Madison
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Madison clear sky chart from 2005-11-06 to 2024-01-31.

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
30%
23296
12%
75160
9%
23241
35%
23241
14%
56107

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
7%
758
6%
2459
2%
757
11%
757
5%
2157
January11th to 20thNight
11%
760
5%
2470
3%
760
13%
760
5%
2125
January21st to endNight
12%
835
6%
2711
2%
835
17%
835
5%
2349
February1st to 10thNight
13%
720
5%
2340
2%
720
17%
720
6%
1980
February11th to 20thNight
13%
703
7%
2261
3%
700
18%
700
7%
1851
February21st to endNight
11%
592
10%
1776
1%
592
20%
592
9%
1441
March1st to 10thNight
20%
720
13%
2012
7%
720
25%
720
13%
1559
March11th to 20thNight
23%
720
16%
1980
8%
720
30%
720
17%
1461
March21st to endNight
26%
792
15%
2178
8%
792
32%
792
16%
1662
April1st to 10thNight
26%
720
12%
1918
4%
720
31%
720
18%
1426
April11th to 20thNight
29%
601
16%
1665
7%
601
35%
601
21%
1178
April21st to endNight
32%
540
16%
1620
7%
540
40%
540
20%
1142
May1st to 10thNight
37%
540
12%
1620
8%
540
39%
540
18%
1150
May11th to 20thNight
41%
531
16%
1592
11%
531
46%
531
21%
1092
May21st to endNight
53%
451
15%
1613
14%
450
58%
450
28%
947
June1st to 10thNight
46%
360
15%
1440
16%
360
53%
360
21%
851
June11th to 20thNight
49%
360
16%
1440
19%
360
56%
360
21%
860
June21st to endNight
51%
360
16%
1440
19%
360
57%
360
22%
852
July1st to 10thNight
63%
417
16%
1467
18%
417
66%
417
30%
831
July11th to 20thNight
59%
522
16%
1566
16%
522
62%
522
31%
944
July21st to endNight
59%
591
17%
1672
14%
558
61%
558
29%
1037
August1st to 10thNight
63%
537
18%
1600
16%
534
64%
534
30%
976
August11th to 20thNight
62%
534
20%
1598
16%
534
65%
534
28%
1005
August21st to endNight
54%
630
19%
1818
13%
630
57%
630
30%
1148
September1st to 10thNight
55%
720
19%
1849
12%
720
57%
720
31%
1221
September11th to 20thNight
57%
720
24%
1980
17%
720
60%
720
31%
1260
September21st to endNight
43%
720
18%
1980
14%
720
47%
720
24%
1376
October1st to 10thNight
42%
720
18%
2124
16%
720
45%
720
23%
1426
October11th to 20thNight
28%
720
13%
2160
9%
720
34%
720
15%
1593
October21st to endNight
19%
792
13%
2376
8%
792
26%
792
11%
1858
November1st to 10thNight
28%
740
14%
2392
12%
740
33%
740
16%
1700
November11th to 20thNight
16%
760
11%
2571
7%
760
23%
760
9%
2036
November21st to endNight
15%
760
8%
2660
5%
760
20%
760
7%
2186
December1st to 10thNight
10%
760
3%
2660
3%
760
12%
760
5%
2321
December11th to 20thNight
10%
760
5%
3281
2%
759
15%
759
4%
2764
December21st to endNight
9%
830
3%
4871
1%
817
14%
817
2%
4342

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
16%12%5%8%6%345%5%7%31%
74754
Night
16%13%5%8%6%3445%6%29%
75379
TransparencyDay
52%7%12%18%10%1
74474
Night
56%7%11%16%9%1
75179
SeeingDay
22%14%29%22%10%3
13481
Night
23%14%26%24%11%1
23305

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
16%19%10%13%8%3443415%
1706
11th to 20thDay
16%23%9%14%7%3433413%
1710
21st to endDay
16%21%11%16%9%4443310%
1872
February1st to 10thDay
17%19%7%14%10%3433317%
1620
11th to 20thDay
16%16%9%13%10%4444417%
1583
21st to endDay
18%18%413%5%35%45%5%21%
1480
March1st to 10thDay
17%15%7%9%5%3345%7%25%
1948
11th to 20thDay
15%14%7%9%6%24446%29%
1980
21st to endDay
21%13%48%5%34345%29%
2178
April1st to 10thDay
15%14%46%5%245%5%7%32%
2042
11th to 20thDay
19%11%36%435%446%33%
2259
21st to endDay
20%11%5%7%5%33345%35%
2340
May1st to 10thDay
17%10%47%5%35%5%5%6%32%
2340
11th to 20thDay
18%7%36%6%35%5%6%8%34%
2301
21st to endDay
11%5%35%6%46%6%6%8%40%
2659
June1st to 10thDay
16%6%25%5%35%6%6%9%37%
2520
11th to 20thDay
13%6%36%5%35%5%6%9%39%
2520
21st to endDay
12%5%245%36%5%6%10%41%
2520
July1st to 10thDay
9%5%25%5%345%6%9%45%
2445
11th to 20thDay
12%6%35%435%5%6%11%41%
2340
21st to endDay
10%5%247%45%6%6%10%42%
2547
August1st to 10thDay
9%5%25%6%35%6%7%10%42%
2327
11th to 20thDay
10%5%35%6%36%7%8%10%36%
2303
21st to endDay
12%5%36%5%35%6%6%9%40%
2520
September1st to 10thDay
16%6%35%5%35%5%5%9%40%
2107
11th to 20thDay
12%6%25%5%35%5%6%9%42%
1980
21st to endDay
18%8%26%6%345%5%6%38%
1980
October1st to 10thDay
17%6%37%6%345%6%8%35%
1836
11th to 20thDay
22%10%37%7%3445%7%28%
1800
21st to endDay
25%12%48%6%445%46%23%
1980
November1st to 10thDay
14%13%48%6%45%446%32%
1683
11th to 20thDay
17%21%38%7%345%45%23%
1606
21st to endDay
18%23%7%7%6%4435%6%15%
1520
December1st to 10thDay
16%26%11%10%6%3444413%
1520
11th to 20thDay
16%22%9%14%6%3445%5%12%
1910
21st to endDay
23%26%7%12%8%3333310%
2772
January1st to 10thNight
17%20%9%15%7%4433414%
2459
11th to 20thNight
17%20%10%14%7%3334415%
2470
21st to endNight
16%21%8%14%9%4443413%
2711
February1st to 10thNight
19%17%6%12%9%4443416%
2340
11th to 20thNight
17%16%7%13%8%45%33420%
2259
21st to endNight
19%13%7%12%6%35%5%4421%
1776
March1st to 10thNight
14%13%7%9%8%445%5%5%27%
2012
11th to 20thNight
17%11%5%8%6%34446%33%
1980
21st to endNight
18%14%6%8%6%34445%29%
2178
April1st to 10thNight
16%14%47%5%3445%6%32%
1918
11th to 20thNight
17%12%35%5%35%6%5%6%34%
1665
21st to endNight
15%9%47%5%35%5%5%8%34%
1620
May1st to 10thNight
18%9%37%7%345%6%7%32%
1620
11th to 20thNight
13%9%47%6%35%46%8%35%
1592
21st to endNight
12%5%245%346%6%11%44%
1612
June1st to 10thNight
10%6%37%6%35%6%6%7%42%
1440
11th to 20thNight
9%5%37%6%45%5%5%8%43%
1440
21st to endNight
11%436%6%35%46%10%43%
1440
July1st to 10thNight
7%5%25%5%345%6%8%51%
1510
11th to 20thNight
8%5%25%5%35%5%7%10%45%
1620
21st to endNight
9%5%26%5%35%6%7%8%44%
1771
August1st to 10thNight
7%5%25%5%45%6%7%8%47%
1611
11th to 20thNight
9%5%36%6%36%5%7%8%43%
1598
21st to endNight
11%6%25%435%5%6%9%44%
1818
September1st to 10thNight
13%425%5%345%6%8%44%
1849
11th to 20thNight
12%5%245%25%45%6%49%
1980
21st to endNight
16%6%36%6%35%5%5%7%38%
1980
October1st to 10thNight
16%7%26%5%3445%7%40%
2124
11th to 20thNight
21%9%37%7%35%5%5%6%30%
2160
21st to endNight
28%10%37%6%4445%5%25%
2376
November1st to 10thNight
16%13%46%5%35%446%33%
2392
11th to 20thNight
17%17%5%9%6%4445%5%22%
2571
21st to endNight
20%20%7%8%6%34345%19%
2660
December1st to 10thNight
20%24%9%8%6%3443414%
2660
11th to 20thNight
18%21%8%11%7%45%33416%
3285
21st to endNight
22%23%7%10%8%45%445%9%
4882

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
76%6%9%7%2
1707
11th to 20thDay
77%5%10%7%2
1710
21st to endDay
79%5%6%7%2
1872
February1st to 10thDay
74%5%8%10%3
1620
11th to 20thDay
72%5%7%11%5%
1592
21st to endDay
63%6%11%12%6%2
1480
March1st to 10thDay
57%6%13%19%5%
1948
11th to 20thDay
56%7%10%16%9%2
1980
21st to endDay
57%6%7%19%9%2
2178
April1st to 10thDay
51%5%13%18%13%
2042
11th to 20thDay
51%5%11%18%13%2
2259
21st to endDay
52%5%11%19%9%3
2340
May1st to 10thDay
51%7%9%20%10%2
2340
11th to 20thDay
47%8%12%18%13%3
2305
21st to endDay
39%9%15%24%12%1
2659
June1st to 10thDay
41%8%13%24%13%1
2520
11th to 20thDay
40%8%15%22%13%1
2520
21st to endDay
37%8%13%26%15%2
2520
July1st to 10thDay
34%8%13%25%18%2
2379
11th to 20thDay
36%7%15%25%15%1
2271
21st to endDay
35%8%16%23%15%2
2405
August1st to 10thDay
35%9%16%28%12%
2314
11th to 20thDay
38%11%17%23%10%1
2303
21st to endDay
38%8%15%22%16%2
2520
September1st to 10thDay
41%7%15%20%13%2
2107
11th to 20thDay
38%8%14%25%15%1
1980
21st to endDay
46%7%11%23%12%1
1980
October1st to 10thDay
45%9%14%18%13%1
1836
11th to 20thDay
55%7%13%18%7%1
1800
21st to endDay
63%7%11%13%6%1
1980
November1st to 10thDay
52%7%11%17%11%1
1683
11th to 20thDay
63%7%10%12%7%2
1606
21st to endDay
69%6%9%11%4
1520
December1st to 10thDay
76%6%8%8%2
1520
11th to 20thDay
75%6%8%9%2
1906
21st to endDay
80%6%7%6%1
2772
January1st to 10thNight
76%6%7%8%3
2459
11th to 20thNight
75%5%9%8%2
2470
21st to endNight
76%5%7%8%31
2711
February1st to 10thNight
71%6%9%10%3
2340
11th to 20thNight
69%48%13%5%
2261
21st to endNight
65%6%8%13%7%1
1776
March1st to 10thNight
58%7%10%18%7%
2012
11th to 20thNight
54%5%11%18%11%2
1980
21st to endNight
58%5%7%17%12%2
2178
April1st to 10thNight
53%6%11%17%10%2
1918
11th to 20thNight
48%7%12%19%12%3
1665
21st to endNight
48%7%11%19%11%3
1620
May1st to 10thNight
51%6%12%17%11%3
1620
11th to 20thNight
46%7%10%19%14%4
1593
21st to endNight
34%8%17%25%14%2
1613
June1st to 10thNight
39%7%11%25%15%3
1440
11th to 20thNight
39%8%13%20%19%3
1440
21st to endNight
37%9%13%24%17%1
1440
July1st to 10thNight
32%7%12%25%19%4
1467
11th to 20thNight
32%9%13%24%19%3
1566
21st to endNight
34%9%15%23%17%2
1672
August1st to 10thNight
33%9%13%29%15%1
1600
11th to 20thNight
37%8%15%28%12%1
1598
21st to endNight
36%8%15%23%16%3
1818
September1st to 10thNight
37%8%15%23%14%3
1849
11th to 20thNight
35%8%13%24%19%1
1980
21st to endNight
45%7%12%20%15%1
1980
October1st to 10thNight
43%8%11%20%17%1
2124
11th to 20thNight
53%7%12%18%10%1
2160
21st to endNight
61%6%11%13%7%1
2376
November1st to 10thNight
52%7%12%17%10%2
2392
11th to 20thNight
64%6%9%13%5%2
2571
21st to endNight
69%6%9%12%4
2660
December1st to 10thNight
76%6%8%7%3
2660
11th to 20thNight
73%7%10%8%2
3288
21st to endNight
78%8%8%5%1
4882

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
30%27%29%10%3
270
11th to 20thDay
33%28%27%9%31
270
21st to endDay
28%31%31%9%2
294
February1st to 10thDay
34%23%36%7%
240
11th to 20thDay
35%27%30%8%
240
21st to endDay
34%29%30%7%
198
March1st to 10thDay
28%20%36%13%31
388
11th to 20thDay
25%20%35%16%31
420
21st to endDay
35%18%26%17%4
462
April1st to 10thDay
24%21%31%17%6%
420
11th to 20thDay
30%14%30%17%7%2
412
21st to endDay
26%16%34%18%5%1
420
May1st to 10thDay
25%16%30%20%6%2
423
11th to 20thDay
19%11%32%27%9%2
447
21st to endDay
14%6%30%29%15%6%
485
June1st to 10thDay
17%7%36%28%10%2
450
11th to 20thDay
16%10%28%31%13%2
450
21st to endDay
14%7%32%32%14%2
450
July1st to 10thDay
10%6%24%31%21%9%
445
11th to 20thDay
14%6%28%28%17%7%
444
21st to endDay
10%5%33%31%17%5%
488
August1st to 10thDay
10%7%22%33%21%7%
446
11th to 20thDay
13%7%23%31%19%7%
439
21st to endDay
13%7%22%31%20%6%
495
September1st to 10thDay
18%7%22%27%20%6%
450
11th to 20thDay
12%6%20%30%22%10%
450
21st to endDay
18%12%29%23%12%6%
450
October1st to 10thDay
17%12%25%24%17%4
450
11th to 20thDay
26%18%32%17%5%1
450
21st to endDay
37%14%29%17%3
495
November1st to 10thDay
23%24%26%17%9%1
281
11th to 20thDay
36%24%24%11%41
221
21st to endDay
30%27%31%12%
180
December1st to 10thDay
33%28%26%10%31
180
11th to 20thDay
24%30%33%12%1
180
21st to endDay
32%27%29%10%1
198
January1st to 10thNight
29%27%30%11%3
760
11th to 20thNight
33%22%27%16%2
760
21st to endNight
28%22%31%16%3
835
February1st to 10thNight
31%21%28%17%3
720
11th to 20thNight
28%21%33%17%2
703
21st to endNight
31%21%31%16%1
592
March1st to 10thNight
24%18%35%21%3
720
11th to 20thNight
24%19%31%20%5%1
720
21st to endNight
24%14%30%23%7%1
792
April1st to 10thNight
24%15%29%26%6%
720
11th to 20thNight
24%11%32%23%8%1
601
21st to endNight
18%11%34%30%7%1
540
May1st to 10thNight
21%11%24%31%12%1
540
11th to 20thNight
17%8%26%37%10%2
531
21st to endNight
12%5%24%36%21%3
452
June1st to 10thNight
13%429%38%15%1
360
11th to 20thNight
13%7%23%39%18%1
360
21st to endNight
11%7%24%39%19%
360
July1st to 10thNight
7%418%39%26%6%
417
11th to 20thNight
9%420%36%25%5%
522
21st to endNight
11%421%37%25%3
591
August1st to 10thNight
9%418%39%26%5%
537
11th to 20thNight
12%215%36%31%4
534
21st to endNight
14%6%19%30%28%3
630
September1st to 10thNight
15%7%17%31%25%5%
720
11th to 20thNight
14%5%16%34%27%5%
720
21st to endNight
19%9%23%26%18%4
720
October1st to 10thNight
20%10%23%26%18%3
720
11th to 20thNight
26%16%26%25%7%1
720
21st to endNight
32%19%26%19%3
792
November1st to 10thNight
26%15%28%23%8%1
740
11th to 20thNight
30%21%28%15%5%1
760
21st to endNight
34%21%27%14%4
760
December1st to 10thNight
36%22%27%11%4
760
11th to 20thNight
31%26%27%13%2
760
21st to endNight
33%21%32%13%1
836
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