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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 2016-03-19.

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%
14177
34%
41248
29%
14137
75%
14137
50%
20866

By Month

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
JanuaryNight
60%
1361
31%
4264
28%
1360
67%
1360
38%
2279
FebruaryNight
60%
1218
31%
3670
30%
1218
65%
1218
35%
2113
MarchNight
61%
1312
32%
3716
28%
1312
67%
1312
41%
2078
AprilNight
56%
1199
31%
2999
17%
1199
62%
1199
46%
1737
MayNight
68%
932
34%
2764
24%
932
72%
932
55%
1323
JuneNight
82%
900
36%
2700
30%
900
84%
900
74%
1076
JulyNight
88%
922
31%
2609
25%
887
88%
887
61%
1189
AugustNight
90%
1233
39%
3080
26%
1229
90%
1229
72%
1466
SeptemberNight
88%
1196
44%
3217
37%
1196
91%
1196
76%
1407
OctoberNight
74%
1240
39%
3571
36%
1240
78%
1240
55%
1728
NovemberNight
71%
1300
35%
4225
35%
1300
76%
1300
47%
2032
DecemberNight
59%
1364
32%
4433
30%
1364
65%
1364
35%
2438

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%
41524
Night
3413313335%65%
41447
TransparencyDay
19%35%14%27%29%
41223
Night
21%3413%26%30%
41250
SeeingDay
6%13%37%32%8%2
3782
Night
6%413%30%33%11%
14189

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
MonthOccurrence of each ForecastData
Points
JanuaryDay
6%6%1332335%5%59%
3215
Night
5%6%24423435%58%
4264
FebruaryDay
6%7%23323346%55%
3050
Night
5%8%2432443454%
3660
MarchDay
4423323347%58%
3498
Night
36%2341445%7%55%
3716
AprilDay
4413313336%64%
3589
Night
36%23423445%59%
2999
MayDay
2212212235%74%
3935
Night
1213213336%69%
2763
JuneDay
11111112481%
3900
Night
11111112383%
2700
JulyDay
2212313447%66%
3997
Night
1113213347%69%
2809
AugustDay
11221334473%
3708
Night
11211223477%
3090
SeptemberDay
11121223477%
3383
Night
1111122382%
3217
OctoberDay
2312313235%69%
3246
Night
131331233470%
3571
NovemberDay
4313313335%65%
2934
Night
2423313335%65%
4225
DecemberDay
8%6%14323347%53%
3069
Night
7%6%24423335%55%
4433

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthOccurrence of each ForecastData
Points
JanuaryDay
27%45%12%24%25%
3216
Night
28%35%12%23%27%
4264
FebruaryDay
30%3415%25%19%
3050
Night
33%3312%24%22%
3671
MarchDay
25%37%19%26%18%
3498
Night
27%46%18%23%19%
3716
AprilDay
22%26%21%30%15%
3589
Night
25%46%18%27%17%
2999
MayDay
15%25%17%35%22%
3938
Night
16%35%17%32%24%
2765
JuneDay
10%139%23%52%
3900
Night
8%138%24%54%
2700
JulyDay
16%46%16%21%33%
3706
Night
14%37%15%22%36%
2609
AugustDay
13%3412%30%35%
3694
Night
10%2314%30%38%
3080
SeptemberDay
11%238%30%42%
3383
Night
8%139%31%45%
3217
OctoberDay
18%2411%26%35%
3246
Night
18%2311%26%37%
3571
NovemberDay
21%25%12%28%28%
2934
Night
22%2413%25%31%
4225
DecemberDay
30%36%16%22%18%
3069
Night
31%36%14%23%20%
4433

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
MonthOccurrence of each ForecastData
Points
JanuaryDay
14%15%35%28%7%
248
Night
9%6%14%34%25%9%
1364
FebruaryDay
11%18%33%25%8%1
392
Night
11%7%15%34%24%7%
1224
MarchDay
11%22%38%20%7%
383
Night
8%6%17%34%25%7%
1312
AprilDay
10%29%40%15%4
299
Night
7%9%24%30%21%7%
1199
MayDay
7%18%42%24%5%1
370
Night
26%18%35%29%7%
935
JuneDay
210%48%30%5%3
390
Night
1112%40%37%5%
900
JulyDay
234%49%9%3
392
Night
2326%54%13%
922
AugustDay
1232%47%9%7%
399
Night
1216%53%24%
1233
SeptemberDay
27%35%43%7%4
390
Night
16%22%51%18%
1196
OctoberDay
5%14%38%28%12%
336
Night
4312%31%32%15%
1240
NovemberDay
8%18%17%33%17%3
90
Night
6%312%31%32%14%
1300
DecemberDay
7%15%19%41%13%2
93
Night
13%6%14%32%24%9%
1364
Page generated at 2016-03-19 13:04:57. Version ac04

Copyright 2016 A. Danko


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