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 2018-04-23.

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%
15475
14%
49538
9%
15443
40%
15443
18%
35081

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
21%
780
10%
2716
5%
776
27%
776
10%
2083
January16th to endNight
26%
832
11%
2912
6%
832
33%
832
13%
2131
February1st to 15thNight
23%
764
10%
2517
5%
761
30%
761
12%
1939
February16th to endNight
27%
683
14%
2049
8%
683
35%
683
16%
1510
March1st to 15thNight
24%
780
13%
2340
9%
780
30%
780
14%
1790
March16th to endNight
36%
832
20%
2165
10%
832
42%
832
25%
1510
April1st to 15thNight
28%
778
16%
1946
5%
778
34%
778
21%
1468
April16th to endNight
31%
638
17%
1752
7%
638
38%
638
22%
1229
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
50%
717
22%
1971
15%
717
55%
717
33%
1244
October1st to 15thNight
39%
720
19%
2118
12%
720
49%
720
24%
1422
October16th to endNight
30%
768
13%
2466
8%
768
38%
768
16%
1783
November1st to 15thNight
29%
760
17%
2472
11%
760
38%
760
18%
1736
November16th to endNight
25%
780
14%
2720
9%
780
33%
780
13%
1995
December1st to 15thNight
22%
780
9%
2730
4%
780
29%
780
11%
2086
December16th to endNight
17%
832
12%
2912
5%
832
26%
832
10%
2249

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%33%
49982
Night
18%9%36%5%34446%34%
49707
Cloud CoverDay
17%8%36%5%3445%6%33%
49992
Night
18%9%36%5%24445%33%
49712
TransparencyDay
49%6%12%19%10%1
49669
Night
51%6%11%19%10%1
49538
SeeingDay
21%6%25%26%14%4
6230
Night
23%6%28%30%10%
15475

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%13%49%5%3444425%
1552
16th to endDay
12%14%48%6%3345%5%30%
1664
February1st to 15thDay
13%14%5%8%6%35%5%5%5%26%
1671
16th to endDay
16%12%5%9%7%2435%427%
1710
March1st to 15thDay
17%12%47%6%5%5%345%27%
1940
16th to endDay
14%8%35%5%24346%39%
2408
April1st to 15thDay
20%8%35%5%35%34433%
2332
16th to endDay
20%6%25%5%24336%38%
2322
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%6%41%
2160
16th to endDay
14%424414346%51%
1988
October1st to 15thDay
20%7%25%5%25%35%6%35%
1839
16th to endDay
21%8%46%6%34445%29%
1757
November1st to 15thDay
16%8%46%5%245%5%6%34%
1716
16th to endDay
21%9%26%5%24447%30%
1566
December1st to 15thDay
24%11%47%5%25%446%23%
1560
16th to endDay
23%14%47%42443425%
1664
January1st to 15thNight
17%14%5%8%6%3445%6%23%
2716
16th to endNight
13%12%5%7%7%45%5%45%28%
2912
February1st to 15thNight
12%12%7%10%7%445%5%425%
2515
16th to endNight
17%10%48%5%35%445%30%
2049
March1st to 15thNight
20%12%46%5%24445%27%
2327
16th to endNight
14%8%45%5%3443441%
2165
April1st to 15thNight
24%8%36%423435%32%
1946
16th to endNight
22%6%35%42345%5%38%
1752
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
15%41331345%6%49%
1971
October1st to 15thNight
16%6%25%424445%42%
2118
16th to endNight
23%9%36%423346%33%
2466
November1st to 15thNight
20%8%36%434445%34%
2472
16th to endNight
22%11%37%5%34335%31%
2720
December1st to 15thNight
22%12%5%6%5%23345%27%
2730
16th to endNight
21%14%6%7%5%2334424%
2912

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%13%5%7%6%34445%24%
1552
16th to endDay
12%14%38%7%3435%5%30%
1664
February1st to 15thDay
14%15%39%7%35%45%5%26%
1671
16th to endDay
17%13%5%8%6%3345%427%
1710
March1st to 15thDay
18%12%47%7%45%34427%
1950
16th to endDay
16%9%35%5%23445%39%
2408
April1st to 15thDay
21%9%45%6%35%335%32%
2332
16th to endDay
20%7%25%5%24335%38%
2322
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%
2160
16th to endDay
13%424333345%51%
1988
October1st to 15thDay
20%6%35%43445%6%35%
1839
16th to endDay
22%8%36%5%34445%30%
1757
November1st to 15thDay
16%9%36%43445%7%33%
1716
16th to endDay
22%9%35%5%35%446%30%
1566
December1st to 15thDay
25%10%46%6%3444424%
1560
16th to endDay
24%14%46%433335%24%
1664
January1st to 15thNight
17%15%6%8%6%34445%23%
2716
16th to endNight
13%12%5%8%6%35%5%45%27%
2912
February1st to 15thNight
13%12%7%10%8%445%5%424%
2508
16th to endNight
18%10%47%5%35%445%30%
2049
March1st to 15thNight
21%12%46%5%2444427%
2340
16th to endNight
16%8%45%42443441%
2164
April1st to 15thNight
24%9%45%5%23435%32%
1946
16th to endNight
23%6%25%423436%37%
1752
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
15%424423446%49%
1971
October1st to 15thNight
17%6%26%424446%41%
2118
16th to endNight
23%9%35%423346%32%
2466
November1st to 15thNight
20%7%35%5%24445%34%
2472
16th to endNight
22%11%46%5%3424430%
2720
December1st to 15thNight
22%13%47%5%23345%26%
2730
16th to endNight
22%15%5%7%5%2433424%
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
63%5%9%14%7%
1553
16th to endDay
54%6%12%17%8%
1664
February1st to 15thDay
59%5%11%17%5%
1673
16th to endDay
59%310%15%8%1
1710
March1st to 15thDay
60%411%14%9%1
1950
16th to endDay
46%412%18%14%4
2408
April1st to 15thDay
55%48%18%11%2
2332
16th to endDay
48%5%7%19%14%3
2322
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%
2160
16th to endDay
35%413%32%12%
1988
October1st to 15thDay
49%6%11%23%10%
1839
16th to endDay
56%5%13%17%6%
1757
November1st to 15thDay
49%6%14%19%9%
1716
16th to endDay
54%5%13%18%8%
1566
December1st to 15thDay
61%6%11%15%5%
1560
16th to endDay
62%5%10%12%8%
1664
January1st to 15thNight
61%5%10%15%5%
2716
16th to endNight
56%6%12%15%8%1
2912
February1st to 15thNight
60%6%10%15%6%
2517
16th to endNight
56%5%8%17%11%
2049
March1st to 15thNight
59%5%7%16%8%1
2340
16th to endNight
46%49%17%16%4
2165
April1st to 15thNight
55%35%19%14%1
1946
16th to endNight
48%47%19%15%4
1752
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
35%6%12%31%13%
1971
October1st to 15thNight
44%5%10%25%12%
2118
16th to endNight
53%6%12%20%8%
2466
November1st to 15thNight
51%5%12%19%9%2
2472
16th to endNight
57%49%19%7%
2720
December1st to 15thNight
60%5%12%16%4
2730
16th to endNight
63%48%13%7%
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
23%11%22%32%11%
90
16th to endDay
23%11%36%18%6%3
96
February1st to 15thDay
31%11%34%20%1
126
16th to endDay
28%332%27%6%
291
March1st to 15thDay
28%7%30%26%6%
330
16th to endDay
21%6%29%28%11%2
352
April1st to 15thDay
25%13%24%23%9%3
330
16th to endDay
20%7%29%24%14%3
289
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%12%
315
16th to endDay
14%6%23%20%22%12%
314
October1st to 15thDay
20%6%25%25%17%3
315
16th to endDay
25%8%29%23%12%
295
November1st to 15thDay
23%7%27%25%13%2
280
16th to endDay
33%8%27%19%11%
96
December1st to 15thDay
26%7%30%25%7%2
90
16th to endDay
33%12%33%16%4
96
January1st to 15thNight
24%10%31%26%7%
780
16th to endNight
18%8%35%29%7%
832
February1st to 15thNight
19%7%35%30%6%
764
16th to endNight
23%434%31%5%
683
March1st to 15thNight
28%7%31%26%5%
780
16th to endNight
20%5%30%33%10%
832
April1st to 15thNight
27%8%27%29%6%
778
16th to endNight
27%7%30%25%8%
638
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
18%323%31%21%2
717
October1st to 15thNight
19%5%28%33%12%
720
16th to endNight
28%8%26%26%8%
768
November1st to 15thNight
24%6%30%25%11%
760
16th to endNight
27%8%29%22%10%1
780
December1st to 15thNight
30%7%30%25%5%
780
16th to endNight
31%7%31%22%5%
832
Page generated at 2018-04-24 10:03:00. Version ac04

Copyright 2018 A. Danko


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