Alpine
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Alpine clear sky chart from 2005-11-05 to 2017-09-10.

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
74%
16201
33%
46897
29%
16158
77%
16158
49%
24211

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
63%
717
29%
2327
28%
716
69%
716
39%
1218
January16th to endNight
59%
768
34%
2304
27%
768
69%
768
36%
1304
February1st to 15thNight
62%
699
32%
2110
28%
699
70%
699
39%
1168
February16th to endNight
54%
632
27%
1895
29%
632
57%
632
29%
1187
March1st to 15thNight
63%
720
29%
2151
29%
720
68%
720
40%
1187
March16th to endNight
70%
768
29%
2052
25%
768
72%
768
42%
1189
April1st to 15thNight
63%
719
27%
1799
19%
719
65%
719
44%
1081
April16th to endNight
69%
720
31%
1800
20%
720
72%
720
52%
998
May1st to 15thNight
73%
575
30%
1655
22%
575
75%
575
48%
878
May16th to endNight
72%
561
28%
1685
22%
561
74%
561
48%
869
June1st to 15thNight
83%
540
32%
1620
28%
540
84%
540
63%
726
June16th to endNight
92%
540
38%
1620
34%
540
93%
540
80%
621
July1st to 15thNight
91%
510
29%
1530
24%
510
91%
510
65%
663
July16th to endNight
89%
623
33%
1647
26%
585
89%
585
57%
797
August1st to 15thNight
94%
717
37%
1790
24%
713
95%
713
78%
812
August16th to endNight
93%
764
43%
1910
31%
764
93%
764
74%
902
September1st to 15thNight
91%
700
38%
1826
32%
700
91%
700
69%
860
September16th to endNight
88%
656
46%
1815
42%
656
90%
656
74%
780
October1st to 15thNight
75%
660
36%
1815
32%
660
78%
660
52%
944
October16th to endNight
75%
704
36%
2095
36%
704
79%
704
49%
1040
November1st to 15thNight
74%
700
33%
2275
34%
700
79%
700
49%
1080
November16th to endNight
71%
720
34%
2340
35%
720
75%
720
44%
1156
December1st to 15thNight
62%
720
31%
2340
31%
720
67%
720
35%
1300
December16th to endNight
55%
768
30%
2496
27%
768
63%
768
31%
1451

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
6%312213335%66%
47713
Night
6%313213335%64%
47100
TransparencyDay
20%35%15%26%28%
47414
Night
22%36%15%22%29%
46900
SeeingDay
7%9%30%36%11%4
5879
Night
7%210%30%36%12%
16212

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
9%413213336%58%
1611
16th to endDay
12%423323446%54%
1917
February1st to 15thDay
9%413313345%57%
1751
16th to endDay
15%6%24424347%43%
1579
March1st to 15thDay
8%313313447%57%
1807
16th to endDay
7%314223346%58%
2169
April1st to 15thDay
9%324413346%56%
2149
16th to endDay
6%312112236%67%
2160
May1st to 15thDay
5%312213226%66%
2292
16th to endDay
432213235%71%
2429
June1st to 15thDay
221221223474%
2340
16th to endDay
11112287%
2340
July1st to 15thDay
212212346%71%
2340
16th to endDay
21122345%8%65%
2405
August1st to 15thDay
112222479%
2160
16th to endDay
11222233476%
2292
September1st to 15thDay
112212335%74%
2019
16th to endDay
1211222380%
1815
October1st to 15thDay
6%31221233465%
1815
16th to endDay
5%31221223370%
1771
November1st to 15thDay
6%322212236%65%
1584
16th to endDay
7%422312345%61%
1620
December1st to 15thDay
10%423333348%52%
1620
16th to endDay
14%5%13422435%51%
1728
January1st to 15thNight
7%41342335%5%58%
2327
16th to endNight
11%5%23313336%55%
2304
February1st to 15thNight
8%5%23323336%56%
2101
16th to endNight
14%7%2442443447%
1895
March1st to 15thNight
9%5%23323347%54%
2151
16th to endNight
7%4232235%5%8%53%
2052
April1st to 15thNight
9%7%13213346%54%
1799
16th to endNight
7%413322237%62%
1800
May1st to 15thNight
441332335%5%61%
1655
16th to endNight
35%22423436%62%
1684
June1st to 15thNight
1312212246%71%
1620
16th to endNight
1122286%
1620
July1st to 15thNight
11112345%75%
1620
16th to endNight
211213346%69%
1760
August1st to 15thNight
112246%78%
1800
16th to endNight
1121223479%
1910
September1st to 15thNight
1211323478%
1826
16th to endNight
2111112283%
1815
October1st to 15thNight
5%312213326%66%
1815
16th to endNight
4313223335%66%
2095
November1st to 15thNight
5%31222333467%
2275
16th to endNight
6%5%13312336%61%
2340
December1st to 15thNight
11%42332235%6%53%
2340
16th to endNight
13%42442333452%
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
27%35%12%24%27%
1612
16th to endDay
31%36%11%18%28%
1917
February1st to 15thDay
27%3413%22%28%
1751
16th to endDay
38%45%13%22%14%
1579
March1st to 15thDay
25%45%15%25%23%
1807
16th to endDay
26%37%20%24%17%
2169
April1st to 15thDay
29%35%21%26%12%
2149
16th to endDay
18%27%22%27%20%
2160
May1st to 15thDay
20%36%17%28%22%
2292
16th to endDay
17%27%21%36%15%
2432
June1st to 15thDay
14%2417%27%33%
2340
16th to endDay
6%127%20%61%
2340
July1st to 15thDay
13%36%12%26%38%
2201
16th to endDay
14%7%9%23%28%16%
2255
August1st to 15thDay
9%3415%34%33%
2146
16th to endDay
11%3412%35%32%
2292
September1st to 15thDay
12%3410%31%37%
2019
16th to endDay
10%237%34%41%
1815
October1st to 15thDay
22%25%14%26%28%
1815
16th to endDay
19%3310%19%42%
1771
November1st to 15thDay
21%26%12%21%35%
1584
16th to endDay
24%3411%21%34%
1620
December1st to 15thDay
30%47%13%17%25%
1620
16th to endDay
34%46%14%22%18%
1728
January1st to 15thNight
26%35%11%21%30%
2327
16th to endNight
31%36%11%16%31%
2304
February1st to 15thNight
29%35%11%20%28%
2112
16th to endNight
39%4313%19%20%
1895
March1st to 15thNight
29%36%15%20%24%
2151
16th to endNight
27%5%7%16%23%18%
2052
April1st to 15thNight
30%28%19%25%14%
1799
16th to endNight
23%29%19%19%25%
1800
May1st to 15thNight
23%39%17%21%23%
1656
16th to endNight
23%311%18%24%19%
1685
June1st to 15thNight
14%27%21%24%30%
1620
16th to endNight
5%1210%17%61%
1620
July1st to 15thNight
12%25%13%25%40%
1530
16th to endNight
14%6%7%27%26%17%
1647
August1st to 15thNight
6%36%21%32%30%
1790
16th to endNight
9%2316%30%37%
1910
September1st to 15thNight
12%2314%30%36%
1826
16th to endNight
9%138%36%41%
1815
October1st to 15thNight
21%35%15%26%27%
1815
16th to endNight
21%3410%18%41%
2095
November1st to 15thNight
20%3413%20%37%
2275
16th to endNight
24%25%13%20%33%
2340
December1st to 15thNight
31%46%13%18%25%
2340
16th to endNight
34%48%11%18%22%
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
37%216%32%11%
90
16th to endDay
16%15%33%28%5%1
285
February1st to 15thDay
8%15%37%27%9%1
266
16th to endDay
16%20%35%18%7%1
238
March1st to 15thDay
8%18%32%25%10%3
270
16th to endDay
9%18%36%25%7%2
288
April1st to 15thDay
12%20%40%17%6%2
269
16th to endDay
7%20%40%22%5%2
270
May1st to 15thDay
14%13%33%27%8%3
288
16th to endDay
9%10%37%33%7%2
330
June1st to 15thDay
28%35%37%11%4
315
16th to endDay
1125%42%18%10%
315
July1st to 15thDay
1118%51%19%7%
305
16th to endDay
312%57%15%10%
327
August1st to 15thDay
124%49%13%10%
315
16th to endDay
17%55%16%9%
332
September1st to 15thDay
3229%50%8%5%
294
16th to endDay
46%34%45%5%4
255
October1st to 15thDay
5%12%45%26%8%1
255
16th to endDay
10%6%33%29%16%2
206
November1st to 15thDay
6%10%16%30%31%5%
90
16th to endDay
15%10%22%31%21%
90
December1st to 15thDay
38%17%44%20%5%
90
16th to endDay
19%8%30%30%11%
96
January1st to 15thNight
8%5%15%36%24%9%
720
16th to endNight
13%5%14%32%26%6%
768
February1st to 15thNight
11%315%34%27%7%
704
16th to endNight
16%5%15%35%20%6%
632
March1st to 15thNight
11%415%36%25%7%
720
16th to endNight
8%311%37%30%8%
768
April1st to 15thNight
11%415%38%24%6%
719
16th to endNight
8%313%36%28%9%
720
May1st to 15thNight
7%112%37%33%7%
576
16th to endNight
6%113%32%38%6%
563
June1st to 15thNight
29%37%41%7%
540
16th to endNight
1328%56%8%
540
July1st to 15thNight
1117%65%14%
510
16th to endNight
2112%59%22%
623
August1st to 15thNight
117%56%23%
717
16th to endNight
119%55%31%
764
September1st to 15thNight
1218%57%20%
700
16th to endNight
26%27%44%18%
656
October1st to 15thNight
6%211%34%35%10%
660
16th to endNight
6%19%33%30%18%
704
November1st to 15thNight
7%112%37%29%12%
700
16th to endNight
9%210%33%29%14%
720
December1st to 15thNight
13%313%33%25%9%
720
16th to endNight
16%417%31%22%7%
768
Page generated at 2017-09-11 16:35:15. Version ac04

Copyright 2017 A. Danko


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