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San Diego
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the San Diego 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
71%
16918
27%
48923
26%
16873
72%
16873
39%
28162

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
73%
777
28%
2495
30%
776
75%
776
40%
1319
January16th to endNight
70%
832
32%
2496
32%
832
73%
832
39%
1403
February1st to 15thNight
72%
758
30%
2288
32%
758
74%
758
39%
1268
February16th to endNight
62%
660
27%
1979
30%
660
64%
660
29%
1239
March1st to 15thNight
68%
720
25%
2160
28%
720
69%
720
37%
1219
March16th to endNight
68%
768
23%
2032
21%
768
69%
768
35%
1277
April1st to 15thNight
64%
719
24%
1799
17%
719
65%
719
38%
1136
April16th to endNight
67%
720
26%
1800
17%
720
68%
720
40%
1119
May1st to 15thNight
61%
599
21%
1680
16%
599
62%
599
30%
1119
May16th to endNight
57%
561
18%
1685
14%
561
57%
561
26%
1147
June1st to 15thNight
61%
540
15%
1620
14%
540
61%
540
26%
1116
June16th to endNight
76%
540
22%
1620
19%
540
76%
540
43%
903
July1st to 15thNight
74%
510
19%
1530
16%
510
74%
510
37%
915
July16th to endNight
74%
657
22%
1679
16%
617
73%
617
36%
1046
August1st to 15thNight
73%
717
23%
1790
16%
713
74%
713
43%
1091
August16th to endNight
80%
764
32%
1910
23%
764
80%
764
53%
1067
September1st to 15thNight
79%
720
29%
1869
25%
720
79%
720
49%
1057
September16th to endNight
81%
716
37%
1980
36%
716
81%
716
54%
1009
October1st to 15thNight
77%
720
30%
1980
30%
720
78%
720
47%
1067
October16th to endNight
75%
768
35%
2287
37%
768
76%
768
43%
1207
November1st to 15thNight
78%
760
30%
2470
35%
760
78%
760
44%
1220
November16th to endNight
75%
780
33%
2535
38%
780
76%
780
40%
1332
December1st to 15thNight
69%
780
30%
2535
32%
780
71%
780
35%
1395
December16th to endNight
68%
832
31%
2704
33%
832
71%
832
36%
1491

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%423323448%57%
49316
Night
6%7%24323447%51%
49129
TransparencyDay
24%49%16%23%21%
49020
Night
30%48%14%19%22%
48927
SeeingDay
7%219%40%24%5%
6506
Night
9%17%28%39%13%
16930

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
7%414323347%56%
1772
16th to endDay
9%424313347%56%
2080
February1st to 15thDay
6%424323447%56%
1901
16th to endDay
9%426%4345%5%8%46%
1641
March1st to 15thDay
5%42432245%9%56%
1800
16th to endDay
5%42442435%8%54%
2189
April1st to 15thDay
6%5%2442335%8%53%
2149
16th to endDay
4313212348%62%
2160
May1st to 15thDay
6%6%23323448%55%
2268
16th to endDay
5%6%2331335%9%56%
2429
June1st to 15thDay
5%9%23323349%51%
2340
16th to endDay
25%23212348%61%
2340
July1st to 15thDay
46%243245%6%11%49%
2340
16th to endDay
35%1332346%10%55%
2371
August1st to 15thDay
25%13213348%63%
2160
16th to endDay
131332345%9%62%
2292
September1st to 15thDay
13233145%5%8%59%
2091
16th to endDay
2313213449%64%
1980
October1st to 15thDay
4224323347%60%
1980
16th to endDay
5%313213437%63%
1932
November1st to 15thDay
5%313323347%59%
1719
16th to endDay
5%423313347%60%
1755
December1st to 15thDay
6%425%323448%54%
1755
16th to endDay
10%314323348%54%
1872
January1st to 15thNight
7%42331445%8%54%
2495
16th to endNight
9%5%14313346%56%
2496
February1st to 15thNight
7%424424346%55%
2281
16th to endNight
10%8%36%424345%46%
1979
March1st to 15thNight
7%5%15%424349%50%
2160
16th to endNight
6%7%35%42345%7%47%
2032
April1st to 15thNight
11%7%24313239%49%
1799
16th to endNight
8%9%34323345%51%
1800
May1st to 15thNight
10%11%37%43345%7%38%
1679
16th to endNight
12%13%46%423347%36%
1684
June1st to 15thNight
8%15%46%425%5%5%9%31%
1620
16th to endNight
210%45%32446%11%43%
1620
July1st to 15thNight
5%10%35%42445%11%41%
1620
16th to endNight
6%9%3442445%10%43%
1794
August1st to 15thNight
311%35%4235%5%9%46%
1800
16th to endNight
25%234225%49%55%
1910
September1st to 15thNight
25%24323448%57%
1869
16th to endNight
3423223437%62%
1980
October1st to 15thNight
342432345%8%56%
1980
16th to endNight
6%6%23212446%58%
2287
November1st to 15thNight
45%23212347%61%
2470
16th to endNight
45%25%324346%57%
2535
December1st to 15thNight
8%5%2442345%6%52%
2535
16th to endNight
10%323323345%56%
2704

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
28%47%14%20%24%
1773
16th to endDay
28%38%15%14%28%
2080
February1st to 15thDay
26%38%14%20%25%
1901
16th to endDay
36%5%7%15%23%11%
1641
March1st to 15thDay
24%5%9%18%20%20%
1800
16th to endDay
26%5%11%23%19%13%
2189
April1st to 15thDay
28%49%23%24%8%
2149
16th to endDay
19%5%12%23%20%18%
2160
May1st to 15thDay
27%5%8%22%20%15%
2268
16th to endDay
24%411%22%28%8%
2432
June1st to 15thDay
27%5%10%17%22%17%
2340
16th to endDay
18%29%10%22%36%
2340
July1st to 15thDay
25%39%14%24%22%
2201
16th to endDay
22%5%15%21%24%10%
2224
August1st to 15thDay
19%38%14%31%22%
2146
16th to endDay
16%38%14%31%23%
2292
September1st to 15thDay
19%37%14%29%24%
2091
16th to endDay
15%38%13%32%27%
1980
October1st to 15thDay
23%37%15%25%24%
1980
16th to endDay
20%36%13%20%34%
1932
November1st to 15thDay
24%49%15%16%30%
1719
16th to endDay
23%38%14%18%31%
1755
December1st to 15thDay
28%310%13%17%26%
1755
16th to endDay
29%5%9%15%20%19%
1872
January1st to 15thNight
27%48%13%20%25%
2495
16th to endNight
29%48%12%13%31%
2496
February1st to 15thNight
28%48%13%18%26%
2292
16th to endNight
39%45%12%22%15%
1979
March1st to 15thNight
30%49%16%17%21%
2160
16th to endNight
33%6%10%17%18%13%
2032
April1st to 15thNight
34%48%22%21%10%
1799
16th to endNight
32%49%16%19%17%
1800
May1st to 15thNight
41%5%10%13%14%15%
1680
16th to endNight
44%5%9%14%15%10%
1685
June1st to 15thNight
45%5%11%11%15%10%
1620
16th to endNight
29%29%12%16%29%
1620
July1st to 15thNight
33%39%11%21%20%
1530
16th to endNight
34%5%12%20%20%6%
1679
August1st to 15thNight
31%310%16%25%13%
1790
16th to endNight
23%29%13%26%24%
1910
September1st to 15thNight
25%37%11%28%24%
1869
16th to endNight
21%2410%34%26%
1980
October1st to 15thNight
24%38%16%23%23%
1980
16th to endNight
26%35%11%18%34%
2287
November1st to 15thNight
23%38%16%15%31%
2470
16th to endNight
26%46%14%17%30%
2535
December1st to 15thNight
31%37%14%17%24%
2535
16th to endNight
30%49%14%18%22%
2704

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
21%16%36%19%5%
161
16th to endDay
11%5%26%37%15%3
352
February1st to 15thDay
7%423%37%21%5%
326
16th to endDay
8%9%32%32%14%2
264
March1st to 15thDay
7%428%39%15%4
270
16th to endDay
5%6%27%41%15%3
288
April1st to 15thDay
10%433%35%12%4
269
16th to endDay
5%6%35%37%10%4
270
May1st to 15thDay
11%429%36%14%2
288
16th to endDay
11%5%25%38%17%1
330
June1st to 15thDay
6%23%43%23%2
315
16th to endDay
38%47%34%5%
315
July1st to 15thDay
7%7%40%37%6%
305
16th to endDay
5%234%47%10%
327
August1st to 15thDay
36%46%37%6%
315
16th to endDay
4341%43%7%
332
September1st to 15thDay
5%13%52%26%1
315
16th to endDay
415%53%21%5%
315
October1st to 15thDay
4225%45%18%3
315
16th to endDay
9%19%37%24%8%
285
November1st to 15thDay
45%14%36%29%10%
135
16th to endDay
11%5%17%25%29%11%
135
December1st to 15thDay
4212%43%30%5%
135
16th to endDay
11%413%32%27%9%
144
January1st to 15thNight
8%19%36%33%10%
780
16th to endNight
11%110%32%35%8%
832
February1st to 15thNight
9%28%31%36%12%
764
16th to endNight
13%211%40%26%6%
660
March1st to 15thNight
9%210%37%33%7%
720
16th to endNight
10%28%32%37%8%
768
April1st to 15thNight
12%310%34%33%5%
719
16th to endNight
12%210%33%31%9%
720
May1st to 15thNight
12%111%30%35%8%
600
16th to endNight
15%113%26%33%8%
563
June1st to 15thNight
14%9%33%35%6%
540
16th to endNight
5%422%56%10%
540
July1st to 15thNight
10%213%53%19%
510
16th to endNight
9%211%47%28%
657
August1st to 15thNight
9%113%50%24%
717
16th to endNight
6%18%46%37%
764
September1st to 15thNight
6%215%53%22%
720
16th to endNight
6%423%49%16%
716
October1st to 15thNight
6%15%31%45%9%
720
16th to endNight
11%15%26%36%20%
768
November1st to 15thNight
7%15%32%40%13%
760
16th to endNight
6%15%32%37%16%
780
December1st to 15thNight
12%17%36%32%9%
780
16th to endNight
12%210%32%32%10%
832
Page generated at 2018-02-23 08:21:40. Version ac04

Copyright 2018 A. Danko


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