Artis Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Artis Observatory clear sky chart from 2005-11-05 to 2018-01-12.

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
75%
15864
31%
48354
29%
15831
77%
15831
49%
24025

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
66%
760
20%
2637
23%
760
68%
760
31%
1512
January16th to endNight
66%
768
25%
2496
28%
768
67%
768
30%
1484
February1st to 15thNight
67%
698
25%
2178
27%
698
69%
698
35%
1254
February16th to endNight
65%
632
24%
1895
27%
632
66%
632
34%
1120
March1st to 15thNight
66%
720
19%
2118
21%
720
67%
720
38%
1207
March16th to endNight
66%
768
24%
2016
20%
768
69%
768
46%
1153
April1st to 15thNight
60%
719
26%
1799
15%
719
64%
719
45%
1068
April16th to endNight
66%
720
28%
1800
14%
720
70%
720
55%
970
May1st to 15thNight
73%
629
30%
1709
21%
629
76%
629
62%
809
May16th to endNight
70%
411
33%
1534
30%
411
76%
411
51%
624
June1st to 15thNight
76%
360
32%
1440
35%
360
84%
360
59%
515
June16th to endNight
90%
360
40%
1440
50%
360
94%
360
81%
417
July1st to 15thNight
92%
340
36%
1360
47%
340
93%
340
74%
414
July16th to endNight
91%
477
41%
1509
40%
447
92%
447
68%
577
August1st to 15thNight
89%
662
38%
1736
26%
659
89%
659
80%
746
August16th to endNight
94%
764
45%
1910
30%
764
94%
764
86%
841
September1st to 15thNight
91%
720
43%
1800
31%
720
93%
720
82%
802
September16th to endNight
87%
716
47%
1947
42%
716
89%
716
77%
824
October1st to 15thNight
84%
720
34%
2118
36%
720
86%
720
60%
967
October16th to endNight
82%
768
41%
2307
45%
768
84%
768
59%
1048
November1st to 15thNight
78%
760
31%
2470
35%
760
80%
760
49%
1172
November16th to endNight
75%
780
30%
2535
32%
780
76%
780
42%
1309
December1st to 15thNight
71%
780
24%
2688
27%
780
72%
780
34%
1472
December16th to endNight
61%
832
24%
2912
27%
832
65%
832
28%
1720

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
7%212212335%66%
48983
Night
8%212212235%66%
48541
TransparencyDay
20%38%19%25%22%
48663
Night
21%39%20%24%19%
48361
SeeingDay
8%5%20%35%22%7%
6217
Night
9%19%35%35%9%
15876

By Month

Percentage Cloud Cover SW (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
13%42432335%7%48%
1541
16th to endDay
17%5%2332336%6%44%
1728
February1st to 15thDay
14%5%13324446%47%
1676
16th to endDay
18%5%23323346%46%
1579
March1st to 15thDay
12%5%23325%5%6%8%44%
1841
16th to endDay
12%4233245%5%7%49%
2207
April1st to 15thDay
11%5%23313236%54%
2149
16th to endDay
8%212313346%61%
2160
May1st to 15thDay
3213222235%72%
2241
16th to endDay
5%22213347%67%
2576
June1st to 15thDay
221112225%75%
2520
16th to endDay
1111288%
2520
July1st to 15thDay
111212384%
2520
16th to endDay
11111222381%
2553
August1st to 15thDay
11111287%
2214
16th to endDay
1111112385%
2292
September1st to 15thDay
111122285%
2160
16th to endDay
111122482%
2013
October1st to 15thDay
311221324470%
1839
16th to endDay
5%112212235%70%
1917
November1st to 15thDay
7%312324346%60%
1719
16th to endDay
10%313334336%56%
1755
December1st to 15thDay
15%423333336%49%
1599
16th to endDay
16%434424347%44%
1664
January1st to 15thNight
14%424322346%51%
2637
16th to endNight
16%5%23323346%49%
2496
February1st to 15thNight
14%414213447%50%
2173
16th to endNight
18%412222346%50%
1895
March1st to 15thNight
12%413313345%54%
2118
16th to endNight
11%212312437%57%
2016
April1st to 15thNight
10%313213347%57%
1799
16th to endNight
6%212223225%68%
1800
May1st to 15thNight
3112112235%73%
1709
16th to endNight
412212235%72%
1533
June1st to 15thNight
211112225%77%
1440
16th to endNight
111289%
1440
July1st to 15thNight
111121384%
1440
16th to endNight
2212122479%
1613
August1st to 15thNight
11111286%
1745
16th to endNight
11112386%
1910
September1st to 15thNight
11112286%
1800
16th to endNight
111111384%
1947
October1st to 15thNight
4211112235%72%
2118
16th to endNight
5%1212235%73%
2307
November1st to 15thNight
7%212312136%66%
2470
16th to endNight
8%223213447%59%
2535
December1st to 15thNight
12%413323347%53%
2688
16th to endNight
18%423323337%47%
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
34%7%14%18%19%5%
1541
16th to endDay
40%5%11%17%14%10%
1728
February1st to 15thDay
37%6%10%24%17%3
1676
16th to endDay
37%6%13%26%14%1
1579
March1st to 15thDay
33%6%15%20%17%5%
1841
16th to endDay
30%7%15%24%17%3
2207
April1st to 15thDay
31%311%27%18%6%
2149
16th to endDay
23%5%12%25%26%7%
2160
May1st to 15thDay
15%28%24%35%13%
2241
16th to endDay
16%39%30%30%10%
2580
June1st to 15thDay
12%310%18%30%26%
2520
16th to endDay
5%128%33%48%
2520
July1st to 15thDay
6%126%22%61%
2371
16th to endDay
9%248%21%54%
2394
August1st to 15thDay
6%19%27%54%
2198
16th to endDay
7%28%34%47%
2292
September1st to 15thDay
7%1311%31%44%
2160
16th to endDay
7%1322%39%25%
2013
October1st to 15thDay
15%36%21%26%25%
1839
16th to endDay
17%18%25%27%20%
1917
November1st to 15thDay
26%315%24%23%6%
1719
16th to endDay
28%5%12%23%25%4
1755
December1st to 15thDay
36%6%8%20%19%8%
1599
16th to endDay
38%6%14%19%17%3
1664
January1st to 15thNight
34%411%24%18%5%
2637
16th to endNight
36%5%11%16%18%11%
2496
February1st to 15thNight
31%5%12%26%17%5%
2184
16th to endNight
34%414%27%16%2
1895
March1st to 15thNight
30%418%20%22%4
2118
16th to endNight
26%316%26%20%5%
2016
April1st to 15thNight
27%414%28%18%5%
1799
16th to endNight
19%314%26%28%7%
1800
May1st to 15thNight
14%29%23%35%14%
1710
16th to endNight
15%38%27%33%11%
1534
June1st to 15thNight
12%28%23%27%26%
1440
16th to endNight
41210%27%53%
1440
July1st to 15thNight
6%12423%61%
1360
16th to endNight
10%137%21%55%
1509
August1st to 15thNight
7%18%27%54%
1736
16th to endNight
5%28%32%49%
1910
September1st to 15thNight
6%139%30%48%
1800
16th to endNight
8%1316%42%28%
1947
October1st to 15thNight
14%36%22%26%26%
2118
16th to endNight
15%26%24%28%22%
2307
November1st to 15thNight
21%212%26%26%9%
2470
16th to endNight
24%5%12%25%24%8%
2535
December1st to 15thNight
30%5%13%20%20%9%
2688
16th to endNight
38%413%22%16%5%
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
32%20%25%14%7%
103
16th to endDay
22%213%32%18%10%
256
February1st to 15thDay
20%318%24%20%11%
253
16th to endDay
20%7%21%28%16%5%
238
March1st to 15thDay
14%6%22%28%21%7%
270
16th to endDay
17%8%25%28%17%3
288
April1st to 15thDay
17%15%26%26%11%2
269
16th to endDay
8%16%29%30%11%3
270
May1st to 15thDay
5%9%29%36%13%5%
288
16th to endDay
6%10%24%32%19%6%
330
June1st to 15thDay
26%28%36%20%3
315
16th to endDay
1217%42%25%10%
315
July1st to 15thDay
10%44%32%11%
305
16th to endDay
112%46%29%9%
327
August1st to 15thDay
3118%49%19%8%
315
16th to endDay
112%46%27%12%
332
September1st to 15thDay
1115%48%24%8%
315
16th to endDay
2422%38%26%4
315
October1st to 15thDay
35%29%34%24%4
315
16th to endDay
6%5%16%30%31%9%
333
November1st to 15thDay
8%110%25%34%20%
135
16th to endDay
8%5%17%28%32%6%
135
December1st to 15thDay
13%116%34%24%11%
99
16th to endDay
14%414%23%32%10%
96
January1st to 15thNight
15%17%34%30%12%
764
16th to endNight
19%17%33%29%9%
768
February1st to 15thNight
16%7%35%28%10%
704
16th to endNight
19%19%35%27%6%
632
March1st to 15thNight
13%110%36%29%7%
720
16th to endNight
12%114%36%30%4
768
April1st to 15thNight
10%319%35%26%4
719
16th to endNight
6%320%35%27%7%
720
May1st to 15thNight
4216%46%26%4
630
16th to endNight
5%218%38%32%1
412
June1st to 15thNight
316%44%33%1
360
16th to endNight
16%52%38%1
360
July1st to 15thNight
1241%52%2
340
16th to endNight
1225%59%10%
477
August1st to 15thNight
15%35%49%8%
662
16th to endNight
228%58%10%
764
September1st to 15thNight
429%52%13%
720
16th to endNight
26%33%42%14%
716
October1st to 15thNight
5%6%39%36%12%
720
16th to endNight
7%5%30%35%20%
768
November1st to 15thNight
8%15%33%36%13%
760
16th to endNight
8%9%36%32%13%
780
December1st to 15thNight
13%17%39%28%9%
780
16th to endNight
20%19%39%23%6%
832
Page generated at 2018-01-12 19:01:34. Version ac04

Copyright 2018 A. Danko


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