Oakley Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Oakley 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
43%
15825
19%
46827
13%
15782
48%
15782
25%
30883

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
24%
900
15%
2506
7%
895
31%
895
19%
1841
January16th to endNight
23%
960
14%
2632
5%
960
30%
960
19%
1942
February1st to 15thNight
25%
709
12%
2118
6%
707
31%
707
17%
1538
February16th to endNight
26%
631
16%
1893
7%
631
34%
631
18%
1338
March1st to 15thNight
26%
720
15%
2160
9%
720
31%
720
19%
1512
March16th to endNight
34%
660
16%
2024
10%
660
41%
660
21%
1416
April1st to 15thNight
35%
539
19%
1797
12%
539
46%
539
24%
1143
April16th to endNight
40%
540
20%
1743
14%
540
49%
540
24%
1136
May1st to 15thNight
41%
540
15%
1620
10%
540
46%
540
22%
1127
May16th to endNight
55%
561
18%
1590
13%
561
58%
561
28%
1040
June1st to 15thNight
62%
540
19%
1440
16%
540
64%
540
38%
881
June16th to endNight
63%
540
20%
1440
15%
540
66%
540
37%
889
July1st to 15thNight
68%
510
18%
1360
15%
510
69%
510
38%
826
July16th to endNight
78%
564
26%
1420
22%
531
80%
531
47%
788
August1st to 15thNight
73%
539
22%
1678
22%
536
75%
536
38%
933
August16th to endNight
72%
573
24%
1910
26%
573
75%
573
37%
1029
September1st to 15thNight
63%
574
26%
1834
25%
574
67%
574
34%
1055
September16th to endNight
62%
665
27%
1837
21%
665
65%
665
36%
1103
October1st to 15thNight
56%
660
31%
1845
24%
660
61%
660
37%
1094
October16th to endNight
36%
704
21%
2240
15%
704
45%
704
25%
1395
November1st to 15thNight
43%
700
27%
2276
21%
700
53%
700
30%
1334
November16th to endNight
33%
720
19%
2340
15%
720
41%
720
21%
1565
December1st to 15thNight
24%
816
11%
2436
6%
816
30%
816
16%
1840
December16th to endNight
20%
960
12%
2688
5%
960
28%
960
14%
2118

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
14%6%35%5%3445%7%39%
47953
Night
14%7%35%424446%41%
46998
Cloud CoverDay
14%6%35%5%3445%7%39%
47962
Night
14%7%35%424446%41%
47003
TransparencyDay
44%6%12%21%13%2
47641
Night
43%5%11%21%15%2
46828
SeeingDay
15%5%22%25%21%10%
5845
Night
18%6%26%31%15%1
15828

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
20%10%49%6%33335%28%
1432
16th to endDay
14%12%6%6%6%24345%32%
1590
February1st to 15thDay
14%10%6%8%6%2445%431%
1744
16th to endDay
15%11%47%6%44446%30%
1580
March1st to 15thDay
20%9%45%424445%33%
1790
16th to endDay
17%9%37%5%33446%32%
2208
April1st to 15thDay
18%7%34423446%39%
2151
16th to endDay
19%6%25%434446%36%
2217
May1st to 15thDay
22%6%26%435%45%6%33%
2331
16th to endDay
12%6%36%6%25%5%6%7%38%
2521
June1st to 15thDay
10%4244245%6%9%45%
2520
16th to endDay
10%3245%25%5%6%9%43%
2520
July1st to 15thDay
10%425%6%25%5%6%9%41%
2520
16th to endDay
6%314447%6%7%9%42%
2652
August1st to 15thDay
8%4245%345%7%10%43%
2268
16th to endDay
7%5%245%45%46%8%45%
2292
September1st to 15thDay
12%4245%345%5%6%44%
2112
16th to endDay
12%4245%23446%49%
1829
October1st to 15thDay
15%41442335%7%46%
1784
16th to endDay
18%5%25%423346%42%
1631
November1st to 15thDay
14%5%23424347%48%
1582
16th to endDay
21%8%44413335%39%
1620
December1st to 15thDay
23%11%37%6%23345%28%
1523
16th to endDay
23%12%45%433345%28%
1536
January1st to 15thNight
19%10%37%5%24345%33%
2506
16th to endNight
16%12%5%7%5%33445%32%
2632
February1st to 15thNight
17%10%5%7%5%34445%32%
2116
16th to endNight
17%9%46%424445%35%
1893
March1st to 15thNight
18%9%45%425%336%36%
2147
16th to endNight
17%8%36%5%24346%36%
2024
April1st to 15thNight
16%6%35%423445%43%
1797
16th to endNight
15%6%35%424446%40%
1743
May1st to 15thNight
18%7%345%34447%36%
1620
16th to endNight
10%425%5%4446%9%41%
1589
June1st to 15thNight
9%414424349%50%
1440
16th to endNight
8%4234235%7%10%47%
1440
July1st to 15thNight
8%3234235%6%10%48%
1440
16th to endNight
5%22432435%9%56%
1516
August1st to 15thNight
5%3234245%5%10%51%
1689
16th to endNight
5%5%1342445%8%53%
1910
September1st to 15thNight
10%5%24433247%51%
1834
16th to endNight
11%424323447%50%
1837
October1st to 15thNight
11%41432335%6%53%
1845
16th to endNight
18%6%14423436%44%
2240
November1st to 15thNight
11%6%23424445%50%
2276
16th to endNight
19%8%35%423345%38%
2340
December1st to 15thNight
21%11%5%7%5%23445%28%
2436
16th to endNight
25%11%46%5%2433427%
2688

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
20%10%5%8%6%24335%28%
1432
16th to endDay
14%13%6%6%6%2434432%
1590
February1st to 15thDay
14%10%6%8%6%3345%5%31%
1744
16th to endDay
15%11%5%8%5%34346%31%
1580
March1st to 15thDay
21%8%45%425%345%33%
1800
16th to endDay
18%9%36%5%34447%32%
2207
April1st to 15thDay
19%7%34414346%39%
2151
16th to endDay
19%6%25%5%34446%36%
2217
May1st to 15thDay
22%6%35%5%35%446%33%
2331
16th to endDay
12%6%36%5%35%5%5%7%37%
2521
June1st to 15thDay
9%4244245%6%9%45%
2520
16th to endDay
10%3245%25%5%6%10%42%
2520
July1st to 15thDay
10%5%245%35%5%6%9%41%
2520
16th to endDay
7%3145%47%6%7%10%42%
2652
August1st to 15thDay
8%324435%5%7%11%43%
2268
16th to endDay
7%5%246%35%45%9%45%
2292
September1st to 15thDay
12%4245%345%5%6%44%
2112
16th to endDay
12%5%2442335%6%48%
1829
October1st to 15thDay
15%42443335%7%46%
1784
16th to endDay
18%5%25%433346%42%
1631
November1st to 15thDay
13%5%23424346%49%
1582
16th to endDay
22%8%44423335%39%
1620
December1st to 15thDay
23%11%37%6%13345%28%
1523
16th to endDay
23%12%46%333345%28%
1536
January1st to 15thNight
19%10%37%5%24335%33%
2506
16th to endNight
16%12%5%7%5%33345%32%
2632
February1st to 15thNight
17%10%5%7%424445%31%
2109
16th to endNight
16%10%37%424445%35%
1893
March1st to 15thNight
19%9%44434336%36%
2160
16th to endNight
17%8%36%424446%36%
2024
April1st to 15thNight
16%6%3442345%5%43%
1797
16th to endNight
15%5%35%42445%6%40%
1743
May1st to 15thNight
18%7%345%245%48%36%
1619
16th to endNight
10%4245%35%5%6%8%41%
1589
June1st to 15thNight
9%424414349%50%
1440
16th to endNight
8%4134245%6%10%47%
1440
July1st to 15thNight
8%3244235%6%9%49%
1440
16th to endNight
5%2143244410%56%
1516
August1st to 15thNight
5%324425%5%5%9%51%
1689
16th to endNight
5%41442445%8%53%
1910
September1st to 15thNight
10%4145%33238%51%
1834
16th to endNight
11%424423447%50%
1837
October1st to 15thNight
12%41332345%5%53%
1845
16th to endNight
18%5%24423436%44%
2240
November1st to 15thNight
11%6%24424345%50%
2276
16th to endNight
19%9%35%423345%39%
2340
December1st to 15thNight
22%11%5%7%5%2344429%
2436
16th to endNight
25%11%45%5%33335%27%
2688

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
58%49%18%8%
1433
16th to endDay
54%413%20%6%
1590
February1st to 15thDay
54%413%18%8%1
1746
16th to endDay
54%5%11%21%6%
1580
March1st to 15thDay
53%413%19%7%
1800
16th to endDay
51%5%13%21%6%
2208
April1st to 15thDay
45%5%10%24%13%1
2151
16th to endDay
47%5%10%20%10%4
2217
May1st to 15thDay
52%6%11%18%11%
2331
16th to endDay
43%8%11%18%14%2
2525
June1st to 15thDay
33%7%13%24%17%3
2520
16th to endDay
35%7%15%20%17%3
2520
July1st to 15thDay
38%8%11%21%17%2
2371
16th to endDay
33%10%16%25%13%1
2485
August1st to 15thDay
32%8%14%25%17%2
2255
16th to endDay
34%5%13%23%15%6%
2292
September1st to 15thDay
38%5%10%21%18%5%
2112
16th to endDay
35%5%8%25%22%3
1829
October1st to 15thDay
37%411%25%19%2
1784
16th to endDay
42%411%24%16%
1631
November1st to 15thDay
37%312%22%18%5%
1582
16th to endDay
48%49%21%14%1
1620
December1st to 15thDay
57%5%10%16%8%
1523
16th to endDay
58%411%18%5%
1536
January1st to 15thNight
54%310%20%10%
2506
16th to endNight
53%413%20%7%
2632
February1st to 15thNight
54%414%17%8%
2118
16th to endNight
50%6%12%21%9%
1893
March1st to 15thNight
50%410%22%10%2
2160
16th to endNight
48%5%13%21%8%1
2024
April1st to 15thNight
41%5%10%23%16%2
1797
16th to endNight
43%5%9%21%14%6%
1743
May1st to 15thNight
46%7%12%21%12%
1620
16th to endNight
38%8%13%17%17%4
1591
June1st to 15thNight
31%6%11%27%20%3
1440
16th to endNight
30%8%13%21%20%5%
1440
July1st to 15thNight
29%8%16%21%19%5%
1360
16th to endNight
24%414%33%19%2
1420
August1st to 15thNight
26%7%16%24%20%4
1678
16th to endNight
27%5%13%23%21%7%
1910
September1st to 15thNight
32%5%9%25%20%7%
1834
16th to endNight
33%49%21%25%6%
1837
October1st to 15thNight
31%49%26%23%4
1845
16th to endNight
41%410%25%16%2
2240
November1st to 15thNight
36%48%23%21%6%
2276
16th to endNight
48%39%22%15%
2340
December1st to 15thNight
57%5%10%16%9%
2436
16th to endNight
61%5%9%15%7%
2688

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
31%11%33%16%6%1
90
16th to endDay
13%19%46%15%4
96
February1st to 15thDay
21%17%38%14%7%
90
16th to endDay
19%8%39%24%7%
81
March1st to 15thDay
27%14%37%16%3
90
16th to endDay
19%12%34%23%8%1
267
April1st to 15thDay
19%11%28%25%13%1
270
16th to endDay
21%7%25%24%15%5%
270
May1st to 15thDay
23%7%26%25%12%4
288
16th to endDay
15%428%24%17%9%
421
June1st to 15thDay
12%220%31%25%7%
495
16th to endDay
12%326%29%20%7%
495
July1st to 15thDay
13%217%32%21%12%
475
16th to endDay
6%111%28%32%20%
512
August1st to 15thDay
12%7%19%35%24%
313
16th to endDay
7%110%24%36%18%
332
September1st to 15thDay
13%212%23%32%16%
315
16th to endDay
15%214%23%26%17%
259
October1st to 15thDay
12%224%25%25%9%
224
16th to endDay
19%336%29%11%
96
November1st to 15thDay
8%11%15%25%28%10%
90
16th to endDay
35%10%25%17%10%1
90
December1st to 15thDay
16%13%36%22%8%2
90
16th to endDay
32%6%44%14%2
96
January1st to 15thNight
23%13%33%25%4
900
16th to endNight
21%10%38%26%2
960
February1st to 15thNight
21%11%35%29%2
710
16th to endNight
22%9%36%28%2
631
March1st to 15thNight
22%11%35%26%4
720
16th to endNight
21%7%31%30%8%1
660
April1st to 15thNight
18%10%30%31%9%
539
16th to endNight
19%5%28%35%10%1
540
May1st to 15thNight
20%5%26%34%12%
540
16th to endNight
12%223%35%23%3
563
June1st to 15thNight
11%115%47%22%
540
16th to endNight
8%217%43%26%
540
July1st to 15thNight
9%112%40%33%1
510
16th to endNight
5%16%39%39%6%
564
August1st to 15thNight
6%10%38%39%4
539
16th to endNight
7%10%33%41%6%
573
September1st to 15thNight
12%214%34%30%6%
574
16th to endNight
13%213%33%31%5%
665
October1st to 15thNight
13%420%34%21%5%
660
16th to endNight
22%7%29%29%10%
704
November1st to 15thNight
15%6%29%33%13%1
700
16th to endNight
23%9%29%27%9%
720
December1st to 15thNight
27%8%32%23%7%
816
16th to endNight
31%8%32%22%4
960
Page generated at 2017-09-18 08:38:20. Version ac04

Copyright 2017 A. Danko


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