Spradlin Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Spradlin Observatory clear sky chart from 2005-11-06 to 2024-01-16.

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
51%
23551
23%
74491
18%
23497
58%
23497
28%
45777

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
28%
760
22%
2459
11%
757
41%
757
23%
1528
January11th to 20thNight
31%
744
24%
2371
12%
744
43%
744
20%
1573
January21st to endNight
29%
792
29%
2376
14%
792
43%
792
25%
1527
February1st to 10thNight
33%
720
24%
2160
13%
720
43%
720
24%
1409
February11th to 20thNight
29%
703
20%
2098
10%
699
38%
699
23%
1392
February21st to endNight
26%
592
21%
1776
10%
592
37%
592
23%
1188
March1st to 10thNight
35%
720
24%
2160
14%
720
43%
720
29%
1326
March11th to 20thNight
33%
720
20%
2038
10%
720
40%
720
24%
1356
March21st to endNight
37%
744
24%
2130
12%
744
47%
744
28%
1338
April1st to 10thNight
44%
540
25%
1800
20%
540
53%
540
30%
1060
April11th to 20thNight
42%
533
26%
1775
18%
533
55%
533
31%
1016
April21st to endNight
50%
540
27%
1800
23%
540
59%
540
32%
1005
May1st to 10thNight
55%
540
25%
1625
18%
540
62%
540
37%
938
May11th to 20thNight
59%
531
19%
1592
15%
531
63%
531
29%
1008
May21st to endNight
71%
582
22%
1744
19%
582
73%
582
34%
1045
June1st to 10thNight
68%
540
16%
1620
14%
540
69%
540
26%
1066
June11th to 20thNight
78%
540
17%
1620
15%
540
80%
540
41%
905
June21st to endNight
77%
540
18%
1620
16%
540
78%
540
33%
978
July1st to 10thNight
74%
525
13%
1575
12%
525
75%
525
27%
1030
July11th to 20thNight
80%
522
15%
1566
15%
522
80%
522
29%
1010
July21st to endNight
73%
591
16%
1680
16%
558
74%
558
30%
1054
August1st to 10thNight
79%
537
17%
1778
20%
534
79%
534
31%
1055
August11th to 20thNight
72%
534
16%
1776
18%
534
73%
534
25%
1137
August21st to endNight
68%
594
19%
1980
23%
594
68%
594
24%
1295
September1st to 10thNight
71%
589
21%
1849
23%
589
71%
589
28%
1173
September11th to 20thNight
63%
720
23%
1980
20%
720
64%
720
31%
1267
September21st to endNight
67%
720
29%
1980
23%
720
72%
720
39%
1174
October1st to 10thNight
64%
720
32%
1980
25%
720
68%
720
44%
1117
October11th to 20thNight
55%
720
35%
1980
25%
720
64%
720
40%
1156
October21st to endNight
51%
792
29%
2474
27%
792
57%
792
31%
1459
November1st to 10thNight
59%
740
27%
2406
26%
740
66%
740
36%
1297
November11th to 20thNight
47%
760
30%
2470
23%
760
58%
760
34%
1378
November21st to endNight
45%
760
25%
2470
20%
760
53%
760
28%
1476
December1st to 10thNight
34%
760
24%
2470
17%
760
45%
760
22%
1590
December11th to 20thNight
36%
759
24%
2904
17%
758
44%
758
21%
1749
December21st to endNight
33%
827
14%
4409
15%
817
41%
817
13%
2702

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
12%6%35%5%35%5%6%8%42%
74859
Night
12%6%25%5%345%5%8%46%
74962
TransparencyDay
40%7%11%19%18%5%
74583
Night
37%6%11%19%20%6%
74757
SeeingDay
14%8%20%24%21%12%
13500
Night
14%7%21%31%23%5%
23563

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
19%7%35%5%24346%42%
1706
11th to 20thDay
18%10%4441344443%
1715
21st to endDay
18%6%34424435%46%
1980
February1st to 10thDay
18%8%36%5%35%45%5%39%
1800
11th to 20thDay
23%7%34434345%40%
1748
21st to endDay
20%8%37%434445%38%
1480
March1st to 10thDay
15%5%27%434446%46%
1800
11th to 20thDay
16%8%47%5%3445%7%37%
1921
21st to endDay
15%6%36%5%35%5%5%7%40%
2240
April1st to 10thDay
12%5%35%5%345%47%47%
2160
11th to 20thDay
13%5%25%5%45%5%47%46%
2134
21st to endDay
8%4245%345%6%8%50%
2160
May1st to 10thDay
10%5%25%3345%6%8%49%
2333
11th to 20thDay
8%5%36%5%35%5%7%9%44%
2301
21st to endDay
7%5%25%6%46%6%6%8%44%
2531
June1st to 10thDay
11%5%27%6%5%7%7%7%10%33%
2340
11th to 20thDay
6%4245%46%7%8%10%44%
2340
21st to endDay
6%436%6%36%7%9%12%38%
2340
July1st to 10thDay
8%5%36%8%5%8%7%9%12%31%
2340
11th to 20thDay
6%5%36%8%6%7%8%8%13%31%
2340
21st to endDay
6%426%7%5%9%8%9%11%32%
2534
August1st to 10thDay
6%325%7%5%9%9%9%13%32%
2148
11th to 20thDay
10%6%36%7%5%6%7%8%11%32%
2125
21st to endDay
11%6%26%7%46%7%7%10%34%
2376
September1st to 10thDay
9%6%36%7%46%6%6%8%40%
2092
11th to 20thDay
12%7%35%5%35%5%6%7%43%
1980
21st to endDay
10%5%25%5%345%5%7%49%
1980
October1st to 10thDay
10%424425%5%47%53%
1980
11th to 20thDay
9%5%24433446%56%
1980
21st to endDay
13%424423345%55%
1876
November1st to 10thDay
12%5%345%2334454%
1672
11th to 20thDay
13%5%24424345%53%
1710
21st to endDay
15%6%25%5%235%5%6%46%
1710
December1st to 10thDay
21%6%26%5%3445%6%38%
1710
11th to 20thDay
17%8%36%6%3433443%
2153
21st to endDay
19%8%37%5%345%46%36%
3124
January1st to 10thNight
17%8%25%42345%5%45%
2459
11th to 20thNight
17%9%45%5%34347%39%
2371
21st to endNight
16%7%35%5%345%45%44%
2376
February1st to 10thNight
16%6%36%6%34446%42%
2160
11th to 20thNight
21%7%26%33434444%
2098
21st to endNight
19%7%25%6%3345%7%39%
1776
March1st to 10thNight
16%6%24424447%47%
2160
11th to 20thNight
15%7%25%445%45%7%42%
2038
21st to endNight
14%5%246%35%5%48%45%
2130
April1st to 10thNight
10%6%245%35%5%5%8%47%
1800
11th to 20thNight
13%5%25%42435%7%50%
1775
21st to endNight
8%425%5%235%5%6%54%
1800
May1st to 10thNight
8%425%4345%5%8%53%
1625
11th to 20thNight
8%5%26%6%45%5%6%9%44%
1592
21st to endNight
7%424435%5%7%12%47%
1744
June1st to 10thNight
5%5%36%6%46%7%8%12%37%
1620
11th to 20thNight
42135%35%5%8%13%51%
1620
21st to endNight
4315%7%35%7%8%11%45%
1620
July1st to 10thNight
5%5%35%6%38%7%9%12%36%
1620
11th to 20thNight
4425%6%47%6%9%13%41%
1620
21st to endNight
45%36%6%45%7%8%12%40%
1779
August1st to 10thNight
35%246%45%7%9%13%41%
1790
11th to 20thNight
7%5%26%6%45%6%7%10%42%
1776
21st to endNight
9%7%37%7%46%5%6%8%40%
1980
September1st to 10thNight
7%435%6%36%6%7%8%43%
1849
11th to 20thNight
11%6%35%5%245%6%9%45%
1980
21st to endNight
7%5%25%5%35%46%8%52%
1980
October1st to 10thNight
8%5%24433336%60%
1980
11th to 20thNight
10%5%245%23446%55%
1980
21st to endNight
13%6%2443333454%
2474
November1st to 10thNight
12%42332345%5%57%
2406
11th to 20thNight
12%434423346%55%
2470
21st to endNight
13%5%25%5%35%45%6%48%
2470
December1st to 10thNight
18%6%35%5%345%5%6%41%
2470
11th to 20thNight
17%7%25%424335%48%
3042
21st to endNight
19%8%35%5%345%5%8%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
44%47%17%24%5%
1707
11th to 20thDay
45%47%18%21%5%
1715
21st to endDay
41%45%21%24%6%
1980
February1st to 10thDay
49%47%18%19%4
1800
11th to 20thDay
47%45%18%20%6%
1758
21st to endDay
49%5%6%12%21%7%
1480
March1st to 10thDay
41%5%7%17%20%10%
1800
11th to 20thDay
47%5%11%14%17%6%
1921
21st to endDay
43%5%10%18%20%3
2240
April1st to 10thDay
38%5%9%21%19%8%
2160
11th to 20thDay
38%5%7%19%24%7%
2134
21st to endDay
31%5%10%25%25%3
2160
May1st to 10thDay
32%7%12%22%22%5%
2333
11th to 20thDay
36%8%15%22%16%2
2305
21st to endDay
36%8%12%23%18%3
2531
June1st to 10thDay
44%9%14%19%14%1
2340
11th to 20thDay
31%11%18%25%13%2
2340
21st to endDay
36%11%18%22%10%3
2340
July1st to 10thDay
41%12%21%16%9%1
2275
11th to 20thDay
39%13%20%17%9%1
2271
21st to endDay
38%13%20%20%8%
2392
August1st to 10thDay
38%13%19%23%7%
2136
11th to 20thDay
43%10%17%17%10%3
2125
21st to endDay
43%11%14%18%10%3
2376
September1st to 10thDay
39%9%15%16%16%6%
2092
11th to 20thDay
40%7%11%19%19%4
1980
21st to endDay
34%5%11%21%22%7%
1980
October1st to 10thDay
31%6%10%19%26%9%
1980
11th to 20thDay
30%37%24%27%8%
1980
21st to endDay
34%45%16%32%10%
1876
November1st to 10thDay
34%37%15%29%11%
1672
11th to 20thDay
34%47%17%27%11%
1710
21st to endDay
39%5%6%19%23%7%
1710
December1st to 10thDay
46%5%8%16%19%6%
1710
11th to 20thDay
47%26%17%21%6%
2150
21st to endDay
49%49%17%19%2
3124
January1st to 10thNight
42%47%19%23%5%
2459
11th to 20thNight
46%47%18%19%5%
2371
21st to endNight
44%35%19%24%6%
2376
February1st to 10thNight
45%46%18%20%7%
2160
11th to 20thNight
46%4417%20%9%
2099
21st to endNight
44%5%9%14%19%9%
1776
March1st to 10thNight
38%38%17%21%12%
2160
11th to 20thNight
42%6%10%16%20%6%
2038
21st to endNight
38%5%8%23%20%5%
2130
April1st to 10thNight
35%6%11%21%19%8%
1800
11th to 20thNight
34%5%8%20%23%11%
1775
21st to endNight
31%6%10%25%22%7%
1800
May1st to 10thNight
29%6%11%23%26%5%
1625
11th to 20thNight
36%9%16%20%17%2
1593
21st to endNight
30%10%13%26%17%5%
1745
June1st to 10thNight
37%12%14%20%17%1
1620
11th to 20thNight
23%10%23%27%14%3
1620
21st to endNight
31%9%19%21%16%4
1620
July1st to 10thNight
35%12%21%19%10%2
1575
11th to 20thNight
30%15%22%20%10%2
1566
21st to endNight
32%11%25%21%10%1
1680
August1st to 10thNight
29%11%21%29%9%
1778
11th to 20thNight
36%12%21%16%11%4
1776
21st to endNight
41%9%15%19%12%4
1980
September1st to 10thNight
35%11%15%17%17%5%
1849
11th to 20thNight
34%10%11%19%21%5%
1980
21st to endNight
30%6%10%22%24%8%
1980
October1st to 10thNight
27%49%23%25%12%
1980
11th to 20thNight
30%48%20%26%11%
1980
21st to endNight
36%35%13%30%12%
2474
November1st to 10thNight
29%48%18%26%15%
2406
11th to 20thNight
33%36%19%27%13%
2470
21st to endNight
38%47%18%24%9%
2470
December1st to 10thNight
43%5%8%18%21%5%
2470
11th to 20thNight
41%36%15%29%5%
3044
21st to endNight
46%5%9%20%18%3
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
24%23%30%19%5%
270
11th to 20thDay
22%20%33%15%9%1
257
21st to endDay
23%21%34%15%5%1
264
February1st to 10thDay
24%24%30%16%6%
240
11th to 20thDay
35%18%28%18%1
240
21st to endDay
23%19%43%15%1
198
March1st to 10thDay
24%15%33%23%41
240
11th to 20thDay
20%16%32%21%10%1
361
21st to endDay
19%16%31%24%10%
462
April1st to 10thDay
16%14%28%27%12%2
420
11th to 20thDay
16%12%29%25%15%3
412
21st to endDay
11%11%30%30%16%2
420
May1st to 10thDay
13%9%23%30%18%7%
423
11th to 20thDay
9%423%30%22%14%
447
21st to endDay
10%414%29%24%19%
485
June1st to 10thDay
13%212%29%27%16%
450
11th to 20thDay
8%212%22%27%30%
450
21st to endDay
8%310%25%30%24%
450
July1st to 10thDay
8%27%20%31%32%
445
11th to 20thDay
6%6%19%29%40%
444
21st to endDay
6%26%17%38%32%
488
August1st to 10thDay
9%18%20%32%30%
446
11th to 20thDay
10%15%23%37%24%
439
21st to endDay
15%17%21%33%23%
495
September1st to 10thDay
8%39%24%39%18%
450
11th to 20thDay
12%411%23%36%15%
450
21st to endDay
11%214%25%35%13%
450
October1st to 10thDay
13%319%32%25%9%
450
11th to 20thDay
10%8%20%32%26%4
450
21st to endDay
16%11%20%30%20%3
357
November1st to 10thDay
20%6%24%30%15%5%
270
11th to 20thDay
15%14%31%29%9%1
270
21st to endDay
11%16%32%28%11%3
270
December1st to 10thDay
25%16%32%20%8%
270
11th to 20thDay
23%17%30%20%8%2
270
21st to endDay
27%14%28%22%8%
297
January1st to 10thNight
21%14%33%27%5%
760
11th to 20thNight
22%15%29%27%8%
744
21st to endNight
20%13%35%28%4
792
February1st to 10thNight
19%11%32%34%4
720
11th to 20thNight
25%12%31%28%4
703
21st to endNight
21%13%35%28%3
592
March1st to 10thNight
19%12%32%33%5%
720
11th to 20thNight
18%12%33%27%10%1
720
21st to endNight
15%11%32%30%11%1
744
April1st to 10thNight
12%8%32%31%15%
540
11th to 20thNight
14%10%29%31%15%1
533
21st to endNight
11%8%25%37%19%2
540
May1st to 10thNight
8%5%26%35%24%2
540
11th to 20thNight
8%418%37%27%5%
531
21st to endNight
8%210%35%38%8%
584
June1st to 10thNight
8%111%37%37%7%
540
11th to 20thNight
319%27%44%17%
540
21st to endNight
5%16%31%45%11%
540
July1st to 10thNight
7%15%21%49%17%
525
11th to 20thNight
5%1419%50%22%
522
21st to endNight
6%5%26%46%17%
591
August1st to 10thNight
41423%51%17%
537
11th to 20thNight
9%1426%48%11%
534
21st to endNight
12%26%24%43%13%
594
September1st to 10thNight
9%17%25%47%11%
589
11th to 20thNight
12%312%27%41%5%
720
21st to endNight
8%214%34%38%4
720
October1st to 10thNight
9%317%37%28%5%
720
11th to 20thNight
13%421%35%24%3
720
21st to endNight
15%7%20%36%20%2
792
November1st to 10thNight
13%6%18%38%22%3
740
11th to 20thNight
14%9%26%36%14%1
760
21st to endNight
16%10%25%36%12%1
760
December1st to 10thNight
21%10%30%30%9%1
760
11th to 20thNight
23%8%29%28%11%1
760
21st to endNight
26%11%26%32%6%
836
Page generated at 2024-01-13 18:28:31. Version ac07

Copyright 2024 Attilla Danko


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