Observatoire de La Sitelle
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire de La Sitelle clear sky chart from 2005-11-05 to 2017-09-18.

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
26%
14604
13%
46849
6%
14572
33%
14572
15%
33603

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
13%
720
8%
2506
2%
716
21%
716
8%
1979
January16th to endNight
18%
768
11%
2688
4%
768
26%
768
11%
1994
February1st to 15thNight
15%
704
10%
2308
3%
701
24%
701
11%
1759
February16th to endNight
18%
631
13%
1910
5%
631
29%
631
12%
1425
March1st to 15thNight
16%
720
13%
2159
6%
720
25%
720
12%
1639
March16th to endNight
26%
768
20%
1992
7%
768
35%
768
21%
1383
April1st to 15thNight
21%
718
16%
1796
4%
718
28%
718
19%
1325
April16th to endNight
24%
630
16%
1710
6%
630
31%
630
20%
1197
May1st to 15thNight
24%
364
14%
1444
10%
364
35%
364
15%
997
May16th to endNight
26%
375
13%
1497
9%
374
40%
374
16%
992
June1st to 15thNight
28%
360
7%
1440
5%
360
36%
360
13%
1010
June16th to endNight
40%
360
7%
1440
9%
360
44%
360
16%
966
July1st to 15thNight
46%
340
11%
1360
15%
340
53%
340
24%
788
July16th to endNight
47%
376
11%
1418
12%
354
53%
354
21%
872
August1st to 15thNight
52%
362
13%
1433
12%
360
58%
360
20%
903
August16th to endNight
46%
747
19%
1893
9%
747
51%
747
33%
1213
September1st to 15thNight
41%
720
13%
1800
6%
720
44%
720
29%
1246
September16th to endNight
41%
669
20%
1824
12%
669
46%
669
31%
1177
October1st to 15thNight
28%
660
18%
1962
9%
660
38%
660
18%
1371
October16th to endNight
21%
704
11%
2249
5%
704
30%
704
13%
1698
November1st to 15thNight
24%
700
17%
2292
9%
700
34%
700
14%
1655
November16th to endNight
20%
720
12%
2520
7%
720
27%
720
10%
1888
December1st to 15thNight
14%
720
8%
2520
2%
720
21%
720
8%
1990
December16th to endNight
10%
768
10%
2688
2%
768
19%
768
7%
2136

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%10%47%6%3445%6%28%
47955
Night
16%10%47%5%3445%6%31%
47018
Cloud CoverDay
18%9%47%6%3445%6%29%
47964
Night
16%9%46%5%3445%6%32%
47024
TransparencyDay
54%6%11%17%8%1
47642
Night
51%7%11%19%9%1
46849
SeeingDay
23%15%30%19%7%2
5535
Night
21%15%31%22%8%
14604

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
19%15%6%9%7%4443419%
1432
16th to endDay
11%14%7%10%6%35%445%25%
1536
February1st to 15thDay
10%15%7%10%8%45%445%23%
1554
16th to endDay
13%19%5%8%7%25%34424%
1562
March1st to 15thDay
14%13%5%10%7%45%335%25%
1790
16th to endDay
15%9%46%5%24437%35%
2231
April1st to 15thDay
21%11%35%5%23345%31%
2152
16th to endDay
20%10%45%424445%33%
2256
May1st to 15thDay
22%10%37%5%34446%28%
2511
16th to endDay
23%8%35%5%3445%6%29%
2618
June1st to 15thDay
23%7%26%6%35%46%6%25%
2520
16th to endDay
21%7%35%6%45%5%6%6%26%
2520
July1st to 15thDay
16%5%36%6%35%46%7%32%
2520
16th to endDay
14%6%36%6%46%5%6%9%29%
2654
August1st to 15thDay
16%8%28%6%36%6%7%6%27%
2514
16th to endDay
12%5%26%5%4445%8%38%
2297
September1st to 15thDay
19%5%35%6%2445%7%35%
2160
16th to endDay
18%6%25%322346%43%
1859
October1st to 15thDay
23%9%26%424346%29%
1667
16th to endDay
26%11%47%7%3443421%
1623
November1st to 15thDay
17%11%36%6%435%5%6%29%
1563
16th to endDay
23%14%37%5%23345%25%
1440
December1st to 15thDay
22%18%6%8%5%23435%19%
1440
16th to endDay
20%17%7%9%6%33435%18%
1536
January1st to 15thNight
15%16%6%8%8%3445%6%17%
2506
16th to endNight
9%14%7%8%7%45%45%7%24%
2688
February1st to 15thNight
9%14%6%11%8%45%445%25%
2306
16th to endNight
13%14%5%10%5%35%45%6%25%
1910
March1st to 15thNight
17%11%49%5%35%45%5%27%
2146
16th to endNight
13%9%45%5%24446%39%
1992
April1st to 15thNight
23%7%36%433346%32%
1796
16th to endNight
18%8%345%235%5%6%36%
1710
May1st to 15thNight
20%8%45%6%23446%33%
1444
16th to endNight
20%6%3443336%7%35%
1495
June1st to 15thNight
22%7%445%345%5%7%29%
1440
16th to endNight
19%6%245%35%5%5%7%35%
1440
July1st to 15thNight
12%42442445%8%44%
1440
16th to endNight
9%5%25%335%7%6%7%42%
1514
August1st to 15thNight
10%5%25%6%25%5%7%9%38%
1443
16th to endNight
11%5%1342345%7%48%
1893
September1st to 15thNight
15%6%2443446%7%41%
1800
16th to endNight
18%414322436%46%
1824
October1st to 15thNight
18%7%35%6%34336%36%
1962
16th to endNight
24%9%26%5%24446%26%
2249
November1st to 15thNight
17%9%37%5%35%45%7%29%
2292
16th to endNight
19%14%5%8%5%24345%25%
2520
December1st to 15thNight
19%14%6%10%6%35%445%20%
2520
16th to endNight
19%16%6%8%7%34435%19%
2688

Percentage Cloud Cover SE (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
19%14%5%8%7%44345%20%
1432
16th to endDay
11%14%7%9%6%35%44426%
1536
February1st to 15thDay
10%16%6%10%8%35%446%23%
1554
16th to endDay
13%18%5%8%6%3443425%
1562
March1st to 15thDay
16%13%5%10%8%34425%26%
1800
16th to endDay
16%9%36%5%24346%36%
2230
April1st to 15thDay
21%11%35%5%23345%31%
2152
16th to endDay
20%10%45%5%24445%34%
2256
May1st to 15thDay
22%9%36%6%3445%6%27%
2511
16th to endDay
23%7%35%6%34446%29%
2618
June1st to 15thDay
22%7%36%6%36%5%5%7%25%
2520
16th to endDay
21%6%37%6%35%6%7%5%26%
2520
July1st to 15thDay
15%6%35%6%36%5%5%8%32%
2520
16th to endDay
14%6%26%7%36%5%7%8%30%
2654
August1st to 15thDay
16%7%36%6%46%6%6%6%28%
2514
16th to endDay
11%5%26%6%35%45%9%39%
2297
September1st to 15thDay
18%6%25%5%24446%37%
2160
16th to endDay
18%5%34423336%44%
1859
October1st to 15thDay
23%8%26%5%23346%31%
1667
16th to endDay
25%11%38%6%34345%22%
1623
November1st to 15thDay
16%9%36%5%35%45%7%30%
1563
16th to endDay
22%12%46%5%24345%27%
1440
December1st to 15thDay
22%16%7%8%5%2444420%
1440
16th to endDay
20%16%6%9%5%2434420%
1536
January1st to 15thNight
15%15%6%9%7%35%45%6%20%
2506
16th to endNight
10%14%6%8%7%45%446%27%
2688
February1st to 15thNight
9%13%6%10%9%45%5%5%426%
2299
16th to endNight
13%13%5%8%6%25%446%27%
1910
March1st to 15thNight
17%11%47%5%36%45%6%27%
2159
16th to endNight
12%8%45%5%24345%40%
1992
April1st to 15thNight
22%8%35%5%34445%33%
1796
16th to endNight
19%7%25%414447%36%
1710
May1st to 15thNight
19%8%45%6%23445%34%
1444
16th to endNight
21%5%35%414348%35%
1495
June1st to 15thNight
22%7%445%335%6%6%30%
1440
16th to endNight
19%5%25%425%5%5%7%35%
1440
July1st to 15thNight
12%41443445%8%44%
1440
16th to endNight
10%5%35%5%25%5%6%8%43%
1514
August1st to 15thNight
11%425%5%446%7%8%39%
1443
16th to endNight
11%5%1443345%7%49%
1893
September1st to 15thNight
13%6%244335%5%7%42%
1800
16th to endNight
17%41432335%5%48%
1824
October1st to 15thNight
18%7%35%6%24446%37%
1962
16th to endNight
25%8%35%5%24446%28%
2249
November1st to 15thNight
17%9%36%6%35%45%6%31%
2292
16th to endNight
19%13%47%425%345%28%
2520
December1st to 15thNight
19%13%6%9%6%25%446%22%
2520
16th to endNight
19%16%6%8%6%33345%22%
2688

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
66%6%7%14%5%
1433
16th to endDay
59%5%9%15%9%1
1536
February1st to 15thDay
61%410%16%6%
1556
16th to endDay
61%5%7%14%8%1
1562
March1st to 15thDay
61%48%14%9%1
1800
16th to endDay
47%5%9%17%14%4
2231
April1st to 15thDay
54%48%18%11%3
2152
16th to endDay
51%6%7%18%12%3
2256
May1st to 15thDay
56%5%8%16%11%1
2511
16th to endDay
54%7%10%16%10%1
2622
June1st to 15thDay
56%7%11%14%8%1
2520
16th to endDay
55%7%11%17%7%1
2520
July1st to 15thDay
46%8%14%21%8%
2371
16th to endDay
49%8%15%17%8%
2487
August1st to 15thDay
51%11%14%17%5%
2500
16th to endDay
40%8%18%22%9%
2297
September1st to 15thDay
46%7%13%21%11%
2160
16th to endDay
42%412%29%9%
1859
October1st to 15thDay
53%6%10%19%9%
1667
16th to endDay
63%7%11%12%5%
1623
November1st to 15thDay
51%8%15%14%9%
1563
16th to endDay
58%7%10%16%6%
1440
December1st to 15thDay
65%6%10%12%4
1440
16th to endDay
66%6%8%10%8%
1536
January1st to 15thNight
63%7%10%13%4
2506
16th to endNight
56%7%10%15%8%1
2688
February1st to 15thNight
59%6%10%16%6%
2308
16th to endNight
55%6%10%16%9%1
1910
March1st to 15thNight
56%7%8%16%9%1
2159
16th to endNight
45%5%10%18%17%2
1992
April1st to 15thNight
52%38%20%12%1
1796
16th to endNight
46%6%12%17%14%2
1710
May1st to 15thNight
51%6%9%15%13%3
1444
16th to endNight
47%6%11%21%11%1
1497
June1st to 15thNight
52%7%11%19%8%
1440
16th to endNight
46%8%11%20%12%
1440
July1st to 15thNight
35%7%18%25%12%
1360
16th to endNight
37%9%17%23%10%
1418
August1st to 15thNight
39%10%19%23%7%
1433
16th to endNight
33%7%17%30%10%
1893
September1st to 15thNight
39%9%14%25%11%
1800
16th to endNight
36%6%14%31%10%
1824
October1st to 15thNight
47%6%11%21%11%
1962
16th to endNight
55%8%11%17%7%
2249
November1st to 15thNight
52%7%12%18%7%2
2292
16th to endNight
57%7%10%16%6%
2520
December1st to 15thNight
62%8%11%14%3
2520
16th to endNight
64%7%9%11%6%1
2688

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%16%35%20%1
60
16th to endDay
25%20%35%12%33
64
February1st to 15thDay
32%27%32%5%2
87
16th to endDay
26%21%31%17%3
221
March1st to 15thDay
23%22%31%18%3
270
16th to endDay
22%19%29%18%7%2
288
April1st to 15thDay
30%19%27%14%6%1
270
16th to endDay
25%15%32%17%7%1
270
May1st to 15thDay
31%17%28%15%42
288
16th to endDay
28%16%32%16%6%
331
June1st to 15thDay
27%14%34%16%6%
315
16th to endDay
21%13%36%22%5%1
315
July1st to 15thDay
16%10%39%23%7%2
305
16th to endDay
15%7%31%32%11%1
326
August1st to 15thDay
17%8%30%28%11%3
313
16th to endDay
14%9%30%22%12%9%
332
September1st to 15thDay
19%11%26%23%12%6%
315
16th to endDay
19%13%25%20%13%7%
262
October1st to 15thDay
26%14%26%20%9%2
255
16th to endDay
32%15%27%16%7%
247
November1st to 15thDay
21%19%30%20%6%1
217
16th to endDay
35%23%25%15%1
60
December1st to 15thDay
28%26%28%13%3
60
16th to endDay
40%28%28%3
64
January1st to 15thNight
24%20%33%16%4
720
16th to endNight
16%18%36%22%41
768
February1st to 15thNight
17%20%37%18%5%
704
16th to endNight
21%16%37%19%3
631
March1st to 15thNight
24%18%36%18%2
720
16th to endNight
17%18%32%23%6%1
768
April1st to 15thNight
26%17%29%21%4
718
16th to endNight
24%17%29%20%6%
630
May1st to 15thNight
24%10%34%22%6%1
364
16th to endNight
22%10%37%22%7%
375
June1st to 15thNight
24%8%33%26%6%
360
16th to endNight
22%328%30%13%1
360
July1st to 15thNight
13%8%27%33%15%1
340
16th to endNight
12%428%39%13%1
376
August1st to 15thNight
13%422%39%18%1
362
16th to endNight
14%7%27%29%19%1
747
September1st to 15thNight
17%7%29%31%12%1
720
16th to endNight
19%11%25%24%16%2
669
October1st to 15thNight
22%14%28%23%10%
660
16th to endNight
30%13%29%19%6%
704
November1st to 15thNight
22%17%29%21%8%1
700
16th to endNight
25%22%25%17%6%1
720
December1st to 15thNight
28%20%29%17%3
720
16th to endNight
29%19%32%14%31
768
Page generated at 2017-09-19 07:32:21. Version ac04

Copyright 2017 A. Danko


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