Santa Monica Canyon Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Santa Monica Canyon Observatory clear sky chart from 2005-11-05 to 2017-10-06.

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
65%
15927
31%
47028
25%
15877
72%
15877
41%
24309

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
59%
716
28%
2452
23%
716
69%
716
33%
1222
January16th to endNight
54%
768
34%
2380
26%
768
67%
768
34%
1249
February1st to 15thNight
60%
700
34%
2103
31%
697
68%
697
39%
1089
February16th to endNight
52%
632
26%
1895
21%
632
62%
632
29%
1109
March1st to 15thNight
58%
720
28%
2160
25%
720
67%
720
39%
1106
March16th to endNight
60%
768
27%
1994
20%
768
65%
768
37%
1167
April1st to 15thNight
57%
719
29%
1799
16%
719
62%
719
42%
1035
April16th to endNight
60%
720
31%
1800
14%
720
67%
720
45%
998
May1st to 15thNight
62%
641
25%
1721
15%
641
66%
641
38%
994
May16th to endNight
64%
561
26%
1685
18%
561
69%
561
43%
881
June1st to 15thNight
68%
438
25%
1518
21%
438
71%
438
35%
783
June16th to endNight
73%
360
31%
1440
31%
360
79%
360
39%
626
July1st to 15thNight
76%
340
30%
1360
33%
340
79%
340
37%
593
July16th to endNight
72%
631
25%
1650
19%
588
80%
588
42%
904
August1st to 15thNight
77%
717
31%
1790
20%
713
78%
713
49%
985
August16th to endNight
80%
764
37%
1910
22%
764
83%
764
56%
999
September1st to 15thNight
81%
720
35%
1815
27%
720
82%
720
54%
956
September16th to endNight
81%
716
40%
1980
35%
716
86%
716
56%
938
October1st to 15thNight
73%
684
33%
1914
33%
684
76%
684
50%
972
October16th to endNight
71%
704
38%
2117
34%
704
79%
704
47%
1017
November1st to 15thNight
68%
700
35%
2275
35%
700
74%
700
47%
1008
November16th to endNight
62%
720
36%
2340
30%
720
73%
720
39%
1112
December1st to 15thNight
56%
720
34%
2340
27%
720
67%
720
31%
1225
December16th to endNight
50%
768
31%
2590
25%
768
62%
768
31%
1341

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
4312212247%67%
48145
Night
5%313212347%64%
47232
TransparencyDay
20%38%18%26%22%
47839
Night
23%37%16%24%23%
47038
SeeingDay
412%19%36%21%5%
6037
Night
5%15%7%26%34%10%
15938

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
6%41342333462%
1485
16th to endDay
10%423313336%59%
1841
February1st to 15thDay
6%322312246%62%
1751
16th to endDay
10%423323347%55%
1579
March1st to 15thDay
431331345%7%62%
1800
16th to endDay
431332445%9%56%
2226
April1st to 15thDay
5%31321335%8%61%
2149
16th to endDay
2312212247%70%
2160
May1st to 15thDay
3312212348%65%
2229
16th to endDay
3412212248%67%
2429
June1st to 15thDay
5%6%1321247%64%
2438
16th to endDay
1311112136%75%
2520
July1st to 15thDay
3211213238%68%
2520
16th to endDay
2212212247%70%
2398
August1st to 15thDay
2211111126%76%
2160
16th to endDay
11112236%77%
2292
September1st to 15thDay
211111246%76%
2143
16th to endDay
1211111236%76%
1980
October1st to 15thDay
4212212336%70%
1840
16th to endDay
2212212335%71%
1752
November1st to 15thDay
3213212235%69%
1584
16th to endDay
4213322347%65%
1620
December1st to 15thDay
7%31321435%8%58%
1620
16th to endDay
9%314313336%59%
1629
January1st to 15thNight
6%412313346%61%
2452
16th to endNight
10%313212236%60%
2380
February1st to 15thNight
5%323212346%63%
2101
16th to endNight
12%324413345%54%
1895
March1st to 15thNight
5%31331235%8%60%
2160
16th to endNight
442232435%8%57%
1994
April1st to 15thNight
7%5%23212226%63%
1799
16th to endNight
3313213347%66%
1800
May1st to 15thNight
5%6%1331235%7%60%
1721
16th to endNight
3413312248%64%
1684
June1st to 15thNight
25%222233410%58%
1518
16th to endNight
141211236%10%63%
1440
July1st to 15thNight
2312323249%64%
1440
16th to endNight
331321345%11%58%
1767
August1st to 15thNight
34221225%9%65%
1800
16th to endNight
12122113410%67%
1910
September1st to 15thNight
2212112247%70%
1815
16th to endNight
12212246%74%
1980
October1st to 15thNight
3212313345%69%
1914
16th to endNight
3312212235%70%
2117
November1st to 15thNight
2312212235%73%
2275
16th to endNight
4312213237%67%
2340
December1st to 15thNight
6%424313237%60%
2340
16th to endNight
10%313212235%61%
2590

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
26%35%14%22%27%
1485
16th to endDay
27%29%15%16%27%
1841
February1st to 15thDay
23%36%16%25%23%
1751
16th to endDay
29%47%20%27%10%
1579
March1st to 15thDay
21%311%22%20%20%
1800
16th to endDay
24%413%24%18%14%
2226
April1st to 15thDay
22%412%25%23%12%
2149
16th to endDay
15%5%11%24%26%17%
2160
May1st to 15thDay
20%5%11%21%25%15%
2229
16th to endDay
19%411%28%27%7%
2432
June1st to 15thDay
23%49%17%30%14%
2438
16th to endDay
15%25%11%33%31%
2520
July1st to 15thDay
19%27%12%28%30%
2371
16th to endDay
17%39%22%28%18%
2252
August1st to 15thDay
14%15%18%34%26%
2146
16th to endDay
10%15%16%39%25%
2292
September1st to 15thDay
15%27%15%29%29%
2143
16th to endDay
14%26%15%33%27%
1980
October1st to 15thDay
18%26%21%25%24%
1840
16th to endDay
17%35%17%21%34%
1752
November1st to 15thDay
19%26%15%22%33%
1584
16th to endDay
20%47%15%21%30%
1620
December1st to 15thDay
25%310%16%20%22%
1620
16th to endDay
27%310%16%21%20%
1629
January1st to 15thNight
25%37%14%21%27%
2452
16th to endNight
26%38%15%16%30%
2380
February1st to 15thNight
23%46%17%22%25%
2112
16th to endNight
33%48%14%23%14%
1895
March1st to 15thNight
22%410%19%23%19%
2160
16th to endNight
27%5%12%19%22%13%
1994
April1st to 15thNight
25%39%25%23%13%
1799
16th to endNight
22%29%23%22%18%
1800
May1st to 15thNight
28%310%18%25%13%
1722
16th to endNight
22%311%25%25%10%
1685
June1st to 15thNight
26%413%16%26%11%
1518
16th to endNight
21%27%13%28%26%
1440
July1st to 15thNight
22%15%13%24%31%
1360
16th to endNight
26%39%22%21%16%
1650
August1st to 15thNight
23%1413%33%23%
1790
16th to endNight
18%15%11%36%25%
1910
September1st to 15thNight
18%26%9%32%29%
1815
16th to endNight
17%1314%31%31%
1980
October1st to 15thNight
20%25%17%27%25%
1914
16th to endNight
19%25%13%22%35%
2117
November1st to 15thNight
17%27%16%20%36%
2275
16th to endNight
21%27%17%19%31%
2340
December1st to 15thNight
27%37%15%20%24%
2340
16th to endNight
27%38%15%23%21%
2590

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
15%12%31%34%5%
113
16th to endDay
11%18%24%33%12%1
275
February1st to 15thDay
10%15%26%29%15%3
266
16th to endDay
12%19%27%27%11%1
238
March1st to 15thDay
6%19%29%20%21%2
270
16th to endDay
420%27%33%11%2
288
April1st to 15thDay
5%22%30%27%10%4
269
16th to endDay
23%35%29%7%3
270
May1st to 15thDay
5%19%26%34%12%2
288
16th to endDay
313%26%41%12%2
330
June1st to 15thDay
8%12%19%39%17%3
315
16th to endDay
10%8%40%29%11%
315
July1st to 15thDay
36%6%36%38%8%
305
16th to endDay
19%335%37%12%
327
August1st to 15thDay
26%6%40%34%7%
315
16th to endDay
145%35%43%10%
332
September1st to 15thDay
4411%49%24%5%
315
16th to endDay
25%13%48%23%6%
315
October1st to 15thDay
29%24%43%17%2
278
16th to endDay
49%20%42%19%4
264
November1st to 15thDay
447%24%38%20%
90
16th to endDay
36%18%38%30%2
90
December1st to 15thDay
38%13%35%37%1
90
16th to endDay
11%13%20%30%21%2
79
January1st to 15thNight
7%17%10%34%22%6%
720
16th to endNight
10%18%10%30%25%4
768
February1st to 15thNight
5%17%10%32%25%7%
704
16th to endNight
11%17%11%29%25%4
632
March1st to 15thNight
5%17%12%33%24%6%
720
16th to endNight
5%18%10%31%29%5%
768
April1st to 15thNight
7%18%11%31%26%3
719
16th to endNight
419%11%30%27%6%
720
May1st to 15thNight
7%17%6%30%31%5%
642
16th to endNight
317%11%32%31%3
563
June1st to 15thNight
216%6%29%39%4
438
16th to endNight
316%118%51%8%
360
July1st to 15thNight
311%16%53%22%
340
16th to endNight
316%19%49%20%
631
August1st to 15thNight
49%116%50%17%
717
16th to endNight
28%112%50%24%
764
September1st to 15thNight
48%217%47%20%
720
16th to endNight
38%321%48%15%
716
October1st to 15thNight
48%6%27%41%11%
684
16th to endNight
5%10%7%23%37%14%
704
November1st to 15thNight
315%7%29%31%13%
700
16th to endNight
6%17%8%27%29%10%
720
December1st to 15thNight
7%18%9%32%25%6%
720
16th to endNight
12%20%12%31%17%5%
768
Page generated at 2017-10-07 11:07:54. Version ac04

Copyright 2017 A. Danko


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