Seaman Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Seaman 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
45%
24178
22%
74649
14%
24129
54%
24129
27%
46421

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
29%
757
23%
2459
12%
757
43%
757
25%
1486
January11th to 20thNight
30%
732
23%
2378
12%
732
45%
732
22%
1541
January21st to endNight
29%
792
28%
2574
15%
792
47%
792
29%
1515
February1st to 10thNight
28%
720
20%
2340
11%
720
41%
720
24%
1455
February11th to 20thNight
19%
700
20%
2201
7%
699
35%
699
21%
1429
February21st to endNight
28%
592
28%
1716
14%
592
44%
592
27%
1076
March1st to 10thNight
34%
720
27%
1980
15%
720
47%
720
33%
1204
March11th to 20thNight
28%
720
20%
1980
10%
720
38%
720
26%
1319
March21st to endNight
33%
792
22%
2178
11%
792
42%
792
28%
1414
April1st to 10thNight
34%
720
24%
1815
9%
720
44%
720
32%
1172
April11th to 20thNight
39%
711
25%
1775
9%
711
47%
711
35%
1137
April21st to endNight
45%
720
25%
1800
11%
720
50%
720
36%
1129
May1st to 10thNight
41%
662
18%
1742
8%
662
45%
662
33%
1111
May11th to 20thNight
48%
531
16%
1592
10%
531
52%
531
24%
1058
May21st to endNight
61%
556
17%
1718
14%
556
63%
556
28%
1073
June1st to 10thNight
63%
360
17%
1440
22%
360
65%
360
26%
829
June11th to 20thNight
61%
360
15%
1440
16%
360
64%
360
21%
886
June21st to endNight
68%
425
18%
1505
18%
425
70%
425
24%
953
July1st to 10thNight
68%
525
14%
1575
12%
525
70%
525
26%
1039
July11th to 20thNight
72%
522
14%
1566
12%
522
73%
522
29%
1020
July21st to endNight
66%
591
17%
1672
14%
558
69%
558
28%
1073
August1st to 10thNight
63%
537
12%
1600
10%
534
63%
534
24%
1096
August11th to 20thNight
64%
642
15%
1706
11%
642
65%
642
26%
1178
August21st to endNight
64%
792
16%
1980
11%
792
64%
792
29%
1371
September1st to 10thNight
69%
720
22%
1800
16%
720
70%
720
35%
1165
September11th to 20thNight
61%
720
25%
1822
19%
720
63%
720
31%
1222
September21st to endNight
49%
720
17%
2070
14%
720
53%
720
22%
1452
October1st to 10thNight
56%
720
24%
2160
23%
720
62%
720
31%
1320
October11th to 20thNight
50%
720
29%
2160
24%
720
61%
720
34%
1270
October21st to endNight
50%
792
32%
2376
24%
792
63%
792
37%
1344
November1st to 10thNight
47%
740
26%
2221
20%
740
56%
740
31%
1350
November11th to 20thNight
43%
760
26%
2362
17%
760
54%
760
30%
1396
November21st to endNight
45%
760
26%
2590
21%
760
56%
760
31%
1449
December1st to 10thNight
33%
760
21%
2660
13%
760
47%
760
22%
1675
December11th to 20thNight
38%
760
24%
3171
17%
758
51%
758
22%
1816
December21st to endNight
34%
827
17%
4525
14%
817
47%
817
17%
2398

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%35%5%6%8%44%
74600
Night
14%5%25%5%3445%7%45%
75126
TransparencyDay
39%5%12%22%17%4
74321
Night
39%5%11%21%19%5%
74924
SeeingDay
16%7%22%26%20%10%
14175
Night
16%6%25%33%18%2
24195

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
16%6%246%35%336%46%
1706
11th to 20thDay
18%6%345%24346%43%
1638
21st to endDay
15%6%25%423446%48%
1782
February1st to 10thDay
15%6%35%5%35%5%5%6%43%
1620
11th to 20thDay
22%5%24424335%47%
1645
21st to endDay
17%6%35%6%2445%7%41%
1537
March1st to 10thDay
14%6%24334445%51%
1980
11th to 20thDay
16%6%26%43435%8%43%
1980
21st to endDay
16%7%36%5%35%45%6%40%
2178
April1st to 10thDay
11%42342445%8%53%
2143
11th to 20thDay
11%5%24435%45%8%50%
2134
21st to endDay
13%6%25%5%35%45%6%46%
2160
May1st to 10thDay
10%5%35%6%46%37%9%43%
2232
11th to 20thDay
13%6%36%6%45%46%8%39%
2301
21st to endDay
12%5%26%5%35%6%6%9%41%
2553
June1st to 10thDay
10%426%6%46%6%7%9%40%
2520
11th to 20thDay
9%5%25%6%36%6%7%11%42%
2520
21st to endDay
7%5%26%6%36%7%8%10%40%
2446
July1st to 10thDay
8%436%6%46%7%8%12%36%
2340
11th to 20thDay
8%6%35%6%46%6%8%11%38%
2340
21st to endDay
7%426%7%47%7%8%10%36%
2547
August1st to 10thDay
10%6%27%6%45%7%9%11%33%
2327
11th to 20thDay
11%6%36%7%36%7%7%9%34%
2174
21st to endDay
10%7%37%6%46%6%6%10%37%
2376
September1st to 10thDay
10%5%25%5%35%6%7%9%43%
2160
11th to 20thDay
13%6%35%435%46%8%44%
2134
21st to endDay
19%7%26%6%4445%7%37%
1890
October1st to 10thDay
15%5%35%5%24445%49%
1800
11th to 20thDay
14%5%25%4235%35%53%
1800
21st to endDay
12%5%25%43433454%
1980
November1st to 10thDay
13%6%24423346%53%
1857
11th to 20thDay
13%6%23333437%52%
1814
21st to endDay
14%5%2342435%6%52%
1587
December1st to 10thDay
15%8%25%5%4345%7%41%
1520
11th to 20thDay
15%5%24322345%55%
1910
21st to endDay
16%7%35%434447%43%
2969
January1st to 10thNight
16%6%25%424446%46%
2459
11th to 20thNight
15%8%36%5%3445%5%42%
2378
21st to endNight
16%425%433446%49%
2574
February1st to 10thNight
18%6%25%43445%6%44%
2340
11th to 20thNight
20%6%35%424446%42%
2201
21st to endNight
16%6%244245%5%6%46%
1716
March1st to 10thNight
13%435%323445%53%
1980
11th to 20thNight
17%5%25%5%3446%8%40%
1980
21st to endNight
16%6%245%3435%6%45%
2178
April1st to 10thNight
13%5%25%42445%7%48%
1815
11th to 20thNight
13%5%2443435%8%49%
1775
21st to endNight
11%4245%4445%8%48%
1800
May1st to 10thNight
11%6%26%5%2446%10%44%
1742
11th to 20thNight
15%6%36%6%45%447%41%
1592
21st to endNight
11%4246%45%46%11%42%
1718
June1st to 10thNight
9%434435%6%8%11%40%
1440
11th to 20thNight
9%5%27%7%35%7%8%9%39%
1440
21st to endNight
8%5%26%6%36%7%9%11%38%
1505
July1st to 10thNight
6%5%36%7%45%7%8%11%39%
1620
11th to 20thNight
8%427%6%46%5%8%13%38%
1620
21st to endNight
7%5%35%6%46%6%7%11%38%
1771
August1st to 10thNight
12%6%36%6%37%5%7%9%35%
1611
11th to 20thNight
8%6%36%7%5%5%6%8%11%33%
1706
21st to endNight
11%7%26%6%35%6%7%10%38%
1980
September1st to 10thNight
11%425%43446%10%46%
1800
11th to 20thNight
12%6%36%5%35%448%45%
1822
21st to endNight
19%6%37%5%35%447%36%
2070
October1st to 10thNight
15%5%2442445%6%48%
2160
11th to 20thNight
14%424424336%53%
2160
21st to endNight
12%424423446%55%
2376
November1st to 10thNight
14%5%35%433445%50%
2221
11th to 20thNight
14%5%24334446%50%
2362
21st to endNight
13%42442445%6%52%
2590
December1st to 10thNight
17%6%36%5%335%47%42%
2660
11th to 20thNight
18%6%2442345%5%48%
3285
21st to endNight
15%7%25%433447%47%
4679

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
41%38%23%19%6%
1707
11th to 20thDay
44%46%20%22%5%
1638
21st to endDay
39%36%23%23%6%
1782
February1st to 10thDay
41%411%22%17%5%
1620
11th to 20thDay
43%27%20%22%6%
1654
21st to endDay
44%411%16%19%6%
1537
March1st to 10thDay
36%48%23%22%6%
1980
11th to 20thDay
41%5%10%22%16%7%
1980
21st to endDay
45%5%10%20%16%4
2178
April1st to 10thDay
31%310%27%22%7%
2143
11th to 20thDay
33%412%23%22%6%
2134
21st to endDay
38%5%12%23%18%4
2160
May1st to 10thDay
37%5%17%21%17%3
2232
11th to 20thDay
43%6%13%24%13%1
2305
21st to endDay
39%7%15%26%13%
2553
June1st to 10thDay
38%7%14%23%16%2
2520
11th to 20thDay
35%8%17%24%14%2
2520
21st to endDay
35%10%17%22%14%2
2446
July1st to 10thDay
37%9%17%22%11%3
2275
11th to 20thDay
37%8%20%22%11%2
2271
21st to endDay
39%8%20%22%11%
2405
August1st to 10thDay
42%8%19%22%8%1
2314
11th to 20thDay
44%8%16%22%9%1
2174
21st to endDay
43%7%16%21%10%3
2376
September1st to 10thDay
37%8%16%18%17%4
2160
11th to 20thDay
38%5%11%23%21%2
2134
21st to endDay
48%410%21%14%4
1890
October1st to 10thDay
38%410%24%20%4
1800
11th to 20thDay
35%47%25%23%6%
1800
21st to endDay
35%36%22%25%9%
1980
November1st to 10thDay
34%37%24%27%5%
1857
11th to 20thDay
35%310%20%25%7%
1814
21st to endDay
34%37%24%26%5%
1587
December1st to 10thDay
43%312%21%17%4
1520
11th to 20thDay
34%36%28%20%9%
1906
21st to endDay
42%38%24%21%2
2969
January1st to 10thNight
40%38%20%23%6%
2459
11th to 20thNight
44%49%20%18%5%
2378
21st to endNight
38%36%23%25%6%
2574
February1st to 10thNight
42%39%20%21%6%
2340
11th to 20thNight
45%47%17%21%7%
2203
21st to endNight
39%48%23%19%8%
1716
March1st to 10thNight
34%48%23%23%8%
1980
11th to 20thNight
43%5%9%19%18%5%
1980
21st to endNight
40%5%10%21%20%5%
2178
April1st to 10thNight
36%5%9%18%26%7%
1815
11th to 20thNight
35%5%9%24%21%7%
1775
21st to endNight
35%411%28%18%5%
1800
May1st to 10thNight
36%5%15%23%17%3
1742
11th to 20thNight
43%6%12%21%16%2
1593
21st to endNight
37%7%16%25%14%1
1719
June1st to 10thNight
34%8%18%22%16%2
1440
11th to 20thNight
38%10%17%18%15%2
1440
21st to endNight
38%10%14%21%14%2
1505
July1st to 10thNight
37%11%18%21%11%2
1575
11th to 20thNight
35%11%21%23%9%2
1566
21st to endNight
37%9%19%25%10%1
1672
August1st to 10thNight
43%9%20%21%7%1
1600
11th to 20thNight
41%10%19%20%9%1
1706
21st to endNight
40%9%16%23%10%2
1980
September1st to 10thNight
34%8%17%22%14%5%
1800
11th to 20thNight
39%7%10%21%20%3
1822
21st to endNight
49%5%10%18%15%3
2070
October1st to 10thNight
37%5%8%24%23%4
2160
11th to 20thNight
35%37%23%25%7%
2160
21st to endNight
32%37%23%26%9%
2376
November1st to 10thNight
38%46%19%28%5%
2221
11th to 20thNight
36%49%16%25%10%
2362
21st to endNight
34%47%23%26%7%
2590
December1st to 10thNight
44%410%20%19%4
2660
11th to 20thNight
39%28%20%23%7%
3288
21st to endNight
39%37%25%23%3
4679

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%37%20%6%
270
11th to 20thDay
19%22%32%20%8%
246
21st to endDay
19%17%40%18%5%1
264
February1st to 10thDay
20%16%34%23%5%1
240
11th to 20thDay
32%11%37%17%4
312
21st to endDay
23%15%32%23%7%
346
March1st to 10thDay
18%12%35%26%8%1
420
11th to 20thDay
20%16%34%22%7%1
420
21st to endDay
21%10%33%24%10%2
462
April1st to 10thDay
17%14%28%26%13%2
420
11th to 20thDay
13%12%28%28%16%4
412
21st to endDay
16%10%24%29%20%2
420
May1st to 10thDay
11%11%34%23%14%7%
423
11th to 20thDay
16%421%29%20%9%
447
21st to endDay
16%412%26%26%15%
485
June1st to 10thDay
12%214%30%29%14%
450
11th to 20thDay
12%317%24%25%19%
450
21st to endDay
9%312%30%33%14%
450
July1st to 10thDay
10%17%25%35%22%
445
11th to 20thDay
9%16%25%36%22%
444
21st to endDay
8%29%31%34%16%
488
August1st to 10thDay
12%212%27%29%18%
446
11th to 20thDay
12%19%23%31%24%
439
21st to endDay
12%19%26%27%25%
495
September1st to 10thDay
13%211%20%29%24%
450
11th to 20thDay
13%413%27%30%15%
450
21st to endDay
22%6%17%27%20%8%
450
October1st to 10thDay
17%320%22%25%12%
450
11th to 20thDay
15%5%22%30%22%6%
450
21st to endDay
13%6%25%30%20%5%
495
November1st to 10thDay
19%6%24%29%16%6%
455
11th to 20thDay
18%7%32%29%12%2
419
21st to endDay
17%10%25%28%17%4
247
December1st to 10thDay
19%12%39%18%9%2
180
11th to 20thDay
18%8%37%20%15%2
180
21st to endDay
22%12%31%19%13%3
255
January1st to 10thNight
19%11%36%28%6%1
760
11th to 20thNight
19%10%34%30%7%
732
21st to endNight
18%7%42%29%4
792
February1st to 10thNight
22%8%38%29%4
720
11th to 20thNight
24%13%41%21%1
703
21st to endNight
20%9%37%30%3
592
March1st to 10thNight
16%11%36%32%5%
720
11th to 20thNight
20%9%38%25%7%1
720
21st to endNight
19%10%34%30%7%
792
April1st to 10thNight
15%11%35%33%6%
720
11th to 20thNight
15%9%34%32%11%
711
21st to endNight
15%5%30%41%9%1
720
May1st to 10thNight
13%8%32%35%12%
662
11th to 20thNight
18%5%21%40%15%1
531
21st to endNight
13%213%40%32%2
558
June1st to 10thNight
9%317%43%27%1
360
11th to 20thNight
10%415%39%29%4
360
21st to endNight
7%312%44%31%3
425
July1st to 10thNight
9%110%37%39%5%
525
11th to 20thNight
8%26%39%39%6%
522
21st to endNight
8%210%42%34%4
591
August1st to 10thNight
11%29%39%37%4
537
11th to 20thNight
11%27%35%39%5%
642
21st to endNight
14%38%30%39%6%
792
September1st to 10thNight
12%27%34%39%6%
720
11th to 20thNight
15%311%35%31%5%
720
21st to endNight
23%313%33%26%1
720
October1st to 10thNight
16%316%33%27%4
720
11th to 20thNight
16%5%22%35%20%2
720
21st to endNight
14%428%32%20%2
792
November1st to 10thNight
17%426%33%17%3
740
11th to 20thNight
17%7%29%33%13%1
760
21st to endNight
15%6%29%34%15%1
760
December1st to 10thNight
19%8%32%33%8%
760
11th to 20thNight
18%7%31%35%8%
760
21st to endNight
18%8%32%32%9%
836
Page generated at 2024-01-10 10:16:10. Version ac07

Copyright 2024 Attilla Danko


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