Barrington Hills
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Barrington Hills clear sky chart from 2005-11-06 to 2024-01-12.

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%
24619
17%
74647
10%
24564
41%
24564
22%
50298

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
17%
950
15%
2648
3%
946
28%
946
17%
1903
January11th to 20thNight
17%
910
13%
2547
5%
910
25%
910
14%
1942
January21st to endNight
18%
990
11%
2732
3%
990
25%
990
15%
2091
February1st to 10thNight
16%
873
12%
2313
2%
873
22%
873
16%
1744
February11th to 20thNight
21%
700
17%
2099
7%
700
30%
700
17%
1457
February21st to endNight
18%
592
19%
1776
5%
592
30%
592
16%
1247
March1st to 10thNight
23%
720
13%
2160
6%
720
29%
720
17%
1533
March11th to 20thNight
28%
700
19%
2119
9%
700
37%
700
24%
1367
March21st to endNight
27%
594
16%
1980
11%
594
35%
594
15%
1417
April1st to 10thNight
27%
540
15%
1800
9%
540
38%
540
19%
1208
April11th to 20thNight
29%
533
19%
1775
12%
533
39%
533
18%
1191
April21st to endNight
31%
540
17%
1699
9%
540
41%
540
21%
1146
May1st to 10thNight
33%
540
15%
1620
8%
540
38%
540
21%
1121
May11th to 20thNight
39%
531
18%
1457
10%
531
46%
531
27%
967
May21st to endNight
44%
582
16%
1552
8%
582
49%
582
29%
1042
June1st to 10thNight
51%
540
17%
1440
10%
540
55%
540
36%
899
June11th to 20thNight
46%
540
20%
1440
12%
540
51%
540
34%
901
June21st to endNight
47%
540
17%
1440
9%
540
53%
540
32%
931
July1st to 10thNight
65%
525
16%
1400
11%
525
67%
525
40%
844
July11th to 20thNight
58%
522
21%
1392
13%
522
63%
522
38%
839
July21st to endNight
65%
591
22%
1487
15%
558
70%
558
41%
879
August1st to 10thNight
68%
537
22%
1458
18%
534
70%
534
39%
866
August11th to 20thNight
66%
534
22%
1755
22%
534
70%
534
35%
977
August21st to endNight
63%
594
24%
1980
23%
594
68%
594
37%
1060
September1st to 10thNight
54%
540
24%
1800
23%
540
60%
540
31%
1045
September11th to 20thNight
57%
633
34%
1893
27%
633
64%
633
38%
1067
September21st to endNight
47%
720
25%
1980
16%
720
53%
720
32%
1224
October1st to 10thNight
47%
720
24%
2031
18%
720
52%
720
31%
1253
October11th to 20thNight
29%
720
21%
2173
9%
720
42%
720
24%
1390
October21st to endNight
27%
792
17%
2574
10%
792
37%
792
19%
1745
November1st to 10thNight
29%
740
26%
2406
16%
740
43%
740
25%
1460
November11th to 20thNight
23%
760
19%
2470
8%
760
36%
760
17%
1642
November21st to endNight
21%
837
18%
2547
7%
837
32%
837
18%
1744
December1st to 10thNight
20%
950
14%
2660
4%
950
28%
950
17%
1928
December11th to 20thNight
19%
950
14%
3213
4%
948
28%
948
14%
2315
December21st to endNight
12%
1039
7%
4831
2%
1026
20%
1026
6%
3913

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%46%6%35%5%5%7%37%
74802
Night
14%9%46%5%3445%7%39%
74949
TransparencyDay
46%6%11%22%13%2
74503
Night
46%5%11%22%14%2
74769
SeeingDay
17%14%31%24%11%4
14651
Night
18%11%32%27%11%1
24630

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
14%11%6%7%7%345%5%6%32%
1517
11th to 20thDay
14%14%8%12%6%345%47%25%
1453
21st to endDay
14%17%7%10%7%44446%23%
1624
February1st to 10thDay
14%14%6%7%7%46%5%5%6%26%
1647
11th to 20thDay
14%11%5%7%6%4445%5%35%
1748
21st to endDay
15%12%6%10%7%33445%31%
1480
March1st to 10thDay
15%13%5%10%6%35%446%30%
1800
11th to 20thDay
13%9%46%6%35%45%8%37%
1856
21st to endDay
20%12%48%6%45%45%6%26%
2376
April1st to 10thDay
18%11%5%7%6%3445%7%31%
2160
11th to 20thDay
16%11%36%5%35%46%6%35%
2134
21st to endDay
20%10%36%6%345%5%6%33%
2259
May1st to 10thDay
17%9%46%6%35%5%6%8%31%
2340
11th to 20thDay
19%8%36%5%3446%7%34%
2435
21st to endDay
13%7%36%6%37%5%5%8%36%
2725
June1st to 10thDay
9%5%36%5%35%5%6%7%46%
2520
11th to 20thDay
11%5%25%435%46%10%44%
2520
21st to endDay
12%5%26%6%36%5%7%8%39%
2520
July1st to 10thDay
9%3245%26%6%8%10%45%
2520
11th to 20thDay
9%5%25%435%6%6%9%46%
2520
21st to endDay
7%425%6%45%5%7%9%45%
2743
August1st to 10thDay
8%5%36%5%36%5%6%9%43%
2471
11th to 20thDay
9%6%26%6%46%5%7%9%41%
2142
21st to endDay
9%425%5%45%5%7%8%47%
2376
September1st to 10thDay
13%5%25%5%35%45%8%46%
2160
11th to 20thDay
13%4234245%5%7%52%
2048
21st to endDay
11%6%35%5%35%5%6%8%43%
1980
October1st to 10thDay
13%6%36%6%2446%6%45%
1926
11th to 20thDay
20%9%35%6%3445%7%34%
1787
21st to endDay
22%9%35%5%2445%5%37%
1782
November1st to 10thDay
13%8%35%4345%5%7%44%
1672
11th to 20thDay
16%11%47%5%3445%7%34%
1710
21st to endDay
18%10%47%5%34435%36%
1630
December1st to 10thDay
14%14%5%9%6%35%445%32%
1520
11th to 20thDay
12%14%5%9%6%36%5%6%6%29%
1918
21st to endDay
20%23%9%10%6%3333415%
2783
January1st to 10thNight
14%12%6%8%6%33345%36%
2648
11th to 20thNight
16%14%6%9%6%34446%29%
2547
21st to endNight
15%13%7%9%6%345%5%7%26%
2732
February1st to 10thNight
15%14%6%7%8%34346%30%
2313
11th to 20thNight
14%11%37%6%3445%6%35%
2098
21st to endNight
18%12%38%5%24345%36%
1776
March1st to 10thNight
16%9%5%7%6%35%45%6%34%
2160
11th to 20thNight
13%8%346%35%5%5%7%41%
2119
21st to endNight
20%10%47%6%35%446%32%
1980
April1st to 10thNight
17%7%36%5%46%5%46%39%
1800
11th to 20thNight
20%8%35%5%35%45%6%37%
1775
21st to endNight
20%7%25%5%35%45%6%39%
1699
May1st to 10thNight
15%7%37%6%45%6%7%7%34%
1620
11th to 20thNight
17%6%25%5%3446%8%40%
1457
21st to endNight
12%6%47%5%3445%8%42%
1551
June1st to 10thNight
10%425%5%35%5%6%7%48%
1440
11th to 20thNight
10%5%25%5%35%45%9%48%
1440
21st to endNight
9%5%35%5%35%6%7%9%43%
1440
July1st to 10thNight
6%314435%6%8%10%50%
1440
11th to 20thNight
7%4244345%8%8%52%
1440
21st to endNight
7%324435%5%8%9%51%
1575
August1st to 10thNight
5%4135%36%6%7%10%50%
1467
11th to 20thNight
9%3145%345%5%8%54%
1755
21st to endNight
8%5%24423448%55%
1980
September1st to 10thNight
12%5%26%434347%51%
1800
11th to 20thNight
11%424423346%55%
1893
21st to endNight
12%6%25%43445%7%48%
1980
October1st to 10thNight
12%5%25%424446%50%
2031
11th to 20thNight
17%8%25%333446%43%
2173
21st to endNight
21%9%3442445%6%38%
2574
November1st to 10thNight
11%8%35%5%34345%49%
2406
11th to 20thNight
14%11%47%5%35%35%6%37%
2470
21st to endNight
16%10%46%5%3445%5%38%
2547
December1st to 10thNight
16%11%47%6%35%5%5%6%32%
2660
11th to 20thNight
15%12%6%8%5%3345%7%32%
3279
21st to endNight
23%17%7%8%5%3445%5%18%
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%412%18%11%
1518
11th to 20thDay
60%6%12%16%6%1
1453
21st to endDay
63%410%14%9%
1624
February1st to 10thDay
59%411%15%9%1
1647
11th to 20thDay
52%5%10%21%10%2
1758
21st to endDay
55%6%9%17%11%1
1480
March1st to 10thDay
56%6%10%19%8%1
1800
11th to 20thDay
47%5%13%22%11%2
1856
21st to endDay
60%6%11%17%6%1
2376
April1st to 10thDay
55%410%19%11%
2160
11th to 20thDay
49%6%9%21%12%4
2134
21st to endDay
51%7%12%17%12%2
2259
May1st to 10thDay
50%7%12%22%8%
2340
11th to 20thDay
49%7%10%22%12%1
2439
21st to endDay
46%6%12%19%15%2
2725
June1st to 10thDay
36%6%12%26%18%2
2520
11th to 20thDay
35%8%11%23%20%3
2520
21st to endDay
41%7%13%23%14%2
2520
July1st to 10thDay
31%9%13%29%14%4
2451
11th to 20thDay
34%8%13%26%17%2
2445
21st to endDay
33%8%15%25%15%4
2591
August1st to 10thDay
36%9%14%28%12%2
2456
11th to 20thDay
38%6%14%26%14%1
2142
21st to endDay
31%7%13%25%20%4
2376
September1st to 10thDay
37%6%12%23%17%3
2160
11th to 20thDay
31%6%11%32%18%3
2048
21st to endDay
39%5%9%28%18%1
1980
October1st to 10thDay
40%6%10%26%17%1
1926
11th to 20thDay
51%311%21%12%1
1787
21st to endDay
50%410%23%10%2
1782
November1st to 10thDay
41%413%23%17%2
1672
11th to 20thDay
51%412%22%10%1
1710
21st to endDay
52%411%23%9%
1630
December1st to 10thDay
55%412%20%8%1
1520
11th to 20thDay
54%6%13%18%7%2
1915
21st to endDay
75%5%6%10%4
2783
January1st to 10thNight
53%310%20%12%1
2648
11th to 20thNight
58%5%12%15%10%
2547
21st to endNight
59%411%15%10%1
2732
February1st to 10thNight
58%39%17%12%1
2313
11th to 20thNight
50%5%11%20%13%1
2099
21st to endNight
53%39%21%10%4
1776
March1st to 10thNight
51%5%13%20%9%1
2160
11th to 20thNight
42%5%13%21%16%3
2119
21st to endNight
54%5%10%19%10%1
1980
April1st to 10thNight
47%5%11%22%13%2
1800
11th to 20thNight
48%5%7%20%16%4
1775
21st to endNight
47%5%10%22%14%2
1699
May1st to 10thNight
47%6%11%23%12%
1620
11th to 20thNight
41%6%11%25%15%2
1458
21st to endNight
41%6%13%21%17%2
1552
June1st to 10thNight
32%7%12%26%19%3
1440
11th to 20thNight
36%5%10%25%23%2
1440
21st to endNight
37%7%16%22%17%2
1440
July1st to 10thNight
27%9%16%28%16%5%
1400
11th to 20thNight
29%8%13%29%19%3
1392
21st to endNight
26%8%15%26%19%5%
1487
August1st to 10thNight
27%9%16%31%16%2
1458
11th to 20thNight
27%8%16%29%18%1
1755
21st to endNight
29%5%12%30%20%5%
1980
September1st to 10thNight
34%6%10%25%23%3
1800
11th to 20thNight
30%47%33%23%2
1893
21st to endNight
35%5%11%31%16%2
1980
October1st to 10thNight
36%5%9%27%21%2
2031
11th to 20thNight
42%410%23%18%2
2173
21st to endNight
48%5%10%23%12%2
2574
November1st to 10thNight
39%48%27%19%3
2406
11th to 20thNight
48%411%23%12%2
2470
21st to endNight
49%5%12%23%12%1
2547
December1st to 10thNight
53%5%11%21%9%1
2660
11th to 20thNight
54%413%18%10%1
3281
21st to endNight
68%5%8%13%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
20%17%39%21%21
270
11th to 20thDay
23%20%36%18%21
245
21st to endDay
23%22%35%15%5%
264
February1st to 10thDay
24%21%42%11%3
240
11th to 20thDay
29%23%31%15%2
240
21st to endDay
28%22%37%9%31
198
March1st to 10thDay
23%29%35%12%1
240
11th to 20thDay
27%17%35%15%6%
260
21st to endDay
28%16%29%20%6%2
462
April1st to 10thDay
25%17%31%23%4
420
11th to 20thDay
23%23%23%20%9%2
412
21st to endDay
23%18%30%20%9%1
420
May1st to 10thDay
21%17%32%22%6%3
423
11th to 20thDay
21%14%32%23%8%3
581
21st to endDay
16%11%30%22%15%5%
679
June1st to 10thDay
8%10%35%29%13%4
630
11th to 20thDay
12%10%32%29%12%4
630
21st to endDay
12%12%31%30%12%4
630
July1st to 10thDay
7%5%25%31%20%12%
621
11th to 20thDay
10%6%31%32%14%7%
618
21st to endDay
6%7%31%34%16%6%
684
August1st to 10thDay
9%425%32%21%9%
590
11th to 20thDay
9%5%22%31%22%11%
439
21st to endDay
9%5%24%32%21%9%
495
September1st to 10thDay
17%7%24%28%20%5%
450
11th to 20thDay
10%6%21%30%22%10%
450
21st to endDay
12%15%24%26%16%7%
450
October1st to 10thDay
16%13%28%26%13%4
396
11th to 20thDay
24%25%30%16%5%
270
21st to endDay
32%19%32%12%5%
297
November1st to 10thDay
17%18%38%18%7%2
270
11th to 20thDay
23%24%32%15%6%
270
21st to endDay
23%16%40%18%2
270
December1st to 10thDay
17%24%41%13%4
270
11th to 20thDay
19%23%37%16%4
270
21st to endDay
25%26%35%13%1
297
January1st to 10thNight
19%18%38%21%4
950
11th to 20thNight
22%17%37%20%41
910
21st to endNight
22%14%37%24%3
990
February1st to 10thNight
23%15%37%21%4
873
11th to 20thNight
22%17%35%23%3
703
21st to endNight
25%18%34%19%3
592
March1st to 10thNight
21%15%36%21%7%
720
11th to 20thNight
17%10%41%23%8%
700
21st to endNight
23%13%30%25%8%1
594
April1st to 10thNight
21%13%35%25%6%
540
11th to 20thNight
22%15%31%23%7%1
533
21st to endNight
24%11%30%28%7%1
540
May1st to 10thNight
18%9%36%30%7%1
540
11th to 20thNight
18%9%29%31%13%
531
21st to endNight
14%6%28%33%18%1
584
June1st to 10thNight
10%5%28%39%17%1
540
11th to 20thNight
12%5%31%38%14%
540
21st to endNight
10%6%31%35%17%1
540
July1st to 10thNight
6%321%39%29%3
525
11th to 20thNight
7%427%38%22%2
522
21st to endNight
6%124%44%24%1
591
August1st to 10thNight
5%217%47%26%4
537
11th to 20thNight
7%315%39%32%4
534
21st to endNight
8%321%38%29%2
594
September1st to 10thNight
11%6%21%33%25%4
540
11th to 20thNight
10%5%23%31%27%4
633
21st to endNight
12%10%26%28%22%3
720
October1st to 10thNight
15%7%26%31%19%2
720
11th to 20thNight
21%14%32%24%8%
720
21st to endNight
26%13%31%22%7%
792
November1st to 10thNight
16%14%38%23%9%1
740
11th to 20thNight
20%19%34%22%5%1
760
21st to endNight
21%14%39%20%6%
837
December1st to 10thNight
21%16%37%21%5%
950
11th to 20thNight
22%15%36%23%4
950
21st to endNight
29%16%35%18%2
1045
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