This page made possible by the sponsorship of: Bruce Waddington, Kevin Morefield.

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 2017-05-24.

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
71%
15795
34%
45892
29%
15755
75%
15755
50%
23262

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%
717
30%
2327
28%
716
68%
716
38%
1208
January16th to endNight
56%
768
31%
2325
27%
768
64%
768
34%
1336
February1st to 15thNight
64%
698
32%
2111
29%
698
70%
698
38%
1168
February16th to endNight
54%
632
28%
1895
28%
632
59%
632
29%
1174
March1st to 15thNight
61%
720
31%
2151
31%
720
66%
720
40%
1166
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%
540
32%
1622
24%
540
70%
540
54%
775
June1st to 15thNight
79%
495
37%
1485
30%
495
82%
495
70%
613
June16th to endNight
87%
495
35%
1485
31%
495
88%
495
80%
565
July1st to 15thNight
90%
465
32%
1395
28%
465
90%
465
68%
591
July16th to endNight
88%
553
31%
1496
25%
518
88%
518
59%
707
August1st to 15thNight
91%
657
39%
1640
26%
653
91%
653
75%
765
August16th to endNight
91%
700
40%
1750
28%
700
91%
700
72%
831
September1st to 15thNight
90%
660
41%
1724
33%
660
91%
660
74%
789
September16th to endNight
85%
656
46%
1815
41%
656
89%
656
76%
769
October1st to 15thNight
74%
660
39%
1815
34%
660
79%
660
55%
909
October16th to endNight
75%
704
40%
2114
38%
704
79%
704
54%
996
November1st to 15thNight
73%
700
34%
2275
35%
700
79%
700
52%
1046
November16th to endNight
69%
720
35%
2340
36%
720
74%
720
43%
1170
December1st to 15thNight
61%
720
31%
2340
30%
720
67%
720
35%
1281
December16th to endNight
57%
768
32%
2496
29%
768
63%
768
33%
1390

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%
46378
Night
3413313335%65%
46091
TransparencyDay
19%35%14%27%29%
46077
Night
21%35%13%26%30%
45894
SeeingDay
7%12%33%30%11%4
5424
Night
6%412%30%33%11%
15807

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%60%
1611
16th to endDay
8%7%1341335%5%54%
1898
February1st to 15thDay
5%6%22324336%58%
1751
16th to endDay
8%9%25%323347%47%
1579
March1st to 15thDay
5%313213348%61%
1808
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
22121223474%
2335
June1st to 15thDay
121112225%77%
2145
16th to endDay
111111385%
2145
July1st to 15thDay
2112212336%72%
2145
16th to endDay
22123245%47%64%
2251
August1st to 15thDay
111213335%75%
1980
16th to endDay
11222245%373%
2100
September1st to 15thDay
211213235%74%
1906
16th to endDay
2111122281%
1815
October1st to 15thDay
2413212235%69%
1815
16th to endDay
2311313335%70%
1755
November1st to 15thDay
331231333469%
1584
16th to endDay
5%313323336%63%
1620
December1st to 15thDay
6%5%1433335%9%52%
1620
16th to endDay
9%7%14323335%54%
1728
January1st to 15thNight
45%24422436%59%
2327
16th to endNight
7%7%24424335%53%
2325
February1st to 15thNight
48%23224445%57%
2101
16th to endNight
7%8%35%434435%48%
1895
March1st to 15thNight
46%2341435%7%56%
2151
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
1213313345%69%
1621
June1st to 15thNight
112111235%77%
1485
16th to endNight
11112287%
1485
July1st to 15thNight
1112112336%74%
1485
16th to endNight
2113224246%68%
1606
August1st to 15thNight
12113325%77%
1650
16th to endNight
11111123380%
1750
September1st to 15thNight
11211235%79%
1724
16th to endNight
1111112185%
1815
October1st to 15thNight
2313213336%68%
1815
16th to endNight
121332233470%
2114
November1st to 15thNight
242321223469%
2275
16th to endNight
3424413445%61%
2340
December1st to 15thNight
5%6%2442345%7%52%
2340
16th to endNight
8%7%3432333455%
2496

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
26%45%12%27%23%
1612
16th to endDay
30%36%12%21%25%
1898
February1st to 15thDay
27%3315%24%24%
1751
16th to endDay
36%35%15%24%13%
1579
March1st to 15thDay
22%26%19%26%21%
1808
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%
2338
June1st to 15thDay
12%2413%27%40%
2145
16th to endDay
7%125%20%62%
2145
July1st to 15thDay
13%3312%21%45%
2006
16th to endDay
17%5%9%18%24%25%
2099
August1st to 15thDay
11%3313%27%42%
1966
16th to endDay
13%45%10%32%33%
2100
September1st to 15thDay
13%348%28%41%
1906
16th to endDay
10%127%31%46%
1815
October1st to 15thDay
19%2414%29%30%
1815
16th to endDay
17%35%10%23%40%
1755
November1st to 15thDay
19%25%13%29%28%
1584
16th to endDay
22%35%10%27%29%
1620
December1st to 15thDay
29%47%16%20%22%
1620
16th to endDay
32%46%16%23%16%
1728
January1st to 15thNight
26%4413%25%26%
2327
16th to endNight
32%36%11%20%26%
2325
February1st to 15thNight
29%4312%23%26%
2112
16th to endNight
38%3313%23%16%
1895
March1st to 15thNight
27%3417%24%21%
2151
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%18%34%19%
1622
June1st to 15thNight
10%1412%27%44%
1485
16th to endNight
5%12420%65%
1485
July1st to 15thNight
10%35%9%21%50%
1395
16th to endNight
16%38%20%25%26%
1496
August1st to 15thNight
9%1315%27%43%
1640
16th to endNight
10%2310%32%39%
1750
September1st to 15thNight
9%2410%28%44%
1724
16th to endNight
8%127%31%48%
1815
October1st to 15thNight
18%2314%30%29%
1815
16th to endNight
18%239%22%42%
2114
November1st to 15thNight
19%2412%29%31%
2275
16th to endNight
24%2413%22%32%
2340
December1st to 15thNight
29%5%6%14%21%23%
2340
16th to endNight
33%27%13%24%19%
2496

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
24%11%26%32%5%
90
16th to endDay
17%16%32%25%6%1
266
February1st to 15thDay
9%15%34%27%12%1
266
16th to endDay
18%22%27%22%6%2
238
March1st to 15thDay
12%18%29%22%12%4
270
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%15%40%25%8%3
301
June1st to 15thDay
29%49%27%7%3
255
16th to endDay
26%37%34%12%5%
255
July1st to 15thDay
234%44%11%6%
245
16th to endDay
224%50%14%8%
271
August1st to 15thDay
1232%41%12%9%
255
16th to endDay
1125%47%12%11%
268
September1st to 15thDay
3238%41%7%5%
255
16th to endDay
213%32%37%12%2
255
October1st to 15thDay
5%13%41%28%9%1
255
16th to endDay
5%8%29%29%24%2
198
November1st to 15thDay
413%13%33%27%7%
90
16th to endDay
12%13%25%28%17%2
90
December1st to 15thDay
5%7%22%44%16%3
90
16th to endDay
13%13%25%35%12%
96
January1st to 15thNight
9%5%15%35%22%10%
720
16th to endNight
12%6%14%33%26%6%
768
February1st to 15thNight
9%5%14%36%25%7%
704
16th to endNight
13%8%16%32%22%6%
632
March1st to 15thNight
9%7%16%35%24%5%
720
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%32%30%7%
542
June1st to 15thNight
1214%41%34%4
495
16th to endNight
18%38%42%7%
495
July1st to 15thNight
1328%55%10%
465
16th to endNight
2223%55%15%
553
August1st to 15thNight
1220%53%20%
657
16th to endNight
1213%54%27%
700
September1st to 15thNight
1318%57%18%
660
16th to endNight
29%28%41%16%
656
October1st to 15thNight
5%311%34%33%11%
660
16th to endNight
4211%28%35%17%
704
November1st to 15thNight
5%213%33%32%12%
700
16th to endNight
7%412%29%32%14%
720
December1st to 15thNight
10%5%14%33%26%9%
720
16th to endNight
15%7%14%33%22%7%
768
Page generated at 2017-05-25 10:27:39. Version ac04

Copyright 2017 A. Danko


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