Seven Sisters Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Seven Sisters Observatory clear sky chart from 2005-11-06 to 2024-01-12.

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%
24449
16%
74618
10%
24392
42%
24392
20%
52195

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
17%
950
13%
2648
4%
946
24%
946
13%
2065
January11th to 20thNight
16%
908
8%
2541
3%
908
21%
908
12%
2064
January21st to endNight
20%
860
8%
2642
3%
860
24%
860
11%
2097
February1st to 10thNight
16%
720
7%
2340
3%
720
22%
720
9%
1859
February11th to 20thNight
20%
700
13%
2102
6%
700
27%
700
13%
1561
February21st to endNight
17%
592
14%
1776
4%
592
27%
592
15%
1296
March1st to 10thNight
26%
720
16%
2147
9%
720
32%
720
18%
1499
March11th to 20thNight
29%
720
20%
1980
8%
720
38%
720
23%
1365
March21st to endNight
30%
792
17%
2178
10%
792
36%
792
19%
1582
April1st to 10thNight
26%
583
16%
1843
8%
583
36%
583
20%
1249
April11th to 20thNight
30%
533
20%
1665
9%
533
42%
533
22%
1124
April21st to endNight
33%
540
16%
1620
6%
540
41%
540
22%
1109
May1st to 10thNight
33%
540
13%
1620
7%
540
38%
540
19%
1157
May11th to 20thNight
40%
531
17%
1593
10%
531
47%
531
23%
1067
May21st to endNight
53%
583
14%
1717
11%
582
57%
582
30%
1070
June1st to 10thNight
55%
540
17%
1440
11%
540
61%
540
36%
893
June11th to 20thNight
54%
540
18%
1440
14%
540
58%
540
31%
945
June21st to endNight
59%
540
20%
1440
14%
540
64%
540
35%
899
July1st to 10thNight
67%
525
17%
1400
15%
525
68%
525
39%
848
July11th to 20thNight
64%
522
22%
1392
18%
522
68%
522
40%
844
July21st to endNight
68%
591
20%
1597
16%
558
72%
558
40%
906
August1st to 10thNight
66%
537
22%
1600
19%
534
68%
534
36%
933
August11th to 20thNight
66%
534
22%
1598
18%
534
70%
534
34%
950
August21st to endNight
63%
594
23%
1858
20%
594
66%
594
35%
1063
September1st to 10thNight
60%
620
21%
1880
19%
620
62%
620
31%
1134
September11th to 20thNight
62%
720
29%
1980
23%
720
65%
720
37%
1179
September21st to endNight
51%
720
23%
1980
16%
720
55%
720
29%
1290
October1st to 10thNight
46%
720
22%
1996
17%
720
51%
720
29%
1277
October11th to 20thNight
30%
720
17%
2160
9%
720
40%
720
19%
1507
October21st to endNight
27%
792
17%
2551
11%
792
36%
792
17%
1783
November1st to 10thNight
33%
740
20%
2406
15%
740
42%
740
22%
1529
November11th to 20thNight
25%
760
16%
2470
10%
760
34%
760
17%
1703
November21st to endNight
25%
760
14%
2470
9%
760
31%
760
15%
1815
December1st to 10thNight
18%
760
9%
2470
5%
760
22%
760
11%
1937
December11th to 20thNight
17%
902
10%
3200
2%
900
25%
900
10%
2450
December21st to endNight
14%
1040
5%
4878
2%
1026
20%
1026
5%
4146

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%9%47%6%45%5%6%7%33%
74883
Night
15%10%47%6%345%5%7%35%
74845
TransparencyDay
48%7%12%20%12%1
74592
Night
49%6%12%20%12%1
74657
SeeingDay
17%11%28%23%14%6%
14507
Night
19%9%29%29%13%1
24458

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
15%13%6%11%8%5%6%5%47%19%
1517
11th to 20thDay
16%16%7%12%9%45%5%5%5%17%
1448
21st to endDay
15%18%9%10%8%5%5%435%18%
1711
February1st to 10thDay
14%15%7%11%11%36%5%5%5%19%
1620
11th to 20thDay
16%10%5%11%9%5%6%5%5%5%24%
1744
21st to endDay
17%13%6%9%8%25%45%6%24%
1480
March1st to 10thDay
14%10%5%8%9%46%5%6%7%27%
1812
11th to 20thDay
13%11%5%9%7%34447%34%
1980
21st to endDay
19%12%5%8%6%35%446%28%
2178
April1st to 10thDay
16%11%6%8%5%45%5%5%6%30%
2132
11th to 20thDay
16%9%36%5%36%46%7%34%
2244
21st to endDay
18%9%47%6%25%45%7%34%
2340
May1st to 10thDay
17%8%36%6%35%6%5%7%33%
2340
11th to 20thDay
18%9%37%6%4445%6%34%
2301
21st to endDay
12%5%36%5%45%6%6%9%40%
2555
June1st to 10thDay
10%5%36%5%46%5%6%9%41%
2520
11th to 20thDay
10%5%35%5%36%6%7%10%40%
2520
21st to endDay
9%5%35%6%46%6%7%10%39%
2520
July1st to 10thDay
6%5%35%5%45%6%7%10%45%
2520
11th to 20thDay
9%5%26%5%36%6%5%9%45%
2520
21st to endDay
7%5%25%7%46%6%7%9%42%
2625
August1st to 10thDay
8%425%7%45%6%7%8%43%
2327
11th to 20thDay
10%6%36%7%46%6%7%8%38%
2303
21st to endDay
9%6%35%5%35%5%7%9%43%
2496
September1st to 10thDay
12%5%26%5%45%6%6%9%39%
2062
11th to 20thDay
10%425%5%36%6%6%9%45%
1980
21st to endDay
13%5%35%5%445%6%9%39%
1980
October1st to 10thDay
12%7%35%6%45%5%6%7%41%
1962
11th to 20thDay
17%9%36%7%45%5%5%6%33%
1800
21st to endDay
20%9%47%6%35%5%46%30%
1800
November1st to 10thDay
12%7%38%5%445%5%6%40%
1672
11th to 20thDay
14%12%5%8%8%445%46%30%
1710
21st to endDay
19%12%47%6%45%45%6%27%
1710
December1st to 10thDay
14%14%8%12%6%5%5%446%22%
1710
11th to 20thDay
14%14%6%11%6%35%5%7%6%22%
1961
21st to endDay
22%20%7%12%8%44445%11%
2783
January1st to 10thNight
17%12%6%10%7%45%5%5%7%23%
2648
11th to 20thNight
18%14%7%11%9%4445%5%20%
2541
21st to endNight
13%13%8%12%8%45%5%5%6%20%
2642
February1st to 10thNight
17%14%6%10%9%45%446%22%
2340
11th to 20thNight
14%13%5%8%7%5%5%46%5%27%
2101
21st to endNight
19%12%5%9%5%34446%29%
1776
March1st to 10thNight
15%9%48%7%3445%6%34%
2147
11th to 20thNight
14%9%345%36%5%5%7%38%
1980
21st to endNight
21%9%37%6%3435%6%33%
2178
April1st to 10thNight
14%8%37%6%35%6%5%7%36%
1843
11th to 20thNight
18%8%26%5%25%45%7%38%
1665
21st to endNight
17%10%35%5%35%5%5%7%36%
1620
May1st to 10thNight
18%7%47%7%35%46%7%32%
1620
11th to 20thNight
19%7%245%35%46%7%38%
1592
21st to endNight
10%7%3443446%9%45%
1716
June1st to 10thNight
9%4246%345%6%9%46%
1440
11th to 20thNight
10%6%26%6%3445%9%43%
1440
21st to endNight
8%425%5%345%7%9%47%
1440
July1st to 10thNight
6%425%4345%5%7%54%
1440
11th to 20thNight
7%5%3442445%8%54%
1440
21st to endNight
43245%35%6%7%10%51%
1691
August1st to 10thNight
6%425%5%3435%10%50%
1611
11th to 20thNight
7%5%245%35%5%6%9%48%
1598
21st to endNight
9%4245%335%5%7%51%
1858
September1st to 10thNight
9%6%345%345%5%8%48%
1880
11th to 20thNight
9%5%244335%5%7%53%
1980
21st to endNight
12%7%35%435%5%6%7%43%
1980
October1st to 10thNight
12%7%35%5%3445%7%45%
1996
11th to 20thNight
16%10%47%6%44445%36%
2160
21st to endNight
20%9%37%5%345%5%5%33%
2551
November1st to 10thNight
12%9%46%5%345%5%6%42%
2406
11th to 20thNight
15%10%46%7%35%5%5%7%33%
2470
21st to endNight
17%12%5%8%6%3445%6%29%
2470
December1st to 10thNight
16%14%6%10%7%35%45%6%22%
2470
11th to 20thNight
15%13%5%10%7%45%5%5%7%23%
3231
21st to endNight
26%20%7%9%6%3444412%
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
64%7%10%14%5%
1518
11th to 20thDay
70%6%12%8%4
1448
21st to endDay
69%5%9%11%6%1
1711
February1st to 10thDay
65%7%9%12%7%1
1620
11th to 20thDay
61%6%10%15%8%1
1754
21st to endDay
60%6%12%15%6%2
1480
March1st to 10thDay
55%6%12%18%8%1
1812
11th to 20thDay
51%411%19%12%3
1980
21st to endDay
58%5%10%19%7%1
2178
April1st to 10thDay
54%5%11%18%12%
2132
11th to 20thDay
49%6%11%20%13%2
2244
21st to endDay
50%6%12%17%14%1
2340
May1st to 10thDay
49%8%11%19%11%1
2340
11th to 20thDay
51%6%9%18%15%2
2305
21st to endDay
39%9%13%25%13%2
2555
June1st to 10thDay
38%7%12%26%14%2
2520
11th to 20thDay
37%9%13%22%18%2
2520
21st to endDay
38%9%14%21%16%3
2520
July1st to 10thDay
33%8%12%25%18%4
2451
11th to 20thDay
34%7%13%25%18%2
2445
21st to endDay
34%8%14%24%18%2
2479
August1st to 10thDay
34%8%15%28%13%1
2314
11th to 20thDay
40%9%12%23%13%2
2303
21st to endDay
36%7%11%24%18%3
2496
September1st to 10thDay
40%8%16%20%14%2
2062
11th to 20thDay
34%7%12%31%16%1
1980
21st to endDay
40%7%12%24%16%
1980
October1st to 10thDay
40%7%11%26%15%2
1962
11th to 20thDay
50%6%12%19%12%
1800
21st to endDay
54%6%13%18%9%1
1800
November1st to 10thDay
44%6%11%24%15%1
1672
11th to 20thDay
54%6%12%18%8%2
1710
21st to endDay
57%6%13%17%7%1
1710
December1st to 10thDay
64%7%11%13%5%
1710
11th to 20thDay
60%7%13%16%4
1958
21st to endDay
77%5%9%6%4
2783
January1st to 10thNight
60%6%10%16%7%
2648
11th to 20thNight
65%5%12%11%6%
2541
21st to endNight
64%6%12%12%6%1
2642
February1st to 10thNight
65%5%10%13%6%1
2340
11th to 20thNight
58%5%11%17%9%1
2102
21st to endNight
56%413%17%9%2
1776
March1st to 10thNight
50%5%11%22%10%1
2147
11th to 20thNight
44%6%12%20%15%2
1980
21st to endNight
53%5%9%21%11%2
2178
April1st to 10thNight
46%7%10%22%15%1
1843
11th to 20thNight
46%5%11%18%18%2
1665
21st to endNight
47%6%12%18%15%3
1620
May1st to 10thNight
51%6%10%20%11%2
1620
11th to 20thNight
45%6%9%19%19%2
1593
21st to endNight
35%8%14%26%15%3
1717
June1st to 10thNight
33%7%12%28%19%3
1440
11th to 20thNight
38%7%12%25%17%3
1440
21st to endNight
32%8%13%26%19%1
1440
July1st to 10thNight
29%7%12%27%21%3
1400
11th to 20thNight
29%7%12%29%20%3
1392
21st to endNight
26%8%17%24%21%4
1597
August1st to 10thNight
30%7%14%32%16%2
1600
11th to 20thNight
30%9%15%28%14%3
1598
21st to endNight
31%6%14%25%22%3
1858
September1st to 10thNight
34%7%12%26%17%3
1880
11th to 20thNight
31%6%10%31%21%1
1980
21st to endNight
38%7%12%27%15%1
1980
October1st to 10thNight
39%5%11%24%19%1
1996
11th to 20thNight
49%5%11%19%15%1
2160
21st to endNight
50%6%10%23%9%1
2551
November1st to 10thNight
42%6%12%23%16%1
2406
11th to 20thNight
49%6%14%20%9%1
2470
21st to endNight
56%6%12%19%7%
2470
December1st to 10thNight
62%6%11%14%6%
2470
11th to 20thNight
59%7%13%14%7%1
3233
21st to endNight
75%5%10%7%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
23%18%36%18%41
270
11th to 20thDay
20%14%43%18%41
243
21st to endDay
26%17%34%18%6%
264
February1st to 10thDay
25%18%38%18%3
240
11th to 20thDay
25%20%40%13%3
240
21st to endDay
28%24%37%10%2
198
March1st to 10thDay
25%21%35%16%4
252
11th to 20thDay
23%12%35%22%8%1
420
21st to endDay
26%16%29%21%6%1
462
April1st to 10thDay
20%14%33%24%9%1
420
11th to 20thDay
25%16%32%15%8%4
412
21st to endDay
23%13%31%21%10%3
420
May1st to 10thDay
23%13%30%19%12%3
423
11th to 20thDay
21%10%28%21%14%6%
447
21st to endDay
13%7%24%26%19%12%
509
June1st to 10thDay
11%6%29%32%17%4
630
11th to 20thDay
13%6%27%30%17%6%
630
21st to endDay
11%7%29%31%17%5%
630
July1st to 10thDay
9%418%27%27%14%
621
11th to 20thDay
12%423%29%22%10%
618
21st to endDay
8%423%30%24%11%
566
August1st to 10thDay
9%217%28%24%19%
446
11th to 20thDay
13%415%27%27%13%
439
21st to endDay
11%321%27%24%14%
495
September1st to 10thDay
14%422%22%25%12%
450
11th to 20thDay
11%318%25%28%15%
450
21st to endDay
16%11%20%23%20%9%
450
October1st to 10thDay
15%7%29%24%15%10%
450
11th to 20thDay
19%16%28%27%9%1
450
21st to endDay
27%16%36%15%41
315
November1st to 10thDay
14%17%33%25%9%2
270
11th to 20thDay
21%22%29%21%5%1
270
21st to endDay
26%14%41%15%4
270
December1st to 10thDay
24%23%30%15%7%1
270
11th to 20thDay
21%20%42%13%4
270
21st to endDay
27%22%33%16%2
297
January1st to 10thNight
22%15%36%21%5%1
950
11th to 20thNight
24%11%38%21%6%1
908
21st to endNight
19%11%38%26%6%
860
February1st to 10thNight
26%12%35%24%3
720
11th to 20thNight
23%14%35%24%3
703
21st to endNight
26%13%39%20%3
592
March1st to 10thNight
20%12%34%27%7%
720
11th to 20thNight
21%14%33%26%6%1
720
21st to endNight
24%10%30%27%8%
792
April1st to 10thNight
17%14%37%27%5%1
583
11th to 20thNight
20%8%37%25%8%1
533
21st to endNight
21%8%32%30%8%1
540
May1st to 10thNight
19%8%29%33%9%1
540
11th to 20thNight
24%229%31%12%1
531
21st to endNight
14%323%36%22%2
584
June1st to 10thNight
11%324%45%17%1
540
11th to 20thNight
13%323%41%20%1
540
21st to endNight
10%320%43%23%2
540
July1st to 10thNight
9%215%41%29%5%
525
11th to 20thNight
10%315%43%26%3
522
21st to endNight
6%119%44%30%1
591
August1st to 10thNight
9%215%43%27%4
537
11th to 20thNight
10%116%36%31%5%
534
21st to endNight
12%116%35%31%4
594
September1st to 10thNight
11%318%36%27%5%
620
11th to 20thNight
11%317%35%30%4
720
21st to endNight
14%6%21%31%22%5%
720
October1st to 10thNight
15%7%24%33%18%3
720
11th to 20thNight
21%13%29%27%9%1
720
21st to endNight
25%12%33%24%6%
792
November1st to 10thNight
18%11%31%27%12%1
740
11th to 20thNight
21%14%35%22%7%1
760
21st to endNight
24%10%34%26%5%
760
December1st to 10thNight
23%15%36%20%6%
760
11th to 20thNight
24%12%38%21%5%
902
21st to endNight
31%12%34%21%2
1045
Page generated at 2024-01-09 07:14:41. Version ac07

Copyright 2024 Attilla Danko


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