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Carr Astronomical Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Carr Astronomical 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
30%
10771
10%
33506
7%
10736
33%
10736
13%
26034

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
10%
1208
2%
3810
1%
1208
12%
1208
2%
3525
FebruaryNight
15%
992
4%
3195
1%
992
19%
992
6%
2732
MarchNight
29%
1116
15%
3084
9%
1116
34%
1116
17%
2332
AprilNight
31%
886
15%
2458
8%
886
36%
886
20%
1773
MayNight
48%
584
17%
2043
17%
584
54%
584
23%
1281
JuneNight
48%
480
13%
1742
15%
480
54%
480
20%
1155
JulyNight
61%
557
17%
1767
18%
525
63%
525
30%
1026
AugustNight
57%
755
17%
2233
12%
752
60%
752
30%
1397
SeptemberNight
48%
957
15%
2550
10%
957
50%
957
25%
1769
OctoberNight
27%
992
10%
2986
7%
992
31%
992
12%
2359
NovemberNight
22%
1060
10%
3664
8%
1060
25%
1060
8%
2993
DecemberNight
8%
1184
1%
3974
0%
1184
9%
1184
2%
3692

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
14%10%5%8%7%5%5%6%28%
33850
Night
14%10%5%8%7%5%5%5%6%26%
33677
Cloud CoverDay
14%10%8%6%5%5%6%28%
33860
Night
14%10%5%8%7%5%5%5%6%26%
33681
TransparencyDay
8%12%18%9%
29383
Night
9%11%16%8%
29105
SeeingDay
7%23%29%17%6%
2189
Night
13%29%26%10%
10430

By Month

Percentage Cloud Cover NE (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%15%8%16%13%6%7%5%7%
2300
Night
13%14%7%14%12%5%7%5%5%5%7%
3810
FebruaryDay
13%16%9%13%11%5%6%12%
2268
Night
11%12%6%12%10%5%7%5%6%6%15%
3193
MarchDay
11%11%5%9%7%5%5%6%29%
3042
Night
11%11%6%8%6%5%5%5%32%
3072
AprilDay
16%10%6%5%5%7%32%
3178
Night
17%8%6%6%6%34%
2458
MayDay
14%8%5%5%6%6%38%
3294
Night
13%6%5%5%7%41%
2041
JuneDay
15%6%5%5%5%6%6%7%36%
3536
Night
13%5%5%5%6%6%5%8%37%
1742
JulyDay
11%5%5%5%6%7%10%37%
3499
Night
8%5%7%9%48%
1943
AugustDay
12%5%6%6%5%5%8%39%
3203
Night
10%5%5%7%47%
2244
SeptemberDay
20%6%5%5%5%8%32%
2728
Night
17%5%5%6%8%38%
2550
OctoberDay
23%12%6%7%5%5%22%
2468
Night
22%11%6%6%5%6%25%
2986
NovemberDay
14%15%7%8%7%6%5%5%19%
2174
Night
16%14%6%8%6%5%5%5%6%20%
3664
DecemberDay
16%17%10%12%9%5%5%5%7%
2160
Night
17%15%9%13%8%6%5%5%7%
3974

Percentage Cloud Cover SE (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%15%8%16%13%6%7%5%7%
2300
Night
13%14%7%14%12%5%7%5%5%5%7%
3810
FebruaryDay
13%16%8%13%11%5%5%12%
2268
Night
11%13%6%12%10%5%6%5%6%6%15%
3186
MarchDay
11%10%5%9%7%5%5%6%29%
3052
Night
11%11%6%8%6%5%5%32%
3084
AprilDay
16%10%5%5%5%5%7%33%
3178
Night
17%8%6%5%6%34%
2458
MayDay
14%8%5%5%6%38%
3294
Night
13%6%5%5%5%7%41%
2040
JuneDay
14%5%6%5%5%6%6%7%36%
3536
Night
13%5%5%5%6%5%5%8%37%
1742
JulyDay
10%5%5%5%5%5%7%9%37%
3499
Night
8%5%7%9%48%
1943
AugustDay
11%5%6%6%5%5%8%39%
3203
Night
10%5%7%47%
2244
SeptemberDay
20%6%5%6%5%8%32%
2728
Night
17%5%5%6%8%38%
2550
OctoberDay
23%12%6%6%5%5%22%
2468
Night
22%10%5%6%5%6%25%
2986
NovemberDay
14%15%7%9%6%6%5%5%5%19%
2174
Night
17%14%6%9%5%5%5%6%6%21%
3664
DecemberDay
16%17%10%12%8%5%5%8%
2160
Night
17%15%9%13%8%6%5%5%7%
3974

Transparency (when cloud cover <= 30%)
Color Meanings:
Poor Below Average Average Above average Transparent
MonthOccurrence of each ForecastData
Points
JanuaryDay
7%8%5%
1874
Night
11%7%
3120
FebruaryDay
7%9%9%
1870
Night
10%12%10%
2648
MarchDay
8%14%18%10%
2633
Night
8%11%21%10%
2678
AprilDay
6%10%23%14%
2724
Night
5%10%19%18%
2133
MayDay
7%12%23%16%
2902
Night
7%13%25%15%
1842
JuneDay
9%15%23%12%
3174
Night
10%15%23%13%
1561
JulyDay
10%15%22%13%
2889
Night
10%15%28%19%
1630
AugustDay
8%14%22%13%
3041
Night
7%14%27%16%
2123
SeptemberDay
7%13%23%7%
2492
Night
10%15%27%9%
2330
OctoberDay
7%10%12%7%
2236
Night
8%11%14%8%
2734
NovemberDay
9%10%12%
1803
Night
11%12%13%
3074
DecemberDay
10%7%
1745
Night
10%8%
3232

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
JanuaryNight
22%37%20%
1145
FebruaryNight
17%38%22%5%
968
MarchDay
7%30%32%12%
254
Night
11%34%25%10%
1100
AprilDay
12%28%22%15%
245
Night
11%31%27%10%
848
MayDay
8%20%25%22%8%
237
Night
24%38%16%
570
JuneDay
6%23%34%17%
407
Night
23%37%19%
471
JulyDay
5%21%33%19%9%
343
Night
20%44%21%
550
AugustDay
17%30%25%13%
242
Night
19%38%23%
747
SeptemberDay
7%22%24%17%9%
234
Night
6%21%33%15%6%
931
OctoberDay
14%25%25%9%
227
Night
14%26%21%10%
958
NovemberNight
18%29%20%8%
1012
DecemberNight
22%36%17%
1130
Page generated at 2014-04-18 00:20:01. Version ac01


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