Observatoire Magenta
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire Magenta clear sky chart from 2005-11-05 to 2017-09-16.

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%
14648
11%
46820
8%
14617
35%
14617
14%
35160

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
17%
720
6%
2506
3%
716
20%
716
7%
2108
January16th to endNight
20%
768
7%
2688
5%
768
24%
768
8%
2167
February1st to 15thNight
19%
704
6%
2306
4%
701
23%
701
7%
1939
February16th to endNight
23%
631
9%
1893
6%
631
28%
631
10%
1533
March1st to 15thNight
25%
720
13%
2160
10%
720
30%
720
13%
1671
March16th to endNight
30%
768
18%
2005
9%
768
36%
768
19%
1484
April1st to 15thNight
25%
718
13%
1796
4%
718
30%
718
16%
1411
April16th to endNight
29%
603
16%
1683
6%
603
35%
603
20%
1202
May1st to 15thNight
31%
432
16%
1512
14%
432
37%
432
17%
1042
May16th to endNight
35%
374
11%
1497
10%
374
44%
374
15%
1032
June1st to 15thNight
33%
360
8%
1440
8%
360
40%
360
13%
1035
June16th to endNight
44%
360
9%
1440
12%
360
50%
360
18%
927
July1st to 15thNight
50%
340
11%
1360
16%
340
54%
340
20%
849
July16th to endNight
55%
376
11%
1418
15%
354
57%
354
21%
889
August1st to 15thNight
53%
392
13%
1463
13%
390
54%
390
19%
958
August16th to endNight
56%
732
18%
1878
11%
732
58%
732
32%
1229
September1st to 15thNight
49%
720
13%
1812
8%
720
50%
720
28%
1256
September16th to endNight
45%
658
18%
1818
13%
658
48%
658
29%
1194
October1st to 15thNight
32%
660
16%
1914
9%
660
40%
660
18%
1386
October16th to endNight
23%
704
9%
2275
7%
704
27%
704
11%
1776
November1st to 15thNight
27%
700
14%
2277
11%
700
33%
700
13%
1724
November16th to endNight
22%
720
11%
2471
9%
720
27%
720
10%
1934
December1st to 15thNight
14%
720
4%
2520
2%
720
17%
720
5%
2141
December16th to endNight
12%
768
6%
2688
3%
768
17%
768
5%
2273

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%
47932
Night
20%11%47%5%34345%29%
46990
Cloud CoverDay
21%10%36%5%34446%29%
47942
Night
21%11%47%5%34345%28%
46995
TransparencyDay
55%6%12%17%7%
47620
Night
57%5%10%16%8%
46820
SeeingDay
26%9%25%22%11%3
5631
Night
27%9%26%26%10%
14649

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
24%17%6%9%5%3434415%
1432
16th to endDay
14%16%5%8%7%46%5%45%20%
1536
February1st to 15thDay
14%16%7%12%7%46%445%18%
1555
16th to endDay
17%15%7%8%7%45%345%22%
1580
March1st to 15thDay
18%14%5%8%6%35%33425%
1790
16th to endDay
20%9%47%5%33335%33%
2215
April1st to 15thDay
24%10%45%42433429%
2152
16th to endDay
23%7%25%433435%35%
2277
May1st to 15thDay
22%6%36%5%24447%32%
2448
16th to endDay
22%6%25%5%3446%6%31%
2618
June1st to 15thDay
27%6%2443445%7%29%
2520
16th to endDay
21%5%26%5%35%5%5%8%30%
2520
July1st to 15thDay
15%435%5%36%5%6%8%35%
2520
16th to endDay
15%5%25%5%35%5%7%8%34%
2654
August1st to 15thDay
17%6%26%6%45%5%6%8%30%
2475
16th to endDay
13%5%144245%5%9%42%
2321
September1st to 15thDay
19%5%25%423346%40%
2148
16th to endDay
16%6%14323348%43%
1815
October1st to 15thDay
25%7%35%5%2435%7%29%
1716
16th to endDay
28%11%26%5%33436%23%
1595
November1st to 15thDay
20%11%45%424446%29%
1581
16th to endDay
24%14%46%6%23345%24%
1488
December1st to 15thDay
26%16%48%6%2434416%
1440
16th to endDay
27%20%5%9%5%3332413%
1536
January1st to 15thNight
20%17%6%12%6%3433417%
2506
16th to endNight
15%16%7%9%7%45%33421%
2688
February1st to 15thNight
16%14%7%14%8%35%345%16%
2305
16th to endNight
17%16%5%9%6%45%32423%
1893
March1st to 15thNight
22%13%5%7%5%2333327%
2147
16th to endNight
19%12%45%42433435%
2005
April1st to 15thNight
26%10%46%5%3333428%
1796
16th to endNight
22%7%26%423336%37%
1683
May1st to 15thNight
22%8%35%5%24345%35%
1512
16th to endNight
22%5%245%3446%7%33%
1495
June1st to 15thNight
30%6%25%325%347%29%
1440
16th to endNight
17%6%345%2445%9%36%
1440
July1st to 15thNight
13%4345%26%5%7%9%36%
1440
16th to endNight
13%325%5%36%5%7%7%39%
1514
August1st to 15thNight
13%5%25%6%335%6%8%37%
1473
16th to endNight
13%41442445%7%44%
1878
September1st to 15thNight
17%6%245%2345%6%41%
1812
16th to endNight
20%5%14313336%45%
1818
October1st to 15thNight
22%7%36%5%23445%33%
1914
16th to endNight
29%9%37%5%24335%25%
2275
November1st to 15thNight
21%11%35%5%35%5%46%27%
2277
16th to endNight
24%13%48%5%2433425%
2471
December1st to 15thNight
26%16%6%9%7%2333415%
2520
16th to endNight
24%22%5%8%6%2232318%
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%5%11%5%36%33314%
1432
16th to endDay
12%17%6%10%7%37%5%5%5%18%
1536
February1st to 15thDay
14%16%7%13%7%46%44316%
1555
16th to endDay
17%16%7%9%6%35%43420%
1580
March1st to 15thDay
18%15%6%8%6%35%33424%
1800
16th to endDay
20%11%5%7%5%2222433%
2215
April1st to 15thDay
24%11%46%423335%29%
2152
16th to endDay
23%9%34423435%34%
2277
May1st to 15thDay
23%6%36%5%23447%30%
2448
16th to endDay
22%6%35%5%3445%6%30%
2618
June1st to 15thDay
29%6%15%42445%6%29%
2520
16th to endDay
22%5%25%5%25%5%48%30%
2520
July1st to 15thDay
16%5%25%5%35%6%5%9%34%
2520
16th to endDay
15%6%25%6%35%6%6%9%32%
2654
August1st to 15thDay
17%7%36%6%45%45%8%29%
2475
16th to endDay
14%5%245%3445%8%41%
2321
September1st to 15thDay
21%5%25%423346%39%
2148
16th to endDay
18%43442435%7%42%
1815
October1st to 15thDay
26%9%2443445%6%28%
1716
16th to endDay
29%13%26%5%3433423%
1595
November1st to 15thDay
21%13%445%24445%29%
1581
16th to endDay
23%15%48%5%2334324%
1488
December1st to 15thDay
26%17%5%8%6%2443415%
1440
16th to endDay
26%22%6%9%6%2432313%
1536
January1st to 15thNight
20%17%7%11%7%3433316%
2506
16th to endNight
15%16%7%10%7%45%43319%
2688
February1st to 15thNight
15%15%7%15%8%35%335%16%
2298
16th to endNight
16%17%6%11%6%4432422%
1893
March1st to 15thNight
22%14%5%7%6%2333327%
2160
16th to endNight
19%12%5%6%42333434%
2004
April1st to 15thNight
27%11%46%5%2433428%
1796
16th to endNight
22%7%25%423335%37%
1683
May1st to 15thNight
23%8%35%5%23336%34%
1512
16th to endNight
22%6%245%35%5%47%32%
1495
June1st to 15thNight
30%6%2442335%7%28%
1440
16th to endNight
18%5%244245%6%9%35%
1440
July1st to 15thNight
14%4245%36%5%6%10%35%
1440
16th to endNight
13%5%24437%6%6%7%38%
1514
August1st to 15thNight
15%5%26%5%435%6%8%36%
1473
16th to endNight
14%4145%2445%7%45%
1878
September1st to 15thNight
19%5%245%23446%41%
1812
16th to endNight
22%423323236%45%
1818
October1st to 15thNight
23%7%35%5%34345%33%
1914
16th to endNight
30%10%36%434335%24%
2275
November1st to 15thNight
22%11%36%5%35%445%26%
2277
16th to endNight
24%14%48%42333325%
2471
December1st to 15thNight
26%18%6%9%6%2333315%
2520
16th to endNight
24%22%6%8%42322416%
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
73%49%10%2
1433
16th to endDay
63%7%13%11%3
1536
February1st to 15thDay
70%6%9%12%1
1558
16th to endDay
66%5%12%10%6%
1580
March1st to 15thDay
63%5%10%14%5%
1800
16th to endDay
55%410%18%9%1
2215
April1st to 15thDay
58%47%17%9%1
2152
16th to endDay
51%5%10%18%11%3
2277
May1st to 15thDay
52%5%11%17%12%
2448
16th to endDay
52%7%11%18%9%1
2622
June1st to 15thDay
54%6%12%17%7%
2520
16th to endDay
51%7%11%21%8%
2520
July1st to 15thDay
43%8%15%25%7%
2371
16th to endDay
45%8%17%22%6%
2487
August1st to 15thDay
50%9%16%18%5%
2461
16th to endDay
40%6%17%25%10%
2321
September1st to 15thDay
45%5%13%24%11%
2148
16th to endDay
40%6%13%29%10%
1815
October1st to 15thDay
54%6%13%18%6%
1716
16th to endDay
63%5%12%13%4
1595
November1st to 15thDay
57%5%12%15%8%
1581
16th to endDay
63%5%12%11%7%
1488
December1st to 15thDay
71%7%10%9%1
1440
16th to endDay
77%5%7%5%4
1536
January1st to 15thNight
72%5%9%9%2
2506
16th to endNight
67%5%9%12%4
2688
February1st to 15thNight
71%5%8%11%2
2306
16th to endNight
66%48%11%8%
1893
March1st to 15thNight
61%48%17%6%1
2160
16th to endNight
54%47%17%13%2
2005
April1st to 15thNight
61%36%16%11%1
1796
16th to endNight
49%5%8%18%14%2
1683
May1st to 15thNight
51%46%18%15%3
1512
16th to endNight
49%8%9%20%9%1
1497
June1st to 15thNight
55%6%10%18%7%1
1440
16th to endNight
43%8%14%19%12%
1440
July1st to 15thNight
40%9%14%24%10%
1360
16th to endNight
39%9%15%23%10%
1418
August1st to 15thNight
43%9%16%22%8%
1463
16th to endNight
37%6%16%26%12%
1878
September1st to 15thNight
43%6%12%25%11%
1812
16th to endNight
41%5%11%27%13%
1818
October1st to 15thNight
52%5%10%20%10%
1914
16th to endNight
62%5%9%15%5%
2275
November1st to 15thNight
57%6%12%14%6%2
2277
16th to endNight
64%49%13%6%
2471
December1st to 15thNight
73%5%9%9%1
2520
16th to endNight
73%49%8%3
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
30%16%21%21%8%1
60
16th to endDay
37%14%28%12%6%1
64
February1st to 15thDay
26%25%26%16%4
112
16th to endDay
28%14%29%20%6%
239
March1st to 15thDay
28%15%28%22%5%
270
16th to endDay
28%10%27%19%10%3
288
April1st to 15thDay
33%12%23%20%8%1
270
16th to endDay
28%9%29%15%11%4
270
May1st to 15thDay
34%427%19%10%4
288
16th to endDay
23%9%32%19%12%1
331
June1st to 15thDay
33%7%26%22%7%2
315
16th to endDay
25%5%31%27%7%1
315
July1st to 15thDay
19%428%30%12%4
305
16th to endDay
20%319%36%17%2
326
August1st to 15thDay
23%5%21%27%18%5%
313
16th to endDay
19%5%19%24%20%10%
332
September1st to 15thDay
20%6%22%21%19%9%
315
16th to endDay
18%7%24%24%16%9%
254
October1st to 15thDay
25%9%26%19%14%4
255
16th to endDay
38%14%17%20%9%
242
November1st to 15thDay
27%11%29%17%11%1
235
16th to endDay
32%20%18%16%10%1
108
December1st to 15thDay
43%10%16%26%11
60
16th to endDay
51%17%20%10%
64
January1st to 15thNight
27%14%31%21%5%
720
16th to endNight
24%13%29%24%7%
768
February1st to 15thNight
24%10%33%25%5%
704
16th to endNight
27%12%29%25%5%
631
March1st to 15thNight
31%11%26%25%5%
720
16th to endNight
26%12%25%25%8%1
768
April1st to 15thNight
31%11%26%25%5%
718
16th to endNight
26%13%27%23%9%
603
May1st to 15thNight
25%7%31%23%11%1
432
16th to endNight
26%330%30%7%1
375
June1st to 15thNight
33%5%22%26%11%
360
16th to endNight
19%426%36%13%
360
July1st to 15thNight
14%226%38%17%1
340
16th to endNight
15%123%42%18%
376
August1st to 15thNight
18%218%37%21%1
392
16th to endNight
17%218%35%23%2
732
September1st to 15thNight
21%419%35%16%1
720
16th to endNight
24%5%22%27%17%2
658
October1st to 15thNight
27%6%25%25%12%1
660
16th to endNight
37%8%25%21%6%
704
November1st to 15thNight
28%9%28%23%8%1
700
16th to endNight
32%15%23%17%9%1
720
December1st to 15thNight
35%12%29%17%4
720
16th to endNight
35%13%27%17%41
768
Page generated at 2017-09-16 17:06:59. Version ac04

Copyright 2017 A. Danko


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