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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 2019-07-11.

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
74%
18269
33%
54033
29%
18222
78%
18222
50%
27109

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%
836
28%
2887
26%
836
73%
836
39%
1464
January16th to endNight
63%
896
34%
2735
29%
896
72%
896
42%
1432
February1st to 15thNight
68%
818
35%
2465
34%
817
75%
817
46%
1276
February16th to endNight
60%
736
28%
2207
27%
736
66%
736
38%
1233
March1st to 15thNight
64%
840
27%
2520
25%
840
71%
840
42%
1360
March16th to endNight
71%
896
28%
2339
23%
896
74%
896
48%
1296
April1st to 15thNight
66%
839
30%
2099
18%
839
70%
839
47%
1211
April16th to endNight
67%
832
30%
2080
15%
832
72%
832
53%
1134
May1st to 15thNight
67%
724
27%
1984
19%
724
69%
724
44%
1120
May16th to endNight
68%
657
29%
1973
23%
657
70%
657
50%
1006
June1st to 15thNight
82%
544
30%
1804
29%
544
84%
544
53%
826
June16th to endNight
89%
420
33%
1680
41%
420
89%
420
50%
674
July1st to 15thNight
90%
392
35%
1568
43%
392
90%
392
53%
597
July16th to endNight
90%
682
29%
1798
23%
640
91%
640
56%
902
August1st to 15thNight
90%
765
35%
1910
24%
761
90%
761
66%
948
August16th to endNight
91%
828
40%
2070
27%
828
91%
828
68%
1025
September1st to 15thNight
88%
780
39%
1979
32%
780
88%
780
64%
995
September16th to endNight
90%
776
42%
2145
41%
776
91%
776
70%
946
October1st to 15thNight
78%
780
37%
2161
35%
780
81%
780
56%
1097
October16th to endNight
80%
832
39%
2522
41%
832
83%
832
55%
1181
November1st to 15thNight
78%
820
37%
2665
39%
820
84%
820
55%
1179
November16th to endNight
76%
840
35%
2730
37%
840
80%
840
48%
1307
December1st to 15thNight
67%
840
34%
2730
31%
840
74%
840
40%
1414
December16th to endNight
61%
896
33%
2982
30%
896
70%
896
40%
1486

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%67%
55143
Night
5%212222336%67%
54234
TransparencyDay
19%37%17%27%25%
54836
Night
20%37%16%26%25%
54041
SeeingDay
6%8%28%37%14%4
8353
Night
5%212%34%35%8%
18282

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
8%413413335%60%
1709
16th to endDay
11%312313335%58%
2187
February1st to 15thDay
9%323212346%61%
2051
16th to endDay
12%313323246%55%
1839
March1st to 15thDay
7%31432335%6%57%
2100
16th to endDay
6%21232445%8%56%
2585
April1st to 15thDay
5%313324348%60%
2509
16th to endDay
5%312212235%68%
2485
May1st to 15thDay
7%413312346%61%
2626
16th to endDay
6%313323246%62%
2845
June1st to 15thDay
4312322237%67%
2811
16th to endDay
11121122479%
2940
July1st to 15thDay
2112312236%72%
2874
16th to endDay
2111212336%73%
2600
August1st to 15thDay
11111212383%
2293
16th to endDay
112235%80%
2484
September1st to 15thDay
1111122481%
2310
16th to endDay
2111123480%
2145
October1st to 15thDay
6%2231223469%
2126
16th to endDay
4221233473%
2051
November1st to 15thDay
331231223470%
1854
16th to endDay
5%213323347%63%
1890
December1st to 15thDay
7%312213439%59%
1890
16th to endDay
10%312212337%58%
1939
January1st to 15thNight
8%313223436%60%
2887
16th to endNight
10%312312235%62%
2735
February1st to 15thNight
8%313212235%64%
2461
16th to endNight
12%312324335%57%
2207
March1st to 15thNight
7%313223448%58%
2520
16th to endNight
5%21232445%7%60%
2339
April1st to 15thNight
6%412233336%61%
2099
16th to endNight
3211323336%67%
2080
May1st to 15thNight
43135%22337%61%
1984
16th to endNight
4212422235%67%
1972
June1st to 15thNight
111323347%70%
1804
16th to endNight
11131223476%
1680
July1st to 15thNight
12121233474%
1648
16th to endNight
21121235%8%68%
1914
August1st to 15thNight
211112225%77%
1920
16th to endNight
111111245%79%
2070
September1st to 15thNight
11221222377%
1979
16th to endNight
11111122482%
2145
October1st to 15thNight
421222333471%
2161
16th to endNight
42121223473%
2522
November1st to 15thNight
3312212235%72%
2665
16th to endNight
5%21221335%6%64%
2730
December1st to 15thNight
7%213423247%60%
2730
16th to endNight
10%312212335%63%
2982

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
27%45%13%22%26%
1709
16th to endDay
27%38%14%18%27%
2187
February1st to 15thDay
25%26%15%25%25%
2051
16th to endDay
28%28%18%28%11%
1839
March1st to 15thDay
25%410%20%19%19%
2100
16th to endDay
23%5%12%22%21%14%
2585
April1st to 15thDay
23%411%24%23%12%
2509
16th to endDay
18%210%22%29%15%
2485
May1st to 15thDay
25%49%19%26%14%
2626
16th to endDay
24%38%25%28%8%
2848
June1st to 15thDay
21%38%15%31%19%
2811
16th to endDay
13%248%32%38%
2940
July1st to 15thDay
15%36%11%26%37%
2725
16th to endDay
12%48%22%31%20%
2453
August1st to 15thDay
9%2212%35%36%
2279
16th to endDay
8%2412%41%30%
2484
September1st to 15thDay
9%2412%34%35%
2310
16th to endDay
9%2413%35%34%
2145
October1st to 15thDay
18%36%19%25%27%
2126
16th to endDay
14%35%12%23%40%
2051
November1st to 15thDay
17%36%16%23%33%
1854
16th to endDay
21%48%14%22%29%
1890
December1st to 15thDay
23%49%18%18%26%
1890
16th to endDay
26%39%17%21%21%
1939
January1st to 15thNight
26%47%14%21%26%
2887
16th to endNight
25%37%15%17%29%
2735
February1st to 15thNight
24%37%15%22%26%
2472
16th to endNight
29%47%15%25%16%
2207
March1st to 15thNight
26%49%19%22%18%
2520
16th to endNight
22%5%12%21%23%14%
2339
April1st to 15thNight
25%310%24%21%14%
2099
16th to endNight
20%410%22%27%15%
2080
May1st to 15thNight
25%5%10%20%25%12%
1985
16th to endNight
21%310%27%27%9%
1973
June1st to 15thNight
18%211%16%34%16%
1804
16th to endNight
17%26%10%31%32%
1680
July1st to 15thNight
14%35%11%28%36%
1568
16th to endNight
15%6%9%21%27%19%
1798
August1st to 15thNight
12%3310%37%31%
1910
16th to endNight
12%3310%41%28%
2070
September1st to 15thNight
15%249%32%34%
1979
16th to endNight
9%3312%34%35%
2145
October1st to 15thNight
18%3418%29%25%
2161
16th to endNight
17%3411%23%40%
2522
November1st to 15thNight
16%37%15%23%34%
2665
16th to endNight
21%37%17%20%30%
2730
December1st to 15thNight
25%5%7%15%19%26%
2730
16th to endNight
25%38%15%25%21%
2982

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%7%31%29%12%2
157
16th to endDay
11%12%30%30%13%1
401
February1st to 15thDay
13%10%26%30%12%4
386
16th to endDay
12%20%30%26%9%
342
March1st to 15thDay
10%16%35%23%12%1
390
16th to endDay
8%12%35%31%9%1
416
April1st to 15thDay
8%16%37%24%10%2
389
16th to endDay
6%19%38%25%7%2
378
May1st to 15thDay
13%13%32%27%8%3
408
16th to endDay
10%12%38%27%9%1
458
June1st to 15thDay
6%5%25%43%13%5%
435
16th to endDay
2125%46%14%8%
435
July1st to 15thDay
116%50%21%8%
406
16th to endDay
112%52%23%10%
391
August1st to 15thDay
2119%54%14%7%
359
16th to endDay
16%56%19%6%
396
September1st to 15thDay
2230%48%11%4
375
16th to endDay
2432%41%13%5%
375
October1st to 15thDay
6%10%34%34%11%1
375
16th to endDay
5%5%25%38%19%6%
371
November1st to 15thDay
4419%36%27%7%
180
16th to endDay
5%6%26%35%18%8%
180
December1st to 15thDay
45%22%42%21%3
180
16th to endDay
8%7%26%31%21%4
170
January1st to 15thNight
9%117%42%24%4
840
16th to endNight
12%217%38%26%3
896
February1st to 15thNight
8%214%40%27%6%
824
16th to endNight
12%219%37%24%3
736
March1st to 15thNight
7%220%41%23%4
840
16th to endNight
5%314%43%28%4
896
April1st to 15thNight
7%417%40%26%3
839
16th to endNight
3420%35%29%6%
832
May1st to 15thNight
5%317%35%32%5%
725
16th to endNight
5%220%38%29%4
659
June1st to 15thNight
1110%37%45%3
544
16th to endNight
2429%56%7%
420
July1st to 15thNight
2210%68%16%
392
16th to endNight
21120%57%17%
682
August1st to 15thNight
11320%54%17%
765
16th to endNight
1317%54%23%
828
September1st to 15thNight
16%25%48%17%
780
16th to endNight
1430%48%13%
776
October1st to 15thNight
411%38%38%6%
780
16th to endNight
5%19%31%38%13%
832
November1st to 15thNight
3110%40%34%9%
820
16th to endNight
6%111%38%33%8%
840
December1st to 15thNight
7%215%42%26%5%
840
16th to endNight
11%5%16%41%21%4
896
Page generated at 2019-07-12 04:32:35. Version ac04

Copyright 2019 A. Danko


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