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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 2016-11-15.

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%
15057
34%
43702
29%
15017
75%
15017
50%
22008

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
62%
1364
31%
3853
27%
1364
67%
1364
41%
2148
AprilNight
56%
1319
30%
3299
16%
1319
62%
1319
46%
1910
MayNight
67%
1026
33%
3044
24%
1026
70%
1026
53%
1478
JuneNight
83%
990
36%
2970
31%
990
85%
990
75%
1178
JulyNight
89%
1018
31%
2891
26%
983
89%
983
63%
1298
AugustNight
91%
1357
39%
3390
27%
1353
91%
1353
73%
1596
SeptemberNight
87%
1316
44%
3539
37%
1316
90%
1316
75%
1558
OctoberNight
75%
1364
39%
3929
36%
1364
79%
1364
55%
1905
NovemberNight
71%
1360
35%
4420
36%
1360
77%
1360
48%
2107
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%
44388
Night
3413313335%66%
43901
TransparencyDay
19%35%14%27%29%
44087
Night
21%3413%26%30%
43704
SeeingDay
6%12%35%31%10%4
4726
Night
6%412%30%34%11%
15069

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%59%
3645
Night
36%2341445%7%56%
3853
AprilDay
4413313336%63%
3949
Night
36%23323446%59%
3299
MayDay
2212212235%73%
4337
Night
1213323346%67%
3043
JuneDay
11111212481%
4290
Night
111113482%
2970
JulyDay
2212313446%68%
4396
Night
1112213346%71%
3091
AugustDay
11121334474%
4080
Night
11111222478%
3400
SeptemberDay
21121223477%
3721
Night
11121122382%
3539
OctoberDay
2312313235%69%
3570
Night
1313322335%69%
3929
NovemberDay
4312313335%66%
3066
Night
242331333466%
4420
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%17%
3645
Night
27%46%18%24%19%
3853
AprilDay
23%26%21%30%15%
3949
Night
25%46%19%27%17%
3299
MayDay
15%26%18%35%21%
4340
Night
18%36%18%31%22%
3045
JuneDay
10%139%24%51%
4290
Night
8%138%24%54%
2970
JulyDay
15%46%15%23%35%
4105
Night
13%37%14%23%38%
2891
AugustDay
12%3411%30%37%
4066
Night
10%2312%30%41%
3390
SeptemberDay
11%238%29%44%
3721
Night
8%138%30%46%
3539
OctoberDay
18%2412%26%35%
3570
Night
18%2311%26%36%
3929
NovemberDay
20%25%12%29%28%
3066
Night
21%2413%26%32%
4420
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
10%23%36%20%8%1
434
Night
8%7%17%34%25%7%
1364
AprilDay
12%26%39%14%5%2
419
Night
7%9%23%29%22%7%
1319
MayDay
7%18%40%25%6%2
494
Night
26%19%35%28%6%
1029
JuneDay
28%43%30%10%4
510
Night
1111%40%38%6%
990
JulyDay
229%47%12%7%
516
Night
2225%55%13%
1018
AugustDay
1229%44%12%10%
523
Night
1217%54%24%
1357
SeptemberDay
28%35%39%10%4
510
Night
16%23%49%17%
1316
OctoberDay
5%11%36%29%15%1
453
Night
4211%31%34%14%
1364
NovemberDay
5%14%18%32%22%6%
134
Night
5%312%31%32%14%
1360
DecemberDay
7%15%19%41%13%2
93
Night
13%6%14%32%24%9%
1364
Page generated at 2016-11-16 09:29:36. Version ac04

Copyright 2016 A. Danko


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