Streator
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Streator clear sky chart from 2005-11-06 to 2024-03-28.

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
36%
24856
17%
80881
11%
24754
43%
24754
21%
55007

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%
942
10%
4387
4%
926
29%
926
11%
3135
January11th to 20thNight
17%
950
11%
4377
4%
930
24%
930
9%
3450
January21st to endNight
19%
1039
8%
4646
3%
1023
25%
1023
9%
3713
February1st to 10thNight
20%
932
13%
2452
3%
932
27%
932
18%
1825
February11th to 20thNight
25%
740
19%
2219
9%
740
34%
740
19%
1527
February21st to endNight
19%
628
16%
1884
4%
628
30%
628
17%
1330
March1st to 10thNight
24%
760
15%
2280
6%
760
32%
760
18%
1584
March11th to 20thNight
28%
691
19%
2211
10%
691
38%
691
22%
1427
March21st to endNight
23%
615
13%
2059
7%
615
31%
615
14%
1518
April1st to 10thNight
27%
540
16%
1800
9%
540
38%
540
20%
1190
April11th to 20thNight
30%
533
21%
1775
14%
533
42%
533
23%
1143
April21st to endNight
32%
540
15%
1758
8%
540
42%
540
21%
1183
May1st to 10thNight
33%
540
15%
1620
8%
540
40%
540
23%
1126
May11th to 20thNight
39%
531
19%
1452
10%
531
46%
531
27%
984
May21st to endNight
47%
584
17%
1552
8%
582
53%
582
29%
1043
June1st to 10thNight
56%
540
17%
1440
10%
540
61%
540
36%
899
June11th to 20thNight
54%
540
20%
1440
13%
540
58%
540
37%
897
June21st to endNight
51%
540
17%
1440
9%
540
56%
540
31%
956
July1st to 10thNight
67%
525
18%
1400
14%
525
68%
525
37%
856
July11th to 20thNight
67%
522
23%
1392
16%
522
71%
522
43%
813
July21st to endNight
71%
591
25%
1487
19%
558
75%
558
41%
870
August1st to 10thNight
69%
537
22%
1512
19%
534
70%
534
40%
881
August11th to 20thNight
70%
534
22%
1776
23%
534
73%
534
34%
988
August21st to endNight
68%
594
24%
1980
26%
594
72%
594
36%
1078
September1st to 10thNight
57%
540
24%
1800
23%
540
63%
540
33%
1007
September11th to 20thNight
62%
607
33%
1867
30%
607
67%
607
38%
1028
September21st to endNight
52%
720
24%
1980
15%
720
58%
720
33%
1236
October1st to 10thNight
50%
720
25%
2065
18%
720
54%
720
33%
1243
October11th to 20thNight
32%
720
24%
2160
12%
720
45%
720
28%
1338
October21st to endNight
26%
792
18%
2536
10%
792
35%
792
20%
1693
November1st to 10thNight
32%
740
26%
2406
16%
740
44%
740
27%
1407
November11th to 20thNight
28%
760
19%
2470
9%
760
40%
760
20%
1618
November21st to endNight
26%
833
19%
2543
10%
833
36%
833
21%
1728
December1st to 10thNight
21%
950
13%
2660
5%
950
28%
950
19%
1925
December11th to 20thNight
24%
949
15%
3192
6%
948
31%
948
15%
2285
December21st to endNight
14%
1037
6%
4863
2%
1026
22%
1026
6%
4083

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
14%9%47%6%35%5%5%7%36%
78724
Night
14%9%47%5%3445%6%38%
81313
TransparencyDay
46%6%12%22%12%2
78425
Night
47%6%11%21%13%2
81133
SeeingDay
16%10%28%26%15%5%
14829
Night
17%10%31%29%12%1
24882

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
13%12%9%12%8%45%445%25%
2527
11th to 20thDay
13%13%5%13%9%5%6%6%8%418%
2530
21st to endDay
18%20%9%11%7%33345%17%
2979
February1st to 10thDay
17%12%6%9%6%35%445%28%
1725
11th to 20thDay
15%9%5%7%7%45%5%5%7%33%
1848
21st to endDay
14%13%7%10%5%34446%30%
1570
March1st to 10thDay
16%13%5%7%5%3435%6%33%
1900
11th to 20thDay
13%9%48%6%346%7%8%33%
1985
21st to endDay
21%11%6%7%6%35%45%7%24%
2450
April1st to 10thDay
16%11%5%6%6%3436%6%35%
2160
11th to 20thDay
17%9%36%5%34447%37%
2134
21st to endDay
21%8%36%6%35%5%5%7%33%
2200
May1st to 10thDay
18%8%37%6%35%5%5%8%32%
2340
11th to 20thDay
19%8%36%5%45%5%5%8%34%
2438
21st to endDay
15%6%36%6%35%5%6%8%36%
2725
June1st to 10thDay
9%425%5%35%5%7%9%45%
2520
11th to 20thDay
9%5%25%6%35%6%6%8%45%
2520
21st to endDay
9%6%36%6%46%6%6%9%39%
2520
July1st to 10thDay
8%5%25%435%6%7%9%46%
2520
11th to 20thDay
9%4244245%7%11%47%
2520
21st to endDay
7%425%5%45%6%6%10%45%
2743
August1st to 10thDay
7%5%25%5%45%6%7%11%43%
2410
11th to 20thDay
8%5%25%435%5%7%8%48%
2125
21st to endDay
8%5%245%245%7%9%49%
2376
September1st to 10thDay
12%5%25%5%35%45%8%47%
2160
11th to 20thDay
12%4243235%5%7%53%
2073
21st to endDay
8%7%26%44446%8%47%
1980
October1st to 10thDay
11%7%25%6%34447%46%
1891
11th to 20thDay
18%7%36%5%335%46%41%
1800
21st to endDay
20%8%46%6%2445%5%37%
1818
November1st to 10thDay
11%8%3442446%7%48%
1672
11th to 20thDay
17%10%5%6%5%34446%36%
1710
21st to endDay
18%10%48%5%3335%436%
1634
December1st to 10thDay
15%12%5%7%7%34445%33%
1520
11th to 20thDay
14%12%410%7%45%45%7%28%
1918
21st to endDay
23%19%9%12%6%34335%14%
2783
January1st to 10thNight
15%14%7%9%6%34445%30%
4428
11th to 20thNight
14%18%7%11%7%345%7%420%
4440
21st to endNight
22%16%8%9%6%2343422%
4683
February1st to 10thNight
16%12%5%8%7%35%346%32%
2452
11th to 20thNight
13%10%37%6%4445%6%36%
2218
21st to endNight
18%10%6%7%6%34446%34%
1884
March1st to 10thNight
15%10%47%6%35%345%37%
2280
11th to 20thNight
14%7%36%6%3445%8%39%
2211
21st to endNight
20%10%48%6%35%5%5%6%29%
2059
April1st to 10thNight
15%8%45%6%2445%7%38%
1800
11th to 20thNight
18%8%35%43445%6%42%
1775
21st to endNight
18%7%36%5%345%6%8%36%
1758
May1st to 10thNight
17%7%36%5%345%6%9%34%
1620
11th to 20thNight
16%6%36%5%2446%8%41%
1452
21st to endNight
12%5%36%6%35%6%6%9%39%
1551
June1st to 10thNight
10%5%245%3445%9%50%
1440
11th to 20thNight
8%5%25%5%4447%11%45%
1440
21st to endNight
9%5%35%6%46%6%6%8%43%
1440
July1st to 10thNight
6%425%5%35%45%11%50%
1440
11th to 20thNight
6%423426%5%5%7%56%
1440
21st to endNight
34245%35%6%6%9%53%
1575
August1st to 10thNight
5%424445%5%7%10%50%
1521
11th to 20thNight
6%5%246%25%5%6%9%51%
1776
21st to endNight
6%4245%2446%8%56%
1980
September1st to 10thNight
12%5%245%23338%54%
1800
11th to 20thNight
9%42443445%7%55%
1867
21st to endNight
9%5%26%4445%6%8%48%
1980
October1st to 10thNight
10%5%25%5%25%446%53%
2065
11th to 20thNight
16%7%35%423446%46%
2160
21st to endNight
19%9%35%5%33446%38%
2536
November1st to 10thNight
11%7%2443445%7%50%
2406
11th to 20thNight
13%9%37%6%35%35%6%39%
2470
21st to endNight
17%8%46%5%34446%39%
2543
December1st to 10thNight
16%10%49%5%34446%34%
2660
11th to 20thNight
15%11%6%8%6%34446%33%
3279
21st to endNight
23%17%7%10%7%4444416%
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
61%411%17%6%1
2528
11th to 20thDay
65%5%9%12%8%1
2530
21st to endDay
71%38%12%5%
2979
February1st to 10thDay
58%5%11%17%7%2
1725
11th to 20thDay
50%5%13%21%10%1
1858
21st to endDay
56%5%10%21%6%2
1570
March1st to 10thDay
52%5%11%22%8%1
1900
11th to 20thDay
48%7%14%20%10%1
1985
21st to endDay
59%6%11%18%41
2450
April1st to 10thDay
50%6%12%21%12%
2160
11th to 20thDay
48%5%9%23%11%3
2134
21st to endDay
50%6%13%18%11%2
2200
May1st to 10thDay
50%7%13%22%8%
2340
11th to 20thDay
49%6%12%21%12%
2442
21st to endDay
44%8%12%19%16%2
2725
June1st to 10thDay
34%8%13%26%16%2
2520
11th to 20thDay
35%8%10%22%22%3
2520
21st to endDay
40%8%13%22%15%2
2520
July1st to 10thDay
33%8%15%27%14%4
2451
11th to 20thDay
30%10%16%28%14%2
2445
21st to endDay
32%9%15%26%16%2
2591
August1st to 10thDay
32%9%16%30%12%2
2395
11th to 20thDay
32%7%16%26%17%2
2125
21st to endDay
30%8%13%26%19%4
2376
September1st to 10thDay
36%5%13%24%18%5%
2160
11th to 20thDay
30%6%11%28%21%4
2073
21st to endDay
34%7%10%26%21%2
1980
October1st to 10thDay
38%6%12%23%19%2
1891
11th to 20thDay
45%410%24%15%2
1800
21st to endDay
49%5%11%22%10%2
1818
November1st to 10thDay
36%5%14%26%17%3
1672
11th to 20thDay
49%5%11%23%12%1
1710
21st to endDay
51%5%11%22%10%
1634
December1st to 10thDay
55%412%20%8%1
1520
11th to 20thDay
56%5%10%21%6%1
1915
21st to endDay
74%5%8%9%4
2783
January1st to 10thNight
56%6%12%18%9%
4428
11th to 20thNight
66%410%12%8%
4440
21st to endNight
66%5%9%14%6%
4683
February1st to 10thNight
55%411%18%11%2
2452
11th to 20thNight
49%5%11%22%12%1
2219
21st to endNight
52%411%19%11%3
1884
March1st to 10thNight
50%5%11%22%11%1
2280
11th to 20thNight
43%5%12%21%15%3
2211
21st to endNight
56%6%10%18%8%1
2059
April1st to 10thNight
45%6%12%22%13%2
1800
11th to 20thNight
44%5%9%23%15%5%
1775
21st to endNight
45%7%13%21%11%4
1758
May1st to 10thNight
46%7%11%24%11%1
1620
11th to 20thNight
41%7%12%23%15%1
1453
21st to endNight
39%8%14%19%16%3
1552
June1st to 10thNight
32%7%13%25%19%4
1440
11th to 20thNight
32%6%14%23%22%3
1440
21st to endNight
36%9%14%22%15%4
1440
July1st to 10thNight
30%8%14%28%15%4
1400
11th to 20thNight
26%7%13%29%21%4
1392
21st to endNight
26%8%15%26%21%4
1487
August1st to 10thNight
27%8%18%29%17%2
1512
11th to 20thNight
29%7%14%26%22%2
1776
21st to endNight
27%7%11%28%22%5%
1980
September1st to 10thNight
31%5%11%25%22%5%
1800
11th to 20thNight
28%5%10%28%24%5%
1867
21st to endNight
34%7%12%25%20%3
1980
October1st to 10thNight
33%6%10%24%23%3
2065
11th to 20thNight
38%5%8%26%20%3
2160
21st to endNight
48%49%23%14%2
2536
November1st to 10thNight
35%6%10%26%19%4
2406
11th to 20thNight
46%5%12%21%14%2
2470
21st to endNight
47%410%25%12%1
2543
December1st to 10thNight
52%5%12%21%9%1
2660
11th to 20thNight
54%5%10%21%10%1
3281
21st to endNight
72%6%8%10%4
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
21%15%32%24%7%1
270
11th to 20thDay
25%17%37%13%7%1
270
21st to endDay
19%17%34%22%8%
297
February1st to 10thDay
24%13%39%20%4
270
11th to 20thDay
21%16%37%19%7%
270
21st to endDay
20%18%44%14%3
225
March1st to 10thDay
24%19%37%16%3
270
11th to 20thDay
24%17%37%17%5%1
270
21st to endDay
29%15%33%15%7%2
480
April1st to 10thDay
22%13%34%23%6%1
420
11th to 20thDay
19%17%32%18%12%2
412
21st to endDay
23%12%33%22%8%2
420
May1st to 10thDay
22%13%32%22%9%3
423
11th to 20thDay
22%10%27%26%12%3
584
21st to endDay
16%8%28%25%15%9%
679
June1st to 10thDay
9%5%26%32%21%7%
630
11th to 20thDay
10%5%27%34%20%5%
630
21st to endDay
11%7%32%30%16%4
630
July1st to 10thDay
9%416%31%24%16%
621
11th to 20thDay
10%420%31%23%11%
618
21st to endDay
7%220%37%25%8%
684
August1st to 10thDay
7%317%36%26%12%
597
11th to 20thDay
10%416%27%30%13%
439
21st to endDay
7%318%33%27%12%
495
September1st to 10thDay
14%419%30%27%6%
450
11th to 20thDay
11%315%30%27%13%
450
21st to endDay
10%10%25%26%21%7%
450
October1st to 10thDay
17%5%26%32%16%4
361
11th to 20thDay
18%22%33%20%6%
270
21st to endDay
33%13%28%21%4
297
November1st to 10thDay
13%14%39%22%8%4
270
11th to 20thDay
23%18%34%17%7%1
270
21st to endDay
23%12%37%23%6%
270
December1st to 10thDay
16%19%38%18%8%2
270
11th to 20thDay
17%16%37%26%4
270
21st to endDay
24%21%39%13%2
297
January1st to 10thNight
19%13%39%23%5%
950
11th to 20thNight
21%14%40%19%5%
950
21st to endNight
22%12%35%27%4
1045
February1st to 10thNight
23%11%39%23%4
932
11th to 20thNight
19%14%36%27%3
743
21st to endNight
24%15%38%19%4
628
March1st to 10thNight
20%17%36%22%5%
760
11th to 20thNight
17%12%37%27%5%1
691
21st to endNight
26%10%36%21%7%1
615
April1st to 10thNight
19%13%37%25%5%
540
11th to 20thNight
21%12%32%28%7%
533
21st to endNight
22%10%32%28%7%1
540
May1st to 10thNight
20%7%36%29%8%1
540
11th to 20thNight
18%8%30%34%10%1
531
21st to endNight
13%429%36%16%1
584
June1st to 10thNight
11%325%47%13%1
540
11th to 20thNight
11%425%44%15%1
540
21st to endNight
9%329%39%19%
540
July1st to 10thNight
8%216%37%32%5%
525
11th to 20thNight
7%218%43%27%2
522
21st to endNight
4115%50%28%2
591
August1st to 10thNight
6%215%44%28%5%
537
11th to 20thNight
8%212%39%34%4
534
21st to endNight
7%316%40%32%2
594
September1st to 10thNight
13%419%34%27%3
540
11th to 20thNight
9%419%37%27%4
607
21st to endNight
9%8%25%34%23%2
720
October1st to 10thNight
12%6%27%34%19%2
720
11th to 20thNight
18%13%34%25%11%1
720
21st to endNight
24%12%34%23%7%
792
November1st to 10thNight
15%10%40%24%10%1
740
11th to 20thNight
18%14%35%25%7%
760
21st to endNight
21%12%36%25%6%
833
December1st to 10thNight
21%13%39%23%5%
950
11th to 20thNight
21%12%35%26%5%
950
21st to endNight
29%15%34%20%2
1045
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