Shiloh School Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Shiloh School Observatory clear sky chart from 2005-11-06 to 2024-01-13.

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
42%
23630
21%
74625
13%
23582
51%
23582
25%
46668

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
25%
757
24%
2602
8%
757
44%
757
22%
1563
January11th to 20thNight
30%
732
21%
2378
9%
732
44%
732
20%
1539
January21st to endNight
27%
792
26%
2574
13%
792
44%
792
25%
1553
February1st to 10thNight
25%
720
18%
2340
10%
720
38%
720
23%
1471
February11th to 20thNight
19%
700
21%
2148
7%
699
37%
699
21%
1382
February21st to endNight
27%
592
26%
1776
13%
592
44%
592
25%
1122
March1st to 10thNight
32%
720
23%
2061
11%
720
46%
720
29%
1261
March11th to 20thNight
30%
720
21%
1980
10%
720
41%
720
25%
1320
March21st to endNight
31%
792
21%
2109
9%
792
40%
792
26%
1432
April1st to 10thNight
29%
720
20%
1800
6%
720
38%
720
27%
1210
April11th to 20thNight
42%
711
24%
1775
9%
711
48%
711
37%
1131
April21st to endNight
43%
720
20%
1800
10%
720
46%
720
31%
1190
May1st to 10thNight
40%
713
16%
1793
7%
713
44%
713
26%
1241
May11th to 20thNight
44%
405
17%
1467
14%
405
49%
405
21%
924
May21st to endNight
56%
389
17%
1551
17%
388
60%
388
21%
940
June1st to 10thNight
58%
360
17%
1440
20%
360
62%
360
23%
857
June11th to 20thNight
62%
360
16%
1440
18%
360
65%
360
22%
858
June21st to endNight
64%
360
17%
1440
19%
360
69%
360
23%
844
July1st to 10thNight
65%
350
16%
1400
20%
350
66%
350
22%
831
July11th to 20thNight
75%
412
18%
1456
20%
412
76%
412
31%
834
July21st to endNight
68%
591
18%
1672
14%
558
70%
558
27%
1070
August1st to 10thNight
67%
537
13%
1600
11%
534
68%
534
24%
1086
August11th to 20thNight
62%
687
15%
1751
10%
687
62%
687
28%
1198
August21st to endNight
64%
792
17%
1980
9%
792
65%
792
31%
1349
September1st to 10thNight
64%
720
22%
1800
14%
720
66%
720
34%
1189
September11th to 20thNight
62%
720
27%
1800
19%
720
65%
720
35%
1168
September21st to endNight
48%
720
18%
2029
13%
720
53%
720
23%
1414
October1st to 10thNight
49%
720
21%
2160
18%
720
55%
720
27%
1377
October11th to 20thNight
45%
720
26%
2160
22%
720
54%
720
28%
1318
October21st to endNight
41%
792
28%
2376
21%
792
52%
792
29%
1433
November1st to 10thNight
43%
740
23%
2339
15%
740
54%
740
28%
1392
November11th to 20thNight
36%
760
24%
2470
16%
760
48%
760
25%
1505
November21st to endNight
40%
760
27%
2560
17%
760
55%
760
28%
1448
December1st to 10thNight
29%
760
20%
2660
10%
760
42%
760
19%
1677
December11th to 20thNight
28%
760
22%
3183
12%
759
43%
759
19%
1921
December21st to endNight
35%
826
16%
4755
14%
817
48%
817
15%
2620

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%5%25%5%345%6%8%44%
74685
Night
14%6%25%5%3445%7%44%
75052
TransparencyDay
37%7%13%24%16%3
74395
Night
39%6%12%23%17%3
74861
SeeingDay
16%7%23%30%20%5%
14023
Night
17%8%26%31%16%2
23646

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
15%5%245%35%5%47%44%
1559
11th to 20thDay
16%7%35%5%345%5%6%42%
1638
21st to endDay
17%6%3442345%7%44%
1782
February1st to 10thDay
13%8%35%6%35%5%7%7%39%
1620
11th to 20thDay
20%5%25%424336%46%
1695
21st to endDay
17%8%445%36%5%5%6%37%
1480
March1st to 10thDay
14%5%35%423446%50%
1897
11th to 20thDay
17%6%2442345%7%45%
1980
21st to endDay
16%6%346%35%5%5%6%42%
2245
April1st to 10thDay
12%6%25%32346%7%49%
2160
11th to 20thDay
10%5%245%45%45%6%50%
2134
21st to endDay
13%6%35%4345%48%45%
2160
May1st to 10thDay
13%6%34435%46%10%42%
2182
11th to 20thDay
16%5%25%5%35%6%6%8%39%
2424
21st to endDay
13%5%14425%5%6%9%45%
2725
June1st to 10thDay
11%415%5%345%7%11%44%
2520
11th to 20thDay
10%425%5%35%6%7%11%43%
2520
21st to endDay
7%4245%36%5%7%11%45%
2520
July1st to 10thDay
7%5%25%6%35%5%7%10%43%
2520
11th to 20thDay
5%325%446%7%8%12%43%
2450
21st to endDay
7%425%6%46%7%10%11%39%
2547
August1st to 10thDay
9%5%25%5%35%6%8%11%40%
2327
11th to 20thDay
11%436%6%36%6%6%10%39%
2131
21st to endDay
11%425%5%45%47%10%44%
2376
September1st to 10thDay
13%425%4346%7%8%44%
2160
11th to 20thDay
11%5%36%5%2446%8%46%
2160
21st to endDay
18%7%35%5%3435%7%40%
1926
October1st to 10thDay
14%5%35%43345%7%45%
1800
11th to 20thDay
16%5%23424445%51%
1800
21st to endDay
12%6%25%5%4445%7%48%
1980
November1st to 10thDay
15%5%24423346%52%
1739
11th to 20thDay
13%6%245%2445%7%48%
1710
21st to endDay
15%4245%2445%5%50%
1616
December1st to 10thDay
15%7%35%42445%8%43%
1520
11th to 20thDay
16%6%2443333450%
1910
21st to endDay
16%7%25%5%2445%7%43%
2772
January1st to 10thNight
15%6%35%5%34347%45%
2602
11th to 20thNight
17%6%26%435%5%5%6%40%
2378
21st to endNight
16%7%24324446%47%
2574
February1st to 10thNight
16%9%25%33445%6%42%
2340
11th to 20thNight
19%6%24434446%43%
2148
21st to endNight
18%7%34423346%46%
1776
March1st to 10thNight
14%5%25%424346%50%
2061
11th to 20thNight
19%6%245%2446%7%41%
1980
21st to endNight
16%7%36%5%2445%6%42%
2109
April1st to 10thNight
14%6%35%5%346%6%7%42%
1800
11th to 20thNight
12%5%25%5%2345%8%49%
1775
21st to endNight
16%5%25%42445%7%45%
1800
May1st to 10thNight
13%7%26%6%35%5%5%8%39%
1793
11th to 20thNight
15%7%36%5%3446%7%41%
1466
21st to endNight
12%7%25%4345%5%9%42%
1550
June1st to 10thNight
13%425%5%35%5%6%9%43%
1440
11th to 20thNight
10%425%5%46%6%8%9%40%
1440
21st to endNight
7%5%35%5%37%6%7%10%42%
1440
July1st to 10thNight
8%437%6%45%6%8%10%40%
1440
11th to 20thNight
4435%5%45%7%7%12%44%
1504
21st to endNight
7%436%7%36%7%7%9%40%
1771
August1st to 10thNight
8%426%7%5%7%7%7%11%36%
1611
11th to 20thNight
10%6%27%5%45%6%7%9%38%
1751
21st to endNight
9%5%36%6%46%5%6%10%40%
1980
September1st to 10thNight
13%5%25%42445%7%47%
1800
11th to 20thNight
10%5%36%6%2445%9%47%
1800
21st to endNight
19%6%35%5%35%45%6%38%
2029
October1st to 10thNight
16%5%245%3445%7%44%
2160
11th to 20thNight
17%5%24423445%50%
2160
21st to endNight
16%5%24423447%49%
2376
November1st to 10thNight
14%6%35%423346%49%
2339
11th to 20thNight
16%6%34424445%47%
2470
21st to endNight
12%5%2433445%7%50%
2560
December1st to 10thNight
16%8%35%43445%6%41%
2660
11th to 20thNight
17%6%25%5%34447%44%
3285
21st to endNight
14%7%35%4345%6%8%42%
4884

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
39%6%11%25%15%4
1560
11th to 20thDay
42%412%24%16%3
1638
21st to endDay
38%5%11%25%17%4
1782
February1st to 10thDay
43%412%26%13%3
1620
11th to 20thDay
41%49%22%20%4
1704
21st to endDay
45%7%11%17%15%5%
1480
March1st to 10thDay
37%412%24%21%3
1897
11th to 20thDay
39%5%12%21%18%5%
1980
21st to endDay
42%7%10%20%18%3
2245
April1st to 10thDay
33%5%13%22%20%6%
2160
11th to 20thDay
34%6%11%23%21%5%
2134
21st to endDay
38%6%12%23%16%6%
2160
May1st to 10thDay
38%8%13%25%15%3
2182
11th to 20thDay
41%8%13%23%12%3
2428
21st to endDay
35%9%15%28%13%1
2725
June1st to 10thDay
33%8%17%28%12%2
2520
11th to 20thDay
32%10%18%24%15%2
2520
21st to endDay
32%10%16%24%17%2
2520
July1st to 10thDay
34%10%15%22%16%2
2450
11th to 20thDay
29%11%19%30%11%1
2375
21st to endDay
33%11%18%22%15%1
2405
August1st to 10thDay
35%10%18%26%10%1
2314
11th to 20thDay
39%9%15%23%13%1
2131
21st to endDay
34%9%14%25%14%3
2376
September1st to 10thDay
35%9%16%21%16%3
2160
11th to 20thDay
36%7%10%26%20%2
2160
21st to endDay
44%6%7%23%17%3
1926
October1st to 10thDay
39%5%10%25%18%3
1800
11th to 20thDay
36%5%9%26%21%4
1800
21st to endDay
37%5%7%25%22%5%
1980
November1st to 10thDay
35%49%28%20%4
1739
11th to 20thDay
37%5%12%19%22%6%
1710
21st to endDay
36%410%27%20%4
1616
December1st to 10thDay
41%5%13%25%14%3
1520
11th to 20thDay
38%48%28%16%6%
1906
21st to endDay
41%5%11%27%14%1
2772
January1st to 10thNight
40%410%23%19%5%
2602
11th to 20thNight
44%5%12%22%14%3
2378
21st to endNight
39%39%26%19%4
2574
February1st to 10thNight
42%411%24%16%2
2340
11th to 20thNight
44%38%22%18%5%
2150
21st to endNight
41%49%21%19%6%
1776
March1st to 10thNight
37%49%27%20%3
2061
11th to 20thNight
42%5%11%21%17%4
1980
21st to endNight
43%5%8%21%17%5%
2109
April1st to 10thNight
40%6%11%18%21%5%
1800
11th to 20thNight
34%411%23%22%5%
1775
21st to endNight
39%5%13%22%16%4
1800
May1st to 10thNight
42%7%11%23%14%3
1793
11th to 20thNight
42%7%15%21%15%1
1467
21st to endNight
39%9%15%25%12%1
1551
June1st to 10thNight
37%9%13%24%16%1
1440
11th to 20thNight
37%9%16%22%14%2
1440
21st to endNight
35%9%15%23%16%2
1440
July1st to 10thNight
38%8%17%21%13%3
1400
11th to 20thNight
30%9%21%28%10%1
1456
21st to endNight
35%11%15%26%13%
1672
August1st to 10thNight
40%11%17%21%10%
1600
11th to 20thNight
39%9%18%20%13%1
1751
21st to endNight
38%8%15%22%14%2
1980
September1st to 10thNight
35%8%17%20%16%4
1800
11th to 20thNight
35%7%10%26%21%2
1800
21st to endNight
46%7%10%17%17%3
2029
October1st to 10thNight
40%6%10%25%17%3
2160
11th to 20thNight
38%48%24%23%3
2160
21st to endNight
36%49%26%21%4
2376
November1st to 10thNight
38%411%25%19%4
2339
11th to 20thNight
39%410%21%19%7%
2470
21st to endNight
34%49%27%22%4
2560
December1st to 10thNight
44%411%23%14%3
2660
11th to 20thNight
41%410%22%18%4
3288
21st to endNight
39%5%13%27%14%2
4884

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
19%17%32%28%6%
200
11th to 20thDay
17%17%39%21%6%
246
21st to endDay
20%11%36%28%5%
264
February1st to 10thDay
18%14%35%27%6%
240
11th to 20thDay
26%10%39%21%4
363
21st to endDay
23%10%41%23%4
346
March1st to 10thDay
16%14%35%29%7%
420
11th to 20thDay
19%11%36%27%6%1
420
21st to endDay
17%11%32%32%7%1
462
April1st to 10thDay
14%13%36%27%10%1
420
11th to 20thDay
10%10%29%36%12%3
412
21st to endDay
16%9%28%34%12%1
420
May1st to 10thDay
16%9%26%34%13%2
423
11th to 20thDay
20%224%32%19%3
447
21st to endDay
20%314%29%27%7%
485
June1st to 10thDay
13%213%37%29%6%
450
11th to 20thDay
12%216%36%25%10%
450
21st to endDay
10%313%37%32%6%
450
July1st to 10thDay
10%210%32%35%12%
445
11th to 20thDay
5%5%31%48%10%
444
21st to endDay
10%112%36%32%9%
488
August1st to 10thDay
9%113%33%34%9%
446
11th to 20thDay
13%211%29%35%10%
439
21st to endDay
11%211%30%33%14%
495
September1st to 10thDay
16%211%28%29%14%
450
11th to 20thDay
13%314%30%30%10%
450
21st to endDay
25%6%20%25%19%5%
450
October1st to 10thDay
19%321%25%23%9%
450
11th to 20thDay
17%7%23%28%21%3
450
21st to endDay
13%11%28%32%13%4
495
November1st to 10thDay
18%8%25%27%17%6%
399
11th to 20thDay
15%15%28%31%10%1
370
21st to endDay
17%14%25%28%14%2
276
December1st to 10thDay
23%8%35%24%8%1
180
11th to 20thDay
21%8%36%27%8%
180
21st to endDay
20%10%30%30%10%1
198
January1st to 10thNight
17%16%37%26%4
760
11th to 20thNight
20%13%33%27%7%
732
21st to endNight
20%14%35%28%3
792
February1st to 10thNight
20%10%40%27%4
720
11th to 20thNight
23%16%38%21%2
703
21st to endNight
20%13%35%28%3
592
March1st to 10thNight
17%13%34%29%7%
720
11th to 20thNight
22%9%34%27%7%1
720
21st to endNight
18%9%36%29%7%
792
April1st to 10thNight
18%10%39%27%7%
720
11th to 20thNight
14%8%32%36%10%1
711
21st to endNight
19%7%26%37%10%1
720
May1st to 10thNight
17%9%28%35%11%1
713
11th to 20thNight
18%425%37%14%2
405
21st to endNight
15%220%31%30%4
389
June1st to 10thNight
14%118%38%27%3
360
11th to 20thNight
10%317%38%28%4
360
21st to endNight
7%317%43%27%4
360
July1st to 10thNight
10%211%42%31%4
350
11th to 20thNight
5%18%38%42%6%
412
21st to endNight
8%211%42%34%4
591
August1st to 10thNight
10%110%38%35%5%
537
11th to 20thNight
14%211%32%36%5%
687
21st to endNight
11%213%31%34%8%
792
September1st to 10thNight
16%111%32%33%8%
720
11th to 20thNight
12%215%31%33%7%
720
21st to endNight
22%5%16%32%23%2
720
October1st to 10thNight
18%5%20%27%23%7%
720
11th to 20thNight
19%9%22%30%18%2
720
21st to endNight
19%10%26%27%16%3
792
November1st to 10thNight
18%7%25%30%17%4
740
11th to 20thNight
18%12%29%28%12%1
760
21st to endNight
14%13%30%30%12%2
760
December1st to 10thNight
19%11%36%23%10%2
760
11th to 20thNight
18%10%38%25%8%
760
21st to endNight
18%10%31%33%7%
836
Page generated at 2024-01-10 10:16:11. Version ac07

Copyright 2024 Attilla Danko


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