Charleston
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Charleston clear sky chart from 2005-11-05 to 2017-08-12.

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
46%
15832
21%
46512
14%
15793
54%
15793
25%
29223

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
29%
716
22%
2327
9%
716
44%
716
19%
1445
January16th to endNight
29%
768
23%
2496
13%
768
42%
768
23%
1501
February1st to 15thNight
32%
704
22%
2255
12%
701
46%
701
21%
1364
February16th to endNight
32%
631
26%
1795
12%
631
45%
631
24%
1138
March1st to 15thNight
36%
720
26%
1980
15%
720
47%
720
29%
1208
March16th to endNight
39%
768
21%
2112
12%
768
47%
768
27%
1319
April1st to 15thNight
44%
718
25%
1898
14%
718
52%
718
32%
1148
April16th to endNight
47%
720
26%
1800
13%
720
54%
720
33%
1113
May1st to 15thNight
52%
578
21%
1659
13%
578
56%
578
30%
990
May16th to endNight
54%
561
19%
1684
12%
561
59%
561
25%
1020
June1st to 15thNight
60%
540
14%
1620
11%
540
62%
540
25%
1028
June16th to endNight
60%
540
13%
1620
9%
540
62%
540
24%
1040
July1st to 15thNight
64%
510
13%
1530
12%
510
64%
510
25%
979
July16th to endNight
63%
564
11%
1595
10%
531
68%
531
23%
1058
August1st to 15thNight
63%
527
13%
1575
11%
524
64%
524
20%
1089
August16th to endNight
57%
678
13%
1728
9%
678
59%
678
20%
1300
September1st to 15thNight
62%
660
18%
1760
15%
660
63%
660
24%
1238
September16th to endNight
50%
657
12%
1815
6%
657
55%
657
17%
1319
October1st to 15thNight
51%
660
27%
1963
25%
660
57%
660
30%
1174
October16th to endNight
54%
704
32%
2112
25%
704
65%
704
34%
1191
November1st to 15thNight
47%
700
30%
2101
21%
700
59%
700
34%
1166
November16th to endNight
43%
720
26%
2251
17%
720
55%
720
27%
1318
December1st to 15thNight
37%
720
21%
2340
14%
720
46%
720
20%
1474
December16th to endNight
32%
768
22%
2496
13%
768
44%
768
18%
1603

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
10%5%25%5%35%5%6%8%42%
47453
Night
10%5%25%5%3446%8%44%
46709
TransparencyDay
36%7%15%21%14%4
47154
Night
37%6%13%20%16%6%
46512
SeeingDay
10%10%14%25%25%11%
5660
Night
11%18%15%26%23%5%
15839

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
14%6%25%5%3335%7%43%
1611
16th to endDay
15%5%25%5%22346%45%
1728
February1st to 15thDay
14%6%15%433446%44%
1604
16th to endDay
12%5%35%423335%48%
1676
March1st to 15thDay
12%424424347%50%
1980
16th to endDay
10%5%2442446%6%47%
2111
April1st to 15thDay
9%31432345%6%55%
2047
16th to endDay
6%3143245%5%9%53%
2160
May1st to 15thDay
7%4245%345%6%8%46%
2301
16th to endDay
9%425%435%6%7%9%42%
2431
June1st to 15thDay
7%325%5%36%7%8%12%36%
2340
16th to endDay
6%425%5%48%6%9%11%35%
2340
July1st to 15thDay
8%5%345%47%8%7%11%34%
2340
16th to endDay
7%5%26%6%47%8%8%11%31%
2465
August1st to 15thDay
8%436%8%47%8%9%12%27%
2288
16th to endDay
11%6%27%7%5%7%8%8%10%23%
2110
September1st to 15thDay
12%4247%36%6%7%10%35%
1867
16th to endDay
15%9%37%5%25%5%6%8%30%
1815
October1st to 15thDay
13%424423345%51%
1667
16th to endDay
9%413423345%57%
1760
November1st to 15thDay
9%5%23323345%56%
1757
16th to endDay
10%42432435%5%53%
1707
December1st to 15thDay
14%6%25%434436%44%
1620
16th to endDay
13%6%2432445%7%44%
1728
January1st to 15thNight
11%6%15%5%34447%44%
2327
16th to endNight
14%6%34423345%47%
2496
February1st to 15thNight
14%5%25%42344448%
2246
16th to endNight
10%7%25%5%24346%46%
1795
March1st to 15thNight
8%5%25%424447%48%
1980
16th to endNight
10%5%245%2335%8%47%
2112
April1st to 15thNight
11%314423347%52%
1898
16th to endNight
8%42432446%9%50%
1800
May1st to 15thNight
6%5%1443446%8%49%
1658
16th to endNight
7%314435%5%6%10%45%
1682
June1st to 15thNight
7%4235%45%7%7%13%38%
1620
16th to endNight
4425%5%45%7%9%13%37%
1620
July1st to 15thNight
6%425%5%35%6%9%12%37%
1620
16th to endNight
7%425%7%36%6%9%12%34%
1703
August1st to 15thNight
8%4246%36%8%11%13%29%
1586
16th to endNight
10%6%36%8%46%5%7%11%28%
1728
September1st to 15thNight
9%425%6%445%7%9%38%
1760
16th to endNight
15%6%26%5%446%7%10%30%
1815
October1st to 15thNight
13%5%23423347%49%
1963
16th to endNight
8%41432345%457%
2112
November1st to 15thNight
9%5%13313346%57%
2101
16th to endNight
11%5%25%424346%50%
2251
December1st to 15thNight
14%5%25%42435%6%44%
2340
16th to endNight
14%6%35%5%34446%40%
2496

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
41%410%18%19%6%
1612
16th to endDay
40%47%20%20%6%
1728
February1st to 15thDay
41%37%18%21%7%
1606
16th to endDay
38%47%21%20%6%
1676
March1st to 15thDay
35%310%22%18%8%
1980
16th to endDay
35%5%13%22%16%5%
2112
April1st to 15thDay
28%414%25%19%7%
2047
16th to endDay
26%6%14%23%20%8%
2160
May1st to 15thDay
33%6%14%26%16%2
2301
16th to endDay
33%8%18%26%12%
2435
June1st to 15thDay
33%10%25%21%8%
2340
16th to endDay
35%12%20%24%7%
2340
July1st to 15thDay
36%10%24%22%4
2201
16th to endDay
38%11%25%18%4
2310
August1st to 15thDay
42%12%20%19%5%
2275
16th to endDay
46%13%18%17%3
2110
September1st to 15thDay
40%10%17%17%10%3
1867
16th to endDay
47%7%15%16%10%2
1815
October1st to 15thDay
33%411%20%21%7%
1667
16th to endDay
28%48%20%27%10%
1760
November1st to 15thDay
31%38%21%23%10%
1757
16th to endDay
32%410%21%21%10%
1707
December1st to 15thDay
41%411%21%14%6%
1620
16th to endDay
40%414%19%15%6%
1728
January1st to 15thNight
40%5%8%18%19%7%
2327
16th to endNight
39%38%16%22%9%
2496
February1st to 15thNight
38%37%20%18%10%
2255
16th to endNight
40%39%17%19%9%
1795
March1st to 15thNight
33%5%11%21%18%8%
1980
16th to endNight
35%5%14%19%16%8%
2112
April1st to 15thNight
32%411%22%21%8%
1898
16th to endNight
30%6%12%23%21%6%
1800
May1st to 15thNight
32%6%14%25%19%2
1659
16th to endNight
32%9%18%27%12%1
1684
June1st to 15thNight
35%9%23%22%8%
1620
16th to endNight
33%13%22%23%6%
1620
July1st to 15thNight
35%11%24%22%6%
1530
16th to endNight
36%13%21%22%4
1595
August1st to 15thNight
40%13%20%20%5%
1575
16th to endNight
46%12%18%18%3
1728
September1st to 15thNight
41%11%16%18%10%2
1760
16th to endNight
48%9%15%14%9%1
1815
October1st to 15thNight
35%411%20%21%7%
1963
16th to endNight
29%48%18%25%13%
2112
November1st to 15thNight
29%39%20%24%12%
2101
16th to endNight
34%410%16%22%11%
2251
December1st to 15thNight
41%412%17%15%6%
2340
16th to endNight
44%49%20%13%7%
2496

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
12%12%26%28%14%5%
90
16th to endDay
14%9%41%25%8%1
96
February1st to 15thDay
14%14%34%27%8%
90
16th to endDay
8%15%37%32%6%
177
March1st to 15thDay
11%15%32%24%14%1
270
16th to endDay
11%15%25%30%13%3
288
April1st to 15thDay
12%19%21%22%18%6%
270
16th to endDay
312%20%27%21%14%
270
May1st to 15thDay
5%12%25%29%19%7%
288
16th to endDay
9%12%8%22%27%17%
331
June1st to 15thDay
8%10%5%27%27%19%
315
16th to endDay
8%9%7%28%28%17%
315
July1st to 15thDay
6%7%222%39%20%
305
16th to endDay
8%10%22%40%17%
326
August1st to 15thDay
10%7%223%39%16%
297
16th to endDay
10%7%322%35%20%
268
September1st to 15thDay
12%5%223%36%18%
255
16th to endDay
20%6%6%21%31%14%
254
October1st to 15thDay
20%7%14%27%20%9%
255
16th to endDay
11%7%15%25%29%11%
272
November1st to 15thDay
13%13%19%23%25%4
265
16th to endDay
9%10%23%28%21%6%
177
December1st to 15thDay
16%224%38%13%4
90
16th to endDay
15%425%29%22%3
96
January1st to 15thNight
11%26%24%27%9%
720
16th to endNight
12%22%31%27%5%
768
February1st to 15thNight
15%24%22%29%8%
704
16th to endNight
12%22%26%30%8%
631
March1st to 15thNight
10%21%26%29%11%
720
16th to endNight
11%21%21%27%16%1
768
April1st to 15thNight
11%21%18%25%20%2
718
16th to endNight
8%19%19%25%23%3
720
May1st to 15thNight
7%18%15%33%20%4
579
16th to endNight
8%17%8%21%29%14%
563
June1st to 15thNight
7%17%323%35%13%
540
16th to endNight
5%17%5%24%36%11%
540
July1st to 15thNight
7%12%322%40%13%
510
16th to endNight
6%16%119%45%11%
564
August1st to 15thNight
12%10%18%43%13%
527
16th to endNight
11%9%221%37%17%
678
September1st to 15thNight
9%9%421%41%13%
660
16th to endNight
17%9%6%24%32%9%
657
October1st to 15thNight
15%9%15%26%26%6%
660
16th to endNight
9%13%17%27%26%6%
704
November1st to 15thNight
9%18%19%31%19%2
700
16th to endNight
11%21%18%29%16%3
720
December1st to 15thNight
14%22%19%25%16%2
720
16th to endNight
14%23%21%29%10%
768
Page generated at 2017-08-13 14:16:16. Version ac04

Copyright 2017 A. Danko


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