Breton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Breton clear sky chart from 2005-11-06 to 2024-02-10.

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
39%
23456
12%
80189
8%
23393
43%
23393
18%
54668

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 10thNight
31%
936
13%
4680
6%
926
36%
926
10%
3160
January11th to 20thNight
32%
937
20%
4598
7%
930
39%
930
12%
2973
January21st to endNight
28%
888
11%
4932
8%
876
37%
876
9%
3156
February1st to 10thNight
34%
758
13%
2652
10%
758
40%
758
14%
1909
February11th to 20thNight
33%
700
12%
2347
9%
700
38%
700
14%
1717
February21st to endNight
41%
592
16%
1830
13%
592
47%
592
19%
1297
March1st to 10thNight
38%
720
16%
2160
12%
720
44%
720
19%
1543
March11th to 20thNight
40%
720
17%
2029
9%
720
45%
720
22%
1436
March21st to endNight
36%
792
11%
2111
5%
792
39%
792
17%
1611
April1st to 10thNight
33%
664
12%
1744
4%
664
37%
664
18%
1325
April11th to 20thNight
34%
533
14%
1601
9%
533
40%
533
18%
1162
April21st to endNight
38%
540
12%
1620
11%
540
41%
540
21%
1099
May1st to 10thNight
40%
360
7%
1348
8%
360
43%
360
15%
943
May11th to 20thNight
45%
354
7%
1239
6%
354
47%
354
21%
819
May21st to endNight
41%
389
1%
1358
0%
388
42%
388
17%
953
June1st to 10thNight
40%
360
0%
1260
0%
360
40%
360
17%
891
June11th to 20thNight
40%
360
0%
1142
0%
360
40%
360
14%
862
June21st to endNight
51%
360
0%
1080
0%
360
51%
360
22%
742
July1st to 10thNight
58%
350
0%
1122
0%
350
58%
350
23%
739
July11th to 20thNight
53%
348
0%
1218
0%
348
53%
348
18%
817
July21st to endNight
61%
394
5%
1302
4%
372
61%
372
22%
823
August1st to 10thNight
58%
358
7%
1414
10%
356
60%
356
18%
881
August11th to 20thNight
58%
435
11%
1503
13%
435
60%
435
24%
933
August21st to endNight
54%
594
16%
1782
13%
594
57%
594
28%
1115
September1st to 10thNight
54%
625
15%
1705
10%
625
57%
625
30%
1111
September11th to 20thNight
50%
720
17%
1963
10%
720
53%
720
29%
1301
September21st to endNight
45%
720
20%
1980
12%
720
50%
720
31%
1264
October1st to 10thNight
43%
720
16%
2059
10%
720
49%
720
24%
1408
October11th to 20thNight
37%
720
17%
2340
10%
720
44%
720
22%
1541
October21st to endNight
34%
792
16%
2574
9%
792
43%
792
18%
1801
November1st to 10thNight
30%
883
14%
2548
9%
883
36%
883
16%
1938
November11th to 20thNight
29%
950
14%
2835
6%
950
36%
950
17%
2081
November21st to endNight
30%
950
11%
2850
5%
950
36%
950
19%
2043
December1st to 10thNight
32%
950
15%
2850
9%
950
37%
950
18%
2052
December11th to 20thNight
35%
949
13%
3476
8%
949
39%
949
15%
2488
December21st to endNight
35%
1035
11%
4937
7%
1026
42%
1026
14%
2734

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
10%9%47%6%46%6%6%8%34%
78072
Night
9%10%5%8%7%46%5%6%8%32%
80849
TransparencyDay
47%7%17%21%8%1
77772
Night
49%6%14%21%9%1
80729
SeeingDay
14%6%24%30%19%6%
14683
Night
14%6%29%35%15%2
23508

By Month

Percentage Cloud Cover NW (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 10thDay
313%5%11%9%45%6%5%8%30%
2219
11th to 20thDay
6%9%5%9%6%35%9%7%9%32%
2199
21st to endDay
6%11%5%8%6%5%6%6%5%8%34%
2711
February1st to 10thDay
10%12%5%10%7%5%6%6%7%7%24%
1512
11th to 20thDay
5%14%7%11%7%46%5%6%7%27%
1502
21st to endDay
311%7%13%9%5%7%8%7%7%23%
1422
March1st to 10thDay
6%13%6%10%9%46%5%7%6%27%
1800
11th to 20thDay
8%10%5%7%6%45%5%7%9%34%
1930
21st to endDay
7%15%6%8%7%46%5%6%9%26%
2242
April1st to 10thDay
9%11%6%7%8%5%5%7%8%7%27%
2216
11th to 20thDay
12%13%5%7%7%46%6%5%8%27%
2310
21st to endDay
11%9%47%7%5%6%6%6%9%31%
2340
May1st to 10thDay
13%10%47%8%47%6%6%8%29%
2608
11th to 20thDay
9%7%37%6%45%5%7%9%39%
2654
21st to endDay
19%7%36%6%35%5%6%8%34%
2917
June1st to 10thDay
17%8%26%6%45%6%7%9%31%
2700
11th to 20thDay
20%8%47%7%46%7%6%7%23%
2813
21st to endDay
11%5%26%5%46%7%7%9%37%
2880
July1st to 10thDay
12%6%36%6%35%5%7%9%36%
2801
11th to 20thDay
12%6%36%6%46%6%7%9%36%
2700
21st to endDay
10%425%6%36%6%7%9%43%
2938
August1st to 10thDay
10%6%25%5%46%6%8%10%37%
2517
11th to 20thDay
9%5%25%6%35%6%6%10%43%
2396
21st to endDay
12%6%26%435%6%6%9%41%
2574
September1st to 10thDay
14%6%26%5%35%5%6%8%41%
2253
11th to 20thDay
16%7%2443435%9%42%
1996
21st to endDay
11%7%35%446%5%6%8%42%
1980
October1st to 10thDay
12%10%48%7%35%446%38%
1900
11th to 20thDay
11%10%36%5%35%6%6%7%37%
1620
21st to endDay
9%14%48%8%46%45%7%32%
1782
November1st to 10thDay
10%15%5%10%6%5%5%5%5%7%26%
1511
11th to 20thDay
7%13%410%7%35%447%35%
1345
21st to endDay
6%9%6%9%8%45%7%7%8%29%
1330
December1st to 10thDay
8%12%6%12%9%47%45%8%27%
1330
11th to 20thDay
411%6%10%9%5%7%5%6%9%28%
1682
21st to endDay
49%48%6%46%5%6%9%39%
2442
January1st to 10thNight
412%6%12%9%45%5%5%7%29%
4726
11th to 20thNight
49%5%10%9%6%6%6%7%7%32%
4699
21st to endNight
7%14%5%9%7%46%5%6%7%31%
4976
February1st to 10thNight
7%13%6%11%8%45%5%6%7%26%
2652
11th to 20thNight
6%13%5%10%9%5%7%6%6%7%25%
2345
21st to endNight
6%13%5%9%8%47%6%5%7%31%
1830
March1st to 10thNight
6%11%5%9%8%47%5%7%9%28%
2160
11th to 20thNight
7%10%5%9%7%5%7%5%6%9%30%
2029
21st to endNight
6%15%5%12%7%47%5%5%7%26%
2111
April1st to 10thNight
9%12%47%10%46%6%8%7%26%
1744
11th to 20thNight
11%12%48%8%46%7%6%7%28%
1601
21st to endNight
13%10%47%6%345%6%9%33%
1620
May1st to 10thNight
14%12%38%7%27%6%5%8%27%
1348
11th to 20thNight
10%9%37%6%45%5%6%7%36%
1239
21st to endNight
19%10%37%6%35%5%5%7%31%
1358
June1st to 10thNight
18%8%37%6%46%6%6%8%28%
1260
11th to 20thNight
19%9%47%8%46%6%7%7%23%
1142
21st to endNight
14%6%26%7%36%8%7%8%33%
1080
July1st to 10thNight
13%5%25%7%446%7%8%37%
1156
11th to 20thNight
10%7%26%6%47%6%8%11%31%
1260
21st to endNight
12%5%25%5%36%6%7%9%39%
1379
August1st to 10thNight
11%7%26%5%5%5%6%7%10%36%
1421
11th to 20thNight
9%5%36%5%46%6%7%10%38%
1503
21st to endNight
12%6%36%5%345%8%9%40%
1782
September1st to 10thNight
14%5%26%5%346%6%9%41%
1705
11th to 20thNight
14%6%36%5%35%46%6%43%
1963
21st to endNight
11%6%35%5%445%6%9%42%
1980
October1st to 10thNight
11%9%38%6%35%6%5%7%37%
2059
11th to 20thNight
11%9%47%6%35%46%7%37%
2340
21st to endNight
8%11%49%9%45%5%6%7%31%
2574
November1st to 10thNight
12%14%6%9%7%36%5%5%7%26%
2548
11th to 20thNight
8%12%6%10%8%46%5%5%7%29%
2835
21st to endNight
7%11%5%9%8%45%6%6%9%28%
2850
December1st to 10thNight
8%13%6%9%8%45%5%6%7%31%
2850
11th to 20thNight
6%13%6%10%8%5%5%6%6%7%29%
3510
21st to endNight
49%47%6%45%5%6%7%43%
5214

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 10thDay
50%5%15%21%8%1
2219
11th to 20thDay
47%5%9%16%19%4
2220
21st to endDay
48%6%15%25%5%1
2711
February1st to 10thDay
56%6%12%15%10%1
1512
11th to 20thDay
55%7%14%16%8%
1510
21st to endDay
57%6%11%17%9%
1422
March1st to 10thDay
56%6%13%18%6%1
1800
11th to 20thDay
44%5%13%24%12%1
1931
21st to endDay
54%7%15%17%6%1
2242
April1st to 10thDay
51%9%14%17%8%1
2216
11th to 20thDay
54%6%12%21%7%
2310
21st to endDay
49%6%14%22%7%2
2340
May1st to 10thDay
51%7%14%20%8%
2608
11th to 20thDay
40%6%15%29%10%
2658
21st to endDay
48%7%15%21%9%
2918
June1st to 10thDay
48%6%18%22%5%
2700
11th to 20thDay
58%7%14%15%5%
2813
21st to endDay
39%9%23%23%5%1
2880
July1st to 10thDay
42%8%19%24%6%1
2726
11th to 20thDay
43%8%26%21%3
2619
21st to endDay
36%7%28%25%3
2775
August1st to 10thDay
40%8%26%23%3
2499
11th to 20thDay
36%7%27%24%7%
2396
21st to endDay
38%7%23%24%8%
2574
September1st to 10thDay
40%6%21%25%7%2
2253
11th to 20thDay
41%5%17%28%9%
1996
21st to endDay
40%7%16%24%10%2
1980
October1st to 10thDay
47%5%16%22%8%1
1900
11th to 20thDay
43%7%15%23%11%
1620
21st to endDay
52%5%11%23%9%1
1782
November1st to 10thDay
57%5%14%17%6%1
1511
11th to 20thDay
51%6%15%18%9%
1345
21st to endDay
49%8%16%18%7%2
1330
December1st to 10thDay
57%412%16%8%2
1330
11th to 20thDay
51%6%16%18%7%1
1684
21st to endDay
39%6%11%21%19%3
2442
January1st to 10thNight
54%5%13%17%9%2
4726
11th to 20thNight
50%5%10%15%16%4
4740
21st to endNight
51%6%16%19%8%1
4976
February1st to 10thNight
56%410%19%9%2
2652
11th to 20thNight
56%6%12%15%10%1
2347
21st to endNight
52%5%10%20%10%2
1830
March1st to 10thNight
51%6%13%23%6%1
2160
11th to 20thNight
50%5%11%21%13%1
2029
21st to endNight
56%6%12%18%7%1
2111
April1st to 10thNight
53%9%11%18%8%1
1744
11th to 20thNight
53%6%12%19%8%2
1601
21st to endNight
46%6%15%23%9%1
1620
May1st to 10thNight
53%6%13%20%7%1
1348
11th to 20thNight
46%6%11%23%13%1
1239
21st to endNight
52%6%13%17%9%2
1358
June1st to 10thNight
52%7%15%20%6%
1260
11th to 20thNight
56%8%17%15%4
1142
21st to endNight
44%9%19%22%5%1
1080
July1st to 10thNight
41%9%19%23%7%1
1122
11th to 20thNight
43%11%23%17%5%
1218
21st to endNight
40%9%22%24%5%
1302
August1st to 10thNight
41%9%23%23%4
1414
11th to 20thNight
39%8%22%24%6%1
1503
21st to endNight
38%6%18%28%9%1
1782
September1st to 10thNight
39%7%18%25%9%2
1705
11th to 20thNight
41%6%14%28%8%3
1963
21st to endNight
38%6%14%26%13%2
1980
October1st to 10thNight
46%5%14%24%10%1
2059
11th to 20thNight
45%6%14%25%9%1
2340
21st to endNight
50%7%13%22%8%1
2574
November1st to 10thNight
57%6%11%18%8%1
2548
11th to 20thNight
54%7%12%18%9%1
2835
21st to endNight
52%6%15%19%6%2
2850
December1st to 10thNight
53%5%10%20%9%3
2850
11th to 20thNight
54%6%15%19%6%
3507
21st to endNight
40%412%25%16%3
5214

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 10thDay
5%6%31%33%18%7%
180
11th to 20thDay
7%8%37%25%16%7%
180
21st to endDay
13%8%29%31%14%5%
198
February1st to 10thDay
15%10%30%26%16%4
178
11th to 20thDay
16%6%33%33%9%3
206
21st to endDay
7%6%34%30%18%6%
288
March1st to 10thDay
12%10%32%28%16%3
420
11th to 20thDay
9%6%34%30%14%6%
420
21st to endDay
16%7%28%28%17%4
462
April1st to 10thDay
10%13%31%30%12%3
420
11th to 20thDay
18%6%23%31%17%5%
412
21st to endDay
15%9%25%33%14%4
420
May1st to 10thDay
16%9%20%32%18%5%
514
11th to 20thDay
11%7%21%33%23%6%
625
21st to endDay
18%420%30%22%7%
679
June1st to 10thDay
18%7%21%35%16%3
630
11th to 20thDay
22%6%19%29%20%5%
743
21st to endDay
12%421%29%25%9%
810
July1st to 10thDay
14%320%33%22%8%
721
11th to 20thDay
15%5%18%32%24%6%
618
21st to endDay
10%416%31%27%12%
684
August1st to 10thDay
9%5%20%30%23%12%
457
11th to 20thDay
9%422%33%26%7%
437
21st to endDay
17%5%15%30%24%9%
495
September1st to 10thDay
17%6%26%24%21%6%
450
11th to 20thDay
20%323%30%18%7%
450
21st to endDay
14%9%29%26%19%4
450
October1st to 10thDay
19%5%27%27%16%7%
374
11th to 20thDay
12%10%31%30%13%5%
270
21st to endDay
15%12%34%28%10%2
297
November1st to 10thDay
20%6%27%33%12%3
270
11th to 20thDay
12%6%33%36%10%3
187
21st to endDay
8%8%34%34%11%5%
180
December1st to 10thDay
11%7%34%31%11%6%
180
11th to 20thDay
10%10%33%30%15%2
180
21st to endDay
8%5%29%30%21%7%
198
January1st to 10thNight
11%8%34%31%15%1
950
11th to 20thNight
12%8%33%33%13%1
950
21st to endNight
14%11%33%29%11%2
898
February1st to 10thNight
12%11%27%31%17%2
758
11th to 20thNight
13%8%31%34%13%1
704
21st to endNight
11%5%26%34%18%5%
592
March1st to 10thNight
11%5%33%33%15%3
720
11th to 20thNight
11%5%32%38%13%2
720
21st to endNight
13%6%29%37%14%3
792
April1st to 10thNight
14%7%31%33%13%2
664
11th to 20thNight
17%6%31%33%13%1
533
21st to endNight
16%8%26%37%11%1
540
May1st to 10thNight
21%6%22%36%14%2
360
11th to 20thNight
15%425%36%18%1
354
21st to endNight
21%322%35%16%1
389
June1st to 10thNight
21%423%37%12%2
360
11th to 20thNight
23%318%37%17%2
360
21st to endNight
16%419%36%23%3
360
July1st to 10thNight
15%313%44%23%1
350
11th to 20thNight
14%317%45%18%2
348
21st to endNight
14%5%12%42%25%3
394
August1st to 10thNight
16%217%35%25%4
358
11th to 20thNight
13%317%39%27%2
435
21st to endNight
14%318%42%22%1
594
September1st to 10thNight
16%317%45%18%2
625
11th to 20thNight
15%421%40%19%1
720
21st to endNight
13%5%30%36%13%3
720
October1st to 10thNight
17%427%38%14%1
720
11th to 20thNight
16%433%31%15%1
720
21st to endNight
14%7%32%35%11%1
792
November1st to 10thNight
19%8%31%30%11%2
883
11th to 20thNight
14%7%40%28%10%1
950
21st to endNight
13%5%39%31%10%2
950
December1st to 10thNight
14%9%33%29%12%3
950
11th to 20thNight
12%7%34%33%13%1
950
21st to endNight
11%5%33%34%15%2
1045
Page generated at 2024-02-07 04:11:55. Version ac07

Copyright 2024 Attilla Danko


Breton Clear Sky Chart |Charts Home