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 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
46%
16103
23%
48795
15%
16061
55%
16061
27%
30127

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%
780
22%
2522
9%
776
43%
776
18%
1582
January16th to endNight
26%
832
26%
2675
11%
832
44%
832
21%
1655
February1st to 15thNight
28%
759
25%
2279
10%
757
44%
757
24%
1400
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
36%
768
20%
2112
10%
768
44%
768
28%
1338
April1st to 15thNight
39%
641
25%
1899
14%
641
50%
641
32%
1088
April16th to endNight
48%
540
25%
1686
17%
540
57%
540
31%
985
May1st to 15thNight
50%
540
19%
1620
11%
540
57%
540
27%
1016
May16th to endNight
60%
561
20%
1683
14%
561
64%
561
30%
1024
June1st to 15thNight
64%
540
14%
1620
10%
540
67%
540
28%
1039
June16th to endNight
75%
540
16%
1620
13%
540
77%
540
34%
984
July1st to 15thNight
67%
510
13%
1530
11%
510
68%
510
27%
996
July16th to endNight
72%
564
17%
1595
14%
531
75%
531
29%
1020
August1st to 15thNight
67%
539
17%
1612
16%
536
69%
536
27%
1048
August16th to endNight
66%
573
19%
1910
20%
573
68%
573
23%
1260
September1st to 15thNight
61%
708
19%
1968
17%
708
62%
708
28%
1304
September16th to endNight
59%
717
25%
1980
19%
717
64%
717
32%
1244
October1st to 15thNight
52%
720
32%
1998
24%
720
60%
720
36%
1170
October16th to endNight
49%
768
35%
2304
25%
768
63%
768
35%
1270
November1st to 15thNight
48%
760
30%
2456
23%
760
59%
760
33%
1338
November16th to endNight
40%
780
28%
2535
18%
780
53%
780
27%
1463
December1st to 15thNight
35%
780
23%
2535
13%
780
48%
780
20%
1587
December16th to endNight
28%
832
21%
2704
11%
832
40%
832
17%
1805

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%
49272
Night
13%42442445%7%45%
48994
TransparencyDay
41%6%11%19%17%4
48973
Night
37%5%11%20%19%5%
48797
SeeingDay
17%7%18%22%19%12%
5873
Night
16%9%20%27%21%4
16106

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%2442334443%
1746
16th to endDay
17%5%2442434447%
1898
February1st to 15thDay
19%5%2322345%8%41%
1883
16th to endDay
18%5%2333435%7%41%
1580
March1st to 15thDay
18%435%425%35%7%40%
1899
16th to endDay
16%5%25%43445%6%41%
2111
April1st to 15thDay
13%5%144345%6%6%42%
2058
16th to endDay
13%415%4245%5%7%44%
2272
May1st to 15thDay
12%5%25%6%35%45%7%41%
2331
16th to endDay
12%425%6%46%5%6%9%36%
2431
June1st to 15thDay
9%5%27%7%47%7%7%9%31%
2340
16th to endDay
5%3146%38%7%8%12%37%
2340
July1st to 15thDay
11%436%8%5%8%8%9%10%25%
2340
16th to endDay
7%436%8%5%9%8%9%9%27%
2465
August1st to 15thDay
11%5%25%6%47%8%8%10%30%
2334
16th to endDay
13%7%36%5%5%6%7%7%10%25%
2292
September1st to 15thDay
14%6%25%6%35%6%6%7%34%
1980
16th to endDay
15%415%4345%5%7%41%
1980
October1st to 15thDay
13%5%13323335%54%
1961
16th to endDay
13%31341232459%
1920
November1st to 15thDay
14%413312336%53%
1729
16th to endDay
16%5%23423345%48%
1755
December1st to 15thDay
20%7%23323345%41%
1755
16th to endDay
26%6%2442343437%
1872
January1st to 15thNight
19%42432345%5%43%
2522
16th to endNight
17%5%34424345%45%
2675
February1st to 15thNight
16%423424345%47%
2271
16th to endNight
16%42442445%5%43%
1893
March1st to 15thNight
15%6%14424445%45%
2059
16th to endNight
13%5%25%42335%6%47%
2112
April1st to 15thNight
14%313333447%51%
1899
16th to endNight
11%425%32435%7%49%
1686
May1st to 15thNight
12%4245%15%5%6%7%43%
1619
16th to endNight
10%4135%3436%9%46%
1682
June1st to 15thNight
8%3246%35%7%8%10%38%
1620
16th to endNight
5%3145%36%6%9%11%43%
1620
July1st to 15thNight
8%4246%37%6%9%10%35%
1620
16th to endNight
5%4245%36%7%9%12%38%
1703
August1st to 15thNight
10%5%345%346%6%10%39%
1623
16th to endNight
12%6%25%5%25%6%7%10%34%
1910
September1st to 15thNight
10%5%36%5%245%7%8%39%
1968
16th to endNight
13%41442345%7%47%
1980
October1st to 15thNight
13%5%13322335%55%
1998
16th to endNight
10%214413335%58%
2304
November1st to 15thNight
12%423312247%55%
2456
16th to endNight
16%423323345%51%
2535
December1st to 15thNight
17%5%24424345%42%
2535
16th to endNight
23%6%25%32345%5%35%
2704

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%
1747
16th to endDay
40%26%20%20%8%
1898
February1st to 15thDay
41%38%20%22%3
1885
16th to endDay
42%37%22%18%6%
1580
March1st to 15thDay
43%48%17%20%6%
1899
16th to endDay
42%5%11%21%16%3
2112
April1st to 15thDay
38%410%21%18%5%
2058
16th to endDay
36%6%9%21%21%5%
2272
May1st to 15thDay
41%5%12%20%16%3
2331
16th to endDay
41%8%14%19%13%2
2435
June1st to 15thDay
42%9%19%20%6%1
2340
16th to endDay
36%9%16%21%13%2
2340
July1st to 15thDay
46%10%18%16%5%2
2201
16th to endDay
44%11%17%16%8%1
2310
August1st to 15thDay
43%10%16%20%8%1
2321
16th to endDay
49%9%14%17%8%1
2292
September1st to 15thDay
45%8%12%17%13%3
1980
16th to endDay
40%5%10%17%21%3
1980
October1st to 15thDay
32%39%17%27%8%
1961
16th to endDay
30%2419%30%12%
1920
November1st to 15thDay
32%36%16%31%10%
1729
16th to endDay
37%36%15%28%8%
1755
December1st to 15thDay
44%37%18%19%7%
1755
16th to endDay
50%37%17%14%5%
1872
January1st to 15thNight
42%37%17%22%6%
2522
16th to endNight
41%36%18%23%7%
2675
February1st to 15thNight
39%36%21%22%6%
2280
16th to endNight
40%36%21%22%4
1893
March1st to 15thNight
39%49%18%19%7%
2059
16th to endNight
38%411%24%18%2
2112
April1st to 15thNight
32%311%25%21%5%
1899
16th to endNight
33%410%23%21%6%
1686
May1st to 15thNight
36%7%14%21%18%1
1620
16th to endNight
33%7%15%27%12%2
1684
June1st to 15thNight
34%11%21%21%9%1
1620
16th to endNight
30%9%20%24%13%2
1620
July1st to 15thNight
37%9%23%19%9%1
1530
16th to endNight
32%11%20%21%9%2
1595
August1st to 15thNight
37%9%18%22%11%1
1612
16th to endNight
40%10%16%19%12%1
1910
September1st to 15thNight
39%7%15%18%15%3
1968
16th to endNight
35%6%12%22%17%4
1980
October1st to 15thNight
32%310%19%26%7%
1998
16th to endNight
29%3419%29%12%
2304
November1st to 15thNight
30%36%19%28%11%
2456
16th to endNight
35%35%19%25%9%
2535
December1st to 15thNight
42%38%18%18%8%
2535
16th to endNight
49%38%16%16%5%
2704

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%34%14%4
135
16th to endDay
22%28%30%13%4
144
February1st to 15thDay
25%22%36%15%
130
16th to endDay
28%19%40%8%2
81
March1st to 15thDay
26%13%27%21%9%1
189
16th to endDay
22%11%29%23%11%1
288
April1st to 15thDay
18%12%26%22%16%2
270
16th to endDay
16%7%21%26%20%7%
270
May1st to 15thDay
17%7%25%20%14%13%
288
16th to endDay
17%6%12%25%19%17%
331
June1st to 15thDay
12%11%25%26%22%
315
16th to endDay
9%117%25%20%25%
315
July1st to 15thDay
11%19%22%28%25%
305
16th to endDay
7%16%17%34%33%
326
August1st to 15thDay
20%27%20%25%24%
313
16th to endDay
18%27%21%30%19%
332
September1st to 15thDay
15%5%10%24%27%16%
315
16th to endDay
16%212%26%30%11%
314
October1st to 15thDay
17%421%27%21%7%
315
16th to endDay
15%8%19%27%23%4
336
November1st to 15thDay
27%10%21%23%13%2
147
16th to endDay
12%14%33%25%11%2
135
December1st to 15thDay
28%18%25%21%5%
135
16th to endDay
35%16%33%13%
144
January1st to 15thNight
26%20%22%24%7%
780
16th to endNight
22%16%30%25%4
832
February1st to 15thNight
21%16%29%27%5%
760
16th to endNight
20%19%33%22%3
631
March1st to 15thNight
20%14%32%25%5%
720
16th to endNight
17%11%28%29%12%
768
April1st to 15thNight
16%13%27%26%14%1
641
16th to endNight
13%7%22%32%21%2
540
May1st to 15thNight
14%7%20%32%21%4
540
16th to endNight
14%213%29%33%6%
563
June1st to 15thNight
10%13%28%35%11%
540
16th to endNight
5%18%32%39%12%
540
July1st to 15thNight
10%16%24%45%12%
510
16th to endNight
6%18%22%48%13%
564
August1st to 15thNight
14%17%21%41%13%
539
16th to endNight
15%6%23%41%11%
573
September1st to 15thNight
13%311%25%35%10%
708
16th to endNight
15%214%35%28%3
717
October1st to 15thNight
16%6%19%28%23%5%
720
16th to endNight
13%10%20%29%22%3
768
November1st to 15thNight
15%9%21%29%20%3
760
16th to endNight
19%13%23%27%15%
780
December1st to 15thNight
20%15%23%28%10%1
780
16th to endNight
28%11%27%25%6%
832
Page generated at 2018-02-15 10:58:48. Version ac04

Copyright 2018 A. Danko


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