Vienna
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Vienna clear sky chart from 2005-11-05 to 2017-10-16.

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
39%
15367
21%
47234
12%
15330
49%
15330
25%
29819

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
22%
717
22%
2410
9%
716
40%
716
20%
1519
January16th to endNight
22%
768
23%
2496
8%
768
40%
768
21%
1575
February1st to 15thNight
24%
701
20%
2287
6%
701
41%
701
21%
1415
February16th to endNight
20%
631
24%
1919
6%
631
41%
631
23%
1202
March1st to 15thNight
24%
720
22%
1998
9%
720
38%
720
25%
1292
March16th to endNight
25%
768
21%
2091
9%
768
34%
768
24%
1418
April1st to 15thNight
27%
718
19%
1796
5%
718
35%
718
29%
1193
April16th to endNight
41%
720
20%
1800
8%
720
46%
720
31%
1201
May1st to 15thNight
38%
565
17%
1645
9%
565
45%
565
23%
1118
May16th to endNight
53%
374
17%
1497
16%
374
60%
374
22%
895
June1st to 15thNight
57%
360
19%
1440
21%
360
64%
360
25%
828
June16th to endNight
58%
360
17%
1440
17%
360
64%
360
25%
824
July1st to 15thNight
54%
340
13%
1360
14%
340
57%
340
19%
869
July16th to endNight
72%
559
17%
1590
15%
526
76%
526
37%
918
August1st to 15thNight
66%
539
18%
1609
14%
536
67%
536
30%
1026
August16th to endNight
65%
754
19%
1900
12%
754
66%
754
32%
1273
September1st to 15thNight
56%
720
25%
1800
14%
720
60%
720
33%
1204
September16th to endNight
55%
717
23%
1977
18%
717
58%
717
29%
1309
October1st to 15thNight
47%
720
23%
2160
20%
720
54%
720
27%
1382
October16th to endNight
37%
708
28%
2123
16%
708
53%
708
32%
1254
November1st to 15thNight
37%
700
25%
2216
15%
700
52%
700
28%
1305
November16th to endNight
33%
720
21%
2472
12%
720
47%
720
23%
1482
December1st to 15thNight
28%
720
19%
2520
8%
720
42%
720
19%
1615
December16th to endNight
24%
768
21%
2688
8%
768
41%
768
19%
1702

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
14%5%2443445%7%41%
48177
Night
14%5%2442445%7%43%
47416
Cloud CoverDay
14%5%2443445%7%41%
48187
Night
14%5%2442445%7%44%
47420
TransparencyDay
40%6%11%22%16%2
47877
Night
38%6%11%22%17%3
47234
SeeingDay
17%6%23%25%18%8%
5795
Night
17%8%29%29%14%1
15374

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
16%5%3442435%6%41%
1526
16th to endDay
15%7%25%5%34346%42%
1728
February1st to 15thDay
14%6%25%6%3345%7%40%
1575
16th to endDay
13%7%35%5%34346%41%
1553
March1st to 15thDay
16%5%25%434346%44%
1948
16th to endDay
17%6%25%5%24345%40%
2133
April1st to 15thDay
14%5%2442435%7%44%
2152
16th to endDay
18%5%25%42335%5%44%
2160
May1st to 15thDay
17%5%25%5%35%46%7%37%
2313
16th to endDay
15%4244345%6%8%39%
2618
June1st to 15thDay
11%425%425%47%10%41%
2520
16th to endDay
9%4245%35%5%7%9%42%
2520
July1st to 15thDay
10%325%6%46%5%7%9%37%
2520
16th to endDay
7%3245%47%6%7%11%38%
2468
August1st to 15thDay
11%5%25%6%46%6%7%8%35%
2337
16th to endDay
12%3144445%7%8%41%
2292
September1st to 15thDay
13%425%43445%9%44%
2160
16th to endDay
14%6%25%42445%7%41%
1980
October1st to 15thDay
20%5%23323345%45%
1800
16th to endDay
15%424424446%48%
1770
November1st to 15thDay
15%414324445%48%
1640
16th to endDay
17%5%1432445%6%44%
1488
December1st to 15thDay
15%415%435%45%7%42%
1440
16th to endDay
18%6%25%42345%6%39%
1536
January1st to 15thNight
17%5%25%5%23347%42%
2410
16th to endNight
16%6%24423446%43%
2496
February1st to 15thNight
14%6%2442445%5%44%
2285
16th to endNight
14%6%24424345%45%
1919
March1st to 15thNight
16%424324447%44%
1986
16th to endNight
15%6%36%423446%41%
2091
April1st to 15thNight
14%5%25%5%245%5%6%43%
1796
16th to endNight
15%5%244245%5%8%43%
1800
May1st to 15thNight
18%5%25%42445%7%39%
1645
16th to endNight
13%5%233245%6%9%42%
1495
June1st to 15thNight
10%314425%6%5%8%45%
1440
16th to endNight
8%436%42446%10%43%
1440
July1st to 15thNight
9%5%26%6%36%6%6%9%37%
1440
16th to endNight
6%3134346%9%12%43%
1697
August1st to 15thNight
9%415%6%35%5%6%8%43%
1620
16th to endNight
10%4235%345%5%9%43%
1900
September1st to 15thNight
12%5%25%42446%6%45%
1800
16th to endNight
13%5%25%5%24447%43%
1977
October1st to 15thNight
19%415%423345%45%
2160
16th to endNight
14%423313446%52%
2123
November1st to 15thNight
13%5%35%32223452%
2216
16th to endNight
16%4234245%46%46%
2472
December1st to 15thNight
16%5%26%5%3445%6%39%
2520
16th to endNight
17%6%2442445%6%41%
2688

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%34423447%41%
1526
16th to endDay
15%7%25%5%24346%42%
1728
February1st to 15thDay
14%6%246%2435%7%40%
1575
16th to endDay
13%7%35%344446%41%
1553
March1st to 15thDay
15%435%5%33346%44%
1959
16th to endDay
16%6%35%435%346%40%
2132
April1st to 15thDay
14%4345%34347%44%
2152
16th to endDay
18%5%24423346%44%
2160
May1st to 15thDay
17%6%24435%45%7%36%
2313
16th to endDay
15%4145%35%5%7%8%39%
2618
June1st to 15thDay
11%424425%5%6%10%41%
2520
16th to endDay
8%415%5%35%6%6%10%42%
2520
July1st to 15thDay
10%415%6%35%6%7%9%37%
2520
16th to endDay
7%3245%46%7%8%11%38%
2468
August1st to 15thDay
11%5%26%6%46%6%7%8%34%
2337
16th to endDay
12%3145%45%5%7%8%41%
2292
September1st to 15thDay
13%315%42445%8%44%
2160
16th to endDay
14%6%25%4235%5%7%41%
1980
October1st to 15thDay
19%423334345%45%
1800
16th to endDay
15%414433446%48%
1770
November1st to 15thDay
15%423324347%48%
1640
16th to endDay
17%42332445%6%45%
1488
December1st to 15thDay
15%424435%5%47%42%
1440
16th to endDay
19%7%1442435%7%39%
1536
January1st to 15thNight
17%5%25%423347%42%
2410
16th to endNight
16%6%34424437%43%
2496
February1st to 15thNight
14%6%2442445%5%45%
2278
16th to endNight
14%6%34333346%45%
1919
March1st to 15thNight
16%424324447%44%
1998
16th to endNight
15%5%35%425%346%41%
2091
April1st to 15thNight
14%425%5%2345%5%44%
1796
16th to endNight
16%42332445%7%43%
1800
May1st to 15thNight
18%5%24424447%38%
1644
16th to endNight
13%5%234335%6%9%42%
1495
June1st to 15thNight
10%314425%6%5%10%45%
1440
16th to endNight
9%335%425%46%10%43%
1440
July1st to 15thNight
8%5%27%6%35%6%7%8%38%
1440
16th to endNight
6%223435%7%8%12%44%
1697
August1st to 15thNight
9%425%5%45%5%5%8%44%
1620
16th to endNight
10%4245%45%5%6%9%42%
1900
September1st to 15thNight
12%5%25%4245%5%7%44%
1800
16th to endNight
13%6%25%43435%7%42%
1977
October1st to 15thNight
19%425%423345%45%
2160
16th to endNight
14%32332335%5%52%
2123
November1st to 15thNight
13%5%25%32323452%
2216
16th to endNight
16%3144245%46%45%
2472
December1st to 15thNight
16%6%25%5%3445%6%39%
2520
16th to endNight
17%5%25%42445%6%41%
2688

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%5%11%22%14%3
1527
16th to endDay
42%410%24%13%3
1728
February1st to 15thDay
42%411%24%14%2
1577
16th to endDay
42%312%24%14%1
1553
March1st to 15thDay
41%410%24%15%3
1959
16th to endDay
45%5%10%18%17%2
2133
April1st to 15thDay
39%411%22%18%3
2152
16th to endDay
41%5%8%18%19%6%
2160
May1st to 15thDay
44%6%11%20%15%1
2313
16th to endDay
40%9%12%24%11%2
2622
June1st to 15thDay
35%8%13%26%14%1
2520
16th to endDay
34%8%14%23%16%2
2520
July1st to 15thDay
39%9%13%18%15%3
2371
16th to endDay
34%9%14%24%14%2
2312
August1st to 15thDay
43%8%11%20%15%1
2324
16th to endDay
37%8%13%23%14%2
2292
September1st to 15thDay
36%6%13%19%21%3
2160
16th to endDay
41%48%23%19%2
1980
October1st to 15thDay
41%49%24%17%3
1800
16th to endDay
37%38%26%21%1
1770
November1st to 15thDay
35%5%11%22%18%6%
1640
16th to endDay
39%48%26%17%2
1488
December1st to 15thDay
40%7%12%23%12%3
1440
16th to endDay
45%5%10%24%12%1
1536
January1st to 15thNight
42%410%19%18%4
2410
16th to endNight
41%49%25%17%1
2496
February1st to 15thNight
39%5%10%24%16%3
2287
16th to endNight
39%410%25%18%1
1919
March1st to 15thNight
39%5%11%26%14%2
1998
16th to endNight
42%5%9%21%16%3
2091
April1st to 15thNight
39%410%20%21%3
1796
16th to endNight
37%6%10%20%17%8%
1800
May1st to 15thNight
43%7%10%20%13%3
1645
16th to endNight
36%9%14%21%14%2
1497
June1st to 15thNight
35%7%12%27%15%1
1440
16th to endNight
35%7%15%20%18%2
1440
July1st to 15thNight
40%10%14%17%12%4
1360
16th to endNight
26%9%17%26%17%1
1590
August1st to 15thNight
36%8%12%23%17%1
1609
16th to endNight
36%8%12%23%16%3
1900
September1st to 15thNight
37%7%9%21%20%4
1800
16th to endNight
40%6%8%20%19%4
1977
October1st to 15thNight
41%48%23%19%3
2160
16th to endNight
32%5%8%27%22%3
2123
November1st to 15thNight
37%28%22%21%7%
2216
16th to endNight
37%6%9%22%19%4
2472
December1st to 15thNight
44%5%11%21%14%2
2520
16th to endNight
43%5%12%23%13%2
2688

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
26%15%39%15%11
76
16th to endDay
19%22%34%17%5%
96
February1st to 15thDay
28%20%35%13%2
90
16th to endDay
17%17%38%25%
212
March1st to 15thDay
20%12%34%25%7%
270
16th to endDay
20%13%34%21%7%2
288
April1st to 15thDay
18%12%27%25%14%2
270
16th to endDay
22%6%23%24%16%5%
270
May1st to 15thDay
27%11%26%15%14%4
288
16th to endDay
21%221%26%21%7%
331
June1st to 15thDay
14%324%24%21%11%
315
16th to endDay
11%126%35%17%6%
315
July1st to 15thDay
13%118%31%25%9%
305
16th to endDay
7%111%30%34%13%
326
August1st to 15thDay
15%13%25%32%12%
313
16th to endDay
9%110%27%29%21%
332
September1st to 15thDay
15%219%21%20%21%
315
16th to endDay
21%215%27%18%15%
314
October1st to 15thDay
24%315%24%23%9%
315
16th to endDay
15%10%28%26%15%3
276
November1st to 15thDay
18%8%25%26%16%5%
246
16th to endDay
20%9%30%24%13%1
108
December1st to 15thDay
16%10%41%16%10%5%
60
16th to endDay
39%6%26%26%1
64
January1st to 15thNight
20%15%36%22%5%
720
16th to endNight
21%13%39%23%1
768
February1st to 15thNight
19%13%38%26%2
704
16th to endNight
21%17%38%21%1
631
March1st to 15thNight
20%12%38%24%3
720
16th to endNight
18%13%38%22%5%1
768
April1st to 15thNight
16%15%38%24%5%
718
16th to endNight
18%7%28%32%11%
720
May1st to 15thNight
21%5%28%30%12%
565
16th to endNight
13%321%38%21%1
375
June1st to 15thNight
10%123%39%25%1
360
16th to endNight
8%221%48%18%1
360
July1st to 15thNight
11%20%41%25%1
340
16th to endNight
7%12%40%34%5%
559
August1st to 15thNight
11%13%44%27%2
539
16th to endNight
12%13%38%31%3
754
September1st to 15thNight
15%118%29%31%3
720
16th to endNight
15%117%31%30%2
717
October1st to 15thNight
21%5%19%27%22%3
720
16th to endNight
15%9%33%26%13%
708
November1st to 15thNight
15%9%31%28%13%1
700
16th to endNight
18%12%31%25%10%
720
December1st to 15thNight
20%11%33%25%8%
720
16th to endNight
21%12%37%25%3
768
Page generated at 2017-10-17 16:35:23. Version ac04

Copyright 2017 A. Danko


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