LAS Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the LAS Observatory clear sky chart from 2005-11-05 to 2018-02-22.

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
36%
16360
20%
48800
12%
16315
44%
16315
22%
31759

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
18%
975
15%
2716
6%
970
27%
970
16%
1986
January16th to endNight
18%
940
17%
2762
5%
940
29%
940
15%
1958
February1st to 15thNight
15%
764
15%
2292
4%
761
24%
761
13%
1675
February16th to endNight
15%
659
15%
1977
5%
659
24%
659
14%
1419
March1st to 15thNight
20%
720
16%
2151
7%
720
28%
720
16%
1497
March16th to endNight
26%
708
14%
2052
6%
708
34%
708
17%
1446
April1st to 15thNight
30%
539
22%
1797
12%
539
44%
539
22%
1086
April16th to endNight
32%
540
20%
1728
10%
540
43%
540
20%
1100
May1st to 15thNight
32%
540
15%
1619
8%
539
39%
539
19%
1121
May16th to endNight
45%
561
19%
1683
10%
561
53%
561
21%
1094
June1st to 15thNight
53%
540
21%
1458
13%
540
60%
540
31%
886
June16th to endNight
55%
540
21%
1440
13%
540
61%
540
35%
853
July1st to 15thNight
58%
510
18%
1360
13%
510
61%
510
33%
850
July16th to endNight
62%
564
23%
1500
16%
531
72%
531
36%
877
August1st to 15thNight
67%
539
24%
1661
22%
536
71%
536
35%
916
August16th to endNight
69%
573
26%
1910
25%
573
73%
573
37%
988
September1st to 15thNight
60%
606
26%
1866
23%
606
64%
606
32%
1090
September16th to endNight
56%
717
29%
1980
20%
717
61%
717
33%
1192
October1st to 15thNight
50%
720
31%
1980
21%
720
58%
720
33%
1182
October16th to endNight
36%
768
25%
2438
18%
768
47%
768
25%
1495
November1st to 15thNight
35%
760
26%
2471
18%
760
48%
760
25%
1461
November16th to endNight
28%
780
24%
2535
13%
780
41%
780
19%
1607
December1st to 15thNight
25%
780
15%
2535
8%
780
34%
780
14%
1777
December16th to endNight
15%
1017
14%
2889
4%
1017
24%
1017
12%
2203

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
14%6%35%5%3445%7%39%
49455
Night
14%7%35%424447%41%
48984
TransparencyDay
43%5%11%22%14%2
49141
Night
42%5%10%22%15%3
48802
SeeingDay
16%14%22%21%15%7%
6231
Night
16%20%21%24%14%2
16362

By Month

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
21%9%38%423345%32%
1552
16th to endDay
13%10%47%5%23346%37%
1811
February1st to 15thDay
16%11%5%7%5%23336%35%
1900
16th to endDay
16%9%37%5%345%5%6%31%
1643
March1st to 15thDay
23%8%25%424245%36%
1809
16th to endDay
17%7%36%43446%7%33%
2180
April1st to 15thDay
15%8%25%433447%40%
2151
16th to endDay
17%6%35%5%34447%38%
2232
May1st to 15thDay
20%6%35%5%34347%34%
2331
16th to endDay
11%6%25%6%37%6%5%8%35%
2431
June1st to 15thDay
9%325%5%35%5%5%9%44%
2499
16th to endDay
7%334436%5%6%9%43%
2520
July1st to 15thDay
12%6%26%5%346%6%9%36%
2520
16th to endDay
7%425%5%46%6%8%9%39%
2562
August1st to 15thDay
8%415%5%36%6%6%10%41%
2286
16th to endDay
7%425%3345%7%9%44%
2292
September1st to 15thDay
12%6%25%5%2446%6%43%
2082
16th to endDay
12%5%245%34445%48%
1980
October1st to 15thDay
13%5%24423445%49%
1980
16th to endDay
16%6%14423345%46%
1784
November1st to 15thDay
14%6%2432445%5%46%
1717
16th to endDay
19%7%33313346%42%
1755
December1st to 15thDay
22%10%46%423335%33%
1755
16th to endDay
20%11%5%7%5%24335%31%
1683
January1st to 15thNight
18%9%48%6%2344433%
2716
16th to endNight
16%10%46%5%2435%5%33%
2762
February1st to 15thNight
19%9%47%5%24435%32%
2283
16th to endNight
18%10%46%42445%6%31%
1977
March1st to 15thNight
17%9%45%5%3334437%
2151
16th to endNight
15%8%36%6%3445%7%34%
2052
April1st to 15thNight
13%5%3441445%8%44%
1797
16th to endNight
16%5%345%25%446%42%
1728
May1st to 15thNight
16%7%35%6%25%347%37%
1619
16th to endNight
8%4247%45%6%6%8%40%
1682
June1st to 15thNight
6%315%425%45%8%50%
1458
16th to endNight
5%213435%5%5%10%50%
1440
July1st to 15thNight
9%415%5%2445%9%47%
1440
16th to endNight
6%3133245%7%10%49%
1603
August1st to 15thNight
6%31433446%10%51%
1672
16th to endNight
432432446%11%52%
1910
September1st to 15thNight
12%324423349%49%
1866
16th to endNight
10%5%24433346%51%
1980
October1st to 15thNight
10%423423346%53%
1980
16th to endNight
16%6%24423335%47%
2438
November1st to 15thNight
14%5%24424436%48%
2471
16th to endNight
17%7%34324336%43%
2535
December1st to 15thNight
20%9%5%6%423336%34%
2535
16th to endNight
22%12%46%424336%28%
2889

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
53%410%19%11%1
1553
16th to endDay
47%5%11%26%8%1
1811
February1st to 15thDay
51%39%23%9%1
1902
16th to endDay
52%5%13%20%8%
1643
March1st to 15thDay
51%310%19%12%1
1809
16th to endDay
49%7%12%22%7%1
2181
April1st to 15thDay
44%5%9%22%18%
2151
16th to endDay
44%6%9%23%12%3
2232
May1st to 15thDay
50%6%11%19%11%
2331
16th to endDay
44%8%13%17%13%2
2435
June1st to 15thDay
36%6%11%24%17%2
2499
16th to endDay
34%8%13%21%19%3
2520
July1st to 15thDay
42%7%12%19%14%4
2371
16th to endDay
35%10%14%22%14%2
2402
August1st to 15thDay
36%7%12%22%18%2
2273
16th to endDay
32%7%14%21%18%4
2292
September1st to 15thDay
39%6%9%21%18%5%
2082
16th to endDay
37%5%8%22%23%3
1980
October1st to 15thDay
35%48%25%22%2
1980
16th to endDay
40%39%27%18%2
1784
November1st to 15thDay
38%39%24%17%7%
1717
16th to endDay
43%38%24%17%2
1755
December1st to 15thDay
54%310%20%9%1
1755
16th to endDay
56%410%19%7%1
1683
January1st to 15thNight
53%48%17%13%1
2716
16th to endNight
51%411%21%9%1
2762
February1st to 15thNight
55%49%21%7%1
2292
16th to endNight
52%5%12%19%9%
1977
March1st to 15thNight
50%49%21%11%3
2151
16th to endNight
48%5%14%21%8%1
2052
April1st to 15thNight
37%5%11%22%19%3
1797
16th to endNight
42%49%24%14%5%
1728
May1st to 15thNight
46%6%10%22%11%1
1620
16th to endNight
38%9%12%18%17%4
1684
June1st to 15thNight
30%7%12%24%21%3
1458
16th to endNight
28%6%16%20%21%6%
1440
July1st to 15thNight
33%6%12%23%18%4
1360
16th to endNight
26%7%15%28%18%3
1500
August1st to 15thNight
26%6%16%25%21%3
1661
16th to endNight
24%6%14%29%20%5%
1910
September1st to 15thNight
32%5%8%24%21%7%
1866
16th to endNight
33%47%23%25%5%
1980
October1st to 15thNight
32%49%23%25%5%
1980
16th to endNight
39%37%25%19%4
2438
November1st to 15thNight
37%39%21%21%6%
2471
16th to endNight
42%48%23%18%1
2535
December1st to 15thNight
53%310%20%10%1
2535
16th to endNight
58%410%17%8%1
2889

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
30%20%31%14%4
135
16th to endDay
20%26%39%11%2
144
February1st to 15thDay
26%26%36%8%1
135
16th to endDay
29%19%39%12%1
100
March1st to 15thDay
30%18%35%14%2
99
16th to endDay
21%23%33%13%6%1
288
April1st to 15thDay
18%21%27%22%9%
270
16th to endDay
21%18%27%17%11%4
270
May1st to 15thDay
22%21%26%15%10%3
288
16th to endDay
16%16%24%21%10%9%
331
June1st to 15thDay
10%15%16%30%18%8%
474
16th to endDay
8%17%24%25%16%7%
495
July1st to 15thDay
15%11%17%25%20%9%
475
16th to endDay
6%12%9%28%27%15%
422
August1st to 15thDay
14%6%10%23%24%20%
313
16th to endDay
11%5%14%26%25%16%
332
September1st to 15thDay
13%7%14%21%27%14%
315
16th to endDay
13%7%13%18%33%13%
314
October1st to 15thDay
15%9%22%25%18%8%
315
16th to endDay
14%14%34%25%7%2
167
November1st to 15thDay
20%9%34%20%11%3
135
16th to endDay
29%12%32%20%4
135
December1st to 15thDay
19%22%31%18%5%2
135
16th to endDay
36%25%34%21
144
January1st to 15thNight
20%26%30%19%3
975
16th to endNight
21%28%27%19%2
940
February1st to 15thNight
23%26%29%19%
764
16th to endNight
22%25%31%18%1
659
March1st to 15thNight
20%26%28%20%3
720
16th to endNight
17%25%27%22%6%
708
April1st to 15thNight
15%23%29%23%8%
539
16th to endNight
18%22%21%28%8%1
540
May1st to 15thNight
17%21%22%26%11%1
540
16th to endNight
10%19%16%30%17%5%
563
June1st to 15thNight
7%17%14%35%21%2
540
16th to endNight
5%17%14%35%25%1
540
July1st to 15thNight
11%12%9%29%34%2
510
16th to endNight
5%17%8%25%34%8%
564
August1st to 15thNight
8%9%7%30%35%7%
539
16th to endNight
49%9%29%41%6%
573
September1st to 15thNight
12%9%12%26%31%6%
606
16th to endNight
11%11%12%26%31%5%
717
October1st to 15thNight
13%12%19%24%24%5%
720
16th to endNight
17%14%27%25%12%1
768
November1st to 15thNight
14%20%25%22%15%
760
16th to endNight
20%25%22%21%8%
780
December1st to 15thNight
22%25%21%20%8%1
780
16th to endNight
26%25%28%17%2
1017
Page generated at 2018-02-23 11:21:30. Version ac04

Copyright 2018 A. Danko


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