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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 2014-06-18.

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%
10848
13%
34131
8%
10815
35%
10815
15%
25071

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
13%
995
8%
3148
2%
992
21%
992
8%
2572
MarchNight
23%
1116
15%
3088
8%
1116
29%
1116
14%
2333
AprilNight
26%
1071
16%
2689
6%
1071
30%
1071
21%
1942
MayNight
43%
582
18%
2227
18%
582
49%
582
20%
1394
JuneNight
48%
514
14%
2058
17%
514
55%
514
19%
1273
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%48%6%35%45%6%27%
34596
Night
16%11%5%8%6%35%446%28%
34303
Cloud CoverDay
17%10%47%6%35%45%6%27%
34606
Night
17%10%5%8%6%34446%28%
34308
TransparencyDay
56%311%19%8%
34286
Night
57%311%18%8%
34131
SeeingDay
23%9%21%21%17%7%
2255
Night
25%13%23%25%10%
10849

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%35%44414%
2332
Night
16%15%7%11%9%46%445%14%
3783
FebruaryDay
16%15%7%15%10%3423316%
2317
Night
14%15%8%14%8%35%33418%
3146
MarchDay
16%14%7%9%5%24345%25%
3037
Night
16%13%6%8%5%24335%29%
3076
AprilDay
18%11%35%423446%33%
3245
Night
19%9%35%5%24445%35%
2689
MayDay
16%7%25%5%35%5%5%7%35%
3793
Night
14%5%25%5%35%46%6%38%
2225
JuneDay
18%7%35%5%35%5%6%7%30%
3598
Night
15%6%346%25%46%7%36%
2058
JulyDay
12%5%25%6%37%6%6%9%33%
3455
Night
10%5%25%5%35%47%9%40%
1988
AugustDay
15%6%26%6%45%5%6%8%31%
3112
Night
12%5%25%6%3446%8%41%
2336
SeptemberDay
20%7%26%5%35%446%33%
2770
Night
16%6%35%5%35%5%35%39%
2509
OctoberDay
23%12%25%5%34446%26%
2458
Night
24%9%36%5%34345%29%
2998
NovemberDay
16%14%5%8%6%245%5%6%24%
2247
Night
16%13%5%7%5%34346%27%
3589
DecemberDay
17%18%8%12%7%3434414%
2232
Night
19%15%8%11%7%35%44414%
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%35%445%14%
2332
Night
16%15%7%11%9%36%5%4414%
3783
FebruaryDay
16%16%6%15%10%3323316%
2317
Night
14%15%7%14%8%35%33418%
3139
MarchDay
17%14%7%8%5%33345%25%
3047
Night
17%13%6%8%5%24335%29%
3088
AprilDay
18%11%35%424347%33%
3245
Night
19%9%345%24345%35%
2689
MayDay
16%7%35%5%35%45%7%35%
3793
Night
15%6%25%5%3446%6%38%
2225
JuneDay
19%7%36%5%35%5%6%8%30%
3598
Night
15%6%345%3446%7%36%
2058
JulyDay
13%5%25%6%37%6%6%9%33%
3455
Night
10%425%5%35%5%6%9%40%
1988
AugustDay
16%6%36%6%35%5%6%8%31%
3112
Night
12%5%25%5%245%6%8%40%
2336
SeptemberDay
20%6%36%5%35%346%33%
2770
Night
16%6%25%5%345%46%39%
2509
OctoberDay
24%11%35%5%34445%26%
2458
Night
24%9%36%433446%29%
2998
NovemberDay
16%14%5%7%6%2445%6%25%
2247
Night
17%13%5%7%6%34446%28%
3589
DecemberDay
18%18%9%11%6%3443414%
2232
Night
19%14%8%12%7%35%34415%
3906

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthOccurrence of each ForecastData
Points
JanuaryDay
72%310%11%2
2333
Night
72%48%11%3
3783
FebruaryDay
74%26%11%4
2319
Night
70%210%12%4
3148
MarchDay
61%211%17%6%
3048
Night
59%210%19%7%
3088
AprilDay
51%29%21%12%2
3245
Night
50%210%21%11%2
2689
MayDay
47%313%22%11%1
3797
Night
44%412%23%13%1
2227
JuneDay
51%413%21%8%
3598
Night
44%414%26%10%
2058
JulyDay
45%5%13%23%10%1
3140
Night
39%415%23%15%1
1811
AugustDay
48%310%24%11%1
3099
Night
39%415%26%12%1
2325
SeptemberDay
51%39%23%11%
2770
Night
46%310%25%12%1
2509
OctoberDay
59%311%17%8%
2458
Night
56%312%17%9%
2998
NovemberDay
58%313%16%6%1
2247
Night
58%311%18%6%1
3589
DecemberDay
74%211%9%1
2232
Night
72%311%9%1
3906

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
JanuaryNight
31%18%27%19%3
1116
FebruaryDay
37%23%20%12%41
85
Night
28%22%27%18%3
995
MarchDay
26%18%21%18%11%2
279
Night
27%19%24%20%7%
1116
AprilDay
28%12%22%17%15%2
270
Night
28%14%25%24%7%
1071
MayDay
17%7%27%22%17%6%
274
Night
16%7%23%37%13%1
583
JuneDay
23%421%26%19%4
257
Night
18%6%17%40%16%
514
JulyDay
13%423%26%21%10%
236
Night
12%214%43%25%1
482
AugustDay
19%416%17%23%17%
246
Night
15%316%36%26%2
847
SeptemberDay
24%7%16%15%20%16%
239
Night
20%6%20%26%20%3
957
OctoberDay
32%10%16%23%14%2
248
Night
30%10%23%24%11%
992
NovemberDay
20%12%23%27%15%
121
Night
28%14%24%21%8%1
1060
DecemberNight
32%18%28%17%2
1116
Page generated at 2014-06-18 17:01:28. Version ac04

Copyright 2014 A. Danko


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