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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 2014-04-17.

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
69%
11550
35%
33573
30%
11510
74%
11510
49%
17041

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%
1026
31%
2568
17%
1026
61%
1026
46%
1481
MayNight
69%
742
39%
2202
28%
742
73%
742
59%
1002
JuneNight
81%
720
41%
2160
34%
720
83%
720
74%
863
JulyNight
89%
730
33%
2045
27%
695
89%
695
63%
915
AugustNight
91%
989
40%
2470
27%
985
91%
985
73%
1170
SeptemberNight
88%
956
45%
2574
39%
956
90%
956
76%
1124
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
5%67%
33788
Night
5%65%
33772
TransparencyDay
5%15%28%30%
31896
Night
5%15%27%31%
31862
SeeingDay
17%42%31%
2264
Night
13%30%33%11%
11466

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%5%62%
2629
Night
5%5%5%59%
3486
FebruaryDay
8%8%7%48%
2480
Night
5%10%5%5%50%
2976
MarchDay
8%57%
2983
Night
7%5%7%55%
3152
AprilDay
6%64%
3063
Night
6%6%59%
2568
MayDay
78%
3133
Night
5%73%
2201
JuneDay
82%
3120
Night
83%
2160
JulyDay
6%66%
3197
Night
7%70%
2245
AugustDay
72%
2976
Night
77%
2480
SeptemberDay
78%
2706
Night
82%
2574
OctoberDay
70%
2596
Night
5%70%
2858
NovemberDay
5%64%
2394
Night
5%64%
3445
DecemberDay
8%6%7%53%
2511
Night
7%6%5%54%
3627

Transparency (when cloud cover <= 30%)
Color Meanings:
Poor Below Average Average Above average Transparent
MonthOccurrence of each ForecastData
Points
JanuaryDay
5%14%26%27%
2502
Night
5%13%24%30%
3292
FebruaryDay
5%19%25%14%
2269
Night
15%25%19%
2723
MarchDay
8%23%28%18%
2695
Night
6%21%26%19%
2871
AprilDay
6%24%34%16%
2803
Night
6%21%30%19%
2347
MayDay
6%17%39%25%
3029
Night
6%17%36%26%
2116
JuneDay
10%23%54%
3028
Night
10%23%54%
2110
JulyDay
6%16%21%37%
2800
Night
7%16%22%40%
1953
AugustDay
13%29%36%
2938
Night
14%30%39%
2451
SeptemberDay
8%29%46%
2681
Night
9%27%49%
2553
OctoberDay
11%27%37%
2519
Night
10%27%41%
2770
NovemberDay
6%13%30%26%
2276
Night
14%28%29%
3257
DecemberDay
6%19%23%19%
2356
Night
6%15%25%20%
3419

Seeing (when cloud cover <= 80%)
Color Meanings:
Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
MonthOccurrence of each ForecastData
Points
JanuaryDay
19%41%22%
124
Night
7%15%33%25%9%
1100
FebruaryDay
25%37%21%
236
Night
8%17%33%22%7%
980
MarchDay
27%43%17%
265
Night
7%19%36%24%6%
1089
AprilDay
32%42%15%
242
Night
9%25%30%21%6%
1012
MayDay
24%43%26%
241
Night
6%19%35%29%7%
743
JuneDay
12%58%27%
240
Night
13%39%37%6%
720
JulyDay
37%56%
236
Night
26%54%13%
728
AugustDay
39%51%
248
Night
15%54%25%
988
SeptemberDay
7%39%46%
240
Night
6%22%50%19%
956
OctoberDay
18%42%25%7%
192
Night
13%30%31%15%
987
NovemberNight
12%30%33%14%
1056
DecemberNight
5%14%32%24%10%
1107
Page generated at 2014-04-17 21:20:00. Version ac01


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