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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 2015-03-27.

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%
12840
34%
37355
29%
12800
75%
12800
50%
18888

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%
1224
31%
3463
28%
1224
66%
1224
41%
1944
AprilNight
54%
1079
31%
2699
16%
1079
61%
1079
46%
1566
MayNight
69%
837
36%
2483
26%
837
73%
837
59%
1130
JuneNight
82%
810
36%
2430
30%
810
84%
810
75%
960
JulyNight
89%
826
31%
2327
26%
791
89%
791
62%
1049
AugustNight
90%
1113
39%
2780
27%
1109
90%
1109
72%
1325
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%
37583
Night
3423313335%65%
37554
TransparencyDay
19%35%14%27%29%
37282
Night
21%3414%26%30%
37357
SeeingDay
6%16%42%31%3
2570
Night
6%413%30%33%11%
12852

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
4423323348%58%
3265
Night
37%2341445%7%55%
3463
AprilDay
4413313236%64%
3229
Night
45%23423446%59%
2699
MayDay
111212225%77%
3534
Night
112212335%73%
2482
JuneDay
11111112482%
3510
Night
111113383%
2430
JulyDay
2212313447%65%
3597
Night
1112213247%69%
2527
AugustDay
21222334472%
3348
Night
11221223477%
2790
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%
3265
Night
27%46%18%24%19%
3463
AprilDay
22%26%22%30%14%
3229
Night
25%46%19%27%17%
2699
MayDay
12%26%16%37%24%
3537
Night
13%35%17%33%27%
2484
JuneDay
9%139%24%51%
3510
Night
8%139%24%53%
2430
JulyDay
16%47%16%21%33%
3306
Night
13%37%16%21%37%
2327
AugustDay
13%3413%27%36%
3334
Night
10%2314%29%39%
2780
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%16%4
306
Night
8%6%18%35%24%6%
1224
AprilDay
10%30%39%15%3
269
Night
7%9%25%29%21%6%
1079
MayDay
224%44%27%1
273
Night
17%19%35%29%7%
840
JuneDay
12%59%26%1
270
Night
1113%40%36%5%
810
JulyDay
136%57%3
268
Night
2225%54%14%
826
AugustDay
2238%51%4
279
Night
1315%53%25%
1113
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 2015-03-28 10:47:24. Version ac04

Copyright 2015 A. Danko


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