Broken Oak Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Broken Oak Observatory clear sky chart from 2005-11-06 to 2024-01-14.

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
54%
24420
20%
74534
15%
24366
60%
24366
28%
47097

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
37%
758
22%
2459
14%
757
50%
757
26%
1491
January11th to 20thNight
46%
736
25%
2391
18%
736
57%
736
28%
1414
January21st to endNight
32%
792
22%
2455
13%
792
43%
792
24%
1561
February1st to 10thNight
39%
720
22%
2160
15%
720
47%
720
28%
1355
February11th to 20thNight
42%
700
23%
2099
13%
700
53%
700
32%
1223
February21st to endNight
37%
592
26%
1723
14%
592
49%
592
31%
1053
March1st to 10thNight
41%
720
30%
1980
16%
720
53%
720
41%
1120
March11th to 20thNight
45%
720
27%
1980
17%
720
54%
720
35%
1178
March21st to endNight
43%
792
29%
2178
17%
792
52%
792
38%
1254
April1st to 10thNight
44%
720
23%
1980
15%
720
50%
720
39%
1150
April11th to 20thNight
42%
711
21%
1953
12%
711
50%
711
35%
1166
April21st to endNight
53%
699
29%
1793
17%
699
60%
699
44%
1046
May1st to 10thNight
67%
540
29%
1620
22%
540
72%
540
48%
813
May11th to 20thNight
65%
531
17%
1592
11%
531
70%
531
33%
982
May21st to endNight
69%
582
23%
1744
18%
582
72%
582
34%
1053
June1st to 10thNight
64%
540
14%
1620
12%
540
66%
540
24%
1129
June11th to 20thNight
77%
540
12%
1620
11%
540
78%
540
27%
1061
June21st to endNight
70%
540
8%
1620
7%
540
70%
540
21%
1172
July1st to 10thNight
72%
525
6%
1575
5%
525
72%
525
19%
1164
July11th to 20thNight
75%
522
4%
1566
4%
522
75%
522
19%
1176
July21st to endNight
72%
591
7%
1672
7%
558
74%
558
20%
1235
August1st to 10thNight
75%
537
6%
1600
6%
534
75%
534
22%
1150
August11th to 20thNight
77%
534
6%
1738
7%
534
77%
534
19%
1248
August21st to endNight
63%
774
9%
2160
9%
774
63%
774
18%
1607
September1st to 10thNight
66%
720
8%
1980
8%
720
66%
720
18%
1481
September11th to 20thNight
60%
720
9%
1980
9%
720
60%
720
19%
1464
September21st to endNight
59%
720
19%
1980
17%
720
61%
720
23%
1386
October1st to 10thNight
54%
720
21%
1980
16%
720
59%
720
27%
1321
October11th to 20thNight
65%
720
30%
2134
28%
720
70%
720
39%
1189
October21st to endNight
54%
792
27%
2376
23%
792
62%
792
33%
1397
November1st to 10thNight
51%
740
26%
2221
19%
740
61%
740
37%
1244
November11th to 20thNight
46%
760
28%
2280
22%
760
56%
760
31%
1374
November21st to endNight
45%
760
25%
2441
19%
760
55%
760
29%
1459
December1st to 10thNight
47%
760
27%
2470
19%
760
59%
760
31%
1414
December11th to 20thNight
46%
760
25%
2940
21%
758
54%
758
24%
1716
December21st to endNight
44%
832
15%
4474
20%
817
51%
817
15%
2851

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
8%5%36%7%46%6%7%9%38%
74864
Night
8%5%35%5%35%5%6%9%44%
74902
TransparencyDay
40%10%14%17%14%6%
74587
Night
35%10%16%19%14%6%
74698
SeeingDay
9%7%21%26%22%16%
14319
Night
9%6%23%31%23%7%
24431

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
10%5%26%5%3446%9%45%
1706
11th to 20thDay
8%5%25%5%35%5%5%9%48%
1647
21st to endDay
11%7%25%5%345%6%7%44%
1897
February1st to 10thDay
14%5%36%5%345%5%7%44%
1800
11th to 20thDay
9%435%4346%46%54%
1748
21st to endDay
8%5%35%6%25%5%5%8%48%
1530
March1st to 10thDay
5%4144345%6%8%57%
1980
11th to 20thDay
7%425%5%345%6%8%51%
1980
21st to endDay
7%5%25%6%35%5%5%5%53%
2178
April1st to 10thDay
8%4145%46%5%6%8%49%
1980
11th to 20thDay
8%5%36%7%46%6%6%7%43%
1956
21st to endDay
5%3145%36%5%5%10%52%
2180
May1st to 10thDay
5%3135%35%5%6%9%55%
2340
11th to 20thDay
8%5%26%7%5%6%6%6%9%40%
2301
21st to endDay
6%5%27%8%5%6%6%8%9%37%
2531
June1st to 10thDay
11%8%48%8%6%7%7%7%10%24%
2340
11th to 20thDay
5%437%10%6%10%8%10%10%26%
2340
21st to endDay
8%6%38%8%5%9%8%9%9%27%
2340
July1st to 10thDay
9%6%49%10%6%9%9%9%10%22%
2340
11th to 20thDay
7%7%49%9%7%10%8%8%11%21%
2340
21st to endDay
6%7%39%10%6%9%9%8%11%22%
2547
August1st to 10thDay
7%5%38%10%6%8%8%9%11%25%
2327
11th to 20thDay
6%7%38%10%7%9%10%8%12%20%
2156
21st to endDay
9%7%39%10%5%9%8%8%10%22%
2178
September1st to 10thDay
7%6%49%10%6%9%9%9%10%21%
1980
11th to 20thDay
9%7%5%9%9%6%8%7%7%8%26%
1980
21st to endDay
8%6%37%9%5%8%7%7%8%31%
1980
October1st to 10thDay
10%6%47%7%45%6%6%7%37%
1980
11th to 20thDay
5%435%5%45%5%6%7%50%
1823
21st to endDay
7%5%34436%5%6%9%49%
1980
November1st to 10thDay
7%5%36%5%345%5%7%50%
1857
11th to 20thDay
9%6%26%5%35%5%5%7%47%
1900
21st to endDay
9%6%36%435%5%6%9%44%
1735
December1st to 10thDay
7%5%35%6%345%7%8%47%
1710
11th to 20thDay
11%6%36%6%3445%7%45%
2153
21st to endDay
12%8%37%7%35%6%6%7%36%
3124
January1st to 10thNight
11%6%26%5%3446%8%45%
2459
11th to 20thNight
9%6%34435%6%5%9%47%
2391
21st to endNight
13%6%35%5%35%45%7%43%
2455
February1st to 10thNight
11%6%35%5%245%5%6%46%
2160
11th to 20thNight
9%4245%3446%8%51%
2098
21st to endNight
8%6%46%6%35%45%9%46%
1723
March1st to 10thNight
5%42442445%8%58%
1980
11th to 20thNight
7%5%245%345%6%9%50%
1980
21st to endNight
6%5%25%42345%7%55%
2178
April1st to 10thNight
7%42442347%9%52%
1980
11th to 20thNight
7%6%25%5%2446%10%49%
1953
21st to endNight
6%323435%45%8%57%
1793
May1st to 10thNight
432342345%9%61%
1620
11th to 20thNight
45%25%5%45%6%6%10%49%
1592
21st to endNight
5%425%5%45%5%7%9%50%
1744
June1st to 10thNight
10%6%36%6%47%6%8%11%34%
1620
11th to 20thNight
5%5%245%5%6%8%10%14%37%
1620
21st to endNight
7%5%27%7%5%7%8%9%12%33%
1620
July1st to 10thNight
6%5%36%7%48%7%9%14%32%
1620
11th to 20thNight
5%437%8%5%7%8%11%14%28%
1620
21st to endNight
4447%8%5%8%8%10%12%31%
1771
August1st to 10thNight
45%36%7%47%8%11%12%33%
1611
11th to 20thNight
5%5%36%6%48%9%10%14%31%
1738
21st to endNight
9%8%37%6%47%7%8%11%30%
2160
September1st to 10thNight
6%5%28%8%6%8%7%9%12%30%
1980
11th to 20thNight
9%7%37%7%5%7%6%8%11%29%
1980
21st to endNight
8%7%37%8%45%7%7%9%35%
1980
October1st to 10thNight
8%7%36%6%45%6%5%9%42%
1980
11th to 20thNight
6%5%2442446%8%55%
2134
21st to endNight
8%6%35%5%3435%8%50%
2376
November1st to 10thNight
8%425%43445%8%53%
2221
11th to 20thNight
8%6%35%5%35%447%50%
2280
21st to endNight
8%5%37%5%3446%8%46%
2441
December1st to 10thNight
7%5%25%5%35%45%8%49%
2470
11th to 20thNight
11%7%26%424448%48%
3042
21st to endNight
15%8%36%6%35%5%5%8%36%
4532

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
35%6%11%20%19%9%
1707
11th to 20thDay
32%5%9%22%23%9%
1647
21st to endDay
38%5%9%16%23%10%
1897
February1st to 10thDay
39%7%9%15%18%12%
1800
11th to 20thDay
31%5%9%18%25%12%
1758
21st to endDay
34%6%12%16%22%10%
1530
March1st to 10thDay
25%7%11%23%25%10%
1980
11th to 20thDay
30%7%12%24%17%10%
1980
21st to endDay
32%6%10%22%22%8%
2178
April1st to 10thDay
31%7%14%20%20%8%
1980
11th to 20thDay
37%8%11%16%21%7%
1956
21st to endDay
26%7%13%23%23%8%
2180
May1st to 10thDay
24%7%13%22%24%10%
2340
11th to 20thDay
37%9%16%20%14%4
2305
21st to endDay
40%9%15%18%16%3
2531
June1st to 10thDay
51%13%16%15%4
2340
11th to 20thDay
46%15%20%16%3
2340
21st to endDay
48%15%19%13%4
2340
July1st to 10thDay
53%16%21%9%1
2275
11th to 20thDay
52%17%23%8%1
2271
21st to endDay
49%18%22%11%1
2405
August1st to 10thDay
46%18%26%9%
2314
11th to 20thDay
50%19%22%9%1
2156
21st to endDay
52%17%18%12%2
2178
September1st to 10thDay
51%18%18%11%3
1980
11th to 20thDay
50%14%20%12%4
1980
21st to endDay
46%13%13%15%10%3
1980
October1st to 10thDay
44%10%10%16%12%9%
1980
11th to 20thDay
31%7%11%21%23%7%
1823
21st to endDay
30%7%11%18%21%12%
1980
November1st to 10thDay
32%8%10%20%18%12%
1857
11th to 20thDay
35%7%11%17%21%10%
1900
21st to endDay
35%7%9%21%20%8%
1735
December1st to 10thDay
33%6%14%25%16%6%
1710
11th to 20thDay
37%6%10%17%17%13%
2150
21st to endDay
45%8%10%18%14%5%
3124
January1st to 10thNight
36%7%11%18%18%9%
2459
11th to 20thNight
34%7%10%21%21%8%
2391
21st to endNight
40%6%10%16%19%9%
2455
February1st to 10thNight
36%8%10%17%18%12%
2160
11th to 20thNight
30%8%11%19%23%10%
2099
21st to endNight
35%6%13%19%21%7%
1723
March1st to 10thNight
25%7%12%25%23%9%
1980
11th to 20thNight
30%7%14%26%14%9%
1980
21st to endNight
27%7%11%29%20%7%
2178
April1st to 10thNight
26%8%20%21%18%7%
1980
11th to 20thNight
29%8%14%25%19%6%
1953
21st to endNight
25%6%15%24%23%6%
1793
May1st to 10thNight
19%6%16%28%22%9%
1620
11th to 20thNight
30%11%22%20%15%2
1593
21st to endNight
29%10%16%22%20%2
1745
June1st to 10thNight
40%13%21%21%6%
1620
11th to 20thNight
32%15%29%21%2
1620
21st to endNight
40%17%24%14%5%
1620
July1st to 10thNight
41%19%29%9%2
1575
11th to 20thNight
40%21%30%9%1
1566
21st to endNight
37%22%29%11%1
1672
August1st to 10thNight
36%19%32%11%1
1600
11th to 20thNight
38%20%29%12%1
1738
21st to endNight
45%16%23%15%2
2160
September1st to 10thNight
42%19%23%13%4
1980
11th to 20thNight
46%14%20%16%31
1980
21st to endNight
41%13%16%17%10%2
1980
October1st to 10thNight
38%11%13%19%13%7%
1980
11th to 20thNight
25%8%14%24%23%5%
2134
21st to endNight
31%7%11%18%22%10%
2376
November1st to 10thNight
29%6%13%21%20%11%
2221
11th to 20thNight
35%6%11%20%20%9%
2280
21st to endNight
36%6%10%22%18%8%
2441
December1st to 10thNight
31%7%13%27%15%6%
2470
11th to 20thNight
35%7%9%19%18%12%
3044
21st to endNight
44%8%12%17%14%4
4532

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
11%16%46%20%6%
270
11th to 20thDay
9%15%37%26%9%3
249
21st to endDay
15%19%44%19%3
264
February1st to 10thDay
14%16%33%27%8%2
240
11th to 20thDay
13%10%36%28%8%4
240
21st to endDay
9%16%29%32%14%
248
March1st to 10thDay
5%15%39%28%11%1
420
11th to 20thDay
12%13%28%29%16%2
420
21st to endDay
6%13%31%32%16%2
462
April1st to 10thDay
11%13%30%27%17%2
420
11th to 20thDay
9%13%31%27%16%3
412
21st to endDay
6%7%28%32%20%7%
420
May1st to 10thDay
6%7%23%33%21%10%
423
11th to 20thDay
9%318%33%22%15%
447
21st to endDay
8%312%25%32%20%
485
June1st to 10thDay
14%411%24%29%19%
450
11th to 20thDay
6%29%28%28%27%
450
21st to endDay
6%17%19%29%37%
450
July1st to 10thDay
6%17%14%27%45%
445
11th to 20thDay
6%16%15%31%42%
444
21st to endDay
7%19%22%26%35%
488
August1st to 10thDay
7%26%16%33%37%
446
11th to 20thDay
7%16%12%33%40%
439
21st to endDay
9%210%23%26%30%
495
September1st to 10thDay
8%27%18%32%33%
450
11th to 20thDay
9%210%25%31%23%
450
21st to endDay
10%29%27%31%22%
450
October1st to 10thDay
12%5%22%33%22%6%
450
11th to 20thDay
7%6%16%36%26%8%
450
21st to endDay
9%5%23%37%21%5%
495
November1st to 10thDay
9%7%26%34%20%4
455
11th to 20thDay
13%8%27%35%14%3
460
21st to endDay
8%11%36%31%12%1
295
December1st to 10thDay
7%12%37%27%13%4
270
11th to 20thDay
13%12%36%29%10%1
270
21st to endDay
9%11%35%34%9%2
297
January1st to 10thNight
13%13%32%32%10%
760
11th to 20thNight
12%10%28%39%12%1
736
21st to endNight
15%14%34%31%6%
792
February1st to 10thNight
14%10%32%31%13%
720
11th to 20thNight
9%12%30%38%10%1
703
21st to endNight
10%10%36%36%9%
592
March1st to 10thNight
6%9%40%34%11%
720
11th to 20thNight
9%9%32%36%13%
720
21st to endNight
7%10%36%36%11%
792
April1st to 10thNight
8%9%34%38%12%
720
11th to 20thNight
9%9%36%34%11%1
711
21st to endNight
7%6%30%39%17%
699
May1st to 10thNight
6%320%44%24%2
540
11th to 20thNight
6%319%41%28%3
531
21st to endNight
6%314%36%35%7%
584
June1st to 10thNight
11%113%30%35%9%
540
11th to 20thNight
7%16%25%40%21%
540
21st to endNight
8%17%18%42%24%
540
July1st to 10thNight
8%414%43%30%
525
11th to 20thNight
41314%46%32%
522
21st to endNight
5%15%13%50%26%
591
August1st to 10thNight
5%15%12%50%28%
537
11th to 20thNight
6%15%9%47%33%
534
21st to endNight
12%111%19%36%22%
774
September1st to 10thNight
8%19%24%38%19%
720
11th to 20thNight
11%114%27%35%12%
720
21st to endNight
11%213%29%38%7%
720
October1st to 10thNight
13%322%38%21%3
720
11th to 20thNight
6%5%19%38%30%2
720
21st to endNight
11%5%24%36%22%2
792
November1st to 10thNight
9%5%30%34%19%3
740
11th to 20thNight
11%6%29%38%14%2
760
21st to endNight
9%7%32%39%13%1
760
December1st to 10thNight
10%8%29%33%19%1
760
11th to 20thNight
10%10%27%37%15%1
760
21st to endNight
12%9%29%34%14%1
836
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Copyright 2024 Attilla Danko


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