Arkansas Tech University Astronomical Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Arkansas Tech University Astronomical Observatory clear sky chart from 2005-11-05 to 2017-09-10.

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
54%
15663
25%
47140
19%
15619
60%
15619
33%
27654

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
38%
898
29%
2327
13%
895
49%
895
33%
1432
January16th to endNight
38%
960
29%
2496
12%
960
48%
960
36%
1536
February1st to 15thNight
37%
880
21%
2288
8%
876
44%
876
31%
1468
February16th to endNight
35%
594
28%
1856
12%
594
48%
594
31%
1079
March1st to 15thNight
40%
540
22%
1980
17%
540
47%
540
22%
1199
March16th to endNight
43%
576
20%
2112
19%
576
48%
576
23%
1305
April1st to 15thNight
43%
539
25%
1818
18%
539
55%
539
31%
1028
April16th to endNight
44%
540
23%
1800
19%
540
54%
540
28%
1067
May1st to 15thNight
54%
539
19%
1702
17%
539
59%
539
27%
1055
May16th to endNight
64%
562
21%
1685
21%
561
67%
561
32%
1026
June1st to 15thNight
78%
540
23%
1620
23%
540
81%
540
47%
838
June16th to endNight
80%
540
25%
1620
26%
540
82%
540
45%
848
July1st to 15thNight
75%
510
18%
1530
19%
510
76%
510
36%
890
July16th to endNight
85%
564
25%
1594
29%
531
86%
531
44%
851
August1st to 15thNight
77%
539
24%
1622
28%
536
78%
536
40%
888
August16th to endNight
77%
573
24%
1910
29%
573
78%
573
35%
1054
September1st to 15thNight
72%
525
26%
1750
28%
525
73%
525
34%
983
September16th to endNight
71%
528
32%
1828
32%
528
75%
528
36%
972
October1st to 15thNight
65%
660
31%
1980
26%
660
67%
660
38%
1117
October16th to endNight
59%
704
35%
2112
26%
704
66%
704
41%
1144
November1st to 15thNight
57%
700
31%
2100
24%
700
64%
700
38%
1159
November16th to endNight
45%
792
29%
2349
19%
792
53%
792
31%
1419
December1st to 15thNight
42%
900
21%
2520
12%
900
48%
900
29%
1608
December16th to endNight
39%
960
24%
2541
13%
960
46%
960
27%
1688

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%45%
47473
Night
12%424323347%50%
47335
TransparencyDay
38%5%10%23%17%4
47173
Night
33%410%24%21%5%
47140
SeeingDay
13%213%25%30%15%
5707
Night
15%418%35%22%2
15667

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
19%41442222450%
1611
16th to endDay
15%5%24423345%49%
1728
February1st to 15thDay
18%6%3331322349%
1575
16th to endDay
18%7%24423335%43%
1626
March1st to 15thDay
19%5%14424335%44%
1980
16th to endDay
19%6%35%325%33441%
2110
April1st to 15thDay
16%5%2442345%5%45%
2128
16th to endDay
18%5%24425%446%40%
2160
May1st to 15thDay
17%7%35%5%3445%5%39%
2247
16th to endDay
12%436%6%36%5%6%8%36%
2430
June1st to 15thDay
7%4246%45%5%6%9%42%
2340
16th to endDay
6%3145%36%6%7%9%45%
2340
July1st to 15thDay
7%5%26%7%47%5%6%10%36%
2340
16th to endDay
5%3245%36%6%7%11%44%
2466
August1st to 15thDay
8%3145%46%6%6%10%41%
2325
16th to endDay
8%425%5%46%5%6%8%42%
2292
September1st to 15thDay
12%5%134345%5%6%46%
2097
16th to endDay
10%314434446%51%
1788
October1st to 15thDay
13%5%14423246%51%
1650
16th to endDay
15%31321343456%
1760
November1st to 15thDay
13%413213345%56%
1758
16th to endDay
18%5%24222336%48%
1605
December1st to 15thDay
18%5%24323246%46%
1440
16th to endDay
22%6%14313335%44%
1677
January1st to 15thNight
17%423212235%53%
2327
16th to endNight
14%5%23322235%53%
2496
February1st to 15thNight
15%6%23422346%48%
2278
16th to endNight
15%5%23313245%51%
1856
March1st to 15thNight
19%424423346%44%
1980
16th to endNight
18%5%24423335%44%
2112
April1st to 15thNight
11%324423337%51%
1818
16th to endNight
14%5%1442445%6%47%
1800
May1st to 15thNight
14%42442445%7%44%
1701
16th to endNight
9%434335%45%10%45%
1683
June1st to 15thNight
421332345%9%59%
1620
16th to endNight
42222245%5%9%57%
1620
July1st to 15thNight
3325%426%5%8%11%44%
1620
16th to endNight
3113325%5%6%12%54%
1702
August1st to 15thNight
43145%3447%10%51%
1632
16th to endNight
5%314435%5%6%10%48%
1910
September1st to 15thNight
10%42342345%6%53%
1750
16th to endNight
8%31343445%7%54%
1828
October1st to 15thNight
12%313323346%55%
1980
16th to endNight
12%31231222462%
2112
November1st to 15thNight
10%323323346%56%
2100
16th to endNight
18%5%13312235%50%
2349
December1st to 15thNight
20%5%14323245%46%
2520
16th to endNight
20%6%25%31233445%
2541

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
39%27%25%19%5%
1612
16th to endDay
37%37%28%19%3
1728
February1st to 15thDay
40%39%25%16%4
1576
16th to endDay
44%37%21%17%4
1626
March1st to 15thDay
43%39%19%16%7%
1980
16th to endDay
46%49%24%13%2
2112
April1st to 15thDay
39%49%21%20%4
2128
16th to endDay
44%5%8%20%18%3
2160
May1st to 15thDay
46%5%9%17%18%2
2247
16th to endDay
43%6%13%22%12%1
2434
June1st to 15thDay
36%6%12%25%17%
2340
16th to endDay
32%8%14%24%17%2
2340
July1st to 15thDay
40%7%13%25%10%1
2201
16th to endDay
30%8%16%29%13%1
2311
August1st to 15thDay
34%9%13%25%15%2
2311
16th to endDay
36%8%16%20%14%4
2292
September1st to 15thDay
37%6%10%22%16%7%
2097
16th to endDay
32%410%20%26%5%
1788
October1st to 15thDay
35%37%22%23%7%
1650
16th to endDay
30%45%25%26%8%
1760
November1st to 15thDay
30%47%27%21%8%
1758
16th to endDay
38%37%21%24%5%
1605
December1st to 15thDay
38%410%24%18%3
1440
16th to endDay
45%27%23%16%4
1677
January1st to 15thNight
35%26%24%27%4
2327
16th to endNight
35%28%25%22%5%
2496
February1st to 15thNight
37%48%25%19%4
2288
16th to endNight
35%39%26%18%7%
1856
March1st to 15thNight
41%410%16%20%6%
1980
16th to endNight
42%49%22%18%2
2112
April1st to 15thNight
33%310%23%20%7%
1818
16th to endNight
36%5%8%23%22%3
1800
May1st to 15thNight
38%6%11%20%18%5%
1702
16th to endNight
34%6%17%24%15%1
1685
June1st to 15thNight
21%5%13%32%24%2
1620
16th to endNight
22%5%14%27%23%5%
1620
July1st to 15thNight
28%8%18%25%16%2
1530
16th to endNight
21%8%17%31%18%2
1594
August1st to 15thNight
25%6%14%31%17%2
1622
16th to endNight
29%6%18%23%18%4
1910
September1st to 15thNight
30%5%9%26%18%8%
1750
16th to endNight
28%5%8%22%26%8%
1828
October1st to 15thNight
30%49%20%24%11%
1980
16th to endNight
27%35%22%30%11%
2112
November1st to 15thNight
28%38%24%23%10%
2100
16th to endNight
37%25%21%26%5%
2349
December1st to 15thNight
41%29%22%18%5%
2520
16th to endNight
43%28%22%17%4
2541

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
25%322%33%13%2
90
16th to endDay
16%7%34%30%8%3
96
February1st to 15thDay
15%8%31%32%11%1
90
16th to endDay
19%7%35%22%13%1
81
March1st to 15thDay
22%10%30%27%10%
90
16th to endDay
14%9%32%20%22%
96
April1st to 15thDay
18%7%27%28%15%2
247
16th to endDay
27%220%27%18%4
270
May1st to 15thDay
20%5%19%30%19%4
384
16th to endDay
15%217%35%21%7%
517
June1st to 15thDay
9%19%22%37%18%
495
16th to endDay
6%110%28%32%20%
495
July1st to 15thDay
7%6%29%35%19%
475
16th to endDay
4217%41%32%
515
August1st to 15thDay
10%16%19%40%22%
478
16th to endDay
13%114%42%26%
332
September1st to 15thDay
9%6%16%44%23%
294
16th to endDay
12%120%40%23%
110
October1st to 15thDay
7%115%28%34%12%
90
16th to endDay
18%25%33%28%12%
96
November1st to 15thDay
12%111%34%30%11%
90
16th to endDay
33%7%21%14%21%2
90
December1st to 15thDay
18%322%28%20%6%
90
16th to endDay
20%10%27%31%10%
96
January1st to 15thNight
21%10%24%34%8%
900
16th to endNight
18%6%32%36%5%
960
February1st to 15thNight
19%8%28%39%4
880
16th to endNight
17%10%34%34%3
594
March1st to 15thNight
20%6%26%40%5%
540
16th to endNight
20%6%23%38%10%
576
April1st to 15thNight
13%5%31%36%12%
539
16th to endNight
17%5%27%35%14%
540
May1st to 15thNight
15%318%41%20%
540
16th to endNight
11%213%42%27%2
563
June1st to 15thNight
5%9%37%42%5%
540
16th to endNight
46%32%50%5%
540
July1st to 15thNight
47%31%48%7%
510
16th to endNight
4223%56%13%
564
August1st to 15thNight
7%328%51%9%
539
16th to endNight
8%428%52%7%
573
September1st to 15thNight
12%5%27%49%4
525
16th to endNight
9%19%34%39%5%
528
October1st to 15thNight
14%112%37%30%3
660
16th to endNight
13%417%38%23%1
704
November1st to 15thNight
12%6%19%40%20%1
700
16th to endNight
20%7%21%32%16%
792
December1st to 15thNight
23%5%23%38%8%
900
16th to endNight
24%7%22%39%6%
960
Page generated at 2017-09-11 18:35:18. Version ac04

Copyright 2017 A. Danko


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