Belen Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Belen Observatory clear sky chart from 2005-11-05 to 2017-09-23.

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
62%
16298
18%
47012
15%
16258
66%
16258
29%
30253

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
53%
716
17%
2327
13%
716
59%
716
26%
1445
January16th to endNight
51%
768
25%
2460
19%
768
60%
768
32%
1413
February1st to 15thNight
51%
703
27%
2091
21%
699
58%
699
35%
1227
February16th to endNight
57%
631
31%
1735
20%
631
66%
631
40%
982
March1st to 15thNight
54%
720
26%
1980
16%
720
62%
720
38%
1168
March16th to endNight
60%
768
25%
2112
20%
768
64%
768
39%
1226
April1st to 15thNight
66%
718
25%
1976
21%
718
70%
718
49%
1062
April16th to endNight
60%
720
24%
1809
14%
720
65%
720
41%
1101
May1st to 15thNight
70%
719
24%
1799
16%
719
72%
719
47%
1040
May16th to endNight
66%
619
16%
1741
13%
619
67%
619
27%
1177
June1st to 15thNight
62%
540
9%
1620
8%
540
62%
540
16%
1232
June16th to endNight
77%
540
7%
1620
7%
540
77%
540
23%
1129
July1st to 15thNight
75%
510
5%
1530
5%
510
75%
510
21%
1093
July16th to endNight
82%
564
9%
1595
9%
531
82%
531
30%
1008
August1st to 15thNight
75%
617
8%
1687
7%
614
74%
614
27%
1131
August16th to endNight
69%
764
6%
2032
5%
764
69%
764
22%
1480
September1st to 15thNight
66%
720
5%
1980
5%
720
66%
720
18%
1504
September16th to endNight
64%
689
7%
1903
7%
689
64%
689
16%
1476
October1st to 15thNight
64%
660
14%
1917
16%
660
66%
660
21%
1346
October16th to endNight
54%
704
18%
2112
16%
704
59%
704
22%
1452
November1st to 15thNight
60%
700
24%
2101
20%
700
67%
700
30%
1303
November16th to endNight
54%
720
26%
2160
21%
720
61%
720
28%
1375
December1st to 15thNight
58%
720
22%
2229
19%
720
63%
720
25%
1430
December16th to endNight
63%
768
24%
2496
23%
768
67%
768
31%
1453

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
9%6%37%8%5%7%7%7%9%27%
47876
Night
6%425%5%35%6%7%10%41%
47218
TransparencyDay
48%9%13%15%10%2
47577
Night
36%8%18%21%12%2
47021
SeeingDay
9%316%24%24%21%
6106
Night
7%215%31%29%13%
16306

By Month

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
11%5%26%7%46%6%6%9%31%
1611
16th to endDay
9%5%35%6%46%5%7%10%36%
1761
February1st to 15thDay
10%5%35%6%45%45%9%39%
1763
16th to endDay
7%425%5%45%5%6%9%43%
1738
March1st to 15thDay
7%426%5%36%7%6%11%37%
1980
16th to endDay
8%5%36%6%45%6%6%9%38%
2111
April1st to 15thDay
6%4245%47%6%8%13%36%
1972
16th to endDay
7%326%6%47%6%7%10%35%
2151
May1st to 15thDay
4325%6%47%6%7%9%40%
2152
16th to endDay
10%6%48%9%6%8%7%8%9%20%
2381
June1st to 15thDay
15%8%49%10%5%9%7%7%6%13%
2340
16th to endDay
9%7%49%9%6%11%8%9%8%15%
2340
July1st to 15thDay
8%7%49%9%5%9%8%9%9%17%
2340
16th to endDay
7%5%38%9%6%10%8%9%11%18%
2465
August1st to 15thDay
7%7%38%9%5%8%8%9%11%19%
2247
16th to endDay
12%6%39%9%6%8%9%8%11%15%
2166
September1st to 15thDay
9%7%310%10%6%10%8%8%8%14%
1980
16th to endDay
14%9%5%9%11%6%8%7%5%7%14%
1894
October1st to 15thDay
11%6%39%9%5%6%7%9%10%19%
1711
16th to endDay
15%6%27%7%46%5%7%10%27%
1760
November1st to 15thDay
9%5%27%6%46%5%7%8%35%
1757
16th to endDay
11%6%26%6%47%5%6%8%35%
1800
December1st to 15thDay
10%7%37%6%45%5%6%8%33%
1728
16th to endDay
7%5%35%6%46%6%7%10%35%
1728
January1st to 15thNight
8%425%5%36%6%7%10%39%
2327
16th to endNight
5%325%425%47%9%47%
2460
February1st to 15thNight
8%5%2442335%7%51%
2089
16th to endNight
421433445%10%54%
1735
March1st to 15thNight
33245%35%5%6%8%52%
1980
16th to endNight
5%3134346%6%9%52%
2112
April1st to 15thNight
21134235%5%9%59%
1976
16th to endNight
6%313425%46%9%50%
1809
May1st to 15thNight
2113425%5%5%10%57%
1799
16th to endNight
7%5%35%6%46%6%7%11%37%
1740
June1st to 15thNight
12%5%26%7%5%8%7%7%10%25%
1620
16th to endNight
5%325%6%47%8%11%14%30%
1620
July1st to 15thNight
4437%7%37%6%8%14%33%
1620
16th to endNight
4335%5%36%6%8%14%39%
1703
August1st to 15thNight
3426%6%36%7%8%13%37%
1698
16th to endNight
5%436%6%46%8%9%12%30%
2032
September1st to 15thNight
6%326%8%47%9%10%11%27%
1980
16th to endNight
8%6%28%9%47%7%9%10%24%
1903
October1st to 15thNight
7%435%7%47%7%8%11%31%
1917
16th to endNight
12%7%35%6%36%47%7%36%
2112
November1st to 15thNight
6%425%5%25%5%6%8%46%
2101
16th to endNight
8%325%5%36%5%5%8%44%
2160
December1st to 15thNight
8%5%25%435%5%6%11%40%
2229
16th to endNight
6%323435%6%6%10%47%
2496

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
46%7%11%18%10%5%
1612
16th to endDay
41%6%11%18%16%5%
1761
February1st to 15thDay
40%5%8%21%18%5%
1765
16th to endDay
34%6%10%26%17%4
1738
March1st to 15thDay
38%7%10%23%16%3
1980
16th to endDay
38%8%10%21%14%5%
2112
April1st to 15thDay
33%9%14%24%16%2
1972
16th to endDay
38%8%11%20%17%4
2151
May1st to 15thDay
34%8%13%23%14%5%
2152
16th to endDay
54%10%12%17%5%
2385
June1st to 15thDay
65%10%12%8%3
2340
16th to endDay
59%12%16%9%1
2340
July1st to 15thDay
55%14%21%8%
2201
16th to endDay
49%13%26%9%
2310
August1st to 15thDay
51%13%19%13%1
2234
16th to endDay
55%13%19%10%
2166
September1st to 15thDay
59%13%18%7%1
1980
16th to endDay
64%12%12%6%3
1894
October1st to 15thDay
53%11%14%12%7%1
1711
16th to endDay
49%6%11%14%13%4
1760
November1st to 15thDay
44%6%10%15%18%5%
1757
16th to endDay
45%6%8%11%20%7%
1800
December1st to 15thDay
48%6%8%16%17%2
1728
16th to endDay
40%7%10%21%16%3
1728
January1st to 15thNight
38%6%16%22%11%3
2327
16th to endNight
31%6%12%27%17%4
2460
February1st to 15thNight
32%49%25%20%7%
2098
16th to endNight
26%6%13%26%21%5%
1735
March1st to 15thNight
30%412%28%19%5%
1980
16th to endNight
28%6%15%26%19%3
2112
April1st to 15thNight
21%5%18%33%18%2
1976
16th to endNight
29%5%15%24%20%3
1809
May1st to 15thNight
22%7%14%33%17%4
1800
16th to endNight
40%8%16%26%8%
1742
June1st to 15thNight
52%11%19%13%3
1620
16th to endNight
38%14%32%13%
1620
July1st to 15thNight
40%15%32%11%
1530
16th to endNight
32%10%38%16%1
1595
August1st to 15thNight
35%12%31%17%1
1687
16th to endNight
42%14%29%12%
2032
September1st to 15thNight
46%15%25%10%1
1980
16th to endNight
50%14%20%11%3
1903
October1st to 15thNight
44%10%17%15%10%1
1917
16th to endNight
46%6%10%19%12%4
2112
November1st to 15thNight
38%5%10%19%22%4
2101
16th to endNight
39%5%9%18%19%7%
2160
December1st to 15thNight
39%7%13%19%17%2
2229
16th to endNight
33%6%11%27%19%2
2496

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
18%13%38%24%4
90
16th to endDay
12%19%38%23%32
96
February1st to 15thDay
7%14%41%20%15%
104
16th to endDay
8%7%30%29%22%1
239
March1st to 15thDay
5%10%31%34%15%2
270
16th to endDay
5%7%35%23%21%6%
288
April1st to 15thDay
5%5%30%24%24%10%
270
16th to endDay
6%230%27%23%10%
270
May1st to 15thDay
4322%26%27%15%
288
16th to endDay
6%210%28%29%21%
331
June1st to 15thDay
13%211%21%23%27%
315
16th to endDay
6%318%28%41%
315
July1st to 15thDay
5%119%33%39%
305
16th to endDay
6%1218%24%46%
326
August1st to 15thDay
7%120%24%44%
313
16th to endDay
12%1416%29%35%
332
September1st to 15thDay
9%2414%24%45%
315
16th to endDay
12%1116%28%40%
283
October1st to 15thDay
7%211%30%32%15%
255
16th to endDay
15%223%29%17%11%
272
November1st to 15thDay
7%220%33%29%7%
265
16th to endDay
12%7%26%32%17%3
270
December1st to 15thDay
20%318%35%18%4
198
16th to endDay
8%7%22%51%9%1
96
January1st to 15thNight
9%5%22%36%22%3
720
16th to endNight
6%5%29%40%15%1
768
February1st to 15thNight
10%328%37%19%
704
16th to endNight
6%5%26%41%19%
631
March1st to 15thNight
5%428%40%18%2
720
16th to endNight
5%324%43%20%1
768
April1st to 15thNight
3222%43%25%2
718
16th to endNight
6%323%42%22%2
720
May1st to 15thNight
3116%45%29%3
720
16th to endNight
8%19%33%34%11%
621
June1st to 15thNight
13%1420%39%21%
540
16th to endNight
4214%40%37%
540
July1st to 15thNight
5%1110%49%32%
510
16th to endNight
38%38%47%
564
August1st to 15thNight
6%11%44%35%
617
16th to endNight
7%1316%39%31%
764
September1st to 15thNight
9%1214%32%39%
720
16th to endNight
9%1116%37%33%
689
October1st to 15thNight
9%19%31%37%11%
660
16th to endNight
15%116%29%26%10%
704
November1st to 15thNight
8%218%38%26%5%
700
16th to endNight
10%321%36%23%4
720
December1st to 15thNight
10%418%38%25%2
720
16th to endNight
8%318%41%25%4
768
Page generated at 2017-09-24 09:15:45. Version ac04

Copyright 2017 A. Danko


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