Belleville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Belleville clear sky chart from 2005-11-06 to 2024-01-31.

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
30%
22795
15%
75016
8%
22756
38%
22756
17%
51880

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
15%
760
11%
2649
4%
757
25%
757
8%
2037
January11th to 20thNight
16%
760
8%
2660
4%
760
22%
760
8%
2107
January21st to endNight
20%
835
12%
2711
5%
835
29%
835
12%
2028
February1st to 10thNight
13%
720
10%
2340
2%
720
22%
720
10%
1799
February11th to 20thNight
16%
701
14%
2275
4%
700
29%
700
13%
1649
February21st to endNight
18%
592
15%
1821
5%
592
31%
592
14%
1309
March1st to 10thNight
20%
720
18%
2063
7%
720
30%
720
18%
1473
March11th to 20thNight
22%
720
16%
1979
6%
720
31%
720
18%
1409
March21st to endNight
26%
792
21%
2126
7%
792
36%
792
24%
1445
April1st to 10thNight
22%
720
17%
1800
4%
720
29%
720
21%
1304
April11th to 20thNight
26%
711
17%
1775
5%
711
32%
711
23%
1277
April21st to endNight
29%
600
16%
1680
7%
600
36%
600
21%
1184
May1st to 10thNight
36%
424
16%
1504
12%
424
43%
424
19%
976
May11th to 20thNight
37%
354
22%
1416
15%
354
54%
354
24%
818
May21st to endNight
44%
388
15%
1551
15%
388
53%
388
25%
884
June1st to 10thNight
37%
360
13%
1440
10%
360
48%
360
19%
900
June11th to 20thNight
41%
360
16%
1440
18%
360
53%
360
23%
824
June21st to endNight
45%
360
13%
1440
16%
360
54%
360
21%
868
July1st to 10thNight
54%
350
16%
1400
21%
350
62%
350
28%
752
July11th to 20thNight
53%
348
17%
1392
21%
348
60%
348
28%
771
July21st to endNight
55%
397
19%
1489
17%
375
61%
375
29%
804
August1st to 10thNight
57%
537
17%
1600
12%
534
60%
534
33%
970
August11th to 20thNight
57%
534
19%
1598
13%
534
62%
534
32%
979
August21st to endNight
49%
754
20%
1942
8%
754
55%
754
35%
1233
September1st to 10thNight
46%
720
17%
1800
6%
720
51%
720
34%
1183
September11th to 20thNight
55%
720
27%
1800
15%
720
59%
720
39%
1123
September21st to endNight
46%
720
21%
2066
15%
720
51%
720
27%
1344
October1st to 10thNight
34%
720
16%
2160
11%
720
41%
720
20%
1475
October11th to 20thNight
26%
720
14%
2160
8%
720
34%
720
17%
1548
October21st to endNight
21%
792
15%
2420
7%
792
32%
792
14%
1787
November1st to 10thNight
32%
740
18%
2443
13%
740
41%
740
20%
1605
November11th to 20thNight
22%
760
16%
2660
9%
760
33%
760
15%
1794
November21st to endNight
20%
760
10%
2660
5%
760
28%
760
11%
1942
December1st to 10thNight
16%
760
9%
2660
4%
760
23%
760
9%
2032
December11th to 20thNight
15%
759
10%
3248
3%
759
25%
759
8%
2378
December21st to endNight
13%
827
5%
4848
1%
817
20%
817
4%
3869

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
16%8%36%5%35%5%5%7%35%
74859
Night
17%9%46%6%35%5%5%7%35%
75265
TransparencyDay
47%7%13%21%11%1
74565
Night
49%6%12%20%11%1
75093
SeeingDay
20%15%31%21%10%3
13417
Night
21%12%30%25%10%1
22808

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 10thDay
17%14%48%7%35%45%6%28%
1517
11th to 20thDay
18%17%5%8%5%35%5%5%5%24%
1520
21st to endDay
14%13%6%10%9%45%6%5%5%24%
1869
February1st to 10thDay
14%14%5%11%8%45%6%5%6%22%
1620
11th to 20thDay
14%13%5%10%8%45%445%28%
1573
21st to endDay
20%12%48%6%446%35%27%
1434
March1st to 10thDay
15%11%39%7%46%5%5%6%30%
1891
11th to 20thDay
16%11%48%5%35%45%5%34%
1980
21st to endDay
20%8%36%5%44445%37%
2228
April1st to 10thDay
19%10%46%7%34446%33%
2160
11th to 20thDay
20%7%26%434346%40%
2134
21st to endDay
20%9%36%7%35%446%33%
2294
May1st to 10thDay
16%7%36%6%35%5%6%7%35%
2456
11th to 20thDay
14%6%35%5%35%5%5%8%41%
2478
21st to endDay
12%5%25%5%36%6%6%9%42%
2725
June1st to 10thDay
18%5%36%5%36%5%6%9%35%
2520
11th to 20thDay
13%5%25%435%6%7%9%41%
2520
21st to endDay
15%6%35%5%35%5%5%9%39%
2520
July1st to 10thDay
10%425%435%6%6%10%46%
2520
11th to 20thDay
11%5%245%46%6%7%10%41%
2520
21st to endDay
10%5%36%5%36%6%8%10%39%
2738
August1st to 10thDay
9%5%345%45%6%6%10%42%
2327
11th to 20thDay
10%5%25%6%46%6%7%9%41%
2303
21st to endDay
12%5%25%5%35%6%6%8%43%
2395
September1st to 10thDay
12%5%35%435%5%5%8%45%
2160
11th to 20thDay
11%43442445%8%50%
2160
21st to endDay
14%6%36%5%45%45%8%41%
1890
October1st to 10thDay
17%8%36%6%345%5%7%35%
1800
11th to 20thDay
20%7%37%6%35%5%5%7%32%
1800
21st to endDay
25%10%45%6%45%446%27%
1936
November1st to 10thDay
15%9%36%5%445%5%7%36%
1633
11th to 20thDay
15%10%47%6%35%5%5%7%32%
1520
21st to endDay
21%11%48%6%35%45%6%26%
1520
December1st to 10thDay
21%13%5%7%7%5%5%5%5%6%22%
1520
11th to 20thDay
19%13%5%7%6%445%45%28%
1906
21st to endDay
30%12%47%6%34345%21%
2772
January1st to 10thNight
19%13%6%9%7%45%445%25%
2649
11th to 20thNight
19%14%5%9%7%45%5%45%22%
2660
21st to endNight
15%13%5%9%7%45%5%5%5%28%
2711
February1st to 10thNight
17%14%5%10%7%45%445%24%
2340
11th to 20thNight
16%12%5%8%6%35%46%5%29%
2273
21st to endNight
17%10%46%6%445%5%7%31%
1821
March1st to 10thNight
15%9%47%6%445%5%6%34%
2053
11th to 20thNight
18%10%5%6%5%34446%35%
1979
21st to endNight
17%8%46%434446%40%
2126
April1st to 10thNight
20%8%36%5%35%45%6%35%
1800
11th to 20thNight
18%7%36%6%3445%5%38%
1775
21st to endNight
20%8%35%6%345%5%6%35%
1680
May1st to 10thNight
19%6%35%5%26%5%6%6%38%
1504
11th to 20thNight
12%6%35%6%35%5%6%8%43%
1415
21st to endNight
10%425%436%46%7%47%
1550
June1st to 10thNight
14%6%35%6%35%6%6%9%37%
1440
11th to 20thNight
10%5%35%6%3447%8%44%
1440
21st to endNight
12%7%25%6%35%46%8%42%
1440
July1st to 10thNight
8%425%435%5%6%7%52%
1440
11th to 20thNight
10%5%245%35%5%6%9%46%
1440
21st to endNight
10%5%244345%6%8%49%
1577
August1st to 10thNight
8%6%25%5%35%46%9%48%
1611
11th to 20thNight
8%6%36%435%46%10%46%
1598
21st to endNight
9%5%245%35%5%6%9%47%
1942
September1st to 10thNight
12%5%36%5%3446%8%45%
1800
11th to 20thNight
12%32342445%8%52%
1800
21st to endNight
17%6%25%5%345%47%44%
2066
October1st to 10thNight
16%7%36%6%445%5%7%37%
2160
11th to 20thNight
21%7%47%6%35%5%47%32%
2160
21st to endNight
23%9%36%6%345%5%7%30%
2420
November1st to 10thNight
19%6%35%5%3445%7%39%
2443
11th to 20thNight
18%9%35%5%45%5%6%7%33%
2660
21st to endNight
22%10%35%6%35%5%6%6%28%
2660
December1st to 10thNight
21%13%5%7%6%45%45%7%24%
2660
11th to 20thNight
19%14%38%6%34445%29%
3288
21st to endNight
30%15%47%5%3445%5%17%
4884

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
58%5%12%17%7%1
1518
11th to 20thDay
63%5%10%12%9%1
1520
21st to endDay
62%6%9%13%8%1
1869
February1st to 10thDay
62%7%11%13%5%1
1620
11th to 20thDay
59%6%9%14%10%1
1582
21st to endDay
60%5%10%15%10%1
1434
March1st to 10thDay
53%7%13%17%9%2
1894
11th to 20thDay
53%6%10%19%11%2
1980
21st to endDay
50%48%18%15%4
2228
April1st to 10thDay
53%48%20%11%3
2160
11th to 20thDay
46%49%24%16%2
2134
21st to endDay
51%5%10%18%13%3
2294
May1st to 10thDay
47%7%10%19%15%3
2456
11th to 20thDay
40%6%10%26%15%2
2482
21st to endDay
37%8%17%22%13%2
2725
June1st to 10thDay
44%8%13%20%13%2
2520
11th to 20thDay
38%6%14%26%14%2
2520
21st to endDay
41%7%15%23%13%1
2520
July1st to 10thDay
32%8%13%29%17%1
2450
11th to 20thDay
35%7%18%29%10%
2445
21st to endDay
38%8%16%25%11%1
2585
August1st to 10thDay
35%9%17%26%11%1
2314
11th to 20thDay
36%9%18%25%12%1
2303
21st to endDay
35%8%15%30%11%1
2395
September1st to 10thDay
35%8%16%28%12%1
2160
11th to 20thDay
32%5%14%31%15%1
2160
21st to endDay
42%7%14%28%9%
1890
October1st to 10thDay
47%6%14%20%12%1
1800
11th to 20thDay
50%7%16%19%7%1
1800
21st to endDay
59%5%11%16%8%
1936
November1st to 10thDay
46%7%15%22%10%1
1633
11th to 20thDay
51%7%14%18%9%1
1520
21st to endDay
58%6%13%15%8%
1520
December1st to 10thDay
63%6%13%13%5%
1520
11th to 20thDay
59%8%13%13%7%
1906
21st to endDay
66%7%9%14%4
2772
January1st to 10thNight
63%5%9%16%7%
2649
11th to 20thNight
64%7%10%12%7%1
2660
21st to endNight
58%6%10%16%10%1
2711
February1st to 10thNight
62%5%12%15%5%1
2340
11th to 20thNight
55%5%11%19%9%1
2275
21st to endNight
52%6%13%19%9%1
1821
March1st to 10thNight
51%5%12%19%11%2
2063
11th to 20thNight
51%412%21%11%1
1980
21st to endNight
45%49%21%17%4
2126
April1st to 10thNight
49%5%9%21%13%3
1800
11th to 20thNight
47%6%9%19%18%1
1775
21st to endNight
48%6%10%17%15%3
1680
May1st to 10thNight
46%6%8%20%17%3
1504
11th to 20thNight
38%5%11%27%16%3
1416
21st to endNight
35%7%15%21%19%4
1551
June1st to 10thNight
43%7%11%23%15%2
1440
11th to 20thNight
36%6%13%22%20%3
1440
21st to endNight
41%6%13%24%14%2
1440
July1st to 10thNight
29%9%11%26%24%2
1400
11th to 20thNight
33%6%13%30%16%
1392
21st to endNight
31%7%15%33%13%1
1489
August1st to 10thNight
34%6%17%29%13%1
1600
11th to 20thNight
34%7%17%26%14%2
1598
21st to endNight
32%8%14%31%14%1
1942
September1st to 10thNight
35%7%17%26%13%1
1800
11th to 20thNight
31%6%14%32%17%1
1800
21st to endNight
40%6%13%27%13%1
2066
October1st to 10thNight
46%7%11%20%14%1
2160
11th to 20thNight
52%5%14%21%7%
2160
21st to endNight
55%6%13%15%10%1
2420
November1st to 10thNight
45%5%15%22%12%1
2443
11th to 20thNight
48%6%15%19%10%2
2660
21st to endNight
54%8%17%16%5%1
2660
December1st to 10thNight
60%7%13%15%4
2660
11th to 20thNight
58%6%12%17%6%1
3288
21st to endNight
69%6%11%11%3
4884

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
26%20%32%12%8%2
180
11th to 20thDay
26%23%31%17%31
180
21st to endDay
22%22%35%16%41
293
February1st to 10thDay
30%26%35%9%1
240
11th to 20thDay
28%26%36%9%1
240
21st to endDay
36%19%34%10%1
300
March1st to 10thDay
23%19%38%16%3
420
11th to 20thDay
27%20%31%18%4
420
21st to endDay
32%15%31%14%7%1
462
April1st to 10thDay
25%22%33%13%6%1
420
11th to 20thDay
26%19%28%17%7%4
412
21st to endDay
27%18%35%14%5%1
420
May1st to 10thDay
23%15%30%22%8%4
423
11th to 20thDay
18%12%37%20%10%3
447
21st to endDay
14%14%33%23%12%4
485
June1st to 10thDay
19%13%36%23%8%2
450
11th to 20thDay
15%13%33%24%12%3
450
21st to endDay
18%9%32%26%12%3
450
July1st to 10thDay
9%9%28%29%21%4
445
11th to 20thDay
15%9%27%28%17%5%
444
21st to endDay
12%9%35%29%11%4
488
August1st to 10thDay
11%7%30%30%16%7%
446
11th to 20thDay
10%7%27%31%18%7%
439
21st to endDay
14%12%29%24%14%8%
495
September1st to 10thDay
12%10%30%27%13%7%
450
11th to 20thDay
10%8%29%24%19%10%
450
21st to endDay
16%13%27%26%14%5%
450
October1st to 10thDay
21%17%23%20%14%6%
450
11th to 20thDay
23%19%32%18%8%1
450
21st to endDay
30%16%29%20%4
473
November1st to 10thDay
25%17%27%21%9%1
327
11th to 20thDay
27%18%36%13%41
180
21st to endDay
27%20%34%14%41
180
December1st to 10thDay
26%22%32%16%41
180
11th to 20thDay
31%22%32%13%3
180
21st to endDay
34%20%32%12%2
198
January1st to 10thNight
28%20%30%18%5%
760
11th to 20thNight
30%16%29%18%6%
760
21st to endNight
22%16%34%24%4
835
February1st to 10thNight
24%19%36%19%2
720
11th to 20thNight
22%18%36%18%4
703
21st to endNight
25%19%34%19%3
592
March1st to 10thNight
20%15%39%23%3
720
11th to 20thNight
25%16%32%22%5%1
720
21st to endNight
22%13%34%23%7%1
792
April1st to 10thNight
23%14%35%23%5%
720
11th to 20thNight
22%15%33%21%9%1
711
21st to endNight
24%11%30%23%11%1
600
May1st to 10thNight
24%6%27%28%14%1
424
11th to 20thNight
15%7%35%32%11%
354
21st to endNight
11%6%34%33%14%2
389
June1st to 10thNight
14%6%34%33%13%1
360
11th to 20thNight
11%8%32%31%17%1
360
21st to endNight
16%5%28%39%12%1
360
July1st to 10thNight
6%7%26%40%20%1
350
11th to 20thNight
12%325%37%22%1
348
21st to endNight
11%227%45%15%1
397
August1st to 10thNight
9%422%38%25%3
537
11th to 20thNight
9%6%20%37%25%4
534
21st to endNight
11%5%28%34%21%2
754
September1st to 10thNight
14%6%28%31%20%3
720
11th to 20thNight
14%5%22%29%25%5%
720
21st to endNight
19%8%23%29%18%4
720
October1st to 10thNight
20%12%29%21%16%2
720
11th to 20thNight
23%13%33%23%8%1
720
21st to endNight
27%14%31%23%5%
792
November1st to 10thNight
24%14%25%28%9%1
740
11th to 20thNight
23%18%31%21%6%1
760
21st to endNight
30%16%28%20%6%
760
December1st to 10thNight
29%18%30%19%3
760
11th to 20thNight
27%17%35%18%3
760
21st to endNight
34%16%30%18%2
836
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