Sept-Īles
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Sept-Īles clear sky chart from 2005-11-05 to 2017-09-16.

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
29%
14512
12%
46762
6%
14483
37%
14483
15%
33499

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%
750
14%
2685
4%
746
32%
746
12%
1943
January16th to endNight
21%
783
15%
2781
6%
783
33%
783
14%
1918
February1st to 15thNight
26%
702
15%
2322
7%
701
38%
701
16%
1600
February16th to endNight
23%
631
9%
2030
4%
631
31%
631
11%
1545
March1st to 15thNight
24%
720
19%
2058
7%
720
36%
720
15%
1495
March16th to endNight
27%
768
18%
2112
6%
768
37%
768
18%
1494
April1st to 15thNight
23%
575
13%
1704
5%
575
30%
575
14%
1271
April16th to endNight
28%
540
17%
1620
8%
540
38%
540
20%
1103
May1st to 15thNight
36%
531
8%
1473
5%
531
39%
531
17%
1118
May16th to endNight
31%
374
9%
1309
5%
374
36%
374
13%
951
June1st to 15thNight
40%
360
3%
1260
2%
360
41%
360
16%
868
June16th to endNight
40%
360
2%
1260
1%
360
40%
360
15%
907
July1st to 15thNight
42%
340
3%
1190
2%
340
42%
340
18%
829
July16th to endNight
50%
376
9%
1241
8%
354
53%
354
20%
839
August1st to 15thNight
49%
488
7%
1539
6%
486
51%
486
18%
1105
August16th to endNight
43%
573
12%
1719
8%
573
47%
573
19%
1205
September1st to 15thNight
39%
585
14%
1806
8%
585
45%
585
22%
1215
September16th to endNight
36%
661
17%
1825
10%
661
42%
661
25%
1236
October1st to 15thNight
30%
660
19%
1974
9%
660
41%
660
20%
1348
October16th to endNight
25%
705
11%
2244
7%
705
31%
705
12%
1731
November1st to 15thNight
24%
730
14%
2453
6%
730
34%
730
12%
1817
November16th to endNight
24%
750
12%
2577
4%
750
33%
750
12%
1923
December1st to 15thNight
19%
750
10%
2700
4%
750
28%
750
11%
1955
December16th to endNight
18%
800
13%
2880
4%
800
29%
800
11%
2083

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
21%8%36%5%34446%31%
48025
Night
20%10%46%5%24445%32%
46911
TransparencyDay
54%5%11%18%8%1
47691
Night
54%411%19%9%1
46763
SeeingDay
28%11%25%22%10%2
6802
Night
25%11%24%26%11%1
14515

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
16%13%36%6%34435%30%
1253
16th to endDay
11%14%6%8%5%24245%34%
1440
February1st to 15thDay
7%10%5%8%8%45%45%6%33%
1538
16th to endDay
12%17%6%9%5%34345%27%
1443
March1st to 15thDay
14%11%47%333445%36%
1891
16th to endDay
13%14%5%6%6%33335%36%
2112
April1st to 15thDay
21%10%46%5%44345%28%
2244
16th to endDay
20%7%25%434446%38%
2340
May1st to 15thDay
25%6%25%5%24446%31%
2487
16th to endDay
27%6%35%5%24345%30%
2805
June1st to 15thDay
24%6%25%425%5%45%31%
2700
16th to endDay
30%5%245%245%5%7%26%
2700
July1st to 15thDay
20%6%35%5%345%6%7%31%
2700
16th to endDay
20%5%25%5%35%5%5%8%31%
2843
August1st to 15thDay
22%6%26%5%35%6%5%7%29%
2398
16th to endDay
20%5%36%6%35%45%8%30%
2483
September1st to 15thDay
23%5%25%434345%36%
2153
16th to endDay
23%4243235%36%38%
1825
October1st to 15thDay
19%6%25%5%35%45%5%35%
1656
16th to endDay
34%8%25%414335%25%
1625
November1st to 15thDay
27%9%14424445%31%
1405
16th to endDay
21%14%5%45%3443427%
1380
December1st to 15thDay
20%13%46%324445%30%
1260
16th to endDay
13%17%6%8%5%2433429%
1344
January1st to 15thNight
17%13%6%7%5%33435%29%
2685
16th to endNight
12%14%6%7%6%33345%32%
2781
February1st to 15thNight
8%10%5%9%7%34446%34%
2321
16th to endNight
14%17%6%8%6%3444326%
2030
March1st to 15thNight
14%12%6%8%5%3344432%
2046
16th to endNight
14%12%5%6%5%33446%35%
2112
April1st to 15thNight
22%11%36%6%3343429%
1704
16th to endNight
24%6%2442332341%
1620
May1st to 15thNight
27%6%35%5%335%5%5%27%
1473
16th to endNight
26%7%45%435%345%30%
1308
June1st to 15thNight
24%5%245%245%6%5%31%
1260
16th to endNight
28%5%25%4345%5%5%29%
1260
July1st to 15thNight
23%6%35%5%3346%7%30%
1260
16th to endNight
19%5%35%4346%5%6%34%
1325
August1st to 15thNight
22%5%35%43446%7%31%
1548
16th to endNight
20%5%25%6%345%6%7%31%
1719
September1st to 15thNight
22%5%244136%45%38%
1806
16th to endNight
22%5%13323445%41%
1825
October1st to 15thNight
24%5%25%412446%37%
1974
16th to endNight
32%9%35%42333426%
2244
November1st to 15thNight
25%11%245%345%4429%
2453
16th to endNight
24%13%5%5%324345%27%
2577
December1st to 15thNight
21%14%5%6%32323432%
2700
16th to endNight
17%13%6%7%5%2434430%
2880

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
56%312%17%7%
1254
16th to endDay
53%27%23%11%1
1440
February1st to 15thDay
51%313%21%7%1
1541
16th to endDay
59%37%19%8%1
1443
March1st to 15thDay
49%310%18%13%2
1902
16th to endDay
52%36%18%15%3
2112
April1st to 15thDay
59%48%13%11%2
2244
16th to endDay
47%410%20%14%2
2340
May1st to 15thDay
55%6%9%18%9%
2487
16th to endDay
57%5%8%17%9%1
2809
June1st to 15thDay
53%6%10%17%10%1
2700
16th to endDay
56%7%10%17%6%
2700
July1st to 15thDay
50%8%15%17%7%1
2541
16th to endDay
51%6%12%23%6%
2664
August1st to 15thDay
53%8%18%15%3
2383
16th to endDay
53%7%16%18%3
2483
September1st to 15thDay
49%6%14%20%8%
2153
16th to endDay
46%7%13%24%7%
1825
October1st to 15thDay
49%5%13%19%9%1
1656
16th to endDay
63%48%16%7%
1625
November1st to 15thDay
55%5%12%17%8%
1405
16th to endDay
61%410%17%5%
1380
December1st to 15thDay
57%412%20%4
1260
16th to endDay
59%211%16%8%
1344
January1st to 15thNight
57%311%17%8%
2685
16th to endNight
54%28%22%11%1
2781
February1st to 15thNight
51%39%21%10%2
2322
16th to endNight
62%37%16%10%
2030
March1st to 15thNight
54%36%19%16%
2058
16th to endNight
50%46%18%17%2
2112
April1st to 15thNight
58%38%12%13%4
1704
16th to endNight
49%27%18%20%1
1620
May1st to 15thNight
57%410%17%9%1
1473
16th to endNight
57%48%19%9%1
1310
June1st to 15thNight
50%5%11%18%12%1
1260
16th to endNight
55%5%11%19%8%
1260
July1st to 15thNight
50%6%16%18%7%
1190
16th to endNight
46%6%13%22%9%
1241
August1st to 15thNight
51%6%18%19%3
1539
16th to endNight
49%6%16%21%4
1719
September1st to 15thNight
45%5%13%26%7%
1806
16th to endNight
44%414%27%8%
1825
October1st to 15thNight
48%313%23%9%1
1974
16th to endNight
62%48%18%6%
2244
November1st to 15thNight
58%49%18%8%
2453
16th to endNight
59%413%17%5%
2577
December1st to 15thNight
58%313%18%6%
2700
16th to endNight
58%29%19%8%
2880

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
18%18%38%16%8%
60
16th to endDay
32%12%25%20%7%1
64
February1st to 15thDay
14%10%35%26%12%1
199
16th to endDay
21%16%24%24%8%4
216
March1st to 15thDay
25%14%31%17%8%2
270
16th to endDay
20%20%25%19%12%2
288
April1st to 15thDay
29%17%28%15%7%1
270
16th to endDay
26%12%32%17%8%2
270
May1st to 15thDay
32%8%24%18%12%4
426
16th to endDay
31%12%25%21%8%1
519
June1st to 15thDay
30%8%25%20%11%2
495
16th to endDay
34%7%18%23%11%3
495
July1st to 15thDay
21%10%26%25%14%2
475
16th to endDay
26%421%29%14%3
514
August1st to 15thDay
27%9%19%29%9%3
332
16th to endDay
28%8%24%24%9%3
332
September1st to 15thDay
29%10%27%22%6%3
315
16th to endDay
26%10%34%14%10%4
257
October1st to 15thDay
21%17%24%21%12%1
226
16th to endDay
43%8%17%14%12%2
240
November1st to 15thDay
36%14%18%24%5%
235
16th to endDay
31%8%24%21%13%
180
December1st to 15thDay
20%16%16%35%11%
60
16th to endDay
21%18%37%18%3
64
January1st to 15thNight
24%13%29%24%7%
750
16th to endNight
19%14%32%25%7%
783
February1st to 15thNight
13%14%32%25%12%1
704
16th to endNight
22%14%27%21%10%3
631
March1st to 15thNight
20%16%28%23%8%2
720
16th to endNight
20%15%26%26%10%
768
April1st to 15thNight
28%11%23%25%8%1
575
16th to endNight
27%10%26%23%10%2
540
May1st to 15thNight
31%6%17%31%10%3
531
16th to endNight
29%9%18%29%11%1
375
June1st to 15thNight
26%5%17%34%14%1
360
16th to endNight
30%6%14%32%14%1
360
July1st to 15thNight
27%318%29%19%1
340
16th to endNight
20%5%12%38%20%1
376
August1st to 15thNight
26%410%32%23%3
488
16th to endNight
21%5%19%31%19%2
573
September1st to 15thNight
25%6%22%31%12%2
585
16th to endNight
25%8%23%29%12%1
661
October1st to 15thNight
27%11%22%24%13%
660
16th to endNight
39%6%18%21%12%1
705
November1st to 15thNight
32%10%25%23%6%1
730
16th to endNight
30%12%24%23%8%1
750
December1st to 15thNight
26%15%27%21%8%
750
16th to endNight
24%18%30%17%8%1
800
Page generated at 2017-09-17 12:05:46. Version ac04

Copyright 2017 A. Danko


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