San Clemente Island (North)
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the San Clemente Island (North) clear sky chart from 2005-11-05 to 2017-10-31.

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
57%
16230
30%
47287
23%
16177
64%
16177
35%
26139

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
56%
717
27%
2413
21%
716
66%
716
32%
1223
January16th to endNight
51%
768
33%
2304
24%
768
64%
768
32%
1256
February1st to 15thNight
53%
700
32%
2101
29%
696
61%
696
35%
1154
February16th to endNight
45%
632
25%
1895
18%
632
56%
632
24%
1170
March1st to 15thNight
56%
720
29%
2160
25%
720
65%
720
39%
1115
March16th to endNight
53%
768
29%
1992
20%
768
60%
768
36%
1175
April1st to 15thNight
50%
719
29%
1799
17%
719
56%
719
37%
1070
April16th to endNight
48%
720
32%
1800
14%
720
56%
720
40%
1013
May1st to 15thNight
52%
674
24%
1754
13%
674
56%
674
33%
1071
May16th to endNight
50%
561
26%
1685
16%
561
57%
561
32%
971
June1st to 15thNight
47%
505
17%
1585
12%
505
50%
505
19%
1057
June16th to endNight
61%
360
28%
1440
27%
360
69%
360
27%
734
July1st to 15thNight
60%
340
24%
1360
25%
340
62%
340
25%
731
July16th to endNight
59%
733
23%
1751
13%
689
65%
689
35%
1084
August1st to 15thNight
65%
717
26%
1790
16%
713
67%
713
41%
1054
August16th to endNight
73%
764
33%
1910
20%
764
76%
764
48%
1058
September1st to 15thNight
71%
720
31%
1818
25%
720
72%
720
43%
1057
September16th to endNight
70%
716
36%
1980
30%
716
76%
716
47%
1023
October1st to 15thNight
69%
720
34%
2006
31%
720
73%
720
50%
1017
October16th to endNight
67%
768
38%
2304
34%
768
76%
768
44%
1170
November1st to 15thNight
63%
700
34%
2261
33%
700
70%
700
41%
1076
November16th to endNight
56%
720
33%
2340
29%
720
65%
720
33%
1201
December1st to 15thNight
50%
720
30%
2340
25%
720
60%
720
26%
1294
December16th to endNight
47%
768
30%
2499
23%
768
58%
768
27%
1365

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
5%6%2442446%12%46%
48424
Night
6%6%2432335%9%51%
47494
TransparencyDay
29%48%16%23%18%
48120
Night
28%37%15%23%22%
47299
SeeingDay
6%11%12%28%31%9%
6224
Night
8%17%8%20%30%14%
16240

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%6%235%23247%54%
1522
16th to endDay
10%5%23323246%53%
1913
February1st to 15thDay
7%5%245%2335%9%49%
1751
16th to endDay
10%425%5%345%6%10%41%
1579
March1st to 15thDay
442432448%11%50%
1800
16th to endDay
5%7%25%32445%11%46%
2228
April1st to 15thDay
6%5%2332345%9%53%
2149
16th to endDay
6%5%1321345%10%55%
2160
May1st to 15thDay
5%8%3442345%10%46%
2193
16th to endDay
5%8%3442346%13%44%
2429
June1st to 15thDay
9%11%46%6%3436%11%33%
2370
16th to endDay
26%244245%7%17%41%
2520
July1st to 15thDay
5%9%24425%6%9%16%32%
2520
16th to endDay
35%25%5%25%6%9%17%35%
2293
August1st to 15thDay
15%25%32448%19%40%
2160
16th to endDay
23134245%7%17%47%
2292
September1st to 15thDay
35%244345%8%11%45%
2142
16th to endDay
25%2342435%12%53%
1980
October1st to 15thDay
5%5%2322435%8%55%
1951
16th to endDay
5%42442446%9%50%
1918
November1st to 15thDay
341432426%10%55%
1598
16th to endDay
5%425%6%35%5%5%9%48%
1620
December1st to 15thDay
8%6%2432445%10%47%
1620
16th to endDay
9%42432445%9%49%
1716
January1st to 15thNight
5%423423448%54%
2413
16th to endNight
8%423323447%55%
2304
February1st to 15thNight
7%42442435%7%53%
2101
16th to endNight
11%7%245%24447%44%
1895
March1st to 15thNight
45%2332346%9%55%
2160
16th to endNight
5%6%25%32335%8%52%
1992
April1st to 15thNight
7%6%23313246%57%
1799
16th to endNight
7%7%22211247%60%
1800
May1st to 15thNight
8%10%242133410%49%
1754
16th to endNight
7%10%43312346%53%
1684
June1st to 15thNight
11%13%37%424349%35%
1585
16th to endNight
310%25%42345%14%43%
1440
July1st to 15thNight
8%8%35%42445%16%35%
1440
16th to endNight
6%9%4442346%15%37%
1869
August1st to 15thNight
38%25%42348%15%40%
1800
16th to endNight
25%2432337%18%45%
1910
September1st to 15thNight
5%6%2433346%11%48%
1818
16th to endNight
2414323349%59%
1980
October1st to 15thNight
341321335%10%59%
2006
16th to endNight
6%413212349%59%
2304
November1st to 15thNight
4412223347%62%
2261
16th to endNight
342442445%7%56%
2340
December1st to 15thNight
8%5%34423446%52%
2340
16th to endNight
10%423324348%53%
2499

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
29%37%15%22%20%
1522
16th to endDay
31%38%15%17%23%
1913
February1st to 15thDay
31%36%18%20%19%
1751
16th to endDay
35%6%9%19%19%9%
1579
March1st to 15thDay
26%312%21%20%16%
1800
16th to endDay
31%5%12%22%17%11%
2228
April1st to 15thDay
27%411%24%23%8%
2149
16th to endDay
24%48%22%25%14%
2160
May1st to 15thDay
31%48%17%22%15%
2193
16th to endDay
31%48%21%25%8%
2432
June1st to 15thDay
42%5%8%9%22%11%
2370
16th to endDay
26%27%9%24%28%
2520
July1st to 15thDay
32%48%11%22%20%
2371
16th to endDay
29%410%19%23%12%
2149
August1st to 15thDay
23%38%12%30%21%
2146
16th to endDay
21%36%12%32%23%
2292
September1st to 15thDay
26%37%10%25%26%
2142
16th to endDay
23%2411%34%22%
1980
October1st to 15thDay
25%47%16%23%21%
1951
16th to endDay
26%5%6%13%20%26%
1918
November1st to 15thDay
23%48%16%20%26%
1598
16th to endDay
30%5%8%16%17%21%
1620
December1st to 15thDay
32%49%16%22%14%
1620
16th to endDay
31%5%10%18%20%14%
1716
January1st to 15thNight
25%49%13%24%22%
2413
16th to endNight
27%48%14%17%26%
2304
February1st to 15thNight
28%36%15%22%23%
2112
16th to endNight
38%46%15%22%13%
1895
March1st to 15thNight
23%39%20%23%18%
2160
16th to endNight
29%49%22%20%14%
1992
April1st to 15thNight
29%36%23%24%12%
1799
16th to endNight
25%26%23%26%16%
1800
May1st to 15thNight
33%37%16%23%15%
1755
16th to endNight
32%36%19%25%12%
1685
June1st to 15thNight
46%47%10%18%12%
1585
16th to endNight
33%15%7%22%30%
1440
July1st to 15thNight
34%35%8%21%26%
1360
16th to endNight
33%37%19%21%14%
1751
August1st to 15thNight
28%26%11%29%20%
1790
16th to endNight
23%25%8%30%29%
1910
September1st to 15thNight
27%36%6%25%31%
1818
16th to endNight
22%238%30%32%
1980
October1st to 15thNight
19%35%15%29%26%
2006
16th to endNight
23%3414%21%32%
2304
November1st to 15thNight
21%25%17%19%32%
2261
16th to endNight
25%46%17%20%25%
2340
December1st to 15thNight
32%38%15%21%18%
2340
16th to endNight
30%39%17%21%16%
2499

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
12%13%20%26%26%2
150
16th to endDay
10%18%14%29%21%5%
287
February1st to 15thDay
9%18%16%21%28%4
266
16th to endDay
11%14%20%28%20%4
238
March1st to 15thDay
315%18%33%21%6%
270
16th to endDay
5%20%11%30%25%6%
288
April1st to 15thDay
6%16%18%35%18%5%
269
16th to endDay
419%17%33%20%4
270
May1st to 15thDay
8%13%17%30%23%7%
288
16th to endDay
9%15%16%32%21%3
330
June1st to 15thDay
11%12%12%28%26%9%
315
16th to endDay
29%5%32%37%12%
315
July1st to 15thDay
6%7%419%41%19%
305
16th to endDay
5%9%213%46%22%
327
August1st to 15thDay
26%323%49%14%
315
16th to endDay
14224%52%14%
332
September1st to 15thDay
5%5%7%37%37%7%
315
16th to endDay
36%8%27%43%9%
315
October1st to 15thDay
37%13%36%33%5%
315
16th to endDay
6%6%13%29%27%16%
336
November1st to 15thDay
16%12%22%38%18%
104
16th to endDay
312%18%22%37%5%
90
December1st to 15thDay
11%10%15%32%25%5%
90
16th to endDay
11%14%22%24%25%1
94
January1st to 15thNight
7%18%9%24%28%11%
720
16th to endNight
10%20%11%21%27%9%
768
February1st to 15thNight
8%19%12%22%28%8%
704
16th to endNight
12%21%13%23%21%7%
632
March1st to 15thNight
5%20%13%26%26%7%
720
16th to endNight
5%20%11%24%28%9%
768
April1st to 15thNight
7%20%16%26%20%7%
719
16th to endNight
9%22%14%20%24%9%
720
May1st to 15thNight
10%20%10%24%24%9%
675
16th to endNight
7%20%14%25%25%7%
563
June1st to 15thNight
13%19%6%26%24%9%
505
16th to endNight
8%17%218%36%15%
360
July1st to 15thNight
12%12%26%33%32%
340
16th to endNight
8%17%110%30%31%
733
August1st to 15thNight
9%10%216%35%26%
717
16th to endNight
5%8%29%39%33%
764
September1st to 15thNight
7%9%316%40%22%
720
16th to endNight
410%6%20%38%19%
716
October1st to 15thNight
410%9%25%36%13%
720
16th to endNight
8%10%8%19%31%21%
768
November1st to 15thNight
5%17%8%21%32%15%
700
16th to endNight
6%20%9%17%34%12%
720
December1st to 15thNight
11%21%9%25%26%5%
720
16th to endNight
11%24%11%20%24%7%
768
Page generated at 2017-11-01 14:23:30. Version ac04

Copyright 2017 A. Danko


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