Observatoire du Geai Bleu
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire du Geai Bleu clear sky chart from 2005-11-05 to 2017-09-15.

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
34%
14606
14%
46813
9%
14574
40%
14574
18%
33156

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
20%
720
10%
2506
5%
716
26%
716
10%
1923
January16th to endNight
27%
768
11%
2688
7%
768
34%
768
13%
1969
February1st to 15thNight
24%
704
9%
2319
5%
701
30%
701
12%
1788
February16th to endNight
27%
631
14%
1893
7%
631
35%
631
15%
1414
March1st to 15thNight
26%
720
14%
2160
10%
720
32%
720
15%
1623
March16th to endNight
35%
768
19%
1998
10%
768
41%
768
25%
1400
April1st to 15thNight
29%
718
16%
1796
5%
718
35%
718
21%
1349
April16th to endNight
31%
617
17%
1697
7%
617
38%
617
22%
1192
May1st to 15thNight
33%
390
15%
1470
12%
390
42%
390
17%
995
May16th to endNight
34%
375
13%
1497
13%
374
43%
374
17%
983
June1st to 15thNight
39%
360
8%
1440
8%
360
45%
360
15%
999
June16th to endNight
44%
360
8%
1440
10%
360
48%
360
17%
950
July1st to 15thNight
55%
340
13%
1360
18%
340
60%
340
25%
784
July16th to endNight
55%
376
12%
1418
15%
354
58%
354
24%
840
August1st to 15thNight
56%
359
14%
1430
18%
357
59%
357
20%
893
August16th to endNight
55%
751
19%
1897
11%
751
58%
751
35%
1223
September1st to 15thNight
53%
720
14%
1800
7%
720
55%
720
30%
1239
September16th to endNight
48%
657
20%
1807
14%
657
52%
657
31%
1154
October1st to 15thNight
38%
660
20%
1941
12%
660
47%
660
23%
1320
October16th to endNight
30%
704
12%
2260
8%
704
37%
704
15%
1649
November1st to 15thNight
30%
700
17%
2277
11%
700
39%
700
17%
1606
November16th to endNight
25%
720
14%
2511
9%
720
33%
720
13%
1842
December1st to 15thNight
23%
720
9%
2520
4%
720
29%
720
11%
1928
December16th to endNight
17%
768
11%
2688
5%
768
25%
768
9%
2093

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
17%7%36%5%35%45%6%34%
47919
Night
18%8%36%5%34446%34%
46982
Cloud CoverDay
17%8%36%5%3445%6%33%
47929
Night
18%9%36%5%24446%33%
46987
TransparencyDay
49%6%12%19%10%1
47606
Night
51%6%11%19%10%1
46813
SeeingDay
21%6%25%27%15%4
5560
Night
22%6%28%30%10%
14606

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
20%12%49%5%34445%25%
1432
16th to endDay
12%15%48%6%34445%30%
1536
February1st to 15thDay
13%14%5%8%6%35%5%5%5%26%
1539
16th to endDay
16%12%5%9%7%2434428%
1580
March1st to 15thDay
16%10%47%6%5%5%35%5%28%
1790
16th to endDay
15%8%35%424346%39%
2223
April1st to 15thDay
21%8%35%435%34434%
2152
16th to endDay
20%6%25%5%24336%37%
2262
May1st to 15thDay
21%6%36%5%3445%5%32%
2491
16th to endDay
21%5%25%5%3445%7%33%
2618
June1st to 15thDay
21%6%25%5%2445%8%30%
2520
16th to endDay
18%5%35%6%36%6%5%8%29%
2520
July1st to 15thDay
13%4245%37%6%6%8%37%
2520
16th to endDay
12%425%5%35%6%6%9%36%
2654
August1st to 15thDay
13%426%7%46%6%7%8%33%
2507
16th to endDay
10%4144345%5%8%47%
2303
September1st to 15thDay
16%4244245%5%7%41%
2149
16th to endDay
15%424414336%48%
1823
October1st to 15thDay
21%7%345%25%45%5%35%
1686
16th to endDay
22%8%46%6%34445%28%
1611
November1st to 15thDay
16%8%45%5%245%5%6%34%
1581
16th to endDay
22%9%16%5%24447%31%
1446
December1st to 15thDay
25%11%5%7%425%446%23%
1440
16th to endDay
24%14%47%42443425%
1536
January1st to 15thNight
16%14%5%8%6%3445%6%23%
2506
16th to endNight
12%12%5%7%7%45%5%45%28%
2688
February1st to 15thNight
12%12%7%10%7%345%5%425%
2317
16th to endNight
17%11%48%5%35%445%29%
1893
March1st to 15thNight
20%10%46%5%25%445%29%
2147
16th to endNight
15%8%45%5%24435%40%
1998
April1st to 15thNight
24%8%36%423435%33%
1796
16th to endNight
21%6%35%42345%5%37%
1697
May1st to 15thNight
21%6%45%5%24445%35%
1470
16th to endNight
22%5%25%434447%34%
1495
June1st to 15thNight
24%5%25%5%24447%31%
1440
16th to endNight
16%6%245%35%5%5%8%35%
1440
July1st to 15thNight
11%424425%6%6%8%43%
1440
16th to endNight
11%4243345%7%9%42%
1514
August1st to 15thNight
11%426%5%445%6%8%39%
1440
16th to endNight
12%42432435%7%48%
1897
September1st to 15thNight
14%5%25%5%2345%7%43%
1800
16th to endNight
16%41331345%6%48%
1807
October1st to 15thNight
17%6%35%424445%40%
1941
16th to endNight
24%9%36%423345%33%
2260
November1st to 15thNight
19%8%36%4345%45%34%
2277
16th to endNight
22%10%37%5%34335%31%
2511
December1st to 15thNight
23%11%46%5%23345%26%
2520
16th to endNight
22%14%6%7%5%2334424%
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
21%12%5%7%6%33445%24%
1432
16th to endDay
13%14%38%6%3435%5%29%
1536
February1st to 15thDay
13%15%49%7%35%45%6%25%
1539
16th to endDay
16%13%5%8%6%3344328%
1580
March1st to 15thDay
17%10%47%7%45%34428%
1800
16th to endDay
17%9%35%423445%38%
2223
April1st to 15thDay
22%8%35%5%35%335%33%
2152
16th to endDay
20%7%25%5%24335%38%
2262
May1st to 15thDay
21%6%35%5%34446%32%
2491
16th to endDay
20%6%25%5%35%5%6%7%32%
2618
June1st to 15thDay
22%6%25%4345%5%8%30%
2520
16th to endDay
18%5%36%5%36%6%6%8%29%
2520
July1st to 15thDay
13%335%5%46%5%6%8%37%
2520
16th to endDay
11%5%26%5%35%6%6%8%37%
2654
August1st to 15thDay
12%427%7%36%5%7%7%34%
2507
16th to endDay
9%4234345%5%8%47%
2303
September1st to 15thDay
15%5%25%4245%5%7%41%
2149
16th to endDay
14%5%24333345%48%
1823
October1st to 15thDay
21%6%35%434445%35%
1686
16th to endDay
22%8%36%5%34445%29%
1611
November1st to 15thDay
15%9%37%43445%7%33%
1581
16th to endDay
22%10%25%425%436%31%
1446
December1st to 15thDay
26%10%46%6%3444423%
1440
16th to endDay
25%14%46%433335%24%
1536
January1st to 15thNight
16%15%6%8%6%34446%23%
2506
16th to endNight
13%13%5%8%6%35%5%45%27%
2688
February1st to 15thNight
13%12%7%10%8%345%5%424%
2310
16th to endNight
17%11%5%8%6%35%445%28%
1893
March1st to 15thNight
21%10%46%5%35%44429%
2160
16th to endNight
16%9%45%42443440%
1997
April1st to 15thNight
24%9%45%423435%32%
1796
16th to endNight
22%7%25%423446%37%
1697
May1st to 15thNight
21%6%36%5%24445%35%
1470
16th to endNight
20%6%35%42445%8%33%
1495
June1st to 15thNight
25%6%25%5%2345%7%30%
1440
16th to endNight
16%6%25%5%35%6%5%8%35%
1440
July1st to 15thNight
11%424435%5%7%9%42%
1440
16th to endNight
11%325%435%5%7%8%41%
1514
August1st to 15thNight
11%5%26%6%345%6%7%39%
1440
16th to endNight
12%4144235%5%7%48%
1897
September1st to 15thNight
14%5%35%42445%6%43%
1800
16th to endNight
16%424413446%48%
1807
October1st to 15thNight
17%6%26%424446%39%
1941
16th to endNight
24%10%35%423345%32%
2260
November1st to 15thNight
20%7%36%5%24445%33%
2277
16th to endNight
22%10%47%5%3424430%
2511
December1st to 15thNight
23%13%47%5%24345%25%
2520
16th to endNight
23%15%5%7%5%2433423%
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
62%5%9%14%6%
1433
16th to endDay
54%5%12%17%8%
1536
February1st to 15thDay
58%5%11%17%5%
1541
16th to endDay
59%410%15%8%1
1580
March1st to 15thDay
58%412%14%9%1
1800
16th to endDay
47%412%17%14%4
2223
April1st to 15thDay
54%47%19%11%2
2152
16th to endDay
48%5%8%19%14%3
2262
May1st to 15thDay
52%410%17%12%2
2491
16th to endDay
48%7%12%18%11%1
2622
June1st to 15thDay
50%6%12%18%10%1
2520
16th to endDay
49%8%11%20%8%1
2520
July1st to 15thDay
40%8%14%24%11%
2371
16th to endDay
41%9%17%22%8%
2487
August1st to 15thDay
45%8%17%21%7%
2493
16th to endDay
33%7%18%28%11%
2303
September1st to 15thDay
40%6%14%25%12%
2149
16th to endDay
38%413%31%11%
1823
October1st to 15thDay
50%6%10%22%10%
1686
16th to endDay
57%5%12%17%6%
1611
November1st to 15thDay
48%6%14%19%10%
1581
16th to endDay
54%5%13%19%7%
1446
December1st to 15thDay
61%6%11%15%4
1440
16th to endDay
63%5%10%12%8%
1536
January1st to 15thNight
61%5%10%15%5%
2506
16th to endNight
56%6%12%15%7%1
2688
February1st to 15thNight
60%6%10%15%6%
2319
16th to endNight
57%5%8%17%10%
1893
March1st to 15thNight
56%6%8%17%9%1
2160
16th to endNight
47%410%18%16%3
1998
April1st to 15thNight
54%35%20%13%1
1796
16th to endNight
48%5%8%19%15%4
1697
May1st to 15thNight
50%5%8%17%14%4
1470
16th to endNight
48%5%10%20%12%1
1497
June1st to 15thNight
53%5%10%18%10%
1440
16th to endNight
44%9%11%18%14%1
1440
July1st to 15thNight
34%8%14%26%14%1
1360
16th to endNight
36%8%19%22%13%
1418
August1st to 15thNight
40%8%16%22%11%
1430
16th to endNight
33%7%15%29%12%
1897
September1st to 15thNight
40%6%13%24%14%
1800
16th to endNight
37%6%12%31%13%
1807
October1st to 15thNight
45%6%10%24%12%
1941
16th to endNight
54%6%11%19%8%
2260
November1st to 15thNight
51%5%12%18%9%2
2277
16th to endNight
57%49%19%7%
2511
December1st to 15thNight
60%6%12%16%3
2520
16th to endNight
64%49%13%7%
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
16%15%23%33%11%
60
16th to endDay
28%9%29%21%6%4
64
February1st to 15thDay
30%13%30%22%2
84
16th to endDay
25%332%28%8%
239
March1st to 15thDay
23%7%32%28%7%
270
16th to endDay
23%5%28%28%11%2
288
April1st to 15thDay
25%12%24%23%9%3
270
16th to endDay
19%8%30%25%12%3
270
May1st to 15thDay
27%5%28%22%11%4
288
16th to endDay
22%7%29%22%15%2
331
June1st to 15thDay
26%6%25%26%11%2
315
16th to endDay
19%5%21%35%16%1
315
July1st to 15thDay
15%324%29%20%6%
305
16th to endDay
14%215%39%22%5%
326
August1st to 15thDay
15%316%32%24%7%
313
16th to endDay
9%418%29%21%15%
332
September1st to 15thDay
15%321%25%22%11%
311
16th to endDay
17%7%25%18%17%11%
254
October1st to 15thDay
21%7%24%26%17%2
255
16th to endDay
26%7%28%23%13%
245
November1st to 15thDay
22%5%30%25%13%2
235
16th to endDay
34%6%24%21%13%
66
December1st to 15thDay
28%330%28%6%3
60
16th to endDay
37%10%39%12%
64
January1st to 15thNight
23%11%32%25%7%
720
16th to endNight
18%7%35%29%8%
768
February1st to 15thNight
19%6%35%30%7%
704
16th to endNight
23%434%31%5%
631
March1st to 15thNight
26%7%33%27%5%
720
16th to endNight
20%5%30%32%10%
768
April1st to 15thNight
27%8%27%30%6%
718
16th to endNight
26%7%31%25%8%
617
May1st to 15thNight
24%430%31%8%
390
16th to endNight
23%432%31%8%
375
June1st to 15thNight
29%421%34%10%
360
16th to endNight
20%228%34%13%
360
July1st to 15thNight
11%425%39%19%
340
16th to endNight
12%121%46%16%1
376
August1st to 15thNight
14%215%42%23%1
359
16th to endNight
15%220%37%23%1
751
September1st to 15thNight
18%318%41%16%1
720
16th to endNight
19%324%31%19%1
657
October1st to 15thNight
20%5%29%33%10%
660
16th to endNight
29%7%26%26%9%
704
November1st to 15thNight
23%6%31%26%11%
700
16th to endNight
27%9%29%22%10%1
720
December1st to 15thNight
30%6%29%26%5%
720
16th to endNight
32%8%31%22%5%
768
Page generated at 2017-09-16 00:58:31. Version ac04

Copyright 2017 A. Danko


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