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 2017-08-12.

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%
14754
13%
46508
9%
14721
36%
14721
16%
33580

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
18%
631
12%
1937
6%
631
26%
631
10%
1535
March1st to 15thNight
20%
720
12%
2058
7%
720
26%
720
12%
1580
March16th to endNight
25%
768
16%
2058
8%
768
31%
768
15%
1546
April1st to 15thNight
23%
718
14%
1796
5%
718
27%
718
18%
1353
April16th to endNight
33%
711
17%
1791
8%
711
37%
711
25%
1225
May1st to 15thNight
40%
405
17%
1485
16%
405
47%
405
17%
980
May16th to endNight
47%
374
17%
1497
18%
374
53%
374
22%
892
June1st to 15thNight
43%
360
14%
1440
15%
360
52%
360
18%
913
June16th to endNight
55%
360
14%
1440
20%
360
60%
360
23%
836
July1st to 15thNight
60%
340
14%
1360
19%
340
62%
340
26%
756
July16th to endNight
62%
391
16%
1432
18%
368
65%
368
27%
814
August1st to 15thNight
57%
527
15%
1575
11%
524
60%
524
32%
959
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%
47471
Night
15%10%48%6%35%45%6%29%
46680
Cloud CoverDay
16%10%47%6%35%45%6%28%
47481
Night
16%10%47%6%34446%30%
46685
TransparencyDay
55%311%19%9%
47161
Night
55%311%19%9%
46508
SeeingDay
24%11%26%19%12%5%
5414
Night
24%13%23%26%11%1
14755

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
15%15%5%13%11%35%23419%
1536
March1st to 15thDay
17%15%7%10%6%24345%22%
1888
16th to endDay
16%12%6%8%6%3435%6%26%
2166
April1st to 15thDay
18%12%47%434346%30%
2152
16th to endDay
15%11%25%5%23346%37%
2178
May1st to 15thDay
16%9%36%5%35%5%5%6%33%
2466
16th to endDay
15%6%25%6%35%5%6%8%34%
2618
June1st to 15thDay
20%8%35%5%345%5%7%31%
2520
16th to endDay
13%6%36%6%45%6%6%9%32%
2520
July1st to 15thDay
11%5%25%6%36%6%7%8%36%
2520
16th to endDay
11%5%36%7%36%6%6%10%32%
2637
August1st to 15thDay
14%6%25%6%45%5%7%9%31%
2288
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%5%14%7%35%445%20%
1937
March1st to 15thNight
15%13%6%10%6%34445%25%
2046
16th to endNight
15%13%5%7%6%34435%30%
2058
April1st to 15thNight
19%11%45%5%3445%5%29%
1796
16th to endNight
18%8%24413345%41%
1791
May1st to 15thNight
16%7%36%6%345%5%6%34%
1485
16th to endNight
11%5%26%5%35%5%7%8%39%
1495
June1st to 15thNight
17%8%35%5%2346%6%36%
1440
16th to endNight
11%3345%35%5%5%9%41%
1440
July1st to 15thNight
7%5%246%35%46%9%44%
1440
16th to endNight
11%414435%47%9%42%
1529
August1st to 15thNight
10%415%6%3446%8%44%
1586
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
16%14%5%13%10%45%24419%
1536
March1st to 15thDay
18%15%7%10%5%33345%22%
1899
16th to endDay
16%13%6%7%6%44445%27%
2165
April1st to 15thDay
19%12%5%6%424337%30%
2152
16th to endDay
16%11%25%5%24346%37%
2178
May1st to 15thDay
17%8%36%5%35%45%6%33%
2466
16th to endDay
15%6%36%6%25%45%8%34%
2618
June1st to 15thDay
22%7%25%5%25%45%8%30%
2520
16th to endDay
14%6%26%5%36%5%7%9%31%
2520
July1st to 15thDay
12%425%5%36%6%6%8%35%
2520
16th to endDay
12%5%26%7%36%6%6%9%33%
2637
August1st to 15thDay
16%5%346%35%5%6%9%32%
2288
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%13%8%35%345%20%
1937
March1st to 15thNight
16%12%6%9%6%2434425%
2058
16th to endNight
16%13%6%7%5%24335%31%
2058
April1st to 15thNight
20%11%445%2445%5%30%
1796
16th to endNight
19%7%24423345%41%
1791
May1st to 15thNight
17%7%36%7%2446%5%35%
1485
16th to endNight
12%425%5%35%5%6%8%39%
1495
June1st to 15thNight
18%7%35%42346%5%37%
1440
16th to endNight
12%4235%35%5%6%9%41%
1440
July1st to 15thNight
7%4246%35%5%5%10%44%
1440
16th to endNight
12%4244345%7%9%42%
1529
August1st to 15thNight
10%415%6%3446%8%44%
1586
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
70%26%14%5%
1536
March1st to 15thDay
65%311%13%6%
1899
16th to endDay
59%29%18%9%
2166
April1st to 15thDay
56%29%20%9%1
2152
16th to endDay
48%28%21%16%1
2178
May1st to 15thDay
50%310%23%10%1
2466
16th to endDay
46%314%21%12%
2622
June1st to 15thDay
51%410%21%10%
2520
16th to endDay
46%413%23%10%
2520
July1st to 15thDay
43%5%11%26%12%1
2371
16th to endDay
45%415%23%10%
2471
August1st to 15thDay
46%413%23%10%
2275
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
66%210%14%5%
1937
March1st to 15thNight
62%211%17%6%
2058
16th to endNight
57%28%18%11%1
2058
April1st to 15thNight
55%39%19%10%1
1796
16th to endNight
45%210%22%16%2
1791
May1st to 15thNight
48%410%21%14%1
1485
16th to endNight
40%413%24%13%1
1497
June1st to 15thNight
47%211%26%10%
1440
16th to endNight
38%5%12%27%14%1
1440
July1st to 15thNight
35%5%13%27%16%1
1360
16th to endNight
36%416%25%14%2
1432
August1st to 15thNight
36%417%29%11%
1575
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
31%21%31%12%3
195
March1st to 15thDay
35%15%25%18%4
270
16th to endDay
27%18%25%16%9%2
288
April1st to 15thDay
32%13%26%17%7%2
270
16th to endDay
26%12%25%16%14%4
270
May1st to 15thDay
29%12%24%18%10%3
288
16th to endDay
18%11%32%19%13%4
331
June1st to 15thDay
25%9%24%24%13%1
315
16th to endDay
20%10%32%21%13%2
315
July1st to 15thDay
14%5%33%24%16%5%
305
16th to endDay
11%426%30%19%6%
326
August1st to 15thDay
17%424%22%21%9%
297
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
30%19%25%20%3
631
March1st to 15thNight
28%20%24%22%4
720
16th to endNight
26%20%22%21%9%
768
April1st to 15thNight
31%14%25%23%4
718
16th to endNight
25%12%24%25%11%
711
May1st to 15thNight
21%9%18%36%13%
405
16th to endNight
11%6%25%39%16%1
375
June1st to 15thNight
21%9%15%37%15%
360
16th to endNight
14%320%45%17%
360
July1st to 15thNight
8%219%45%22%1
340
16th to endNight
13%113%43%25%2
391
August1st to 15thNight
12%216%37%26%3
527
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 2017-08-13 14:16:36. Version ac04

Copyright 2017 A. Danko


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