La Cienega Alta Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the La Cienega Alta Observatory clear sky chart from 2005-11-05 to 2017-09-24.

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
60%
15289
33%
46931
24%
15248
71%
15248
46%
23261

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
57%
718
31%
2327
26%
716
67%
716
43%
1153
January16th to endNight
53%
768
36%
2496
28%
768
68%
768
42%
1236
February1st to 15thNight
54%
700
35%
2266
25%
698
69%
698
49%
1046
February16th to endNight
42%
632
42%
1802
22%
632
62%
632
47%
901
March1st to 15thNight
47%
720
40%
1980
20%
720
63%
720
51%
986
March16th to endNight
53%
768
38%
2112
19%
768
68%
768
56%
1002
April1st to 15thNight
42%
578
35%
1837
16%
578
65%
578
46%
840
April16th to endNight
43%
540
42%
1800
22%
540
72%
540
57%
698
May1st to 15thNight
50%
539
33%
1766
21%
539
67%
539
55%
743
May16th to endNight
55%
562
35%
1684
22%
561
69%
561
55%
782
June1st to 15thNight
69%
540
29%
1620
23%
540
73%
540
54%
754
June16th to endNight
70%
540
23%
1620
18%
540
74%
540
45%
819
July1st to 15thNight
74%
510
18%
1530
16%
510
75%
510
32%
931
July16th to endNight
73%
564
15%
1593
14%
531
74%
531
29%
992
August1st to 15thNight
75%
539
19%
1662
19%
536
75%
536
31%
990
August16th to endNight
75%
573
22%
1910
24%
573
76%
573
28%
1175
September1st to 15thNight
73%
540
24%
1800
25%
540
75%
540
31%
1043
September16th to endNight
74%
686
37%
1935
27%
686
80%
686
55%
963
October1st to 15thNight
70%
660
37%
1980
27%
660
76%
660
55%
937
October16th to endNight
73%
704
42%
2112
30%
704
81%
704
67%
883
November1st to 15thNight
67%
700
42%
2100
30%
700
77%
700
63%
905
November16th to endNight
60%
720
41%
2163
30%
720
69%
720
49%
1058
December1st to 15thNight
59%
720
36%
2340
29%
720
69%
720
44%
1133
December16th to endNight
50%
768
33%
2496
25%
768
61%
768
39%
1291

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
431332445%6%58%
47986
Night
4313323446%61%
47134
TransparencyDay
24%37%16%27%21%
47681
Night
21%37%17%28%20%
46940
SeeingDay
8%12%27%30%16%4
5198
Night
5%6%21%35%26%5%
15297

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
5%4233125%3462%
1611
16th to endDay
9%5%13322237%58%
1728
February1st to 15thDay
3423212345%65%
1588
16th to endDay
342331344463%
1670
March1st to 15thDay
4423413336%62%
1980
16th to endDay
321221225%5%69%
2112
April1st to 15thDay
2312322346%67%
2111
16th to endDay
221221223475%
2160
May1st to 15thDay
2112313446%69%
2181
16th to endDay
322213435%69%
2429
June1st to 15thDay
2212213348%67%
2340
16th to endDay
32134245%6%6%59%
2340
July1st to 15thDay
5%425%7%47%6%8%10%37%
2340
16th to endDay
8%6%36%7%48%9%9%10%26%
2467
August1st to 15thDay
8%425%6%47%7%7%10%34%
2287
16th to endDay
6%5%36%6%46%6%7%8%37%
2292
September1st to 15thDay
8%6%25%6%35%6%7%8%39%
2160
16th to endDay
421333435%6%61%
1879
October1st to 15thDay
421232345%5%64%
1650
16th to endDay
322221335%71%
1760
November1st to 15thDay
223213235%71%
1759
16th to endDay
432331233465%
1794
December1st to 15thDay
6%5%11223446%61%
1620
16th to endDay
6%7%23323336%57%
1728
January1st to 15thNight
6%413324335%62%
2327
16th to endNight
7%5%23313345%60%
2496
February1st to 15thNight
2322323436%64%
2262
16th to endNight
431232333466%
1802
March1st to 15thNight
3312213446%66%
1980
16th to endNight
3311212235%72%
2112
April1st to 15thNight
3213214445%66%
1837
16th to endNight
11121213478%
1800
May1st to 15thNight
212212435%70%
1766
16th to endNight
2112322345%70%
1684
June1st to 15thNight
2212223445%68%
1620
16th to endNight
2123425%6%6%8%56%
1620
July1st to 15thNight
4225%6%46%8%8%13%36%
1620
16th to endNight
3425%6%37%8%9%12%34%
1701
August1st to 15thNight
5%4245%35%7%10%13%36%
1671
16th to endNight
44246%5%7%8%7%9%39%
1910
September1st to 15thNight
5%4246%45%7%7%9%42%
1800
16th to endNight
4212312325%69%
1935
October1st to 15thNight
321222334468%
1980
16th to endNight
12111123478%
2112
November1st to 15thNight
112222236%74%
2100
16th to endNight
5%314312235%66%
2163
December1st to 15thNight
6%413223347%61%
2340
16th to endNight
6%6%2432325%6%56%
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
24%2415%33%19%
1612
16th to endDay
26%1316%33%18%
1728
February1st to 15thDay
19%2416%31%25%
1588
16th to endDay
21%2218%33%21%
1670
March1st to 15thDay
22%2313%34%23%
1980
16th to endDay
16%1414%38%25%
2112
April1st to 15thDay
18%1314%38%23%
2111
16th to endDay
12%1212%34%36%
2160
May1st to 15thDay
15%15%14%32%29%
2181
16th to endDay
16%3410%30%34%
2432
June1st to 15thDay
16%2211%26%40%
2340
16th to endDay
22%46%13%20%32%
2340
July1st to 15thDay
37%7%13%18%10%12%
2201
16th to endDay
44%9%21%17%5%
2312
August1st to 15thDay
38%7%16%21%13%3
2272
16th to endDay
37%7%15%17%15%6%
2292
September1st to 15thDay
37%5%10%20%19%7%
2160
16th to endDay
21%35%18%34%16%
1879
October1st to 15thDay
19%36%15%31%23%
1650
16th to endDay
15%1415%33%29%
1760
November1st to 15thDay
16%1418%32%26%
1759
16th to endDay
22%1414%35%21%
1794
December1st to 15thDay
21%27%21%30%15%
1620
16th to endDay
27%27%21%30%9%
1728
January1st to 15thNight
24%25%15%34%17%
2327
16th to endNight
25%1319%33%16%
2496
February1st to 15thNight
18%35%19%28%24%
2273
16th to endNight
20%1320%33%19%
1802
March1st to 15thNight
18%2415%35%22%
1980
16th to endNight
15%1415%38%24%
2112
April1st to 15thNight
17%2317%38%19%
1837
16th to endNight
11%1314%36%33%
1800
May1st to 15thNight
15%15%12%34%30%
1767
16th to endNight
16%25%11%29%33%
1685
June1st to 15thNight
17%2310%26%38%
1620
16th to endNight
22%48%12%20%31%
1620
July1st to 15thNight
32%9%15%20%12%10%
1530
16th to endNight
34%9%28%21%41
1593
August1st to 15thNight
31%9%21%20%12%4
1662
16th to endNight
35%8%16%18%15%5%
1910
September1st to 15thNight
31%7%15%21%14%9%
1800
16th to endNight
18%3420%36%16%
1935
October1st to 15thNight
17%37%16%31%23%
1980
16th to endNight
10%1419%31%32%
2112
November1st to 15thNight
13%1418%36%25%
2100
16th to endNight
21%1415%29%27%
2163
December1st to 15thNight
22%26%21%29%16%
2340
16th to endNight
28%110%21%27%11%
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
18%14%32%23%8%2
90
16th to endDay
10%14%29%22%15%7%
96
February1st to 15thDay
7%7%20%34%22%7%
90
16th to endDay
7%35%28%18%9%1
171
March1st to 15thDay
11%20%35%22%8%2
270
16th to endDay
7%30%35%18%6%2
288
April1st to 15thDay
8%27%36%19%5%1
269
16th to endDay
10%26%41%16%31
270
May1st to 15thDay
6%24%38%24%5%
288
16th to endDay
313%44%29%6%1
330
June1st to 15thDay
47%36%36%12%2
315
16th to endDay
6%226%39%22%3
315
July1st to 15thDay
5%113%44%27%7%
305
16th to endDay
12%19%28%32%16%
327
August1st to 15thDay
12%18%37%31%9%
315
16th to endDay
7%112%35%31%11%
332
September1st to 15thDay
12%117%40%24%4
315
16th to endDay
7%5%30%40%13%3
260
October1st to 15thDay
7%5%26%25%24%10%
90
16th to endDay
9%321%29%29%7%
96
November1st to 15thDay
5%16%21%33%18%4
90
16th to endDay
11%18%31%28%8%1
90
December1st to 15thDay
412%28%25%24%4
90
16th to endDay
15%20%23%32%5%2
96
January1st to 15thNight
7%6%23%35%20%6%
720
16th to endNight
9%8%22%35%18%4
768
February1st to 15thNight
47%28%34%19%4
704
16th to endNight
5%13%34%34%11%1
632
March1st to 15thNight
411%32%30%18%3
720
16th to endNight
311%27%38%16%2
768
April1st to 15thNight
413%35%33%11%1
578
16th to endNight
114%37%32%11%2
540
May1st to 15thNight
39%33%41%11%1
540
16th to endNight
3332%40%18%1
563
June1st to 15thNight
3319%48%22%2
540
16th to endNight
3216%43%31%3
540
July1st to 15thNight
5%5%35%42%9%
510
16th to endNight
5%15%21%52%13%
564
August1st to 15thNight
7%221%50%17%
539
16th to endNight
416%24%51%11%
573
September1st to 15thNight
7%16%31%48%5%
540
16th to endNight
4114%38%33%7%
686
October1st to 15thNight
4119%41%27%5%
660
16th to endNight
2318%39%28%8%
704
November1st to 15thNight
2322%35%28%6%
700
16th to endNight
6%6%20%31%27%7%
720
December1st to 15thNight
8%7%20%35%22%5%
720
16th to endNight
9%10%23%37%15%3
768
Page generated at 2017-09-25 07:02:24. Version ac04

Copyright 2017 A. Danko


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