Observatoire Vandal
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire Vandal clear sky chart from 2005-11-05 to

2017-09-12
.

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
28%
14618
11%
46779
8%
14587
33%
14587
14%
34948

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
15%
720
6%
2506
4%
716
18%
716
7%
2074
January16th to endNight
18%
768
7%
2688
5%
768
22%
768
8%
2174
February1st to 15thNight
15%
704
6%
2313
3%
701
20%
701
8%
1919
February16th to endNight
19%
631
9%
1893
6%
631
24%
631
10%
1532
March1st to 15thNight
24%
720
13%
2160
10%
720
29%
720
13%
1670
March16th to endNight
29%
768
18%
2007
8%
768
36%
768
19%
1468
April1st to 15thNight
22%
718
13%
1796
4%
718
27%
718
15%
1426
April16th to endNight
28%
595
16%
1675
6%
595
35%
595
19%
1177
May1st to 15thNight
28%
433
16%
1513
12%
433
37%
433
16%
1049
May16th to endNight
32%
374
11%
1497
9%
374
40%
374
15%
1005
June1st to 15thNight
33%
360
8%
1440
8%
360
41%
360
12%
1024
June16th to endNight
42%
360
9%
1440
10%
360
48%
360
18%
925
July1st to 15thNight
48%
340
11%
1360
17%
340
52%
340
19%
863
July16th to endNight
49%
376
11%
1418
14%
354
53%
354
20%
869
August1st to 15thNight
49%
392
13%
1463
13%
390
52%
390
19%
936
August16th to endNight
52%
723
18%
1869
11%
723
55%
723
31%
1240
September1st to 15thNight
43%
707
12%
1782
7%
707
44%
707
27%
1243
September16th to endNight
42%
657
18%
1815
12%
657
46%
657
29%
1191
October1st to 15thNight
30%
660
16%
1908
9%
660
38%
660
18%
1375
October16th to endNight
23%
704
9%
2281
6%
704
27%
704
11%
1768
November1st to 15thNight
24%
700
14%
2277
10%
700
30%
700
13%
1724
November16th to endNight
21%
720
12%
2470
8%
720
27%
720
10%
1903
December1st to 15thNight
13%
720
5%
2520
1%
720
17%
720
5%
2127
December16th to endNight
10%
768
7%
2688
3%
768
16%
768
5%
2266

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
20%9%36%5%34446%29%
47887
Night
20%11%47%5%34345%29%
46949
Cloud CoverDay
20%10%46%5%34446%28%
47897
Night
20%11%47%5%34345%28%
46954
TransparencyDay
56%6%11%17%7%
47575
Night
57%5%10%17%8%
46779
SeeingDay
27%11%27%20%9%3
5613
Night
26%11%27%24%9%
14619

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
22%18%7%10%5%45%33315%
1432
16th to endDay
15%14%7%9%7%36%5%45%19%
1536
February1st to 15thDay
14%16%7%11%8%5%5%44417%
1546
16th to endDay
16%16%6%10%6%35%44421%
1580
March1st to 15thDay
18%12%6%8%7%35%435%25%
1790
16th to endDay
19%11%47%5%3333434%
2215
April1st to 15thDay
23%13%36%42334429%
2152
16th to endDay
23%8%25%424345%35%
2284
May1st to 15thDay
23%7%26%5%3445%5%31%
2448
16th to endDay
21%6%45%5%345%5%7%30%
2618
June1st to 15thDay
27%7%24434447%29%
2520
16th to endDay
21%5%36%5%35%5%6%7%30%
2520
July1st to 15thDay
15%425%5%36%5%6%7%35%
2520
16th to endDay
15%6%35%5%35%6%6%8%32%
2654
August1st to 15thDay
16%7%26%7%45%5%5%8%30%
2473
16th to endDay
13%425%5%2446%8%42%
2332
September1st to 15thDay
20%6%35%434345%39%
2098
16th to endDay
17%6%23323446%42%
1815
October1st to 15thDay
26%8%25%43345%6%28%
1719
16th to endDay
26%13%36%425%435%23%
1590
November1st to 15thDay
21%11%35%5%24445%30%
1581
16th to endDay
22%15%5%7%43443425%
1488
December1st to 15thDay
26%16%49%7%2443415%
1440
16th to endDay
26%19%6%7%6%3432314%
1536
January1st to 15thNight
20%15%7%9%7%3443417%
2506
16th to endNight
15%16%6%10%7%45%44420%
2688
February1st to 15thNight
15%15%6%14%8%3444417%
2312
16th to endNight
16%15%7%9%7%35%32424%
1893
March1st to 15thNight
21%14%47%5%2324427%
2147
16th to endNight
18%12%5%6%42333436%
2007
April1st to 15thNight
26%10%36%5%2434427%
1796
16th to endNight
22%7%25%5%23346%36%
1675
May1st to 15thNight
23%6%35%434346%33%
1513
16th to endNight
22%6%35%335%35%7%33%
1495
June1st to 15thNight
28%7%25%324447%28%
1440
16th to endNight
17%5%25%325%46%8%35%
1440
July1st to 15thNight
14%6%25%5%35%5%7%8%36%
1440
16th to endNight
13%4235%36%6%6%9%38%
1514
August1st to 15thNight
13%6%27%6%2446%9%37%
1473
16th to endNight
13%416%42445%8%43%
1869
September1st to 15thNight
19%6%25%424346%40%
1782
16th to endNight
20%413423346%45%
1815
October1st to 15thNight
20%8%36%5%24345%34%
1908
16th to endNight
29%10%36%5%2333426%
2281
November1st to 15thNight
21%11%26%6%35%5%46%27%
2277
16th to endNight
24%14%5%8%33333425%
2470
December1st to 15thNight
26%16%6%8%6%3333416%
2520
16th to endNight
23%21%5%8%5%3322218%
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%20%6%10%6%3433414%
1432
16th to endDay
13%15%6%10%7%36%45%5%19%
1536
February1st to 15thDay
14%17%8%11%8%5%5%44415%
1546
16th to endDay
16%17%8%8%8%34435%19%
1580
March1st to 15thDay
19%13%5%9%7%35%33424%
1800
16th to endDay
19%11%5%7%6%2224433%
2215
April1st to 15thDay
23%13%45%42333429%
2152
16th to endDay
23%9%2442433435%
2284
May1st to 15thDay
24%6%36%5%2435%6%31%
2448
16th to endDay
21%7%36%5%3445%7%29%
2618
June1st to 15thDay
28%6%2443445%6%28%
2520
16th to endDay
22%6%36%4345%5%7%30%
2520
July1st to 15thDay
16%5%25%6%35%5%6%7%34%
2520
16th to endDay
16%6%26%6%346%5%8%31%
2654
August1st to 15thDay
16%7%27%6%35%5%5%9%28%
2473
16th to endDay
14%425%5%3345%8%41%
2332
September1st to 15thDay
21%6%245%34346%38%
2098
16th to endDay
18%6%243235%47%41%
1815
October1st to 15thDay
27%7%35%433447%28%
1719
16th to endDay
28%13%37%325%335%22%
1590
November1st to 15thDay
21%12%4443445%5%29%
1581
16th to endDay
22%16%5%6%5%2433425%
1488
December1st to 15thDay
25%18%5%8%8%3423414%
1440
16th to endDay
25%22%6%8%6%3433313%
1536
January1st to 15thNight
19%16%8%9%7%4434417%
2506
16th to endNight
14%16%6%11%8%45%44419%
2688
February1st to 15thNight
14%15%7%13%9%3444418%
2305
16th to endNight
16%16%6%11%6%35%32423%
1893
March1st to 15thNight
21%15%5%7%5%2334427%
2160
16th to endNight
17%12%5%6%32333435%
2006
April1st to 15thNight
26%11%46%5%3423427%
1796
16th to endNight
22%7%245%23336%36%
1675
May1st to 15thNight
22%7%36%5%24446%33%
1513
16th to endNight
23%5%35%5%24448%32%
1495
June1st to 15thNight
29%6%344245%47%27%
1440
16th to endNight
18%5%344245%6%9%35%
1440
July1st to 15thNight
14%5%25%6%345%6%10%35%
1440
16th to endNight
13%425%5%35%6%6%8%38%
1514
August1st to 15thNight
14%5%26%5%3446%8%36%
1473
16th to endNight
14%415%43435%8%44%
1869
September1st to 15thNight
19%6%24423446%40%
1782
16th to endNight
20%413423236%45%
1815
October1st to 15thNight
21%9%25%5%24346%33%
1908
16th to endNight
30%10%35%433445%25%
2281
November1st to 15thNight
21%11%36%5%35%45%6%25%
2277
16th to endNight
24%15%5%8%5%2333425%
2470
December1st to 15thNight
25%18%5%8%7%2433416%
2520
16th to endNight
23%21%6%9%5%2322317%
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
75%38%9%3
1433
16th to endDay
65%6%11%12%3
1536
February1st to 15thDay
70%6%9%12%1
1549
16th to endDay
66%5%10%10%6%
1580
March1st to 15thDay
63%5%10%13%6%
1800
16th to endDay
55%310%18%10%1
2215
April1st to 15thDay
58%5%7%17%9%1
2152
16th to endDay
52%49%17%12%2
2284
May1st to 15thDay
54%5%9%18%12%
2448
16th to endDay
52%7%11%18%9%1
2622
June1st to 15thDay
55%6%13%16%8%
2520
16th to endDay
52%6%11%21%7%
2520
July1st to 15thDay
44%8%15%25%6%
2371
16th to endDay
48%9%16%20%6%
2487
August1st to 15thDay
50%9%15%20%4
2459
16th to endDay
40%7%16%24%10%
2332
September1st to 15thDay
47%5%11%23%10%
2098
16th to endDay
41%5%13%28%10%
1815
October1st to 15thDay
55%5%13%19%6%
1719
16th to endDay
64%5%11%14%4
1590
November1st to 15thDay
55%7%12%16%8%
1581
16th to endDay
63%5%10%12%6%
1488
December1st to 15thDay
74%5%9%9%1
1440
16th to endDay
77%47%5%5%
1536
January1st to 15thNight
70%410%9%3
2506
16th to endNight
68%49%12%4
2688
February1st to 15thNight
69%6%8%12%3
2313
16th to endNight
66%48%11%8%
1893
March1st to 15thNight
61%48%17%7%1
2160
16th to endNight
53%48%17%13%3
2007
April1st to 15thNight
61%35%15%11%1
1796
16th to endNight
49%49%18%14%2
1675
May1st to 15thNight
51%5%6%17%15%3
1513
16th to endNight
49%7%11%20%9%1
1497
June1st to 15thNight
55%6%10%19%7%
1440
16th to endNight
44%7%13%22%11%
1440
July1st to 15thNight
40%10%13%24%10%
1360
16th to endNight
39%8%17%22%10%
1418
August1st to 15thNight
43%7%17%22%8%
1463
16th to endNight
37%7%15%27%10%
1869
September1st to 15thNight
45%413%25%10%
1782
16th to endNight
40%5%12%28%13%
1815
October1st to 15thNight
51%6%11%20%9%
1908
16th to endNight
61%5%10%15%5%
2281
November1st to 15thNight
57%6%12%14%5%2
2277
16th to endNight
63%49%15%6%
2470
December1st to 15thNight
73%49%10%2
2520
16th to endNight
73%48%8%4
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
28%11%31%21%6%
60
16th to endDay
32%17%29%14%41
64
February1st to 15thDay
36%21%21%14%5%
111
16th to endDay
27%20%29%17%3
239
March1st to 15thDay
29%17%28%20%4
270
16th to endDay
26%14%30%16%9%3
288
April1st to 15thDay
33%15%25%18%42
270
16th to endDay
30%11%28%15%10%4
270
May1st to 15thDay
35%9%26%14%9%3
288
16th to endDay
23%14%30%19%9%2
331
June1st to 15thDay
36%6%27%21%6%1
315
16th to endDay
25%7%36%20%7%1
315
July1st to 15thDay
21%8%31%23%11%3
305
16th to endDay
20%426%32%12%1
326
August1st to 15thDay
21%8%24%25%15%3
313
16th to endDay
18%8%25%19%18%9%
332
September1st to 15thDay
22%6%26%21%14%8%
299
16th to endDay
19%10%24%24%12%8%
254
October1st to 15thDay
25%12%27%19%10%5%
255
16th to endDay
40%12%18%19%8%
241
November1st to 15thDay
28%15%27%17%10%1
235
16th to endDay
29%19%19%18%11%1
108
December1st to 15thDay
43%11%21%20%3
60
16th to endDay
45%18%29%41
64
January1st to 15thNight
29%15%32%17%4
720
16th to endNight
23%18%29%21%5%
768
February1st to 15thNight
23%15%33%22%4
704
16th to endNight
25%14%33%22%3
631
March1st to 15thNight
30%13%27%25%3
720
16th to endNight
24%13%27%24%8%1
768
April1st to 15thNight
32%12%26%22%5%
718
16th to endNight
27%14%25%22%9%
595
May1st to 15thNight
25%9%32%21%9%1
433
16th to endNight
26%6%29%29%7%
375
June1st to 15thNight
34%6%20%28%10%
360
16th to endNight
18%430%33%12%
360
July1st to 15thNight
14%5%25%36%16%1
340
16th to endNight
17%223%38%17%
376
August1st to 15thNight
19%221%33%21%1
392
16th to endNight
16%5%20%35%19%2
723
September1st to 15thNight
22%5%23%30%15%1
707
16th to endNight
22%6%26%25%17%1
657
October1st to 15thNight
26%9%28%22%12%1
660
16th to endNight
38%10%25%20%5%
704
November1st to 15thNight
27%12%29%20%9%
700
16th to endNight
32%16%23%16%9%1
720
December1st to 15thNight
35%14%30%14%3
720
16th to endNight
35%16%26%16%31
768
Page generated at 2017-09-13 07:39:12. Version ac04

Copyright 2017 A. Danko


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