Addison Oaks Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Addison Oaks Observatory clear sky chart from 2005-11-06 to 2024-01-10.

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
35%
23984
15%
74827
10%
23932
42%
23932
20%
51953

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
18%
947
11%
2647
4%
946
24%
946
14%
2041
January11th to 20thNight
19%
900
8%
2520
3%
900
23%
900
11%
2034
January21st to endNight
22%
814
10%
2596
5%
814
28%
814
13%
1980
February1st to 10thNight
17%
720
8%
2340
2%
720
23%
720
10%
1842
February11th to 20thNight
21%
700
13%
2164
6%
699
28%
699
13%
1614
February21st to endNight
16%
592
15%
1776
4%
592
27%
592
15%
1296
March1st to 10thNight
25%
720
16%
2111
9%
720
31%
720
18%
1509
March11th to 20thNight
28%
720
21%
1980
9%
720
37%
720
22%
1365
March21st to endNight
29%
792
16%
2178
7%
792
36%
792
19%
1581
April1st to 10thNight
27%
635
15%
1895
7%
635
34%
635
21%
1300
April11th to 20thNight
32%
533
20%
1615
9%
533
41%
533
23%
1088
April21st to endNight
37%
540
19%
1620
7%
540
46%
540
24%
1075
May1st to 10thNight
39%
540
14%
1620
9%
540
43%
540
22%
1130
May11th to 20thNight
42%
531
18%
1592
11%
531
49%
531
25%
1038
May21st to endNight
56%
583
15%
1745
12%
582
61%
582
32%
1063
June1st to 10thNight
54%
392
18%
1301
17%
392
60%
392
29%
774
June11th to 20thNight
54%
360
20%
1260
20%
360
62%
360
27%
732
June21st to endNight
56%
417
21%
1317
18%
417
63%
417
31%
775
July1st to 10thNight
64%
525
17%
1400
14%
525
67%
525
40%
824
July11th to 20thNight
64%
522
21%
1392
17%
522
68%
522
40%
832
July21st to endNight
65%
591
17%
1630
12%
558
69%
558
38%
956
August1st to 10thNight
64%
537
20%
1600
16%
534
68%
534
37%
920
August11th to 20thNight
63%
534
23%
1598
17%
534
68%
534
34%
946
August21st to endNight
60%
594
24%
1782
16%
594
65%
594
35%
1047
September1st to 10thNight
56%
652
19%
1911
15%
652
59%
652
30%
1181
September11th to 20thNight
61%
720
27%
1980
21%
720
64%
720
38%
1177
September21st to endNight
51%
720
22%
1980
16%
720
55%
720
30%
1269
October1st to 10thNight
44%
720
20%
2040
16%
720
50%
720
28%
1313
October11th to 20thNight
31%
720
15%
2160
8%
720
40%
720
19%
1505
October21st to endNight
26%
792
15%
2510
10%
792
33%
792
16%
1806
November1st to 10thNight
36%
740
21%
2406
16%
740
45%
740
24%
1511
November11th to 20thNight
25%
760
15%
2470
9%
760
34%
760
16%
1721
November21st to endNight
23%
760
13%
2619
8%
760
30%
760
14%
1891
December1st to 10thNight
17%
760
8%
2660
4%
760
23%
760
10%
2046
December11th to 20thNight
17%
864
9%
3401
3%
862
24%
862
9%
2507
December21st to endNight
15%
1037
4%
5011
1%
1026
21%
1026
5%
4264

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%8%33%
74590
Night
14%9%47%6%35%5%5%7%35%
75059
TransparencyDay
48%7%12%20%11%1
74299
Night
48%6%12%20%12%1
74871
SeeingDay
17%11%29%23%14%6%
14210
Night
18%10%29%30%12%1
23999

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
14%12%7%12%8%45%45%7%22%
1509
11th to 20thDay
14%15%8%11%8%46%6%5%5%18%
1440
21st to endDay
15%16%8%10%9%45%5%45%18%
1758
February1st to 10thDay
14%13%6%11%11%5%6%45%5%20%
1620
11th to 20thDay
13%13%6%10%9%45%5%5%7%23%
1679
21st to endDay
14%15%5%11%8%35%5%5%5%25%
1480
March1st to 10thDay
15%11%5%8%7%45%5%5%6%29%
1847
11th to 20thDay
12%13%5%8%7%3445%6%32%
1980
21st to endDay
18%12%49%7%45%45%5%28%
2178
April1st to 10thDay
16%11%5%7%6%35%5%5%7%30%
2081
11th to 20thDay
16%10%37%5%35%5%6%7%33%
2294
21st to endDay
17%8%38%6%35%45%7%34%
2340
May1st to 10thDay
16%8%47%6%36%5%5%7%34%
2340
11th to 20thDay
18%8%36%5%35%45%7%36%
2301
21st to endDay
12%6%36%5%35%5%6%9%40%
2531
June1st to 10thDay
10%6%26%6%45%6%6%9%41%
2651
11th to 20thDay
10%5%35%6%35%5%5%9%42%
2700
21st to endDay
10%5%35%5%46%7%7%9%38%
2636
July1st to 10thDay
7%425%6%35%6%7%10%45%
2520
11th to 20thDay
8%5%25%5%45%6%7%11%42%
2520
21st to endDay
6%5%26%5%46%7%7%10%40%
2587
August1st to 10thDay
8%5%25%6%47%6%8%10%39%
2327
11th to 20thDay
9%5%26%6%46%6%7%9%40%
2303
21st to endDay
10%6%26%6%45%5%6%7%42%
2572
September1st to 10thDay
11%6%36%6%37%6%6%9%38%
2028
11th to 20thDay
11%4245%35%6%6%10%44%
1980
21st to endDay
14%6%35%6%45%5%7%9%36%
1980
October1st to 10thDay
12%8%36%5%45%5%5%6%41%
1918
11th to 20thDay
17%9%47%5%46%45%7%32%
1800
21st to endDay
19%12%46%6%4445%6%29%
1841
November1st to 10thDay
12%8%47%6%35%5%6%8%37%
1672
11th to 20thDay
13%11%47%8%36%5%5%6%31%
1710
21st to endDay
17%12%5%7%6%35%45%7%29%
1558
December1st to 10thDay
13%13%7%11%9%45%5%46%23%
1520
11th to 20thDay
16%14%5%9%7%35%5%7%7%24%
1756
21st to endDay
24%20%7%9%7%3445%5%12%
2633
January1st to 10thNight
16%10%6%10%7%45%5%5%7%26%
2647
11th to 20thNight
17%15%6%10%8%45%5%5%6%22%
2520
21st to endNight
12%11%7%12%9%5%5%5%5%6%24%
2596
February1st to 10thNight
14%15%6%9%8%46%5%5%5%23%
2340
11th to 20thNight
13%11%5%10%7%46%46%6%27%
2164
21st to endNight
19%12%47%7%3445%6%29%
1776
March1st to 10thNight
15%10%48%6%35%45%6%34%
2111
11th to 20thNight
12%8%46%5%45%6%5%7%38%
1980
21st to endNight
19%8%38%5%35%5%45%34%
2178
April1st to 10thNight
15%9%37%5%45%5%6%6%35%
1895
11th to 20thNight
18%7%26%6%3345%7%38%
1615
21st to endNight
17%7%35%44446%7%39%
1620
May1st to 10thNight
15%8%36%6%45%5%5%9%33%
1620
11th to 20thNight
17%5%35%4345%6%7%41%
1592
21st to endNight
9%5%26%5%345%6%9%46%
1744
June1st to 10thNight
9%6%35%5%3446%9%47%
1301
11th to 20thNight
8%6%35%435%5%6%10%45%
1260
21st to endNight
8%6%35%5%345%5%9%48%
1317
July1st to 10thNight
7%42444445%8%54%
1440
11th to 20thNight
9%4234345%6%10%51%
1440
21st to endNight
5%4145%35%5%8%10%50%
1726
August1st to 10thNight
7%324425%5%7%11%49%
1611
11th to 20thNight
6%425%5%346%7%8%49%
1598
21st to endNight
9%4245%345%5%7%52%
1782
September1st to 10thNight
9%6%36%4445%6%7%46%
1911
11th to 20thNight
9%425%42446%7%52%
1980
21st to endNight
14%427%5%245%5%8%44%
1980
October1st to 10thNight
15%7%25%43445%7%44%
2040
11th to 20thNight
18%9%35%5%45%5%5%6%35%
2160
21st to endNight
20%9%37%6%45%5%5%5%31%
2510
November1st to 10thNight
13%7%35%5%345%5%7%43%
2406
11th to 20thNight
15%9%38%6%45%7%7%6%31%
2470
21st to endNight
18%11%5%7%6%36%5%5%7%28%
2619
December1st to 10thNight
17%13%5%10%8%45%5%6%6%22%
2660
11th to 20thNight
13%12%6%11%7%45%5%5%6%25%
3436
21st to endNight
25%23%7%8%5%3344413%
5014

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
63%6%10%13%7%1
1510
11th to 20thDay
67%8%12%9%5%
1440
21st to endDay
69%5%8%11%6%1
1758
February1st to 10thDay
65%6%8%13%7%
1620
11th to 20thDay
61%411%16%7%1
1688
21st to endDay
59%6%11%15%7%2
1480
March1st to 10thDay
55%6%13%17%8%1
1847
11th to 20thDay
51%6%11%18%11%3
1980
21st to endDay
59%5%10%17%8%1
2178
April1st to 10thDay
52%6%12%19%11%1
2081
11th to 20thDay
49%6%12%19%13%2
2294
21st to endDay
50%6%14%16%13%2
2340
May1st to 10thDay
49%7%12%20%10%2
2340
11th to 20thDay
48%6%11%20%13%2
2305
21st to endDay
40%7%14%22%14%2
2531
June1st to 10thDay
38%7%13%25%14%2
2651
11th to 20thDay
38%6%14%24%16%3
2700
21st to endDay
39%9%12%22%16%2
2636
July1st to 10thDay
33%9%11%25%18%3
2451
11th to 20thDay
34%8%14%25%17%2
2445
21st to endDay
36%10%14%21%17%3
2443
August1st to 10thDay
36%10%14%26%12%1
2314
11th to 20thDay
38%10%15%24%12%2
2303
21st to endDay
39%7%11%25%16%1
2572
September1st to 10thDay
40%9%14%23%12%2
2028
11th to 20thDay
34%7%12%33%13%
1980
21st to endDay
43%7%14%24%12%1
1980
October1st to 10thDay
42%6%12%25%13%2
1918
11th to 20thDay
51%7%13%19%10%1
1800
21st to endDay
54%7%13%17%8%
1841
November1st to 10thDay
44%7%13%24%11%1
1672
11th to 20thDay
52%6%13%18%9%1
1710
21st to endDay
56%6%13%18%7%1
1558
December1st to 10thDay
63%5%12%16%4
1520
11th to 20thDay
58%7%14%15%6%
1752
21st to endDay
75%5%11%6%3
2633
January1st to 10thNight
58%6%11%17%7%1
2647
11th to 20thNight
64%6%12%12%6%
2520
21st to endNight
60%6%13%16%6%1
2596
February1st to 10thNight
63%6%9%13%7%1
2340
11th to 20thNight
56%6%12%16%9%1
2166
21st to endNight
55%413%18%9%1
1776
March1st to 10thNight
51%6%11%21%10%1
2111
11th to 20thNight
45%6%11%21%15%2
1980
21st to endNight
52%6%9%21%11%1
2178
April1st to 10thNight
48%5%12%21%13%2
1895
11th to 20thNight
44%6%12%17%18%2
1615
21st to endNight
43%6%12%20%16%3
1620
May1st to 10thNight
47%7%11%21%12%2
1620
11th to 20thNight
42%6%10%20%19%3
1593
21st to endNight
33%8%15%24%17%3
1745
June1st to 10thNight
35%6%10%29%17%3
1301
11th to 20thNight
34%8%14%24%18%2
1260
21st to endNight
33%7%12%26%21%1
1317
July1st to 10thNight
28%7%11%28%23%3
1400
11th to 20thNight
29%6%13%32%17%3
1392
21st to endNight
26%9%19%22%20%3
1630
August1st to 10thNight
28%8%16%32%14%2
1600
11th to 20thNight
30%9%14%32%12%3
1598
21st to endNight
30%8%13%30%18%1
1782
September1st to 10thNight
35%7%14%26%15%2
1911
11th to 20thNight
30%6%13%31%19%1
1980
21st to endNight
38%6%13%31%12%1
1980
October1st to 10thNight
39%6%11%24%19%1
2040
11th to 20thNight
48%7%14%19%12%1
2160
21st to endNight
53%6%12%20%8%1
2510
November1st to 10thNight
39%7%13%25%15%1
2406
11th to 20thNight
50%7%14%20%8%1
2470
21st to endNight
56%5%14%18%6%
2619
December1st to 10thNight
62%6%12%15%5%
2660
11th to 20thNight
57%7%14%14%7%1
3439
21st to endNight
75%5%11%7%3
5014

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
18%22%37%16%7%
267
11th to 20thDay
22%14%45%14%5%1
240
21st to endDay
26%12%39%18%41
264
February1st to 10thDay
25%20%41%13%1
240
11th to 20thDay
24%19%40%13%3
240
21st to endDay
24%22%42%11%1
198
March1st to 10thDay
26%21%34%15%31
287
11th to 20thDay
21%13%34%24%7%1
420
21st to endDay
27%13%31%22%5%1
462
April1st to 10thDay
16%16%36%21%9%1
420
11th to 20thDay
25%16%29%15%9%6%
412
21st to endDay
23%13%28%22%10%3
420
May1st to 10thDay
23%10%29%24%11%3
423
11th to 20thDay
20%10%28%21%13%7%
447
21st to endDay
14%6%22%28%19%9%
485
June1st to 10thDay
12%9%32%29%15%4
617
11th to 20thDay
11%6%32%29%18%3
630
21st to endDay
12%7%29%30%18%5%
630
July1st to 10thDay
8%5%19%31%23%14%
621
11th to 20thDay
9%6%25%32%19%8%
618
21st to endDay
7%5%24%29%24%10%
528
August1st to 10thDay
9%420%25%27%14%
446
11th to 20thDay
12%319%27%24%15%
439
21st to endDay
12%5%21%29%20%13%
495
September1st to 10thDay
13%425%24%22%12%
450
11th to 20thDay
10%420%23%27%16%
450
21st to endDay
15%11%24%23%20%8%
450
October1st to 10thDay
18%10%26%21%16%10%
450
11th to 20thDay
21%15%31%25%8%1
450
21st to endDay
27%13%36%19%41
356
November1st to 10thDay
15%21%34%21%9%1
270
11th to 20thDay
20%20%34%17%7%1
270
21st to endDay
23%17%37%19%4
198
December1st to 10thDay
22%18%38%14%7%1
180
11th to 20thDay
27%21%37%12%41
180
21st to endDay
26%21%35%15%3
257
January1st to 10thNight
21%14%37%22%5%1
950
11th to 20thNight
25%13%33%24%41
900
21st to endNight
18%13%35%28%6%
814
February1st to 10thNight
22%13%39%24%2
720
11th to 20thNight
20%15%35%25%5%
703
21st to endNight
26%16%37%20%2
592
March1st to 10thNight
20%12%36%26%5%
720
11th to 20thNight
17%14%37%26%6%1
720
21st to endNight
22%11%31%28%8%1
792
April1st to 10thNight
20%14%33%28%41
635
11th to 20thNight
22%9%32%27%8%2
533
21st to endNight
20%8%31%31%9%
540
May1st to 10thNight
18%8%29%35%9%1
540
11th to 20thNight
21%5%26%32%15%1
531
21st to endNight
11%223%41%20%2
584
June1st to 10thNight
12%426%44%15%
392
11th to 20thNight
11%424%50%11%1
360
21st to endNight
10%322%47%18%
417
July1st to 10thNight
7%318%40%29%3
525
11th to 20thNight
10%218%41%25%4
522
21st to endNight
6%319%47%23%2
591
August1st to 10thNight
8%217%38%31%3
537
11th to 20thNight
9%118%38%30%4
534
21st to endNight
11%318%33%32%3
594
September1st to 10thNight
12%5%18%34%25%5%
652
11th to 20thNight
11%5%17%35%27%6%
720
21st to endNight
16%6%22%30%21%5%
720
October1st to 10thNight
18%7%25%30%18%3
720
11th to 20thNight
22%13%28%28%8%1
720
21st to endNight
24%12%32%26%4
792
November1st to 10thNight
19%11%30%27%14%1
740
11th to 20thNight
20%15%33%24%7%1
760
21st to endNight
24%14%34%22%6%
760
December1st to 10thNight
23%14%36%21%6%1
760
11th to 20thNight
22%14%37%23%3
864
21st to endNight
29%13%33%22%3
1045
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Copyright 2024 Attilla Danko


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