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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 2023-05-20.

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
72%
23317
33%
68956
28%
23262
76%
23262
48%
35074

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%
713
26%
2492
27%
713
68%
713
37%
1276
January11th to 20thNight
63%
716
34%
2335
28%
716
74%
716
44%
1164
January21st to endNight
57%
781
38%
2347
29%
781
69%
781
42%
1245
February1st to 10thNight
64%
710
36%
2145
32%
710
72%
710
44%
1109
February11th to 20thNight
61%
680
33%
2047
28%
678
71%
678
45%
1053
February21st to endNight
57%
591
28%
1773
26%
590
65%
590
38%
985
March1st to 10thNight
59%
719
26%
2159
23%
719
66%
719
38%
1216
March11th to 20thNight
63%
711
25%
2083
23%
711
68%
711
40%
1170
March21st to endNight
62%
792
30%
1980
20%
792
69%
792
46%
1142
April1st to 10thNight
66%
713
28%
1781
19%
713
69%
713
43%
1066
April11th to 20thNight
64%
698
32%
1745
17%
698
69%
698
51%
965
April21st to endNight
65%
712
29%
1782
14%
712
69%
712
48%
1011
May1st to 10thNight
64%
660
26%
1733
16%
660
66%
660
43%
1019
May11th to 20thNight
70%
523
28%
1569
22%
523
72%
523
42%
866
May21st to endNight
67%
535
31%
1597
24%
535
70%
535
53%
791
June1st to 10thNight
76%
487
27%
1503
23%
485
77%
485
48%
768
June11th to 20thNight
87%
337
36%
1359
43%
337
88%
337
51%
533
June21st to endNight
88%
329
33%
1344
41%
329
88%
329
46%
560
July1st to 10thNight
89%
328
36%
1312
45%
328
89%
328
51%
518
July11th to 20thNight
91%
343
33%
1297
37%
340
91%
340
51%
546
July21st to endNight
89%
700
29%
1683
21%
658
89%
658
56%
893
August1st to 10thNight
88%
662
33%
1670
22%
658
89%
658
64%
833
August11th to 20thNight
91%
659
36%
1655
23%
659
91%
659
67%
823
August21st to endNight
90%
742
40%
1856
28%
742
90%
742
63%
945
September1st to 10thNight
87%
680
38%
1700
30%
680
87%
680
62%
870
September11th to 20thNight
88%
676
43%
1813
39%
676
89%
676
70%
828
September21st to endNight
86%
667
42%
1851
40%
667
89%
667
66%
840
October1st to 10thNight
78%
679
36%
1869
33%
679
82%
679
54%
965
October11th to 20thNight
77%
674
38%
1964
37%
674
81%
674
54%
956
October21st to endNight
77%
747
41%
2274
40%
746
82%
746
57%
1039
November1st to 10thNight
76%
697
35%
2265
36%
697
81%
697
52%
1031
November11th to 20thNight
77%
717
36%
2328
36%
717
83%
717
53%
1052
November21st to endNight
70%
717
35%
2327
35%
717
74%
717
44%
1164
December1st to 10thNight
63%
715
31%
2330
28%
715
70%
715
38%
1244
December11th to 20thNight
59%
720
31%
2340
29%
720
65%
720
35%
1278
December21st to endNight
56%
787
33%
2648
28%
787
67%
787
40%
1310

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%
70043
Night
5%312212235%67%
69203
TransparencyDay
18%46%16%27%26%
69743
Night
20%5%7%16%25%25%
69006
SeeingDay
6%8%27%36%15%4
13494
Night
5%214%36%32%7%
23337

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
10%313413346%57%
1423
11th to 20thDay
8%412323336%61%
1601
21st to endDay
11%42242223459%
1927
February1st to 10thDay
8%32322235%65%
1771
11th to 20thDay
9%312212346%62%
1721
21st to endDay
9%413413246%57%
1471
March1st to 10thDay
8%5%1443336%7%50%
1800
11th to 20thDay
8%41222335%7%57%
1819
21st to endDay
6%312324447%58%
2352
April1st to 10thDay
6%313223348%60%
2129
11th to 20thDay
4313213236%66%
2097
21st to endDay
5%312212235%68%
2158
May1st to 10thDay
7%5%12222336%61%
2206
11th to 20thDay
5%313313237%63%
2234
21st to endDay
6%313222245%65%
2332
June1st to 10thDay
4312322238%66%
2223
11th to 20thDay
221211225%76%
2380
21st to endDay
11121223478%
2363
July1st to 10thDay
121212235%74%
2379
11th to 20thDay
211211225%78%
2322
21st to endDay
111112347%72%
2220
August1st to 10thDay
11111122481%
1997
11th to 20thDay
111112384%
1947
21st to endDay
1212235%78%
2230
September1st to 10thDay
2111123479%
2028
11th to 20thDay
211112483%
1912
21st to endDay
11121123478%
1858
October1st to 10thDay
421231223470%
1861
11th to 20thDay
3121222476%
1733
21st to endDay
42211133473%
1823
November1st to 10thDay
321231224471%
1584
11th to 20thDay
422212245%70%
1612
21st to endDay
5%113323247%63%
1607
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%413222337%58%
2491
11th to 20thNight
7%313212235%64%
2335
21st to endNight
10%31231222463%
2347
February1st to 10thNight
7%31321223466%
2145
11th to 20thNight
8%313313235%63%
2044
21st to endNight
11%31332333458%
1774
March1st to 10thNight
9%5%1322335%8%54%
2159
11th to 20thNight
8%31232345%6%57%
2084
21st to endNight
7%312324347%59%
1980
April1st to 10thNight
7%413333336%60%
1781
11th to 20thNight
45%11213335%67%
1750
21st to endNight
4412322335%65%
1785
May1st to 10thNight
5%5%13412336%60%
1734
11th to 20thNight
45%12423236%62%
1568
21st to endNight
3313312125%71%
1597
June1st to 10thNight
122423347%66%
1511
11th to 20thNight
2232222476%
1360
21st to endNight
112212245%75%
1344
July1st to 10thNight
121211225%77%
1360
11th to 20thNight
112213336%74%
1355
21st to endNight
31121235%7%69%
1792
August1st to 10thNight
121111222477%
1680
11th to 20thNight
2111135%79%
1655
21st to endNight
11111123479%
1856
September1st to 10thNight
12221222377%
1700
11th to 20thNight
1111111384%
1814
21st to endNight
11111122482%
1851
October1st to 10thNight
321232223371%
1868
11th to 20thNight
41111222475%
1964
21st to endNight
321221223374%
2276
November1st to 10thNight
4311212235%70%
2265
11th to 20thNight
3212212235%72%
2328
21st to endNight
5%21232345%6%62%
2327
December1st to 10thNight
8%314313247%59%
2330
11th to 20thNight
11%323322346%56%
2340
21st to endNight
10%312212335%62%
2653

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%
1424
11th to 20thDay
24%46%10%25%27%
1601
21st to endDay
28%27%16%16%28%
1926
February1st to 10thDay
24%25%14%23%29%
1772
11th to 20thDay
22%35%15%27%25%
1722
21st to endDay
25%39%18%24%19%
1471
March1st to 10thDay
30%49%17%17%20%
1800
11th to 20thDay
23%5%11%19%22%17%
1836
21st to endDay
22%6%12%22%22%14%
2348
April1st to 10thDay
22%5%12%25%21%11%
2127
11th to 20thDay
18%39%21%28%18%
2098
21st to endDay
18%38%25%30%13%
2158
May1st to 10thDay
22%6%9%19%27%13%
2205
11th to 20thDay
21%6%7%21%30%12%
2242
21st to endDay
22%37%27%29%9%
2332
June1st to 10thDay
20%5%8%18%30%16%
2220
11th to 20thDay
14%35%11%33%32%
2380
21st to endDay
14%338%30%38%
2365
July1st to 10thDay
14%45%9%23%43%
2287
11th to 20thDay
12%46%17%30%28%
2233
21st to endDay
11%5%8%21%32%19%
2085
August1st to 10thDay
10%2313%32%38%
1984
11th to 20thDay
7%3212%37%35%
1947
21st to endDay
9%35%10%37%32%
2231
September1st to 10thDay
9%25%9%33%39%
2029
11th to 20thDay
8%2212%34%38%
1914
21st to endDay
10%35%14%34%32%
1858
October1st to 10thDay
17%35%17%23%31%
1861
11th to 20thDay
13%45%15%28%33%
1735
21st to endDay
14%3411%21%44%
1822
November1st to 10thDay
15%35%18%24%31%
1584
11th to 20thDay
16%36%16%19%37%
1612
21st to endDay
20%48%11%23%30%
1611
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%
2492
11th to 20thNight
23%37%14%19%30%
2339
21st to endNight
26%37%15%17%29%
2350
February1st to 10thNight
25%26%14%21%29%
2145
11th to 20thNight
23%36%16%23%26%
2054
21st to endNight
28%47%15%22%21%
1774
March1st to 10thNight
29%47%21%18%18%
2160
11th to 20thNight
25%7%9%16%23%17%
2096
21st to endNight
23%5%11%22%23%13%
1980
April1st to 10thNight
26%6%10%24%18%13%
1781
11th to 20thNight
18%6%9%22%24%18%
1750
21st to endNight
20%7%10%23%28%10%
1782
May1st to 10thNight
24%8%9%21%23%11%
1737
11th to 20thNight
23%8%8%25%23%11%
1569
21st to endNight
17%410%29%28%8%
1597
June1st to 10thNight
19%7%12%19%27%14%
1503
11th to 20thNight
13%5%5%14%37%23%
1359
21st to endNight
18%46%8%30%32%
1344
July1st to 10thNight
13%5%49%27%39%
1312
11th to 20thNight
14%6%6%19%26%26%
1299
21st to endNight
15%7%9%21%28%17%
1684
August1st to 10thNight
13%35%9%36%31%
1670
11th to 20thNight
10%5%413%35%30%
1658
21st to endNight
11%6%410%37%29%
1860
September1st to 10thNight
14%45%8%29%38%
1700
11th to 20thNight
9%4310%34%38%
1813
21st to endNight
11%4413%35%30%
1851
October1st to 10thNight
18%4416%23%32%
1869
11th to 20thNight
16%5%315%26%32%
1965
21st to endNight
15%3410%23%42%
2274
November1st to 10thNight
16%46%15%24%31%
2265
11th to 20thNight
17%37%14%19%38%
2328
21st to endNight
23%46%17%17%31%
2328
December1st to 10thNight
25%6%7%13%18%29%
2330
11th to 20thNight
30%48%16%24%15%
2340
21st to endNight
25%38%15%25%22%
2648

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%29%32%11%1
454
February1st to 10thDay
11%10%29%30%13%3
415
11th to 20thDay
11%16%31%31%7%1
412
21st to endDay
11%19%31%28%8%
345
March1st to 10thDay
13%17%34%23%10%
420
11th to 20thDay
13%14%33%27%9%1
418
21st to endDay
11%18%33%27%8%
460
April1st to 10thDay
9%14%34%26%14%2
414
11th to 20thDay
7%19%37%25%7%2
403
21st to endDay
5%16%33%27%13%3
420
May1st to 10thDay
11%14%34%27%10%2
421
11th to 20thDay
7%11%31%33%12%3
442
21st to endDay
10%10%35%29%12%2
425
June1st to 10thDay
37%28%41%14%4
410
11th to 20thDay
5%5%24%41%15%7%
410
21st to endDay
2225%44%17%8%
410
July1st to 10thDay
115%50%24%6%
402
11th to 20thDay
110%49%25%12%
399
21st to endDay
113%49%24%11%
440
August1st to 10thDay
2117%50%19%8%
397
11th to 20thDay
112%50%24%9%
383
21st to endDay
18%50%23%5%
450
September1st to 10thDay
1124%46%18%6%
409
11th to 20thDay
2329%42%18%4
409
21st to endDay
16%30%37%18%6%
408
October1st to 10thDay
49%30%34%17%3
409
11th to 20thDay
39%28%38%16%2
408
21st to endDay
5%7%24%36%21%5%
412
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
713
11th to 20thNight
9%220%42%23%2
717
21st to endNight
12%321%41%18%2
782
February1st to 10thNight
8%318%41%23%4
710
11th to 20thNight
8%421%38%22%4
687
21st to endNight
11%421%40%19%2
591
March1st to 10thNight
9%422%41%19%2
719
11th to 20thNight
8%417%37%25%5%
712
21st to endNight
7%420%41%21%3
792
April1st to 10thNight
7%415%45%23%2
713
11th to 20thNight
5%6%18%39%27%2
701
21st to endNight
35%20%37%26%6%
712
May1st to 10thNight
5%420%39%26%4
660
11th to 20thNight
5%216%39%31%4
523
21st to endNight
4221%38%29%3
536
June1st to 10thNight
1114%39%40%2
487
11th to 20thNight
115%32%54%4
337
21st to endNight
21433%51%6%
329
July1st to 10thNight
2314%67%11%
328
11th to 20thNight
1315%65%13%
345
21st to endNight
21227%51%15%
700
August1st to 10thNight
21427%51%13%
662
11th to 20thNight
1418%55%19%
661
21st to endNight
1422%53%17%
744
September1st to 10thNight
27%25%48%15%
680
11th to 20thNight
216%32%46%11%
676
21st to endNight
117%33%46%9%
667
October1st to 10thNight
4110%40%39%3
679
11th to 20thNight
4112%37%35%7%
674
21st to endNight
4213%34%33%11%
747
November1st to 10thNight
5%112%41%30%8%
697
11th to 20thNight
3211%44%30%7%
717
21st to endNight
6%117%43%25%5%
717
December1st to 10thNight
8%318%41%23%4
715
11th to 20thNight
12%417%43%19%2
720
21st to endNight
10%5%23%39%17%3
787
Page generated at 2023-05-22 03:21:22. Version ac06

Copyright 2023 Attilla Danko


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