Ibis Observatoire
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Ibis Observatoire clear sky chart from 2005-11-05 to 2017-09-24.

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
23%
14680
11%
46907
5%
14649
30%
14649
13%
35004

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
10%
722
9%
2520
3%
718
18%
718
6%
2045
January16th to endNight
15%
768
11%
2688
2%
768
27%
768
9%
1998
February1st to 15thNight
13%
703
8%
2351
2%
701
21%
701
8%
1851
February16th to endNight
13%
631
12%
1893
3%
631
23%
631
10%
1473
March1st to 15thNight
17%
720
14%
2134
7%
720
25%
720
13%
1581
March16th to endNight
26%
768
16%
2061
6%
768
33%
768
17%
1535
April1st to 15thNight
19%
691
15%
1769
4%
691
26%
691
14%
1351
April16th to endNight
25%
540
15%
1620
7%
540
32%
540
16%
1165
May1st to 15thNight
27%
500
11%
1580
8%
500
33%
500
14%
1159
May16th to endNight
25%
375
9%
1416
6%
374
34%
374
11%
1040
June1st to 15thNight
27%
360
7%
1260
5%
360
32%
360
11%
950
June16th to endNight
33%
360
7%
1260
6%
360
37%
360
16%
898
July1st to 15thNight
36%
340
8%
1273
8%
340
40%
340
17%
865
July16th to endNight
40%
376
9%
1418
10%
354
43%
354
17%
952
August1st to 15thNight
41%
451
11%
1522
9%
449
45%
449
18%
1041
August16th to endNight
39%
603
17%
1749
9%
603
45%
603
25%
1146
September1st to 15thNight
33%
720
11%
1873
4%
720
37%
720
24%
1323
September16th to endNight
36%
693
18%
1913
11%
693
41%
693
26%
1271
October1st to 15thNight
25%
660
16%
1897
6%
660
34%
660
18%
1362
October16th to endNight
16%
704
8%
2288
4%
704
22%
704
10%
1800
November1st to 15thNight
22%
700
15%
2277
9%
700
31%
700
11%
1697
November16th to endNight
21%
745
12%
2565
7%
745
28%
745
10%
1961
December1st to 15thNight
11%
750
6%
2700
1%
750
17%
750
5%
2220
December16th to endNight
12%
800
10%
2880
3%
800
21%
800
5%
2320

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%11%47%6%35%446%26%
48031
Night
16%10%47%6%35%45%6%29%
47074
TransparencyDay
58%7%10%16%7%
47716
Night
54%8%11%17%7%
46907
SeeingDay
25%16%30%18%7%1
6275
Night
22%17%31%20%7%
14681

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
14%13%6%10%10%45%5%36%20%
1417
16th to endDay
9%13%6%10%8%46%45%5%24%
1536
February1st to 15thDay
9%14%6%10%10%6%7%5%4419%
1509
16th to endDay
13%15%5%10%8%35%345%22%
1580
March1st to 15thDay
15%14%6%9%5%34445%25%
1815
16th to endDay
14%11%5%9%6%45%43429%
2163
April1st to 15thDay
20%14%46%5%24345%28%
2179
16th to endDay
19%12%36%5%33345%31%
2340
May1st to 15thDay
22%10%37%5%24345%28%
2382
16th to endDay
21%10%37%7%35%446%25%
2696
June1st to 15thDay
24%9%36%5%35%5%47%23%
2700
16th to endDay
23%9%47%6%35%5%46%22%
2700
July1st to 15thDay
17%7%46%5%45%5%6%8%26%
2609
16th to endDay
20%8%46%6%46%6%5%7%24%
2654
August1st to 15thDay
19%7%37%6%45%5%6%8%23%
2415
16th to endDay
14%6%36%6%35%5%5%8%33%
2450
September1st to 15thDay
20%7%36%5%33336%35%
2086
16th to endDay
16%8%24432447%40%
1906
October1st to 15thDay
22%10%37%6%33435%29%
1730
16th to endDay
24%15%47%6%33445%20%
1584
November1st to 15thDay
19%13%47%5%33435%27%
1581
16th to endDay
18%15%5%7%5%3444426%
1395
December1st to 15thDay
19%19%7%9%7%2434417%
1260
16th to endDay
20%14%7%10%5%4444420%
1344
January1st to 15thNight
12%12%6%11%9%46%5%5%421%
2520
16th to endNight
8%10%6%9%8%46%6%6%7%24%
2688
February1st to 15thNight
7%11%5%10%10%46%6%6%5%23%
2350
16th to endNight
14%12%6%9%7%35%445%26%
1893
March1st to 15thNight
16%10%48%4345%46%30%
2121
16th to endNight
11%10%46%7%45%45%5%33%
2061
April1st to 15thNight
16%13%5%5%6%25%45%5%29%
1769
16th to endNight
20%10%26%5%24345%33%
1620
May1st to 15thNight
21%9%35%5%25%45%5%31%
1580
16th to endNight
22%7%35%7%45%44430%
1414
June1st to 15thNight
23%9%35%6%26%45%5%26%
1260
16th to endNight
17%8%25%5%25%5%5%7%32%
1260
July1st to 15thNight
15%7%26%5%3446%9%34%
1350
16th to endNight
13%6%35%435%5%5%8%36%
1514
August1st to 15thNight
15%6%36%4246%7%7%35%
1532
16th to endNight
13%5%25%4346%410%39%
1749
September1st to 15thNight
18%6%244245%5%7%38%
1873
16th to endNight
16%6%13423346%45%
1913
October1st to 15thNight
19%7%35%5%24447%35%
1897
16th to endNight
21%12%46%6%3445%5%26%
2288
November1st to 15thNight
16%10%46%5%35%45%7%30%
2277
16th to endNight
16%11%48%6%34446%27%
2565
December1st to 15thNight
18%14%5%10%7%45%44419%
2700
16th to endNight
18%14%5%9%6%35%45%5%21%
2880

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%5%8%12%6%
1418
16th to endDay
59%7%7%16%8%
1536
February1st to 15thDay
66%7%8%10%6%
1512
16th to endDay
63%6%6%14%7%1
1580
March1st to 15thDay
61%48%13%10%1
1825
16th to endDay
58%49%15%10%1
2163
April1st to 15thDay
58%5%7%16%9%3
2179
16th to endDay
54%5%7%17%12%2
2340
May1st to 15thDay
57%6%8%17%9%
2382
16th to endDay
58%9%10%16%5%
2700
June1st to 15thDay
60%6%11%15%5%
2700
16th to endDay
61%8%9%14%5%
2700
July1st to 15thDay
52%10%14%16%5%
2457
16th to endDay
59%9%11%14%4
2487
August1st to 15thDay
56%11%15%13%3
2401
16th to endDay
45%11%14%22%6%
2450
September1st to 15thDay
49%7%12%19%10%
2086
16th to endDay
42%6%12%25%11%
1906
October1st to 15thDay
56%6%11%19%6%
1730
16th to endDay
65%6%8%14%4
1584
November1st to 15thDay
58%7%10%14%7%
1581
16th to endDay
62%7%8%16%5%
1395
December1st to 15thDay
69%6%9%11%2
1260
16th to endDay
67%6%7%10%8%
1344
January1st to 15thNight
64%9%8%11%6%
2520
16th to endNight
56%7%9%18%7%
2688
February1st to 15thNight
59%9%9%13%6%
2351
16th to endNight
60%6%7%13%10%
1893
March1st to 15thNight
53%7%9%17%9%2
2134
16th to endNight
51%7%9%18%10%1
2061
April1st to 15thNight
54%6%6%17%11%2
1769
16th to endNight
51%7%9%16%13%2
1620
May1st to 15thNight
53%8%10%16%11%
1580
16th to endNight
56%7%10%15%10%
1416
June1st to 15thNight
57%8%10%16%6%
1260
16th to endNight
49%9%14%17%7%
1260
July1st to 15thNight
44%10%16%20%6%
1273
16th to endNight
45%10%17%19%7%
1418
August1st to 15thNight
43%11%17%23%2
1522
16th to endNight
38%10%18%27%6%
1749
September1st to 15thNight
42%9%13%24%8%1
1873
16th to endNight
39%8%15%26%10%
1913
October1st to 15thNight
48%7%12%22%8%
1897
16th to endNight
59%9%10%15%5%
2288
November1st to 15thNight
52%10%12%15%7%
2277
16th to endNight
57%9%10%17%5%
2565
December1st to 15thNight
67%8%8%12%3
2700
16th to endNight
65%8%7%11%7%
2880

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%33%35%6%
60
16th to endDay
25%26%34%9%31
64
February1st to 15thDay
23%19%32%19%5%
155
16th to endDay
22%18%38%15%4
239
March1st to 15thDay
25%25%29%13%5%
270
16th to endDay
21%21%23%19%12%2
288
April1st to 15thDay
28%22%27%13%6%
270
16th to endDay
28%18%30%14%5%3
270
May1st to 15thDay
33%12%34%15%31
288
16th to endDay
26%17%33%18%4
409
June1st to 15thDay
28%14%28%19%8%
495
16th to endDay
27%9%32%21%7%
495
July1st to 15thDay
23%12%34%19%9%
391
16th to endDay
23%9%34%24%6%1
326
August1st to 15thDay
21%10%32%23%8%3
313
16th to endDay
19%15%29%19%12%4
332
September1st to 15thDay
20%14%29%20%10%3
315
16th to endDay
18%14%31%16%14%5%
287
October1st to 15thDay
26%17%25%18%9%3
244
16th to endDay
36%18%24%14%5%
240
November1st to 15thDay
26%18%29%17%7%
235
16th to endDay
26%21%24%16%8%1
165
December1st to 15thDay
33%23%33%6%3
60
16th to endDay
42%31%23%3
64
January1st to 15thNight
22%27%34%13%2
722
16th to endNight
17%22%37%18%3
768
February1st to 15thNight
13%25%39%17%3
704
16th to endNight
23%20%36%14%4
631
March1st to 15thNight
24%20%35%16%3
720
16th to endNight
18%19%29%23%7%1
768
April1st to 15thNight
26%19%30%17%6%
691
16th to endNight
28%12%29%21%7%
540
May1st to 15thNight
24%13%28%22%9%
500
16th to endNight
27%10%29%25%6%1
375
June1st to 15thNight
26%9%28%25%9%
360
16th to endNight
18%8%32%30%8%
360
July1st to 15thNight
17%9%32%25%13%
340
16th to endNight
16%332%35%10%
376
August1st to 15thNight
16%6%28%28%18%1
451
16th to endNight
16%7%31%29%12%1
603
September1st to 15thNight
20%9%31%25%10%1
720
16th to endNight
20%10%30%24%13%
693
October1st to 15thNight
24%15%31%20%7%1
660
16th to endNight
31%17%29%14%6%
704
November1st to 15thNight
24%22%26%20%5%
700
16th to endNight
25%20%28%17%6%1
745
December1st to 15thNight
25%26%30%13%3
750
16th to endNight
29%25%26%14%4
800
Page generated at 2017-09-25 09:02:21. Version ac04

Copyright 2017 A. Danko


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