Oak Beach Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Oak Beach 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
35%
23858
9%
74915
6%
23803
38%
23803
10%
61389

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
16%
949
5%
2648
1%
946
20%
946
6%
2353
January11th to 20thNight
19%
906
3%
2535
1%
906
21%
906
5%
2317
January21st to endNight
21%
882
5%
2664
2%
882
24%
882
7%
2308
February1st to 10thNight
19%
720
6%
2340
2%
720
23%
720
7%
1986
February11th to 20thNight
23%
701
6%
2192
2%
699
27%
699
7%
1875
February21st to endNight
21%
592
8%
1776
2%
592
27%
592
7%
1513
March1st to 10thNight
29%
720
11%
2118
6%
720
34%
720
11%
1704
March11th to 20thNight
30%
720
13%
1980
7%
720
35%
720
13%
1585
March21st to endNight
34%
792
9%
2178
6%
792
37%
792
12%
1797
April1st to 10thNight
32%
622
10%
1882
6%
622
36%
622
13%
1481
April11th to 20thNight
40%
533
15%
1597
9%
533
44%
533
14%
1226
April21st to endNight
41%
540
12%
1620
8%
540
45%
540
13%
1282
May1st to 10thNight
47%
540
10%
1620
8%
540
49%
540
13%
1279
May11th to 20thNight
48%
531
13%
1593
13%
531
50%
531
13%
1233
May21st to endNight
59%
485
13%
1575
13%
484
63%
484
17%
1139
June1st to 10thNight
53%
360
11%
1260
12%
360
55%
360
12%
951
June11th to 20thNight
58%
360
13%
1260
15%
360
61%
360
15%
899
June21st to endNight
60%
360
11%
1260
13%
360
63%
360
13%
933
July1st to 10thNight
71%
435
12%
1310
12%
435
72%
435
19%
936
July11th to 20thNight
68%
522
11%
1392
11%
522
69%
522
19%
1050
July21st to endNight
65%
591
10%
1572
8%
558
65%
558
17%
1187
August1st to 10thNight
67%
537
10%
1600
8%
534
68%
534
17%
1186
August11th to 20thNight
64%
534
17%
1598
12%
534
68%
534
21%
1098
August21st to endNight
56%
594
14%
1782
11%
594
58%
594
17%
1297
September1st to 10thNight
56%
643
11%
1875
8%
643
58%
643
16%
1398
September11th to 20thNight
60%
720
17%
1980
12%
720
63%
720
19%
1497
September21st to endNight
47%
720
12%
1980
8%
720
50%
720
14%
1570
October1st to 10thNight
42%
720
12%
2052
10%
720
45%
720
15%
1607
October11th to 20thNight
29%
720
7%
2160
4%
720
32%
720
7%
1841
October21st to endNight
25%
792
6%
2536
4%
792
28%
792
6%
2183
November1st to 10thNight
32%
740
11%
2406
9%
740
35%
740
10%
1896
November11th to 20thNight
20%
760
8%
2522
6%
760
24%
760
6%
2170
November21st to endNight
17%
760
4%
2660
3%
760
19%
760
5%
2337
December1st to 10thNight
14%
769
3%
2669
1%
769
17%
769
3%
2425
December11th to 20thNight
13%
949
3%
3519
1%
949
16%
949
4%
3031
December21st to endNight
12%
1039
1%
5204
0%
1026
15%
1026
1%
4819

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%35%5%5%7%35%
74585
Night
15%11%5%8%6%35%45%6%31%
75108
TransparencyDay
32%39%9%13%7%1
74291
Night
35%38%8%12%6%1
74924
SeeingDay
16%7%24%30%18%5%
14232
Night
19%8%28%29%14%2
23869

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%14%8%12%8%46%5%45%18%
1517
11th to 20thDay
14%15%7%13%10%6%6%5%5%6%13%
1448
21st to endDay
14%14%7%12%8%45%6%7%5%18%
1690
February1st to 10thDay
13%14%6%11%8%46%5%47%21%
1620
11th to 20thDay
11%11%6%10%10%5%6%5%5%6%25%
1650
21st to endDay
14%11%5%7%8%45%5%7%7%27%
1480
March1st to 10thDay
13%10%39%9%46%5%5%7%29%
1841
11th to 20thDay
10%10%5%10%6%46%6%6%7%32%
1980
21st to endDay
17%10%48%7%45%45%6%31%
2178
April1st to 10thDay
16%10%5%7%6%345%6%8%31%
2093
11th to 20thDay
16%8%36%5%3445%7%38%
2311
21st to endDay
16%8%37%5%35%45%7%36%
2340
May1st to 10thDay
15%7%36%6%345%6%8%38%
2340
11th to 20thDay
14%6%36%6%45%45%7%40%
2301
21st to endDay
11%6%245%25%46%8%46%
2694
June1st to 10thDay
11%6%345%345%7%8%44%
2700
11th to 20thDay
10%5%345%35%47%9%45%
2700
21st to endDay
11%5%25%5%346%5%9%45%
2700
July1st to 10thDay
7%42432447%11%52%
2607
11th to 20thDay
8%425%5%35%6%6%9%47%
2520
21st to endDay
8%4245%35%6%7%10%46%
2649
August1st to 10thDay
9%5%35%5%36%5%6%10%44%
2327
11th to 20thDay
9%425%445%5%5%9%48%
2303
21st to endDay
11%6%35%4245%5%8%47%
2574
September1st to 10thDay
11%6%36%5%35%6%5%8%43%
2062
11th to 20thDay
14%6%243335%5%8%46%
1980
21st to endDay
14%6%36%6%36%6%6%8%36%
1980
October1st to 10thDay
16%9%36%7%34446%38%
1908
11th to 20thDay
22%12%37%5%445%47%27%
1800
21st to endDay
23%11%47%7%45%5%5%7%22%
1818
November1st to 10thDay
13%13%47%7%5%5%46%8%29%
1672
11th to 20thDay
15%15%6%9%7%46%5%5%8%21%
1656
21st to endDay
17%18%6%12%8%45%436%18%
1520
December1st to 10thDay
12%20%10%13%9%5%5%44414%
1506
11th to 20thDay
14%17%6%11%9%5%5%5%5%5%18%
1675
21st to endDay
25%21%7%11%7%35%4349%
2445
January1st to 10thNight
16%12%7%12%8%35%5%5%6%20%
2648
11th to 20thNight
17%15%7%11%9%5%5%45%6%17%
2535
21st to endNight
11%13%7%12%9%5%5%5%5%6%21%
2664
February1st to 10thNight
14%14%7%10%7%45%5%6%6%21%
2340
11th to 20thNight
15%14%5%10%7%35%45%6%27%
2192
21st to endNight
16%14%6%9%7%345%45%27%
1776
March1st to 10thNight
12%11%6%7%6%44445%37%
2118
11th to 20thNight
12%10%48%7%345%46%36%
1980
21st to endNight
18%11%5%7%6%35%345%33%
2178
April1st to 10thNight
18%11%5%5%5%345%47%34%
1882
11th to 20thNight
18%7%35%5%345%5%9%38%
1597
21st to endNight
17%9%36%6%4445%6%35%
1620
May1st to 10thNight
12%8%46%5%4446%8%37%
1620
11th to 20thNight
16%7%36%5%45%45%7%38%
1592
21st to endNight
10%5%25%435%46%7%49%
1574
June1st to 10thNight
13%6%35%5%345%5%9%42%
1260
11th to 20thNight
10%6%245%35%5%6%8%45%
1260
21st to endNight
8%6%36%5%35%5%6%8%45%
1260
July1st to 10thNight
6%42443445%8%55%
1349
11th to 20thNight
8%4235%35%6%6%10%48%
1440
21st to endNight
8%5%25%6%345%6%9%48%
1665
August1st to 10thNight
8%4245%345%7%11%47%
1611
11th to 20thNight
9%415%5%245%6%10%50%
1598
21st to endNight
10%5%36%435%47%7%47%
1782
September1st to 10thNight
11%5%27%5%3445%8%45%
1875
11th to 20thNight
12%5%25%42446%7%49%
1980
21st to endNight
15%7%36%6%2445%7%41%
1980
October1st to 10thNight
17%7%26%6%25%447%40%
2052
11th to 20thNight
22%11%47%6%35%346%30%
2160
21st to endNight
24%12%48%6%34446%23%
2536
November1st to 10thNight
15%12%48%5%35%446%34%
2406
11th to 20thNight
15%14%7%11%8%45%5%5%5%21%
2522
21st to endNight
21%17%6%10%6%44445%20%
2660
December1st to 10thNight
18%16%9%12%6%35%45%5%16%
2669
11th to 20thNight
14%15%7%12%9%5%5%6%5%6%16%
3522
21st to endNight
24%21%8%9%7%3444411%
5205

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
44%42%7%6%1
1518
11th to 20thDay
43%44%6%5%2
1448
21st to endDay
42%40%8%6%21
1690
February1st to 10thDay
40%38%8%11%2
1620
11th to 20thDay
39%40%8%9%41
1659
21st to endDay
39%38%8%12%3
1480
March1st to 10thDay
36%39%8%12%5%
1841
11th to 20thDay
35%39%7%13%5%2
1980
21st to endDay
36%37%9%13%41
2178
April1st to 10thDay
34%38%9%12%7%1
2093
11th to 20thDay
29%37%9%13%11%1
2311
21st to endDay
32%38%10%11%8%1
2340
May1st to 10thDay
28%38%8%15%10%1
2340
11th to 20thDay
27%38%6%14%12%2
2305
21st to endDay
24%39%10%14%11%2
2694
June1st to 10thDay
24%39%10%17%9%1
2700
11th to 20thDay
20%38%9%19%14%1
2700
21st to endDay
23%39%10%18%9%1
2700
July1st to 10thDay
19%39%10%20%11%1
2538
11th to 20thDay
21%40%9%17%10%2
2445
21st to endDay
22%40%11%16%10%1
2502
August1st to 10thDay
25%39%10%18%7%1
2314
11th to 20thDay
18%38%11%20%11%2
2303
21st to endDay
23%38%9%20%9%1
2574
September1st to 10thDay
25%39%8%19%8%1
2062
11th to 20thDay
24%39%11%20%6%
1980
21st to endDay
31%38%10%15%6%
1980
October1st to 10thDay
30%38%7%17%7%1
1908
11th to 20thDay
39%38%8%11%4
1800
21st to endDay
39%40%9%8%3
1818
November1st to 10thDay
32%44%7%12%5%
1672
11th to 20thDay
36%42%9%8%5%
1656
21st to endDay
43%41%7%8%1
1520
December1st to 10thDay
47%42%7%41
1506
11th to 20thDay
45%35%9%9%1
1671
21st to endDay
67%26%42
2445
January1st to 10thNight
42%41%6%10%1
2648
11th to 20thNight
43%43%7%5%1
2535
21st to endNight
41%39%9%9%3
2664
February1st to 10thNight
40%38%7%11%3
2340
11th to 20thNight
40%38%8%9%41
2194
21st to endNight
41%37%7%11%3
1776
March1st to 10thNight
33%37%8%16%5%1
2118
11th to 20thNight
32%37%8%13%8%1
1980
21st to endNight
36%36%8%14%5%1
2178
April1st to 10thNight
32%36%7%15%9%1
1882
11th to 20thNight
29%36%7%14%13%1
1597
21st to endNight
32%37%6%12%11%2
1620
May1st to 10thNight
30%38%6%14%11%1
1620
11th to 20thNight
30%37%5%13%12%4
1593
21st to endNight
21%39%9%16%12%3
1575
June1st to 10thNight
28%38%7%15%10%1
1260
11th to 20thNight
22%39%8%14%16%1
1260
21st to endNight
26%38%10%14%11%2
1260
July1st to 10thNight
20%37%8%18%16%1
1310
11th to 20thNight
20%41%10%17%11%1
1392
21st to endNight
22%41%11%15%9%2
1572
August1st to 10thNight
21%40%11%21%7%
1600
11th to 20thNight
17%36%11%20%13%2
1598
21st to endNight
22%38%9%20%10%2
1782
September1st to 10thNight
25%37%7%19%11%1
1875
11th to 20thNight
23%38%8%24%7%
1980
21st to endNight
30%38%9%17%7%1
1980
October1st to 10thNight
29%38%8%16%9%
2052
11th to 20thNight
40%38%6%11%5%
2160
21st to endNight
42%38%8%8%4
2536
November1st to 10thNight
27%43%8%16%6%1
2406
11th to 20thNight
39%41%8%9%3
2522
21st to endNight
41%42%8%9%
2660
December1st to 10thNight
46%41%6%6%1
2669
11th to 20thNight
45%36%11%6%1
3525
21st to endNight
62%29%6%3
5205

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
16%14%39%21%8%1
270
11th to 20thDay
21%9%36%23%10%
243
21st to endDay
23%6%35%27%8%2
264
February1st to 10thDay
23%12%43%20%3
240
11th to 20thDay
17%14%41%24%4
240
21st to endDay
19%16%41%21%3
198
March1st to 10thDay
17%14%34%27%7%1
281
11th to 20thDay
15%12%31%31%9%2
420
21st to endDay
21%11%28%31%8%2
462
April1st to 10thDay
20%8%31%30%10%1
420
11th to 20thDay
21%11%22%27%13%5%
412
21st to endDay
20%6%30%30%12%2
420
May1st to 10thDay
16%7%29%31%13%3
423
11th to 20thDay
15%424%30%21%6%
447
21st to endDay
12%319%32%27%8%
552
June1st to 10thDay
12%319%38%23%4
630
11th to 20thDay
12%220%38%21%6%
630
21st to endDay
11%319%40%22%5%
630
July1st to 10thDay
8%212%35%33%10%
621
11th to 20thDay
11%315%39%24%8%
618
21st to endDay
8%215%42%27%7%
590
August1st to 10thDay
11%213%33%29%12%
446
11th to 20thDay
10%210%31%35%12%
439
21st to endDay
14%417%28%29%7%
495
September1st to 10thDay
12%421%30%23%10%
450
11th to 20thDay
13%417%26%28%12%
450
21st to endDay
17%6%23%20%24%10%
450
October1st to 10thDay
20%8%24%24%18%6%
450
11th to 20thDay
25%12%29%25%7%1
450
21st to endDay
30%12%27%25%5%1
333
November1st to 10thDay
18%9%34%25%12%1
270
11th to 20thDay
19%17%35%22%5%2
244
21st to endDay
24%16%37%21%2
180
December1st to 10thDay
21%17%36%24%3
180
11th to 20thDay
25%21%32%18%31
180
21st to endDay
27%16%37%17%2
204
January1st to 10thNight
21%12%36%23%6%1
950
11th to 20thNight
22%12%35%23%7%1
906
21st to endNight
18%7%38%27%9%
882
February1st to 10thNight
21%8%39%27%4
720
11th to 20thNight
22%9%36%27%7%
703
21st to endNight
22%11%38%25%4
592
March1st to 10thNight
17%8%36%29%11%
720
11th to 20thNight
17%9%36%28%8%1
720
21st to endNight
21%9%28%29%11%1
792
April1st to 10thNight
21%9%31%29%10%
622
11th to 20thNight
21%6%28%30%13%3
533
21st to endNight
21%5%23%35%14%1
540
May1st to 10thNight
15%424%41%14%3
540
11th to 20thNight
18%420%35%22%2
531
21st to endNight
14%217%35%29%3
486
June1st to 10thNight
14%219%39%23%2
360
11th to 20thNight
11%319%39%25%2
360
21st to endNight
10%320%38%25%4
360
July1st to 10thNight
7%213%44%31%3
435
11th to 20thNight
9%315%38%28%8%
522
21st to endNight
8%214%46%27%3
591
August1st to 10thNight
11%112%38%33%5%
537
11th to 20thNight
10%215%30%35%8%
534
21st to endNight
13%318%31%31%5%
594
September1st to 10thNight
12%419%34%23%8%
643
11th to 20thNight
14%218%31%27%8%
720
21st to endNight
17%7%22%27%20%8%
720
October1st to 10thNight
20%6%27%27%18%3
720
11th to 20thNight
29%12%25%25%9%
720
21st to endNight
31%11%26%25%5%1
792
November1st to 10thNight
23%12%28%25%11%1
740
11th to 20thNight
23%13%35%20%8%
760
21st to endNight
30%13%32%20%4
760
December1st to 10thNight
28%15%34%17%6%
769
11th to 20thNight
24%15%37%20%31
950
21st to endNight
28%13%36%20%2
1045
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