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 2018-10-08.

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%
17235
19%
50980
14%
17192
49%
17192
25%
33550

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
25%
975
15%
2716
7%
970
32%
970
19%
1982
January16th to endNight
24%
1040
14%
2851
5%
1040
31%
1040
19%
2094
February1st to 15thNight
24%
769
12%
2298
6%
767
30%
767
16%
1679
February16th to endNight
26%
683
16%
2049
7%
683
33%
683
17%
1466
March1st to 15thNight
26%
780
16%
2340
9%
780
32%
780
20%
1618
March16th to endNight
33%
715
16%
2193
10%
715
41%
715
20%
1543
April1st to 15thNight
35%
584
19%
1947
13%
584
45%
584
23%
1257
April16th to endNight
40%
579
20%
1866
14%
579
48%
579
24%
1221
May1st to 15thNight
42%
585
15%
1755
11%
585
47%
585
23%
1196
May16th to endNight
56%
609
17%
1726
12%
609
59%
609
27%
1138
June1st to 15thNight
63%
585
20%
1560
16%
585
65%
585
37%
957
June16th to endNight
63%
585
20%
1560
15%
585
67%
585
37%
963
July1st to 15thNight
70%
555
20%
1480
17%
555
71%
555
39%
891
July16th to endNight
77%
612
26%
1548
21%
579
79%
579
45%
871
August1st to 15thNight
74%
575
23%
1787
23%
572
75%
572
39%
987
August16th to endNight
71%
621
23%
2070
25%
621
74%
621
37%
1118
September1st to 15thNight
63%
622
27%
1987
26%
622
67%
622
33%
1146
September16th to endNight
63%
777
28%
2145
22%
777
65%
777
37%
1274
October1st to 15thNight
56%
752
29%
2101
23%
752
60%
752
35%
1266
October16th to endNight
36%
768
22%
2444
16%
768
46%
768
25%
1519
November1st to 15thNight
42%
760
26%
2471
20%
760
52%
760
28%
1476
November16th to endNight
34%
780
21%
2535
15%
780
43%
780
22%
1655
December1st to 15thNight
25%
884
11%
2639
6%
884
31%
884
17%
1946
December16th to endNight
20%
1040
13%
2912
5%
1040
28%
1040
14%
2287

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%
52161
Night
14%7%35%424446%41%
51151
Cloud CoverDay
15%6%35%5%3445%7%39%
52170
Night
14%7%35%424446%41%
51156
TransparencyDay
44%6%12%21%13%2
51849
Night
42%5%11%22%15%2
50981
SeeingDay
16%5%22%25%20%9%
7276
Night
18%6%25%31%16%1
17238

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%48%6%33335%29%
1552
16th to endDay
14%12%6%6%6%34345%33%
1723
February1st to 15thDay
15%10%6%8%6%2444431%
1894
16th to endDay
17%11%47%5%33346%30%
1710
March1st to 15thDay
19%8%46%5%24345%35%
1940
16th to endDay
19%9%36%5%2345%6%31%
2392
April1st to 15thDay
18%7%35%423446%38%
2331
16th to endDay
19%7%25%434446%37%
2369
May1st to 15thDay
20%6%26%435%45%6%34%
2526
16th to endDay
12%6%36%6%25%5%6%7%37%
2736
June1st to 15thDay
9%4244345%6%9%45%
2730
16th to endDay
10%3245%35%5%6%9%43%
2730
July1st to 15thDay
10%4245%25%5%6%9%42%
2730
16th to endDay
8%314437%6%7%9%41%
2876
August1st to 15thDay
8%3245%345%7%10%44%
2412
16th to endDay
7%5%245%45%46%8%44%
2484
September1st to 15thDay
12%4245%345%5%6%44%
2288
16th to endDay
11%4245%2345%6%49%
2145
October1st to 15thDay
15%41443435%7%44%
2028
16th to endDay
18%5%25%423346%43%
1779
November1st to 15thDay
15%5%23424346%47%
1717
16th to endDay
20%7%34413335%40%
1755
December1st to 15thDay
21%11%37%6%23346%30%
1650
16th to endDay
24%12%45%433445%27%
1664
January1st to 15thNight
19%9%37%5%24345%33%
2716
16th to endNight
16%11%47%5%33445%32%
2851
February1st to 15thNight
17%11%5%7%5%24445%31%
2296
16th to endNight
19%10%46%424445%34%
2049
March1st to 15thNight
18%9%35%435%336%37%
2327
16th to endNight
19%8%36%424346%35%
2193
April1st to 15thNight
17%7%25%423445%42%
1947
16th to endNight
15%6%36%424446%40%
1866
May1st to 15thNight
16%6%345%34447%38%
1755
16th to endNight
9%426%5%4446%9%40%
1725
June1st to 15thNight
9%4144244410%49%
1560
16th to endNight
8%4144235%7%10%47%
1560
July1st to 15thNight
7%3244235%6%9%49%
1560
16th to endNight
5%22442445%9%55%
1644
August1st to 15thNight
5%3234245%5%10%52%
1798
16th to endNight
5%5%1342445%8%53%
2070
September1st to 15thNight
11%424433247%50%
1987
16th to endNight
10%424423347%51%
2145
October1st to 15thNight
11%5%1432345%6%51%
2101
16th to endNight
17%6%14423436%45%
2444
November1st to 15thNight
11%7%24424445%48%
2471
16th to endNight
18%8%35%423345%40%
2535
December1st to 15thNight
20%11%47%5%23345%31%
2639
16th to endNight
24%11%46%5%2433427%
2912

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%11%48%6%24335%29%
1552
16th to endDay
14%13%6%5%6%3434433%
1723
February1st to 15thDay
15%10%6%8%6%33345%30%
1894
16th to endDay
17%11%47%5%34345%30%
1710
March1st to 15thDay
20%8%46%424345%34%
1950
16th to endDay
20%9%36%5%33447%31%
2391
April1st to 15thDay
19%7%34414346%38%
2331
16th to endDay
19%6%35%5%24446%37%
2369
May1st to 15thDay
20%6%35%5%34446%34%
2526
16th to endDay
12%6%36%5%35%5%5%7%37%
2736
June1st to 15thDay
9%4244345%6%9%45%
2730
16th to endDay
10%4245%25%5%6%10%42%
2730
July1st to 15thDay
9%4245%35%5%6%9%42%
2730
16th to endDay
8%3145%37%6%7%9%41%
2876
August1st to 15thDay
8%324435%5%7%11%43%
2412
16th to endDay
8%5%245%35%45%9%44%
2484
September1st to 15thDay
12%4245%346%5%6%44%
2288
16th to endDay
12%42442335%6%49%
2145
October1st to 15thDay
15%42443335%7%44%
2028
16th to endDay
18%5%25%433346%42%
1779
November1st to 15thDay
15%5%23424346%47%
1717
16th to endDay
20%7%34323335%40%
1755
December1st to 15thDay
21%10%37%6%13345%30%
1650
16th to endDay
24%12%46%333445%27%
1664
January1st to 15thNight
19%10%37%5%24335%33%
2716
16th to endNight
16%11%47%5%33345%32%
2851
February1st to 15thNight
17%10%5%7%424445%31%
2289
16th to endNight
18%10%37%424445%34%
2049
March1st to 15thNight
18%9%34434336%36%
2340
16th to endNight
19%7%36%424346%35%
2193
April1st to 15thNight
17%7%35%42335%5%42%
1947
16th to endNight
15%5%36%42445%6%40%
1866
May1st to 15thNight
16%7%345%245%48%37%
1754
16th to endNight
10%425%5%35%5%6%9%41%
1725
June1st to 15thNight
9%424424449%50%
1560
16th to endNight
8%4134245%6%10%47%
1560
July1st to 15thNight
7%3244235%7%9%49%
1560
16th to endNight
5%224424449%55%
1644
August1st to 15thNight
5%324425%5%5%9%52%
1798
16th to endNight
6%41342445%8%52%
2070
September1st to 15thNight
11%4145%33248%50%
1987
16th to endNight
10%5%24423447%51%
2145
October1st to 15thNight
12%41332345%6%51%
2101
16th to endNight
17%5%24423446%44%
2444
November1st to 15thNight
11%7%24424345%48%
2471
16th to endNight
18%8%34423345%40%
2535
December1st to 15thNight
21%11%5%7%5%2344431%
2639
16th to endNight
24%11%46%5%23335%27%
2912

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%17%9%
1553
16th to endDay
53%413%21%6%
1723
February1st to 15thDay
55%412%18%7%1
1896
16th to endDay
55%5%10%20%7%
1710
March1st to 15thDay
52%412%20%8%1
1950
16th to endDay
52%5%13%21%6%
2392
April1st to 15thDay
46%5%11%23%12%1
2331
16th to endDay
47%5%10%20%11%5%
2369
May1st to 15thDay
50%6%12%19%11%
2526
16th to endDay
43%8%11%19%14%2
2740
June1st to 15thDay
33%7%13%24%17%3
2730
16th to endDay
36%7%15%21%16%3
2730
July1st to 15thDay
36%8%11%23%16%3
2581
16th to endDay
34%9%15%25%13%1
2709
August1st to 15thDay
32%8%15%25%17%2
2399
16th to endDay
35%5%14%22%15%5%
2484
September1st to 15thDay
38%5%12%21%17%5%
2288
16th to endDay
34%5%10%24%22%3
2145
October1st to 15thDay
39%410%24%17%2
2028
16th to endDay
42%411%24%16%
1779
November1st to 15thDay
39%312%21%17%5%
1717
16th to endDay
46%48%23%15%1
1755
December1st to 15thDay
56%5%10%17%8%
1650
16th to endDay
59%411%18%5%
1664
January1st to 15thNight
54%39%19%11%1
2716
16th to endNight
53%412%20%7%
2851
February1st to 15thNight
55%414%16%8%1
2298
16th to endNight
52%5%11%20%9%
2049
March1st to 15thNight
49%410%22%11%2
2340
16th to endNight
49%5%13%21%8%1
2193
April1st to 15thNight
43%5%9%23%15%1
1947
16th to endNight
43%5%9%20%14%6%
1866
May1st to 15thNight
44%7%13%21%12%
1755
16th to endNight
38%8%12%18%17%4
1727
June1st to 15thNight
31%6%11%26%20%3
1560
16th to endNight
30%8%13%22%19%5%
1560
July1st to 15thNight
28%8%15%22%19%5%
1480
16th to endNight
25%5%14%32%19%2
1548
August1st to 15thNight
26%6%16%24%21%4
1787
16th to endNight
28%5%13%24%21%6%
2070
September1st to 15thNight
33%5%10%24%20%6%
1987
16th to endNight
32%410%21%25%5%
2145
October1st to 15thNight
32%5%10%25%21%4
2101
16th to endNight
40%49%25%17%2
2444
November1st to 15thNight
37%38%23%20%5%
2471
16th to endNight
46%310%23%15%
2535
December1st to 15thNight
55%410%17%10%
2639
16th to endNight
61%49%16%7%
2912

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
33%8%31%15%10%1
135
16th to endDay
17%18%38%21%3
144
February1st to 15thDay
26%15%37%14%5%
135
16th to endDay
29%11%33%20%5%
120
March1st to 15thDay
25%12%38%20%2
135
16th to endDay
23%11%33%22%7%1
329
April1st to 15thDay
20%12%29%24%11%
330
16th to endDay
21%8%26%24%15%4
319
May1st to 15thDay
20%8%25%27%13%4
348
16th to endDay
16%425%25%18%11%
492
June1st to 15thDay
11%219%31%25%8%
570
16th to endDay
13%324%28%22%7%
570
July1st to 15thDay
12%115%29%23%17%
550
16th to endDay
8%112%28%31%18%
592
August1st to 15thDay
11%7%21%37%22%
358
16th to endDay
9%112%26%33%17%
396
September1st to 15thDay
13%211%22%33%16%
375
16th to endDay
14%217%22%27%17%
374
October1st to 15thDay
16%222%28%22%7%
311
16th to endDay
19%5%34%26%13%
144
November1st to 15thDay
19%9%16%26%20%8%
135
16th to endDay
26%8%33%21%8%
135
December1st to 15thDay
12%20%35%20%8%1
135
16th to endDay
34%8%43%13%1
144
January1st to 15thNight
23%12%32%25%5%
975
16th to endNight
21%10%38%26%2
1040
February1st to 15thNight
22%10%35%28%2
770
16th to endNight
24%9%35%26%3
683
March1st to 15thNight
22%11%36%26%4
780
16th to endNight
23%7%30%30%7%
715
April1st to 15thNight
19%10%30%30%8%
584
16th to endNight
18%6%28%34%10%1
579
May1st to 15thNight
18%427%34%13%1
585
16th to endNight
12%221%35%25%3
611
June1st to 15thNight
11%115%48%22%
585
16th to endNight
9%217%42%28%
585
July1st to 15thNight
9%111%39%34%3
555
16th to endNight
5%17%40%38%6%
612
August1st to 15thNight
6%9%39%40%4
575
16th to endNight
7%11%33%40%6%
621
September1st to 15thNight
12%113%32%32%5%
622
16th to endNight
12%213%33%32%5%
777
October1st to 15thNight
14%419%34%22%4
752
16th to endNight
21%7%29%28%11%
768
November1st to 15thNight
16%6%29%33%13%1
760
16th to endNight
22%9%30%27%9%
780
December1st to 15thNight
26%8%32%23%7%
884
16th to endNight
30%8%33%23%4
1040
Page generated at 2018-10-09 10:39:15. Version ac04

Copyright 2018 A. Danko


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