El Segundo
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the El Segundo clear sky chart from 2005-11-05 to 2017-09-21.

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
64%
15892
33%
46851
26%
15840
71%
15840
42%
23815

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
61%
716
29%
2452
26%
716
70%
716
35%
1184
January16th to endNight
56%
768
35%
2362
27%
768
68%
768
35%
1234
February1st to 15thNight
60%
700
35%
2101
33%
696
67%
696
39%
1081
February16th to endNight
51%
632
27%
1895
22%
632
61%
632
28%
1099
March1st to 15thNight
61%
720
30%
2160
28%
720
69%
720
41%
1092
March16th to endNight
57%
768
28%
1996
20%
768
63%
768
37%
1155
April1st to 15thNight
57%
719
30%
1799
18%
719
62%
719
42%
1020
April16th to endNight
60%
720
32%
1800
15%
720
65%
720
47%
971
May1st to 15thNight
61%
638
28%
1718
16%
638
65%
638
41%
952
May16th to endNight
61%
561
28%
1685
19%
561
66%
561
43%
858
June1st to 15thNight
64%
454
26%
1534
23%
454
67%
454
37%
786
June16th to endNight
67%
360
30%
1440
30%
360
73%
360
36%
635
July1st to 15thNight
70%
340
32%
1360
35%
340
73%
340
36%
604
July16th to endNight
67%
643
26%
1661
19%
599
75%
599
43%
910
August1st to 15thNight
72%
717
33%
1790
21%
713
73%
713
51%
969
August16th to endNight
77%
764
38%
1910
23%
764
80%
764
54%
1005
September1st to 15thNight
79%
720
37%
1819
29%
720
81%
720
56%
945
September16th to endNight
76%
680
40%
1881
35%
680
82%
680
57%
880
October1st to 15thNight
74%
660
38%
1842
36%
660
77%
660
53%
901
October16th to endNight
71%
704
40%
2120
36%
704
80%
704
49%
990
November1st to 15thNight
69%
700
36%
2275
37%
700
75%
700
49%
990
November16th to endNight
63%
720
38%
2340
33%
720
74%
720
42%
1062
December1st to 15thNight
55%
720
35%
2340
30%
720
65%
720
33%
1191
December16th to endNight
53%
768
33%
2571
27%
768
64%
768
31%
1301

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
4312212348%63%
47977
Night
5%423313347%59%
47058
TransparencyDay
19%15%19%29%23%
47672
Night
23%15%18%26%23%
46863
SeeingDay
5%14%24%34%15%5%
5980
Night
6%16%5%26%33%11%
15903

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
7%32331325%5%60%
1483
16th to endDay
10%422313346%57%
1858
February1st to 15thDay
7%31321235%5%62%
1751
16th to endDay
10%323313348%53%
1579
March1st to 15thDay
331321436%7%62%
1800
16th to endDay
442332445%10%55%
2223
April1st to 15thDay
4322313348%60%
2149
16th to endDay
2311211347%68%
2160
May1st to 15thDay
35%1222335%8%62%
2229
16th to endDay
3413212249%63%
2429
June1st to 15thDay
6%6%13213349%57%
2421
16th to endDay
232222338%69%
2520
July1st to 15thDay
341221335%11%60%
2520
16th to endDay
221221235%9%65%
2383
August1st to 15thDay
23112249%70%
2160
16th to endDay
12112348%71%
2292
September1st to 15thDay
12121225%9%68%
2139
16th to endDay
232112238%70%
1871
October1st to 15thDay
4213212246%67%
1787
16th to endDay
2212323345%69%
1752
November1st to 15thDay
3213222245%69%
1584
16th to endDay
4313222247%65%
1620
December1st to 15thDay
6%42321345%8%56%
1620
16th to endDay
9%313313336%59%
1647
January1st to 15thNight
6%31321345%6%59%
2452
16th to endNight
10%413222336%59%
2362
February1st to 15thNight
6%324313336%60%
2101
16th to endNight
11%5%245%23345%52%
1895
March1st to 15thNight
5%423213348%59%
2160
16th to endNight
46%2431436%8%53%
1996
April1st to 15thNight
7%5%23213245%61%
1799
16th to endNight
3424212337%63%
1800
May1st to 15thNight
5%7%33222448%55%
1718
16th to endNight
46%23213347%59%
1684
June1st to 15thNight
38%23325%46%8%51%
1534
16th to endNight
26%3432345%8%54%
1440
July1st to 15thNight
35%2432336%7%57%
1440
16th to endNight
45%3343445%10%50%
1779
August1st to 15thNight
35%2431246%9%57%
1800
16th to endNight
141222345%10%59%
1910
September1st to 15thNight
2312323448%63%
1819
16th to endNight
25%12212237%68%
1881
October1st to 15thNight
3312313445%66%
1842
16th to endNight
4412212247%67%
2120
November1st to 15thNight
2412212237%68%
2275
16th to endNight
4312312347%63%
2340
December1st to 15thNight
6%424422336%58%
2340
16th to endNight
10%413212236%59%
2571

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%25%14%24%27%
1483
16th to endDay
28%16%18%16%27%
1858
February1st to 15thDay
23%2418%26%24%
1751
16th to endDay
29%26%22%29%10%
1579
March1st to 15thDay
20%29%22%25%20%
1800
16th to endDay
24%111%27%20%14%
2223
April1st to 15thDay
22%110%28%25%12%
2149
16th to endDay
15%19%26%28%18%
2160
May1st to 15thDay
20%19%24%28%16%
2229
16th to endDay
19%17%33%29%8%
2432
June1st to 15thDay
24%17%17%34%14%
2421
16th to endDay
15%210%35%34%
2520
July1st to 15thDay
19%1212%30%33%
2371
16th to endDay
15%27%22%33%18%
2238
August1st to 15thDay
13%117%38%28%
2146
16th to endDay
11%1114%43%27%
2292
September1st to 15thDay
12%1215%34%32%
2139
16th to endDay
13%117%35%30%
1871
October1st to 15thDay
17%1425%26%24%
1787
16th to endDay
16%1418%24%35%
1752
November1st to 15thDay
17%2417%25%33%
1584
16th to endDay
21%16%15%23%31%
1620
December1st to 15thDay
25%28%16%22%23%
1620
16th to endDay
26%28%17%22%21%
1647
January1st to 15thNight
24%26%14%23%28%
2452
16th to endNight
26%26%16%17%29%
2362
February1st to 15thNight
25%15%16%24%26%
2112
16th to endNight
35%26%16%25%14%
1895
March1st to 15thNight
24%17%21%25%19%
2160
16th to endNight
28%311%21%21%14%
1996
April1st to 15thNight
25%17%27%24%12%
1799
16th to endNight
21%18%25%24%18%
1800
May1st to 15thNight
27%18%23%26%13%
1719
16th to endNight
22%29%30%25%9%
1685
June1st to 15thNight
26%29%17%32%11%
1534
16th to endNight
24%1311%33%26%
1440
July1st to 15thNight
23%2112%28%32%
1360
16th to endNight
26%25%22%26%16%
1661
August1st to 15thNight
22%111%39%23%
1790
16th to endNight
19%211%40%25%
1910
September1st to 15thNight
17%239%36%30%
1819
16th to endNight
16%1117%32%31%
1881
October1st to 15thNight
18%1422%29%23%
1842
16th to endNight
18%1315%23%36%
2120
November1st to 15thNight
16%15%17%21%36%
2275
16th to endNight
20%15%19%22%31%
2340
December1st to 15thNight
27%17%16%21%25%
2340
16th to endNight
27%28%16%24%21%
2571

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%12%26%31%11%
111
16th to endDay
11%20%26%28%11%2
278
February1st to 15thDay
10%18%26%23%14%5%
266
16th to endDay
12%23%32%21%7%2
238
March1st to 15thDay
5%23%30%21%13%4
270
16th to endDay
6%23%32%24%8%4
288
April1st to 15thDay
5%26%37%17%8%4
269
16th to endDay
127%38%25%24
270
May1st to 15thDay
421%31%29%9%2
288
16th to endDay
5%18%33%30%8%3
330
June1st to 15thDay
10%14%23%34%13%3
315
16th to endDay
10%19%45%14%9%
315
July1st to 15thDay
5%8%12%43%21%8%
305
16th to endDay
210%10%44%20%12%
327
August1st to 15thDay
36%14%47%20%7%
315
16th to endDay
15%12%47%24%9%
332
September1st to 15thDay
26%24%41%17%6%
315
16th to endDay
17%26%43%13%7%
276
October1st to 15thDay
5%13%29%34%14%2
255
16th to endDay
411%25%37%16%4
264
November1st to 15thDay
36%6%23%32%27%
90
16th to endDay
37%18%33%34%2
90
December1st to 15thDay
36%14%35%33%6%
90
16th to endDay
14%10%16%30%22%4
83
January1st to 15thNight
9%17%5%32%26%8%
720
16th to endNight
11%18%7%29%25%7%
768
February1st to 15thNight
6%19%6%30%29%7%
704
16th to endNight
12%18%7%30%25%5%
632
March1st to 15thNight
5%18%6%36%25%6%
720
16th to endNight
420%7%32%27%7%
768
April1st to 15thNight
7%21%9%30%26%5%
719
16th to endNight
5%20%8%31%28%7%
720
May1st to 15thNight
5%18%7%28%31%7%
639
16th to endNight
419%9%32%29%5%
563
June1st to 15thNight
418%7%26%36%7%
454
16th to endNight
418%16%49%10%
360
July1st to 15thNight
5%12%249%29%
340
16th to endNight
417%11%38%26%
643
August1st to 15thNight
6%10%116%43%21%
717
16th to endNight
49%112%45%27%
764
September1st to 15thNight
49%18%45%21%
720
16th to endNight
410%119%48%15%
680
October1st to 15thNight
39%5%26%42%12%
660
16th to endNight
7%10%423%37%16%
704
November1st to 15thNight
315%426%35%13%
700
16th to endNight
6%18%427%31%11%
720
December1st to 15thNight
8%19%5%33%26%7%
720
16th to endNight
12%20%7%33%20%5%
768
Page generated at 2017-09-22 04:35:38. Version ac04

Copyright 2017 A. Danko


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