J. Stephen Schmidt Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the J. Stephen Schmidt Observatory clear sky chart from 2005-11-06 to 2024-01-15.

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
45%
23823
22%
74470
15%
23767
53%
23767
25%
46857

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
22%
760
21%
2459
8%
757
38%
757
18%
1568
January11th to 20thNight
25%
739
21%
2399
9%
739
39%
739
17%
1599
January21st to endNight
25%
792
28%
2505
12%
792
43%
792
22%
1555
February1st to 10thNight
29%
720
23%
2160
12%
720
41%
720
23%
1387
February11th to 20thNight
21%
702
20%
2098
6%
699
34%
699
19%
1398
February21st to endNight
19%
592
21%
1776
7%
592
32%
592
19%
1218
March1st to 10thNight
30%
720
25%
2116
12%
720
41%
720
26%
1315
March11th to 20thNight
29%
720
19%
1980
9%
720
37%
720
24%
1319
March21st to endNight
33%
792
21%
2178
11%
792
40%
792
24%
1444
April1st to 10thNight
39%
670
25%
1930
13%
670
50%
670
30%
1162
April11th to 20thNight
40%
533
26%
1775
17%
533
53%
533
28%
1031
April21st to endNight
50%
540
29%
1655
20%
540
58%
540
32%
956
May1st to 10thNight
50%
540
22%
1620
13%
540
58%
540
31%
975
May11th to 20thNight
51%
531
16%
1593
10%
531
55%
531
26%
1021
May21st to endNight
63%
582
19%
1744
15%
582
65%
582
29%
1106
June1st to 10thNight
65%
540
16%
1620
13%
540
66%
540
24%
1086
June11th to 20thNight
70%
540
15%
1620
13%
540
71%
540
34%
964
June21st to endNight
72%
540
16%
1620
14%
540
74%
540
29%
1023
July1st to 10thNight
67%
525
14%
1575
13%
525
68%
525
24%
1059
July11th to 20thNight
70%
522
12%
1566
11%
522
70%
522
25%
1038
July21st to endNight
69%
591
15%
1672
13%
558
70%
558
25%
1124
August1st to 10thNight
69%
537
14%
1600
13%
534
69%
534
24%
1063
August11th to 20thNight
63%
534
18%
1731
18%
534
64%
534
24%
1144
August21st to endNight
60%
594
18%
1980
19%
594
62%
594
20%
1346
September1st to 10thNight
63%
686
19%
1946
18%
686
63%
686
28%
1280
September11th to 20thNight
58%
720
22%
1980
17%
720
61%
720
30%
1297
September21st to endNight
61%
720
27%
1980
19%
720
66%
720
34%
1221
October1st to 10thNight
56%
720
31%
1980
23%
720
63%
720
39%
1144
October11th to 20thNight
47%
720
31%
2077
22%
720
58%
720
35%
1205
October21st to endNight
48%
792
31%
2376
25%
792
59%
792
33%
1363
November1st to 10thNight
48%
740
28%
2403
23%
740
59%
740
33%
1320
November11th to 20thNight
40%
760
29%
2470
18%
760
55%
760
30%
1402
November21st to endNight
38%
760
24%
2470
17%
760
49%
760
25%
1511
December1st to 10thNight
28%
760
22%
2470
12%
760
41%
760
18%
1636
December11th to 20thNight
33%
759
24%
2934
15%
758
44%
758
20%
1743
December21st to endNight
27%
830
14%
4412
12%
817
37%
817
11%
2834

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
14%6%35%5%35%5%6%8%40%
74885
Night
14%6%25%5%345%5%7%44%
74906
TransparencyDay
41%7%12%19%17%4
74608
Night
39%6%11%20%19%5%
74702
SeeingDay
20%10%22%23%17%9%
13736
Night
17%9%22%28%20%4
23833

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
21%8%25%5%24445%42%
1706
11th to 20thDay
20%7%24434445%43%
1656
21st to endDay
18%6%36%434445%44%
1849
February1st to 10thDay
19%9%35%5%4445%7%37%
1800
11th to 20thDay
25%6%343245%5%5%40%
1748
21st to endDay
24%7%35%424345%39%
1480
March1st to 10thDay
16%5%25%43446%7%44%
1844
11th to 20thDay
20%7%35%5%35%5%46%37%
1980
21st to endDay
16%6%36%6%345%5%7%39%
2178
April1st to 10thDay
12%5%35%5%35%5%6%6%44%
2044
11th to 20thDay
13%5%35%6%3445%6%45%
2134
21st to endDay
11%5%244345%6%9%48%
2304
May1st to 10thDay
11%5%35%5%3445%8%47%
2340
11th to 20thDay
11%6%26%6%46%5%6%8%39%
2301
21st to endDay
9%6%26%6%46%6%7%9%39%
2531
June1st to 10thDay
10%6%36%7%46%6%7%10%34%
2340
11th to 20thDay
6%325%7%46%7%9%12%39%
2340
21st to endDay
8%435%6%47%7%9%10%37%
2340
July1st to 10thDay
9%6%37%7%5%7%8%8%11%29%
2340
11th to 20thDay
8%5%37%9%5%8%8%8%12%26%
2340
21st to endDay
6%5%37%8%6%9%7%8%11%29%
2547
August1st to 10thDay
8%6%27%7%5%7%9%9%10%30%
2327
11th to 20thDay
11%6%36%7%5%7%7%7%9%31%
2165
21st to endDay
12%7%37%7%5%7%7%8%8%28%
2376
September1st to 10thDay
10%6%36%7%45%6%5%9%39%
1994
11th to 20thDay
14%7%26%5%35%5%5%8%41%
1980
21st to endDay
12%5%25%6%345%47%47%
1980
October1st to 10thDay
12%424434435%55%
1980
11th to 20thDay
13%5%23323447%54%
1882
21st to endDay
15%5%25%423345%54%
1980
November1st to 10thDay
13%424324235%57%
1672
11th to 20thDay
14%42442445%5%52%
1710
21st to endDay
16%6%345%3445%6%45%
1710
December1st to 10thDay
24%6%3443446%6%37%
1710
11th to 20thDay
18%6%36%5%35%345%43%
2153
21st to endDay
22%8%3443446%6%34%
3124
January1st to 10thNight
20%6%35%433345%43%
2459
11th to 20thNight
18%8%46%5%4445%5%37%
2399
21st to endNight
17%7%35%423345%46%
2505
February1st to 10thNight
17%6%36%5%3345%7%42%
2160
11th to 20thNight
22%6%35%43334442%
2098
21st to endNight
23%6%35%425%45%5%38%
1776
March1st to 10thNight
16%6%3443445%6%48%
2116
11th to 20thNight
15%6%36%5%25%45%7%41%
1980
21st to endNight
14%6%36%5%3445%6%44%
2178
April1st to 10thNight
12%4245%25%5%6%8%48%
1930
11th to 20thNight
13%6%2442446%6%49%
1775
21st to endNight
9%5%35%42446%8%51%
1655
May1st to 10thNight
9%4245%35%5%6%8%49%
1620
11th to 20thNight
12%6%25%6%45%6%5%9%41%
1592
21st to endNight
9%6%25%5%35%5%6%10%43%
1744
June1st to 10thNight
7%5%36%7%5%6%7%8%10%36%
1620
11th to 20thNight
5%425%5%347%7%13%45%
1620
21st to endNight
6%435%5%46%6%8%12%42%
1620
July1st to 10thNight
8%5%36%7%36%7%8%11%35%
1620
11th to 20thNight
6%426%6%5%7%6%9%13%36%
1620
21st to endNight
7%426%8%46%8%9%11%35%
1771
August1st to 10thNight
8%5%36%6%47%6%8%13%36%
1611
11th to 20thNight
10%6%36%7%36%5%6%9%39%
1731
21st to endNight
12%7%35%6%46%6%7%9%35%
1980
September1st to 10thNight
8%6%36%7%45%5%6%9%42%
1946
11th to 20thNight
13%5%25%6%35%46%7%44%
1980
21st to endNight
11%5%244245%5%7%50%
1980
October1st to 10thNight
12%414323346%58%
1980
11th to 20thNight
11%5%24433346%55%
2077
21st to endNight
13%5%24422346%54%
2376
November1st to 10thNight
12%5%23323336%56%
2403
11th to 20thNight
14%5%244235%46%53%
2470
21st to endNight
16%6%244345%5%6%44%
2470
December1st to 10thNight
20%7%26%5%3445%6%38%
2470
11th to 20thNight
17%8%25%424345%46%
3042
21st to endNight
21%8%36%5%3445%7%34%
4532

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
45%47%19%21%4
1707
11th to 20thDay
45%47%19%20%5%
1656
21st to endDay
43%36%20%21%6%
1849
February1st to 10thDay
48%38%17%20%4
1800
11th to 20thDay
46%48%19%18%5%
1758
21st to endDay
50%37%14%20%7%
1480
March1st to 10thDay
39%5%10%16%21%9%
1844
11th to 20thDay
48%410%15%18%5%
1980
21st to endDay
45%5%11%21%16%3
2178
April1st to 10thDay
39%5%9%22%19%5%
2044
11th to 20thDay
39%48%18%22%8%
2134
21st to endDay
33%5%12%27%19%4
2304
May1st to 10thDay
35%6%13%22%20%4
2340
11th to 20thDay
42%8%15%20%13%2
2305
21st to endDay
38%8%13%23%16%2
2531
June1st to 10thDay
43%9%16%20%10%2
2340
11th to 20thDay
34%9%20%25%11%2
2340
21st to endDay
38%12%17%20%12%2
2340
July1st to 10thDay
44%12%18%16%8%2
2275
11th to 20thDay
46%12%18%13%8%3
2271
21st to endDay
44%12%18%17%8%
2405
August1st to 10thDay
43%13%18%20%5%1
2314
11th to 20thDay
46%10%16%17%9%2
2165
21st to endDay
50%10%13%15%9%2
2376
September1st to 10thDay
42%8%13%16%17%4
1994
11th to 20thDay
41%8%12%17%20%2
1980
21st to endDay
37%6%11%17%22%7%
1980
October1st to 10thDay
33%5%9%17%28%8%
1980
11th to 20thDay
31%410%22%24%10%
1882
21st to endDay
34%35%20%28%10%
1980
November1st to 10thDay
33%37%16%32%9%
1672
11th to 20thDay
34%48%17%26%11%
1710
21st to endDay
40%47%17%25%7%
1710
December1st to 10thDay
48%48%18%17%5%
1710
11th to 20thDay
45%36%16%23%7%
2150
21st to endDay
47%5%9%19%17%3
3124
January1st to 10thNight
44%5%7%17%23%5%
2459
11th to 20thNight
48%49%16%19%4
2399
21st to endNight
41%35%21%25%5%
2505
February1st to 10thNight
42%49%19%20%6%
2160
11th to 20thNight
46%46%18%20%6%
2099
21st to endNight
48%48%15%18%7%
1776
March1st to 10thNight
39%48%18%20%11%
2116
11th to 20thNight
42%6%11%17%19%6%
1980
21st to endNight
42%5%8%22%19%3
2178
April1st to 10thNight
34%5%11%20%24%6%
1930
11th to 20thNight
36%48%21%22%10%
1775
21st to endNight
33%5%10%28%20%4
1655
May1st to 10thNight
33%7%12%23%22%3
1620
11th to 20thNight
39%7%17%22%14%1
1593
21st to endNight
36%9%12%25%16%3
1745
June1st to 10thNight
38%12%15%21%11%2
1620
11th to 20thNight
30%9%24%24%12%1
1620
21st to endNight
33%11%18%22%12%4
1620
July1st to 10thNight
39%12%18%19%11%1
1575
11th to 20thNight
35%14%22%17%9%3
1566
21st to endNight
38%13%20%20%8%2
1672
August1st to 10thNight
36%14%20%22%7%1
1600
11th to 20thNight
40%10%18%17%14%1
1731
21st to endNight
43%11%15%18%11%2
1980
September1st to 10thNight
38%9%14%18%16%5%
1946
11th to 20thNight
37%8%13%19%21%2
1980
21st to endNight
32%8%10%21%20%9%
1980
October1st to 10thNight
29%6%10%19%29%8%
1980
11th to 20thNight
32%49%21%24%10%
2077
21st to endNight
32%45%19%28%12%
2376
November1st to 10thNight
32%37%19%27%12%
2403
11th to 20thNight
34%45%19%27%12%
2470
21st to endNight
39%47%19%24%6%
2470
December1st to 10thNight
47%48%19%17%5%
2470
11th to 20thNight
40%49%16%26%6%
3044
21st to endNight
50%5%7%22%14%2
4532

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
34%19%33%11%2
270
11th to 20thDay
35%20%25%15%5%
252
21st to endDay
31%23%33%10%21
264
February1st to 10thDay
30%23%35%10%3
240
11th to 20thDay
43%27%21%8%
240
21st to endDay
40%20%32%7%2
198
March1st to 10thDay
30%14%35%16%4
284
11th to 20thDay
31%18%23%20%7%
420
21st to endDay
25%16%35%17%7%
462
April1st to 10thDay
27%10%28%23%9%2
420
11th to 20thDay
18%16%30%22%13%1
412
21st to endDay
20%12%27%23%15%3
420
May1st to 10thDay
18%11%30%24%12%5%
423
11th to 20thDay
15%9%21%28%18%10%
447
21st to endDay
16%6%14%32%21%12%
485
June1st to 10thDay
13%320%28%24%12%
450
11th to 20thDay
8%5%15%25%25%20%
450
21st to endDay
12%415%30%23%15%
450
July1st to 10thDay
13%29%27%26%22%
445
11th to 20thDay
9%210%21%34%23%
444
21st to endDay
8%29%26%31%24%
488
August1st to 10thDay
12%6%12%24%25%22%
446
11th to 20thDay
14%39%27%30%17%
439
21st to endDay
17%311%22%30%17%
495
September1st to 10thDay
10%7%14%28%26%15%
450
11th to 20thDay
16%6%13%26%28%11%
450
21st to endDay
12%5%20%27%27%9%
450
October1st to 10thDay
16%6%21%32%17%9%
450
11th to 20thDay
17%10%22%28%18%4
450
21st to endDay
20%10%26%26%15%3
495
November1st to 10thDay
20%11%26%28%10%4
270
11th to 20thDay
21%20%34%17%6%1
270
21st to endDay
19%15%37%21%7%1
270
December1st to 10thDay
34%20%25%16%31
270
11th to 20thDay
29%15%34%19%3
270
21st to endDay
35%18%28%15%4
297
January1st to 10thNight
27%18%28%22%5%
760
11th to 20thNight
26%15%28%23%7%
739
21st to endNight
24%16%33%25%3
792
February1st to 10thNight
23%14%30%27%6%
720
11th to 20thNight
28%17%31%22%2
703
21st to endNight
28%15%34%20%3
592
March1st to 10thNight
20%16%30%29%4
720
11th to 20thNight
20%15%31%25%9%1
720
21st to endNight
21%13%29%29%8%
792
April1st to 10thNight
16%13%28%31%11%
670
11th to 20thNight
17%12%28%29%14%1
533
21st to endNight
12%8%25%36%18%1
540
May1st to 10thNight
11%9%24%33%22%1
540
11th to 20thNight
15%5%20%31%24%5%
531
21st to endNight
13%312%32%34%6%
584
June1st to 10thNight
9%112%39%34%5%
540
11th to 20thNight
6%312%32%34%14%
540
21st to endNight
6%19%37%38%8%
540
July1st to 10thNight
10%27%24%44%13%
525
11th to 20thNight
8%27%24%45%13%
522
21st to endNight
8%27%25%46%13%
591
August1st to 10thNight
9%27%27%44%11%
537
11th to 20thNight
11%210%24%42%10%
534
21st to endNight
14%410%24%37%10%
594
September1st to 10thNight
11%410%28%37%9%
686
11th to 20thNight
14%315%28%35%3
720
21st to endNight
13%218%35%31%2
720
October1st to 10thNight
14%5%20%32%23%6%
720
11th to 20thNight
13%9%25%31%20%3
720
21st to endNight
17%10%20%34%17%2
792
November1st to 10thNight
16%9%22%32%19%1
740
11th to 20thNight
16%13%27%30%13%1
760
21st to endNight
21%12%26%28%12%1
760
December1st to 10thNight
23%16%28%25%8%
760
11th to 20thNight
24%13%27%27%8%1
760
21st to endNight
32%11%26%25%6%
836
Page generated at 2024-01-12 07:31:49. Version ac07

Copyright 2024 Attilla Danko


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