Walter E. Schuele Planetarium
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Walter E. Schuele Planetarium clear sky chart from 2005-11-06 to 2024-01-31.

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
35%
23481
13%
74746
9%
23431
39%
23431
16%
55085

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
10%
758
9%
2459
3%
757
17%
757
7%
2032
January11th to 20thNight
11%
760
4%
2470
2%
760
14%
760
6%
2129
January21st to endNight
16%
835
7%
2711
4%
835
20%
835
7%
2302
February1st to 10thNight
16%
720
6%
2340
3%
720
20%
720
8%
1929
February11th to 20thNight
19%
701
9%
2203
4%
700
24%
700
9%
1762
February21st to endNight
17%
592
10%
1776
2%
592
24%
592
11%
1414
March1st to 10thNight
26%
720
14%
2048
8%
720
31%
720
16%
1531
March11th to 20thNight
30%
720
17%
1980
9%
720
36%
720
20%
1443
March21st to endNight
32%
792
15%
2178
9%
792
36%
792
18%
1651
April1st to 10thNight
32%
720
11%
1959
5%
720
36%
720
20%
1436
April11th to 20thNight
32%
547
17%
1611
8%
547
39%
547
21%
1120
April21st to endNight
36%
540
17%
1620
8%
540
42%
540
23%
1097
May1st to 10thNight
40%
540
10%
1620
8%
540
42%
540
18%
1185
May11th to 20thNight
43%
531
15%
1592
11%
531
46%
531
21%
1094
May21st to endNight
60%
582
14%
1745
12%
582
62%
582
29%
1091
June1st to 10thNight
53%
360
14%
1440
16%
360
59%
360
21%
865
June11th to 20thNight
53%
360
17%
1377
18%
360
59%
360
22%
826
June21st to endNight
57%
400
19%
1300
19%
400
62%
400
28%
804
July1st to 10thNight
68%
525
15%
1433
14%
525
69%
525
34%
893
July11th to 20thNight
62%
522
16%
1566
15%
522
64%
522
32%
933
July21st to endNight
63%
591
17%
1672
15%
558
65%
558
30%
1055
August1st to 10thNight
65%
537
18%
1600
16%
534
65%
534
34%
950
August11th to 20thNight
62%
534
20%
1598
17%
534
64%
534
28%
1016
August21st to endNight
60%
594
21%
1782
17%
594
62%
594
29%
1122
September1st to 10thNight
57%
720
18%
1916
12%
720
60%
720
29%
1286
September11th to 20thNight
61%
720
24%
1980
18%
720
63%
720
33%
1236
September21st to endNight
47%
720
19%
1980
15%
720
50%
720
25%
1366
October1st to 10thNight
47%
720
17%
2083
15%
720
50%
720
24%
1395
October11th to 20thNight
29%
720
14%
2160
9%
720
35%
720
17%
1555
October21st to endNight
23%
792
14%
2407
10%
792
29%
792
12%
1872
November1st to 10thNight
31%
740
15%
2406
13%
740
36%
740
18%
1689
November11th to 20thNight
20%
760
12%
2470
8%
760
26%
760
11%
1918
November21st to endNight
18%
760
9%
2655
6%
760
23%
760
9%
2123
December1st to 10thNight
14%
760
4%
2660
3%
760
17%
760
6%
2256
December11th to 20thNight
15%
760
6%
3271
3%
759
20%
759
6%
2627
December21st to endNight
14%
828
3%
4678
3%
817
18%
817
3%
4082

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%35%5%5%7%32%
75132
Night
17%12%5%8%6%35%45%6%30%
74975
TransparencyDay
50%8%13%18%11%1
74851
Night
53%8%11%16%10%1
74777
SeeingDay
19%10%26%27%14%4
13873
Night
22%11%26%27%13%2
23495

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%18%8%11%8%45%43417%
1706
11th to 20thDay
19%20%8%13%8%4443412%
1710
21st to endDay
19%20%9%13%9%44435%12%
1872
February1st to 10thDay
17%18%6%10%9%4434420%
1620
11th to 20thDay
15%14%8%14%8%45%5%36%19%
1641
21st to endDay
19%12%6%10%6%45%46%6%22%
1480
March1st to 10thDay
19%13%6%8%5%3445%6%27%
1911
11th to 20thDay
16%12%5%8%6%44346%31%
1980
21st to endDay
21%13%5%8%6%35%345%27%
2178
April1st to 10thDay
15%12%46%6%345%5%6%33%
2000
11th to 20thDay
19%10%45%5%35%45%6%35%
2312
21st to endDay
21%10%36%5%34446%34%
2340
May1st to 10thDay
17%9%36%6%46%45%6%33%
2340
11th to 20thDay
17%8%36%5%35%5%6%7%35%
2301
21st to endDay
10%6%35%6%46%5%6%10%40%
2531
June1st to 10thDay
13%6%35%5%45%5%6%8%39%
2514
11th to 20thDay
12%5%26%6%35%5%6%9%41%
2575
21st to endDay
10%5%35%5%35%5%7%10%41%
2654
July1st to 10thDay
9%5%25%5%35%5%5%9%47%
2480
11th to 20thDay
11%5%24435%5%7%12%43%
2340
21st to endDay
10%5%245%36%6%7%11%42%
2547
August1st to 10thDay
8%5%26%5%45%6%7%9%44%
2327
11th to 20thDay
10%6%35%6%36%6%7%9%39%
2303
21st to endDay
11%5%35%5%45%6%6%9%42%
2555
September1st to 10thDay
14%5%35%6%35%6%5%8%41%
2041
11th to 20thDay
11%6%35%6%35%46%8%44%
1980
21st to endDay
17%8%35%4335%5%7%39%
1980
October1st to 10thDay
15%6%47%5%3446%8%38%
1876
11th to 20thDay
20%8%36%5%45%46%6%33%
1800
21st to endDay
24%10%47%6%4446%5%25%
1946
November1st to 10thDay
14%12%37%5%4436%7%35%
1672
11th to 20thDay
18%17%47%5%3345%6%26%
1710
21st to endDay
19%18%6%8%7%35%45%7%18%
1520
December1st to 10thDay
18%21%8%11%8%44345%15%
1520
11th to 20thDay
18%18%7%14%6%35%5%46%15%
1910
21st to endDay
23%23%8%11%7%334449%
2960
January1st to 10thNight
20%17%8%11%7%34435%19%
2459
11th to 20thNight
20%19%8%13%8%4433415%
2470
21st to endNight
19%18%7%12%8%3433417%
2711
February1st to 10thNight
21%14%6%12%8%3443420%
2340
11th to 20thNight
18%15%6%11%6%45%445%21%
2201
21st to endNight
21%13%6%11%6%35%445%23%
1776
March1st to 10thNight
18%12%5%8%6%35%445%30%
2048
11th to 20thNight
16%10%5%6%5%345%5%6%34%
1980
21st to endNight
20%12%47%5%34445%31%
2178
April1st to 10thNight
16%12%5%6%6%346%6%6%32%
1959
11th to 20thNight
16%9%37%6%35%5%6%7%34%
1611
21st to endNight
16%8%45%6%35%5%6%7%36%
1620
May1st to 10thNight
18%10%47%6%35%5%6%8%29%
1620
11th to 20thNight
16%9%36%6%35%5%5%7%35%
1592
21st to endNight
10%425%5%45%6%8%10%42%
1744
June1st to 10thNight
10%5%46%5%46%5%7%6%43%
1440
11th to 20thNight
11%5%26%6%35%5%6%10%40%
1377
21st to endNight
10%435%6%35%46%11%43%
1300
July1st to 10thNight
9%425%5%35%5%7%8%48%
1474
11th to 20thNight
8%4245%345%7%10%47%
1620
21st to endNight
8%6%35%5%45%6%6%9%43%
1771
August1st to 10thNight
7%5%35%5%345%5%10%49%
1611
11th to 20thNight
9%6%25%5%45%46%8%43%
1598
21st to endNight
11%5%26%5%35%5%5%8%44%
1782
September1st to 10thNight
11%6%35%5%36%5%5%7%43%
1916
11th to 20thNight
11%5%25%5%3446%8%48%
1980
21st to endNight
16%6%36%7%35%45%6%40%
1980
October1st to 10thNight
15%6%35%5%345%5%7%41%
2083
11th to 20thNight
21%10%37%5%3445%7%33%
2160
21st to endNight
28%10%47%5%3445%6%26%
2407
November1st to 10thNight
16%12%46%6%3446%5%34%
2406
11th to 20thNight
19%15%5%9%5%34445%26%
2470
21st to endNight
23%15%5%8%5%35%445%22%
2655
December1st to 10thNight
20%20%8%10%6%34445%17%
2660
11th to 20thNight
18%19%7%10%6%34446%20%
3285
21st to endNight
25%20%7%9%7%44445%11%
4691

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
72%6%10%9%3
1707
11th to 20thDay
76%7%10%5%2
1710
21st to endDay
75%6%7%9%4
1872
February1st to 10thDay
67%6%13%10%4
1620
11th to 20thDay
65%8%10%12%41
1650
21st to endDay
60%8%14%12%6%1
1480
March1st to 10thDay
57%6%12%18%6%1
1911
11th to 20thDay
53%7%11%17%10%2
1980
21st to endDay
58%6%9%18%8%1
2178
April1st to 10thDay
48%7%13%17%14%1
2000
11th to 20thDay
48%7%12%17%14%2
2312
21st to endDay
50%6%12%20%10%3
2340
May1st to 10thDay
49%8%11%19%11%2
2340
11th to 20thDay
46%9%11%18%14%3
2305
21st to endDay
36%10%15%23%14%2
2531
June1st to 10thDay
40%8%12%24%14%1
2514
11th to 20thDay
37%10%16%21%14%2
2575
21st to endDay
35%9%14%23%16%3
2654
July1st to 10thDay
32%9%12%26%18%3
2413
11th to 20thDay
32%9%16%27%16%1
2271
21st to endDay
32%9%17%25%15%2
2405
August1st to 10thDay
34%9%16%27%14%
2314
11th to 20thDay
37%10%18%24%10%2
2303
21st to endDay
35%10%15%22%16%3
2555
September1st to 10thDay
39%8%17%19%14%3
2041
11th to 20thDay
36%8%14%25%16%1
1980
21st to endDay
43%8%12%20%17%
1980
October1st to 10thDay
44%8%13%20%14%1
1876
11th to 20thDay
50%8%13%19%9%1
1800
21st to endDay
58%8%13%13%8%1
1946
November1st to 10thDay
48%7%13%18%12%1
1672
11th to 20thDay
58%6%11%15%8%1
1710
21st to endDay
65%9%9%12%5%
1520
December1st to 10thDay
72%7%10%8%3
1520
11th to 20thDay
71%7%10%9%2
1906
21st to endDay
79%6%9%5%1
2960
January1st to 10thNight
69%6%9%11%4
2459
11th to 20thNight
75%5%9%9%2
2470
21st to endNight
72%6%9%9%3
2711
February1st to 10thNight
68%7%10%11%3
2340
11th to 20thNight
65%7%9%13%6%
2203
21st to endNight
63%7%10%13%7%1
1776
March1st to 10thNight
55%6%11%19%8%
2048
11th to 20thNight
49%8%11%18%12%2
1980
21st to endNight
54%7%8%19%10%2
2178
April1st to 10thNight
51%6%13%16%12%2
1959
11th to 20thNight
47%7%12%16%14%3
1611
21st to endNight
45%7%13%18%14%3
1620
May1st to 10thNight
51%9%11%16%11%3
1620
11th to 20thNight
47%7%11%15%17%4
1593
21st to endNight
34%10%16%24%14%2
1745
June1st to 10thNight
39%8%11%25%14%3
1440
11th to 20thNight
36%9%15%20%17%2
1377
21st to endNight
34%10%13%25%17%1
1300
July1st to 10thNight
33%8%13%22%20%5%
1433
11th to 20thNight
31%10%14%24%20%2
1566
21st to endNight
34%10%14%20%18%4
1672
August1st to 10thNight
30%9%16%27%17%1
1600
11th to 20thNight
36%9%14%26%12%2
1598
21st to endNight
37%7%13%23%17%3
1782
September1st to 10thNight
39%8%13%22%14%4
1916
11th to 20thNight
34%8%14%24%20%1
1980
21st to endNight
44%7%11%20%17%1
1980
October1st to 10thNight
41%8%13%18%18%1
2083
11th to 20thNight
51%7%12%18%12%1
2160
21st to endNight
59%7%9%15%8%1
2407
November1st to 10thNight
50%7%12%17%12%2
2406
11th to 20thNight
61%6%10%14%7%2
2470
21st to endNight
66%6%10%13%4
2655
December1st to 10thNight
72%7%9%8%4
2660
11th to 20thNight
67%8%13%11%2
3288
21st to endNight
74%9%9%6%1
4691

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
26%18%35%13%7%1
270
11th to 20thDay
25%21%39%10%4
270
21st to endDay
27%20%33%17%21
294
February1st to 10thDay
25%20%40%14%1
240
11th to 20thDay
28%18%36%18%
240
21st to endDay
24%26%36%13%1
198
March1st to 10thDay
22%20%30%24%4
351
11th to 20thDay
21%15%34%23%6%1
420
21st to endDay
29%13%30%23%5%
462
April1st to 10thDay
19%12%36%23%8%1
420
11th to 20thDay
21%14%29%24%9%4
412
21st to endDay
26%10%31%24%7%2
420
May1st to 10thDay
25%10%26%27%9%2
423
11th to 20thDay
20%5%28%28%16%3
447
21st to endDay
12%424%33%21%6%
485
June1st to 10thDay
15%226%39%14%4
450
11th to 20thDay
12%6%23%34%20%4
505
21st to endDay
11%6%25%36%19%3
630
July1st to 10thDay
9%319%33%27%9%
583
11th to 20thDay
13%416%35%24%7%
444
21st to endDay
9%422%35%25%5%
488
August1st to 10thDay
10%318%33%28%9%
446
11th to 20thDay
13%318%36%24%7%
439
21st to endDay
11%5%19%32%24%8%
495
September1st to 10thDay
17%419%28%25%8%
450
11th to 20thDay
13%315%31%25%12%
450
21st to endDay
20%8%22%26%15%8%
450
October1st to 10thDay
14%7%24%27%20%7%
450
11th to 20thDay
21%14%31%23%9%2
450
21st to endDay
28%18%28%21%6%
461
November1st to 10thDay
18%20%25%24%10%3
270
11th to 20thDay
27%21%29%15%8%
270
21st to endDay
28%18%34%18%2
180
December1st to 10thDay
25%21%31%17%6%1
180
11th to 20thDay
23%26%32%17%2
180
21st to endDay
28%20%34%17%1
250
January1st to 10thNight
30%19%32%15%4
760
11th to 20thNight
32%17%30%17%4
760
21st to endNight
27%15%31%23%4
835
February1st to 10thNight
30%13%32%22%3
720
11th to 20thNight
25%15%34%23%4
703
21st to endNight
27%15%36%20%2
592
March1st to 10thNight
23%12%33%26%7%
720
11th to 20thNight
21%12%33%26%8%1
720
21st to endNight
25%8%28%28%10%1
792
April1st to 10thNight
21%12%30%30%7%1
720
11th to 20thNight
19%9%34%26%10%2
547
21st to endNight
19%8%32%32%8%1
540
May1st to 10thNight
22%7%22%34%13%1
540
11th to 20thNight
20%5%24%31%17%2
531
21st to endNight
13%217%35%28%4
584
June1st to 10thNight
12%423%41%20%1
360
11th to 20thNight
11%321%40%24%1
360
21st to endNight
9%321%39%27%1
400
July1st to 10thNight
10%311%39%33%5%
525
11th to 20thNight
12%416%34%28%6%
522
21st to endNight
10%316%39%29%2
591
August1st to 10thNight
10%314%39%30%5%
537
11th to 20thNight
12%413%37%30%5%
534
21st to endNight
14%316%32%30%5%
594
September1st to 10thNight
14%5%17%33%27%6%
720
11th to 20thNight
13%415%30%32%6%
720
21st to endNight
19%7%21%28%20%5%
720
October1st to 10thNight
18%9%21%28%20%4
720
11th to 20thNight
25%14%28%23%9%1
720
21st to endNight
32%15%24%24%5%
792
November1st to 10thNight
24%13%27%25%9%1
740
11th to 20thNight
29%18%29%17%6%2
760
21st to endNight
32%17%30%16%5%
760
December1st to 10thNight
31%18%30%16%5%
760
11th to 20thNight
29%20%31%16%4
760
21st to endNight
31%16%31%19%3
836
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