Observatoire de Mirabilis
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Observatoire de Mirabilis clear sky chart from 2005-11-05 to 2018-03-21.

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
26%
15340
13%
49242
7%
15308
33%
15308
15%
35526

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%
780
7%
2716
2%
776
20%
776
7%
2193
January16th to endNight
16%
832
10%
2912
5%
832
24%
832
10%
2197
February1st to 15thNight
15%
764
10%
2492
3%
761
24%
761
10%
1917
February16th to endNight
18%
683
12%
2077
5%
683
27%
683
11%
1573
March1st to 15thNight
16%
780
12%
2327
6%
780
23%
780
11%
1803
March16th to endNight
27%
792
21%
2067
7%
792
37%
792
22%
1420
April1st to 15thNight
23%
718
16%
1796
5%
718
28%
718
19%
1331
April16th to endNight
25%
631
16%
1711
6%
631
32%
631
19%
1207
May1st to 15thNight
27%
360
15%
1440
11%
360
39%
360
15%
979
May16th to endNight
28%
375
13%
1497
9%
374
40%
374
17%
979
June1st to 15thNight
30%
360
7%
1440
5%
360
37%
360
13%
996
June16th to endNight
41%
360
8%
1440
11%
360
45%
360
16%
941
July1st to 15thNight
49%
340
11%
1360
15%
340
54%
340
26%
763
July16th to endNight
52%
376
12%
1418
14%
354
56%
354
24%
830
August1st to 15thNight
52%
375
13%
1446
13%
373
57%
373
21%
904
August16th to endNight
46%
737
19%
1883
10%
737
51%
737
34%
1195
September1st to 15thNight
44%
720
14%
1800
6%
720
46%
720
28%
1244
September16th to endNight
45%
717
21%
1950
13%
717
50%
717
31%
1248
October1st to 15thNight
30%
720
17%
2152
10%
720
39%
720
19%
1485
October16th to endNight
22%
768
11%
2445
6%
768
29%
768
13%
1845
November1st to 15thNight
24%
760
16%
2501
10%
760
34%
760
14%
1806
November16th to endNight
18%
780
11%
2730
7%
780
25%
780
9%
2124
December1st to 15thNight
12%
780
8%
2730
2%
780
19%
780
7%
2204
December16th to endNight
10%
832
10%
2912
3%
832
18%
832
6%
2342

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%10%46%5%34446%28%
49618
Night
18%11%46%5%24445%30%
49411
Cloud CoverDay
20%10%46%5%34446%28%
49627
Night
18%11%47%5%34445%30%
49417
TransparencyDay
56%410%18%8%1
49305
Night
55%410%19%9%
49242
SeeingDay
27%14%28%18%8%2
6057
Night
25%13%27%23%8%
15340

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%19%6%11%7%3432317%
1552
16th to endDay
12%16%7%10%7%35%5%5%5%21%
1664
February1st to 15thDay
12%16%6%11%9%24345%21%
1697
16th to endDay
15%19%6%8%6%34345%22%
1681
March1st to 15thDay
18%16%5%9%5%34335%24%
1952
16th to endDay
15%9%46%423447%36%
2285
April1st to 15thDay
23%12%45%423335%31%
2152
16th to endDay
22%8%36%5%2444334%
2259
May1st to 15thDay
23%9%36%424446%28%
2511
16th to endDay
23%8%35%5%34346%29%
2618
June1st to 15thDay
24%8%35%5%36%5%5%6%25%
2520
16th to endDay
22%6%36%5%35%6%5%7%27%
2520
July1st to 15thDay
18%5%25%5%35%45%8%33%
2520
16th to endDay
16%6%25%6%35%5%7%8%30%
2654
August1st to 15thDay
18%7%26%6%45%5%5%7%29%
2502
16th to endDay
15%5%25%5%346%5%8%38%
2306
September1st to 15thDay
22%5%25%434346%36%
2160
16th to endDay
21%5%23313347%43%
2010
October1st to 15thDay
25%9%2443435%6%31%
1806
16th to endDay
29%13%27%5%24335%20%
1779
November1st to 15thDay
18%11%47%6%345%5%6%27%
1686
16th to endDay
25%15%47%5%2323423%
1560
December1st to 15thDay
23%19%5%7%6%24335%16%
1560
16th to endDay
21%18%7%8%6%2434317%
1664
January1st to 15thNight
19%18%8%10%7%24345%16%
2716
16th to endNight
12%16%6%9%7%3445%5%21%
2912
February1st to 15thNight
10%16%7%10%8%4444422%
2490
16th to endNight
16%14%6%10%6%1445%6%23%
2077
March1st to 15thNight
20%13%5%7%6%34245%25%
2314
16th to endNight
15%9%35%424335%40%
2067
April1st to 15thNight
25%9%35%323335%33%
1796
16th to endNight
21%9%25%5%23445%36%
1711
May1st to 15thNight
22%7%45%5%24436%34%
1440
16th to endNight
19%6%35%4245%5%6%36%
1495
June1st to 15thNight
21%7%36%6%2346%6%29%
1440
16th to endNight
20%425%435%6%5%6%36%
1440
July1st to 15thNight
13%5%244245%6%8%44%
1440
16th to endNight
11%4235%345%6%9%42%
1514
August1st to 15thNight
13%5%246%345%6%8%39%
1456
16th to endNight
12%4245%2346%7%47%
1883
September1st to 15thNight
18%6%2442445%6%40%
1800
16th to endNight
17%5%23223336%46%
1950
October1st to 15thNight
20%7%36%433446%35%
2152
16th to endNight
28%12%35%424346%24%
2445
November1st to 15thNight
21%9%36%5%3445%5%29%
2501
16th to endNight
23%16%6%8%42433422%
2730
December1st to 15thNight
22%18%6%8%6%3334418%
2730
16th to endNight
21%18%7%9%6%3434417%
2912

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
21%18%6%10%6%3433217%
1552
16th to endDay
13%15%8%9%7%345%45%22%
1664
February1st to 15thDay
12%17%6%10%10%34445%21%
1697
16th to endDay
16%18%5%8%7%3434422%
1681
March1st to 15thDay
18%16%6%9%5%35%24424%
1962
16th to endDay
16%9%46%5%23346%36%
2284
April1st to 15thDay
23%12%45%5%22335%31%
2152
16th to endDay
22%9%36%42444433%
2259
May1st to 15thDay
22%9%47%5%24446%28%
2511
16th to endDay
22%9%36%5%34346%29%
2618
June1st to 15thDay
23%8%35%6%35%5%5%6%25%
2520
16th to endDay
22%7%26%5%35%5%5%7%26%
2520
July1st to 15thDay
17%6%26%5%345%6%7%33%
2520
16th to endDay
16%5%36%5%36%6%7%8%29%
2654
August1st to 15thDay
17%7%36%7%45%45%7%29%
2502
16th to endDay
13%6%25%5%3446%8%38%
2306
September1st to 15thDay
21%6%245%33446%36%
2160
16th to endDay
20%6%23322347%43%
2010
October1st to 15thDay
25%8%25%423446%31%
1806
16th to endDay
28%13%36%6%2443421%
1779
November1st to 15thDay
18%12%46%5%25%5%46%28%
1686
16th to endDay
25%14%46%6%3333423%
1560
December1st to 15thDay
23%20%5%6%5%25%335%17%
1560
16th to endDay
21%18%7%9%6%2443317%
1664
January1st to 15thNight
18%18%7%9%7%24345%16%
2716
16th to endNight
12%15%7%9%7%4445%6%22%
2912
February1st to 15thNight
10%16%6%10%8%35%44423%
2483
16th to endNight
16%13%6%10%5%24446%24%
2077
March1st to 15thNight
20%13%48%6%35%24425%
2327
16th to endNight
15%9%345%24335%40%
2067
April1st to 15thNight
25%9%36%42333433%
1796
16th to endNight
20%10%25%423446%36%
1711
May1st to 15thNight
21%8%36%5%2243435%
1440
16th to endNight
20%6%26%5%25%446%35%
1495
June1st to 15thNight
21%9%36%5%25%447%29%
1440
16th to endNight
20%5%245%35%5%47%36%
1440
July1st to 15thNight
12%6%2442446%8%43%
1440
16th to endNight
11%5%25%425%5%6%7%43%
1514
August1st to 15thNight
12%5%346%4447%7%39%
1456
16th to endNight
12%5%145%2336%7%47%
1883
September1st to 15thNight
18%5%24334446%41%
1800
16th to endNight
18%5%23323436%47%
1950
October1st to 15thNight
19%7%36%5%33445%36%
2152
16th to endNight
27%11%26%424336%25%
2445
November1st to 15thNight
22%9%36%5%34345%30%
2501
16th to endNight
22%15%5%8%5%3333423%
2730
December1st to 15thNight
21%18%6%7%7%2433418%
2730
16th to endNight
20%18%6%8%7%3344418%
2912

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%25%12%5%
1553
16th to endDay
62%47%16%8%
1664
February1st to 15thDay
65%28%17%5%
1699
16th to endDay
65%27%14%8%1
1681
March1st to 15thDay
64%38%14%8%1
1962
16th to endDay
48%38%19%15%4
2285
April1st to 15thDay
55%27%19%11%2
2152
16th to endDay
53%37%18%12%3
2259
May1st to 15thDay
56%46%18%12%1
2511
16th to endDay
56%310%18%9%1
2622
June1st to 15thDay
57%410%16%9%
2520
16th to endDay
55%5%11%19%7%1
2520
July1st to 15thDay
46%415%23%9%
2371
16th to endDay
50%5%16%18%8%
2487
August1st to 15thDay
53%5%16%19%5%
2488
16th to endDay
42%417%25%9%
2306
September1st to 15thDay
48%312%23%11%
2160
16th to endDay
41%412%30%10%
2010
October1st to 15thDay
53%311%22%8%
1806
16th to endDay
66%311%14%4
1779
November1st to 15thDay
55%5%13%16%7%1
1686
16th to endDay
64%310%14%6%
1560
December1st to 15thDay
70%39%12%3
1560
16th to endDay
70%36%11%7%
1664
January1st to 15thNight
70%38%12%4
2716
16th to endNight
62%38%15%8%1
2912
February1st to 15thNight
63%39%17%5%
2492
16th to endNight
60%39%15%10%
2077
March1st to 15thNight
62%38%15%8%1
2327
16th to endNight
46%310%18%18%2
2067
April1st to 15thNight
54%26%21%12%2
1796
16th to endNight
49%49%18%15%2
1711
May1st to 15thNight
52%37%18%13%3
1440
16th to endNight
48%410%21%13%1
1497
June1st to 15thNight
53%5%11%20%8%
1440
16th to endNight
46%7%10%22%12%
1440
July1st to 15thNight
36%418%27%12%
1360
16th to endNight
37%6%18%26%10%
1418
August1st to 15thNight
41%7%18%24%7%
1446
16th to endNight
35%417%31%9%
1883
September1st to 15thNight
43%5%13%26%10%
1800
16th to endNight
38%413%32%10%
1950
October1st to 15thNight
49%311%23%10%
2152
16th to endNight
60%312%17%6%
2445
November1st to 15thNight
55%412%18%8%1
2501
16th to endNight
65%38%16%5%
2730
December1st to 15thNight
70%38%13%4
2730
16th to endNight
69%27%11%7%
2912

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
32%14%34%15%3
90
16th to endDay
33%20%32%9%4
96
February1st to 15thDay
32%27%34%32
132
16th to endDay
32%24%27%12%2
262
March1st to 15thDay
31%20%30%15%1
330
16th to endDay
27%18%28%15%8%2
311
April1st to 15thDay
32%18%25%15%6%1
270
16th to endDay
29%16%25%17%8%1
270
May1st to 15thDay
34%14%27%14%7%
288
16th to endDay
27%15%32%17%6%
331
June1st to 15thDay
31%12%33%15%6%
315
16th to endDay
23%13%35%20%6%1
315
July1st to 15thDay
21%8%34%25%7%2
305
16th to endDay
18%6%32%32%8%2
326
August1st to 15thDay
18%8%27%29%11%4
313
16th to endDay
18%9%28%21%13%8%
332
September1st to 15thDay
25%6%23%21%15%6%
315
16th to endDay
20%10%21%22%17%7%
314
October1st to 15thDay
30%16%21%18%11%2
315
16th to endDay
37%14%25%14%7%
301
November1st to 15thDay
31%14%23%23%6%1
250
16th to endDay
36%27%24%11%
90
December1st to 15thDay
38%17%31%11%1
90
16th to endDay
35%29%26%6%3
96
January1st to 15thNight
30%18%30%16%4
780
16th to endNight
22%17%33%18%5%1
832
February1st to 15thNight
20%20%34%19%4
764
16th to endNight
25%19%31%19%4
683
March1st to 15thNight
28%17%31%19%2
780
16th to endNight
23%15%30%22%6%1
792
April1st to 15thNight
31%14%25%23%4
718
16th to endNight
28%16%26%18%9%
631
May1st to 15thNight
26%9%29%23%8%1
360
16th to endNight
22%9%35%22%9%
375
June1st to 15thNight
24%10%28%28%6%1
360
16th to endNight
20%6%22%34%15%1
360
July1st to 15thNight
15%7%22%36%16%1
340
16th to endNight
12%5%24%39%16%1
376
August1st to 15thNight
16%219%40%19%1
375
16th to endNight
15%6%24%30%20%2
737
September1st to 15thNight
20%5%23%33%15%
720
16th to endNight
20%7%21%28%19%1
717
October1st to 15thNight
23%12%25%25%11%
720
16th to endNight
34%13%24%21%6%
768
November1st to 15thNight
28%14%26%21%8%1
760
16th to endNight
31%19%23%15%8%1
780
December1st to 15thNight
33%20%25%16%3
780
16th to endNight
34%17%27%15%31
832
Page generated at 2018-03-22 11:34:27. Version ac04

Copyright 2018 A. Danko


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