Dunwoody
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Dunwoody clear sky chart from 2005-11-05 to 2017-03-15.

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
50%
14895
23%
45174
16%
14854
57%
14854
29%
27952

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%
719
23%
2327
10%
716
43%
716
23%
1444
January16th to endNight
28%
768
24%
2442
12%
768
43%
768
23%
1547
February1st to 15thNight
32%
703
26%
2112
11%
701
47%
701
27%
1296
February16th to endNight
27%
631
24%
1893
10%
631
40%
631
26%
1183
March1st to 15thNight
33%
720
23%
2067
12%
720
42%
720
29%
1303
March16th to endNight
41%
704
20%
1936
12%
704
47%
704
30%
1216
April1st to 15thNight
43%
579
26%
1732
19%
579
52%
579
32%
1025
April16th to endNight
50%
495
25%
1565
18%
495
58%
495
33%
903
May1st to 15thNight
53%
495
21%
1485
13%
495
59%
495
29%
924
May16th to endNight
65%
513
20%
1538
14%
513
69%
513
32%
940
June1st to 15thNight
74%
495
18%
1485
16%
495
75%
495
31%
923
June16th to endNight
81%
495
17%
1485
14%
495
82%
495
35%
872
July1st to 15thNight
71%
465
14%
1395
13%
465
72%
465
26%
930
July16th to endNight
73%
522
15%
1469
13%
489
74%
489
28%
957
August1st to 15thNight
73%
494
19%
1508
20%
491
73%
491
27%
972
August16th to endNight
67%
525
17%
1750
19%
525
68%
525
21%
1199
September1st to 15thNight
67%
643
20%
1798
19%
643
68%
643
27%
1210
September16th to endNight
61%
657
22%
1815
18%
657
65%
657
29%
1181
October1st to 15thNight
58%
660
32%
1818
25%
660
64%
660
37%
1078
October16th to endNight
55%
704
33%
2112
26%
704
66%
704
39%
1167
November1st to 15thNight
51%
700
30%
2266
26%
700
62%
700
36%
1221
November16th to endNight
42%
720
27%
2340
19%
720
55%
720
30%
1350
December1st to 15thNight
36%
720
23%
2340
14%
720
47%
720
26%
1431
December16th to endNight
32%
768
20%
2496
14%
768
41%
768
19%
1680

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
12%5%245%345%6%8%41%
45558
Night
12%5%2442445%7%45%
45373
TransparencyDay
38%7%12%19%17%4
45259
Night
36%6%11%19%19%6%
45176
SeeingDay
14%5%16%22%23%17%
4634
Night
14%6%22%29%23%4
14899

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%34314445%42%
1611
16th to endDay
18%6%23423446%43%
1779
February1st to 15thDay
15%6%235%145%5%7%42%
1750
16th to endDay
18%5%2443345%5%42%
1580
March1st to 15thDay
15%6%25%5%34448%41%
1891
16th to endDay
17%42433445%7%41%
1935
April1st to 15thDay
12%5%35%42345%6%45%
1895
16th to endDay
9%324434347%50%
2065
May1st to 15thDay
10%5%25%43446%9%43%
2136
16th to endDay
9%5%25%5%345%6%8%43%
2223
June1st to 15thDay
8%4246%45%5%8%11%37%
2145
16th to endDay
3214426%7%8%11%47%
2145
July1st to 15thDay
11%4247%5%8%8%8%11%28%
2145
16th to endDay
7%335%7%48%9%9%11%30%
2283
August1st to 15thDay
8%415%6%48%7%9%10%33%
2109
16th to endDay
13%6%36%7%46%6%6%9%27%
2100
September1st to 15thDay
11%7%244347%7%9%36%
1821
16th to endDay
16%5%25%42335%7%43%
1815
October1st to 15thDay
13%413223345%54%
1812
16th to endDay
11%323312235%58%
1760
November1st to 15thDay
12%5%13223345%54%
1590
16th to endDay
14%425%314445%48%
1620
December1st to 15thDay
17%6%25%5%24348%39%
1620
16th to endDay
24%8%34324335%35%
1728
January1st to 15thNight
18%6%23324336%44%
2327
16th to endNight
16%5%25%5%2335%5%44%
2442
February1st to 15thNight
15%5%14423345%48%
2103
16th to endNight
16%5%35%423346%45%
1893
March1st to 15thNight
13%5%25%32445%5%47%
2067
16th to endNight
11%5%25%5%23447%47%
1936
April1st to 15thNight
12%5%2332445%7%48%
1732
16th to endNight
10%41342346%7%50%
1565
May1st to 15thNight
9%425%5%345%6%7%46%
1484
16th to endNight
6%3245%35%46%8%47%
1538
June1st to 15thNight
5%3146%35%7%7%14%41%
1485
16th to endNight
3214435%7%8%11%45%
1485
July1st to 15thNight
6%5%25%6%47%6%7%12%34%
1485
16th to endNight
4426%6%37%7%8%11%37%
1577
August1st to 15thNight
6%4345%45%6%9%11%38%
1519
16th to endNight
12%5%26%6%35%6%8%9%33%
1750
September1st to 15thNight
9%5%25%5%46%5%6%10%38%
1798
16th to endNight
14%41443445%7%43%
1815
October1st to 15thNight
11%413323447%53%
1818
16th to endNight
10%31432333359%
2112
November1st to 15thNight
12%313313236%58%
2266
16th to endNight
14%5%23313345%51%
2340
December1st to 15thNight
13%7%24423346%45%
2340
16th to endNight
22%6%25%5%2335%7%35%
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
42%410%14%24%4
1612
16th to endDay
41%37%19%20%6%
1779
February1st to 15thDay
40%39%20%22%3
1752
16th to endDay
43%47%19%19%6%
1580
March1st to 15thDay
41%5%9%18%19%4
1891
16th to endDay
41%5%13%20%15%3
1936
April1st to 15thDay
38%410%21%19%4
1895
16th to endDay
32%5%10%24%23%4
2065
May1st to 15thDay
37%7%14%20%17%2
2136
16th to endDay
34%9%14%25%14%2
2227
June1st to 15thDay
37%10%19%24%7%1
2145
16th to endDay
26%9%19%27%14%2
2145
July1st to 15thDay
41%12%19%17%6%1
2006
16th to endDay
39%15%18%17%7%1
2128
August1st to 15thDay
39%11%18%19%9%1
2096
16th to endDay
49%11%14%15%9%
2100
September1st to 15thDay
40%11%15%16%13%2
1821
16th to endDay
40%5%11%17%20%4
1815
October1st to 15thDay
31%5%8%18%26%8%
1812
16th to endDay
29%36%17%31%11%
1760
November1st to 15thDay
31%26%16%32%9%
1590
16th to endDay
37%47%16%26%7%
1620
December1st to 15thDay
43%5%8%20%15%7%
1620
16th to endDay
51%47%16%14%5%
1728
January1st to 15thNight
41%38%17%23%5%
2327
16th to endNight
42%36%17%22%7%
2442
February1st to 15thNight
38%37%20%21%9%
2112
16th to endNight
39%46%19%23%5%
1893
March1st to 15thNight
37%5%10%19%19%8%
2067
16th to endNight
36%5%10%22%20%5%
1936
April1st to 15thNight
34%410%22%21%6%
1732
16th to endNight
31%5%9%21%21%9%
1565
May1st to 15thNight
35%7%14%20%19%2
1485
16th to endNight
32%8%13%26%15%3
1540
June1st to 15thNight
30%11%21%24%9%1
1485
16th to endNight
27%10%19%23%16%2
1485
July1st to 15thNight
37%11%19%21%7%2
1395
16th to endNight
34%12%21%19%10%1
1469
August1st to 15thNight
34%12%14%24%11%1
1508
16th to endNight
42%11%16%16%11%1
1750
September1st to 15thNight
38%10%15%17%13%4
1798
16th to endNight
38%7%11%19%16%6%
1815
October1st to 15thNight
31%5%11%16%26%8%
1818
16th to endNight
29%25%16%31%13%
2112
November1st to 15thNight
29%35%16%31%13%
2266
16th to endNight
35%36%17%27%10%
2340
December1st to 15thNight
39%410%20%18%7%
2340
16th to endNight
48%48%15%18%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
20%13%32%24%7%2
90
16th to endDay
18%22%40%12%5%
96
February1st to 15thDay
14%21%36%25%2
90
16th to endDay
22%14%39%20%2
81
March1st to 15thDay
17%14%28%30%8%1
182
16th to endDay
20%6%28%27%15%2
224
April1st to 15thDay
16%14%30%18%18%1
210
16th to endDay
13%418%32%26%3
210
May1st to 15thDay
10%7%21%27%17%14%
228
16th to endDay
13%112%21%31%20%
267
June1st to 15thDay
11%8%16%31%32%
255
16th to endDay
35%23%25%41%
255
July1st to 15thDay
12%418%27%36%
245
16th to endDay
7%412%32%42%
270
August1st to 15thDay
13%1417%33%29%
253
16th to endDay
13%27%20%29%26%
268
September1st to 15thDay
14%15%20%31%25%
255
16th to endDay
21%111%26%30%9%
254
October1st to 15thDay
15%319%26%26%8%
255
16th to endDay
13%5%18%26%28%8%
272
November1st to 15thDay
29%10%23%15%19%2
98
16th to endDay
10%10%33%23%18%4
90
December1st to 15thDay
24%12%33%18%11%
90
16th to endDay
36%11%28%18%5%
96
January1st to 15thNight
22%13%31%24%7%
720
16th to endNight
18%13%35%28%4
768
February1st to 15thNight
18%11%32%31%5%
704
16th to endNight
17%12%39%26%3
631
March1st to 15thNight
16%10%36%30%6%
720
16th to endNight
14%9%28%32%14%
704
April1st to 15thNight
16%7%29%31%14%
579
16th to endNight
12%427%34%20%1
495
May1st to 15thNight
10%325%32%25%2
495
16th to endNight
9%114%30%37%7%
515
June1st to 15thNight
8%9%33%38%10%
495
16th to endNight
28%29%44%13%
495
July1st to 15thNight
7%16%23%48%12%
465
16th to endNight
6%6%19%53%14%
522
August1st to 15thNight
7%6%23%51%11%
494
16th to endNight
13%6%26%43%9%
525
September1st to 15thNight
11%16%25%44%9%
643
16th to endNight
17%110%35%32%2
657
October1st to 15thNight
14%318%31%25%5%
660
16th to endNight
11%5%22%32%23%4
704
November1st to 15thNight
14%5%23%30%24%1
700
16th to endNight
17%8%30%28%14%
720
December1st to 15thNight
16%9%32%30%10%1
720
16th to endNight
25%10%27%29%7%
768
Page generated at 2017-03-16 11:05:29. Version ac04

Copyright 2017 A. Danko


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