Cottageville Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cottageville 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
46%
24474
21%
74353
14%
24417
54%
24417
26%
46675

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
29%
760
22%
2459
10%
757
44%
757
22%
1502
January11th to 20thNight
34%
728
25%
2365
14%
728
49%
728
23%
1450
January21st to endNight
23%
792
24%
2574
11%
792
41%
792
22%
1606
February1st to 10thNight
29%
720
20%
2340
10%
720
43%
720
22%
1466
February11th to 20thNight
25%
703
20%
2098
8%
699
39%
699
22%
1348
February21st to endNight
25%
592
24%
1664
9%
592
38%
592
25%
1076
March1st to 10thNight
32%
720
28%
1980
16%
720
43%
720
32%
1219
March11th to 20thNight
32%
720
22%
1980
11%
720
42%
720
27%
1260
March21st to endNight
32%
792
22%
2178
9%
792
43%
792
29%
1358
April1st to 10thNight
35%
720
24%
1980
13%
720
43%
720
32%
1195
April11th to 20thNight
38%
711
26%
1777
13%
711
45%
711
36%
1117
April21st to endNight
43%
720
28%
1800
14%
720
49%
720
39%
1090
May1st to 10thNight
49%
545
23%
1625
13%
545
56%
545
37%
913
May11th to 20thNight
53%
531
17%
1593
10%
531
57%
531
31%
977
May21st to endNight
60%
582
19%
1745
13%
582
65%
582
30%
1087
June1st to 10thNight
58%
540
14%
1620
11%
540
60%
540
26%
1075
June11th to 20thNight
68%
540
13%
1620
10%
540
70%
540
28%
1041
June21st to endNight
65%
540
12%
1620
8%
540
68%
540
24%
1072
July1st to 10thNight
69%
525
12%
1575
11%
525
70%
525
25%
1047
July11th to 20thNight
67%
522
10%
1566
8%
522
67%
522
23%
1070
July21st to endNight
71%
591
12%
1672
9%
558
74%
558
26%
1104
August1st to 10thNight
71%
537
12%
1600
11%
534
71%
534
23%
1089
August11th to 20thNight
66%
550
11%
1614
9%
550
67%
550
19%
1173
August21st to endNight
61%
792
14%
1980
11%
792
62%
792
22%
1482
September1st to 10thNight
66%
720
17%
1943
14%
720
67%
720
27%
1308
September11th to 20thNight
60%
720
17%
1980
16%
720
62%
720
26%
1347
September21st to endNight
55%
720
17%
1980
15%
720
57%
720
26%
1354
October1st to 10thNight
53%
720
26%
2105
23%
720
59%
720
32%
1284
October11th to 20thNight
54%
720
31%
2160
26%
720
64%
720
37%
1207
October21st to endNight
50%
792
31%
2376
24%
792
60%
792
35%
1355
November1st to 10thNight
49%
740
29%
2221
21%
740
60%
740
36%
1261
November11th to 20thNight
40%
760
29%
2284
18%
760
53%
760
30%
1369
November21st to endNight
41%
760
25%
2470
17%
760
52%
760
27%
1467
December1st to 10thNight
35%
760
23%
2470
15%
760
47%
760
22%
1585
December11th to 20thNight
37%
759
25%
2932
16%
758
48%
758
21%
1718
December21st to endNight
31%
830
15%
4407
13%
817
43%
817
13%
2603

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
12%6%36%6%45%5%6%8%40%
74933
Night
11%6%35%5%35%5%6%8%44%
74795
TransparencyDay
40%7%13%18%16%6%
74656
Night
37%8%13%19%17%6%
74591
SeeingDay
14%11%26%25%17%7%
14341
Night
13%9%25%31%19%3
24483

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
13%5%35%5%445%6%7%44%
1706
11th to 20thDay
12%7%35%5%3445%8%45%
1635
21st to endDay
16%7%36%423336%46%
1782
February1st to 10thDay
16%6%34435%5%6%7%40%
1620
11th to 20thDay
18%6%25%42345%7%45%
1744
21st to endDay
16%6%35%43345%5%45%
1589
March1st to 10thDay
13%5%24323346%52%
1980
11th to 20thDay
13%5%35%5%3345%7%46%
1980
21st to endDay
12%6%25%6%35%5%5%6%44%
2178
April1st to 10thDay
9%4245%35%5%5%7%51%
1980
11th to 20thDay
11%5%26%5%35%45%8%46%
2129
21st to endDay
7%4244345%6%8%53%
2168
May1st to 10thDay
8%425%6%45%6%6%7%48%
2340
11th to 20thDay
10%6%36%7%45%6%7%8%39%
2301
21st to endDay
11%5%36%7%5%7%6%8%9%33%
2531
June1st to 10thDay
11%6%37%8%48%8%7%9%29%
2340
11th to 20thDay
8%426%7%48%7%8%12%33%
2340
21st to endDay
7%427%8%6%8%8%8%12%30%
2340
July1st to 10thDay
9%6%27%8%5%7%8%8%10%29%
2340
11th to 20thDay
8%5%38%8%5%8%8%8%11%26%
2340
21st to endDay
8%6%37%8%5%8%8%9%11%27%
2547
August1st to 10thDay
10%6%37%8%6%7%8%8%11%26%
2327
11th to 20thDay
10%6%38%10%6%8%8%8%10%23%
2267
21st to endDay
12%9%49%9%5%6%6%8%9%24%
2376
September1st to 10thDay
10%5%37%7%5%7%7%7%10%33%
2013
11th to 20thDay
14%7%36%7%46%6%6%7%33%
1980
21st to endDay
15%6%36%6%45%5%6%8%37%
1980
October1st to 10thDay
12%6%26%5%36%45%7%44%
1854
11th to 20thDay
10%415%43345%6%54%
1800
21st to endDay
10%5%24424445%55%
1980
November1st to 10thDay
12%5%2442345%6%54%
1857
11th to 20thDay
13%8%34333336%49%
1892
21st to endDay
14%5%235%23447%50%
1710
December1st to 10thDay
14%5%36%6%345%6%6%43%
1710
11th to 20thDay
16%5%25%323346%52%
2153
21st to endDay
18%9%35%433346%44%
3124
January1st to 10thNight
12%7%35%435%5%46%46%
2459
11th to 20thNight
12%7%35%5%3445%6%45%
2365
21st to endNight
16%7%36%42445%5%45%
2574
February1st to 10thNight
16%6%246%3446%6%42%
2340
11th to 20thNight
17%6%25%43445%6%44%
2098
21st to endNight
14%7%45%5%3445%7%43%
1664
March1st to 10thNight
10%5%35%435%5%6%8%48%
1980
11th to 20thNight
12%5%36%44446%8%45%
1980
21st to endNight
11%6%25%5%35%45%9%46%
2178
April1st to 10thNight
10%5%245%245%47%51%
1980
11th to 20thNight
12%3244335%5%9%50%
1777
21st to endNight
8%42443445%8%55%
1800
May1st to 10thNight
7%4344335%6%9%52%
1625
11th to 20thNight
8%6%33435%5%6%10%46%
1592
21st to endNight
9%425%5%45%6%7%9%44%
1744
June1st to 10thNight
9%6%46%6%35%6%7%13%35%
1620
11th to 20thNight
7%5%25%5%5%6%6%8%12%39%
1620
21st to endNight
6%425%6%47%7%10%13%35%
1620
July1st to 10thNight
7%5%35%7%36%7%9%13%35%
1620
11th to 20thNight
7%5%37%8%36%6%8%12%34%
1620
21st to endNight
5%437%6%48%8%7%13%35%
1771
August1st to 10thNight
6%6%26%7%47%8%9%14%32%
1611
11th to 20thNight
7%5%27%8%5%7%8%8%11%31%
1614
21st to endNight
10%7%37%6%47%7%8%10%32%
1980
September1st to 10thNight
8%426%7%46%6%7%11%40%
1943
11th to 20thNight
9%6%27%6%45%6%7%9%39%
1980
21st to endNight
15%7%35%435%5%7%8%38%
1980
October1st to 10thNight
13%6%35%334446%50%
2105
11th to 20thNight
11%42442435%6%56%
2160
21st to endNight
9%6%24433445%56%
2376
November1st to 10thNight
11%5%24423446%55%
2221
11th to 20thNight
14%7%2442335%5%51%
2284
21st to endNight
11%6%26%5%3445%8%47%
2470
December1st to 10thNight
14%6%35%5%3445%8%41%
2470
11th to 20thNight
18%5%24323445%49%
3042
21st to endNight
18%7%36%5%245%5%6%40%
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
39%6%9%19%21%6%
1707
11th to 20thDay
38%49%18%23%7%
1635
21st to endDay
41%36%19%23%8%
1782
February1st to 10thDay
41%6%10%19%18%6%
1620
11th to 20thDay
40%48%17%23%8%
1754
21st to endDay
41%49%19%17%10%
1589
March1st to 10thDay
34%49%20%19%14%
1980
11th to 20thDay
38%6%13%19%16%8%
1980
21st to endDay
40%5%11%18%19%7%
2178
April1st to 10thDay
32%5%13%20%22%9%
1980
11th to 20thDay
37%49%21%18%11%
2129
21st to endDay
28%6%11%28%22%5%
2168
May1st to 10thDay
33%6%12%22%20%7%
2340
11th to 20thDay
41%7%17%18%16%2
2305
21st to endDay
44%9%14%19%13%1
2531
June1st to 10thDay
48%10%17%15%11%
2340
11th to 20thDay
40%10%21%22%6%1
2340
21st to endDay
41%13%20%16%9%1
2340
July1st to 10thDay
44%12%20%16%6%2
2275
11th to 20thDay
46%13%22%13%5%
2271
21st to endDay
45%13%21%17%31
2405
August1st to 10thDay
47%11%20%17%4
2314
11th to 20thDay
51%13%17%15%3
2267
21st to endDay
53%11%16%13%6%1
2376
September1st to 10thDay
45%10%16%13%13%3
2013
11th to 20thDay
46%9%11%16%14%4
1980
21st to endDay
45%7%12%17%14%5%
1980
October1st to 10thDay
39%6%9%16%22%7%
1854
11th to 20thDay
31%5%9%22%25%9%
1800
21st to endDay
31%5%8%16%28%13%
1980
November1st to 10thDay
31%49%17%25%13%
1857
11th to 20thDay
37%47%17%22%13%
1892
21st to endDay
35%48%23%21%8%
1710
December1st to 10thDay
41%5%12%18%15%8%
1710
11th to 20thDay
34%47%21%25%8%
2150
21st to endDay
43%48%17%25%4
3124
January1st to 10thNight
38%5%9%19%21%8%
2459
11th to 20thNight
39%5%8%18%23%8%
2365
21st to endNight
41%5%6%17%22%9%
2574
February1st to 10thNight
42%49%17%19%9%
2340
11th to 20thNight
41%5%9%15%20%10%
2099
21st to endNight
41%5%11%18%14%11%
1664
March1st to 10thNight
34%6%9%19%21%12%
1980
11th to 20thNight
37%6%14%18%16%8%
1980
21st to endNight
36%5%15%20%17%7%
2178
April1st to 10thNight
33%5%13%19%21%9%
1980
11th to 20thNight
32%6%9%23%20%11%
1777
21st to endNight
28%6%12%27%22%5%
1800
May1st to 10thNight
28%6%16%23%21%5%
1625
11th to 20thNight
33%9%20%21%17%1
1593
21st to endNight
34%9%16%27%13%1
1745
June1st to 10thNight
38%11%22%20%9%
1620
11th to 20thNight
34%12%23%24%7%1
1620
21st to endNight
34%15%24%20%5%1
1620
July1st to 10thNight
36%14%23%19%6%2
1575
11th to 20thNight
38%15%25%15%7%1
1566
21st to endNight
34%14%26%22%3
1672
August1st to 10thNight
36%16%26%18%4
1600
11th to 20thNight
42%17%20%18%3
1614
21st to endNight
44%14%18%18%5%1
1980
September1st to 10thNight
36%12%19%18%11%3
1943
11th to 20thNight
39%11%15%18%14%3
1980
21st to endNight
42%8%14%18%15%2
1980
October1st to 10thNight
35%5%10%21%22%6%
2105
11th to 20thNight
28%6%10%22%24%10%
2160
21st to endNight
31%48%18%26%13%
2376
November1st to 10thNight
31%49%17%25%14%
2221
11th to 20thNight
36%47%17%23%13%
2284
21st to endNight
37%49%18%22%10%
2470
December1st to 10thNight
41%6%13%16%16%7%
2470
11th to 20thNight
37%5%7%16%27%7%
3044
21st to endNight
44%5%7%18%22%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
17%24%45%11%3
270
11th to 20thDay
14%20%41%17%7%1
245
21st to endDay
28%26%36%9%2
264
February1st to 10thDay
23%23%36%16%2
240
11th to 20thDay
28%27%36%7%2
240
21st to endDay
18%21%41%16%3
307
March1st to 10thDay
19%18%34%22%8%
420
11th to 20thDay
16%25%35%16%7%1
420
21st to endDay
15%19%38%18%9%1
462
April1st to 10thDay
18%19%34%19%9%1
420
11th to 20thDay
12%20%29%19%14%5%
412
21st to endDay
8%14%32%24%15%7%
420
May1st to 10thDay
9%17%35%20%12%6%
423
11th to 20thDay
11%6%29%27%19%9%
447
21st to endDay
12%420%32%20%12%
485
June1st to 10thDay
12%423%31%20%10%
450
11th to 20thDay
10%418%27%25%15%
450
21st to endDay
8%318%34%24%12%
450
July1st to 10thDay
8%211%30%32%16%
445
11th to 20thDay
8%111%31%33%16%
444
21st to endDay
6%314%37%30%11%
488
August1st to 10thDay
12%215%27%27%17%
446
11th to 20thDay
10%38%31%31%17%
439
21st to endDay
14%312%28%28%15%
495
September1st to 10thDay
10%215%30%28%14%
450
11th to 20thDay
16%416%36%20%8%
450
21st to endDay
18%120%31%22%9%
450
October1st to 10thDay
15%6%26%28%16%9%
450
11th to 20thDay
11%7%23%32%20%7%
450
21st to endDay
14%8%26%29%18%4
495
November1st to 10thDay
17%9%31%23%17%3
455
11th to 20thDay
19%13%36%20%10%2
452
21st to endDay
13%17%35%27%7%
270
December1st to 10thDay
18%19%36%21%6%1
270
11th to 20thDay
20%20%36%17%7%1
270
21st to endDay
27%17%31%18%7%1
297
January1st to 10thNight
15%17%34%28%7%
760
11th to 20thNight
16%14%31%29%9%
728
21st to endNight
20%17%36%24%3
792
February1st to 10thNight
18%15%34%27%5%
720
11th to 20thNight
19%17%35%25%4
703
21st to endNight
17%16%38%24%5%
592
March1st to 10thNight
13%13%39%29%7%
720
11th to 20thNight
16%13%36%27%7%
720
21st to endNight
13%16%34%28%8%
792
April1st to 10thNight
13%15%34%30%8%1
720
11th to 20thNight
13%12%32%28%14%1
711
21st to endNight
11%11%32%33%13%
720
May1st to 10thNight
7%8%30%38%17%
545
11th to 20thNight
10%426%36%20%2
531
21st to endNight
10%216%37%30%5%
584
June1st to 10thNight
10%120%42%23%4
540
11th to 20thNight
9%311%36%31%10%
540
21st to endNight
5%215%39%32%6%
540
July1st to 10thNight
7%211%41%32%7%
525
11th to 20thNight
9%17%34%42%7%
522
21st to endNight
5%28%41%38%6%
591
August1st to 10thNight
7%26%35%41%9%
537
11th to 20thNight
8%28%31%40%10%
550
21st to endNight
13%310%30%34%11%
792
September1st to 10thNight
8%211%33%39%7%
720
11th to 20thNight
12%313%36%31%6%
720
21st to endNight
18%314%31%29%5%
720
October1st to 10thNight
16%322%31%22%5%
720
11th to 20thNight
13%6%23%32%23%3
720
21st to endNight
12%8%26%32%21%3
792
November1st to 10thNight
13%8%26%33%18%3
740
11th to 20thNight
17%11%29%29%13%1
760
21st to endNight
14%10%29%28%17%1
760
December1st to 10thNight
18%11%29%31%11%
760
11th to 20thNight
19%11%28%29%12%1
760
21st to endNight
21%12%30%27%9%
836
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