The Carolinian Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the The Carolinian Observatory clear sky chart from 2005-11-05 to 2017-12-04.

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
37%
15270
14%
47614
10%
15232
42%
15232
19%
33234

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
14%
717
9%
2371
4%
716
20%
716
7%
1911
January16th to endNight
16%
768
9%
2496
4%
768
21%
768
9%
1992
February1st to 15thNight
16%
702
8%
2287
2%
701
24%
701
9%
1800
February16th to endNight
24%
631
11%
1958
4%
631
32%
631
13%
1491
March1st to 15thNight
25%
720
14%
2005
7%
720
31%
720
17%
1511
March16th to endNight
33%
768
19%
2112
10%
768
40%
768
22%
1471
April1st to 15thNight
28%
692
15%
1839
7%
692
34%
692
21%
1332
April16th to endNight
40%
540
21%
1620
9%
540
49%
540
26%
1043
May1st to 15thNight
43%
540
16%
1620
11%
540
48%
540
22%
1107
May16th to endNight
51%
425
17%
1548
16%
425
57%
425
26%
909
June1st to 15thNight
51%
360
14%
1438
16%
360
58%
360
24%
826
June16th to endNight
54%
360
17%
1260
16%
360
61%
360
27%
744
July1st to 15thNight
66%
384
18%
1300
21%
384
69%
384
36%
695
July16th to endNight
65%
564
15%
1595
15%
531
67%
531
34%
944
August1st to 15thNight
70%
539
18%
1609
14%
536
72%
536
34%
947
August16th to endNight
64%
591
23%
1737
16%
591
69%
591
36%
1011
September1st to 15thNight
59%
720
21%
1881
13%
720
62%
720
34%
1197
September16th to endNight
60%
717
23%
1980
17%
717
63%
717
32%
1227
October1st to 15thNight
45%
720
18%
2142
17%
720
50%
720
25%
1408
October16th to endNight
28%
768
15%
2310
9%
768
36%
768
16%
1680
November1st to 15thNight
39%
760
18%
2514
15%
760
44%
760
20%
1660
November16th to endNight
23%
780
10%
2730
6%
780
28%
780
11%
2030
December1st to 15thNight
16%
736
5%
2574
2%
736
20%
736
8%
2044
December16th to endNight
14%
768
5%
2688
1%
768
18%
768
7%
2254

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
15%8%36%6%35%45%7%32%
48860
Night
15%8%36%5%3445%7%34%
47796
Cloud CoverDay
15%8%36%6%35%45%7%32%
48870
Night
15%8%36%5%3445%7%34%
47800
TransparencyDay
49%7%13%18%9%1
48561
Night
48%6%12%19%10%1
47614
SeeingDay
17%6%25%25%16%6%
5839
Night
19%8%27%28%13%1
15276

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
20%12%6%9%9%45%44417%
1564
16th to endDay
16%16%6%12%8%45%44416%
1728
February1st to 15thDay
17%16%6%8%8%5%5%445%19%
1575
16th to endDay
16%12%7%10%7%46%45%6%19%
1512
March1st to 15thDay
17%12%5%9%7%34346%24%
1942
16th to endDay
17%10%6%6%6%25%346%30%
2112
April1st to 15thDay
18%10%47%6%35%45%6%27%
2119
16th to endDay
18%8%25%5%23347%36%
2340
May1st to 15thDay
17%6%26%5%25%5%6%7%33%
2331
16th to endDay
12%5%25%5%3446%9%39%
2567
June1st to 15thDay
12%435%5%345%6%8%39%
2520
16th to endDay
10%4245%35%6%8%9%38%
2697
July1st to 15thDay
9%424425%6%6%9%43%
2575
16th to endDay
9%4245%36%6%7%10%38%
2465
August1st to 15thDay
8%415%6%45%7%7%9%38%
2340
16th to endDay
11%5%25%435%5%6%8%42%
2453
September1st to 15thDay
11%5%26%6%35%46%8%39%
2076
16th to endDay
14%5%2443446%7%41%
1980
October1st to 15thDay
16%7%36%6%35%5%5%5%34%
1818
16th to endDay
24%9%37%6%34346%26%
1911
November1st to 15thDay
14%7%36%6%3445%7%36%
1671
16th to endDay
20%11%47%7%345%5%6%23%
1560
December1st to 15thDay
18%15%6%10%6%34445%21%
1468
16th to endDay
22%15%8%11%7%4444414%
1536
January1st to 15thNight
22%12%5%9%6%4444421%
2371
16th to endNight
16%15%8%9%7%43446%20%
2496
February1st to 15thNight
16%13%6%9%6%45%45%5%22%
2285
16th to endNight
17%10%5%8%7%35%6%5%5%25%
1958
March1st to 15thNight
19%9%46%6%34448%28%
1993
16th to endNight
16%9%35%43445%5%37%
2112
April1st to 15thNight
20%8%35%425%45%7%33%
1839
16th to endNight
11%6%36%5%345%5%7%41%
1620
May1st to 15thNight
15%6%36%5%35%5%6%7%34%
1620
16th to endNight
10%5%24426%5%5%6%46%
1546
June1st to 15thNight
11%425%3345%7%9%42%
1438
16th to endNight
9%5%235%25%5%6%9%44%
1260
July1st to 15thNight
5%423433447%55%
1379
16th to endNight
7%412435%5%6%8%48%
1703
August1st to 15thNight
6%314435%46%11%47%
1620
16th to endNight
8%41442335%7%53%
1737
September1st to 15thNight
11%5%234245%6%6%47%
1881
16th to endNight
11%3144345%5%7%47%
1980
October1st to 15thNight
16%5%35%424445%42%
2142
16th to endNight
20%8%26%5%3435%6%32%
2310
November1st to 15thNight
15%5%35%5%25%5%5%8%37%
2514
16th to endNight
21%10%37%5%345%5%6%26%
2730
December1st to 15thNight
21%13%6%7%5%33447%22%
2574
16th to endNight
22%13%6%9%7%34445%17%
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
20%12%6%9%9%45%435%17%
1564
16th to endDay
16%16%7%12%8%44435%16%
1728
February1st to 15thDay
17%16%6%7%8%5%5%345%19%
1575
16th to endDay
16%12%6%10%7%46%45%5%19%
1512
March1st to 15thDay
17%12%5%8%7%25%346%24%
1953
16th to endDay
17%10%6%6%6%25%346%30%
2111
April1st to 15thDay
18%10%5%7%5%3445%6%27%
2119
16th to endDay
18%8%25%423448%37%
2340
May1st to 15thDay
17%6%25%5%25%5%6%7%34%
2331
16th to endDay
12%5%25%5%3445%9%39%
2567
June1st to 15thDay
12%5%25%5%245%6%9%39%
2520
16th to endDay
11%425%435%6%8%9%39%
2697
July1st to 15thDay
9%3245%35%6%6%9%44%
2575
16th to endDay
9%4245%36%6%7%10%38%
2465
August1st to 15thDay
8%415%7%35%7%7%9%38%
2340
16th to endDay
11%4244445%5%8%42%
2453
September1st to 15thDay
12%426%6%35%46%9%39%
2076
16th to endDay
15%5%2443346%8%41%
1980
October1st to 15thDay
16%6%36%6%35%45%5%34%
1818
16th to endDay
24%9%37%5%34346%26%
1911
November1st to 15thDay
14%7%26%5%35%45%6%36%
1671
16th to endDay
20%11%47%7%345%5%7%23%
1560
December1st to 15thDay
18%15%6%9%7%34345%20%
1468
16th to endDay
22%15%8%10%7%44345%14%
1536
January1st to 15thNight
22%12%5%9%5%3444421%
2371
16th to endNight
16%15%8%8%7%43446%20%
2496
February1st to 15thNight
15%14%6%8%6%45%45%5%23%
2278
16th to endNight
17%10%5%7%7%25%5%5%5%26%
1958
March1st to 15thNight
19%9%46%6%34448%28%
2005
16th to endNight
16%8%45%43445%5%37%
2112
April1st to 15thNight
20%8%45%425%45%7%33%
1839
16th to endNight
11%6%36%5%25%45%7%41%
1620
May1st to 15thNight
15%6%36%5%25%5%6%7%34%
1619
16th to endNight
11%5%244245%5%6%46%
1546
June1st to 15thNight
11%5%25%335%5%6%9%42%
1438
16th to endNight
9%5%235%245%6%9%44%
1260
July1st to 15thNight
5%3234335%5%7%55%
1379
16th to endNight
7%42343446%8%48%
1703
August1st to 15thNight
6%314435%36%12%47%
1620
16th to endNight
8%41442335%7%53%
1737
September1st to 15thNight
11%42343445%7%47%
1881
16th to endNight
11%3145%345%5%6%47%
1980
October1st to 15thNight
16%5%26%424445%42%
2142
16th to endNight
20%8%26%5%3445%6%32%
2310
November1st to 15thNight
15%5%35%5%25%45%7%38%
2514
16th to endNight
21%10%37%6%245%47%26%
2730
December1st to 15thNight
21%13%6%7%5%2345%6%22%
2574
16th to endNight
22%13%6%9%7%35%45%5%17%
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
69%5%10%10%3
1565
16th to endDay
70%6%10%8%3
1728
February1st to 15thDay
67%5%10%12%3
1577
16th to endDay
64%7%12%11%3
1512
March1st to 15thDay
61%6%11%14%6%
1953
16th to endDay
55%411%18%9%1
2112
April1st to 15thDay
56%5%10%18%9%
2119
16th to endDay
46%412%19%14%2
2340
May1st to 15thDay
47%7%13%19%11%1
2331
16th to endDay
40%8%14%21%13%1
2571
June1st to 15thDay
39%7%15%23%12%1
2520
16th to endDay
37%10%15%21%14%
2697
July1st to 15thDay
34%7%13%25%16%2
2426
16th to endDay
37%10%15%21%13%1
2310
August1st to 15thDay
37%10%16%21%12%1
2327
16th to endDay
37%7%17%23%12%2
2453
September1st to 15thDay
40%8%14%24%11%
2076
16th to endDay
39%6%15%24%12%
1980
October1st to 15thDay
49%6%14%17%11%
1818
16th to endDay
59%6%14%12%5%
1911
November1st to 15thDay
47%7%15%19%8%1
1671
16th to endDay
59%7%15%13%3
1560
December1st to 15thDay
66%8%14%8%2
1468
16th to endDay
73%6%10%8%
1536
January1st to 15thNight
65%6%9%11%6%
2371
16th to endNight
65%5%12%13%3
2496
February1st to 15thNight
62%6%11%13%4
2287
16th to endNight
57%7%13%16%5%
1958
March1st to 15thNight
55%6%11%19%6%1
2005
16th to endNight
48%5%11%21%12%2
2112
April1st to 15thNight
50%5%10%20%12%1
1839
16th to endNight
40%6%9%21%18%3
1620
May1st to 15thNight
46%5%10%21%12%2
1620
16th to endNight
36%6%13%23%16%3
1548
June1st to 15thNight
35%7%13%27%13%1
1438
16th to endNight
35%7%13%23%17%1
1260
July1st to 15thNight
28%6%10%30%21%3
1300
16th to endNight
31%7%15%24%18%2
1595
August1st to 15thNight
28%9%14%30%14%1
1609
16th to endNight
30%6%13%30%16%2
1737
September1st to 15thNight
34%6%14%25%16%2
1881
16th to endNight
34%6%12%29%15%
1980
October1st to 15thNight
42%5%11%22%16%
2142
16th to endNight
52%6%13%18%7%
2310
November1st to 15thNight
44%7%14%21%11%1
2514
16th to endNight
56%7%16%15%3
2730
December1st to 15thNight
62%8%15%10%3
2574
16th to endNight
68%8%11%8%2
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
19%19%41%10%7%1
82
16th to endDay
30%19%34%14%1
96
February1st to 15thDay
22%14%53%10%
90
16th to endDay
16%19%48%14%1
81
March1st to 15thDay
23%10%31%25%9%
243
16th to endDay
24%7%35%22%8%1
288
April1st to 15thDay
26%11%27%22%10%2
270
16th to endDay
22%430%22%11%7%
270
May1st to 15thDay
25%5%25%23%15%4
288
16th to endDay
14%5%27%29%15%6%
331
June1st to 15thDay
15%225%33%18%3
315
16th to endDay
11%429%33%16%4
492
July1st to 15thDay
11%420%33%22%8%
406
16th to endDay
10%217%30%27%11%
326
August1st to 15thDay
9%116%30%27%14%
313
16th to endDay
13%316%23%25%17%
332
September1st to 15thDay
12%118%26%26%15%
315
16th to endDay
14%414%24%23%17%
314
October1st to 15thDay
21%6%22%24%19%4
315
16th to endDay
29%8%32%22%7%1
327
November1st to 15thDay
16%12%33%21%12%3
124
16th to endDay
20%23%34%15%5%1
90
December1st to 15thDay
23%23%26%19%5%
67
16th to endDay
26%34%29%7%1
64
January1st to 15thNight
27%16%33%16%4
720
16th to endNight
23%13%36%21%5%
768
February1st to 15thNight
23%14%35%21%4
704
16th to endNight
22%11%32%26%6%
631
March1st to 15thNight
23%10%33%25%7%
720
16th to endNight
21%6%33%26%11%
768
April1st to 15thNight
23%11%31%26%7%
692
16th to endNight
14%6%32%32%11%1
540
May1st to 15thNight
17%5%25%34%15%1
540
16th to endNight
13%226%36%18%2
426
June1st to 15thNight
13%127%40%16%
360
16th to endNight
10%125%44%16%
360
July1st to 15thNight
7%18%43%26%2
384
16th to endNight
9%215%43%26%2
564
August1st to 15thNight
9%12%41%31%4
539
16th to endNight
9%116%34%32%4
591
September1st to 15thNight
13%416%32%28%5%
720
16th to endNight
12%417%29%27%8%
717
October1st to 15thNight
19%6%21%30%19%2
720
16th to endNight
24%11%30%26%7%
768
November1st to 15thNight
18%8%28%29%12%1
760
16th to endNight
27%12%30%19%8%1
780
December1st to 15thNight
29%14%33%16%4
736
16th to endNight
26%13%36%19%4
768
Page generated at 2017-12-05 10:19:01. Version ac04

Copyright 2017 A. Danko


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