Ex Nihilo Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ex Nihilo Observatory clear sky chart from 2005-11-05 to 2017-09-16.

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
48%
15555
23%
46923
15%
15511
56%
15511
28%
29063

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
28%
720
23%
2327
10%
716
44%
716
20%
1439
January16th to endNight
26%
768
25%
2478
11%
768
43%
768
21%
1531
February1st to 15thNight
30%
704
27%
2111
10%
700
47%
700
27%
1276
February16th to endNight
25%
631
24%
1893
9%
631
39%
631
25%
1171
March1st to 15thNight
34%
720
24%
2040
12%
720
45%
720
27%
1291
March16th to endNight
38%
768
22%
2112
12%
768
46%
768
30%
1301
April1st to 15thNight
43%
677
25%
1935
15%
677
52%
677
34%
1133
April16th to endNight
49%
540
25%
1676
15%
540
58%
540
32%
989
May1st to 15thNight
49%
540
20%
1620
10%
540
56%
540
29%
1005
May16th to endNight
60%
561
21%
1683
15%
561
64%
561
30%
1040
June1st to 15thNight
67%
540
17%
1620
14%
540
69%
540
31%
1016
June16th to endNight
74%
540
16%
1620
14%
540
75%
540
32%
991
July1st to 15thNight
69%
510
12%
1530
10%
510
70%
510
27%
1010
July16th to endNight
75%
564
15%
1595
13%
531
78%
531
27%
1052
August1st to 15thNight
67%
539
17%
1609
17%
536
68%
536
25%
1081
August16th to endNight
66%
580
17%
1906
18%
580
67%
580
21%
1300
September1st to 15thNight
63%
720
19%
1980
17%
720
64%
720
27%
1321
September16th to endNight
55%
661
23%
1826
17%
661
60%
661
28%
1206
October1st to 15thNight
52%
660
31%
1842
24%
660
59%
660
34%
1121
October16th to endNight
53%
704
34%
2112
26%
704
66%
704
38%
1155
November1st to 15thNight
51%
700
31%
2232
25%
700
62%
700
37%
1190
November16th to endNight
42%
720
27%
2340
18%
720
54%
720
29%
1337
December1st to 15thNight
37%
720
24%
2340
15%
720
48%
720
23%
1451
December16th to endNight
32%
768
22%
2496
14%
768
43%
768
20%
1656

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
13%425%5%35%45%7%42%
47827
Night
13%42442445%7%45%
47122
TransparencyDay
39%6%11%19%17%4
47528
Night
36%6%11%19%19%6%
46925
SeeingDay
17%6%19%22%22%12%
5425
Night
15%7%21%28%22%3
15557

By Month

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
16%5%34414445%44%
1611
16th to endDay
18%5%24323346%45%
1743
February1st to 15thDay
15%6%2432345%446%
1750
16th to endDay
17%6%24323436%45%
1580
March1st to 15thDay
15%424424345%46%
1919
16th to endDay
16%424424446%45%
2111
April1st to 15thDay
12%435%5%3445%6%45%
2023
16th to endDay
11%425%424449%47%
2283
May1st to 15thDay
11%425%5%2445%8%44%
2331
16th to endDay
11%4245%45%5%5%8%40%
2431
June1st to 15thDay
9%325%6%47%6%8%10%34%
2340
16th to endDay
4215%438%7%8%10%42%
2340
July1st to 15thDay
9%426%6%48%8%9%10%30%
2340
16th to endDay
7%436%7%5%8%8%7%10%31%
2465
August1st to 15thDay
9%5%25%7%5%7%7%8%10%30%
2340
16th to endDay
14%6%27%7%46%6%7%9%26%
2279
September1st to 15thDay
13%5%25%5%445%6%7%38%
1980
16th to endDay
18%6%24324347%41%
1824
October1st to 15thDay
15%31331224456%
1786
16th to endDay
11%32431323459%
1760
November1st to 15thDay
12%413314245%56%
1623
16th to endDay
15%414223336%50%
1620
December1st to 15thDay
18%5%245%23446%41%
1620
16th to endDay
24%7%24424235%37%
1728
January1st to 15thNight
18%6%2432433446%
2327
16th to endNight
18%5%23324345%45%
2478
February1st to 15thNight
15%414424345%50%
2103
16th to endNight
17%423434335%48%
1893
March1st to 15thNight
14%4235%2435%5%47%
2040
16th to endNight
12%42441335%6%49%
2112
April1st to 15thNight
12%31332345%7%52%
1935
16th to endNight
10%32442336%7%49%
1676
May1st to 15thNight
10%5%24425%45%8%45%
1619
16th to endNight
8%424436%46%8%46%
1682
June1st to 15thNight
6%414426%7%8%12%40%
1620
16th to endNight
5%324436%8%8%12%41%
1620
July1st to 15thNight
7%5%26%6%25%6%8%14%34%
1620
16th to endNight
5%215%5%48%8%9%15%33%
1703
August1st to 15thNight
9%5%25%5%35%6%6%12%35%
1620
16th to endNight
13%4145%36%6%7%9%34%
1906
September1st to 15thNight
10%5%25%6%45%5%6%8%40%
1980
16th to endNight
15%415%42345%7%43%
1826
October1st to 15thNight
14%423323245%53%
1842
16th to endNight
9%32332433460%
2112
November1st to 15thNight
12%312213236%58%
2232
16th to endNight
16%312323346%51%
2340
December1st to 15thNight
15%6%25%423436%45%
2340
16th to endNight
20%6%24433346%38%
2496

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
41%49%15%24%4
1612
16th to endDay
39%46%19%22%7%
1743
February1st to 15thDay
40%38%20%23%4
1752
16th to endDay
41%36%21%20%7%
1580
March1st to 15thDay
39%48%19%21%6%
1919
16th to endDay
40%5%10%21%17%4
2112
April1st to 15thDay
38%39%21%21%6%
2023
16th to endDay
33%6%8%21%23%6%
2283
May1st to 15thDay
37%5%12%21%19%3
2331
16th to endDay
40%7%12%22%13%2
2435
June1st to 15thDay
39%11%17%20%8%1
2340
16th to endDay
31%9%17%23%15%2
2340
July1st to 15thDay
42%12%16%19%7%2
2201
16th to endDay
41%11%17%19%7%1
2310
August1st to 15thDay
44%10%15%19%9%1
2327
16th to endDay
51%10%13%13%9%1
2279
September1st to 15thDay
42%9%11%18%15%2
1980
16th to endDay
42%411%18%17%5%
1824
October1st to 15thDay
32%410%19%26%7%
1786
16th to endDay
30%25%18%31%11%
1760
November1st to 15thDay
31%37%15%31%11%
1623
16th to endDay
36%36%16%28%7%
1620
December1st to 15thDay
43%5%7%19%15%8%
1620
16th to endDay
50%36%18%13%7%
1728
January1st to 15thNight
42%27%17%24%6%
2327
16th to endNight
41%35%17%23%8%
2478
February1st to 15thNight
37%26%20%22%10%
2112
16th to endNight
38%37%19%23%6%
1893
March1st to 15thNight
37%5%9%17%21%9%
2040
16th to endNight
35%410%22%20%5%
2112
April1st to 15thNight
31%49%24%23%7%
1935
16th to endNight
32%5%9%21%20%9%
1676
May1st to 15thNight
36%6%13%20%19%3
1620
16th to endNight
32%9%13%26%14%3
1684
June1st to 15thNight
32%10%20%25%10%1
1620
16th to endNight
30%10%18%23%13%3
1620
July1st to 15thNight
36%12%21%20%7%2
1530
16th to endNight
34%13%21%19%8%2
1595
August1st to 15thNight
40%9%16%21%11%
1609
16th to endNight
41%12%16%17%11%
1906
September1st to 15thNight
39%8%14%18%15%3
1980
16th to endNight
38%7%11%18%16%6%
1826
October1st to 15thNight
34%49%17%25%8%
1842
16th to endNight
28%35%17%30%13%
2112
November1st to 15thNight
28%36%17%30%14%
2232
16th to endNight
34%36%17%26%10%
2340
December1st to 15thNight
40%47%20%18%8%
2340
16th to endNight
46%49%15%18%6%
2496

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%10%36%17%5%1
90
16th to endDay
25%23%36%12%2
96
February1st to 15thDay
21%22%37%18%
90
16th to endDay
29%16%37%14%2
81
March1st to 15thDay
21%14%30%21%11%
209
16th to endDay
17%11%27%27%14%2
288
April1st to 15thDay
19%9%27%18%22%3
270
16th to endDay
14%6%26%26%21%4
270
May1st to 15thDay
13%10%29%17%14%13%
288
16th to endDay
17%318%21%23%14%
331
June1st to 15thDay
11%29%26%31%19%
315
16th to endDay
7%114%26%25%24%
315
July1st to 15thDay
10%9%26%28%24%
305
16th to endDay
7%8%21%38%23%
326
August1st to 15thDay
18%7%23%27%21%
313
16th to endDay
17%110%21%29%19%
332
September1st to 15thDay
15%313%21%31%15%
315
16th to endDay
24%213%24%24%11%
257
October1st to 15thDay
20%421%25%20%8%
255
16th to endDay
16%6%14%25%29%7%
272
November1st to 15thDay
28%9%19%22%17%3
131
16th to endDay
12%15%24%30%14%3
90
December1st to 15thDay
27%10%35%18%7%
90
16th to endDay
40%11%29%12%5%1
96
January1st to 15thNight
25%15%26%24%8%
720
16th to endNight
21%16%32%25%3
768
February1st to 15thNight
20%12%32%30%4
704
16th to endNight
19%15%34%26%3
631
March1st to 15thNight
18%13%30%30%7%
720
16th to endNight
16%9%30%29%12%
768
April1st to 15thNight
15%10%29%27%15%
677
16th to endNight
12%6%25%33%20%1
540
May1st to 15thNight
12%5%25%30%22%2
540
16th to endNight
11%217%30%33%4
563
June1st to 15thNight
9%115%30%32%10%
540
16th to endNight
6%10%33%38%10%
540
July1st to 15thNight
10%7%27%41%12%
510
16th to endNight
417%28%48%9%
564
August1st to 15thNight
13%15%25%44%9%
539
16th to endNight
15%16%25%39%11%
580
September1st to 15thNight
12%111%23%41%9%
720
16th to endNight
18%115%31%30%2
661
October1st to 15thNight
17%322%26%25%4
660
16th to endNight
11%6%22%31%24%3
704
November1st to 15thNight
13%6%23%32%22%1
700
16th to endNight
17%10%25%28%16%1
720
December1st to 15thNight
18%11%25%30%12%
720
16th to endNight
25%11%25%30%7%
768
Page generated at 2017-09-17 12:05:46. Version ac04

Copyright 2017 A. Danko


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