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Old Town Pasadena
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Old Town Pasadena 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
75%
15706
33%
46425
29%
15659
79%
15659
50%
23164

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
65%
716
28%
2473
26%
716
74%
716
42%
1205
January16th to endNight
61%
768
35%
2345
28%
768
71%
768
42%
1236
February1st to 15thNight
69%
698
35%
2105
34%
697
76%
697
47%
1080
February16th to endNight
60%
632
27%
1895
26%
632
66%
632
36%
1080
March1st to 15thNight
67%
720
29%
2160
26%
720
75%
720
48%
1094
March16th to endNight
71%
768
28%
2004
23%
768
75%
768
48%
1111
April1st to 15thNight
66%
719
29%
1799
18%
719
69%
719
49%
1024
April16th to endNight
67%
720
31%
1800
15%
720
72%
720
54%
975
May1st to 15thNight
68%
620
28%
1700
19%
620
70%
620
46%
940
May16th to endNight
71%
561
30%
1685
24%
561
73%
561
52%
840
June1st to 15thNight
81%
466
29%
1546
28%
466
83%
466
51%
720
June16th to endNight
91%
360
35%
1440
43%
360
91%
360
54%
551
July1st to 15thNight
91%
340
33%
1360
41%
340
91%
340
55%
512
July16th to endNight
90%
629
31%
1649
25%
587
91%
587
56%
829
August1st to 15thNight
90%
701
34%
1750
23%
697
90%
697
66%
870
August16th to endNight
92%
700
40%
1750
27%
700
92%
700
68%
865
September1st to 15thNight
88%
660
40%
1675
32%
660
88%
660
64%
833
September16th to endNight
89%
656
42%
1815
41%
656
90%
656
68%
813
October1st to 15thNight
78%
660
36%
1829
34%
660
81%
660
56%
929
October16th to endNight
79%
704
38%
2134
40%
704
82%
704
52%
1021
November1st to 15thNight
78%
700
36%
2275
37%
700
84%
700
56%
1001
November16th to endNight
76%
720
37%
2340
38%
720
80%
720
50%
1101
December1st to 15thNight
66%
720
33%
2340
30%
720
73%
720
39%
1229
December16th to endNight
58%
768
32%
2556
29%
768
67%
768
38%
1305

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%212212235%68%
47523
Night
5%212212235%68%
46626
TransparencyDay
18%37%16%27%25%
47216
Night
20%37%16%26%26%
46433
SeeingDay
6%9%30%38%11%3
5788
Night
5%212%34%36%8%
15719

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%31341223463%
1463
16th to endDay
12%322312335%57%
1875
February1st to 15thDay
7%323212336%62%
1751
16th to endDay
13%413324236%52%
1579
March1st to 15thDay
5%21332335%7%60%
1800
16th to endDay
5%21332435%9%56%
2217
April1st to 15thDay
6%312224347%60%
2149
16th to endDay
5%212212335%70%
2160
May1st to 15thDay
5%312312345%65%
2250
16th to endDay
5%312323336%65%
2429
June1st to 15thDay
5%312322137%65%
2409
16th to endDay
121112383%
2520
July1st to 15thDay
212312235%72%
2520
16th to endDay
2111212336%73%
2397
August1st to 15thDay
11111212382%
2114
16th to endDay
11223481%
2100
September1st to 15thDay
1111112482%
1955
16th to endDay
11111123380%
1815
October1st to 15thDay
6%112312235%69%
1799
16th to endDay
421311233472%
1735
November1st to 15thDay
33231223471%
1584
16th to endDay
6%212323236%65%
1620
December1st to 15thDay
8%312313449%56%
1620
16th to endDay
12%312212337%57%
1662
January1st to 15thNight
7%313222335%63%
2473
16th to endNight
10%312312235%62%
2345
February1st to 15thNight
6%31331223465%
2101
16th to endNight
13%32232434455%
1895
March1st to 15thNight
5%312223348%63%
2160
16th to endNight
421222445%7%60%
2004
April1st to 15thNight
6%412322325%64%
1799
16th to endNight
3211323336%69%
1800
May1st to 15thNight
33125%22337%64%
1700
16th to endNight
3212422235%69%
1684
June1st to 15thNight
121323247%69%
1546
16th to endNight
1121223380%
1440
July1st to 15thNight
22121223475%
1440
16th to endNight
21121235%7%68%
1765
August1st to 15thNight
1211112225%77%
1760
16th to endNight
11111123480%
1750
September1st to 15thNight
12221222478%
1675
16th to endNight
121122482%
1815
October1st to 15thNight
321222323472%
1829
16th to endNight
42122223472%
2134
November1st to 15thNight
321221222473%
2275
16th to endNight
5%212213346%66%
2340
December1st to 15thNight
7%213423237%60%
2340
16th to endNight
11%312212235%61%
2556

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
24%45%12%24%28%
1463
16th to endDay
28%28%14%18%27%
1875
February1st to 15thDay
23%26%17%24%25%
1751
16th to endDay
30%29%18%28%10%
1579
March1st to 15thDay
21%410%20%21%21%
1800
16th to endDay
22%5%13%23%20%14%
2217
April1st to 15thDay
22%311%25%24%11%
2149
16th to endDay
17%210%22%28%17%
2160
May1st to 15thDay
22%39%19%28%16%
2250
16th to endDay
22%37%26%30%10%
2432
June1st to 15thDay
22%38%13%31%20%
2409
16th to endDay
11%237%34%41%
2520
July1st to 15thDay
14%35%9%26%39%
2371
16th to endDay
12%5%7%20%32%21%
2250
August1st to 15thDay
9%2213%36%35%
2100
16th to endDay
8%2412%40%31%
2100
September1st to 15thDay
9%2411%33%38%
1955
16th to endDay
9%2412%35%35%
1815
October1st to 15thDay
18%26%19%26%26%
1799
16th to endDay
15%35%13%22%39%
1735
November1st to 15thDay
17%26%15%23%33%
1584
16th to endDay
21%36%13%23%31%
1620
December1st to 15thDay
25%49%17%18%24%
1620
16th to endDay
27%310%17%20%21%
1662
January1st to 15thNight
24%36%13%22%28%
2473
16th to endNight
26%37%15%16%31%
2345
February1st to 15thNight
23%36%16%22%27%
2112
16th to endNight
31%48%15%24%15%
1895
March1st to 15thNight
21%39%20%23%20%
2160
16th to endNight
21%6%12%21%22%15%
2004
April1st to 15thNight
25%29%26%22%13%
1799
16th to endNight
19%410%23%26%16%
1800
May1st to 15thNight
24%5%9%20%26%14%
1701
16th to endNight
19%39%27%28%11%
1685
June1st to 15thNight
19%311%15%33%16%
1546
16th to endNight
14%25%9%32%35%
1440
July1st to 15thNight
13%35%10%27%39%
1360
16th to endNight
16%5%7%20%28%20%
1649
August1st to 15thNight
12%3310%39%30%
1750
16th to endNight
11%4211%39%31%
1750
September1st to 15thNight
14%348%32%37%
1675
16th to endNight
10%3312%34%36%
1815
October1st to 15thNight
18%3418%30%25%
1829
16th to endNight
18%4410%24%38%
2134
November1st to 15thNight
15%35%14%24%36%
2275
16th to endNight
20%36%17%19%33%
2340
December1st to 15thNight
25%5%7%15%19%25%
2340
16th to endNight
26%38%15%23%21%
2556

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
18%8%38%26%7%
91
16th to endDay
12%13%35%29%8%
281
February1st to 15thDay
11%10%29%33%12%2
266
16th to endDay
15%21%30%25%6%
238
March1st to 15thDay
7%15%33%27%14%1
270
16th to endDay
7%15%36%29%8%1
288
April1st to 15thDay
10%17%42%20%5%3
269
16th to endDay
421%42%23%42
270
May1st to 15thDay
10%15%35%29%6%2
288
16th to endDay
8%10%40%29%10%1
330
June1st to 15thDay
8%8%29%42%7%3
315
16th to endDay
1128%46%13%9%
315
July1st to 15thDay
1118%54%18%6%
305
16th to endDay
113%55%20%8%
327
August1st to 15thDay
3122%57%10%5%
300
16th to endDay
117%61%13%5%
268
September1st to 15thDay
2227%54%8%3
255
16th to endDay
2337%41%9%5%
255
October1st to 15thDay
5%11%36%36%7%1
255
16th to endDay
6%6%30%40%14%2
247
November1st to 15thDay
47%13%27%33%13%
90
16th to endDay
47%32%40%13%2
90
December1st to 15thDay
25%22%45%23%1
90
16th to endDay
16%8%29%29%16%
85
January1st to 15thNight
8%118%43%23%4
720
16th to endNight
12%217%36%26%4
768
February1st to 15thNight
7%214%41%27%5%
704
16th to endNight
13%218%36%24%4
632
March1st to 15thNight
5%220%40%25%5%
720
16th to endNight
5%315%41%29%4
768
April1st to 15thNight
7%316%42%25%3
719
16th to endNight
3420%36%29%5%
720
May1st to 15thNight
4318%35%32%5%
621
16th to endNight
4219%38%31%4
563
June1st to 15thNight
1110%39%43%2
466
16th to endNight
1430%57%6%
360
July1st to 15thNight
2210%70%15%
340
16th to endNight
21120%57%17%
629
August1st to 15thNight
11320%56%16%
701
16th to endNight
2216%55%23%
700
September1st to 15thNight
15%23%50%19%
660
16th to endNight
15%28%49%13%
656
October1st to 15thNight
412%36%38%7%
660
16th to endNight
6%19%32%37%12%
704
November1st to 15thNight
3111%38%34%11%
700
16th to endNight
5%112%39%32%8%
720
December1st to 15thNight
7%215%41%27%5%
720
16th to endNight
12%6%16%41%20%3
768
Page generated at 2017-08-13 11:16:58. Version ac04

Copyright 2017 A. Danko


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