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 2024-02-05.

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%
24670
19%
79991
16%
24582
54%
24582
27%
50139

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
38%
936
11%
4380
11%
926
40%
926
13%
3161
January11th to 20thNight
33%
827
13%
4217
15%
807
38%
807
11%
3069
January21st to endNight
32%
826
10%
4478
13%
814
37%
814
10%
3156
February1st to 10thNight
27%
738
10%
2398
8%
738
31%
738
14%
1808
February11th to 20thNight
30%
701
13%
2231
8%
700
36%
700
18%
1579
February21st to endNight
31%
592
17%
1776
11%
592
37%
592
18%
1267
March1st to 10thNight
38%
720
19%
2068
11%
720
44%
720
26%
1363
March11th to 20thNight
50%
720
23%
1980
16%
720
55%
720
33%
1250
March21st to endNight
37%
736
15%
2122
9%
736
42%
736
23%
1506
April1st to 10thNight
39%
540
16%
1800
13%
540
46%
540
22%
1150
April11th to 20thNight
39%
533
17%
1777
14%
533
46%
533
22%
1134
April21st to endNight
46%
540
18%
1800
16%
540
51%
540
26%
1098
May1st to 10thNight
46%
540
17%
1630
14%
540
51%
540
25%
1062
May11th to 20thNight
57%
531
18%
1418
15%
531
59%
531
32%
910
May21st to endNight
56%
584
18%
1552
13%
582
60%
582
36%
946
June1st to 10thNight
65%
540
24%
1440
19%
540
68%
540
49%
774
June11th to 20thNight
61%
540
26%
1440
17%
540
66%
540
46%
787
June21st to endNight
74%
540
28%
1440
24%
540
76%
540
58%
708
July1st to 10thNight
81%
525
21%
1400
19%
525
82%
525
49%
758
July11th to 20thNight
80%
522
25%
1392
22%
522
81%
522
50%
746
July21st to endNight
79%
591
21%
1636
20%
558
79%
558
42%
892
August1st to 10thNight
76%
537
21%
1602
20%
534
77%
534
40%
880
August11th to 20thNight
77%
534
30%
1664
29%
534
80%
534
45%
847
August21st to endNight
79%
594
29%
1980
33%
594
80%
594
42%
1008
September1st to 10thNight
75%
540
31%
1800
32%
540
79%
540
45%
853
September11th to 20thNight
72%
540
33%
1800
35%
540
75%
540
43%
897
September21st to endNight
66%
657
32%
2037
26%
657
71%
657
48%
1006
October1st to 10thNight
58%
720
26%
2160
18%
720
63%
720
38%
1218
October11th to 20thNight
54%
720
31%
2160
18%
720
63%
720
40%
1162
October21st to endNight
50%
792
26%
2376
17%
792
57%
792
34%
1403
November1st to 10thNight
46%
882
24%
2362
14%
882
51%
882
36%
1432
November11th to 20thNight
42%
950
23%
2527
14%
950
46%
950
31%
1615
November21st to endNight
44%
950
20%
2660
14%
950
48%
950
30%
1698
December1st to 10thNight
33%
950
14%
2660
8%
950
37%
950
22%
1881
December11th to 20thNight
33%
949
17%
3102
10%
949
35%
949
18%
2048
December21st to endNight
27%
1033
8%
4726
7%
1026
31%
1026
11%
3067

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
6%10%47%5%345%5%7%44%
78334
Night
6%12%5%7%5%2345%6%46%
80590
TransparencyDay
36%8%13%20%16%6%
78046
Night
37%8%13%21%16%5%
80400
SeeingDay
12%15%29%28%14%3
14480
Night
11%8%25%38%17%1
24710

By Month

Percentage Cloud Cover SW (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
414%9%17%8%33345%30%
2538
11th to 20thDay
423%7%15%9%3333426%
2770
21st to endDay
319%9%11%5%3343435%
3146
February1st to 10thDay
6%21%9%12%6%23335%30%
1656
11th to 20thDay
6%17%8%10%6%24436%32%
1615
21st to endDay
418%8%13%7%3335%7%29%
1480
March1st to 10thDay
6%16%6%10%5%33346%39%
1890
11th to 20thDay
414%6%7%43445%7%41%
1980
21st to endDay
5%15%6%9%6%36%5%5%7%33%
2233
April1st to 10thDay
7%13%5%7%6%3445%7%38%
2160
11th to 20thDay
8%15%48%6%35%5%5%7%34%
2131
21st to endDay
6%12%46%6%35%5%5%7%40%
2160
May1st to 10thDay
10%10%36%6%35%6%7%8%35%
2327
11th to 20thDay
10%7%26%5%45%6%7%9%39%
2478
21st to endDay
8%6%25%6%36%6%7%9%42%
2724
June1st to 10thDay
43134446%7%9%55%
2520
11th to 20thDay
5%2135%345%47%61%
2520
21st to endDay
32134335%6%8%62%
2520
July1st to 10thDay
4314435%6%7%8%55%
2520
11th to 20thDay
3214436%6%8%9%53%
2520
21st to endDay
44245%46%7%9%9%46%
2581
August1st to 10thDay
5%5%25%5%46%7%8%10%43%
2328
11th to 20thDay
43244445%6%9%55%
2237
21st to endDay
5%3245%35%5%7%9%54%
2376
September1st to 10thDay
5%32343445%7%61%
2160
11th to 20thDay
6%4235%345%5%6%57%
2160
21st to endDay
8%413323345%62%
1918
October1st to 10thDay
9%8%25%5%33445%52%
1800
11th to 20thDay
9%8%23223347%56%
1800
21st to endDay
9%10%35%32445%5%50%
1980
November1st to 10thDay
6%10%35%424347%52%
1696
11th to 20thDay
9%15%47%313346%45%
1650
21st to endDay
5%11%5%10%412335%50%
1520
December1st to 10thDay
7%16%8%10%7%33345%36%
1520
11th to 20thDay
6%17%7%8%5%23446%38%
1926
21st to endDay
419%6%11%8%33446%32%
2794
January1st to 10thNight
416%8%16%9%3234431%
4417
11th to 20thNight
424%9%10%8%2233430%
4229
21st to endNight
423%9%12%5%2333432%
4521
February1st to 10thNight
7%17%9%12%7%34435%29%
2398
11th to 20thNight
6%18%10%10%5%3335%6%33%
2230
21st to endNight
417%8%12%6%3335%6%32%
1776
March1st to 10thNight
5%15%5%8%5%2335%6%42%
2068
11th to 20thNight
5%11%5%5%434446%49%
1980
21st to endNight
5%17%6%7%5%35%5%5%6%37%
2122
April1st to 10thNight
9%14%36%425%5%5%6%42%
1800
11th to 20thNight
8%14%5%6%43345%6%40%
1777
21st to endNight
9%13%4443347%6%44%
1800
May1st to 10thNight
9%9%345%35%6%6%8%41%
1630
11th to 20thNight
7%6%25%5%346%7%8%45%
1417
21st to endNight
6%5%245%45%6%6%8%51%
1552
June1st to 10thNight
44224235%6%9%59%
1440
11th to 20thNight
431442345%7%63%
1440
21st to endNight
32123245%5%7%68%
1440
July1st to 10thNight
31133245%6%9%62%
1440
11th to 20thNight
222343447%10%60%
1440
21st to endNight
2224435%6%8%10%54%
1732
August1st to 10thNight
4313435%5%8%10%53%
1611
11th to 20thNight
332342445%10%59%
1664
21st to endNight
43144346%6%8%58%
1980
September1st to 10thNight
5%3134225%6%7%63%
1800
11th to 20thNight
5%42343435%6%62%
1800
21st to endNight
8%313322345%66%
2037
October1st to 10thNight
8%6%13423446%58%
2160
11th to 20thNight
8%8%24312335%62%
2160
21st to endNight
10%10%35%222345%54%
2376
November1st to 10thNight
7%11%44223346%53%
2362
11th to 20thNight
8%13%5%6%32335%6%46%
2527
21st to endNight
5%11%6%7%5%33346%47%
2660
December1st to 10thNight
7%17%6%9%6%32245%38%
2660
11th to 20thNight
6%15%7%9%5%23347%38%
3271
21st to endNight
415%6%11%7%34446%37%
4873

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
50%10%13%17%9%1
2539
11th to 20thDay
56%11%14%11%6%1
2770
21st to endDay
49%10%16%16%8%1
3146
February1st to 10thDay
56%6%14%14%9%1
1656
11th to 20thDay
51%7%12%19%9%2
1624
21st to endDay
53%8%14%13%11%1
1480
March1st to 10thDay
46%5%14%23%11%1
1890
11th to 20thDay
41%8%15%23%11%2
1980
21st to endDay
50%8%12%20%8%3
2233
April1st to 10thDay
41%9%15%18%13%4
2160
11th to 20thDay
47%8%13%18%13%1
2134
21st to endDay
40%8%13%27%11%
2160
May1st to 10thDay
42%10%13%20%14%1
2327
11th to 20thDay
37%12%16%24%11%1
2482
21st to endDay
33%12%15%23%15%2
2724
June1st to 10thDay
22%9%15%22%23%8%
2520
11th to 20thDay
21%6%11%18%26%17%
2520
21st to endDay
17%6%11%20%27%19%
2520
July1st to 10thDay
22%8%13%18%24%14%
2451
11th to 20thDay
22%10%16%19%19%14%
2445
21st to endDay
28%11%16%19%16%10%
2437
August1st to 10thDay
30%13%16%19%15%8%
2313
11th to 20thDay
23%9%13%20%24%11%
2237
21st to endDay
24%9%12%22%22%11%
2376
September1st to 10thDay
22%6%10%17%24%22%
2160
11th to 20thDay
24%6%13%20%25%12%
2160
21st to endDay
24%47%28%30%6%
1918
October1st to 10thDay
34%7%12%22%18%6%
1800
11th to 20thDay
28%5%11%30%21%4
1800
21st to endDay
34%6%14%28%14%3
1980
November1st to 10thDay
33%5%13%24%23%1
1696
11th to 20thDay
40%6%15%23%14%2
1650
21st to endDay
38%412%29%15%2
1520
December1st to 10thDay
51%7%17%16%8%2
1520
11th to 20thDay
44%7%14%26%8%
1924
21st to endDay
49%9%10%17%14%1
2794
January1st to 10thNight
52%10%12%19%7%1
4417
11th to 20thNight
55%9%13%13%8%1
4229
21st to endNight
50%12%14%15%8%1
4521
February1st to 10thNight
57%7%11%16%8%1
2398
11th to 20thNight
50%7%12%20%9%2
2231
21st to endNight
48%9%13%17%12%2
1776
March1st to 10thNight
41%7%13%26%13%1
2068
11th to 20thNight
33%8%12%27%16%4
1980
21st to endNight
44%10%13%23%9%1
2122
April1st to 10thNight
39%9%13%18%16%4
1800
11th to 20thNight
41%8%14%21%15%1
1777
21st to endNight
36%8%13%24%18%1
1800
May1st to 10thNight
38%11%14%22%14%1
1630
11th to 20thNight
33%11%18%26%11%2
1418
21st to endNight
27%10%15%26%18%3
1552
June1st to 10thNight
19%7%16%29%21%9%
1440
11th to 20thNight
21%7%11%17%23%21%
1440
21st to endNight
13%7%9%20%28%22%
1440
July1st to 10thNight
18%10%15%20%20%18%
1400
11th to 20thNight
18%8%15%24%19%16%
1392
21st to endNight
21%10%20%21%18%10%
1636
August1st to 10thNight
23%10%16%26%15%10%
1602
11th to 20thNight
19%9%13%19%25%15%
1664
21st to endNight
21%9%13%19%26%14%
1980
September1st to 10thNight
19%6%11%16%25%22%
1800
11th to 20thNight
23%5%11%22%23%16%
1800
21st to endNight
21%49%25%33%8%
2037
October1st to 10thNight
27%8%11%25%20%9%
2160
11th to 20thNight
25%6%8%32%24%5%
2160
21st to endNight
33%5%14%26%18%4
2376
November1st to 10thNight
30%7%14%24%22%3
2362
11th to 20thNight
37%5%14%26%15%2
2527
21st to endNight
37%7%12%26%15%2
2660
December1st to 10thNight
48%7%14%18%12%2
2660
11th to 20thNight
44%7%13%25%11%
3272
21st to endNight
46%10%12%16%15%1
4873

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
18%14%24%29%12%2
270
11th to 20thDay
17%16%33%25%8%
270
21st to endDay
11%16%38%26%7%1
297
February1st to 10thDay
19%25%35%19%3
252
11th to 20thDay
18%20%33%23%5%
240
21st to endDay
16%24%38%20%3
198
March1st to 10thDay
19%28%26%22%5%1
330
11th to 20thDay
15%24%32%23%5%1
420
21st to endDay
19%31%34%14%3
462
April1st to 10thDay
20%26%29%18%6%1
420
11th to 20thDay
23%29%28%16%41
412
21st to endDay
15%26%32%19%7%1
420
May1st to 10thDay
17%23%31%19%9%1
441
11th to 20thDay
15%11%28%28%16%2
625
21st to endDay
13%13%29%29%14%3
679
June1st to 10thDay
5%11%27%31%22%4
630
11th to 20thDay
7%14%33%29%15%2
630
21st to endDay
48%30%33%22%2
630
July1st to 10thDay
5%421%38%29%4
621
11th to 20thDay
45%22%37%27%5%
618
21st to endDay
5%423%40%24%5%
523
August1st to 10thDay
6%434%34%17%5%
447
11th to 20thDay
35%30%36%21%4
437
21st to endDay
5%6%26%38%20%5%
495
September1st to 10thDay
7%10%31%28%19%5%
450
11th to 20thDay
410%35%30%18%3
450
21st to endDay
11%13%27%26%16%7%
329
October1st to 10thDay
14%12%21%27%17%7%
270
11th to 20thDay
12%17%27%29%13%2
270
21st to endDay
17%19%32%24%7%1
297
November1st to 10thDay
16%23%27%23%10%3
270
11th to 20thDay
14%18%28%29%10%1
270
21st to endDay
14%13%32%31%9%1
270
December1st to 10thDay
16%16%33%23%9%1
270
11th to 20thDay
16%12%36%27%8%
270
21st to endDay
20%16%34%23%6%1
297
January1st to 10thNight
16%12%25%35%11%1
950
11th to 20thNight
16%12%32%30%8%1
827
21st to endNight
14%11%32%32%11%1
836
February1st to 10thNight
16%11%35%31%6%
738
11th to 20thNight
13%12%34%34%7%
704
21st to endNight
12%13%35%36%3
592
March1st to 10thNight
12%11%32%35%9%1
720
11th to 20thNight
10%7%24%46%13%
720
21st to endNight
13%9%34%34%10%
736
April1st to 10thNight
14%14%28%37%6%
540
11th to 20thNight
17%10%29%34%10%1
533
21st to endNight
14%9%25%36%14%1
540
May1st to 10thNight
13%6%29%39%12%1
540
11th to 20thNight
10%423%39%23%1
531
21st to endNight
8%7%21%40%21%3
584
June1st to 10thNight
5%419%41%29%1
540
11th to 20thNight
6%6%22%47%19%1
540
21st to endNight
3316%49%28%2
540
July1st to 10thNight
329%46%38%3
525
11th to 20thNight
228%47%38%3
522
21st to endNight
317%42%46%2
591
August1st to 10thNight
5%19%42%42%1
537
11th to 20thNight
4110%46%37%1
534
21st to endNight
418%44%38%4
594
September1st to 10thNight
6%212%45%31%3
540
11th to 20thNight
5%412%43%33%3
540
21st to endNight
8%318%35%29%6%
657
October1st to 10thNight
10%5%23%38%20%3
720
11th to 20thNight
9%8%25%39%16%2
720
21st to endNight
15%6%26%36%15%2
792
November1st to 10thNight
12%10%28%34%14%1
882
11th to 20thNight
15%11%27%37%9%1
950
21st to endNight
11%9%28%38%12%
950
December1st to 10thNight
16%11%33%32%8%1
950
11th to 20thNight
14%13%29%36%7%
950
21st to endNight
17%12%32%31%7%1
1045
Page generated at 2024-02-02 03:20:29. Version ac07

Copyright 2024 Attilla Danko


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