This page made possible by the sponsorship of: Tim Kearsley.

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 2019-09-17.

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
24%
17798
11%
54455
6%
17753
29%
17753
12%
41621

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
12%
874
6%
2835
2%
870
17%
870
6%
2339
January16th to endNight
11%
896
5%
2912
1%
896
16%
896
5%
2461
February1st to 15thNight
10%
824
6%
2676
1%
821
16%
821
5%
2286
February16th to endNight
13%
735
8%
2316
3%
735
21%
735
9%
1803
March1st to 15thNight
16%
840
13%
2328
5%
840
24%
840
12%
1829
March16th to endNight
19%
896
14%
2464
5%
896
28%
896
15%
1803
April1st to 15thNight
17%
689
14%
2128
5%
689
26%
689
13%
1567
April16th to endNight
24%
623
14%
1869
7%
623
31%
623
17%
1347
May1st to 15thNight
23%
630
12%
1890
6%
630
29%
630
13%
1438
May16th to endNight
25%
657
9%
1752
4%
656
30%
656
14%
1366
June1st to 15thNight
29%
609
10%
1659
6%
609
33%
609
15%
1296
June16th to endNight
32%
420
9%
1470
7%
420
36%
420
12%
1075
July1st to 15thNight
39%
465
10%
1465
9%
465
43%
465
15%
1087
July16th to endNight
32%
661
7%
1860
6%
628
36%
628
12%
1496
August1st to 15thNight
39%
619
12%
1848
10%
615
42%
615
17%
1327
August16th to endNight
42%
669
16%
2051
10%
669
48%
669
20%
1418
September1st to 15thNight
43%
689
18%
2159
15%
689
47%
689
21%
1437
September16th to endNight
39%
782
20%
2159
13%
782
45%
782
23%
1455
October1st to 15thNight
31%
780
16%
2337
9%
780
38%
780
19%
1610
October16th to endNight
23%
832
15%
2496
6%
832
32%
832
16%
1802
November1st to 15thNight
28%
848
13%
2765
8%
848
34%
848
13%
2028
November16th to endNight
17%
900
8%
2940
3%
900
23%
900
8%
2315
December1st to 15thNight
17%
900
7%
2940
3%
900
22%
900
8%
2388
December16th to endNight
12%
960
6%
3136
1%
960
17%
960
5%
2648

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%3445%6%29%
56226
Night
21%10%47%5%3445%6%26%
54634
TransparencyDay
56%5%10%17%9%
55923
Night
59%5%10%15%7%
54455
SeeingDay
25%17%26%20%7%1
10049
Night
24%22%23%20%8%
17798

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%5%7%8%46%6%5%5%16%
1761
16th to endDay
20%9%49%8%36%6%5%7%18%
2016
February1st to 15thDay
19%12%6%8%8%46%6%5%7%14%
1845
16th to endDay
17%9%39%6%46%5%47%25%
1726
March1st to 15thDay
20%10%36%6%34447%27%
2281
16th to endDay
17%8%37%5%34347%34%
2464
April1st to 15thDay
22%8%46%5%2435%6%30%
2481
16th to endDay
23%7%25%433447%32%
2696
May1st to 15thDay
26%9%36%5%24345%27%
2722
16th to endDay
25%7%35%423447%30%
3066
June1st to 15thDay
27%7%35%324445%29%
2971
16th to endDay
23%9%35%4235%5%7%30%
3150
July1st to 15thDay
21%8%35%5%2445%6%32%
3063
16th to endDay
21%12%46%5%3445%7%24%
2902
August1st to 15thDay
19%9%25%5%245%5%7%32%
2683
16th to endDay
16%7%25%42345%7%40%
2854
September1st to 15thDay
15%6%25%423347%43%
2458
16th to endDay
19%7%24413345%43%
2156
October1st to 15thDay
19%7%24424435%40%
1952
16th to endDay
20%7%25%6%35%5%6%6%30%
2077
November1st to 15thDay
21%8%345%35%5%47%28%
1750
16th to endDay
20%10%46%8%45%5%5%5%21%
1680
December1st to 15thDay
24%11%5%7%7%35%5%5%5%17%
1680
16th to endDay
24%11%5%6%7%35%5%5%6%18%
1792
January1st to 15thNight
18%12%5%9%8%35%447%18%
2835
16th to endNight
19%12%6%9%8%45%5%6%7%15%
2912
February1st to 15thNight
19%11%7%11%8%45%5%45%15%
2675
16th to endNight
15%10%5%9%6%36%6%6%6%24%
2316
March1st to 15thNight
22%9%46%5%35%45%5%26%
2316
16th to endNight
16%9%46%6%345%45%33%
2464
April1st to 15thNight
24%9%35%5%24345%30%
2128
16th to endNight
25%8%35%423347%30%
1869
May1st to 15thNight
26%12%35%324446%25%
1890
16th to endNight
27%9%36%5%2445%5%26%
1750
June1st to 15thNight
26%10%47%423347%25%
1659
16th to endNight
27%10%35%423345%29%
1470
July1st to 15thNight
22%8%36%4345%5%8%26%
1540
16th to endNight
26%12%46%43445%5%22%
1967
August1st to 15thNight
19%9%38%5%23346%32%
1860
16th to endNight
17%9%25%434446%36%
2051
September1st to 15thNight
19%7%24423446%38%
2159
16th to endNight
19%7%2442345%6%39%
2159
October1st to 15thNight
21%7%35%423346%37%
2337
16th to endNight
20%6%35%5%3445%5%35%
2496
November1st to 15thNight
19%8%35%5%35%5%47%31%
2765
16th to endNight
19%11%47%7%35%5%5%6%23%
2940
December1st to 15thNight
21%12%5%7%6%35%46%8%19%
2940
16th to endNight
23%12%5%8%6%35%5%6%5%17%
3136

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
70%6%10%8%3
1762
16th to endDay
67%7%10%12%2
2016
February1st to 15thDay
70%7%10%9%2
1848
16th to endDay
59%6%11%15%5%
1726
March1st to 15thDay
57%5%11%16%7%1
2292
16th to endDay
50%5%12%17%12%1
2464
April1st to 15thDay
53%5%9%16%13%
2481
16th to endDay
51%5%10%18%12%1
2696
May1st to 15thDay
59%48%16%9%1
2722
16th to endDay
54%6%11%18%8%
3070
June1st to 15thDay
56%6%8%17%9%1
2971
16th to endDay
55%5%10%16%10%1
3150
July1st to 15thDay
53%411%18%9%1
2910
16th to endDay
61%6%8%15%6%
2746
August1st to 15thDay
52%6%10%19%10%1
2670
16th to endDay
45%5%13%21%14%
2854
September1st to 15thDay
41%5%11%23%16%1
2458
16th to endDay
44%5%8%23%16%1
2156
October1st to 15thDay
46%5%12%22%11%1
1952
16th to endDay
53%6%13%17%8%
2077
November1st to 15thDay
56%7%11%16%6%
1750
16th to endDay
65%5%13%12%3
1680
December1st to 15thDay
69%6%10%10%3
1680
16th to endDay
70%411%9%3
1792
January1st to 15thNight
69%5%12%10%2
2835
16th to endNight
70%6%12%7%2
2912
February1st to 15thNight
72%6%9%8%3
2676
16th to endNight
61%5%12%13%5%
2316
March1st to 15thNight
60%5%11%13%8%
2328
16th to endNight
53%410%18%12%1
2464
April1st to 15thNight
56%48%16%12%2
2128
16th to endNight
54%39%19%10%2
1869
May1st to 15thNight
60%36%18%9%
1890
16th to endNight
59%5%10%15%8%
1752
June1st to 15thNight
60%46%19%8%
1659
16th to endNight
57%5%7%16%11%
1470
July1st to 15thNight
56%5%10%18%8%
1465
16th to endNight
63%6%8%14%5%1
1860
August1st to 15thNight
54%39%22%9%
1848
16th to endNight
48%5%10%20%13%
2051
September1st to 15thNight
46%48%22%15%2
2159
16th to endNight
43%5%9%23%16%
2159
October1st to 15thNight
48%411%21%11%1
2337
16th to endNight
52%5%11%20%9%
2496
November1st to 15thNight
55%5%14%17%7%
2765
16th to endNight
63%5%13%12%4
2940
December1st to 15thNight
66%5%13%11%2
2940
16th to endNight
71%5%10%8%2
3136

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
21%31%31%14%
330
16th to endDay
22%28%32%13%1
352
February1st to 15thDay
25%28%32%12%1
326
16th to endDay
21%25%33%15%3
310
March1st to 15thDay
23%30%29%13%2
390
16th to endDay
20%25%32%15%5%
416
April1st to 15thDay
27%23%32%13%2
390
16th to endDay
27%14%30%21%4
379
May1st to 15thDay
28%17%32%15%41
408
16th to endDay
32%14%26%19%6%
679
June1st to 15thDay
27%12%26%25%7%
645
16th to endDay
28%13%23%25%8%1
645
July1st to 15thDay
27%8%22%29%11%1
625
16th to endDay
28%9%15%30%14%1
475
August1st to 15thDay
26%6%20%28%14%2
418
16th to endDay
21%7%21%29%15%5%
460
September1st to 15thDay
18%9%23%30%15%1
435
16th to endDay
23%7%30%21%11%5%
378
October1st to 15thDay
25%12%25%24%10%2
315
16th to endDay
22%24%29%16%7%
336
November1st to 15thDay
22%25%24%19%7%1
325
16th to endDay
23%32%21%17%4
330
December1st to 15thDay
30%24%25%16%3
330
16th to endDay
28%28%29%12%1
352
January1st to 15thNight
23%31%27%15%2
874
16th to endNight
24%29%27%15%2
896
February1st to 15thNight
25%31%27%13%1
824
16th to endNight
20%29%32%12%4
735
March1st to 15thNight
24%26%27%16%4
840
16th to endNight
19%26%28%18%5%1
896
April1st to 15thNight
24%22%29%18%4
689
16th to endNight
26%19%23%20%9%1
623
May1st to 15thNight
29%18%23%20%6%1
630
16th to endNight
29%18%19%22%8%1
657
June1st to 15thNight
26%17%19%25%10%
609
16th to endNight
26%16%15%25%15%1
420
July1st to 15thNight
26%10%15%31%15%
465
16th to endNight
27%15%16%26%13%
661
August1st to 15thNight
27%9%14%28%17%1
619
16th to endNight
22%8%20%26%19%4
669
September1st to 15thNight
22%9%18%30%14%3
689
16th to endNight
23%11%19%25%16%3
782
October1st to 15thNight
24%14%22%25%10%1
780
16th to endNight
22%21%28%18%7%
832
November1st to 15thNight
20%24%22%22%8%
848
16th to endNight
24%29%23%16%5%
900
December1st to 15thNight
27%28%22%17%4
900
16th to endNight
28%32%23%13%1
960
Page generated at 2019-09-17 22:12:17. Version ac04

Copyright 2019 A. Danko


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