SETEC Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the SETEC Observatory clear sky chart from 2005-11-05 to 2019-06-19.

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
44%
18244
27%
53997
16%
18199
54%
18199
37%
30039

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
37%
1050
30%
2717
14%
1045
48%
1045
39%
1599
January16th to endNight
37%
1120
34%
2912
13%
1120
49%
1120
44%
1621
February1st to 15thNight
32%
961
24%
2609
9%
957
42%
957
32%
1612
February16th to endNight
32%
736
27%
2206
10%
736
45%
736
32%
1250
March1st to 15thNight
33%
682
26%
2362
15%
682
47%
682
31%
1281
March16th to endNight
31%
672
20%
2464
12%
672
43%
672
25%
1417
April1st to 15thNight
29%
629
24%
2239
14%
629
47%
629
28%
1247
April16th to endNight
33%
624
22%
1871
14%
624
44%
624
30%
1106
May1st to 15thNight
37%
629
22%
1890
16%
629
47%
629
31%
1124
May16th to endNight
48%
657
19%
1972
16%
657
54%
657
36%
1127
June1st to 15thNight
53%
630
20%
1890
12%
630
61%
630
45%
974
June16th to endNight
59%
597
23%
1791
15%
597
66%
597
52%
880
July1st to 15thNight
71%
555
20%
1665
18%
555
74%
555
46%
876
July16th to endNight
74%
612
25%
1738
25%
579
76%
579
46%
906
August1st to 15thNight
75%
575
25%
1717
27%
572
78%
572
43%
919
August16th to endNight
69%
621
26%
1921
27%
621
72%
621
42%
1011
September1st to 15thNight
56%
585
25%
2145
25%
585
64%
585
32%
1158
September16th to endNight
56%
582
32%
2145
28%
582
66%
582
38%
1044
October1st to 15thNight
45%
673
31%
2233
21%
673
53%
673
32%
1238
October16th to endNight
46%
832
35%
2496
17%
832
59%
832
48%
1217
November1st to 15thNight
42%
1002
30%
2642
12%
1002
53%
1002
45%
1457
November16th to endNight
42%
1050
31%
2730
12%
1050
53%
1050
42%
1557
December1st to 15thNight
38%
1050
28%
2730
12%
1050
48%
1050
38%
1609
December16th to endNight
35%
1120
28%
2912
12%
1120
46%
1120
34%
1809

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
9%5%2442445%7%51%
54723
Night
8%423323347%54%
54193
Cloud CoverDay
9%5%2442445%7%51%
54721
Night
8%413323447%54%
54193
TransparencyDay
32%312%27%18%4
54421
Night
29%312%27%21%5%
53998
SeeingDay
12%6%27%31%18%4
8138
Night
11%7%31%35%13%1
18247

By Month

Percentage Cloud Cover SW (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
7%7%23412337%54%
1881
16th to endDay
7%6%24323347%53%
2016
February1st to 15thDay
8%7%25%424446%48%
1924
16th to endDay
8%7%2442345%6%50%
1840
March1st to 15thDay
9%6%14424446%50%
2257
16th to endDay
16%7%23323346%45%
2464
April1st to 15thDay
12%5%14423447%47%
2365
16th to endDay
15%5%245%24346%44%
2694
May1st to 15thDay
12%5%25%434446%46%
2721
16th to endDay
12%5%25%5%25%45%7%43%
2846
June1st to 15thDay
6%31342345%8%54%
2730
16th to endDay
5%21242346%8%57%
2577
July1st to 15thDay
6%314425%5%6%9%49%
2535
16th to endDay
42144345%6%9%51%
2674
August1st to 15thDay
5%424435%6%6%9%47%
2486
16th to endDay
6%32442446%8%53%
2628
September1st to 15thDay
10%5%2433445%6%48%
2145
16th to endDay
9%313324347%56%
2145
October1st to 15thDay
15%312323445%53%
2044
16th to endDay
8%423322335%60%
2080
November1st to 15thDay
8%323324337%58%
1875
16th to endDay
9%412212235%62%
1890
December1st to 15thDay
11%5%24323446%51%
1890
16th to endDay
11%8%35%324345%45%
2016
January1st to 15thNight
7%5%24422346%55%
2717
16th to endNight
7%42331333463%
2912
February1st to 15thNight
10%7%34413446%48%
2599
16th to endNight
10%6%23323345%53%
2206
March1st to 15thNight
8%6%15%32345%6%51%
2362
16th to endNight
15%5%23324346%48%
2464
April1st to 15thNight
12%32442345%8%47%
2239
16th to endNight
14%5%1342435%6%49%
1871
May1st to 15thNight
13%415%323348%47%
1889
16th to endNight
9%31332446%9%48%
1971
June1st to 15thNight
5%31232446%11%54%
1890
16th to endNight
4122245%6%9%60%
1791
July1st to 15thNight
4213325%5%7%10%53%
1755
16th to endNight
43133245%6%13%52%
1846
August1st to 15thNight
4213335%5%6%9%53%
1727
16th to endNight
432342445%8%56%
1921
September1st to 15thNight
9%423423446%53%
2145
16th to endNight
6%31332346%7%57%
2145
October1st to 15thNight
13%424312336%53%
2233
16th to endNight
6%313212235%67%
2496
November1st to 15thNight
7%324222337%60%
2642
16th to endNight
10%313214325%60%
2730
December1st to 15thNight
9%5%2431335%7%53%
2730
16th to endNight
10%7%35%423347%49%
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
7%6%23412337%54%
1881
16th to endDay
7%6%14323347%53%
2016
February1st to 15thDay
8%8%25%434446%48%
1924
16th to endDay
8%6%2442345%6%51%
1840
March1st to 15thDay
9%6%244245%46%50%
2257
16th to endDay
16%6%24323346%44%
2462
April1st to 15thDay
12%5%24423447%47%
2365
16th to endDay
15%5%245%24346%44%
2694
May1st to 15thDay
11%6%25%424446%46%
2721
16th to endDay
12%5%25%435%45%7%43%
2846
June1st to 15thDay
6%323423448%54%
2730
16th to endDay
5%21332446%9%57%
2577
July1st to 15thDay
6%314425%5%7%9%49%
2535
16th to endDay
4213435%5%7%9%51%
2674
August1st to 15thDay
5%424435%6%6%9%47%
2486
16th to endDay
6%31442446%8%53%
2628
September1st to 15thDay
10%5%2443445%7%48%
2145
16th to endDay
8%323424346%55%
2145
October1st to 15thDay
15%312323445%53%
2044
16th to endDay
8%423322335%60%
2080
November1st to 15thDay
7%423324337%57%
1875
16th to endDay
9%422212235%62%
1890
December1st to 15thDay
10%5%24313347%51%
1890
16th to endDay
11%8%35%424345%46%
2016
January1st to 15thNight
7%5%24422345%55%
2717
16th to endNight
6%41331333463%
2912
February1st to 15thNight
9%8%35%41345%6%48%
2599
16th to endNight
10%6%23323345%53%
2206
March1st to 15thNight
8%6%15%42345%6%51%
2362
16th to endNight
15%6%14323246%48%
2464
April1st to 15thNight
11%41442345%8%48%
2239
16th to endNight
13%5%2332435%5%49%
1871
May1st to 15thNight
14%414423448%47%
1889
16th to endNight
9%4133245%6%9%48%
1971
June1st to 15thNight
5%31232346%11%54%
1890
16th to endNight
4122245%5%9%60%
1791
July1st to 15thNight
4213325%5%6%10%53%
1755
16th to endNight
43133245%6%12%52%
1846
August1st to 15thNight
42133445%6%9%53%
1727
16th to endNight
431442445%8%55%
1921
September1st to 15thNight
9%423424346%53%
2145
16th to endNight
6%31432335%8%57%
2145
October1st to 15thNight
13%423312336%53%
2233
16th to endNight
7%313212235%67%
2496
November1st to 15thNight
7%324213337%60%
2642
16th to endNight
10%313214325%61%
2730
December1st to 15thNight
9%5%24313347%53%
2730
16th to endNight
9%6%35%423347%48%
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
30%212%31%19%2
1882
16th to endDay
30%214%30%18%3
2016
February1st to 15thDay
36%314%28%12%3
1925
16th to endDay
32%212%28%18%4
1840
March1st to 15thDay
35%310%23%21%5%
2257
16th to endDay
40%311%25%15%2
2464
April1st to 15thDay
36%312%28%15%3
2365
16th to endDay
41%311%28%13%2
2694
May1st to 15thDay
38%412%22%19%2
2721
16th to endDay
39%415%26%13%2
2850
June1st to 15thDay
27%416%28%17%4
2730
16th to endDay
22%415%28%23%5%
2577
July1st to 15thDay
29%5%15%30%17%3
2396
16th to endDay
24%5%15%29%20%3
2519
August1st to 15thDay
31%5%16%26%16%4
2472
16th to endDay
27%5%14%29%17%6%
2628
September1st to 15thDay
34%411%26%15%7%
2145
16th to endDay
28%39%30%22%4
2145
October1st to 15thDay
33%39%24%24%5%
2044
16th to endDay
26%38%29%25%6%
2080
November1st to 15thDay
27%39%26%25%7%
1875
16th to endDay
25%210%31%25%5%
1890
December1st to 15thDay
33%212%31%17%2
1890
16th to endDay
40%211%25%16%3
2016
January1st to 15thNight
30%29%30%23%3
2717
16th to endNight
25%211%30%25%4
2912
February1st to 15thNight
36%314%25%15%4
2609
16th to endNight
33%211%26%18%7%
2206
March1st to 15thNight
33%210%24%21%7%
2362
16th to endNight
38%311%26%17%3
2464
April1st to 15thNight
33%311%26%21%3
2239
16th to endNight
35%313%24%19%4
1871
May1st to 15thNight
35%313%25%17%2
1890
16th to endNight
29%5%20%27%14%2
1973
June1st to 15thNight
23%419%30%19%3
1890
16th to endNight
18%415%31%22%7%
1791
July1st to 15thNight
23%414%29%22%4
1665
16th to endNight
23%5%14%32%22%3
1738
August1st to 15thNight
24%5%15%30%18%5%
1717
16th to endNight
24%5%13%28%21%6%
1921
September1st to 15thNight
33%310%25%18%9%
2145
16th to endNight
24%410%26%27%6%
2145
October1st to 15thNight
34%29%22%23%8%
2233
16th to endNight
20%27%28%31%8%
2496
November1st to 15thNight
25%210%26%26%8%
2642
16th to endNight
27%26%31%25%6%
2730
December1st to 15thNight
30%212%29%20%3
2730
16th to endNight
35%212%26%15%6%
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
14%9%33%30%11%1
180
16th to endDay
11%11%44%28%2
192
February1st to 15thDay
13%12%53%13%5%1
180
16th to endDay
13%12%47%20%5%
159
March1st to 15thDay
12%15%44%22%5%
180
16th to endDay
21%9%38%24%5%1
192
April1st to 15thDay
18%16%33%23%9%
244
16th to endDay
20%10%37%19%9%1
586
May1st to 15thDay
13%9%32%28%12%2
618
16th to endDay
17%7%29%27%14%3
677
June1st to 15thDay
7%227%37%21%3
645
16th to endDay
6%324%42%19%3
587
July1st to 15thDay
7%110%37%33%9%
550
16th to endDay
6%9%38%35%8%
595
August1st to 15thDay
7%112%41%32%5%
549
16th to endDay
6%217%37%28%5%
540
September1st to 15thDay
10%113%37%29%8%
180
16th to endDay
15%125%28%20%9%
180
October1st to 15thDay
19%8%30%25%13%3
180
16th to endDay
10%8%32%29%16%3
192
November1st to 15thDay
16%7%27%26%15%6%
180
16th to endDay
15%15%30%25%12%
180
December1st to 15thDay
10%11%39%27%8%1
180
16th to endDay
15%15%40%21%6%
192
January1st to 15thNight
11%11%34%33%8%
1050
16th to endNight
10%10%38%32%7%
1120
February1st to 15thNight
14%11%36%33%4
961
16th to endNight
13%12%36%31%5%
736
March1st to 15thNight
11%11%39%31%6%
682
16th to endNight
16%11%35%29%5%
672
April1st to 15thNight
16%10%40%24%7%
629
16th to endNight
16%9%37%27%7%
624
May1st to 15thNight
15%7%34%31%9%1
630
16th to endNight
11%431%33%16%2
659
June1st to 15thNight
6%332%37%19%1
630
16th to endNight
5%229%45%16%
597
July1st to 15thNight
5%14%51%24%3
555
16th to endNight
6%11%47%31%1
612
August1st to 15thNight
4111%49%30%1
575
16th to endNight
5%114%43%31%2
621
September1st to 15thNight
10%122%37%24%3
585
16th to endNight
9%425%35%22%2
582
October1st to 15thNight
16%5%30%28%17%1
673
16th to endNight
8%7%34%35%12%
832
November1st to 15thNight
10%8%34%34%12%
1002
16th to endNight
12%10%32%34%10%
1050
December1st to 15thNight
13%10%34%34%7%
1050
16th to endNight
14%9%35%35%5%
1120
Page generated at 2019-06-20 07:02:30. Version ac04

Copyright 2019 A. Danko


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