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 2005-11-05 to 2017-09-17.

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
37%
15486
13%
46809
9%
15445
41%
15445
18%
33775

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 15thNight
16%
898
7%
2506
2%
895
21%
895
10%
2092
January16th to endNight
20%
888
9%
2616
4%
888
26%
888
12%
2095
February1st to 15thNight
19%
702
8%
2287
2%
701
24%
701
11%
1789
February16th to endNight
27%
631
12%
1898
5%
631
34%
631
14%
1442
March1st to 15thNight
29%
720
14%
2072
9%
720
33%
720
17%
1524
March16th to endNight
38%
768
17%
2112
10%
768
43%
768
22%
1504
April1st to 15thNight
35%
593
15%
1791
9%
593
40%
593
21%
1237
April16th to endNight
44%
540
18%
1620
12%
540
48%
540
24%
1076
May1st to 15thNight
48%
540
15%
1620
13%
540
50%
540
24%
1080
May16th to endNight
54%
496
16%
1570
15%
495
58%
495
28%
971
June1st to 15thNight
53%
360
14%
1260
16%
360
56%
360
24%
774
June16th to endNight
62%
360
15%
1260
16%
360
66%
360
27%
743
July1st to 15thNight
69%
450
16%
1300
17%
450
70%
450
38%
751
July16th to endNight
67%
564
14%
1473
12%
531
67%
531
34%
913
August1st to 15thNight
66%
539
17%
1609
16%
536
67%
536
33%
959
August16th to endNight
60%
573
22%
1719
16%
573
63%
573
32%
1028
September1st to 15thNight
56%
669
19%
1911
14%
669
59%
669
30%
1208
September16th to endNight
56%
665
20%
1837
15%
665
59%
665
30%
1188
October1st to 15thNight
40%
660
16%
1914
12%
660
45%
660
21%
1356
October16th to endNight
25%
704
9%
2210
6%
704
31%
704
12%
1710
November1st to 15thNight
30%
700
14%
2276
13%
700
33%
700
15%
1671
November16th to endNight
20%
720
7%
2493
5%
720
23%
720
8%
2031
December1st to 15thNight
13%
786
5%
2586
1%
786
16%
786
6%
2175
December16th to endNight
14%
960
7%
2869
1%
960
19%
960
7%
2458

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%8%36%5%35%5%5%7%35%
47958
Night
15%9%47%5%34446%32%
46984
Cloud CoverDay
13%8%36%6%35%5%5%7%34%
47968
Night
15%9%47%5%3445%6%32%
46988
TransparencyDay
47%7%13%20%10%1
47652
Night
52%5%12%19%9%
46809
SeeingDay
16%421%31%18%6%
5870
Night
20%6%27%28%14%2
15491

By Month

Percentage Cloud Cover NE (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 15thDay
16%13%7%9%8%46%6%35%17%
1432
16th to endDay
13%14%7%12%8%46%6%6%414%
1606
February1st to 15thDay
12%14%6%9%8%36%5%46%22%
1575
16th to endDay
13%8%5%7%8%37%5%6%6%26%
1572
March1st to 15thDay
14%9%38%7%46%6%36%28%
1876
16th to endDay
14%8%48%6%35%5%46%32%
2112
April1st to 15thDay
18%8%36%43345%7%34%
2167
16th to endDay
14%6%24435%36%7%40%
2340
May1st to 15thDay
16%6%245%3445%7%39%
2331
16th to endDay
11%5%25%5%34448%45%
2542
June1st to 15thDay
10%5%245%3446%8%43%
2700
16th to endDay
10%5%245%345%6%9%42%
2700
July1st to 15thDay
6%3143245%6%11%50%
2577
16th to endDay
8%3144345%7%9%46%
2592
August1st to 15thDay
8%415%5%25%5%6%9%45%
2340
16th to endDay
9%6%14423448%48%
2483
September1st to 15thDay
14%4244235%5%7%44%
2034
16th to endDay
14%6%244345%48%41%
1829
October1st to 15thDay
18%8%36%5%34336%36%
1716
16th to endDay
24%8%37%6%36%5%5%6%23%
1661
November1st to 15thDay
16%12%5%5%7%25%447%27%
1582
16th to endDay
16%15%5%11%8%45%44417%
1467
December1st to 15thDay
15%16%7%10%8%45%45%5%15%
1371
16th to endDay
19%15%7%10%8%445%45%13%
1353
January1st to 15thNight
20%12%6%9%8%45%45%6%17%
2506
16th to endNight
13%12%6%11%9%45%446%20%
2616
February1st to 15thNight
14%15%7%8%7%35%446%22%
2285
16th to endNight
15%12%49%7%245%5%6%25%
1898
March1st to 15thNight
13%11%5%8%5%34445%32%
2060
16th to endNight
15%9%46%5%35%345%36%
2112
April1st to 15thNight
20%9%4432345%7%33%
1791
16th to endNight
17%7%25%5%34446%39%
1620
May1st to 15thNight
13%7%26%5%35%5%47%38%
1620
16th to endNight
12%423435%45%6%45%
1568
June1st to 15thNight
12%5%35%4245%5%8%41%
1260
16th to endNight
9%5%245%35%5%5%8%43%
1260
July1st to 15thNight
7%3145%245%5%7%51%
1379
16th to endNight
7%4245%25%5%5%9%47%
1574
August1st to 15thNight
8%315%4246%6%9%46%
1620
16th to endNight
10%5%2442445%7%49%
1719
September1st to 15thNight
14%6%15%42235%6%46%
1911
16th to endNight
13%6%3442445%6%43%
1837
October1st to 15thNight
17%7%36%5%34336%37%
1914
16th to endNight
26%10%37%434346%25%
2210
November1st to 15thNight
15%12%47%5%3435%6%30%
2276
16th to endNight
22%15%6%9%7%3443418%
2493
December1st to 15thNight
20%16%7%10%7%35%335%15%
2586
16th to endNight
19%16%10%8%6%35%45%5%14%
2869

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 15thDay
17%14%6%10%7%5%6%5%45%17%
1432
16th to endDay
13%14%7%12%9%45%6%6%413%
1606
February1st to 15thDay
13%14%6%10%6%45%5%46%21%
1575
16th to endDay
13%10%48%9%46%5%6%6%26%
1572
March1st to 15thDay
13%9%39%8%36%5%36%28%
1887
16th to endDay
14%8%48%7%45%45%5%31%
2111
April1st to 15thDay
17%9%46%42345%7%33%
2167
16th to endDay
14%6%25%435%45%7%39%
2340
May1st to 15thDay
16%6%25%5%3445%7%38%
2331
16th to endDay
11%5%25%5%25%35%7%45%
2542
June1st to 15thDay
10%5%245%345%6%8%43%
2700
16th to endDay
10%5%245%345%6%9%42%
2700
July1st to 15thDay
7%3244245%6%10%49%
2577
16th to endDay
8%3145%346%7%9%45%
2592
August1st to 15thDay
8%425%435%5%5%10%44%
2340
16th to endDay
9%6%25%42445%8%45%
2483
September1st to 15thDay
13%5%25%3245%5%8%43%
2034
16th to endDay
15%5%25%42445%7%40%
1829
October1st to 15thDay
17%9%36%6%23436%36%
1716
16th to endDay
24%9%37%6%35%446%23%
1661
November1st to 15thDay
16%13%46%6%35%45%7%27%
1582
16th to endDay
17%15%5%11%8%45%435%16%
1467
December1st to 15thDay
14%17%7%11%9%35%44416%
1371
16th to endDay
19%16%7%10%7%445%45%14%
1353
January1st to 15thNight
20%12%6%9%8%45%45%6%17%
2506
16th to endNight
13%12%6%10%9%45%45%6%20%
2616
February1st to 15thNight
14%14%6%8%6%35%45%5%23%
2278
16th to endNight
16%12%410%7%2445%6%26%
1898
March1st to 15thNight
13%11%6%8%6%34445%32%
2072
16th to endNight
15%9%5%6%5%35%445%36%
2112
April1st to 15thNight
20%9%44422448%33%
1791
16th to endNight
17%8%25%5%33346%39%
1620
May1st to 15thNight
13%6%36%5%3445%7%39%
1619
16th to endNight
12%5%24435%5%5%6%45%
1568
June1st to 15thNight
12%5%35%425%46%8%41%
1260
16th to endNight
8%5%245%35%6%5%9%43%
1260
July1st to 15thNight
6%42443445%7%52%
1379
16th to endNight
7%4245%245%6%9%46%
1574
August1st to 15thNight
8%3145%345%7%9%46%
1620
16th to endNight
10%425%42435%6%49%
1719
September1st to 15thNight
13%6%16%423346%46%
1911
16th to endNight
12%5%35%42445%6%44%
1837
October1st to 15thNight
17%7%36%6%24437%36%
1914
16th to endNight
24%10%46%5%34446%25%
2210
November1st to 15thNight
15%11%5%8%5%35%346%29%
2276
16th to endNight
22%14%6%9%6%3444418%
2493
December1st to 15thNight
20%15%7%10%6%34445%16%
2586
16th to endNight
19%15%10%9%6%345%4415%
2869

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 15thDay
68%6%11%11%2
1433
16th to endDay
69%8%10%8%2
1606
February1st to 15thDay
63%6%11%14%3
1577
16th to endDay
54%8%14%15%5%
1572
March1st to 15thDay
57%7%11%16%7%
1887
16th to endDay
52%6%14%17%7%
2112
April1st to 15thDay
50%5%12%19%11%
2167
16th to endDay
42%6%17%17%14%2
2340
May1st to 15thDay
43%6%11%24%12%2
2331
16th to endDay
37%6%13%24%15%1
2546
June1st to 15thDay
36%7%14%25%15%
2700
16th to endDay
36%8%15%25%13%
2700
July1st to 15thDay
27%6%15%28%18%2
2428
16th to endDay
32%8%16%24%15%2
2430
August1st to 15thDay
34%7%16%27%12%1
2327
16th to endDay
34%8%15%27%12%1
2483
September1st to 15thDay
36%8%13%30%9%
2034
16th to endDay
40%7%17%25%9%
1829
October1st to 15thDay
48%6%10%22%10%1
1716
16th to endDay
60%8%16%11%3
1661
November1st to 15thDay
56%7%12%16%7%
1582
16th to endDay
69%6%10%9%3
1467
December1st to 15thDay
71%7%11%8%1
1371
16th to endDay
72%7%10%7%1
1353
January1st to 15thNight
68%5%9%12%3
2506
16th to endNight
63%6%14%13%2
2616
February1st to 15thNight
62%6%11%14%4
2287
16th to endNight
58%5%13%15%6%
1898
March1st to 15thNight
53%6%11%20%6%1
2072
16th to endNight
49%411%22%11%1
2112
April1st to 15thNight
49%410%21%13%1
1791
16th to endNight
45%49%18%18%3
1620
May1st to 15thNight
44%6%10%22%14%2
1620
16th to endNight
37%6%11%25%14%4
1570
June1st to 15thNight
39%6%11%23%17%1
1260
16th to endNight
35%7%15%21%18%1
1260
July1st to 15thNight
29%6%12%28%20%2
1300
16th to endNight
33%7%17%23%16%2
1473
August1st to 15thNight
31%8%15%29%13%1
1609
16th to endNight
33%6%12%29%16%1
1719
September1st to 15thNight
38%411%29%14%
1911
16th to endNight
38%6%13%29%10%
1837
October1st to 15thNight
49%5%10%22%11%
1914
16th to endNight
61%5%13%15%4
2210
November1st to 15thNight
55%6%13%17%7%
2276
16th to endNight
68%5%12%11%1
2493
December1st to 15thNight
71%5%11%8%3
2586
16th to endNight
72%5%9%9%2
2869

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 15thDay
18%10%40%24%6%
90
16th to endDay
29%227%35%6%
96
February1st to 15thDay
25%8%40%23%2
90
16th to endDay
13%16%32%28%9%
81
March1st to 15thDay
22%8%33%25%9%
177
16th to endDay
20%5%26%31%12%3
288
April1st to 15thDay
26%6%24%28%11%3
270
16th to endDay
21%329%27%12%5%
270
May1st to 15thDay
18%425%28%17%5%
288
16th to endDay
13%222%33%22%6%
376
June1st to 15thDay
14%117%40%19%5%
495
16th to endDay
11%222%37%19%7%
495
July1st to 15thDay
9%113%38%28%8%
475
16th to endDay
10%117%37%24%9%
452
August1st to 15thDay
10%11%35%29%12%
313
16th to endDay
15%213%28%28%12%
332
September1st to 15thDay
14%217%26%22%16%
315
16th to endDay
20%216%22%26%11%
259
October1st to 15thDay
21%6%25%27%15%3
255
16th to endDay
32%10%27%22%5%
173
November1st to 15thDay
18%428%30%14%3
90
16th to endDay
24%15%26%29%31
65
December1st to 15thDay
25%20%36%18%
60
16th to endDay
27%21%38%12%
65
January1st to 15thNight
26%9%35%21%5%
900
16th to endNight
17%8%39%25%8%
888
February1st to 15thNight
22%6%39%25%5%
704
16th to endNight
20%8%32%30%8%
631
March1st to 15thNight
20%6%33%28%10%
720
16th to endNight
19%5%29%31%12%2
768
April1st to 15thNight
23%6%27%29%10%1
593
16th to endNight
21%325%31%16%2
540
May1st to 15thNight
15%223%37%17%3
540
16th to endNight
15%219%35%25%2
497
June1st to 15thNight
15%19%39%22%2
360
16th to endNight
11%18%38%26%3
360
July1st to 15thNight
9%12%44%27%5%
450
16th to endNight
7%113%43%27%6%
564
August1st to 15thNight
11%11%39%32%4
539
16th to endNight
13%215%28%33%6%
573
September1st to 15thNight
16%317%30%21%10%
669
16th to endNight
16%317%29%23%9%
665
October1st to 15thNight
21%6%25%26%17%1
660
16th to endNight
32%8%26%26%4
704
November1st to 15thNight
23%9%30%22%12%1
700
16th to endNight
31%11%28%20%7%
720
December1st to 15thNight
29%14%34%17%4
786
16th to endNight
27%10%36%20%3
960
Page generated at 2017-09-18 08:38:26. Version ac04

Copyright 2017 A. Danko


Oak Beach Observatory Clear Sky Chart | Charts Home