Shelby
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Shelby clear sky chart from 2005-11-06 to 2024-01-14.

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
40%
23706
16%
74616
10%
23675
46%
23675
25%
46651

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
30%
950
12%
2836
6%
946
36%
946
18%
1959
January11th to 20thNight
30%
889
16%
2723
8%
889
38%
889
20%
1859
January21st to endNight
30%
792
19%
2772
10%
792
41%
792
20%
1709
February1st to 10thNight
27%
720
13%
2354
8%
720
34%
720
17%
1606
February11th to 20thNight
28%
701
10%
2273
6%
700
35%
700
16%
1595
February21st to endNight
33%
592
14%
1860
8%
592
41%
592
20%
1274
March1st to 10thNight
35%
720
13%
2098
7%
720
41%
720
22%
1444
March11th to 20thNight
40%
720
17%
1980
10%
720
47%
720
24%
1359
March21st to endNight
33%
792
9%
2178
3%
792
38%
792
18%
1592
April1st to 10thNight
35%
625
14%
1795
6%
625
41%
625
21%
1244
April11th to 20thNight
33%
533
14%
1601
7%
533
38%
533
19%
1108
April21st to endNight
40%
540
14%
1620
11%
540
44%
540
22%
1079
May1st to 10thNight
45%
540
11%
1580
8%
540
49%
540
26%
1021
May11th to 20thNight
53%
486
16%
1371
15%
486
56%
486
30%
866
May21st to endNight
43%
389
9%
1358
7%
388
47%
388
16%
934
June1st to 10thNight
46%
360
9%
1260
5%
360
52%
360
26%
762
June11th to 20thNight
36%
360
8%
1260
4%
360
39%
360
23%
778
June21st to endNight
61%
360
12%
1260
10%
360
65%
360
40%
630
July1st to 10thNight
65%
350
15%
1225
13%
350
69%
350
48%
556
July11th to 20thNight
59%
348
19%
1218
16%
348
68%
348
45%
565
July21st to endNight
68%
394
26%
1373
31%
372
76%
372
52%
563
August1st to 10thNight
61%
505
22%
1571
20%
503
67%
503
46%
776
August11th to 20thNight
62%
534
25%
1602
18%
534
68%
534
44%
843
August21st to endNight
57%
594
27%
1782
20%
594
62%
594
39%
988
September1st to 10thNight
57%
559
22%
1747
17%
559
61%
559
38%
961
September11th to 20thNight
57%
720
22%
1980
16%
720
61%
720
40%
1166
September21st to endNight
49%
720
24%
1980
15%
720
55%
720
36%
1200
October1st to 10thNight
48%
720
20%
2110
11%
720
55%
720
29%
1318
October11th to 20thNight
42%
720
21%
2160
11%
720
53%
720
26%
1356
October21st to endNight
35%
792
17%
2566
10%
792
44%
792
24%
1603
November1st to 10thNight
32%
856
15%
2521
7%
856
40%
856
21%
1733
November11th to 20thNight
30%
950
18%
2660
7%
950
41%
950
23%
1750
November21st to endNight
34%
950
14%
2685
7%
950
40%
950
27%
1740
December1st to 10thNight
34%
950
14%
2850
7%
950
40%
950
21%
1930
December11th to 20thNight
32%
948
14%
3430
7%
948
38%
948
17%
2195
December21st to endNight
30%
1027
10%
4977
6%
1026
37%
1026
15%
2589

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
8%7%36%5%35%5%6%8%43%
74666
Night
7%8%36%6%35%5%6%8%43%
75094
TransparencyDay
37%8%16%23%13%3
74351
Night
37%8%17%23%12%3
74931
SeeingDay
12%10%26%29%18%5%
14284
Night
11%9%32%34%14%1
23729

By Month

Percentage Cloud Cover SW (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
5%10%5%9%7%46%5%7%8%35%
1329
11th to 20thDay
5%10%5%8%8%46%6%7%9%33%
1326
21st to endDay
310%5%9%7%5%8%6%6%9%32%
1584
February1st to 10thDay
6%11%6%9%8%45%6%7%9%29%
1606
11th to 20thDay
7%13%6%9%7%45%5%5%9%30%
1575
21st to endDay
5%10%6%10%7%36%6%5%7%35%
1394
March1st to 10thDay
5%9%5%9%6%45%5%5%10%37%
1862
11th to 20thDay
6%9%36%6%36%7%7%8%38%
1980
21st to endDay
7%10%410%8%46%7%7%8%31%
2178
April1st to 10thDay
8%11%48%7%45%5%6%8%33%
2159
11th to 20thDay
12%13%47%5%35%45%7%34%
2307
21st to endDay
12%11%36%6%35%5%5%7%37%
2340
May1st to 10thDay
10%8%37%6%45%5%6%7%39%
2380
11th to 20thDay
13%7%26%5%35%6%6%7%39%
2521
21st to endDay
21%8%25%6%45%5%6%7%31%
2917
June1st to 10thDay
15%425%6%45%5%6%9%38%
2700
11th to 20thDay
16%6%25%6%36%6%7%6%37%
2700
21st to endDay
6%313445%5%6%9%54%
2700
July1st to 10thDay
42144345%6%8%59%
2700
11th to 20thDay
33244345%6%7%61%
2700
21st to endDay
311233446%8%65%
2861
August1st to 10thDay
5%4133345%7%8%59%
2360
11th to 20thDay
6%31442445%8%59%
2299
21st to endDay
7%41342445%9%56%
2574
September1st to 10thDay
10%42342345%6%56%
2210
11th to 20thDay
10%5%25%43445%6%52%
1980
21st to endDay
11%5%3443345%6%52%
1980
October1st to 10thDay
12%8%26%6%345%5%7%42%
1850
11th to 20thDay
8%8%37%6%45%5%6%6%42%
1800
21st to endDay
8%9%36%7%35%6%6%9%39%
1787
November1st to 10thDay
11%11%47%435%5%5%8%36%
1538
11th to 20thDay
48%48%7%45%6%9%9%37%
1520
21st to endDay
6%10%47%435%5%5%10%41%
1492
December1st to 10thDay
311%49%7%5%7%5%6%7%36%
1330
11th to 20thDay
410%5%9%6%46%6%6%8%36%
1685
21st to endDay
48%47%5%35%6%7%7%44%
2442
January1st to 10thNight
5%9%5%8%7%46%7%7%8%33%
2836
11th to 20thNight
5%10%47%7%46%5%6%7%38%
2723
21st to endNight
49%48%6%35%5%7%11%38%
2772
February1st to 10thNight
7%10%6%9%7%35%5%6%7%35%
2354
11th to 20thNight
5%13%49%7%5%6%6%6%7%31%
2272
21st to endNight
5%10%5%11%7%45%6%6%7%34%
1860
March1st to 10thNight
310%49%9%5%5%6%7%9%34%
2098
11th to 20thNight
6%9%36%6%46%6%7%11%37%
1980
21st to endNight
9%11%5%8%6%45%6%6%9%31%
2178
April1st to 10thNight
8%10%47%6%46%5%6%8%36%
1795
11th to 20thNight
12%10%46%6%46%5%6%7%35%
1601
21st to endNight
11%9%36%6%35%5%6%7%40%
1620
May1st to 10thNight
10%8%36%5%35%6%6%9%40%
1580
11th to 20thNight
11%5%245%45%5%7%8%44%
1371
21st to endNight
20%8%36%5%345%6%6%34%
1358
June1st to 10thNight
11%6%3443447%9%44%
1260
11th to 20thNight
14%6%24435%5%5%9%43%
1260
21st to endNight
6%323325%46%8%58%
1260
July1st to 10thNight
431332335%7%65%
1260
11th to 20thNight
431342445%8%63%
1260
21st to endNight
321332245%6%69%
1454
August1st to 10thNight
5%323333448%62%
1579
11th to 20thNight
6%2235%235%5%8%58%
1602
21st to endNight
7%425%434447%56%
1782
September1st to 10thNight
10%42333446%7%54%
1747
11th to 20thNight
9%6%2433335%8%53%
1980
21st to endNight
12%42443345%7%51%
1980
October1st to 10thNight
11%6%25%5%345%5%7%46%
2110
11th to 20thNight
7%8%46%5%35%46%7%45%
2160
21st to endNight
6%8%36%6%35%5%6%8%43%
2566
November1st to 10thNight
10%11%46%5%45%46%8%37%
2521
11th to 20thNight
48%36%6%46%7%6%9%41%
2660
21st to endNight
5%10%46%6%346%6%8%42%
2685
December1st to 10thNight
410%47%8%47%5%6%9%36%
2850
11th to 20thNight
49%48%7%35%5%6%8%39%
3506
21st to endNight
48%46%5%35%5%7%8%45%
5214

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
44%8%19%21%5%2
1329
11th to 20thDay
46%9%18%19%6%2
1326
21st to endDay
46%9%17%21%7%1
1584
February1st to 10thDay
49%9%18%16%7%
1606
11th to 20thDay
51%9%17%17%6%1
1584
21st to endDay
46%9%16%18%10%2
1394
March1st to 10thDay
41%8%21%21%8%
1862
11th to 20thDay
40%10%17%24%8%
1980
21st to endDay
46%12%17%17%8%
2178
April1st to 10thDay
47%9%16%20%7%1
2159
11th to 20thDay
48%8%13%21%9%1
2310
21st to endDay
43%9%16%22%8%1
2340
May1st to 10thDay
41%9%16%24%9%1
2380
11th to 20thDay
39%9%17%22%11%2
2525
21st to endDay
50%10%14%18%7%1
2918
June1st to 10thDay
41%9%19%20%11%1
2700
11th to 20thDay
43%9%13%18%15%2
2700
21st to endDay
25%6%17%34%16%2
2700
July1st to 10thDay
21%6%14%30%22%6%
2626
11th to 20thDay
21%6%12%25%23%13%
2619
21st to endDay
15%410%28%31%10%
2702
August1st to 10thDay
20%7%15%26%24%8%
2343
11th to 20thDay
23%6%13%29%24%5%
2299
21st to endDay
24%7%13%26%22%8%
2574
September1st to 10thDay
27%6%12%26%18%10%
2210
11th to 20thDay
32%7%13%26%17%5%
1980
21st to endDay
32%6%13%28%16%5%
1980
October1st to 10thDay
38%7%18%24%11%1
1850
11th to 20thDay
38%9%17%23%10%3
1800
21st to endDay
38%12%16%23%10%1
1787
November1st to 10thDay
44%9%16%20%8%3
1538
11th to 20thDay
39%9%19%23%8%1
1520
21st to endDay
38%9%20%22%9%2
1492
December1st to 10thDay
45%8%16%22%7%2
1330
11th to 20thDay
41%12%24%18%41
1684
21st to endDay
34%8%16%23%15%3
2442
January1st to 10thNight
44%9%18%19%8%1
2836
11th to 20thNight
43%9%17%20%9%2
2723
21st to endNight
38%8%20%22%11%1
2772
February1st to 10thNight
47%7%18%18%9%1
2354
11th to 20thNight
49%8%17%18%8%
2273
21st to endNight
46%8%17%18%9%2
1860
March1st to 10thNight
43%9%20%21%7%
2098
11th to 20thNight
39%11%17%24%8%
1980
21st to endNight
47%11%19%16%7%1
2178
April1st to 10thNight
43%10%16%22%8%
1795
11th to 20thNight
46%8%14%21%10%1
1601
21st to endNight
41%9%16%26%7%1
1620
May1st to 10thNight
38%9%18%27%8%1
1580
11th to 20thNight
35%8%16%26%15%1
1372
21st to endNight
49%8%15%21%7%
1358
June1st to 10thNight
35%9%20%23%12%1
1260
11th to 20thNight
37%9%15%24%13%1
1260
21st to endNight
22%7%17%34%17%2
1260
July1st to 10thNight
18%5%11%32%24%9%
1225
11th to 20thNight
19%6%12%26%27%11%
1218
21st to endNight
14%5%10%23%34%14%
1373
August1st to 10thNight
20%6%12%27%26%9%
1571
11th to 20thNight
23%6%13%27%23%8%
1602
21st to endNight
27%6%10%23%25%10%
1782
September1st to 10thNight
28%5%13%25%17%12%
1747
11th to 20thNight
29%6%14%28%18%6%
1980
21st to endNight
32%6%13%29%16%4
1980
October1st to 10thNight
36%7%16%26%13%2
2110
11th to 20thNight
36%8%15%26%12%3
2160
21st to endNight
36%10%18%22%13%1
2566
November1st to 10thNight
44%8%16%20%9%2
2521
11th to 20thNight
36%11%18%22%12%1
2660
21st to endNight
37%8%22%21%9%2
2685
December1st to 10thNight
42%10%17%21%8%2
2850
11th to 20thNight
39%11%24%21%41
3507
21st to endNight
33%8%16%24%14%6%
5214

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
8%8%28%31%14%11%
180
11th to 20thDay
13%10%28%29%16%5%
166
21st to endDay
7%14%35%30%13%2
176
February1st to 10thDay
15%13%41%23%7%1
234
11th to 20thDay
10%16%29%29%11%4
240
21st to endDay
7%14%32%32%13%2
260
March1st to 10thDay
10%14%33%27%13%3
420
11th to 20thDay
12%12%29%26%15%6%
420
21st to endDay
11%15%28%29%13%4
462
April1st to 10thDay
13%15%32%27%11%1
420
11th to 20thDay
14%16%32%26%11%2
412
21st to endDay
19%14%27%21%16%3
420
May1st to 10thDay
15%10%23%28%16%7%
463
11th to 20thDay
20%7%20%26%21%7%
625
21st to endDay
21%6%19%24%22%7%
679
June1st to 10thDay
14%11%27%24%18%6%
630
11th to 20thDay
17%15%29%24%13%2
630
21st to endDay
7%7%25%32%21%7%
630
July1st to 10thDay
6%423%35%26%7%
621
11th to 20thDay
6%6%25%42%17%3
618
21st to endDay
4323%36%28%7%
607
August1st to 10thDay
6%6%21%36%25%6%
447
11th to 20thDay
8%5%17%31%27%12%
437
21st to endDay
6%6%23%33%24%7%
495
September1st to 10thDay
11%10%26%28%19%6%
450
11th to 20thDay
10%8%25%30%20%7%
450
21st to endDay
15%11%24%28%16%5%
450
October1st to 10thDay
18%6%22%28%20%8%
320
11th to 20thDay
13%10%26%26%17%7%
270
21st to endDay
15%16%32%24%11%3
297
November1st to 10thDay
26%9%26%26%13%1
270
11th to 20thDay
10%10%37%29%13%1
270
21st to endDay
7%14%33%29%13%4
257
December1st to 10thDay
11%9%40%23%13%4
180
11th to 20thDay
17%13%29%26%11%3
180
21st to endDay
11%8%24%35%17%6%
198
January1st to 10thNight
9%12%39%29%10%1
950
11th to 20thNight
10%14%39%26%10%1
889
21st to endNight
8%15%37%29%9%2
792
February1st to 10thNight
13%12%38%27%9%2
720
11th to 20thNight
12%12%35%30%10%1
704
21st to endNight
8%9%34%31%17%2
592
March1st to 10thNight
8%8%37%34%12%2
720
11th to 20thNight
8%9%33%36%12%2
720
21st to endNight
14%8%33%31%13%1
792
April1st to 10thNight
11%10%33%33%12%
625
11th to 20thNight
16%11%35%29%10%
533
21st to endNight
15%8%30%33%14%
540
May1st to 10thNight
13%8%27%32%19%
540
11th to 20thNight
13%5%22%38%20%2
486
21st to endNight
23%5%21%29%19%3
389
June1st to 10thNight
14%5%29%33%17%1
360
11th to 20thNight
19%8%35%26%12%1
360
21st to endNight
6%326%44%19%1
360
July1st to 10thNight
6%323%45%23%
350
11th to 20thNight
7%227%49%15%
348
21st to endNight
4222%55%18%
394
August1st to 10thNight
6%325%45%21%1
505
11th to 20thNight
6%324%43%22%2
534
21st to endNight
8%5%25%43%18%1
594
September1st to 10thNight
13%323%41%18%2
559
11th to 20thNight
13%321%40%22%2
720
21st to endNight
14%6%26%33%18%3
720
October1st to 10thNight
15%5%24%36%19%1
720
11th to 20thNight
11%10%28%34%14%2
720
21st to endNight
10%11%38%31%10%1
792
November1st to 10thNight
16%9%36%31%7%1
856
11th to 20thNight
10%14%39%27%9%1
950
21st to endNight
10%10%39%32%8%1
950
December1st to 10thNight
9%13%33%31%12%2
950
11th to 20thNight
8%12%36%34%9%1
950
21st to endNight
12%10%36%31%10%1
1045
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