Iowa City
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Iowa City clear sky chart from 2005-11-06 to 2024-01-16.

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
37%
24645
18%
74716
11%
24591
45%
24591
24%
49011

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
26%
950
15%
2648
5%
946
34%
946
22%
1836
January11th to 20thNight
23%
930
12%
2548
4%
930
29%
930
16%
1936
January21st to endNight
21%
990
14%
2574
4%
990
29%
990
18%
1915
February1st to 10thNight
22%
900
12%
2340
3%
900
28%
900
19%
1712
February11th to 20thNight
26%
839
18%
2237
7%
838
34%
838
24%
1537
February21st to endNight
22%
592
19%
1776
6%
592
35%
592
20%
1207
March1st to 10thNight
27%
666
18%
2106
8%
666
37%
666
23%
1359
March11th to 20thNight
35%
540
18%
1980
13%
540
43%
540
20%
1252
March21st to endNight
24%
594
10%
2102
6%
594
32%
594
12%
1545
April1st to 10thNight
24%
540
18%
1800
9%
540
37%
540
21%
1164
April11th to 20thNight
29%
533
20%
1775
14%
533
41%
533
21%
1164
April21st to endNight
34%
540
17%
1800
11%
540
45%
540
22%
1191
May1st to 10thNight
31%
540
17%
1545
8%
540
41%
540
26%
1031
May11th to 20thNight
38%
531
17%
1417
10%
531
44%
531
26%
975
May21st to endNight
46%
584
17%
1551
8%
582
51%
582
30%
1031
June1st to 10thNight
56%
540
18%
1440
9%
540
61%
540
36%
896
June11th to 20thNight
53%
540
19%
1440
11%
540
56%
540
36%
882
June21st to endNight
52%
540
19%
1440
10%
540
55%
540
37%
886
July1st to 10thNight
71%
525
17%
1400
12%
525
72%
525
40%
830
July11th to 20thNight
66%
522
24%
1392
16%
522
70%
522
50%
766
July21st to endNight
64%
591
23%
1545
17%
558
67%
558
40%
907
August1st to 10thNight
71%
537
21%
1601
21%
534
73%
534
37%
910
August11th to 20thNight
68%
534
26%
1652
28%
534
72%
534
35%
954
August21st to endNight
67%
594
25%
1980
29%
594
72%
594
38%
1055
September1st to 10thNight
60%
540
23%
1800
22%
540
66%
540
34%
989
September11th to 20thNight
61%
540
32%
1800
31%
540
67%
540
35%
999
September21st to endNight
52%
674
25%
2028
16%
674
61%
674
36%
1136
October1st to 10thNight
46%
720
24%
2160
17%
720
51%
720
32%
1275
October11th to 20thNight
36%
720
23%
2160
12%
720
46%
720
28%
1322
October21st to endNight
30%
792
19%
2405
10%
792
39%
792
22%
1574
November1st to 10thNight
34%
740
25%
2406
15%
740
48%
740
31%
1367
November11th to 20thNight
25%
842
20%
2552
9%
842
37%
842
23%
1648
November21st to endNight
30%
950
18%
2660
8%
950
39%
950
23%
1799
December1st to 10thNight
24%
950
14%
2660
6%
950
32%
950
20%
1875
December11th to 20thNight
27%
948
15%
3157
6%
948
33%
948
17%
2189
December21st to endNight
19%
1037
9%
4839
4%
1026
28%
1026
8%
3897

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%36%6%35%5%5%7%38%
74771
Night
13%8%46%5%3445%6%41%
75070
TransparencyDay
44%6%13%22%13%2
74475
Night
43%6%12%23%14%2
74886
SeeingDay
16%9%29%27%15%4
14667
Night
16%9%31%31%12%1
24658

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
10%12%5%10%8%6%6%5%6%6%27%
1517
11th to 20thDay
13%14%6%9%9%5%5%45%6%25%
1539
21st to endDay
14%13%6%10%9%45%446%26%
1782
February1st to 10thDay
13%12%5%9%7%45%5%5%7%28%
1620
11th to 20thDay
15%11%36%6%46%448%32%
1610
21st to endDay
14%10%5%10%6%3445%6%33%
1480
March1st to 10thDay
16%10%5%8%42435%7%37%
1871
11th to 20thDay
14%9%5%8%5%45%5%5%7%34%
1980
21st to endDay
21%11%46%7%35%45%7%27%
2254
April1st to 10thDay
16%11%47%6%35%446%34%
2160
11th to 20thDay
17%9%46%6%35%5%5%7%34%
2134
21st to endDay
21%8%36%5%34446%35%
2160
May1st to 10thDay
17%8%38%7%45%6%6%8%30%
2411
11th to 20thDay
19%7%35%5%46%5%46%35%
2479
21st to endDay
14%7%46%7%36%5%6%7%34%
2725
June1st to 10thDay
10%425%6%35%6%7%9%44%
2520
11th to 20thDay
10%5%26%435%46%8%47%
2520
21st to endDay
12%5%35%6%36%5%6%10%39%
2520
July1st to 10thDay
8%424435%5%7%9%48%
2520
11th to 20thDay
9%425%5%35%5%7%9%46%
2520
21st to endDay
6%424435%6%7%11%46%
2679
August1st to 10thDay
6%426%6%46%6%9%10%41%
2328
11th to 20thDay
9%5%25%445%6%7%8%45%
2247
21st to endDay
9%5%245%345%5%7%52%
2376
September1st to 10thDay
13%4244345%5%8%48%
2160
11th to 20thDay
10%325%43445%9%51%
2160
21st to endDay
11%5%245%345%5%8%47%
1912
October1st to 10thDay
14%7%26%5%34346%47%
1800
11th to 20thDay
17%6%36%5%2446%6%41%
1800
21st to endDay
18%8%35%5%3345%6%41%
1949
November1st to 10thDay
11%8%35%5%345%6%6%45%
1672
11th to 20thDay
15%10%37%5%2435%8%36%
1625
21st to endDay
17%9%36%5%24447%39%
1520
December1st to 10thDay
15%11%410%5%35%436%33%
1520
11th to 20thDay
14%9%48%7%36%5%5%7%33%
1918
21st to endDay
23%18%7%10%6%3443417%
2783
January1st to 10thNight
11%9%5%8%6%45%45%6%37%
2648
11th to 20thNight
11%13%7%10%7%35%45%6%28%
2548
21st to endNight
13%11%5%10%6%3445%7%31%
2574
February1st to 10thNight
15%12%5%7%6%3445%5%33%
2340
11th to 20thNight
13%9%47%5%4445%6%40%
2236
21st to endNight
15%10%47%6%2445%439%
1776
March1st to 10thNight
16%8%35%5%2445%7%41%
2106
11th to 20thNight
12%7%37%5%45%447%40%
1980
21st to endNight
20%9%5%8%6%45%5%5%5%28%
2102
April1st to 10thNight
14%9%37%42445%6%41%
1800
11th to 20thNight
17%9%36%5%235%46%39%
1775
21st to endNight
17%8%25%5%35%5%5%7%39%
1800
May1st to 10thNight
15%6%36%5%35%46%7%41%
1545
11th to 20thNight
16%6%25%6%4446%7%40%
1416
21st to endNight
11%5%36%6%35%46%8%43%
1551
June1st to 10thNight
8%5%25%5%345%6%9%48%
1440
11th to 20thNight
7%5%36%5%25%5%6%10%46%
1440
21st to endNight
10%5%35%435%45%8%49%
1440
July1st to 10thNight
6%3145%346%6%11%51%
1440
11th to 20thNight
6%21432447%9%59%
1440
21st to endNight
6%325%6%35%6%8%8%50%
1636
August1st to 10thNight
4325%6%45%5%7%8%52%
1611
11th to 20thNight
6%436%4345%5%7%54%
1652
21st to endNight
9%32442345%7%56%
1980
September1st to 10thNight
10%42442445%7%54%
1800
11th to 20thNight
11%42342445%7%54%
1800
21st to endNight
7%425%5%3446%7%54%
2028
October1st to 10thNight
13%5%24423447%52%
2160
11th to 20thNight
15%6%24434447%47%
2160
21st to endNight
17%7%36%5%34435%43%
2405
November1st to 10thNight
10%7%24423347%53%
2406
11th to 20thNight
14%8%46%5%3445%6%43%
2552
21st to endNight
17%7%36%5%34446%40%
2660
December1st to 10thNight
13%11%47%7%35%45%6%35%
2660
11th to 20thNight
14%10%48%6%35%5%5%6%35%
3279
21st to endNight
21%15%7%10%7%4443420%
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
57%6%11%15%10%1
1518
11th to 20thDay
59%5%13%16%6%
1539
21st to endDay
60%5%12%13%8%1
1782
February1st to 10thDay
56%7%13%17%6%1
1620
11th to 20thDay
51%5%14%20%9%1
1619
21st to endDay
52%5%13%20%8%2
1480
March1st to 10thDay
48%5%15%22%9%1
1871
11th to 20thDay
49%6%12%21%11%1
1980
21st to endDay
58%6%11%18%6%1
2254
April1st to 10thDay
52%412%22%9%
2160
11th to 20thDay
49%6%10%23%11%1
2134
21st to endDay
50%5%10%20%13%2
2160
May1st to 10thDay
51%7%12%21%8%1
2411
11th to 20thDay
48%7%11%21%12%1
2483
21st to endDay
47%8%12%19%13%2
2725
June1st to 10thDay
35%9%15%24%16%1
2520
11th to 20thDay
34%8%11%22%22%4
2520
21st to endDay
40%8%14%22%15%2
2520
July1st to 10thDay
30%7%15%30%15%3
2451
11th to 20thDay
31%9%14%27%15%3
2445
21st to endDay
29%8%18%27%16%1
2530
August1st to 10thDay
34%11%16%27%12%1
2314
11th to 20thDay
35%8%13%27%16%1
2247
21st to endDay
31%7%11%28%20%3
2376
September1st to 10thDay
34%6%10%25%21%4
2160
11th to 20thDay
30%6%12%31%18%3
2160
21st to endDay
34%5%10%31%18%2
1912
October1st to 10thDay
40%5%10%25%20%1
1800
11th to 20thDay
43%410%25%16%2
1800
21st to endDay
45%412%23%14%2
1949
November1st to 10thDay
38%6%14%25%14%3
1672
11th to 20thDay
46%415%21%13%1
1625
21st to endDay
46%6%13%24%10%
1520
December1st to 10thDay
52%5%13%21%8%1
1520
11th to 20thDay
50%6%15%19%9%2
1915
21st to endDay
71%410%11%4
2783
January1st to 10thNight
47%5%14%19%15%
2648
11th to 20thNight
57%6%15%14%8%
2548
21st to endNight
53%5%13%18%9%1
2574
February1st to 10thNight
53%5%12%19%11%1
2340
11th to 20thNight
44%6%12%24%12%2
2237
21st to endNight
48%412%21%13%2
1776
March1st to 10thNight
44%413%27%11%1
2106
11th to 20thNight
44%6%13%22%13%3
1980
21st to endNight
58%6%11%17%8%1
2102
April1st to 10thNight
44%5%10%25%15%2
1800
11th to 20thNight
45%5%9%22%16%4
1775
21st to endNight
44%7%11%22%13%3
1800
May1st to 10thNight
42%6%13%25%13%1
1545
11th to 20thNight
42%7%14%21%14%2
1417
21st to endNight
39%6%13%22%16%3
1552
June1st to 10thNight
31%8%13%27%17%3
1440
11th to 20thNight
32%6%12%24%20%5%
1440
21st to endNight
32%6%17%23%17%4
1440
July1st to 10thNight
27%8%15%30%15%5%
1400
11th to 20thNight
20%7%16%33%21%2
1392
21st to endNight
28%7%16%29%18%3
1545
August1st to 10thNight
27%8%16%32%14%3
1601
11th to 20thNight
29%8%9%31%20%2
1652
21st to endNight
27%6%10%28%23%7%
1980
September1st to 10thNight
30%6%11%25%25%4
1800
11th to 20thNight
31%5%9%32%19%4
1800
21st to endNight
30%5%10%30%24%2
2028
October1st to 10thNight
34%5%10%24%24%3
2160
11th to 20thNight
38%412%23%19%4
2160
21st to endNight
45%411%21%17%2
2405
November1st to 10thNight
32%6%14%26%19%4
2406
11th to 20thNight
44%412%25%14%2
2552
21st to endNight
45%412%27%11%1
2660
December1st to 10thNight
49%5%13%23%9%1
2660
11th to 20thNight
50%5%13%24%7%1
3281
21st to endNight
67%5%9%13%6%
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
22%13%31%24%9%1
270
11th to 20thDay
22%15%40%19%4
257
21st to endDay
20%12%42%20%6%1
264
February1st to 10thDay
20%19%40%18%4
240
11th to 20thDay
25%17%33%19%7%
240
21st to endDay
20%17%44%15%31
198
March1st to 10thDay
17%22%42%12%8%
240
11th to 20thDay
22%17%33%19%8%1
240
21st to endDay
32%15%30%16%5%1
340
April1st to 10thDay
21%16%36%20%6%1
420
11th to 20thDay
21%15%31%21%11%1
412
21st to endDay
24%14%33%18%10%1
420
May1st to 10thDay
20%11%37%24%7%2
589
11th to 20thDay
20%13%27%26%12%2
625
21st to endDay
16%8%27%27%16%6%
679
June1st to 10thDay
7%327%33%23%6%
630
11th to 20thDay
12%5%27%33%19%3
630
21st to endDay
12%8%29%31%14%5%
630
July1st to 10thDay
8%316%32%26%14%
621
11th to 20thDay
10%323%34%23%6%
618
21st to endDay
6%324%38%24%6%
684
August1st to 10thDay
6%323%36%24%8%
626
11th to 20thDay
9%419%35%25%9%
561
21st to endDay
9%418%35%25%9%
495
September1st to 10thDay
14%7%19%30%23%7%
450
11th to 20thDay
9%319%39%21%9%
450
21st to endDay
13%10%27%22%23%5%
354
October1st to 10thDay
19%8%27%30%11%4
270
11th to 20thDay
20%22%33%17%9%
270
21st to endDay
29%13%29%22%6%1
297
November1st to 10thDay
15%10%43%19%10%3
270
11th to 20thDay
21%16%32%21%7%2
270
21st to endDay
24%10%36%24%6%
270
December1st to 10thDay
15%13%41%23%6%3
270
11th to 20thDay
16%14%37%24%9%
270
21st to endDay
28%15%37%16%3
297
January1st to 10thNight
15%12%39%27%7%1
950
11th to 20thNight
18%13%35%28%6%
930
21st to endNight
18%12%38%27%6%
990
February1st to 10thNight
23%11%37%25%4
900
11th to 20thNight
18%13%36%28%5%
842
21st to endNight
22%12%39%22%31
592
March1st to 10thNight
20%12%38%24%6%1
666
11th to 20thNight
17%11%32%32%9%
540
21st to endNight
23%11%35%25%5%1
594
April1st to 10thNight
19%14%39%24%4
540
11th to 20thNight
22%13%31%28%7%
533
21st to endNight
20%9%32%29%9%1
540
May1st to 10thNight
18%7%39%27%7%1
540
11th to 20thNight
19%8%28%34%10%
531
21st to endNight
14%430%34%18%1
584
June1st to 10thNight
10%325%44%16%1
540
11th to 20thNight
8%427%46%15%
540
21st to endNight
12%228%39%17%1
540
July1st to 10thNight
8%211%41%33%5%
525
11th to 20thNight
5%220%43%26%3
522
21st to endNight
6%219%44%27%1
591
August1st to 10thNight
5%215%47%29%2
537
11th to 20thNight
6%314%43%29%5%
534
21st to endNight
9%216%43%28%3
594
September1st to 10thNight
11%5%19%37%24%3
540
11th to 20thNight
12%119%37%24%5%
540
21st to endNight
9%7%26%37%19%2
674
October1st to 10thNight
16%6%27%31%18%2
720
11th to 20thNight
18%11%30%30%10%
720
21st to endNight
21%11%33%27%8%
792
November1st to 10thNight
15%9%37%29%10%1
740
11th to 20thNight
18%13%39%23%6%
842
21st to endNight
21%11%33%27%7%
950
December1st to 10thNight
18%13%37%26%6%1
950
11th to 20thNight
21%10%33%29%6%
950
21st to endNight
25%14%33%24%3
1045
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