This page made possible by the sponsorship of: Russell Sipe.

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 2015-08-20.

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%
13333
34%
38718
29%
13293
75%
13293
50%
19611

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%
1237
32%
3875
28%
1236
67%
1236
39%
2043
FebruaryNight
57%
1102
29%
3322
28%
1102
63%
1102
33%
1962
MarchNight
61%
1240
31%
3503
28%
1240
67%
1240
41%
1962
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%
1189
40%
2970
27%
1185
91%
1185
72%
1410
SeptemberNight
88%
1076
45%
2896
38%
1076
91%
1076
77%
1253
OctoberNight
74%
1116
40%
3215
37%
1116
79%
1116
56%
1533
NovemberNight
71%
1180
34%
3835
35%
1180
76%
1180
46%
1865
DecemberNight
58%
1240
31%
4030
29%
1240
64%
1240
34%
2258

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%
39408
Night
3423313335%65%
38917
TransparencyDay
19%35%14%27%29%
39107
Night
21%3414%26%30%
38720
SeeingDay
6%14%40%31%5%1
3021
Night
6%413%30%33%11%
13345

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
5%6%13313345%61%
2922
Night
5%5%24423335%59%
3875
FebruaryDay
7%8%24323346%52%
2760
Night
5%9%34324435%52%
3312
MarchDay
4423323347%58%
3313
Night
36%2341445%7%55%
3503
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%
3574
Night
11211223477%
2980
SeptemberDay
11121223379%
3044
Night
1111122383%
2896
OctoberDay
231221223471%
2920
Night
131321233471%
3215
NovemberDay
4313313335%65%
2664
Night
2423313335%64%
3835
DecemberDay
8%6%14323347%52%
2790
Night
7%6%24423345%53%
4030

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthOccurrence of each ForecastData
Points
JanuaryDay
26%35%13%25%26%
2923
Night
27%3412%23%28%
3875
FebruaryDay
33%35%17%25%15%
2760
Night
34%3413%25%18%
3323
MarchDay
25%37%19%25%18%
3313
Night
27%45%18%24%19%
3503
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%3413%29%35%
3560
Night
10%2314%29%39%
2970
SeptemberDay
10%238%29%45%
3044
Night
7%139%29%48%
2896
OctoberDay
17%2410%26%37%
2920
Night
17%2310%26%39%
3215
NovemberDay
22%26%13%29%26%
2664
Night
23%2414%26%29%
3835
DecemberDay
32%46%17%21%17%
2790
Night
32%36%14%23%19%
4030

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
15%18%39%21%4
141
Night
9%6%15%32%26%9%
1240
FebruaryDay
15%23%36%21%2
276
Night
12%7%16%34%22%7%
1108
MarchDay
11%25%41%17%4
310
Night
8%6%17%35%24%6%
1240
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
1235%49%6%4
355
Night
1216%53%24%
1189
SeptemberDay
28%39%45%4
270
Night
16%22%50%19%
1076
OctoberDay
5%16%43%25%8%
218
Night
5%311%30%32%16%
1116
NovemberNight
5%312%30%33%14%
1180
DecemberNight
13%5%14%32%23%9%
1240
Page generated at 2015-08-21 09:03:21. Version ac04

Copyright 2015 A. Danko


OCA Anza Observatory Clear Sky Chart | Charts Home