Walker County Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Walker County Observatory clear sky chart from 2005-11-05 to 2017-08-12.

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
49%
15250
22%
46568
16%
15208
56%
15208
28%
28915

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
27%
720
22%
2327
10%
716
40%
716
21%
1516
January16th to endNight
29%
768
23%
2418
12%
768
41%
768
22%
1591
February1st to 15thNight
27%
702
21%
2112
9%
700
40%
700
26%
1342
February16th to endNight
24%
631
21%
1893
9%
631
35%
631
23%
1244
March1st to 15thNight
31%
720
21%
2106
12%
720
38%
720
24%
1380
March16th to endNight
37%
768
19%
2112
12%
768
43%
768
28%
1374
April1st to 15thNight
44%
560
25%
1818
16%
560
56%
560
34%
1018
April16th to endNight
47%
540
26%
1734
18%
540
57%
540
33%
994
May1st to 15thNight
52%
540
21%
1620
13%
540
59%
540
30%
998
May16th to endNight
67%
561
20%
1683
15%
561
70%
561
32%
1029
June1st to 15thNight
73%
540
17%
1620
15%
540
75%
540
36%
954
June16th to endNight
78%
540
18%
1620
15%
540
80%
540
38%
940
July1st to 15thNight
71%
510
15%
1530
13%
510
72%
510
29%
980
July16th to endNight
74%
564
19%
1595
17%
531
77%
531
33%
970
August1st to 15thNight
75%
527
20%
1648
22%
524
76%
524
29%
1027
August16th to endNight
67%
525
18%
1750
21%
525
68%
525
24%
1125
September1st to 15thNight
67%
605
19%
1760
17%
605
68%
605
26%
1160
September16th to endNight
61%
657
26%
1815
20%
657
64%
657
33%
1123
October1st to 15thNight
56%
660
34%
1815
27%
660
62%
660
39%
1064
October16th to endNight
51%
704
32%
2140
25%
704
61%
704
36%
1212
November1st to 15thNight
50%
700
29%
2276
25%
700
60%
700
35%
1250
November16th to endNight
37%
720
27%
2340
18%
720
50%
720
28%
1385
December1st to 15thNight
37%
720
21%
2340
16%
720
46%
720
23%
1519
December16th to endNight
32%
768
19%
2496
14%
768
40%
768
19%
1720

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%25%5%35%5%5%7%40%
47400
Night
11%5%25%43445%7%45%
46766
TransparencyDay
41%7%11%19%16%3
47101
Night
36%6%11%21%18%4
46569
SeeingDay
14%6%19%23%22%13%
5121
Night
14%6%23%30%21%3
15254

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%7%36%434445%39%
1611
16th to endDay
15%6%2342444445%
1803
February1st to 15thDay
14%8%35%434445%40%
1750
16th to endDay
15%5%26%5%345%5%7%38%
1580
March1st to 15thDay
15%6%26%5%3445%6%38%
1854
16th to endDay
14%6%35%5%35%45%6%39%
2111
April1st to 15thDay
11%5%25%5%25%45%7%43%
2139
16th to endDay
10%6%25%6%44447%43%
2226
May1st to 15thDay
12%5%25%5%3445%6%43%
2331
16th to endDay
10%425%6%35%6%7%8%39%
2431
June1st to 15thDay
6%426%6%46%6%8%11%35%
2340
16th to endDay
4225%6%46%7%7%11%40%
2340
July1st to 15thDay
9%425%7%48%7%8%10%30%
2340
16th to endDay
6%426%7%49%9%9%10%29%
2465
August1st to 15thDay
6%426%6%5%7%7%7%10%34%
2213
16th to endDay
14%6%27%7%47%7%6%7%29%
2100
September1st to 15thDay
12%5%35%5%46%6%6%7%34%
1857
16th to endDay
14%6%25%424446%44%
1815
October1st to 15thDay
12%423323235%54%
1815
16th to endDay
12%32332333455%
1729
November1st to 15thDay
11%423423335%53%
1582
16th to endDay
18%314423346%47%
1620
December1st to 15thDay
15%7%36%43445%5%38%
1620
16th to endDay
20%8%37%5%2332436%
1728
January1st to 15thNight
16%6%25%5%24445%41%
2327
16th to endNight
15%6%35%4345%5%5%40%
2418
February1st to 15thNight
13%6%25%5%33445%45%
2103
16th to endNight
16%5%25%6%25%446%40%
1893
March1st to 15thNight
13%7%2443445%6%42%
2106
16th to endNight
10%6%35%6%34435%45%
2112
April1st to 15thNight
11%31342445%8%50%
1818
16th to endNight
9%424424447%51%
1734
May1st to 15thNight
10%32443436%8%46%
1619
16th to endNight
7%3244445%7%10%46%
1682
June1st to 15thNight
42245%35%5%5%11%47%
1620
16th to endNight
3214425%6%7%13%47%
1620
July1st to 15thNight
8%315%6%36%6%6%10%40%
1620
16th to endNight
43245%37%6%8%13%40%
1703
August1st to 15thNight
5%325%435%7%8%10%43%
1659
16th to endNight
11%425%5%445%7%9%40%
1750
September1st to 15thNight
9%5%25%6%346%6%10%39%
1760
16th to endNight
11%5%2442345%7%47%
1815
October1st to 15thNight
12%314323235%56%
1815
16th to endNight
11%42442333457%
2140
November1st to 15thNight
11%5%13222336%55%
2276
16th to endNight
14%425%5%23335%50%
2340
December1st to 15thNight
15%5%35%5%34446%41%
2340
16th to endNight
19%7%36%5%24436%36%
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
46%47%18%19%2
1612
16th to endDay
42%48%22%18%3
1803
February1st to 15thDay
45%5%7%22%16%2
1752
16th to endDay
44%5%9%19%17%3
1580
March1st to 15thDay
46%48%18%17%3
1854
16th to endDay
44%5%13%22%12%1
2112
April1st to 15thDay
39%5%10%22%17%4
2139
16th to endDay
40%6%8%23%17%3
2226
May1st to 15thDay
40%6%13%23%14%3
2331
16th to endDay
39%9%13%20%14%2
2435
June1st to 15thDay
37%11%17%21%11%
2340
16th to endDay
34%9%16%20%15%3
2340
July1st to 15thDay
42%12%15%17%7%3
2201
16th to endDay
41%13%17%17%8%1
2310
August1st to 15thDay
38%12%16%20%11%1
2200
16th to endDay
49%10%12%13%11%2
2100
September1st to 15thDay
44%10%12%15%12%4
1857
16th to endDay
39%5%9%18%21%5%
1815
October1st to 15thDay
32%5%8%19%25%8%
1815
16th to endDay
32%36%21%28%7%
1729
November1st to 15thDay
33%35%19%30%7%
1582
16th to endDay
37%37%22%24%4
1620
December1st to 15thDay
47%5%6%19%16%3
1620
16th to endDay
52%39%17%13%2
1728
January1st to 15thNight
44%47%18%20%3
2327
16th to endNight
44%47%20%17%4
2418
February1st to 15thNight
40%49%20%18%5%
2112
16th to endNight
44%48%22%17%2
1893
March1st to 15thNight
42%5%8%19%17%6%
2106
16th to endNight
40%411%25%15%1
2112
April1st to 15thNight
31%411%25%21%5%
1818
16th to endNight
31%5%10%25%21%5%
1734
May1st to 15thNight
34%7%15%20%19%2
1620
16th to endNight
30%10%17%24%14%2
1684
June1st to 15thNight
29%8%21%27%12%2
1620
16th to endNight
25%10%20%23%16%4
1620
July1st to 15thNight
35%10%16%22%11%4
1530
16th to endNight
30%9%21%22%12%2
1595
August1st to 15thNight
31%12%15%23%14%2
1648
16th to endNight
38%9%16%19%13%1
1750
September1st to 15thNight
37%11%18%15%12%4
1760
16th to endNight
34%6%10%22%21%5%
1815
October1st to 15thNight
30%48%21%24%9%
1815
16th to endNight
32%3419%28%12%
2140
November1st to 15thNight
30%35%20%28%11%
2276
16th to endNight
37%36%20%24%6%
2340
December1st to 15thNight
43%5%9%17%19%4
2340
16th to endNight
50%49%17%15%2
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
17%25%28%15%11%1
90
16th to endDay
16%29%42%10%1
96
February1st to 15thDay
17%28%37%14%1
90
16th to endDay
23%13%46%14%1
81
March1st to 15thDay
18%20%29%27%22
144
16th to endDay
18%9%33%25%13%
288
April1st to 15thDay
15%11%30%24%17%1
270
16th to endDay
13%9%24%23%24%4
270
May1st to 15thDay
13%9%26%24%14%12%
288
16th to endDay
16%317%22%24%15%
331
June1st to 15thDay
7%210%25%28%25%
315
16th to endDay
10%112%21%26%26%
315
July1st to 15thDay
10%18%27%28%23%
305
16th to endDay
8%5%18%31%35%
326
August1st to 15thDay
12%110%25%29%20%
297
16th to endDay
19%16%19%32%20%
268
September1st to 15thDay
10%39%20%35%20%
255
16th to endDay
18%212%25%32%7%
254
October1st to 15thDay
16%117%31%25%7%
255
16th to endDay
13%5%22%23%29%5%
217
November1st to 15thDay
21%13%20%32%12%1
90
16th to endDay
15%16%30%20%17%
90
December1st to 15thDay
21%17%42%14%4
90
16th to endDay
31%17%31%15%4
96
January1st to 15thNight
21%12%35%24%6%
720
16th to endNight
18%11%35%32%2
768
February1st to 15thNight
17%11%38%29%2
704
16th to endNight
20%13%38%24%3
631
March1st to 15thNight
17%13%33%30%5%
720
16th to endNight
15%10%30%29%12%1
768
April1st to 15thNight
12%7%32%33%12%
560
16th to endNight
10%7%29%38%12%
540
May1st to 15thNight
11%5%25%33%21%3
540
16th to endNight
10%113%35%33%5%
563
June1st to 15thNight
5%10%36%39%7%
540
16th to endNight
49%29%44%11%
540
July1st to 15thNight
11%6%30%39%11%
510
16th to endNight
6%7%23%50%12%
564
August1st to 15thNight
7%16%26%47%10%
527
16th to endNight
13%17%25%43%8%
525
September1st to 15thNight
11%17%31%40%7%
605
16th to endNight
14%113%33%34%2
657
October1st to 15thNight
13%321%29%26%5%
660
16th to endNight
13%5%24%33%20%2
704
November1st to 15thNight
13%8%24%31%20%1
700
16th to endNight
16%11%30%28%12%
720
December1st to 15thNight
18%11%27%32%9%
720
16th to endNight
22%10%30%29%7%
768
Page generated at 2017-08-13 14:16:23. Version ac04

Copyright 2017 A. Danko


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