Observatoire Le Valhalla
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire Le Valhalla 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
25%
14629
13%
46791
7%
14597
32%
14597
14%
33655

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
13%
720
7%
2506
3%
716
18%
716
7%
2023
January16th to endNight
16%
768
9%
2688
4%
768
24%
768
9%
2031
February1st to 15thNight
13%
704
9%
2287
3%
701
20%
701
8%
1795
February16th to endNight
18%
631
13%
1907
5%
631
27%
631
11%
1441
March1st to 15thNight
16%
720
13%
2151
6%
720
24%
720
11%
1629
March16th to endNight
25%
768
20%
1998
8%
768
33%
768
19%
1403
April1st to 15thNight
21%
718
16%
1796
5%
718
27%
718
17%
1337
April16th to endNight
21%
645
16%
1725
3%
645
30%
645
16%
1229
May1st to 15thNight
26%
372
16%
1452
11%
372
38%
372
13%
980
May16th to endNight
26%
375
12%
1497
7%
374
41%
374
14%
974
June1st to 15thNight
26%
360
8%
1440
6%
360
36%
360
11%
1014
June16th to endNight
34%
360
9%
1440
8%
360
42%
360
14%
925
July1st to 15thNight
44%
340
14%
1360
18%
340
52%
340
22%
786
July16th to endNight
42%
376
12%
1418
13%
354
51%
354
22%
824
August1st to 15thNight
49%
386
14%
1457
12%
384
56%
384
20%
894
August16th to endNight
44%
750
19%
1896
9%
750
49%
750
31%
1234
September1st to 15thNight
43%
707
14%
1768
7%
707
45%
707
27%
1231
September16th to endNight
42%
657
20%
1790
12%
657
47%
657
28%
1160
October1st to 15thNight
27%
660
18%
1966
10%
660
37%
660
18%
1354
October16th to endNight
21%
704
10%
2238
6%
704
27%
704
12%
1687
November1st to 15thNight
24%
700
16%
2283
9%
700
33%
700
13%
1644
November16th to endNight
17%
720
11%
2520
6%
720
25%
720
9%
1879
December1st to 15thNight
13%
720
8%
2520
3%
720
19%
720
7%
2014
December16th to endNight
8%
768
9%
2688
2%
768
16%
768
5%
2167

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%7%36%5%35%45%6%33%
47885
Night
18%9%36%5%34445%32%
46960
Cloud CoverDay
17%7%36%5%3445%7%33%
47894
Night
18%9%46%5%34446%32%
46966
TransparencyDay
50%7%12%19%9%1
47572
Night
52%6%11%18%9%1
46791
SeeingDay
20%20%27%19%9%2
5528
Night
20%24%24%21%8%
14629

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
21%14%5%8%7%3444421%
1432
16th to endDay
15%16%5%6%5%35%5%46%25%
1536
February1st to 15thDay
15%12%411%6%46%5%46%22%
1575
16th to endDay
18%11%5%7%6%35%445%26%
1565
March1st to 15thDay
17%11%49%8%3433427%
1799
16th to endDay
18%7%35%5%23445%38%
2226
April1st to 15thDay
23%8%36%5%33345%33%
2152
16th to endDay
21%6%25%5%34446%35%
2235
May1st to 15thDay
20%6%36%5%35%445%33%
2511
16th to endDay
20%5%25%435%45%7%35%
2618
June1st to 15thDay
23%6%35%5%34447%31%
2520
16th to endDay
19%425%5%36%5%6%8%32%
2520
July1st to 15thDay
12%435%5%36%5%5%8%39%
2520
16th to endDay
12%5%25%436%5%7%9%36%
2654
August1st to 15thDay
13%426%6%45%5%5%9%36%
2492
16th to endDay
11%3144346%5%9%45%
2294
September1st to 15thDay
16%5%2442445%7%41%
2112
16th to endDay
15%5%25%324346%46%
1840
October1st to 15thDay
20%6%26%5%245%5%5%35%
1662
16th to endDay
23%9%36%7%35%445%25%
1634
November1st to 15thDay
16%7%45%436%5%5%6%33%
1572
16th to endDay
22%9%46%6%3435%5%27%
1440
December1st to 15thDay
25%12%37%6%35%45%6%19%
1440
16th to endDay
26%14%5%7%5%2443421%
1536
January1st to 15thNight
19%14%5%9%7%345%45%20%
2506
16th to endNight
13%14%5%7%7%44435%26%
2688
February1st to 15thNight
14%12%5%10%8%46%5%5%5%21%
2285
16th to endNight
16%11%5%8%5%35%5%5%5%27%
1907
March1st to 15thNight
20%10%5%6%6%34345%29%
2138
16th to endNight
16%10%35%43433441%
1998
April1st to 15thNight
25%7%35%5%23335%33%
1796
16th to endNight
21%6%24434345%37%
1725
May1st to 15thNight
22%6%35%6%24345%36%
1452
16th to endNight
18%5%35%5%2445%6%37%
1495
June1st to 15thNight
23%7%245%25%45%6%31%
1440
16th to endNight
15%5%25%426%5%6%8%36%
1440
July1st to 15thNight
10%315%436%5%7%9%42%
1440
16th to endNight
11%5%14435%5%6%7%44%
1514
August1st to 15thNight
9%6%26%5%245%7%8%41%
1467
16th to endNight
11%4235%34447%48%
1896
September1st to 15thNight
15%5%25%5%35%446%40%
1768
16th to endNight
17%423423345%47%
1790
October1st to 15thNight
19%6%26%42445%6%36%
1966
16th to endNight
24%8%46%5%34445%28%
2238
November1st to 15thNight
20%8%36%5%345%45%33%
2283
16th to endNight
22%9%48%5%34445%27%
2520
December1st to 15thNight
22%15%5%7%6%3435%422%
2520
16th to endNight
25%16%47%5%3433421%
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%13%5%8%5%4444421%
1432
16th to endDay
14%14%5%8%5%35%45%6%25%
1536
February1st to 15thDay
14%12%5%10%7%36%5%5%6%22%
1575
16th to endDay
18%11%6%6%7%35%35%427%
1565
March1st to 15thDay
17%10%6%8%7%36%33427%
1809
16th to endDay
19%6%36%434345%38%
2225
April1st to 15thDay
22%8%35%5%34445%32%
2152
16th to endDay
19%6%35%5%24446%36%
2235
May1st to 15thDay
19%6%37%5%34446%33%
2511
16th to endDay
18%6%26%5%35%447%35%
2618
June1st to 15thDay
22%6%35%43445%7%31%
2520
16th to endDay
18%425%5%36%5%6%9%31%
2520
July1st to 15thDay
12%426%5%25%5%6%8%39%
2520
16th to endDay
12%425%5%36%48%10%36%
2654
August1st to 15thDay
12%5%26%7%35%5%5%8%35%
2492
16th to endDay
10%3144445%6%8%45%
2294
September1st to 15thDay
16%5%25%42345%7%41%
2112
16th to endDay
14%5%25%424347%45%
1840
October1st to 15thDay
20%7%345%3446%435%
1662
16th to endDay
22%10%47%5%3445%6%24%
1634
November1st to 15thDay
15%8%35%5%35%5%5%6%32%
1572
16th to endDay
21%9%37%6%35%446%27%
1440
December1st to 15thDay
25%12%37%5%445%5%5%19%
1440
16th to endDay
26%14%48%6%23345%20%
1536
January1st to 15thNight
18%15%6%9%7%3445%419%
2506
16th to endNight
13%15%6%8%6%45%445%26%
2688
February1st to 15thNight
14%12%5%12%7%46%5%45%21%
2278
16th to endNight
16%11%5%8%5%35%44428%
1907
March1st to 15thNight
20%10%46%6%35%345%28%
2151
16th to endNight
16%10%45%423345%40%
1998
April1st to 15thNight
25%7%35%5%2325%5%32%
1796
16th to endNight
21%7%25%424436%36%
1725
May1st to 15thNight
21%8%45%5%23336%35%
1452
16th to endNight
18%435%5%34448%36%
1495
June1st to 15thNight
23%7%245%26%45%6%30%
1440
16th to endNight
15%5%25%5%25%6%5%9%36%
1440
July1st to 15thNight
10%3236%35%5%7%10%42%
1440
16th to endNight
10%5%25%435%6%7%7%42%
1514
August1st to 15thNight
10%426%5%345%6%9%40%
1467
16th to endNight
12%4244245%5%8%46%
1896
September1st to 15thNight
15%5%26%5%24346%41%
1768
16th to endNight
17%423433345%46%
1790
October1st to 15thNight
18%7%26%424446%36%
1966
16th to endNight
24%8%47%6%23445%28%
2238
November1st to 15thNight
19%8%36%5%44446%32%
2283
16th to endNight
22%10%48%5%24445%26%
2520
December1st to 15thNight
22%15%5%7%5%2444422%
2520
16th to endNight
25%15%5%7%5%3333421%
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
65%6%8%13%4
1433
16th to endDay
58%7%12%13%7%
1536
February1st to 15thDay
61%5%10%17%3
1577
16th to endDay
60%5%9%14%9%1
1565
March1st to 15thDay
60%5%11%14%7%1
1809
16th to endDay
47%5%9%17%15%4
2226
April1st to 15thDay
53%47%19%12%2
2152
16th to endDay
49%5%8%18%14%4
2235
May1st to 15thDay
50%6%9%17%13%2
2511
16th to endDay
47%6%12%20%11%1
2622
June1st to 15thDay
51%6%11%19%10%
2520
16th to endDay
48%8%13%18%9%
2520
July1st to 15thDay
38%9%14%25%12%
2371
16th to endDay
41%10%17%22%8%
2487
August1st to 15thDay
43%9%16%22%7%
2478
16th to endDay
33%9%17%26%12%
2294
September1st to 15thDay
41%7%13%25%12%
2112
16th to endDay
39%412%32%10%
1840
October1st to 15thDay
49%6%11%22%9%
1662
16th to endDay
59%7%12%14%6%
1634
November1st to 15thDay
49%8%14%18%8%
1572
16th to endDay
57%8%11%16%5%
1440
December1st to 15thDay
64%9%12%11%2
1440
16th to endDay
67%6%10%10%5%
1536
January1st to 15thNight
65%7%10%12%4
2506
16th to endNight
59%6%11%15%6%
2688
February1st to 15thNight
62%6%10%15%3
2287
16th to endNight
57%5%10%16%9%
1907
March1st to 15thNight
58%5%10%17%7%1
2151
16th to endNight
47%39%19%15%4
1998
April1st to 15thNight
53%47%19%13%1
1796
16th to endNight
48%5%7%18%15%3
1725
May1st to 15thNight
50%5%8%16%15%4
1452
16th to endNight
46%7%11%19%13%1
1497
June1st to 15thNight
53%6%11%19%8%
1440
16th to endNight
42%9%13%18%14%
1440
July1st to 15thNight
33%9%13%28%15%
1360
16th to endNight
36%7%18%22%13%
1418
August1st to 15thNight
36%9%19%22%11%
1457
16th to endNight
34%7%15%29%12%
1896
September1st to 15thNight
43%6%11%24%13%
1768
16th to endNight
38%5%11%31%12%
1790
October1st to 15thNight
47%5%12%23%10%
1966
16th to endNight
57%6%13%16%5%
2238
November1st to 15thNight
52%6%13%16%8%1
2283
16th to endNight
58%6%13%16%5%
2520
December1st to 15thNight
64%6%11%14%2
2520
16th to endNight
67%5%9%12%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
25%25%18%25%6%
60
16th to endDay
32%23%25%14%4
64
February1st to 15thDay
34%28%30%5%1
90
16th to endDay
29%24%27%16%3
224
March1st to 15thDay
22%30%27%17%2
270
16th to endDay
22%26%25%16%5%2
288
April1st to 15thDay
25%28%27%11%5%1
270
16th to endDay
18%27%25%17%9%1
270
May1st to 15thDay
22%27%24%15%6%2
288
16th to endDay
19%25%30%14%8%1
331
June1st to 15thDay
24%20%31%18%41
315
16th to endDay
19%17%31%21%8%1
315
July1st to 15thDay
14%15%29%23%14%1
305
16th to endDay
14%13%25%29%13%3
326
August1st to 15thDay
12%11%26%32%12%5%
313
16th to endDay
10%10%29%25%16%8%
332
September1st to 15thDay
16%12%23%21%17%8%
299
16th to endDay
15%17%25%18%14%9%
254
October1st to 15thDay
21%20%21%21%14%1
255
16th to endDay
25%25%23%19%5%
249
November1st to 15thDay
17%25%23%21%10%1
226
16th to endDay
31%15%30%21%1
60
December1st to 15thDay
28%15%38%16%1
60
16th to endDay
42%18%35%3
64
January1st to 15thNight
19%32%29%15%3
720
16th to endNight
19%30%27%17%4
768
February1st to 15thNight
18%31%28%18%3
704
16th to endNight
20%30%25%19%4
631
March1st to 15thNight
24%29%25%17%3
720
16th to endNight
19%27%23%24%4
768
April1st to 15thNight
23%28%23%21%3
718
16th to endNight
22%27%24%17%7%
645
May1st to 15thNight
21%24%22%22%7%2
372
16th to endNight
16%22%31%21%8%
375
June1st to 15thNight
21%23%22%27%5%
360
16th to endNight
15%21%24%24%13%1
360
July1st to 15thNight
11%16%24%29%16%
340
16th to endNight
11%18%24%31%13%1
376
August1st to 15thNight
12%11%19%34%20%1
386
16th to endNight
12%14%23%27%19%2
750
September1st to 15thNight
16%13%22%31%14%1
707
16th to endNight
19%15%20%22%20%1
657
October1st to 15thNight
21%20%25%22%10%
660
16th to endNight
26%20%25%21%5%
704
November1st to 15thNight
18%25%26%20%8%
700
16th to endNight
20%32%23%14%8%
720
December1st to 15thNight
28%30%21%16%3
720
16th to endNight
29%31%22%10%4
768
Page generated at 2017-09-13 07:39:15. Version ac04

Copyright 2017 A. Danko


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