ASKC Dark Site
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the ASKC Dark Site clear sky chart from 2005-11-06 to 2024-03-23.

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
42%
24695
23%
80497
15%
24587
51%
24587
29%
48421

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
31%
940
20%
4052
7%
926
43%
926
20%
2496
January11th to 20thNight
25%
949
20%
4043
8%
930
36%
930
17%
2696
January21st to endNight
30%
1039
16%
4491
9%
1023
40%
1023
17%
2980
February1st to 10thNight
24%
950
19%
2470
6%
950
32%
950
26%
1692
February11th to 20thNight
26%
929
19%
2404
6%
925
33%
925
28%
1575
February21st to endNight
23%
568
26%
1824
10%
568
37%
568
25%
1124
March1st to 10thNight
28%
570
26%
2090
13%
570
44%
570
26%
1185
March11th to 20thNight
31%
570
21%
2090
13%
570
42%
570
22%
1262
March21st to endNight
25%
600
16%
2200
8%
600
37%
600
17%
1452
April1st to 10thNight
32%
540
22%
1882
13%
540
46%
540
27%
1062
April11th to 20thNight
31%
533
24%
1775
17%
533
45%
533
26%
1061
April21st to endNight
30%
540
21%
1702
12%
540
44%
540
25%
1081
May1st to 10thNight
37%
540
18%
1620
12%
540
46%
540
25%
1073
May11th to 20thNight
45%
531
21%
1594
19%
531
51%
531
32%
967
May21st to endNight
47%
584
20%
1746
15%
582
55%
582
30%
1054
June1st to 10thNight
69%
540
23%
1449
16%
540
73%
540
48%
796
June11th to 20thNight
63%
540
24%
1440
17%
540
66%
540
44%
837
June21st to endNight
63%
540
27%
1519
20%
540
67%
540
51%
783
July1st to 10thNight
72%
525
19%
1575
18%
525
73%
525
40%
874
July11th to 20thNight
76%
522
23%
1566
23%
522
78%
522
50%
791
July21st to endNight
71%
591
25%
1673
26%
558
74%
558
42%
905
August1st to 10thNight
70%
537
23%
1601
27%
534
73%
534
42%
857
August11th to 20thNight
71%
534
30%
1600
34%
534
74%
534
43%
869
August21st to endNight
76%
594
30%
1945
35%
594
78%
594
46%
952
September1st to 10thNight
66%
540
28%
1800
29%
540
69%
540
37%
949
September11th to 20thNight
63%
540
30%
1957
28%
540
70%
540
34%
1030
September21st to endNight
61%
540
33%
1980
30%
540
68%
540
39%
956
October1st to 10thNight
54%
715
28%
2155
21%
715
59%
715
40%
1164
October11th to 20thNight
35%
720
30%
2160
15%
720
47%
720
35%
1241
October21st to endNight
34%
792
27%
2376
14%
792
45%
792
31%
1415
November1st to 10thNight
41%
740
33%
2220
17%
740
55%
740
40%
1179
November11th to 20thNight
35%
911
28%
2463
12%
911
47%
911
35%
1476
November21st to endNight
32%
950
25%
2660
10%
950
43%
950
31%
1631
December1st to 10thNight
31%
950
22%
2660
9%
950
42%
950
31%
1659
December11th to 20thNight
30%
949
23%
3132
9%
948
40%
948
24%
1935
December21st to endNight
26%
1042
15%
4583
9%
1026
38%
1026
13%
3362

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%7%35%5%3445%7%44%
78827
Night
12%7%35%43445%6%48%
81096
TransparencyDay
40%412%26%16%2
78550
Night
38%311%26%18%3
80893
SeeingDay
15%9%27%28%18%5%
14656
Night
15%8%30%33%13%1
24716

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
15%9%38%6%34445%39%
2847
11th to 20thDay
11%11%48%7%45%335%39%
2850
21st to endDay
18%14%46%433336%36%
3135
February1st to 10thDay
15%11%36%5%34236%40%
1710
11th to 20thDay
14%8%46%5%35%345%43%
1664
21st to endDay
14%9%36%5%35%45%7%41%
1644
March1st to 10thDay
14%7%46%6%34345%44%
2090
11th to 20thDay
21%8%36%42445%6%37%
2090
21st to endDay
21%11%36%5%345%45%33%
2200
April1st to 10thDay
13%7%25%5%345%5%6%44%
2078
11th to 20thDay
15%7%36%5%3446%7%40%
2134
21st to endDay
20%8%35%5%3445%6%36%
2254
May1st to 10thDay
19%8%35%6%35%446%36%
2340
11th to 20thDay
16%7%25%5%25%5%5%8%39%
2302
21st to endDay
15%7%36%6%46%5%5%9%34%
2531
June1st to 10thDay
6%4145%35%6%6%10%48%
2506
11th to 20thDay
8%5%246%35%6%6%8%48%
2520
21st to endDay
6%31342446%9%56%
2432
July1st to 10thDay
8%5%35%5%45%7%6%9%43%
2340
11th to 20thDay
43145%346%6%9%54%
2340
21st to endDay
9%5%25%5%36%6%6%10%43%
2546
August1st to 10thDay
7%425%5%45%5%7%11%44%
2328
11th to 20thDay
7%425%5%35%47%9%49%
2301
21st to endDay
8%3244346%6%9%53%
2408
September1st to 10thDay
13%5%24423447%53%
2160
11th to 20thDay
10%5%234345%7%6%51%
1998
21st to endDay
8%42443435%6%56%
1965
October1st to 10thDay
12%5%2442445%7%52%
1800
11th to 20thDay
13%5%24423435%55%
1800
21st to endDay
18%7%35%42343448%
1980
November1st to 10thDay
9%6%35%323447%55%
1858
11th to 20thDay
15%5%34323347%50%
1711
21st to endDay
17%7%25%423336%49%
1520
December1st to 10thDay
12%7%35%5%24447%47%
1520
11th to 20thDay
13%9%47%6%2432445%
1918
21st to endDay
18%14%6%7%5%34446%28%
3007
January1st to 10thNight
11%9%49%5%33435%43%
4108
11th to 20thNight
11%8%37%8%6%7%5%45%38%
4120
21st to endNight
20%11%47%323335%38%
4532
February1st to 10thNight
13%10%36%5%3445%7%39%
2470
11th to 20thNight
13%8%36%424447%44%
2403
21st to endNight
14%8%35%5%24345%47%
1824
March1st to 10thNight
13%6%35%43435%6%48%
2090
11th to 20thNight
16%7%26%424446%45%
2090
21st to endNight
19%9%35%5%345%5%7%35%
2200
April1st to 10thNight
10%6%35%43345%7%50%
1882
11th to 20thNight
15%7%25%5%23346%46%
1775
21st to endNight
16%6%36%5%34447%43%
1702
May1st to 10thNight
16%5%36%5%445%46%42%
1620
11th to 20thNight
13%6%245%2345%7%48%
1593
21st to endNight
11%6%26%4245%7%10%42%
1745
June1st to 10thNight
6%3134235%7%11%55%
1449
11th to 20thNight
44245%35%6%8%9%51%
1440
21st to endNight
5%31333335%8%62%
1519
July1st to 10thNight
7%3145%435%7%9%52%
1620
11th to 20thNight
32134345%6%9%60%
1620
21st to endNight
6%424435%5%6%9%51%
1772
August1st to 10thNight
6%314435%5%6%10%53%
1611
11th to 20thNight
6%4145%25%45%8%57%
1600
21st to endNight
5%32433446%7%60%
1945
September1st to 10thNight
10%41433445%7%56%
1800
11th to 20thNight
9%414335%5%5%7%53%
1957
21st to endNight
7%42342345%7%59%
1980
October1st to 10thNight
9%324434446%58%
2155
11th to 20thNight
14%6%24323335%55%
2160
21st to endNight
16%6%34423335%52%
2376
November1st to 10thNight
10%423323345%61%
2220
11th to 20thNight
12%6%24324346%53%
2463
21st to endNight
17%6%23323335%52%
2660
December1st to 10thNight
12%7%35%42445%7%47%
2660
11th to 20thNight
14%8%35%43435%6%45%
3279
21st to endNight
20%15%5%7%5%2333431%
4656

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%39%27%14%1
2848
11th to 20thDay
50%311%23%12%
2850
21st to endDay
52%210%19%16%1
3135
February1st to 10thDay
49%410%25%9%3
1710
11th to 20thDay
45%212%22%15%3
1673
21st to endDay
44%29%25%14%6%
1644
March1st to 10thDay
44%310%22%17%4
2090
11th to 20thDay
50%39%23%12%3
2090
21st to endDay
54%314%19%9%1
2200
April1st to 10thDay
41%412%25%17%2
2078
11th to 20thDay
45%311%26%15%1
2134
21st to endDay
49%311%25%11%
2254
May1st to 10thDay
49%412%21%13%1
2340
11th to 20thDay
43%5%14%25%12%
2306
21st to endDay
47%5%15%23%9%1
2531
June1st to 10thDay
31%6%18%28%17%1
2506
11th to 20thDay
33%5%14%30%16%2
2520
21st to endDay
25%415%35%18%3
2432
July1st to 10thDay
36%5%14%27%15%3
2276
11th to 20thDay
24%5%16%31%19%3
2271
21st to endDay
34%5%15%31%14%1
2405
August1st to 10thDay
33%6%19%27%15%1
2314
11th to 20thDay
32%413%33%16%2
2301
21st to endDay
28%5%12%28%21%6%
2408
September1st to 10thDay
33%412%30%16%7%
2160
11th to 20thDay
32%49%26%26%2
1998
21st to endDay
30%49%28%25%5%
1965
October1st to 10thDay
34%311%27%22%4
1800
11th to 20thDay
33%36%29%24%6%
1800
21st to endDay
42%29%24%19%5%
1980
November1st to 10thDay
31%311%30%21%5%
1858
11th to 20thDay
36%28%26%23%4
1711
21st to endDay
40%28%28%19%1
1520
December1st to 10thDay
39%310%33%13%1
1520
11th to 20thDay
45%310%26%14%2
1915
21st to endDay
58%211%20%8%2
3007
January1st to 10thNight
44%314%25%13%1
4108
11th to 20thNight
50%310%23%13%1
4120
21st to endNight
51%211%22%12%2
4532
February1st to 10thNight
45%411%23%15%2
2470
11th to 20thNight
41%211%25%17%3
2404
21st to endNight
42%37%23%18%7%
1824
March1st to 10thNight
38%310%24%21%6%
2090
11th to 20thNight
42%410%23%18%3
2090
21st to endNight
50%311%23%12%2
2200
April1st to 10thNight
35%310%24%23%4
1882
11th to 20thNight
40%28%26%19%4
1775
21st to endNight
43%310%26%17%1
1702
May1st to 10thNight
44%5%11%23%16%2
1620
11th to 20thNight
37%314%29%16%2
1594
21st to endNight
36%6%17%29%11%1
1746
June1st to 10thNight
24%420%31%18%3
1449
11th to 20thNight
26%6%17%29%20%2
1440
21st to endNight
21%413%35%23%4
1519
July1st to 10thNight
29%415%32%16%4
1575
11th to 20thNight
21%414%33%25%4
1566
21st to endNight
27%415%31%21%1
1673
August1st to 10thNight
26%5%16%36%14%3
1601
11th to 20thNight
27%310%33%25%2
1600
21st to endNight
22%413%28%26%7%
1945
September1st to 10thNight
29%410%30%20%8%
1800
11th to 20thNight
30%48%25%27%5%
1957
21st to endNight
26%38%29%29%5%
1980
October1st to 10thNight
28%39%27%26%7%
2155
11th to 20thNight
33%35%27%25%7%
2160
21st to endNight
37%37%24%24%5%
2376
November1st to 10thNight
27%311%29%24%6%
2220
11th to 20thNight
34%27%27%26%4
2463
21st to endNight
37%38%27%22%3
2660
December1st to 10thNight
38%312%28%18%1
2660
11th to 20thNight
41%39%29%17%1
3281
21st to endNight
58%37%20%10%2
4656

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
22%13%36%24%4
270
11th to 20thDay
30%13%36%20%2
270
21st to endDay
18%13%43%22%4
297
February1st to 10thDay
23%19%37%18%4
270
11th to 20thDay
19%18%44%14%5%1
270
21st to endDay
24%24%38%12%3
225
March1st to 10thDay
20%17%41%19%3
270
11th to 20thDay
25%15%32%22%5%
270
21st to endDay
31%18%36%13%21
270
April1st to 10thDay
17%19%36%21%7%1
338
11th to 20thDay
19%15%34%24%8%
412
21st to endDay
23%13%33%23%8%
514
May1st to 10thDay
22%12%34%22%10%1
603
11th to 20thDay
20%8%29%28%12%3
625
21st to endDay
16%7%27%27%17%5%
679
June1st to 10thDay
7%317%36%28%9%
630
11th to 20thDay
9%423%35%24%5%
630
21st to endDay
6%430%35%21%3
630
July1st to 10thDay
10%212%31%32%13%
621
11th to 20thDay
4118%35%34%8%
618
21st to endDay
9%211%33%35%11%
684
August1st to 10thDay
9%412%38%31%7%
626
11th to 20thDay
7%215%35%33%7%
615
21st to endDay
9%210%29%35%13%
527
September1st to 10thDay
14%214%32%31%7%
450
11th to 20thDay
7%119%37%29%7%
288
21st to endDay
11%5%26%34%17%7%
270
October1st to 10thDay
14%9%25%29%16%8%
270
11th to 20thDay
12%13%42%26%6%1
270
21st to endDay
26%14%32%21%7%
297
November1st to 10thDay
15%10%36%24%11%4
270
11th to 20thDay
18%17%29%25%10%1
270
21st to endDay
24%14%33%22%7%1
270
December1st to 10thDay
14%11%42%23%6%4
270
11th to 20thDay
20%16%32%26%7%
270
21st to endDay
23%21%39%16%1
297
January1st to 10thNight
15%11%37%30%6%1
950
11th to 20thNight
17%12%39%27%41
950
21st to endNight
15%13%38%30%4
1045
February1st to 10thNight
19%12%41%25%3
950
11th to 20thNight
18%13%38%28%2
929
21st to endNight
21%13%39%24%3
568
March1st to 10thNight
18%11%40%27%4
570
11th to 20thNight
21%11%34%28%6%1
570
21st to endNight
23%12%36%26%3
600
April1st to 10thNight
14%11%38%30%6%
540
11th to 20thNight
18%13%33%29%7%
533
21st to endNight
18%7%39%26%9%
540
May1st to 10thNight
18%6%32%36%8%
540
11th to 20thNight
17%330%34%15%1
531
21st to endNight
14%6%27%32%19%2
584
June1st to 10thNight
6%316%44%30%1
540
11th to 20thNight
4224%49%19%2
540
21st to endNight
5%424%47%19%1
540
July1st to 10thNight
8%210%40%36%4
525
11th to 20thNight
4113%45%34%3
522
21st to endNight
8%211%40%38%2
591
August1st to 10thNight
6%212%44%33%2
537
11th to 20thNight
8%110%48%29%3
534
21st to endNight
7%110%40%39%4
594
September1st to 10thNight
13%114%44%24%3
540
11th to 20thNight
10%217%38%28%5%
540
21st to endNight
10%321%41%21%4
540
October1st to 10thNight
10%426%37%22%2
715
11th to 20thNight
16%6%38%30%9%
720
21st to endNight
20%10%32%29%8%
792
November1st to 10thNight
12%9%34%32%12%1
740
11th to 20thNight
16%10%35%29%9%
911
21st to endNight
20%10%34%29%7%
950
December1st to 10thNight
16%10%38%28%6%1
950
11th to 20thNight
21%9%34%30%5%
950
21st to endNight
19%14%36%27%4
1045
Page generated at 2024-03-19 22:31:03. Version ac07

Copyright © 2024 Attilla Danko.


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