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 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
48%
16414
23%
49526
15%
16370
56%
16370
28%
30641

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%
780
23%
2522
10%
776
44%
776
20%
1557
January16th to endNight
27%
832
26%
2684
12%
832
44%
832
22%
1640
February1st to 15thNight
29%
764
26%
2291
10%
760
45%
760
25%
1414
February16th to endNight
25%
683
24%
2049
9%
683
39%
683
25%
1284
March1st to 15thNight
33%
780
25%
2210
11%
780
45%
780
28%
1384
March16th to endNight
36%
832
22%
2288
11%
832
45%
832
29%
1425
April1st to 15thNight
44%
734
25%
2097
15%
734
52%
734
34%
1232
April16th to endNight
48%
558
25%
1731
15%
558
58%
558
32%
1020
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
57%
717
25%
1980
19%
717
62%
717
30%
1284
October1st to 15thNight
53%
720
30%
2010
23%
720
60%
720
35%
1218
October16th to endNight
52%
768
36%
2304
26%
768
66%
768
38%
1252
November1st to 15thNight
51%
760
30%
2423
24%
760
62%
760
36%
1313
November16th to endNight
44%
780
28%
2535
20%
780
56%
780
30%
1434
December1st to 15thNight
37%
780
24%
2535
14%
780
49%
780
23%
1573
December16th to endNight
31%
832
22%
2704
14%
832
43%
832
20%
1795

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%435%45%7%42%
49982
Night
13%42442445%7%46%
49725
TransparencyDay
39%6%11%19%17%5%
49683
Night
36%6%10%19%19%6%
49528
SeeingDay
17%6%20%22%21%11%
6168
Night
15%7%22%28%21%3
16416

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
17%5%34414345%45%
1746
16th to endDay
17%5%24323345%47%
1888
February1st to 15thDay
16%6%2433445%5%44%
1900
16th to endDay
18%6%24324436%43%
1710
March1st to 15thDay
16%424423345%47%
2079
16th to endDay
17%424424446%44%
2287
April1st to 15thDay
12%425%5%3445%6%45%
2192
16th to endDay
11%425%324449%47%
2342
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
16%5%24324347%43%
1980
October1st to 15thDay
15%41331224455%
1948
16th to endDay
11%31331323460%
1920
November1st to 15thDay
12%413314345%55%
1762
16th to endDay
14%414323336%51%
1755
December1st to 15thDay
18%5%245%23445%41%
1755
16th to endDay
24%7%25%424235%36%
1872
January1st to 15thNight
17%6%2442433447%
2522
16th to endNight
18%5%23324345%46%
2684
February1st to 15thNight
16%414423335%48%
2283
16th to endNight
17%423434435%47%
2049
March1st to 15thNight
14%4235%2435%5%48%
2210
16th to endNight
13%42442345%7%47%
2288
April1st to 15thNight
12%31332345%7%51%
2097
16th to endNight
11%32442336%7%49%
1731
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
14%41442345%7%45%
1980
October1st to 15thNight
14%5%13323245%53%
2010
16th to endNight
9%32332333460%
2304
November1st to 15thNight
12%313313236%57%
2423
16th to endNight
15%31232335%6%52%
2535
December1st to 15thNight
15%6%25%423436%46%
2535
16th to endNight
20%7%25%433346%38%
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
41%39%16%23%4
1747
16th to endDay
39%35%19%22%8%
1888
February1st to 15thDay
42%38%19%22%4
1902
16th to endDay
42%37%20%19%6%
1710
March1st to 15thDay
39%38%19%21%8%
2079
16th to endDay
40%5%10%21%17%4
2288
April1st to 15thDay
39%38%21%20%6%
2192
16th to endDay
34%6%8%20%23%6%
2342
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
40%411%19%18%4
1980
October1st to 15thDay
32%49%19%26%7%
1948
16th to endDay
29%25%18%31%12%
1920
November1st to 15thDay
32%38%15%30%10%
1762
16th to endDay
35%36%16%28%8%
1755
December1st to 15thDay
44%5%6%19%16%8%
1755
16th to endDay
51%36%19%12%6%
1872
January1st to 15thNight
42%26%17%24%6%
2522
16th to endNight
40%35%18%23%9%
2684
February1st to 15thNight
39%26%19%21%9%
2292
16th to endNight
39%48%20%22%6%
2049
March1st to 15thNight
36%48%17%21%10%
2210
16th to endNight
36%411%21%20%5%
2288
April1st to 15thNight
32%48%24%22%7%
2097
16th to endNight
32%5%9%20%21%9%
1731
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
37%7%12%19%17%5%
1980
October1st to 15thNight
34%48%19%25%7%
2010
16th to endNight
28%35%17%31%13%
2304
November1st to 15thNight
29%36%18%28%13%
2423
16th to endNight
33%36%17%26%11%
2535
December1st to 15thNight
40%48%20%18%7%
2535
16th to endNight
46%49%16%17%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
27%14%33%20%4
135
16th to endDay
25%20%33%16%3
144
February1st to 15thDay
26%18%38%15%
135
16th to endDay
31%14%37%14%2
120
March1st to 15thDay
23%16%30%18%10%
264
16th to endDay
19%13%28%24%12%1
352
April1st to 15thDay
21%9%27%20%18%2
330
16th to endDay
15%6%25%25%21%4
289
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
20%211%25%26%14%
314
October1st to 15thDay
20%320%25%20%8%
315
16th to endDay
15%8%18%23%27%6%
336
November1st to 15thDay
25%8%21%22%20%2
180
16th to endDay
8%14%26%28%16%5%
135
December1st to 15thDay
30%10%32%20%5%
135
16th to endDay
38%15%27%13%4
144
January1st to 15thNight
24%15%26%24%8%
780
16th to endNight
21%16%31%26%4
832
February1st to 15thNight
21%12%31%30%4
764
16th to endNight
19%15%35%26%3
683
March1st to 15thNight
18%13%31%30%6%
780
16th to endNight
17%10%30%28%12%
832
April1st to 15thNight
15%9%28%29%15%
734
16th to endNight
12%6%25%32%20%1
558
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
17%14%30%32%3
717
October1st to 15thNight
16%322%27%26%4
720
16th to endNight
11%7%22%31%24%2
768
November1st to 15thNight
14%5%22%32%23%1
760
16th to endNight
16%10%24%29%17%2
780
December1st to 15thNight
18%11%25%30%11%
780
16th to endNight
25%11%25%30%6%
832
Page generated at 2018-04-24 10:03:01. Version ac04

Copyright 2018 A. Danko


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