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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 2015-05-26.

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%
12067
12%
37935
8%
12034
35%
12034
15%
27773

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%
1240
7%
4205
3%
1236
20%
1236
6%
3485
FebruaryNight
14%
1107
8%
3503
3%
1104
20%
1104
8%
2863
MarchNight
23%
1240
14%
3432
8%
1240
29%
1240
14%
2592
AprilNight
26%
1191
16%
2989
6%
1191
31%
1191
21%
2159
MayNight
43%
638
18%
2439
17%
638
50%
638
20%
1518
JuneNight
48%
540
14%
2160
16%
540
55%
540
19%
1333
JulyNight
60%
545
13%
2060
16%
522
63%
522
25%
1189
AugustNight
56%
953
16%
2617
10%
950
59%
950
31%
1666
SeptemberNight
45%
1077
19%
2822
11%
1077
49%
1077
27%
1908
OctoberNight
27%
1116
13%
3373
9%
1116
34%
1116
15%
2489
NovemberNight
23%
1180
14%
3995
10%
1180
31%
1180
12%
2939
DecemberNight
15%
1240
5%
4340
2%
1240
17%
1240
6%
3632

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%48%6%35%45%6%27%
38333
Night
16%11%48%6%35%45%6%28%
38107
Cloud CoverDay
17%10%47%6%35%45%6%27%
38343
Night
17%10%47%6%34446%29%
38112
TransparencyDay
56%311%19%8%
38023
Night
56%311%18%8%
37935
SeeingDay
23%9%21%21%16%7%
2551
Night
25%13%23%25%10%
12068

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%10%14%10%35%44414%
2592
Night
16%15%6%11%9%46%445%14%
4205
FebruaryDay
16%15%6%15%10%3423316%
2578
Night
14%15%7%14%8%35%33418%
3501
MarchDay
17%14%7%9%6%24345%25%
3375
Night
16%13%6%8%5%24335%29%
3420
AprilDay
17%11%36%5%23446%33%
3606
Night
19%9%35%5%24345%35%
2989
MayDay
15%7%25%5%35%5%5%7%36%
4150
Night
14%5%25%5%35%5%6%7%38%
2437
JuneDay
17%7%35%5%35%6%6%8%30%
3780
Night
15%6%346%2446%7%37%
2160
JulyDay
12%5%25%6%36%6%6%9%33%
3888
Night
9%5%25%5%35%47%9%41%
2237
AugustDay
15%7%26%6%35%5%6%9%31%
3501
Night
12%425%5%3446%8%41%
2628
SeptemberDay
18%6%26%5%35%446%34%
3117
Night
15%5%245%35%446%41%
2822
OctoberDay
23%11%26%5%3445%6%26%
2765
Night
24%9%36%5%34445%28%
3373
NovemberDay
16%13%5%8%6%245%5%6%24%
2501
Night
16%13%5%7%6%34346%27%
3995
DecemberDay
17%19%8%11%7%3434414%
2480
Night
19%16%8%11%7%35%44414%
4340

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%14%10%35%44415%
2592
Night
16%15%7%11%9%36%5%4415%
4205
FebruaryDay
16%15%6%15%10%4423316%
2578
Night
14%15%7%13%8%36%33418%
3494
MarchDay
17%14%7%9%5%3334425%
3385
Night
17%13%6%8%5%24335%29%
3432
AprilDay
18%12%35%5%24347%33%
3606
Night
20%9%345%24345%35%
2989
MayDay
15%6%35%5%35%45%7%36%
4150
Night
15%5%25%5%35%5%6%6%39%
2437
JuneDay
18%7%26%5%35%5%6%8%30%
3780
Night
15%6%345%3446%7%37%
2160
JulyDay
13%5%25%6%36%6%6%9%33%
3888
Night
10%4245%35%5%6%10%41%
2237
AugustDay
16%6%35%6%45%5%6%8%31%
3501
Night
12%5%25%5%345%6%8%41%
2628
SeptemberDay
19%6%26%5%35%35%7%34%
3117
Night
15%5%244345%46%41%
2822
OctoberDay
23%11%25%5%3445%5%26%
2765
Night
24%9%36%5%33446%29%
3373
NovemberDay
17%14%5%7%5%2445%6%25%
2501
Night
17%13%47%6%34446%28%
3995
DecemberDay
18%19%9%11%6%3433414%
2480
Night
19%16%8%11%7%35%34415%
4340

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%11%3
2593
Night
71%48%11%3
4205
FebruaryDay
74%26%12%4
2580
Night
70%29%12%4
3503
MarchDay
62%210%16%7%
3386
Night
59%210%19%8%
3432
AprilDay
52%28%21%13%2
3606
Night
51%39%20%12%2
2989
MayDay
46%313%23%11%1
4154
Night
43%411%23%13%1
2439
JuneDay
50%413%21%8%
3780
Night
44%414%25%11%
2160
JulyDay
45%5%14%24%9%1
3573
Night
38%416%24%14%1
2060
AugustDay
49%310%24%11%
3488
Night
38%415%28%12%
2617
SeptemberDay
50%210%25%11%
3117
Night
43%411%26%12%1
2822
OctoberDay
58%311%18%7%
2765
Night
57%312%17%8%
3373
NovemberDay
58%313%16%6%1
2501
Night
59%211%18%6%1
3995
DecemberDay
74%211%9%1
2480
Night
73%311%9%1
4340

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
30%18%27%19%3
1240
FebruaryDay
36%22%19%15%5%1
94
Night
28%21%27%19%3
1107
MarchDay
27%17%21%20%10%2
310
Night
27%20%24%21%7%
1240
AprilDay
28%12%22%19%14%3
300
Night
28%14%25%24%7%
1191
MayDay
17%8%29%21%15%6%
350
Night
16%7%23%35%15%1
639
JuneDay
23%420%27%20%4
270
Night
17%6%18%40%16%
540
JulyDay
13%323%26%21%10%
267
Night
12%214%43%25%1
545
AugustDay
20%316%16%23%19%
277
Night
15%316%35%26%2
953
SeptemberDay
23%6%15%15%20%17%
269
Night
19%6%21%27%21%3
1077
OctoberDay
31%10%18%24%13%2
279
Night
30%10%22%24%11%
1116
NovemberDay
21%13%22%27%14%
135
Night
28%15%25%21%7%1
1180
DecemberNight
33%18%27%16%3
1240
Page generated at 2015-05-27 12:02:39. Version ac04

Copyright 2015 A. Danko


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