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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 2017-02-18.

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
31%
14250
13%
44909
9%
14217
36%
14217
16%
32506

By Month

MonthDays of 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
January1st to 15thNight
17%
720
7%
2506
5%
716
20%
716
7%
2061
January16th to endNight
14%
768
10%
2542
4%
768
21%
768
7%
2090
February1st to 15thNight
13%
704
8%
2287
2%
701
20%
701
7%
1862
February16th to endNight
17%
588
10%
1805
5%
588
24%
588
9%
1457
March1st to 15thNight
21%
660
12%
1887
7%
660
27%
660
13%
1439
March16th to endNight
25%
704
16%
1887
8%
704
31%
704
16%
1408
April1st to 15thNight
22%
658
14%
1646
5%
658
27%
658
17%
1245
April16th to endNight
33%
652
17%
1642
8%
652
37%
652
25%
1123
May1st to 15thNight
42%
371
19%
1361
17%
371
49%
371
19%
878
May16th to endNight
47%
342
17%
1369
18%
342
54%
342
22%
811
June1st to 15thNight
40%
330
15%
1320
15%
330
50%
330
17%
856
June16th to endNight
57%
330
13%
1320
19%
330
62%
330
24%
757
July1st to 15thNight
59%
310
14%
1240
20%
310
62%
310
26%
688
July16th to endNight
61%
362
14%
1319
16%
339
65%
339
27%
749
August1st to 15thNight
56%
494
16%
1474
12%
491
60%
491
31%
904
August16th to endNight
59%
668
19%
1718
11%
668
61%
668
36%
1081
September1st to 15thNight
50%
660
19%
1650
10%
660
52%
660
31%
1109
September16th to endNight
48%
657
21%
1800
15%
657
51%
657
29%
1169
October1st to 15thNight
35%
660
17%
1980
15%
660
41%
660
19%
1377
October16th to endNight
22%
704
10%
2142
5%
704
29%
704
13%
1644
November1st to 15thNight
28%
700
16%
2286
12%
700
37%
700
16%
1617
November16th to endNight
23%
720
13%
2520
9%
720
30%
720
11%
1854
December1st to 15thNight
16%
720
6%
2520
4%
720
19%
720
7%
2040
December16th to endNight
14%
768
5%
2688
2%
768
18%
768
5%
2287

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%
45264
Night
15%11%48%6%35%45%6%29%
45081
Cloud CoverDay
16%10%47%6%35%45%6%28%
45274
Night
16%10%47%6%34446%30%
45086
TransparencyDay
55%311%19%9%
44954
Night
55%311%18%9%
44909
SeeingDay
24%10%25%20%13%5%
4723
Night
24%13%23%25%11%1
14251

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
14%13%8%15%9%36%45%414%
1432
16th to endDay
10%14%10%14%11%46%44414%
1680
February1st to 15thDay
16%14%8%16%9%3433316%
1575
16th to endDay
16%16%5%13%11%35%23317%
1427
March1st to 15thDay
17%16%7%10%5%23345%22%
1730
16th to endDay
15%12%7%8%6%3335%5%26%
1985
April1st to 15thDay
19%12%5%7%424446%29%
1972
16th to endDay
16%10%25%5%23346%37%
1996
May1st to 15thDay
15%8%35%5%35%5%5%7%35%
2260
16th to endDay
15%5%25%6%25%5%6%8%35%
2394
June1st to 15thDay
21%8%345%345%5%7%29%
2310
16th to endDay
13%6%36%6%35%6%6%9%32%
2310
July1st to 15thDay
12%425%6%36%6%7%8%36%
2310
16th to endDay
11%5%26%7%36%6%6%10%32%
2443
August1st to 15thDay
14%6%25%6%45%5%7%9%31%
2145
16th to endDay
14%6%25%6%35%6%5%9%33%
2121
September1st to 15thDay
16%7%26%5%24447%37%
1980
16th to endDay
17%6%245%35%446%40%
1829
October1st to 15thDay
20%9%25%5%3435%6%32%
1650
16th to endDay
23%14%27%6%34445%22%
1730
November1st to 15thDay
15%12%46%5%245%5%6%30%
1569
16th to endDay
16%15%5%9%6%2435%7%21%
1440
December1st to 15thDay
15%20%7%10%6%34345%18%
1440
16th to endDay
18%18%9%12%7%2444411%
1536
January1st to 15thNight
17%15%5%12%8%45%445%15%
2506
16th to endNight
12%15%7%11%10%46%445%15%
2542
February1st to 15thNight
13%15%8%13%9%45%43418%
2285
16th to endNight
14%14%6%14%7%35%445%18%
1805
March1st to 15thNight
15%13%6%10%5%34345%26%
1875
16th to endNight
15%14%5%6%5%24435%31%
1887
April1st to 15thNight
19%11%45%5%35%45%5%29%
1646
16th to endNight
19%8%24413345%41%
1642
May1st to 15thNight
15%6%35%5%345%5%6%37%
1361
16th to endNight
11%5%26%5%35%5%7%7%40%
1367
June1st to 15thNight
18%8%35%5%2446%6%34%
1320
16th to endNight
11%3345%36%5%5%9%42%
1320
July1st to 15thNight
7%5%246%36%46%9%44%
1320
16th to endNight
11%41443448%9%41%
1416
August1st to 15thNight
10%425%6%345%6%9%42%
1485
16th to endNight
11%41443446%8%45%
1718
September1st to 15thNight
15%5%245%25%446%43%
1650
16th to endNight
14%5%244345%46%43%
1800
October1st to 15thNight
20%8%26%433345%35%
1980
16th to endNight
25%11%46%5%34446%23%
2142
November1st to 15thNight
15%13%45%5%34346%32%
2286
16th to endNight
15%14%5%8%6%34446%26%
2520
December1st to 15thNight
20%16%6%9%6%3444417%
2520
16th to endNight
18%16%8%13%8%35%34412%
2688

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
14%12%9%15%9%35%44414%
1432
16th to endDay
12%13%9%14%11%45%5%4414%
1680
February1st to 15thDay
16%15%7%15%9%4433316%
1575
16th to endDay
17%15%5%13%10%45%13418%
1427
March1st to 15thDay
18%15%7%11%42334423%
1741
16th to endDay
15%14%6%7%6%34445%27%
1984
April1st to 15thDay
19%12%5%6%424347%29%
1972
16th to endDay
16%11%25%6%24346%37%
1996
May1st to 15thDay
16%8%35%5%35%45%6%35%
2260
16th to endDay
15%6%36%6%25%45%8%35%
2394
June1st to 15thDay
22%7%25%5%25%45%8%28%
2310
16th to endDay
14%6%26%5%36%5%6%9%32%
2310
July1st to 15thDay
12%425%5%36%6%6%8%36%
2310
16th to endDay
12%5%26%7%36%6%6%9%33%
2443
August1st to 15thDay
16%5%346%36%5%6%8%31%
2145
16th to endDay
15%6%25%5%35%5%5%9%33%
2121
September1st to 15thDay
18%6%26%5%2435%7%36%
1980
16th to endDay
17%5%245%34446%40%
1829
October1st to 15thDay
22%8%25%5%3335%6%32%
1650
16th to endDay
23%14%36%6%345%45%23%
1730
November1st to 15thDay
16%12%36%43445%6%31%
1569
16th to endDay
17%14%6%8%6%34447%22%
1440
December1st to 15thDay
16%20%7%10%5%34335%18%
1440
16th to endDay
19%18%9%11%6%34445%12%
1536
January1st to 15thNight
17%14%6%11%8%45%5%4415%
2506
16th to endNight
13%16%7%11%10%46%44416%
2542
February1st to 15thNight
13%14%8%13%8%46%43419%
2278
16th to endNight
14%15%5%14%8%25%345%19%
1805
March1st to 15thNight
17%12%6%10%5%3434426%
1887
16th to endNight
16%13%6%6%5%24335%32%
1887
April1st to 15thNight
20%11%446%2445%6%30%
1646
16th to endNight
19%7%24323245%42%
1642
May1st to 15thNight
15%6%35%6%2446%5%37%
1361
16th to endNight
12%425%5%35%5%6%7%40%
1367
June1st to 15thNight
19%8%36%43346%5%34%
1320
16th to endNight
11%4245%35%5%6%9%42%
1320
July1st to 15thNight
7%4146%35%5%5%10%44%
1320
16th to endNight
12%4244345%7%9%42%
1416
August1st to 15thNight
10%415%6%3446%8%42%
1485
16th to endNight
12%4244235%5%8%45%
1718
September1st to 15thNight
15%5%24434446%43%
1650
16th to endNight
15%5%25%4245%46%44%
1800
October1st to 15thNight
21%7%26%5%33445%35%
1980
16th to endNight
26%11%36%424446%24%
2142
November1st to 15thNight
17%11%36%5%24446%33%
2286
16th to endNight
16%14%5%7%6%34446%26%
2520
December1st to 15thNight
20%16%6%9%6%34445%18%
2520
16th to endNight
19%16%8%12%8%35%34413%
2688

Transparency (when cloud cover <= 30%)
Color Meanings:
Too cloudy to forecast Poor Below Average Average Above average Transparent
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
73%37%11%4
1433
16th to endDay
72%310%9%4
1680
February1st to 15thDay
74%26%12%4
1577
16th to endDay
72%26%13%5%
1427
March1st to 15thDay
65%312%14%5%
1741
16th to endDay
58%29%18%9%
1985
April1st to 15thDay
56%29%20%9%1
1972
16th to endDay
48%27%21%17%2
1996
May1st to 15thDay
48%311%24%11%1
2260
16th to endDay
46%314%21%13%1
2398
June1st to 15thDay
53%410%20%9%
2310
16th to endDay
47%413%22%11%
2310
July1st to 15thDay
43%5%11%26%12%1
2161
16th to endDay
44%415%23%10%
2277
August1st to 15thDay
47%412%23%10%
2132
16th to endDay
46%310%25%12%1
2121
September1st to 15thDay
46%39%25%14%
1980
16th to endDay
45%210%24%15%1
1829
October1st to 15thDay
52%39%21%12%1
1650
16th to endDay
64%212%15%4
1730
November1st to 15thDay
52%413%18%8%2
1569
16th to endDay
62%213%15%6%
1440
December1st to 15thDay
69%212%11%3
1440
16th to endDay
76%29%9%2
1536
January1st to 15thNight
71%39%9%6%
2506
16th to endNight
70%47%13%4
2542
February1st to 15thNight
69%39%12%5%
2287
16th to endNight
68%29%13%5%
1805
March1st to 15thNight
61%211%17%5%
1887
16th to endNight
56%28%19%11%1
1887
April1st to 15thNight
56%39%19%10%1
1646
16th to endNight
46%29%22%17%2
1642
May1st to 15thNight
46%5%10%22%14%1
1361
16th to endNight
40%413%24%14%2
1369
June1st to 15thNight
49%212%24%9%
1320
16th to endNight
37%5%12%28%14%1
1320
July1st to 15thNight
35%413%27%16%1
1240
16th to endNight
36%416%24%14%2
1319
August1st to 15thNight
37%416%29%12%
1474
16th to endNight
35%415%29%14%1
1718
September1st to 15thNight
41%413%24%14%2
1650
16th to endNight
40%410%27%15%1
1800
October1st to 15thNight
50%49%21%13%
1980
16th to endNight
62%214%14%5%
2142
November1st to 15thNight
54%211%18%10%2
2286
16th to endNight
59%312%18%6%
2520
December1st to 15thNight
70%311%11%3
2520
16th to endNight
75%39%9%2
2688

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
MonthDays in MonthOccurrence of each ForecastData
Points
January1st to 15thDay
35%18%33%5%5%3
60
16th to endDay
28%29%30%7%3
88
February1st to 15thDay
36%28%31%21
90
16th to endDay
35%20%27%11%3
152
March1st to 15thDay
30%15%25%21%6%
210
16th to endDay
25%20%21%19%10%2
224
April1st to 15thDay
34%13%22%17%9%2
210
16th to endDay
28%10%21%18%15%5%
210
May1st to 15thDay
25%12%24%19%13%4
228
16th to endDay
16%9%31%20%16%5%
267
June1st to 15thDay
28%9%23%23%13%2
255
16th to endDay
20%6%29%24%16%3
255
July1st to 15thDay
13%431%24%18%6%
245
16th to endDay
11%5%25%32%18%7%
270
August1st to 15thDay
17%423%23%21%8%
253
16th to endDay
16%5%17%22%18%20%
268
September1st to 15thDay
19%7%16%21%20%15%
255
16th to endDay
18%7%23%20%15%14%
254
October1st to 15thDay
27%6%23%20%18%3
255
16th to endDay
35%12%26%18%7%
267
November1st to 15thDay
23%13%21%26%13%
223
16th to endDay
25%20%41%11%1
60
December1st to 15thDay
35%15%30%13%33
60
16th to endDay
39%18%34%7%
64
January1st to 15thNight
29%20%27%17%4
720
16th to endNight
28%17%28%21%3
768
February1st to 15thNight
22%23%30%20%2
704
16th to endNight
31%19%25%19%3
588
March1st to 15thNight
27%19%25%23%4
660
16th to endNight
26%20%22%20%9%
704
April1st to 15thNight
30%15%25%23%4
658
16th to endNight
25%12%23%25%12%
652
May1st to 15thNight
19%8%19%36%14%
371
16th to endNight
11%5%25%39%16%1
343
June1st to 15thNight
22%10%16%36%14%
330
16th to endNight
13%318%45%18%
330
July1st to 15thNight
8%219%44%23%1
310
16th to endNight
13%114%43%24%1
362
August1st to 15thNight
11%217%38%26%3
494
16th to endNight
15%315%33%29%3
668
September1st to 15thNight
19%418%30%24%2
660
16th to endNight
17%7%21%25%22%5%
657
October1st to 15thNight
25%9%21%25%17%1
660
16th to endNight
33%12%24%22%5%
704
November1st to 15thNight
26%11%26%24%10%1
700
16th to endNight
28%18%22%22%6%1
720
December1st to 15thNight
35%17%25%16%4
720
16th to endNight
32%20%27%17%2
768
Page generated at 2017-02-18 16:04:31. Version ac04

Copyright 2017 A. Danko


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