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 2005-11-05 to

2017-09-12
.

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
48%
15562
24%
46875
16%
15518
57%
15518
29%
28619

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
28%
720
24%
2327
11%
716
45%
716
21%
1431
January16th to endNight
26%
768
26%
2490
11%
768
44%
768
22%
1527
February1st to 15thNight
29%
704
27%
2111
10%
700
47%
700
27%
1273
February16th to endNight
26%
631
26%
1893
9%
631
42%
631
25%
1165
March1st to 15thNight
34%
720
25%
2031
13%
720
46%
720
29%
1272
March16th to endNight
40%
768
23%
2112
12%
768
49%
768
32%
1281
April1st to 15thNight
40%
691
25%
1949
15%
691
50%
691
35%
1119
April16th to endNight
50%
540
26%
1667
17%
540
59%
540
32%
972
May1st to 15thNight
48%
540
20%
1620
10%
540
56%
540
30%
988
May16th to endNight
61%
561
22%
1682
15%
561
65%
561
32%
1013
June1st to 15thNight
67%
540
17%
1620
15%
540
68%
540
34%
982
June16th to endNight
73%
540
17%
1620
14%
540
74%
540
34%
972
July1st to 15thNight
69%
510
12%
1530
10%
510
70%
510
28%
985
July16th to endNight
73%
564
16%
1595
13%
531
75%
531
28%
1027
August1st to 15thNight
67%
539
18%
1609
18%
536
68%
536
26%
1072
August16th to endNight
65%
590
17%
1900
17%
590
66%
590
22%
1273
September1st to 15thNight
65%
707
19%
1944
17%
707
67%
707
30%
1263
September16th to endNight
56%
657
23%
1815
17%
657
61%
657
30%
1174
October1st to 15thNight
53%
660
31%
1851
25%
660
60%
660
35%
1117
October16th to endNight
54%
704
35%
2112
27%
704
66%
704
40%
1145
November1st to 15thNight
52%
700
32%
2221
25%
700
63%
700
37%
1184
November16th to endNight
41%
720
28%
2340
19%
720
54%
720
29%
1331
December1st to 15thNight
39%
720
25%
2340
17%
720
50%
720
24%
1426
December16th to endNight
33%
768
23%
2496
15%
768
44%
768
21%
1627

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%245%35%5%5%7%42%
47776
Night
12%42442445%7%46%
47075
TransparencyDay
39%5%11%20%18%5%
47477
Night
36%411%20%20%6%
46878
SeeingDay
16%5%18%23%22%12%
5427
Night
15%7%20%30%22%4
15564

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
16%6%34313446%44%
1611
16th to endDay
18%5%23313346%46%
1732
February1st to 15thDay
16%5%24433445%46%
1750
16th to endDay
17%6%33323336%46%
1580
March1st to 15thDay
16%424433346%46%
1928
16th to endDay
16%42442345%5%44%
2111
April1st to 15thDay
12%4245%3445%6%47%
2008
16th to endDay
10%42442445%8%48%
2292
May1st to 15thDay
11%425%5%3446%7%44%
2331
16th to endDay
10%425%6%46%46%9%40%
2431
June1st to 15thDay
8%4146%47%8%8%10%34%
2340
16th to endDay
42145%47%7%8%10%43%
2340
July1st to 15thDay
8%426%6%5%8%8%7%10%30%
2340
16th to endDay
7%425%6%5%8%7%10%10%30%
2465
August1st to 15thDay
9%5%26%6%5%7%6%8%10%30%
2340
16th to endDay
14%6%36%7%46%7%7%8%26%
2285
September1st to 15thDay
12%5%25%6%35%5%6%7%38%
1936
16th to endDay
18%5%24424445%42%
1815
October1st to 15thDay
14%414312235%55%
1778
16th to endDay
11%31332333459%
1760
November1st to 15thDay
11%313323345%55%
1635
16th to endDay
15%423324345%50%
1620
December1st to 15thDay
17%7%24435%34442%
1620
16th to endDay
23%8%24423345%37%
1728
January1st to 15thNight
18%6%2342334447%
2327
16th to endNight
18%5%14424345%45%
2490
February1st to 15thNight
14%423424345%50%
2103
16th to endNight
15%415%423435%48%
1893
March1st to 15thNight
13%4245%24446%47%
2031
16th to endNight
12%42342445%5%50%
2112
April1st to 15thNight
12%41331335%7%52%
1949
16th to endNight
10%42443445%7%49%
1667
May1st to 15thNight
9%5%145%35%46%7%46%
1619
16th to endNight
7%4145%35%5%8%8%45%
1682
June1st to 15thNight
6%325%436%6%8%12%40%
1620
16th to endNight
5%3145%36%7%8%10%42%
1620
July1st to 15thNight
8%336%5%25%6%9%12%35%
1620
16th to endNight
4315%7%37%7%9%12%35%
1703
August1st to 15thNight
9%5%25%6%45%6%7%12%33%
1620
16th to endNight
11%5%245%37%6%7%10%34%
1900
September1st to 15thNight
9%5%25%5%35%46%10%40%
1944
16th to endNight
15%5%244245%47%44%
1815
October1st to 15thNight
13%414323335%52%
1851
16th to endNight
10%22232343459%
2112
November1st to 15thNight
11%323322336%58%
2221
16th to endNight
15%423323345%51%
2340
December1st to 15thNight
15%6%24424345%46%
2340
16th to endNight
20%7%25%433346%39%
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%48%16%24%5%
1612
16th to endDay
40%26%20%22%8%
1732
February1st to 15thDay
41%27%21%23%4
1752
16th to endDay
40%25%22%21%7%
1580
March1st to 15thDay
39%28%21%20%7%
1928
16th to endDay
40%311%22%17%4
2112
April1st to 15thDay
37%38%22%22%6%
2008
16th to endDay
33%48%22%24%6%
2292
May1st to 15thDay
37%412%22%19%3
2331
16th to endDay
40%5%13%24%14%2
2435
June1st to 15thDay
39%8%18%22%8%1
2340
16th to endDay
31%8%17%25%15%2
2340
July1st to 15thDay
42%8%17%20%7%2
2201
16th to endDay
41%9%18%21%7%2
2310
August1st to 15thDay
44%8%14%21%10%1
2327
16th to endDay
51%8%13%15%9%1
2285
September1st to 15thDay
42%6%10%20%17%2
1936
16th to endDay
42%49%19%18%4
1815
October1st to 15thDay
33%210%19%27%6%
1778
16th to endDay
29%25%19%31%11%
1760
November1st to 15thDay
31%36%16%30%11%
1635
16th to endDay
35%36%18%28%7%
1620
December1st to 15thDay
44%37%20%15%9%
1620
16th to endDay
49%26%19%13%7%
1728
January1st to 15thNight
42%26%17%24%6%
2327
16th to endNight
41%2418%23%9%
2490
February1st to 15thNight
37%26%20%22%10%
2112
16th to endNight
39%25%20%24%7%
1893
March1st to 15thNight
38%39%17%22%9%
2031
16th to endNight
34%311%23%21%6%
2112
April1st to 15thNight
31%29%25%22%8%
1949
16th to endNight
33%49%22%21%9%
1667
May1st to 15thNight
36%5%13%21%20%3
1620
16th to endNight
33%6%14%27%14%3
1684
June1st to 15thNight
33%6%21%26%10%1
1620
16th to endNight
32%7%18%25%14%2
1620
July1st to 15thNight
37%8%23%21%8%2
1530
16th to endNight
34%11%23%19%8%2
1595
August1st to 15thNight
39%8%16%23%10%
1609
16th to endNight
42%9%17%17%12%
1900
September1st to 15thNight
38%7%15%18%16%4
1944
16th to endNight
39%5%12%19%17%6%
1815
October1st to 15thNight
35%39%18%25%8%
1851
16th to endNight
28%35%18%30%14%
2112
November1st to 15thNight
28%25%18%30%14%
2221
16th to endNight
35%25%17%27%11%
2340
December1st to 15thNight
40%37%21%18%8%
2340
16th to endNight
47%28%17%18%6%
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
24%8%38%23%4
90
16th to endDay
26%19%37%13%3
96
February1st to 15thDay
23%17%41%17%
90
16th to endDay
27%17%37%16%2
81
March1st to 15thDay
21%13%27%24%12%
218
16th to endDay
17%11%25%29%15%1
288
April1st to 15thDay
18%9%27%18%22%4
270
16th to endDay
14%5%24%25%22%5%
270
May1st to 15thDay
15%8%29%16%16%12%
288
16th to endDay
14%5%17%22%26%13%
331
June1st to 15thDay
11%38%26%27%22%
315
16th to endDay
7%114%27%23%25%
315
July1st to 15thDay
9%19%24%28%27%
305
16th to endDay
7%1423%38%25%
326
August1st to 15thDay
17%17%23%26%23%
313
16th to endDay
17%17%22%29%21%
332
September1st to 15thDay
15%29%21%36%14%
299
16th to endDay
23%114%26%25%8%
254
October1st to 15thDay
20%322%25%19%7%
255
16th to endDay
14%6%16%26%28%8%
272
November1st to 15thDay
27%6%22%25%13%4
143
16th to endDay
12%10%27%36%10%3
90
December1st to 15thDay
24%12%34%22%6%
90
16th to endDay
43%6%30%13%42
96
January1st to 15thNight
24%15%23%26%9%
720
16th to endNight
21%15%32%25%4
768
February1st to 15thNight
19%12%32%30%4
704
16th to endNight
18%15%34%26%3
631
March1st to 15thNight
17%12%31%31%7%
720
16th to endNight
15%10%28%32%12%
768
April1st to 15thNight
15%10%30%26%16%
691
16th to endNight
11%7%24%33%21%1
540
May1st to 15thNight
13%6%24%31%21%3
540
16th to endNight
10%215%32%34%4
563
June1st to 15thNight
10%12%32%33%10%
540
16th to endNight
5%9%33%39%11%
540
July1st to 15thNight
9%1428%44%11%
510
16th to endNight
5%5%30%46%11%
564
August1st to 15thNight
12%325%46%10%
539
16th to endNight
14%15%26%40%10%
590
September1st to 15thNight
12%9%23%43%10%
707
16th to endNight
17%114%32%30%3
657
October1st to 15thNight
15%420%29%26%4
660
16th to endNight
12%5%21%34%23%3
704
November1st to 15thNight
13%6%22%33%21%2
700
16th to endNight
17%12%23%29%14%2
720
December1st to 15thNight
17%10%24%32%12%1
720
16th to endNight
24%10%25%31%8%
768
Page generated at 2017-09-13 07:39:11. Version ac04

Copyright 2017 A. Danko


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