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 2018-01-12.

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%
16130
31%
48317
24%
16091
65%
16091
43%
25126

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%
760
22%
2637
16%
760
56%
760
28%
1493
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
88%
720
42%
1809
30%
720
91%
720
75%
839
September16th to endNight
77%
716
47%
1980
37%
716
87%
716
73%
837
October1st to 15thNight
65%
720
34%
2034
27%
720
74%
720
54%
1001
October16th to endNight
65%
768
39%
2325
36%
768
72%
768
49%
1128
November1st to 15thNight
61%
760
30%
2470
28%
760
68%
760
39%
1283
November16th to endNight
57%
780
30%
2535
29%
780
63%
780
38%
1340
December1st to 15thNight
49%
780
28%
2535
22%
780
59%
780
34%
1415
December16th to endNight
45%
832
26%
2893
23%
832
52%
832
24%
1751

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
4412212335%65%
49013
Night
6%5%13312336%62%
48504
TransparencyDay
21%27%16%27%24%
48699
Night
24%26%17%26%20%
48318
SeeingDay
10%15%39%25%7%1
6260
Night
9%8%21%31%24%5%
16141

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
8%6%25%4235%47%50%
1542
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
1111112484%
2151
16th to endDay
1111112384%
1980
October1st to 15thDay
5%312212245%67%
1923
16th to endDay
431221325%5%66%
1897
November1st to 15thDay
6%6%23323246%58%
1719
16th to endDay
5%7%23413347%56%
1755
December1st to 15thDay
8%5%233235%5%7%53%
1755
16th to endDay
11%9%34413346%46%
1680
January1st to 15thNight
8%8%3442345%6%48%
2637
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
1111122483%
1809
16th to endNight
11111122383%
1980
October1st to 15thNight
4312212235%69%
2034
16th to endNight
5%33212335%66%
2325
November1st to 15thNight
6%7%23323346%57%
2470
16th to endNight
7%6%2231425%8%53%
2535
December1st to 15thNight
8%7%24313447%52%
2535
16th to endNight
11%10%34422446%44%
2893

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
33%47%18%21%14%
1542
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%41%
2151
16th to endDay
8%1211%40%34%
1980
October1st to 15thDay
19%15%17%28%27%
1923
16th to endDay
18%26%15%26%31%
1897
November1st to 15thDay
24%39%16%28%17%
1719
16th to endDay
27%48%15%24%20%
1755
December1st to 15thDay
29%48%17%20%19%
1755
16th to endDay
38%29%17%18%12%
1680
January1st to 15thNight
35%36%17%20%15%
2637
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%38%
1809
16th to endNight
8%1218%40%29%
1980
October1st to 15thNight
19%1419%29%26%
2034
16th to endNight
20%3415%27%28%
2325
November1st to 15thNight
28%26%17%27%18%
2470
16th to endNight
28%37%15%23%22%
2535
December1st to 15thNight
31%46%15%23%18%
2535
16th to endNight
40%48%17%17%12%
2893

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
25%24%33%10%31
104
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
36%48%32%7%2
315
16th to endDay
39%46%29%8%1
315
October1st to 15thDay
7%18%40%28%4
315
16th to endDay
7%14%35%32%8%
313
November1st to 15thDay
14%5%29%30%18%
135
16th to endDay
12%14%30%28%13%
135
December1st to 15thDay
15%15%30%30%7%
135
16th to endDay
20%14%27%27%11%1
100
January1st to 15thNight
11%8%26%33%13%5%
764
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
17%34%44%11%
720
16th to endNight
2413%32%36%10%
716
October1st to 15thNight
5%5%20%37%25%5%
720
16th to endNight
7%6%17%30%26%11%
768
November1st to 15thNight
10%420%33%24%7%
760
16th to endNight
10%5%21%33%23%6%
780
December1st to 15thNight
11%8%25%32%18%2
780
16th to endNight
17%10%22%31%15%2
832
Page generated at 2018-01-12 19:01:38. Version ac04

Copyright 2018 A. Danko


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