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OCA Anza Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the OCA Anza Observatory clear sky chart from 2005-11-05 to 2020-06-03.

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
70%
19919
34%
57889
29%
19879
75%
19879
49%
29491

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
62%
897
31%
2912
29%
896
68%
896
38%
1527
January16th to endNight
57%
960
33%
2907
28%
960
65%
960
36%
1635
February1st to 15thNight
63%
878
32%
2651
30%
878
69%
878
38%
1457
February16th to endNight
53%
792
31%
2375
29%
792
60%
792
31%
1441
March1st to 15thNight
57%
900
27%
2689
26%
900
62%
900
33%
1566
March16th to endNight
62%
960
29%
2565
23%
960
67%
960
40%
1507
April1st to 15thNight
55%
899
29%
2249
17%
899
60%
899
39%
1372
April16th to endNight
60%
892
33%
2230
17%
892
66%
892
51%
1232
May1st to 15thNight
67%
700
33%
2050
23%
700
70%
700
50%
1037
May16th to endNight
65%
705
33%
2117
25%
705
69%
705
50%
1043
June1st to 15thNight
80%
637
37%
1911
31%
637
82%
637
72%
777
June16th to endNight
86%
630
36%
1890
31%
630
88%
630
78%
733
July1st to 15thNight
91%
600
33%
1800
28%
600
91%
600
71%
740
July16th to endNight
88%
700
31%
1919
25%
665
88%
665
59%
910
August1st to 15thNight
91%
825
38%
2060
25%
821
91%
821
76%
954
August16th to endNight
92%
892
42%
2230
30%
892
92%
892
75%
1037
September1st to 15thNight
90%
840
41%
2194
34%
840
91%
840
74%
1003
September16th to endNight
83%
836
44%
2310
39%
836
88%
836
73%
1001
October1st to 15thNight
75%
840
39%
2310
34%
840
79%
840
57%
1135
October16th to endNight
75%
896
42%
2690
39%
896
81%
896
58%
1226
November1st to 15thNight
75%
880
36%
2860
37%
880
81%
880
53%
1297
November16th to endNight
67%
900
34%
2925
34%
900
72%
900
40%
1516
December1st to 15thNight
58%
900
30%
2925
28%
900
64%
900
33%
1634
December16th to endNight
58%
960
32%
3120
29%
960
65%
960
35%
1711

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
3312213336%67%
58521
Night
3413313345%65%
58088
TransparencyDay
19%35%14%27%29%
58220
Night
21%3413%26%30%
57891
SeeingDay
6%12%30%30%14%5%
9556
Night
6%413%31%33%10%
19931

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
6%6%12323346%59%
2016
16th to endDay
7%6%1241335%6%56%
2372
February1st to 15thDay
6%6%22323335%59%
2201
16th to endDay
7%10%25%323346%49%
1979
March1st to 15thDay
6%41332435%8%55%
2260
16th to endDay
35%23323447%58%
2711
April1st to 15thDay
5%6%23424336%57%
2689
16th to endDay
232212337%68%
2665
May1st to 15thDay
2313212236%68%
2889
16th to endDay
222212235%72%
3053
June1st to 15thDay
111112225%78%
2758
16th to endDay
111111386%
2730
July1st to 15thDay
2112312336%72%
2730
16th to endDay
12123245%5%7%64%
2840
August1st to 15thDay
111213325%76%
2473
16th to endDay
11221234475%
2676
September1st to 15thDay
111213235%74%
2426
16th to endDay
11111122381%
2310
October1st to 15thDay
231321223472%
2310
16th to endDay
12131322473%
2234
November1st to 15thDay
3312312335%69%
1989
16th to endDay
5%413323347%59%
2025
December1st to 15thDay
6%5%1433336%8%52%
2025
16th to endDay
9%7%24323435%53%
2160
January1st to 15thNight
5%5%24423446%58%
2912
16th to endNight
6%7%24423335%55%
2907
February1st to 15thNight
48%23224445%58%
2641
16th to endNight
6%9%25%434335%50%
2375
March1st to 15thNight
5%8%2342445%8%50%
2689
16th to endNight
27%2442445%7%53%
2565
April1st to 15thNight
49%24423447%52%
2249
16th to endNight
3423323346%63%
2230
May1st to 15thNight
142432335%7%63%
2050
16th to endNight
131331335%6%66%
2116
June1st to 15thNight
12111136%78%
1911
16th to endNight
111112386%
1890
July1st to 15thNight
112112335%77%
1890
16th to endNight
2112223346%68%
2029
August1st to 15thNight
1112225%79%
2070
16th to endNight
11111122382%
2230
September1st to 15thNight
11211225%79%
2194
16th to endNight
11111112283%
2310
October1st to 15thNight
2312212335%69%
2310
16th to endNight
121331233373%
2690
November1st to 15thNight
1323212235%69%
2860
16th to endNight
4424413446%57%
2925
December1st to 15thNight
6%6%25%42345%7%50%
2925
16th to endNight
7%6%24423335%56%
3120

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%27%22%
2017
16th to endDay
28%36%13%23%23%
2372
February1st to 15thDay
27%3314%25%24%
2201
16th to endDay
34%45%15%25%14%
1979
March1st to 15thDay
27%36%19%25%18%
2260
16th to endDay
26%48%19%28%13%
2711
April1st to 15thDay
28%36%20%29%11%
2689
16th to endDay
16%37%20%33%18%
2665
May1st to 15thDay
19%26%16%32%22%
2889
16th to endDay
16%35%20%36%17%
3056
June1st to 15thDay
11%2313%31%37%
2758
16th to endDay
7%2420%63%
2730
July1st to 15thDay
13%3411%22%44%
2591
16th to endDay
16%5%10%18%25%23%
2688
August1st to 15thDay
10%3312%27%43%
2459
16th to endDay
11%35%11%31%35%
2676
September1st to 15thDay
12%348%28%42%
2426
16th to endDay
10%227%33%43%
2310
October1st to 15thDay
18%2312%26%36%
2310
16th to endDay
14%248%26%43%
2234
November1st to 15thDay
18%25%12%29%31%
1989
16th to endDay
24%35%11%25%28%
2025
December1st to 15thDay
29%47%16%20%22%
2025
16th to endDay
32%45%15%24%16%
2160
January1st to 15thNight
27%4414%25%24%
2912
16th to endNight
30%35%11%22%24%
2907
February1st to 15thNight
28%3311%23%27%
2652
16th to endNight
36%3312%25%17%
2375
March1st to 15thNight
32%45%16%22%18%
2689
16th to endNight
28%5%7%17%26%14%
2565
April1st to 15thNight
31%47%18%25%13%
2249
16th to endNight
21%35%16%31%20%
2230
May1st to 15thNight
20%35%16%28%24%
2051
16th to endNight
19%37%17%33%18%
2117
June1st to 15thNight
9%1312%30%42%
1911
16th to endNight
7%12419%65%
1890
July1st to 15thNight
8%35%9%22%51%
1800
16th to endNight
15%39%20%25%25%
1919
August1st to 15thNight
9%1313%29%42%
2060
16th to endNight
9%2311%31%41%
2230
September1st to 15thNight
9%2410%27%46%
2194
16th to endNight
10%127%32%45%
2310
October1st to 15thNight
17%2313%27%35%
2310
16th to endNight
16%238%22%46%
2690
November1st to 15thNight
18%2411%29%33%
2860
16th to endNight
26%3413%21%29%
2925
December1st to 15thNight
31%5%5%13%20%23%
2925
16th to endNight
31%26%12%25%20%
3120

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%23%33%14%2
225
16th to endDay
13%13%27%28%13%2
452
February1st to 15thDay
10%17%28%24%15%4
446
16th to endDay
14%22%31%21%9%1
398
March1st to 15thDay
12%22%31%20%10%2
450
16th to endDay
6%24%33%21%11%1
480
April1st to 15thDay
12%22%34%18%9%3
449
16th to endDay
6%21%37%20%8%4
438
May1st to 15thDay
8%14%34%27%10%4
468
16th to endDay
5%18%36%24%11%3
522
June1st to 15thDay
17%39%29%14%7%
444
16th to endDay
1432%33%20%8%
435
July1st to 15thDay
2124%41%19%11%
425
16th to endDay
1119%45%19%12%
455
August1st to 15thDay
2228%38%15%12%
419
16th to endDay
1123%43%16%15%
460
September1st to 15thDay
2233%39%14%7%
435
16th to endDay
112%31%35%15%3
435
October1st to 15thDay
412%40%30%11%1
435
16th to endDay
37%30%30%22%5%
370
November1st to 15thDay
47%17%40%26%4
225
16th to endDay
10%15%23%26%15%8%
225
December1st to 15thDay
8%11%26%32%18%3
225
16th to endDay
9%16%25%27%18%2
240
January1st to 15thNight
9%5%16%36%23%9%
900
16th to endNight
11%6%15%33%26%5%
960
February1st to 15thNight
10%6%14%35%24%7%
884
16th to endNight
13%8%17%32%22%5%
792
March1st to 15thNight
10%9%17%36%22%4
900
16th to endNight
7%8%16%33%26%7%
960
April1st to 15thNight
9%9%22%31%22%4
899
16th to endNight
5%8%23%28%26%8%
892
May1st to 15thNight
35%18%35%29%6%
701
16th to endNight
36%20%33%29%6%
707
June1st to 15thNight
1214%37%38%6%
637
16th to endNight
19%35%45%7%
630
July1st to 15thNight
1326%56%12%
600
16th to endNight
2223%55%15%
700
August1st to 15thNight
1321%53%20%
825
16th to endNight
1114%55%26%
892
September1st to 15thNight
1422%56%15%
840
16th to endNight
219%30%41%14%
836
October1st to 15thNight
5%312%39%31%8%
840
16th to endNight
3213%29%34%15%
896
November1st to 15thNight
4212%38%32%10%
880
16th to endNight
7%413%30%31%13%
900
December1st to 15thNight
11%6%16%34%24%7%
900
16th to endNight
13%6%15%35%21%7%
960
Page generated at 2020-06-04 00:18:53. Version ac04

Copyright 2020 A. Danko


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