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 2018-11-30.

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
44%
17547
26%
51711
14%
17501
56%
17501
37%
28188

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%
975
29%
2716
12%
970
52%
970
42%
1375
January16th to endNight
33%
838
35%
2710
17%
838
55%
838
44%
1253
February1st to 15thNight
26%
763
26%
2431
8%
759
45%
759
34%
1242
February16th to endNight
24%
684
33%
2050
8%
684
50%
684
37%
1042
March1st to 15thNight
35%
780
26%
2278
10%
780
49%
780
39%
1204
March16th to endNight
34%
743
27%
2199
11%
743
49%
743
34%
1221
April1st to 15thNight
33%
584
23%
1948
11%
584
51%
584
30%
1019
April16th to endNight
32%
579
21%
1929
9%
579
50%
579
27%
1125
May1st to 15thNight
42%
585
19%
1788
14%
585
50%
585
25%
1138
May16th to endNight
46%
610
16%
1626
9%
609
53%
609
32%
1019
June1st to 15thNight
61%
585
23%
1560
16%
585
67%
585
46%
837
June16th to endNight
67%
585
22%
1560
18%
585
71%
585
47%
848
July1st to 15thNight
66%
555
16%
1480
14%
555
67%
555
29%
980
July16th to endNight
71%
612
15%
1613
15%
579
72%
579
27%
1064
August1st to 15thNight
68%
575
15%
1787
16%
572
69%
572
27%
1106
August16th to endNight
70%
621
20%
2070
22%
621
72%
621
30%
1213
September1st to 15thNight
64%
585
24%
1950
23%
585
69%
585
31%
1131
September16th to endNight
59%
582
32%
2090
25%
582
69%
582
39%
1014
October1st to 15thNight
49%
773
29%
2333
16%
773
60%
773
41%
1251
October16th to endNight
52%
843
35%
2507
18%
843
63%
843
46%
1279
November1st to 15thNight
43%
1025
33%
2665
15%
1025
54%
1025
48%
1397
November16th to endNight
41%
1050
35%
2779
14%
1050
55%
1050
51%
1404
December1st to 15thNight
31%
975
25%
2730
8%
975
46%
975
39%
1426
December16th to endNight
27%
1040
28%
2912
10%
1040
44%
1040
35%
1600

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%25%5%345%6%8%49%
52597
Night
242442445%8%56%
51889
Cloud CoverDay
45%25%5%35%5%6%8%49%
52595
Night
242442445%8%56%
51889
TransparencyDay
30%6%13%22%19%6%
52278
Night
24%6%14%26%21%6%
51711
SeeingDay
10%16%32%23%13%3
7373
Night
5%11%32%33%15%1
17549

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
424413448%61%
1555
16th to endDay
424313348%61%
1872
February1st to 15thDay
5%25%42336%10%53%
1760
16th to endDay
5%344235%5%7%56%
1710
March1st to 15thDay
16%35%5%2435%9%51%
2011
16th to endDay
27%36%4345%6%9%47%
2376
April1st to 15thDay
37%26%5%345%6%8%46%
2330
16th to endDay
6%11%37%6%4445%6%39%
2306
May1st to 15thDay
7%8%46%7%35%6%7%7%36%
2490
16th to endDay
6%5%25%5%35%6%6%9%41%
2840
June1st to 15thDay
4434426%5%7%10%46%
2730
16th to endDay
32145%35%6%6%8%50%
2730
July1st to 15thDay
7%425%6%35%7%7%8%38%
2730
16th to endDay
7%5%36%7%47%6%6%8%34%
2803
August1st to 15thDay
9%6%35%6%46%6%6%8%35%
2414
16th to endDay
7%426%5%36%5%6%8%42%
2484
September1st to 15thDay
8%5%25%7%35%5%5%6%45%
2340
16th to endDay
4414423445%59%
2200
October1st to 15thDay
441441345%7%56%
1953
16th to endDay
35%24223346%61%
2054
November1st to 15thDay
142331335%8%62%
1853
16th to endDay
22332335%7%64%
1832
December1st to 15thDay
325%42345%7%60%
1560
16th to endDay
132432447%9%54%
1664
January1st to 15thNight
21332345%7%64%
2716
16th to endNight
313323336%68%
2710
February1st to 15thNight
435%413448%58%
2421
16th to endNight
5%2432335%6%61%
2050
March1st to 15thNight
132442445%9%57%
2278
16th to endNight
24345%23347%57%
2199
April1st to 15thNight
26%24424437%56%
1948
16th to endNight
5%7%26%433446%49%
1929
May1st to 15thNight
5%9%35%5%3445%7%42%
1787
16th to endNight
45%25%5%3447%8%48%
1625
June1st to 15thNight
22133145%6%9%58%
1560
16th to endNight
2212325%5%8%7%57%
1560
July1st to 15thNight
5%437%5%35%6%6%8%42%
1560
16th to endNight
5%425%447%7%9%12%36%
1714
August1st to 15thNight
5%325%5%45%7%7%9%43%
1796
16th to endNight
5%4235%35%6%7%10%44%
2070
September1st to 15thNight
5%425%5%345%7%10%45%
1950
16th to endNight
331442335%6%60%
2090
October1st to 15thNight
33123235%5%6%60%
2333
16th to endNight
33123235%5%6%62%
2507
November1st to 15thNight
323314347%64%
2665
16th to endNight
312323348%66%
2779
December1st to 15thNight
13144134410%60%
2730
16th to endNight
435%33446%8%55%
2912

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
32341345%8%60%
1555
16th to endDay
434313348%61%
1872
February1st to 15thDay
5%25%43346%8%54%
1760
16th to endDay
5%3442345%7%57%
1710
March1st to 15thDay
15%35%5%2435%8%52%
2011
16th to endDay
17%35%43446%8%48%
2374
April1st to 15thDay
36%25%5%35%45%9%46%
2330
16th to endDay
5%10%47%5%35%45%6%40%
2306
May1st to 15thDay
6%8%37%6%36%5%5%8%36%
2490
16th to endDay
6%5%25%5%36%6%7%8%42%
2840
June1st to 15thDay
4425%425%5%8%10%47%
2730
16th to endDay
3214435%6%7%8%50%
2730
July1st to 15thDay
7%425%6%37%7%7%7%39%
2730
16th to endDay
7%6%27%6%37%7%7%8%33%
2803
August1st to 15thDay
8%6%26%6%46%7%6%8%35%
2414
16th to endDay
6%426%7%35%5%6%9%42%
2484
September1st to 15thDay
7%426%5%35%5%5%7%45%
2340
16th to endDay
4414424345%60%
2200
October1st to 15thDay
441432445%8%56%
1953
16th to endDay
35%24323445%61%
2054
November1st to 15thDay
42331335%7%63%
1853
16th to endDay
22432335%7%64%
1832
December1st to 15thDay
335%32335%8%60%
1560
16th to endDay
1324325%47%9%54%
1664
January1st to 15thNight
21331345%7%64%
2716
16th to endNight
313323346%67%
2710
February1st to 15thNight
435%41345%9%58%
2421
16th to endNight
5%2332345%7%61%
2050
March1st to 15thNight
142442446%8%57%
2278
16th to endNight
25%25%423447%57%
2199
April1st to 15thNight
26%24324347%56%
1948
16th to endNight
5%8%35%5%23446%50%
1929
May1st to 15thNight
5%7%45%435%449%42%
1787
16th to endNight
4425%5%2447%9%48%
1625
June1st to 15thNight
221322446%9%59%
1560
16th to endNight
2112425%6%8%7%57%
1560
July1st to 15thNight
4437%5%35%6%8%8%42%
1560
16th to endNight
5%3245%5%7%7%9%11%37%
1714
August1st to 15thNight
5%315%6%36%7%7%8%44%
1796
16th to endNight
5%414435%6%7%10%44%
2070
September1st to 15thNight
5%425%5%346%7%10%45%
1950
16th to endNight
3314324447%60%
2090
October1st to 15thNight
33133235%5%7%59%
2333
16th to endNight
331331345%7%61%
2507
November1st to 15thNight
323223447%64%
2665
16th to endNight
312323348%66%
2779
December1st to 15thNight
131441345%9%60%
2730
16th to endNight
425%43445%8%55%
2912

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%30%19%5%
1556
16th to endDay
20%416%31%20%6%
1872
February1st to 15thDay
24%419%30%16%4
1761
16th to endDay
23%410%27%26%6%
1710
March1st to 15thDay
28%313%26%22%6%
2011
16th to endDay
31%6%13%25%19%3
2376
April1st to 15thDay
33%6%13%24%16%6%
2330
16th to endDay
42%5%11%20%15%3
2306
May1st to 15thDay
42%9%13%18%13%1
2490
16th to endDay
35%9%15%18%15%6%
2844
June1st to 15thDay
29%8%13%16%21%11%
2730
16th to endDay
26%8%11%19%24%10%
2730
July1st to 15thDay
37%9%12%17%16%7%
2581
16th to endDay
41%11%16%18%9%2
2642
August1st to 15thDay
42%10%13%14%13%5%
2399
16th to endDay
35%8%13%21%17%3
2484
September1st to 15thDay
35%6%12%18%17%9%
2340
16th to endDay
25%49%23%30%7%
2200
October1st to 15thDay
24%6%11%22%26%8%
1953
16th to endDay
23%410%26%27%7%
2054
November1st to 15thDay
18%313%25%27%11%
1853
16th to endDay
17%410%30%29%9%
1832
December1st to 15thDay
22%5%17%28%19%5%
1560
16th to endDay
22%6%18%25%19%6%
1664
January1st to 15thNight
17%5%17%31%24%4
2716
16th to endNight
17%413%30%26%7%
2710
February1st to 15thNight
23%5%17%35%15%3
2431
16th to endNight
21%311%28%28%6%
2050
March1st to 15thNight
22%5%13%27%26%4
2278
16th to endNight
26%5%12%28%22%3
2199
April1st to 15thNight
26%5%14%28%19%5%
1948
16th to endNight
34%6%14%25%15%3
1929
May1st to 15thNight
38%7%13%23%13%2
1788
16th to endNight
31%8%16%21%14%5%
1626
June1st to 15thNight
20%6%18%22%16%15%
1560
16th to endNight
19%8%14%21%21%13%
1560
July1st to 15thNight
35%11%14%19%12%6%
1480
16th to endNight
32%14%20%21%8%1
1613
August1st to 15thNight
34%10%17%19%12%5%
1787
16th to endNight
30%10%17%25%13%2
2070
September1st to 15thNight
31%8%15%21%14%8%
1950
16th to endNight
23%5%11%27%26%6%
2090
October1st to 15thNight
22%7%13%21%26%8%
2333
16th to endNight
20%5%10%27%28%7%
2507
November1st to 15thNight
17%5%12%26%26%12%
2665
16th to endNight
16%411%30%28%8%
2779
December1st to 15thNight
19%5%19%28%20%5%
2730
16th to endNight
24%5%18%24%21%5%
2912

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
11%16%38%20%13%
135
16th to endDay
222%38%28%6%1
144
February1st to 15thDay
13%37%34%13%1
135
16th to endDay
7%35%33%16%5%
120
March1st to 15thDay
12%22%43%15%6%
196
16th to endDay
15%34%36%11%1
352
April1st to 15thDay
14%40%29%11%3
329
16th to endDay
24%35%25%10%21
318
May1st to 15thDay
11%19%35%24%7%1
465
16th to endDay
10%17%29%25%13%2
597
June1st to 15thDay
6%13%30%26%18%4
570
16th to endDay
47%36%26%20%5%
570
July1st to 15thDay
10%423%27%26%8%
550
16th to endDay
10%221%30%27%7%
518
August1st to 15thDay
16%5%29%30%12%4
359
16th to endDay
10%6%35%28%15%3
396
September1st to 15thDay
11%11%34%27%11%4
375
16th to endDay
8%12%36%26%12%2
235
October1st to 15thDay
9%16%33%23%12%3
180
16th to endDay
8%17%32%23%15%2
192
November1st to 15thDay
7%14%37%21%16%3
180
16th to endDay
10%19%42%20%6%
178
December1st to 15thDay
8%27%44%14%5%
135
16th to endDay
6%27%40%20%4
144
January1st to 15thNight
417%38%27%9%1
975
16th to endNight
213%45%28%7%1
838
February1st to 15thNight
414%49%27%3
764
16th to endNight
420%46%25%3
684
March1st to 15thNight
215%42%31%7%
780
16th to endNight
6%15%39%32%6%
743
April1st to 15thNight
7%20%36%30%5%
584
16th to endNight
11%14%37%27%8%
579
May1st to 15thNight
10%8%30%38%10%1
585
16th to endNight
6%8%31%36%16%1
611
June1st to 15thNight
4424%44%17%3
585
16th to endNight
3120%44%27%1
585
July1st to 15thNight
7%11%39%38%3
555
16th to endNight
6%8%35%42%5%
612
August1st to 15thNight
8%111%37%37%3
575
16th to endNight
7%111%37%37%4
621
September1st to 15thNight
8%117%36%30%6%
585
16th to endNight
45%25%38%23%2
582
October1st to 15thNight
5%8%33%36%13%2
773
16th to endNight
5%5%31%35%17%2
843
November1st to 15thNight
312%35%35%10%1
1025
16th to endNight
314%37%33%9%1
1050
December1st to 15thNight
318%41%28%6%
975
16th to endNight
5%17%42%26%6%
1040
Page generated at 2018-12-01 09:35:38. Version ac04

Copyright 2018 A. Danko


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