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 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
71%
15861
36%
46623
29%
15820
78%
15820
58%
21352

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
64%
716
30%
2327
26%
716
72%
716
44%
1137
January16th to endNight
62%
768
35%
2325
28%
768
72%
768
43%
1208
February1st to 15thNight
66%
699
34%
2107
32%
698
73%
698
47%
1052
February16th to endNight
56%
632
31%
1895
30%
632
64%
632
41%
1017
March1st to 15thNight
63%
720
31%
2160
28%
720
72%
720
48%
1057
March16th to endNight
61%
768
33%
2025
23%
768
70%
768
53%
1048
April1st to 15thNight
54%
719
32%
1799
14%
719
64%
719
54%
939
April16th to endNight
60%
720
37%
1800
17%
720
69%
720
67%
859
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%
656
47%
1816
41%
656
91%
656
83%
729
October1st to 15thNight
75%
660
41%
1815
34%
660
83%
660
66%
830
October16th to endNight
78%
704
42%
2147
40%
704
85%
704
64%
909
November1st to 15thNight
77%
700
36%
2275
37%
700
83%
700
59%
966
November16th to endNight
74%
720
38%
2340
38%
720
80%
720
52%
1060
December1st to 15thNight
66%
720
34%
2340
31%
720
74%
720
45%
1148
December16th to endNight
57%
768
32%
2496
27%
768
67%
768
38%
1298

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
111112236%75%
48099
Night
111112236%75%
46819
TransparencyDay
12%46%15%26%33%
47790
Night
12%5%7%17%28%29%
46629
SeeingDay
314%30%31%15%5%
5881
Night
15%18%34%31%7%
15873

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
2214313247%66%
1611
16th to endDay
2323313447%64%
1896
February1st to 15thDay
1213212347%68%
1751
16th to endDay
223334347%63%
1579
March1st to 15thDay
21221235%10%67%
1800
16th to endDay
11111335%9%69%
2194
April1st to 15thDay
1111212237%72%
2149
16th to endDay
11111135%80%
2160
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
11213384%
1816
October1st to 15thDay
2113335%77%
1815
16th to endDay
11111235%79%
1720
November1st to 15thDay
111213235%76%
1584
16th to endDay
1111223336%72%
1620
December1st to 15thDay
121132235%10%64%
1620
16th to endDay
4213323347%63%
1728
January1st to 15thNight
221221335%8%65%
2327
16th to endNight
3212213337%67%
2325
February1st to 15thNight
1212112346%69%
2101
16th to endNight
221232345%8%63%
1895
March1st to 15thNight
1112213349%68%
2160
16th to endNight
112213349%71%
2025
April1st to 15thNight
122212338%71%
1799
16th to endNight
111147%80%
1800
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%
1816
October1st to 15thNight
11112236%78%
1815
16th to endNight
11112235%80%
2147
November1st to 15thNight
11212235%77%
2275
16th to endNight
211222347%73%
2340
December1st to 15thNight
221222325%9%65%
2340
16th to endNight
3213313337%65%
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
20%5%8%19%27%18%
1612
16th to endDay
22%6%8%19%22%20%
1896
February1st to 15thDay
18%6%6%19%26%23%
1751
16th to endDay
22%7%7%19%29%12%
1579
March1st to 15thDay
14%7%7%24%26%20%
1800
16th to endDay
14%6%10%24%26%16%
2194
April1st to 15thDay
16%5%6%21%32%17%
2149
16th to endDay
9%48%22%31%24%
2160
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%138%30%48%
1816
October1st to 15thDay
11%45%14%30%33%
1815
16th to endDay
9%36%12%28%39%
1720
November1st to 15thDay
13%47%16%32%26%
1584
16th to endDay
16%5%7%17%27%26%
1620
December1st to 15thDay
17%7%12%21%23%17%
1620
16th to endDay
24%7%10%22%20%14%
1728
January1st to 15thNight
19%7%8%18%26%20%
2327
16th to endNight
20%7%9%17%21%22%
2325
February1st to 15thNight
17%7%8%19%24%22%
2112
16th to endNight
20%9%9%19%26%14%
1895
March1st to 15thNight
16%7%9%22%23%20%
2160
16th to endNight
14%7%10%25%27%14%
2025
April1st to 15thNight
15%49%28%25%16%
1799
16th to endNight
7%5%8%26%33%18%
1800
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%34%46%
1816
October1st to 15thNight
9%45%13%35%30%
1815
16th to endNight
9%45%10%30%38%
2147
November1st to 15thNight
11%46%15%34%27%
2275
16th to endNight
14%6%7%18%25%27%
2340
December1st to 15thNight
18%7%9%18%25%19%
2340
16th to endNight
22%7%10%20%23%14%
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
7%18%26%33%13%
90
16th to endDay
7%19%28%31%10%3
264
February1st to 15thDay
421%29%26%14%3
266
16th to endDay
7%27%26%24%13%
238
March1st to 15thDay
5%21%31%24%14%2
270
16th to endDay
423%34%22%13%1
288
April1st to 15thDay
5%25%35%19%9%4
269
16th to endDay
234%31%20%9%2
270
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
18%26%37%23%2
256
October1st to 15thDay
218%30%31%13%2
255
16th to endDay
311%29%29%22%3
207
November1st to 15thDay
11%15%28%27%16%
90
16th to endDay
216%24%36%20%
90
December1st to 15thDay
112%24%34%24%3
90
16th to endDay
9%19%18%36%14%1
96
January1st to 15thNight
37%20%37%24%6%
720
16th to endNight
48%22%35%25%5%
768
February1st to 15thNight
27%20%37%25%5%
704
16th to endNight
411%25%31%22%4
632
March1st to 15thNight
19%22%38%23%4
720
16th to endNight
18%25%34%25%4
768
April1st to 15thNight
212%29%28%23%4
719
16th to endNight
18%29%31%22%6%
720
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%31%42%13%
656
October1st to 15thNight
15%16%35%33%7%
660
16th to endNight
1214%33%33%14%
704
November1st to 15thNight
1414%36%33%11%
700
16th to endNight
2415%35%31%10%
720
December1st to 15thNight
36%20%35%26%6%
720
16th to endNight
5%9%23%35%21%4
768
Page generated at 2017-09-16 14:07:01. Version ac04

Copyright 2017 A. Danko


Luz Observatory Clear Sky Chart | Charts Home