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Mount Wilson Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Mount Wilson Observatory clear sky chart from 2005-11-05 to 2014-12-13.

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%
12169
34%
35944
27%
12121
76%
12121
51%
17604

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
54%
1113
33%
3609
24%
1112
68%
1112
44%
1755
FebruaryNight
54%
991
30%
2980
25%
989
63%
989
37%
1659
MarchNight
59%
1116
29%
3125
22%
1116
67%
1116
43%
1700
AprilNight
61%
1079
30%
2699
15%
1079
66%
1079
47%
1544
MayNight
70%
875
31%
2521
21%
875
74%
875
55%
1217
JuneNight
87%
623
34%
2243
36%
623
89%
623
64%
850
JulyNight
90%
719
32%
2214
31%
678
91%
678
60%
933
AugustNight
92%
1113
40%
2780
27%
1109
92%
1109
78%
1273
SeptemberNight
91%
1076
43%
2857
38%
1076
92%
1076
75%
1256
OctoberNight
74%
1116
39%
3244
36%
1116
80%
1116
56%
1546
NovemberNight
67%
1180
34%
3835
32%
1180
76%
1180
49%
1798
DecemberNight
54%
1168
32%
3837
25%
1168
65%
1168
34%
2073

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
6%212212235%70%
36678
Night
5%212212235%71%
36144
TransparencyDay
17%47%16%27%26%
36370
Night
18%47%16%25%27%
35952
SeeingDay
5%14%43%35%1
2573
Night
5%315%34%32%8%
12180

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
10%312312225%63%
2501
Night
8%313212245%65%
3609
FebruaryDay
13%423213236%55%
2480
Night
11%5%23212235%57%
2976
MarchDay
8%31322345%8%55%
3009
Night
6%31221335%7%61%
3125
AprilDay
7%422212236%64%
3229
Night
7%312212235%68%
2699
MayDay
3211112235%74%
3495
Night
22111126%78%
2520
JuneDay
3111122382%
3694
Night
12486%
2243
JulyDay
31111223475%
3712
Night
31121223476%
2409
AugustDay
1111121384%
3348
Night
111112383%
2790
SeptemberDay
111112285%
3082
Night
111112286%
2857
OctoberDay
6%21121222472%
2890
Night
421211111376%
3244
NovemberDay
7%21332323465%
2664
Night
6%212212235%67%
3835
DecemberDay
12%412312337%56%
2574
Night
10%413323336%57%
3837

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%36%12%23%28%
2501
Night
22%37%14%22%30%
3609
FebruaryDay
29%5%7%18%26%12%
2480
Night
28%5%7%17%25%15%
2987
MarchDay
24%6%12%21%21%14%
3009
Night
22%6%11%21%22%15%
3125
AprilDay
21%5%11%22%26%12%
3229
Night
23%48%22%24%15%
2699
MayDay
14%5%10%21%32%16%
3498
Night
13%6%10%20%30%17%
2522
JuneDay
12%36%12%32%33%
3694
Night
9%49%14%28%33%
2243
JulyDay
12%46%16%26%34%
3415
Night
12%47%17%22%35%
2214
AugustDay
7%25%13%35%35%
3334
Night
7%26%13%34%35%
2780
SeptemberDay
7%25%11%32%41%
3082
Night
8%15%10%28%43%
2857
OctoberDay
16%35%15%24%34%
2890
Night
17%2412%26%36%
3244
NovemberDay
22%36%14%25%27%
2664
Night
19%37%15%23%31%
3835
DecemberDay
27%6%7%18%19%19%
2574
Night
28%5%7%16%22%20%
3837

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%17%43%21%2
162
Night
9%5%24%39%18%3
1116
FebruaryDay
14%23%41%19%1
248
Night
11%6%21%36%20%3
996
MarchDay
10%23%46%18%1
279
Night
5%5%25%37%21%4
1116
AprilDay
7%29%43%19%
269
Night
6%6%22%38%22%3
1079
MayDay
319%45%30%1
273
Night
3419%37%29%5%
878
JuneDay
29%50%36%
270
Night
8%40%44%4
623
JulyDay
229%64%2
268
Night
11217%62%15%
719
AugustDay
1335%58%
279
Night
1318%55%20%
1113
SeptemberDay
1450%42%
270
Night
1427%48%18%
1076
OctoberDay
5%12%45%34%1
255
Night
5%213%32%35%10%
1116
NovemberNight
6%217%37%27%7%
1180
DecemberNight
10%7%19%43%16%2
1168
Page generated at 2014-12-14 01:50:27. Version ac04

Copyright 2014 A. Danko


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