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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 2014-09-04.

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%
12024
35%
34887
29%
11984
74%
11984
50%
17656

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
59%
1113
32%
3486
29%
1112
66%
1112
39%
1831
FebruaryNight
55%
990
29%
2986
27%
990
60%
990
31%
1802
MarchNight
60%
1116
32%
3152
29%
1116
66%
1116
40%
1782
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%
972
45%
2614
39%
972
90%
972
76%
1140
OctoberNight
72%
992
40%
2858
37%
992
77%
992
56%
1371
NovemberNight
71%
1060
34%
3445
36%
1060
76%
1060
46%
1690
DecemberNight
59%
1116
32%
3627
30%
1116
65%
1116
34%
2010

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%
35555
Night
3423313335%65%
35086
TransparencyDay
19%35%15%27%29%
35254
Night
21%3414%25%30%
34889
SeeingDay
6%16%41%31%3
2451
Night
6%413%30%33%11%
12036

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%62%
2629
Night
5%5%23323435%59%
3486
FebruaryDay
8%8%24334347%48%
2480
Night
5%10%35%334435%50%
2976
MarchDay
4423323348%57%
2983
Night
37%3341445%7%55%
3152
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
11121223378%
2744
Night
1121122382%
2614
OctoberDay
241331222470%
2596
Night
1313212335%70%
2858
NovemberDay
4413313335%64%
2394
Night
2424413335%64%
3445
DecemberDay
8%6%14323347%53%
2511
Night
7%6%24423345%54%
3627

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthOccurrence of each ForecastData
Points
JanuaryDay
25%35%13%25%26%
2630
Night
26%3412%23%28%
3486
FebruaryDay
35%45%18%23%13%
2480
Night
36%3414%22%17%
2987
MarchDay
25%37%20%25%16%
2983
Night
28%46%19%24%17%
3152
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
11%238%28%46%
2744
Night
8%139%27%49%
2614
OctoberDay
18%2410%26%36%
2596
Night
18%2310%26%39%
2858
NovemberDay
23%26%13%29%25%
2394
Night
23%2414%27%28%
3445
DecemberDay
30%36%18%22%18%
2511
Night
32%36%14%24%19%
3627

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%18%40%22%3
127
Night
9%6%15%32%25%9%
1116
FebruaryDay
16%24%35%20%2
248
Night
13%8%16%32%21%7%
996
MarchDay
11%26%41%16%4
279
Night
8%6%18%35%23%6%
1116
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
27%39%46%4
244
Night
16%22%50%19%
972
OctoberDay
6%18%41%25%7%
194
Night
5%313%30%31%15%
992
NovemberNight
5%312%30%33%14%
1060
DecemberNight
12%5%14%32%23%9%
1116
Page generated at 2014-09-04 23:15:50. Version ac04

Copyright 2014 A. Danko


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