Riverwoods Field Laboratory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Riverwoods Field Laboratory clear sky chart from 2005-11-06 to 2024-01-15.

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
61%
24730
20%
74517
16%
24677
65%
24677
29%
46942

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
48%
758
22%
2459
17%
757
58%
757
32%
1424
January11th to 20thNight
51%
737
25%
2393
21%
737
60%
737
32%
1388
January21st to endNight
45%
792
24%
2516
17%
792
55%
792
29%
1512
February1st to 10thNight
49%
720
23%
2160
17%
720
55%
720
30%
1341
February11th to 20thNight
53%
700
27%
2084
18%
699
63%
699
41%
1138
February21st to endNight
55%
592
33%
1628
23%
592
63%
592
43%
912
March1st to 10thNight
54%
720
32%
1980
19%
720
64%
720
48%
1047
March11th to 20thNight
56%
720
29%
1980
21%
720
65%
720
43%
1103
March21st to endNight
57%
792
31%
2178
22%
792
65%
792
47%
1179
April1st to 10thNight
59%
720
24%
1980
19%
720
65%
720
45%
1078
April11th to 20thNight
57%
711
20%
1903
14%
711
61%
711
39%
1132
April21st to endNight
60%
720
29%
1800
17%
720
64%
720
43%
1087
May1st to 10thNight
67%
717
26%
1797
17%
717
70%
717
50%
1012
May11th to 20thNight
73%
531
16%
1592
13%
531
74%
531
32%
985
May21st to endNight
75%
582
20%
1744
16%
582
76%
582
32%
1105
June1st to 10thNight
65%
540
11%
1620
9%
540
65%
540
22%
1171
June11th to 20thNight
73%
540
11%
1620
10%
540
73%
540
25%
1119
June21st to endNight
72%
540
10%
1620
9%
540
72%
540
22%
1180
July1st to 10thNight
73%
525
5%
1575
4%
525
73%
525
19%
1191
July11th to 20thNight
77%
522
6%
1566
6%
522
77%
522
20%
1161
July21st to endNight
73%
591
7%
1672
7%
558
73%
558
21%
1241
August1st to 10thNight
78%
537
6%
1600
7%
534
78%
534
22%
1127
August11th to 20thNight
74%
629
4%
1718
4%
629
74%
629
23%
1240
August21st to endNight
62%
792
7%
2178
6%
792
62%
792
17%
1632
September1st to 10thNight
65%
720
6%
1980
6%
720
66%
720
18%
1455
September11th to 20thNight
63%
720
6%
1980
7%
720
63%
720
18%
1474
September21st to endNight
59%
720
13%
1980
11%
720
60%
720
20%
1448
October1st to 10thNight
62%
720
20%
2022
19%
720
65%
720
28%
1330
October11th to 20thNight
66%
720
25%
2160
24%
720
70%
720
32%
1320
October21st to endNight
63%
792
25%
2376
24%
792
67%
792
34%
1400
November1st to 10thNight
58%
740
26%
2221
22%
740
65%
740
34%
1298
November11th to 20thNight
59%
760
26%
2280
23%
760
64%
760
32%
1384
November21st to endNight
56%
760
29%
2280
25%
760
63%
760
32%
1387
December1st to 10thNight
59%
760
27%
2460
24%
760
66%
760
34%
1382
December11th to 20thNight
57%
760
23%
2947
22%
758
62%
758
26%
1708
December21st to endNight
57%
830
14%
4468
21%
817
62%
817
16%
2851

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
7%6%37%7%5%7%7%7%9%36%
74888
Night
7%5%36%6%45%6%7%9%43%
74885
TransparencyDay
41%8%15%18%13%4
74611
Night
35%8%17%21%14%5%
74681
SeeingDay
7%416%25%26%22%
14601
Night
8%317%33%29%9%
24743

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
8%5%26%435%6%7%8%44%
1706
11th to 20thDay
7%5%245%36%5%6%12%44%
1656
21st to endDay
10%6%36%5%35%5%6%7%43%
1836
February1st to 10thDay
10%5%25%5%45%46%9%44%
1800
11th to 20thDay
44245%445%6%9%53%
1759
21st to endDay
7%425%5%45%6%6%10%47%
1628
March1st to 10thDay
33145%45%5%7%8%54%
1980
11th to 20thDay
5%325%6%35%5%6%9%51%
1980
21st to endDay
5%425%445%6%5%9%51%
2178
April1st to 10thDay
5%325%6%46%7%7%9%45%
1980
11th to 20thDay
7%5%26%6%47%8%7%8%39%
2003
21st to endDay
5%315%5%46%5%7%9%48%
2160
May1st to 10thDay
5%3244446%7%9%53%
2176
11th to 20thDay
8%5%26%7%5%8%7%8%9%34%
2301
21st to endDay
7%5%39%9%6%8%6%7%9%32%
2531
June1st to 10thDay
12%9%48%9%6%8%8%8%9%19%
2340
11th to 20thDay
6%6%39%9%6%9%9%8%10%24%
2340
21st to endDay
8%7%47%11%6%10%8%7%9%24%
2340
July1st to 10thDay
9%7%49%9%6%8%8%8%9%21%
2340
11th to 20thDay
6%6%39%11%6%9%8%9%9%23%
2340
21st to endDay
7%7%39%9%7%10%8%8%10%21%
2547
August1st to 10thDay
5%6%37%10%6%9%10%9%12%24%
2327
11th to 20thDay
5%5%39%8%7%8%9%8%11%26%
2157
21st to endDay
7%8%411%9%7%8%8%8%10%20%
2178
September1st to 10thDay
7%6%49%10%6%8%9%9%10%22%
1980
11th to 20thDay
8%7%410%10%6%8%8%8%9%21%
1980
21st to endDay
9%8%37%8%5%8%8%8%9%25%
1980
October1st to 10thDay
9%6%37%8%5%6%7%6%11%33%
1936
11th to 20thDay
6%5%36%8%5%7%7%6%8%38%
1800
21st to endDay
7%5%25%7%46%47%10%43%
1980
November1st to 10thDay
7%6%26%6%46%5%6%8%44%
1857
11th to 20thDay
8%6%36%6%46%5%5%10%39%
1900
21st to endDay
8%5%36%446%5%7%9%42%
1900
December1st to 10thDay
8%5%245%45%6%6%8%46%
1715
11th to 20thDay
10%6%35%6%35%46%9%43%
2153
21st to endDay
10%7%37%8%5%7%6%6%9%34%
3124
January1st to 10thNight
8%5%25%5%3447%9%46%
2459
11th to 20thNight
8%5%35%5%345%6%11%45%
2393
21st to endNight
12%6%245%35%5%5%8%46%
2516
February1st to 10thNight
9%6%36%5%345%5%8%44%
2160
11th to 20thNight
7%42442346%8%54%
2084
21st to endNight
6%424425%5%6%8%55%
1628
March1st to 10thNight
431334345%9%60%
1980
11th to 20thNight
5%4244345%5%9%55%
1980
21st to endNight
5%32432445%8%59%
2178
April1st to 10thNight
432442446%10%57%
1980
11th to 20thNight
5%4245%35%5%7%9%49%
1903
21st to endNight
44245%35%5%5%7%55%
1800
May1st to 10thNight
432333445%9%60%
1797
11th to 20thNight
6%435%5%46%6%6%11%45%
1592
21st to endNight
6%5%26%6%45%8%8%9%41%
1744
June1st to 10thNight
10%8%38%7%5%6%7%7%10%29%
1620
11th to 20thNight
5%6%36%7%5%6%7%9%13%32%
1620
21st to endNight
6%6%36%8%47%8%7%10%34%
1620
July1st to 10thNight
9%7%46%6%5%6%8%8%11%30%
1620
11th to 20thNight
6%438%6%5%7%8%9%11%33%
1620
21st to endNight
5%7%39%8%48%8%9%10%30%
1771
August1st to 10thNight
46%26%7%5%7%8%9%13%33%
1611
11th to 20thNight
5%5%37%8%5%7%8%9%12%33%
1718
21st to endNight
9%7%37%8%5%7%6%9%12%28%
2178
September1st to 10thNight
6%6%27%8%5%7%9%9%12%28%
1980
11th to 20thNight
8%6%48%9%5%7%7%7%10%29%
1980
21st to endNight
10%8%39%7%47%6%6%9%31%
1980
October1st to 10thNight
9%7%25%6%45%6%7%10%38%
2022
11th to 20thNight
7%6%35%6%346%7%8%46%
2160
21st to endNight
9%5%25%4335%5%9%48%
2376
November1st to 10thNight
8%5%35%4345%6%8%49%
2221
11th to 20thNight
8%5%35%5%45%6%6%8%45%
2280
21st to endNight
9%5%35%5%35%5%6%8%45%
2280
December1st to 10thNight
7%4246%345%6%8%50%
2460
11th to 20thNight
12%6%25%4345%5%7%47%
3042
21st to endNight
11%8%37%7%46%6%6%9%34%
4532

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
35%6%9%23%20%8%
1707
11th to 20thDay
33%5%10%24%21%6%
1656
21st to endDay
39%5%9%20%19%9%
1836
February1st to 10thDay
36%5%8%21%21%8%
1800
11th to 20thDay
28%49%26%21%11%
1769
21st to endDay
32%5%11%18%25%8%
1628
March1st to 10thDay
26%5%13%24%23%9%
1980
11th to 20thDay
29%412%27%20%7%
1980
21st to endDay
28%6%9%27%22%8%
2178
April1st to 10thDay
30%8%15%24%17%6%
1980
11th to 20thDay
37%7%12%19%20%4
2003
21st to endDay
31%6%10%21%25%7%
2160
May1st to 10thDay
26%6%13%22%24%9%
2176
11th to 20thDay
41%8%15%20%14%1
2305
21st to endDay
46%8%12%18%15%1
2531
June1st to 10thDay
57%9%18%13%4
2340
11th to 20thDay
48%13%20%16%2
2340
21st to endDay
54%11%21%11%2
2340
July1st to 10thDay
54%14%25%7%1
2275
11th to 20thDay
52%13%25%9%1
2271
21st to endDay
52%14%22%11%1
2405
August1st to 10thDay
46%15%30%8%1
2314
11th to 20thDay
47%13%31%9%1
2157
21st to endDay
55%13%21%9%2
2178
September1st to 10thDay
51%14%21%13%1
1980
11th to 20thDay
54%13%20%11%2
1980
21st to endDay
49%12%17%13%8%2
1980
October1st to 10thDay
43%8%13%18%12%5%
1936
11th to 20thDay
40%8%10%21%17%4
1800
21st to endDay
34%6%11%19%20%9%
1980
November1st to 10thDay
37%6%12%18%17%10%
1857
11th to 20thDay
40%6%10%22%16%7%
1900
21st to endDay
36%6%11%22%19%6%
1900
December1st to 10thDay
33%6%15%24%17%4
1715
11th to 20thDay
37%6%11%20%16%11%
2150
21st to endDay
45%7%11%18%15%4
3124
January1st to 10thNight
34%5%14%23%18%7%
2459
11th to 20thNight
33%5%10%29%17%6%
2393
21st to endNight
36%5%11%22%17%8%
2516
February1st to 10thNight
36%6%12%19%19%8%
2160
11th to 20thNight
27%5%11%24%24%10%
2085
21st to endNight
26%5%12%22%28%6%
1628
March1st to 10thNight
22%5%13%30%24%7%
1980
11th to 20thNight
26%5%14%31%18%7%
1980
21st to endNight
22%5%14%29%22%8%
2178
April1st to 10thNight
23%6%20%28%16%7%
1980
11th to 20thNight
29%6%17%23%20%4
1903
21st to endNight
27%6%12%26%23%6%
1800
May1st to 10thNight
22%6%13%29%22%9%
1797
11th to 20thNight
32%9%19%26%13%1
1593
21st to endNight
34%9%18%22%17%
1745
June1st to 10thNight
48%8%22%17%5%
1620
11th to 20thNight
40%12%27%19%2
1620
21st to endNight
41%16%24%16%4
1620
July1st to 10thNight
45%16%26%11%2
1575
11th to 20thNight
43%16%29%12%1
1566
21st to endNight
42%16%28%13%1
1672
August1st to 10thNight
38%17%33%13%
1600
11th to 20thNight
39%16%36%7%1
1718
21st to endNight
46%15%26%11%2
2178
September1st to 10thNight
43%17%27%12%2
1980
11th to 20thNight
47%14%22%15%2
1980
21st to endNight
48%11%18%15%7%
1980
October1st to 10thNight
38%9%18%18%14%4
2022
11th to 20thNight
33%8%13%21%21%3
2160
21st to endNight
32%6%13%19%20%9%
2376
November1st to 10thNight
32%6%12%21%20%9%
2221
11th to 20thNight
34%7%12%24%16%7%
2280
21st to endNight
36%6%10%23%20%6%
2280
December1st to 10thNight
31%5%13%30%15%6%
2460
11th to 20thNight
36%5%11%20%17%11%
3044
21st to endNight
46%6%14%16%13%5%
4532

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
8%7%42%30%11%2
270
11th to 20thDay
7%9%35%30%13%6%
252
21st to endDay
14%13%39%24%8%1
264
February1st to 10thDay
11%8%27%32%20%3
240
11th to 20thDay
6%7%26%35%19%7%
251
21st to endDay
8%6%23%34%26%4
346
March1st to 10thDay
47%29%37%20%2
420
11th to 20thDay
6%5%27%31%27%4
420
21st to endDay
5%425%33%28%5%
462
April1st to 10thDay
5%5%32%31%21%6%
420
11th to 20thDay
7%7%22%33%24%7%
412
21st to endDay
7%317%34%29%11%
420
May1st to 10thDay
5%116%31%31%15%
423
11th to 20thDay
10%315%24%30%18%
447
21st to endDay
7%27%21%32%30%
485
June1st to 10thDay
14%39%16%30%27%
450
11th to 20thDay
7%25%15%30%41%
450
21st to endDay
6%2312%24%53%
450
July1st to 10thDay
7%137%25%57%
445
11th to 20thDay
31312%28%53%
444
21st to endDay
10%2213%25%48%
488
August1st to 10thDay
415%12%26%53%
446
11th to 20thDay
429%28%57%
439
21st to endDay
8%36%17%26%40%
495
September1st to 10thDay
6%37%10%26%48%
450
11th to 20thDay
6%36%19%27%40%
450
21st to endDay
8%37%17%33%32%
450
October1st to 10thDay
11%311%32%31%12%
450
11th to 20thDay
6%315%34%30%12%
450
21st to endDay
7%316%35%30%9%
495
November1st to 10thDay
9%7%18%28%28%9%
455
11th to 20thDay
13%5%24%32%21%5%
460
21st to endDay
8%420%40%24%5%
460
December1st to 10thDay
5%8%28%33%19%7%
275
11th to 20thDay
8%8%27%36%18%4
270
21st to endDay
6%9%29%35%16%6%
297
January1st to 10thNight
9%6%29%37%18%1
760
11th to 20thNight
10%5%26%43%14%2
737
21st to endNight
13%6%30%39%11%
792
February1st to 10thNight
11%7%25%42%15%
720
11th to 20thNight
8%6%27%42%17%1
703
21st to endNight
9%327%47%14%
592
March1st to 10thNight
5%5%32%43%15%
720
11th to 20thNight
7%5%26%42%19%1
720
21st to endNight
6%427%47%16%
792
April1st to 10thNight
5%5%26%47%18%
720
11th to 20thNight
7%426%43%20%1
711
21st to endNight
6%324%46%21%1
720
May1st to 10thNight
5%317%48%25%2
717
11th to 20thNight
7%18%44%35%4
531
21st to endNight
7%16%34%44%8%
584
June1st to 10thNight
12%35%24%46%9%
540
11th to 20thNight
7%1318%49%22%
540
21st to endNight
7%2213%44%32%
540
July1st to 10thNight
8%226%49%33%
525
11th to 20thNight
5%1110%43%40%
522
21st to endNight
5%2210%45%36%
591
August1st to 10thNight
5%29%52%32%
537
11th to 20thNight
5%239%48%33%
629
21st to endNight
12%26%16%40%25%
792
September1st to 10thNight
8%25%15%44%24%
720
11th to 20thNight
9%25%20%44%20%
720
21st to endNight
14%27%23%42%13%
720
October1st to 10thNight
12%312%35%33%6%
720
11th to 20thNight
8%311%36%37%5%
720
21st to endNight
11%315%37%30%4
792
November1st to 10thNight
9%321%38%26%3
740
11th to 20thNight
8%421%43%21%3
760
21st to endNight
10%321%43%22%1
760
December1st to 10thNight
8%321%41%26%2
760
11th to 20thNight
10%5%21%39%24%2
760
21st to endNight
9%423%39%24%1
836
Page generated at 2024-01-11 22:33:47. Version ac07

Copyright 2024 Attilla Danko


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