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Ithaca
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ithaca clear sky chart from 2005-11-05 to 2014-02-03.

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%
10405
13%
32779
8%
10372
35%
10372
15%
24107

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
14%
1116
7%
3783
3%
1112
19%
1112
6%
3160
FebruaryNight
14%
895
8%
2829
2%
892
20%
892
7%
2335
MarchNight
23%
992
15%
2744
8%
992
29%
992
15%
2075
AprilNight
26%
952
15%
2390
6%
952
30%
952
21%
1735
MayNight
43%
516
19%
1975
19%
516
50%
516
21%
1222
JuneNight
48%
480
15%
1920
19%
480
56%
480
19%
1183
JulyNight
59%
482
15%
1811
18%
459
63%
459
24%
1061
AugustNight
55%
847
16%
2325
9%
844
58%
844
30%
1497
SeptemberNight
44%
957
19%
2509
11%
957
48%
957
26%
1732
OctoberNight
28%
992
13%
2998
9%
992
34%
992
15%
2207
NovemberNight
24%
1060
15%
3589
11%
1060
32%
1060
13%
2643
DecemberNight
15%
1116
5%
3906
2%
1116
18%
1116
6%
3257

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
17%10%7%6%5%5%6%27%
32986
Night
17%11%5%8%6%5%6%28%
32951
Cloud CoverDay
17%10%7%6%5%5%6%27%
32996
Night
17%11%5%8%6%6%28%
32956
TransparencyDay
13%21%9%
28612
Night
13%20%9%
28584
SeeingDay
9%21%21%18%7%
2049
Night
13%25%26%11%
9863

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
12%14%10%14%10%5%14%
2332
Night
16%15%7%11%9%6%5%14%
3783
FebruaryDay
17%16%7%15%10%15%
2074
Night
14%16%8%14%7%5%16%
2827
MarchDay
17%14%8%8%5%25%
2699
Night
17%13%6%8%5%29%
2732
AprilDay
18%11%6%6%34%
2884
Night
20%9%5%6%34%
2390
MayDay
16%7%5%5%5%5%5%7%36%
3363
Night
14%5%5%5%5%6%40%
1973
JuneDay
18%7%6%5%5%6%6%7%30%
3360
Night
15%6%6%5%5%6%7%37%
1920
JulyDay
12%5%5%6%7%6%6%9%33%
3455
Night
10%5%5%5%5%7%9%40%
1988
AugustDay
15%6%6%6%5%5%6%8%31%
3112
Night
12%5%5%6%6%8%41%
2336
SeptemberDay
20%7%6%5%5%6%33%
2770
Night
16%6%5%5%5%5%5%39%
2509
OctoberDay
23%12%5%5%6%26%
2458
Night
24%9%6%5%5%29%
2998
NovemberDay
16%14%5%8%6%5%5%6%24%
2247
Night
16%13%5%7%5%6%27%
3589
DecemberDay
17%18%8%12%7%14%
2232
Night
19%15%8%11%7%5%14%
3906

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
13%13%9%14%10%5%5%14%
2332
Night
16%15%7%11%9%6%5%14%
3783
FebruaryDay
17%16%7%15%10%15%
2074
Night
14%16%7%14%8%5%17%
2820
MarchDay
17%14%8%8%5%26%
2709
Night
18%13%7%8%29%
2744
AprilDay
18%11%5%5%7%33%
2884
Night
20%9%5%5%5%34%
2390
MayDay
16%7%5%5%5%6%36%
3363
Night
14%5%5%5%5%5%6%40%
1973
JuneDay
18%7%6%5%5%5%6%8%30%
3360
Night
15%6%5%6%7%37%
1920
JulyDay
13%5%5%6%7%6%6%9%33%
3455
Night
10%5%5%5%5%6%9%40%
1988
AugustDay
16%6%6%6%5%5%6%8%31%
3112
Night
12%5%5%5%5%6%8%40%
2336
SeptemberDay
20%6%6%5%5%6%33%
2770
Night
16%6%5%5%5%6%39%
2509
OctoberDay
24%11%5%5%5%26%
2458
Night
24%9%6%6%29%
2998
NovemberDay
16%14%5%7%6%5%6%25%
2247
Night
17%13%5%7%6%6%28%
3589
DecemberDay
18%18%9%11%6%14%
2232
Night
19%14%8%12%7%5%15%
3906

Transparency (when cloud cover <= 30%)
Color Meanings:
Poor Below Average Average Above average Transparent
MonthOccurrence of each ForecastData
Points
JanuaryDay
12%13%
1913
Night
5%10%13%
3106
FebruaryDay
8%13%
1677
Night
12%14%
2307
MarchDay
13%21%8%
2234
Night
13%23%8%
2298
AprilDay
10%24%15%
2463
Night
13%22%14%
2044
MayDay
15%24%14%
2994
Night
5%14%25%15%
1795
JuneDay
5%16%23%9%
2944
Night
16%29%11%
1685
JulyDay
5%15%25%11%
2865
Night
5%16%25%16%
1658
AugustDay
10%25%12%
2930
Night
16%28%13%
2176
SeptemberDay
9%26%12%
2520
Night
10%27%13%
2317
OctoberDay
12%19%8%
2264
Night
13%18%9%
2798
NovemberDay
16%18%7%
1943
Night
12%21%7%
3117
DecemberDay
13%11%
1865
Night
13%11%
3283

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
20%30%21%
1015
FebruaryDay
25%20%12%5%
70
Night
23%29%19%
826
MarchDay
18%23%19%13%
237
Night
19%25%21%9%
943
AprilDay
13%25%19%15%
222
Night
15%27%27%7%
885
MayDay
8%27%23%18%7%
237
Night
7%25%36%14%
505
JuneDay
5%23%26%20%
230
Night
6%18%43%16%
455
JulyDay
23%26%22%10%
231
Night
15%44%25%
468
AugustDay
16%18%23%18%
242
Night
16%36%26%
827
SeptemberDay
7%17%15%21%17%
227
Night
7%21%28%21%
921
OctoberDay
11%17%24%14%
240
Night
11%23%24%11%
957
NovemberDay
13%24%29%16%
113
Night
15%25%22%9%
1009
DecemberNight
19%30%18%
1052
Page generated at 2014-02-03 20:56:43. Version ac01


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