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 2018-03-11.

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%
16929
33%
49121
29%
16886
77%
16886
48%
25359

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
62%
777
29%
2522
27%
776
68%
776
37%
1345
January16th to endNight
60%
832
35%
2496
28%
832
69%
832
37%
1394
February1st to 15thNight
63%
759
32%
2290
29%
759
70%
759
39%
1261
February16th to endNight
55%
684
28%
2051
30%
684
58%
684
30%
1268
March1st to 15thNight
63%
764
27%
2283
28%
764
67%
764
38%
1283
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
90%
720
37%
1881
31%
720
91%
720
68%
891
September16th to endNight
87%
716
47%
1980
43%
716
90%
716
72%
859
October1st to 15thNight
77%
720
36%
1980
32%
720
80%
720
54%
1006
October16th to endNight
76%
768
39%
2286
38%
768
79%
768
50%
1123
November1st to 15thNight
73%
760
31%
2470
33%
760
78%
760
45%
1212
November16th to endNight
71%
780
36%
2535
37%
780
75%
780
44%
1254
December1st to 15thNight
61%
780
31%
2535
30%
780
66%
780
35%
1386
December16th to endNight
57%
832
31%
2704
28%
832
65%
832
33%
1541

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%
49490
Night
6%313213335%63%
49324
TransparencyDay
20%35%14%26%28%
49191
Night
22%36%15%22%30%
49124
SeeingDay
7%9%29%35%12%4
6524
Night
7%210%30%36%12%
16940

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
10%413213346%57%
1746
16th to endDay
11%423323436%55%
2077
February1st to 15thDay
8%413323345%59%
1901
16th to endDay
15%6%23424347%44%
1709
March1st to 15thDay
9%3123135%47%56%
1911
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
111212335%74%
2077
16th to endDay
11111222380%
1980
October1st to 15thDay
6%31221223468%
1980
16th to endDay
5%31221223370%
1932
November1st to 15thDay
6%422222336%62%
1719
16th to endDay
7%422312345%61%
1755
December1st to 15thDay
9%412333348%54%
1755
16th to endDay
13%5%13423435%52%
1872
January1st to 15thNight
8%41442335%6%56%
2522
16th to endNight
10%5%23313336%56%
2496
February1st to 15thNight
8%5%23323336%57%
2281
16th to endNight
13%7%2432433448%
2051
March1st to 15thNight
10%5%23323347%53%
2283
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
11221323477%
1881
16th to endNight
21111212282%
1980
October1st to 15thNight
5%312212326%68%
1980
16th to endNight
4313222335%67%
2286
November1st to 15thNight
6%41222333464%
2470
16th to endNight
6%5%13312336%61%
2535
December1st to 15thNight
10%42332235%6%54%
2535
16th to endNight
12%424323335%53%
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
28%35%13%24%25%
1747
16th to endDay
30%36%12%17%28%
2077
February1st to 15thDay
26%3413%22%28%
1901
16th to endDay
39%45%12%22%15%
1709
March1st to 15thDay
26%45%15%24%23%
1911
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%36%
2077
16th to endDay
10%227%35%40%
1980
October1st to 15thDay
20%25%13%26%31%
1980
16th to endDay
19%3310%19%43%
1932
November1st to 15thDay
24%25%13%20%33%
1719
16th to endDay
24%3411%21%34%
1755
December1st to 15thDay
28%47%13%17%28%
1755
16th to endDay
33%45%13%22%19%
1872
January1st to 15thNight
28%35%12%21%28%
2522
16th to endNight
30%35%12%16%31%
2496
February1st to 15thNight
29%3411%21%29%
2292
16th to endNight
38%4312%20%20%
2051
March1st to 15thNight
30%36%15%20%23%
2283
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%35%
1881
16th to endNight
10%137%36%40%
1980
October1st to 15thNight
19%25%15%26%30%
1980
16th to endNight
20%3410%17%42%
2286
November1st to 15thNight
22%4414%20%34%
2470
16th to endNight
24%2413%20%34%
2535
December1st to 15thNight
30%46%13%17%27%
2535
16th to endNight
32%47%11%19%23%
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
33%113%31%18%1
135
16th to endDay
14%14%30%28%8%3
349
February1st to 15thDay
6%14%33%28%12%4
326
16th to endDay
18%18%32%19%9%1
290
March1st to 15thDay
9%17%33%26%9%3
312
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
3130%49%9%4
315
16th to endDay
47%31%43%8%4
315
October1st to 15thDay
49%42%29%11%1
315
16th to endDay
9%6%30%28%20%5%
264
November1st to 15thDay
8%8%19%34%25%3
135
16th to endDay
14%8%18%29%22%5%
135
December1st to 15thDay
210%22%38%22%3
135
16th to endDay
13%8%24%25%22%4
144
January1st to 15thNight
9%5%15%35%25%8%
780
16th to endNight
13%5%14%32%27%6%
832
February1st to 15thNight
11%314%33%27%9%
764
16th to endNight
16%5%15%35%20%5%
684
March1st to 15thNight
11%414%36%25%6%
764
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
1219%56%19%
720
16th to endNight
36%28%43%17%
716
October1st to 15thNight
6%210%34%36%10%
720
16th to endNight
6%19%33%31%18%
768
November1st to 15thNight
7%111%38%29%11%
760
16th to endNight
9%210%33%30%14%
780
December1st to 15thNight
12%414%33%25%9%
780
16th to endNight
15%416%31%24%8%
832
Page generated at 2018-03-12 10:28:09. Version ac04

Copyright 2018 A. Danko


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