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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 2005-11-06 to 2023-06-24.

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%
23634
33%
69829
28%
23588
76%
23588
48%
35572

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 10thNight
62%
716
26%
2506
27%
716
68%
716
37%
1281
January11th to 20thNight
64%
720
34%
2350
29%
720
74%
720
44%
1167
January21st to endNight
57%
792
38%
2376
29%
792
69%
792
42%
1258
February1st to 10thNight
64%
720
36%
2160
32%
720
72%
720
45%
1121
February11th to 20thNight
61%
700
33%
2098
28%
700
71%
700
45%
1083
February21st to endNight
57%
592
28%
1776
26%
592
64%
592
38%
987
March1st to 10thNight
59%
720
26%
2160
23%
720
66%
720
38%
1216
March11th to 20thNight
64%
720
25%
2109
23%
720
69%
720
40%
1180
March21st to endNight
62%
792
30%
1980
20%
792
69%
792
46%
1142
April1st to 10thNight
66%
720
28%
1800
19%
720
69%
720
43%
1076
April11th to 20thNight
64%
711
32%
1779
17%
711
69%
711
51%
981
April21st to endNight
65%
720
29%
1800
15%
720
69%
720
49%
1019
May1st to 10thNight
64%
662
26%
1742
16%
662
66%
662
43%
1021
May11th to 20thNight
70%
531
28%
1595
22%
531
71%
531
43%
874
May21st to endNight
67%
582
30%
1746
24%
582
69%
582
51%
882
June1st to 10thNight
75%
520
25%
1600
22%
520
76%
520
46%
839
June11th to 20thNight
86%
360
35%
1440
42%
360
86%
360
47%
590
June21st to endNight
87%
348
34%
1392
42%
348
88%
348
47%
587
July1st to 10thNight
90%
330
36%
1320
45%
330
90%
330
51%
520
July11th to 20thNight
91%
349
33%
1333
37%
349
91%
349
51%
560
July21st to endNight
88%
713
30%
1721
21%
671
89%
671
56%
910
August1st to 10thNight
89%
676
33%
1680
22%
672
89%
672
65%
846
August11th to 20thNight
90%
672
36%
1680
23%
672
90%
672
68%
831
August21st to endNight
90%
748
40%
1870
28%
748
90%
748
63%
949
September1st to 10thNight
87%
680
38%
1700
30%
680
87%
680
62%
870
September11th to 20thNight
88%
680
43%
1823
39%
680
89%
680
69%
837
September21st to endNight
86%
680
42%
1870
40%
680
89%
680
66%
856
October1st to 10thNight
78%
680
36%
1870
33%
680
82%
680
54%
966
October11th to 20thNight
77%
680
38%
1976
37%
680
81%
680
53%
969
October21st to endNight
77%
748
41%
2278
40%
748
82%
748
57%
1042
November1st to 10thNight
76%
700
35%
2275
36%
700
81%
700
52%
1035
November11th to 20thNight
77%
720
36%
2340
36%
720
83%
720
53%
1057
November21st to endNight
70%
720
35%
2340
36%
720
74%
720
44%
1167
December1st to 10thNight
64%
720
31%
2340
28%
720
71%
720
38%
1249
December11th to 20thNight
59%
720
31%
2340
29%
720
65%
720
35%
1278
December21st to endNight
56%
792
33%
2664
28%
792
67%
792
40%
1326

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%212212236%68%
71158
Night
5%312212235%67%
70034
TransparencyDay
18%47%16%27%26%
70884
Night
20%5%7%16%25%25%
69830
SeeingDay
6%8%27%36%15%4
13737
Night
5%214%36%32%7%
23644

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 10thDay
9%313413346%57%
1439
11th to 20thDay
8%412323336%61%
1601
21st to endDay
11%42232223460%
1980
February1st to 10thDay
9%323212235%64%
1800
11th to 20thDay
9%212212346%62%
1750
21st to endDay
9%413413246%57%
1480
March1st to 10thDay
8%5%1443336%7%50%
1800
11th to 20thDay
8%41222335%7%57%
1845
21st to endDay
6%312324447%58%
2376
April1st to 10thDay
6%312223348%60%
2160
11th to 20thDay
4313213235%66%
2129
21st to endDay
5%312212235%68%
2160
May1st to 10thDay
7%5%12222336%61%
2218
11th to 20thDay
5%313313237%63%
2301
21st to endDay
6%313322245%63%
2530
June1st to 10thDay
4312322238%65%
2354
11th to 20thDay
331212225%74%
2520
21st to endDay
11121223478%
2425
July1st to 10thDay
121212235%74%
2380
11th to 20thDay
211211225%78%
2355
21st to endDay
111112347%72%
2244
August1st to 10thDay
1111122481%
2029
11th to 20thDay
111112384%
2002
21st to endDay
1212235%78%
2244
September1st to 10thDay
2111123480%
2040
11th to 20thDay
211112483%
1916
21st to endDay
11121123479%
1870
October1st to 10thDay
421231223470%
1870
11th to 20thDay
4121222476%
1760
21st to endDay
42211133474%
1833
November1st to 10thDay
321231224471%
1584
11th to 20thDay
422212245%70%
1620
21st to endDay
5%113323247%63%
1620
December1st to 10thDay
8%313323436%58%
1620
11th to 20thDay
11%3123123410%53%
1620
21st to endDay
11%312223336%58%
1683
January1st to 10thNight
10%413222437%58%
2506
11th to 20thNight
7%313212236%64%
2350
21st to endNight
10%31231222464%
2376
February1st to 10thNight
7%31321223466%
2160
11th to 20thNight
8%313313235%63%
2098
21st to endNight
11%31332333459%
1776
March1st to 10thNight
9%5%1322335%8%54%
2160
11th to 20thNight
8%31232345%7%57%
2109
21st to endNight
7%312324347%59%
1980
April1st to 10thNight
6%413333336%60%
1800
11th to 20thNight
45%11213335%67%
1779
21st to endNight
4412322335%65%
1800
May1st to 10thNight
5%5%13412336%61%
1742
11th to 20thNight
45%13423236%62%
1594
21st to endNight
4413311225%69%
1746
June1st to 10thNight
2312423347%64%
1600
11th to 20thNight
12232222475%
1440
21st to endNight
112212245%74%
1392
July1st to 10thNight
121211225%77%
1360
11th to 20thNight
112213346%74%
1381
21st to endNight
31121235%7%69%
1829
August1st to 10thNight
121111222477%
1690
11th to 20thNight
2111135%79%
1680
21st to endNight
11111123479%
1870
September1st to 10thNight
12221222377%
1700
11th to 20thNight
1111111384%
1823
21st to endNight
111111225%81%
1870
October1st to 10thNight
321232223371%
1870
11th to 20thNight
42111222474%
1976
21st to endNight
321221223374%
2278
November1st to 10thNight
4311212235%70%
2275
11th to 20thNight
3212212225%72%
2340
21st to endNight
5%21232345%6%62%
2340
December1st to 10thNight
8%314312247%59%
2340
11th to 20thNight
11%323322346%56%
2340
21st to endNight
10%412212335%62%
2664

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 10thDay
28%46%17%21%21%
1439
11th to 20thDay
24%46%10%25%27%
1601
21st to endDay
28%27%17%17%27%
1980
February1st to 10thDay
24%25%14%24%28%
1800
11th to 20thDay
22%35%16%27%24%
1760
21st to endDay
25%39%18%24%19%
1480
March1st to 10thDay
30%49%17%17%20%
1800
11th to 20thDay
23%5%10%19%22%17%
1845
21st to endDay
22%5%11%22%22%14%
2376
April1st to 10thDay
22%5%12%25%22%12%
2160
11th to 20thDay
18%39%21%29%17%
2132
21st to endDay
18%38%25%30%13%
2160
May1st to 10thDay
22%6%9%19%27%13%
2218
11th to 20thDay
21%6%7%22%30%12%
2304
21st to endDay
21%5%7%27%29%8%
2530
June1st to 10thDay
21%5%9%18%29%15%
2354
11th to 20thDay
15%35%12%32%30%
2520
21st to endDay
14%338%30%38%
2425
July1st to 10thDay
13%45%9%23%43%
2311
11th to 20thDay
12%5%6%17%29%28%
2280
21st to endDay
11%5%8%21%32%19%
2112
August1st to 10thDay
10%2312%32%38%
2015
11th to 20thDay
7%3212%38%35%
2002
21st to endDay
9%35%10%37%33%
2244
September1st to 10thDay
9%25%9%33%39%
2040
11th to 20thDay
9%2212%34%38%
1916
21st to endDay
10%35%14%34%32%
1870
October1st to 10thDay
17%35%17%23%31%
1870
11th to 20thDay
13%45%15%27%33%
1760
21st to endDay
14%3411%22%43%
1833
November1st to 10thDay
15%35%18%24%31%
1584
11th to 20thDay
16%36%16%19%37%
1620
21st to endDay
20%48%11%24%30%
1620
December1st to 10thDay
26%5%6%15%18%26%
1620
11th to 20thDay
27%310%18%22%16%
1620
21st to endDay
27%38%17%21%21%
1683
January1st to 10thNight
26%46%16%24%20%
2506
11th to 20thNight
23%38%14%19%30%
2350
21st to endNight
26%37%16%17%28%
2376
February1st to 10thNight
24%26%14%22%29%
2160
11th to 20thNight
23%36%16%23%25%
2099
21st to endNight
28%47%15%22%21%
1776
March1st to 10thNight
29%47%21%18%18%
2160
11th to 20thNight
25%7%9%16%23%17%
2109
21st to endNight
23%5%11%22%23%13%
1980
April1st to 10thNight
26%6%10%24%19%13%
1800
11th to 20thNight
19%6%9%22%24%17%
1779
21st to endNight
20%7%10%23%28%10%
1800
May1st to 10thNight
23%8%9%21%24%11%
1742
11th to 20thNight
22%8%7%24%24%11%
1595
21st to endNight
17%6%10%30%27%8%
1746
June1st to 10thNight
19%8%13%19%26%13%
1600
11th to 20thNight
14%6%6%14%35%22%
1440
21st to endNight
17%46%8%30%32%
1392
July1st to 10thNight
13%5%49%27%39%
1320
11th to 20thNight
14%6%7%19%25%27%
1333
21st to endNight
15%7%9%21%29%17%
1721
August1st to 10thNight
13%35%9%36%31%
1680
11th to 20thNight
10%5%413%36%30%
1680
21st to endNight
11%6%410%37%29%
1870
September1st to 10thNight
14%45%8%29%38%
1700
11th to 20thNight
9%4310%34%37%
1823
21st to endNight
11%4413%35%30%
1870
October1st to 10thNight
18%4416%23%32%
1870
11th to 20thNight
16%5%314%26%32%
1976
21st to endNight
15%3410%23%42%
2278
November1st to 10thNight
16%46%15%24%31%
2275
11th to 20thNight
17%37%14%19%38%
2340
21st to endNight
23%46%17%17%30%
2340
December1st to 10thNight
25%6%7%13%18%28%
2340
11th to 20thNight
30%48%16%24%15%
2340
21st to endNight
25%38%15%24%21%
2664

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 10thDay
16%328%35%13%2
160
11th to 20thDay
11%11%32%31%11%1
309
21st to endDay
9%14%30%32%11%1
462
February1st to 10thDay
11%10%29%30%13%3
420
11th to 20thDay
11%17%31%31%6%1
415
21st to endDay
11%19%31%28%8%
346
March1st to 10thDay
13%17%34%23%10%
420
11th to 20thDay
13%14%34%26%9%1
420
21st to endDay
11%18%33%27%8%
462
April1st to 10thDay
9%14%34%26%14%2
420
11th to 20thDay
7%19%38%24%7%2
412
21st to endDay
5%16%33%27%13%3
420
May1st to 10thDay
11%13%34%27%10%2
423
11th to 20thDay
7%12%31%33%12%3
448
21st to endDay
9%10%35%29%13%2
485
June1st to 10thDay
47%28%40%15%4
450
11th to 20thDay
5%5%25%40%16%6%
450
21st to endDay
2225%43%17%8%
423
July1st to 10thDay
115%50%24%6%
406
11th to 20thDay
10%49%25%12%
404
21st to endDay
113%49%24%11%
443
August1st to 10thDay
2117%51%19%8%
407
11th to 20thDay
112%50%24%9%
397
21st to endDay
18%50%23%5%
451
September1st to 10thDay
1124%46%18%6%
410
11th to 20thDay
2329%42%18%4
410
21st to endDay
16%30%37%18%6%
410
October1st to 10thDay
49%30%34%17%3
410
11th to 20thDay
39%28%38%16%2
410
21st to endDay
5%7%24%36%21%5%
414
November1st to 10thDay
5%7%19%39%23%5%
240
11th to 20thDay
5%419%41%23%5%
240
21st to endDay
5%6%27%37%17%6%
240
December1st to 10thDay
10%5%23%41%16%3
240
11th to 20thDay
5%5%27%37%20%4
240
21st to endDay
16%9%27%33%12%1
220
January1st to 10thNight
11%118%42%21%4
720
11th to 20thNight
9%220%42%23%2
720
21st to endNight
12%320%41%18%2
792
February1st to 10thNight
8%318%41%23%4
720
11th to 20thNight
8%421%37%22%4
704
21st to endNight
11%421%40%19%2
592
March1st to 10thNight
9%422%41%19%2
720
11th to 20thNight
8%417%38%25%5%
720
21st to endNight
7%420%41%21%3
792
April1st to 10thNight
7%415%46%23%2
720
11th to 20thNight
5%6%19%38%27%2
711
21st to endNight
35%20%37%27%6%
720
May1st to 10thNight
5%420%39%26%4
662
11th to 20thNight
5%316%38%31%4
531
21st to endNight
3221%38%29%3
584
June1st to 10thNight
1215%37%40%2
520
11th to 20thNight
216%31%53%5%
360
21st to endNight
21434%51%6%
348
July1st to 10thNight
2313%67%11%
330
11th to 20thNight
1315%65%13%
349
21st to endNight
21226%51%16%
713
August1st to 10thNight
21426%51%14%
676
11th to 20thNight
1418%55%19%
672
21st to endNight
1422%53%17%
748
September1st to 10thNight
27%25%48%15%
680
11th to 20thNight
216%32%45%11%
680
21st to endNight
117%33%46%9%
680
October1st to 10thNight
4110%40%38%3
680
11th to 20thNight
5%112%37%35%7%
680
21st to endNight
4213%34%33%11%
748
November1st to 10thNight
5%112%41%30%8%
700
11th to 20thNight
3211%43%30%7%
720
21st to endNight
6%117%43%25%5%
720
December1st to 10thNight
8%318%41%23%4
720
11th to 20thNight
12%417%43%19%2
720
21st to endNight
10%5%23%39%17%3
792
Page generated at 2023-06-21 16:40:08. Version ac06

Copyright 2023 Attilla Danko


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