Las Brisas Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Las Brisas Observatory clear sky chart from 2005-11-05 to 2017-04-26.

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%
15476
26%
45622
13%
15430
55%
15430
36%
24992

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
34%
900
29%
2506
12%
895
51%
895
40%
1279
January16th to endNight
32%
774
34%
2502
16%
774
54%
774
42%
1170
February1st to 15thNight
25%
703
26%
2241
8%
699
45%
699
34%
1161
February16th to endNight
25%
632
34%
1894
9%
632
50%
632
38%
960
March1st to 15thNight
34%
720
26%
2103
10%
720
48%
720
38%
1123
March16th to endNight
33%
686
28%
2030
11%
686
49%
686
34%
1131
April1st to 15thNight
35%
539
23%
1798
11%
539
52%
539
30%
940
April16th to endNight
32%
528
21%
1760
9%
528
49%
528
27%
1026
May1st to 15thNight
39%
495
18%
1513
13%
495
47%
495
23%
974
May16th to endNight
44%
514
14%
1370
7%
513
52%
513
31%
866
June1st to 15thNight
59%
495
22%
1320
14%
495
66%
495
45%
721
June16th to endNight
68%
495
21%
1320
16%
495
71%
495
47%
717
July1st to 15thNight
64%
465
16%
1240
13%
465
66%
465
27%
842
July16th to endNight
71%
522
15%
1361
15%
489
73%
489
29%
881
August1st to 15thNight
65%
494
15%
1536
16%
491
67%
491
25%
963
August16th to endNight
69%
525
19%
1750
21%
525
71%
525
29%
1036
September1st to 15thNight
60%
495
24%
1650
22%
495
66%
495
30%
973
September16th to endNight
60%
492
32%
1768
26%
492
71%
492
40%
846
October1st to 15thNight
50%
654
30%
1974
16%
654
61%
654
42%
1039
October16th to endNight
51%
713
34%
2121
18%
713
62%
713
46%
1081
November1st to 15thNight
44%
875
33%
2275
15%
875
55%
875
48%
1196
November16th to endNight
40%
900
36%
2382
14%
900
54%
900
50%
1221
December1st to 15thNight
30%
900
25%
2520
7%
900
45%
900
37%
1336
December16th to endNight
27%
960
26%
2688
8%
960
43%
960
33%
1510

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
45%35%5%345%6%8%48%
46046
Night
242442445%8%56%
45800
Cloud CoverDay
45%25%5%35%5%6%8%48%
46044
Night
242442445%8%56%
45800
TransparencyDay
30%6%13%22%19%6%
45727
Night
24%6%15%26%20%6%
45622
SeeingDay
12%16%32%22%13%3
5165
Night
5%11%33%32%14%1
15478

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
424413348%61%
1435
16th to endDay
424322347%61%
1728
February1st to 15thDay
5%35%42336%9%53%
1621
16th to endDay
5%345%235%5%7%55%
1580
March1st to 15thDay
16%46%5%2435%8%50%
1856
16th to endDay
27%36%3445%6%9%47%
2193
April1st to 15thDay
37%26%6%345%6%8%46%
2150
16th to endDay
6%10%37%6%445%5%6%39%
2111
May1st to 15thDay
8%9%47%6%35%6%6%7%35%
2106
16th to endDay
6%6%35%6%36%6%6%8%41%
2392
June1st to 15thDay
5%4345%26%5%8%10%44%
2310
16th to endDay
32145%35%6%6%8%51%
2310
July1st to 15thDay
8%425%6%35%8%7%8%37%
2310
16th to endDay
7%6%36%7%47%6%6%8%34%
2395
August1st to 15thDay
10%6%35%7%46%5%6%7%36%
2082
16th to endDay
8%5%26%5%35%5%6%8%42%
2100
September1st to 15thDay
8%6%25%7%35%5%5%6%44%
1980
16th to endDay
4424423435%60%
1862
October1st to 15thDay
431441445%8%56%
1653
16th to endDay
35%23223345%63%
1738
November1st to 15thDay
142332335%7%62%
1583
16th to endDay
32432335%7%63%
1575
December1st to 15thDay
325%42345%7%59%
1440
16th to endDay
1425%4245%7%9%53%
1536
January1st to 15thNight
21332345%7%63%
2506
16th to endNight
323313345%67%
2502
February1st to 15thNight
5%35%413447%58%
2231
16th to endNight
5%2432335%6%61%
1894
March1st to 15thNight
142442445%8%56%
2103
16th to endNight
34345%23347%57%
2030
April1st to 15thNight
27%24424437%57%
1798
16th to endNight
5%7%26%5%33446%49%
1760
May1st to 15thNight
6%10%35%5%3445%7%42%
1512
16th to endNight
45%25%5%3447%8%48%
1369
June1st to 15thNight
23133245%6%8%58%
1320
16th to endNight
2112325%5%8%7%57%
1320
July1st to 15thNight
6%437%5%45%6%7%9%40%
1320
16th to endNight
5%324447%7%8%11%37%
1462
August1st to 15thNight
6%325%6%45%7%6%7%43%
1545
16th to endNight
6%4235%346%6%10%44%
1750
September1st to 15thNight
6%425%5%345%7%10%44%
1650
16th to endNight
331342335%6%61%
1768
October1st to 15thNight
331232345%7%61%
1974
16th to endNight
33223235%46%63%
2121
November1st to 15thNight
32332435%7%64%
2275
16th to endNight
312413337%66%
2382
December1st to 15thNight
1215%41345%10%58%
2520
16th to endNight
1435%43446%8%54%
2688

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
323413448%61%
1435
16th to endDay
133431335%8%61%
1728
February1st to 15thDay
5%25%43346%8%54%
1621
16th to endDay
5%345%2345%7%56%
1580
March1st to 15thDay
16%36%5%2435%8%50%
1856
16th to endDay
17%35%43446%8%47%
2191
April1st to 15thDay
36%25%5%36%46%8%46%
2150
16th to endDay
6%10%47%5%35%45%6%40%
2111
May1st to 15thDay
7%9%38%6%36%5%5%7%35%
2106
16th to endDay
6%5%25%5%36%5%7%8%41%
2392
June1st to 15thDay
4425%425%5%8%10%44%
2310
16th to endDay
3214435%6%7%8%51%
2310
July1st to 15thDay
8%435%6%37%7%8%7%37%
2310
16th to endDay
7%6%36%6%47%7%7%9%33%
2395
August1st to 15thDay
9%6%26%6%46%6%6%7%35%
2082
16th to endDay
7%426%6%35%6%5%9%42%
2100
September1st to 15thDay
7%5%36%5%35%46%7%44%
1980
16th to endDay
431442434460%
1862
October1st to 15thDay
432442445%9%56%
1653
16th to endDay
35%23323345%63%
1738
November1st to 15thDay
42331335%7%63%
1583
16th to endDay
22432335%8%63%
1575
December1st to 15thDay
335%32445%8%58%
1440
16th to endDay
1425%325%48%9%53%
1536
January1st to 15thNight
21341446%7%64%
2506
16th to endNight
323323346%67%
2502
February1st to 15thNight
435%41345%8%57%
2231
16th to endNight
5%2332345%7%61%
1894
March1st to 15thNight
142442446%8%57%
2103
16th to endNight
25%25%423448%56%
2030
April1st to 15thNight
27%24324347%56%
1798
16th to endNight
5%8%35%5%23446%50%
1760
May1st to 15thNight
6%8%46%435%448%42%
1512
16th to endNight
4425%5%2448%9%48%
1369
June1st to 15thNight
222332446%9%58%
1320
16th to endNight
2112425%5%8%7%57%
1320
July1st to 15thNight
5%437%6%25%6%7%8%40%
1320
16th to endNight
5%3245%47%6%9%11%38%
1462
August1st to 15thNight
6%425%6%36%7%6%7%44%
1545
16th to endNight
5%5%24436%6%7%10%44%
1750
September1st to 15thNight
6%425%5%346%7%9%45%
1650
16th to endNight
321432445%7%61%
1768
October1st to 15thNight
33123235%5%7%61%
1974
16th to endNight
331331345%6%62%
2121
November1st to 15thNight
22332345%8%64%
2275
16th to endNight
313323337%66%
2382
December1st to 15thNight
1315%41345%10%58%
2520
16th to endNight
5%35%43445%8%54%
2688

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
20%5%18%31%19%4
1436
16th to endDay
20%415%32%19%7%
1728
February1st to 15thDay
24%5%17%30%16%4
1622
16th to endDay
25%311%29%24%5%
1580
March1st to 15thDay
29%413%25%21%5%
1856
16th to endDay
31%6%13%25%19%3
2193
April1st to 15thDay
33%6%13%24%16%6%
2150
16th to endDay
42%6%12%20%16%2
2111
May1st to 15thDay
44%9%13%17%14%1
2106
16th to endDay
37%9%15%18%13%5%
2396
June1st to 15thDay
31%8%13%17%20%9%
2310
16th to endDay
26%8%10%19%24%10%
2310
July1st to 15thDay
38%9%13%17%13%7%
2161
16th to endDay
41%10%15%19%9%2
2234
August1st to 15thDay
43%9%13%13%13%6%
2067
16th to endDay
35%8%13%22%15%4
2100
September1st to 15thDay
36%6%11%18%17%8%
1980
16th to endDay
25%49%23%30%6%
1862
October1st to 15thDay
24%6%12%23%27%6%
1653
16th to endDay
22%310%26%29%7%
1738
November1st to 15thDay
19%413%24%26%12%
1583
16th to endDay
17%310%29%29%9%
1575
December1st to 15thDay
23%5%18%28%20%3
1440
16th to endDay
23%7%19%25%17%6%
1536
January1st to 15thNight
18%5%17%31%23%3
2506
16th to endNight
18%413%31%24%7%
2502
February1st to 15thNight
24%5%15%35%15%3
2241
16th to endNight
21%311%30%26%6%
1894
March1st to 15thNight
22%5%13%27%25%4
2103
16th to endNight
27%5%11%29%22%3
2030
April1st to 15thNight
26%414%28%19%5%
1798
16th to endNight
34%5%15%25%14%3
1760
May1st to 15thNight
39%7%14%21%14%3
1513
16th to endNight
31%9%17%21%13%5%
1370
June1st to 15thNight
21%7%19%21%15%14%
1320
16th to endNight
19%9%15%21%21%13%
1320
July1st to 15thNight
37%11%14%18%9%7%
1240
16th to endNight
31%13%21%21%9%2
1361
August1st to 15thNight
36%10%16%18%12%6%
1536
16th to endNight
30%10%17%24%13%3
1750
September1st to 15thNight
32%8%14%20%15%7%
1650
16th to endNight
22%411%29%25%5%
1768
October1st to 15thNight
21%7%12%23%27%7%
1974
16th to endNight
20%5%10%28%29%6%
2121
November1st to 15thNight
17%5%13%26%24%13%
2275
16th to endNight
17%311%28%29%8%
2382
December1st to 15thNight
20%6%20%29%18%4
2520
16th to endNight
25%6%19%24%19%4
2688

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
15%15%34%14%20%
90
16th to endDay
317%41%29%8%
96
February1st to 15thDay
11%32%43%11%2
90
16th to endDay
9%28%32%20%7%1
81
March1st to 15thDay
13%21%44%14%6%
146
16th to endDay
15%34%36%11%1
288
April1st to 15thDay
15%36%30%12%41
269
16th to endDay
27%35%24%9%2
254
May1st to 15thDay
13%19%36%23%6%1
327
16th to endDay
12%16%30%24%12%3
437
June1st to 15thDay
6%14%30%25%18%4
420
16th to endDay
47%32%26%22%6%
420
July1st to 15thDay
11%425%26%25%7%
400
16th to endDay
11%221%32%24%7%
380
August1st to 15thDay
20%7%26%27%11%5%
255
16th to endDay
13%6%36%27%11%3
268
September1st to 15thDay
13%16%37%25%5%1
255
16th to endDay
8%8%39%21%17%4
137
October1st to 15thDay
212%28%30%18%7%
90
16th to endDay
9%19%27%28%11%4
96
November1st to 15thDay
6%8%30%20%28%5%
90
16th to endDay
12%20%45%15%6%
90
December1st to 15thDay
10%28%45%13%2
90
16th to endDay
7%25%43%19%31
96
January1st to 15thNight
418%38%26%10%1
900
16th to endNight
213%46%27%7%1
774
February1st to 15thNight
415%49%26%3
704
16th to endNight
320%45%26%3
632
March1st to 15thNight
315%42%30%7%
720
16th to endNight
6%15%39%31%6%
686
April1st to 15thNight
7%20%34%31%5%
539
16th to endNight
10%15%38%27%7%
528
May1st to 15thNight
12%9%31%35%9%1
495
16th to endNight
6%8%31%35%15%1
515
June1st to 15thNight
5%425%45%16%2
495
16th to endNight
3120%43%29%2
495
July1st to 15thNight
7%112%40%34%3
465
16th to endNight
6%9%35%42%5%
522
August1st to 15thNight
9%212%34%37%4
494
16th to endNight
8%111%35%37%4
525
September1st to 15thNight
9%219%38%25%5%
495
16th to endNight
45%23%37%24%3
492
October1st to 15thNight
5%8%32%34%15%3
654
16th to endNight
5%6%32%34%17%3
713
November1st to 15thNight
312%34%35%12%1
875
16th to endNight
414%38%31%10%1
900
December1st to 15thNight
319%42%27%6%
900
16th to endNight
5%17%43%26%6%
960
Page generated at 2017-04-27 15:49:00. Version ac04

Copyright 2017 A. Danko


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