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Los Angeles
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Los Angeles clear sky chart from 2005-11-05 to 2017-09-10.

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
76%
15834
32%
46721
29%
15786
79%
15786
49%
23643

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
72%
716
28%
2464
29%
716
77%
716
42%
1195
January16th to endNight
67%
768
34%
2349
32%
768
73%
768
42%
1246
February1st to 15thNight
71%
697
34%
2101
34%
696
76%
696
46%
1083
February16th to endNight
63%
632
26%
1895
27%
632
68%
632
35%
1106
March1st to 15thNight
70%
720
29%
2160
30%
720
75%
720
48%
1098
March16th to endNight
72%
768
27%
2002
22%
768
75%
768
46%
1137
April1st to 15thNight
67%
719
28%
1799
18%
719
71%
719
48%
1033
April16th to endNight
70%
720
30%
1800
16%
720
73%
720
52%
992
May1st to 15thNight
72%
626
27%
1706
18%
626
73%
626
47%
955
May16th to endNight
72%
561
27%
1685
21%
561
74%
561
50%
862
June1st to 15thNight
79%
463
26%
1543
25%
463
80%
463
48%
747
June16th to endNight
86%
360
32%
1440
38%
360
86%
360
50%
577
July1st to 15thNight
89%
340
32%
1360
39%
340
89%
340
49%
550
July16th to endNight
86%
635
27%
1654
22%
592
86%
592
51%
863
August1st to 15thNight
85%
717
33%
1790
22%
713
85%
713
60%
924
August16th to endNight
89%
764
38%
1910
26%
764
89%
764
66%
959
September1st to 15thNight
86%
700
36%
1772
29%
700
86%
700
61%
907
September16th to endNight
89%
656
41%
1815
40%
656
90%
656
65%
836
October1st to 15thNight
81%
660
36%
1834
35%
660
83%
660
55%
928
October16th to endNight
80%
704
38%
2128
41%
704
82%
704
53%
1014
November1st to 15thNight
81%
700
35%
2275
38%
700
85%
700
56%
1002
November16th to endNight
78%
720
37%
2340
39%
720
82%
720
50%
1097
December1st to 15thNight
69%
720
33%
2340
33%
720
75%
720
40%
1216
December16th to endNight
63%
768
32%
2559
30%
768
69%
768
39%
1316

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
4312212346%68%
47868
Night
5%312212346%66%
46927
TransparencyDay
19%36%17%27%24%
47562
Night
21%38%17%25%24%
46733
SeeingDay
6%7%28%38%14%4
5919
Night
6%19%33%38%10%
15848

By Month

Percentage Cloud Cover SW (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
8%313323345%62%
1471
16th to endDay
10%413213345%59%
1870
February1st to 15thDay
6%314212246%62%
1751
16th to endDay
11%423323338%55%
1579
March1st to 15thDay
431331335%7%62%
1800
16th to endDay
5%32331345%9%58%
2217
April1st to 15thDay
6%313312347%62%
2149
16th to endDay
4313212236%70%
2160
May1st to 15thDay
4412212345%66%
2241
16th to endDay
35%12212245%66%
2429
June1st to 15thDay
6%6%12211246%64%
2412
16th to endDay
13111123379%
2520
July1st to 15thDay
3312212336%70%
2520
16th to endDay
221212347%71%
2391
August1st to 15thDay
22111123479%
2160
16th to endDay
111112335%78%
2292
September1st to 15thDay
2111113479%
2073
16th to endDay
1111133479%
1815
October1st to 15thDay
5%21322224469%
1794
16th to endDay
322212345%71%
1741
November1st to 15thDay
2212322235%71%
1584
16th to endDay
5%213312336%65%
1620
December1st to 15thDay
7%31231445%8%58%
1620
16th to endDay
11%312312336%59%
1659
January1st to 15thNight
6%413223345%63%
2464
16th to endNight
10%413212235%62%
2349
February1st to 15thNight
6%323312235%64%
2101
16th to endNight
12%41322344454%
1895
March1st to 15thNight
5%41321235%8%61%
2160
16th to endNight
441221446%6%59%
2002
April1st to 15thNight
7%422212226%63%
1799
16th to endNight
3423112245%67%
1800
May1st to 15thNight
5%6%11213347%62%
1706
16th to endNight
35%12211245%68%
1684
June1st to 15thNight
35%12212348%64%
1543
16th to endNight
15%1221346%71%
1440
July1st to 15thNight
2312212347%69%
1440
16th to endNight
321222345%8%63%
1771
August1st to 15thNight
2311211347%69%
1800
16th to endNight
122211247%71%
1910
September1st to 15thNight
2311211245%73%
1772
16th to endNight
121111245%76%
1815
October1st to 15thNight
322312335%69%
1834
16th to endNight
4312212235%70%
2128
November1st to 15thNight
2311312225%73%
2275
16th to endNight
3212222346%67%
2340
December1st to 15thNight
6%313423336%60%
2340
16th to endNight
11%41221223462%
2559

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
25%36%13%22%29%
1471
16th to endDay
27%46%16%17%27%
1870
February1st to 15thDay
23%35%16%26%24%
1751
16th to endDay
29%47%20%27%10%
1579
March1st to 15thDay
20%310%20%22%21%
1800
16th to endDay
23%410%24%21%14%
2217
April1st to 15thDay
22%49%25%25%12%
2149
16th to endDay
16%38%24%28%18%
2160
May1st to 15thDay
20%49%21%27%16%
2241
16th to endDay
20%48%28%28%9%
2432
June1st to 15thDay
24%28%15%32%16%
2412
16th to endDay
13%139%34%37%
2520
July1st to 15thDay
18%1411%26%36%
2371
16th to endDay
15%38%20%32%19%
2245
August1st to 15thDay
12%1215%36%31%
2146
16th to endDay
10%2313%40%29%
2292
September1st to 15thDay
11%1413%33%35%
2073
16th to endDay
11%1314%34%33%
1815
October1st to 15thDay
19%25%21%25%25%
1794
16th to endDay
16%35%14%20%39%
1741
November1st to 15thDay
16%26%15%22%34%
1584
16th to endDay
20%36%13%22%32%
1620
December1st to 15thDay
25%49%16%19%24%
1620
16th to endDay
25%49%16%21%22%
1659
January1st to 15thNight
24%27%13%21%29%
2464
16th to endNight
26%37%15%15%31%
2349
February1st to 15thNight
24%27%16%22%27%
2112
16th to endNight
34%37%15%24%15%
1895
March1st to 15thNight
22%39%20%24%19%
2160
16th to endNight
25%413%21%20%14%
2002
April1st to 15thNight
25%39%26%23%12%
1799
16th to endNight
21%310%23%23%17%
1800
May1st to 15thNight
24%5%11%21%24%13%
1707
16th to endNight
19%5%11%28%24%10%
1685
June1st to 15thNight
20%413%17%30%12%
1543
16th to endNight
18%18%12%30%27%
1440
July1st to 15thNight
18%26%14%28%30%
1360
16th to endNight
21%310%23%25%16%
1654
August1st to 15thNight
18%16%11%37%23%
1790
16th to endNight
15%16%12%37%25%
1910
September1st to 15thNight
17%26%9%33%31%
1772
16th to endNight
13%2316%32%32%
1815
October1st to 15thNight
18%35%19%28%23%
1834
16th to endNight
18%35%13%23%36%
2128
November1st to 15thNight
16%26%15%20%37%
2275
16th to endNight
19%36%17%20%32%
2340
December1st to 15thNight
27%38%15%20%25%
2340
16th to endNight
27%38%14%24%21%
2559

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%431%35%11%
99
16th to endDay
12%9%33%33%10%1
280
February1st to 15thDay
11%9%29%29%16%3
266
16th to endDay
15%18%31%24%9%
238
March1st to 15thDay
7%15%32%25%15%3
270
16th to endDay
6%16%35%31%7%2
288
April1st to 15thDay
10%15%41%21%7%3
269
16th to endDay
418%43%25%34
270
May1st to 15thDay
7%14%34%31%10%2
288
16th to endDay
6%9%39%32%11%1
330
June1st to 15thDay
9%7%27%40%12%2
315
16th to endDay
1120%50%17%8%
315
July1st to 15thDay
4115%51%22%5%
305
16th to endDay
213%51%23%9%
327
August1st to 15thDay
5%16%57%14%5%
315
16th to endDay
315%53%19%7%
332
September1st to 15thDay
4125%51%11%4
294
16th to endDay
1335%43%11%5%
255
October1st to 15thDay
5%10%33%35%12%1
255
16th to endDay
6%5%29%39%15%3
253
November1st to 15thDay
45%8%26%33%21%
90
16th to endDay
4321%41%27%2
90
December1st to 15thDay
5%222%37%31%1
90
16th to endDay
14%9%21%34%20%1
85
January1st to 15thNight
8%11%43%28%6%
720
16th to endNight
12%111%36%31%6%
768
February1st to 15thNight
8%111%38%31%8%
704
16th to endNight
13%116%37%26%5%
632
March1st to 15thNight
5%214%44%26%6%
720
16th to endNight
6%212%42%29%6%
768
April1st to 15thNight
8%314%41%27%4
719
16th to endNight
4315%37%32%5%
720
May1st to 15thNight
10%112%38%32%6%
627
16th to endNight
4216%39%32%4
563
June1st to 15thNight
410%37%41%4
463
16th to endNight
31224%60%7%
360
July1st to 15thNight
229%68%16%
340
16th to endNight
4217%56%18%
635
August1st to 15thNight
5%222%51%16%
717
16th to endNight
3116%53%24%
764
September1st to 15thNight
5%221%51%18%
700
16th to endNight
31227%51%13%
656
October1st to 15thNight
48%36%40%9%
660
16th to endNight
6%18%28%41%14%
704
November1st to 15thNight
46%37%37%14%
700
16th to endNight
5%19%34%36%12%
720
December1st to 15thNight
9%211%37%31%7%
720
16th to endNight
12%315%37%24%5%
768
Page generated at 2017-09-11 16:35:23. Version ac04

Copyright 2017 A. Danko


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