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Edwardsville Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Edwardsville Observatory clear sky chart from 2005-11-05 to 2017-09-10.

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
43%
15822
21%
46797
14%
15775
50%
15775
28%
29666

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
26%
900
18%
2506
7%
895
35%
895
22%
1715
January16th to endNight
23%
960
18%
2505
6%
960
31%
960
22%
1769
February1st to 15thNight
26%
818
14%
2226
5%
815
32%
815
20%
1603
February16th to endNight
26%
631
20%
1893
6%
631
36%
631
23%
1223
March1st to 15thNight
25%
678
17%
2118
8%
678
33%
678
20%
1436
March16th to endNight
33%
576
14%
2019
10%
576
40%
576
19%
1362
April1st to 15thNight
32%
539
21%
1797
12%
539
46%
539
26%
1098
April16th to endNight
40%
540
22%
1800
17%
540
49%
540
26%
1117
May1st to 15thNight
43%
540
17%
1657
13%
539
49%
539
24%
1101
May16th to endNight
56%
563
20%
1497
14%
561
60%
561
32%
984
June1st to 15thNight
66%
540
22%
1440
16%
540
69%
540
42%
854
June16th to endNight
63%
540
22%
1440
15%
540
67%
540
42%
846
July1st to 15thNight
71%
510
20%
1360
16%
510
72%
510
42%
804
July16th to endNight
74%
564
23%
1464
20%
531
76%
531
41%
844
August1st to 15thNight
77%
539
23%
1691
26%
536
78%
536
36%
942
August16th to endNight
74%
573
24%
1910
28%
573
76%
573
35%
1050
September1st to 15thNight
65%
525
27%
1750
28%
525
69%
525
33%
990
September16th to endNight
61%
618
31%
1776
23%
618
66%
618
36%
1021
October1st to 15thNight
54%
660
29%
1958
21%
660
61%
660
37%
1121
October16th to endNight
40%
704
25%
2142
17%
704
48%
704
31%
1261
November1st to 15thNight
40%
700
28%
2276
18%
700
53%
700
33%
1272
November16th to endNight
32%
744
22%
2364
13%
744
42%
744
25%
1476
December1st to 15thNight
28%
900
15%
2520
8%
900
34%
900
20%
1810
December16th to endNight
24%
960
15%
2688
6%
960
32%
960
18%
1967

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
12%6%25%5%3445%7%42%
47836
Night
13%6%25%424447%44%
46977
TransparencyDay
40%6%12%23%14%2
47519
Night
39%5%11%23%16%3
46799
SeeingDay
13%5%22%27%21%9%
5841
Night
16%6%27%31%15%1
15822

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 15thDay
15%8%47%6%25%445%34%
1432
16th to endDay
13%9%36%5%2335%6%39%
1718
February1st to 15thDay
15%8%46%33445%6%36%
1636
16th to endDay
12%9%46%44445%5%38%
1580
March1st to 15thDay
17%9%35%5%24445%38%
1851
16th to endDay
17%8%35%5%35%5%5%6%31%
2201
April1st to 15thDay
15%5%15%5%2445%5%43%
2151
16th to endDay
16%8%25%5%35%35%5%38%
2160
May1st to 15thDay
19%425%5%2446%8%36%
2291
16th to endDay
11%6%25%5%25%5%5%8%40%
2617
June1st to 15thDay
8%324435%5%6%9%46%
2520
16th to endDay
6%3145%35%6%6%10%45%
2520
July1st to 15thDay
9%424435%6%6%9%43%
2520
16th to endDay
5%3135%35%5%6%11%47%
2602
August1st to 15thDay
8%315%5%36%6%6%9%42%
2258
16th to endDay
8%4245%35%5%7%9%43%
2292
September1st to 15thDay
13%5%24433447%47%
2097
16th to endDay
9%42443445%8%48%
1843
October1st to 15thDay
13%5%14423445%50%
1669
16th to endDay
13%41332335%6%51%
1727
November1st to 15thDay
14%423323346%51%
1582
16th to endDay
17%8%25%423236%41%
1593
December1st to 15thDay
19%9%45%424436%34%
1440
16th to endDay
19%10%45%423246%34%
1536
January1st to 15thNight
15%7%37%5%34345%39%
2506
16th to endNight
13%10%46%5%33346%37%
2505
February1st to 15thNight
14%9%47%424446%35%
2217
16th to endNight
13%9%36%423335%42%
1893
March1st to 15thNight
19%8%25%5%33335%38%
2118
16th to endNight
18%7%25%435%447%35%
2019
April1st to 15thNight
14%6%24423446%46%
1797
16th to endNight
16%425%5%23346%44%
1800
May1st to 15thNight
16%5%345%2445%7%40%
1657
16th to endNight
7%5%35%6%245%6%7%45%
1496
June1st to 15thNight
6%3234345%5%8%54%
1440
16th to endNight
7%32332446%11%50%
1440
July1st to 15thNight
8%22333446%8%52%
1440
16th to endNight
4214425%5%7%10%51%
1564
August1st to 15thNight
5%2134245%6%8%53%
1701
16th to endNight
5%314425%46%8%53%
1910
September1st to 15thNight
9%424423448%51%
1750
16th to endNight
9%5%2432335%7%53%
1776
October1st to 15thNight
12%313323447%52%
1958
16th to endNight
16%424322335%51%
2142
November1st to 15thNight
11%5%13324346%54%
2276
16th to endNight
17%6%34313345%45%
2364
December1st to 15thNight
22%9%45%423446%32%
2520
16th to endNight
20%9%46%424445%32%
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
51%5%9%20%12%
1433
16th to endDay
45%5%15%24%8%
1718
February1st to 15thDay
47%5%13%23%8%
1638
16th to endDay
46%6%11%22%11%1
1580
March1st to 15thDay
48%5%11%22%11%1
1851
16th to endDay
51%8%13%17%8%
2203
April1st to 15thDay
41%5%10%24%16%1
2151
16th to endDay
46%5%11%23%11%1
2160
May1st to 15thDay
44%7%14%23%9%
2291
16th to endDay
40%8%14%18%15%2
2621
June1st to 15thDay
32%8%15%23%17%2
2520
16th to endDay
31%7%17%21%18%3
2520
July1st to 15thDay
34%8%12%26%14%4
2371
16th to endDay
28%8%16%27%16%1
2439
August1st to 15thDay
35%9%11%25%17%
2244
16th to endDay
33%8%14%20%17%5%
2292
September1st to 15thDay
36%5%9%24%20%4
2097
16th to endDay
32%5%9%27%21%3
1843
October1st to 15thDay
35%410%25%20%4
1669
16th to endDay
33%310%31%17%3
1727
November1st to 15thDay
34%312%22%20%6%
1582
16th to endDay
44%411%26%12%1
1593
December1st to 15thDay
50%5%12%20%9%
1440
16th to endDay
51%412%20%9%1
1536
January1st to 15thNight
47%49%23%13%1
2506
16th to endNight
47%412%22%11%
2505
February1st to 15thNight
50%410%20%12%1
2226
16th to endNight
43%314%24%13%
1893
March1st to 15thNight
48%49%22%12%2
2118
16th to endNight
48%5%13%22%9%
2019
April1st to 15thNight
38%5%10%24%18%2
1797
16th to endNight
41%49%25%16%2
1800
May1st to 15thNight
42%7%11%21%16%1
1658
16th to endNight
35%9%13%21%16%4
1498
June1st to 15thNight
27%6%12%29%21%1
1440
16th to endNight
26%7%14%25%20%6%
1440
July1st to 15thNight
28%5%13%30%15%6%
1360
16th to endNight
25%8%16%29%18%1
1464
August1st to 15thNight
26%9%12%26%22%2
1691
16th to endNight
27%7%10%24%24%5%
1910
September1st to 15thNight
31%5%8%24%21%7%
1750
16th to endNight
30%5%8%24%26%4
1776
October1st to 15thNight
30%410%25%21%6%
1958
16th to endNight
35%39%25%20%4
2142
November1st to 15thNight
32%311%22%22%7%
2276
16th to endNight
41%49%26%17%1
2364
December1st to 15thNight
52%411%21%10%
2520
16th to endNight
53%412%18%9%1
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
30%15%35%13%41
90
16th to endDay
11%19%45%19%3
96
February1st to 15thDay
25%12%36%21%4
90
16th to endDay
14%23%27%30%3
81
March1st to 15thDay
34%7%34%17%41
90
16th to endDay
23%12%31%24%8%
187
April1st to 15thDay
15%12%31%24%15%
270
16th to endDay
20%8%27%25%13%3
270
May1st to 15thDay
17%8%28%29%10%5%
308
16th to endDay
14%6%29%28%14%6%
517
June1st to 15thDay
9%320%31%24%11%
495
16th to endDay
7%324%36%21%7%
495
July1st to 15thDay
12%113%34%25%11%
475
16th to endDay
5%111%30%32%18%
515
August1st to 15thDay
12%8%28%32%18%
411
16th to endDay
10%10%26%35%16%
332
September1st to 15thDay
12%314%19%35%14%
294
16th to endDay
12%5%13%23%28%16%
254
October1st to 15thDay
11%8%21%36%19%2
109
16th to endDay
10%7%32%36%13%
96
November1st to 15thDay
8%427%20%26%12%
90
16th to endDay
33%13%31%15%5%1
90
December1st to 15thDay
15%15%34%21%8%4
90
16th to endDay
28%13%41%13%3
96
January1st to 15thNight
19%12%37%24%5%
900
16th to endNight
19%12%38%26%3
960
February1st to 15thNight
18%13%35%27%3
818
16th to endNight
19%9%39%29%1
631
March1st to 15thNight
24%9%37%24%4
678
16th to endNight
21%5%34%29%8%
576
April1st to 15thNight
17%10%37%25%9%
539
16th to endNight
19%430%33%11%
540
May1st to 15thNight
18%5%26%35%13%1
540
16th to endNight
9%223%41%21%1
563
June1st to 15thNight
8%18%44%25%1
540
16th to endNight
10%17%43%26%1
540
July1st to 15thNight
10%10%43%32%3
510
16th to endNight
5%18%37%42%4
564
August1st to 15thNight
6%17%38%41%5%
539
16th to endNight
6%10%35%40%6%
573
September1st to 15thNight
10%212%34%33%6%
525
16th to endNight
11%5%15%29%32%6%
618
October1st to 15thNight
13%225%29%24%3
660
16th to endNight
19%7%30%32%9%
704
November1st to 15thNight
13%6%36%29%14%1
700
16th to endNight
22%9%33%26%8%
744
December1st to 15thNight
27%10%30%26%5%
900
16th to endNight
24%10%34%27%2
960
Page generated at 2017-09-11 18:35:21. Version ac04

Copyright 2017 A. Danko


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