Heidelberg College
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Heidelberg College clear sky chart from 2005-11-06 to 2024-01-27.

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%
24183
15%
74541
10%
24128
42%
24128
20%
52357

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
15%
949
12%
2648
4%
946
22%
946
12%
2101
January11th to 20thNight
13%
801
7%
2511
3%
801
18%
801
8%
2062
January21st to endNight
18%
820
11%
2664
5%
820
24%
820
10%
2105
February1st to 10thNight
17%
720
8%
2340
4%
720
22%
720
11%
1861
February11th to 20thNight
21%
701
12%
2129
6%
700
27%
700
12%
1621
February21st to endNight
16%
592
13%
1776
4%
592
25%
592
12%
1364
March1st to 10thNight
25%
720
14%
2101
8%
720
31%
720
17%
1551
March11th to 20thNight
27%
720
19%
1980
9%
720
35%
720
22%
1367
March21st to endNight
30%
792
17%
2178
9%
792
37%
792
20%
1570
April1st to 10thNight
26%
658
14%
1918
6%
658
34%
658
20%
1344
April11th to 20thNight
30%
533
19%
1637
9%
533
39%
533
21%
1100
April21st to endNight
32%
540
17%
1620
5%
540
42%
540
23%
1117
May1st to 10thNight
34%
540
11%
1620
5%
540
38%
540
17%
1197
May11th to 20thNight
40%
531
16%
1593
10%
531
46%
531
23%
1090
May21st to endNight
56%
583
16%
1745
12%
582
60%
582
30%
1073
June1st to 10thNight
53%
540
15%
1594
13%
540
56%
540
30%
995
June11th to 20thNight
57%
540
18%
1440
14%
540
62%
540
33%
917
June21st to endNight
57%
540
20%
1440
14%
540
62%
540
34%
904
July1st to 10thNight
64%
525
16%
1400
15%
525
65%
525
35%
890
July11th to 20thNight
64%
522
19%
1468
16%
522
66%
522
37%
878
July21st to endNight
67%
591
18%
1672
16%
558
70%
558
36%
999
August1st to 10thNight
70%
537
20%
1600
18%
534
70%
534
35%
936
August11th to 20thNight
65%
534
22%
1598
18%
534
68%
534
33%
961
August21st to endNight
67%
594
23%
1813
18%
594
70%
594
35%
1050
September1st to 10thNight
59%
670
22%
1930
16%
670
63%
670
32%
1194
September11th to 20thNight
63%
720
28%
1980
21%
720
67%
720
38%
1176
September21st to endNight
52%
720
24%
1980
19%
720
56%
720
30%
1278
October1st to 10thNight
50%
720
21%
2027
18%
720
53%
720
29%
1301
October11th to 20thNight
34%
720
18%
2160
12%
720
41%
720
21%
1473
October21st to endNight
28%
792
18%
2471
13%
792
35%
792
18%
1723
November1st to 10thNight
35%
740
21%
2406
16%
740
42%
740
24%
1518
November11th to 20thNight
26%
760
19%
2470
10%
760
37%
760
18%
1694
November21st to endNight
25%
760
14%
2470
9%
760
31%
760
14%
1839
December1st to 10thNight
18%
760
10%
2470
5%
760
24%
760
11%
1923
December11th to 20thNight
19%
759
10%
3001
3%
758
27%
758
10%
2198
December21st to endNight
14%
939
4%
4691
3%
926
19%
926
4%
3987

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
15%10%47%6%45%5%5%7%33%
75233
Night
16%10%47%6%3445%7%35%
74792
TransparencyDay
50%7%12%19%11%2
74946
Night
49%6%11%20%12%2
74599
SeeingDay
19%10%27%23%15%6%
14339
Night
19%9%28%29%13%1
24194

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
18%15%7%12%9%5%5%445%16%
1517
11th to 20thDay
18%18%8%13%7%46%34415%
1660
21st to endDay
17%17%9%11%9%45%5%35%16%
1836
February1st to 10thDay
18%16%7%11%8%44435%20%
1620
11th to 20thDay
15%12%6%11%7%5%6%5%4423%
1716
21st to endDay
17%14%6%9%7%35%346%25%
1480
March1st to 10thDay
19%12%7%9%7%3445%6%26%
1858
11th to 20thDay
16%13%5%9%5%4445%7%28%
1980
21st to endDay
24%12%5%8%6%35%346%24%
2178
April1st to 10thDay
14%11%47%7%45%5%6%6%30%
2056
11th to 20thDay
17%10%36%6%45%5%5%7%34%
2271
21st to endDay
20%9%36%5%3445%6%34%
2340
May1st to 10thDay
17%8%38%7%45%5%5%7%32%
2340
11th to 20thDay
19%8%36%6%35%5%6%6%33%
2301
21st to endDay
10%5%36%7%45%6%7%9%39%
2531
June1st to 10thDay
13%6%35%7%36%6%5%9%38%
2361
11th to 20thDay
11%6%37%6%36%5%7%8%40%
2520
21st to endDay
11%5%25%6%46%6%8%9%38%
2520
July1st to 10thDay
9%5%26%5%45%5%6%9%42%
2520
11th to 20thDay
8%4246%35%6%7%10%45%
2440
21st to endDay
8%5%25%6%46%5%6%10%42%
2547
August1st to 10thDay
9%4245%36%6%7%10%43%
2327
11th to 20thDay
9%5%25%6%5%6%6%8%10%39%
2303
21st to endDay
10%5%26%5%35%5%7%10%42%
2538
September1st to 10thDay
14%5%245%35%5%5%8%43%
2011
11th to 20thDay
10%5%25%6%35%5%7%7%45%
1980
21st to endDay
16%7%25%5%3445%7%43%
1980
October1st to 10thDay
13%9%37%6%345%5%6%40%
1931
11th to 20thDay
17%7%36%5%45%5%5%7%37%
1800
21st to endDay
19%10%47%6%35%6%47%29%
1882
November1st to 10thDay
12%10%35%5%345%5%7%41%
1672
11th to 20thDay
18%12%46%6%24446%34%
1710
21st to endDay
18%14%5%8%6%3435%6%27%
1710
December1st to 10thDay
17%18%9%11%6%35%335%20%
1710
11th to 20thDay
16%16%6%10%6%45%447%22%
2153
21st to endDay
22%22%8%11%7%4433411%
2934
January1st to 10thNight
19%15%6%10%6%3445%5%23%
2648
11th to 20thNight
18%19%5%11%7%45%445%19%
2511
21st to endNight
17%16%7%11%7%3443422%
2664
February1st to 10thNight
20%13%6%10%6%45%5%45%22%
2340
11th to 20thNight
16%13%6%9%8%35%446%26%
2128
21st to endNight
20%13%5%8%6%44436%26%
1776
March1st to 10thNight
17%10%5%8%7%35%445%32%
2101
11th to 20thNight
15%9%26%6%3446%7%38%
1980
21st to endNight
19%10%37%5%35%347%34%
2178
April1st to 10thNight
15%11%47%5%445%47%34%
1918
11th to 20thNight
16%8%36%5%445%6%7%37%
1637
21st to endNight
18%8%26%6%4445%7%37%
1620
May1st to 10thNight
19%7%48%7%36%5%5%6%31%
1620
11th to 20thNight
17%8%35%43446%7%39%
1592
21st to endNight
10%5%24435%6%6%11%44%
1744
June1st to 10thNight
10%6%25%5%445%6%7%46%
1594
11th to 20thNight
10%5%25%4346%8%9%44%
1440
21st to endNight
9%4246%35%46%9%46%
1440
July1st to 10thNight
8%5%246%35%5%6%9%47%
1440
11th to 20thNight
8%424435%46%10%49%
1516
21st to endNight
7%415%5%36%6%5%10%48%
1771
August1st to 10thNight
7%325%6%45%6%7%9%47%
1611
11th to 20thNight
8%5%26%6%345%5%9%47%
1598
21st to endNight
7%4245%25%6%6%8%51%
1813
September1st to 10thNight
11%5%345%3345%8%48%
1930
11th to 20thNight
10%4245%34447%53%
1980
21st to endNight
12%6%36%5%3445%6%47%
1980
October1st to 10thNight
12%6%25%6%4445%6%46%
2027
11th to 20thNight
19%8%26%5%2445%6%38%
2160
21st to endNight
22%8%36%5%3445%6%34%
2471
November1st to 10thNight
14%8%36%5%245%5%7%42%
2406
11th to 20thNight
16%12%47%5%345%5%7%33%
2470
21st to endNight
19%13%5%7%6%3445%6%27%
2470
December1st to 10thNight
18%15%7%9%7%345%46%23%
2470
11th to 20thNight
19%14%6%9%5%3445%6%26%
3042
21st to endNight
25%18%8%9%6%34445%12%
4706

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
70%5%9%12%3
1518
11th to 20thDay
73%6%9%9%3
1660
21st to endDay
71%48%11%41
1836
February1st to 10thDay
67%5%10%11%5%1
1620
11th to 20thDay
64%5%9%14%7%1
1726
21st to endDay
60%5%12%14%7%2
1480
March1st to 10thDay
60%5%11%17%6%
1858
11th to 20thDay
56%5%11%16%9%1
1980
21st to endDay
62%5%9%18%6%1
2178
April1st to 10thDay
53%7%11%17%11%1
2056
11th to 20thDay
49%7%12%18%12%2
2271
21st to endDay
50%6%13%20%10%2
2340
May1st to 10thDay
51%8%11%18%11%1
2340
11th to 20thDay
50%8%11%17%12%2
2305
21st to endDay
40%8%14%23%13%2
2531
June1st to 10thDay
41%8%11%25%12%3
2361
11th to 20thDay
40%8%14%21%15%2
2520
21st to endDay
38%9%16%19%14%4
2520
July1st to 10thDay
38%8%11%23%17%3
2451
11th to 20thDay
32%9%14%27%16%2
2365
21st to endDay
36%9%14%24%15%2
2405
August1st to 10thDay
33%10%16%27%14%1
2314
11th to 20thDay
36%10%16%25%11%2
2303
21st to endDay
35%9%14%22%18%4
2538
September1st to 10thDay
38%7%13%22%16%4
2011
11th to 20thDay
36%7%12%26%18%2
1980
21st to endDay
41%5%12%23%18%
1980
October1st to 10thDay
43%7%11%22%16%1
1931
11th to 20thDay
46%7%11%22%13%1
1800
21st to endDay
53%6%12%18%10%1
1882
November1st to 10thDay
42%5%11%24%16%1
1672
11th to 20thDay
52%5%11%19%11%2
1710
21st to endDay
57%5%11%18%8%
1710
December1st to 10thDay
69%5%9%13%3
1710
11th to 20thDay
62%6%11%17%5%
2150
21st to endDay
77%6%7%7%3
2934
January1st to 10thNight
64%5%9%16%7%
2648
11th to 20thNight
69%5%11%12%4
2511
21st to endNight
65%5%10%14%6%1
2664
February1st to 10thNight
64%6%11%13%5%1
2340
11th to 20thNight
59%6%9%17%8%1
2129
21st to endNight
60%6%9%15%9%2
1776
March1st to 10thNight
55%5%11%19%10%1
2101
11th to 20thNight
45%6%12%20%14%3
1980
21st to endNight
52%410%23%10%1
2178
April1st to 10thNight
49%5%12%18%14%2
1918
11th to 20thNight
44%7%12%17%17%3
1637
21st to endNight
47%5%11%21%13%3
1620
May1st to 10thNight
54%7%10%16%11%3
1620
11th to 20thNight
44%8%11%17%18%2
1593
21st to endNight
34%8%14%26%15%3
1745
June1st to 10thNight
36%7%11%26%16%4
1594
11th to 20thNight
33%9%15%24%16%3
1440
21st to endNight
33%8%14%26%15%3
1440
July1st to 10thNight
34%7%12%24%19%4
1400
11th to 20thNight
29%8%15%27%19%2
1468
21st to endNight
30%8%17%24%18%4
1672
August1st to 10thNight
30%8%15%29%17%1
1600
11th to 20thNight
33%7%14%30%14%2
1598
21st to endNight
29%9%15%23%21%5%
1813
September1st to 10thNight
34%8%13%24%17%5%
1930
11th to 20thNight
30%7%11%27%24%1
1980
21st to endNight
37%7%10%24%20%2
1980
October1st to 10thNight
39%6%11%23%19%2
2027
11th to 20thNight
47%6%9%23%15%1
2160
21st to endNight
51%5%10%22%10%2
2471
November1st to 10thNight
41%6%11%23%16%2
2406
11th to 20thNight
49%5%11%21%12%1
2470
21st to endNight
58%5%12%17%7%
2470
December1st to 10thNight
62%6%11%14%7%
2470
11th to 20thNight
58%5%14%17%5%
3044
21st to endNight
73%7%9%8%2
4706

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
23%23%27%20%6%1
270
11th to 20thDay
28%15%39%12%41
270
21st to endDay
31%17%28%19%5%
282
February1st to 10thDay
31%19%37%13%
240
11th to 20thDay
25%18%36%17%3
240
21st to endDay
24%20%43%11%2
198
March1st to 10thDay
23%16%37%17%6%
298
11th to 20thDay
23%14%37%18%7%2
420
21st to endDay
33%11%30%19%6%1
462
April1st to 10thDay
21%14%30%23%11%
420
11th to 20thDay
22%15%31%17%11%4
412
21st to endDay
26%13%30%21%9%1
420
May1st to 10thDay
26%8%32%20%10%3
423
11th to 20thDay
23%7%28%24%12%6%
447
21st to endDay
12%7%26%25%20%11%
485
June1st to 10thDay
14%426%31%18%6%
471
11th to 20thDay
12%6%28%27%21%6%
630
21st to endDay
14%7%27%28%19%6%
630
July1st to 10thDay
11%419%30%21%15%
621
11th to 20thDay
10%323%28%22%14%
538
21st to endDay
10%5%18%25%28%13%
488
August1st to 10thDay
11%414%28%26%18%
446
11th to 20thDay
11%415%31%26%13%
439
21st to endDay
9%419%26%26%16%
495
September1st to 10thDay
16%416%28%24%12%
450
11th to 20thDay
10%217%24%29%18%
450
21st to endDay
17%11%22%22%19%10%
450
October1st to 10thDay
15%7%26%24%21%8%
450
11th to 20thDay
18%16%32%23%10%2
450
21st to endDay
23%15%36%19%5%1
397
November1st to 10thDay
19%12%33%21%11%3
270
11th to 20thDay
26%18%29%17%10%
270
21st to endDay
26%16%34%21%3
270
December1st to 10thDay
21%19%35%16%7%1
270
11th to 20thDay
23%19%37%17%3
270
21st to endDay
31%18%32%15%4
297
January1st to 10thNight
25%16%35%20%4
950
11th to 20thNight
29%14%35%17%31
801
21st to endNight
23%15%35%23%4
820
February1st to 10thNight
29%11%35%23%2
720
11th to 20thNight
25%12%35%25%3
703
21st to endNight
27%14%38%19%3
592
March1st to 10thNight
22%11%34%27%7%
720
11th to 20thNight
19%15%35%25%6%1
720
21st to endNight
23%11%31%26%9%
792
April1st to 10thNight
21%12%36%26%5%
658
11th to 20thNight
20%10%36%23%9%1
533
21st to endNight
21%8%34%29%8%1
540
May1st to 10thNight
23%7%28%32%9%1
540
11th to 20thNight
22%6%26%32%13%1
531
21st to endNight
12%222%40%21%3
584
June1st to 10thNight
11%325%44%18%
540
11th to 20thNight
11%322%44%20%1
540
21st to endNight
11%323%39%23%1
540
July1st to 10thNight
10%214%40%31%3
525
11th to 20thNight
9%417%40%26%5%
522
21st to endNight
8%216%42%30%2
591
August1st to 10thNight
7%112%45%31%3
537
11th to 20thNight
10%212%40%31%5%
534
21st to endNight
8%313%37%35%5%
594
September1st to 10thNight
14%414%36%28%5%
670
11th to 20thNight
10%314%36%32%4
720
21st to endNight
13%6%22%34%23%2
720
October1st to 10thNight
16%7%22%34%19%3
720
11th to 20thNight
23%12%28%28%8%2
720
21st to endNight
26%11%31%26%6%1
792
November1st to 10thNight
17%10%32%28%11%1
740
11th to 20thNight
21%14%33%22%8%1
760
21st to endNight
26%12%32%24%6%1
760
December1st to 10thNight
27%13%35%21%5%
760
11th to 20thNight
26%13%36%21%4
760
21st to endNight
29%14%34%19%3
945
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