Georgia Shore Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Georgia Shore Observatory clear sky chart from 2005-11-05 to 2017-12-20.

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
24%
15068
12%
48039
7%
15037
31%
15037
13%
35489

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
10%
720
7%
2506
3%
716
14%
716
5%
2078
January16th to endNight
16%
768
9%
2688
5%
768
22%
768
7%
2117
February1st to 15thNight
13%
704
7%
2286
3%
701
19%
701
6%
1929
February16th to endNight
19%
631
10%
1893
5%
631
26%
631
9%
1515
March1st to 15thNight
19%
720
12%
2160
7%
720
26%
720
11%
1658
March16th to endNight
22%
768
19%
2003
7%
768
30%
768
15%
1488
April1st to 15thNight
18%
718
15%
1796
4%
718
23%
718
13%
1397
April16th to endNight
21%
616
16%
1696
4%
616
29%
616
15%
1207
May1st to 15thNight
23%
435
18%
1515
10%
435
34%
435
14%
1012
May16th to endNight
29%
374
13%
1497
9%
374
41%
374
14%
988
June1st to 15thNight
26%
360
9%
1440
7%
360
35%
360
11%
1018
June16th to endNight
35%
360
9%
1440
9%
360
42%
360
18%
916
July1st to 15thNight
41%
340
12%
1360
15%
340
47%
340
21%
815
July16th to endNight
47%
376
13%
1418
16%
354
55%
354
20%
854
August1st to 15thNight
45%
392
14%
1463
13%
390
50%
390
20%
912
August16th to endNight
49%
753
20%
1899
10%
753
52%
753
33%
1211
September1st to 15thNight
43%
720
15%
1806
7%
720
46%
720
29%
1206
September16th to endNight
42%
717
23%
1980
16%
717
47%
717
30%
1244
October1st to 15thNight
27%
720
16%
2094
10%
720
34%
720
18%
1479
October16th to endNight
20%
768
10%
2470
6%
768
27%
768
11%
1919
November1st to 15thNight
20%
760
15%
2472
10%
760
27%
760
12%
1821
November16th to endNight
18%
780
11%
2672
6%
780
25%
780
8%
2072
December1st to 15thNight
10%
780
5%
2730
2%
780
14%
780
4%
2303
December16th to endNight
11%
788
6%
2755
3%
788
15%
788
4%
2330

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
18%9%36%5%34446%30%
48808
Night
19%11%47%5%34445%29%
48209
Cloud CoverDay
19%9%36%5%35%446%30%
48818
Night
20%11%47%5%24445%28%
48214
TransparencyDay
55%310%20%9%
48496
Night
58%310%18%8%
48039
SeeingDay
24%19%25%18%9%3
5929
Night
23%24%21%20%9%1
15069

By Month

Percentage Cloud Cover NE (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
18%17%7%10%7%37%33415%
1432
16th to endDay
13%15%6%11%7%26%5%5%6%20%
1536
February1st to 15thDay
14%13%6%13%9%5%6%43418%
1573
16th to endDay
15%16%7%10%7%34335%22%
1580
March1st to 15thDay
17%14%5%8%7%35%335%24%
1790
16th to endDay
20%10%5%7%423345%32%
2218
April1st to 15thDay
21%11%36%433345%30%
2152
16th to endDay
20%7%36%434346%36%
2262
May1st to 15thDay
21%6%26%5%3445%7%31%
2445
16th to endDay
19%6%246%345%6%7%33%
2618
June1st to 15thDay
25%6%25%4245%6%7%27%
2520
16th to endDay
18%5%25%6%35%5%6%8%31%
2520
July1st to 15thDay
13%5%26%5%36%46%8%36%
2520
16th to endDay
13%5%25%5%36%6%6%10%35%
2654
August1st to 15thDay
13%6%27%6%345%6%8%33%
2474
16th to endDay
11%5%15%4345%6%8%44%
2300
September1st to 15thDay
19%6%14422346%43%
2154
16th to endDay
14%424324447%47%
1980
October1st to 15thDay
22%8%36%43445%5%32%
1866
16th to endDay
26%12%36%42443425%
1752
November1st to 15thDay
20%12%37%5%24446%28%
1716
16th to endDay
19%12%5%9%5%35%5%4424%
1618
December1st to 15thDay
23%17%5%7%7%35%33417%
1560
16th to endDay
25%18%6%8%8%2432413%
1568
January1st to 15thNight
18%17%7%11%6%35%43416%
2506
16th to endNight
14%16%6%9%7%35%44421%
2688
February1st to 15thNight
15%15%8%15%8%4433316%
2285
16th to endNight
16%15%7%10%6%2443422%
1893
March1st to 15thNight
22%13%6%7%6%2233328%
2147
16th to endNight
19%11%5%7%5%2323433%
2003
April1st to 15thNight
24%12%5%6%5%23335%27%
1796
16th to endNight
21%9%35%5%2334436%
1696
May1st to 15thNight
21%8%35%5%23337%33%
1515
16th to endNight
20%425%5%345%5%7%34%
1495
June1st to 15thNight
26%7%36%42445%7%28%
1440
16th to endNight
18%6%25%4245%7%8%35%
1440
July1st to 15thNight
11%5%25%6%35%47%9%37%
1440
16th to endNight
14%425%435%5%7%8%38%
1514
August1st to 15thNight
12%5%26%6%345%5%9%37%
1473
16th to endNight
12%423425%448%47%
1899
September1st to 15thNight
17%424433346%42%
1806
16th to endNight
17%42431335%5%47%
1980
October1st to 15thNight
22%7%25%5%23335%35%
2094
16th to endNight
28%10%36%6%2343424%
2470
November1st to 15thNight
22%11%37%5%23336%28%
2472
16th to endNight
22%14%5%8%5%25%34424%
2672
December1st to 15thNight
22%18%6%10%6%3433415%
2730
16th to endNight
22%20%6%10%6%3433314%
2755

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
18%17%6%11%8%37%33415%
1432
16th to endDay
13%16%6%11%7%35%5%46%19%
1536
February1st to 15thDay
15%13%6%12%9%5%6%43417%
1573
16th to endDay
15%16%7%10%7%34335%22%
1580
March1st to 15thDay
18%15%5%8%6%35%33424%
1800
16th to endDay
20%12%47%5%23235%32%
2218
April1st to 15thDay
22%12%35%5%33345%30%
2152
16th to endDay
21%9%35%5%24336%35%
2262
May1st to 15thDay
22%7%26%5%25%447%30%
2445
16th to endDay
20%5%25%5%35%5%5%8%32%
2618
June1st to 15thDay
27%6%25%425%46%7%26%
2520
16th to endDay
20%5%25%5%36%5%6%8%32%
2520
July1st to 15thDay
13%5%25%5%35%5%5%9%35%
2520
16th to endDay
14%5%245%35%6%7%9%34%
2654
August1st to 15thDay
15%5%27%5%45%5%7%7%33%
2474
16th to endDay
12%425%4345%6%8%43%
2300
September1st to 15thDay
20%7%13413346%41%
2154
16th to endDay
14%424434447%47%
1980
October1st to 15thDay
23%9%35%334446%31%
1866
16th to endDay
26%13%35%434335%25%
1752
November1st to 15thDay
21%13%47%424445%28%
1716
16th to endDay
20%14%6%8%5%3444424%
1618
December1st to 15thDay
23%17%6%8%7%2433417%
1560
16th to endDay
25%19%7%8%7%3333413%
1568
January1st to 15thNight
18%18%7%12%5%35%34415%
2506
16th to endNight
14%16%6%10%7%35%5%4421%
2688
February1st to 15thNight
15%15%7%15%9%4433316%
2278
16th to endNight
16%17%6%10%6%2434322%
1893
March1st to 15thNight
23%14%5%7%6%2323328%
2160
16th to endNight
19%12%5%6%5%2223433%
2002
April1st to 15thNight
24%13%5%6%424335%27%
1796
16th to endNight
22%9%26%42334436%
1696
May1st to 15thNight
22%8%25%423346%34%
1515
16th to endNight
20%5%15%5%35%5%6%6%34%
1495
June1st to 15thNight
27%6%35%43345%7%28%
1440
16th to endNight
19%5%244246%5%8%35%
1440
July1st to 15thNight
12%425%6%35%5%6%10%36%
1440
16th to endNight
14%5%25%5%25%5%7%9%37%
1514
August1st to 15thNight
13%6%25%5%245%5%9%37%
1473
16th to endNight
13%5%14424448%46%
1899
September1st to 15thNight
18%5%145%2335%6%42%
1806
16th to endNight
18%42332335%6%46%
1980
October1st to 15thNight
23%7%35%423336%34%
2094
16th to endNight
30%10%26%6%3334424%
2470
November1st to 15thNight
22%12%46%5%23346%28%
2472
16th to endNight
22%15%48%42334423%
2672
December1st to 15thNight
23%19%7%10%6%2433315%
2730
16th to endNight
22%22%6%9%5%3433314%
2755

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
74%36%11%3
1433
16th to endDay
65%312%12%5%
1536
February1st to 15thDay
71%36%14%3
1576
16th to endDay
66%29%11%8%1
1580
March1st to 15thDay
64%29%14%7%1
1800
16th to endDay
56%27%17%12%2
2218
April1st to 15thDay
57%26%19%11%1
2152
16th to endDay
51%38%20%12%3
2262
May1st to 15thDay
52%38%20%13%
2445
16th to endDay
49%410%21%11%1
2622
June1st to 15thDay
55%411%19%8%
2520
16th to endDay
49%5%10%23%9%
2520
July1st to 15thDay
43%5%12%27%10%
2371
16th to endDay
45%5%14%25%8%
2487
August1st to 15thDay
47%5%16%21%7%
2460
16th to endDay
38%413%29%14%
2300
September1st to 15thDay
43%39%29%12%
2154
16th to endDay
37%313%31%12%1
1980
October1st to 15thDay
53%310%22%9%
1866
16th to endDay
62%311%16%5%
1752
November1st to 15thDay
58%312%17%7%1
1716
16th to endDay
64%310%13%7%
1618
December1st to 15thDay
71%311%10%2
1560
16th to endDay
77%37%6%5%
1568
January1st to 15thNight
72%39%10%3
2506
16th to endNight
66%38%13%6%
2688
February1st to 15thNight
73%36%11%4
2286
16th to endNight
66%28%12%8%
1893
March1st to 15thNight
62%28%18%7%1
2160
16th to endNight
56%27%17%14%2
2003
April1st to 15thNight
60%25%17%12%1
1796
16th to endNight
52%27%18%16%2
1696
May1st to 15thNight
51%25%19%17%3
1515
16th to endNight
48%5%10%21%11%1
1497
June1st to 15thNight
56%49%20%8%
1440
16th to endNight
45%412%23%11%
1440
July1st to 15thNight
40%5%15%26%11%
1360
16th to endNight
41%5%15%24%12%
1418
August1st to 15thNight
43%417%23%10%
1463
16th to endNight
36%314%30%14%
1899
September1st to 15thNight
41%313%30%10%1
1806
16th to endNight
38%311%32%13%1
1980
October1st to 15thNight
51%310%23%10%
2094
16th to endNight
63%310%16%5%
2470
November1st to 15thNight
58%311%16%8%2
2472
16th to endNight
64%310%15%5%
2672
December1st to 15thNight
75%28%10%1
2730
16th to endNight
76%28%8%3
2755

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
20%25%31%15%6%1
60
16th to endDay
32%21%25%15%4
64
February1st to 15thDay
25%27%32%10%4
115
16th to endDay
22%32%25%14%5%
239
March1st to 15thDay
29%27%20%18%3
270
16th to endDay
27%30%18%13%7%2
288
April1st to 15thDay
28%25%24%16%31
270
16th to endDay
25%27%23%14%6%3
270
May1st to 15thDay
32%18%24%15%6%3
288
16th to endDay
18%23%29%17%8%1
331
June1st to 15thDay
32%16%26%18%6%
315
16th to endDay
20%17%33%20%6%1
315
July1st to 15thDay
17%13%28%27%9%3
305
16th to endDay
17%13%26%30%10%2
326
August1st to 15thDay
18%11%25%25%15%4
313
16th to endDay
15%11%22%24%17%8%
332
September1st to 15thDay
20%12%23%18%16%9%
315
16th to endDay
13%14%20%20%20%10%
314
October1st to 15thDay
25%16%22%15%16%3
315
16th to endDay
32%19%24%15%7%
294
November1st to 15thDay
28%21%26%11%11%1
280
16th to endDay
27%28%20%13%8%1
148
December1st to 15thDay
31%23%25%15%31
90
16th to endDay
45%18%31%4
72
January1st to 15thNight
21%33%26%15%3
720
16th to endNight
22%32%19%20%4
768
February1st to 15thNight
21%27%27%20%3
704
16th to endNight
22%30%21%19%6%
631
March1st to 15thNight
28%28%18%20%3
720
16th to endNight
24%28%19%19%7%
768
April1st to 15thNight
26%27%22%19%4
718
16th to endNight
23%30%21%16%7%
616
May1st to 15thNight
24%23%23%18%9%1
435
16th to endNight
16%22%26%24%8%1
375
June1st to 15thNight
24%21%20%25%8%
360
16th to endNight
19%18%22%26%12%
360
July1st to 15thNight
11%15%25%27%18%2
340
16th to endNight
14%18%13%40%13%
376
August1st to 15thNight
15%11%18%33%18%2
392
16th to endNight
14%11%17%30%22%2
753
September1st to 15thNight
19%13%19%28%17%2
720
16th to endNight
19%12%22%19%21%4
717
October1st to 15thNight
24%17%24%20%11%1
720
16th to endNight
30%20%22%19%6%
768
November1st to 15thNight
25%25%23%16%7%1
760
16th to endNight
27%31%16%14%7%
780
December1st to 15thNight
31%30%20%12%4
780
16th to endNight
31%30%17%15%3
788
Page generated at 2017-12-21 07:04:50. Version ac04

Copyright 2017 A. Danko


Georgia Shore Observatory Clear Sky Chart |Charts Home