
July1st to 15thNight
6%4245%346%6%9%44%
1755
16th to endNight
4225%437%6%9%11%41%
1847
August1st to 15thNight
9%5%25%5%246%5%9%42%
1726
16th to endNight
8%3146%46%5%6%11%41%
1957
September1st to 15thNight
9%5%25%6%3445%7%45%
2072
16th to endNight
16%5%145%3445%7%40%
2145
October1st to 15thNight
12%6%25%5%23346%46%
2311
16th to endNight
10%5%25%42445%6%48%
2496
November1st to 15thNight
14%6%24423345%47%
2524
16th to endNight
11%5%344245%5%6%47%
2730
December1st to 15thNight
14%7%36%6%35%447%35%
2730
16th to endNight
15%9%46%5%35%5%5%7%31%
2912

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
14%7%26%5%35%45%7%35%
1881
16th to endDay
12%7%36%5%345%45%39%
2016
February1st to 15thDay
12%7%36%6%36%6%5%5%35%
1845
16th to endDay
16%6%37%7%245%5%6%33%
1866
March1st to 15thDay
15%6%345%34447%40%
2310
16th to endDay
16%8%35%5%34446%37%
2463
April1st to 15thDay
11%5%35%5%2345%8%44%
2400
16th to endDay
14%6%25%5%35%5%6%6%38%
2614
May1st to 15thDay
15%6%36%5%45%6%6%7%31%
2721
16th to endDay
11%6%26%6%46%5%6%10%33%
2847
June1st to 15thDay
9%5%25%5%46%5%7%9%35%
2652
16th to endDay
7%5%35%6%46%6%7%10%36%
2535
July1st to 15thDay
10%6%36%6%5%7%7%7%9%30%
2535
16th to endDay
9%5%26%7%48%7%8%9%29%
2673
August1st to 15thDay
13%5%25%6%47%7%7%10%28%
2487
16th to endDay
10%5%25%5%36%6%6%9%35%
2584
September1st to 15thDay
13%6%25%6%35%46%7%38%
2215
16th to endDay
19%6%25%5%35%5%6%6%33%
2145
October1st to 15thDay
16%5%14423346%45%
1977
16th to endDay
12%6%25%423436%48%
2080
November1st to 15thDay
14%5%24433447%45%
1990
16th to endDay
11%7%26%434446%45%
1890
December1st to 15thDay
13%7%26%5%25%46%7%38%
1890
16th to endDay
17%9%35%4245%5%6%34%
2016
January1st to 15thNight
13%7%26%6%35%5%47%36%
2717
16th to endNight
13%8%35%5%345%5%7%37%
2912
February1st to 15thNight
13%7%26%5%2446%7%38%
2668
16th to endNight
13%6%36%5%35%5%6%7%35%
2175
March1st to 15thNight
13%6%26%4345%6%7%39%
2310
16th to endNight
14%6%35%5%35%447%39%
2464
April1st to 15thNight
11%6%245%25%5%6%9%41%
2206
16th to endNight
13%5%245%35%45%6%43%
1963
May1st to 15thNight
12%5%35%5%25%448%41%
1889
16th to endNight
9%5%26%6%345%6%9%40%
1970
June1st to 15thNight
7%424435%5%6%11%44%
1836
16th to endNight
5%325%435%5%7%10%47%
1755
July1st to 15thNight
6%4245%35%6%7%8%45%
1755
16th to endNight
4224446%6%9%11%41%
1847
August1st to 15thNight
9%435%5%246%6%10%42%
1726
16th to endNight
8%3146%46%5%6%11%41%
1957
September1st to 15thNight
8%5%26%5%2445%7%46%
2072
16th to endNight
15%5%245%3445%6%41%
2145
October1st to 15thNight
12%5%25%5%23337%47%
2311
16th to endNight
10%5%25%433446%48%
2496
November1st to 15thNight
14%7%24323345%47%
2524
16th to endNight
11%5%343245%46%47%
2730
December1st to 15thNight
14%7%36%6%345%47%35%
2730
16th to endNight
15%9%47%5%35%5%5%7%31%
2912

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
46%6%10%21%12%3
1882
16th to endDay
45%49%23%14%2
2016
February1st to 15thDay
48%5%10%20%14%1
1847
16th to endDay
49%5%12%18%12%1
1866
March1st to 15thDay
44%49%21%15%3
2310
16th to endDay
47%7%9%22%12%2
2464
April1st to 15thDay
38%5%12%25%12%4
2400
16th to endDay
44%7%10%20%13%4
2614
May1st to 15thDay
49%7%14%17%8%1
2721
16th to endDay
45%9%16%20%7%1
2851
June1st to 15thDay
41%11%16%19%10%
2652
16th to endDay
40%11%14%18%13%2
2535
July1st to 15thDay
46%10%13%15%11%2
2396
16th to endDay
45%12%15%16%9%
2518
August1st to 15thDay
48%10%15%17%8%
2474
16th to endDay
42%11%16%16%10%1
2584
September1st to 15thDay
43%8%12%18%14%2
2215
16th to endDay
49%6%9%19%13%1
2145
October1st to 15thDay
40%5%11%23%15%3
1977
16th to endDay
37%48%26%19%3
2080
November1st to 15thDay
38%49%19%22%5%
1990
16th to endDay
40%49%23%20%1
1890
December1st to 15thDay
45%6%11%17%15%3
1890
16th to endDay
47%6%12%18%12%1
2016
January1st to 15thNight
46%6%10%16%15%4
2717
16th to endNight
43%5%10%22%15%2
2912
February1st to 15thNight
44%411%22%13%2
2677
16th to endNight
46%6%10%23%10%2
2175
March1st to 15thNight
43%6%10%23%13%2
2310
16th to endNight
44%6%11%21%13%1
2464
April1st to 15thNight
38%6%14%22%14%3
2206
16th to endNight
40%6%12%20%16%4
1963
May1st to 15thNight
41%7%16%23%10%
1890
16th to endNight
38%9%20%23%6%1
1972
June1st to 15thNight
32%12%19%23%11%
1836
16th to endNight
29%12%17%24%14%1
1755
July1st to 15thNight
33%12%16%20%12%4
1665
16th to endNight
30%12%21%23%11%1
1739
August1st to 15thNight
36%10%17%21%13%
1715
16th to endNight
34%10%17%24%11%1
1957
September1st to 15thNight
37%8%13%21%16%3
2072
16th to endNight
42%6%10%23%16%1
2145
October1st to 15thNight
37%5%11%25%16%3
2311
16th to endNight
35%48%27%19%4
2496
November1st to 15thNight
39%49%18%20%7%
2524
16th to endNight
36%49%25%20%3
2730
December1st to 15thNight
47%6%10%20%12%3
2730
16th to endNight
50%6%11%18%12%1
2912

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
31%25%25%13%3
180
16th to endDay
34%23%26%11%3
192
February1st to 15thDay
30%25%33%7%3
180
16th to endDay
31%23%31%8%4
191
March1st to 15thDay
25%24%27%15%6%
390
16th to endDay
23%17%27%23%6%1
416
April1st to 15thDay
19%19%25%22%12%1
390
16th to endDay
22%10%27%18%13%7%
379
May1st to 15thDay
18%15%27%18%13%6%
408
16th to endDay
15%5%26%22%18%12%
459
June1st to 15thDay
11%420%26%22%13%
411
16th to endDay
10%6%25%25%19%11%
375
July1st to 15thDay
13%216%29%22%15%
365
16th to endDay
9%211%27%31%17%
390
August1st to 15thDay
16%115%24%23%19%
358
16th to endDay
10%29%20%28%29%
396
September1st to 15thDay
14%6%13%18%27%20%
375
16th to endDay
20%413%25%22%12%
374
October1st to 15thDay
18%9%14%23%27%6%
375
16th to endDay
15%15%24%23%17%4
400
November1st to 15thDay
26%10%23%22%14%3
318
16th to endDay
20%21%18%27%8%2
180
December1st to 15thDay
26%25%27%13%6%
180
16th to endDay
36%17%26%15%3
192
January1st to 15thNight
24%21%28%20%4
840
16th to endNight
20%23%31%21%1
896
February1st to 15thNight
25%19%31%21%2
824
16th to endNight
24%22%31%19%2
735
March1st to 15thNight
21%17%32%24%3
840
16th to endNight
19%14%31%26%7%
896
April1st to 15thNight
18%16%29%26%7%
838
16th to endNight
17%11%25%32%13%
717
May1st to 15thNight
14%8%26%30%18%1
630
16th to endNight
10%316%31%33%3
659
June1st to 15thNight
9%115%36%32%4
612
16th to endNight
7%113%37%35%5%
585
July1st to 15thNight
9%9%37%38%4
555
16th to endNight
5%16%36%42%7%
612
August1st to 15thNight
10%17%40%35%5%
575
16th to endNight
10%6%29%44%7%
715
September1st to 15thNight
11%212%30%36%6%
780
16th to endNight
18%315%29%29%3
777
October1st to 15thNight
15%7%18%30%24%3
780
16th to endNight
14%12%26%30%15%1
832
November1st to 15thNight
19%10%21%31%15%1
820
16th to endNight
19%16%25%26%12%
840
December1st to 15thNight
21%17%28%24%7%
840
16th to endNight
22%18%30%25%3
896
Page generated at 2019-06-10 19:29:50. Version ac04

Copyright 2019 A. Danko


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