Alapaha River Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Alapaha River 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
53%
24086
22%
74389
16%
24029
60%
24029
28%
46300

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
31%
759
22%
2458
9%
757
47%
757
23%
1524
January11th to 20thNight
41%
720
27%
2340
18%
720
53%
720
28%
1360
January21st to endNight
29%
792
24%
2485
11%
792
44%
792
23%
1589
February1st to 10thNight
37%
720
22%
2160
13%
720
47%
720
27%
1354
February11th to 20thNight
36%
703
23%
2098
10%
699
49%
699
27%
1322
February21st to endNight
38%
592
27%
1776
15%
592
49%
592
30%
1088
March1st to 10thNight
46%
720
30%
2026
18%
720
55%
720
36%
1199
March11th to 20thNight
42%
720
25%
1980
14%
720
51%
720
32%
1233
March21st to endNight
42%
792
25%
2178
11%
792
53%
792
34%
1311
April1st to 10thNight
46%
720
25%
1980
15%
720
53%
720
33%
1206
April11th to 20thNight
48%
663
24%
1905
16%
663
55%
663
34%
1133
April21st to endNight
58%
540
34%
1640
24%
540
67%
540
41%
881
May1st to 10thNight
59%
540
28%
1620
19%
540
67%
540
40%
877
May11th to 20thNight
63%
531
18%
1592
13%
531
67%
531
32%
992
May21st to endNight
69%
582
21%
1744
17%
582
71%
582
31%
1076
June1st to 10thNight
67%
540
14%
1620
12%
540
68%
540
26%
1080
June11th to 20thNight
76%
540
15%
1620
12%
540
77%
540
30%
1041
June21st to endNight
74%
540
13%
1620
11%
540
75%
540
24%
1105
July1st to 10thNight
69%
525
10%
1575
9%
525
70%
525
21%
1122
July11th to 20thNight
73%
522
11%
1566
11%
522
73%
522
23%
1077
July21st to endNight
80%
591
14%
1672
14%
558
80%
558
29%
1090
August1st to 10thNight
72%
537
9%
1600
9%
534
72%
534
22%
1128
August11th to 20thNight
71%
534
11%
1728
12%
534
71%
534
19%
1222
August21st to endNight
65%
661
13%
2047
14%
661
65%
661
18%
1488
September1st to 10thNight
63%
720
15%
1980
14%
720
63%
720
22%
1412
September11th to 20thNight
62%
720
15%
1980
14%
720
62%
720
24%
1379
September21st to endNight
63%
720
23%
1980
20%
720
66%
720
31%
1270
October1st to 10thNight
59%
720
28%
1980
24%
720
64%
720
38%
1179
October11th to 20thNight
60%
720
33%
2108
29%
720
67%
720
38%
1179
October21st to endNight
57%
792
30%
2376
27%
792
64%
792
36%
1349
November1st to 10thNight
54%
740
29%
2221
23%
740
62%
740
36%
1260
November11th to 20thNight
46%
760
27%
2459
21%
760
57%
760
32%
1389
November21st to endNight
45%
760
26%
2470
19%
760
55%
760
31%
1425
December1st to 10thNight
42%
760
24%
2470
17%
760
53%
760
27%
1487
December11th to 20thNight
39%
759
25%
2914
16%
758
50%
758
23%
1706
December21st to endNight
39%
831
15%
4421
17%
817
47%
817
13%
2767

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
10%6%25%6%45%5%6%8%42%
74842
Night
10%5%25%5%35%5%6%8%45%
74837
TransparencyDay
38%8%12%18%17%6%
74565
Night
36%7%12%18%18%8%
74633
SeeingDay
12%6%20%24%23%15%
14002
Night
12%5%22%33%24%4
24095

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
12%6%25%5%4437%7%43%
1697
11th to 20thDay
10%5%25%5%2446%8%48%
1620
21st to endDay
16%7%35%424446%45%
1868
February1st to 10thDay
16%7%36%6%24447%41%
1800
11th to 20thDay
15%5%2443346%6%47%
1748
21st to endDay
15%6%345%3445%7%45%
1480
March1st to 10thDay
10%6%25%43445%7%52%
1933
11th to 20thDay
11%7%25%5%35%5%6%8%44%
1980
21st to endDay
12%5%24435%5%46%49%
2178
April1st to 10thDay
11%425%5%35%5%6%6%48%
1980
11th to 20thDay
12%5%245%345%6%7%48%
2017
21st to endDay
7%3244245%5%6%57%
2317
May1st to 10thDay
6%323435%5%6%8%56%
2340
11th to 20thDay
8%5%36%6%35%6%7%9%42%
2301
21st to endDay
8%426%8%46%6%6%10%41%
2531
June1st to 10thDay
10%5%36%6%5%6%8%8%11%32%
2340
11th to 20thDay
5%426%7%5%7%7%7%11%39%
2340
21st to endDay
7%5%36%7%5%8%8%9%11%30%
2340
July1st to 10thDay
7%5%36%8%6%7%9%9%11%29%
2340
11th to 20thDay
7%6%27%8%6%7%8%8%10%29%
2340
21st to endDay
7%5%26%8%5%7%8%9%11%31%
2547
August1st to 10thDay
9%6%37%8%5%9%7%7%13%26%
2327
11th to 20thDay
9%7%38%8%5%7%8%9%10%26%
2169
21st to endDay
11%7%38%9%47%6%8%8%28%
2288
September1st to 10thDay
8%7%37%8%46%7%8%10%31%
1980
11th to 20thDay
11%6%36%7%46%6%6%9%34%
1980
21st to endDay
10%5%25%6%46%5%6%8%43%
1980
October1st to 10thDay
12%5%25%42445%7%50%
1980
11th to 20thDay
9%414434447%56%
1850
21st to endDay
9%4245%3445%6%54%
1980
November1st to 10thDay
10%43443445%6%55%
1857
11th to 20thDay
11%5%2433344456%
1717
21st to endDay
12%6%3442445%6%49%
1710
December1st to 10thDay
13%6%25%6%345%5%6%45%
1710
11th to 20thDay
17%6%2443445%7%44%
2153
21st to endDay
18%10%35%5%24435%42%
3124
January1st to 10thNight
13%6%26%5%345%47%44%
2458
11th to 20thNight
11%6%345%3445%7%49%
2340
21st to endNight
17%6%35%4345%46%43%
2485
February1st to 10thNight
15%6%3443445%8%44%
2160
11th to 20thNight
15%6%25%6%245%45%47%
2098
21st to endNight
13%5%25%435%5%5%6%48%
1776
March1st to 10thNight
12%42443345%7%53%
2026
11th to 20thNight
12%6%35%42445%8%48%
1980
21st to endNight
8%6%245%2445%7%53%
2178
April1st to 10thNight
11%4245%36%448%50%
1980
11th to 20thNight
7%5%345%35%5%5%8%50%
1905
21st to endNight
6%3144345%5%7%59%
1640
May1st to 10thNight
6%32442446%9%56%
1620
11th to 20thNight
6%425%6%35%7%7%9%46%
1592
21st to endNight
6%426%6%36%6%5%10%45%
1744
June1st to 10thNight
8%435%7%46%6%10%11%35%
1620
11th to 20thNight
6%325%5%46%8%8%12%41%
1620
21st to endNight
6%426%6%5%8%9%9%11%34%
1620
July1st to 10thNight
8%5%35%8%48%8%9%13%30%
1620
11th to 20thNight
6%5%36%7%47%7%10%12%33%
1620
21st to endNight
5%425%6%47%7%9%13%38%
1771
August1st to 10thNight
5%5%27%7%47%8%10%13%33%
1611
11th to 20thNight
7%6%37%6%46%7%9%14%30%
1728
21st to endNight
8%7%37%7%5%7%7%8%10%31%
2047
September1st to 10thNight
9%7%48%7%45%7%7%12%31%
1980
11th to 20thNight
11%6%36%6%46%6%7%9%37%
1980
21st to endNight
9%6%36%6%45%5%6%8%43%
1980
October1st to 10thNight
9%6%25%43345%7%53%
1980
11th to 20thNight
10%42442335%6%58%
2108
21st to endNight
8%5%244345%5%5%55%
2376
November1st to 10thNight
10%5%2342435%6%55%
2221
11th to 20thNight
12%5%24423446%53%
2459
21st to endNight
12%6%3442446%8%48%
2470
December1st to 10thNight
12%5%35%435%45%8%46%
2470
11th to 20thNight
15%6%35%423345%50%
3042
21st to endNight
17%8%36%5%35%446%38%
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
40%5%8%18%19%10%
1698
11th to 20thDay
34%49%20%24%9%
1620
21st to endDay
42%46%17%22%9%
1868
February1st to 10thDay
44%5%7%15%20%9%
1800
11th to 20thDay
38%46%15%27%9%
1758
21st to endDay
39%6%7%19%18%12%
1480
March1st to 10thDay
31%5%8%20%24%12%
1933
11th to 20thDay
38%7%13%16%18%9%
1980
21st to endDay
35%7%10%21%20%8%
2178
April1st to 10thDay
36%6%9%20%18%11%
1980
11th to 20thDay
35%6%7%19%23%9%
2017
21st to endDay
27%5%10%27%23%8%
2317
May1st to 10thDay
26%6%11%25%25%8%
2340
11th to 20thDay
35%9%17%20%15%4
2305
21st to endDay
38%8%12%21%18%3
2531
June1st to 10thDay
43%10%16%19%11%1
2340
11th to 20thDay
36%11%17%22%13%1
2340
21st to endDay
42%14%20%15%8%2
2340
July1st to 10thDay
42%16%22%14%5%1
2275
11th to 20thDay
45%14%21%14%5%1
2271
21st to endDay
40%14%21%20%4
2405
August1st to 10thDay
46%13%20%17%3
2314
11th to 20thDay
47%14%20%14%4
2169
21st to endDay
50%11%18%15%5%1
2288
September1st to 10thDay
44%12%13%17%11%2
1980
11th to 20thDay
46%9%14%14%14%3
1980
21st to endDay
38%7%11%20%19%6%
1980
October1st to 10thDay
34%6%10%16%24%11%
1980
11th to 20thDay
29%47%21%30%9%
1850
21st to endDay
31%47%16%27%16%
1980
November1st to 10thDay
30%5%8%16%25%16%
1857
11th to 20thDay
32%47%17%25%15%
1717
21st to endDay
36%5%8%18%24%10%
1710
December1st to 10thDay
39%6%10%17%19%9%
1710
11th to 20thDay
41%38%15%25%8%
2150
21st to endDay
46%45%16%24%6%
3124
January1st to 10thNight
40%5%7%16%21%10%
2458
11th to 20thNight
35%48%15%28%10%
2340
21st to endNight
42%5%6%15%22%11%
2485
February1st to 10thNight
39%5%8%17%20%11%
2160
11th to 20thNight
39%5%7%14%20%15%
2099
21st to endNight
36%6%7%21%16%15%
1776
March1st to 10thNight
31%5%8%21%21%14%
2026
11th to 20thNight
35%6%11%18%18%11%
1980
21st to endNight
31%6%12%20%21%11%
2178
April1st to 10thNight
32%6%11%17%20%13%
1980
11th to 20thNight
32%6%9%18%24%10%
1905
21st to endNight
25%6%11%25%24%9%
1640
May1st to 10thNight
24%7%10%24%23%12%
1620
11th to 20thNight
32%9%18%18%16%6%
1593
21st to endNight
34%9%14%22%19%4
1745
June1st to 10thNight
38%11%20%18%12%1
1620
11th to 20thNight
31%14%23%21%10%1
1620
21st to endNight
38%14%22%18%7%2
1620
July1st to 10thNight
40%16%23%15%5%1
1575
11th to 20thNight
39%13%25%16%5%1
1566
21st to endNight
32%14%27%23%31
1672
August1st to 10thNight
37%17%25%17%3
1600
11th to 20thNight
40%17%23%16%5%
1728
21st to endNight
45%14%18%16%42
2047
September1st to 10thNight
44%12%16%15%12%2
1980
11th to 20thNight
42%11%14%15%15%3
1980
21st to endNight
37%7%14%17%18%6%
1980
October1st to 10thNight
31%5%12%20%19%13%
1980
11th to 20thNight
29%5%7%21%28%10%
2108
21st to endNight
31%5%7%15%25%18%
2376
November1st to 10thNight
31%47%17%24%16%
2221
11th to 20thNight
33%47%15%26%15%
2459
21st to endNight
34%5%9%20%20%12%
2470
December1st to 10thNight
37%5%13%15%21%8%
2470
11th to 20thNight
38%47%15%25%10%
3044
21st to endNight
48%47%16%21%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
13%19%40%22%41
267
11th to 20thDay
13%13%30%32%8%4
240
21st to endDay
24%16%42%13%5%
264
February1st to 10thDay
20%15%37%20%7%1
240
11th to 20thDay
21%10%40%23%5%1
240
21st to endDay
14%16%40%24%5%2
198
March1st to 10thDay
13%10%34%29%13%1
373
11th to 20thDay
16%10%34%28%11%1
420
21st to endDay
13%13%31%27%14%1
462
April1st to 10thDay
16%12%25%27%17%2
420
11th to 20thDay
12%12%26%25%17%7%
412
21st to endDay
8%7%23%32%22%9%
420
May1st to 10thDay
7%9%23%29%22%10%
423
11th to 20thDay
10%215%30%29%16%
447
21st to endDay
11%29%23%31%24%
485
June1st to 10thDay
11%210%26%29%24%
450
11th to 20thDay
6%212%22%28%29%
450
21st to endDay
6%39%20%31%31%
450
July1st to 10thDay
7%15%17%31%38%
445
11th to 20thDay
7%15%11%32%43%
444
21st to endDay
8%6%16%37%33%
488
August1st to 10thDay
11%17%18%32%32%
446
11th to 20thDay
8%15%13%35%38%
439
21st to endDay
11%210%18%34%26%
495
September1st to 10thDay
10%211%20%31%25%
450
11th to 20thDay
12%28%32%30%15%
450
21st to endDay
12%210%22%32%21%
450
October1st to 10thDay
13%324%30%22%8%
450
11th to 20thDay
10%418%30%29%11%
450
21st to endDay
10%7%22%33%23%4
495
November1st to 10thDay
15%422%32%20%7%
455
11th to 20thDay
16%8%37%25%10%3
277
21st to endDay
10%13%30%32%12%3
270
December1st to 10thDay
15%14%32%24%13%2
270
11th to 20thDay
19%13%37%23%8%1
270
21st to endDay
19%12%31%25%11%2
297
January1st to 10thNight
16%12%35%30%6%1
760
11th to 20thNight
13%10%29%33%13%
720
21st to endNight
19%9%38%27%6%
792
February1st to 10thNight
19%8%32%33%8%
720
11th to 20thNight
17%9%33%35%6%
703
21st to endNight
15%8%34%38%5%
592
March1st to 10thNight
13%8%30%41%9%
720
11th to 20thNight
13%7%33%32%13%1
720
21st to endNight
11%9%34%34%12%1
792
April1st to 10thNight
13%8%29%36%14%1
720
11th to 20thNight
8%10%29%37%15%1
663
21st to endNight
6%5%27%39%23%1
540
May1st to 10thNight
6%5%25%40%21%2
540
11th to 20thNight
7%320%41%24%5%
531
21st to endNight
8%111%36%38%6%
584
June1st to 10thNight
9%19%40%36%5%
540
11th to 20thNight
7%28%33%36%14%
540
21st to endNight
6%16%32%44%10%
540
July1st to 10thNight
7%16%25%44%17%
525
11th to 20thNight
7%420%49%20%
522
21st to endNight
5%1425%53%12%
591
August1st to 10thNight
9%427%48%12%
537
11th to 20thNight
9%1419%51%16%
534
21st to endNight
11%17%27%38%15%
661
September1st to 10thNight
11%210%24%43%11%
720
11th to 20thNight
13%110%32%38%5%
720
21st to endNight
11%213%32%38%4
720
October1st to 10thNight
13%218%35%28%4
720
11th to 20thNight
12%317%37%27%4
720
21st to endNight
10%5%23%35%25%1
792
November1st to 10thNight
12%6%21%39%20%2
740
11th to 20thNight
14%8%28%34%16%1
760
21st to endNight
14%7%29%35%15%
760
December1st to 10thNight
15%7%30%31%16%1
760
11th to 20thNight
17%7%30%31%14%1
760
21st to endNight
20%8%26%34%11%
836
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