Arkansas Sky Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Arkansas Sky Observatory clear sky chart from 2005-11-05 to 2018-03-11.

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
50%
16433
25%
49207
19%
16387
57%
16387
33%
29191

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
33%
975
27%
2522
11%
970
43%
970
33%
1603
January16th to endNight
33%
1040
28%
2704
11%
1040
43%
1040
34%
1695
February1st to 15thNight
31%
938
20%
2467
8%
935
38%
935
29%
1623
February16th to endNight
28%
664
26%
2030
12%
664
40%
664
29%
1232
March1st to 15thNight
32%
573
22%
2101
15%
573
42%
573
23%
1266
March16th to endNight
39%
576
20%
2112
18%
576
46%
576
23%
1309
April1st to 15thNight
39%
539
25%
1797
17%
539
53%
539
31%
1020
April16th to endNight
41%
540
25%
1800
19%
540
53%
540
30%
1041
May1st to 15thNight
51%
540
20%
1745
17%
540
58%
540
27%
1083
May16th to endNight
59%
563
21%
1675
20%
561
63%
561
31%
1030
June1st to 15thNight
79%
540
26%
1440
23%
540
82%
540
51%
776
June16th to endNight
76%
540
27%
1502
25%
540
78%
540
44%
839
July1st to 15thNight
75%
510
18%
1530
19%
510
76%
510
34%
906
July16th to endNight
85%
564
25%
1594
27%
531
86%
531
43%
857
August1st to 15thNight
79%
539
23%
1652
27%
536
79%
536
41%
887
August16th to endNight
77%
573
23%
1910
29%
573
78%
573
32%
1089
September1st to 15thNight
71%
540
26%
1800
29%
540
73%
540
34%
1027
September16th to endNight
70%
597
33%
1971
33%
597
73%
597
37%
1062
October1st to 15thNight
62%
720
31%
2160
25%
720
65%
720
39%
1205
October16th to endNight
53%
768
37%
2304
25%
768
63%
768
42%
1229
November1st to 15thNight
51%
760
30%
2280
21%
760
59%
760
36%
1303
November16th to endNight
43%
819
30%
2567
21%
819
52%
819
31%
1487
December1st to 15thNight
39%
975
22%
2730
12%
975
47%
975
29%
1737
December16th to endNight
35%
1040
23%
2814
11%
1040
43%
1040
26%
1885

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%2443445%7%44%
49397
Night
12%424323346%50%
49403
TransparencyDay
38%6%10%22%17%4
49097
Night
34%410%23%21%5%
49208
SeeingDay
13%418%26%26%10%
6253
Night
14%5%23%33%20%2
16433

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
21%5%2331223448%
1746
16th to endDay
15%5%24313435%49%
1872
February1st to 15thDay
17%7%15%31323448%
1724
16th to endDay
20%7%35%433346%39%
1739
March1st to 15thDay
19%5%24424345%43%
2095
16th to endDay
17%6%25%42435%5%41%
2110
April1st to 15thDay
15%6%25%423347%44%
2151
16th to endDay
16%5%145%35%446%39%
2160
May1st to 15thDay
16%6%36%433447%38%
2204
16th to endDay
10%5%25%7%46%5%6%9%35%
2433
June1st to 15thDay
5%3245%35%6%7%10%43%
2520
16th to endDay
6%315%5%35%7%7%10%43%
2453
July1st to 15thDay
6%5%36%8%37%7%6%9%35%
2340
16th to endDay
5%3145%46%6%7%9%43%
2466
August1st to 15thDay
8%4245%35%6%7%10%41%
2295
16th to endDay
8%415%5%46%6%7%8%42%
2292
September1st to 15thDay
12%5%24435%447%44%
2160
16th to endDay
10%31343445%7%49%
1974
October1st to 15thDay
13%5%24323346%50%
1800
16th to endDay
14%21322343457%
1920
November1st to 15thDay
13%5%23213235%55%
1908
16th to endDay
18%6%24413235%48%
1719
December1st to 15thDay
18%6%14322335%47%
1560
16th to endDay
19%6%35%423235%42%
1756
January1st to 15thNight
19%5%23312245%50%
2522
16th to endNight
15%42432333453%
2704
February1st to 15thNight
18%5%34422345%46%
2457
16th to endNight
16%5%23423235%49%
2030
March1st to 15thNight
18%6%24323246%45%
2101
16th to endNight
17%5%25%424436%43%
2112
April1st to 15thNight
11%41442445%6%50%
1797
16th to endNight
12%5%14324447%48%
1800
May1st to 15thNight
14%415%4245%48%44%
1744
16th to endNight
9%4245%3445%9%45%
1674
June1st to 15thNight
321232446%11%57%
1440
16th to endNight
432342446%10%54%
1502
July1st to 15thNight
43245%26%7%7%11%43%
1620
16th to endNight
313325%6%6%10%55%
1702
August1st to 15thNight
431442446%9%52%
1662
16th to endNight
5%3145%35%6%7%12%44%
1910
September1st to 15thNight
8%425%434348%51%
1800
16th to endNight
7%41342345%6%55%
1971
October1st to 15thNight
10%323323335%57%
2160
16th to endNight
12%21231322363%
2304
November1st to 15thNight
11%5%24323337%53%
2280
16th to endNight
16%5%1421223453%
2567
December1st to 15thNight
18%5%2441334447%
2730
16th to endNight
20%6%24423335%44%
2814

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%26%26%17%5%
1747
16th to endDay
37%38%25%20%4
1872
February1st to 15thDay
41%410%25%15%3
1725
16th to endDay
46%47%19%16%4
1739
March1st to 15thDay
43%410%17%17%7%
2095
16th to endDay
44%5%10%24%13%1
2112
April1st to 15thDay
39%49%22%19%4
2151
16th to endDay
42%5%9%21%17%3
2160
May1st to 15thDay
44%7%10%17%17%2
2204
16th to endDay
42%9%13%21%12%1
2437
June1st to 15thDay
32%8%14%26%17%
2520
16th to endDay
30%9%14%24%17%2
2453
July1st to 15thDay
39%9%14%23%11%1
2201
16th to endDay
31%9%15%26%15%1
2311
August1st to 15thDay
35%8%13%24%15%2
2281
16th to endDay
35%9%14%21%14%4
2292
September1st to 15thDay
38%7%10%18%17%8%
2160
16th to endDay
31%6%10%21%24%5%
1974
October1st to 15thDay
34%48%23%23%6%
1800
16th to endDay
29%35%25%26%10%
1920
November1st to 15thDay
32%38%25%22%8%
1908
16th to endDay
38%36%20%25%5%
1719
December1st to 15thDay
39%311%23%17%4
1560
16th to endDay
45%410%20%14%4
1756
January1st to 15thNight
37%37%22%25%3
2522
16th to endNight
36%36%24%23%6%
2704
February1st to 15thNight
41%38%23%17%5%
2467
16th to endNight
38%28%24%17%7%
2030
March1st to 15thNight
41%310%15%20%8%
2101
16th to endNight
42%49%23%17%2
2112
April1st to 15thNight
32%5%9%23%20%7%
1797
16th to endNight
34%5%10%22%23%3
1800
May1st to 15thNight
38%5%11%21%17%5%
1745
16th to endNight
35%7%15%23%16%1
1676
June1st to 15thNight
20%5%14%31%25%2
1440
16th to endNight
25%5%13%26%23%5%
1502
July1st to 15thNight
29%9%17%26%15%2
1530
16th to endNight
20%10%16%31%18%2
1594
August1st to 15thNight
25%5%18%29%18%2
1652
16th to endNight
30%7%16%23%17%3
1910
September1st to 15thNight
31%5%11%23%20%8%
1800
16th to endNight
28%5%8%23%25%8%
1971
October1st to 15thNight
29%48%22%24%10%
2160
16th to endNight
27%2421%33%10%
2304
November1st to 15thNight
31%38%23%22%9%
2280
16th to endNight
34%36%21%27%6%
2567
December1st to 15thNight
39%310%21%19%5%
2730
16th to endNight
44%38%21%18%4
2814

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
23%8%31%28%6%
135
16th to endDay
11%22%35%20%9%
144
February1st to 15thDay
12%17%42%20%5%
135
16th to endDay
25%10%37%19%5%
120
March1st to 15thDay
22%12%38%23%2
121
16th to endDay
16%20%21%29%11%
96
April1st to 15thDay
20%8%29%25%15%
270
16th to endDay
22%426%27%16%3
270
May1st to 15thDay
19%5%28%26%16%3
341
16th to endDay
12%5%21%33%20%5%
517
June1st to 15thDay
8%13%26%35%15%
495
16th to endDay
5%112%33%34%12%
495
July1st to 15thDay
8%110%31%33%14%
475
16th to endDay
6%320%40%28%
515
August1st to 15thDay
10%6%27%36%18%
448
16th to endDay
13%1319%43%18%
332
September1st to 15thDay
11%28%18%40%19%
315
16th to endDay
9%18%26%38%14%
201
October1st to 15thDay
9%320%34%24%7%
135
16th to endDay
13%422%35%18%5%
144
November1st to 15thDay
17%5%24%30%20%2
135
16th to endDay
23%8%28%21%15%2
135
December1st to 15thDay
19%8%34%20%14%2
135
16th to endDay
27%12%34%22%2
144
January1st to 15thNight
21%8%32%30%6%
975
16th to endNight
18%7%37%32%4
1040
February1st to 15thNight
19%10%34%31%3
938
16th to endNight
19%10%39%28%2
664
March1st to 15thNight
19%9%34%33%3
573
16th to endNight
18%5%32%33%9%
576
April1st to 15thNight
13%7%36%32%9%
539
16th to endNight
13%5%34%35%11%
540
May1st to 15thNight
16%224%41%14%
540
16th to endNight
9%218%38%26%3
563
June1st to 15thNight
39%41%39%4
540
16th to endNight
5%7%37%43%5%
540
July1st to 15thNight
5%8%34%45%5%
510
16th to endNight
4325%54%11%
564
August1st to 15thNight
5%5%30%46%11%
539
16th to endNight
8%430%49%6%
573
September1st to 15thNight
10%17%32%43%4
540
16th to endNight
8%111%36%37%4
597
October1st to 15thNight
12%119%32%30%3
720
16th to endNight
13%425%34%20%1
768
November1st to 15thNight
13%6%24%37%17%
760
16th to endNight
17%9%26%30%15%
819
December1st to 15thNight
21%6%27%36%7%
975
16th to endNight
23%8%28%32%5%
1040
Page generated at 2018-03-12 12:28:13. Version ac04

Copyright 2018 A. Danko


Arkansas Sky Observatory Clear Sky Chart |Charts Home