San Clemente
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the San Clemente clear sky chart from 2005-11-05 to 2017-09-18.

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
73%
16088
28%
46780
27%
16043
75%
16043
41%
26135

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
72%
716
29%
2300
30%
716
75%
716
41%
1201
January16th to endNight
69%
768
31%
2304
30%
768
71%
768
39%
1283
February1st to 15thNight
73%
697
32%
2105
34%
697
76%
697
43%
1124
February16th to endNight
62%
632
25%
1895
28%
632
64%
632
30%
1195
March1st to 15thNight
72%
720
27%
2160
31%
720
74%
720
41%
1175
March16th to endNight
72%
768
24%
2019
21%
768
74%
768
41%
1204
April1st to 15thNight
64%
719
24%
1799
17%
719
66%
719
40%
1127
April16th to endNight
74%
720
27%
1800
17%
720
75%
720
45%
1076
May1st to 15thNight
66%
608
22%
1689
16%
608
66%
608
33%
1090
May16th to endNight
65%
561
20%
1685
16%
561
66%
561
31%
1074
June1st to 15thNight
63%
540
17%
1620
15%
540
63%
540
27%
1091
June16th to endNight
76%
425
25%
1505
27%
425
76%
425
37%
783
July1st to 15thNight
76%
412
21%
1432
21%
412
76%
412
34%
780
July16th to endNight
78%
662
23%
1683
17%
621
78%
621
41%
997
August1st to 15thNight
79%
717
26%
1790
17%
713
79%
713
46%
1051
August16th to endNight
84%
764
33%
1910
23%
764
84%
764
57%
1026
September1st to 15thNight
83%
720
32%
1848
27%
720
83%
720
52%
1010
September16th to endNight
83%
667
38%
1847
38%
667
83%
667
55%
915
October1st to 15thNight
80%
660
35%
1815
34%
660
81%
660
51%
959
October16th to endNight
77%
704
35%
2123
37%
704
78%
704
46%
1084
November1st to 15thNight
80%
700
32%
2275
37%
700
82%
700
48%
1076
November16th to endNight
75%
720
33%
2340
37%
720
77%
720
43%
1187
December1st to 15thNight
69%
720
31%
2340
33%
720
73%
720
35%
1279
December16th to endNight
62%
768
31%
2496
30%
768
68%
768
36%
1348

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
4313313348%61%
47990
Night
6%5%24323347%57%
46986
TransparencyDay
21%49%17%23%22%
47691
Night
28%48%15%21%22%
46787
SeeingDay
6%214%35%34%6%
5967
Night
8%16%27%40%15%
16102

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
8%313323347%57%
1636
16th to endDay
9%413322346%56%
1920
February1st to 15thDay
7%313322447%59%
1751
16th to endDay
10%414323448%52%
1579
March1st to 15thDay
421332345%9%59%
1800
16th to endDay
43133244410%57%
2202
April1st to 15thDay
5%41232345%7%58%
2149
16th to endDay
431221235%9%64%
2160
May1st to 15thDay
5%41432335%9%57%
2262
16th to endDay
45%1431235%8%58%
2429
June1st to 15thDay
6%6%25%312249%54%
2340
16th to endDay
1313212247%69%
2447
July1st to 15thDay
242331346%9%58%
2436
16th to endDay
221322345%9%62%
2366
August1st to 15thDay
122212249%69%
2160
16th to endDay
12221235%10%68%
2292
September1st to 15thDay
121221236%8%68%
2110
16th to endDay
1213212238%69%
1838
October1st to 15thDay
5%413212347%61%
1815
16th to endDay
5%312212347%65%
1746
November1st to 15thDay
4111323346%66%
1584
16th to endDay
5%223213448%62%
1620
December1st to 15thDay
6%324423349%55%
1620
16th to endDay
11%313323447%56%
1728
January1st to 15thNight
6%424322437%59%
2300
16th to endNight
10%423313335%57%
2304
February1st to 15thNight
7%313313336%60%
2101
16th to endNight
12%5%25%433435%48%
1895
March1st to 15thNight
6%5%24323349%55%
2160
16th to endNight
5%6%2332335%9%53%
2019
April1st to 15thNight
8%7%35%312237%52%
1799
16th to endNight
6%423313437%59%
1800
May1st to 15thNight
8%9%35%322247%48%
1688
16th to endNight
8%11%36%323347%46%
1684
June1st to 15thNight
7%12%49%5%22448%39%
1620
16th to endNight
26%36%424449%50%
1505
July1st to 15thNight
36%36%4145%5%10%46%
1518
16th to endNight
47%25%42345%10%49%
1799
August1st to 15thNight
2435%423448%56%
1800
16th to endNight
2413212249%63%
1910
September1st to 15thNight
3413413447%63%
1848
16th to endNight
2323211225%70%
1847
October1st to 15thNight
3314312246%65%
1815
16th to endNight
6%313312345%63%
2123
November1st to 15thNight
4313322325%67%
2275
16th to endNight
6%31431235%6%61%
2340
December1st to 15thNight
8%324423446%55%
2340
16th to endNight
11%5%1331224459%
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
26%5%8%13%20%25%
1637
16th to endDay
29%38%15%15%28%
1920
February1st to 15thDay
25%48%14%23%23%
1751
16th to endDay
31%5%9%18%25%9%
1579
March1st to 15thDay
22%411%20%20%19%
1800
16th to endDay
23%6%14%23%20%12%
2202
April1st to 15thDay
24%5%11%27%21%10%
2149
16th to endDay
19%5%14%21%22%17%
2160
May1st to 15thDay
26%5%10%22%20%15%
2262
16th to endDay
24%312%26%25%7%
2432
June1st to 15thDay
27%49%16%27%13%
2340
16th to endDay
15%37%11%26%36%
2447
July1st to 15thDay
21%48%13%22%29%
2294
16th to endDay
19%5%12%21%25%16%
2219
August1st to 15thDay
13%27%16%32%27%
2146
16th to endDay
12%39%15%32%25%
2292
September1st to 15thDay
14%48%13%31%27%
2110
16th to endDay
16%27%13%30%30%
1838
October1st to 15thDay
22%28%19%23%23%
1815
16th to endDay
20%37%14%19%34%
1746
November1st to 15thDay
19%48%17%18%32%
1584
16th to endDay
21%48%15%20%29%
1620
December1st to 15thDay
26%5%12%16%17%22%
1620
16th to endDay
29%5%9%15%20%18%
1728
January1st to 15thNight
26%38%13%19%28%
2300
16th to endNight
29%49%12%13%30%
2304
February1st to 15thNight
25%47%15%21%25%
2112
16th to endNight
39%45%12%22%15%
1895
March1st to 15thNight
27%49%19%18%20%
2160
16th to endNight
28%5%13%18%19%13%
2019
April1st to 15thNight
32%48%21%19%12%
1799
16th to endNight
26%5%10%20%19%16%
1800
May1st to 15thNight
37%49%16%16%14%
1689
16th to endNight
38%49%18%18%10%
1685
June1st to 15thNight
44%48%11%21%10%
1620
16th to endNight
26%5%7%11%23%24%
1505
July1st to 15thNight
30%5%6%14%20%22%
1432
16th to endNight
28%6%10%20%21%12%
1683
August1st to 15thNight
27%47%17%27%16%
1790
16th to endNight
18%48%13%29%26%
1910
September1st to 15thNight
21%45%10%30%26%
1848
16th to endNight
19%2312%31%30%
1847
October1st to 15thNight
22%36%19%28%20%
1815
16th to endNight
23%45%11%22%33%
2123
November1st to 15thNight
21%26%15%18%35%
2275
16th to endNight
24%48%16%16%30%
2340
December1st to 15thNight
29%5%8%15%18%22%
2340
16th to endNight
29%410%14%21%20%
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
20%220%37%18%
115
16th to endDay
12%221%36%23%2
288
February1st to 15thDay
9%317%33%31%3
266
16th to endDay
14%325%33%20%2
238
March1st to 15thDay
7%321%33%28%5%
270
16th to endDay
5%422%39%22%4
288
April1st to 15thDay
7%5%25%41%15%4
269
16th to endDay
2427%43%17%4
270
May1st to 15thDay
6%322%37%27%3
288
16th to endDay
9%114%43%26%4
330
June1st to 15thDay
8%15%37%32%5%
315
16th to endDay
1430%53%10%
315
July1st to 15thDay
2328%51%13%
305
16th to endDay
419%59%15%
327
August1st to 15thDay
3332%51%8%
315
16th to endDay
2223%56%13%
332
September1st to 15thDay
36%45%40%4
315
16th to endDay
310%44%34%7%
264
October1st to 15thDay
4220%46%23%3
255
16th to endDay
8%111%41%27%8%
236
November1st to 15thDay
48%22%41%23%
90
16th to endDay
48%13%35%32%5%
90
December1st to 15thDay
4411%38%35%5%
90
16th to endDay
13%6%13%34%30%2
96
January1st to 15thNight
8%29%38%29%12%
720
16th to endNight
11%110%33%34%8%
768
February1st to 15thNight
8%17%31%38%11%
704
16th to endNight
14%110%36%29%7%
632
March1st to 15thNight
9%28%36%34%9%
720
16th to endNight
9%18%30%40%9%
768
April1st to 15thNight
11%311%32%33%7%
719
16th to endNight
7%28%35%37%9%
720
May1st to 15thNight
12%110%29%35%10%
609
16th to endNight
11%38%27%39%9%
563
June1st to 15thNight
11%18%30%39%7%
540
16th to endNight
6%416%58%13%
425
July1st to 15thNight
7%115%49%26%
412
16th to endNight
4210%46%35%
662
August1st to 15thNight
5%115%50%26%
717
16th to endNight
5%18%47%37%
764
September1st to 15thNight
5%213%53%25%
720
16th to endNight
5%221%50%19%
667
October1st to 15thNight
415%34%42%13%
660
16th to endNight
9%15%23%41%18%
704
November1st to 15thNight
5%5%30%40%17%
700
16th to endNight
7%7%30%36%17%
720
December1st to 15thNight
10%18%33%35%9%
720
16th to endNight
13%312%31%29%8%
768
Page generated at 2017-09-19 04:32:27. Version ac04

Copyright 2017 A. Danko


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