Saint-Zénon
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Saint-Zénon clear sky chart from 2005-11-05 to 2018-02-14.

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
25%
15164
12%
48822
6%
15132
32%
15132
14%
35186

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
12%
780
9%
2716
2%
776
20%
776
7%
2130
January16th to endNight
16%
832
10%
2912
4%
832
25%
832
9%
2182
February1st to 15thNight
15%
760
11%
2513
2%
757
26%
757
10%
1891
February16th to endNight
15%
631
13%
1905
4%
631
27%
631
12%
1405
March1st to 15thNight
17%
720
12%
2160
6%
720
25%
720
12%
1651
March16th to endNight
25%
768
20%
1997
7%
768
34%
768
19%
1400
April1st to 15thNight
21%
718
15%
1796
5%
718
27%
718
16%
1360
April16th to endNight
23%
612
15%
1692
5%
612
31%
612
19%
1174
May1st to 15thNight
28%
367
14%
1447
13%
367
36%
367
14%
989
May16th to endNight
25%
375
13%
1497
8%
374
38%
374
14%
1008
June1st to 15thNight
28%
360
6%
1440
4%
360
35%
360
13%
1011
June16th to endNight
42%
360
6%
1440
7%
360
45%
360
16%
953
July1st to 15thNight
44%
340
9%
1360
12%
340
48%
340
22%
805
July16th to endNight
46%
376
11%
1418
13%
354
52%
354
21%
861
August1st to 15thNight
55%
359
13%
1430
15%
357
60%
357
20%
894
August16th to endNight
44%
729
18%
1875
9%
729
48%
729
30%
1234
September1st to 15thNight
41%
720
13%
1800
6%
720
44%
720
28%
1248
September16th to endNight
39%
717
20%
1966
12%
717
45%
717
30%
1251
October1st to 15thNight
27%
720
17%
2129
8%
720
38%
720
18%
1464
October16th to endNight
18%
768
10%
2469
5%
768
26%
768
11%
1917
November1st to 15thNight
23%
760
16%
2488
8%
760
33%
760
12%
1823
November16th to endNight
17%
780
12%
2730
6%
780
25%
780
9%
2057
December1st to 15thNight
13%
780
8%
2730
3%
780
19%
780
8%
2166
December16th to endNight
11%
832
10%
2912
3%
832
20%
832
6%
2312

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
18%11%47%6%34446%27%
49263
Night
16%11%47%6%3445%6%28%
48991
TransparencyDay
56%5%10%17%8%1
48950
Night
54%5%11%18%8%
48822
SeeingDay
25%16%29%17%8%2
5929
Night
23%15%29%22%8%
15164

By Month

Percentage Cloud Cover NE (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
15%18%7%9%8%5%444418%
1552
16th to endDay
10%13%7%11%8%35%6%47%21%
1664
February1st to 15thDay
8%16%5%11%9%5%6%445%21%
1646
16th to endDay
14%18%6%9%7%3434422%
1566
March1st to 15thDay
13%15%6%9%7%3443425%
1790
16th to endDay
14%11%48%5%35%336%33%
2226
April1st to 15thDay
20%14%46%5%23335%29%
2152
16th to endDay
20%11%46%5%2343432%
2271
May1st to 15thDay
21%11%37%5%34346%28%
2511
16th to endDay
23%10%46%5%24345%28%
2618
June1st to 15thDay
25%9%26%5%25%5%47%25%
2520
16th to endDay
22%8%37%5%45%45%7%24%
2520
July1st to 15thDay
17%7%45%6%46%5%5%7%28%
2520
16th to endDay
15%8%47%6%35%5%5%8%28%
2654
August1st to 15thDay
19%8%47%6%45%5%6%7%23%
2520
16th to endDay
13%7%26%6%35%5%5%9%34%
2314
September1st to 15thDay
19%8%26%5%33447%33%
2160
16th to endDay
18%8%23424236%41%
1993
October1st to 15thDay
24%10%36%5%4345%5%27%
1830
16th to endDay
26%15%5%8%6%2333420%
1754
November1st to 15thDay
17%15%5%7%6%25%45%5%24%
1698
16th to endDay
18%17%6%7%6%3323424%
1560
December1st to 15thDay
22%15%6%8%6%24445%19%
1560
16th to endDay
19%17%7%10%6%3434419%
1664
January1st to 15thNight
15%16%7%12%8%345%5%5%16%
2716
16th to endNight
10%12%6%10%10%5%5%5%5%6%20%
2912
February1st to 15thNight
7%14%7%11%9%5%6%45%6%21%
2511
16th to endNight
13%12%5%9%7%345%6%6%23%
1905
March1st to 15thNight
17%12%6%7%7%35%446%23%
2147
16th to endNight
12%11%36%5%25%45%5%36%
1997
April1st to 15thNight
22%10%5%6%5%23445%29%
1796
16th to endNight
18%9%35%424445%35%
1692
May1st to 15thNight
19%9%36%5%3424434%
1447
16th to endNight
22%7%35%5%24448%32%
1495
June1st to 15thNight
22%8%45%5%35%45%7%28%
1440
16th to endNight
17%7%25%435%5%7%7%33%
1440
July1st to 15thNight
12%435%4345%5%8%41%
1440
16th to endNight
11%5%26%6%2445%8%42%
1514
August1st to 15thNight
12%6%25%5%245%7%8%38%
1440
16th to endNight
12%6%25%5%3445%7%42%
1875
September1st to 15thNight
16%7%25%5%245%5%6%38%
1800
16th to endNight
16%6%2442335%6%45%
1966
October1st to 15thNight
17%8%47%434336%36%
2129
16th to endNight
24%13%48%5%32436%23%
2469
November1st to 15thNight
18%11%47%7%24446%28%
2488
16th to endNight
20%14%6%9%6%24345%22%
2730
December1st to 15thNight
19%16%7%10%7%34345%17%
2730
16th to endNight
17%16%7%10%6%45%5%45%15%
2912

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
67%47%13%6%
1553
16th to endDay
59%5%8%17%8%1
1664
February1st to 15thDay
63%29%15%7%
1648
16th to endDay
63%37%14%9%2
1566
March1st to 15thDay
61%39%12%11%1
1800
16th to endDay
51%38%18%14%4
2226
April1st to 15thDay
57%28%17%10%3
2152
16th to endDay
54%47%16%14%3
2271
May1st to 15thDay
56%47%17%11%1
2511
16th to endDay
57%5%9%16%9%1
2622
June1st to 15thDay
57%6%9%16%8%
2520
16th to endDay
56%6%11%17%7%
2520
July1st to 15thDay
50%6%14%20%7%
2371
16th to endDay
52%7%13%18%8%
2487
August1st to 15thDay
55%8%14%17%3
2506
16th to endDay
43%6%16%23%9%
2314
September1st to 15thDay
49%413%21%9%
2160
16th to endDay
44%412%28%10%
1993
October1st to 15thDay
56%411%19%6%
1830
16th to endDay
66%410%13%4
1754
November1st to 15thDay
59%5%11%15%8%
1698
16th to endDay
61%310%15%7%
1560
December1st to 15thDay
66%310%14%4
1560
16th to endDay
66%36%11%10%
1664
January1st to 15thNight
65%39%14%5%
2716
16th to endNight
60%49%14%9%1
2912
February1st to 15thNight
60%410%17%6%
2513
16th to endNight
57%49%16%11%1
1905
March1st to 15thNight
59%5%8%16%8%1
2160
16th to endNight
47%5%9%19%16%2
1997
April1st to 15thNight
56%37%18%11%1
1796
16th to endNight
48%410%20%13%3
1692
May1st to 15thNight
53%39%17%12%3
1447
16th to endNight
50%5%10%21%11%1
1497
June1st to 15thNight
52%6%13%18%7%
1440
16th to endNight
46%7%13%20%10%
1440
July1st to 15thNight
38%6%20%23%10%1
1360
16th to endNight
40%6%18%25%9%
1418
August1st to 15thNight
40%8%20%25%5%
1430
16th to endNight
38%6%17%29%8%
1875
September1st to 15thNight
42%6%16%22%11%
1800
16th to endNight
38%416%30%9%
1966
October1st to 15thNight
48%412%23%10%
2129
16th to endNight
60%5%11%16%5%
2469
November1st to 15thNight
55%5%11%18%7%1
2488
16th to endNight
61%411%16%5%
2730
December1st to 15thNight
66%411%13%4
2730
16th to endNight
66%48%11%7%1
2912

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
28%14%34%17%4
90
16th to endDay
20%22%40%11%31
96
February1st to 15thDay
29%28%32%8%
119
16th to endDay
26%25%26%17%3
225
March1st to 15thDay
25%23%29%17%3
270
16th to endDay
23%19%29%16%8%2
288
April1st to 15thDay
30%21%25%14%7%
270
16th to endDay
26%22%27%13%8%1
270
May1st to 15thDay
34%18%24%13%5%2
288
16th to endDay
27%18%28%17%6%
331
June1st to 15thDay
33%14%28%15%6%1
315
16th to endDay
23%13%36%20%5%
315
July1st to 15thDay
21%10%35%23%6%2
305
16th to endDay
15%7%34%29%11%2
326
August1st to 15thDay
21%7%31%25%10%4
313
16th to endDay
17%9%29%21%14%7%
332
September1st to 15thDay
23%9%27%18%14%5%
315
16th to endDay
19%13%25%21%13%7%
314
October1st to 15thDay
27%15%27%15%11%2
315
16th to endDay
36%16%24%13%7%
294
November1st to 15thDay
25%18%27%20%6%1
262
16th to endDay
33%26%27%6%41
90
December1st to 15thDay
27%22%38%8%2
90
16th to endDay
32%25%32%8%2
96
January1st to 15thNight
24%20%32%16%5%
780
16th to endNight
16%20%36%21%4
832
February1st to 15thNight
16%22%37%18%4
760
16th to endNight
21%18%35%18%4
631
March1st to 15thNight
27%19%30%18%3
720
16th to endNight
19%19%30%20%8%1
768
April1st to 15thNight
29%16%27%20%5%
718
16th to endNight
25%16%30%19%7%
612
May1st to 15thNight
26%10%28%24%8%1
367
16th to endNight
24%13%33%20%8%
375
June1st to 15thNight
26%11%26%27%6%1
360
16th to endNight
21%6%24%35%11%1
360
July1st to 15thNight
12%7%27%35%14%2
340
16th to endNight
15%425%37%15%
376
August1st to 15thNight
14%5%17%40%21%
359
16th to endNight
15%9%24%30%17%2
729
September1st to 15thNight
19%6%27%32%11%1
720
16th to endNight
18%10%27%24%16%1
717
October1st to 15thNight
23%16%27%20%10%1
720
16th to endNight
32%16%26%18%5%
768
November1st to 15thNight
26%16%27%17%9%1
760
16th to endNight
28%22%24%16%6%1
780
December1st to 15thNight
28%20%29%16%3
780
16th to endNight
29%21%28%15%41
832
Page generated at 2018-02-15 10:58:50. Version ac04

Copyright 2018 A. Danko


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