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 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
54%
16443
26%
49398
20%
16399
60%
16399
33%
28987

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%
973
28%
2522
12%
970
48%
970
33%
1572
January16th to endNight
40%
1040
30%
2704
13%
1040
49%
1040
37%
1649
February1st to 15thNight
38%
955
21%
2483
9%
951
44%
951
31%
1607
February16th to endNight
34%
643
26%
2009
11%
643
46%
643
29%
1201
March1st to 15thNight
41%
573
22%
2101
17%
573
48%
573
23%
1265
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%
540
26%
1800
29%
540
73%
540
34%
1008
September16th to endNight
72%
576
34%
1994
34%
576
75%
576
36%
1050
October1st to 15thNight
65%
720
30%
2160
25%
720
67%
720
39%
1204
October16th to endNight
59%
768
37%
2304
28%
768
67%
768
43%
1226
November1st to 15thNight
56%
760
30%
2280
23%
760
63%
760
37%
1282
November16th to endNight
47%
858
30%
2545
21%
858
56%
858
33%
1500
December1st to 15thNight
44%
975
22%
2730
13%
975
50%
975
30%
1717
December16th to endNight
38%
1040
23%
2753
12%
1040
45%
1040
26%
1856

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%6%45%
49216
Night
12%424323347%51%
49593
TransparencyDay
38%5%10%23%17%4
48916
Night
33%410%24%21%5%
49398
SeeingDay
13%214%25%29%14%
6259
Night
15%418%36%22%2
16447

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%5%1441222449%
1746
16th to endDay
14%5%24423345%50%
1872
February1st to 15thDay
18%6%3432323349%
1710
16th to endDay
20%7%25%5%23335%41%
1760
March1st to 15thDay
18%5%14424335%45%
2095
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%46%47%
2160
16th to endDay
9%314424447%52%
1951
October1st to 15thDay
13%5%15%423246%50%
1800
16th to endDay
14%31322333457%
1920
November1st to 15thDay
14%423223345%53%
1908
16th to endDay
17%5%24222335%50%
1739
December1st to 15thDay
17%5%24313246%47%
1560
16th to endDay
21%7%14313335%43%
1817
January1st to 15thNight
18%5%23212235%52%
2522
16th to endNight
14%5%2332223454%
2704
February1st to 15thNight
15%6%24422346%47%
2473
16th to endNight
17%5%23313245%49%
2009
March1st to 15thNight
19%424413345%45%
2101
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
9%42342345%6%53%
1800
16th to endNight
7%31343435%7%55%
1994
October1st to 15thNight
11%313322446%56%
2160
16th to endNight
12%21231222464%
2304
November1st to 15thNight
11%323323347%54%
2280
16th to endNight
17%413312235%52%
2545
December1st to 15thNight
19%5%14323245%47%
2730
16th to endNight
20%7%2441333443%
2753

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
40%26%25%19%5%
1747
16th to endDay
36%37%27%20%4
1872
February1st to 15thDay
40%310%24%15%4
1711
16th to endDay
46%37%20%16%4
1760
March1st to 15thDay
42%310%19%16%8%
2095
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
36%6%9%22%17%7%
2160
16th to endDay
31%411%22%24%4
1951
October1st to 15thDay
34%38%22%22%7%
1800
16th to endDay
29%35%25%26%9%
1920
November1st to 15thDay
32%48%26%20%7%
1908
16th to endDay
37%37%21%25%5%
1739
December1st to 15thDay
37%410%24%19%4
1560
16th to endDay
45%38%23%15%4
1817
January1st to 15thNight
36%27%23%25%3
2522
16th to endNight
34%27%24%24%6%
2704
February1st to 15thNight
38%48%25%18%4
2483
16th to endNight
37%38%24%18%7%
2009
March1st to 15thNight
41%39%16%20%8%
2101
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%25%19%8%
1800
16th to endNight
28%48%23%26%7%
1994
October1st to 15thNight
29%410%21%23%11%
2160
16th to endNight
26%35%22%31%11%
2304
November1st to 15thNight
30%38%24%22%9%
2280
16th to endNight
35%26%22%27%6%
2545
December1st to 15thNight
39%29%22%19%5%
2730
16th to endNight
45%28%22%16%4
2753

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
28%223%31%11%1
135
16th to endDay
15%6%34%28%11%2
144
February1st to 15thDay
16%7%32%32%10%
135
16th to endDay
28%7%34%19%10%
120
March1st to 15thDay
19%8%35%28%8%
121
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
10%6%15%43%23%
315
16th to endDay
8%1121%46%20%
157
October1st to 15thDay
8%17%28%33%11%
135
16th to endDay
15%413%29%25%11%
144
November1st to 15thDay
17%16%31%26%7%
135
16th to endDay
27%5%18%21%23%3
135
December1st to 15thDay
15%231%25%20%5%
135
16th to endDay
23%9%27%30%9%
144
January1st to 15thNight
21%10%24%35%8%
975
16th to endNight
18%6%31%37%6%
1040
February1st to 15thNight
20%7%27%39%4
955
16th to endNight
19%9%33%33%2
643
March1st to 15thNight
20%6%26%40%5%
573
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%50%4
540
16th to endNight
8%19%33%41%5%
576
October1st to 15thNight
13%112%38%30%3
720
16th to endNight
13%418%38%23%1
768
November1st to 15thNight
12%6%19%40%19%1
760
16th to endNight
19%6%20%35%16%
858
December1st to 15thNight
22%5%23%40%8%
975
16th to endNight
24%6%22%39%6%
1040
Page generated at 2018-03-12 12:28:08. Version ac04

Copyright 2018 A. Danko


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