Northern Cross Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Northern Cross Observatory 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
37%
15848
15%
46988
10%
15806
42%
15806
20%
32978

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%
900
9%
2506
3%
895
22%
895
11%
2025
January16th to endNight
21%
874
9%
2602
4%
874
26%
874
12%
2064
February1st to 15thNight
18%
701
9%
2255
3%
701
24%
701
11%
1741
February16th to endNight
23%
631
14%
1893
6%
631
30%
631
14%
1426
March1st to 15thNight
26%
720
15%
2084
9%
720
31%
720
17%
1514
March16th to endNight
34%
768
18%
2112
10%
768
40%
768
21%
1490
April1st to 15thNight
28%
578
14%
1806
8%
578
35%
578
18%
1262
April16th to endNight
35%
540
20%
1620
9%
540
45%
540
25%
1072
May1st to 15thNight
39%
540
14%
1620
7%
540
45%
540
22%
1125
May16th to endNight
50%
562
15%
1660
11%
561
55%
561
28%
1061
June1st to 15thNight
56%
502
15%
1402
12%
502
60%
502
32%
878
June16th to endNight
57%
525
16%
1425
13%
525
61%
525
34%
895
July1st to 15thNight
65%
510
16%
1360
14%
510
67%
510
40%
805
July16th to endNight
68%
564
19%
1487
15%
531
72%
531
38%
881
August1st to 15thNight
64%
539
20%
1609
17%
536
67%
536
34%
977
August16th to endNight
62%
573
23%
1746
17%
573
66%
573
34%
1025
September1st to 15thNight
58%
660
24%
1920
19%
660
63%
660
35%
1127
September16th to endNight
58%
661
23%
1826
17%
661
61%
661
32%
1142
October1st to 15thNight
46%
660
20%
1892
15%
660
51%
660
26%
1262
October16th to endNight
25%
704
14%
2214
7%
704
33%
704
15%
1606
November1st to 15thNight
36%
700
19%
2276
16%
700
42%
700
21%
1491
November16th to endNight
25%
720
13%
2378
9%
720
32%
720
14%
1752
December1st to 15thNight
16%
756
7%
2556
3%
756
21%
756
9%
2022
December16th to endNight
15%
960
6%
2739
1%
960
19%
960
8%
2335

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
14%9%47%6%35%45%7%32%
47704
Night
15%9%46%5%24446%35%
47165
Cloud CoverDay
14%9%47%6%35%45%7%32%
47714
Night
15%9%46%5%34446%35%
47169
TransparencyDay
50%6%11%19%10%1
47399
Night
48%5%11%20%11%1
46988
SeeingDay
17%7%26%24%16%8%
5852
Night
19%8%28%29%12%1
15852

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
16%17%7%11%7%34445%16%
1432
16th to endDay
16%18%9%11%8%4433415%
1620
February1st to 15thDay
14%15%6%10%8%46%34418%
1605
16th to endDay
13%14%8%11%7%3445%5%20%
1580
March1st to 15thDay
16%11%5%8%6%3435%6%27%
1864
16th to endDay
17%11%5%7%5%44335%30%
2112
April1st to 15thDay
20%10%45%5%34446%30%
2151
16th to endDay
16%8%26%5%2435%6%37%
2340
May1st to 15thDay
20%7%36%5%35%446%33%
2331
16th to endDay
14%6%25%5%25%5%5%9%38%
2452
June1st to 15thDay
10%6%35%5%35%5%5%8%39%
2520
16th to endDay
10%5%26%6%46%6%6%9%34%
2520
July1st to 15thDay
8%4345%445%5%9%43%
2520
16th to endDay
8%425%6%46%6%7%9%38%
2577
August1st to 15thDay
10%5%25%6%35%6%6%8%37%
2340
16th to endDay
11%5%25%5%35%5%5%9%39%
2454
September1st to 15thDay
12%5%26%5%345%5%8%40%
2027
16th to endDay
12%6%25%425%6%6%9%38%
1824
October1st to 15thDay
15%8%35%6%24437%38%
1738
16th to endDay
22%10%35%5%33446%30%
1656
November1st to 15thDay
15%9%25%43445%7%35%
1582
16th to endDay
17%13%6%8%5%35%436%25%
1579
December1st to 15thDay
16%13%9%12%7%23335%21%
1401
16th to endDay
20%18%9%10%5%3333316%
1479
January1st to 15thNight
21%13%6%7%7%34445%22%
2506
16th to endNight
13%13%8%10%7%345%5%5%20%
2602
February1st to 15thNight
15%15%6%9%6%3444425%
2253
16th to endNight
15%12%49%8%35%345%26%
1893
March1st to 15thNight
16%11%46%5%24445%32%
2072
16th to endNight
15%8%36%5%25%437%36%
2112
April1st to 15thNight
19%9%35%42445%6%33%
1806
16th to endNight
15%7%25%5%24447%40%
1620
May1st to 15thNight
18%6%26%5%3445%7%35%
1620
16th to endNight
12%5%245%35%438%45%
1658
June1st to 15thNight
10%43443446%8%46%
1402
16th to endNight
9%5%25%425%46%10%44%
1425
July1st to 15thNight
7%314424448%53%
1440
16th to endNight
6%32442445%10%50%
1589
August1st to 15thNight
6%315%5%35%5%6%9%47%
1620
16th to endNight
9%43442335%7%51%
1746
September1st to 15thNight
12%41422335%6%51%
1920
16th to endNight
10%6%245%2445%6%46%
1826
October1st to 15thNight
16%5%25%5%24447%40%
1892
16th to endNight
22%8%36%6%34345%31%
2214
November1st to 15thNight
15%9%25%5%245%5%5%39%
2276
16th to endNight
22%11%46%434445%27%
2378
December1st to 15thNight
20%14%7%9%5%34345%22%
2556
16th to endNight
21%16%8%10%6%24445%15%
2739

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
17%17%7%11%7%34445%16%
1432
16th to endDay
15%18%9%12%8%35%33414%
1620
February1st to 15thDay
14%15%7%10%8%46%45%5%18%
1605
16th to endDay
13%14%8%12%7%25%445%20%
1580
March1st to 15thDay
16%11%5%8%6%3435%6%27%
1875
16th to endDay
18%11%5%7%5%44345%30%
2111
April1st to 15thDay
20%10%45%434447%30%
2151
16th to endDay
16%8%26%5%2435%6%37%
2340
May1st to 15thDay
20%7%36%435%445%33%
2331
16th to endDay
14%6%25%5%2445%8%38%
2452
June1st to 15thDay
10%6%26%5%35%5%5%8%39%
2520
16th to endDay
11%416%6%45%7%7%9%34%
2520
July1st to 15thDay
7%5%245%45%5%5%8%44%
2520
16th to endDay
8%425%6%46%6%7%9%38%
2577
August1st to 15thDay
10%5%25%7%36%6%5%8%37%
2340
16th to endDay
11%5%25%5%36%5%5%9%39%
2454
September1st to 15thDay
12%426%5%345%6%8%40%
2027
16th to endDay
12%6%25%425%6%6%9%38%
1824
October1st to 15thDay
14%8%35%6%24446%38%
1738
16th to endDay
22%10%345%33436%30%
1656
November1st to 15thDay
15%8%25%5%25%45%7%35%
1582
16th to endDay
17%14%5%8%5%34336%26%
1579
December1st to 15thDay
16%13%9%12%7%24335%21%
1401
16th to endDay
20%18%8%9%6%3333316%
1479
January1st to 15thNight
22%12%6%8%6%34445%22%
2506
16th to endNight
14%13%8%11%8%35%5%5%5%20%
2602
February1st to 15thNight
15%15%7%8%6%34345%25%
2246
16th to endNight
15%12%49%8%35%445%26%
1893
March1st to 15thNight
17%11%46%5%335%45%32%
2084
16th to endNight
15%8%36%5%25%447%35%
2112
April1st to 15thNight
19%9%35%42445%6%33%
1806
16th to endNight
15%7%25%5%2445%7%40%
1620
May1st to 15thNight
18%6%26%5%3445%7%35%
1619
16th to endNight
12%5%245%35%438%45%
1658
June1st to 15thNight
10%425%42445%7%46%
1402
16th to endNight
9%42442446%9%45%
1425
July1st to 15thNight
8%31442445%8%53%
1440
16th to endNight
6%3144245%5%10%50%
1589
August1st to 15thNight
6%315%5%35%5%7%8%47%
1620
16th to endNight
9%42442335%7%51%
1746
September1st to 15thNight
12%42332435%6%51%
1920
16th to endNight
10%5%245%335%5%6%47%
1826
October1st to 15thNight
16%5%35%5%33447%40%
1892
16th to endNight
21%9%26%6%34345%31%
2214
November1st to 15thNight
14%8%245%245%5%5%39%
2276
16th to endNight
22%11%46%424445%28%
2378
December1st to 15thNight
20%14%6%9%6%24345%22%
2556
16th to endNight
21%15%9%10%5%2444415%
2739

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
69%6%9%10%3
1433
16th to endDay
73%5%7%8%4
1620
February1st to 15thDay
67%6%8%12%5%
1607
16th to endDay
64%5%9%13%6%1
1580
March1st to 15thDay
56%6%12%16%7%
1875
16th to endDay
56%410%18%8%1
2112
April1st to 15thDay
54%5%10%19%10%
2151
16th to endDay
46%5%13%16%14%2
2340
May1st to 15thDay
51%6%9%20%9%2
2331
16th to endDay
42%6%13%23%12%1
2456
June1st to 15thDay
40%8%11%24%14%1
2520
16th to endDay
41%8%12%19%16%
2520
July1st to 15thDay
35%7%11%24%18%2
2371
16th to endDay
37%9%13%20%15%2
2416
August1st to 15thDay
40%8%12%23%12%2
2327
16th to endDay
40%7%10%24%15%1
2454
September1st to 15thDay
39%7%12%25%13%
2027
16th to endDay
40%7%11%29%12%
1824
October1st to 15thDay
45%5%11%22%13%1
1738
16th to endDay
54%5%13%18%6%
1656
November1st to 15thDay
46%6%12%21%11%1
1582
16th to endDay
59%412%17%5%
1579
December1st to 15thDay
65%5%11%13%3
1401
16th to endDay
73%310%8%3
1479
January1st to 15thNight
64%410%12%6%
2506
16th to endNight
63%5%12%13%4
2602
February1st to 15thNight
61%5%11%14%6%
2255
16th to endNight
58%5%11%17%7%
1893
March1st to 15thNight
52%5%10%18%10%1
2084
16th to endNight
48%5%11%22%10%1
2112
April1st to 15thNight
50%5%10%19%14%
1806
16th to endNight
42%6%10%19%17%3
1620
May1st to 15thNight
47%6%11%20%11%2
1620
16th to endNight
39%6%12%23%15%3
1660
June1st to 15thNight
34%7%12%28%15%1
1402
16th to endNight
34%6%15%25%17%1
1425
July1st to 15thNight
29%5%9%29%22%2
1360
16th to endNight
29%6%15%23%21%2
1487
August1st to 15thNight
31%8%10%31%15%2
1609
16th to endNight
32%5%11%29%17%2
1746
September1st to 15thNight
32%5%11%30%19%1
1920
16th to endNight
35%6%11%28%17%
1826
October1st to 15thNight
41%6%10%22%17%1
1892
16th to endNight
53%5%11%20%7%
2214
November1st to 15thNight
44%6%12%22%12%1
2276
16th to endNight
57%412%18%6%
2378
December1st to 15thNight
64%5%11%12%5%
2556
16th to endNight
70%6%9%9%3
2739

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
17%15%43%17%5%
90
16th to endDay
32%8%40%14%4
96
February1st to 15thDay
24%17%48%8%
90
16th to endDay
22%17%37%18%4
81
March1st to 15thDay
28%11%30%21%7%
165
16th to endDay
25%6%31%25%10%1
288
April1st to 15thDay
23%9%30%25%8%2
270
16th to endDay
21%10%30%20%11%7%
270
May1st to 15thDay
27%7%26%19%15%4
288
16th to endDay
18%5%26%24%16%8%
352
June1st to 15thDay
12%5%30%31%15%4
495
16th to endDay
12%7%30%25%17%6%
495
July1st to 15thDay
9%5%22%29%20%11%
475
16th to endDay
8%323%31%21%11%
437
August1st to 15thDay
11%115%27%21%23%
313
16th to endDay
15%316%19%24%20%
332
September1st to 15thDay
11%5%19%20%25%17%
315
16th to endDay
16%217%21%29%12%
257
October1st to 15thDay
17%7%22%26%20%6%
255
16th to endDay
26%12%30%23%6%
168
November1st to 15thDay
15%14%22%28%16%2
90
16th to endDay
30%19%30%15%4
83
December1st to 15thDay
21%21%33%21%1
60
16th to endDay
27%25%37%9%
87
January1st to 15thNight
27%12%35%19%5%
900
16th to endNight
20%10%35%27%5%
874
February1st to 15thNight
23%12%37%22%4
704
16th to endNight
21%12%32%29%3
631
March1st to 15thNight
23%11%30%26%6%
720
16th to endNight
18%9%31%29%9%1
768
April1st to 15thNight
23%11%32%25%6%1
578
16th to endNight
19%6%34%27%9%1
540
May1st to 15thNight
21%428%35%8%1
540
16th to endNight
13%425%37%17%2
563
June1st to 15thNight
10%224%48%13%
502
16th to endNight
11%221%45%16%1
525
July1st to 15thNight
10%116%40%27%2
510
16th to endNight
5%117%47%23%3
564
August1st to 15thNight
9%16%41%27%4
539
16th to endNight
12%117%31%31%5%
573
September1st to 15thNight
13%320%30%26%5%
660
16th to endNight
13%5%16%32%27%5%
661
October1st to 15thNight
18%5%24%33%15%2
660
16th to endNight
26%11%31%24%5%
704
November1st to 15thNight
20%9%29%27%12%1
700
16th to endNight
27%11%29%23%7%
720
December1st to 15thNight
26%13%34%20%4
756
16th to endNight
28%11%36%19%3
960
Page generated at 2017-09-17 12:05:42. Version ac04

Copyright 2017 A. Danko


Northern Cross Observatory Clear Sky Chart | Charts Home