Lake Zurich
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Lake Zurich clear sky chart from 2005-11-05 to 2018-03-21.

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%
16794
18%
49211
10%
16753
43%
16753
23%
32901

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
19%
975
15%
2716
4%
970
29%
970
18%
1956
January16th to endNight
19%
1040
13%
2886
4%
1040
27%
1040
16%
2145
February1st to 15thNight
19%
869
15%
2400
4%
869
28%
869
18%
1715
February16th to endNight
24%
683
18%
2049
8%
683
33%
683
16%
1446
March1st to 15thNight
26%
780
14%
2340
7%
780
33%
780
19%
1626
March16th to endNight
33%
646
16%
2080
12%
646
39%
646
19%
1436
April1st to 15thNight
29%
539
15%
1797
9%
539
38%
539
18%
1237
April16th to endNight
34%
540
19%
1729
11%
540
44%
540
22%
1147
May1st to 15thNight
35%
540
15%
1587
8%
540
41%
540
21%
1121
May16th to endNight
46%
561
17%
1498
9%
561
51%
561
30%
971
June1st to 15thNight
51%
540
16%
1440
9%
540
55%
540
34%
906
June16th to endNight
50%
540
16%
1440
9%
540
54%
540
31%
946
July1st to 15thNight
63%
510
17%
1360
11%
510
66%
510
39%
823
July16th to endNight
67%
564
21%
1417
15%
531
70%
531
41%
845
August1st to 15thNight
75%
539
22%
1558
21%
536
77%
536
42%
861
August16th to endNight
63%
573
21%
1910
21%
573
68%
573
34%
1053
September1st to 15thNight
60%
543
28%
1803
27%
543
65%
543
36%
979
September16th to endNight
56%
717
28%
1980
19%
717
62%
717
36%
1188
October1st to 15thNight
47%
720
24%
2073
17%
720
53%
720
30%
1294
October16th to endNight
29%
768
19%
2448
10%
768
40%
768
21%
1606
November1st to 15thNight
31%
760
23%
2471
15%
760
42%
760
23%
1562
November16th to endNight
25%
832
18%
2587
8%
832
36%
832
19%
1727
December1st to 15thNight
20%
975
14%
2730
4%
975
29%
975
16%
2001
December16th to endNight
14%
1040
12%
2912
2%
1040
23%
1040
12%
2310

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%3445%7%37%
49641
Night
14%7%35%424446%40%
49379
Cloud CoverDay
13%8%36%5%3445%7%36%
49650
Night
14%8%36%424446%40%
49384
TransparencyDay
45%6%12%22%12%1
49327
Night
44%5%11%22%14%1
49211
SeeingDay
16%9%29%25%13%5%
6567
Night
18%9%29%28%12%1
16799

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
14%11%48%5%35%446%30%
1552
16th to endDay
11%15%7%8%7%34445%26%
1688
February1st to 15thDay
13%15%6%7%435%445%30%
1790
16th to endDay
14%12%48%5%43346%31%
1710
March1st to 15thDay
14%12%5%7%5%24446%32%
1940
16th to endDay
17%9%47%6%34446%31%
2280
April1st to 15thDay
19%11%46%5%34345%31%
2151
16th to endDay
19%8%245%3345%6%35%
2229
May1st to 15thDay
17%8%46%5%35%45%6%30%
2361
16th to endDay
12%5%35%6%45%5%5%7%38%
2617
June1st to 15thDay
10%6%25%435%46%7%43%
2520
16th to endDay
9%5%35%6%35%5%7%9%37%
2520
July1st to 15thDay
8%324435%5%8%9%44%
2520
16th to endDay
8%3246%35%5%7%9%42%
2655
August1st to 15thDay
7%5%26%5%36%5%6%9%41%
2389
16th to endDay
10%5%245%35%5%6%8%41%
2292
September1st to 15thDay
12%41342445%6%49%
2144
16th to endDay
9%5%245%345%6%9%43%
1980
October1st to 15thDay
16%5%25%5%3345%5%42%
1886
16th to endDay
18%8%35%5%33445%37%
1776
November1st to 15thDay
15%9%35%42445%7%38%
1717
16th to endDay
16%9%46%5%23335%39%
1700
December1st to 15thDay
16%12%47%6%3445%5%30%
1560
16th to endDay
19%15%6%7%5%24345%24%
1664
January1st to 15thNight
16%11%47%5%24335%36%
2716
16th to endNight
12%13%6%8%5%24447%29%
2886
February1st to 15thNight
14%12%46%434335%35%
2398
16th to endNight
16%11%36%5%24336%34%
2049
March1st to 15thNight
15%9%47%5%24445%37%
2327
16th to endNight
15%8%36%5%25%45%7%34%
2080
April1st to 15thNight
18%7%36%6%25%445%35%
1797
16th to endNight
20%6%25%413345%41%
1729
May1st to 15thNight
17%6%35%6%4445%7%34%
1587
16th to endNight
10%436%42346%8%43%
1496
June1st to 15thNight
11%3244245%5%6%48%
1440
16th to endNight
8%4245%36%5%8%9%39%
1440
July1st to 15thNight
7%23425%5%7%8%51%
1440
16th to endNight
5%313335%5%7%9%50%
1513
August1st to 15thNight
3213335%5%6%9%54%
1567
16th to endNight
9%225%32345%8%52%
1910
September1st to 15thNight
9%423323346%56%
1803
16th to endNight
8%423425%448%51%
1980
October1st to 15thNight
13%424423447%47%
2073
16th to endNight
18%8%25%323345%41%
2448
November1st to 15thNight
13%7%36%5%23345%44%
2471
16th to endNight
15%9%35%5%24336%38%
2587
December1st to 15thNight
19%9%47%5%34445%31%
2730
16th to endNight
21%14%47%5%33445%23%
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
14%12%5%8%5%34446%30%
1552
16th to endDay
12%15%7%9%6%24445%26%
1688
February1st to 15thDay
13%15%5%7%5%35%445%29%
1790
16th to endDay
14%12%48%5%4335%5%31%
1710
March1st to 15thDay
14%12%47%5%34446%31%
1950
16th to endDay
17%9%47%6%34446%31%
2279
April1st to 15thDay
19%11%36%5%34345%31%
2151
16th to endDay
19%8%235%4345%6%35%
2229
May1st to 15thDay
16%9%47%5%35%45%6%29%
2361
16th to endDay
12%5%35%6%45%5%5%7%37%
2617
June1st to 15thDay
10%5%25%5%35%5%7%6%42%
2520
16th to endDay
9%5%36%5%35%5%8%9%37%
2520
July1st to 15thDay
8%325%445%5%7%10%44%
2520
16th to endDay
7%4246%35%5%7%9%42%
2655
August1st to 15thDay
7%5%25%5%36%5%6%9%41%
2389
16th to endDay
9%5%25%5%35%5%6%8%41%
2292
September1st to 15thDay
12%3143245%5%6%49%
2144
16th to endDay
9%4245%35%5%6%9%43%
1980
October1st to 15thDay
16%5%25%5%2345%6%42%
1886
16th to endDay
18%8%35%5%33445%37%
1776
November1st to 15thDay
15%9%35%424447%38%
1717
16th to endDay
16%8%46%5%23336%39%
1700
December1st to 15thDay
16%12%46%6%3445%6%30%
1560
16th to endDay
20%15%7%7%5%24345%24%
1664
January1st to 15thNight
16%11%47%5%23335%35%
2716
16th to endNight
12%13%6%8%6%25%447%29%
2886
February1st to 15thNight
14%12%46%434345%35%
2391
16th to endNight
16%11%46%5%24346%34%
2049
March1st to 15thNight
15%9%37%5%34445%37%
2340
16th to endNight
15%8%36%5%3445%7%34%
2080
April1st to 15thNight
17%7%36%6%25%45%5%35%
1797
16th to endNight
20%6%25%413335%41%
1729
May1st to 15thNight
17%6%36%5%345%5%7%33%
1586
16th to endNight
10%436%5%2346%8%43%
1496
June1st to 15thNight
12%3144245%5%6%48%
1440
16th to endNight
8%425%5%36%5%7%9%40%
1440
July1st to 15thNight
6%313425%6%6%9%51%
1440
16th to endNight
5%313335%5%7%9%50%
1513
August1st to 15thNight
3213326%5%6%9%53%
1567
16th to endNight
9%315%31345%8%52%
1910
September1st to 15thNight
9%423323345%56%
1803
16th to endNight
8%4235%24438%51%
1980
October1st to 15thNight
13%5%24423447%47%
2073
16th to endNight
18%8%24413336%41%
2448
November1st to 15thNight
13%7%36%423336%44%
2471
16th to endNight
15%10%45%5%23336%38%
2587
December1st to 15thNight
19%10%36%5%2445%5%31%
2730
16th to endNight
22%14%48%5%33445%23%
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
53%414%16%9%
1553
16th to endDay
59%410%16%7%
1688
February1st to 15thDay
56%411%17%9%1
1792
16th to endDay
53%5%10%19%8%1
1710
March1st to 15thDay
53%6%11%20%8%1
1950
16th to endDay
54%413%20%5%
2280
April1st to 15thDay
55%48%20%10%
2151
16th to endDay
48%6%11%18%12%3
2229
May1st to 15thDay
53%6%11%21%7%
2361
16th to endDay
43%6%12%21%14%1
2621
June1st to 15thDay
38%8%9%24%17%1
2520
16th to endDay
39%9%13%20%15%2
2520
July1st to 15thDay
32%8%13%28%14%2
2371
16th to endDay
35%7%16%22%15%3
2488
August1st to 15thDay
37%7%12%28%12%1
2374
16th to endDay
37%6%13%23%16%2
2292
September1st to 15thDay
33%6%11%25%20%2
2144
16th to endDay
35%6%10%29%16%
1980
October1st to 15thDay
42%5%10%25%13%1
1886
16th to endDay
47%5%11%23%10%1
1776
November1st to 15thDay
45%411%22%13%2
1717
16th to endDay
48%412%26%7%
1700
December1st to 15thDay
54%5%11%19%7%
1560
16th to endDay
62%411%13%7%
1664
January1st to 15thNight
51%49%19%13%1
2716
16th to endNight
54%413%15%10%
2886
February1st to 15thNight
51%311%20%12%
2400
16th to endNight
51%49%22%8%2
2049
March1st to 15thNight
49%5%11%19%11%2
2340
16th to endNight
48%5%13%21%8%1
2080
April1st to 15thNight
49%5%8%20%14%1
1797
16th to endNight
45%410%21%13%4
1729
May1st to 15thNight
47%6%10%22%12%
1587
16th to endNight
37%6%12%22%18%2
1498
June1st to 15thNight
34%6%11%26%18%2
1440
16th to endNight
37%7%13%22%18%1
1440
July1st to 15thNight
28%8%13%28%18%3
1360
16th to endNight
27%7%16%25%18%4
1417
August1st to 15thNight
24%7%15%31%19%1
1558
16th to endNight
29%5%13%28%18%4
1910
September1st to 15thNight
29%48%27%27%1
1803
16th to endNight
31%5%9%33%17%1
1980
October1st to 15thNight
36%5%9%27%19%1
2073
16th to endNight
44%412%23%13%1
2448
November1st to 15thNight
42%47%24%16%3
2471
16th to endNight
47%313%23%11%
2587
December1st to 15thNight
53%5%9%20%9%1
2730
16th to endNight
63%410%14%6%
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
17%15%36%27%2
135
16th to endDay
21%13%32%22%7%1
144
February1st to 15thDay
24%17%44%11%1
135
16th to endDay
28%16%31%15%5%2
120
March1st to 15thDay
31%13%31%17%5%
135
16th to endDay
26%9%29%20%12%2
262
April1st to 15thDay
25%12%27%24%9%1
270
16th to endDay
24%13%25%20%11%4
270
May1st to 15thDay
23%13%31%18%8%5%
318
16th to endDay
15%10%32%24%11%4
517
June1st to 15thDay
12%8%33%27%14%4
495
16th to endDay
12%8%35%26%11%5%
495
July1st to 15thDay
6%5%33%29%16%9%
475
16th to endDay
8%327%33%17%9%
515
August1st to 15thDay
10%419%30%20%14%
406
16th to endDay
9%6%15%31%23%13%
332
September1st to 15thDay
9%221%28%25%11%
315
16th to endDay
10%421%26%26%10%
314
October1st to 15thDay
19%9%20%32%14%3
221
16th to endDay
29%11%34%20%4
144
November1st to 15thDay
14%12%29%27%13%2
135
16th to endDay
21%14%42%15%5%
135
December1st to 15thDay
17%21%40%15%31
135
16th to endDay
28%25%38%6%1
144
January1st to 15thNight
20%16%36%20%4
975
16th to endNight
19%13%39%24%3
1040
February1st to 15thNight
22%12%37%22%4
872
16th to endNight
22%14%31%25%4
683
March1st to 15thNight
19%12%36%23%8%
780
16th to endNight
19%8%31%27%11%1
646
April1st to 15thNight
21%11%33%25%6%
539
16th to endNight
23%9%28%28%8%1
540
May1st to 15thNight
20%7%31%30%9%1
540
16th to endNight
12%5%27%33%19%1
563
June1st to 15thNight
13%324%41%16%
540
16th to endNight
10%430%34%19%1
540
July1st to 15thNight
9%120%39%26%3
510
16th to endNight
5%219%42%26%3
564
August1st to 15thNight
412%46%31%4
539
16th to endNight
9%216%35%31%4
573
September1st to 15thNight
10%319%31%29%5%
543
16th to endNight
10%6%20%31%26%4
717
October1st to 15thNight
17%7%24%30%18%2
720
16th to endNight
23%13%31%22%8%
768
November1st to 15thNight
17%11%35%23%9%1
760
16th to endNight
21%14%33%23%7%
832
December1st to 15thNight
25%14%33%21%4
975
16th to endNight
28%13%33%20%2
1040
Page generated at 2018-03-22 10:34:23. Version ac04

Copyright 2018 A. Danko


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