Emory University Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Emory University Observatory clear sky chart from 2005-11-06 to 2024-11-04.

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%
24731
21%
96006
16%
24459
56%
24459
23%
57478

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%
755
23%
4005
10%
737
40%
737
14%
2294
January11th to 20thNight
29%
756
28%
3932
11%
740
44%
740
15%
2154
January21st to endNight
25%
833
19%
4315
12%
814
44%
814
14%
2770
February1st to 10thNight
34%
760
25%
2280
14%
760
45%
760
26%
1458
February11th to 20thNight
24%
742
21%
2218
7%
739
37%
739
23%
1457
February21st to endNight
24%
628
21%
1884
9%
628
35%
628
22%
1238
March1st to 10thNight
33%
757
20%
3626
13%
745
43%
745
16%
2394
March11th to 20thNight
31%
754
27%
3413
10%
740
42%
740
22%
1673
March21st to endNight
38%
832
17%
3706
12%
814
46%
814
19%
2226
April1st to 10thNight
41%
720
25%
2050
15%
720
51%
720
32%
1230
April11th to 20thNight
42%
563
26%
1875
17%
563
55%
563
31%
1062
April21st to endNight
53%
570
28%
1755
20%
570
61%
570
37%
986
May1st to 10thNight
54%
566
22%
2781
14%
559
62%
559
21%
1552
May11th to 20thNight
55%
553
17%
2763
13%
541
59%
541
18%
1608
May21st to endNight
65%
599
18%
3031
17%
593
68%
593
25%
1356
June1st to 10thNight
70%
570
17%
1710
16%
570
71%
570
27%
1110
June11th to 20thNight
71%
570
18%
1710
15%
570
73%
570
38%
984
June21st to endNight
73%
570
14%
1710
12%
570
74%
570
32%
1039
July1st to 10thNight
68%
542
10%
2753
13%
535
69%
535
15%
1848
July11th to 20thNight
71%
534
10%
2635
12%
533
71%
533
17%
1670
July21st to endNight
70%
614
9%
2974
12%
569
71%
569
13%
2240
August1st to 10thNight
70%
553
19%
2629
14%
545
70%
545
19%
1543
August11th to 20thNight
68%
554
16%
2688
20%
544
69%
544
18%
1524
August21st to endNight
66%
606
18%
2956
20%
605
66%
605
19%
1587
September1st to 10thNight
67%
731
21%
2061
18%
731
69%
731
31%
1312
September11th to 20thNight
61%
760
21%
2090
18%
760
63%
760
30%
1370
September21st to endNight
62%
760
25%
2090
20%
760
65%
760
34%
1306
October1st to 10thNight
60%
760
24%
2422
23%
740
65%
740
30%
1518
October11th to 20thNight
53%
760
33%
2107
24%
740
63%
740
38%
1210
October21st to endNight
55%
836
29%
2694
27%
814
64%
814
32%
1585
November1st to 10thNight
52%
755
29%
2428
25%
755
61%
755
35%
1312
November11th to 20thNight
42%
760
30%
2470
21%
760
56%
760
32%
1381
November21st to endNight
43%
760
26%
2470
19%
760
54%
760
29%
1452
December1st to 10thNight
34%
760
24%
2470
16%
760
47%
760
23%
1569
December11th to 20thNight
35%
759
26%
2911
16%
758
46%
758
22%
1673
December21st to endNight
31%
829
15%
4394
14%
817
41%
817
12%
2787

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%6%26%445%46%8%41%
100960
Night
13%7%26%44446%7%44%
98018
TransparencyDay
38%6%12%21%19%5%
104790
Night
37%5%10%19%21%7%
102326
SeeingDay
15%8%20%23%21%13%
14880
Night
15%7%22%30%22%4
24881

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%10%36%44445%5%37%
2836
11th to 20thDay
13%6%15%333446%51%
2840
21st to endDay
26%9%25%33324439%
3261
February1st to 10thDay
16%8%37%45%4446%38%
1900
11th to 20thDay
21%8%26%344345%41%
1848
21st to endDay
21%7%26%44435%6%38%
1570
March1st to 10thDay
24%12%36%43335%5%33%
3211
11th to 20thDay
12%6%26%44436%6%46%
3480
21st to endDay
19%6%26%44446%6%41%
3815
April1st to 10thDay
12%7%25%4445%5%7%45%
2145
11th to 20thDay
12%6%26%5%44347%47%
2254
21st to endDay
10%425%44446%8%50%
2422
May1st to 10thDay
10%6%36%44446%9%43%
4082
11th to 20thDay
16%8%36%4445%6%8%36%
4081
21st to endDay
8%5%26%445%46%10%46%
4476
June1st to 10thDay
10%6%37%6%5%5%5%7%10%35%
2470
11th to 20thDay
5%4245%5%6%5%8%11%45%
2470
21st to endDay
6%5%26%6%5%7%6%7%10%40%
2470
July1st to 10thDay
8%6%38%7%7%8%7%9%11%26%
4120
11th to 20thDay
8%5%27%6%6%7%6%8%11%35%
4120
21st to endDay
10%9%310%7%7%8%7%9%10%20%
4466
August1st to 10thDay
6%6%26%46%6%6%9%12%38%
4104
11th to 20thDay
7%5%26%45%45%7%10%46%
3767
21st to endDay
7%5%25%345%46%10%49%
4180
September1st to 10thDay
10%6%25%5%5%6%46%8%42%
2097
11th to 20thDay
15%6%26%43447%8%41%
2090
21st to endDay
14%5%25%433347%49%
2090
October1st to 10thDay
12%5%24343345%57%
2090
11th to 20thDay
11%42432435%7%55%
1990
21st to endDay
13%5%15%333335%55%
2090
November1st to 10thDay
12%6%25%333345%55%
1718
11th to 20thDay
14%5%2433435%452%
1710
21st to endDay
13%7%25%445%35%6%46%
1710
December1st to 10thDay
19%8%26%44435%7%37%
1710
11th to 20thDay
17%7%37%444345%43%
2153
21st to endDay
22%8%36%44436%6%35%
3124
January1st to 10thNight
18%8%35%34436%6%41%
4109
11th to 20thNight
12%8%26%44435%5%46%
4120
21st to endNight
23%13%25%32323440%
4390
February1st to 10thNight
17%7%36%43435%6%43%
2280
11th to 20thNight
21%8%25%34235%5%42%
2218
21st to endNight
20%7%26%5%43346%40%
1884
March1st to 10thNight
23%9%36%433346%35%
3640
11th to 20thNight
11%6%2433346%7%50%
3480
21st to endNight
16%6%26%44445%5%43%
3817
April1st to 10thNight
12%5%25%445%46%7%47%
2050
11th to 20thNight
14%5%25%33435%7%49%
1875
21st to endNight
8%5%25%33435%8%53%
1755
May1st to 10thNight
9%6%27%5%46%47%8%42%
2813
11th to 20thNight
15%7%26%44446%7%40%
2812
21st to endNight
6%425%445%46%11%48%
3079
June1st to 10thNight
7%6%36%5%6%6%5%8%12%37%
1710
11th to 20thNight
4415%6%5%5%48%13%45%
1710
21st to endNight
5%415%5%5%6%5%10%11%42%
1710
July1st to 10thNight
8%6%39%6%6%7%5%8%11%30%
2840
11th to 20thNight
5%5%28%6%5%7%6%9%13%34%
2840
21st to endNight
10%10%410%7%6%7%6%8%10%23%
3087
August1st to 10thNight
7%437%5%5%6%5%9%13%36%
2825
11th to 20thNight
7%5%26%445%46%9%48%
3059
21st to endNight
7%5%35%45%445%7%52%
3476
September1st to 10thNight
8%5%26%446%6%7%9%42%
2061
11th to 20thNight
14%6%26%44436%8%43%
2090
21st to endNight
12%5%25%44435%7%48%
2090
October1st to 10thNight
10%5%25%333446%55%
2090
11th to 20thNight
10%5%25%323245%59%
2188
21st to endNight
12%424333345%58%
2508
November1st to 10thNight
12%5%24333345%56%
2428
11th to 20thNight
13%5%24333246%53%
2470
21st to endNight
15%6%2443435%6%47%
2470
December1st to 10thNight
17%7%27%44435%6%41%
2470
11th to 20thNight
17%8%24333245%48%
3042
21st to endNight
20%9%36%5%4445%7%34%
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
46%38%16%21%6%
2837
11th to 20thDay
34%37%25%24%6%
2840
21st to endDay
49%2418%21%6%
3261
February1st to 10thDay
46%47%17%21%5%
1900
11th to 20thDay
46%26%18%21%6%
1858
21st to endDay
48%38%14%20%8%
1570
March1st to 10thDay
54%29%12%14%8%
3211
11th to 20thDay
38%49%18%24%8%
3480
21st to endDay
44%39%21%19%4
3815
April1st to 10thDay
38%49%23%20%6%
2145
11th to 20thDay
37%48%20%25%7%
2254
21st to endDay
31%5%11%28%23%2
2422
May1st to 10thDay
36%414%24%19%2
4120
11th to 20thDay
44%5%13%25%11%1
4085
21st to endDay
32%6%15%26%20%1
4489
June1st to 10thDay
41%7%17%23%10%2
2470
11th to 20thDay
28%7%21%27%15%1
2470
21st to endDay
35%9%18%22%13%3
2470
July1st to 10thDay
44%14%21%16%5%1
4055
11th to 20thDay
39%11%21%22%5%1
4051
21st to endDay
53%13%16%13%4
4324
August1st to 10thDay
34%8%17%32%8%
4091
11th to 20thDay
31%8%17%27%14%2
3804
21st to endDay
29%7%17%23%21%3
4179
September1st to 10thDay
38%7%16%18%17%4
2097
11th to 20thDay
40%7%11%18%23%1
2090
21st to endDay
36%5%9%21%23%6%
2090
October1st to 10thDay
25%37%14%38%13%
3480
11th to 20thDay
19%35%17%30%27%
3282
21st to endDay
27%36%20%32%12%
3428
November1st to 10thDay
32%48%15%31%11%
1718
11th to 20thDay
34%37%20%26%10%
1710
21st to endDay
38%47%19%25%7%
1710
December1st to 10thDay
47%47%19%17%6%
1710
11th to 20thDay
45%25%17%24%7%
2150
21st to endDay
47%38%20%19%3
3124
January1st to 10thNight
43%35%17%26%6%
4109
11th to 20thNight
39%46%22%21%8%
4120
21st to endNight
50%2412%25%6%
4390
February1st to 10thNight
42%38%18%20%9%
2280
11th to 20thNight
46%35%17%21%8%
2219
21st to endNight
46%38%16%17%10%
1884
March1st to 10thNight
51%39%16%14%7%
3640
11th to 20thNight
33%39%16%27%12%
3480
21st to endNight
41%46%19%20%9%
3817
April1st to 10thNight
35%310%20%23%8%
2050
11th to 20thNight
35%37%20%24%11%
1875
21st to endNight
30%5%10%28%22%6%
1755
May1st to 10thNight
37%5%16%22%17%2
2840
11th to 20thNight
42%413%26%13%1
2813
21st to endNight
27%6%17%27%21%3
3087
June1st to 10thNight
37%10%18%21%13%2
1710
11th to 20thNight
28%8%21%29%14%2
1710
21st to endNight
31%11%21%19%15%4
1710
July1st to 10thNight
44%12%20%17%5%1
2795
11th to 20thNight
35%14%23%18%7%2
2786
21st to endNight
52%12%17%12%5%1
2988
August1st to 10thNight
35%9%18%30%7%1
2814
11th to 20thNight
31%9%15%27%16%1
3088
21st to endNight
30%7%14%21%25%3
3476
September1st to 10thNight
35%8%17%18%17%5%
2061
11th to 20thNight
39%7%12%21%19%3
2090
21st to endNight
35%6%12%18%21%9%
2090
October1st to 10thNight
25%5%8%13%35%13%
3480
11th to 20thNight
17%2418%32%27%
3635
21st to endNight
22%3422%31%18%
4120
November1st to 10thNight
31%38%17%28%13%
2428
11th to 20thNight
33%35%18%28%13%
2470
21st to endNight
37%37%19%26%8%
2470
December1st to 10thNight
43%49%19%20%6%
2470
11th to 20thNight
39%28%16%28%7%
3044
21st to endNight
49%36%20%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
22%21%37%18%2
270
11th to 20thDay
25%18%30%19%7%1
270
21st to endDay
24%21%35%15%5%1
297
February1st to 10thDay
21%19%34%21%5%
270
11th to 20thDay
36%14%33%14%3
270
21st to endDay
31%14%38%14%3
225
March1st to 10thDay
23%16%29%23%7%2
322
11th to 20thDay
20%15%30%26%8%
460
21st to endDay
20%14%33%24%8%1
506
April1st to 10thDay
18%15%28%21%15%2
460
11th to 20thDay
12%13%31%25%17%2
452
21st to endDay
15%8%24%28%21%5%
460
May1st to 10thDay
11%9%26%26%21%7%
463
11th to 20thDay
13%419%25%24%15%
487
21st to endDay
13%413%25%26%19%
529
June1st to 10thDay
12%311%25%31%18%
490
11th to 20thDay
7%212%24%22%32%
490
21st to endDay
11%210%27%27%23%
490
July1st to 10thDay
8%25%19%34%32%
485
11th to 20thDay
8%25%17%30%39%
484
21st to endDay
6%27%17%39%29%
532
August1st to 10thDay
11%311%21%27%27%
486
11th to 20thDay
11%38%21%33%24%
479
21st to endDay
16%25%24%29%24%
539
September1st to 10thDay
9%412%24%30%21%
490
11th to 20thDay
16%5%11%20%33%15%
490
21st to endDay
16%316%21%32%12%
490
October1st to 10thDay
16%318%32%21%10%
490
11th to 20thDay
11%9%23%24%25%8%
490
21st to endDay
17%7%19%29%22%5%
539
November1st to 10thDay
19%7%25%24%19%5%
298
11th to 20thDay
17%14%33%24%10%2
270
21st to endDay
12%13%32%29%11%2
270
December1st to 10thDay
28%14%33%16%9%
270
11th to 20thDay
23%16%29%24%8%1
270
21st to endDay
31%13%31%19%6%1
297
January1st to 10thNight
23%14%34%24%5%1
760
11th to 20thNight
19%15%31%26%8%
760
21st to endNight
21%13%36%26%4
836
February1st to 10thNight
19%10%32%33%6%
760
11th to 20thNight
24%11%37%25%3
743
21st to endNight
23%14%35%25%4
628
March1st to 10thNight
17%13%32%33%6%
760
11th to 20thNight
18%10%35%26%10%
760
21st to endNight
17%12%29%32%11%
836
April1st to 10thNight
14%10%30%33%13%1
720
11th to 20thNight
16%8%29%31%15%1
563
21st to endNight
11%5%26%35%21%2
570
May1st to 10thNight
10%7%22%35%24%1
570
11th to 20thNight
12%420%34%26%5%
561
21st to endNight
12%211%34%34%8%
617
June1st to 10thNight
10%18%39%36%7%
570
11th to 20thNight
4212%28%39%15%
570
21st to endNight
6%27%32%43%10%
570
July1st to 10thNight
10%17%21%46%14%
555
11th to 20thNight
7%2418%51%17%
552
21st to endNight
7%25%27%46%13%
624
August1st to 10thNight
7%27%25%45%13%
567
11th to 20thNight
11%17%27%45%9%
564
21st to endNight
13%35%27%42%10%
627
September1st to 10thNight
10%29%26%40%12%
731
11th to 20thNight
16%211%26%42%4
760
21st to endNight
16%311%31%36%4
760
October1st to 10thNight
12%316%35%27%7%
760
11th to 20thNight
12%6%23%34%22%3
760
21st to endNight
14%5%21%36%21%3
836
November1st to 10thNight
15%6%22%34%22%2
755
11th to 20thNight
16%9%30%30%14%1
760
21st to endNight
17%8%27%33%14%1
760
December1st to 10thNight
19%10%29%32%9%1
760
11th to 20thNight
22%8%30%30%10%
760
21st to endNight
27%10%27%29%7%
836
Page generated at 2024-11-01 22:47:47. Version ac07

Copyright © 2024 Attilla Danko.


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