Skyline Observatory
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Skyline Observatory clear sky chart from 2005-11-06 to 2024-01-12.

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
49%
23535
23%
74436
17%
23482
55%
23482
27%
45979

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
25%
759
22%
2459
11%
757
38%
757
19%
1586
January11th to 20thNight
27%
727
20%
2360
11%
727
38%
727
16%
1631
January21st to endNight
29%
792
28%
2394
14%
792
42%
792
23%
1534
February1st to 10thNight
31%
720
22%
2160
12%
720
41%
720
23%
1411
February11th to 20thNight
25%
703
18%
2098
9%
699
33%
699
19%
1428
February21st to endNight
24%
592
21%
1776
10%
592
32%
592
17%
1242
March1st to 10thNight
33%
720
23%
2160
14%
720
41%
720
23%
1377
March11th to 20thNight
33%
720
18%
2034
10%
720
39%
720
23%
1373
March21st to endNight
35%
748
21%
2134
12%
748
42%
748
25%
1396
April1st to 10thNight
44%
540
26%
1800
19%
540
54%
540
30%
1004
April11th to 20thNight
43%
533
28%
1775
20%
533
56%
533
29%
1013
April21st to endNight
49%
540
26%
1759
20%
540
58%
540
30%
995
May1st to 10thNight
53%
540
23%
1620
15%
540
60%
540
35%
954
May11th to 20thNight
57%
531
19%
1592
13%
531
61%
531
29%
1009
May21st to endNight
68%
582
20%
1744
18%
582
69%
582
34%
1039
June1st to 10thNight
64%
540
18%
1620
15%
540
66%
540
30%
1010
June11th to 20thNight
78%
540
21%
1620
17%
540
80%
540
45%
853
June21st to endNight
74%
540
18%
1620
17%
540
75%
540
36%
954
July1st to 10thNight
70%
525
14%
1575
14%
525
71%
525
29%
997
July11th to 20thNight
74%
522
17%
1566
16%
522
75%
522
33%
951
July21st to endNight
70%
591
18%
1672
17%
558
72%
558
30%
1049
August1st to 10thNight
77%
537
17%
1707
19%
534
77%
534
33%
999
August11th to 20thNight
68%
534
16%
1776
19%
534
69%
534
28%
1073
August21st to endNight
68%
594
21%
1980
24%
594
69%
594
26%
1242
September1st to 10thNight
70%
587
23%
1847
24%
587
71%
587
33%
1108
September11th to 20thNight
64%
720
23%
1980
20%
720
65%
720
33%
1231
September21st to endNight
62%
720
30%
1980
23%
720
67%
720
38%
1169
October1st to 10thNight
63%
720
34%
1980
28%
720
67%
720
42%
1110
October11th to 20thNight
48%
720
31%
1980
21%
720
57%
720
33%
1222
October21st to endNight
51%
792
29%
2527
27%
792
59%
792
31%
1473
November1st to 10thNight
52%
740
28%
2406
25%
740
60%
740
32%
1338
November11th to 20thNight
43%
760
30%
2470
21%
760
57%
760
31%
1410
November21st to endNight
41%
760
26%
2470
20%
760
51%
760
25%
1522
December1st to 10thNight
32%
760
22%
2470
15%
760
43%
760
19%
1644
December11th to 20thNight
38%
759
26%
2912
19%
758
47%
758
20%
1747
December21st to endNight
30%
827
13%
4413
13%
817
39%
817
10%
2885

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%36%5%35%5%6%8%40%
74828
Night
14%6%35%5%345%5%7%44%
74894
TransparencyDay
42%411%22%17%4
74551
Night
40%411%22%19%5%
74690
SeeingDay
19%10%21%22%19%9%
13472
Night
17%8%19%30%22%4
23548

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
23%7%3442435%6%39%
1706
11th to 20thDay
24%8%35%425%335%37%
1629
21st to endDay
18%5%35%434446%45%
1958
February1st to 10thDay
19%11%36%423347%38%
1800
11th to 20thDay
24%7%36%5%25%345%36%
1748
21st to endDay
25%8%26%434335%36%
1480
March1st to 10thDay
17%6%35%5%3446%6%40%
1800
11th to 20thDay
21%8%45%5%35%5%45%35%
1926
21st to endDay
16%7%37%5%35%5%6%8%36%
2236
April1st to 10thDay
14%6%35%435%5%5%7%44%
2160
11th to 20thDay
16%6%25%434447%45%
2134
21st to endDay
11%6%26%5%35%46%8%43%
2200
May1st to 10thDay
14%6%25%5%35%5%5%8%44%
2340
11th to 20thDay
12%7%37%6%45%46%7%39%
2301
21st to endDay
12%5%35%5%46%5%6%10%38%
2531
June1st to 10thDay
10%5%36%6%47%6%7%10%34%
2340
11th to 20thDay
5%325%5%35%9%8%11%43%
2340
21st to endDay
7%5%25%8%46%7%7%11%40%
2340
July1st to 10thDay
9%5%37%8%5%7%7%9%10%29%
2340
11th to 20thDay
10%436%7%5%8%8%7%10%32%
2340
21st to endDay
8%5%36%8%47%7%8%12%32%
2547
August1st to 10thDay
8%437%7%5%8%8%8%12%31%
2216
11th to 20thDay
10%5%27%7%5%7%7%7%9%33%
2125
21st to endDay
13%5%26%8%5%6%6%7%9%32%
2376
September1st to 10thDay
12%5%35%6%45%7%7%9%38%
2093
11th to 20thDay
13%5%26%6%35%6%6%7%42%
1980
21st to endDay
12%5%25%6%3445%6%49%
1980
October1st to 10thDay
11%5%24434336%55%
1980
11th to 20thDay
10%6%2443435%7%53%
1980
21st to endDay
15%6%24333346%51%
1823
November1st to 10thDay
12%5%2432444455%
1672
11th to 20thDay
13%5%245%35%35%6%49%
1710
21st to endDay
19%6%25%424446%44%
1710
December1st to 10thDay
24%7%25%5%346%45%35%
1710
11th to 20thDay
17%7%36%5%4445%5%40%
2153
21st to endDay
19%9%5%6%6%4446%7%31%
3124
January1st to 10thNight
22%7%25%5%24346%41%
2459
11th to 20thNight
21%8%46%5%445%46%33%
2360
21st to endNight
16%8%35%5%34445%44%
2394
February1st to 10thNight
19%8%35%5%33346%41%
2160
11th to 20thNight
22%7%36%5%34445%39%
2098
21st to endNight
26%7%35%435%5%45%34%
1776
March1st to 10thNight
17%6%25%43445%7%42%
2160
11th to 20thNight
16%8%36%5%3445%7%38%
2034
21st to endNight
15%6%36%5%3445%6%42%
2134
April1st to 10thNight
12%5%245%245%6%8%47%
1800
11th to 20thNight
15%5%24423438%50%
1775
21st to endNight
10%4245%35%5%47%50%
1759
May1st to 10thNight
11%425%425%35%8%51%
1620
11th to 20thNight
10%6%25%6%36%5%7%9%42%
1592
21st to endNight
7%5%25%5%45%6%8%10%45%
1744
June1st to 10thNight
9%5%25%6%35%7%6%10%41%
1620
11th to 20thNight
5%223415%6%6%12%54%
1620
21st to endNight
6%4345%35%6%6%12%47%
1620
July1st to 10thNight
8%5%45%6%5%6%6%7%11%38%
1620
11th to 20thNight
9%3235%36%7%7%12%42%
1620
21st to endNight
6%5%36%6%37%6%7%13%38%
1771
August1st to 10thNight
5%4246%45%6%9%13%42%
1718
11th to 20thNight
10%5%36%5%35%5%6%11%41%
1776
21st to endNight
10%5%36%6%36%5%6%9%41%
1980
September1st to 10thNight
8%5%25%6%25%5%6%7%48%
1847
11th to 20thNight
11%435%5%3447%8%45%
1980
21st to endNight
8%5%25%5%2445%7%53%
1980
October1st to 10thNight
11%323413346%59%
1980
11th to 20thNight
12%6%35%5%34446%50%
1980
21st to endNight
16%5%25%323445%51%
2527
November1st to 10thNight
13%42442445%6%53%
2406
11th to 20thNight
13%5%35%424446%51%
2470
21st to endNight
18%6%25%42445%6%44%
2470
December1st to 10thNight
20%8%36%5%3445%6%37%
2470
11th to 20thNight
18%7%25%423446%45%
3042
21st to endNight
20%8%47%6%35%5%5%7%29%
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
47%27%21%19%4
1707
11th to 20thDay
52%27%18%18%3
1629
21st to endDay
41%37%25%20%3
1958
February1st to 10thDay
49%27%21%18%3
1800
11th to 20thDay
53%26%20%15%4
1758
21st to endDay
52%17%14%18%6%
1480
March1st to 10thDay
43%38%17%21%8%
1800
11th to 20thDay
51%310%15%17%4
1926
21st to endDay
46%411%24%13%2
2236
April1st to 10thDay
39%311%24%17%5%
2160
11th to 20thDay
40%37%21%24%5%
2134
21st to endDay
39%39%30%16%3
2200
May1st to 10thDay
39%412%26%15%4
2340
11th to 20thDay
44%415%22%13%
2305
21st to endDay
40%5%13%26%15%1
2531
June1st to 10thDay
43%6%14%21%15%1
2340
11th to 20thDay
31%6%20%26%15%2
2340
21st to endDay
36%6%19%21%14%3
2340
July1st to 10thDay
44%8%16%20%10%2
2275
11th to 20thDay
42%8%19%19%9%3
2271
21st to endDay
41%8%19%23%8%1
2405
August1st to 10thDay
42%8%20%21%8%1
2203
11th to 20thDay
44%7%14%21%13%1
2125
21st to endDay
47%7%13%19%11%3
2376
September1st to 10thDay
39%7%15%18%16%4
2093
11th to 20thDay
40%5%12%19%21%3
1980
21st to endDay
35%49%23%21%7%
1980
October1st to 10thDay
34%37%21%27%8%
1980
11th to 20thDay
32%48%23%24%10%
1980
21st to endDay
36%25%21%28%8%
1823
November1st to 10thDay
33%37%19%30%8%
1672
11th to 20thDay
37%25%23%25%8%
1710
21st to endDay
42%26%21%24%5%
1710
December1st to 10thDay
52%26%19%18%4
1710
11th to 20thDay
47%27%20%20%4
2150
21st to endDay
53%28%23%12%3
3124
January1st to 10thNight
47%27%21%19%4
2459
11th to 20thNight
52%38%19%15%3
2360
21st to endNight
44%25%24%21%4
2394
February1st to 10thNight
46%28%20%20%4
2160
11th to 20thNight
50%26%19%16%6%
2099
21st to endNight
52%36%18%15%6%
1776
March1st to 10thNight
43%37%18%20%9%
2160
11th to 20thNight
45%411%18%17%4
2034
21st to endNight
44%39%25%17%2
2134
April1st to 10thNight
34%313%24%21%4
1800
11th to 20thNight
36%36%22%22%10%
1775
21st to endNight
34%411%30%18%4
1759
May1st to 10thNight
33%412%23%25%3
1620
11th to 20thNight
38%6%17%23%16%1
1593
21st to endNight
33%6%17%25%16%3
1745
June1st to 10thNight
36%7%16%22%17%2
1620
11th to 20thNight
23%5%20%32%16%2
1620
21st to endNight
30%7%18%23%16%4
1620
July1st to 10thNight
38%6%21%20%12%3
1575
11th to 20thNight
31%9%23%20%12%4
1566
21st to endNight
36%8%21%24%11%1
1672
August1st to 10thNight
31%8%23%25%12%
1707
11th to 20thNight
36%7%21%19%14%3
1776
21st to endNight
40%6%15%24%11%3
1980
September1st to 10thNight
33%7%17%21%17%4
1847
11th to 20thNight
35%6%14%19%23%3
1980
21st to endNight
31%5%8%24%23%9%
1980
October1st to 10thNight
27%47%26%27%9%
1980
11th to 20thNight
37%36%23%21%10%
1980
21st to endNight
36%2421%28%9%
2527
November1st to 10thNight
33%37%23%24%10%
2406
11th to 20thNight
35%35%20%28%10%
2470
21st to endNight
43%25%21%24%6%
2470
December1st to 10thNight
49%38%20%17%3
2470
11th to 20thNight
41%36%19%26%5%
3044
21st to endNight
52%37%22%13%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%20%28%14%3
270
11th to 20thDay
31%22%29%12%5%2
243
21st to endDay
26%23%34%13%3
264
February1st to 10thDay
30%23%30%14%3
240
11th to 20thDay
41%24%26%9%
240
21st to endDay
42%20%29%8%2
198
March1st to 10thDay
28%20%35%13%41
240
11th to 20thDay
31%17%28%17%6%1
366
21st to endDay
28%16%31%16%8%1
462
April1st to 10thDay
23%14%25%24%12%2
420
11th to 20thDay
22%15%27%23%12%1
412
21st to endDay
21%11%31%21%14%2
420
May1st to 10thDay
18%11%30%23%12%6%
423
11th to 20thDay
13%7%26%26%17%11%
447
21st to endDay
16%416%27%21%15%
485
June1st to 10thDay
15%5%16%26%24%13%
450
11th to 20thDay
5%414%28%27%21%
450
21st to endDay
10%417%24%28%17%
450
July1st to 10thDay
10%312%22%33%20%
445
11th to 20thDay
9%311%24%33%21%
444
21st to endDay
9%47%24%34%21%
488
August1st to 10thDay
12%210%25%31%19%
446
11th to 20thDay
13%29%29%34%13%
439
21st to endDay
16%39%23%31%18%
495
September1st to 10thDay
12%312%26%30%16%
450
11th to 20thDay
15%414%21%29%17%
450
21st to endDay
14%5%14%26%32%8%
450
October1st to 10thDay
14%5%21%28%23%9%
450
11th to 20thDay
14%10%27%29%18%2
450
21st to endDay
25%8%24%27%13%4
338
November1st to 10thDay
22%11%26%25%14%2
270
11th to 20thDay
14%18%38%24%6%
270
21st to endDay
21%16%31%20%11%2
270
December1st to 10thDay
34%15%26%18%6%1
270
11th to 20thDay
26%20%32%14%7%1
270
21st to endDay
35%14%32%13%5%
297
January1st to 10thNight
28%15%27%23%6%
760
11th to 20thNight
26%17%24%26%7%
727
21st to endNight
22%14%31%29%4
792
February1st to 10thNight
25%12%26%32%5%
720
11th to 20thNight
27%17%27%26%3
703
21st to endNight
33%12%28%25%3
592
March1st to 10thNight
22%15%25%33%5%
720
11th to 20thNight
22%13%27%29%9%1
720
21st to endNight
20%12%29%28%12%
748
April1st to 10thNight
15%10%26%34%14%
540
11th to 20thNight
19%9%24%31%15%2
533
21st to endNight
13%7%25%38%16%1
540
May1st to 10thNight
12%6%23%34%22%2
540
11th to 20thNight
12%5%18%33%27%5%
531
21st to endNight
10%38%35%38%6%
584
June1st to 10thNight
12%111%31%36%7%
540
11th to 20thNight
5%26%33%41%13%
540
21st to endNight
7%27%31%43%10%
540
July1st to 10thNight
10%25%25%42%17%
525
11th to 20thNight
10%2423%42%19%
522
21st to endNight
8%25%23%48%14%
591
August1st to 10thNight
7%1225%49%16%
537
11th to 20thNight
12%35%24%47%9%
534
21st to endNight
12%25%26%44%11%
594
September1st to 10thNight
10%28%26%46%9%
587
11th to 20thNight
12%412%28%39%6%
720
21st to endNight
9%413%29%42%3
720
October1st to 10thNight
13%415%32%30%6%
720
11th to 20thNight
15%8%20%33%23%1
720
21st to endNight
19%8%17%36%19%2
792
November1st to 10thNight
16%8%19%33%23%3
740
11th to 20thNight
15%11%26%31%15%1
760
21st to endNight
23%9%22%33%13%1
760
December1st to 10thNight
26%12%24%29%9%
760
11th to 20thNight
24%12%21%34%9%
760
21st to endNight
28%12%24%29%7%
836
Page generated at 2024-01-09 06:14:42. Version ac07

Copyright 2024 Attilla Danko


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