Cincinnati Astronomical Society Dark Sky Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cincinnati Astronomical Society Dark Sky Site clear sky chart from 2005-11-05 to 2018-04-23.

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
39%
16325
18%
49529
12%
16283
45%
16283
22%
33328

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
16%
780
12%
2522
5%
776
24%
776
9%
1984
January16th to endNight
17%
832
14%
2704
6%
832
26%
832
12%
1993
February1st to 15thNight
18%
762
12%
2389
4%
761
26%
761
13%
1777
February16th to endNight
16%
683
12%
2049
5%
683
24%
683
13%
1547
March1st to 15thNight
23%
780
16%
2230
9%
780
30%
780
16%
1609
March16th to endNight
28%
832
16%
2288
9%
832
33%
832
20%
1630
April1st to 15thNight
27%
678
18%
2035
9%
678
36%
678
22%
1356
April16th to endNight
34%
558
20%
1672
10%
558
43%
558
22%
1133
May1st to 15thNight
35%
540
15%
1620
8%
540
40%
540
20%
1117
May16th to endNight
58%
562
16%
1684
12%
561
61%
561
28%
1076
June1st to 15thNight
64%
540
18%
1620
14%
540
68%
540
35%
948
June16th to endNight
61%
540
17%
1620
13%
540
65%
540
34%
948
July1st to 15thNight
59%
510
15%
1530
13%
510
60%
510
29%
954
July16th to endNight
71%
564
18%
1595
15%
531
75%
531
36%
940
August1st to 15thNight
71%
539
23%
1609
18%
536
73%
536
34%
955
August16th to endNight
72%
573
25%
1788
23%
573
74%
573
38%
992
September1st to 15thNight
62%
695
26%
1955
20%
695
66%
695
35%
1173
September16th to endNight
59%
717
28%
1980
22%
717
63%
717
33%
1234
October1st to 15thNight
51%
720
27%
2051
22%
720
57%
720
34%
1226
October16th to endNight
37%
768
24%
2343
18%
768
46%
768
23%
1529
November1st to 15thNight
40%
760
24%
2471
20%
760
49%
760
27%
1481
November16th to endNight
31%
780
20%
2535
14%
780
39%
780
18%
1716
December1st to 15thNight
24%
780
11%
2535
7%
780
30%
780
13%
1885
December16th to endNight
18%
832
12%
2704
5%
832
25%
832
10%
2125

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%8%35%5%3445%6%36%
49970
Night
15%8%35%42445%7%38%
49722
Cloud CoverDay
16%8%35%5%3445%6%36%
49980
Night
15%8%35%42445%7%38%
49726
TransparencyDay
47%6%11%19%12%1
49681
Night
45%6%11%20%14%2
49529
SeeingDay
20%11%25%20%14%7%
6060
Night
19%10%24%26%15%2
16328

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
21%10%6%9%6%2444424%
1746
16th to endDay
18%13%6%6%5%23445%27%
1872
February1st to 15thDay
20%12%49%5%2334428%
1799
16th to endDay
19%14%46%5%34435%27%
1710
March1st to 15thDay
20%10%46%43343432%
2047
16th to endDay
21%10%45%5%33345%33%
2288
April1st to 15thDay
18%9%35%422346%39%
2251
16th to endDay
17%6%25%5%33347%38%
2402
May1st to 15thDay
23%7%35%434445%32%
2331
16th to endDay
11%5%35%6%45%5%6%8%37%
2431
June1st to 15thDay
10%425%5%35%5%6%8%41%
2340
16th to endDay
10%5%25%5%46%6%6%9%37%
2340
July1st to 15thDay
15%5%35%6%35%5%6%7%34%
2340
16th to endDay
10%5%245%36%6%7%10%35%
2465
August1st to 15thDay
8%5%25%6%45%6%7%10%38%
2340
16th to endDay
8%4245%36%6%7%8%43%
2411
September1st to 15thDay
14%5%244345%5%6%44%
1992
16th to endDay
15%6%25%5%24345%45%
1980
October1st to 15thDay
13%5%244245%46%46%
1908
16th to endDay
21%7%13323235%44%
1878
November1st to 15thDay
12%9%3442433446%
1717
16th to endDay
16%10%35%424346%37%
1755
December1st to 15thDay
23%12%5%7%5%2344424%
1755
16th to endDay
22%13%6%7%5%23335%25%
1872
January1st to 15thNight
19%13%5%11%6%3443423%
2522
16th to endNight
18%13%47%5%2434429%
2704
February1st to 15thNight
21%12%47%5%23345%29%
2387
16th to endNight
19%15%37%6%34345%28%
2049
March1st to 15thNight
17%9%47%5%3445%6%31%
2218
16th to endNight
17%8%36%5%3345%7%34%
2288
April1st to 15thNight
16%6%36%42345%6%38%
2035
16th to endNight
16%5%26%5%24446%39%
1672
May1st to 15thNight
18%7%35%43345%8%36%
1620
16th to endNight
9%324435%5%7%10%42%
1682
June1st to 15thNight
5%214435%5%6%10%49%
1620
16th to endNight
7%413335%5%7%10%46%
1620
July1st to 15thNight
10%5%35%33445%10%44%
1620
16th to endNight
5%314436%5%7%8%49%
1703
August1st to 15thNight
5%315%5%25%5%6%10%48%
1620
16th to endNight
5%3134245%5%10%52%
1788
September1st to 15thNight
11%413413347%52%
1955
16th to endNight
12%425%423445%50%
1980
October1st to 15thNight
10%5%134235%48%49%
2051
16th to endNight
18%6%24434345%42%
2343
November1st to 15thNight
15%5%24423446%46%
2471
16th to endNight
19%8%35%424336%37%
2535
December1st to 15thNight
22%10%47%5%24346%27%
2535
16th to endNight
20%15%6%7%5%3443423%
2704

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
21%11%6%9%6%2444424%
1746
16th to endDay
18%14%5%7%5%23445%27%
1872
February1st to 15thDay
20%12%5%8%5%2344428%
1799
16th to endDay
19%14%46%5%34435%27%
1710
March1st to 15thDay
20%11%46%43343432%
2058
16th to endDay
21%10%35%5%33345%33%
2287
April1st to 15thDay
18%9%35%422346%39%
2251
16th to endDay
17%7%25%5%3335%7%38%
2402
May1st to 15thDay
23%7%35%434445%31%
2331
16th to endDay
11%6%25%6%45%5%6%8%37%
2431
June1st to 15thDay
10%426%5%36%5%5%8%41%
2340
16th to endDay
10%4245%46%7%6%9%37%
2340
July1st to 15thDay
15%5%25%6%36%5%6%8%34%
2340
16th to endDay
10%5%245%46%6%7%10%35%
2465
August1st to 15thDay
8%5%246%45%6%7%10%38%
2340
16th to endDay
8%4235%36%6%7%8%43%
2411
September1st to 15thDay
14%5%245%25%45%6%44%
1992
16th to endDay
15%6%245%24345%45%
1980
October1st to 15thDay
14%5%14424446%46%
1908
16th to endDay
21%7%13322335%43%
1878
November1st to 15thDay
12%9%3442434446%
1717
16th to endDay
17%10%35%423436%38%
1755
December1st to 15thDay
23%12%5%7%5%23445%24%
1755
16th to endDay
22%13%6%7%5%23335%25%
1872
January1st to 15thNight
19%12%5%11%6%3444423%
2522
16th to endNight
18%13%47%5%2434429%
2704
February1st to 15thNight
21%12%46%433345%29%
2380
16th to endNight
19%14%47%5%34335%28%
2049
March1st to 15thNight
17%9%46%5%345%5%6%31%
2230
16th to endNight
17%8%36%5%3435%7%34%
2288
April1st to 15thNight
16%6%45%43346%6%38%
2035
16th to endNight
16%5%25%6%2445%6%39%
1672
May1st to 15thNight
18%7%35%43336%8%35%
1619
16th to endNight
8%324435%5%7%11%42%
1682
June1st to 15thNight
5%214435%5%6%11%49%
1620
16th to endNight
7%313325%5%7%10%47%
1620
July1st to 15thNight
10%5%344335%5%10%44%
1620
16th to endNight
5%314435%5%7%9%49%
1703
August1st to 15thNight
5%3145%25%5%6%10%48%
1620
16th to endNight
5%3134246%5%10%52%
1788
September1st to 15thNight
11%414423347%52%
1955
16th to endNight
12%325%42445%5%50%
1980
October1st to 15thNight
10%5%13424448%49%
2051
16th to endNight
18%6%14424345%42%
2343
November1st to 15thNight
16%5%24423446%46%
2471
16th to endNight
19%9%35%424336%37%
2535
December1st to 15thNight
22%10%48%5%23346%27%
2535
16th to endNight
20%16%6%7%5%2434423%
2704

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
62%49%14%9%
1747
16th to endDay
58%413%17%5%
1872
February1st to 15thDay
58%412%14%8%
1801
16th to endDay
58%5%10%19%6%
1710
March1st to 15thDay
54%411%20%8%1
2058
16th to endDay
54%5%8%20%9%1
2288
April1st to 15thDay
46%410%24%11%2
2251
16th to endDay
45%5%10%19%14%4
2402
May1st to 15thDay
53%6%12%17%8%2
2331
16th to endDay
42%9%14%19%12%1
2435
June1st to 15thDay
38%8%13%22%15%
2340
16th to endDay
40%9%13%18%15%2
2340
July1st to 15thDay
46%7%12%16%15%2
2201
16th to endDay
40%9%16%19%12%1
2310
August1st to 15thDay
37%9%15%21%14%1
2327
16th to endDay
34%8%14%23%15%3
2411
September1st to 15thDay
39%6%11%19%18%4
1992
16th to endDay
41%5%8%19%24%1
1980
October1st to 15thDay
37%5%10%24%19%2
1908
16th to endDay
44%310%26%13%1
1878
November1st to 15thDay
41%39%23%16%5%
1717
16th to endDay
47%310%22%14%
1755
December1st to 15thDay
60%5%11%14%6%
1755
16th to endDay
62%410%14%7%
1872
January1st to 15thNight
64%46%13%9%
2522
16th to endNight
57%410%18%7%1
2704
February1st to 15thNight
57%410%17%7%1
2389
16th to endNight
59%411%16%8%
2049
March1st to 15thNight
51%5%9%20%11%1
2230
16th to endNight
49%5%12%21%10%
2288
April1st to 15thNight
44%5%10%20%16%2
2035
16th to endNight
44%6%9%17%15%6%
1672
May1st to 15thNight
46%7%13%20%9%2
1620
16th to endNight
34%10%16%19%15%3
1684
June1st to 15thNight
27%9%16%24%19%2
1620
16th to endNight
29%8%17%22%19%2
1620
July1st to 15thNight
35%7%12%21%18%4
1530
16th to endNight
27%9%17%25%17%2
1595
August1st to 15thNight
29%9%15%24%18%3
1609
16th to endNight
26%8%14%25%20%4
1788
September1st to 15thNight
31%6%12%21%22%5%
1955
16th to endNight
35%6%6%21%29%1
1980
October1st to 15thNight
32%5%12%26%19%3
2051
16th to endNight
43%49%25%15%2
2343
November1st to 15thNight
38%310%21%21%4
2471
16th to endNight
49%38%22%14%1
2535
December1st to 15thNight
58%410%17%8%
2535
16th to endNight
63%5%9%15%5%
2704

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
28%25%28%11%3
135
16th to endDay
37%22%31%7%
144
February1st to 15thDay
34%28%28%5%1
135
16th to endDay
34%18%39%7%
120
March1st to 15thDay
32%20%29%14%2
243
16th to endDay
28%19%28%16%7%
352
April1st to 15thDay
24%19%28%18%9%
330
16th to endDay
21%11%31%15%13%5%
289
May1st to 15thDay
28%13%29%12%11%4
288
16th to endDay
14%9%30%22%12%10%
331
June1st to 15thDay
9%7%23%32%16%10%
315
16th to endDay
12%12%26%22%14%11%
315
July1st to 15thDay
21%5%19%25%14%13%
305
16th to endDay
10%214%28%23%20%
326
August1st to 15thDay
9%216%25%27%18%
313
16th to endDay
9%121%25%26%14%
332
September1st to 15thDay
13%416%23%29%11%
315
16th to endDay
18%415%20%30%11%
314
October1st to 15thDay
15%7%22%26%19%8%
315
16th to endDay
22%11%30%23%9%2
294
November1st to 15thDay
22%14%25%25%8%2
135
16th to endDay
25%22%31%15%5%
135
December1st to 15thDay
27%25%29%8%8%
135
16th to endDay
32%29%32%5%
144
January1st to 15thNight
29%18%30%16%4
780
16th to endNight
27%19%32%19%1
832
February1st to 15thNight
30%17%29%21%
764
16th to endNight
27%18%33%18%1
683
March1st to 15thNight
25%16%29%22%4
780
16th to endNight
21%12%32%23%9%
832
April1st to 15thNight
21%14%32%22%7%
678
16th to endNight
19%9%31%28%10%1
558
May1st to 15thNight
21%9%28%26%13%
540
16th to endNight
9%422%33%26%3
563
June1st to 15thNight
5%222%42%26%1
540
16th to endNight
8%222%36%27%2
540
July1st to 15thNight
13%217%35%27%3
510
16th to endNight
6%12%35%38%6%
564
August1st to 15thNight
6%111%38%36%6%
539
16th to endNight
6%12%36%36%7%
573
September1st to 15thNight
14%312%30%32%6%
695
16th to endNight
12%415%28%32%5%
717
October1st to 15thNight
13%6%24%29%22%4
720
16th to endNight
22%12%25%25%12%1
768
November1st to 15thNight
18%11%24%25%18%1
760
16th to endNight
25%13%25%23%10%1
780
December1st to 15thNight
29%16%24%22%7%
780
16th to endNight
29%16%30%20%3
832
Page generated at 2018-04-24 10:03:04. Version ac04

Copyright 2018 A. Danko


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