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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 2016-07-10.

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%
14563
34%
42325
29%
14523
75%
14523
50%
21399

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
88%
952
32%
2699
27%
917
88%
917
62%
1222
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%
42946
Night
3413313335%65%
42524
TransparencyDay
19%35%14%27%29%
42645
Night
21%35%13%26%30%
42327
SeeingDay
6%13%36%31%8%3
4235
Night
6%413%30%33%11%
14575

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%67%
4120
Night
1113213346%70%
2899
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%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
16%46%16%22%34%
3829
Night
13%37%15%22%37%
2699
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
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
233%49%9%4
430
Night
2326%54%13%
952
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 2016-07-11 04:01:09. Version ac04

Copyright 2016 A. Danko


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