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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 2016-09-27.

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
31%
13677
13%
43014
9%
13644
36%
13644
16%
31060

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
15%
1364
8%
4627
4%
1360
20%
1360
7%
3815
FebruaryNight
15%
1223
9%
3870
4%
1220
22%
1220
8%
3129
MarchNight
23%
1364
14%
3774
8%
1364
29%
1364
14%
2847
AprilNight
28%
1310
16%
3288
6%
1310
32%
1310
21%
2368
MayNight
45%
713
18%
2730
17%
713
51%
713
20%
1689
JuneNight
48%
660
14%
2640
17%
660
56%
660
20%
1613
JulyNight
60%
672
14%
2559
18%
649
63%
649
27%
1437
AugustNight
58%
1162
17%
3192
11%
1159
60%
1159
34%
1985
SeptemberNight
49%
1305
20%
3413
13%
1305
52%
1305
30%
2252
OctoberNight
28%
1240
13%
3747
9%
1240
35%
1240
15%
2753
NovemberNight
24%
1300
15%
4400
10%
1300
32%
1300
13%
3190
DecemberNight
15%
1364
5%
4774
3%
1364
18%
1364
6%
3982

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
16%10%47%6%35%45%6%28%
44006
Night
15%10%47%6%35%45%6%29%
43186
Cloud CoverDay
16%10%47%6%35%45%6%28%
44016
Night
16%10%47%6%34446%30%
43191
TransparencyDay
55%311%19%9%
43696
Night
55%311%19%9%
43014
SeeingDay
23%10%24%21%14%6%
4327
Night
24%13%23%25%11%1
13678

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%13%9%14%11%46%44414%
2852
Night
14%15%6%12%9%46%445%14%
4627
FebruaryDay
16%14%6%15%10%35%33316%
2849
Night
13%14%7%13%8%35%445%18%
3868
MarchDay
16%14%7%9%6%33345%24%
3715
Night
15%13%6%8%5%34335%29%
3762
AprilDay
17%11%36%5%23346%33%
3968
Night
19%9%35%5%24345%35%
3288
MayDay
15%7%25%6%35%5%5%7%35%
4654
Night
13%6%25%5%35%5%6%7%38%
2728
JuneDay
17%7%35%5%35%5%6%8%30%
4620
Night
15%6%345%25%46%7%38%
2640
JulyDay
11%5%25%6%36%6%6%9%34%
4753
Night
9%4145%35%47%9%43%
2736
AugustDay
14%6%25%6%45%5%6%9%32%
4266
Night
11%4145%3446%8%44%
3203
SeptemberDay
16%6%25%5%35%447%38%
3773
Night
14%5%24435%5%46%43%
3413
OctoberDay
22%11%26%5%3445%6%26%
3073
Night
23%9%36%5%3445%5%29%
3747
NovemberDay
16%13%5%8%6%2445%6%26%
2755
Night
16%13%47%6%34346%28%
4400
DecemberDay
17%18%8%11%7%3434414%
2728
Night
19%16%8%11%7%35%44414%
4774

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%12%9%15%10%45%44414%
2852
Night
15%14%7%11%9%46%5%4415%
4627
FebruaryDay
16%15%6%14%10%4423317%
2849
Night
14%15%6%13%8%36%43419%
3861
MarchDay
16%14%7%9%5%33345%25%
3725
Night
16%13%6%8%5%24345%29%
3774
AprilDay
18%12%36%5%24346%33%
3968
Night
20%9%34424345%36%
3288
MayDay
15%7%35%5%35%45%7%35%
4654
Night
14%5%25%6%345%6%6%39%
2728
JuneDay
18%7%26%5%35%5%6%8%30%
4620
Night
15%6%35%5%3446%7%38%
2640
JulyDay
12%5%25%6%36%6%6%9%35%
4753
Night
10%4145%345%6%9%43%
2736
AugustDay
16%5%25%6%35%5%6%8%32%
4266
Night
11%415%5%2446%8%44%
3203
SeptemberDay
17%6%25%5%3445%7%38%
3773
Night
15%5%24434446%44%
3413
OctoberDay
23%11%35%5%3445%5%27%
3073
Night
24%9%36%5%33446%29%
3747
NovemberDay
17%13%5%7%5%3445%6%26%
2755
Night
17%12%46%6%34446%29%
4400
DecemberDay
18%19%9%10%6%34335%15%
2728
Night
20%16%7%11%7%35%34415%
4774

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%39%10%4
2853
Night
71%38%11%4
4627
FebruaryDay
73%26%12%4
2851
Night
68%29%13%5%
3870
MarchDay
61%310%16%7%
3726
Night
59%210%18%8%
3774
AprilDay
52%28%20%13%1
3968
Night
51%29%20%13%2
3288
MayDay
46%312%22%12%1
4658
Night
43%411%23%14%1
2730
JuneDay
50%412%21%10%
4620
Night
43%412%26%12%
2640
JulyDay
44%413%24%11%1
4438
Night
36%415%26%15%2
2559
AugustDay
47%411%24%11%1
4253
Night
36%415%29%13%1
3192
SeptemberDay
45%39%25%14%1
3773
Night
40%412%26%15%1
3413
OctoberDay
58%311%18%7%
3073
Night
56%312%18%8%
3747
NovemberDay
57%313%16%7%1
2755
Night
57%312%18%7%1
4400
DecemberDay
73%211%9%2
2728
Night
73%310%10%2
4774

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
24%28%31%8%5%2
74
Night
29%19%28%19%3
1364
FebruaryDay
34%21%29%10%3
191
Night
27%21%28%19%3
1223
MarchDay
27%17%23%20%8%1
434
Night
26%19%24%21%7%
1364
AprilDay
31%11%22%18%12%4
420
Night
28%13%24%24%8%
1310
MayDay
20%10%28%20%14%5%
495
Night
15%7%22%37%15%1
714
JuneDay
24%7%26%23%14%2
510
Night
17%6%17%40%16%
660
JulyDay
12%5%28%28%18%6%
515
Night
11%216%44%24%1
672
AugustDay
17%420%22%20%14%
521
Night
13%316%35%27%3
1162
SeptemberDay
17%6%20%21%18%15%
495
Night
18%5%20%28%23%3
1305
OctoberDay
30%9%22%21%13%1
401
Night
30%11%22%24%11%
1240
NovemberDay
22%16%24%24%11%
209
Night
28%15%25%21%8%1
1300
DecemberDay
41%11%22%17%33
62
Night
33%18%27%17%3
1364
Page generated at 2016-09-28 06:54:37. Version ac04

Copyright 2016 A. Danko


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