Alpine Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Alpine Observatory clear sky chart from 2005-11-05 to 2018-02-22.

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
52%
15980
32%
48835
21%
15936
65%
15936
39%
24413

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
50%
780
31%
2522
24%
776
63%
776
38%
1225
January16th to endNight
47%
832
35%
2704
24%
832
64%
832
36%
1316
February1st to 15thNight
46%
761
31%
2479
22%
758
62%
758
38%
1160
February16th to endNight
35%
660
39%
1888
18%
660
57%
660
36%
959
March1st to 15thNight
42%
720
37%
1980
18%
720
59%
720
41%
999
March16th to endNight
44%
768
37%
2112
17%
768
61%
768
47%
1025
April1st to 15thNight
36%
605
33%
1864
13%
605
56%
605
36%
870
April16th to endNight
38%
540
40%
1800
18%
540
66%
540
43%
716
May1st to 15thNight
45%
539
32%
1682
19%
539
61%
539
43%
744
May16th to endNight
44%
562
34%
1684
17%
561
60%
561
48%
743
June1st to 15thNight
56%
540
32%
1620
23%
540
63%
540
53%
714
June16th to endNight
62%
540
23%
1620
17%
540
67%
540
42%
805
July1st to 15thNight
63%
510
15%
1530
14%
510
63%
510
25%
960
July16th to endNight
62%
564
9%
1593
9%
531
67%
531
22%
1059
August1st to 15thNight
69%
539
15%
1611
14%
536
70%
536
25%
1021
August16th to endNight
69%
573
21%
1904
21%
573
71%
573
26%
1166
September1st to 15thNight
66%
591
24%
1851
22%
591
68%
591
29%
1131
September16th to endNight
65%
716
36%
1982
21%
716
76%
716
49%
996
October1st to 15thNight
61%
720
35%
2160
23%
720
70%
720
52%
1006
October16th to endNight
69%
768
43%
2304
29%
768
81%
768
59%
995
November1st to 15thNight
55%
760
39%
2280
26%
760
66%
760
52%
1005
November16th to endNight
51%
780
40%
2426
26%
780
66%
780
40%
1138
December1st to 15thNight
46%
780
35%
2535
23%
780
62%
780
35%
1239
December16th to endNight
42%
832
32%
2704
23%
832
55%
832
31%
1421

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
5%424424446%55%
49409
Night
3313323446%62%
49035
TransparencyDay
26%5%8%15%26%16%
49104
Night
20%5%9%18%29%16%
48841
SeeingDay
10%23%24%24%13%3
5720
Night
420%16%29%24%4
15985

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
36%1232345%6%60%
1746
16th to endDay
45%13223446%61%
1872
February1st to 15thDay
25%14313245%65%
1710
16th to endDay
27%14314445%58%
1728
March1st to 15thDay
36%13323446%60%
1980
16th to endDay
3423313346%63%
2112
April1st to 15thDay
2312323447%64%
2084
16th to endDay
3314323325%64%
2160
May1st to 15thDay
2314323345%63%
2265
16th to endDay
5%21332333465%
2429
June1st to 15thDay
3312324346%66%
2340
16th to endDay
43146%35%45%5%55%
2340
July1st to 15thDay
10%6%36%8%46%6%6%7%32%
2340
16th to endDay
13%6%37%8%5%8%7%8%9%20%
2467
August1st to 15thDay
13%6%49%8%5%7%6%5%6%26%
2340
16th to endDay
11%5%47%7%37%6%6%6%32%
2295
September1st to 15thDay
10%5%28%6%46%5%5%6%37%
2106
16th to endDay
6%423424436%56%
1977
October1st to 15thDay
5%21321333467%
1800
16th to endDay
322212225%72%
1920
November1st to 15thDay
2312312245%69%
1909
16th to endDay
341231223468%
1862
December1st to 15thDay
36%2331335%5%60%
1755
16th to endDay
28%2431345%457%
1872
January1st to 15thNight
25%22323446%61%
2522
16th to endNight
4413323335%63%
2704
February1st to 15thNight
2413323346%66%
2472
16th to endNight
241232345%7%62%
1888
March1st to 15thNight
2413213335%68%
1980
16th to endNight
2222212237%70%
2112
April1st to 15thNight
211332345%5%65%
1864
16th to endNight
11121223476%
1800
May1st to 15thNight
1212222237%70%
1682
16th to endNight
321112245%72%
1684
June1st to 15thNight
2112122235%73%
1620
16th to endNight
2222425%46%6%61%
1620
July1st to 15thNight
3425%7%47%7%6%9%40%
1620
16th to endNight
3325%6%46%9%10%14%31%
1701
August1st to 15thNight
45%145%45%7%9%10%40%
1620
16th to endNight
5%5%15%5%35%6%8%9%42%
1904
September1st to 15thNight
6%5%25%5%345%6%8%47%
1851
16th to endNight
421321233469%
1982
October1st to 15thNight
32221333472%
2160
16th to endNight
21121222477%
2304
November1st to 15thNight
2211213345%71%
2280
16th to endNight
4313213235%68%
2426
December1st to 15thNight
45%13223346%62%
2535
16th to endNight
36%1442445%6%56%
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
23%37%17%32%15%
1747
16th to endDay
23%36%14%36%15%
1872
February1st to 15thDay
20%37%20%27%20%
1710
16th to endDay
25%37%18%32%13%
1728
March1st to 15thDay
21%36%15%37%16%
1980
16th to endDay
21%25%15%39%15%
2112
April1st to 15thDay
18%36%17%35%17%
2084
16th to endDay
20%35%16%32%22%
2160
May1st to 15thDay
20%37%14%29%24%
2265
16th to endDay
20%46%12%32%23%
2432
June1st to 15thDay
16%35%11%25%37%
2340
16th to endDay
24%6%7%11%21%28%
2340
July1st to 15thDay
44%9%14%12%9%9%
2201
16th to endDay
50%15%19%11%2
2312
August1st to 15thDay
50%10%12%11%12%2
2325
16th to endDay
43%10%12%15%14%3
2295
September1st to 15thDay
40%9%10%15%16%6%
2106
16th to endDay
25%5%6%16%29%17%
1977
October1st to 15thDay
20%37%13%33%22%
1800
16th to endDay
14%27%16%35%23%
1920
November1st to 15thDay
16%26%21%32%20%
1909
16th to endDay
19%2414%35%22%
1862
December1st to 15thDay
22%5%8%22%26%14%
1755
16th to endDay
27%5%9%21%27%9%
1872
January1st to 15thNight
22%37%19%34%13%
2522
16th to endNight
22%38%16%36%12%
2704
February1st to 15thNight
19%37%22%28%18%
2483
16th to endNight
20%37%20%34%13%
1888
March1st to 15thNight
18%36%16%40%14%
1980
16th to endNight
16%26%19%39%16%
2112
April1st to 15thNight
17%36%23%34%15%
1864
16th to endNight
11%25%19%39%20%
1800
May1st to 15thNight
15%37%16%38%19%
1683
16th to endNight
13%38%17%34%23%
1685
June1st to 15thNight
13%2410%29%37%
1620
16th to endNight
19%5%9%11%21%31%
1620
July1st to 15thNight
32%12%16%15%12%11%
1530
16th to endNight
33%16%31%13%4
1593
August1st to 15thNight
32%14%20%14%14%4
1611
16th to endNight
32%11%19%17%14%4
1904
September1st to 15thNight
33%8%15%17%17%6%
1851
16th to endNight
18%37%21%28%20%
1982
October1st to 15thNight
16%37%18%33%21%
2160
16th to endNight
11%26%19%35%24%
2304
November1st to 15thNight
13%26%23%33%19%
2280
16th to endNight
18%25%16%33%23%
2426
December1st to 15thNight
22%37%22%27%17%
2535
16th to endNight
25%5%12%20%27%8%
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
14%20%24%23%14%1
135
16th to endDay
9%19%23%22%19%5%
144
February1st to 15thDay
11%14%22%28%17%5%
135
16th to endDay
11%45%22%12%6%
227
March1st to 15thDay
10%37%26%16%7%1
270
16th to endDay
11%39%28%12%6%1
288
April1st to 15thDay
10%45%24%12%5%1
269
16th to endDay
15%45%24%10%3
270
May1st to 15thDay
7%37%31%16%32
288
16th to endDay
6%36%35%13%6%1
330
June1st to 15thDay
6%23%33%24%7%3
315
16th to endDay
6%15%25%31%16%4
315
July1st to 15thDay
12%8%19%33%22%3
305
16th to endDay
13%10%14%22%27%12%
327
August1st to 15thDay
12%6%12%36%24%6%
315
16th to endDay
10%6%16%35%25%6%
332
September1st to 15thDay
11%10%26%34%15%2
315
16th to endDay
8%18%30%27%12%2
312
October1st to 15thDay
5%16%30%26%11%8%
135
16th to endDay
411%25%34%18%6%
144
November1st to 15thDay
8%20%29%26%14%
135
16th to endDay
14%15%28%28%11%1
135
December1st to 15thDay
6%18%24%31%14%5%
135
16th to endDay
17%17%20%33%7%3
144
January1st to 15thNight
421%17%33%18%5%
780
16th to endNight
6%24%16%26%20%5%
832
February1st to 15thNight
423%22%30%16%3
764
16th to endNight
5%30%25%29%9%
660
March1st to 15thNight
329%20%27%16%2
720
16th to endNight
327%21%30%14%2
768
April1st to 15thNight
335%22%28%9%
605
16th to endNight
331%25%25%12%2
540
May1st to 15thNight
225%23%33%13%1
540
16th to endNight
424%24%27%17%1
563
June1st to 15thNight
218%19%35%20%2
540
16th to endNight
218%10%32%33%3
540
July1st to 15thNight
412%424%46%7%
510
16th to endNight
317%317%48%10%
564
August1st to 15thNight
39%415%54%12%
539
16th to endNight
6%8%418%51%11%
573
September1st to 15thNight
6%8%6%27%45%5%
591
16th to endNight
5%11%10%32%34%5%
716
October1st to 15thNight
213%18%36%23%5%
720
16th to endNight
211%13%37%28%7%
768
November1st to 15thNight
218%19%29%24%5%
760
16th to endNight
6%24%15%27%21%5%
780
December1st to 15thNight
8%23%16%30%17%2
780
16th to endNight
7%24%21%29%13%2
832
Page generated at 2018-02-23 09:21:28. Version ac04

Copyright 2018 A. Danko


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