Owens Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Owens Observatory clear sky chart from 2005-11-05 to 2018-02-14.

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
49%
16093
23%
48801
16%
16051
57%
16051
29%
30065

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
26%
780
23%
2522
9%
776
43%
776
22%
1554
January16th to endNight
28%
832
26%
2654
13%
832
44%
832
23%
1652
February1st to 15thNight
31%
759
25%
2280
10%
757
46%
757
26%
1421
February16th to endNight
26%
631
25%
1893
9%
631
40%
631
25%
1184
March1st to 15thNight
32%
720
23%
2064
12%
720
42%
720
28%
1311
March16th to endNight
40%
768
21%
2112
13%
768
46%
768
30%
1320
April1st to 15thNight
43%
635
25%
1893
17%
635
53%
635
34%
1090
April16th to endNight
52%
540
26%
1701
19%
540
60%
540
34%
984
May1st to 15thNight
53%
540
20%
1620
13%
540
59%
540
29%
1001
May16th to endNight
65%
561
21%
1682
14%
561
69%
561
32%
1033
June1st to 15thNight
72%
540
16%
1620
15%
540
74%
540
30%
1021
June16th to endNight
76%
540
17%
1620
15%
540
77%
540
33%
967
July1st to 15thNight
70%
510
13%
1530
12%
510
71%
510
27%
1004
July16th to endNight
74%
564
16%
1595
14%
531
75%
531
28%
1033
August1st to 15thNight
71%
539
19%
1637
19%
536
71%
536
26%
1072
August16th to endNight
66%
573
19%
1910
21%
573
66%
573
22%
1282
September1st to 15thNight
63%
704
19%
1964
18%
704
65%
704
28%
1319
September16th to endNight
64%
717
25%
1980
20%
717
68%
717
31%
1247
October1st to 15thNight
58%
720
32%
1987
26%
720
64%
720
39%
1165
October16th to endNight
52%
768
35%
2304
27%
768
65%
768
39%
1256
November1st to 15thNight
51%
760
29%
2459
25%
760
61%
760
36%
1341
November16th to endNight
43%
780
29%
2535
20%
780
56%
780
31%
1442
December1st to 15thNight
36%
780
24%
2535
14%
780
48%
780
26%
1550
December16th to endNight
31%
832
20%
2704
13%
832
40%
832
19%
1816

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%5%244345%6%7%42%
49271
Night
12%42442445%7%46%
49000
TransparencyDay
38%7%12%20%17%4
48972
Night
36%6%10%20%20%6%
48803
SeeingDay
15%6%17%22%22%15%
5867
Night
14%6%22%28%23%4
16096

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 15thDay
17%6%35%423346%43%
1746
16th to endDay
18%6%14323336%45%
1921
February1st to 15thDay
17%5%14325%447%42%
1883
16th to endDay
19%433424345%42%
1580
March1st to 15thDay
16%5%2442435%7%41%
1895
16th to endDay
17%424325%5%5%7%42%
2111
April1st to 15thDay
13%425%42436%6%45%
2064
16th to endDay
11%32442445%7%49%
2259
May1st to 15thDay
10%5%25%43346%8%45%
2331
16th to endDay
10%424435%6%7%9%42%
2431
June1st to 15thDay
8%426%5%36%6%9%11%35%
2340
16th to endDay
6%214436%6%8%12%43%
2340
July1st to 15thDay
10%5%35%6%47%7%9%11%29%
2340
16th to endDay
7%426%6%47%8%9%9%31%
2465
August1st to 15thDay
10%425%6%47%8%8%9%32%
2310
16th to endDay
14%6%26%7%45%6%7%9%27%
2292
September1st to 15thDay
14%5%25%5%25%5%7%7%38%
1983
16th to endDay
15%424423446%45%
1980
October1st to 15thDay
12%413322335%55%
1971
16th to endDay
11%423322235%59%
1920
November1st to 15thDay
14%423323345%53%
1727
16th to endDay
14%425%323345%49%
1755
December1st to 15thDay
19%7%15%313446%41%
1755
16th to endDay
25%7%25%43333436%
1872
January1st to 15thNight
18%5%24314345%45%
2522
16th to endNight
17%6%34423345%44%
2654
February1st to 15thNight
17%424423345%46%
2271
16th to endNight
17%424423445%45%
1893
March1st to 15thNight
14%424424446%46%
2064
16th to endNight
12%425%424447%47%
2112
April1st to 15thNight
12%41431445%7%51%
1893
16th to endNight
9%413424448%49%
1701
May1st to 15thNight
9%425%5%25%6%5%7%45%
1619
16th to endNight
7%414435%5%5%8%47%
1682
June1st to 15thNight
6%325%445%7%8%12%39%
1620
16th to endNight
4315%5%35%6%8%11%44%
1620
July1st to 15thNight
6%425%6%5%6%7%7%10%38%
1620
16th to endNight
5%325%6%47%7%9%11%37%
1703
August1st to 15thNight
6%426%436%6%7%11%39%
1648
16th to endNight
11%5%25%6%45%6%6%9%36%
1910
September1st to 15thNight
11%426%5%36%5%5%8%40%
1964
16th to endNight
13%324325%45%8%46%
1980
October1st to 15thNight
10%423222347%55%
1987
16th to endNight
9%414413235%59%
2304
November1st to 15thNight
11%413313247%56%
2459
16th to endNight
14%413423345%52%
2535
December1st to 15thNight
15%6%245%23337%44%
2535
16th to endNight
22%6%25%5%23347%35%
2704

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
42%49%15%23%3
1747
16th to endDay
40%37%19%21%7%
1921
February1st to 15thDay
42%48%20%21%3
1885
16th to endDay
42%37%20%19%6%
1580
March1st to 15thDay
41%5%9%19%19%4
1895
16th to endDay
39%6%13%20%16%3
2112
April1st to 15thDay
37%410%22%20%4
2064
16th to endDay
33%5%10%24%21%3
2259
May1st to 15thDay
36%7%13%20%19%3
2331
16th to endDay
34%9%13%25%14%2
2435
June1st to 15thDay
36%10%19%24%7%1
2340
16th to endDay
29%9%17%27%14%2
2340
July1st to 15thDay
39%12%20%18%7%1
2201
16th to endDay
39%14%17%19%8%1
2310
August1st to 15thDay
40%12%17%19%9%1
2297
16th to endDay
48%10%13%16%9%
2292
September1st to 15thDay
40%10%13%17%15%2
1983
16th to endDay
38%5%11%19%21%4
1980
October1st to 15thDay
31%5%8%19%27%8%
1971
16th to endDay
28%36%17%31%11%
1920
November1st to 15thDay
32%37%15%31%8%
1727
16th to endDay
36%46%16%27%8%
1755
December1st to 15thDay
43%48%20%15%7%
1755
16th to endDay
51%48%16%13%5%
1872
January1st to 15thNight
40%38%17%23%5%
2522
16th to endNight
41%35%18%22%7%
2654
February1st to 15thNight
39%37%19%20%8%
2280
16th to endNight
40%36%20%23%5%
1893
March1st to 15thNight
37%5%9%19%19%8%
2064
16th to endNight
35%5%10%23%19%4
2112
April1st to 15thNight
32%49%23%23%6%
1893
16th to endNight
31%6%9%22%21%8%
1701
May1st to 15thNight
35%7%13%20%20%2
1620
16th to endNight
32%8%13%26%14%3
1684
June1st to 15thNight
32%11%20%24%9%1
1620
16th to endNight
28%10%19%22%16%2
1620
July1st to 15thNight
35%11%19%23%8%2
1530
16th to endNight
33%12%20%19%10%2
1595
August1st to 15thNight
36%11%14%24%11%1
1637
16th to endNight
41%10%16%17%12%1
1910
September1st to 15thNight
38%9%12%19%15%4
1964
16th to endNight
35%7%11%20%18%5%
1980
October1st to 15thNight
29%5%10%19%27%7%
1987
16th to endNight
29%25%16%32%13%
2304
November1st to 15thNight
29%37%16%30%11%
2459
16th to endNight
33%36%18%27%10%
2535
December1st to 15thNight
39%49%20%18%7%
2535
16th to endNight
48%38%16%17%4
2704

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
19%17%33%23%5%1
135
16th to endDay
21%25%31%14%5%1
144
February1st to 15thDay
20%24%35%16%2
130
16th to endDay
24%14%39%18%2
81
March1st to 15thDay
20%16%27%26%8%1
185
16th to endDay
16%9%31%27%13%2
288
April1st to 15thDay
16%11%29%20%19%2
270
16th to endDay
14%5%18%32%24%4
270
May1st to 15thDay
12%7%26%23%15%14%
288
16th to endDay
13%214%25%26%17%
331
June1st to 15thDay
9%29%17%28%32%
315
16th to endDay
8%8%24%24%33%
315
July1st to 15thDay
10%419%31%33%
305
16th to endDay
9%5%15%32%36%
326
August1st to 15thDay
15%15%20%30%25%
313
16th to endDay
15%17%22%28%22%
332
September1st to 15thDay
15%29%21%27%23%
315
16th to endDay
16%111%26%30%13%
314
October1st to 15thDay
17%316%28%25%8%
315
16th to endDay
13%7%19%25%27%7%
336
November1st to 15thDay
26%10%18%21%20%3
145
16th to endDay
7%11%32%25%18%4
135
December1st to 15thDay
26%14%26%22%8%
135
16th to endDay
35%12%32%15%3
144
January1st to 15thNight
22%14%32%23%7%
780
16th to endNight
20%13%34%26%5%
832
February1st to 15thNight
20%12%31%30%4
760
16th to endNight
18%13%37%26%3
631
March1st to 15thNight
17%10%35%29%6%
720
16th to endNight
14%10%28%31%14%
768
April1st to 15thNight
15%8%29%29%16%
635
16th to endNight
11%426%35%20%1
540
May1st to 15thNight
10%424%33%24%2
540
16th to endNight
10%114%31%35%7%
563
June1st to 15thNight
8%9%30%39%11%
540
16th to endNight
48%32%41%12%
540
July1st to 15thNight
8%16%21%48%13%
510
16th to endNight
6%16%20%52%12%
564
August1st to 15thNight
7%7%24%49%10%
539
16th to endNight
13%6%25%43%9%
573
September1st to 15thNight
13%19%24%42%9%
704
16th to endNight
15%110%34%34%2
717
October1st to 15thNight
14%319%31%25%6%
720
16th to endNight
11%6%23%31%23%3
768
November1st to 15thNight
13%5%24%30%23%2
760
16th to endNight
16%10%27%28%16%
780
December1st to 15thNight
18%9%30%30%10%1
780
16th to endNight
24%10%28%28%6%
832
Page generated at 2018-02-15 10:58:40. Version ac04

Copyright 2018 A. Danko


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