Observatoire de Val-Des-Bois
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire de Val-Des-Bois clear sky chart from 2005-11-05 to 2017-08-12.

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
27%
14475
13%
46493
7%
14443
35%
14443
16%
33108

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
16%
720
7%
2506
2%
716
22%
716
7%
2024
January16th to endNight
20%
768
12%
2659
5%
768
28%
768
11%
1981
February1st to 15thNight
16%
704
11%
2287
4%
701
26%
701
10%
1749
February16th to endNight
21%
631
14%
1949
6%
631
32%
631
13%
1462
March1st to 15thNight
20%
720
13%
2109
7%
720
28%
720
14%
1598
March16th to endNight
26%
768
20%
2028
9%
768
35%
768
20%
1398
April1st to 15thNight
23%
718
16%
1796
5%
718
29%
718
19%
1313
April16th to endNight
26%
627
17%
1707
7%
627
33%
627
20%
1193
May1st to 15thNight
31%
360
16%
1440
15%
360
42%
360
15%
941
May16th to endNight
33%
375
14%
1497
9%
374
47%
374
17%
969
June1st to 15thNight
32%
360
8%
1440
7%
360
40%
360
14%
963
June16th to endNight
42%
360
9%
1440
11%
360
48%
360
19%
907
July1st to 15thNight
49%
340
13%
1360
16%
340
57%
340
26%
752
July16th to endNight
51%
376
13%
1418
16%
354
56%
354
27%
798
August1st to 15thNight
47%
410
13%
1459
12%
408
52%
408
25%
883
August16th to endNight
41%
649
16%
1699
8%
649
46%
649
37%
1043
September1st to 15thNight
40%
660
15%
1650
6%
660
44%
660
28%
1147
September16th to endNight
42%
657
21%
1793
12%
657
47%
657
31%
1148
October1st to 15thNight
27%
660
18%
1980
10%
660
38%
660
18%
1390
October16th to endNight
24%
704
11%
2211
6%
704
31%
704
13%
1685
November1st to 15thNight
25%
700
17%
2337
10%
700
35%
700
15%
1647
November16th to endNight
18%
720
9%
2520
6%
720
24%
720
8%
1964
December1st to 15thNight
16%
720
9%
2520
3%
720
23%
720
8%
2000
December16th to endNight
12%
768
10%
2688
4%
768
21%
768
7%
2153

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
18%10%46%5%34446%30%
47493
Night
17%11%47%5%34445%31%
46662
Cloud CoverDay
23%9%36%5%24345%30%
47502
Night
20%9%36%5%23345%33%
46668
TransparencyDay
54%311%20%9%1
47180
Night
54%310%20%9%
46493
SeeingDay
25%13%29%20%8%3
5321
Night
24%13%27%24%9%1
14475

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
23%16%6%10%7%3423318%
1432
16th to endDay
14%15%7%9%6%35%445%23%
1563
February1st to 15thDay
11%16%6%12%8%44345%21%
1575
16th to endDay
16%16%7%8%6%34335%25%
1524
March1st to 15thDay
17%14%5%8%6%35%335%26%
1839
16th to endDay
14%8%46%5%33346%37%
2196
April1st to 15thDay
24%11%45%422335%30%
2152
16th to endDay
21%8%46%5%2343434%
2261
May1st to 15thDay
22%9%36%6%24346%31%
2511
16th to endDay
19%7%36%5%3445%6%32%
2618
June1st to 15thDay
21%8%35%5%35%45%7%28%
2520
16th to endDay
19%6%35%5%25%5%6%8%30%
2520
July1st to 15thDay
15%5%35%5%45%5%6%8%34%
2520
16th to endDay
13%7%25%6%35%5%7%8%32%
2654
August1st to 15thDay
15%6%36%6%35%5%5%8%33%
2404
16th to endDay
13%6%25%5%3446%8%38%
2140
September1st to 15thDay
18%7%35%5%23347%37%
1980
16th to endDay
19%6%24323446%43%
1837
October1st to 15thDay
23%8%35%5%34346%31%
1650
16th to endDay
29%14%37%6%2343421%
1660
November1st to 15thDay
16%11%46%5%24447%30%
1521
16th to endDay
23%15%6%7%5%2433422%
1440
December1st to 15thDay
21%18%7%10%5%35%445%13%
1440
16th to endDay
21%20%7%7%6%3423318%
1536
January1st to 15thNight
19%16%7%9%8%35%43416%
2506
16th to endNight
13%15%7%8%7%35%445%24%
2659
February1st to 15thNight
10%14%7%12%9%45%43422%
2285
16th to endNight
14%15%5%9%6%35%5%4425%
1949
March1st to 15thNight
19%11%5%7%6%3443427%
2096
16th to endNight
14%9%36%5%2433440%
2028
April1st to 15thNight
23%10%34424345%33%
1796
16th to endNight
18%9%36%5%14335%36%
1707
May1st to 15thNight
21%9%35%5%23345%35%
1440
16th to endNight
16%6%35%5%35%5%5%5%36%
1495
June1st to 15thNight
19%9%25%5%345%5%7%32%
1440
16th to endNight
16%5%245%36%5%5%7%37%
1440
July1st to 15thNight
11%5%243245%6%7%45%
1440
16th to endNight
8%5%244345%6%9%44%
1514
August1st to 15thNight
10%436%6%345%6%8%39%
1469
16th to endNight
10%43442345%7%47%
1699
September1st to 15thNight
16%6%26%5%2445%5%39%
1650
16th to endNight
17%6%25%423235%48%
1793
October1st to 15thNight
20%8%36%5%33437%33%
1980
16th to endNight
25%12%37%5%34345%26%
2211
November1st to 15thNight
19%9%47%6%3435%6%29%
2337
16th to endNight
22%14%5%9%5%3443322%
2520
December1st to 15thNight
21%18%6%8%6%3334418%
2520
16th to endNight
21%18%6%8%6%3433418%
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
22%16%5%9%7%3332321%
1432
16th to endDay
14%14%7%8%7%3435%5%25%
1563
February1st to 15thDay
13%15%6%12%8%4333423%
1575
16th to endDay
18%14%7%8%6%3333425%
1524
March1st to 15thDay
25%11%35%42423430%
1849
16th to endDay
25%6%35%323235%37%
2195
April1st to 15thDay
27%10%44322235%32%
2152
16th to endDay
23%8%35%42333436%
2261
May1st to 15thDay
33%7%25%42333429%
2511
16th to endDay
32%6%24423335%31%
2618
June1st to 15thDay
25%7%35%42345%6%30%
2520
16th to endDay
24%42442445%7%34%
2520
July1st to 15thDay
15%5%35%5%35%5%7%8%34%
2520
16th to endDay
14%6%35%6%35%6%6%8%33%
2654
August1st to 15thDay
31%425%5%34446%28%
2404
16th to endDay
32%314423346%33%
2140
September1st to 15thDay
18%5%26%42335%7%39%
1980
16th to endDay
18%5%23312346%45%
1837
October1st to 15thDay
22%8%35%43335%6%34%
1650
16th to endDay
28%12%37%5%2343423%
1660
November1st to 15thDay
20%10%35%5%24446%31%
1521
16th to endDay
26%13%5%6%5%1443324%
1440
December1st to 15thDay
21%18%5%9%5%44345%16%
1440
16th to endDay
21%18%7%6%6%3432321%
1536
January1st to 15thNight
18%16%6%7%7%35%34421%
2506
16th to endNight
12%15%7%7%7%3444429%
2659
February1st to 15thNight
13%13%6%11%7%5%443424%
2278
16th to endNight
17%14%5%9%5%3434427%
1949
March1st to 15thNight
30%7%35%42432330%
2109
16th to endNight
24%7%2442323341%
2028
April1st to 15thNight
26%8%44323335%35%
1796
16th to endNight
20%8%35%423335%37%
1707
May1st to 15thNight
27%8%25%31223337%
1440
16th to endNight
20%5%34433346%40%
1495
June1st to 15thNight
20%8%25%5%335%5%5%34%
1440
16th to endNight
19%6%13435%6%5%6%37%
1440
July1st to 15thNight
11%5%25%42445%7%47%
1440
16th to endNight
8%5%25%4345%6%8%45%
1514
August1st to 15thNight
24%325%42345%7%34%
1469
16th to endNight
25%413313346%40%
1699
September1st to 15thNight
16%6%25%5%335%36%41%
1650
16th to endNight
17%5%24322235%50%
1793
October1st to 15thNight
20%7%25%5%23446%36%
1980
16th to endNight
24%10%37%5%3233429%
2211
November1st to 15thNight
25%7%35%43333433%
2337
16th to endNight
25%12%47%5%2432327%
2520
December1st to 15thNight
22%15%5%7%6%3334424%
2520
16th to endNight
23%16%5%7%5%2333424%
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
71%27%12%5%
1433
16th to endDay
62%39%16%8%
1563
February1st to 15thDay
64%29%17%5%
1577
16th to endDay
62%29%14%10%1
1524
March1st to 15thDay
60%29%17%8%1
1849
16th to endDay
47%38%18%16%4
2196
April1st to 15thDay
55%27%18%13%2
2152
16th to endDay
53%26%20%13%3
2261
May1st to 15thDay
55%35%20%13%1
2511
16th to endDay
51%411%20%10%1
2622
June1st to 15thDay
54%410%22%8%
2520
16th to endDay
49%413%21%9%
2520
July1st to 15thDay
43%413%27%11%
2371
16th to endDay
46%5%15%22%9%
2487
August1st to 15thDay
48%5%15%23%7%
2390
16th to endDay
41%416%26%10%1
2140
September1st to 15thDay
46%312%26%10%
1980
16th to endDay
41%413%30%9%
1837
October1st to 15thDay
53%211%21%10%
1650
16th to endDay
66%49%14%4
1660
November1st to 15thDay
51%414%19%8%
1521
16th to endDay
65%211%13%5%
1440
December1st to 15thDay
71%310%11%2
1440
16th to endDay
70%38%10%6%
1536
January1st to 15thNight
69%39%12%4
2506
16th to endNight
61%39%17%8%
2659
February1st to 15thNight
63%29%18%5%
2287
16th to endNight
60%18%18%10%
1949
March1st to 15thNight
60%27%19%8%1
2109
16th to endNight
47%28%21%16%3
2028
April1st to 15thNight
53%26%20%15%1
1796
16th to endNight
50%37%20%15%2
1707
May1st to 15thNight
51%26%20%15%3
1440
16th to endNight
48%310%22%12%1
1497
June1st to 15thNight
51%411%23%8%
1440
16th to endNight
43%5%12%23%13%
1440
July1st to 15thNight
35%414%29%15%
1360
16th to endNight
35%416%29%13%
1418
August1st to 15thNight
39%5%18%26%9%
1459
16th to endNight
33%319%32%11%
1699
September1st to 15thNight
45%412%27%10%
1650
16th to endNight
40%212%35%8%
1793
October1st to 15thNight
51%39%24%11%
1980
16th to endNight
60%312%18%5%
2211
November1st to 15thNight
54%313%18%9%
2337
16th to endNight
64%410%15%4
2520
December1st to 15thNight
68%210%14%3
2520
16th to endNight
68%38%13%5%
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
35%15%26%18%5%
60
16th to endDay
33%7%39%15%21
69
February1st to 15thDay
33%20%37%7%1
90
16th to endDay
31%21%25%18%3
183
March1st to 15thDay
29%17%29%16%5%
270
16th to endDay
24%20%26%17%9%2
288
April1st to 15thDay
30%19%28%17%4
270
16th to endDay
26%20%25%16%8%2
270
May1st to 15thDay
34%11%28%16%7%2
288
16th to endDay
26%14%32%15%8%2
331
June1st to 15thDay
27%12%32%20%6%
315
16th to endDay
19%11%34%22%9%1
315
July1st to 15thDay
18%7%33%27%9%4
305
16th to endDay
14%6%33%29%12%3
326
August1st to 15thDay
18%5%22%34%13%6%
297
16th to endDay
14%5%31%26%12%10%
268
September1st to 15thDay
18%9%25%18%16%10%
255
16th to endDay
22%9%25%22%13%7%
254
October1st to 15thDay
27%14%22%21%12%1
255
16th to endDay
35%14%26%14%8%
253
November1st to 15thDay
22%13%32%22%8%1
175
16th to endDay
40%15%28%16%
60
December1st to 15thDay
30%18%31%16%3
60
16th to endDay
42%26%28%3
64
January1st to 15thNight
30%13%32%18%4
720
16th to endNight
21%14%30%23%8%1
768
February1st to 15thNight
19%18%34%21%5%
704
16th to endNight
24%19%28%22%4
631
March1st to 15thNight
26%17%28%23%3
720
16th to endNight
21%18%27%23%8%
768
April1st to 15thNight
28%16%26%23%4
718
16th to endNight
26%15%28%22%7%
627
May1st to 15thNight
28%8%25%26%8%1
360
16th to endNight
19%11%32%24%12%
375
June1st to 15thNight
22%8%28%32%8%
360
16th to endNight
18%5%27%35%11%1
360
July1st to 15thNight
11%5%27%39%15%
340
16th to endNight
10%426%40%16%1
376
August1st to 15thNight
13%321%37%21%2
410
16th to endNight
12%5%25%35%19%1
649
September1st to 15thNight
20%5%28%26%17%1
660
16th to endNight
20%6%27%26%17%1
657
October1st to 15thNight
25%11%27%24%9%
660
16th to endNight
31%13%25%21%6%
704
November1st to 15thNight
26%13%28%19%10%1
700
16th to endNight
31%18%23%18%6%
720
December1st to 15thNight
29%17%28%20%3
720
16th to endNight
33%14%29%15%5%1
768
Page generated at 2017-08-13 14:16:43. Version ac04

Copyright 2017 A. Danko


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