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

2017-09-12
.

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%
15964
18%
46784
10%
15923
43%
15923
23%
31321

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
18%
900
14%
2506
4%
895
28%
895
17%
1821
January16th to endNight
18%
960
12%
2664
4%
960
26%
960
16%
1991
February1st to 15thNight
19%
801
15%
2212
4%
801
28%
801
19%
1573
February16th to endNight
25%
631
19%
1893
8%
631
34%
631
16%
1332
March1st to 15thNight
25%
720
13%
2160
6%
720
31%
720
17%
1529
March16th to endNight
32%
624
15%
2012
11%
624
38%
624
19%
1395
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
59%
533
28%
1770
27%
533
65%
533
36%
964
September16th to endNight
56%
657
26%
1815
18%
657
61%
657
35%
1100
October1st to 15thNight
48%
660
25%
1900
18%
660
54%
660
31%
1174
October16th to endNight
28%
704
18%
2244
9%
704
39%
704
21%
1478
November1st to 15thNight
32%
700
23%
2276
16%
700
44%
700
24%
1417
November16th to endNight
25%
768
17%
2388
8%
768
35%
768
18%
1617
December1st to 15thNight
20%
900
14%
2520
4%
900
28%
900
16%
1868
December16th to endNight
14%
960
12%
2688
2%
960
22%
960
12%
2152

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%36%
47879
Night
14%7%35%424446%40%
46952
Cloud CoverDay
13%8%36%5%3445%7%36%
47888
Night
14%8%35%424446%40%
46957
TransparencyDay
46%6%12%21%12%1
47565
Night
44%5%11%22%14%1
46784
SeeingDay
15%9%29%25%13%6%
5967
Night
18%9%29%28%12%1
15969

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%12%48%5%35%446%29%
1432
16th to endDay
12%16%7%8%7%34445%26%
1558
February1st to 15thDay
13%14%6%7%436%445%29%
1648
16th to endDay
13%12%48%6%43346%31%
1580
March1st to 15thDay
15%12%5%7%5%24446%30%
1790
16th to endDay
17%9%47%5%34446%31%
2220
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%
2098
16th to endDay
10%5%245%35%46%9%42%
1815
October1st to 15thDay
14%5%25%5%3345%5%43%
1729
16th to endDay
18%8%35%433445%36%
1628
November1st to 15thDay
13%9%35%424447%40%
1582
16th to endDay
17%9%46%5%23335%36%
1569
December1st to 15thDay
17%12%47%6%3435%5%29%
1440
16th to endDay
20%15%6%7%5%24345%23%
1536
January1st to 15thNight
17%11%47%5%23335%34%
2506
16th to endNight
13%13%6%8%5%24447%28%
2664
February1st to 15thNight
14%12%5%6%434335%35%
2210
16th to endNight
15%11%36%5%24346%35%
1893
March1st to 15thNight
15%9%47%5%24445%36%
2147
16th to endNight
16%8%36%5%25%45%7%34%
2012
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%424323346%56%
1770
16th to endNight
9%423425%448%50%
1815
October1st to 15thNight
12%5%24423447%49%
1900
16th to endNight
19%8%24323345%41%
2244
November1st to 15thNight
12%7%35%5%23345%46%
2276
16th to endNight
16%9%45%5%24346%37%
2388
December1st to 15thNight
20%9%47%5%34445%31%
2520
16th to endNight
23%14%47%5%33445%22%
2688

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%35%45%6%28%
1432
16th to endDay
12%16%7%9%6%24445%25%
1558
February1st to 15thDay
13%14%5%7%5%35%445%29%
1648
16th to endDay
13%11%48%6%4435%5%32%
1580
March1st to 15thDay
15%12%5%7%5%34446%30%
1800
16th to endDay
18%9%47%6%44446%31%
2219
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%48%
2098
16th to endDay
10%5%245%35%5%6%9%42%
1815
October1st to 15thDay
14%5%25%5%2345%5%43%
1729
16th to endDay
18%8%35%434445%36%
1628
November1st to 15thDay
13%9%35%424347%40%
1582
16th to endDay
16%9%46%5%24335%36%
1569
December1st to 15thDay
17%12%47%6%34345%28%
1440
16th to endDay
21%15%6%6%5%24345%23%
1536
January1st to 15thNight
17%11%47%5%23335%34%
2506
16th to endNight
13%13%6%8%5%25%447%28%
2664
February1st to 15thNight
14%12%46%434345%35%
2203
16th to endNight
16%11%47%5%24346%34%
1893
March1st to 15thNight
15%9%48%5%34445%35%
2160
16th to endNight
16%8%36%5%3445%7%34%
2012
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%
1770
16th to endNight
9%4235%24438%50%
1815
October1st to 15thNight
12%5%24423447%48%
1900
16th to endNight
19%8%24413336%41%
2244
November1st to 15thNight
13%7%35%423346%45%
2276
16th to endNight
16%10%45%5%24336%37%
2388
December1st to 15thNight
20%10%46%5%24445%31%
2520
16th to endNight
23%14%47%5%33435%23%
2688

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
54%414%15%9%
1433
16th to endDay
60%5%9%16%7%
1558
February1st to 15thDay
55%411%18%8%1
1650
16th to endDay
53%6%10%19%8%1
1580
March1st to 15thDay
54%6%11%18%7%1
1800
16th to endDay
54%413%20%5%
2220
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%24%20%2
2098
16th to endDay
37%6%10%28%15%
1815
October1st to 15thDay
40%5%10%27%13%1
1729
16th to endDay
48%5%11%22%9%1
1628
November1st to 15thDay
43%411%23%14%2
1582
16th to endDay
50%412%24%6%
1569
December1st to 15thDay
56%5%11%19%6%
1440
16th to endDay
63%411%12%7%
1536
January1st to 15thNight
52%410%20%11%1
2506
16th to endNight
55%413%15%10%
2664
February1st to 15thNight
51%311%20%11%
2212
16th to endNight
51%410%22%8%2
1893
March1st to 15thNight
50%5%12%17%11%2
2160
16th to endNight
49%5%13%21%8%1
2012
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%2
1770
16th to endNight
32%5%9%33%16%1
1815
October1st to 15thNight
35%5%9%27%20%1
1900
16th to endNight
44%412%24%12%1
2244
November1st to 15thNight
40%48%24%17%3
2276
16th to endNight
48%413%22%11%
2388
December1st to 15thNight
54%5%10%20%9%
2520
16th to endNight
63%49%14%6%
2688

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
20%16%36%24%2
90
16th to endDay
26%13%25%26%7%2
96
February1st to 15thDay
21%15%48%13%1
90
16th to endDay
24%12%32%18%8%3
81
March1st to 15thDay
38%12%30%14%31
90
16th to endDay
27%9%28%19%11%2
243
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
10%323%29%23%10%
299
16th to endDay
12%5%21%25%24%10%
254
October1st to 15thDay
13%10%23%32%16%4
169
16th to endDay
30%12%34%19%3
96
November1st to 15thDay
6%14%26%33%15%3
90
16th to endDay
25%11%43%12%6%1
90
December1st to 15thDay
17%20%38%17%41
90
16th to endDay
30%26%37%42
96
January1st to 15thNight
21%16%36%19%4
900
16th to endNight
19%13%38%23%3
960
February1st to 15thNight
22%12%37%22%5%
804
16th to endNight
21%15%30%26%5%
631
March1st to 15thNight
19%12%35%22%9%
720
16th to endNight
19%8%32%27%10%1
624
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
11%319%32%28%5%
533
16th to endNight
11%6%20%31%26%4
657
October1st to 15thNight
16%7%24%30%18%2
660
16th to endNight
23%13%31%21%8%
704
November1st to 15thNight
17%12%34%24%10%1
700
16th to endNight
22%14%31%23%7%
768
December1st to 15thNight
26%14%33%21%4
900
16th to endNight
30%13%32%20%2
960
Page generated at 2017-09-13 06:39:24. Version ac04

Copyright 2017 A. Danko


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