Topanga
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Topanga clear sky chart from 2005-11-05 to 2017-12-20.

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
66%
16213
33%
47978
27%
16164
73%
16164
45%
23730

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
57%
716
29%
2446
25%
716
67%
716
35%
1188
January16th to endNight
53%
768
34%
2393
25%
768
66%
768
34%
1255
February1st to 15thNight
60%
700
35%
2103
32%
697
68%
697
40%
1072
February16th to endNight
55%
632
27%
1895
22%
632
64%
632
30%
1088
March1st to 15thNight
59%
720
28%
2160
25%
720
68%
720
41%
1092
March16th to endNight
62%
768
28%
1993
20%
768
68%
768
41%
1118
April1st to 15thNight
59%
719
30%
1799
18%
719
64%
719
45%
1013
April16th to endNight
63%
720
31%
1800
15%
720
68%
720
51%
945
May1st to 15thNight
64%
644
27%
1724
16%
644
67%
644
42%
957
May16th to endNight
67%
561
28%
1685
19%
561
71%
561
44%
845
June1st to 15thNight
70%
426
27%
1506
25%
426
74%
426
40%
711
June16th to endNight
75%
360
34%
1440
34%
360
81%
360
47%
533
July1st to 15thNight
77%
340
33%
1360
37%
340
81%
340
45%
532
July16th to endNight
74%
627
29%
1647
22%
585
81%
585
51%
815
August1st to 15thNight
79%
717
34%
1790
21%
713
80%
713
59%
909
August16th to endNight
81%
764
41%
1910
25%
764
85%
764
64%
916
September1st to 15thNight
81%
720
38%
1812
29%
720
83%
720
60%
909
September16th to endNight
81%
716
43%
1980
37%
716
87%
716
65%
869
October1st to 15thNight
74%
720
35%
2022
34%
720
77%
720
52%
993
October16th to endNight
73%
768
42%
2307
39%
768
81%
768
51%
1073
November1st to 15thNight
70%
760
34%
2470
34%
760
75%
760
48%
1100
November16th to endNight
62%
780
38%
2535
33%
780
72%
780
42%
1169
December1st to 15thNight
57%
780
35%
2535
29%
780
67%
780
36%
1265
December16th to endNight
50%
787
33%
2666
26%
787
63%
787
32%
1363

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
4312212236%68%
48842
Night
5%312212346%66%
48181
TransparencyDay
18%48%18%26%24%
48535
Night
20%38%16%25%25%
47988
SeeingDay
410%15%34%28%6%
6290
Night
5%14%7%25%35%11%
16224

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%413322235%62%
1489
16th to endDay
10%423213236%59%
1828
February1st to 15thDay
7%323312246%63%
1751
16th to endDay
10%413223346%56%
1579
March1st to 15thDay
5%313213446%62%
1800
16th to endDay
431332445%9%57%
2229
April1st to 15thDay
5%422223348%62%
2149
16th to endDay
331122336%71%
2160
May1st to 15thDay
4412112348%65%
2223
16th to endDay
3412112337%68%
2429
June1st to 15thDay
5%6%1322237%65%
2450
16th to endDay
121111112478%
2520
July1st to 15thDay
232212335%71%
2520
16th to endDay
221212236%72%
2401
August1st to 15thDay
221211112478%
2160
16th to endDay
11111235%79%
2292
September1st to 15thDay
211111225%79%
2148
16th to endDay
221111225%78%
1980
October1st to 15thDay
431121133472%
1935
16th to endDay
221221234472%
1917
November1st to 15thDay
3312223335%68%
1719
16th to endDay
4212313347%65%
1755
December1st to 15thDay
6%31231336%8%59%
1755
16th to endDay
9%313313336%59%
1653
January1st to 15thNight
7%313213246%61%
2446
16th to endNight
11%312222335%60%
2393
February1st to 15thNight
6%323312245%64%
2101
16th to endNight
13%313314335%55%
1895
March1st to 15thNight
5%413213447%62%
2160
16th to endNight
44123235%5%6%59%
1993
April1st to 15thNight
7%5%22211235%64%
1799
16th to endNight
3312212337%68%
1800
May1st to 15thNight
5%6%12223346%61%
1724
16th to endNight
3412212337%66%
1684
June1st to 15thNight
341331335%8%62%
1506
16th to endNight
1321213246%71%
1440
July1st to 15thNight
1313222337%69%
1440
16th to endNight
231222245%7%64%
1763
August1st to 15thNight
331221225%6%69%
1800
16th to endNight
1212211346%72%
1910
September1st to 15thNight
312112235%74%
1812
16th to endNight
121211123477%
1980
October1st to 15thNight
421321323470%
2022
16th to endNight
431112235%71%
2307
November1st to 15thNight
3212212335%71%
2470
16th to endNight
4212213346%66%
2535
December1st to 15thNight
6%313223246%62%
2535
16th to endNight
10%313213235%62%
2666

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
25%46%12%24%27%
1489
16th to endDay
27%48%16%17%26%
1828
February1st to 15thDay
22%37%15%25%25%
1751
16th to endDay
29%49%17%27%10%
1579
March1st to 15thDay
21%5%9%22%20%20%
1800
16th to endDay
23%5%14%22%18%14%
2229
April1st to 15thDay
21%5%13%24%23%12%
2149
16th to endDay
15%5%11%22%27%17%
2160
May1st to 15thDay
17%7%11%20%26%17%
2223
16th to endDay
16%414%27%27%9%
2432
June1st to 15thDay
21%410%17%29%16%
2450
16th to endDay
12%16%12%34%33%
2520
July1st to 15thDay
14%37%14%28%32%
2371
16th to endDay
14%39%22%29%19%
2254
August1st to 15thDay
12%15%16%34%29%
2146
16th to endDay
8%15%15%39%29%
2292
September1st to 15thDay
10%26%15%30%33%
2148
16th to endDay
11%25%17%32%30%
1980
October1st to 15thDay
15%37%20%24%27%
1935
16th to endDay
15%45%15%21%37%
1917
November1st to 15thDay
19%36%16%23%30%
1719
16th to endDay
20%48%13%22%31%
1755
December1st to 15thDay
22%5%9%15%20%26%
1755
16th to endDay
27%48%16%23%19%
1653
January1st to 15thNight
23%37%14%22%27%
2446
16th to endNight
26%38%15%15%30%
2393
February1st to 15thNight
22%46%16%23%26%
2112
16th to endNight
32%38%15%24%14%
1895
March1st to 15thNight
21%410%19%24%19%
2160
16th to endNight
23%5%13%20%21%15%
1993
April1st to 15thNight
23%39%25%23%13%
1799
16th to endNight
16%413%22%23%19%
1800
May1st to 15thNight
22%5%9%19%25%15%
1725
16th to endNight
18%5%11%26%25%11%
1685
June1st to 15thNight
20%5%14%17%27%14%
1506
16th to endNight
14%29%14%30%30%
1440
July1st to 15thNight
16%15%14%26%35%
1360
16th to endNight
17%48%23%25%19%
1647
August1st to 15thNight
16%16%12%34%28%
1790
16th to endNight
12%5%14%37%29%
1910
September1st to 15thNight
14%26%10%30%35%
1812
16th to endNight
11%15%14%32%35%
1980
October1st to 15thNight
17%36%16%27%28%
2022
16th to endNight
16%25%13%21%39%
2307
November1st to 15thNight
16%38%16%21%34%
2470
16th to endNight
18%37%16%21%33%
2535
December1st to 15thNight
24%37%15%20%28%
2535
16th to endNight
26%47%14%25%21%
2666

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
14%11%23%42%6%
117
16th to endDay
10%16%21%34%14%1
273
February1st to 15thDay
9%13%22%33%19%2
266
16th to endDay
13%13%25%31%13%1
238
March1st to 15thDay
5%17%23%26%25%2
270
16th to endDay
415%25%34%18%2
288
April1st to 15thDay
5%17%23%36%12%5%
269
16th to endDay
119%29%32%13%3
270
May1st to 15thDay
5%13%23%34%18%3
288
16th to endDay
412%18%43%18%3
330
June1st to 15thDay
8%11%12%36%26%5%
315
16th to endDay
19%430%41%12%
315
July1st to 15thDay
26%425%47%12%
305
16th to endDay
29%220%49%15%
327
August1st to 15thDay
25%5%31%45%9%
315
16th to endDay
4325%53%13%
332
September1st to 15thDay
35%5%40%37%6%
315
16th to endDay
2410%43%32%6%
315
October1st to 15thDay
26%18%44%24%4
315
16th to endDay
46%15%37%28%7%
333
November1st to 15thDay
5%211%31%34%13%
135
16th to endDay
2217%35%30%11%
135
December1st to 15thDay
2217%35%34%6%
135
16th to endDay
6%13%17%32%23%5%
89
January1st to 15thNight
8%17%10%33%23%6%
720
16th to endNight
11%17%11%28%26%4
768
February1st to 15thNight
6%17%9%31%27%7%
704
16th to endNight
12%17%9%30%25%4
632
March1st to 15thNight
418%11%32%26%5%
720
16th to endNight
5%17%9%31%30%5%
768
April1st to 15thNight
6%18%10%31%28%4
719
16th to endNight
418%9%30%30%6%
720
May1st to 15thNight
7%16%7%25%34%7%
645
16th to endNight
317%9%30%34%4
563
June1st to 15thNight
317%427%39%8%
426
16th to endNight
216%117%50%11%
360
July1st to 15thNight
411%1448%28%
340
16th to endNight
316%6%48%23%
627
August1st to 15thNight
49%12%49%22%
717
16th to endNight
28%10%48%29%
764
September1st to 15thNight
38%215%46%24%
720
16th to endNight
28%219%49%17%
716
October1st to 15thNight
48%5%25%44%11%
720
16th to endNight
5%9%7%20%41%15%
768
November1st to 15thNight
313%7%33%30%11%
760
16th to endNight
6%15%8%26%32%10%
780
December1st to 15thNight
7%16%11%30%27%6%
780
16th to endNight
11%19%13%31%18%5%
787
Page generated at 2017-12-21 04:04:56. Version ac04

Copyright 2017 A. Danko


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