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 2018-02-14.

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%
15495
13%
48831
9%
15462
36%
15462
16%
35222

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%
780
7%
2716
5%
776
20%
776
7%
2241
January16th to endNight
15%
832
9%
2754
4%
832
22%
832
8%
2247
February1st to 15thNight
12%
760
7%
2468
2%
757
19%
757
7%
2018
February16th to endNight
19%
631
12%
1937
6%
631
27%
631
10%
1535
March1st to 15thNight
20%
720
12%
2058
7%
720
25%
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
36%
711
25%
1225
May1st to 15thNight
41%
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
59%
360
23%
836
July1st to 15thNight
59%
340
14%
1360
19%
340
61%
340
26%
756
July16th to endNight
61%
391
16%
1432
18%
368
65%
368
27%
814
August1st to 15thNight
56%
539
15%
1609
11%
536
60%
536
32%
978
August16th to endNight
60%
729
20%
1875
12%
729
61%
729
37%
1167
September1st to 15thNight
49%
720
18%
1800
10%
720
51%
720
30%
1213
September16th to endNight
51%
717
24%
1964
18%
717
54%
717
30%
1253
October1st to 15thNight
36%
720
17%
2160
14%
720
42%
720
20%
1485
October16th to endNight
23%
768
12%
2337
7%
768
30%
768
14%
1765
November1st to 15thNight
27%
760
16%
2482
11%
760
36%
760
16%
1762
November16th to endNight
23%
780
14%
2730
9%
780
31%
780
12%
1984
December1st to 15thNight
17%
780
6%
2730
4%
780
20%
780
7%
2199
December16th to endNight
13%
832
5%
2912
2%
832
17%
832
5%
2480

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
15%10%47%6%35%45%7%28%
49252
Night
15%10%48%6%35%45%6%29%
49003
Cloud CoverDay
16%10%47%6%35%45%6%29%
49262
Night
16%10%47%6%34446%30%
49008
TransparencyDay
55%310%19%9%
48942
Night
55%311%19%9%
48831
SeeingDay
24%11%26%19%12%5%
5985
Night
24%13%23%26%11%1
15496

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%14%9%46%45%414%
1552
16th to endDay
11%14%10%13%11%36%44415%
1820
February1st to 15thDay
17%13%7%15%9%35%33315%
1695
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%
2340
16th to endDay
13%6%26%6%45%6%6%9%33%
2315
September1st to 15thDay
17%6%26%5%24448%36%
2160
16th to endDay
15%5%145%35%446%41%
1995
October1st to 15thDay
19%9%25%5%3445%6%33%
1800
16th to endDay
22%13%27%6%34445%24%
1887
November1st to 15thDay
16%12%46%5%245%5%6%30%
1703
16th to endDay
16%15%5%9%6%3435%7%22%
1560
December1st to 15thDay
15%19%7%11%7%34345%18%
1560
16th to endDay
18%18%9%12%7%3444411%
1664
January1st to 15thNight
17%14%5%11%9%5%6%445%15%
2716
16th to endNight
12%15%7%11%10%46%445%16%
2754
February1st to 15thNight
13%14%8%13%9%45%43417%
2466
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
9%415%6%345%6%8%43%
1620
16th to endNight
11%41443446%8%46%
1875
September1st to 15thNight
14%5%245%36%446%42%
1800
16th to endNight
13%5%244345%46%45%
1964
October1st to 15thNight
20%7%26%433345%36%
2160
16th to endNight
24%11%36%5%3445%6%25%
2337
November1st to 15thNight
15%12%46%6%34346%31%
2482
16th to endNight
15%14%5%7%6%3435%6%26%
2730
December1st to 15thNight
19%16%6%10%6%3444417%
2730
16th to endNight
18%16%8%13%8%45%34412%
2912

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%8%14%9%46%445%14%
1552
16th to endDay
12%13%9%13%10%45%5%45%15%
1820
February1st to 15thDay
17%14%7%14%10%4433315%
1695
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%
2340
16th to endDay
14%6%25%5%35%5%6%9%34%
2315
September1st to 15thDay
18%6%26%5%35%45%7%36%
2160
16th to endDay
16%5%245%34446%41%
1995
October1st to 15thDay
21%7%25%5%3445%6%33%
1800
16th to endDay
22%13%26%6%345%45%25%
1887
November1st to 15thDay
17%12%36%5%3445%6%30%
1703
16th to endDay
17%15%6%7%6%3445%7%23%
1560
December1st to 15thDay
16%19%7%11%6%34335%18%
1560
16th to endDay
19%18%9%11%6%44445%11%
1664
January1st to 15thNight
17%13%6%11%9%5%6%5%4415%
2716
16th to endNight
13%15%7%11%9%46%5%4417%
2754
February1st to 15thNight
14%14%7%13%8%46%5%3318%
2459
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%43%
1620
16th to endNight
11%41442345%8%46%
1875
September1st to 15thNight
14%5%244345%46%42%
1800
16th to endNight
14%5%244245%46%45%
1964
October1st to 15thNight
20%7%26%5%23446%36%
2160
16th to endNight
26%11%36%424346%26%
2337
November1st to 15thNight
16%11%36%6%34445%32%
2482
16th to endNight
16%14%5%6%6%34346%27%
2730
December1st to 15thNight
19%15%6%9%7%44345%18%
2730
16th to endNight
18%16%8%12%8%45%34413%
2912

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
72%37%11%4
1553
16th to endDay
71%311%9%4
1820
February1st to 15thDay
74%26%12%4
1697
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%24%10%
2327
16th to endDay
45%310%26%12%1
2315
September1st to 15thDay
47%38%25%14%
2160
16th to endDay
43%210%26%15%1
1995
October1st to 15thDay
51%39%22%12%1
1800
16th to endDay
62%212%17%5%
1887
November1st to 15thDay
53%313%17%8%2
1703
16th to endDay
61%213%15%6%
1560
December1st to 15thDay
69%311%11%3
1560
16th to endDay
76%29%8%2
1664
January1st to 15thNight
72%38%9%6%
2716
16th to endNight
69%48%13%4
2754
February1st to 15thNight
70%39%11%5%
2468
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%
1609
16th to endNight
34%415%30%15%1
1875
September1st to 15thNight
41%413%23%14%2
1800
16th to endNight
39%410%28%17%1
1964
October1st to 15thNight
49%410%21%13%
2160
16th to endNight
60%213%16%6%
2337
November1st to 15thNight
54%211%18%10%2
2482
16th to endNight
58%312%19%6%
2730
December1st to 15thNight
69%311%11%3
2730
16th to endNight
75%38%9%2
2912

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
33%22%33%5%32
90
16th to endDay
25%25%35%10%3
132
February1st to 15thDay
36%28%33%1
130
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
16%5%26%21%20%9%
313
16th to endDay
14%6%21%22%18%17%
332
September1st to 15thDay
20%7%18%20%19%13%
315
16th to endDay
15%7%20%22%20%13%
314
October1st to 15thDay
25%6%25%21%16%5%
315
16th to endDay
31%14%27%18%7%
328
November1st to 15thDay
27%13%22%23%12%1
267
16th to endDay
31%22%36%8%1
90
December1st to 15thDay
31%18%32%13%22
90
16th to endDay
44%16%31%7%
96
January1st to 15thNight
29%21%27%17%4
780
16th to endNight
28%17%28%23%3
832
February1st to 15thNight
24%23%29%20%2
760
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
11%217%37%26%3
539
16th to endNight
14%315%34%29%3
729
September1st to 15thNight
19%5%18%30%24%2
720
16th to endNight
16%7%20%24%25%6%
717
October1st to 15thNight
25%9%20%25%17%1
720
16th to endNight
33%13%24%23%5%
768
November1st to 15thNight
26%12%26%24%10%1
760
16th to endNight
28%18%23%22%6%1
780
December1st to 15thNight
34%18%24%18%4
780
16th to endNight
31%21%27%17%1
832
Page generated at 2018-02-15 10:58:48. Version ac04

Copyright 2018 A. Danko


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