Astro-chalet West
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Astro-chalet West 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
58%
15638
31%
46774
23%
15599
65%
15599
43%
24377

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
46%
716
23%
2482
17%
716
57%
716
29%
1385
January16th to endNight
44%
768
28%
2442
21%
768
55%
768
29%
1431
February1st to 15thNight
45%
700
27%
2112
22%
700
53%
700
31%
1268
February16th to endNight
45%
632
24%
1895
21%
632
52%
632
28%
1192
March1st to 15thNight
46%
720
20%
2160
18%
720
53%
720
29%
1312
March16th to endNight
45%
768
23%
1994
13%
768
54%
768
34%
1245
April1st to 15thNight
39%
719
24%
1799
10%
719
46%
719
32%
1125
April16th to endNight
45%
720
29%
1800
11%
720
52%
720
44%
997
May1st to 15thNight
46%
617
30%
1697
15%
617
54%
617
49%
867
May16th to endNight
42%
561
30%
1685
15%
561
53%
561
40%
819
June1st to 15thNight
54%
367
33%
1447
26%
367
70%
367
53%
546
June16th to endNight
66%
360
41%
1440
39%
360
79%
360
75%
440
July1st to 15thNight
85%
340
34%
1360
37%
340
90%
340
63%
472
July16th to endNight
85%
541
39%
1568
34%
506
86%
506
68%
650
August1st to 15thNight
80%
717
38%
1790
23%
713
81%
713
78%
808
August16th to endNight
87%
764
45%
1910
28%
764
88%
764
79%
867
September1st to 15thNight
89%
700
42%
1758
31%
700
92%
700
77%
806
September16th to endNight
78%
656
45%
1815
36%
656
86%
656
73%
772
October1st to 15thNight
64%
660
35%
1864
28%
660
74%
660
51%
940
October16th to endNight
64%
704
37%
2131
34%
704
71%
704
48%
1043
November1st to 15thNight
61%
700
31%
2275
29%
700
69%
700
40%
1170
November16th to endNight
56%
720
28%
2340
26%
720
62%
720
37%
1245
December1st to 15thNight
47%
720
27%
2340
20%
720
57%
720
32%
1342
December16th to endNight
43%
768
25%
2670
22%
768
51%
768
23%
1635

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%412212335%65%
47846
Night
6%5%13312335%62%
46961
TransparencyDay
21%27%16%27%24%
47532
Night
25%26%17%26%20%
46775
SeeingDay
11%15%39%25%6%1
5867
Night
9%8%21%31%24%5%
15649

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
7%6%25%3235%47%51%
1454
16th to endDay
10%10%24423345%47%
1779
February1st to 15thDay
9%8%23323446%49%
1751
16th to endDay
10%9%3433345%5%44%
1579
March1st to 15thDay
8%10%133246%5%8%45%
1800
16th to endDay
6%8%2332445%8%50%
2226
April1st to 15thDay
8%8%23323336%53%
2149
16th to endDay
5%6%22213338%61%
2160
May1st to 15thDay
4412213336%66%
2251
16th to endDay
5%411212336%66%
2429
June1st to 15thDay
211112335%76%
2509
16th to endDay
1111287%
2520
July1st to 15thDay
111112225%80%
2520
16th to endDay
21211223476%
2486
August1st to 15thDay
1111112384%
2160
16th to endDay
11212385%
2292
September1st to 15thDay
11112484%
2089
16th to endDay
111112384%
1815
October1st to 15thDay
5%312312246%65%
1763
16th to endDay
4412313246%65%
1739
November1st to 15thDay
6%6%23323236%59%
1584
16th to endDay
5%8%23413346%56%
1620
December1st to 15thDay
8%5%343235%5%7%50%
1620
16th to endDay
12%10%34413336%46%
1551
January1st to 15thNight
8%8%34323347%50%
2482
16th to endNight
8%9%24324347%48%
2442
February1st to 15thNight
7%11%25%422247%48%
2101
16th to endNight
12%9%245%24345%45%
1895
March1st to 15thNight
7%9%3443445%8%46%
2160
16th to endNight
8%8%23424348%48%
1994
April1st to 15thNight
10%7%2341245%5%52%
1799
16th to endNight
7%413213336%63%
1800
May1st to 15thNight
5%212212247%67%
1697
16th to endNight
6%212211235%69%
1684
June1st to 15thNight
211212325%76%
1447
16th to endNight
1111388%
1440
July1st to 15thNight
11121123479%
1440
16th to endNight
21111122479%
1677
August1st to 15thNight
111112385%
1800
16th to endNight
11122386%
1910
September1st to 15thNight
111122484%
1758
16th to endNight
11111122383%
1815
October1st to 15thNight
5%31321234467%
1864
16th to endNight
6%313212435%66%
2131
November1st to 15thNight
6%7%23312246%58%
2275
16th to endNight
7%6%2331325%8%53%
2340
December1st to 15thNight
8%8%24323447%50%
2340
16th to endNight
12%11%34422446%43%
2670

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
32%47%18%22%15%
1454
16th to endDay
39%37%12%18%17%
1779
February1st to 15thDay
34%46%19%20%14%
1751
16th to endDay
40%38%18%24%3
1579
March1st to 15thDay
35%412%16%18%12%
1800
16th to endDay
32%411%23%18%8%
2226
April1st to 15thDay
32%311%25%19%9%
2149
16th to endDay
20%316%23%26%9%
2160
May1st to 15thDay
19%29%23%32%12%
2251
16th to endDay
20%27%26%34%8%
2432
June1st to 15thDay
13%26%16%32%28%
2509
16th to endDay
6%136%31%49%
2520
July1st to 15thDay
10%129%21%53%
2371
16th to endDay
14%2413%31%34%
2332
August1st to 15thDay
8%128%28%50%
2146
16th to endDay
7%127%41%39%
2292
September1st to 15thDay
7%1411%32%42%
2089
16th to endDay
8%1212%38%36%
1815
October1st to 15thDay
21%16%18%28%23%
1763
16th to endDay
18%36%15%27%28%
1739
November1st to 15thDay
24%39%14%29%18%
1584
16th to endDay
28%48%15%22%20%
1620
December1st to 15thDay
31%5%9%18%20%14%
1620
16th to endDay
40%39%18%17%10%
1551
January1st to 15thNight
34%36%17%21%16%
2482
16th to endNight
36%38%12%19%19%
2442
February1st to 15thNight
37%26%14%21%17%
2112
16th to endNight
40%39%18%22%6%
1895
March1st to 15thNight
36%410%18%17%12%
2160
16th to endNight
34%413%21%19%6%
1994
April1st to 15thNight
34%311%24%20%6%
1799
16th to endNight
22%211%31%24%6%
1800
May1st to 15thNight
19%37%29%32%7%
1698
16th to endNight
19%38%28%34%5%
1685
June1st to 15thNight
14%17%20%32%23%
1447
16th to endNight
5%139%35%43%
1440
July1st to 15thNight
10%1310%24%48%
1360
16th to endNight
11%1418%29%33%
1568
August1st to 15thNight
7%1210%33%44%
1790
16th to endNight
7%1110%47%31%
1910
September1st to 15thNight
8%25%12%33%39%
1758
16th to endNight
8%1218%38%31%
1815
October1st to 15thNight
20%2420%29%22%
1864
16th to endNight
20%3416%29%25%
2131
November1st to 15thNight
28%26%15%27%19%
2275
16th to endNight
28%37%15%22%21%
2340
December1st to 15thNight
33%47%16%24%14%
2340
16th to endNight
41%48%17%16%11%
2670

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%25%35%8%21
82
16th to endDay
23%21%36%14%31
265
February1st to 15thDay
16%23%31%24%31
266
16th to endDay
19%26%36%15%2
238
March1st to 15thDay
18%25%28%19%7%
270
16th to endDay
18%21%36%17%5%1
288
April1st to 15thDay
23%24%31%14%5%1
269
16th to endDay
14%31%35%14%21
270
May1st to 15thDay
13%22%39%18%41
288
16th to endDay
16%17%36%23%4
330
June1st to 15thDay
6%17%45%23%6%
315
16th to endDay
211%48%28%7%1
315
July1st to 15thDay
1445%36%8%2
305
16th to endDay
2140%39%12%3
327
August1st to 15thDay
26%48%30%8%3
315
16th to endDay
441%37%9%6%
332
September1st to 15thDay
35%47%33%8%2
294
16th to endDay
39%47%29%9%1
255
October1st to 15thDay
9%19%37%30%3
255
16th to endDay
7%17%36%31%6%
251
November1st to 15thDay
17%121%35%23%1
90
16th to endDay
15%16%36%23%7%
90
December1st to 15thDay
22%12%35%25%4
90
16th to endDay
28%16%29%17%5%1
67
January1st to 15thNight
11%8%27%32%13%6%
720
16th to endNight
14%12%22%30%15%4
768
February1st to 15thNight
11%10%26%28%17%5%
704
16th to endNight
17%9%23%28%15%4
632
March1st to 15thNight
12%12%23%30%16%4
720
16th to endNight
13%12%25%28%17%2
768
April1st to 15thNight
13%17%26%24%15%3
719
16th to endNight
10%17%25%25%17%3
720
May1st to 15thNight
8%10%31%30%16%1
618
16th to endNight
11%17%25%27%16%1
563
June1st to 15thNight
47%32%37%16%1
367
16th to endNight
130%41%24%1
360
July1st to 15thNight
28%40%45%2
340
16th to endNight
27%31%50%7%
541
August1st to 15thNight
114%35%39%7%
717
16th to endNight
9%30%45%12%
764
September1st to 15thNight
16%33%46%11%
700
16th to endNight
2413%31%37%11%
656
October1st to 15thNight
5%5%20%36%26%6%
660
16th to endNight
8%6%18%30%26%10%
704
November1st to 15thNight
10%418%32%25%8%
700
16th to endNight
10%6%22%33%21%6%
720
December1st to 15thNight
12%8%26%32%17%2
720
16th to endNight
18%11%22%30%13%2
768
Page generated at 2017-09-11 16:35:21. Version ac04

Copyright 2017 A. Danko


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