El Centro
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the El Centro clear sky chart from 2005-11-05 to 2017-09-16.

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
77%
16086
41%
46953
33%
16047
83%
16047
68%
19963

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
76%
718
35%
2327
35%
716
82%
716
56%
1027
January16th to endNight
69%
768
41%
2364
35%
768
79%
768
55%
1072
February1st to 15thNight
75%
699
41%
2107
36%
698
85%
698
62%
919
February16th to endNight
67%
632
37%
1895
35%
632
75%
632
51%
916
March1st to 15thNight
68%
720
38%
2106
33%
720
79%
720
64%
916
March16th to endNight
69%
768
41%
2112
29%
768
81%
768
70%
925
April1st to 15thNight
61%
719
41%
1820
20%
719
74%
719
71%
832
April16th to endNight
66%
699
46%
1779
22%
699
78%
699
80%
771
May1st to 15thNight
68%
539
44%
1619
29%
539
77%
539
77%
612
May16th to endNight
68%
561
43%
1684
28%
561
76%
561
80%
624
June1st to 15thNight
73%
540
38%
1620
28%
540
78%
540
86%
578
June16th to endNight
85%
540
39%
1620
34%
540
86%
540
83%
604
July1st to 15thNight
88%
510
32%
1530
27%
510
89%
510
67%
647
July16th to endNight
88%
564
39%
1593
32%
531
89%
531
63%
705
August1st to 15thNight
91%
693
37%
1767
25%
690
92%
690
76%
810
August16th to endNight
90%
764
44%
1910
31%
764
90%
764
73%
899
September1st to 15thNight
89%
720
39%
1926
33%
720
91%
720
73%
859
September16th to endNight
85%
660
48%
1826
39%
660
91%
660
85%
723
October1st to 15thNight
76%
660
46%
1815
35%
660
86%
660
75%
777
October16th to endNight
83%
704
46%
2082
42%
704
90%
704
75%
829
November1st to 15thNight
81%
700
42%
2275
39%
700
90%
700
72%
868
November16th to endNight
79%
720
44%
2340
45%
720
85%
720
66%
929
December1st to 15thNight
77%
720
41%
2340
41%
720
84%
720
59%
999
December16th to endNight
69%
768
39%
2496
37%
768
77%
768
52%
1122

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
211112235%76%
47798
Night
111112235%77%
47154
TransparencyDay
10%2411%24%46%
47493
Night
10%1311%24%47%
46960
SeeingDay
25%13%23%33%20%
5796
Night
2214%34%39%6%
16096

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
2212313245%69%
1611
16th to endDay
313313346%67%
1857
February1st to 15thDay
222113336%71%
1751
16th to endDay
211321345%7%66%
1579
March1st to 15thDay
2111112246%74%
1851
16th to endDay
1111111335%76%
2112
April1st to 15thDay
1122445%76%
2124
16th to endDay
1125%85%
2181
May1st to 15thDay
111215%84%
2331
16th to endDay
12388%
2429
June1st to 15thDay
111487%
2340
16th to endDay
111112287%
2340
July1st to 15thDay
1113322247%69%
2340
16th to endDay
211232446%9%62%
2467
August1st to 15thDay
2111212236%73%
2181
16th to endDay
3112212345%70%
2292
September1st to 15thDay
21221325%5%73%
2034
16th to endDay
111112385%
1823
October1st to 15thDay
1111222481%
1815
16th to endDay
111122384%
1788
November1st to 15thDay
111112335%78%
1584
16th to endDay
211112235%76%
1620
December1st to 15thDay
3212223348%65%
1620
16th to endDay
4213213446%65%
1728
January1st to 15thNight
1111323445%69%
2327
16th to endNight
5%21321223470%
2364
February1st to 15thNight
11221335%5%72%
2101
16th to endNight
3212324445%65%
1895
March1st to 15thNight
211213235%74%
2106
16th to endNight
211112247%74%
2112
April1st to 15thNight
11111122481%
1820
16th to endNight
1112387%
1779
May1st to 15thNight
122485%
1619
16th to endNight
111289%
1684
June1st to 15thNight
112488%
1620
16th to endNight
111288%
1620
July1st to 15thNight
1111213235%74%
1620
16th to endNight
212312247%71%
1701
August1st to 15thNight
11112336%78%
1776
16th to endNight
112111145%77%
1910
September1st to 15thNight
11112235%78%
1926
16th to endNight
112289%
1826
October1st to 15thNight
11111226%79%
1815
16th to endNight
111123479%
2082
November1st to 15thNight
11111223480%
2275
16th to endNight
111212235%76%
2340
December1st to 15thNight
2112222337%69%
2340
16th to endNight
4212213346%66%
2496

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
16%26%15%28%30%
1612
16th to endDay
17%26%14%30%28%
1857
February1st to 15thDay
14%25%12%29%36%
1751
16th to endDay
15%37%17%30%26%
1579
March1st to 15thDay
11%1312%28%42%
1851
16th to endDay
10%2311%32%38%
2112
April1st to 15thDay
8%249%33%42%
2124
16th to endDay
4128%28%55%
2181
May1st to 15thDay
6%126%23%59%
2331
16th to endDay
418%25%59%
2432
June1st to 15thDay
415%17%69%
2340
16th to endDay
7%127%79%
2340
July1st to 15thDay
15%25%10%17%49%
2201
16th to endDay
16%49%19%22%27%
2312
August1st to 15thDay
12%2412%26%42%
2166
16th to endDay
15%35%8%23%44%
2292
September1st to 15thDay
12%25%10%21%47%
2034
16th to endDay
6%25%18%67%
1823
October1st to 15thDay
8%148%26%50%
1815
16th to endDay
7%1310%20%57%
1788
November1st to 15thDay
9%1411%28%45%
1584
16th to endDay
10%2312%27%43%
1620
December1st to 15thDay
18%25%17%26%28%
1620
16th to endDay
17%48%22%28%20%
1728
January1st to 15thNight
15%35%11%25%38%
2327
16th to endNight
17%25%15%23%36%
2364
February1st to 15thNight
13%2315%22%42%
2112
16th to endNight
19%35%14%23%33%
1895
March1st to 15thNight
12%1311%28%41%
2106
16th to endNight
9%1413%28%42%
2112
April1st to 15thNight
8%1311%30%43%
1820
16th to endNight
5%118%26%55%
1779
May1st to 15thNight
5%118%24%57%
1620
16th to endNight
5%15%28%58%
1685
June1st to 15thNight
315%19%70%
1620
16th to endNight
5%127%82%
1620
July1st to 15thNight
11%1310%18%54%
1530
16th to endNight
13%25%17%29%31%
1593
August1st to 15thNight
8%2411%28%44%
1767
16th to endNight
9%249%22%50%
1910
September1st to 15thNight
9%248%22%53%
1926
16th to endNight
425%17%69%
1826
October1st to 15thNight
7%1310%25%50%
1815
16th to endNight
7%139%19%58%
2082
November1st to 15thNight
9%1210%26%49%
2275
16th to endNight
11%1311%28%44%
2340
December1st to 15thNight
15%15%16%27%32%
2340
16th to endNight
17%26%20%27%25%
2496

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
12%221%32%26%5%
90
16th to endDay
46%19%32%25%12%
225
February1st to 15thDay
46%13%32%31%11%
266
16th to endDay
412%19%28%25%9%
238
March1st to 15thDay
111%18%25%29%13%
270
16th to endDay
29%22%25%21%17%
288
April1st to 15thDay
413%20%26%24%11%
269
16th to endDay
14%25%28%22%8%
270
May1st to 15thDay
27%22%25%27%15%
288
16th to endDay
28%19%25%33%10%
330
June1st to 15thDay
16%14%26%34%16%
315
16th to endDay
19%24%34%29%
315
July1st to 15thDay
17%18%38%33%
305
16th to endDay
2316%35%41%
327
August1st to 15thDay
3317%40%33%
315
16th to endDay
3411%41%38%
332
September1st to 15thDay
45%22%48%18%
315
16th to endDay
2210%23%40%20%
258
October1st to 15thDay
17%16%23%38%12%
255
16th to endDay
138%22%40%23%
159
November1st to 15thDay
15%12%21%31%28%
90
16th to endDay
45%20%28%28%12%
90
December1st to 15thDay
18%8%18%38%23%
90
16th to endDay
5%320%33%32%5%
96
January1st to 15thNight
2114%45%30%5%
720
16th to endNight
6%117%39%31%2
768
February1st to 15thNight
1214%41%35%3
704
16th to endNight
4320%44%23%3
632
March1st to 15thNight
2421%38%29%3
720
16th to endNight
2321%35%31%4
768
April1st to 15thNight
17%27%34%25%3
719
16th to endNight
15%24%36%29%2
699
May1st to 15thNight
1324%34%33%2
540
16th to endNight
5%23%33%32%3
563
June1st to 15thNight
322%37%33%2
540
16th to endNight
110%38%45%2
540
July1st to 15thNight
1429%56%6%
510
16th to endNight
2221%63%9%
564
August1st to 15thNight
1317%62%14%
693
16th to endNight
2317%58%18%
764
September1st to 15thNight
15%23%57%11%
720
16th to endNight
1110%31%48%7%
660
October1st to 15thNight
2216%38%37%3
660
16th to endNight
11%33%42%11%
704
November1st to 15thNight
112%40%39%5%
700
16th to endNight
113%36%37%10%
720
December1st to 15thNight
2113%43%35%3
720
16th to endNight
5%218%41%27%4
768
Page generated at 2017-09-17 09:05:40. Version ac04

Copyright 2017 A. Danko


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