Luz Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Luz Observatory clear sky chart from 2005-11-05 to 2018-04-23.

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
72%
16733
37%
49225
30%
16692
78%
16692
58%
22532

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
65%
776
30%
2522
27%
776
72%
776
44%
1240
January16th to endNight
63%
832
35%
2519
29%
832
73%
832
44%
1298
February1st to 15thNight
67%
759
35%
2287
32%
758
75%
758
49%
1122
February16th to endNight
56%
684
32%
2051
31%
684
64%
684
42%
1083
March1st to 15thNight
62%
780
30%
2340
27%
780
71%
780
47%
1156
March16th to endNight
61%
832
32%
2194
22%
832
69%
832
51%
1148
April1st to 15thNight
54%
779
33%
1949
15%
779
65%
779
54%
1020
April16th to endNight
59%
744
38%
1860
17%
744
68%
744
66%
896
May1st to 15thNight
65%
566
37%
1646
23%
566
70%
566
70%
669
May16th to endNight
59%
561
35%
1685
22%
561
68%
561
68%
688
June1st to 15thNight
71%
540
35%
1620
28%
540
75%
540
76%
630
June16th to endNight
89%
360
43%
1440
50%
360
92%
360
83%
414
July1st to 15thNight
93%
362
35%
1382
41%
362
93%
362
69%
468
July16th to endNight
86%
601
33%
1627
26%
565
87%
565
63%
739
August1st to 15thNight
89%
717
38%
1790
25%
713
90%
713
81%
798
August16th to endNight
92%
764
44%
1910
29%
764
92%
764
82%
856
September1st to 15thNight
90%
720
41%
1856
31%
720
92%
720
77%
833
September16th to endNight
86%
716
49%
1980
43%
716
92%
716
83%
793
October1st to 15thNight
76%
720
40%
1980
34%
720
83%
720
67%
893
October16th to endNight
79%
768
45%
2343
43%
768
86%
768
65%
981
November1st to 15thNight
78%
760
35%
2470
36%
760
83%
760
58%
1055
November16th to endNight
75%
780
39%
2535
40%
780
80%
780
52%
1149
December1st to 15thNight
66%
780
34%
2535
31%
780
74%
780
47%
1217
December16th to endNight
59%
832
33%
2704
29%
832
68%
832
39%
1386

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
111212236%75%
50273
Night
111112236%75%
49421
TransparencyDay
12%46%15%26%33%
49964
Night
12%5%7%17%28%29%
49231
SeeingDay
314%29%31%15%5%
6662
Night
15%17%34%31%7%
16745

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
2214323247%65%
1746
16th to endDay
2313313347%65%
2054
February1st to 15thDay
1212212346%70%
1901
16th to endDay
223323347%65%
1709
March1st to 15thDay
21221235%10%66%
1950
16th to endDay
11121335%9%68%
2377
April1st to 15thDay
1211212237%72%
2329
16th to endDay
11111135%80%
2214
May1st to 15thDay
111236%80%
2301
16th to endDay
11111122482%
2429
June1st to 15thDay
1225%84%
2340
16th to endDay
1111288%
2514
July1st to 15thDay
11112245%77%
2490
16th to endDay
112213346%71%
2427
August1st to 15thDay
11123483%
2160
16th to endDay
1212235%78%
2292
September1st to 15thDay
11112235%79%
2103
16th to endDay
11213285%
1980
October1st to 15thDay
1112225%78%
1980
16th to endDay
1111235%80%
1876
November1st to 15thDay
111213235%75%
1719
16th to endDay
1111223336%71%
1755
December1st to 15thDay
121122235%10%66%
1755
16th to endDay
3213323347%63%
1872
January1st to 15thNight
221322345%8%64%
2522
16th to endNight
2212213337%68%
2519
February1st to 15thNight
1212112446%70%
2281
16th to endNight
221232345%8%64%
2051
March1st to 15thNight
11112133410%67%
2340
16th to endNight
113213349%69%
2194
April1st to 15thNight
122211339%71%
1949
16th to endNight
111146%79%
1860
May1st to 15thNight
11146%82%
1646
16th to endNight
111225%83%
1684
June1st to 15thNight
122486%
1620
16th to endNight
1291%
1440
July1st to 15thNight
111122383%
1464
16th to endNight
1111213146%74%
1738
August1st to 15thNight
1112385%
1800
16th to endNight
1122485%
1910
September1st to 15thNight
111212383%
1856
16th to endNight
12389%
1980
October1st to 15thNight
1112236%79%
1980
16th to endNight
1111223480%
2343
November1st to 15thNight
11212335%76%
2470
16th to endNight
211222347%72%
2535
December1st to 15thNight
221221325%8%66%
2535
16th to endNight
3213313347%65%
2704

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%8%21%26%17%
1747
16th to endDay
21%6%8%20%23%19%
2054
February1st to 15thDay
16%6%6%18%27%24%
1901
16th to endDay
21%7%6%20%29%14%
1709
March1st to 15thDay
15%7%7%24%25%19%
1950
16th to endDay
15%6%10%24%27%16%
2377
April1st to 15thDay
16%5%6%20%31%18%
2329
16th to endDay
8%37%22%32%24%
2214
May1st to 15thDay
7%38%19%31%28%
2301
16th to endDay
9%25%18%39%24%
2432
June1st to 15thDay
6%3310%28%47%
2340
16th to endDay
5%12415%71%
2514
July1st to 15thDay
9%348%18%55%
2343
16th to endDay
13%5%6%15%21%37%
2275
August1st to 15thDay
6%238%18%59%
2146
16th to endDay
8%348%24%49%
2292
September1st to 15thDay
8%36%8%26%46%
2103
16th to endDay
7%128%31%48%
1980
October1st to 15thDay
10%45%13%29%37%
1980
16th to endDay
8%35%12%27%41%
1876
November1st to 15thDay
13%47%17%32%24%
1719
16th to endDay
15%5%7%16%28%26%
1755
December1st to 15thDay
15%7%11%21%23%20%
1755
16th to endDay
23%7%9%21%22%15%
1872
January1st to 15thNight
19%7%9%19%25%19%
2522
16th to endNight
20%7%8%18%23%22%
2519
February1st to 15thNight
16%6%8%18%25%23%
2292
16th to endNight
19%9%9%18%27%15%
2051
March1st to 15thNight
16%8%10%22%23%19%
2340
16th to endNight
15%7%10%24%27%13%
2194
April1st to 15thNight
15%5%9%27%25%16%
1949
16th to endNight
8%5%8%26%33%18%
1860
May1st to 15thNight
5%38%25%33%21%
1647
16th to endNight
7%38%23%38%18%
1685
June1st to 15thNight
5%35%14%30%41%
1620
16th to endNight
326%22%63%
1440
July1st to 15thNight
7%239%17%58%
1382
16th to endNight
13%37%12%25%36%
1627
August1st to 15thNight
5%239%26%52%
1790
16th to endNight
6%149%32%45%
1910
September1st to 15thNight
7%25%7%32%44%
1856
16th to endNight
41211%35%45%
1980
October1st to 15thNight
9%45%12%35%32%
1980
16th to endNight
8%45%10%29%41%
2343
November1st to 15thNight
12%46%17%33%25%
2470
16th to endNight
14%6%7%18%26%27%
2535
December1st to 15thNight
17%7%9%18%25%22%
2535
16th to endNight
21%7%10%19%25%16%
2704

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
6%15%21%32%21%2
135
16th to endDay
5%18%26%31%14%4
326
February1st to 15thDay
419%26%26%17%5%
326
16th to endDay
6%27%26%26%12%
290
March1st to 15thDay
422%32%24%13%2
330
16th to endDay
424%32%24%13%1
352
April1st to 15thDay
5%22%34%21%10%4
329
16th to endDay
233%31%19%10%2
288
May1st to 15thDay
120%34%29%10%4
288
16th to endDay
315%36%27%12%4
330
June1st to 15thDay
113%38%28%13%4
315
16th to endDay
5%38%33%14%7%
315
July1st to 15thDay
429%39%18%7%
305
16th to endDay
1125%42%18%10%
327
August1st to 15thDay
3333%33%14%11%
315
16th to endDay
1125%40%17%12%
332
September1st to 15thDay
2429%40%18%4
315
16th to endDay
8%27%37%22%2
315
October1st to 15thDay
216%30%34%13%2
315
16th to endDay
210%25%30%23%7%
265
November1st to 15thDay
28%20%31%25%11%
135
16th to endDay
113%20%37%22%5%
135
December1st to 15thDay
13%21%32%28%3
135
16th to endDay
6%16%14%32%22%6%
144
January1st to 15thNight
37%19%38%24%6%
780
16th to endNight
38%21%35%26%5%
832
February1st to 15thNight
27%19%36%27%6%
764
16th to endNight
412%25%32%22%3
684
March1st to 15thNight
29%22%38%22%4
780
16th to endNight
18%25%34%24%4
832
April1st to 15thNight
212%29%28%23%3
779
16th to endNight
19%28%31%22%6%
744
May1st to 15thNight
7%26%38%22%4
567
16th to endNight
7%30%34%24%2
563
June1st to 15thNight
323%44%25%2
540
16th to endNight
8%47%40%3
360
July1st to 15thNight
233%54%7%
362
16th to endNight
16%38%45%6%
601
August1st to 15thNight
16%32%46%12%
717
16th to endNight
427%51%15%
764
September1st to 15thNight
15%29%47%15%
720
16th to endNight
110%32%41%13%
716
October1st to 15thNight
416%36%34%7%
720
16th to endNight
1213%32%35%14%
768
November1st to 15thNight
1314%38%32%10%
760
16th to endNight
2415%34%33%9%
780
December1st to 15thNight
36%20%36%27%6%
780
16th to endNight
5%8%22%35%22%5%
832
Page generated at 2018-04-24 07:03:04. Version ac04

Copyright 2018 A. Danko


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