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 2005-11-06 to 2024-02-25.

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
47%
23817
21%
79689
16%
23716
54%
23716
25%
49419

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
23%
755
21%
4012
10%
737
37%
737
13%
2429
January11th to 20thNight
27%
757
25%
3957
10%
740
38%
740
13%
2329
January21st to endNight
27%
831
17%
4266
13%
814
41%
814
13%
2811
February1st to 10thNight
29%
760
22%
2280
11%
760
40%
760
25%
1491
February11th to 20thNight
22%
742
17%
2218
7%
739
31%
739
19%
1533
February21st to endNight
19%
611
19%
1831
8%
611
29%
611
19%
1262
March1st to 10thNight
30%
720
23%
2160
13%
720
39%
720
26%
1358
March11th to 20thNight
29%
720
18%
1990
9%
720
36%
720
23%
1358
March21st to endNight
33%
792
20%
2178
10%
792
40%
792
25%
1461
April1st to 10thNight
40%
573
26%
1833
17%
573
51%
573
30%
1058
April11th to 20thNight
40%
533
28%
1775
18%
533
55%
533
33%
1005
April21st to endNight
48%
540
26%
1702
18%
540
57%
540
32%
995
May1st to 10thNight
49%
540
22%
1620
14%
540
57%
540
33%
964
May11th to 20thNight
56%
531
18%
1593
11%
531
61%
531
29%
1014
May21st to endNight
68%
582
19%
1744
17%
582
69%
582
30%
1088
June1st to 10thNight
65%
540
17%
1620
14%
540
67%
540
29%
1030
June11th to 20thNight
77%
540
18%
1620
15%
540
78%
540
42%
880
June21st to endNight
75%
540
16%
1620
13%
540
77%
540
35%
971
July1st to 10thNight
69%
525
15%
1575
13%
525
70%
525
26%
1044
July11th to 20thNight
73%
522
15%
1566
15%
522
75%
522
30%
980
July21st to endNight
70%
591
17%
1672
15%
558
72%
558
29%
1067
August1st to 10thNight
76%
537
17%
1623
18%
534
76%
534
28%
1047
August11th to 20thNight
68%
534
16%
1776
18%
534
69%
534
26%
1124
August21st to endNight
65%
594
19%
1980
22%
594
66%
594
23%
1284
September1st to 10thNight
66%
630
19%
1890
18%
630
67%
630
28%
1202
September11th to 20thNight
62%
720
22%
1980
17%
720
64%
720
29%
1279
September21st to endNight
60%
720
28%
1980
21%
720
65%
720
36%
1194
October1st to 10thNight
59%
720
32%
1980
25%
720
65%
720
41%
1127
October11th to 20thNight
47%
720
29%
2029
20%
720
57%
720
34%
1234
October21st to endNight
51%
792
31%
2463
26%
792
59%
792
34%
1403
November1st to 10thNight
52%
740
27%
2406
24%
740
60%
740
32%
1351
November11th to 20thNight
40%
760
28%
2470
19%
760
54%
760
32%
1400
November21st to endNight
39%
760
25%
2470
18%
760
50%
760
26%
1515
December1st to 10thNight
32%
760
21%
2470
14%
760
42%
760
19%
1662
December11th to 20thNight
35%
759
25%
2925
17%
758
44%
758
21%
1734
December21st to endNight
31%
826
13%
4415
12%
817
39%
817
12%
2735

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%36%6%35%5%6%7%40%
78855
Night
13%6%35%5%345%5%7%44%
80456
TransparencyDay
41%8%11%20%17%4
78578
Night
38%7%11%21%19%5%
80252
SeeingDay
17%10%23%23%18%9%
13715
Night
15%8%24%30%20%3
23844

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
15%10%37%5%345%5%5%37%
2836
11th to 20thDay
17%7%47%6%3443441%
2840
21st to endDay
23%10%34423445%39%
3321
February1st to 10thDay
17%10%35%4345%5%6%38%
1900
11th to 20thDay
18%9%36%6%34445%37%
1848
21st to endDay
21%7%36%43445%6%37%
1520
March1st to 10thDay
14%5%36%5%345%6%7%43%
1800
11th to 20thDay
18%7%36%5%25%5%5%6%37%
1970
21st to endDay
13%7%46%6%46%5%5%7%37%
2178
April1st to 10thDay
10%5%36%6%46%5%6%7%44%
2142
11th to 20thDay
12%7%35%6%3446%6%45%
2134
21st to endDay
11%5%25%6%445%5%8%45%
2256
May1st to 10thDay
11%5%25%435%5%6%6%47%
2340
11th to 20thDay
10%6%37%7%46%6%7%8%39%
2301
21st to endDay
10%426%6%45%7%7%10%39%
2531
June1st to 10thDay
9%5%36%7%46%6%8%10%36%
2340
11th to 20thDay
4325%6%47%7%8%12%41%
2340
21st to endDay
6%426%7%47%7%7%12%38%
2340
July1st to 10thDay
8%5%38%8%5%9%7%8%10%31%
2340
11th to 20thDay
10%5%26%7%5%7%8%9%11%30%
2340
21st to endDay
6%5%36%8%5%9%9%9%11%30%
2547
August1st to 10thDay
7%5%27%7%5%9%9%9%10%30%
2300
11th to 20thDay
10%6%37%8%5%7%6%7%9%34%
2125
21st to endDay
13%6%37%7%46%7%7%9%32%
2376
September1st to 10thDay
10%5%37%5%46%7%6%8%38%
2051
11th to 20thDay
14%6%246%45%6%5%7%41%
1980
21st to endDay
12%5%26%4245%5%6%49%
1980
October1st to 10thDay
11%5%24424445%54%
1980
11th to 20thDay
10%5%3433435%6%54%
1930
21st to endDay
14%42442445%6%51%
1890
November1st to 10thDay
11%5%2432335%5%55%
1672
11th to 20thDay
13%5%25%5%3445%6%50%
1710
21st to endDay
16%5%25%5%34447%45%
1710
December1st to 10thDay
20%8%46%5%3445%5%37%
1710
11th to 20thDay
12%6%47%7%45%446%40%
2153
21st to endDay
18%9%46%5%345%47%34%
3124
January1st to 10thNight
17%8%37%5%34445%40%
4109
11th to 20thNight
17%8%46%5%23446%42%
4120
21st to endNight
20%12%36%43444436%
4331
February1st to 10thNight
15%7%37%5%34445%43%
2280
11th to 20thNight
19%7%36%6%44445%39%
2218
21st to endNight
21%8%36%5%2445%6%36%
1831
March1st to 10thNight
14%7%345%3445%7%45%
2160
11th to 20thNight
14%8%35%6%35%5%6%6%39%
1990
21st to endNight
11%7%37%7%35%5%46%42%
2178
April1st to 10thNight
11%4245%35%5%5%8%49%
1833
11th to 20thNight
11%5%25%423448%50%
1775
21st to endNight
10%424425%45%8%51%
1702
May1st to 10thNight
9%425%43446%7%50%
1620
11th to 20thNight
9%5%345%345%8%10%43%
1592
21st to endNight
8%426%5%45%5%7%10%44%
1744
June1st to 10thNight
5%437%7%5%7%5%6%10%41%
1620
11th to 20thNight
4224435%5%6%14%53%
1620
21st to endNight
5%3145%36%7%7%13%45%
1620
July1st to 10thNight
8%437%6%47%6%7%11%36%
1620
11th to 20thNight
8%5%245%36%7%8%11%41%
1620
21st to endNight
5%436%6%47%7%8%12%38%
1771
August1st to 10thNight
6%4245%5%6%8%8%11%41%
1634
11th to 20thNight
9%5%26%5%45%6%8%10%41%
1776
21st to endNight
12%425%6%45%5%7%9%40%
1980
September1st to 10thNight
8%6%26%6%346%6%10%41%
1890
11th to 20thNight
13%6%25%4345%6%8%44%
1980
21st to endNight
11%425%43345%7%52%
1980
October1st to 10thNight
11%423323346%59%
1980
11th to 20thNight
12%426%434345%53%
2029
21st to endNight
13%5%24423445%54%
2463
November1st to 10thNight
12%5%23333446%55%
2406
11th to 20thNight
11%6%25%423447%52%
2470
21st to endNight
15%5%25%5%345%46%46%
2470
December1st to 10thNight
18%7%35%6%345%5%6%37%
2470
11th to 20thNight
15%6%25%434346%46%
3042
21st to endNight
17%7%47%6%46%6%6%7%32%
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
45%7%7%18%21%2
2837
11th to 20thDay
46%5%7%16%24%2
2840
21st to endDay
48%39%20%18%2
3321
February1st to 10thDay
47%5%7%19%17%3
1900
11th to 20thDay
50%5%6%19%16%5%
1858
21st to endDay
48%5%9%14%18%6%
1520
March1st to 10thDay
41%5%9%17%21%7%
1800
11th to 20thDay
48%7%10%16%16%4
1970
21st to endDay
46%5%11%23%13%2
2178
April1st to 10thDay
39%7%10%23%17%5%
2142
11th to 20thDay
40%48%20%22%6%
2134
21st to endDay
37%6%10%28%17%2
2256
May1st to 10thDay
36%7%14%26%15%3
2340
11th to 20thDay
41%9%15%20%13%1
2305
21st to endDay
37%10%13%23%15%2
2531
June1st to 10thDay
39%10%16%21%13%1
2340
11th to 20thDay
31%11%18%25%14%2
2340
21st to endDay
36%12%18%19%13%3
2340
July1st to 10thDay
42%13%16%18%9%2
2275
11th to 20thDay
41%13%18%16%8%4
2271
21st to endDay
41%15%17%19%8%
2405
August1st to 10thDay
41%15%17%19%7%1
2287
11th to 20thDay
42%12%15%17%12%1
2125
21st to endDay
46%11%14%14%12%3
2376
September1st to 10thDay
40%11%13%16%15%5%
2051
11th to 20thDay
41%8%11%20%18%2
1980
21st to endDay
35%6%10%19%22%8%
1980
October1st to 10thDay
32%6%8%20%26%8%
1980
11th to 20thDay
31%5%8%24%23%8%
1930
21st to endDay
34%46%22%27%7%
1890
November1st to 10thDay
32%47%19%29%8%
1672
11th to 20thDay
35%47%21%26%7%
1710
21st to endDay
40%5%7%22%23%4
1710
December1st to 10thDay
50%5%7%18%17%3
1710
11th to 20thDay
45%5%7%19%21%3
2150
21st to endDay
48%410%21%14%3
3124
January1st to 10thNight
45%5%6%20%21%2
4109
11th to 20thNight
43%5%7%19%18%7%
4120
21st to endNight
51%46%18%18%3
4331
February1st to 10thNight
43%5%10%19%20%4
2280
11th to 20thNight
49%5%7%17%16%6%
2219
21st to endNight
49%5%8%16%16%6%
1831
March1st to 10thNight
40%48%18%22%8%
2160
11th to 20thNight
44%7%10%18%17%4
1990
21st to endNight
43%5%9%24%16%2
2178
April1st to 10thNight
33%6%12%24%21%5%
1833
11th to 20thNight
33%47%24%22%10%
1775
21st to endNight
32%6%11%28%20%2
1702
May1st to 10thNight
32%7%13%22%22%3
1620
11th to 20thNight
33%11%19%22%14%1
1593
21st to endNight
33%10%15%24%16%2
1745
June1st to 10thNight
35%10%17%21%14%3
1620
11th to 20thNight
22%9%21%30%15%2
1620
21st to endNight
28%10%21%22%14%5%
1620
July1st to 10thNight
37%11%17%20%12%3
1575
11th to 20thNight
32%12%22%18%12%4
1566
21st to endNight
33%12%21%23%10%2
1672
August1st to 10thNight
32%14%20%24%9%1
1623
11th to 20thNight
35%11%20%18%13%2
1776
21st to endNight
40%10%17%18%13%3
1980
September1st to 10thNight
36%9%18%18%14%4
1890
11th to 20thNight
36%9%13%19%21%2
1980
21st to endNight
31%6%10%23%22%7%
1980
October1st to 10thNight
28%48%24%26%9%
1980
11th to 20thNight
34%5%8%21%22%10%
2029
21st to endNight
32%46%22%26%10%
2463
November1st to 10thNight
32%5%7%22%24%10%
2406
11th to 20thNight
33%47%20%27%9%
2470
21st to endNight
40%5%6%22%22%5%
2470
December1st to 10thNight
47%6%10%17%17%3
2470
11th to 20thNight
39%5%8%18%27%3
3044
21st to endNight
47%6%11%21%15%2
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
28%24%29%17%3
270
11th to 20thDay
29%22%31%11%6%1
270
21st to endDay
22%25%37%13%3
297
February1st to 10thDay
28%20%35%13%4
270
11th to 20thDay
39%21%27%11%2
270
21st to endDay
36%21%33%9%1
210
March1st to 10thDay
24%24%31%17%31
240
11th to 20thDay
24%20%30%20%6%1
410
21st to endDay
21%17%35%19%8%
462
April1st to 10thDay
16%18%30%20%12%2
420
11th to 20thDay
15%18%30%23%13%1
412
21st to endDay
17%12%31%22%15%3
420
May1st to 10thDay
15%11%28%27%14%5%
423
11th to 20thDay
11%7%23%29%19%11%
447
21st to endDay
14%417%27%24%14%
485
June1st to 10thDay
13%417%29%23%14%
450
11th to 20thDay
5%412%30%27%22%
450
21st to endDay
10%319%24%25%19%
450
July1st to 10thDay
11%211%25%28%24%
445
11th to 20thDay
11%210%23%33%21%
444
21st to endDay
7%28%27%30%25%
488
August1st to 10thDay
12%411%23%33%18%
446
11th to 20thDay
11%213%28%31%15%
439
21st to endDay
15%311%23%32%17%
495
September1st to 10thDay
9%413%27%32%16%
450
11th to 20thDay
16%412%23%32%14%
450
21st to endDay
15%5%15%27%31%7%
450
October1st to 10thDay
14%5%19%29%23%9%
450
11th to 20thDay
12%10%27%29%20%2
450
21st to endDay
19%10%24%29%15%4
405
November1st to 10thDay
21%10%26%27%12%3
270
11th to 20thDay
17%15%34%27%6%
270
21st to endDay
15%19%35%22%8%1
270
December1st to 10thDay
27%18%34%17%31
270
11th to 20thDay
19%17%38%19%7%1
270
21st to endDay
29%20%30%16%41
297
January1st to 10thNight
23%14%35%23%5%
760
11th to 20thNight
20%15%32%27%6%
760
21st to endNight
19%14%35%29%3
836
February1st to 10thNight
19%13%35%29%4
760
11th to 20thNight
24%15%35%24%1
743
21st to endNight
27%15%36%20%2
611
March1st to 10thNight
18%13%35%31%4
720
11th to 20thNight
18%15%33%24%8%1
720
21st to endNight
17%12%33%28%9%
792
April1st to 10thNight
13%11%32%33%11%
573
11th to 20thNight
13%10%34%32%10%1
533
21st to endNight
12%8%27%40%12%1
540
May1st to 10thNight
9%7%28%34%20%2
540
11th to 20thNight
13%421%32%24%4
531
21st to endNight
10%212%38%34%5%
584
June1st to 10thNight
7%113%38%35%5%
540
11th to 20thNight
4211%36%37%10%
540
21st to endNight
6%110%31%43%8%
540
July1st to 10thNight
10%27%26%43%12%
525
11th to 20thNight
9%26%27%43%13%
522
21st to endNight
7%18%26%48%10%
591
August1st to 10thNight
7%25%24%50%11%
537
11th to 20thNight
11%110%29%42%7%
534
21st to endNight
14%18%25%43%8%
594
September1st to 10thNight
10%210%30%40%8%
630
11th to 20thNight
15%311%30%37%4
720
21st to endNight
13%215%33%34%3
720
October1st to 10thNight
13%418%29%28%7%
720
11th to 20thNight
14%5%28%31%20%1
720
21st to endNight
16%6%22%37%17%2
792
November1st to 10thNight
14%9%21%34%20%1
740
11th to 20thNight
13%9%34%31%12%1
760
21st to endNight
18%11%28%33%10%1
760
December1st to 10thNight
22%13%28%29%8%
760
11th to 20thNight
19%11%30%31%8%1
760
21st to endNight
22%11%30%30%6%
836
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