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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 2019-09-17.

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%
18510
21%
54764
14%
18463
50%
18463
27%
34841

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%
1050
18%
2926
8%
1045
35%
1045
21%
2025
January16th to endNight
23%
1120
18%
2923
6%
1120
31%
1120
22%
2076
February1st to 15thNight
25%
956
15%
2604
5%
953
31%
953
20%
1877
February16th to endNight
24%
735
19%
2205
6%
735
34%
735
21%
1462
March1st to 15thNight
24%
792
19%
2472
8%
792
34%
792
20%
1663
March16th to endNight
32%
672
14%
2356
9%
672
39%
672
18%
1601
April1st to 15thNight
32%
629
21%
2097
13%
629
46%
629
25%
1300
April16th to endNight
38%
624
20%
2078
15%
624
47%
624
25%
1303
May1st to 15thNight
45%
630
18%
1933
14%
629
50%
629
24%
1266
May16th to endNight
56%
659
19%
1753
13%
657
60%
657
31%
1156
June1st to 15thNight
66%
630
22%
1680
16%
630
70%
630
41%
1004
June16th to endNight
64%
630
22%
1680
16%
630
67%
630
41%
995
July1st to 15thNight
73%
600
20%
1600
17%
600
74%
600
43%
935
July16th to endNight
73%
660
23%
1728
20%
627
75%
627
42%
987
August1st to 15thNight
77%
620
24%
1942
27%
617
78%
617
37%
1071
August16th to endNight
70%
669
23%
2230
26%
669
73%
669
34%
1244
September1st to 15thNight
67%
630
28%
2100
30%
630
70%
630
34%
1179
September16th to endNight
62%
734
32%
2111
24%
734
67%
734
37%
1211
October1st to 15thNight
53%
780
27%
2314
20%
780
59%
780
34%
1364
October16th to endNight
40%
832
26%
2532
18%
832
49%
832
32%
1480
November1st to 15thNight
37%
820
27%
2666
17%
820
50%
820
29%
1563
November16th to endNight
33%
868
23%
2758
14%
868
44%
868
26%
1709
December1st to 15thNight
29%
1050
16%
2940
9%
1050
35%
1050
20%
2086
December16th to endNight
25%
1120
15%
3136
6%
1120
33%
1120
18%
2284

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%6%25%5%3445%7%41%
55931
Night
13%6%25%424446%44%
54944
TransparencyDay
40%6%12%23%14%2
55614
Night
39%5%11%23%16%2
54766
SeeingDay
15%6%22%26%20%8%
8588
Night
17%6%27%31%15%1
18510

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%10%47%6%25%445%33%
1672
16th to endDay
13%9%37%6%2335%6%37%
2004
February1st to 15thDay
16%9%46%43445%5%34%
1917
16th to endDay
15%9%46%43445%5%35%
1840
March1st to 15thDay
17%9%36%5%2444438%
2159
16th to endDay
19%9%36%6%345%5%6%30%
2568
April1st to 15thDay
15%6%25%5%2445%5%41%
2511
16th to endDay
17%8%25%5%34345%39%
2487
May1st to 15thDay
18%425%5%2446%8%36%
2674
16th to endDay
10%5%25%5%25%5%5%9%40%
3065
June1st to 15thDay
7%3244345%6%9%46%
2940
16th to endDay
6%3245%46%6%6%10%44%
2940
July1st to 15thDay
8%314435%6%6%9%45%
2940
16th to endDay
5%4135%35%5%6%10%49%
3042
August1st to 15thDay
8%3145%36%6%6%9%44%
2589
16th to endDay
8%4245%35%5%7%8%42%
2676
September1st to 15thDay
12%5%14423447%48%
2520
16th to endDay
8%3244345%5%7%49%
2190
October1st to 15thDay
14%5%24423445%46%
1973
16th to endDay
14%413323346%52%
2041
November1st to 15thDay
15%424323346%48%
1852
16th to endDay
16%8%26%423236%42%
1859
December1st to 15thDay
18%9%45%424446%35%
1680
16th to endDay
19%9%46%5%3335%6%32%
1792
January1st to 15thNight
16%7%37%6%34345%38%
2926
16th to endNight
13%10%46%6%33446%36%
2923
February1st to 15thNight
15%9%47%424446%35%
2595
16th to endNight
15%9%36%5%23335%40%
2205
March1st to 15thNight
18%8%25%5%23335%39%
2472
16th to endNight
19%7%26%424446%35%
2356
April1st to 15thNight
14%6%25%423446%45%
2097
16th to endNight
16%6%25%5%23346%43%
2078
May1st to 15thNight
15%5%2442445%8%41%
1933
16th to endNight
7%5%25%5%346%6%7%44%
1752
June1st to 15thNight
6%313435%5%5%8%53%
1680
16th to endNight
7%3233235%6%10%50%
1680
July1st to 15thNight
7%22333445%9%53%
1680
16th to endNight
5%214425%5%6%10%52%
1828
August1st to 15thNight
5%2124245%6%8%53%
1952
16th to endNight
6%414425%45%8%52%
2230
September1st to 15thNight
9%424423348%53%
2100
16th to endNight
8%42432335%7%53%
2111
October1st to 15thNight
13%413423447%50%
2314
16th to endNight
15%424322335%52%
2532
November1st to 15thNight
13%6%14324336%50%
2666
16th to endNight
17%6%34312445%46%
2758
December1st to 15thNight
20%8%36%5%23446%33%
2940
16th to endNight
19%10%46%424445%32%
3136

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
52%5%9%20%11%1
1673
16th to endDay
47%5%14%23%9%
2004
February1st to 15thDay
50%5%13%21%8%
1919
16th to endDay
49%6%10%21%11%1
1840
March1st to 15thDay
48%5%10%22%11%1
2159
16th to endDay
53%7%12%18%8%
2570
April1st to 15thDay
43%5%12%23%14%1
2511
16th to endDay
47%5%10%23%11%1
2487
May1st to 15thDay
44%8%14%23%9%
2674
16th to endDay
38%8%15%20%13%2
3069
June1st to 15thDay
31%8%15%24%17%2
2940
16th to endDay
32%8%17%21%16%3
2940
July1st to 15thDay
32%8%13%26%14%4
2791
16th to endDay
29%7%15%28%17%2
2879
August1st to 15thDay
33%8%12%27%17%
2575
16th to endDay
35%9%14%20%16%4
2676
September1st to 15thDay
35%411%24%19%4
2520
16th to endDay
32%5%9%27%21%3
2190
October1st to 15thDay
38%410%23%18%3
1973
16th to endDay
33%49%30%19%3
2041
November1st to 15thDay
37%311%22%18%5%
1852
16th to endDay
44%310%26%12%1
1859
December1st to 15thDay
49%5%12%20%10%
1680
16th to endDay
52%412%19%9%1
1792
January1st to 15thNight
48%48%23%14%1
2926
16th to endNight
48%412%21%11%
2923
February1st to 15thNight
50%411%19%12%1
2604
16th to endNight
46%313%22%13%1
2205
March1st to 15thNight
47%49%22%13%2
2472
16th to endNight
49%412%22%10%
2356
April1st to 15thNight
39%5%10%25%16%2
2097
16th to endNight
42%49%23%16%3
2078
May1st to 15thNight
41%7%12%21%15%1
1934
16th to endNight
35%9%13%22%15%3
1754
June1st to 15thNight
27%7%12%27%22%1
1680
16th to endNight
27%7%14%27%18%5%
1680
July1st to 15thNight
26%6%15%30%14%6%
1600
16th to endNight
24%7%15%29%20%2
1728
August1st to 15thNight
25%8%12%28%22%2
1942
16th to endNight
28%7%11%24%22%4
2230
September1st to 15thNight
31%5%9%25%21%7%
2100
16th to endNight
30%5%8%25%25%4
2111
October1st to 15thNight
33%410%24%20%6%
2314
16th to endNight
35%39%26%21%4
2532
November1st to 15thNight
36%310%21%20%7%
2666
16th to endNight
40%49%27%17%1
2758
December1st to 15thNight
50%411%21%12%
2940
16th to endNight
53%412%18%10%1
3136

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
31%13%31%15%8%
180
16th to endDay
15%19%40%20%4
192
February1st to 15thDay
29%14%32%19%4
180
16th to endDay
28%18%28%22%1
159
March1st to 15thDay
29%12%37%15%5%
180
16th to endDay
27%10%30%23%7%
298
April1st to 15thDay
17%14%32%22%12%
390
16th to endDay
22%10%27%22%14%2
379
May1st to 15thDay
16%8%29%28%13%4
431
16th to endDay
13%6%28%28%16%7%
677
June1st to 15thDay
9%320%31%24%10%
645
16th to endDay
7%222%35%22%8%
645
July1st to 15thDay
11%111%29%27%18%
625
16th to endDay
7%212%30%32%15%
675
August1st to 15thDay
11%8%31%32%15%
532
16th to endDay
12%14%29%30%12%
460
September1st to 15thDay
12%312%20%35%14%
435
16th to endDay
10%413%26%28%15%
378
October1st to 15thDay
16%8%20%37%14%1
203
16th to endDay
16%9%31%30%10%1
192
November1st to 15thDay
21%6%31%19%15%6%
180
16th to endDay
24%12%30%21%10%1
180
December1st to 15thDay
16%21%31%18%7%4
180
16th to endDay
25%12%42%15%4
192
January1st to 15thNight
20%12%35%25%5%
1050
16th to endNight
20%12%38%25%3
1120
February1st to 15thNight
20%13%36%26%3
956
16th to endNight
21%10%37%28%1
735
March1st to 15thNight
24%9%37%24%3
792
16th to endNight
23%6%33%28%8%
672
April1st to 15thNight
17%9%37%25%9%
629
16th to endNight
20%5%31%31%11%
624
May1st to 15thNight
17%5%25%36%13%1
630
16th to endNight
10%223%39%21%2
659
June1st to 15thNight
8%118%43%27%1
630
16th to endNight
9%16%42%28%2
630
July1st to 15thNight
9%9%39%36%5%
600
16th to endNight
6%110%36%41%3
660
August1st to 15thNight
6%7%40%39%4
620
16th to endNight
7%12%36%37%5%
669
September1st to 15thNight
10%211%35%33%7%
630
16th to endNight
10%416%30%32%6%
734
October1st to 15thNight
15%324%31%21%3
780
16th to endNight
18%6%31%32%10%
832
November1st to 15thNight
17%6%35%28%12%
820
16th to endNight
21%9%32%27%8%
868
December1st to 15thNight
25%10%30%26%5%
1050
16th to endNight
25%9%34%27%3
1120
Page generated at 2019-09-17 20:12:19. Version ac04

Copyright 2019 A. Danko


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