Tujunga Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tujunga Observatory clear sky chart from 2005-11-05 to 2017-09-17.

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
72%
15823
35%
46811
29%
15775
78%
15775
53%
22352

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
29%
2467
24%
716
68%
716
40%
1201
January16th to endNight
54%
768
34%
2371
26%
768
66%
768
39%
1247
February1st to 15thNight
62%
700
35%
2105
30%
698
72%
698
46%
1076
February16th to endNight
57%
632
29%
1895
26%
632
64%
632
35%
1069
March1st to 15thNight
61%
720
29%
2160
24%
720
71%
720
46%
1080
March16th to endNight
66%
768
31%
2000
23%
768
72%
768
47%
1089
April1st to 15thNight
64%
719
30%
1799
18%
719
69%
719
50%
1002
April16th to endNight
66%
720
33%
1800
16%
720
72%
720
60%
910
May1st to 15thNight
69%
623
29%
1703
19%
623
72%
623
52%
879
May16th to endNight
73%
561
32%
1685
25%
561
76%
561
60%
754
June1st to 15thNight
85%
444
33%
1524
32%
444
88%
444
65%
588
June16th to endNight
96%
360
41%
1440
51%
360
96%
360
79%
425
July1st to 15thNight
92%
340
36%
1360
44%
340
92%
340
66%
453
July16th to endNight
90%
614
35%
1635
29%
573
91%
573
65%
737
August1st to 15thNight
92%
717
37%
1790
25%
713
92%
713
81%
807
August16th to endNight
93%
764
46%
1910
31%
764
93%
764
81%
856
September1st to 15thNight
91%
720
41%
1821
33%
720
91%
720
76%
835
September16th to endNight
90%
664
46%
1837
44%
664
91%
664
78%
765
October1st to 15thNight
76%
660
37%
1840
34%
660
80%
660
57%
905
October16th to endNight
76%
704
41%
2131
41%
704
81%
704
54%
987
November1st to 15thNight
71%
700
36%
2275
34%
700
80%
700
56%
993
November16th to endNight
72%
720
37%
2340
35%
720
79%
720
48%
1101
December1st to 15thNight
61%
720
33%
2340
28%
720
71%
720
37%
1238
December16th to endNight
51%
768
32%
2583
26%
768
64%
768
33%
1355

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
4212212335%68%
47941
Night
4212212235%69%
47011
TransparencyDay
17%36%16%28%27%
47633
Night
17%36%15%27%29%
46819
SeeingDay
6%9%28%38%12%3
5935
Night
6%313%32%35%8%
15833

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%223322245%62%
1468
16th to endDay
12%5%13312236%56%
1850
February1st to 15thDay
8%323212347%59%
1751
16th to endDay
12%5%24322335%52%
1579
March1st to 15thDay
6%31322345%9%57%
1800
16th to endDay
6%31432346%8%55%
2220
April1st to 15thDay
6%323322447%59%
2149
16th to endDay
4212212336%68%
2160
May1st to 15thDay
3312312336%66%
2244
16th to endDay
422212337%68%
2429
June1st to 15thDay
3211212237%71%
2433
16th to endDay
111111386%
2520
July1st to 15thDay
111221232476%
2520
16th to endDay
211212345%73%
2413
August1st to 15thDay
1111122384%
2160
16th to endDay
11122484%
2292
September1st to 15thDay
1111222382%
2137
16th to endDay
1112122381%
1828
October1st to 15thDay
5%11221224469%
1788
16th to endDay
321222234470%
1741
November1st to 15thDay
331331233469%
1584
16th to endDay
5%323322245%63%
1620
December1st to 15thDay
7%41332345%10%54%
1620
16th to endDay
11%413313345%55%
1635
January1st to 15thNight
8%313212346%61%
2467
16th to endNight
9%423212345%59%
2371
February1st to 15thNight
6%413313346%61%
2101
16th to endNight
13%424313335%54%
1895
March1st to 15thNight
5%42221325%8%61%
2160
16th to endNight
42123135%5%8%60%
2000
April1st to 15thNight
6%313223235%65%
1799
16th to endNight
3211212346%72%
1800
May1st to 15thNight
2212323247%66%
1703
16th to endNight
112213226%73%
1684
June1st to 15thNight
11212247%75%
1524
16th to endNight
111288%
1440
July1st to 15thNight
1211213380%
1440
16th to endNight
211212235%74%
1750
August1st to 15thNight
111114382%
1800
16th to endNight
111112385%
1910
September1st to 15thNight
11111123480%
1821
16th to endNight
11122385%
1837
October1st to 15thNight
42331222372%
1840
16th to endNight
32232222474%
2131
November1st to 15thNight
3212212235%72%
2275
16th to endNight
4213213345%66%
2340
December1st to 15thNight
7%324423336%58%
2340
16th to endNight
11%413312236%58%
2583

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%25%13%23%28%
1468
16th to endDay
30%37%13%19%26%
1850
February1st to 15thDay
23%45%15%25%25%
1751
16th to endDay
34%45%16%27%12%
1579
March1st to 15thDay
23%5%9%19%22%20%
1800
16th to endDay
24%6%11%22%21%14%
2220
April1st to 15thDay
24%410%24%24%11%
2149
16th to endDay
17%49%21%30%17%
2160
May1st to 15thDay
19%310%19%28%18%
2244
16th to endDay
17%49%25%32%11%
2432
June1st to 15thDay
14%39%15%33%23%
2433
16th to endDay
6%137%35%44%
2520
July1st to 15thDay
12%2310%28%43%
2371
16th to endDay
12%36%20%30%26%
2265
August1st to 15thDay
6%1312%35%40%
2146
16th to endDay
6%1212%39%36%
2292
September1st to 15thDay
8%15%12%32%39%
2137
16th to endDay
9%1313%35%37%
1828
October1st to 15thDay
18%35%17%27%27%
1788
16th to endDay
16%4312%22%39%
1741
November1st to 15thDay
19%25%14%28%30%
1584
16th to endDay
23%25%12%23%32%
1620
December1st to 15thDay
25%5%8%15%21%22%
1620
16th to endDay
29%5%7%16%21%19%
1635
January1st to 15thNight
24%36%14%23%28%
2467
16th to endNight
26%37%12%19%30%
2371
February1st to 15thNight
22%36%15%24%27%
2112
16th to endNight
31%36%16%25%16%
1895
March1st to 15thNight
20%49%18%25%21%
2160
16th to endNight
21%5%9%22%24%16%
2000
April1st to 15thNight
22%48%26%22%15%
1799
16th to endNight
14%29%24%28%20%
1800
May1st to 15thNight
17%6%10%19%29%17%
1704
16th to endNight
13%410%25%32%14%
1685
June1st to 15thNight
8%311%16%31%27%
1524
16th to endNight
5%5%8%30%49%
1440
July1st to 15thNight
9%1311%25%48%
1360
16th to endNight
11%35%20%29%29%
1635
August1st to 15thNight
7%139%38%40%
1790
16th to endNight
6%1211%39%37%
1910
September1st to 15thNight
9%16%9%29%44%
1821
16th to endNight
7%1213%34%40%
1837
October1st to 15thNight
17%3416%30%28%
1840
16th to endNight
16%3312%23%40%
2131
November1st to 15thNight
16%25%13%27%34%
2275
16th to endNight
20%25%15%21%34%
2340
December1st to 15thNight
26%46%15%20%25%
2340
16th to endNight
27%46%14%25%20%
2583

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
16%13%47%16%5%
96
16th to endDay
15%14%38%24%6%
277
February1st to 15thDay
10%15%30%31%9%1
266
16th to endDay
20%18%34%21%6%
238
March1st to 15thDay
11%15%35%22%14%1
270
16th to endDay
8%15%38%30%5%1
288
April1st to 15thDay
11%19%37%23%5%2
269
16th to endDay
426%36%24%5%1
270
May1st to 15thDay
7%15%35%33%43
288
16th to endDay
8%10%36%32%9%3
330
June1st to 15thDay
37%31%42%10%3
315
16th to endDay
2126%44%16%8%
315
July1st to 15thDay
1115%51%21%8%
305
16th to endDay
29%57%20%9%
327
August1st to 15thDay
219%56%13%6%
315
16th to endDay
14%57%18%8%
332
September1st to 15thDay
1226%53%12%3
315
16th to endDay
1329%51%11%1
260
October1st to 15thDay
5%10%34%36%10%2
255
16th to endDay
7%9%29%37%15%1
253
November1st to 15thDay
5%11%12%32%32%6%
90
16th to endDay
7%11%33%36%10%1
90
December1st to 15thDay
6%8%20%43%20%1
90
16th to endDay
19%13%27%29%9%
81
January1st to 15thNight
10%422%42%16%4
720
16th to endNight
13%5%19%36%21%3
768
February1st to 15thNight
8%417%39%24%5%
704
16th to endNight
15%5%17%33%23%4
632
March1st to 15thNight
7%5%20%35%25%5%
720
16th to endNight
5%5%17%37%28%4
768
April1st to 15thNight
7%5%17%39%26%3
719
16th to endNight
37%20%35%27%5%
720
May1st to 15thNight
4320%36%30%5%
624
16th to endNight
3217%37%34%4
563
June1st to 15thNight
110%36%47%3
444
16th to endNight
132%56%8%
360
July1st to 15thNight
2110%69%16%
340
16th to endNight
2215%61%16%
614
August1st to 15thNight
1220%57%16%
717
16th to endNight
2115%57%23%
764
September1st to 15thNight
1321%54%18%
720
16th to endNight
15%26%50%16%
664
October1st to 15thNight
5%210%37%36%7%
660
16th to endNight
5%39%31%36%13%
704
November1st to 15thNight
5%316%35%29%10%
700
16th to endNight
7%314%40%26%8%
720
December1st to 15thNight
10%5%14%41%24%2
720
16th to endNight
13%10%19%39%14%3
768
Page generated at 2017-09-18 05:38:23. Version ac04

Copyright 2017 A. Danko


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