Torrance
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Torrance clear sky chart from 2005-11-05 to 2017-08-12.

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
64%
15752
31%
46427
25%
15700
70%
15700
39%
24638

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
60%
716
27%
2452
23%
716
69%
716
34%
1214
January16th to endNight
55%
768
34%
2347
25%
768
67%
768
34%
1243
February1st to 15thNight
59%
700
34%
2101
32%
696
66%
696
37%
1109
February16th to endNight
52%
632
27%
1895
22%
632
61%
632
28%
1117
March1st to 15thNight
60%
720
29%
2160
26%
720
68%
720
39%
1124
March16th to endNight
59%
768
26%
2000
20%
768
63%
768
37%
1179
April1st to 15thNight
57%
719
28%
1799
17%
719
62%
719
42%
1032
April16th to endNight
59%
720
30%
1800
15%
720
64%
720
41%
1031
May1st to 15thNight
59%
638
26%
1718
15%
638
62%
638
36%
1005
May16th to endNight
64%
561
26%
1685
17%
561
69%
561
38%
924
June1st to 15thNight
67%
468
23%
1548
19%
468
69%
468
32%
868
June16th to endNight
67%
360
28%
1440
29%
360
71%
360
30%
723
July1st to 15thNight
71%
340
28%
1360
31%
340
73%
340
34%
635
July16th to endNight
68%
653
23%
1671
16%
609
75%
609
41%
943
August1st to 15thNight
74%
701
31%
1750
20%
697
75%
697
46%
993
August16th to endNight
78%
700
34%
1750
20%
700
81%
700
50%
948
September1st to 15thNight
76%
660
35%
1669
27%
660
78%
660
49%
908
September16th to endNight
77%
656
38%
1815
34%
656
82%
656
54%
882
October1st to 15thNight
70%
660
34%
1837
34%
660
73%
660
47%
962
October16th to endNight
70%
704
37%
2122
34%
704
78%
704
46%
1041
November1st to 15thNight
68%
700
35%
2275
36%
700
74%
700
46%
1028
November16th to endNight
64%
720
34%
2340
31%
720
72%
720
37%
1150
December1st to 15thNight
54%
720
32%
2340
28%
720
63%
720
29%
1257
December16th to endNight
50%
768
32%
2553
25%
768
62%
768
31%
1322

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
4312212346%65%
47515
Night
5%423313347%59%
46634
TransparencyDay
23%27%18%26%22%
47210
Night
25%36%16%24%22%
46439
SeeingDay
5%12%17%36%23%5%
5822
Night
7%15%6%23%33%13%
15763

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%413423246%59%
1483
16th to endDay
10%423312336%57%
1873
February1st to 15thDay
7%313313346%61%
1751
16th to endDay
10%5%13323347%53%
1579
March1st to 15thDay
331322345%7%61%
1800
16th to endDay
441332445%9%57%
2221
April1st to 15thDay
4412323247%62%
2149
16th to endDay
3212212236%69%
2160
May1st to 15thDay
45%22212347%63%
2232
16th to endDay
4413312337%64%
2429
June1st to 15thDay
6%6%24211338%59%
2408
16th to endDay
231211213474%
2520
July1st to 15thDay
3413212346%65%
2520
16th to endDay
2212213347%68%
2374
August1st to 15thDay
231112235%74%
2114
16th to endDay
1112135%6%74%
2100
September1st to 15thDay
2212311236%72%
1959
16th to endDay
231212236%73%
1815
October1st to 15thDay
5%222213346%66%
1790
16th to endDay
321221335%5%68%
1749
November1st to 15thDay
3212223236%69%
1584
16th to endDay
4313322347%63%
1620
December1st to 15thDay
7%41232345%7%56%
1620
16th to endDay
10%313312337%58%
1665
January1st to 15thNight
6%413323447%59%
2452
16th to endNight
10%413213236%59%
2347
February1st to 15thNight
6%414323236%60%
2101
16th to endNight
11%5%34423445%51%
1895
March1st to 15thNight
5%42322235%9%57%
2160
16th to endNight
5%5%3332445%8%53%
2000
April1st to 15thNight
7%5%32212237%60%
1799
16th to endNight
45%23313346%62%
1800
May1st to 15thNight
6%6%24413338%55%
1718
16th to endNight
45%13323347%60%
1684
June1st to 15thNight
36%2432445%9%52%
1548
16th to endNight
27%333235%5%8%55%
1440
July1st to 15thNight
34244233410%55%
1440
16th to endNight
45%244245%5%9%52%
1789
August1st to 15thNight
341331235%10%58%
1760
16th to endNight
141221245%10%61%
1750
September1st to 15thNight
231431345%9%60%
1669
16th to endNight
2413212236%68%
1815
October1st to 15thNight
3214313335%66%
1837
16th to endNight
4412212247%65%
2122
November1st to 15thNight
3322211247%68%
2275
16th to endNight
341331325%7%63%
2340
December1st to 15thNight
7%424423336%57%
2340
16th to endNight
10%313323235%59%
2553

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
27%26%14%21%26%
1483
16th to endDay
28%27%17%16%26%
1873
February1st to 15thDay
25%25%17%26%22%
1751
16th to endDay
31%37%22%24%10%
1579
March1st to 15thDay
22%311%20%21%19%
1800
16th to endDay
26%311%25%19%13%
2221
April1st to 15thDay
23%212%26%23%11%
2149
16th to endDay
19%210%24%26%16%
2160
May1st to 15thDay
24%39%23%24%15%
2232
16th to endDay
24%37%28%27%8%
2432
June1st to 15thDay
28%26%16%31%13%
2408
16th to endDay
20%139%30%34%
2520
July1st to 15thDay
23%3311%27%30%
2371
16th to endDay
21%37%20%31%16%
2229
August1st to 15thDay
17%2215%34%27%
2100
16th to endDay
16%3314%38%24%
2100
September1st to 15thDay
20%2411%30%30%
1959
16th to endDay
18%2115%33%29%
1815
October1st to 15thDay
21%26%21%25%22%
1790
16th to endDay
19%35%17%20%32%
1749
November1st to 15thDay
19%26%16%22%32%
1584
16th to endDay
22%28%17%20%29%
1620
December1st to 15thDay
26%39%17%19%22%
1620
16th to endDay
28%210%15%21%20%
1665
January1st to 15thNight
24%38%13%22%27%
2452
16th to endNight
27%28%15%15%29%
2347
February1st to 15thNight
26%26%17%22%24%
2112
16th to endNight
34%35%16%24%14%
1895
March1st to 15thNight
24%38%20%24%18%
2160
16th to endNight
28%410%21%21%12%
2000
April1st to 15thNight
26%29%26%23%12%
1799
16th to endNight
25%37%23%22%17%
1800
May1st to 15thNight
30%28%20%23%13%
1719
16th to endNight
26%49%24%26%9%
1685
June1st to 15thNight
31%49%14%28%11%
1548
16th to endNight
29%338%27%27%
1440
July1st to 15thNight
24%3411%26%30%
1360
16th to endNight
27%39%20%22%16%
1671
August1st to 15thNight
24%3212%34%22%
1750
16th to endNight
19%4211%36%25%
1750
September1st to 15thNight
21%349%29%30%
1669
16th to endNight
18%215%32%31%
1815
October1st to 15thNight
22%35%17%29%22%
1837
16th to endNight
21%2414%23%34%
2122
November1st to 15thNight
19%25%17%20%34%
2275
16th to endNight
22%35%17%20%29%
2340
December1st to 15thNight
30%27%15%21%22%
2340
16th to endNight
28%28%17%22%20%
2553

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
9%10%22%37%18%
111
16th to endDay
11%17%19%32%17%2
281
February1st to 15thDay
10%15%21%28%21%3
266
16th to endDay
10%16%27%28%15%2
238
March1st to 15thDay
6%17%24%27%19%4
270
16th to endDay
5%18%24%34%12%5%
288
April1st to 15thDay
421%24%32%13%4
269
16th to endDay
219%32%32%7%4
270
May1st to 15thDay
415%26%35%14%3
288
16th to endDay
6%13%22%42%12%3
330
June1st to 15thDay
8%11%19%37%20%2
315
16th to endDay
19%8%42%29%7%
315
July1st to 15thDay
27%7%39%34%8%
305
16th to endDay
29%333%39%10%
327
August1st to 15thDay
36%7%43%33%6%
300
16th to endDay
16%7%35%43%5%
268
September1st to 15thDay
17%8%46%30%5%
255
16th to endDay
17%11%47%24%7%
255
October1st to 15thDay
5%8%22%39%21%2
255
16th to endDay
48%15%39%24%7%
261
November1st to 15thDay
34427%36%23%
90
16th to endDay
38%8%36%36%5%
90
December1st to 15thDay
5%413%31%41%4
90
16th to endDay
10%9%20%28%28%3
85
January1st to 15thNight
8%17%7%32%27%7%
720
16th to endNight
11%17%9%27%28%5%
768
February1st to 15thNight
6%18%8%28%30%7%
704
16th to endNight
13%17%8%28%25%6%
632
March1st to 15thNight
5%18%9%33%26%6%
720
16th to endNight
6%18%9%28%30%7%
768
April1st to 15thNight
7%19%9%29%27%5%
719
16th to endNight
6%20%9%26%30%7%
720
May1st to 15thNight
8%18%9%23%32%8%
639
16th to endNight
418%7%31%30%7%
563
June1st to 15thNight
418%5%27%36%8%
468
16th to endNight
6%16%214%43%15%
360
July1st to 15thNight
6%12%15%38%35%
340
16th to endNight
6%16%17%38%30%
653
August1st to 15thNight
6%9%112%43%25%
701
16th to endNight
5%9%17%43%33%
700
September1st to 15thNight
49%213%43%26%
660
16th to endNight
5%9%317%45%19%
656
October1st to 15thNight
5%9%6%22%41%14%
660
16th to endNight
6%10%6%19%39%17%
704
November1st to 15thNight
415%5%25%35%13%
700
16th to endNight
7%18%5%25%32%10%
720
December1st to 15thNight
9%18%8%29%27%6%
720
16th to endNight
13%20%12%27%22%5%
768
Page generated at 2017-08-13 11:16:45. Version ac04

Copyright 2017 A. Danko


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