University of Georgia Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the University of Georgia Observatory clear sky chart from 2005-11-06 to 2024-01-11.

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
47%
23967
23%
74369
15%
23910
56%
23910
27%
45703

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 10thNight
24%
760
23%
2459
9%
757
42%
757
20%
1534
January11th to 20thNight
29%
724
25%
2352
12%
724
45%
724
21%
1463
January21st to endNight
25%
792
28%
2565
11%
792
45%
792
23%
1534
February1st to 10thNight
30%
720
25%
2160
12%
720
44%
720
25%
1351
February11th to 20thNight
23%
703
22%
2098
7%
699
39%
699
22%
1363
February21st to endNight
24%
592
23%
1776
9%
592
38%
592
22%
1164
March1st to 10thNight
34%
720
27%
2057
14%
720
46%
720
29%
1265
March11th to 20thNight
31%
720
21%
1980
8%
720
43%
720
27%
1265
March21st to endNight
36%
792
24%
2178
10%
792
46%
792
28%
1371
April1st to 10thNight
37%
720
25%
1980
12%
720
48%
720
33%
1178
April11th to 20thNight
44%
583
27%
1806
16%
583
56%
583
33%
1023
April21st to endNight
51%
540
31%
1620
20%
540
60%
540
36%
913
May1st to 10thNight
49%
540
23%
1620
11%
540
59%
540
34%
923
May11th to 20thNight
52%
531
16%
1592
9%
531
56%
531
27%
1018
May21st to endNight
63%
582
21%
1744
16%
582
65%
582
30%
1078
June1st to 10thNight
63%
540
16%
1620
13%
540
65%
540
30%
1019
June11th to 20thNight
69%
540
17%
1620
15%
540
70%
540
36%
952
June21st to endNight
69%
540
15%
1620
12%
540
70%
540
30%
1014
July1st to 10thNight
65%
525
12%
1575
11%
525
66%
525
25%
1048
July11th to 20thNight
71%
522
12%
1566
11%
522
72%
522
26%
1025
July21st to endNight
72%
591
15%
1672
13%
558
73%
558
28%
1091
August1st to 10thNight
68%
537
14%
1600
14%
534
68%
534
25%
1082
August11th to 20thNight
65%
534
20%
1646
19%
534
66%
534
24%
1107
August21st to endNight
60%
618
16%
2004
16%
618
61%
618
20%
1383
September1st to 10thNight
69%
720
20%
1980
18%
720
70%
720
32%
1251
September11th to 20thNight
60%
720
22%
1980
17%
720
63%
720
29%
1292
September21st to endNight
59%
720
27%
1980
20%
720
65%
720
34%
1234
October1st to 10thNight
57%
720
27%
1980
21%
720
63%
720
36%
1180
October11th to 20thNight
51%
720
31%
2128
24%
720
62%
720
35%
1238
October21st to endNight
53%
792
33%
2376
26%
792
64%
792
37%
1307
November1st to 10thNight
50%
740
30%
2316
23%
740
61%
740
35%
1277
November11th to 20thNight
42%
760
29%
2470
20%
760
56%
760
31%
1366
November21st to endNight
41%
760
27%
2470
18%
760
54%
760
28%
1452
December1st to 10thNight
35%
760
26%
2470
15%
760
49%
760
21%
1573
December11th to 20thNight
36%
759
29%
2897
17%
758
49%
758
23%
1626
December21st to endNight
29%
830
15%
4412
12%
817
41%
817
12%
2743

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%5%25%5%35%5%6%8%42%
74864
Night
13%5%25%5%345%6%7%45%
74843
TransparencyDay
40%5%11%21%19%5%
74587
Night
38%5%11%20%20%6%
74639
SeeingDay
18%8%22%23%20%10%
13870
Night
17%7%21%30%21%4
23976

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 10thDay
17%6%35%434446%45%
1706
11th to 20thDay
17%7%25%4245%46%44%
1620
21st to endDay
19%6%24424345%46%
1789
February1st to 10thDay
17%6%36%6%3445%6%41%
1800
11th to 20thDay
22%5%24324436%44%
1748
21st to endDay
20%7%35%5%34446%41%
1480
March1st to 10thDay
14%5%25%424446%50%
1902
11th to 20thDay
19%5%35%5%3445%7%41%
1980
21st to endDay
16%5%25%5%345%7%7%42%
2178
April1st to 10thDay
12%4246%35%5%6%6%48%
1980
11th to 20thDay
12%5%26%5%34447%47%
2116
21st to endDay
9%42443445%8%52%
2340
May1st to 10thDay
10%425%435%46%8%49%
2340
11th to 20thDay
11%6%36%5%46%46%7%42%
2301
21st to endDay
11%5%26%6%45%5%7%9%40%
2531
June1st to 10thDay
10%5%26%6%47%8%7%10%34%
2340
11th to 20thDay
5%4235%5%7%7%8%11%42%
2340
21st to endDay
5%427%7%5%6%8%8%10%39%
2340
July1st to 10thDay
8%5%37%7%5%8%8%8%10%31%
2340
11th to 20thDay
8%6%26%7%5%8%8%9%12%29%
2340
21st to endDay
6%5%27%6%6%8%8%10%11%32%
2547
August1st to 10thDay
9%6%37%8%5%7%7%8%11%29%
2327
11th to 20thDay
12%5%27%7%47%7%8%9%31%
2250
21st to endDay
14%7%46%8%5%6%7%7%8%30%
2332
September1st to 10thDay
11%6%25%7%46%6%6%9%39%
1980
11th to 20thDay
16%5%35%5%35%6%6%7%41%
1980
21st to endDay
15%6%24434445%48%
1980
October1st to 10thDay
13%5%2432345%6%54%
1980
11th to 20thDay
12%423423346%55%
1830
21st to endDay
12%424432345%56%
1980
November1st to 10thDay
12%42443334456%
1760
11th to 20thDay
14%42332445%7%53%
1710
21st to endDay
14%5%24425%45%6%49%
1710
December1st to 10thDay
19%8%34445%45%5%38%
1710
11th to 20thDay
18%5%25%434345%48%
2153
21st to endDay
22%7%2443345%7%39%
3124
January1st to 10thNight
19%7%2443443446%
2459
11th to 20thNight
18%6%345%25%45%6%43%
2352
21st to endNight
18%6%24423345%48%
2565
February1st to 10thNight
16%5%25%5%35%446%46%
2160
11th to 20thNight
21%5%25%42444444%
2098
21st to endNight
19%6%25%5%33346%43%
1776
March1st to 10thNight
13%6%35%424445%49%
2057
11th to 20thNight
15%5%245%345%6%7%44%
1980
21st to endNight
13%6%245%35%5%5%6%46%
2178
April1st to 10thNight
11%41442446%7%50%
1980
11th to 20thNight
13%5%2442345%8%51%
1806
21st to endNight
9%42443446%7%53%
1620
May1st to 10thNight
9%5%145%35%47%8%50%
1620
11th to 20thNight
10%5%26%6%46%5%7%7%42%
1592
21st to endNight
10%5%25%5%35%5%7%10%43%
1744
June1st to 10thNight
7%436%6%46%6%8%13%37%
1620
11th to 20thNight
5%425%5%36%7%8%11%44%
1620
21st to endNight
7%425%6%46%7%8%11%40%
1620
July1st to 10thNight
9%5%37%6%36%6%9%12%33%
1620
11th to 20thNight
6%436%8%46%7%9%13%34%
1620
21st to endNight
5%5%26%6%48%8%10%13%34%
1771
August1st to 10thNight
8%5%27%7%46%7%8%14%32%
1611
11th to 20thNight
12%5%25%6%46%6%7%11%34%
1646
21st to endNight
13%7%36%7%46%7%7%8%33%
2004
September1st to 10thNight
9%5%26%5%45%5%7%11%42%
1980
11th to 20thNight
13%7%245%35%5%6%7%43%
1980
21st to endNight
12%5%24435%5%5%7%48%
1980
October1st to 10thNight
12%5%244345%46%53%
1980
11th to 20thNight
12%4245%3444455%
2128
21st to endNight
12%423333445%58%
2376
November1st to 10thNight
13%5%23323346%57%
2316
11th to 20thNight
15%423423346%53%
2470
21st to endNight
16%42343445%6%48%
2470
December1st to 10thNight
17%6%35%5%3445%5%43%
2470
11th to 20thNight
17%6%14423345%51%
3042
21st to endNight
19%7%36%6%3445%6%36%
4532

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 10thDay
42%47%19%23%6%
1707
11th to 20thDay
41%38%20%22%6%
1620
21st to endDay
42%25%21%23%8%
1789
February1st to 10thDay
46%37%19%19%6%
1800
11th to 20thDay
44%36%19%22%6%
1758
21st to endDay
45%47%16%19%9%
1480
March1st to 10thDay
37%38%19%23%10%
1902
11th to 20thDay
44%39%19%17%7%
1980
21st to endDay
41%410%22%18%4
2178
April1st to 10thDay
37%49%22%23%6%
1980
11th to 20thDay
37%47%20%23%9%
2116
21st to endDay
31%49%28%24%4
2340
May1st to 10thDay
33%412%24%23%4
2340
11th to 20thDay
41%416%22%15%2
2305
21st to endDay
39%6%11%25%17%2
2531
June1st to 10thDay
42%8%17%21%10%2
2340
11th to 20thDay
33%8%20%26%13%1
2340
21st to endDay
36%8%18%22%12%4
2340
July1st to 10thDay
43%9%18%19%8%3
2275
11th to 20thDay
43%10%21%17%7%3
2271
21st to endDay
40%9%20%22%9%1
2405
August1st to 10thDay
45%10%17%22%6%
2314
11th to 20thDay
44%8%18%17%10%2
2250
21st to endDay
50%7%14%17%10%2
2332
September1st to 10thDay
40%7%13%18%18%4
1980
11th to 20thDay
42%6%9%19%23%2
1980
21st to endDay
38%48%23%20%7%
1980
October1st to 10thDay
32%410%21%28%7%
1980
11th to 20thDay
32%37%24%26%8%
1830
21st to endDay
31%35%18%31%11%
1980
November1st to 10thDay
32%38%15%30%12%
1760
11th to 20thDay
32%37%21%27%10%
1710
21st to endDay
36%47%21%25%7%
1710
December1st to 10thDay
47%46%19%16%7%
1710
11th to 20thDay
41%36%17%24%10%
2150
21st to endDay
44%47%21%22%3
3124
January1st to 10thNight
43%36%18%24%6%
2459
11th to 20thNight
43%37%20%21%7%
2352
21st to endNight
40%2420%25%8%
2565
February1st to 10thNight
40%38%20%20%8%
2160
11th to 20thNight
44%35%19%22%8%
2099
21st to endNight
45%37%16%20%9%
1776
March1st to 10thNight
38%28%17%23%12%
2057
11th to 20thNight
39%412%15%22%7%
1980
21st to endNight
38%49%22%21%6%
2178
April1st to 10thNight
33%411%21%23%8%
1980
11th to 20thNight
32%37%23%24%11%
1806
21st to endNight
30%410%26%24%6%
1620
May1st to 10thNight
31%5%14%23%23%5%
1620
11th to 20thNight
39%7%15%20%17%2
1593
21st to endNight
36%7%12%26%16%3
1745
June1st to 10thNight
37%7%20%22%13%2
1620
11th to 20thNight
31%7%20%28%12%2
1620
21st to endNight
35%8%20%20%12%3
1620
July1st to 10thNight
41%9%22%18%9%2
1575
11th to 20thNight
37%11%24%17%8%2
1566
21st to endNight
34%12%24%21%7%1
1672
August1st to 10thNight
40%10%20%23%6%
1600
11th to 20thNight
41%9%17%18%13%1
1646
21st to endNight
46%9%16%17%10%2
2004
September1st to 10thNight
36%6%17%18%18%4
1980
11th to 20thNight
39%7%12%19%20%4
1980
21st to endNight
36%5%12%19%21%7%
1980
October1st to 10thNight
34%310%19%27%7%
1980
11th to 20thNight
33%47%22%25%10%
2128
21st to endNight
29%35%19%30%14%
2376
November1st to 10thNight
31%37%19%27%14%
2316
11th to 20thNight
33%36%18%26%14%
2470
21st to endNight
38%26%20%26%8%
2470
December1st to 10thNight
43%47%21%19%6%
2470
11th to 20thNight
37%27%18%28%8%
3044
21st to endNight
48%46%21%18%3
4532

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 10thDay
26%19%39%13%3
270
11th to 20thDay
29%15%30%20%6%
240
21st to endDay
30%17%37%13%3
264
February1st to 10thDay
25%17%37%18%4
240
11th to 20thDay
39%17%34%10%1
240
21st to endDay
32%19%35%12%2
198
March1st to 10thDay
22%14%33%22%9%
342
11th to 20thDay
26%15%32%18%7%1
420
21st to endDay
21%16%31%23%9%
462
April1st to 10thDay
21%11%31%22%14%1
420
11th to 20thDay
15%16%29%22%16%3
412
21st to endDay
18%9%27%24%18%4
420
May1st to 10thDay
14%11%32%22%13%7%
423
11th to 20thDay
15%421%29%21%10%
447
21st to endDay
15%5%14%27%26%13%
485
June1st to 10thDay
13%313%29%28%14%
450
11th to 20thDay
8%316%28%24%21%
450
21st to endDay
8%317%30%26%16%
450
July1st to 10thDay
11%27%22%30%28%
445
11th to 20thDay
12%25%22%35%25%
444
21st to endDay
7%27%25%38%23%
488
August1st to 10thDay
15%211%23%26%22%
446
11th to 20thDay
14%26%21%36%20%
439
21st to endDay
17%26%23%31%21%
495
September1st to 10thDay
12%29%28%34%15%
450
11th to 20thDay
20%210%23%31%14%
450
21st to endDay
18%315%26%29%10%
450
October1st to 10thDay
18%420%30%19%10%
450
11th to 20thDay
14%7%26%24%23%6%
450
21st to endDay
17%7%24%27%20%4
495
November1st to 10thDay
20%5%27%28%16%3
358
11th to 20thDay
20%11%38%24%6%1
270
21st to endDay
13%14%33%27%10%2
270
December1st to 10thDay
30%12%32%22%3
270
11th to 20thDay
27%10%37%17%7%1
270
21st to endDay
34%14%27%16%5%2
297
January1st to 10thNight
25%15%28%24%6%1
760
11th to 20thNight
23%14%29%25%9%
724
21st to endNight
22%16%34%25%3
792
February1st to 10thNight
20%13%31%30%5%
720
11th to 20thNight
25%15%32%24%3
703
21st to endNight
23%12%35%27%3
592
March1st to 10thNight
18%13%31%34%5%
720
11th to 20thNight
18%11%33%27%10%1
720
21st to endNight
17%13%29%31%10%
792
April1st to 10thNight
16%13%31%27%13%
720
11th to 20thNight
15%10%27%31%16%1
583
21st to endNight
11%7%25%35%21%1
540
May1st to 10thNight
11%8%25%34%21%1
540
11th to 20thNight
13%5%19%34%24%5%
531
21st to endNight
14%112%34%34%5%
584
June1st to 10thNight
11%114%36%32%6%
540
11th to 20thNight
6%211%32%36%12%
540
21st to endNight
8%110%37%34%9%
540
July1st to 10thNight
13%2426%42%13%
525
11th to 20thNight
7%1426%49%13%
522
21st to endNight
7%15%31%46%9%
591
August1st to 10thNight
11%428%45%11%
537
11th to 20thNight
14%2427%42%11%
534
21st to endNight
17%16%26%40%10%
618
September1st to 10thNight
11%18%27%42%11%
720
11th to 20thNight
19%110%27%39%5%
720
21st to endNight
16%213%32%34%4
720
October1st to 10thNight
15%318%32%26%6%
720
11th to 20thNight
15%5%23%34%21%3
720
21st to endNight
14%7%21%34%21%3
792
November1st to 10thNight
16%6%22%33%21%2
740
11th to 20thNight
18%10%25%33%13%1
760
21st to endNight
18%10%25%31%14%2
760
December1st to 10thNight
21%11%24%34%9%1
760
11th to 20thNight
21%11%27%30%10%1
760
21st to endNight
28%10%27%29%7%
836
Page generated at 2024-01-08 11:14:21. Version ac07

Copyright 2024 Attilla Danko


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