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Cape Negro Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Cape Negro Observatory clear sky chart from 2005-11-05 to 2017-09-10.

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%
15120
11%
46521
6%
15075
29%
15075
12%
35614

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
11%
737
6%
2428
2%
733
17%
733
6%
2007
January16th to endNight
9%
768
5%
2496
0%
768
15%
768
5%
2119
February1st to 15thNight
10%
704
4%
2286
1%
701
14%
701
5%
1977
February16th to endNight
14%
631
8%
1988
3%
631
21%
631
9%
1560
March1st to 15thNight
17%
720
12%
1995
5%
720
23%
720
13%
1561
March16th to endNight
20%
768
16%
2112
6%
768
28%
768
15%
1545
April1st to 15thNight
18%
590
13%
1823
5%
590
26%
590
13%
1350
April16th to endNight
24%
540
14%
1620
7%
540
31%
540
17%
1154
May1st to 15thNight
22%
540
11%
1620
5%
540
28%
540
12%
1246
May16th to endNight
27%
561
10%
1496
4%
560
31%
560
14%
1164
June1st to 15thNight
27%
522
8%
1422
5%
522
30%
522
13%
1140
June16th to endNight
32%
360
9%
1260
6%
360
36%
360
11%
930
July1st to 15thNight
36%
395
8%
1245
7%
395
38%
395
14%
936
July16th to endNight
30%
565
7%
1576
5%
532
35%
532
11%
1272
August1st to 15thNight
39%
539
12%
1608
10%
535
41%
535
17%
1149
August16th to endNight
42%
573
17%
1757
10%
573
48%
573
20%
1208
September1st to 15thNight
41%
572
18%
1796
14%
572
46%
572
21%
1189
September16th to endNight
42%
657
23%
1815
15%
657
49%
657
26%
1171
October1st to 15thNight
29%
660
16%
1977
9%
660
36%
660
18%
1363
October16th to endNight
22%
704
13%
2112
5%
704
30%
704
15%
1545
November1st to 15thNight
29%
714
12%
2361
8%
714
33%
714
14%
1735
November16th to endNight
18%
750
9%
2520
4%
750
24%
750
9%
1958
December1st to 15thNight
16%
750
7%
2520
3%
750
21%
750
7%
2052
December16th to endNight
11%
800
6%
2688
1%
800
17%
800
5%
2283

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
21%9%36%5%34446%29%
48097
Night
21%10%47%5%3445%6%26%
46700
TransparencyDay
56%6%10%16%8%
47794
Night
59%5%10%15%7%
46521
SeeingDay
25%18%25%20%7%1
7296
Night
24%23%22%20%8%1
15120

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
18%14%6%7%8%46%7%5%5%15%
1508
16th to endDay
20%10%49%7%36%6%5%7%17%
1728
February1st to 15thDay
18%12%6%9%8%46%7%5%7%13%
1575
16th to endDay
16%9%39%7%5%6%5%46%24%
1482
March1st to 15thDay
21%9%36%5%34447%28%
1954
16th to endDay
18%8%47%5%33347%33%
2112
April1st to 15thDay
21%8%46%5%34346%30%
2126
16th to endDay
22%7%25%43345%7%33%
2340
May1st to 15thDay
27%9%36%424335%27%
2332
16th to endDay
25%7%35%423447%30%
2618
June1st to 15thDay
29%8%45%424445%27%
2547
16th to endDay
23%9%35%4235%5%7%30%
2700
July1st to 15thDay
23%9%36%5%2445%6%29%
2625
16th to endDay
22%12%46%43445%6%24%
2482
August1st to 15thDay
20%9%25%4245%5%6%32%
2340
16th to endDay
16%6%25%42345%7%39%
2444
September1st to 15thDay
17%6%25%323247%44%
2050
16th to endDay
17%7%33413345%45%
1815
October1st to 15thDay
20%7%34423445%40%
1652
16th to endDay
22%7%35%5%35%46%6%29%
1757
November1st to 15thDay
22%9%345%35%5%47%28%
1494
16th to endDay
21%10%5%6%8%45%5%5%5%20%
1440
December1st to 15thDay
25%12%5%7%6%35%6%6%5%16%
1440
16th to endDay
25%11%5%6%7%25%5%5%6%17%
1536
January1st to 15thNight
19%12%6%9%8%35%447%18%
2428
16th to endNight
19%12%6%10%8%45%5%6%7%14%
2496
February1st to 15thNight
19%11%7%11%9%45%5%5%6%14%
2285
16th to endNight
14%10%410%6%36%6%6%6%23%
1988
March1st to 15thNight
22%10%47%5%35%44427%
1983
16th to endNight
17%9%46%6%345%45%33%
2112
April1st to 15thNight
25%10%35%424345%29%
1823
16th to endNight
24%7%35%5%23447%32%
1620
May1st to 15thNight
27%12%35%324447%24%
1620
16th to endNight
26%8%36%5%25%45%5%26%
1494
June1st to 15thNight
28%10%47%5%23346%22%
1422
16th to endNight
27%10%36%423346%28%
1260
July1st to 15thNight
24%9%37%425%5%48%24%
1320
16th to endNight
28%12%36%42445%5%21%
1683
August1st to 15thNight
20%9%37%5%23347%32%
1620
16th to endNight
18%9%25%434446%36%
1757
September1st to 15thNight
21%8%24422336%39%
1796
16th to endNight
18%5%2432345%6%43%
1815
October1st to 15thNight
20%7%35%423346%37%
1977
16th to endNight
20%6%36%5%3445%5%34%
2112
November1st to 15thNight
19%8%35%5%35%5%47%31%
2361
16th to endNight
20%11%47%7%35%45%6%24%
2520
December1st to 15thNight
22%13%5%6%6%35%46%7%18%
2520
16th to endNight
24%12%5%8%6%35%5%6%5%16%
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
71%6%10%8%2
1509
16th to endDay
68%7%10%12%2
1728
February1st to 15thDay
71%7%10%8%2
1578
16th to endDay
61%7%11%14%4
1482
March1st to 15thDay
57%5%12%16%7%1
1965
16th to endDay
51%5%12%18%10%1
2112
April1st to 15thDay
52%5%9%17%13%
2126
16th to endDay
49%5%11%18%12%1
2340
May1st to 15thDay
59%47%16%9%1
2332
16th to endDay
54%6%12%18%8%
2622
June1st to 15thDay
58%6%8%16%7%1
2547
16th to endDay
55%6%10%16%10%1
2700
July1st to 15thDay
55%5%11%17%8%1
2472
16th to endDay
61%6%8%16%6%
2326
August1st to 15thDay
51%6%9%20%10%1
2327
16th to endDay
44%5%13%22%13%
2444
September1st to 15thDay
40%5%11%23%17%1
2050
16th to endDay
41%5%8%25%18%
1815
October1st to 15thDay
46%5%12%21%12%1
1652
16th to endDay
55%6%13%16%8%
1757
November1st to 15thDay
57%6%11%16%6%1
1494
16th to endDay
66%5%12%11%3
1440
December1st to 15thDay
69%6%11%9%2
1440
16th to endDay
70%5%11%9%3
1536
January1st to 15thNight
69%5%12%10%2
2428
16th to endNight
71%6%12%7%1
2496
February1st to 15thNight
73%6%9%7%2
2286
16th to endNight
62%6%13%13%4
1988
March1st to 15thNight
59%5%11%14%8%
1995
16th to endNight
52%410%19%11%
2112
April1st to 15thNight
57%38%16%11%2
1823
16th to endNight
52%310%19%10%2
1620
May1st to 15thNight
61%37%17%9%
1620
16th to endNight
58%5%10%16%8%
1496
June1st to 15thNight
63%46%18%5%
1422
16th to endNight
58%5%8%15%11%
1260
July1st to 15thNight
57%5%10%18%6%
1245
16th to endNight
63%6%8%15%41
1576
August1st to 15thNight
53%39%22%9%
1608
16th to endNight
47%5%10%21%14%
1757
September1st to 15thNight
46%48%22%15%2
1796
16th to endNight
39%49%25%19%
1815
October1st to 15thNight
48%411%21%11%2
1977
16th to endNight
53%5%10%19%9%
2112
November1st to 15thNight
55%5%14%16%7%
2361
16th to endNight
62%5%13%12%4
2520
December1st to 15thNight
67%5%13%11%2
2520
16th to endNight
72%6%10%8%2
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
19%34%30%15%
240
16th to endDay
23%27%33%13%1
256
February1st to 15thDay
23%27%31%15%1
236
16th to endDay
17%22%35%19%4
222
March1st to 15thDay
25%30%27%14%3
270
16th to endDay
24%25%30%14%5%
288
April1st to 15thDay
25%22%31%15%3
270
16th to endDay
24%15%32%21%5%1
270
May1st to 15thDay
28%18%29%14%5%2
288
16th to endDay
32%16%23%18%7%1
519
June1st to 15thDay
28%14%23%25%7%
495
16th to endDay
28%15%18%25%9%2
495
July1st to 15thDay
30%10%20%24%11%2
475
16th to endDay
29%12%16%25%13%1
343
August1st to 15thDay
29%7%17%27%15%2
313
16th to endDay
21%8%20%28%15%6%
332
September1st to 15thDay
20%11%22%28%14%2
294
16th to endDay
16%9%31%23%13%6%
254
October1st to 15thDay
25%14%22%22%11%3
225
16th to endDay
25%21%28%17%7%
240
November1st to 15thDay
21%24%23%19%8%1
235
16th to endDay
22%33%20%17%5%1
240
December1st to 15thDay
33%26%22%15%2
240
16th to endDay
28%29%28%11%1
256
January1st to 15thNight
23%32%25%15%3
737
16th to endNight
22%32%27%14%2
768
February1st to 15thNight
24%32%26%14%1
704
16th to endNight
19%31%31%12%5%
631
March1st to 15thNight
23%28%26%16%4
720
16th to endNight
20%27%27%18%5%
768
April1st to 15thNight
24%23%28%18%4
590
16th to endNight
23%20%24%19%10%1
540
May1st to 15thNight
29%20%21%19%7%1
540
16th to endNight
28%20%17%22%9%1
561
June1st to 15thNight
26%18%18%24%10%
522
16th to endNight
25%18%13%23%16%1
360
July1st to 15thNight
27%11%15%29%15%
395
16th to endNight
29%17%15%25%12%
565
August1st to 15thNight
27%10%13%27%18%2
539
16th to endNight
21%9%19%26%19%4
573
September1st to 15thNight
23%10%18%29%14%3
572
16th to endNight
20%12%18%26%16%4
657
October1st to 15thNight
23%16%23%24%10%1
660
16th to endNight
23%21%28%19%5%
704
November1st to 15thNight
19%23%23%22%9%1
714
16th to endNight
24%30%22%16%5%
750
December1st to 15thNight
28%29%21%16%3
750
16th to endNight
29%32%22%13%1
800
Page generated at 2017-09-11 20:35:15. Version ac04

Copyright 2017 A. Danko


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