Appleton
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Appleton clear sky chart from 2005-11-06 to 2024-01-15.

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
33%
24779
17%
74687
9%
24726
41%
24726
22%
50156

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
20%
950
13%
2648
4%
946
28%
946
18%
1923
January11th to 20thNight
20%
923
12%
2583
4%
923
28%
923
15%
1961
January21st to endNight
19%
990
12%
2772
2%
990
27%
990
16%
2098
February1st to 10thNight
20%
900
14%
2354
2%
900
28%
900
18%
1711
February11th to 20thNight
23%
741
19%
2139
6%
740
34%
740
19%
1473
February21st to endNight
22%
592
18%
1776
5%
592
34%
592
18%
1257
March1st to 10thNight
31%
720
17%
2160
9%
720
37%
720
21%
1422
March11th to 20thNight
29%
686
21%
2117
10%
686
40%
686
24%
1354
March21st to endNight
33%
594
20%
1980
15%
594
42%
594
20%
1316
April1st to 10thNight
24%
540
15%
1800
8%
540
35%
540
18%
1243
April11th to 20thNight
32%
533
19%
1775
14%
533
40%
533
20%
1156
April21st to endNight
32%
540
17%
1666
8%
540
41%
540
22%
1128
May1st to 10thNight
32%
540
15%
1557
9%
540
37%
540
22%
1087
May11th to 20thNight
34%
531
19%
1416
9%
531
43%
531
25%
986
May21st to endNight
45%
583
14%
1552
7%
582
51%
582
30%
1004
June1st to 10thNight
47%
540
15%
1440
7%
540
52%
540
35%
894
June11th to 20thNight
44%
540
16%
1440
8%
540
49%
540
32%
927
June21st to endNight
53%
540
16%
1440
7%
540
58%
540
38%
874
July1st to 10thNight
64%
525
18%
1400
11%
525
66%
525
46%
798
July11th to 20thNight
53%
522
19%
1392
10%
522
58%
522
41%
833
July21st to endNight
61%
591
23%
1487
14%
558
66%
558
44%
863
August1st to 10thNight
64%
537
22%
1423
17%
534
67%
534
41%
846
August11th to 20thNight
60%
534
21%
1666
16%
534
67%
534
36%
940
August21st to endNight
57%
594
23%
1980
21%
594
63%
594
35%
1092
September1st to 10thNight
53%
540
23%
1800
21%
540
60%
540
32%
1015
September11th to 20thNight
52%
614
28%
1874
22%
614
60%
614
36%
1065
September21st to endNight
44%
720
21%
1980
13%
720
50%
720
31%
1239
October1st to 10thNight
41%
720
22%
2070
14%
720
48%
720
30%
1273
October11th to 20thNight
27%
720
18%
2193
8%
720
38%
720
20%
1487
October21st to endNight
29%
792
15%
2574
9%
792
37%
792
18%
1779
November1st to 10thNight
29%
740
24%
2406
13%
740
44%
740
25%
1469
November11th to 20thNight
19%
762
17%
2472
7%
762
31%
762
15%
1707
November21st to endNight
24%
950
17%
2660
7%
950
34%
950
20%
1831
December1st to 10thNight
17%
950
12%
2660
2%
950
26%
950
16%
1928
December11th to 20thNight
18%
950
13%
3210
3%
948
27%
948
12%
2370
December21st to endNight
15%
1035
8%
4825
3%
1026
24%
1026
7%
3807

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%8%37%6%35%5%5%8%37%
74807
Night
13%9%47%6%3445%7%38%
74998
TransparencyDay
45%5%13%24%11%1
74508
Night
46%412%24%13%1
74818
SeeingDay
17%10%30%26%13%4
14782
Night
18%10%32%29%11%1
24792

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
11%11%5%9%8%45%46%5%31%
1517
11th to 20thDay
13%15%6%12%8%45%45%6%21%
1472
21st to endDay
12%15%6%10%7%445%5%5%25%
1584
February1st to 10thDay
11%11%6%9%7%45%5%6%6%32%
1605
11th to 20thDay
12%10%48%5%45%5%5%6%36%
1708
21st to endDay
14%11%49%6%35%5%5%6%31%
1480
March1st to 10thDay
14%10%46%6%35%448%36%
1800
11th to 20thDay
12%9%47%5%445%5%7%38%
1857
21st to endDay
17%10%37%6%35%5%5%7%32%
2376
April1st to 10thDay
14%13%47%5%46%5%5%7%30%
2160
11th to 20thDay
19%9%46%5%35%446%34%
2134
21st to endDay
18%8%47%6%45%5%5%7%32%
2294
May1st to 10thDay
16%7%37%6%45%5%6%7%34%
2401
11th to 20thDay
16%7%25%5%3447%8%39%
2479
21st to endDay
11%5%26%6%36%6%6%8%40%
2725
June1st to 10thDay
10%6%36%5%35%46%8%45%
2520
11th to 20thDay
13%6%245%35%5%6%9%41%
2520
21st to endDay
9%5%35%5%35%5%7%10%43%
2520
July1st to 10thDay
6%324445%7%6%11%47%
2520
11th to 20thDay
8%4145%35%6%7%9%48%
2520
21st to endDay
8%5%245%35%5%6%9%48%
2743
August1st to 10thDay
7%425%6%46%6%7%10%44%
2507
11th to 20thDay
10%5%36%5%35%5%7%9%43%
2229
21st to endDay
11%6%25%5%3446%9%45%
2376
September1st to 10thDay
11%7%36%5%35%5%6%8%43%
2160
11th to 20thDay
12%435%425%45%9%47%
2067
21st to endDay
12%7%37%5%35%5%6%9%39%
1980
October1st to 10thDay
14%7%36%5%345%46%44%
1887
11th to 20thDay
19%10%37%6%3445%7%31%
1765
21st to endDay
17%10%37%6%44345%36%
1782
November1st to 10thDay
12%8%35%6%35%5%5%7%42%
1672
11th to 20thDay
12%10%5%8%8%35%5%6%7%31%
1706
21st to endDay
16%10%37%5%25%6%5%6%34%
1520
December1st to 10thDay
13%11%5%8%7%46%6%7%7%26%
1520
11th to 20thDay
12%14%6%9%8%46%5%46%26%
1918
21st to endDay
18%16%8%13%8%45%43417%
2783
January1st to 10thNight
12%13%5%9%8%34445%34%
2648
11th to 20thNight
15%13%6%9%6%35%5%45%28%
2583
21st to endNight
12%14%6%10%7%45%5%5%5%27%
2772
February1st to 10thNight
10%13%5%9%7%345%45%34%
2354
11th to 20thNight
11%8%48%7%45%5%5%5%38%
2138
21st to endNight
16%12%46%5%34445%35%
1776
March1st to 10thNight
14%9%36%5%45%46%5%39%
2160
11th to 20thNight
12%9%35%5%45%45%6%42%
2117
21st to endNight
18%8%36%5%35%45%7%36%
1980
April1st to 10thNight
18%9%47%5%45%45%6%34%
1800
11th to 20thNight
21%8%25%5%2436%7%36%
1775
21st to endNight
17%8%46%6%35%5%5%5%38%
1666
May1st to 10thNight
17%8%37%5%4446%8%34%
1557
11th to 20thNight
18%7%26%6%345%5%7%39%
1416
21st to endNight
12%5%35%5%35%6%7%9%42%
1551
June1st to 10thNight
9%425%6%346%5%7%48%
1440
11th to 20thNight
12%7%345%345%5%9%43%
1440
21st to endNight
7%4245%35%5%7%10%48%
1440
July1st to 10thNight
7%4134246%7%9%54%
1440
11th to 20thNight
7%435%5%345%6%9%50%
1440
21st to endNight
5%435%3345%6%8%54%
1575
August1st to 10thNight
8%4244345%7%9%49%
1432
11th to 20thNight
8%5%25%4335%6%8%51%
1666
21st to endNight
9%5%25%4245%5%7%52%
1980
September1st to 10thNight
10%5%244345%5%7%52%
1800
11th to 20thNight
12%425%433347%54%
1874
21st to endNight
12%6%25%5%35%45%7%45%
1980
October1st to 10thNight
13%7%25%42445%6%47%
2070
11th to 20thNight
16%8%36%6%35%5%5%7%36%
2193
21st to endNight
17%10%36%6%345%5%8%33%
2574
November1st to 10thNight
12%8%35%6%34447%45%
2406
11th to 20thNight
14%10%48%7%35%5%46%33%
2472
21st to endNight
14%10%46%6%25%446%38%
2660
December1st to 10thNight
13%13%48%7%35%45%7%30%
2660
11th to 20thNight
12%16%6%8%7%34445%30%
3279
21st to endNight
20%17%6%10%7%34435%21%
4884

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
54%413%20%9%1
1518
11th to 20thDay
63%411%13%8%1
1472
21st to endDay
59%412%17%8%
1584
February1st to 10thDay
52%411%23%10%1
1605
11th to 20thDay
48%411%24%12%2
1718
21st to endDay
53%411%19%11%2
1480
March1st to 10thDay
48%5%15%21%9%2
1800
11th to 20thDay
45%5%15%21%12%2
1857
21st to endDay
53%413%22%7%1
2376
April1st to 10thDay
53%5%12%19%11%
2160
11th to 20thDay
52%48%22%12%2
2134
21st to endDay
51%5%10%21%11%2
2294
May1st to 10thDay
48%414%23%9%1
2401
11th to 20thDay
42%6%12%25%13%2
2483
21st to endDay
41%6%13%26%13%2
2725
June1st to 10thDay
37%413%30%15%2
2520
11th to 20thDay
38%5%14%27%15%1
2520
21st to endDay
36%7%15%26%15%1
2520
July1st to 10thDay
30%6%14%33%15%2
2451
11th to 20thDay
30%6%15%30%16%3
2445
21st to endDay
31%5%15%29%16%3
2591
August1st to 10thDay
34%6%17%31%11%1
2492
11th to 20thDay
35%6%15%30%14%1
2229
21st to endDay
37%5%14%27%17%1
2376
September1st to 10thDay
39%5%13%26%16%1
2160
11th to 20thDay
36%417%33%11%1
2067
21st to endDay
43%413%31%10%
1980
October1st to 10thDay
42%413%29%11%
1887
11th to 20thDay
53%412%22%8%1
1765
21st to endDay
51%414%20%10%
1782
November1st to 10thDay
42%413%25%15%1
1672
11th to 20thDay
52%414%20%8%1
1706
21st to endDay
51%317%21%7%1
1520
December1st to 10thDay
53%5%14%22%41
1520
11th to 20thDay
59%314%15%7%2
1915
21st to endDay
73%28%12%5%
2783
January1st to 10thNight
54%312%19%11%1
2648
11th to 20thNight
59%312%18%7%
2583
21st to endNight
58%411%17%10%1
2772
February1st to 10thNight
53%39%23%10%2
2354
11th to 20thNight
48%410%23%12%2
2139
21st to endNight
52%311%21%11%2
1776
March1st to 10thNight
45%5%14%23%12%1
2160
11th to 20thNight
43%412%25%15%2
2117
21st to endNight
48%410%24%12%2
1980
April1st to 10thNight
51%47%18%18%1
1800
11th to 20thNight
47%39%22%15%4
1775
21st to endNight
48%311%21%15%2
1666
May1st to 10thNight
48%5%14%20%12%1
1557
11th to 20thNight
45%6%10%25%13%2
1417
21st to endNight
38%6%16%24%16%2
1552
June1st to 10thNight
34%5%13%31%16%1
1440
11th to 20thNight
37%6%11%27%18%2
1440
21st to endNight
31%6%18%28%14%4
1440
July1st to 10thNight
26%414%34%18%4
1400
11th to 20thNight
29%5%14%30%17%4
1392
21st to endNight
27%5%15%32%18%3
1487
August1st to 10thNight
30%5%17%30%16%2
1423
11th to 20thNight
30%5%16%32%16%1
1666
21st to endNight
31%412%29%20%3
1980
September1st to 10thNight
32%5%11%28%23%1
1800
11th to 20thNight
33%313%35%16%1
1874
21st to endNight
38%413%31%14%1
1980
October1st to 10thNight
37%411%31%15%2
2070
11th to 20thNight
48%414%22%12%1
2193
21st to endNight
50%5%13%20%12%
2574
November1st to 10thNight
40%412%26%16%2
2406
11th to 20thNight
51%412%20%12%1
2472
21st to endNight
48%415%25%7%1
2660
December1st to 10thNight
53%414%21%7%1
2660
11th to 20thNight
57%312%18%8%1
3281
21st to endNight
68%39%15%5%
4884

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
19%12%32%26%9%2
270
11th to 20thDay
21%13%33%25%7%
252
21st to endDay
23%9%32%26%8%1
264
February1st to 10thDay
15%16%40%25%5%
240
11th to 20thDay
17%19%40%17%8%
240
21st to endDay
21%16%45%17%11
198
March1st to 10thDay
21%13%39%18%8%
240
11th to 20thDay
23%13%32%22%8%2
248
21st to endDay
29%10%26%25%8%1
462
April1st to 10thDay
26%11%34%22%5%1
420
11th to 20thDay
28%14%28%20%8%2
412
21st to endDay
23%12%27%25%11%2
420
May1st to 10thDay
20%11%34%25%9%2
484
11th to 20thDay
19%8%34%27%8%4
625
21st to endDay
15%10%29%25%15%5%
679
June1st to 10thDay
11%9%32%30%13%4
630
11th to 20thDay
15%8%33%28%13%3
630
21st to endDay
13%7%29%32%16%3
630
July1st to 10thDay
8%422%33%25%8%
621
11th to 20thDay
10%6%27%31%19%7%
618
21st to endDay
8%5%27%33%20%7%
684
August1st to 10thDay
9%426%31%23%8%
626
11th to 20thDay
13%418%29%25%11%
473
21st to endDay
17%6%23%27%18%9%
495
September1st to 10thDay
17%6%22%30%18%7%
450
11th to 20thDay
13%424%33%18%7%
450
21st to endDay
18%11%28%21%17%5%
450
October1st to 10thDay
19%11%22%27%18%2
357
11th to 20thDay
20%20%32%19%7%
270
21st to endDay
23%15%37%18%5%1
297
November1st to 10thDay
15%16%39%22%8%1
270
11th to 20thDay
16%18%41%16%9%1
270
21st to endDay
24%14%41%15%6%
270
December1st to 10thDay
20%16%40%19%5%
270
11th to 20thDay
24%14%36%19%5%1
270
21st to endDay
25%19%35%16%4
297
January1st to 10thNight
17%13%37%25%7%1
950
11th to 20thNight
21%12%36%23%7%1
923
21st to endNight
20%10%37%26%7%
990
February1st to 10thNight
17%13%37%28%5%1
900
11th to 20thNight
16%15%37%23%8%
743
21st to endNight
23%14%33%25%5%1
592
March1st to 10thNight
19%11%31%29%8%1
720
11th to 20thNight
18%11%37%27%6%1
686
21st to endNight
22%8%30%30%9%1
594
April1st to 10thNight
24%10%37%24%5%
540
11th to 20thNight
24%11%28%29%8%1
533
21st to endNight
20%8%35%29%8%1
540
May1st to 10thNight
22%9%32%30%7%
540
11th to 20thNight
19%9%32%31%8%1
531
21st to endNight
14%7%27%36%16%1
584
June1st to 10thNight
11%431%38%14%1
540
11th to 20thNight
16%5%29%37%12%1
540
21st to endNight
9%328%44%14%1
540
July1st to 10thNight
9%120%45%23%1
525
11th to 20thNight
10%424%40%21%1
522
21st to endNight
7%323%43%23%1
591
August1st to 10thNight
9%217%45%25%1
537
11th to 20thNight
10%320%36%28%3
534
21st to endNight
11%323%39%22%2
594
September1st to 10thNight
12%425%37%18%5%
540
11th to 20thNight
14%425%33%21%3
614
21st to endNight
14%9%26%31%18%2
720
October1st to 10thNight
18%8%27%28%18%1
720
11th to 20thNight
21%14%32%25%8%
720
21st to endNight
23%12%29%26%8%1
792
November1st to 10thNight
16%10%39%26%7%1
740
11th to 20thNight
21%17%35%22%5%
762
21st to endNight
20%15%36%23%7%
950
December1st to 10thNight
22%13%39%20%6%
950
11th to 20thNight
22%13%35%23%6%1
950
21st to endNight
29%12%33%22%4
1045
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