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 2024-03-23.

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
38%
24729
20%
80595
13%
24619
46%
24619
24%
51698

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
22%
944
14%
4279
6%
926
33%
926
13%
2941
January11th to 20thNight
21%
950
16%
4043
7%
930
30%
930
13%
2889
January21st to endNight
20%
1037
13%
4485
5%
1023
29%
1023
12%
3309
February1st to 10thNight
21%
950
15%
2470
5%
950
26%
950
20%
1801
February11th to 20thNight
21%
882
18%
2357
5%
878
29%
878
24%
1595
February21st to endNight
17%
628
20%
1884
5%
628
29%
628
21%
1246
March1st to 10thNight
24%
613
21%
2133
9%
613
37%
613
22%
1307
March11th to 20thNight
28%
570
18%
2090
10%
570
39%
570
17%
1374
March21st to endNight
21%
600
9%
2173
5%
600
27%
600
12%
1603
April1st to 10thNight
28%
540
21%
1800
11%
540
42%
540
25%
1083
April11th to 20thNight
31%
533
22%
1775
16%
533
43%
533
24%
1095
April21st to endNight
30%
540
20%
1800
11%
540
45%
540
22%
1165
May1st to 10thNight
37%
540
16%
1667
11%
540
44%
540
25%
1088
May11th to 20thNight
47%
531
19%
1494
16%
531
51%
531
27%
995
May21st to endNight
49%
584
19%
1551
12%
582
55%
582
28%
1041
June1st to 10thNight
64%
540
20%
1440
15%
540
67%
540
42%
832
June11th to 20thNight
59%
540
23%
1440
15%
540
63%
540
37%
880
June21st to endNight
62%
540
24%
1440
15%
540
66%
540
47%
803
July1st to 10thNight
68%
525
18%
1400
15%
525
69%
525
39%
838
July11th to 20thNight
72%
522
23%
1478
20%
522
75%
522
47%
799
July21st to endNight
65%
591
23%
1673
21%
558
69%
558
38%
937
August1st to 10thNight
72%
537
23%
1601
24%
534
75%
534
40%
885
August11th to 20thNight
71%
534
26%
1669
30%
534
73%
534
37%
938
August21st to endNight
72%
594
26%
1980
32%
594
75%
594
42%
1019
September1st to 10thNight
64%
540
26%
1800
27%
540
68%
540
37%
962
September11th to 20thNight
62%
540
32%
1800
29%
540
70%
540
36%
979
September21st to endNight
55%
638
29%
2049
22%
638
63%
638
37%
1093
October1st to 10thNight
52%
720
27%
2160
19%
720
58%
720
39%
1191
October11th to 20thNight
33%
720
28%
2160
15%
720
44%
720
30%
1292
October21st to endNight
31%
792
23%
2376
11%
792
42%
792
26%
1493
November1st to 10thNight
37%
740
29%
2305
16%
740
51%
740
34%
1274
November11th to 20thNight
30%
784
26%
2494
13%
784
44%
784
27%
1486
November21st to endNight
27%
950
20%
2660
8%
950
38%
950
25%
1759
December1st to 10thNight
26%
950
18%
2660
7%
950
36%
950
23%
1804
December11th to 20thNight
25%
949
18%
3153
8%
948
33%
948
19%
2087
December21st to endNight
21%
1041
10%
4856
5%
1026
31%
1026
9%
3815

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
13%8%36%5%3445%7%42%
78816
Night
13%8%36%5%3445%6%43%
81117
TransparencyDay
41%7%12%24%15%2
78529
Night
41%6%11%24%16%3
80925
SeeingDay
16%10%27%27%15%4
14705
Night
16%10%31%30%12%1
24748

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
12%13%5%9%5%3445%6%33%
2623
11th to 20thDay
12%12%48%6%5%7%34436%
2850
21st to endDay
16%15%7%9%5%33346%30%
3135
February1st to 10thDay
17%9%5%8%6%33447%34%
1710
11th to 20thDay
13%9%45%4345%5%6%41%
1710
21st to endDay
16%10%46%5%2435%5%40%
1570
March1st to 10thDay
14%10%5%6%5%3345%6%40%
2061
11th to 20thDay
18%9%47%6%34446%36%
2090
21st to endDay
21%13%48%5%35%5%5%6%27%
2226
April1st to 10thDay
13%7%37%6%3435%6%44%
2160
11th to 20thDay
16%10%35%5%3445%6%40%
2134
21st to endDay
23%6%25%5%35%5%6%7%34%
2160
May1st to 10thDay
17%8%35%6%25%5%5%9%35%
2290
11th to 20thDay
17%7%35%6%345%47%40%
2399
21st to endDay
13%7%36%6%45%5%6%9%36%
2725
June1st to 10thDay
7%4245%45%6%7%10%46%
2520
11th to 20thDay
9%4245%35%5%6%10%47%
2520
21st to endDay
6%4246%35%6%6%9%49%
2520
July1st to 10thDay
10%4245%35%5%7%12%43%
2520
11th to 20thDay
5%414435%5%7%10%51%
2430
21st to endDay
8%6%25%435%6%6%9%44%
2546
August1st to 10thDay
7%5%25%6%46%7%7%10%42%
2328
11th to 20thDay
9%435%5%346%7%8%46%
2230
21st to endDay
8%4244345%410%53%
2376
September1st to 10thDay
11%5%2443445%8%50%
2160
11th to 20thDay
10%5%234235%49%53%
2160
21st to endDay
7%425%425%5%5%7%53%
1889
October1st to 10thDay
11%5%25%43335%6%52%
1800
11th to 20thDay
15%7%24422346%51%
1800
21st to endDay
18%9%25%423345%46%
1980
November1st to 10thDay
10%7%34424347%53%
1771
11th to 20thDay
15%7%25%323447%49%
1682
21st to endDay
18%9%45%424346%43%
1520
December1st to 10thDay
12%10%47%32335%7%43%
1520
11th to 20thDay
14%9%46%434346%42%
1918
21st to endDay
19%15%5%9%6%34445%24%
2783
January1st to 10thNight
10%11%8%10%6%34435%35%
4328
11th to 20thNight
13%10%5%9%6%47%6%5%431%
4120
21st to endNight
20%16%6%6%5%3334430%
4532
February1st to 10thNight
15%11%37%5%36%5%5%6%34%
2470
11th to 20thNight
15%8%46%5%235%5%6%41%
2356
21st to endNight
15%11%36%4235%45%41%
1884
March1st to 10thNight
15%9%35%32344447%
2133
11th to 20thNight
19%8%36%4245%5%6%37%
2090
21st to endNight
21%11%36%7%35%45%6%28%
2173
April1st to 10thNight
11%8%35%435%446%47%
1800
11th to 20thNight
14%7%35%5%2435%6%46%
1775
21st to endNight
18%6%35%4345%5%7%42%
1800
May1st to 10thNight
14%6%25%5%36%45%9%42%
1667
11th to 20thNight
15%6%35%434447%44%
1493
21st to endNight
12%5%36%5%45%6%6%8%41%
1551
June1st to 10thNight
5%324435%5%5%10%55%
1440
11th to 20thNight
5%335%5%35%6%5%10%49%
1440
21st to endNight
4223435%5%5%9%58%
1440
July1st to 10thNight
8%325%5%3445%9%52%
1440
11th to 20thNight
441442346%9%59%
1526
21st to endNight
7%425%4335%7%9%51%
1772
August1st to 10thNight
6%3234345%6%9%54%
1611
11th to 20thNight
6%4145%345%6%8%53%
1669
21st to endNight
6%32432445%8%59%
1980
September1st to 10thNight
10%413324446%57%
1800
11th to 20thNight
9%4343345%5%8%53%
1800
21st to endNight
7%425%425%446%58%
2049
October1st to 10thNight
8%5%1332445%7%57%
2160
11th to 20thNight
15%4245%24346%51%
2160
21st to endNight
17%7%24423345%47%
2376
November1st to 10thNight
10%424423346%57%
2305
11th to 20thNight
12%7%35%423446%49%
2494
21st to endNight
17%8%25%5%24445%45%
2660
December1st to 10thNight
13%10%46%6%2445%6%40%
2660
11th to 20thNight
14%10%5%6%5%24446%40%
3279
21st to endNight
19%19%6%9%5%33335%24%
4884

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
50%6%10%24%10%1
2624
11th to 20thDay
52%6%11%20%11%
2850
21st to endDay
57%5%10%15%12%1
3135
February1st to 10thDay
51%5%12%20%12%1
1710
11th to 20thDay
44%6%12%21%15%3
1719
21st to endDay
47%5%9%22%14%3
1570
March1st to 10thDay
45%5%10%24%14%3
2061
11th to 20thDay
49%6%10%21%12%3
2090
21st to endDay
57%6%11%17%8%1
2226
April1st to 10thDay
41%6%11%25%15%1
2160
11th to 20thDay
44%6%10%23%13%3
2134
21st to endDay
48%6%12%20%12%1
2160
May1st to 10thDay
46%8%14%21%10%1
2290
11th to 20thDay
45%7%11%22%14%1
2403
21st to endDay
42%10%14%20%12%2
2725
June1st to 10thDay
31%9%15%29%14%1
2520
11th to 20thDay
32%8%13%25%17%4
2520
21st to endDay
29%9%16%27%15%4
2520
July1st to 10thDay
32%9%16%25%14%4
2451
11th to 20thDay
27%9%16%27%18%2
2356
21st to endDay
34%8%13%31%13%1
2405
August1st to 10thDay
33%10%17%26%12%1
2314
11th to 20thDay
34%8%12%31%14%1
2230
21st to endDay
28%7%15%24%20%6%
2376
September1st to 10thDay
33%6%12%26%18%5%
2160
11th to 20thDay
29%6%10%27%23%4
2160
21st to endDay
29%7%11%26%24%4
1889
October1st to 10thDay
34%5%10%25%23%4
1800
11th to 20thDay
36%49%25%22%4
1800
21st to endDay
43%49%23%18%4
1980
November1st to 10thDay
32%5%12%24%22%5%
1771
11th to 20thDay
37%49%24%22%3
1682
21st to endDay
44%410%27%14%1
1520
December1st to 10thDay
42%6%12%28%12%1
1520
11th to 20thDay
44%6%12%25%12%1
1915
21st to endDay
61%6%10%14%8%1
2783
January1st to 10thNight
52%5%10%22%10%1
4328
11th to 20thNight
54%5%12%19%9%1
4120
21st to endNight
58%410%19%8%1
4532
February1st to 10thNight
50%6%11%19%12%2
2470
11th to 20thNight
44%5%11%21%17%3
2357
21st to endNight
44%5%10%20%17%4
1884
March1st to 10thNight
41%5%10%24%17%3
2133
11th to 20thNight
46%6%10%21%14%3
2090
21st to endNight
58%6%11%17%7%1
2173
April1st to 10thNight
38%5%10%26%18%4
1800
11th to 20thNight
40%5%9%26%15%5%
1775
21st to endNight
43%6%9%23%18%1
1800
May1st to 10thNight
39%9%14%21%15%1
1667
11th to 20thNight
39%9%12%22%17%1
1494
21st to endNight
39%9%13%22%15%2
1552
June1st to 10thNight
24%8%16%31%17%3
1440
11th to 20thNight
30%8%11%26%22%4
1440
21st to endNight
22%7%17%29%19%6%
1440
July1st to 10thNight
29%7%14%31%15%4
1400
11th to 20thNight
21%7%15%31%22%3
1478
21st to endNight
27%7%14%33%17%1
1673
August1st to 10thNight
25%8%18%32%15%2
1601
11th to 20thNight
27%8%11%32%21%2
1669
21st to endNight
23%7%14%27%23%7%
1980
September1st to 10thNight
27%6%12%24%25%6%
1800
11th to 20thNight
28%6%11%26%23%6%
1800
21st to endNight
28%5%8%28%27%4
2049
October1st to 10thNight
27%5%10%26%26%5%
2160
11th to 20thNight
36%47%27%20%6%
2160
21st to endNight
40%49%21%22%3
2376
November1st to 10thNight
29%5%12%28%19%6%
2305
11th to 20thNight
37%48%26%22%4
2494
21st to endNight
43%5%10%24%17%2
2660
December1st to 10thNight
45%5%12%24%13%1
2660
11th to 20thNight
45%5%11%26%13%1
3281
21st to endNight
64%5%9%13%8%1
4884

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
21%18%36%22%2
270
11th to 20thDay
32%18%38%12%1
270
21st to endDay
19%20%45%13%3
297
February1st to 10thDay
27%17%39%14%2
270
11th to 20thDay
24%23%35%13%5%
270
21st to endDay
28%23%35%13%1
225
March1st to 10thDay
18%22%45%14%1
270
11th to 20thDay
27%14%35%21%2
270
21st to endDay
35%21%29%12%3
296
April1st to 10thDay
19%16%38%20%6%1
420
11th to 20thDay
23%17%31%22%7%
412
21st to endDay
25%12%33%23%5%1
420
May1st to 10thDay
18%14%34%25%8%1
553
11th to 20thDay
20%12%26%28%12%2
625
21st to endDay
15%8%29%26%16%5%
679
June1st to 10thDay
7%423%36%23%7%
630
11th to 20thDay
9%324%40%21%3
630
21st to endDay
6%6%31%36%17%4
630
July1st to 10thDay
11%313%32%30%12%
621
11th to 20thDay
6%420%35%28%7%
618
21st to endDay
9%316%37%31%5%
684
August1st to 10thDay
7%317%42%25%7%
626
11th to 20thDay
9%317%36%27%7%
544
21st to endDay
9%213%35%30%10%
495
September1st to 10thDay
13%318%32%28%7%
450
11th to 20thDay
8%418%33%25%12%
450
21st to endDay
7%10%25%30%22%5%
296
October1st to 10thDay
13%8%34%26%16%3
270
11th to 20thDay
20%20%33%22%5%
270
21st to endDay
32%17%27%21%3
297
November1st to 10thDay
13%13%39%24%8%3
270
11th to 20thDay
21%15%34%21%7%2
270
21st to endDay
26%15%30%25%41
270
December1st to 10thDay
17%20%34%19%7%3
270
11th to 20thDay
24%14%39%19%41
270
21st to endDay
24%25%35%15%1
297
January1st to 10thNight
16%17%39%23%5%
950
11th to 20thNight
20%19%36%20%41
950
21st to endNight
19%14%42%24%2
1045
February1st to 10thNight
20%15%39%22%3
950
11th to 20thNight
20%14%40%22%3
882
21st to endNight
21%19%38%19%3
628
March1st to 10thNight
19%15%40%23%3
613
11th to 20thNight
22%13%33%27%5%
570
21st to endNight
28%14%34%21%4
600
April1st to 10thNight
16%15%38%26%4
540
11th to 20thNight
18%14%34%26%8%
533
21st to endNight
19%11%37%27%6%
540
May1st to 10thNight
16%7%34%35%7%
540
11th to 20thNight
17%7%23%38%14%1
531
21st to endNight
13%5%27%34%19%2
584
June1st to 10thNight
7%221%42%27%2
540
11th to 20thNight
5%227%42%23%1
540
21st to endNight
2328%47%18%1
540
July1st to 10thNight
10%211%38%35%4
525
11th to 20thNight
5%116%43%33%2
522
21st to endNight
8%118%42%30%2
591
August1st to 10thNight
7%213%46%31%2
537
11th to 20thNight
6%312%44%32%3
534
21st to endNight
7%214%38%36%3
594
September1st to 10thNight
12%217%38%26%4
540
11th to 20thNight
11%318%37%26%5%
540
21st to endNight
9%5%26%36%20%4
638
October1st to 10thNight
11%5%28%32%20%3
720
11th to 20thNight
17%11%36%28%8%
720
21st to endNight
22%12%32%27%6%1
792
November1st to 10thNight
12%11%37%31%9%
740
11th to 20thNight
16%14%38%26%6%1
784
21st to endNight
22%12%37%24%5%
950
December1st to 10thNight
20%14%37%24%5%
950
11th to 20thNight
23%12%35%25%4
950
21st to endNight
24%17%35%23%2
1045
Page generated at 2024-03-19 22:31:04. Version ac07

Copyright © 2024 Attilla Danko.


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