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 2018-02-14.

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%
16547
21%
48837
13%
16500
48%
16500
28%
30587

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
25%
975
19%
2609
7%
970
34%
970
25%
1738
January16th to endNight
24%
1040
22%
2704
7%
1040
34%
1040
27%
1796
February1st to 15thNight
22%
950
14%
2470
4%
946
27%
946
21%
1778
February16th to endNight
21%
660
22%
1922
6%
660
33%
660
25%
1235
March1st to 15thNight
27%
567
19%
2007
10%
567
38%
567
20%
1270
March16th to endNight
25%
576
12%
2093
8%
576
33%
576
14%
1489
April1st to 15thNight
30%
539
20%
1797
12%
539
43%
539
25%
1092
April16th to endNight
34%
540
22%
1800
14%
540
48%
540
24%
1134
May1st to 15thNight
42%
539
18%
1640
14%
539
48%
539
25%
1086
May16th to endNight
47%
563
21%
1497
14%
561
54%
561
30%
996
June1st to 15thNight
62%
540
20%
1440
13%
540
66%
540
41%
849
June16th to endNight
60%
540
22%
1440
12%
540
64%
540
41%
842
July1st to 15thNight
68%
510
18%
1360
14%
510
69%
510
39%
808
July16th to endNight
71%
564
23%
1592
21%
531
75%
531
43%
854
August1st to 15thNight
77%
539
25%
1610
27%
536
79%
536
43%
864
August16th to endNight
73%
573
24%
1897
30%
573
75%
573
38%
1030
September1st to 15thNight
65%
540
27%
1800
27%
540
70%
540
34%
995
September16th to endNight
59%
603
30%
1968
23%
603
67%
603
36%
1056
October1st to 15thNight
45%
720
27%
2160
18%
720
53%
720
34%
1260
October16th to endNight
36%
768
28%
2304
15%
768
48%
768
32%
1352
November1st to 15thNight
36%
760
27%
2404
16%
760
50%
760
31%
1380
November16th to endNight
28%
926
23%
2681
11%
926
39%
926
27%
1695
December1st to 15thNight
25%
975
16%
2730
7%
975
34%
975
22%
1873
December16th to endNight
21%
1040
17%
2912
5%
1040
30%
1040
18%
2115

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%6%35%42445%7%42%
49237
Night
12%6%24424446%46%
49023
TransparencyDay
40%6%12%23%14%2
48927
Night
37%5%11%24%16%2
48839
SeeingDay
14%7%25%30%18%4
6358
Night
15%9%31%29%12%1
16548

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
13%8%36%423446%40%
1656
16th to endDay
10%10%47%5%34446%38%
1872
February1st to 15thDay
14%9%46%5%33436%36%
1694
16th to endDay
13%9%5%6%5%34345%38%
1550
March1st to 15thDay
14%10%46%6%33446%36%
1962
16th to endDay
20%10%47%4245%45%30%
2128
April1st to 15thDay
15%8%35%424345%41%
2151
16th to endDay
22%6%25%43445%7%33%
2160
May1st to 15thDay
19%6%35%5%24447%35%
2305
16th to endDay
13%6%25%5%3435%8%39%
2617
June1st to 15thDay
9%4245%35%5%5%8%42%
2520
16th to endDay
7%3135%25%5%6%10%47%
2520
July1st to 15thDay
9%313435%5%7%11%43%
2520
16th to endDay
6%424435%5%7%10%46%
2466
August1st to 15thDay
7%3245%35%7%6%9%44%
2340
16th to endDay
8%5%245%245%5%9%47%
2304
September1st to 15thDay
11%5%144245%48%47%
2160
16th to endDay
9%5%24325%5%5%8%48%
1979
October1st to 15thDay
14%5%25%423246%48%
1800
16th to endDay
14%6%14312345%52%
1920
November1st to 15thDay
14%7%23313346%49%
1784
16th to endDay
16%8%24323345%45%
1605
December1st to 15thDay
14%9%46%32335%6%40%
1560
16th to endDay
16%11%5%7%323435%35%
1664
January1st to 15thNight
12%8%45%433445%43%
2609
16th to endNight
11%8%45%434345%44%
2704
February1st to 15thNight
14%9%36%5%245%46%35%
2460
16th to endNight
14%9%35%313446%44%
1922
March1st to 15thNight
17%8%25%323435%43%
2007
16th to endNight
20%8%35%6%3445%7%30%
2093
April1st to 15thNight
13%7%23324345%47%
1797
16th to endNight
18%5%24423446%44%
1800
May1st to 15thNight
15%5%24436%45%7%42%
1640
16th to endNight
13%4244345%47%44%
1496
June1st to 15thNight
43235%25%45%9%53%
1440
16th to endNight
5%224435%5%5%10%51%
1440
July1st to 15thNight
8%31432435%7%53%
1440
16th to endNight
5%2144235%6%10%54%
1699
August1st to 15thNight
42133345%6%9%56%
1620
16th to endNight
6%323324348%55%
1897
September1st to 15thNight
11%413223446%54%
1800
16th to endNight
7%324324448%54%
1968
October1st to 15thNight
11%424324345%52%
2160
16th to endNight
14%413323236%53%
2304
November1st to 15thNight
11%5%24312347%52%
2404
16th to endNight
14%7%24324335%48%
2681
December1st to 15thNight
15%9%35%5%23346%39%
2730
16th to endNight
17%13%46%423335%34%
2912

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
44%410%24%15%1
1657
16th to endDay
45%5%15%22%10%
1872
February1st to 15thDay
48%5%14%20%9%
1695
16th to endDay
48%5%11%22%11%1
1550
March1st to 15thDay
49%5%10%23%9%2
1962
16th to endDay
53%6%12%17%8%
2130
April1st to 15thDay
45%5%10%22%14%1
2151
16th to endDay
49%6%11%19%11%1
2160
May1st to 15thDay
47%6%12%22%10%
2305
16th to endDay
42%7%14%19%13%1
2621
June1st to 15thDay
36%8%13%24%14%1
2520
16th to endDay
29%9%17%27%13%3
2520
July1st to 15thDay
33%9%15%26%12%2
2371
16th to endDay
30%8%16%30%13%
2311
August1st to 15thDay
32%9%13%28%14%1
2326
16th to endDay
33%7%12%22%18%5%
2304
September1st to 15thDay
34%6%10%23%19%4
2160
16th to endDay
32%6%11%29%17%2
1979
October1st to 15thDay
38%49%22%20%4
1800
16th to endDay
34%310%27%20%3
1920
November1st to 15thDay
36%411%21%22%4
1784
16th to endDay
41%410%28%14%1
1605
December1st to 15thDay
44%5%13%24%11%
1560
16th to endDay
50%413%19%10%1
1664
January1st to 15thNight
42%5%12%23%15%1
2609
16th to endNight
41%414%23%14%1
2704
February1st to 15thNight
49%5%11%19%11%1
2470
16th to endNight
40%412%23%17%
1922
March1st to 15thNight
44%411%22%15%1
2007
16th to endNight
53%6%11%19%8%
2093
April1st to 15thNight
38%48%26%17%4
1797
16th to endNight
41%5%9%26%16%2
1800
May1st to 15thNight
40%8%13%21%15%
1641
16th to endNight
37%7%14%21%16%2
1498
June1st to 15thNight
26%7%14%30%18%2
1440
16th to endNight
26%7%15%27%18%4
1440
July1st to 15thNight
30%5%11%31%17%3
1360
16th to endNight
23%7%16%33%17%1
1592
August1st to 15thNight
22%8%14%32%20%2
1610
16th to endNight
26%6%11%25%22%6%
1897
September1st to 15thNight
29%5%10%23%24%6%
1800
16th to endNight
28%5%10%31%21%3
1968
October1st to 15thNight
33%49%24%21%6%
2160
16th to endNight
34%38%26%22%4
2304
November1st to 15thNight
33%311%25%19%6%
2404
16th to endNight
39%49%26%18%1
2681
December1st to 15thNight
46%414%21%12%
2730
16th to endNight
52%410%18%10%2
2912

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
25%12%38%22%
135
16th to endDay
11%17%51%13%5%
144
February1st to 15thDay
19%21%38%16%3
130
16th to endDay
18%20%34%20%4
81
March1st to 15thDay
25%14%44%12%3
90
16th to endDay
27%18%35%17%1
114
April1st to 15thDay
20%16%28%26%8%
270
16th to endDay
25%7%29%27%8%1
270
May1st to 15thDay
17%11%31%27%9%2
435
16th to endDay
17%6%29%28%12%3
517
June1st to 15thDay
7%323%37%21%6%
495
16th to endDay
8%330%35%18%3
495
July1st to 15thDay
12%216%37%24%6%
475
16th to endDay
6%111%35%37%7%
515
August1st to 15thDay
7%113%38%30%9%
493
16th to endDay
9%111%37%30%9%
344
September1st to 15thDay
10%314%28%33%9%
315
16th to endDay
8%5%18%30%26%10%
212
October1st to 15thDay
18%8%28%26%14%2
135
16th to endDay
15%12%31%32%6%
144
November1st to 15thDay
12%7%33%25%14%5%
135
16th to endDay
29%12%26%25%5%
135
December1st to 15thDay
13%19%37%20%5%4
135
16th to endDay
25%18%40%14%1
144
January1st to 15thNight
15%17%37%22%5%
975
16th to endNight
15%13%42%24%3
1040
February1st to 15thNight
17%13%40%24%2
950
16th to endNight
19%14%40%22%3
660
March1st to 15thNight
21%12%35%24%4
567
16th to endNight
24%10%34%24%5%
576
April1st to 15thNight
16%14%36%26%5%
539
16th to endNight
19%9%34%29%7%
540
May1st to 15thNight
16%5%29%36%10%
540
16th to endNight
14%428%34%15%2
563
June1st to 15thNight
6%123%41%25%1
540
16th to endNight
4226%44%20%1
540
July1st to 15thNight
11%111%44%28%3
510
16th to endNight
5%14%37%39%2
564
August1st to 15thNight
5%110%42%38%2
539
16th to endNight
7%111%40%34%4
573
September1st to 15thNight
13%213%37%27%5%
540
16th to endNight
9%321%33%25%6%
603
October1st to 15thNight
14%430%28%18%3
720
16th to endNight
17%9%33%29%9%
768
November1st to 15thNight
14%11%34%29%10%
760
16th to endNight
19%10%39%23%6%
926
December1st to 15thNight
21%14%35%23%4
975
16th to endNight
24%12%37%23%2
1040
Page generated at 2018-02-15 09:58:43. Version ac04

Copyright 2018 A. Danko


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