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 2018-04-23.

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
36%
16741
15%
49676
10%
16699
42%
16699
20%
34878

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
19%
975
9%
2716
3%
970
24%
970
12%
2169
January16th to endNight
20%
947
9%
2819
4%
947
25%
947
12%
2231
February1st to 15thNight
17%
761
9%
2447
3%
761
24%
761
11%
1894
February16th to endNight
22%
683
13%
2049
6%
683
29%
683
14%
1546
March1st to 15thNight
26%
780
16%
2258
9%
780
32%
780
18%
1628
March16th to endNight
34%
832
19%
2288
10%
832
41%
832
22%
1602
April1st to 15thNight
28%
626
14%
1956
8%
626
35%
626
18%
1380
April16th to endNight
36%
558
21%
1672
10%
558
46%
558
25%
1104
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
59%
717
24%
1980
19%
717
63%
717
33%
1224
October1st to 15thNight
45%
720
19%
2064
14%
720
50%
720
25%
1396
October16th to endNight
26%
768
15%
2415
9%
768
35%
768
16%
1732
November1st to 15thNight
35%
760
18%
2471
15%
760
41%
760
20%
1642
November16th to endNight
25%
780
14%
2576
9%
780
33%
780
15%
1869
December1st to 15thNight
17%
819
7%
2769
3%
819
22%
819
9%
2177
December16th to endNight
15%
1040
7%
2967
1%
1040
19%
1040
8%
2510

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%3445%7%32%
49771
Night
15%9%46%5%34446%35%
49853
Cloud CoverDay
14%9%47%6%35%45%7%32%
49781
Night
15%9%46%5%34446%35%
49857
TransparencyDay
50%6%11%19%11%1
49466
Night
49%5%11%20%11%1
49676
SeeingDay
18%7%27%24%15%7%
6553
Night
19%8%28%29%12%1
16745

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%10%8%345%45%16%
1552
16th to endDay
16%18%8%11%8%3433416%
1755
February1st to 15thDay
15%15%6%10%8%46%34418%
1743
16th to endDay
14%14%8%10%7%34445%21%
1710
March1st to 15thDay
16%11%5%8%6%3435%6%27%
2020
16th to endDay
17%11%5%8%5%33335%31%
2288
April1st to 15thDay
20%10%45%5%24446%29%
2331
16th to endDay
15%8%26%5%2435%6%38%
2402
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%24425%5%6%8%40%
1980
October1st to 15thDay
15%7%35%6%24437%38%
1896
16th to endDay
22%10%35%5%33446%31%
1806
November1st to 15thDay
16%9%26%43445%7%35%
1717
16th to endDay
16%14%5%8%5%24336%27%
1710
December1st to 15thDay
15%13%9%11%7%23336%21%
1518
16th to endDay
20%17%9%10%6%3334316%
1602
January1st to 15thNight
21%12%6%7%7%34445%22%
2716
16th to endNight
13%13%8%10%7%45%5%5%6%20%
2819
February1st to 15thNight
15%15%6%9%6%3444425%
2445
16th to endNight
16%12%48%8%35%345%26%
2049
March1st to 15thNight
16%11%46%6%34445%33%
2246
16th to endNight
14%8%36%5%25%437%36%
2288
April1st to 15thNight
20%10%35%5%2445%6%32%
1956
16th to endNight
15%7%25%5%24447%40%
1672
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
9%6%245%2445%6%47%
1980
October1st to 15thNight
17%6%35%5%24447%39%
2064
16th to endNight
21%8%26%6%34345%32%
2415
November1st to 15thNight
15%9%25%5%2445%5%38%
2471
16th to endNight
21%11%46%43445%6%28%
2576
December1st to 15thNight
19%14%7%10%5%34345%22%
2769
16th to endNight
20%16%8%10%5%24445%16%
2967

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
16%17%7%10%8%345%45%16%
1552
16th to endDay
16%18%8%11%8%35%33416%
1755
February1st to 15thDay
15%15%7%9%8%46%34418%
1743
16th to endDay
14%14%7%11%7%24445%21%
1710
March1st to 15thDay
16%11%5%8%6%3435%6%27%
2031
16th to endDay
17%11%48%5%34335%31%
2287
April1st to 15thDay
20%10%45%434447%29%
2331
16th to endDay
15%8%26%5%2435%6%37%
2402
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%244346%6%8%40%
1980
October1st to 15thDay
15%8%35%6%24446%38%
1896
16th to endDay
21%11%345%23436%31%
1806
November1st to 15thDay
16%9%26%5%2445%7%34%
1717
16th to endDay
16%14%5%8%5%34336%27%
1710
December1st to 15thDay
15%13%9%11%7%24335%22%
1518
16th to endDay
20%18%8%9%7%3333316%
1602
January1st to 15thNight
21%12%5%7%6%34445%22%
2716
16th to endNight
13%12%8%11%8%35%5%5%5%20%
2819
February1st to 15thNight
15%15%7%8%6%3434425%
2438
16th to endNight
16%12%49%7%34345%26%
2049
March1st to 15thNight
16%10%46%5%335%45%33%
2258
16th to endNight
15%8%36%5%35%437%36%
2288
April1st to 15thNight
20%10%35%42445%6%32%
1956
16th to endNight
15%7%25%424447%40%
1672
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
9%5%245%335%5%6%47%
1980
October1st to 15thNight
17%5%35%5%33447%39%
2064
16th to endNight
21%9%26%5%34345%32%
2415
November1st to 15thNight
15%9%25%5%245%5%5%37%
2471
16th to endNight
21%11%46%434445%29%
2576
December1st to 15thNight
19%14%7%9%6%24445%22%
2769
16th to endNight
20%16%8%10%5%2444416%
2967

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
68%6%9%10%4
1553
16th to endDay
71%5%8%9%4
1755
February1st to 15thDay
67%6%7%12%5%
1745
16th to endDay
63%5%9%13%6%1
1710
March1st to 15thDay
56%6%12%16%8%
2031
16th to endDay
55%49%19%9%
2288
April1st to 15thDay
54%5%10%19%10%
2331
16th to endDay
46%5%13%16%15%2
2402
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
38%7%11%29%13%
1980
October1st to 15thDay
46%5%11%22%12%1
1896
16th to endDay
53%5%14%18%7%
1806
November1st to 15thDay
47%6%12%21%10%1
1717
16th to endDay
58%412%17%6%
1710
December1st to 15thDay
64%411%14%4
1518
16th to endDay
73%311%8%3
1602
January1st to 15thNight
63%410%12%7%
2716
16th to endNight
63%5%12%13%4
2819
February1st to 15thNight
61%5%10%14%7%
2447
16th to endNight
58%5%10%17%7%
2049
March1st to 15thNight
52%5%10%18%11%1
2258
16th to endNight
48%5%11%22%10%1
2288
April1st to 15thNight
51%5%9%18%14%
1956
16th to endNight
42%5%10%19%18%3
1672
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
34%6%11%29%17%
1980
October1st to 15thNight
43%6%9%21%17%1
2064
16th to endNight
52%5%11%20%8%
2415
November1st to 15thNight
45%6%12%22%12%1
2471
16th to endNight
55%412%19%6%
2576
December1st to 15thNight
63%5%11%12%6%
2769
16th to endNight
69%6%9%9%4
2967

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%14%42%19%5%
135
16th to endDay
33%9%40%14%2
144
February1st to 15thDay
28%15%45%10%
135
16th to endDay
27%18%36%14%3
120
March1st to 15thDay
25%12%32%22%6%
216
16th to endDay
23%7%30%27%9%
352
April1st to 15thDay
25%10%31%23%6%2
330
16th to endDay
21%10%29%21%10%6%
289
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
14%217%20%30%14%
314
October1st to 15thDay
18%6%24%25%19%6%
315
16th to endDay
27%10%28%27%5%
222
November1st to 15thDay
22%12%23%24%14%2
135
16th to endDay
27%20%32%16%4
124
December1st to 15thDay
23%23%32%15%5%
90
16th to endDay
26%24%35%12%
130
January1st to 15thNight
26%12%34%21%5%
975
16th to endNight
19%11%35%27%5%
947
February1st to 15thNight
23%12%38%22%3
764
16th to endNight
22%13%32%28%3
683
March1st to 15thNight
22%11%31%27%6%
780
16th to endNight
18%9%31%30%9%1
832
April1st to 15thNight
24%11%31%26%5%
626
16th to endNight
19%6%34%28%9%1
558
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
12%416%32%27%6%
717
October1st to 15thNight
19%5%24%32%15%2
720
16th to endNight
26%10%31%24%6%
768
November1st to 15thNight
21%9%28%27%11%1
760
16th to endNight
26%12%30%22%7%
780
December1st to 15thNight
25%14%34%21%4
819
16th to endNight
28%11%37%19%2
1040
Page generated at 2018-04-24 10:02:59. Version ac04

Copyright 2018 A. Danko


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