Tinley Park
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Tinley Park clear sky chart from 2005-11-05 to 2018-01-12.

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
36%
16460
17%
48341
11%
16418
43%
16418
23%
32454

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 15thNight
21%
956
13%
2662
4%
951
29%
951
17%
1938
January16th to endNight
20%
960
12%
2661
4%
960
27%
960
15%
2027
February1st to 15thNight
21%
776
13%
2187
3%
776
29%
776
18%
1573
February16th to endNight
25%
631
18%
1893
7%
631
34%
631
17%
1344
March1st to 15thNight
24%
720
12%
2160
8%
720
27%
720
17%
1544
March16th to endNight
30%
639
15%
2019
10%
639
36%
639
18%
1413
April1st to 15thNight
30%
539
15%
1797
10%
539
38%
539
20%
1200
April16th to endNight
31%
540
18%
1728
11%
540
40%
540
21%
1166
May1st to 15thNight
36%
540
16%
1620
9%
540
43%
540
23%
1112
May16th to endNight
49%
562
17%
1499
10%
561
54%
561
31%
982
June1st to 15thNight
49%
540
17%
1440
10%
540
54%
540
36%
899
June16th to endNight
48%
540
17%
1440
9%
540
53%
540
31%
950
July1st to 15thNight
61%
510
17%
1360
11%
510
64%
510
38%
828
July16th to endNight
67%
564
22%
1417
17%
531
71%
531
43%
829
August1st to 15thNight
77%
539
22%
1584
22%
536
78%
536
42%
884
August16th to endNight
65%
573
21%
1910
21%
573
70%
573
34%
1073
September1st to 15thNight
61%
555
28%
1815
27%
555
67%
555
36%
1006
September16th to endNight
59%
717
27%
1980
21%
717
63%
717
36%
1193
October1st to 15thNight
47%
720
25%
2054
18%
720
53%
720
31%
1258
October16th to endNight
29%
768
19%
2451
12%
768
38%
768
21%
1597
November1st to 15thNight
30%
760
22%
2471
15%
760
41%
760
23%
1558
November16th to endNight
25%
796
18%
2551
10%
796
35%
796
20%
1692
December1st to 15thNight
19%
975
13%
2730
4%
975
27%
975
17%
2020
December16th to endNight
15%
1040
10%
2912
2%
1040
22%
1040
11%
2368

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%5%345%5%7%36%
49007
Night
14%8%36%5%2445%6%39%
48509
Cloud CoverDay
14%8%36%5%3445%7%36%
49016
Night
14%8%35%5%24446%39%
48514
TransparencyDay
46%6%12%21%12%1
48693
Night
44%5%12%21%14%2
48341
SeeingDay
15%8%29%25%14%5%
6331
Night
18%9%29%28%12%1
16464

By Month

Percentage Cloud Cover NE (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 15thDay
16%14%46%6%445%5%6%25%
1520
16th to endDay
13%16%8%8%6%34436%25%
1560
February1st to 15thDay
15%13%6%8%6%34446%26%
1672
16th to endDay
15%11%47%7%43345%31%
1580
March1st to 15thDay
15%13%5%7%5%35%5%45%28%
1790
16th to endDay
18%9%47%5%345%46%30%
2216
April1st to 15thDay
18%9%47%5%34346%32%
2151
16th to endDay
19%7%25%5%3445%6%35%
2232
May1st to 15thDay
18%9%36%6%3445%7%29%
2331
16th to endDay
12%5%35%6%35%5%47%39%
2615
June1st to 15thDay
11%5%35%4345%6%7%43%
2520
16th to endDay
10%425%6%45%7%6%9%36%
2520
July1st to 15thDay
7%425%5%35%5%5%10%42%
2520
16th to endDay
6%425%5%35%6%7%10%40%
2655
August1st to 15thDay
6%415%6%45%5%6%9%43%
2364
16th to endDay
8%4246%35%6%6%8%42%
2292
September1st to 15thDay
12%413424448%47%
2133
16th to endDay
8%5%25%4345%6%8%44%
1980
October1st to 15thDay
15%7%24434446%42%
1905
16th to endDay
17%8%35%6%33446%36%
1773
November1st to 15thDay
15%7%35%42335%6%40%
1717
16th to endDay
17%8%37%424436%38%
1737
December1st to 15thDay
16%10%5%8%6%35%35%5%28%
1560
16th to endDay
20%16%5%8%6%34445%22%
1664
January1st to 15thNight
17%11%37%5%24345%33%
2662
16th to endNight
13%12%7%8%6%34445%28%
2661
February1st to 15thNight
15%12%46%5%34435%34%
2185
16th to endNight
16%10%47%6%34345%33%
1893
March1st to 15thNight
15%12%46%6%3443434%
2147
16th to endNight
15%7%37%5%35%5%5%7%33%
2019
April1st to 15thNight
16%7%46%5%23347%37%
1797
16th to endNight
18%8%25%5%2435%5%38%
1728
May1st to 15thNight
18%7%25%42446%8%35%
1620
16th to endNight
10%4145%345%6%8%43%
1497
June1st to 15thNight
9%5%2442345%6%50%
1440
16th to endNight
9%5%245%35%46%10%40%
1440
July1st to 15thNight
6%4244345%7%8%50%
1440
16th to endNight
5%3144235%7%10%50%
1513
August1st to 15thNight
241343446%10%53%
1593
16th to endNight
8%22342445%9%50%
1910
September1st to 15thNight
11%31432335%7%54%
1815
16th to endNight
7%5%15%42446%6%50%
1980
October1st to 15thNight
13%425%424247%49%
2054
16th to endNight
19%7%35%313345%41%
2451
November1st to 15thNight
13%7%35%423445%44%
2471
16th to endNight
17%8%35%5%23347%37%
2551
December1st to 15thNight
19%10%48%5%23445%31%
2730
16th to endNight
21%15%48%7%3433422%
2912

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 15thDay
15%14%46%6%4445%6%25%
1520
16th to endDay
13%16%7%9%6%34345%26%
1560
February1st to 15thDay
15%14%5%7%6%34445%27%
1672
16th to endDay
15%11%48%7%34345%31%
1580
March1st to 15thDay
16%12%5%7%5%35%45%5%28%
1800
16th to endDay
18%9%36%5%3445%6%31%
2215
April1st to 15thDay
18%10%47%5%24346%32%
2151
16th to endDay
20%6%25%5%3445%6%35%
2232
May1st to 15thDay
18%8%36%5%3445%7%30%
2331
16th to endDay
13%5%35%6%345%5%7%39%
2615
June1st to 15thDay
11%4245%335%5%7%44%
2520
16th to endDay
10%425%5%36%6%7%9%37%
2520
July1st to 15thDay
7%4246%35%5%5%9%43%
2520
16th to endDay
7%425%5%36%6%7%9%41%
2655
August1st to 15thDay
6%425%6%45%5%7%8%43%
2364
16th to endDay
9%4245%45%5%5%9%42%
2292
September1st to 15thDay
13%423333447%48%
2133
16th to endDay
9%425%435%5%6%8%44%
1980
October1st to 15thDay
16%6%24424446%42%
1905
16th to endDay
18%8%26%6%23346%36%
1773
November1st to 15thDay
15%8%35%42345%6%41%
1717
16th to endDay
17%8%36%424346%38%
1737
December1st to 15thDay
16%11%48%7%35%345%28%
1560
16th to endDay
20%16%6%7%5%34345%22%
1664
January1st to 15thNight
17%11%47%43334433%
2662
16th to endNight
13%12%7%7%6%35%445%28%
2661
February1st to 15thNight
15%12%46%5%34335%34%
2178
16th to endNight
17%10%46%6%24345%33%
1893
March1st to 15thNight
16%11%47%5%2443434%
2160
16th to endNight
15%8%36%5%35%5%5%7%33%
2019
April1st to 15thNight
16%7%46%423446%37%
1797
16th to endNight
18%7%25%5%2344438%
1728
May1st to 15thNight
19%6%25%4345%5%8%34%
1619
16th to endNight
10%425%5%345%6%8%43%
1497
June1st to 15thNight
10%5%245%2345%7%50%
1440
16th to endNight
10%4245%25%46%10%41%
1440
July1st to 15thNight
6%3145%345%6%8%51%
1440
16th to endNight
5%3234245%7%11%49%
1513
August1st to 15thNight
3313425%46%9%53%
1593
16th to endNight
9%31432435%9%51%
1910
September1st to 15thNight
10%41342335%7%54%
1815
16th to endNight
8%425%4245%5%7%50%
1980
October1st to 15thNight
14%424323346%48%
2054
16th to endNight
19%7%35%323336%40%
2451
November1st to 15thNight
13%7%35%5%33435%43%
2471
16th to endNight
18%7%35%42335%7%38%
2551
December1st to 15thNight
19%9%37%6%23445%31%
2730
16th to endNight
21%15%5%7%6%3434422%
2912

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 15thDay
57%6%12%13%9%
1521
16th to endDay
61%5%11%14%6%
1560
February1st to 15thDay
59%410%14%8%1
1674
16th to endDay
54%5%11%21%5%1
1580
March1st to 15thDay
56%5%12%17%7%
1800
16th to endDay
53%5%13%20%5%
2216
April1st to 15thDay
53%48%20%11%
2151
16th to endDay
48%6%13%16%10%3
2232
May1st to 15thDay
52%5%11%21%6%
2331
16th to endDay
43%6%11%20%15%1
2619
June1st to 15thDay
37%6%12%23%19%1
2520
16th to endDay
39%9%14%20%14%2
2520
July1st to 15thDay
36%7%12%25%15%2
2371
16th to endDay
35%9%15%22%13%2
2488
August1st to 15thDay
35%7%14%25%15%1
2349
16th to endDay
36%7%12%24%15%3
2292
September1st to 15thDay
35%5%11%24%19%3
2133
16th to endDay
34%7%9%27%18%1
1980
October1st to 15thDay
42%5%11%23%14%2
1905
16th to endDay
48%5%12%22%10%1
1773
November1st to 15thDay
43%5%12%21%15%2
1717
16th to endDay
48%412%25%9%
1737
December1st to 15thDay
57%411%18%7%
1560
16th to endDay
64%5%9%12%6%
1664
January1st to 15thNight
53%412%17%11%
2662
16th to endNight
56%5%13%15%8%
2661
February1st to 15thNight
52%412%19%9%1
2187
16th to endNight
51%411%20%9%1
1893
March1st to 15thNight
52%412%18%9%2
2160
16th to endNight
49%6%13%20%8%1
2019
April1st to 15thNight
47%410%21%14%1
1797
16th to endNight
47%5%9%20%13%4
1728
May1st to 15thNight
46%5%12%23%11%
1620
16th to endNight
36%7%14%20%17%3
1499
June1st to 15thNight
34%5%11%26%19%3
1440
16th to endNight
36%7%12%21%18%1
1440
July1st to 15thNight
30%6%13%26%19%3
1360
16th to endNight
25%6%16%28%17%4
1417
August1st to 15thNight
25%6%17%28%19%2
1584
16th to endNight
30%6%13%25%19%4
1910
September1st to 15thNight
29%411%25%25%3
1815
16th to endNight
32%5%9%29%20%2
1980
October1st to 15thNight
36%310%26%20%2
2054
16th to endNight
45%312%22%14%1
2451
November1st to 15thNight
42%49%23%16%3
2471
16th to endNight
46%413%23%10%
2551
December1st to 15thNight
54%5%10%19%10%
2730
16th to endNight
66%49%13%5%1
2912

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 15thDay
23%11%35%23%5%
123
16th to endDay
14%15%38%25%5%1
96
February1st to 15thDay
22%23%42%12%
90
16th to endDay
18%17%37%16%7%3
81
March1st to 15thDay
30%20%33%12%4
90
16th to endDay
28%9%29%20%10%1
252
April1st to 15thDay
24%12%27%22%11%
270
16th to endDay
21%13%30%20%11%2
270
May1st to 15thDay
23%10%30%21%10%4
288
16th to endDay
16%11%31%25%11%3
515
June1st to 15thDay
13%7%32%29%13%4
495
16th to endDay
11%9%37%26%10%5%
495
July1st to 15thDay
10%5%29%29%16%9%
475
16th to endDay
8%426%30%20%10%
515
August1st to 15thDay
7%218%33%23%15%
382
16th to endDay
9%414%33%25%13%
332
September1st to 15thDay
12%320%28%27%8%
315
16th to endDay
9%5%18%28%28%9%
314
October1st to 15thDay
18%6%24%27%17%5%
240
16th to endDay
25%11%36%22%4
144
November1st to 15thDay
20%5%28%26%12%5%
135
16th to endDay
23%10%44%15%5%
135
December1st to 15thDay
14%24%43%12%4
135
16th to endDay
23%25%43%6%1
144
January1st to 15thNight
21%17%34%22%3
956
16th to endNight
21%14%34%26%3
960
February1st to 15thNight
21%12%38%22%4
779
16th to endNight
23%13%31%25%5%
631
March1st to 15thNight
22%14%35%21%5%
720
16th to endNight
18%12%33%26%8%1
639
April1st to 15thNight
22%11%31%27%5%
539
16th to endNight
22%8%33%24%10%
540
May1st to 15thNight
21%6%30%28%12%
540
16th to endNight
12%5%26%37%17%
563
June1st to 15thNight
12%326%43%13%
540
16th to endNight
10%330%34%19%1
540
July1st to 15thNight
8%221%41%24%1
510
16th to endNight
6%215%44%27%3
564
August1st to 15thNight
5%9%48%30%5%
539
16th to endNight
9%116%34%32%4
573
September1st to 15thNight
12%416%33%27%6%
555
16th to endNight
10%5%17%34%28%3
717
October1st to 15thNight
17%6%23%32%17%1
720
16th to endNight
24%13%30%22%8%
768
November1st to 15thNight
18%12%34%22%9%1
760
16th to endNight
21%14%33%22%7%
796
December1st to 15thNight
25%13%35%21%4
975
16th to endNight
29%14%33%19%2
1040
Page generated at 2018-01-12 21:01:36. Version ac04

Copyright 2018 A. Danko


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