Columbia
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Columbia clear sky chart from 2005-11-05 to 2017-10-06.

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
39%
16044
19%
47110
11%
15998
46%
15998
27%
30150

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
28%
900
17%
2446
7%
895
35%
895
24%
1641
January16th to endNight
24%
960
17%
2496
5%
960
33%
960
21%
1782
February1st to 15thNight
23%
879
13%
2288
4%
876
29%
876
20%
1684
February16th to endNight
27%
714
20%
1976
7%
714
38%
714
26%
1293
March1st to 15thNight
34%
552
21%
1992
13%
552
44%
552
23%
1205
March16th to endNight
27%
576
11%
2109
7%
576
34%
576
15%
1479
April1st to 15thNight
31%
539
18%
1797
11%
539
42%
539
23%
1142
April16th to endNight
30%
540
18%
1743
12%
540
42%
540
20%
1185
May1st to 15thNight
36%
540
16%
1584
10%
540
43%
540
25%
1058
May16th to endNight
42%
563
20%
1497
9%
561
51%
561
30%
981
June1st to 15thNight
57%
540
16%
1440
8%
540
60%
540
33%
908
June16th to endNight
53%
540
18%
1440
9%
540
57%
540
39%
862
July1st to 15thNight
69%
510
17%
1360
11%
510
70%
510
44%
789
July16th to endNight
75%
564
21%
1547
19%
531
76%
531
46%
813
August1st to 15thNight
73%
539
21%
1610
22%
536
75%
536
39%
895
August16th to endNight
67%
573
23%
1839
26%
573
71%
573
34%
1047
September1st to 15thNight
58%
540
26%
1800
26%
540
64%
540
33%
987
September16th to endNight
54%
582
27%
1983
21%
582
64%
582
35%
1070
October1st to 15thNight
42%
684
25%
2052
18%
684
48%
684
31%
1236
October16th to endNight
34%
704
22%
2112
11%
704
44%
704
29%
1274
November1st to 15thNight
35%
745
25%
2271
13%
745
47%
745
32%
1310
November16th to endNight
28%
900
17%
2520
7%
900
37%
900
25%
1660
December1st to 15thNight
22%
900
13%
2520
4%
900
30%
900
18%
1834
December16th to endNight
21%
960
16%
2688
4%
960
31%
960
16%
2015

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%7%35%5%3445%7%39%
48079
Night
12%6%35%424446%44%
47291
Cloud CoverDay
13%7%35%5%3445%7%39%
48088
Night
12%6%35%424446%44%
47295
TransparencyDay
43%6%13%22%12%1
47777
Night
39%5%13%24%14%2
47111
SeeingDay
14%7%27%29%16%4
6058
Night
15%8%31%31%12%
16045

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
9%9%5%7%7%35%447%34%
1491
16th to endDay
14%13%48%7%35%446%27%
1728
February1st to 15thDay
14%9%48%6%34447%31%
1575
16th to endDay
13%8%47%5%25%45%5%38%
1497
March1st to 15thDay
13%9%47%5%3446%6%34%
1966
16th to endDay
18%10%47%5%23347%31%
2115
April1st to 15thDay
18%8%35%424446%37%
2151
16th to endDay
23%7%36%5%25%346%31%
2214
May1st to 15thDay
19%7%37%6%3435%6%32%
2366
16th to endDay
14%5%35%445%45%6%39%
2617
June1st to 15thDay
11%6%25%4345%5%8%41%
2520
16th to endDay
7%4245%35%5%7%8%45%
2520
July1st to 15thDay
8%3144245%7%8%47%
2520
16th to endDay
5%3144345%7%9%49%
2511
August1st to 15thDay
7%4245%35%5%7%9%43%
2340
16th to endDay
12%5%2442435%7%46%
2362
September1st to 15thDay
13%42432235%8%50%
2160
16th to endDay
11%41442436%7%49%
1962
October1st to 15thDay
13%6%25%423346%47%
1706
16th to endDay
15%7%24423446%43%
1760
November1st to 15thDay
10%6%14324446%49%
1582
16th to endDay
17%7%34434447%38%
1440
December1st to 15thDay
15%12%6%9%6%25%346%28%
1440
16th to endDay
15%14%5%9%7%3433428%
1536
January1st to 15thNight
10%8%46%5%4435%7%39%
2446
16th to endNight
11%11%5%7%5%34446%36%
2496
February1st to 15thNight
12%11%5%9%434336%34%
2285
16th to endNight
13%8%46%41435%5%43%
1976
March1st to 15thNight
13%7%26%324235%46%
1980
16th to endNight
18%10%46%42445%6%32%
2109
April1st to 15thNight
14%7%25%434346%43%
1797
16th to endNight
20%8%25%5%3334439%
1743
May1st to 15thNight
14%4245%35%46%7%40%
1584
16th to endNight
10%426%5%2445%7%45%
1496
June1st to 15thNight
6%424435%5%6%7%47%
1440
16th to endNight
5%3235%245%7%9%49%
1440
July1st to 15thNight
5%1143245%6%8%56%
1440
16th to endNight
42133245%5%11%55%
1654
August1st to 15thNight
42124346%6%9%54%
1620
16th to endNight
7%324424347%52%
1839
September1st to 15thNight
10%413413346%54%
1800
16th to endNight
9%422323448%54%
1983
October1st to 15thNight
16%414323345%50%
2052
16th to endNight
13%6%24422345%50%
2112
November1st to 15thNight
10%6%13323337%53%
2271
16th to endNight
15%7%35%423345%44%
2520
December1st to 15thNight
16%11%46%6%2434435%
2520
16th to endNight
17%10%5%8%5%2433432%
2688

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
9%10%5%7%6%35%447%34%
1491
16th to endDay
13%13%48%7%26%45%6%26%
1728
February1st to 15thDay
14%10%48%6%44346%31%
1575
16th to endDay
13%8%46%5%26%45%5%37%
1497
March1st to 15thDay
13%9%47%5%3445%7%33%
1977
16th to endDay
18%11%46%5%24337%31%
2113
April1st to 15thDay
18%8%35%434446%37%
2151
16th to endDay
22%7%36%5%24346%31%
2214
May1st to 15thDay
19%8%36%6%3435%6%32%
2366
16th to endDay
14%6%35%5%45%5%5%6%39%
2617
June1st to 15thDay
11%6%25%4345%5%8%40%
2520
16th to endDay
6%4245%36%5%6%9%44%
2520
July1st to 15thDay
7%315%4245%6%9%47%
2520
16th to endDay
5%3144346%7%10%48%
2511
August1st to 15thDay
7%4245%345%7%9%43%
2340
16th to endDay
12%5%2443435%8%45%
2362
September1st to 15thDay
12%42432235%8%50%
2160
16th to endDay
11%42442436%6%49%
1962
October1st to 15thDay
13%6%25%323446%47%
1706
16th to endDay
15%7%24423446%43%
1760
November1st to 15thDay
10%5%24425%436%49%
1582
16th to endDay
18%7%3442445%7%37%
1440
December1st to 15thDay
15%12%6%8%5%25%446%28%
1440
16th to endDay
14%14%5%9%7%34335%27%
1536
January1st to 15thNight
9%7%45%6%35%45%8%39%
2446
16th to endNight
11%11%47%5%34446%36%
2496
February1st to 15thNight
12%10%5%10%5%34337%33%
2278
16th to endNight
12%8%35%42335%5%43%
1976
March1st to 15thNight
13%7%36%323235%46%
1992
16th to endNight
18%10%46%4345%46%31%
2109
April1st to 15thNight
13%7%25%434346%43%
1797
16th to endNight
19%9%25%5%33345%38%
1743
May1st to 15thNight
14%4245%35%46%7%40%
1583
16th to endNight
9%426%5%245%5%7%45%
1496
June1st to 15thNight
6%424435%5%6%7%47%
1440
16th to endNight
5%2245%345%7%9%49%
1440
July1st to 15thNight
5%2133245%7%8%56%
1440
16th to endNight
42133245%5%10%55%
1654
August1st to 15thNight
3213435%5%6%9%54%
1620
16th to endNight
7%3245%3435%7%52%
1839
September1st to 15thNight
10%423413346%54%
1800
16th to endNight
9%413323448%54%
1983
October1st to 15thNight
15%414223345%50%
2052
16th to endNight
13%6%2442243450%
2112
November1st to 15thNight
10%6%13313337%53%
2271
16th to endNight
15%8%35%423345%44%
2520
December1st to 15thNight
16%11%47%5%24345%34%
2520
16th to endNight
18%10%5%8%6%24335%31%
2688

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
49%413%18%11%
1492
16th to endDay
57%6%14%15%6%
1728
February1st to 15thDay
53%414%20%6%
1576
16th to endDay
47%5%15%21%9%1
1497
March1st to 15thDay
48%6%15%19%8%1
1977
16th to endDay
53%5%14%18%6%
2115
April1st to 15thDay
47%6%11%26%8%
2151
16th to endDay
53%6%12%17%9%1
2214
May1st to 15thDay
52%5%12%20%9%
2366
16th to endDay
44%7%13%22%10%1
2621
June1st to 15thDay
39%7%15%22%13%1
2520
16th to endDay
33%9%14%24%15%1
2520
July1st to 15thDay
32%9%15%26%12%3
2371
16th to endDay
28%8%18%26%17%1
2355
August1st to 15thDay
34%8%15%25%15%
2326
16th to endDay
36%6%12%22%16%4
2362
September1st to 15thDay
32%5%12%25%19%3
2160
16th to endDay
34%414%30%14%1
1962
October1st to 15thDay
37%5%9%23%20%2
1706
16th to endDay
41%5%13%24%13%2
1760
November1st to 15thDay
35%413%23%19%2
1582
16th to endDay
45%5%15%22%9%
1440
December1st to 15thDay
57%5%14%15%7%
1440
16th to endDay
59%5%11%14%7%1
1536
January1st to 15thNight
44%416%21%13%
2446
16th to endNight
48%5%15%19%10%
2496
February1st to 15thNight
51%413%21%8%
2288
16th to endNight
42%413%24%13%1
1976
March1st to 15thNight
40%413%25%15%1
1992
16th to endNight
52%5%13%18%8%
2109
April1st to 15thNight
41%5%10%25%14%2
1797
16th to endNight
48%411%20%12%2
1743
May1st to 15thNight
41%7%16%21%12%
1584
16th to endNight
36%8%13%23%14%3
1498
June1st to 15thNight
32%9%13%26%15%2
1440
16th to endNight
28%7%14%23%21%4
1440
July1st to 15thNight
23%8%17%30%14%5%
1360
16th to endNight
21%7%17%32%19%1
1547
August1st to 15thNight
25%8%16%31%16%2
1610
16th to endNight
30%6%10%26%19%6%
1839
September1st to 15thNight
31%49%26%24%4
1800
16th to endNight
28%5%12%30%20%2
1983
October1st to 15thNight
35%5%9%22%23%4
2052
16th to endNight
36%413%25%17%2
2112
November1st to 15thNight
31%413%25%19%4
2271
16th to endNight
43%313%25%12%1
2520
December1st to 15thNight
52%413%19%8%
2520
16th to endNight
56%410%16%10%1
2688

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
21%7%45%20%41
90
16th to endDay
22%10%46%16%3
96
February1st to 15thDay
16%21%28%23%10%
90
16th to endDay
13%14%41%14%13%1
81
March1st to 15thDay
23%17%38%17%11
90
16th to endDay
32%10%33%18%6%
99
April1st to 15thDay
21%10%32%24%10%
270
16th to endDay
29%11%27%20%9%1
324
May1st to 15thDay
19%12%35%22%9%1
468
16th to endDay
17%9%28%28%12%2
517
June1st to 15thDay
12%424%34%20%4
495
16th to endDay
7%6%33%30%18%3
495
July1st to 15thDay
8%124%34%21%9%
475
16th to endDay
4118%42%27%5%
515
August1st to 15thDay
9%119%34%29%5%
493
16th to endDay
12%5%17%34%22%8%
402
September1st to 15thDay
11%220%33%23%8%
315
16th to endDay
12%227%37%16%4
174
October1st to 15thDay
10%6%40%29%5%7%
107
16th to endDay
17%8%36%29%8%
96
November1st to 15thDay
45%37%27%16%7%
90
16th to endDay
37%14%33%12%11
90
December1st to 15thDay
20%22%27%18%6%4
90
16th to endDay
29%22%32%13%2
96
January1st to 15thNight
13%12%40%24%8%
900
16th to endNight
17%11%39%26%5%
960
February1st to 15thNight
17%11%38%26%5%
880
16th to endNight
17%10%39%25%6%
714
March1st to 15thNight
17%8%34%28%10%
552
16th to endNight
22%9%35%26%6%
576
April1st to 15thNight
16%12%36%30%4
539
16th to endNight
23%8%32%26%8%1
540
May1st to 15thNight
15%7%34%33%8%
540
16th to endNight
11%435%33%13%
563
June1st to 15thNight
10%322%46%16%
540
16th to endNight
6%229%42%17%
540
July1st to 15thNight
5%19%41%30%1
510
16th to endNight
5%13%48%30%1
564
August1st to 15thNight
4114%47%29%2
539
16th to endNight
9%113%43%29%2
573
September1st to 15thNight
11%419%32%27%4
540
16th to endNight
10%425%31%25%1
582
October1st to 15thNight
17%7%27%30%15%1
684
16th to endNight
17%9%34%28%9%
704
November1st to 15thNight
14%11%36%27%9%
745
16th to endNight
18%12%37%22%8%
900
December1st to 15thNight
22%14%35%22%4
900
16th to endNight
23%11%34%25%5%
960
Page generated at 2017-10-07 13:07:52. Version ac04

Copyright 2017 A. Danko


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