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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 2018-03-11.

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
71%
16888
34%
49129
29%
16848
75%
16848
50%
24794

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%
777
30%
2522
28%
776
68%
776
37%
1330
January16th to endNight
58%
832
32%
2519
28%
832
65%
832
36%
1420
February1st to 15thNight
65%
758
32%
2291
30%
758
71%
758
39%
1256
February16th to endNight
54%
684
29%
2051
29%
684
59%
684
31%
1253
March1st to 15thNight
61%
764
30%
2283
30%
764
66%
764
38%
1256
March16th to endNight
64%
768
31%
2052
25%
768
69%
768
44%
1160
April1st to 15thNight
57%
719
29%
1799
17%
719
62%
719
43%
1061
April16th to endNight
59%
720
33%
1800
16%
720
66%
720
53%
983
May1st to 15thNight
68%
560
34%
1640
24%
560
71%
560
52%
809
May16th to endNight
67%
561
33%
1685
24%
561
70%
561
54%
800
June1st to 15thNight
78%
540
35%
1620
28%
540
81%
540
70%
665
June16th to endNight
87%
540
38%
1620
33%
540
88%
540
81%
614
July1st to 15thNight
90%
510
31%
1530
26%
510
91%
510
69%
639
July16th to endNight
88%
598
32%
1625
26%
563
88%
563
59%
770
August1st to 15thNight
91%
717
37%
1790
24%
713
92%
713
76%
830
August16th to endNight
92%
764
43%
1910
30%
764
92%
764
74%
895
September1st to 15thNight
90%
720
39%
1881
32%
720
91%
720
72%
873
September16th to endNight
84%
716
47%
1980
42%
716
89%
716
75%
849
October1st to 15thNight
76%
720
38%
1980
34%
720
80%
720
57%
975
October16th to endNight
76%
768
42%
2307
41%
768
80%
768
55%
1076
November1st to 15thNight
73%
760
33%
2470
34%
760
78%
760
49%
1169
November16th to endNight
70%
780
36%
2535
38%
780
74%
780
43%
1267
December1st to 15thNight
61%
780
31%
2535
30%
780
67%
780
37%
1358
December16th to endNight
58%
832
33%
2704
30%
832
65%
832
34%
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
3312213335%67%
49496
Night
3413313335%65%
49328
TransparencyDay
19%35%14%27%29%
49195
Night
21%35%13%26%30%
49131
SeeingDay
6%11%31%30%13%5%
6494
Night
6%412%31%34%11%
16900

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
5%6%1332335%5%59%
1746
16th to endDay
8%6%1241335%6%55%
2056
February1st to 15thDay
5%5%22323335%60%
1901
16th to endDay
8%10%25%323346%48%
1709
March1st to 15thDay
5%313213348%60%
1912
16th to endDay
35%24323347%59%
2169
April1st to 15thDay
5%5%23324336%59%
2149
16th to endDay
232212337%69%
2160
May1st to 15thDay
2313213236%70%
2309
16th to endDay
22121233474%
2429
June1st to 15thDay
121112225%77%
2340
16th to endDay
111111386%
2340
July1st to 15thDay
2112212336%72%
2340
16th to endDay
22123245%5%7%63%
2430
August1st to 15thDay
111213335%76%
2160
16th to endDay
11222235%374%
2292
September1st to 15thDay
212213235%73%
2079
16th to endDay
21111122382%
1980
October1st to 15thDay
231321223471%
1980
16th to endDay
2311313335%71%
1914
November1st to 15thDay
3413313335%66%
1719
16th to endDay
5%313323337%62%
1755
December1st to 15thDay
5%5%1433335%8%54%
1755
16th to endDay
9%6%24323435%54%
1872
January1st to 15thNight
5%5%24423436%57%
2522
16th to endNight
6%7%24423335%55%
2519
February1st to 15thNight
47%23224445%57%
2281
16th to endNight
6%8%35%434335%50%
2051
March1st to 15thNight
5%6%2341435%7%54%
2283
16th to endNight
26%2331345%7%57%
2052
April1st to 15thNight
37%23313447%56%
1799
16th to endNight
3323323345%65%
1800
May1st to 15thNight
1323323347%66%
1640
16th to endNight
1212313346%69%
1684
June1st to 15thNight
12111136%77%
1620
16th to endNight
11112288%
1620
July1st to 15thNight
112112336%75%
1620
16th to endNight
2112224247%68%
1735
August1st to 15thNight
12112225%78%
1800
16th to endNight
11111122381%
1910
September1st to 15thNight
11211235%77%
1881
16th to endNight
1111112284%
1980
October1st to 15thNight
2313213335%69%
1980
16th to endNight
121332233471%
2307
November1st to 15thNight
2423323345%66%
2470
16th to endNight
3424413446%60%
2535
December1st to 15thNight
5%6%2442345%7%54%
2535
16th to endNight
7%6%24423335%56%
2704

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%14%26%21%
1747
16th to endDay
29%36%14%21%24%
2056
February1st to 15thDay
26%3314%26%24%
1901
16th to endDay
36%35%15%24%13%
1709
March1st to 15thDay
22%26%20%26%20%
1912
16th to endDay
25%37%20%27%14%
2169
April1st to 15thDay
27%25%20%31%11%
2149
16th to endDay
16%37%20%31%19%
2160
May1st to 15thDay
18%26%16%32%23%
2309
16th to endDay
14%35%19%37%18%
2432
June1st to 15thDay
11%1313%28%39%
2340
16th to endDay
6%2419%65%
2340
July1st to 15thDay
13%3411%22%44%
2201
16th to endDay
17%5%8%19%24%24%
2278
August1st to 15thDay
11%3312%27%42%
2146
16th to endDay
12%35%9%32%35%
2292
September1st to 15thDay
13%349%29%39%
2079
16th to endDay
10%127%32%45%
1980
October1st to 15thDay
17%2313%28%34%
1980
16th to endDay
16%349%23%41%
1914
November1st to 15thDay
21%25%13%29%27%
1719
16th to endDay
23%35%10%27%29%
1755
December1st to 15thDay
27%37%16%19%25%
1755
16th to endDay
31%46%15%24%17%
1872
January1st to 15thNight
27%4413%25%24%
2522
16th to endNight
31%36%12%20%26%
2519
February1st to 15thNight
28%4412%23%27%
2292
16th to endNight
37%3412%25%16%
2051
March1st to 15thNight
28%35%17%24%20%
2283
16th to endNight
25%47%19%26%16%
2052
April1st to 15thNight
27%46%19%27%14%
1799
16th to endNight
20%46%19%29%21%
1800
May1st to 15thNight
18%35%17%29%25%
1641
16th to endNight
17%27%17%35%19%
1685
June1st to 15thNight
10%1412%28%43%
1620
16th to endNight
5%12418%67%
1620
July1st to 15thNight
9%35%8%22%51%
1530
16th to endNight
16%38%20%25%26%
1625
August1st to 15thNight
9%1314%28%42%
1790
16th to endNight
9%2310%32%41%
1910
September1st to 15thNight
9%2411%29%42%
1881
16th to endNight
9%127%32%47%
1980
October1st to 15thNight
17%2313%30%32%
1980
16th to endNight
17%239%21%44%
2307
November1st to 15thNight
21%2412%29%29%
2470
16th to endNight
24%2413%22%32%
2535
December1st to 15thNight
28%46%14%20%26%
2535
16th to endNight
32%27%12%25%20%
2704

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
22%8%21%28%17%2
135
16th to endDay
14%14%29%26%11%3
328
February1st to 15thDay
7%14%30%26%14%5%
326
16th to endDay
15%23%26%22%10%1
290
March1st to 15thDay
11%18%30%22%12%3
312
16th to endDay
6%23%34%18%13%3
288
April1st to 15thDay
12%24%36%15%7%4
269
16th to endDay
7%23%41%17%7%2
270
May1st to 15thDay
9%18%37%23%7%3
288
16th to endDay
5%14%39%26%10%3
330
June1st to 15thDay
28%44%28%10%5%
315
16th to endDay
25%34%33%16%7%
315
July1st to 15thDay
1129%43%15%8%
305
16th to endDay
1121%47%16%11%
327
August1st to 15thDay
1231%40%13%11%
315
16th to endDay
1124%45%14%12%
332
September1st to 15thDay
2338%39%10%5%
315
16th to endDay
113%30%37%13%2
315
October1st to 15thDay
5%10%40%29%12%1
315
16th to endDay
5%7%25%29%25%5%
255
November1st to 15thDay
6%9%19%36%22%5%
135
16th to endDay
9%11%20%29%17%10%
135
December1st to 15thDay
311%22%37%21%3
135
16th to endDay
9%11%21%34%20%4
144
January1st to 15thNight
9%5%15%35%23%10%
780
16th to endNight
12%6%14%32%27%6%
832
February1st to 15thNight
9%5%14%36%25%8%
764
16th to endNight
13%8%16%32%22%6%
684
March1st to 15thNight
9%7%16%36%24%5%
764
16th to endNight
7%6%16%31%28%8%
768
April1st to 15thNight
8%9%21%32%22%5%
719
16th to endNight
5%8%24%28%24%9%
720
May1st to 15thNight
36%16%39%26%7%
561
16th to endNight
26%20%31%31%7%
563
June1st to 15thNight
1214%39%36%5%
540
16th to endNight
19%37%43%7%
540
July1st to 15thNight
1328%55%11%
510
16th to endNight
2221%55%17%
598
August1st to 15thNight
1220%54%20%
717
16th to endNight
1213%54%27%
764
September1st to 15thNight
1421%56%16%
720
16th to endNight
19%29%42%15%
716
October1st to 15thNight
4311%35%34%10%
720
16th to endNight
4111%28%36%17%
768
November1st to 15thNight
4213%36%31%11%
760
16th to endNight
6%411%30%32%14%
780
December1st to 15thNight
10%5%15%33%26%8%
780
16th to endNight
14%6%13%33%23%8%
832
Page generated at 2018-03-12 10:28:13. Version ac04

Copyright 2018 A. Danko


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