North Georgia Astronomical Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the North Georgia Astronomical Observatory clear sky chart from 2005-11-05 to 2017-03-19.

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
45%
14927
23%
45211
14%
14885
55%
14885
26%
27983

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
26%
720
23%
2327
9%
716
43%
716
17%
1468
January16th to endNight
25%
768
25%
2469
10%
768
43%
768
21%
1547
February1st to 15thNight
29%
703
26%
2111
10%
701
45%
701
25%
1268
February16th to endNight
23%
631
24%
1893
9%
631
38%
631
22%
1194
March1st to 15thNight
29%
720
24%
2059
10%
720
41%
720
25%
1317
March16th to endNight
35%
720
20%
1980
10%
720
43%
720
28%
1250
April1st to 15thNight
38%
588
26%
1741
15%
588
49%
588
30%
1020
April16th to endNight
46%
495
25%
1546
16%
495
55%
495
31%
896
May1st to 15thNight
50%
495
20%
1485
11%
495
57%
495
27%
944
May16th to endNight
60%
513
19%
1539
14%
513
64%
513
31%
933
June1st to 15thNight
64%
495
15%
1485
11%
495
67%
495
28%
943
June16th to endNight
77%
495
16%
1485
13%
495
78%
495
36%
885
July1st to 15thNight
65%
465
13%
1395
11%
465
66%
465
26%
927
July16th to endNight
73%
522
15%
1469
13%
489
75%
489
29%
942
August1st to 15thNight
68%
494
19%
1477
16%
491
70%
491
29%
941
August16th to endNight
65%
525
17%
1750
18%
525
67%
525
22%
1170
September1st to 15thNight
62%
649
19%
1804
18%
649
63%
649
28%
1203
September16th to endNight
56%
657
22%
1815
16%
657
61%
657
30%
1171
October1st to 15thNight
52%
660
34%
1831
24%
660
60%
660
36%
1069
October16th to endNight
50%
704
33%
2112
24%
704
62%
704
35%
1177
November1st to 15thNight
47%
700
31%
2262
24%
700
59%
700
34%
1209
November16th to endNight
37%
720
26%
2340
16%
720
51%
720
25%
1382
December1st to 15thNight
35%
720
23%
2340
14%
720
47%
720
20%
1464
December16th to endNight
28%
768
20%
2496
11%
768
40%
768
17%
1663

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
14%5%25%5%35%5%6%7%39%
45600
Night
13%42442445%7%45%
45410
TransparencyDay
41%6%11%18%17%4
45301
Night
37%5%11%20%19%5%
45213
SeeingDay
17%7%17%22%20%14%
4658
Night
17%9%20%27%20%4
14930

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
20%6%24423345%42%
1611
16th to endDay
17%5%25%42434446%
1752
February1st to 15thDay
18%5%2332435%8%42%
1750
16th to endDay
18%5%2333435%7%41%
1580
March1st to 15thDay
18%435%425%35%7%40%
1899
16th to endDay
17%5%25%43445%6%41%
1974
April1st to 15thDay
13%5%144345%6%7%41%
1886
16th to endDay
12%415%4245%5%7%45%
2082
May1st to 15thDay
12%5%25%6%35%46%7%39%
2136
16th to endDay
12%425%5%46%5%6%9%37%
2223
June1st to 15thDay
9%426%6%47%7%7%10%32%
2145
16th to endDay
33146%49%7%8%12%38%
2145
July1st to 15thDay
12%436%8%5%8%8%8%10%24%
2145
16th to endDay
7%436%8%5%10%8%9%9%26%
2283
August1st to 15thDay
10%4146%48%8%9%10%31%
2140
16th to endDay
14%7%46%6%5%6%7%6%10%24%
2100
September1st to 15thDay
13%6%26%6%36%6%6%7%32%
1815
16th to endDay
17%5%15%435%5%5%7%39%
1815
October1st to 15thDay
13%5%13323335%54%
1798
16th to endDay
13%31341232459%
1760
November1st to 15thDay
14%313212336%55%
1593
16th to endDay
17%5%23423345%47%
1620
December1st to 15thDay
20%7%24323446%40%
1620
16th to endDay
26%5%2432343438%
1728
January1st to 15thNight
20%42432345%5%42%
2327
16th to endNight
17%5%34424346%43%
2469
February1st to 15thNight
14%423324346%48%
2103
16th to endNight
16%42442445%5%43%
1893
March1st to 15thNight
15%6%14424445%45%
2059
16th to endNight
13%425%42335%6%47%
1980
April1st to 15thNight
15%313333447%49%
1741
16th to endNight
12%425%32326%7%50%
1546
May1st to 15thNight
13%4245%15%5%7%7%41%
1484
16th to endNight
10%4135%2445%9%47%
1538
June1st to 15thNight
8%3246%35%7%8%10%39%
1485
16th to endNight
42245%25%6%9%11%45%
1485
July1st to 15thNight
8%4247%37%6%9%10%34%
1485
16th to endNight
5%4245%36%8%9%12%38%
1577
August1st to 15thNight
10%5%244345%6%11%40%
1488
16th to endNight
12%6%26%5%247%7%10%33%
1750
September1st to 15thNight
10%5%36%5%25%5%7%9%38%
1804
16th to endNight
15%415%42345%7%44%
1815
October1st to 15thNight
13%5%13322335%55%
1831
16th to endNight
11%214424335%57%
2112
November1st to 15thNight
12%423312246%57%
2262
16th to endNight
17%423323345%49%
2340
December1st to 15thNight
17%5%25%424345%42%
2340
16th to endNight
23%6%25%32345%5%36%
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
44%27%16%22%5%
1612
16th to endDay
41%36%20%20%7%
1752
February1st to 15thDay
40%38%20%23%3
1752
16th to endDay
42%37%22%18%6%
1580
March1st to 15thDay
43%48%17%20%6%
1899
16th to endDay
42%410%21%16%3
1975
April1st to 15thDay
39%410%21%18%5%
1886
16th to endDay
36%5%8%21%22%6%
2082
May1st to 15thDay
42%5%13%19%15%2
2136
16th to endDay
41%7%14%19%13%2
2227
June1st to 15thDay
41%9%19%21%6%1
2145
16th to endDay
34%9%17%22%13%2
2145
July1st to 15thDay
48%10%17%15%5%2
2006
16th to endDay
45%11%17%16%7%1
2128
August1st to 15thDay
41%10%16%21%8%1
2127
16th to endDay
50%9%14%16%8%1
2100
September1st to 15thDay
46%8%12%17%12%3
1815
16th to endDay
42%5%10%16%20%3
1815
October1st to 15thDay
32%39%17%27%9%
1798
16th to endDay
30%2419%30%11%
1760
November1st to 15thDay
31%25%17%32%10%
1593
16th to endDay
39%36%16%27%7%
1620
December1st to 15thDay
45%37%18%17%7%
1620
16th to endDay
49%37%17%15%6%
1728
January1st to 15thNight
42%37%17%22%6%
2327
16th to endNight
42%36%18%22%6%
2469
February1st to 15thNight
37%37%21%23%7%
2112
16th to endNight
40%36%21%22%4
1893
March1st to 15thNight
39%49%18%19%7%
2059
16th to endNight
38%311%23%19%3
1980
April1st to 15thNight
33%310%25%20%5%
1741
16th to endNight
33%49%22%22%7%
1546
May1st to 15thNight
38%6%15%21%16%1
1485
16th to endNight
33%7%16%28%11%3
1540
June1st to 15thNight
34%11%21%22%8%1
1485
16th to endNight
28%9%20%25%14%2
1485
July1st to 15thNight
39%9%21%18%9%1
1395
16th to endNight
33%12%21%21%9%1
1469
August1st to 15thNight
35%9%18%23%11%1
1477
16th to endNight
41%10%17%17%12%1
1750
September1st to 15thNight
39%8%16%18%13%3
1804
16th to endNight
37%6%12%21%16%5%
1815
October1st to 15thNight
32%311%18%26%8%
1831
16th to endNight
30%3419%29%12%
2112
November1st to 15thNight
29%25%19%30%12%
2262
16th to endNight
36%45%19%24%9%
2340
December1st to 15thNight
42%38%18%18%8%
2340
16th to endNight
48%38%16%17%5%
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
25%20%32%18%21
90
16th to endDay
19%31%37%8%3
96
February1st to 15thDay
22%25%36%15%
90
16th to endDay
28%19%40%8%2
81
March1st to 15thDay
26%13%27%21%9%1
189
16th to endDay
23%11%27%23%12%1
238
April1st to 15thDay
17%14%30%18%17%2
210
16th to endDay
15%8%21%25%19%9%
210
May1st to 15thDay
15%8%23%23%13%16%
228
16th to endDay
16%411%24%22%20%
267
June1st to 15thDay
13%10%25%25%24%
255
16th to endDay
3115%26%22%29%
255
July1st to 15thDay
14%28%21%26%26%
245
16th to endDay
7%2414%33%37%
270
August1st to 15thDay
18%15%19%26%28%
253
16th to endDay
20%25%21%30%20%
268
September1st to 15thDay
14%5%5%24%30%19%
255
16th to endDay
20%312%26%28%8%
254
October1st to 15thDay
18%5%21%25%21%7%
255
16th to endDay
15%7%18%27%25%5%
272
November1st to 15thDay
28%11%23%16%14%3
101
16th to endDay
17%14%31%24%10%2
90
December1st to 15thDay
28%23%21%21%5%
90
16th to endDay
39%12%31%14%11
96
January1st to 15thNight
26%19%21%24%6%
720
16th to endNight
21%16%32%25%3
768
February1st to 15thNight
19%16%30%27%5%
704
16th to endNight
20%19%33%22%3
631
March1st to 15thNight
20%14%32%25%5%
720
16th to endNight
17%12%28%29%12%
720
April1st to 15thNight
17%13%28%26%12%1
588
16th to endNight
13%8%23%31%20%2
495
May1st to 15thNight
15%6%20%31%22%4
495
16th to endNight
13%214%27%34%6%
515
June1st to 15thNight
10%13%30%33%10%
495
16th to endNight
417%32%41%12%
495
July1st to 15thNight
10%26%25%44%10%
465
16th to endNight
6%17%22%47%13%
522
August1st to 15thNight
13%17%21%41%14%
494
16th to endNight
16%6%24%40%11%
525
September1st to 15thNight
12%310%26%36%10%
649
16th to endNight
17%215%36%25%2
657
October1st to 15thNight
16%7%19%28%22%5%
660
16th to endNight
13%9%20%30%22%3
704
November1st to 15thNight
14%10%21%29%20%3
700
16th to endNight
20%14%24%26%14%
720
December1st to 15thNight
20%15%23%29%10%1
720
16th to endNight
28%11%26%25%7%
768
Page generated at 2017-03-20 08:18:34. Version ac04

Copyright 2017 A. Danko


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