Columbia
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Columbia clear sky chart from 2005-11-06 to 2024-01-11.

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
47%
23745
22%
74196
17%
23691
54%
23691
27%
46295

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 10thNight
27%
950
19%
2648
10%
946
35%
946
23%
1801
January11th to 20thNight
24%
817
18%
2432
8%
817
32%
817
16%
1752
January21st to endNight
25%
792
25%
2376
11%
792
39%
792
24%
1550
February1st to 10thNight
25%
720
18%
2160
10%
720
32%
720
19%
1522
February11th to 20thNight
22%
703
17%
2099
8%
700
30%
700
18%
1470
February21st to endNight
22%
592
20%
1776
10%
592
30%
592
19%
1256
March1st to 10thNight
30%
720
20%
2160
11%
720
38%
720
24%
1385
March11th to 20thNight
28%
720
18%
2081
10%
720
35%
720
21%
1461
March21st to endNight
34%
666
20%
2052
12%
666
42%
666
24%
1339
April1st to 10thNight
41%
540
26%
1800
18%
540
52%
540
30%
1020
April11th to 20thNight
41%
533
27%
1775
19%
533
54%
533
30%
1025
April21st to endNight
42%
540
23%
1795
15%
540
52%
540
29%
1060
May1st to 10thNight
47%
540
22%
1620
13%
540
55%
540
31%
994
May11th to 20thNight
52%
531
19%
1593
14%
531
56%
531
29%
1002
May21st to endNight
65%
582
19%
1744
15%
582
67%
582
32%
1065
June1st to 10thNight
65%
540
20%
1620
16%
540
67%
540
33%
971
June11th to 20thNight
77%
540
25%
1443
20%
540
78%
540
48%
789
June21st to endNight
76%
540
23%
1440
17%
540
78%
540
43%
842
July1st to 10thNight
73%
525
15%
1400
12%
525
74%
525
33%
915
July11th to 20thNight
74%
522
20%
1446
18%
522
75%
522
37%
874
July21st to endNight
76%
591
20%
1672
19%
558
78%
558
34%
1008
August1st to 10thNight
76%
537
20%
1752
22%
534
76%
534
33%
993
August11th to 20thNight
75%
534
18%
1776
21%
534
76%
534
31%
1047
August21st to endNight
71%
594
21%
1980
26%
594
72%
594
29%
1196
September1st to 10thNight
69%
540
25%
1800
27%
540
70%
540
30%
1059
September11th to 20thNight
64%
717
26%
1977
22%
717
67%
717
36%
1212
September21st to endNight
63%
720
31%
1980
23%
720
68%
720
39%
1155
October1st to 10thNight
64%
720
34%
1980
28%
720
68%
720
44%
1090
October11th to 20thNight
48%
720
30%
2024
22%
720
56%
720
33%
1232
October21st to endNight
45%
792
29%
2533
25%
792
54%
792
30%
1516
November1st to 10thNight
51%
740
29%
2406
27%
740
57%
740
33%
1339
November11th to 20thNight
42%
760
29%
2470
20%
760
55%
760
33%
1387
November21st to endNight
40%
760
25%
2470
20%
760
50%
760
27%
1514
December1st to 10thNight
32%
760
20%
2470
13%
760
41%
760
19%
1670
December11th to 20thNight
35%
759
27%
2912
17%
758
47%
758
22%
1729
December21st to endNight
27%
888
12%
4534
10%
878
36%
878
11%
3055

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
12%6%36%6%35%5%6%8%41%
75056
Night
13%6%35%5%3445%7%44%
74620
TransparencyDay
41%6%11%22%17%3
74769
Night
39%5%10%22%19%4
74427
SeeingDay
16%8%21%24%20%11%
13973
Night
16%7%24%31%20%3
23757

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 10thDay
17%8%46%5%34446%39%
1517
11th to 20thDay
19%10%47%6%24346%34%
1528
21st to endDay
15%6%36%5%3445%5%44%
1980
February1st to 10thDay
19%11%46%5%33435%37%
1800
11th to 20thDay
19%10%46%5%3435%5%35%
1748
21st to endDay
21%9%46%5%335%36%36%
1480
March1st to 10thDay
13%9%46%6%345%46%40%
1800
11th to 20thDay
19%8%47%6%35%5%5%6%34%
1878
21st to endDay
15%8%37%6%45%5%6%6%35%
2318
April1st to 10thDay
11%5%25%6%35%5%5%7%46%
2160
11th to 20thDay
12%7%46%5%34446%45%
2134
21st to endDay
11%6%36%6%35%5%6%9%41%
2164
May1st to 10thDay
14%5%25%6%345%5%8%41%
2340
11th to 20thDay
13%7%47%6%45%5%5%7%39%
2301
21st to endDay
8%6%37%7%35%6%6%10%39%
2531
June1st to 10thDay
8%6%36%6%35%5%7%10%41%
2340
11th to 20thDay
5%4246%46%7%7%10%45%
2510
21st to endDay
5%425%6%46%7%8%11%42%
2520
July1st to 10thDay
7%6%37%7%5%6%7%8%10%34%
2520
11th to 20thDay
8%5%27%6%47%6%7%10%37%
2462
21st to endDay
6%436%7%5%6%8%9%11%36%
2547
August1st to 10thDay
6%426%7%5%8%8%8%11%35%
2170
11th to 20thDay
8%6%26%6%46%7%8%9%38%
2125
21st to endDay
10%6%36%6%46%6%7%8%38%
2376
September1st to 10thDay
11%5%26%5%45%5%7%8%42%
2143
11th to 20thDay
12%6%246%45%5%5%6%44%
1980
21st to endDay
10%42443446%7%52%
1980
October1st to 10thDay
11%425%5%24436%55%
1980
11th to 20thDay
11%5%2432445%7%52%
1931
21st to endDay
16%5%344345%46%46%
1821
November1st to 10thDay
12%423323445%57%
1672
11th to 20thDay
13%6%345%2445%6%50%
1710
21st to endDay
14%6%45%43446%7%44%
1710
December1st to 10thDay
22%8%36%5%34446%36%
1710
11th to 20thDay
15%8%37%6%445%45%40%
2153
21st to endDay
15%10%5%7%6%345%5%7%33%
3017
January1st to 10thNight
17%8%46%5%34346%40%
2648
11th to 20thNight
18%11%47%6%35%445%32%
2432
21st to endNight
15%8%36%435%45%5%43%
2376
February1st to 10thNight
20%9%36%7%3445%5%35%
2160
11th to 20thNight
20%10%36%5%3434438%
2098
21st to endNight
24%8%36%6%3435%5%34%
1776
March1st to 10thNight
15%6%26%5%3445%8%42%
2160
11th to 20thNight
17%7%37%6%445%47%37%
2081
21st to endNight
13%8%35%6%35%5%6%7%40%
2052
April1st to 10thNight
11%5%245%3445%7%50%
1800
11th to 20thNight
14%5%24433446%50%
1775
21st to endNight
11%5%35%5%35%46%8%45%
1795
May1st to 10thNight
10%436%6%3445%7%48%
1620
11th to 20thNight
9%6%35%445%5%6%9%44%
1592
21st to endNight
6%435%6%36%5%7%10%44%
1744
June1st to 10thNight
7%6%35%5%35%5%6%10%46%
1620
11th to 20thNight
42144345%7%10%57%
1443
21st to endNight
4314435%6%7%12%51%
1440
July1st to 10thNight
9%426%446%6%9%11%39%
1440
11th to 20thNight
7%4245%45%5%8%13%44%
1494
21st to endNight
5%424446%7%9%12%43%
1771
August1st to 10thNight
5%425%5%35%7%8%11%46%
1763
11th to 20thNight
5%5%35%5%36%6%8%9%45%
1776
21st to endNight
8%5%25%6%35%6%7%10%43%
1980
September1st to 10thNight
10%4345%345%6%8%48%
1800
11th to 20thNight
10%435%5%245%5%7%49%
1977
21st to endNight
9%425%42445%6%55%
1980
October1st to 10thNight
9%423322446%60%
1980
11th to 20thNight
13%6%2443435%6%50%
2024
21st to endNight
15%6%25%423346%50%
2533
November1st to 10thNight
10%5%345%33346%54%
2406
11th to 20thNight
11%5%2443337%8%50%
2470
21st to endNight
15%7%35%43435%6%46%
2470
December1st to 10thNight
19%9%35%5%3445%6%37%
2470
11th to 20thNight
15%7%25%5%23345%47%
3042
21st to endNight
16%10%5%7%7%45%45%6%31%
4632

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 10thDay
47%47%23%16%3
1518
11th to 20thDay
53%38%20%14%2
1528
21st to endDay
42%48%24%20%2
1980
February1st to 10thDay
51%47%19%16%3
1800
11th to 20thDay
52%36%21%14%3
1758
21st to endDay
51%47%16%16%7%
1480
March1st to 10thDay
46%48%16%19%6%
1800
11th to 20thDay
51%6%9%17%16%2
1878
21st to endDay
47%6%11%21%13%1
2318
April1st to 10thDay
38%5%10%24%19%4
2160
11th to 20thDay
41%47%21%22%6%
2134
21st to endDay
40%5%10%26%17%2
2164
May1st to 10thDay
40%7%11%24%15%3
2340
11th to 20thDay
43%7%12%23%15%1
2305
21st to endDay
39%7%15%25%13%1
2531
June1st to 10thDay
37%7%13%24%17%2
2340
11th to 20thDay
31%8%16%26%17%3
2510
21st to endDay
33%9%17%20%16%4
2520
July1st to 10thDay
40%9%17%19%11%3
2451
11th to 20thDay
40%8%18%20%11%3
2387
21st to endDay
35%11%17%25%10%1
2405
August1st to 10thDay
37%10%18%22%11%1
2157
11th to 20thDay
39%9%14%21%15%2
2125
21st to endDay
41%7%14%22%13%3
2376
September1st to 10thDay
38%8%12%22%17%4
2143
11th to 20thDay
39%6%9%21%21%3
1980
21st to endDay
31%5%11%24%22%7%
1980
October1st to 10thDay
32%48%24%27%5%
1980
11th to 20thDay
32%5%6%23%25%9%
1931
21st to endDay
39%46%21%24%6%
1821
November1st to 10thDay
30%47%22%31%6%
1672
11th to 20thDay
35%36%22%26%6%
1710
21st to endDay
39%47%24%21%5%
1710
December1st to 10thDay
51%45%21%16%3
1710
11th to 20thDay
48%48%20%18%2
2150
21st to endDay
49%6%11%22%10%3
3017
January1st to 10thNight
47%48%21%17%3
2648
11th to 20thNight
55%46%19%13%3
2432
21st to endNight
44%47%23%19%3
2376
February1st to 10thNight
52%49%17%16%2
2160
11th to 20thNight
52%46%19%16%4
2099
21st to endNight
52%37%16%15%5%
1776
March1st to 10thNight
41%5%8%15%21%9%
2160
11th to 20thNight
48%6%7%20%16%2
2081
21st to endNight
43%6%10%24%15%2
2052
April1st to 10thNight
33%5%12%24%22%4
1800
11th to 20thNight
35%48%21%23%9%
1775
21st to endNight
37%5%11%26%19%2
1795
May1st to 10thNight
36%6%10%25%21%3
1620
11th to 20thNight
36%8%16%22%17%1
1593
21st to endNight
33%8%15%26%15%2
1745
June1st to 10thNight
33%7%15%24%19%2
1620
11th to 20thNight
22%6%18%32%18%3
1443
21st to endNight
24%9%19%28%17%4
1440
July1st to 10thNight
35%9%20%20%13%3
1400
11th to 20thNight
29%9%20%26%12%5%
1446
21st to endNight
28%11%20%28%11%1
1672
August1st to 10thNight
29%9%17%29%15%1
1752
11th to 20thNight
30%10%20%21%16%2
1776
21st to endNight
34%9%14%26%13%4
1980
September1st to 10thNight
34%7%12%25%18%4
1800
11th to 20thNight
33%6%13%19%26%2
1977
21st to endNight
29%6%8%25%25%7%
1980
October1st to 10thNight
26%48%25%28%9%
1980
11th to 20thNight
36%47%23%22%9%
2024
21st to endNight
37%4422%26%6%
2533
November1st to 10thNight
33%37%22%26%8%
2406
11th to 20thNight
32%47%21%27%8%
2470
21st to endNight
41%36%23%22%5%
2470
December1st to 10thNight
48%5%8%18%17%3
2470
11th to 20thNight
41%36%23%24%4
3044
21st to endNight
54%48%19%13%2
4632

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 10thDay
24%17%38%15%5%1
270
11th to 20thDay
25%17%35%16%43
240
21st to endDay
18%20%42%16%4
264
February1st to 10thDay
27%17%35%15%5%1
240
11th to 20thDay
37%14%35%12%2
240
21st to endDay
36%16%35%8%5%1
198
March1st to 10thDay
23%18%37%18%4
240
11th to 20thDay
24%16%34%19%6%1
318
21st to endDay
24%13%30%23%8%1
462
April1st to 10thDay
18%12%29%27%12%2
420
11th to 20thDay
18%11%30%25%13%3
412
21st to endDay
17%10%30%26%13%4
420
May1st to 10thDay
17%10%23%30%14%5%
423
11th to 20thDay
15%6%21%29%18%11%
447
21st to endDay
11%317%28%24%17%
485
June1st to 10thDay
10%6%15%23%25%21%
450
11th to 20thDay
5%216%27%31%19%
620
21st to endDay
7%215%32%27%16%
630
July1st to 10thDay
9%310%27%29%22%
621
11th to 20thDay
8%38%24%31%26%
560
21st to endDay
7%27%25%33%26%
488
August1st to 10thDay
9%17%23%37%23%
446
11th to 20thDay
10%36%31%34%15%
439
21st to endDay
14%36%17%38%22%
495
September1st to 10thDay
12%29%27%34%17%
450
11th to 20thDay
14%29%24%32%19%
450
21st to endDay
15%5%12%28%29%11%
450
October1st to 10thDay
15%218%26%26%12%
450
11th to 20thDay
14%11%29%30%13%4
401
21st to endDay
24%9%27%26%12%2
297
November1st to 10thDay
19%10%27%30%11%3
270
11th to 20thDay
15%14%34%27%10%
270
21st to endDay
20%15%28%22%11%4
270
December1st to 10thDay
26%16%31%21%6%1
270
11th to 20thDay
21%14%34%20%9%1
270
21st to endDay
24%18%34%19%5%
297
January1st to 10thNight
22%12%34%27%5%
950
11th to 20thNight
23%14%33%25%5%
817
21st to endNight
20%10%42%25%3
792
February1st to 10thNight
25%11%35%25%4
720
11th to 20thNight
25%15%33%23%3
703
21st to endNight
31%13%32%22%2
592
March1st to 10thNight
20%12%33%29%5%
720
11th to 20thNight
21%12%34%25%8%1
720
21st to endNight
18%8%34%30%9%
666
April1st to 10thNight
14%9%32%34%11%
540
11th to 20thNight
16%8%30%34%9%1
533
21st to endNight
15%6%32%33%13%1
540
May1st to 10thNight
12%430%34%17%2
540
11th to 20thNight
11%324%35%23%5%
531
21st to endNight
9%213%38%34%6%
584
June1st to 10thNight
10%213%37%33%6%
540
11th to 20thNight
4210%37%41%5%
540
21st to endNight
5%10%38%39%8%
540
July1st to 10thNight
9%36%26%45%12%
525
11th to 20thNight
7%27%28%44%12%
522
21st to endNight
6%26%31%46%10%
591
August1st to 10thNight
7%2328%49%11%
537
11th to 20thNight
7%25%39%43%5%
534
21st to endNight
10%2429%46%10%
594
September1st to 10thNight
11%28%32%43%6%
540
11th to 20thNight
11%211%31%40%5%
717
21st to endNight
10%314%31%37%5%
720
October1st to 10thNight
11%315%35%30%6%
720
11th to 20thNight
16%6%23%35%18%2
720
21st to endNight
18%5%26%32%17%2
792
November1st to 10thNight
12%6%22%39%19%2
740
11th to 20thNight
13%9%34%32%12%1
760
21st to endNight
20%8%28%31%12%1
760
December1st to 10thNight
24%10%29%30%7%
760
11th to 20thNight
21%8%31%32%8%1
760
21st to endNight
25%11%31%27%5%
897
Page generated at 2024-01-08 10:14:20. Version ac07

Copyright 2024 Attilla Danko


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